Multi-robotic construction system for unfired soil masonry by Francesco M. Massetti

Architectural Association / Graduate School / Emergent Technologies & Design

Multi-robotic construction system for unfired soil masonry

Architectural Association School of Architecture Graduate School / Emergent Technologies & Design 2015/2016

Multi-robotic construction system for unfired soil masonry

M.Sc // Francesco M. Massetti

Course directors

Michael Weinstock George Jeronimidis

Studio master

Evan Greenberg

Studio tutors

Elif Erdine Manja van de Worp

In collaboration with M.Arch // JosĂŠ M. Cherem M.Arch // Ekaterina Bryskina

Multi-robotic construction system for unfired soil masonry

Table of contents

ABSTRACT

INTRODUCTION // Industrialisation and machines // Construction industry issues // Resources scarcity and availability // Environmental emissions // Earth construction

10 12 14 16 18 20

DOMAIN

EARTH AND LOAM // Granular materials // Soil mineralogy // Soil phases // Hygroscopic properties // Construction techniques

25 26 32 34 38 42

ROBOTIC FABRICATION // Automation and manufacture // Prefabricated masonry // Selective laser sintering // Solar sinter // Industrial extrusion // Woven clay

50 52 54 56 58 60 62

MOBILE ROBOTS // Robustness, scalability and flexibility // Collaborative behaviour in natural systems // Termes // Spatially targeted communication ROBOTIC CONSTRUCTION // On-site automation // GHG emissions // Site safety // Prior art overview // Vertical slip forming // D-Shape // Big Delta WASPS // Rock print // Minibuilders

66 68 70 72 74

SITE SELECTION METHODS // Control and Dataflow // Parametric Form-finding // Structural Analysis (FEA) // Environmental Analysis // Multi-objective optimization // Cellular Automata (CA) // Agent Based Modeling (ABM) // Physical computing // Material tests

100

78 80 82 84 86 88 90 92 94 96

108 110 112 113 114 115 116 117 118 119

RESEARCH DEVELOPMENT

122

MATERIAL EXPLORATION // Manual forming_Water absorption // Casting_Layers cohesion // Direct extrusion_Overlapping // Direct extrusion_Spanning // Direct extrusion_Masonry // Hydrostatic extrusion_Pneumatic tool // Hydrostatic extrusion_Clay // Hydrostatic extrusion_Clay > Loam > Sand // Hydrostatic extrusion_Loam > Clay > Sand // Hydrostatic extrusion_CNC technologies

123 124 126 128 130 136 142 148 150 154 162

ROBOT CONTROL // Centralized control // Decentralized control // Robotic unit hardware // Path processing // Differential drive kinematics // Path planning // Linear and angular velocity // Continuous path // Discontinuous path

166 168 170 174 176 178 180 182 184 186

CONSTRUCTION STRATEGY // Material manipulation // Soil crystallization // Layering logic // Construction process // Autonomy // Fitness landscape generation // Time/Mass/Cost Projection // Porosity/Energy/Mass Projection DESIGN DEVELOPMENT // Linear component // Components aggregation // Structural analysis // Environmental strategy // Occlusion and radiation analysis // Rainflow analysis // Section resolution and texture

194 196 198 200 202 210 212 214 218

CONCLUSIONS

240

FURTHER DEVELOPMENTS

246

MAP OF CONTRIBUTION

250

Multi-robotic construction system for unfired soil masonry

222 224 226 228 230 232 234 236

Abstract

Construction industry, traditionally afflicted with costs, safety concerns and material scarcity, is taking inspiration from the manufacturing industry in order to increase precision, speed and efficiency of built products. Contemporary achievements in automation and robotics allow fabrication processes to be implemented in construction strategies, while cognitive and computer sciences are suggesting collective behaviour principles as robust and effective approach to complex problem solving. Here we present a construction method that makes use of ground mobile robots to fabricate earth structures from in-situ sourced granular material. Clay powder, one of the main material phase of soil, is mixed with water to produce viscous paste, a medium that, with the employment of specific digital tools, provides flexibility, ease of manipulation and sustainable applications. The proposed system envisions a layer-by-layer approach in which clay is used in different phases. While clay paste materializes the final design, clay powder holds the role of withstanding disruptive forces during fabrication, regulating crystallization and texture of the artefact. Although the use of mobile agents is correlated with scalability propositions, two approaches in control of collaborative behaviours are discussed. If centralized systems are addressed through spatially targeted communication models and parametric form-finding, decentralized system showing emergent properties are questioned in terms of interaction between local and global scale as well as in terms of possibilities in developing scalability strategies.

Multi-robotic construction system for unfired soil masonry

Introduction

Multi-robotic construction system for unfired soil masonry

Industrialisation and machines

Construction industry has been developing for the past decades as a result of the wave of industrialisation that, from the XIX century to nowadays, presented the machine, with its physical interface and digital control, as controversial allied in human activities. During this period, tools exponentially increased their importance within the human society, rising to fundamental elements of our life, from every day activities to large scale construction projects. If on the one hand production volumes of goods and efficiency of fabrication processes experienced an incontrollable growth, on the other hand machinery represents a complex topic because of its implications in the biosphere. Man-machine relationship contributed to the creation of disciplines such as computer science and ergonomy. The distinction here outlined between human and robots - accepted as particular case of machines - should not misdirect the reader towards the idea of a world divided into sectors with specific and unique rules regulating matter and energy flows. Biosphere, a concept introduced by Austrian geologist Eduard Suess, is defined as the existing network between all natural ecosystem on planet Earth. It includes all living organisms and interacts with other systems such as hydrosphere, cryosphere, lithosphere and atmosphere, defined by tangible instances and boundaries. The higher complexity of Biosphere identifies the Hominidae as major modifying agents of the planet. Directly deriving from the attitude of categorising and labelling phenomena, whose roots can be placed between the modern philosophy of Kant and the scientific research of Linnaeus, the influence of technology led to the invention of the technosphere, ‘that includes the world’s large-scale energy and resource extraction systems, power generation and transmission systems, communication, transportation, financial and other networks, governments and bureaucracies, cities, factories, farms and myriad other built systems, as well as all the parts of these systems, including computers, windows, tractors, office memos and humans.’ [1] Technosphere is one of those terms, as well as the wider Anthropocene, that try to identify an ensemble of systems and processes for collecting specialised knowledge on how to render those tools more efficient. In doing so, the elements of the technosphere are by tradition considered as alien to our nature, spreading the idea of technology and its effects as intrinsically artificial products of civilisation. A consideration that forgets how technology is a product of human social development and, as such, a direct offspring of life in the biosphere and its dependencies from all other ‘spheres’. Reminding ourselves how the use of tools is also evident in other animal species, human technology needs to be considered as manifestation of the survival challenge typical of living forms. Throughout this document, machines and robots will be considered as tools forged by humans for the execution of tasks, while the debate about their contributes in the development of technology will try to ‘abandon the apparently natural assumption that the technosphere is primarily a human-created and controlled system and instead develop the idea that workings of modern humanity are a product of a system that operates beyond our control and that imposes its own requirements on human behaviour. The technosphere is a system for which humans are essential but, nonetheless, subordinate parts.’ [1]

Der Mensch als Industriepalast (Man as Industrial Palace). Stuttgart, 1926. Chromolithograph. National Library of Medicine. [2]

Multi-robotic construction system for unfired soil masonry

Construction industry issues

Construction industry, as ensemble of ‘construction activities for buildings and civil engineering works, includes new work, repair, additions and alterations, the erection of prefabricated building or structures on the site and also construction of a temporary nature’. [3] As recent compartment of modern industry, construction is experiencing issues and problems that have been previously central in the discussion of how production systems influence output volumes and workers life in other sectors such as manufacturing. Being these issues of different nature, it is possible to identify some of them as related with the practical aspects of construction and some others with all consequences within the relative business landscape. Direct issues are those connected to workforce consideration and quality of the final product, while indirect ones are usually less visible and are mainly represented by socio-political interactions and environmental repercussions. Given the impressive extent of the subject and the differences among countries in construction management, this research will try to debate those characteristics that are closer to the role of project managers, architects and designers in general, leaving socio-political considerations out of discussion. Being working people necessary condition and main resource for any human activity, current construction industry analysis shows, much better than others sectors, how ‘the workforce is undervalued, under-resourced and frequently treated as a commodity rather than the industry’s single most important asset.’ [4] It seems then plausible to observe how human workforce contributes to the majority of issues in construction, starting from considerations about skills and experience. In addition to skills shortage, ‘there is a crisis in training. The proportion of trainees in the workforce appears to have declined by half since the 1970s and [...] Too few people are being trained to replace the aging skilled workforce, and too few are acquiring the technical and managerial skills required to get full value from new techniques and technologies.’ [3] A matter of fact that has its origin in how people perceive construction, as a dangerous, dirty and hard work, encouraging youth towards safer and cleaner environments and leaving the profession lacking of talented people. The result of this configuration is also related with the productivity of workers, taught to be around 40% of the time, while for the remaining 60% workers would be moving from one task to another or waiting for materials and instructions. [5] Usually, productivity issues are caused by ‘poor management and supervision; disruptions of work; inclement weather conditions; low and discontinuous demand; frequent changes in specification; inefficient construction methods and over-manning.’ [6]

Challenges of construction industry as direct construction issues and peripheral pressures. Adapted. [8]

The challenges of construction

Construction issues

Peripheral pressures

Rising costs

Time

Quality

Environmental

Socio-political

Legal

Wages

Delivery of materials, supplies and equipment

Design criteria

Design Erosion and sedimentation control

Public involvement in planning, design and construction

Claims avoidance, support and mitigation

Materials supply

Government restraints

Inspection

Wetlands and parklands

Civic/community groups

Liability

Productivity

Lack of skilled workers

Lead abatement

Advisory boards

Fiduciary duty

Time delay

Design changes

Supervision

Asbestos

NIMBY syndrome

Labor and safety laws

Capital equipment

Design schedule

Finance

Inflation

Construction schedule

Availability of materials

Multi-robotic construction system for unfired soil masonry

Resources scarcity and availability

At the centre of the construction industry debate, as well as for all production and assembly chains, there is the necessity of evaluating environmental impact and raw material availability. If manufacture mainly deals with the design of specialised components to be produced and assembled in controlled settings, construction, even when based on prefabrication, always presents an element of uncertainty within its completion due to the necessity of providing sheltering functions in natural environments, in which scalability arguments render planning and coordination of difficult management. Control of multiple agents is often coupled with unforeseeable site conditions and cost projections are usually implicitly liable of changes. Material availability, being the main premise to fabrication processes, has great influence on the realisation of a project. Consequently, ‘materials determine technologies and processes employed in construction and architectural forms, as well as supply chain nodes’ [9] A reality that can also be considered as a form of vulnerability of the field for physical limitation and operational constraint. The economic principle of scarcity, usually expressed as related, more than to the real availability of material, to the actual price of a resource within a certain market, finds its conceptual roots in Malthus’ discourse on population and on the concept of price, whose economical interpretation does not refer to an absolute value of goods or services, but to the price that users are willing to pay. This, according to David Ricardo, happens ‘because high quality resources will be extracted before lower quality ones, scarcity is not merely a consequence of resource exhaustion, but instead derives from the increasing difficulty and cost of accessing lower quality resources’, that is to say that a ‘resource becomes scarce when efforts needed to access the marginal amount of material is greater than the amount of effort one would be capable or willing to exert’ [9]. Scarcity therefore is a way of defining the value of a material according to its demand and utilisation, a consideration that should lead the designer to a deep reflection about what materials are currently employed in construction, in what conditions and for which uses.

MARKET FORCES

RATE OF DISCOVERY

Flow analysis for material availability and key drivers of scarcity/availability. Adapted. [9]

RESOURCE RESERVES RATE OF TECHNOLOGICAL CHANGE IN EXTRACTION

RATE OF CONSUMPTION

RATE OF RECYCLING

APPLICATION DEMAND

IN USE

RATE OF SUBSTITUTION

USE OF ALTERNATIVES

Multi-robotic construction system for unfired soil masonry

RATE OF DISSIPATION

LOSS

Environmental emissions

The life-cycle of construction industry products is often thought to be made of all activities from extraction of materials to consignment of the project, while consequent phases of material utilisation are not considered. Almost all current technological activities in construction industry, from extraction and manufacturing to utilisation and recycling, rely on massive consumption of fossil fuel and constitute a primary source of greenhouse gases. A briefing made in 2011 about production emissions in UK shows that more than half of them are due to the construction sector and in particular to the utilisation of buildings and the embodied impact related with the manufacture of buildings components. [10] Manufacturing of construction material is highly industrialised and based on the extraction of resources from renewable and not renewable sources, the latter option entailing emissions of gases such as carbon dioxide and methane. Granular material, aggregates and minerals, among the most employed technologies for construction, imply energy expensive manufacturing processes such as extraction and processing. A composite material made of cement and coarse aggregates - concrete - and its industry are main producers of emissions due to the high temperature requested for the production of raw materials, while its utilisation determines consequences on natural systems feed-back loops. Ceramic materials, even with a simpler processing, need high temperature too for drying. Unfired clay and soil, when conditions are suitable, can constitute an alternative for avoiding to use large amounts of energy and exploiting environmental heat for solidification.

World GHG emissions flow chart for 2005. Detail of carbon dioxide emission related with energy industry and industrial processes (63,4% of total emission). [11]

Multi-robotic construction system for unfired soil masonry

Earth construction

In almost every hot-arid and temperate climates, earth and soil have been considered as fundamental construction materials in virtue of their ease of procurement and use. Earthen houses are widely in use among the human population, in particular in developing countries in which the employment of industrial construction materials, such as steel, concrete or bricks, or the application of industrialised construction techniques do not provide economical and social safeguard. In this contexts, viable solutions are represented by using local building materials and construction techniques of simple management, aiming at lowering costs and need of specialised skills. Consequently, large excavations and energy-intensive processes are not employable nor beneficial due to their complexity and impact on environment and social life. Traditional construction processes are usually based on unspecialised labour that operates through simple and repetitive routines to deposit material in a three-dimensional space. Where tools and machines are not available, buildings are realised as the sum of small portions of wet material brought into place by multiple human agents. Similarities within zoology, neurosciences and robotics lead us to envision a symbiotic collaboration between cutting-edge technologies and low impact design for evaluating energy, costs and material consumption in construction, investigating unbaked soil as a solution to energy consumption and to sustainability issues through the reduction of transportation needs and chemical processing of the material involved.

Shibam, Yemen, high-rise earth buildings. [12]

From top left clockwise. Storage rooms, temple of Ramses II, Gourna, Egypt. [13] Rammed earth house, Weilburg, Germany, 1828. [13] Mosque, Kashan, Iran. [13] Bazaar, Sirdjan, Iran. [13]

Multi-robotic construction system for unfired soil masonry

[1] Haff. P. (2014). HUMANS AND TECHNOLOGY IN THE ANTHROPOCENE: SIX RULES. The Anthropocene Review, 1(2). p. 127. [2] Kahn F. (1926). DER MENSCH ALS INDUSTRIEPALAST (Man as Industrial Palace). Stuttgart. National Library of Medicine. Chromolithograph. [3] Office for National Statistics. (2016). CONSTRUCTION STATISTICS: NO 17. p. 8. [4] Egan. J. (1998). RETHINKING CONSTRUCTION. Construction Task Force: Department of Environment, Transport and the Region. UK., p. 25. [5] Gray C., Flanagan R., (1989). THE CHANGING ROLE OF SPECIALIST AND TRADE CONTRACTORS. Chartered Institute of Building. UK., p. 77. [6] Proverbs D.G., Holt G. D., Cheok H. Y. (2012). CONSTRUCTION INDUSTRY PROBLEMS: THE VIEWS OF UK CONSTRUCTION DIRECTORS. Built Environment Research Unit, School of Engineering and the Built Environment. University of Wolverhampton, West Midlands. UK. p. 5. [7] S. Nishigaki, K. H. Law (1994). SAFETY PROBLEMS IN ON-SITE CONSTRUCTION WORK, in D. A. Chamberlain (editor). (1994). Automation and Robotics in Construction XI. Elsevier Science. p. 13. [8] Muir B. (2005). CHALLENGES FACING TODAY’S CONSTRUCTION MANAGER. Supplemental reading for CIEG 486-010 Construction methods & management. University of Delaware. p. 1. [9] Alonso E., Field F., Gregory J., Kirchain R. (2007). MATERIAL AVAILABILITY AND THE SUPPLY CHAIN: RISKS, EFFECTS AND RESPONSES. Massachusetts Institute of Technology. pp. 2-16. [10] Anderson J. PE International. (2011). MATERIALS, PRODUCTS AND CARBON. Carbon leader briefings. pp. 1-3. [11] World Resources Institute, (2000), WORLD GHG EMISSIONS FLOW CHART. [12] De Freitas W. (2007). SHIBAM. From Flickr account. [13] Minke G. (2013). BUILDING WITH EARTH. DESIGN AND TECHNOLOGY OF A SUSTAINABLE ARCHITECTURE. Basel. Birkhäuser Verlag. pp. 9-13.

Multi-robotic construction system for unfired soil masonry

Domain

Earth and loam

Multi-robotic construction system for unfired soil masonry

Granular materials

Granular materials are employed in several engineering application and they are widely available as natural resource. The group of industries that handle granular materials includes pharmaceutical, agricultural, construction and many others, meaning that many sectors are simultaneously requesting wide investigation in the field. [1] This research is focused on possibilities of using hygroscopic granular materials in fabrication, construction and architectural application as on-site widely available material. Granular materials have significant advantages in energy consumption, recycling, availability, fireproof and durability. At the same time, building with this materials is labor intensive and traditional construction processes tend to be dangerous for workers. Crystallization, sintering and adding a liquid binder are chemical processes of forming a solid mass from granular materials that can be studied for construction needs. Each process is characterized by different material bridges that form a bond between particles with chemical reaction or simply melting. [1] All three processes involve different conditions and devices that can be used to achieve required results. At the same time each process of granular materials solidification can become basis for traditional or alternative construction methods for discrete and non-discrete approaches in terms of assembly strategies.

Negev, Israel.

Multi-robotic construction system for unfired soil masonry

Crystallisation is a process that starts from dissolving a substance, depositing of suspended particles what creates liquid bridges between particles and solidifies a substance. This chemical reaction can be applied to non-discrete and discrete assembly logics and there are many examples of both. The non-discrete approach can be represented by ancient techniques like cob, rammed earth, wattle and daub and others. At the same time, they can be applied to discrete method where components or bricks will be prefabricated like in mud bricks or compressed earth blocks. All techniques use natural materials as sand, clay, water and some kind of fibrous or organic material (sticks, straw and or manure) for reinforcement. [2] It is important to mention that no additional materials are needed accept the ones that can be easily found on-site. These techniques have significant advantages as widely available and durable materials, low energy consumption and low-tech construction process. Granular materials have been used to build for thousands of years and they are still the main construction material in modern architecture. Even today, one third of the entire world construction uses earthen houses, especially in developing countries. [2] Also, modern innovation techniques as extruded unfired masonry units can push construction even further towards popularity of earthen architecture. [1] Sintering process in the brick manufacturing stables initial raw materials and transforms them into complex solid ‘compounds at high temperatures’. [3] This process is the main in the brick fabrication where the quality of the final product will depend on a combination of ‘the type of raw materials, fabrication method, drying procedure, firing temperature and profile’. [3] For example, fired-clay bricks that are sintered on a higher temperature will provide the highest strength and ‘the effect of firing temperature will significantly improve the microstructure in terms of porosity and the quality of physical properties’. [3] This method can be applied to custom-made components, but in this case fabrication will gain a lot of complexity in terms of mould production. Also, the amount of energy that is required for brick fabrication is the main disadvantage of this approach. Conversely, the assembly method, ‘pick and place’, is relevantly easy to perform, because of predefined elements. However, there is a possibility of non-discrete sintering even if currently it exists mainly as a conceptual and novel approach. The idea is to sinter a surface of silica sand dunes. The structure will be supported with a sand basis and the top surface will be solidified. Solar-sinter by Markus Kayser can be taken as a case study and innovative approach in the solar-sintering method. Granule consolidation is widely used for industrial purposes as a soil stabilizer. There is a large number of liquid binders (natural and artificial) that can be applied for granular materials solidification. The granule consolidation is used ‘to develop sufficient interaction forces between solid particles to allow for agglomerate growth’. [4] The result of the chemical reaction can perform remarkably differently and depend on the type of granular material and liquid binder as well as on percentage by weight of material components. This method is applied in brick manufacturing with variety of different binders, for example fly ash with water. Another good example of discrete approach is ‘Hy-fi’

Granular materials Solidification Crystallizing

Liquid binder

Sintering

Onsite Sintering

Casting Discrete Fired bricks Components

Non-discrete

Discrete

Cob Rammed Earth Wattle and Daub 3D contouring

Adobe Mudbricks Compressed Earth Blocks

Alginate Polypavement Cement Rubber Natural Glue

From top left clockwise.

Bacillus Pasteurii

Non-discrete

Discrete

Beehive houses at Hamah. [5] Solar Sinter, Markus Kayser, 2011. [6] Hy-fi, David Benjamin, 2014. [7] Nubian Vaults in Africa. [8] Flight Assembled Architecture, Gramazio & Kohler, 2012. [9] Dune, Magnus Larsson, 2008. [10]

Multi-robotic construction system for unfired soil masonry

pavilion by David Benjamin. The pavilion is represents a bio-design solution from organic blocks. All bricks are fabricated through a mixture of discarded corn stalks and specially developed living root structures from mushrooms. The same liquid binders can be used for non-discrete and discrete approaches, but control over structural performance will be an advantage in the first one. For example, higher amount of binder can be applied in required areas according to a structural analysis. The project â&#x20AC;&#x2DC;Duneâ&#x20AC;&#x2122; by Magnus Larsson can be mentioned as an outstanding example of non-discrete approach where Bacillus Pasteurii bacteria was used to solidify dune surface. As researchers says, it will take a week to saturate the sand enough to achieve a solid sandstone structure. Granule consolidation can provide variety of bio-design solution, but at the same time it will always require an additional material for the fabrication or assembly process. Architecture requires variety of assembly strategies for different purposes and material applications. Assembly issues have to be embedded at the early stage of design as an important input of a final design methodology. The goal is to simplify fabrication and assembly methods with increasing quality of structural performance. In this case, the main difference in discrete and non-discrete approaches is gaining complexity on different stages of design process. Design of a system that is based on discrete elements will force to add complexity at the fabrication level. Of course, it can be simplified towards identical building blocks, but still it will require fabrication process to be developed and performed. Also, the fabrication method can gain complexity to keep design freedom where each component can become customized using parametric design approach and robotic assembly strategy. For example, double-curve blocks or components need to be casted to achieve synclastic or anticlastic curvature. However, the assembly process will be relevantly simple because of predefined geometry of each element and exact place of an element according to the final design. The assembly strategy for non-discrete material deposition would follow a different logic, in which fabrication and assembly processes are merged into the same phase. In this case assembly process will gain complexity, but erase the prefabrication step. This strategy can be more convenient in terms of assembly logics and facilitate the potential utilisation of robotic agents to directly perform construction on site.

Different binding mechanisms. Redrawn. [11]

Granular materials construction

Energy Consumption Recycling, biodegradable Abundance Fireproof Durable

Labor intensive Slow

a) solid bridge and particles are composed by the same materials. b) particles and bridge have different composition.

Crystallizing

-Chemical reaction -Hardering binders -Crystalization of dissolved substances -Deposition of suspended particlesa -Liquid bridges

- Assembly process - No additional material - Durable - Low-tech

Sintering

-Sinter bridges -Partial melting -Crystalization of soluble substances

- Assembly process- No additional material - High structural performance

Multi-robotic construction system for unfired soil masonry

- Size of the robot - Amount of energy - Scale

Liquid binder

c) agglomeration of particles characterized by the formation of binder bridges.

-Chemical reaction -Hardering binders -Highly viscous binders -Adsorption layers

- Assembly process - Control over structural performance

- Additional material

Soil mineralogy

‘Soil is any uncemented or weakly cemented accumulation of mineral particles formed by the weathering of rocks as part of the rock cycle, the void space between the particles containing water and/ or air’ [12]. It is then transformed into sedimentary rock, within a process called lithification, due to cementation between particles displaced by deposition and compression of soil. Particles can vary in size and composition, with diameters that span from 0.001 mm to 100 mm. The structure that derive from interlocking of particles and their frictional contact with each other in a solid state is called single grain and it does not request any chemical bond. Chemical weathering is the responsible for the formation of particles with crystalline arrangement and size less than 0.0002 mm. In this dimension, often referred to as colloidal size, small particles determine the plastic behaviour of soils, derived from cohesion between granules and their chemical composition and micro-structure. Loam is the scientific term for defining earth used as building material and it is composed by a mixture of clay, silt and sand, plus occasionally larger aggregates such as gravel and stones. [12] Techniques that employ this particular material are those related with mud bricks, adobes, soil blocks and rammed earth, all of them realised without any baking process. Compared to industrialised construction materials, loam presents few disadvantages. Given the on-site extraction, loam is not a standardised material, meaning that different sites would mean different composition of the soil, modifying therefore approaches and techniques for building. In addition to this, since moisture is requested to activate the colloidal properties of the material and to increase workability, during evaporation of water shrinkage cracks occur, For similar reasons, loam is not water-resistant, generating the need of sheltering it against rain and frost, especially in temperate areas. On the other hand, loam offers many advantages, such as natural balance of air humidity in enclosed environments. Indoor climate is regulated by the capacity of loam of absorbing and desorbing water from the air more than any standardised material. If the relative humidity of a room made of unbacked bricks is raised from 50% to 80%, moisture absorbed during two days is double the amount than it would be with baked bricks and ‘the first 1.5 cm thick layer of a mud brick wall is able to absorb about 300 g of water per m2 of wall surface in 48 hours’ if the humidity is raised [12]. With loam is possible to store heat during high temperature diurnal hours and release it when radiation is lower, balancing indoor climate. The energy and footprint deriving from the utilisation of on-site loam is contained thanks to the minor involvement of preparation, transportation and handling of typical industrialised materials. Furthermore, dry loam is completely recyclable and reusable employing water, generating no waste during the construction process. Finally, other than removing water solved pollutants in the air and preserving organic building materials such as timber, loam is ideal for self-construction through inexpensive equipments and non-professional intensive labour.

Soil triangle. Allows soil texture identification through ratios of particles types. [13]

Soil particles sizes. [12]

Multi-robotic construction system for unfired soil masonry

Soil phases

‘The basic structural units of most clay minerals’ are a silicon-oxygen tetrahedron and an aluminiumhydroxyl octahedron and ‘do not exist in isolation, but combine to form sheet structures. The tetrahedral units combine by sharing of oxygen ions to form a silica sheet’, while ‘the octahedral units combine through shared hydroxyl ions to form a gibbsite sheet. Layer structures then form by the bonding of a silica sheet with either one or two gibbsite sheets. Clay mineral particles consist of stacks of these layers, with different forms of bonding between the layers.’ [12] At the level of the macro-fabric, all soils may be idealised as a three-phase continuum, the phases being solid particles, water and air. The relative proportions of these three phases are controlled by the closeness of particle packing, described by the voids ratio, water content and saturation ratio. ‘Layers of water molecules are held around a clay mineral particle by hydrogen bonding and (because water molecules are dipolar) by attraction to the negatively charged surfaces. In addition, the exchangeable cations attract water (i.e. they become hydrated). The particle is thus surrounded by a layer of adsorbed water. The water nearest to the particle is strongly held and appears to have a high viscosity, but the viscosity decreases with increasing distance from the particle surface to that of ‘free’ water at the boundary of the adsorbed layer. Adsorbed water molecules can move relatively freely parallel to the particle surface, but movement perpendicular to the surface is restricted.’ [12] When heat is applied to a mass of totally saturated clay, the liquid phase starts to evaporate. During this process, solid particles get closer to each other decreasing the plasticity of the material. Once reached the state of partially saturated soil, solid particles are bonded by the remaining water molecules and empty volumes within the mass are occupied by air. The ratios between volumes of each phase within a unit or material are responsible of physical properties of the material, such as porosity and saturation. [12] Throughout this document and in particular during material exploration, clay will be used as medium for experimenting research topics. In doing so, we need to be aware that current applications in construction industry are not possible with any of these phases of soil taken apart, meaning their interaction and proportions are fundamental for solid and durable shelters.

Steps in drying a clay mass, redrawn, [14] and soil variables representing ratios between the upper half and the lower half of the graphs, adapted. [12]

Dry density

Water content

Porosity

Water content

solid particles

water

Dry density

Water content

Dry density

Water content

Porosity

Water content

Porosity

Void ratio

Porosity

Void ratio

Saturation ratio

Void ratio

Saturation ratio

Air content

Multi-robotic construction system for unfired soil masonry

Porosity

air

Void ratio

Saturation ratio

Air content

Void ratio

Saturation ratio

Air Air content content

Silicon-oxygen tetrahedron

Aluminium-hydroxyl octahedron

Layer of tetrahedra

Layer of octahedra

Silica sheet

Gibbsite sheet

Microscopic structure of clay. Drawn. [15]

Bonding Clay mineral

Clay mineral

Single grain structure

Large dickite plates in sandstone, Cretaceous, West of Shetland. [16] Dimensions: ~130 Âľm wide

Multi-robotic construction system for unfired soil masonry

Hygroscopic properties

Sane (left) and dried out (right) mucous membrane section. Redrawn. [17]

Indoor well-being is highly influenced by humidity levels contained in a closed volume. Researchers such as Grandjean (1972) and Becker (1986) showed that being exposed to levels of 40% or less of relative humidity over time can decrease the resistance to colds and similar diseases since the dried mucous membrane is prevented from absorbing dust and viruses before they can reach the lungs. Maintaining the relative humidity up to 70% can generate conditions for reducing fine dust in the air, activating skin protection mechanisms against bacteria and reducing odour and static charge of the object in a room. An higher level of humidity would increase the development of fungi and spores. In any soil, water has the role of binding agent between aggregates. Absorbed and capillary water are naturally released at 105 degrees Celsius, a process comparable with unbaked items production. Structural water undergoes crystallisation and is chemically tied up to 400 degrees Celsius, threshold after which the bond is dissolved. [17] Because of the correlation between water content and behaviour of the material, atmospheric agents may endanger the artefact during construction as much as during the life cycle of the building. Researches [17] show that determining resistance to rain and frost is the development of hairline cracks, whose appearance encourages penetration of atmospheric water into the material. Sandy loam better responds to frost but is not able to withstand rain; clayey loam is susceptible to frost only in virtue of its ease of cracks development and, in optimal condition, is almost rain-resistant.

[g/m3]

300

250

Absorption capacity of 15 mm thick 1 samples at 21 degrees Celsius with a sudden increase of humidity from 50% (top) to 80% (bottom). Redrawn. [17]

250

200

150

100

2 4

2 3

4 5 6

1 Cement concrete M 25 2 Lime-sand brick 3 Porous concrete

48 [h] 4 Lightweight bricks 5 Solid brick 6 Clinker brick

1 Clayey loam 2 Clayey loam plaster 3 Spruce, planed

48 [h] 4 Lime-cement plaster 5 Gypsum plaster

[g/m3] 300

250

200

150 1

100

2 4

2 3 4

5 6

ent concrete M 25 -sand brick us concrete

48 [h] 4 Lightweight bricks 5 Solid brick 6 Clinker brick

1 Clayey loam 2 Clayey loam plaster 3 Spruce, planed

Multi-robotic construction system for unfired soil masonry

48 [h] 4 Lime-cement plaster 5 Gypsum plaster

35 100% 30 80%

25 20

Relative humidity

Water content in air [ g/m3]

Carrier Diagram and linear shrinkage and drying period of lean loam mortar (clay 4%, silt 25%, sand 71%) with a slump of 42 cm. Redrawn. [17]

60%

15 40% 10 20%

0% -10

-5

Temperature [°C]

30 Water content W [%]

Linear Shrinkage [%]

Water content W [%]

Linear Shrinkage [%]

0.5

1 A

1.5

1 A’

B’

2.5 20

Drying time t (d) A Water content at 20/81 B Water content at 20/44 A’ Shrinkage at 20/81 B’ Shrinkage at 20/44

2.5 20

Drying time t (d)

A’

B’

1.5

A Water content at 20/81 B Water content at 20/44 A’ Shrinkage at 20/81 B’ Shrinkage at 20/44

Water absorption curves in different composition loams and drying period for loams. Redrawn. [17]

Water absorption w [kg/m2]

0.5 2 3

0.4 25

11 8

7 9 6

0.3 2

0.2

5 10

0 0

1 1 2 3 4 5 6 7 8 9 10 11 12

Time t [min]

Clayey loam + sand Clayey loam + 2% cement Clayey loam + 4% cement Clayey loam + 8% cement Lightweight mineral loam 650 Lightweight mineral loam 800 Lightweight straw loam 450 Lightweight straw loam 850 Lightweight straw loam 1150 Clayey loam Silty loam Sandy loam

Multi-robotic construction system for unfired soil masonry

Water content [g/m3]

1 3

0.1

6 7

0.0 0

Drying time [d] 1 2 3 4 5 6 7

Sandy loam 1900 kg/m3 Silty loam 1950 kg/m3 Straw loam 1200 kg/m3 Straw loam 550 kg/m3 Straw loam 450 kg/m3 Mineral loam 750 kg/m3 Mineral loam 600 kg/m3

Construction techniques

Differently from other materials, wet loam and soil in general are liable of being formed into any shape without the employment of complex equipments. Direct forming of wet loam is widespread in the world, especially in Africa and Asia, and consists of directly utilisation of the prepared mixture on site. Its main disadvantage is the ease of cracks formation due to levels of linear shrinkage about 3%-6% for loam with 10%-15% of clay content or more for lager amount of clay and water. Traditionally, shrinkage cracks are prevented or controlled embedding pre-designed cracks of smaller dimensions and using curved element. Plastic loam is directly placed by ramming, beating, pressing and throwing. In southern India, for example, earth is often mixed with water to form paste to be transported on site and applied on the wall. Then, by hands, the material is spread along the objects being continuously built in layers of 2-4 cm, process facilitated by the sun quickly drying the material. In north Yemen, wet loam has been employed to build multi-storey houses with a technique called ‘zabur’, in which clods of straw loam are formed by hand and strongly thrown on to the wall, in such a way that additional compression of the material with tools is only requested at the end of the process. [20] Moving to applications that rely on mechanical tools to be implemented, wet loam has been also used in techniques such as the ‘stranglehm’ (‘loam strand’) developed in 1982 by the Building Research Institute in Germany. Here, wet loam profiles of 8 x 16 cm in section are fabricated using an extrusion machine that can produce 2 meters of element per minute. The extruder employed is activated through a worm gear that, after the earth is mixed with water, pushes the material through its cross-section. [20] The amount of clay in the mixture needs to be about 15% in order to allow safe manipulation of the elements during construction, operation conducted easily stacking the profiles above each others, compressing and finishing the joints by hand and using a stick. In the same way of totally manual techniques, there is a maximum amount of layers that can be built before letting the material dry: only 3 to 5 layers per day are built. Otherwise, the incremental weight added by successive layers would squeeze the profiles, causing instability and local variations in performances. Furthermore, long elements are not suggested as shrinkage of 3% to 5% is most likely detectable.

Variations of external and internal walls using ‘stranglehm’ technique. [17]

From top left clockwise. Wet loam bench and cracks after drying. [17] Multi-storey house built with â&#x20AC;&#x2DC;zaburâ&#x20AC;&#x2122; technique, Yemen. [17] Walls made of extruded loam profiles, University of Kassel, 1982. [17]

Multi-robotic construction system for unfired soil masonry

From top left clockwise Transportation of profiles. [17] Interior wall made with loam profiles. [17] Finishing process with wet sponge. [17] Sculptured joint between elements. [17]

Wall made of loamfilled hoses that act as heat storage and humidity balance mechanism. [17]

When low costs and rapid construction are desired, loam is used as filling material for hoses or bags. Using plastics or fabrics allows to fabricate nearly standard elements filled with earth, rendering the construction process faster and independent from specialised skills. The material used as membrane and its thickness determines how loam dries and its resistance to compression. Fabrics would assure fast drying time but large weight deformation during construction whereas using plastic material would increase the number of buildable layers in virtue of the tension that the membrane deploys as a response to weight addition. Contrary to the â&#x20AC;&#x2DC;stranglehmâ&#x20AC;&#x2122; technique, the utilisation of light-weight mineral loam and elastic cotton hoses has the advantage of increasing plasticity of the elements while providing ease of sculptural manipulation. Made by 70 cm long elements, 3 to 5 layers can be stacked per day, or more with the addition of cement for reducing drying time. Polyester fabrics, jute or sugar and flour bags are employed for their ease of supply at low costs and are typically used for long elements filled with sand or earth.

Multi-robotic construction system for unfired soil masonry

Earth-filled hoses dome, Kassel, Germany. [17]

Fabrication and manipulation of loamfilled hoses. [17]

Earth-filled hoses dome, Kassel, Germany. [17]

Fabrication and manipulation of loamfilled hoses. [17]

Multi-robotic construction system for unfired soil masonry

[1] Heath, A., Walker, P., Fourie, C. and Lawrence, M. (2009). COMPRESSIVE STRENGTH OF EXTRUDED UNFIRED CLAY MASONRY UNITS. Proceedings of the Institution of Civil Engineers: Construction Materials, 162 (3), pp. 105-112. [2] Sruthi G. S. (2013). MUD ARCHITECTURE. Department of Applied Mechanics and Hydraulics. National Institute of Technology Karnataka. Karnataka, India [3] Johari I., Said S., Hisham B. , Bakar A., Ahmad Z. A. (2010). EFFECT OF THE CHANGE OF FIRING TEMPERATURE ON MICROSTRUCTURE AND PHYSICAL PROPERTIES OF CLAY BRICKS FROM BERUAS (MALAYSIA). School of Civil Engineering, University Sains Malaysia. Penang, Malaysia. [4] Simons S.J.R., Fairbrother R.J. (2000). DIRECT OBSERVATIONS OF LIQUID BINDER–PARTICLE INTERACTIONS: THE ROLE OF WETTING BEHAVIOUR IN AGGLOMERATE GROWTH. Powder technologies. pp. 44-58. [5] Demeter D. (2013) BEEHIVE HOUSES. Hama Region. Syria. In Flickr profile. https://www.flickr.com. [6] Kayser M. (2011). SOLAR SINTER. Egypt. www.markuskayser.com [7] Graves K. (2014). HY-FI BY BENJAMIN D. MoMA PS1. New York, USA. [8] United Nations Framework Convention on Climate Change. (2014). NUBIAN VAULTS. http://unfccc.int/ [9] Gramazio F., Kohler M. (2012) FLIGHT ASSEMBLED ARCHITECTURE 2011-2012. FRAC Centre Orléans, Orléans, France. http://www.gramaziokohler.com/. [10] Larsson M. (2008). DUNE. Architectural Association, Thesis. http://www.magnuslarsson.com/ [11] S. J. Antony, W. Hoyle, Y. Ding. (2004). GRANULAR MATERIALS: FUNDAMENTALS AND APPLICATIONS. Royal Society of Chemistry [12] Knappett J., R.F. Craig. (2012). CRAIG’S SOIL MECHANICS, Eighth Edition. [13] United States Department of Agriculture. SOIL TRIANGLE. Natural Resources Conservation Service. [14] Norton F.H. (1976). CLAY, WHY IT ACTS THE WAY IT DOES, Studio Potter, Vol. 4, Num. 2. [15] Jordán A. (2014). LIGHTENING THE CLAY, http://blogs.egu.eu/

[16] Sample by Russell Gray, photo courtesy Evelyne Delbos, James Hutton Institute, LARGE DICKITE PLATES IN SANDSTONE, Cretaceous, West of Shetland, Image reproduced from the ‘Images of Clay Archive’ of the Mineralogical Society of Great Britain & Ireland and The Clay Minerals Society (www.minersoc. org/gallery.php?id=2). [17] Minke G. (2013). BUILDING WITH EARTH. DESIGN AND TECHNOLOGY OF A SUSTAINABLE ARCHI-

TECTURE. Basel. Birkhäuser Verlag.

Multi-robotic construction system for unfired soil masonry

Domain

Robotic fabrication

Multi-robotic construction system for unfired soil masonry

Automation and manufacture

Industrialisation of manufacturing processes has been spreading first in developed countries, later in developing ones, showing great effectiveness in providing goods for the increasing demand in construction materials and building components. Generally, these processes are industrialised, namely enclosing one or more fabrication processes within the same production line, grounded in the contemporary economic models that succeeds in lowering costs only through an increase of production volumes. Results in these terms are achieved through machinery and software design, controlled work environment and countless repetition of highly precise actions. For instance, prefabrication spread in virtue of fast production, low costs and ease of assembly rendering traditional construction techniques not viable solutions within a competitive market. Following high productivity, current industrial activities are cause of hazards and disequilibrium within natural and anthropological systems, employing vast amounts of energy and resources for markets in which the demand has clearly moved far from a logic of necessity. Construction industry contributes to GHG emission statistics in two ways. Initially, industrial production of building components, typical of a rampant global urbanisation, has been involved in the emission of more than 80% of greenhouse gases while distribution, construction and demolition form together about its 14% [1] The large portion of emission produced by manufacturing processes displays disparities of technological innovation rates between industrial sectors as well as limited awareness of the entire life cycle of construction. Because of current similarities between processes in construction and manufacturing, automated and numerically controlled production will be investigated, both in terms of granular material management and embodied energy, aiming at understanding how variations in scale of machinery and products are related to earth and soil manipulation.

Distribution 6%

UK construction industry embodied greenhouse gas (GHG) emissions for sub-sectors in 2010. Adapted. [1]

Construction 5% Refurb/Demolition 3%

Manufacturing 86%

Multi-robotic construction system for unfired soil masonry

Prefabricated masonry

Several applications of prefabrication has been developed from the manufacturing of machines for the production of units for masonry construction. Mechanical and electrical tools are combined into production units able to fabricate portions of buildings by processing raw materials, placing mortar and assembling components. All activities are executed inside a warehouse, from which finished products will be shipped to the site. Guaranteeing timing and economical competitiveness for building blocks of up to 40 kg in mass and allowing fast assembly on site [2], prefabricated systems result more efficient than human labour based masonry in terms of costs and time. On the other side, prefabrication, as all industrialised process, requires high costs for setting equipment and process control softwares, forcing the investor to plan for production volumes, sales amount and price on selected market. The need for plausible forecast causes the plants to be over-sized for justifying the investment, while convenience is reached by the fabrication of identical components and flexibility is denied by trade-off analysis of large volumes. When production of variations of an object is required, removal of current equipment and installation of needed set of tools take time and requires skilled and expensive labour. Large machinery also involve considerable amounts of energy and large working facilities, as well as relative necessities for transportation of manufactured products. On the contrary, prefabrication considerably reduces design flexibility as much as often ignores site specificity, promoting supply of finished components produced by distant manufacturers and made of alien materials.

Industrial unit for production of prefabricated masonry components. Large investments and constant production volumes are usually needed for machinery amortisation. [2]

Multi-robotic construction system for unfired soil masonry

Selective laser sintering

A laser beam is focused on powder particles for sintering them into solid material. This process is repeated for each layer in which geometries are decomposed. Where the laser do not intersect the material, powder is not sintered and can be employed as support material to be removed at the end of the process. Adapted. [3]

Laser scanning direction Sintered powder particles

Laser beam

Pre-placed powder bed

Laser sintering

Unsintered material in previous layers

Selective laser sintering is a computer numerical control system to manufacture objects through sinterization of powder by using a laser beam. Plastics, metals, ceramics and glass powder are distributed on a moving bed, representing the first layer. The laser sinters the grains in specific positions, while leaving behind powder that acts as support for the sintered structures. Then, the platform moves downward and a powder delivery system uses a roller to move powder in place of the last layer realised. Repeating this process for all layers, it is possible to fabricate without the influence of gravity on the employed material, allowing fabrication of concentric structures and porous surfaces. As many other automated systems, selective laser sintering needs to be evaluated considering scale as first design driver. Highly engineered processes requesting high precision are normally built within partially closed structures for safety and material stability. Equipment in controlled environment can usually contain costs and energy through easier forecast and control of processes. Scaling such technology for construction purposes would involve energy and material availability analysis as well as time and performances evaluation. On the other hand, in virtue of the natural potential scalability of sequential sinterization of granules, as long as gravity allows, sintered structures can be maintained in place by neighbouring not sintered powder, permitting more control on matter than usual filament deposition manufacturing.

General tools configuration for selective laser sintering applications. A laser is directed toward the powder to process, while pistons and roller are needed for vertically displacing the material and horizontally recharge the building plate of powder. Redrawn. [4]

Multi-robotic construction system for unfired soil masonry

Solar Sinter

Solar Sinter apparatus composed of Fresnel lens and photovoltaic panels. [5]

Application of natural materials and solar energy has significant advantages in ecological and economical studies. Sand is almost an unlimited source of silica in the form of quartz. Silica sand solidifies as glass during the cooling process after it reaches the melting point. This process is known as sintering. This logic became the origin point for developing a Solar-Sinter in combination with 3D printing technologies, combining high-tech technologies and natural resources that are available in deserts. Solar-sinter by Kayser M. has two photovoltaic panels that produce electricity to charge a battery that provides power for motors. Sintering process happens due to Fresnel lens (1.4 x 1.0 meter) that focus a beam of sunlight and produces temperatures between 1400 and 1600 degrees Celsius. Sun-tracking devise moves the lens in x and y directions, and, at the same time, it rotates the machine towards the sun during the day. The focal point of the lens directs on the center of the printing bed where the geometry is materialised. Simultaneously, two motors move a box that contains sand (the printing bed) according to the a path that allows to fabricate the artefact as made of several layers of sintered sand. Another platform lowers the sand box when a layer is finished, permitting to new sand to be loaded and flattened at the focal point. The top layer is just the one that is visible, because an entire structure goes down

during the printing process. After the process is completed, the object is left inside the sand to cool down and then removed from the printing bed and cleaned. As a final result, the glass artefact has a sandy finish and different material performance can be achieved according to sand composition or particles dimensional range. This research looks towards a vast potential of solar energy and naturally abundant materials usage like silica sand. The project has a novel approach in using this widely available recourses and a great potential for the future development. The size of the devise and mobility are important aspects that will be faced as a problem on a bigger scale application and during future investigation.

The focal point of the lens directs on the center of the printing bed where the geometry is printed. [5]

After the printing is completed the structure stays inside to cool down slowly before it is dug out. [5]

Silica sand solidifies as glass during the cooling process after it reached the melting point. [5]

Multi-robotic construction system for unfired soil masonry

Industrial extrusion

Extrusion is a manufacturing process employed in fabrication of objects with specific cross sectional area. During the process molten metal is forced into a closed shaped die and the methods with which force is applied to the material determines categorization and material properties. Several types of extrusion are used in engineering and industry, categorized according to temperature, direction, equipment. Aim of this chapter is to provide an overview on extrusion processes compared from the perspective of forces application on molten (or viscous) material. In extrusion process, the volume of material to extrude with round or square cross-section,the billet, ‘is placed in a container, pushed through the die opening using a ram and dummy block’ [6], hydrostatic pressure or mechanical drives. Displacing agent and material to extrude are both in movement. Direct or forward extrusion presents a billet that moves along the same direction of force application with ram or similar. Friction, generated between billet and container, varies with ram dimensions. Before extrusion, the billet is compressed to the size of the container and during extrusion friction tends to decrease as amount of material inside the container does. ‘Direct extrusion is employed for generating solid circular or non-circular sections, hollow sections such as tubes or cups.’ [6] Indirect or backward extrusion, a moving die is displaced towards the material to extrude, shaping it in desired sections. Hydrostatic extrusion, contrary, does not include mechanical displacement of material, rather the movement is caused by injection of high pressurised fluids - water, oil, air - able to push the material directly or through a piston. Differently in logic from the previous ones, impact extrusion intermittently releases a weight above material restrained in a bounding box. Within all techniques, direct, indirect and hydrostatic extrusion are the most likely to be employed in on-site construction activities in virtue of their operativity continuity, while hydrostatic extrusion operates through momentary events. DIrect and hydraulic present forces applied towards the material to extrude through the utilisation of a common piston, operated through injection of air in a confined volume behind the piston or through mechanical displacement of a plunger. Both methods are valid, as much as different in operational rules. Extruding using a ram or plunger has many advantages in precision and coherence between control of machinery and material to extrude, meaning it is possible to better control the extrusion thanks to the high control that servos and steppers provide. If a liquid is used for extruding, physical equipment is reduced to minima and electronic control is of simpler configuration than using motors. Nevertheless, this application forces to design against leakages of liquids and loss of pressure, increasing need for accurate assembly and sealing processes.

Industrial extrusion methods with variation of displacing agents. Redrawn. [6]

Multi-robotic construction system for unfired soil masonry

Woven clay

The woven clay facade panels with different light permeability were produced using the 3D printing technique and then assembled together. [7]

This research focused on development of a robotic clay deposition strategy that reevaluates â&#x20AC;&#x153;layer upon layerâ&#x20AC;? traditional 3D printing technique. The Harvard GSD Design Robotics Group used traditional clay coil extrusion and additive manufacturing method with robotic setup to create an opportunity for variety of lattice patterning effects. The woven technique was introduced to incorporate both assembly logics and performance qualities. The pattern was designed from liner fiber arrangement in one layers and it was perpendicular to the next one. The variety of facade components with different patterns and light permeability were produced with using this technique and assembled together. Material investigation was the main aspect of the project in relationship to robotic advantages as speed and size control. The clay extruder was developed as end-effector for 6-axis industrial robotic arm. It was important that clay had enough plasticity and easily to extrude at a constant speed, while still providing the stiffness necessary to retain the coil shape [7] and to form interlaced extrusions with consideration of shrinkage rates. Clays with lower shrinkage rates are less prone to cracking in their green state, and are better in maintaining the coil shape, because they contain less moisture at the moment of deposition. [7] Since the behavior of the clay deposition varies depending on the degree of curvature, the rate of curvature was linked to the speeds of the robot [6] and adapted to degree of curvature to create precise extrusion.

Domain / Granular materials

Assembly logic of multiple panels mounted on frames. [7]

The clay extruder was developed as end-effector for 6-axis industrial robotic arm. [7]

Multi-robotic construction system for unfired soil masonry

[1] HM Government (2010). LOW CARBON CONSTRUCTION, INNOVATION AND GROWTH TEAM – FINAL REPORT. [2] Bock T. (2008). CONSTRUCTION AUTOMATION AND ROBOTICS, Robotics and Automation in Construction, Balaguer C., Abderrahim M. (Ed.). InTech. [3] SELECTIVE LASER SINTERING. https://en.wikipedia.org/wiki/Selective_laser_sintering [4] Byrne J. (2013). A BRIEF INTRODUCTION TO 3D PRINTING. Urban Modelling Group, University College. Dublin, Ireland. http://jonathan-byrne.com/. [5] Kayser M. (2011). SOLAR SINTER. Egypt. www.markuskayser.com. [6] Chandramouli R. (2014). TYPES OF EXTRUSION AND EXTRUSION EQUIPMENT. In NPTEL - Mechanical Engineering - Forming. SASTRA University, Thanjavur. Joint Initiative of IITs and IISc – Funded by MHRD. pp. 1-10. [7] Friedman J., Heamin K., Mesa O. (2013). WOVEN CLAY. Harvard Graduate School of Design.

Multi-robotic construction system for unfired soil masonry

Domain

Mobile robots

Multi-robotic construction system for unfired soil masonry

Robustness, scalability and flexibility

In the past decade, considerable research efforts have been invested in the field of cooperation and coordination of multi-robot systems, fuelled by the continuously expanding range of possible applications. One of the main driving forces in the development of such systems is their ability of replacing humans in dangerous or inaccessible scenarios such as toxic clean-ups, the decommissioning of nuclear power plants, extra-planetary ‘exploration, search and rescue missions’, and security, surveillance, or reconnaissance tasks; ‘or in repetitive types of tasks, such as automated manufacturing or industrial/household maintenance’. [1] A robotic system must work fully autonomously in achieving goals. The traditional approach to designing an autonomous robotic system develops a single robot capable of accomplishing particular goals in a specific environment; however, some tasks may require a range of actions or capabilities too wide to integrate into a single robot. Furthermore, time constraints may require certain tasks to be accomplished in parallel, which can be done by having multiple robots working simultaneously. There are three key features offered by multi-robot systems, and which a single robot approach lacks: robustness, scalability, and flexibility. Robustness refers to the ‘ability of a system to gracefully degrade in the presence of partial system failure’ [1]. In order to achieve a robust system, individual units must not exclusively rely on one ‘higher level’ unit for receiving instructions about tasks to execute. Relying on ‘one, or a few, coordinating robots makes the team much more vulnerable to individual robot failures’ [1]. Additionally, robots must be able to relocate tasks whenever other robots fail. This is particularly essential when dealing with a dynamic environment. A system is said to be scalable when it is possible to increase or decrease the amount of agents of the system without having to modify the plan. In order for a robot to be scalable to large collective sizes, all of its operations must work collectively and not require individual attention. These operations include programming (‘instead of plugging in a programming cable to each robot in order to update its program, each can receive a program via an infrared communication channel. This allows an overhead infrared transmitter to program all the robots in the collective in a fixed amount of time, independent of the number of robots’) [3], battery charging (‘rather than manually plugging in each robot to a charger ,they use an automatic charging dock that allows the robots to charge themselves without human help, thus making the robot charging scalable’) [3] and power control. While these ‘scalable operations are essential for collective operations, they should not have a dramatic impact on the robots capabilities, cost, or ease of manufacturing’. [3] The term flexibility refers to the ability of members of a collective ‘to modify their actions as the environment or robot team changes’. By having multiple robots capable of cooperation, it is possible to design the ideal system, which can respond ‘to changes in individual robot skills and performance as well as dynamic environmental changes’. [1] Since the aim of this project is to develop a robotic construction system capable of operating with very limited human interaction and in a range of dynamic environments, a multi-robot system is a suitable approach.

Termites working on a mound. Small balls, consisting of a mix of earth and saliva, are brought by the workers to extend the construction. Soldier ants equipped with gigantic heads and well-fortified pincers watch over the workers. [4]

Multi-robotic construction system for unfired soil masonry

Collaborative behaviour in natural systems

Social insects, those that live in colonies such as ants, bees, wasps and termites, are capable of integrating simple individual activities into complex, highly coordinated systems without requiring any supervisor. This collective or swarm intelligence gives them the ability to construct specialized shelters with a higher degree of complexity than any of its individual builders and inhabitants. The designs for those shelters are embedded within the behavior of every individual insect, but the only way for these inherent traits to lead to general reproductive success is through cooperation. â&#x20AC;&#x2DC;Theories of self-organization (SO), originally developed in the context of physics and chemistry to describe the emergence of macroscopic patterns out of processes and interactions defined at the microscopic level, can be extended to social insects to show that complex collective behavior may emerge from interactions among individuals that exhibit simple behaviorâ&#x20AC;&#x2122;. [1] Swarm intelligent systems are flexible, which means that they are capable of adapting to changing environments, as well as robust, which gives them the ability to function even though some individuals may fail to perform their tasks.

Australian Spinifex termites mound. This towers can reach heights of more than six meters. A single structure can accommodate two or three million termites. The chimney-like form serves as part of a ventilation system that maintain temperatures around 30Â°. [4]

Median wasps building a masticated wood shell and a nest. The paper-like construction reaches a maximum size of thirty centimeters. The external cover consists of closes air pockets Three to six honeycomb levels, with up to 1,800 cells, are incorporated inside. [4]

Multi-robotic construction system for unfired soil masonry

TERMES

Each robot is able to carry one block at a time dislocating onto the ground or climbing other blocks. [5]

TERMES is a hardware system aimed at researching automated construction by multiple robots. Passive building blocks are liable of being moved and positioned by small robots to generate stable structures. The robotic agents are able to lift and stack the blocks to be used as building components as well as scaffolds to be eventually removed. The projects demonstrates the ability of the robots to perform autonomous construction showing the formation of structures that are sensibly larger than the robots themselves, underlining effectiveness of swarms applications in scalability arguments. Further on, a decentralised control algorithm is developed in order to allow the user to input a high-level description of the desired geometry. The latter is decomposed into a series of brief logical steps consisting of the displacement of one single block, giving to unspecialised users the freedom of defining a geometry without having to manually evaluate the entire sequence of steps for each inputted disposition of the components. Influenced by termites, the units are designed towards simplicity: basic tasks are performed thanks to few actuator and sensors (10 and 3 respectively) and dispose only of local instructions that the agents autonomously follow while avoiding interference with their counterparts. [5] Given the ability of the robots of climbing over height of one block, great attention is given to the evaluation of paths and sequence of blocks displacement that do not present the possibility of having one or more units stuck between insurmountable stack of two or more blocks.

System overview. One physical robot atop a six-block structure and render of multiple units collaborating. [5]

Automation of collective collaboration. The user specify a desired final structure, consequently subdivided into paths. [5]

Multi-robotic construction system for unfired soil masonry

Spatially targeted communication

A schematic highlighting spatially targeted communication. Each flying robot communicates with a subgroup of ground robots. [6]

This project, by N. Mathews, A. Lyhne Christensen, R. O’Grady and M. Dorigo introduces ‘spatially targeted communication – a communication method for multi-robot systems. This method allows an individual message sending robot to isolate selected message recipient robots based on their spatial location’ [6], making possible to control multiple units in achieving positioning tasks. ‘The recipient robots can then be sent information targeted solely at them, even if the sending robot uses a broadcast communication modality’. [6] They also address spatially targeted communication employing ‘heterogeneous multi-robot system’ made of flying and ground ‘self-assembling’ units, the first taking advantage of their wider view of the terrain for collecting, analysing, elaborating and communicating information about tasks to be executed, above all expressed in form of morphologies to pursue, to their ground based counterparts. [6] .

Frames showing a flying robot instructing ground robots how to overstep an obstacles by cooperating through a self-assembled linear morphology. [6]

Example of morphologies that can be formed by the self-assembling robots. [6]

Multi-robotic construction system for unfired soil masonry

[1] Parker L.E. (1994). HETEROGENEOUS MULTI-ROBOT COOPERATION. No. AI-TR-1465. Massachusetts Institute of Technology. Cambridge. Artificial Intelligence Lab. [2] Seyfried J., Szymanski M., Bender N., Estana R., Thiel M., Wörn H. (2004). THE I-SWARM PROJECT: INTELLIGENT SMALL WORLD AUTONOMOUS ROBOTS FOR MICRO-MANIPULATION. In International Workshop on Swarm Robotics. Springer Berlin Heidelberg. (pp. 70-83). [3] Rubenstein, Michael, Christian Ahler, Radhika Nagpal. (2012). KILOBOT: A LOW COST SCALABLE ROBOT SYSTEM FOR COLLECTIVE BEHAVIORS. In Proceedings IEEE International Conference on Robotics and Automation (IRCA 2012). May 14-18. Saint Paul, Minnesota, 3293-3298. Washington, D.C. Computer Society Press of the IEEE. [4] Tautz J. (2013). ANIMAL ARCHITECTURE. Abrams. New York. [5] Petersen K., Nagpal R., Werfe, J. (2011). TERMES: AN AUTONOMOUS ROBOTIC SYSTEM FOR THREE-DIMENSIONAL COLLECTIVE CONSTRUCTION. Proc. Robotics: Science & Systems VIImensional Collective Construction. [6] Mathews N., Christensen A.L., O’Grady R., Dorigo M. (2012). SPATIALLY TARGETED COMMUNICATION AND SELF-ASSEMBLY. In 2012 IEEE/RSJ International Conference on Intelligent Robots and Systems. IEEE. pp. 2678-2679.

Multi-robotic construction system for unfired soil masonry

Domain

Robotic construction

Multi-robotic construction system for unfired soil masonry

On-site automation

For the purpose of clarification, robotic construction is here intended as ensemble of techniques and methods for construction purposes by utilisation of automated systems and machines during manufacturing as well as, if needed, assembly processes. Differently from manufacturing processes for construction materials, we are referring to any method that makes use of robotic agents on site to perform construction tasks in medium and large scale, autonomously or not, starting from a digital representation of the object to build. Implications of CNC and rapid prototyping in construction are currently appearing positive in terms of flexibility and costs. These methodologies rely on informatically computed geometries that, after being evaluated in virtue of tests on their material counterpart, are generated through the manipulation of granular material. Real-time feedback between fabrication and construction can be achieved and control of the final outcome reached with a precision that mostly depend on material and scale employed. Other than facilitating the realisation of multiple designs with the same system, numeric control applications better react to local needs and site characterisation. Where conventional construction ask for selected skilled workers and rudimentary tools, prefabrication reduces necessary competences and relies on large amount of agents for the execution of instructed and standardised tasks. Due to its adaptability and coherence with local conditions, robotic construction promises similar costs to prefabricated solutions and emergency architecture. These two categories, apparently following different logics, share attention in economy of materials employed and tend to direct great attention toward recycling of material. Yet, emergency architecture, due to its innate significance of sheltering need, has great potential for employing robotic construction for computing optimal solutions disposing of limited resources.

labor intensive slow dangerous costly and over budget wastefull and emission causing

Fraction of cost and time Safe Architectural flexibility Use of in-situ materials material and energy efficient

Correlation between cost and architectural flexibility in robot based construction CO2 Emissio processes. Adapted. 7.00E+05 [1]

Conventional

cost

Prefab (modular)

Prefab (manufactured) Robotic Construction Emergency

architectural flexibility

20% - 25% Financing Traditional construction

Short project length Robotic construction

25%labor - 30% Material intensive

Lean Fraction processof cost and time

slow 45%dangerous - 55% Labor costly and over budget wastefull and emission causing

0.00E+00 Traditional Robotic Construction*

Safe Architectural flexibility Automation Use of in-situ materials material and energy efficient

Khoshnevis B. Journal of Automation in Cons AUTOMATED CONSTRUCTION BY CONTOU

20% - 25% Financing

Short project length

25% - 30% Material

Lean process

45% - 55% Labor

Automation

Multi-robotic construction system for unfired soil masonry

GHG emissions

Construction issues related to physical damages of workers and users, including accidental greenhouse emissions and hazards at work, are perfect contestants for automation and robotic applications. Emissions of gases such as carbon dioxide have slowly contributed to major changes in the environment and are currently causes of illness in many biological organisms. Embodied energy is usually referred to as all the energy involved in the production of a good or service, meaning the energy requested by all participants in the construction process. It is often used as a measure of emissions for specific industrial production chains from supply of material and manufacturing to distribution and transportation. A comparative analysis between the life-cycle embodied energy and CO2 emissions of a concrete wall built by two different methods, automated Contour Crafting technology and a standard manual construction process using concrete masonry units, shows a significant reduction both in CO2 emissions and in total embodied energy when using the automated process (75% and 50% respectively). [1] This is possible due to several factors ascribable to different management of material and alternative technologies compared to current industrial activities. On the one side, the viscosity of the extrusion and the ability of the machine to deposit material along specific patterns allows to consistently reduce material employment and waste. On the other side, equipment used is powered by electrical energy and does not require large amount of energy because the material is placed on site and transportation is reduced to its minimum.

nd time Safe exibility aterials efficient

Embodied Energy

CO2 Emissions 7.00E+05

2.00E+04

0.00E+00

CO2 emission and embodied energy in robotic fabrication processes. Adapted. [1]

ction

Traditional Robotic Construction*

Non-residential buildings 18%

Residential buildings 27% Construction process 10% Khoshnevis B. Journal of Automation in Construction – Special Issue: The best of ISARC 2002, Vol 13, Issue 1, January 2004, pp 5-19. AUTOMATED CONSTRUCTION BY CONTOUR CRAFTING –RELATED ROBOTICS AND INFORMATION TECHNOLOGIES

Proportion of total UK CO2 emissions that construction can influence, referring to amount of people that use and buy related goods and services. Construction process contributes are manufacture (8%) and on-site distribution operations (2%). Redrawn. [2]

Other 44%

Multi-robotic construction system for unfired soil masonry

Site safety

Construction industry is main contributor to total deaths and injuries happening at work places, specifically building sites and warehouses. According to an investigation performed on work accidents in China in 2015, 35% of them, the largest sector share, occur in the construction industry while 11% in manufacturing. Differently from manufacturing, in which work environments are mostly controlled and regulated by safety procedures, construction activities take place on site and rely on contemporary ‘facilities, machinery equipment and structural’ elements ‘at high elevated place’ [3], as well as horizontal and vertical movement of heavy loads. In addition, even where verbal or written instruction of safety procedures are listed and imposed, ‘inadequate plans’ and workers’ negligence cause the presence of several tools, packaging and waste material all over the work area, rising the chances of what in Japan is defined as ‘hiyari-hat’ (near-miss), that is ‘a worker’s experience that, luckily, does not result in injury, although under slightly different circumstances, it might have led to a work jury and/or property damage.’ [3], mainly related with stumbling or slipping, physical conditions of workers, people falling ‘or being struck by falling objects’ [3]. Construction automation allows to minimise accidents at work in virtue of less manpower involved and higher degrees of control that users are liable of implementing on employed hardware. Differently from traditional techniques, machinery needs less energy and, because of the higher precision, material is placed where necessary, reducing the amount of tools and material provisions scattered along the construction site, therefore reducing possibilities for operators to incur injuries.

Caught in or between 9.4%

Struck by objects 6.4% Struck by falling objects 6.4%

Collapse (earth falls) 10.6%

The causes of all fatalities in 1992 in the Japanese construction industry. Redrawn. [3]

Other 11.8%

Traffic accidents 13.1%

Person falling 42.9%

Type of Hiyari-Hat

Stumbling or slipping Backache, sprain or strain Person falling Struck by falling objects Step on sharp objects Traffic accidents Exposed to electric shock Misoperate machinery equipment or tools Struck by or against objects Caught in or between Abraded or rubbed Collapse (earth fall, etc.) Other

Multi-robotic construction system for unfired soil masonry

Frequency

Percent

1428 974 737 647 629 548 285 377 267 196 189 141 317

14 10 7 6 6 5 3 3 3 2 2 1 3

Reported frequency of hiyari-hat occurrence from workers with average age of 41 and an average work experience of 13 years. [3]

Prior art overview

Correlation of robotic unit complexity with scale of fabricated or constructed product. The overview is build as a tool for comparing hardware complexity of robotic units involved in fabrication and construction processes to the dimensions of produced artefact. Machines such as industrial robots are able to produce objects that most likely do not oversize them, while applications in which small ground robots are used, scalability is possible thanks to cooperation between agents and decentralised control. In other cases, robot of medium scale are employed for executing building tasks on site, relying on human intervention for supply of material and initial positioning.

robot complexity

Robotic Construction Processes

Solar Sinter 2011

Living Screen 2015

WovenClay 2014

Approach to Automated Construction Using Addaptive Programming 2014

ICD Aggre Pavillio 2015

2013 Pylos Giannakopoulos Iaac, Barcelona Large scale robot Large scale construction 1 unit Contouring Natural soil Extruder

Pylos 2013

mini-builders 2014

Mobile Robotic Fabrication S Filament Structures 2015

Stone Spray 2012

Construction with quadrotor teams 2012

2011 Termes Petersen, Nagpal, Werfel Wyss Institute for Biologically Inspired Engineering, Harvard " Small scale robot Small scale construction Multiple units Blocks Whegs

Termes 2011

colour: relation to our research material

robotic material system manipulation

Contour-Crafting 2004 WovenClay 2014

Approach to Automated Construction Using Addaptive Programming 2014

ICD Aggregate Pavillion 2015

Rock Print 2015 2014 Minibuilders Novikov, Jokic, Jin, Maggs, Nan, Sadan Iaac, Barcelona Medium scale robots Large scale construction

Pylos 2013

3 units Contouring

mini-builders 2014

Mobile Robotic Fabrication System for Filament Structures 2015 2011 Termes

Programmed wall 2006

Artificial marble Tracks, rollers, vacuum generator

Flight Assembled Architecture 2012

SCL 2014

Petersen, Nagpal, Werfel Wyss Institute for Biologically Inspired Engineering, Harvard

In the next pages some examples of robotic application are presented and listed and color mapped according to area of interest within this research. Material interest is in ceramics pastes extruded thanks to their viscosity and deposited in layer by layer or wireframe approach. Material manipulation refers to the analysis of tools and techniques involved in displacing and positioning the material. Beyond the material, robotic systems are examined in term of interaction between agents and local and global control.

" Small scale robot Small scale construction Multiple units Blocks Whegs

XO 2016

size of outcome

Multi-robotic construction system for unfired soil masonry

Vertical slip forming

Vertical slip forming presents the advantage of reducing displacement of machinery on site and it is mainly used for building vertical structures such as chimneys or silos with constant or changing thickness of walls. Norwegian contractors (1991-1993). Sleipner A for Statoil. Sleipner East gas field, North Sea. [4]

Vertical slip forming involves the development of a traditional construction technique, such as the extrusion of concrete paste, in which the material is cast directly on site rather than in short lifts. While the advantage of building a monolithic structure is followed by high speed and low cost, the initial set-up for the equipment and the need of specialist expertise can represent a prohibitive investment. This method can be employed for several typologies of project, from the construction of high-rise buildings and chimneys, to bridge columns and offshore platforms, in which dimensional accuracy requested is lower than in conventional techniques. The development in height of the section is due to a 1 to 1.2 m high formwork and incrementally lifted by hydraulics jacks at a rate of 150 to 350 mm per hour. [4] â&#x20AC;&#x2DC;The jacks climb on smooth rods or structural tubing embedded in the hardened concrete. Reinforcement is fixed just ahead of the form, which is then filled in layers with concrete. The rate of climb is regulated to ensure that the concrete is self-supporting on emerging yet not so slow that the concrete hardens and binds on the forms.â&#x20AC;&#x2122; [4] Virtually, there is no limit to the height of the building or the area of its cross-section, given the possibility of assembling a larger system from manufacture of modular industrial scaffolding.

Vertical slip forming employs hydraulic jack for gradually moving formworks panels to be filled with concrete. This technique requests less time than usual for construction of relatively simple horizontal section and tall buildings, while its main limits are the initial cost for setting up machinery and the large amount of manpower needed for operating it. Adapted. [5]

Multi-robotic construction system for unfired soil masonry

D-Shape

D-Shape technology makes use of minerals in form of powder and liquid binders for manufacturing large scale artefacts with low carbon footprint. [6]

Enrico Dini and his technology - D-Shape - take advantage of additive manufacturing for developing new methods in large scale construction. Particles of granular materials, usually salt and sand, are bound together using a low-impact two components inorganic liquid binder. A metallic frame hosts a 3-axis CNC system for distribution of sprayed binder above a bed of granular material. Similarly to selective laser technologies, the structure is built layer-by-layer but the outcome of the process generates as a single piece. A first layer of 5 to 10 mm of sand is ejected from above the printing head and distributed within the printing boundary in specific locations. A series of nozzles 20 mm apart from each other ejects liquid binder in selected areas of the sand bed. After 24 hours for drying, the first layer is complete and the process repeated for each layer. An electric piston is used for evenly distributing the sand through vibration. Pieces of art, building blocks, houses and bridges have been designed and fabricated with this technique. On the one side, using granular materials allows to benefit from recycling and waste material from building site, on the other side on-site construction would involve displacement of machinery whose productivity is strongly related to sizes of machine and structure to realise. Producing in factory and assembling on-site as alternative, mindful of industrial prefabrication, requests planning and management of transportation of supply material and shipping of products to the building site.

Custom build CNC are used for depositing liquid binder in specific location within a bed of powder. [6]

Liquid binder is dispensed through multiple nozzle of regular diameter while horizontal axis are displaced. [6]

Multi-robotic construction system for unfired soil masonry

Big Delta WASPS

Delta printing technologies are employed for construction of low cost soil and straw shelters, displacing and depositing viscous soil through three numerically controlled rods and an extruder. [7]

WASPS is a company of 3d printers manufacturer whose first aim is to print low-impact and inexpensive houses with clay and soil. Always using a delta printer for increasing speed and precision, they experimented additive manufacturing with ceramic materials in several scale, until the current construction of a 12 meters structure for printing a 1:1 shelter prototype. Within the small scale they developed a double extrusion system for clay artifacts up to 60/100 cm in bounding dimensions. Mixed material is first pushed driven through a hose by pneumatic extruder powered by an air compressor and consequently deposited after being prompted by a plunger displacing upward and downward thanks to a metal screw. This system avoids air bubble formation and forces maximum output pressure from 4 to 40 bar. On the large scale side, they have been set progressively larger structures for printing of shelters through sequential deposition of layers. Material-wise, a wide range of applications is available, depending on phases of soil mixed and amount of water, and structural performances are comparable with those of traditional techniques involving similar materials. What it does not seem as much viable as desired is the necessity of disposing of a - metallic - frame that needs to be larger than the artifact being fabricated. Delta printers are typically much taller than the printed object, while cartesian ones, although optimised for volumes containment, are not able to solve scalability issues, mainly referred to ratio between cost of industrial setting of machinery and cost and durability of extruded material.

The structure is made of 135 layers for 5 five meters of total diameter and 270 cm of total length of the wall. Each layer weighs 40 tons and needs 20 minutes for being extruded. Consumptions are represented by 2 m3 of water and 200 KWh, that also means around 40 GBP for energy and water. [7]

Rock print

Rock Print is a reversible an architectural installation at the inaugural Chicago Architecture Biennial, Chicago, 2015. [8]

This research investigates the field of granular construction and cutting edge robotic fabrication techniques with the intention of creating a material system based on jammed architecture principles. Granular systems have two structural possibilities, being ‘yield and flow’ or ‘jammed and rigid’. [9] The Gramazio Kohler Research group, ETH Zurich and the Self-Assembly Lab, MIT collaborated for this project. They made variety of tests to develop the strategy and built full-scale prototypes, developing a first robotic experimental set up for jammed structures, where they used up to two industrial robots. Digital fabrication process takes in consideration behavior of the structure during the buildup process. Prototypes were fabricated from controlled aggregation of granular materials (gravel or rocks) and assembled in geometrically predetermined structures as additional frameworks. This creates an opportunity for structure to be reversible and can be simply built from local and recycled materials. This is a new cutting age strategy for sustainable and economical approaches in architecture with minimal material waste, easy to recycle and with variety of geometrical possibilities. Three main strategies where developed in rock printing, slip casting and multi-robot fabrication. Rock printing, based on 3D printing logic, presents granular material (gravel) applied layer by layer onto the printing bed where aggregates are reinforced with a rope for increasing friction between particles. Different types of granular materials were tested, but the hardest particles with the strongest edge condition performed the best during the experimentation. The string reinforcement provided

The structure here presented is realised by depositing a rope while adding particles within rigid boundaries. Once these are removed, friction between gravel and rope allows the particles to stay in place and form the column, until the rope is removed for collapsing the structure. [8]

stiffness and different degrees of freedom of particles. [9] At the same time, the structure gains stability by increasing vertical load and compression force. The loose material fell after the bed was removed, but it performed as a support during the build-up process. Slip casting has the same logic as Rock printing, but the bed is replaced with a conical mould. It was placed on top of printed jammed structure and moved upwards. In this method material was placed in thin layers in the mould and no boundaries conditions, as printing bed, were required. Geometrical possibilities are quite limited in this method and mainly represented by circular column prototypes. Square and complex geometries outlines were also tested, but were harder to aggregate successfully. Multi-robot fabrication is a mix of rock printing and slip casting that is defined as a main strategy for scaling up. Two robotic arms robots were working in collaboration, one moving a mould and another depositing the string. The global geometry consisted from columns, which were partly blended between each other during the printing process. Jammed architecture principles were investigated and challenged during this research, but there are still a lot of geometrical limitations, scaling up complexity and robotic mobility.

Multi-robotic construction system for unfired soil masonry

Minibuilders

Minibuilders tries to exploit additive manufacturing and robotics for conceiving a construction process that minimise need of human workers and scalability issues for large scale buildings. [11]

Current fabrication technologies are highly standardized [10] and the cost of construction increases if customize elements are used. Additive manufacture gives variety of possibilities that can be applied in construction and fabrication industries. Three-dimensional printing is mostly used for small-scale objects and the main reason is the size of the machine and positioning device. This research investigates the Fused Deposition Modeling (FDM) method and proposes a system that consists mobile additive manufacturing devices. This multi-robot system can produce objects, independently from the size of the employed machines. The construction process was divided into three steps that were represented in three devices with different functions. The Foundation robot performs the first step and prints the base layers. This robot has sensors to recognize ‘curves on the ground and enables steering’ [11]. Also, it has actuators for positioning the nozzle according the height of printed layer. As a next step, the Grip robot attaches to the printed foundation by clamping between four rollers. It has rotation and steering actuators ‘that allows to position robot precisely over the structure’ [11]. The Vacuum Robot is applied after the structure is finished to reinforce it. The device ‘attaches onto the surface by using vacuum generator and a suction cup’ [11]. All robots have an ability to change the speed of movement and material extrusion speed.

The relationship between two parameters created the variety of possibilities with different thickness of extrusion and layer width. Also, the devices can perform continuous and discontinuous locomotion, according to the design requirements. This project achieved a significant robotic performance with developing methodology that can be applied on-site. It is a novel approach of using a multi-robot system and additive manufacture technique in construction industry. At the same time, the Grip robot need to be placed at the right position by humans at each step of the process and communication and awareness between robots were not developed.

Foundation robot is released on the ground for extruding the first layers on which the structure will be built. [11]

Grip robot is manually placed and fixed on foundations for starting extruding material along a spiral, allowing the robot to continuously move along its own extrusion. [11]

Vacuum robot is vacuum attached to the surface for vertically extrusion of finishing and reinforcing elements. [11]

Multi-robotic construction system for unfired soil masonry

[1] Khoshnevis B. (2013) AUTOMATED CONSTRUCTION BY CONTOUR CRAFTING –RELATED ROBOTICS AND INFORMATION TECHNOLOGIES. In Automation in Construction (2004). Vol 13. pp 5-19. [2] HM Government (2010. LOW CARBON CONSTRUCTION, INNOVATION AND GROWTH TEAM – FINAL REPORT. Department for Business, Innovation and Skills. London. [3] Nishigaki S., Lawb K. H. (1994). SAFETY PROBLEMS IN ON-SITE CONSTRUCTION WORK PROCESSES. Technical Research Institute, Hazama Corporation. Department of Civil Engineering, Stanford University. In D.A. Chamberlain (Editor). (1994). Automation and Robotics in Construction XI. Elsevier Science B.V. [4] Norwegian contractors (1991-1993). Sleipner A for Statoil. Sleipner East gas field, North Sea. http://www. hanling.com.sg/. [5] Concrete Society (2012). SLIP FORMING OF VERTICAL STRUCTURES - GCG6. pp. 1-26. [6] D-Shape. LARGE SCALE FREE-FORM 3D PRINTING. http://d-shape.com/. [7] WASPS Project. BIG DELTA WASPS 12 M. http://www.wasproject.it/. [8] Gramazio Kohler Research, ETH Zurich and the Self-Assembly Lab, MIT. [9] Fauconneau M., Wittel F. K., Herrmann H. J. (2015). CONTINUOUS WIRE REINFORCEMENT FOR JAMMED GRANULAR ARCHITECTURE. [10] Jokić S., Novikov P., Maggs S., Sadan D., Jin S., Nan C. (2014). ROBOTIC POSITIONING DEVICE FOR THREE-DIMENSIONAL PRINTING, Institute for Advanced Architecture of Catalonia ,Open Thesis Fabrication. Barcelona, Spain. [11] Jokić S., Novikov P., Maggs S., Sadan D., Jin S., Nan C. (2014). MINIBUILDERS. SMALL ROBOTS PRINTING BIG STRUCTURES. Institute for Advanced Architecture of Catalonia ,Open Thesis Fabrication. Barcelona, Spain. http://archive.monograph.io/iaac/minibuilders.

Multi-robotic construction system for unfired soil masonry

Domain

100

Site selection

Multi-robotic construction system for unfired soil masonry

101

Site identification arises as natural consequence of involved materials such as granular matter in form of soil particles. Since different mineralogic configurations are possible, properties of dry and wet materials rely on grain size and chemical composition, as well as on binder employed. Mineral grains kinematics allows for similar manipulation of any hygroscopic granular phase as long as it is possible to dispose of homogeneous deposition at the end of the process. Climates, temperatures and precipitations across the globe are analysed and cross-referenced with information about soil with high percentage of clay minerals. Dry and mild climates provide a stable background for unbaked soil, a process that is challenged by high saturation ratios. As a consequence, preferred temperature ranges are the ones that go from hot arid to cool summer, in which heat is used in crystallisation processes between solid clay particles. The relationship between the availability of granular material and water and the possibility of using natural heat as drying agent, leads us to look at desertic areas and steppes in which sporadic precipitations are naturally contained by the landscape or by human intervention. In addition, arid climates naturally generate challenges of promising resolution if contextualised in the developing housing crisis as well as in the increasing density of human settlement, with the consequent consumption and reduction of precious resources. Clay powder is here used for simulating clayey deserts conditions and loam for temperate regions with majority of silty soils. Furthermore, clay is the main colloidal agent in soil particles sinterization, allowing for higher resolution and lower utilisation of water than silt and sand composites. Water is fundamental resource for processing of hygroscopic granular matter. If on the one side deposition methods are influenced by the amount of water mixed with soil, on the other side constructed structures would be made of dry soil, material whose morphology continue to adapt to moisture level variations within the atmosphere. Consequently, while in temperate environments the first concern is relative to how a building would react to atmospheric water, in arid deserts the main need is water supply. In these regions almost no water is available on the ground, except for particular cases in which, thanks both to low temperatures and stable or seasonal water basins, ground water is available in restrained areas and time periods. In some regions water is available in form of rainfalls eventually contained in ponds whose capacity depends on dimensions and coefficient of evaporation, in other cases salty waters are available close to construction site. The employment of freshwater would allow high levels of material purity while saltwater would participate in the overall physical properties of the material due to considerable amounts of dissolved salts. Salt particles, as much as silt, sand and clay, have their specific impact on structural properties of the composite material and investigations in this direction are executed within the current architectural and construction research activity.

102

Namib Desert, Africa. ‘Korea’s Kompsat-2 satellite captured this image over the sand seas of the Namib Desert on 7 January 2012. The blue and white area is the dry river bed of the Tsauchab. Black dots of vegetation are concentrated close to the river’s main route, while salt deposits appear bright white. In this image, there appears to be some shadow on the western side. From this we can deduce that the image was acquired during the late morning.’ [1]

Multi-robotic construction system for unfired soil masonry

103

Namib Desert, Namibia, Africa. [2]

Global climates. Adapted. [3]

Atacama Desert, Chile, South America. [4]

Global temperatures. Adapted. [3]

104

Alxa League, Inner Mongolia, China, Asia. [5]

Global precipitations. Adapted. [3]

Simpson Desert. Australia. [6]

Global clay minerals distribution. Adapted. [7]

Multi-robotic construction system for unfired soil masonry

105

[1] KARI/ESA (2013). NAMIB DESERT. http://www.esa.int/ [2] USGS EROS Data Center. (2010). NAMIB DESERT. Satellite Landsat 7. http://www.crdp-strasbourg.fr/ [3] Rubel, Kottek (2010). KÖPPEN-GEIGER CLIMATE CLASSIFICATION. [4] Allende Labbé J. M. (2011). MIÑIQUES. Atacama desert, Chile. In Flickr profile. https://www.flickr.com [5] Xiao Y. (2008). LAKES IN THE DESERT. Alxa UNESCO Global Geopark. China. https://www.flickr.com/ [6] Sidebottom B. (2013). SIMPSON DESERT. In Flickr profile. https://www.flickr.com [7] Soil Survey Division World Soil Resources (2005). GLOBAL SOIL REGIONS MAP. United States Department of Agriculture.

106

Multi-robotic construction system for unfired soil masonry

107

Methods

108

Multi-robotic construction system for unfired soil masonry

109

Control and Dataflow

The research, starting from an insight in robotic construction processes, has its main focus in terrestrial multi robot systems able to perform tasks and routines. At the same time, granular materials are analysed and soils with high ratios of clay minerals investigated, taking in account microscopic structure and traditional construction techniques. An environmental context is selected and evaluated within the design process. Data extracted from research are used in form-finding procedures aimed at generating parametric geometries to be developed, after physical tests, in material systems. Two different approaches towards the control of the robots are proposed. A first exploration, based on the concept of spatially targeted communication, tends to interpret robotic construction as an explicit process. The geometry previously created is discretized and principle stress lines generated. Following a logic of real-time control, paths of movement are assigned to the robotic units and stress lines synthesized through material redistribution. Information is then sent from modelling environment to the processor that control the robots. In this perspective, movement or tasks in the physical world are based on their digital counterparts, liable to be updated by the user in every moment. A design proposal is elaborated, evaluated through environmental analysis and optimised towards multi criteria satisfaction. A second investigation would instead direct more attention towards the concept of emergence and swarm behaviour. Considered as an implicit construction method, the process takes distance from the security of the previous approach, renouncing to control, within certain limits, the final outcome. In other words, instead of defining a design to be physically realized, individual behaviour is embedded in each unit, whose interaction with its counterparts will generate a design. Differently from what previously said, real-time control here is not of interest and local awareness will be uploaded in form of code into the processor of the units. Once activated, robots execute their task until completion and the outcome is structurally and environmentally evaluated. The lack of a global objective forces us to create sets of rules whose related outcomes are the product of local awareness, local interaction and material manipulation. Cellular automata will be addressed in space discretization and rules codification, while agent based environments will be used to simulate swarming behaviour of multiple units implicitly aimed at common objectives.

110

Map of methods and tools involved in the design process.

Research

System Development

Robot

Parametric Form-Finding

Robotic construction

Spatially targeted communication

Geometry generation

Model discretization

Environmental context

FEA

Swarm

Cellular Automata CA

Granular material Soil Clay

Analysis

Structural Analysis

Explicit construction Emergent construction

Multi robot systems

Material

Control/Simulation

Material properties

Material tests Physical computing

Agent Based Modeling ABM

Material system

Environmental Analysis

Prototyping platform Multi-objective Optimisation

Design proposal Real-time control

Rules set upload

Rover processor

Material redistribution

Multi-robotic construction system for unfired soil masonry

111

Parametric Form-finding

Reciprocal diagram of compression vault for visually analysing reciprocal influence of forces along different portion of the structure.

Compression only shells are explored as possible design solution due to the high compressive strength of unfired clay masonry relative to its tensile strength. Such structures have efficient structural forms, which minimize the use of material and can reduce and even eliminate the need for reinforcement. In the past, designers and engineers such as Antoni Gaudi, Frei Otto, and Heinz Isler have developed powerful physical design techniques using hanging cable nets or cloths as form-finding approaches for compression shells, but these techniques are very time and cost intensive [1]. Different computational approaches have been developed in order to ease the design of such structures. [2] RhinoVAULT, a funicular form-finding method based on Thrust Network Analysis (TNA), uses reciprocal diagrams to provide an intuitive and fast way for creating and exploring compression-only structures. Although it is not integrated within Grasshopperâ&#x20AC;&#x2122;s parametric environment, RhinoVAULT is considerably more flexible in terms of geometric possibilities than any funicular form finding method available for designers. â&#x20AC;&#x2DC;By giving explicit, bidirectional control over the internal force distribution and overall geometry to the designer, free exploration of these statically highly indeterminate systems is made possibleâ&#x20AC;&#x2122;. [3]

112

Structural Analysis (FEA)

Force flow and utilisation analysis.

Structural analysis is used to do a comparative evaluation of the iterations produced by the different parameterized geometric models and form finding methods. This evaluation can be used to optimize the modelâ&#x20AC;&#x2122;s parameters in order to generate geometries that are informed by the properties of unfired clay and by a specific climatic and environmental context. The analysis will be conducted with Karamba, a parametric structural engineering tool that is fully embedded in the Rhino+Grasshopper environment. This makes it easy to combine parametric geometric models, finite element calculations and multi-objective optimization algorithms like Octopus. [4]

Multi-robotic construction system for unfired soil masonry

113

Environmental Analysis

Radiation and sunlight analysis.

In an environmental design approach, it is crucial to define environmental factors at the early stage of design because they will drive the design development. Site environmental conditions and a clear understanding of design problems [5] will help to form environmentally responsive design approach. An understanding of environmental data and the ability to visualize it gives a clear connection between the design and environmental data input. Desert or hot climate buildings are exposed to clear-sky during the whole year. Solar rays penetrate into environment generating a non-uniform daylight distribution and high solar heat gain; affecting both visual and thermal comfort. The objective is to harvest daylight while diffusing direct sun rays. [6] The goal is to bring improvements in daylight distribution and orientations during the design process and to form the optimal solution. Solar access Analysis and shadow analysis will be done and evaluated for archiving defined goals. This study will be the main in adapting the material system geometry and orientation according to environmental conditions for human well being in desert climate. Incident solar radiation on a surface will be measured during the solar access analysis. At the same time, shadow analysis is highly important in desert environment where the goal is to increase shadow pattern with diffusing direct sun rays.

114

Multi-objective Optimization (GA)

Fitness landscape representation.

Global maximum

Local maximum

C O

Multi-objective optimisation involves minimising or maximizing multiple objective functions subject to a set of constraints, aiming at the optimal solution with tradeoffs between two or more conflicting objectives. A genetic algorithm (GA) is a computational and operational metaheuristic aimed at solving optimisation problems through the application of biological evolution inspired processes. Operating with the logic of natural selection, individuals within a population are used for producing offspring through multiple generations. Through combination, mutation and deletion of individuals, the entire population tend to approximate itself to the best solution for the input objective and parameters specified. The theoretical space in which all solutions are searched for is defined fitness landscape. Being the fitness the height of the landscape, the algorithm tries to get closer to a maximum that satisfies the fitness functions considered. The ability of the system to distinguish between local and global maxima is due to the user, that needs to specify how the algorithm will be acting during the research. Multi-objective Optimisation is here employed as evaluation tool aimed at finding global maxima within form-finding, structural analysis and environmental studies. [7] [8]

Multi-robotic construction system for unfired soil masonry

115

Cellular Automata

Structures growth in time.

‘A Cellular automaton’ is a mathematical model in which ‘space is divided into a finite number of cells, while time advances in time steps. Each cell has a state (‘Dead’ or ‘Alive’, ‘True’ or ‘False’, ‘Red’ or ‘Blue’). A cell represents a Finite State Machine. The cells are connected together and a group of connected cells is called a neighbourhood/cluster. The state of the cell is affected by the states of it’s neighbours. In the common scenario, when time changes each cell changes it’s current state in parallel to the other cells in the automaton. A cellular automaton could exist in multiple dimensions: 1-D, 2-D, 3-D. One could think of a cellular automaton as a simplified multi-agent system. Each cell represents an agent. Global emerging behaviour could be observed in result of local interactions between cells’. [9] In this experimentation, being N and K integers, the cellular automaton follows two simple rules: - A cell survives if surrounded by N living neighbours - A cell comes to life if surrounded by K living neighbours Cellular automata will be investigated to define how implicit construction methods can exploit mathematical relations and spatial discretization to generate rules sets to be followed by robotic units. Cells are computed as material deposition targets for discrete or not discrete components, while three-dimensionality is achieved through layering of consecutive configurations through time.

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Agent Based Modeling (ABM)

Agents trajectories in time.

Attractor points

Boundary

Agents

Agent’s path

Agent-Based Modeling (ABM) is usually considered as a variation of Cellular Automata models in which complexity is increased by additional degrees of freedom of the agents. The main feature ‘of ABMs, which distinguishes them from CA, is the potential asynchrony of the interactions among agents and between agents and their environments. In ABM agents typically do not simultaneously perform actions at constant time-steps. Rather, their actions follow discrete-event cues or a sequential schedule of interactions. The discrete-event setup allows for the cohabitation of agents with different environmental experiences. Also ABMs are not necessarily grid-based nor do agents ‘tile’ the environment. In particular, the richness of detail one can take into account in ABM makes this methodology very appealing for the simulation of biological and social systems, where the behaviour and the heterogeneity of the interacting components are not safely reducible to some stylized or simple mechanism. ‘ [10] Within this logic, the agents submit to several forces (alignment, cohesion, separation, gravity) that specify their spatial relationships with the neighbours. [11] ‘Computational methods in science become advantageous when a specific problem is too difficult to be solved analytically, an approximate theoretical result might not be reliable, and it is necessary to check it with a different method, or an experiment is expensive or not feasible to perform’. [10] In this paper, ABM is explored to simulate group dynamics in multi robotic systems aimed at implicit construction methods.

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Physical computing

DFRobotShop Rover V2 - Arduino Compatible Tracked Robot.

Construction tasks that involve on-site granular material manipulation need to be tested through physical tests in credible environmental conditions. Fine-grained soils are physically simulated in order to host multi robot local awareness experimentations. Tracked vehicles define a basic locomotion dynamics framework in which exploring agents communication. An on-board microcontroller, Arduino Uno, accept coded input to be executed on the unit, that becomes able to perform tasks thanks to the employment of sensors (temperature, sonar range finder, line follower, humidity, etc.) and motors (DC, stepper, servo, etc.). The information is coded in a format based on Processing and require to be written into the Arduino software, uploaded into the board and run. Our interest is towards interfaces, that enable communication between parametric modeling environments and micro-controllers, allowing control of robotic units along desired trajectories for deposition of material in specific locations.

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Material tests

Clay spheres samples for absorption tests.

A variety of material tests have to be conducted in order to evaluate the different options based on material properties. During this experimentation, it is important to define the optimal ratio between material selection and testing factors. This data will inform the possibilities for structural development and generate an understanding of functional requirements for robotic prototyping. Also, it will direct engineering properties and requirements for the design of robotic effectors and help to study the relationship between material and outcome performance. Physical modeling will help to develop a better understanding of which approach to take in terms of material system development. Two lines of research will be tested in parallel: material tests and end-effectors performance. The prototype will be used during further investigations to evaluate the systemâ&#x20AC;&#x2122;s performance as a whole. At the same time, prototype shows that the production methods and materials can successfully result in the design approach and demonstrate that the complete construction process is effective.

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[1] Kilian A., Ochsendorf J. (2005). PARTICLE SPRING SYSTEMS FOR STRUCTURAL FORM FINDING. In Journal of the International Association for Shell and Spatial Structures. Vol. 46, No.2. pp. 77-85. [2] Rippmann M., Block P., (2013). FUNICULAR SHELL DESIGN EXPLORATION. Proceedings of the 33rd Annual Conference of the ACADIA. [3] Rippmann M., Lachauer L., Block P. (2013). INTERACTIVE VAULT DESIGN. In International Journal of Space Structures. Vol. 27, No.4. [4] Preisinger C., Bollinger-Grohmann-Schneider ZT GmbH (2016). KARAMBA. Vienna. http://www. karamba3d.com/. [5] Sadeghipour Roudsari M., Pak M., Smith A., Gill G. Architecture (2013) LADYBUG: A PARAMETRIC ENVIRONMENTAL PLUG-IN FOR GRASSHOPPER TO HELP DESIGNERS CREATE AN ENVIRONMENTALLY CONSCIOUS DESIGN. Chicago, U.S.A. [6] Sherif A. H., Sabry H. M., Gadelhak M. I. (2012). THE IMPACT OF CHANGING SOLAR SCREEN ROTATION ANGLE AND ITS OPENING ASPECT RATIOS ON DAYLIGHT AVAILABILITY IN RESIDENTIAL DESERT BUILDINGS. [7] Weinstock M., Hensel M. , Menges A. (2010). EMERGENT TECHNOLOGIES AND DESIGN, TOWARDS A BIOLOGICAL PARADIGM FOR ARCHITECTURE. Routledge. [8] De Jong K. A. (2006). EVOLUTIONARY COMPUTATION: A UNIFIED APPROACH. MIT Press. Cambridge MA. [9] Morphocode Academy. http://morphocode.com/ [10] Castiglione F. (2006) AGENT BASED MODELING. Scholarpedia, 1(10):1562. [11] Fischer A. AGENT-BASED DESIGN FOR GRASSHOPPER. http://quelea.alexjfischer.com/

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Research development

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Material exploration

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Manual forming_Water absorption

Sample are placed in and covered by clay powder for homogeneous drying conditions.

Preliminary tests on water absorption were conducted to dispose of empirical evaluation of how the powder would absorb water during drying process. Three samples of confined volume of wet clay are formed employing different amount of water (moisture content) and evenly buried in three vases containing dry clay powder. The surface of all samples needs to be covered in order to address homogeneity displacement of material and water. Samples presents same amount of wet clay and different percentage of water, therefore they will dry with different speeds and with various effects on the powder around them. As an easily detectable rule, the more water is added to the sample the more its final volume after removal from the powder will increase. This is due to capillarity action of water through particles of clay that force water to move from the centre of the sample to the surface of the containers.

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Variation in volume caused by different moisture content during drying process.

Moisture content: 30ml (24%)

Moisture content: 35ml (28%)

Moisture content: 40ml (32%)

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Moisture content: 40ml (32%)

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Casting_Layers cohesion

Clay disks are stacked and contained by clay powder within a physical bounding box.

The experiment was aimed at exploring fabrication strategies and potential issues in multi layered cylindrical structure. Started as an attempt of column-like morphologies generation, the test showed major advantages and disadvantages of assembly method employed. Three percentages of water per unit of material (20%, 25% and 30%) are tested, as well as three different diameters of cross section. The structures are meant to be built layer by layer, using laser-cut stencils to prefabricate wet clay discs. Once this elements are placed inside a container, clay powder is used to fill the remaining space in the container, leveling the granular material up to the height of the discs. This technique provides a flat surface to stack consequent layers and boundaries to contain bulking material in place. The thickness of the layers is the same for all the samples, as well as their height, and all of them are the consequence of the same technique. After a passive drying process lasted about twenty days, the container is opened and support is slowly removed. As a consequence of manual work and difficulties in uniform application of water between components, several layers separated from their neighbours. In addition, the percentage of water also regulates the amount of support material being active during drying process, determining thickness of the column and texture of external surface.

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6 cm

3 cm

4 cm

6 cm

4 cm

Diameter variation and final absorbed volume before finishing process.

3 cm

Water content: 20% Layer height: 6 mm Diameter: 60 mm, 40mm, 30mm

Water content: 25% Layer height: 6 mm Diameter: 60 mm, 40 mm, 30 mm

Water content: 30% Layer height: 6 mm Diameter: 60 mm, 40 mm, 30 mm

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Direct extrusion_Overlapping

Samples of clay extrusion deposition on an inclined clay powder surface.

Behavioural interaction between viscous clay and clay powder is tested through the utilization of a syringe in order to deposit small scale extrusions above an inclined bed of dry clay. The moisture content about 25% by mass allows the material to be smoothly displaced through the tool while the linear elements are stacked above each others. Once the slope is entirely covered, the extruded mass is dried at room temperature, detached from its support and cleaned from the powder. The capacity of the extrusions to remain connected after drying process relies on several factors like the contact area between each linear element, the angle of repose of the powder mass, the diameter of extrusion and the moisture content. Most of them are directly influenced by gravitational forces and granular support material is used to decrease their influence during fabrication. Given a confined volume of powder in form of a slope, the angle of repose of the material - the angle at which all the powder grains are in static equilibrium - is dependent on confinement geometrical conditions and amount of powder. Granular masses dynamics needs to be taken in account when apertures and holes are materialised depositing linear element in discontinuous and intermittent mode. In this case, fabrication is possible until hydrostatic, frictional and gravitational forces are balanced. Since precise forecast of powder movement is not of simple actuation, in case of collapse of soil the entire structure would be affected by unforeseen displacement of support material.

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Angle of slope and angle of repose of unconstrained clay grains under gravitational forces and tests phases.

xÂ° Moisture content 25%

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x = angle of repose

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Direct extrusion_Spanning

Morphology of test objective and its decomposition in elements.

Proceeding with the idea of support material to be employed as an external constraint for depositing linear elements, our interest moved on the potential of powder in allowing spanning elements and openings during fabrication. A change in scale caused the transition from flat to linear components, realised using off the shelf extrusion tools. The mechanism is based on a plunger activated, through a set of gears, by the user. Closed planar geometries are shaped from clay pipes with 25% of water by mass and stacked on each other. Following the same logic of custom stencils seen in the previous test, in each layer support material is placed in those areas that will sustain dry material in the next layer. Powder efficiency in compression resistance allows to repeat the process at different heights without modifying the stability of lower beams. Main consequence of such porous geometries fabrication is the new functions that powder provides. Given the large amount of voids in the structure and its relative complexity, it is not always possible to completely remove the support material from the artifact. The presence of unremovable powder in some areas reveals possibilities in implementation of powder as infill aimed at structural and environmental performances. If powder contained by a drying mass could represent a way of increasing insulation and stiffness of an object, it also influences velocity and direction of water absorption, with inevitable repercussions on homogeneity of dried outcome.

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Operational section and test phases.

Layers of wet clay Layers of dry clay Absorption

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Mechanical meat extruder that employs a screw for displacing a plunger.

Cross section can be modified by changing plastic funnel at the end of the tool.

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Cleaning and finishing steps after removal of support material.

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Detail of texture of external surface.

Structure after finishing process.

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Detail of apertures and beams of one of three fronts.

Cracks and fissures developed between layers and material detachment following failed cohesion between side by side elements and between stacked layers.

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Direct extrusion_Masonry

Digital and morphological model of sample.

The prototype here presented comes from the will of physically testing feasibility of a portion of masonry, using the already employed mechanical extruder with 25 mm cross section. As previously, the model is built inside a wooden box for containing gravity forces during fabrication. Each layer is generated by depositing two linear elements side by side, while their surroundings are filled with support material. The latter is made of clay powder and rocks deriving from previous tests as waste material representing material scarcity instances in on site applications. The whole geometry is composed by 12 layers that, after drying within the box for a couple of weeks, need to be cleaned to reveal elements spanning above the ground. The final structure, in virtue of its mass, presents a good degree of resistance to compression forces, while, contrary to previous tests, cohesion between pipes in the same layer is high. Yet, critical points are visible where spanning elements connect to the main body of the artifact. In both interior and exterior sides, cracks and fissures are likely generated by the utilisation of composite support material. The fabric of the support material is opened and air is allowed to flow inside, drastically changing how moisture is distributed. As a consequence, conflicting forces produced by different drying rates determines contractions in the material, provoking displacement of elements along the vertical axis and suggesting the importance of using homogeneous material for supporting the process.

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Fabrication process steps. Each layer is made of clay extrusions and support clay rock and powder. Once the extrusions are maintained in place by support material, the layer can be considered ready to withstand the successive one.

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The artifact is 60 cm long, allowing 3 ribs of 20 cm to be placed and is made of 12 layers of 2.5 cm in diameter.

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All cracks occurred around connection points between spanning elements and main body of the structure.

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Detail of a fracture likely caused by not uniform drying process.

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View of the internal partition.

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Hydrostatic extrusion_Pneumatic tool

Exploded axonometry of pneumatic extruder components.

Input alluminium cap 1/4” female thread

Foam gaskets Acrylic hollow tube

Threaded metal rods Felt gasket Aluminium cylinder

Clay paste Output alluminium cap

1/2” female thread

Hexagonal nuts

In order to explore robotic and automated clay deposition, a mechanical tool is designed for extrusion tests. Core of the extruder is an acrylic glass tube of variable length and constant cross-section. Within this volume, here tested as 40 cm in length, 100 mm in internal diameter and 110 mm in external diameter, clay will be placed and pushed towards the extrusion cross-section. The tube is closed at its extremities by two metal caps obtained by milling of aluminium, the one close to the air input flat and the one close to the output showing a slight funnel shape to facilitate material displacement. These components present circular compartments of 2.5 cm in depth to allow the tube to be inserted and to accommodate rubber gaskets for reducing air leakage during actuation. Four M10 threaded metal rods and relative hexagonal nuts hold caps and tube together, avoiding the tool to be taken apart by the air pressure. A third aluminium element, the cylinder, is covered with soft material like felt for facilitating sliding movement and placed into the tube. BSP/Gas connectors of 1/4” (input) and 1/2” (output) are integrated into the caps through the fabrication of threaded holes. As the extruder represents the mean for material displacement, it could be needed to deposit the extrusion faraway from the output of the tool. For this reason, reinforced PVC and plastic hoses are tested for the extension of the path traveled by the material. In this sense, given the presence of the cylinder, when using extensions, it is necessary to take in account that once the paste is all extruded through the tool output, there is no more available movement for the cylinder. Therefore, the length of the hose should be considered while evaluating the total amount of material contained within the acrylic tube.

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High pressure PVC hose with air connectors

Hexagonal nuts

High pressure PVC hose with connector

Threaded metal rods

Metal hose with connector

Components of pneumatic extruder.

Connectors for liquids

Alluminium cylinder

Plexiglas hollow tube

Input alluminium cap

Output alluminium cap

Rubber and foam gaskets

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Caps milled from aluminium present embedded threads for injection and ejection connection.

Aluminium caps and cylinder together weigh around 10 kilograms.

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Dimensions for BSP/Gas threads employed.

Dp P TPI

Pilot hole diameter

Average diameter

Thread pitch

Nominal diameter

Thread per inch

Thread angle

BSP/G Parallel G

TPI

1/4"

13,157

1,337

12,301

11,8

55°

1/2"

20,955

1,814

19,793

55°

BSP/Gas threaded male and female connection for liquids.

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Pneumatic extruder prototype in two sizes.. The extruder has been specifically designed with the intention of disposing of a tool of simple utilisation, made of few and removable components for inspection and cleaning operation. Main feature is the possibility of being used with multiple reservoir lengths, meaning that the hollow plastic tube can be extended in length as much as the metal rods permit, influencing the amount of pressure needed for extruding material. At equal amounts of material and energy, the longer the reservoir is the more efficient would be the tool, distributing the pressure on a smaller surface. Here, input pressure is used during tests for understanding material behaviour and speed of extrusion. Therefore, initial tests will be made on 40 cm length, while the longer tube is fundamental for scaling up phases.

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Hydrostatic extrusion_Clay

Standard output aperture is 19 mm in diameter. The extrusion here presented is made of white clay originally provided in blocks of 22% water by mass blocks. Moisture has been increased up to 25% for manipulation during refill of reservoir and operational pauses. Pressure operates between 2 and 6 bars (30-85 psi) and constitutes a practical way of controlling speed of extrusion. Air bubbles in the reservoir are easily pushed out of the section causing local shortage of material and drops of structural performances, generating bursts of air during extrusion.

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Hydrostatic extrusion_Clay > Loam > Sand

Pneumatic extrusion of soil using loam as support material for feasibility tests of raw clayey soil elements in large scale construction. Compared to previous extrusion tests, viscosity is here increased for ease of process management. The artefact is here generated by overlapping tubular elements, while Support material has been tested in form of dry loam, widely available, because of its larger

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grains and therefore overall pore space, the higher permeability allowing more air to penetrate inside the structure during drying process. Trying to overstep previous criticalities of material fragility, mixture of soil has been here modified introducing fine white powder and fresh loam - the same used as support material - in proportion highly determined by nature of raw materials and their storage conditions. The mixture has been made by inserting sand and loam into a mass of already viscous brown clay at 35% of water by mass, in proportions of about 60% clay, 30% loam and 10% sand in volume, extruded at 5/6 bar.

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The structure is made with 4 layers of 19 mm height, following a pattern that alternates semicircular spanning elements to linear ones, generating counterposed curves along a central longitudinal axis.

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Contrary to expectations, maintaining planarity within each layer is not as simple as thought. As presented in the image, the first layer, instead of being placed onto the ground, is 2/3 cm suspended above it.

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Hydrostatic extrusion_Loam > Clay > Sand

The artefact has been realised as a trial of feasibility for raw clay elements in large scale construction. While methodology of material mixing and amount of water are unchanged, proportion of material have been modified for reducing utilisation of clay powder, using 60% loam, 30% clay and 10% sand by volume, with the same extrusion pressure of previous test.

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Masonry portion prototype. After two weeks of drying inside the wooden box filled with loam, the artefact is ready to be removed from its container. The box is opened and superficial and dry loam easily removed. Noticing that support material close to the extrusions is moist and strongly attached to them, about 6 and 10 further hours for drying of internal spaces are employed. Then, using air pressure from the compressor, up to 4 bar, a second session of loam removal is applied. The next and final phase requests the utilisation of manual tool of contained size for grinding and detaching support material from the finished surface of the structure.

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Detail of connection between 4 extrusions in 4 layers. In this location, removal of support material is rendered more difficult by the presence of sintered material within the multiple interstices between tubular elements.

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The tubular elements, after intersecting, spans longitudinally and transversally for about 10/15 cm above the ground, leaving significant space between each element.

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Multiple and massive fissures and consequent collapse of three elements of the structure. Not being in correspondence to the intersection of the extrusions and occurring only around one node, the crack should not have occurred for material weakness, rather for operational errors.

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Two nodes for five tubular elements generate twenty critical areas corresponding to maximum stress of spanning material. Here, three elements show self-weight collapse that developed from the loam supported part towards the intersection node. Considering their similarity, the issue is likely related to behaviour of support material during drying process. Loam, compared to clay powder, is more difficult to settle or compact in virtue of larger size of grains and consequent larger amount of internal air. Differentials in planarity within each layer are of extreme importance and uncompressed support soil will determine both a decrease of effectiveness of support material and variations of moisture displacement that alter homogeneity of air drying.

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Hydrostatic extrusion_CNC technologies

Extruder connected to 3d printer through reinforced plastic hose.

Considering difficulties in manipulating extruded elements in virtue of their viscosity, the research will make use of computer numerically controlled technologies for experimenting three-dimensional viscous material deposition for gaining a better understanding of layer overlapping, as well as support material and extrusion superimposition. At this stage, clay would be displaced from the extruder to the 20x30x20 cm printing volume of an assembled Prusa i3 Steel XL, while the insertion of support material remains at the expense of the user, whether during machine operations or stopping it at the end of fabrication of each layer. Given the utilisation of a reinforced plastic hose of approximately 1.2 m in length and certain limitations in maximum pressure allowed for the extruder, viscosity would need to be higher than before for avoiding premature solidification of material inside the tube during operational tool setting. Main criticalities lie in synchronising movements and speed of the printer with the amount of material extruded, taking into account potential heterogeneity of clay paste as well as possible differential of electrical current of the machine.

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Hardware components of assembled Prusa i3 Steel XL 3d printer.

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Parametric digital model of increasingly ribbed hollow solids and Printrun control interface for assembled 3d printer.

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From top left clockwise. Control motherboard for 3d printer, configuration and tests of its axes and detail of x axis hardware and 8 mm diameter nozzle.

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Research development

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Robot control

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Centralised control

One of the main challenges in designing a multi-robot system that is composed by small groundbased mobile robots is their inherently restricted environmental perception. The two main limitations are in sensory hardware and in vantage point. Since the perception of every agent within the system is restricted to their immediate surroundings, coordinating a decentralized multi-robot system to perform a specific task becomes extremely difficult, especially for applications outside of a controlled environment. Spatially Targeted Communication is a ‘communication method for multi-robot systems, which allows an individual message-sending robot to isolate selected message recipient robots based on their spatial location. The recipient robots can then be sent information targeted solely at them, even if the sending robot uses a broadcast communication modality’ [1]. An experiment was conducted for determining and communicating information from flying robots to groups of ground units in reference to morphologies to be obtained through grouping of units. ‘A flying robot estimates the parameters of an upcoming task on the ground by computing height maps of the ground based on stereo images. These parameters are then used in on-board simulations that are executed to find a morphology appropriate for the task’ [2]. ‘The flying robot then establishes a communication link with an appropriate number of robots on the ground, and sends the group instructions on how to form the morphology.’ [3] ‘Finally, the self-assembling robots form the morphology using a recruitment and guidance-based approach’ [4] and execute the task. ‘Any robotic platform equipped with LEDs and a standard camera can participate in STC’ [1]. Spatially Targeted Communications hardware is based on off-the-shelf LEDs and cameras, while robot tracking does not include maps, GPS or other specialized tool. ‘Therefore, it is ideally suited to swarms of robots and can be used outside of a laboratory environment’. [1]

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Centralised control strategy. Funicular Form-Finding

Parametric Modeling

Control Global Geometry

Structural Elements

Structural Performance

Climate Analysis

Spatially Targeted Communication* centralized sensory inputs + decentralized control

Structural Performance Slicing Algorithm Rover Instructions from Curves

Tool-Path Curves

Spatially Targeted Communication Centralized Spatial Awareness

Material Processing

Task Distribution

Mixing

Task Allocation

Data Processing Decentralized Microcontrolers

Actuation

Locomotion Move, Rotate

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Deposition

Material Processing

Extrude Powder

Mixing

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Decentralised control

In the world of living creatures, large groups of decentralized closely cooperating entities, commonly called collectives or swarms, can work together to complete tasks that are beyond the capabilities of any of its individuals. Considering this idea in the context of robotics, it becomes possible to design models for programming goal-oriented behaviour into the members of a group of simple robots lacking global supervision. [5] There are unique challenges to developing an application in which by only programming the rules that many agents must follow, the result is an emergent system behaviour [6]. One of the most significant challenges relies on the fact that swarm-robotic agents are decentralized, which means that they have no central controller or memory. In order to be considered fully decentralized, the data gathering (sensory network) as well as the data processing (computing) must be distributed amongst all of the agents. As a consequence of being distributed amongst hundreds or even thousands of agents, both the sensing and computing become limited by size and cost restrictions. This means that each agent can only be aware of its immediate surroundings, and since there is no centralized control or ‘a global map of the environment’ [1], it becomes increasingly difficult to predict what will emerge from the determined set of low-level rules. Because of the high complexity inherent to emergent systems, research on the subject has been practically out of reach to designers and architects, but thanks to collective research efforts, new platforms are being developed in which a collective control algorithm will, in the near future, enable designers to create and implement swarm applications while interacting only with high-level descriptions of their designs. [6] [7] When designing robots that will form part of a swarm, there are two competing factors that have to be considered: cost and functionality. While the robots need to have ‘enough functionality’ to perform its intended task or multiple tasks, ‘it must also be simple enough to keep the cost low’. [8]

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Computational Strategy

Decentralised control strategy.

Emergent

Simulation

Control

Agent Based Modeling (ABM) Interaction + Deposition

Swarm Robotics local decentralized sensory inputs + decentralized control

Material Re-Filling

Sensory Inputs Boundary Detection

State of Clay

Data Processing

Obstacle Detection

Decentralized Microcontrolers

Boolean (wet/dry)

Move, Rotate

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Actuation

Decentralized Microcontrolers

Locomotion

Actuation

Locomotion

Deposition

Material Processing

Extrude Powder

Mixing

Move, Rotate

Deposition

Material Processing

Extrude Powder

Mixing

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Defi Repeat (moves.per.layer) times Move to next layer and use previous one as (lay.below)

Defi Repeat (num.lay) times

Initial seed and five generations. rov 0 rov 2

rov 1

Layer 1 start

Seed Layer Wet (true)

Layer 1 end

Final Geometry num.lay = 5

Dry (false)

Because of the large amount of robots required to function, computer simulations play a key role in the development of a swarm-robotic framework or application. For this project, a cellular automaton is being developed as a tool for testing the multiple parameters that make up the system and as a way of visualizing how they relate with each other and to the final geometrical outcome. These parameters are separated into four classes: robot properties, which include speed, payload capacity, maximum inclination, sensing, and initial position. Rules of interaction, which translate sensory inputs into actions such as moving, rotating and extruding. Workspace properties such as size (rows columns), maximum height (number of layers), and location of the material sources (water and clay). Simulation properties, which are the maximum moves each robot can make per layer, the number of rovers and the state of each cell of the seed layer (wet or dry). When the simulation is finalized, the result is a three dimensional boolean matrix in which the seed layer has a height equal to zero and the final layer has a height equal to the maximum height defined in the workspace properties. The remaining layers are distributed equitably between the two. Subsequently, all of the â&#x20AC;&#x153;trueâ&#x20AC;? cells, which represent wet clay, are extruded until they reach the layer above them. By doing this, all of the layers become connected to form an approximation of the morphology that would result given all of the defined parameters. Afterwards, the resulting morphology can be evaluated for structural and environmental criteria.

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Pseudocode for decentralised control.

Emergent Simulation Pseudocode

Classes yes: change state of current cell to True Is rov (i, between 0 and num.rov) over a wet cell?

yes: Rotate Is rov (i, between 0 and num.rov) in front of an obstruction (Wet Cell, Rover, Boundary)?

no: Move

Repeat (num.rov) times Repeat (moves.per.layer) times

Move to next layer and use previous one as (lay.below)

Repeat (num.lay) times

Define Class: Seed layer state (for each True = Wet False = Dry Define Class: Rover Position (row, col) Orientation (n) (s) (e) (w)

Define Class: Simulation Number of Rovers (num.rov) Number of moves per layer (mov

rov 0

By methodically varying the parameters used for each simulation and comparing the results Layer 1 start change state of current cell to fromyes: the evaluations, it could beTrue possible to exov) over a wet cell? tractno:some relations cell remains False between the values used for each parameter and certain characteristics of the resulting morphologies. Further on, it yes: Rotate ov) in front of an could be possible to integrate the cellular auno: Move Boundary)? tomaton and the morphology into a Repeat (num.rov) evaluation times genetic algorithm (GA) in order to directly relate them with each other in an iterative optimiRepeat (moves.per.layer) times zation process. rov 2

rov 1

revious one as (lay.below)

ayer 1 start

no: cell remains False

Define Class: Work-Space Number of layers (num.lay) Number of rows (num.row) Number of culumns (num.col)

Seed Layer

Wet (true) Dry (false)

Repeat (num.lay) times

Classes

Layer 1 end Define Class: Work-Space Number of layers (num.lay) Number of rows (num.row) Number of culumns (num.col) Define Class: Seed layer state (for each cell) True = Wet False = Dry Define Class: Rover Position (row, col) Orientation (n) (s) (e) (w) Final Geometry Define Class: Simulation num.lay = 5 Number of Rovers (num.rov) Number of moves per layer (movesperlayer)

Layer 1 end

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Robotic unit hardware Sensory Inputs Units sensory inputs.

Photo sensor

Material State Detection

Tilt sensor

Boundary Detection

Ultrasonic range finder

Collision Avoidance

printed structure (obstacle) rover (obstacle) construction area angle of repose area

Actuation Mobile robots are designed to follow several tasks and action, whose effectiveness is linked with hardware and software embedded into their construction process. Hardware is generally composed of a set of wheels or tracks to perform locomotion and all electrical equipments to control their actions. Other than batteries for storing and power suppliers for providing energy, a gear box connectDifferential drive DC Locomotionsystem and motors for actuating potential mounted edMotor to the motors that activates the locomotion with gearbox tools, the core of the units is a printed circuit board called motherboard connected to all sensory Discharge inputs and outputs. The board is able to process information coming from sensors to coordinate actions performed by the vehicle. Given the difference in brightness and color of dry and wet clay, Suction Powder / Liquid VaccumSuction photo sensors can be used to inform the motherboard about the state of the material in a specific Collection location, as well as tilt sensors are able to facilitate the units in boundaries detection. Moreover, ultra Impeller sonic range finders are employed for collision avoidance between units during tasks completion. Volute Channel A further development of the units is related with communication. Information about tasks to be perArchimidean Screw Mixing / Extruding formed Effector can be physically uploaded into the motherboard from a computer or, in cases in which this is not possible or suggested, modules for bluetooth or wi-fi communication can be installed and permit to send information from distance or, in any case, without being directly connected to the robots with wires and cables.

174

Mechatronic hardware for robotic applications.

Wheels and metallic skeleton

Rubber tracks

Gear box and motors for locomotion

Line follower sensor

Ultra sonic range finder sensor

Bluetooth communication module

Vehicle batteries

Bluetooth communication board

Prototyping platform Power supply Arduino Uno motherboard

Motor for embedded tool

Multi-robotic construction system for unfired soil masonry

175

Path processing

The board that constitutes the main core of the vehicle hosts connections for analog Input, analog and digital Output, Input voltage, motor inputs (right and left), several connections for communication modules and an embedded motherboard with USB connector for uploading code. It uses a written code to control connected hardware, to gather local data and to follow generic information about their behaviour. In this case, the code used by an Arduino Uno board for controlling a differential drive robot would first present assignment of identification to two main variables, speed and direction of each of the two motors. By specifying the velocities of the two tracks as an integer between 0 and 255 and their relative boolean value between HIGH and LOW for the direction of rotation the user is able to perform all different and possible trajectories. If planning to input a specific and desired path to follow, the problem is ascribable to finding the aforementioned values of speed and directions for each point in which the robot will be during task execution along the curve. Even though multiple configuration are available, the simplest one to pursue is considering the wheel always rotating forward, while specifying their overall and relative velocity to virtually compose the path. The strategy here explained consists in using visual scripting for decomposing a curve into segments and determining wheels velocities through differential drive kinematics considerations.

int int int int

E1 E2 M1 M2

= = = =

6; 5; 8; 7;

//M1 //M2 //M1 //M2

Speed Control Speed Control Direction Control Direction Control

void setup() { int i; for(i=5;i<=8;i++) pinMode(i, OUTPUT); Serial.begin(9600); }

void loop() { int leftspeed = 255; //255 is maximum speed int rightspeed = 255; analogWrite (E1,255); digitalWrite(M1,HIGH); analogWrite (E2,255); digitalWrite(M2,HIGH); delay(100); }

176

Connection point

Sensors slot

Main digital and analog components within the control board of the unit.

Target LED

Prototyping area

Wi-Fi control

Target LED M2 Left motor input Encoder Input slot

Dual motor driver

+ -

Reset button Digital Input/Output

+ -

M1 Right motor input Bluetooth control

Analog Input Microcontroller Input voltage

Activity indicator LED

Voltage regulator

On/Off switch Target LED USB connector

Multi-robotic construction system for unfired soil masonry

Power Input connector

177

Differential drive kinematics

Mobile robots usually present 6 degrees of freedom, three of them identifying position in a cartesian system, one represented by the angle of rotation around its barycenter, one being the direction of the rotation of the wheel (forward or backwards) and the last being the heading or orientation, that refers to the average speed vector of the robot along its path. In units with differential drive locomotion system, the overall speed of the robot is set by controlling velocity and direction of rotation of right and left motors, whose operation are independent from each other. As a consequence, research on differential drive kinematics leads toward the solution of the problem of finding the pose of the unit at a certain time starting from a previous pose and moment in time, with the only control parameters of left and right wheel velocity. To achieve this goal, forward kinematics equations are derived and used for generalising the behaviour of the robot in all other cases. A single wheel rotating around its center of rotation can be placed in a local coordinate system in which the movement is decomposed in roll and slip, respectively the movement along Y and X axis. For sake of simplicity, we assume that there is no slip and that the only relevant parameter is the velocity of the wheel in the direction of its movement, meaning that the motion is strictly two dimensional and that the ground is flat and even. In robots with multiple rotating wheels, being the latter not allowed to move relative to each other, a common centre of rotation is defined as Instantaneous Centre of Curvature (ICC). This point moves according to pairs of value of wheel speed and following the development of the path. [9] For a differential drive robot, pairs of wheels are placed on the same axis and rotate around the same ICC with same angular velocity along a circle with determined radius. In this configuration, the product of the angular velocity and the radius gives us the overall speed of the robot. Proceeding with mathematical steps, it is possible to deduct the velocity of the two wheels expressed as the product of angular velocity and â&#x20AC;&#x2DC;the distance between ICC and the midpoint of the wheel axisâ&#x20AC;&#x2122; [9] increased or decreased by half of the length of the robot interaxle, depending on the wheel analyzed. From a mathematical point of view, it is possible to evaluate the next position of the robot considering time in the equations and expressing its new heading as sum of current heading and the product of angular velocity and time. Employing trigonometry for decomposing the ICC in its two components decreased and increased by the product of the radius and respectively sine and cosine of the current heading. Therefore, given a starting position, the new position can be computed through a two-dimensional rotational matrix disposing of angular velocity, radius and time of rotation. Increasing accuracy, given the low precision that usually afflicts measurements of right and left wheel speed, would consist in using wheel encoders, devices able to provide a binary signal for counting how many times (steps) the wheel spins on its axis in a certain time frame and determining the distance traveled from the increase in number of steps. This can be expressed with a three-dimensional matrix that is independent from the time of rotation, often hard to estimate accurately.

178

Differential drive kinematics model.

ICC

l/2 θ (x,y)

ω r= v

ω (R+l /2) = vr ω (R - l/2) = vl

R= l/2(vl +vr) / (vr- vl ) ω = (vr – vl) / l

ω r= v

ω (R+l /2) = vr ω (R - l/2) = vl

R= l/2(vl +vr) / (vr- vl ) ω = (vr – vl) / l

θ’

(x’,y’)

ωδt

(x,y)

ICCx θ’=θωδt + θ v = n step/δt θ’= ωδt + θ

θ’

(x’,y’)

ωδt

ICC y

l/2 vr

θ (x,y)

ICC

ICCx

x (x,y) x

ICC = [ICCx, ICCy] = [ x-R sinθ, y+R cosθ]

x’ cos(ωδt) -sin(ωδt ) x-ICCx = + ICCx ICC = [ICCx,cos(ωδt ICCy] =) [ x-R sinθ,y y+RICC cosθ] y’ sin(ωδt) y-ICC y x’ cos(ωδt) = y’ sin(ωδt)

v = n step/δt

-sin(ωδt ) cos(ωδt )

ωδt) x’ l/2 (v cos( - sin(ωδt ) 0 x-ICCx R= l + vr ) / (vr – vl ) = l/2(nl + nr ) / (nr – nl ) y’ = sin(ωδt) cos(ωδt) 0 y-ICCy + θ’ 0 0 1 θ Multi-robotic construction system for unfired soil masonry - sin(ωδt ) cos(ωδt)

0 0

x-ICCx y-ICCy

x-ICCx + ICCx y-ICCy ICC y

ωδt = (vr – vl ) δt / l = (nr – nl ) step / l

R= l/2 (vl + vr ) / (vr – vl ) = l/2(nl + nr ) / (nr – nl )

x’ cos(ωδt) y’ = sin(ωδt)

Rotation of wheeled vehicle around the Instantaneous Center of Curvature (ICC), where interaxle extensions of consequent positions meet. [9]

nrr –) /n(n –n ) l +(n ICCx ωδt = (vr –Rvl=) l/2 δt /(n l= l )rstepl / l ωδt = (nr – nl ) step / l ICCy ICC = [ x-R sinθ, y+R cosθ ] ωδt ICCx ICCy

R = l/2 (nl + nr ) / (nr – nl ) ωδt = (nr – nl ) step / l

179

Path planning

Physical locomotion possibilities of differential drive tracked vehicles.

180

When speaking of path planning, multiple are the parameters to take in account for having awareness of the behaviour of the unit. The robot needs to move from point A to point B detecting and avoiding obstacles. In addition, it should receive and return information to a controller. In order to do that, a possible path made of sub-trajectories is composed and evaluated in efficiency. In straight path motors spin in the same direction and with same velocity, but when a change in direction is requested, many are the ways in which the units can function. Rotation of the rover assumes a center of rotation and at least one spinning motor. In the most basic example, the right track spin forward while the left track its stationary but still able to slip according to the movement of the right track. The rusult of such an operation is that the centre of the rotation moves in a new position, whose detection derives from frictional properties of tracks and terrain, geometrical dimension of the unit and power of the motors. If two motors are involved, they can both spin in the same direction with different speed or they can spin in opposite direction with equal or different speed. In the first case, the centre of the rotation gently moves according to both motors velocities. High resolution is achieved by computing values for direction and velocity of both motors, as well as the duration time of the task, for describing smooth trajectories. Two motors can also be used for rotating the unit around itself by spinning in opposite direction with same velocity. Here, the centre of rotation, except for acceptable errors with rough terrains, does not move in space, allowing precise movement against continuity of execution. [10]

v1 S θ

ω v1 - v0 r v sin(Ω) ω= r S θ= r θ=2πf ω=

VL VR

Potential paths for goal achievement and obstacles avoidance. Goal Vdx Vsx

x x

Vdx Vsx

Straight trajectories

x x

Goal

VR VL

x x

VR VL

0 x

Straight trajectories + Rotation

VR VL VR VL

x x

VR VL

x x

x 0

Goal

VR VL

x x

Straight trajectories + Circular trajectories

VR VL

x x+y

VR VL VR VL

x x

VR VL

x x

x+y x

Goal

VR VL

Σx Σ(x + y)

Circular trajectories VR VL

Multi-robotic construction system for unfired soil masonry

Σ(x + y) Σx

181

Linear and angular velocities

Linear velocity of the sample tracked vehicle is evaluated empirically from tests of maximum velocity on different terrains. The code uploaded turns both tracks forward at a speed of 255, the unit is placed along a measuring tape and the task execution recorded. With a stopwatch, time to reach 200 mm is measured 5 times and averaged. From this information, maximum speed in mm/s for specific surfaces is calculated. Being the results in seconds, the time with this method obtained needs to be converted in milliseconds for inputting the duration of the task into the code. Angular velocity is evaluated with similar techniques and time calculation is made on a 360 degrees rotation. Maximum linear velocity and maximum angular velocity are surely dependent on ground nature, yet, within the scale here employed, the difference is not as much as relevant for adopting separate techniques of data collection. With vehicle of size comparable with tracked tanks, engineering of locomotion components, such as tracks and wheels, provides larger weights and energy amounts for resulting more efficient on irregular and granular terrains. For simpler implementation and control, path planning and task execution will be tested with values velocities deriving from tests on smooth surfaces, guaranteeing precision and rapidity in changes of directions.

int int int int

E1 E2 M1 M2

= = = =

6; 5; 8; 7;

//M1 //M2 //M1 //M2

Speed Right Speed Left Direction Right Direction Left

void setup() { int i; for(i=5;i<=8;i++) pinMode(i, OUTPUT); Serial.begin(9600); }

void loop()

{

{ analogWrite (E1,255); digitalWrite(M1,HIGH); analogWrite (E2,255); digitalWrite(M2,LOW);

analogWrite (E1,255); digitalWrite(M1,HIGH); analogWrite (E2,255); digitalWrite(M2,HIGH); }

182

}

Data collection for linear velocity extrapolation. Two surfaces are employed for locomotion data. Smooth and hard plastic veneer is tested against sandy terrains (1/8 – 1/16 mm grain size). Linear velocity extrapolation

Linear velocity extrapolation

Surface_plastic veneer

Surface_sand

Vmax = S / tmin

S = 200 mm

Vmax = S / tmin

S = 200 mm

tmin = taverage(t1,t2,t3,t4,t5) = 2.34 s

tmin = taverage(t1,t2,t3,t4,t5) = 2.73 s

Vmax = 85.29 mm/s

Vmax = 73.21 mm/s

delay = tmin = (S / Vmax) x 1000 [ms]

Angular velocity extrapolation

Surface_plastic veneer

Surface_sand

Wmax = 360° / tmin

tmin = taverage(t1,t2,t3,t4,t5) = 4.60 s

tmin = taverage(t1,t2,t3,t4,t5) = 5.77 s

Wmax = 78.2°/s

Wmax = 62.39°/s

delay = tmin = (deg° / Wmax) x 1000 [ms]

Multi-robotic construction system for unfired soil masonry

183

Continuous path

As a first attempt to construct a code for controlling a tracked rover, the desired path is divided at zero inflection points and a dimensional projection of the robot is traced along the curve. Following the aforementioned drive kinematics assumptions, we try to plan a path through graphical resolution and visual scripting, aiming at extremely high resolution. Pairs of points representing position of the tracks are compared and relative ICC found, while the specification for motors control are strictly related to the direction of rotation and velocities are computed by the algorithm, whose results are combined with strings of Arduino IDE code and saved into a text file containing a code ready to be used by the robot. The outcome text file contains, other than initial specification for setting the motherboard, a list of commands for the motors, each one representing a sector of path to be covered twisting both motors with slightly different velocities. Within the program, delay remains variable for each sector and does not give us enough information for a precise path planning (X0, X1, ..., Xn, ..., X31) . A possible solution would be empirically evaluating all sub trajectories and manually adding their execution times to the code, partially deleting the utility of such an algorithm.

void setup() { int i; for(i=5;i<=8;i++) pinMode(i, OUTPUT); Serial.begin(9600); } void loop() { analogWrite(E1,235); digitalWrite(M1,HIGH); analogWrite(E2,255); digitalWrite(M2,HIGH); delay(X0); analogWrite(E1,91); digitalWrite(M1,HIGH); analogWrite(E2,111); digitalWrite(M2,HIGH); delay(X1);

184

..... ..... ..... analogWrite(E1,An); digitalWrite(M1,HIGH); analogWrite(E2,Bn); digitalWrite(M2,HIGH); delay(Xn); ..... ..... ..... analogWrite(E1,178); digitalWrite(M1,HIGH); analogWrite(E2,255); digitalWrite(M2,HIGH); delay(X31); }

Path planning through continuous utilisation of servo motors.

Interaxle extensions, ICC and inflection points on planned path.

Multi-robotic construction system for unfired soil masonry

185

Discontinuous path

To simplify the process of path planning, the curve is then divided into sectors whose starting and ending points are connected through segments. Such interpolated path is composed by linear trajectories alternated with angles between consecutive directions. A list of the angles is computed and employed in finding the related delay in milliseconds to input in the Arduino code. Through the length of the segments and the empirical linear velocity, we are able to determine for how many milliseconds - delay - a certain velocity needs to be maintained for describing the related linear movement. Using the amplitude of the angles and the empirical angular velocity, a measure of time and degrees is computed for rotations and strings manipulation returns a list of instructions to be uploaded. As a matter of fact, the trajectory curve is here reduced in degrees of interpolation, rendering it discontinuous for simplifying the management of code writing. In detail, both motors move forward at maximum speed (255) along a straight segment, then both motors stop at the end of the segment. Here, motors move opposite directions but with equal maximum speed. The time employed for these clockwise or counterclockwise rotations will determine the covered angle. Once the rotation is completed, a straight line is executed and the process repeated until completion of the entire path.

void setup() { int i; for(i=5;i<=8;i++) pinMode(i, OUTPUT); Serial.begin(9600); } void loop() { analogWrite (E1,255); digitalWrite(M1,HIGH); analogWrite (E2,255); digitalWrite(M2,HIGH); delay(1688); analogWrite (E1,255); digitalWrite(M1,LOW); analogWrite (E2,255); digitalWrite(M2,HIGH); delay(83);

186

6.5Â° CW

Path planning through intermittent utilisation of servo motors.

2 2

14 44

142

143

142

7 7

8 28

115

15.7° CW 6.5° CW

115

143

134

8 28

144

288

123

115

8 28

142

134

Dimension of interpolation segments and their relative position in degrees.

4 14

288

4 2559 4 14

144

123

143

123 2559 4 14

4 14

14 14

618

144

2559

288

139

138

144

139

138

144

139

142

618

138

142 0 13

618

142 0 13

134

87.7° CW

15.7° CW 6.5° CW

13.0° CWCW 87.7° 27.6° CW

15.7° CW 6.5° CW

17.3° ACW 13.0° CWCW 87.7° 63.5° ACW 13.0° CW

46.6° CW 27.6° CW

17.3° ACW

63.5° ACW

12.1° CW

17.3° ACW 63.5° ACW

15.8° CW

46.6° CW 27.6° CW

37.3° CW

12.1° CW 46.6° CW

3.6° ACW

12.1° CW 2.4° ACW 45.8° ACW

59.4° ACW 3.6° ACW

2.4° ACW 45.8° ACW

59.4° ACW 3.6° ACW

2.4° ACW

45.8° ACW

59.4° ACW

75.4° CW 37.3° CW

75.4° CW 37.3° CW 53.3° ACW 75.4° CW 53.3° ACW

20.5° CW 41.2° CW 58.2° ACW

15.8° CW

3.9° ACW 20.5° CW 41.2° CW

39.2° ACW 51.7° ACW

58.2° ACW 3.9° ACW 20.5° CW

39.2° ACW 51.7° ACW

58.2° ACW 3.9° ACW

53.3° ACW

Multi-robotic construction system for unfired soil masonry

41.2° CW 15.8° CW

39.2° ACW 51.7° ACW

187

analogWrite (E1,255); digitalWrite(M1,HIGH); analogWrite (E2,255); digitalWrite(M2,HIGH); delay(1687); analogWrite (E1,255); digitalWrite(M1,LOW); analogWrite (E2,255); digitalWrite(M2,HIGH); delay(200);

analogWrite (E1,255); digitalWrite(M1,HIGH); analogWrite (E2,255); digitalWrite(M2,HIGH); delay(1628); 15.7° CW

analogWrite (E1,255); digitalWrite(M1,HIGH); analogWrite (E2,255); digitalWrite(M2,HIGH); delay(1664); analogWrite (E1,255); digitalWrite(M1,LOW); analogWrite (E2,255); digitalWrite(M2,HIGH); delay(1121);

87.7° CW

188

analogWrite (E1,255); digitalWrite(M1,LOW); analogWrite (E2,255); digitalWrite(M2,HIGH); delay(353);

27.6° CW

analogWrite (E1,255); digitalWrite(M1,HIGH); analogWrite (E2,255); digitalWrite(M2,HIGH); delay(1617); 13.0° CW

analogWrite (E1,255); digitalWrite(M1,HIGH); analogWrite (E2,255); digitalWrite(M2,HIGH); delay(1665); analogWrite (E1,255); digitalWrite(M1,HIGH); analogWrite (E2,255); digitalWrite(M2,LOW); delay(812);

17.3° ACW

analogWrite (E1,255); digitalWrite(M1,HIGH); analogWrite (E2,255); digitalWrite(M2,HIGH); delay(1688);

analogWrite (E1,255); digitalWrite(M1,HIGH); analogWrite (E2,255); digitalWrite(M2,HIGH); delay(1525); analogWrite (E1,255); digitalWrite(M1,LOW); analogWrite (E2,255); digitalWrite(M2,HIGH); delay(166);

analogWrite (E1,255); digitalWrite(M1,HIGH); analogWrite (E2,255); digitalWrite(M2,LOW); delay(221);

analogWrite (E1,255); digitalWrite(M1,LOW); analogWrite (E2,255); digitalWrite(M2,HIGH); delay(592);

46.6° CW

analogWrite (E1,255); digitalWrite(M1,HIGH); analogWrite (E2,255); digitalWrite(M2,HIGH); delay(1676); 63.5° ACW

analogWrite (E1,255); digitalWrite(M1,LOW); analogWrite (E2,255); digitalWrite(M2,HIGH); delay(154);

12.1° CW

analogWrite (E1,255); digitalWrite(M1,HIGH); analogWrite (E2,255); digitalWrite(M2,HIGH); delay(1688); analogWrite (E1,255); digitalWrite(M1,HIGH); analogWrite (E2,255); digitalWrite(M2,LOW); delay(31);

analogWrite (E1,255); digitalWrite(M1,HIGH); analogWrite (E2,255); digitalWrite(M2,HIGH); delay(1688); 2.4° ACW

analogWrite (E1,255); digitalWrite(M1,HIGH); analogWrite (E2,255); digitalWrite(M2,HIGH); delay(1686); analogWrite (E1,255); digitalWrite(M1,HIGH); analogWrite (E2,255); digitalWrite(M2,LOW); delay(585);

45.8° ACW

analogWrite (E1,255); digitalWrite(M1,LOW); analogWrite (E2,255); digitalWrite(M2,HIGH); delay(965);

75.4° CW

analogWrite (E1,255); digitalWrite(M1,HIGH); analogWrite (E2,255); digitalWrite(M2,HIGH); delay(1686); 59.4° ACW

analogWrite (E1,255); digitalWrite(M1,HIGH); analogWrite (E2,255); digitalWrite(M2,HIGH); delay(1684); analogWrite (E1,255); digitalWrite(M1,HIGH); analogWrite (E2,255); digitalWrite(M2,LOW); delay(46);

37.3° CW

analogWrite (E1,255); digitalWrite(M1,HIGH); analogWrite (E2,255); digitalWrite(M2,HIGH); delay(1435);

analogWrite (E1,255); digitalWrite(M1,HIGH); analogWrite (E2,255); digitalWrite(M2,HIGH); delay(1480); analogWrite (E1,255); digitalWrite(M1,HIGH); analogWrite (E2,255); digitalWrite(M2,LOW); delay(759);

analogWrite (E1,255); digitalWrite(M1,LOW); analogWrite (E2,255); digitalWrite(M2,HIGH); delay(477);

analogWrite (E1,255); digitalWrite(M1,HIGH); analogWrite (E2,255); digitalWrite(M2,LOW); delay(682);

53.3° ACW

analogWrite (E1,255); digitalWrite(M1,HIGH); analogWrite (E2,255); digitalWrite(M2,HIGH); delay(1341); 3.6° ACW

Multi-robotic construction system for unfired soil masonry

analogWrite (E1,255); digitalWrite(M1,HIGH); analogWrite (E2,255); digitalWrite(M2,LOW); delay(745);

58.2° ACW

189

analogWrite (E1,255); digitalWrite(M1,HIGH); analogWrite (E2,255); digitalWrite(M2,HIGH); delay(1687);

analogWrite (E1,255); digitalWrite(M1,HIGH); analogWrite (E2,255); digitalWrite(M2,HIGH); delay(1687); analogWrite (E1,255); digitalWrite(M1,HIGH); analogWrite (E2,255); digitalWrite(M2,LOW); delay(2);

analogWrite (E1,255); digitalWrite(M1,HIGH); analogWrite (E2,255); digitalWrite(M2,LOW); delay(50);

15.8° CW

analogWrite (E1,255); digitalWrite(M1,HIGH); analogWrite (E2,255); digitalWrite(M2,HIGH); delay(1681);

analogWrite (E1,255); digitalWrite(M1,HIGH); analogWrite (E2,255); digitalWrite(M2,HIGH); delay(1688); analogWrite (E1,255); digitalWrite(M1,LOW); analogWrite (E2,255); digitalWrite(M2,HIGH); delay(202);

analogWrite (E1,255); digitalWrite(M1,HIGH); analogWrite (E2,255); digitalWrite(M2,LOW); delay(661);

41.2° CW

analogWrite (E1,255); digitalWrite(M1,HIGH); analogWrite (E2,255); digitalWrite(M2,HIGH); delay(1568);

analogWrite (E1,255); digitalWrite(M1,HIGH); analogWrite (E2,255); digitalWrite(M2,HIGH); delay(1669); analogWrite (E1,255); digitalWrite(M1,LOW); analogWrite (E2,255); digitalWrite(M2,HIGH); delay(527);

20.5° CW }

analogWrite (E1,255); digitalWrite(M1,HIGH); analogWrite (E2,255); digitalWrite(M2,HIGH); delay(1657); analogWrite (E1,255); digitalWrite(M1,LOW); analogWrite (E2,255); digitalWrite(M2,HIGH); delay(262);

190

51.7° ACW

3.9° ACW

39.2° ACW

Execution of tasks of unit with discontinuous utilisation of servo motors.

When the task is executed on the entire path, no errors seem to occur. What appears undeniable is the light construction of sample robot, whose physical integrity and electrical connections are too uncertain and fragile to sustain application in which dirty materials and medium to high weights are involved. In detail, the axis between sprocket wheels tends to lose coplanarity making really challenging to obtain straight trajectories even when all parameters are defined. On the electrical side, the motors are connected through pairs of metallic electrodes, whose dimension and thickness make them quite sensitive to movement of hardware and cables as it can happen during obstacle overtake and rough surface itineraries. Issues of resolution and precision can be controlled with optimal scale between path and robot size. Fixing the size of the robots, the amount of subdivision of the curve is related to the length to be covered by the rover at each time step and its dimensions, meaning that increasing the size of the path would introduce more time and possibility for error spreading. This is why, when small anomalies exist, shortening lengths and times of reaction can improve precision in execution of paths, especially for hardware of small size.

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[1] Mathews N., Christensen A.L., Ferrante E., O’Grady R., Dorigo M. (2010). ESTABLISHING SPATIALLY TARGETED COMMUNICATION IN A HETEROGENEOUS ROBOT SWARM. In Proceedings of the 9th International Conference on Autonomous Agents and Multiagent Systems. International Foundation for Autonomous Agents and Multiagent Systems. Volume 1, pp. 939-946. [2] Mathews N., Stranieri A., Scheidler A., Dorigo M. (2012). SUPERVISED MORPHOGENESIS: MORPHOLOGY CONTROL OF GROUND-BASED SELF-ASSEMBLING ROBOTS BY AERIAL ROBOTS. In Proceedings of the 11th International Conference on Autonomous Agents and Multiagent Systems-Volume 1. pp. 97-104. [3] Christensen A.L., O’Grady R., Dorigo M. (2008). SWARMORPH-SCRIPT: A LANGUAGE FOR ARBITRARY MORPHOLOGY GENERATION IN SELF-ASSEMBLING ROBOTS. Swarm Intelligence, 2(2-4), pp.143-165. [4] Mathews N., Christensen A. L., O’Grady R., Rétornaz P., Bonani M., Mondada F., Dorigo M. (2011). ENHANCED DIRECTIONAL SELF-ASSEMBLY BASED ON ACTIVE RECRUITMENT AND GUIDANCE. In 2011 IEEE/RSJ International Conference on Intelligent Robots and Systems. IEEE. pp. 4762-4769. [5] Wagner I. A., Altshuler Y., Yanovski V., Bruckstein A. M. (2008). COOPERATIVE CLEANERS: A STUDY IN ANT ROBOTICS. The International Journal of Robotics Research, 27(1), pp.127-151. [6] Miner D., Des Jardins M., Hamilton P. (2008). THE SWARM APPLICATION FRAMEWORK. In Proceedings of the 23rd national conference on Artificial intelligence, Volume 3. AAAI Press. pp. 1822-1823. [7] Petersen K., Nagpal R., Werfel J. (2011}. TERMES: AN AUTONOMOUS ROBOTIC SYSTEM FOR THREE-DIMENSIONAL COLLECTIVE CONSTRUCTION. Proc. Robotics: Science & Systems VII. [8] Rubenstein, Michael, Christian Ahler, Radhika Nagpal. (2012). KILOBOT: A LOW COST SCALABLE ROBOT SYSTEM FOR COLLECTIVE BEHAVIORS. In Proceedings IEEE International Conference on Robotics and Automation (IRCA 2012). May 14-18. Saint Paul, Minnesota, 3293-3298. Washington, D.C. Computer Society Press of the IEEE. [9] Hellström T. (2011). KINEMATICS EQUATIONS FOR DIFFERENTIAL DRIVE AND ARTICULATED STEERING. Department of Computing Science, Umeå University. Umeå, Sweden. [10] LaValle S. M. (2006). PLANNING ALGORITHMS. University of Illinois, Cambridge University Press. Chapter 13, Differential models, pp. 715-786.

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Research development

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Construction strategy

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Material manipulation

In order to prepare clay to be employed in design, water and powder are collected from the environment through suction and mixed together into clay paste. From a microscopic view, such composite material is made of a liquid, continuous phase and a solid, granular one. Movement of material is controlled by mechanisms that allow paste extrusion and powder injection. The different nature of materials and their compounds drives the attention to industrial processes that involve manipulation of matter in liquid/plastic and solid/granular state, transition between phases and controlled deposition of multiple materials. On-site water, if available, needs to be found and quantified for checking the possibility of employing it into the construction processes. Since the material system is liable of modifications during the drying process due to the amount of water per unit of material, plasticity of clay mixture employed can also vary according to the ratio between available water and built volume. The difference between groundwater and superficial water conditions leads to different techniques of fluid collection and extraction. Although penetrating the soil requests specific mechanical equipment, the task is mainly focused around devices able to move fluids through suction. Collection of powder, as well as the previous task, is based on two sequential moments: identification of suitable material and its potential discretisation in smaller and easier particles to be used. In physical tests clay is directly supplied in granular form and the technical challenge is related to collection of powder through suction devices or mechanical systems. The powder collected is then divided into two different flows, one going to the mixing process, the other one to the deposition phase. Mixing is rendered possible through the injection of collected water and powder into a container in which spinning mechanisms of specific shapes allow particles of different materials to recombine in what it can be considered a paste, a fluid that show highly plastic behaviour. Unless mixing and deposition are set in the same volume, the paste needs to be moved where an extruder push the material through a defined section. The extrusion obtained is then used to robotically apply material where needed in layers. During the deposition phase clay paste is shaped in pattern of specific height to be filled and enclosed by clay powder. Powder acts as support for the clay paste, that is not allowed to bulk in any direction. Once the first layer is completely solid, the second one is laid on the flat surface of the first one and so on. The presence of powder permits to create voids, spanning elements and porosity without forcing the designer to have a specific plasticity coefficient. Since each bi-material layer is a solid volume, the challenge is reduced to patterns morphology, contact force between layers and diffusion of water in the material. At the end of the process, that includes a period of passive drying, layers will be connected to each others forming a singular three-dimensional structure, filled with and surrounded by with clay powder. Removing the granular material, the dried structure emerges from the solid volume of clay, revealing voids that are generated by the patterns employed.

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Material phases and manipulation Collection

Manipulation

Deposition

Mixing Water Continuous (flow) Liquid

Clay powder -

Discrete (granular) Solid

Liquid suction

Paste Transfer

Water + Clay powder -

Colloidal suspension

Powder suction

Clay paste

Material manipulation stages request appropriate allocation within machinery designed for ease of use, space economy and low costs.

Bingham plastic fluid

Paste extrusion

Clay powder -

Discrete (granular) Solid

Powder injection

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Soil crystallisation

Schematics of employment of granular material as support and falsework for construction operations.

Plan

Section

θ < max. climbing angle

Falsework

Contained falsework

x° θ > max. climbing angle

Contained + free falsework x = angle of repose angle of repose < max. climbing angle x°

Geometry with opening

Contained + free falsework x = angle of repose

As previously mentioned sintering processes, such as Solar Sinter and Selective Laser Sintering, request large amount of energy and/or complex and expensive tools. In both cases, energy is locally and scattered in time directed toward the material in order to generate bonds between granules. If the possibility of selective solidification of matter within a planar surface covered with powder is of great interest for precision in small and medium scale applications, large scale artifacts need to be supported by contemporary robotic coordination argumentations. Disposing of granular material and needing it to be available in dry and wet states, the possibility of providing the system with ready-touse material and leave its collection and manipulation for further developments should be taken in account. The selective and distributed application of material allows the system to be more robust in sensing and reacting. For both open and closed planar surfaces stacked in layers, main question is related to the ability of rovers to climb deposited material and obtain access to consequent layers. The angle of repose of a specific granular material is of interest in forecasting powder slides outside of boundaries and in planning powder addition and subtraction stages. Simulations can be employed in determining how trajectories develop in time and how agents avoid themselves while depositing. Amount of units, position of refilling station, assignment of tasks are all features to define from capacity, speed and practical limitation imposed by scarcity or desired performance.

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Robot Type 1 Functions: Suction Dry clay deposition

Building plot

Robot Type 1 Functions: Suction Mixing Clay extrusion

Clay

Suctioning the material Mixing the material

Water

Dry clay deposition “layer by layer” Clay extrusion Recharging the material Recharging and mix the material

Clay

Water

Dry clay redeposition Clay extrusion

Building plot

Clay

Water

On-site units coordination includes powder material collection, water refill, extrusion deposition, material mixing, as well units avoidance and global data gathering.

Clay

Water

Suctioning the material Mixing the material

Water

Dry clay deposition “layer by layer” Clay extrusion Recharging the material Recharging and mix the material

Clay

Water

Dry clay redeposition Clay extrusion

Building plot

Clay

Water

Dry clay deposition “layer by layer” Clay extrusion Recharging the material Recharging and mix the material

Clay

Water

Dry clay redeposition Clay extrusion

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Layering logic

Simulated construction logic and layering algorithm for discretising the input geometry and evaluating position of powder and extrusion within each layer.

The method is conceived to work with a layer-by-layer approach, depositing linear elements within a containment of powder material. Two typologies of ground robot must coordinate for placement of wet material within each section and surrounding powder material for as supports. This process is presented, in his simplest version, by a set of paste units and a set of powder units moving on-site while collecting material from refill stations and displacing it into place. At each step in height, both categories of units alternate in executing their specific tasks, intermittently and momentarily interrupted by refuelling of material, whose dynamic is dependent on capacity of material loading on each robot. Given the vertical development that the process assumes, much attention has to be directed towards locomotion and kinematics analysis of robot employed - here differential drive - and its performances on operating ground. Even though structures would be sustained by powder during fabrication, in order to be independent from height, powder robots need to deposit material around the structure, generating through time a slope - dune - that allows robot to climb until the last layers. As a general rule, to facilitate calculation angle of repose of the powder should not vary along each layers, meaning that the largest boundary until which powder will be placed is determined by the projection of the extended layer onto the ground. As a consequence, there is a strong correlation between height of the structure and occupied area around it for construction. When all layers are deposited and dry, powder material

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is removed, revealing the final structure as a whole of ceramic material. Surfaces finishing is usually necessary and performed manually or through automation, consisting of local tasks of grinding, peeling, scratching or application of water for smoothing of layers junctions and reducing superficial porosity

Layer 08

Layer 25

Layer 45

Input sliced geometry as vectors Total length of path (volume) / extruder capacity = segment.length Divide path in segments with length = segment.length

Rovers follow directives coded into general rules for internal coordination of the group, being vectors, volumes and lengths main variables .

Identify position and orientation of rovers Generate path from each rover to the initial points Convert paths to rover instructions

Move rovers to initial points Convert segments from vectors to rover instructions. Send Rover instructions to the corresponding rover.

All Layers (57)

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Construction process

The script here drafted, generated by using visual scripting, addresses the animation and partial simulation of the intended construction strategy. Ground robots are divided into units that deposit extrusion of wet clay and units that eject powder. Both categories of rover depart from a material refill station and returns to it after completing a trajectory. Material refill stations are distributed in strategical locations along boundaries of structures to build, in this case paste robots are evenly placed around the first layer while powder ones are located outside the plan and in front of the aperture. An aerial robot collects information and controls the units on the ground. For each step, simultaneous extrusions are placed and powder released around it as support for the next layer. Layer by layer, support material will constitute an inclined powder mass to be climbed by the units with the tracks of the vehicles. Layer 0.0

PASTE rover // regularly placed around the first layer to build, multiple units reach their starting position on the boundary POWDER rover // maintain position or, if previously performed action, refill material for the next step

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Layer 0.1

PASTE rover // simultaneously start depositing material following defined path paths with specific speed

POWDER rover // maintain position or, if previously performed action, refill material for the next step

Layer 0.2

PASTE rover // once reached final point of deposition, return to refill position

POWDER rover // maintain position or, if previously performed action, refill material for the next step

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Layer 0.3

PASTE rover // maintain position or, if previously performed action, refill material for the next step

POWDER rover // multiple units reach their starting position inside and outside the boundary

Layer 0.4

PASTE rover // maintain position or, if previously performed action, refill material for the next step

POWDER rover // units start depositing sand along a single line subdivided in segments, whose amount is the same of rovers employed

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Layer 0.5

PASTE rover // maintain position or, if previously performed action, refill material for the next step POWDER rover // when the entire layer is filled with powder, rovers return to refill stations

Layer 14.0

PASTE rover // using the powder previously deposited by the powder rovers, paste units climb the external granular material and reach their position on next POWDER rover // maintain position or, if previously performed action, refill material for the next step

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Layer 14.1

PASTE rover // as shown before, rovers deposit material in specific patterns over the previous layer of powder and paste POWDER rover // maintain position or, if previously performed action, refill material for the next step

Layer 14.2

PASTE rover // units return to refill stations

POWDER rover // maintain position or, if previously performed action, refill material for the next step

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Layer 14.3

PASTE rover // maintain position

POWDER rover // climbing on powder support, reach starting point for powder deposition around paste volume

Layer 14.4

PASTE rover // maintain position

POWDER rover // deposit powder in concentric patterns inside and outside the paste path

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Layer 14.5

PASTE rover // maintain position

POWDER rover // return to refill station

Consequent layers

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Autonomy

Autonomy of multi-robot system is one of the most challenging areas of investigation. Building materials and energy source are the main requirements for a successful autonomous performance. In terms of this research, clay as a building and support material is widely available on-site and robotic devices have the ability to collect material directly from the ground. However, being water required for clay crystallisation, access to energy and water sources needs to be investigated. The solar exposition is so intense in arid climates that can be used to provide necessary power to the robotic units. As a possible solution for the energy source, each robot has to be featured with solar panels and energy management system with a smart host microcontroller. [1] Thus, ‘it presents the construction of a solar tracking mechanism aimed at increasing the rover’s power regardless of its mobility’. [1] This solar-powered system requires a pack of dual batteries for each robot. ‘The aim is completing the process of charging a battery independently while the other battery provides all the energy consumed by the robotic vehicle’. [2] One battery functions as a primary source and the other one as a backup battery. When needed, the controller automatically switches to the secondary battery with a relay for robot functioning. [2] This gives the opportunity for the system to have continuous performance during the building process. At any given time, the atmosphere contains 3400 trillion gallons of water vapour, which would be enough to cover the entire Earth in 1 inch of water. [3] This creates an opportunity to extract water from humid ambient air for construction process. Air dehumidifiers can be used to provide required amount of water for clay mixing. The device is based on cooling the air below its dew point to remove moisture. [4] ‘The fan pulls a stream of atmospheric air through a filter and through the evaporator to cool the air and exhausts cooled air through the condenser. The water is collected as condensation by the evaporator and directed to the reservoir’. [5] Solar energy can be used to provide power to dehumidifier units. Looking at energy consumes, main factor is the machine efficiency as a ratio between removed water and used energy for such activity, measured in liters per kilowatt hour (L/ kWh). The disadvantage of the device is during performances in arid climates with low humidity. The relative humidity of a region should remain above 50% for effective functioning of the device. At the same time, relative humidity can change significantly during one day from 20% during the day till 100% during the night. In this case, the amount of potential water extraction can be calculated in relation to day and night humidity. Two possible solutions should be discussed in terms of robotic system. The first one is where each robot (paste rover) that performs extrusion needs to be featured with dehumidifiers. This will provide a fully autonomous performance, though significantly increasing the size of the robot. The second solution is to introduce a station that can generate water providing it to the robots. Past rovers will be charged with water when they return from the construction plot to refill stations, able to work in advance to collect a larger amount of water in storing containers and granting temporal continuity to the process.

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Cross sectional view diagrammatically showing a system designed for collecting atmospheric water and processing it to be drinkable. [6]

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Fitness landscape generation

One of the main advantage of employing robotic tools within construction is the relative simple control and overall supervision that the designer is allowed to manage above the entire process. As previously mentioned about construction general issues, costs are not always as much predictable as desired, as well as time and employed energy. Digital fabrication methods facilitate the prediction and simulation of several scenarios while easily tracing the alterations that each decision would determine within the project. As a proof of concept of how digital tools are able to influence construction activities, a simplified example of material deposition algorithm for retrieving optimal conditions during construction is here presented. The first phase of this process is related with the generation of a surface to be materialised and its subdivision in horizontal layers. Each layer, at this point represented by a contour line and hereafter by linear and tubular element to be extruded on site, is then divided into portions that are grouped in sectors, whose number is equal to the amount of robotic units available for task execution. As a consequence, each rover would work within its specific sector following a trajectory composed by three main paths, the first one being a segment connecting material refill station to the extrusion starting point, the second one the curve corresponding to the extrusion and the last being a segment connecting end point of extrusion path with material refill station. These three curves are sufficient for describing what happens within each layer, while for the entire construction process paths for each layer are listed along z axis and weaved in order to obtain a route that from the first layer continuously extends to the final one. This process is repeated for each sector, allowing the extrusion units to work without needing complex hardware to avoid collision and other interferences.

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Sample structure for fitness landscape generation. Dimensions are in millimeters.

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Time/Cost/Mass Projection

Once created the paths for each sector, the anlysis is addressed to the evaluation of the relation between time of construction and total cost of the process. Parameters that highly influence time of task execution are mainly the amount of rovers and their speed, while costs are determined by the amount of material employed, the energy consumed during the operation and all the hardware equipment needed. Construction material costs can be easily tracked evaluating the total extruded volume as the total length of the path by the cross section of the extrusion, whereas calculating energy costs depends on energy consumption of robotic units. Generally, energy employed by mobile robots is distinguished in robotics energy, for the management of all software, control systems and tools actuation, and mobility energy, dedicated to the locomotion system and its motors. Robotics energy is therefore proportional to the time of task execution and to the nominal power of the unit, while mobility energy is related to the distance covered by the rovers. Energy costs are evaluated multiplying energy employed during the entire construction process by unitary cost of energy. A similar procedure is followed to obtain hardware costs: considering the length of the extruder fixed, the extrusion cross-section becomes a measure of quantity of material transported by each unit, that is to say a larger diameter of extrusion would determine a larger amount of material and therefore more weight to be moved needing more power. The total mass of the rovers is then multiplied by a unitary mass cost to evaluate total cost of hardware. A first exploration has been done evaluating extrusion time, operational costs and mass of the structure as objectives to be minimised or maximised. All other parameters such as amount of rovers, thickness of extrusion or rover speed are left free of being manipulated by the script. In virtue of this, evolutionary algorithm here employed is not operating as pure optimisation process, but as a way of computing possible scenarios, whose internal properties are related to each other. Goal objectives, following how the script has been generated, are not as much conflicting as a multi-objectives optimisation would normally be. After 4-5 generations within a population of 20-30 individuals, differences between several methods for building the same geometry arises and start to define a fitness landscape for preliminary analysis and design indications. Within the first projection, time, mass and cost are objective to be minimised, while parameters defining the process show quite wide ranges of definition. The second projection owns the same architecture of the first one, but the mass of the structure is considered to be maximised, as for increasing the overall thermal inertia of the built volume.

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Surface contour along z

Divide contour

Invert matrix for sectors

Weave with base points

Interpolate rover path

7 layers

Extrusion diameter [mm]

Rover amount

250 to 400

Length per layer

Total extrusion time [h]

Extrusion time per layer

1 to 20

Pipe contour

Total extruded volume

Total length

0.1 to 0.4

0.10 to 3.00

Mass multiplier

Rover speed [m/h]

Ground projection

Covered section [m2]

Pseudocode and generative logic of the algorithm investigating on the relationship between variables, constants and objectives of the construction process. Rectangles identify input parameters while rounded shapes represent evaluated variables.

Uncovered section [m2]

1280 - loam

Total extruded mass [kg]

Unit weight

Rover mass

[Kg/m3]

200

Total hardware mass

Total extrusion cost

Material cost [£/Kg]

Mass cost [£/Kg]

Total hardware cost 70

Rover power [W]

Operation energy [kW]

0.04

Total cost [£]

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Total energy cost

Energy cost [£/Kg]

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Time/Cost/Mass Projection 1.

Sampling three individuals from the fitness landscape - projection 1 - in such a way generated, we observe that: to a smaller diameter of extrusion correspond a larger amount of layers and a smaller mass; time of construction is influenced by speed, diameter of extrusion and amount of rovers; more layers, would mean larger production time and less material used; energy saving is achieved decreasing mass of rover - also considering its load of material - and through the reduction of operational time. Diameter has been set to 45, 110 and 319 mm and their relative amount of layers of 94, 39 and 14. As a consequence, path length and extrusion time, in the same

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Extrusion diameter Rover speed Weight multiplier Rovers amount

110 2.4 0.4 1

[mm] [m/h]

Layers amount Extruded volume Path length Rover mass

39 24.2 3845 44.3

[m3] [m] [kg]

Extrusion time Operation cost Structure mass

1,602 33,183 30,979

[h] [£] [kg]

Extrusion diameter Rover speed Weight multiplier Rovers amount

319 1.9 0.38 3

[mm] [m/h]

Layers amount Extruded volume Path length Rover mass

14 76.3 1969 121.2

[m3] [m] [kg]

Extrusion time Operation cost Structure mass

1,036 115,893 97,686

[h] [£] [kg]

Extrusion diameter Rover speed Weight multiplier Rovers amount

45 1 0.06 10

[mm] [m/h]

Layers amount Extruded volume Path length Rover mass

94 9.5 24,300 2.7

[m3] [m] [kg]

Extrusion time Operation cost Structure mass

24,300 13,560 12,169

[h] [£] [kg]

Multi-robotic construction system for unfired soil masonry

Extrusion diameter Rover speed Weight multiplier Rovers amount

87 2.3 0.23 1

[mm] [m/h]

Layers amount Extruded volume Path length Rover mass

49 19.03 4831 20.01

[m3] [m] [kg]

Extrusion time Operation cost Structure mass

2,100 25,361 24,358

[h] [£] [kg]

Extrusion diameter Rover speed Weight multiplier Rovers amount

43 1.4 0.13 16

[mm] [m/h]

Layers amount Extruded volume Path length Rover mass

99 9.3 36,207 5,59

[m3] [m] [kg]

Extrusion time Operation cost Structure mass

2,586 16,526 11,909

[h] [£] [kg]

Extrusion diameter Rover speed Weight multiplier Rovers amount

363 2.5 0,23 7

[mm] [m/h]

Layers amount Extruded volume Path length Rover mass

12 86.9 2,494 7

[m3] [m] [kg]

Extrusion time Operation cost Structure mass

997 140,554 111,296

[h] [£] [kg]

Time/Cost/Mass Projection 2.

order, are 24,300 meters in 24,300 hours at 1 meters/hour; 3,845 meters in 1,602 hours at 2.4 meters/hours; 1,969 meters in 1,036 hours at 1.9 meters/ hour. The amount of rover is not - yet- related with other properties, meaning that for the previous three individuals, it is possible to dispose of less rover for covering more layers and viceversa, with important consequences on operational time and cost of construction. The latter depends on weight of units and their operation al time, as well as on the amount of material used and the overall weight of the structure. 12,169 kilograms costs 13,560 £, 30,979 kg costs 33,183 £ and 97,686 kg costs 115,893 £.

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Porosity/Energy/Mass Projection

Computed variations of construction configurations for equal number of layers and different levels of porosity, amount of energy employed and overall mass of the structure. Black area represents ground projection of the linear components.

Analogous considerations can be followed for interpreting results of a slightly different approach for including time, macro porosity of the structure, its total mass as well as operational costs within the same algorithm. Here the amount of layers is fixed to 7 for reducing the computational load during calculations and further restraints are set by introducing a first evaluation of porosity, variable extracted as difference of total bounding area and sum of area of all vertical projections of linear elements onto the bounding area. Like previously, liable of variation are also dimensions of extrusion, rover speed and rover amount. When pointing at maximum protection of inhabitants, covered area percentage needs to increase. For the shown samples, an optimisation toward maximum coverage submits extrusion diameter and material extruded volume as 374-72, 311-52 and 357-66, respectively mm and m3. Maximum coverage is obtained in the third sample, where operational costs appear to be higher due to a larger number of units and related energy expenses. Costs and overall mass of the structure are not directly related as long as number and properties of rovers can vary during evaluation. Additionally, costs depend on thickness of extrusion - that is to say amount of extruded material - encouraging applications with less units and thinner extrusion.

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Extrusion diameter Rover speed Weight multiplier Rovers amount

374 2.0 0.21 5

[mm] [m/h]

Layers amount Extruded volume Path length Rover mass

7 72.1 1,326 78.5

[m3] [m] [kg]

Total area Covered area

280.9 145.7

[m2] [m2]

Extrusion time Uncovered area Operation cost Structure mass -

663 135.4 111,886 92,234 -

[h] [m2] [£] [kg] -

Extrusion diameter Rover speed Weight multiplier Rovers amount

311 0.6 0.31 1

[mm] [m/h]

Total area Covered area

280.9 153.4

[m2] [m2]

Layers amount Extruded volume Path length Rover mass

7 52.7 892 96.41

[m3] [m] [kg]

Extrusion time Uncovered area Operation cost Structure mass -

1,487 127.6 72,231 67,402 -

[h] [m2] [£] [kg] -

Extrusion diameter Rover speed Weight multiplier Rovers amount

357 2.5 0.21 7

[mm] [m/h]

Total area Covered area

280.9 172.2

[m2] [m2]

Layers amount Extruded volume Path length Rover mass

7 66.6 1,498 74.9

[m3] [m] [kg]

Extrusion time Uncovered area Operation cost Structure mass

599 108.8 111,586 85,327

[h] [m2] [£] [kg]

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Porosity is approximated as the amount of vectors parallel to z axis that end intersecting the ground without touching the extruded material. The most porous sample, with its 92,000 £ for 145 m2 of uncovered ground projections, presents the larger amount of material employed as well as the thicker diameter, revealing how porosity, if not clearly compared with extrusion time, tends to vanish in economic logics of time and money saving. As a general catalogue, these tests are dependent on variables definition and defined relations between parameters. By modifying how definitions interact with each other, a different construction process is described and computed, as well as different would be the ways in which robotic units will cooperate for on-site operations.

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[1] Sanguino T.D.J.M., Ramos J.E.G. (2013). SMART HOST MICROCONTROLLER FOR OPTIMAL BATTERY CHARGING IN A SOLAR-POWERED ROBOTIC VEHICLE. IEEE/ASME Transactions on Mechatronics. 18(3). pp.1039-1049. [2] Seshadri G., Kishore Babu M. (2015). BEST BATTERY CHARGING USING A SOLAR ENERGY FOR ROBOTIC VEHICLE BASED ON RELAY-HOST MICROCONTROLLER. In International Journal of Emerging Trends in Engineering Research (IJETER). Vol. 3, No.6. Special Issue of NCTET 2K15 - Held on June 13, 2015 in SV College of Engineering, Tirupati. pp. 252-256. [3] Pontious K., Weidner B., Guerin N., Dates A., Pierrakos O., Altaii K. (2016). DESIGN OF AN ATMOSPHERIC WATER GENERATOR: HARVESTING WATER OUT OF THIN AIR. In IEEE Systems and Information Engineering Design Symposium (SIEDS). (2016). IEEE. pp. 6-11. [4] Woodford C. (2008). HOW DO DEHUMIDIFIERS WORK?.http://www.explainthatstuff.com/dehumidifier. html. [5] Abrari S. F. (2016). WIND QANAT, AN APPARATUS FOR ATMOSPHERIC MOISTURE RECOVERY. United Stated Patent Application 20160145837. Mississauga, CA. [6] Engel D. R., Clasby M. E. Jr. (1993). APPARATUS AND METHOD FOR EXTRACTING POTABLE WATER FROM ATMOSPHERE. US Patent 5259203 A. Application number US 07/883,415.

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Design development

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Design parameters

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Linear component

The design strategy consists on defining parametric relationships between form and function at different scales, where function is evaluated through a set of analytical tools related to structural and environmental properties and form is defined by sets of variables informed by said evaluations. At a local scale, the fist parameter that has to be defined is the diameter of the extrusion. The size of the extrusion will determine the amount of layers required to reach a specific height, since the height of each layer is equal to the diameter of the extrusion. In addition, increasing the extrusion diameter decreases the amount of force necessary to extrude the clay, but decreases the length of the segment that can be printed with a single charge. It is also important to note that the maximum extrusion diameter is equal to the diameter of the clay container and that increasing the size of said container increases the force needed for extruding. Finally, the relationship between the size of the container and the size of the rover carrying it must be kept in consideration. The next step is to transition from a linear element into a curved ribbing pattern that provides structural depth and self-shading qualities. The parameters that define the pattern are the density or frequency of the pattern, the depth or amplitude of each rib, and the space between them.

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Design Parameters

Linear extrusion parameters.

Linear Extrusion d = extrusion diameter

d extrusion length per container = container volume Ď&#x20AC; (d/2)^2

Extrusion Pattern t = wall thinckness

f = pattern frequency

s = minimum space

w = rib width

Ribbing pattern for structural performances.

s s > size of rover

Multi-robotic construction system for unfired soil masonry Single Path

Main Path Support Path

Multiple Paths

curve length f

Different Layer Paths

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Components aggregation

By stacking a series of segments with the same patterning parameters, the result is a solid wall that doesnâ&#x20AC;&#x2122;t allow light or wind to go through but can take large loads relative to the extrusion thickness. By alternating the direction of the pattern for each layer, the result is a lattice structure that allows for light and wind to go through but has very limited structural capabilities. In both cases, the result is a homogeneous pattern with no differentiation throughout the surface. By selectively altering the pattern at specific points, it becomes possible to have a combination of the two previously described stacking approaches, in which the amount of porosity is distributed throughout the surface in relation to structural and environmental criteria. We call this selective porosity. At a global scale, funicular shells are generated using RhinoVAULT [1], where the designer, responding to specific project requirements and limitations, defines parameters such as maximum span, height, supports and openings. In the future, this form-finding process could become parametric as a way of enabling people with no 3D modeling or design skills to interface with the form-finding process by defining simple parameters such as plot dimensions and geographical location, material quantities, project time, cost restrictions or even programmatic needs. Once an appropriate shell has been selected, it is processed using a slicing algorithm, which returns horizontal sections of the structure at intervals equal to the extrusion diameter. Each horizontal section is then distorted into the ribbing pattern and lofted together to create a ribbed surface. The patterning parameters are then optimized for structural and environmental criteria such as self-shading, solar radiation, water runoff management, and wind speed. After having defined the patterning parameters on the previously selected funicular shell, porosity is applied across the surface suing the selective porosity method while evaluating for criteria such as wind circulation, light penetration and internal comfort.

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Stacked Rain Control

Stacked configuration , suitable for rain control, high structural performances and self-shading.

Structural performance

Self Shading

lume 2

void

uniform distribution

solid

Alternating Ventilation

ency

Lighting

void

uniform distribution

Alternated version of the previous in which voids allow ventilation and light to penetrate the structure.

solid

Selective Porosity Rain Control

Structural performance Self Shading

Selective porosity allows to combine features of previous iterations and to assign specific patterns to specific areas of the structure.

Ventilation non-uniform distribution

t Layer Paths

Multi-robotic construction system for unfired soil masonry

Lighting

227

Structural analysis

We use Finite Element Analysis (FEA) as a way of relating the various parameters that define the ribbing pattern with a structural performance evaluation. Five experiments were conducted in order to understand how each variable affects the structural performance in terms of utilization and maximum displacement. The highly symmetrical vault geometry was kept the same throughout the experiments, apart from variations in span and height. This was done in order to reduce the complexity of the results and make them easier to visualize. Both the pattern density and the pattern depth are directly correlated with structural performance. (If they increase, maximum displacement decreases) When increasing the rib width from 860mm to 950mm, the maximum displacement went down but when increasing it even more, to 1150mm, the displacement became the largest. This is probably an indication that the proportion between depth and width must be kept as small as possible for a more stable structure.

Span

Height

Density/Frequency

Depth

Rib Width

228

span: 5m height: 3.4m density: 35 depth: 750mm rib width: 950

span: 7.5m height: 2.5m density: 35 depth: 750mm rib width: 950

span: 7.5m height: 3.4m density: 25 depth: 750mm rib width: 950

span: 7.5m height: 3.4m density: 35 depth: 375mm rib width: 950

span: 7.5m height: 3.4m density: 35 depth: 750mm rib width: 860mm

Utilization analysis in ribbed shells.

span: 7.5m height: 3.4m density: 35 depth: 750mm rib width: 950

span: 10m height: 3.4m density: 35 depth: 750mm rib width: 950

: 7.5m ht: 2.5m ity: 35 h: 750mm idth: 950

span: 7.5m height: 4.3m density: 35 depth: 750mm rib width: 950

span: 7.5m height: 3.4m density: 35 depth: 750mm rib width: 950

n: 7.5m ht: 3.4m sity: 25 h: 750mm width: 950

span: 7.5m height: 3.4m density: 35 depth: 750mm rib width: 950

span: 7.5m height: 3.4m density: 45 depth: 750mm rib width: 950

n: 7.5m ht: 3.4m sity: 35 th: 375mm width: 950

span: 7.5m height: 3.4m density: 35 depth: 750mm rib width: 950

span: 7.5m height: 3.4m density: 35 depth: 1300mm rib width: 950

n: 7.5m ht: 3.4m sity: 35 h: 750mm width: 860mm

span: 7.5m height: 3.4m density: 35 depth: 750mm rib width: 950mm

span: 7.5m height: 3.4m density: 35 depth: 750mm rib width: 1150mm

utilization

n: 5m ht: 3.4m ity: 35 h: 750mm idth: 950

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Environmental strategy

Almost half of all the energy produced in the developed world is inefficiently used to heat, cool, ventilate and control humidity in buildings, for meeting the increasingly high thermal comfort levels demanded by occupants. [2] In arid climates high priority is using geometrical exploration and material properties as feature of environmental strategy. This brings intelligence and responsiveness, creating potential for an adaptive material system development. The significant complexity and geometrical possibilities that can be performed by multi-robot systems serve towards plenty of design variations based on environmental needs, as long as unfired clay provides consistent improvement to indoor comfort in hot climates thanks to optimal thermal conductance and resistance levels. [3] At the same time, clay is cheap, environmentally friendly and abundantly available on-site. Unfired clay can be utilized in the creation of more sustainable desert architecture, minimizing energy demand while enhancing the quality of the built environment. [3] Environmental strategy of the projects covers few main climatic criteria as temperature, relative humidity, solar radiation, precipitation, wind and rainflow with the intention of creating shelters with high environmental performance driven by geometrical exploration and based on material properties. Climatic requirements will form the design proposal, unit orientation and clustering strategy. Solar radiation, self-shading, natural ventilation and rainflow analysis are defined as starting point for investigation. Selective porosity and pattern with variable depth gives plenty of opportunities for self-shading and creates natural ventilation. It prevents direct sun rays penetration, but at the same time it provides natural illumination of the space during all day. Additionally, selective porosity contributes to air flows topology and helps to create cross-sectional natural ventilation, as a ‘flow generated by temperature differences, wind pressure and this creates a natural air exchange’. [4] ‘The ventilation rate depends on the strength and direction of these forces and the resistance of the flow path’. [5] It is much more efficient in spaces ‘with upper and lower openings’, compared with single openings that ‘generate lower ventilation rates’ avoiding ventilated air from deeply penetrating into the structure. [5]

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Self-shading analysis on different layering patterns.

Stacked Self shading factor: 0.93

Alternating Self shading factor: 0.88

Selective Porosity Self shading factor: 0.77

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Occlusion and radiation analysis

Occlusion analysis is performed projecting vectors from sun position to a plane representing the ground for evaluating the percentage of vectors not intersecting with the geometry of the structure. Two variations are tested against occlusion, both of them employing the same amount of sample points on tested surface - the ground - representing location of intersection between sun rays and uncovered surface. Those vectors that cannot reach the surface without intersecting the geometry of the shelter are subtracted from the total amount of sample points. The ratio between these two numbers is employed for obtaining the occlusion rate of a particular variation. The results show that an increase of cross-sectional dimensions of linear elements allows for larger occlusion percentage with sun rays at specified time and location - in this case Cape Town on July 15 from 1 to 2 pm. Radiation analysis traces values of radiation - direct and reflected - showing, through scale of colors, the amount of kW received every hour by one square meter of material. Being the analysis resolution 0.1 m, values in meters are computed as average between full and empty spaces. Maximum radiation is equal in both analysis, but similarly to what found in the occlusion test, shelter variation with smaller section of tubular elements presents higher levels of total radiation within the selected time frame. On the one side, this is related to a difference in total superficial area of the thinner extrusion, on the other hand larger cross sections allow for higher levels of self-shading instances that reduce the radiation load of those portions that are placed close to the ribs with low permeability.

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Occlusion test and radiation analysis for two design variations.

U count V count Total sample points

300 300 90,601

Grid size

0.1

[m]

Max radiation

0.59

[kWh/m2]

Occluded sample points Occlusion percentage

42,710 47 %

Total radiation

105

[kWh]

U count V count Total sample points

300 300 90,601

Grid size

0.1

[m]

Max radiation

0.59

[kWh/m2]

Total radiation

119

[kWh]

Occluded sample points Occlusion percentage

36,995 41 %

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Rainflow analysis

Most of arid environments have a short rain season that is enough to affect physical properties of unfired clay. One of the aims consists in controlling the waterflows for evaluation of remedial strategies to prevent erosion and water absorption. Ribbed structures concentrates water flow in paths that perform as waterspouts, while porous ribbed structure, though presenting similar considerations, need to take in account percolation, stagnation and water dripping. The latter is particularly important for structures composed of multiple tubular elements where, due to their shape, water is induced by gravity and surface tension to generate slip trajectories along transversal section of the extrusions. A drop of water at its first intersection with a portion of matter tends to describe theoretical semicircular slip trajectories towards the ground, whose length is determined by dimension of drop, cross section of the element and permeability of the material. Rain flows simulation is executed with two methodologies for two variations. Employing the same structures previously tested for occlusion and radiation, a number of virtual particles - drops - of water is specified as well as the position from which they will fall. Particles are placed at specific height named Sky Z - here 5 meters - and disposed in a rectangular and regular grid or in a random grid contained by rectangular boundaries. When simulation is launched, particles start falling as pushed by gravity towards the ground and their trajectories on the structure plotted. 10,000 drops are here tested with both starting settings and slipping trajectories computed. The amount of paths on the extrusions and the amount of released particles are used for calculating coverage percentages, that are clearly not dependent on nature of starting grid, but derive from cross section of extrusions and their amount, revealing how structures with thicker constituent element allow for higher coverage from rain water.

234

Rain flows analysis executed on two design variations with regular and random starting grid with 10,000 particles dropping from 5 meters height.

Particles disposition

Regular

Particles disposition

Random

Curves amount Minimum length Maximum length

3897 0.119 0.532

[m] [m]

Curves amount Minimum length Maximum length

3868 0.133 0.532

[m] [m]

Total length

1621

[m]

Total length

1614

[m]

Coverage percentage

39%

Coverage percentage

38.7%

Particles disposition

Regular

Particles disposition

Random

Curves amount Minimum length Maximum length

3296 0.004 0.188

[m] [m]

Curves amount Minimum length Maximum length

3328 0.003 0.188

[m] [m]

Total length

489

[m]

Total length

492

[m]

Coverage percentage

33%

Coverage percentage

33.3%

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Section resolution and texture

Diagonal sections of input structure built with a resolution of about 300 mm diameter of extrusion. Being faster to build, these sections are preferred for emergency or extreme conditions in virtue of their economical value and lower needed accuracy during operation. The architectural consequence of this approach is the reduction in space for allocating thicker linear components, as well as raw surfaces finish.

236

Diagonal sections of input structure built with a resolution of about 100 mm diameter of extrusion. This projection is time and money demanding in virtue of larger internal space and higher texture complexity. Applications in which time constraints are reduced by larger amount of robots allow to increase resolution of construction while adjusting openness and closure of ribbing pattern is possible to control weathering agents influence on indoor space.

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[1] Rippmann M., Lachauer L., Block P. (1994). INTERACTIVE VAULT DESIGN. International Journal of Space Structures volume 27 number 4, pages 219-230. [2] Hall M. R. ed. (2010). MATERIALS FOR ENERGY EFFICIENCY AND THERMAL COMFORT IN BUILDINGS. Elsevier. [3] Huberman N., Pearlmutter D. (2008). A LIFE-CYCLE ENERGY ANALYSIS OF BUILDING MATERIALS IN THE NEGEV DESERT. Energy and Buildings, 40(5), pp.837-848. [4] Linden P.F. (1999). THE FLUID MECHANICS OF NATURAL VENTILATION. Annual review of fluid mechanics, 31(1), pp.201-238. [5] Allocca C., Chen Q., Glicksman L.R. (2003). DESIGN ANALYSIS OF SINGLE-SIDED NATURAL VENTILATION. Energy and buildings, 35(8), pp.785-795.

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Conclusions

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Tracing the origin of modern fabrication and construction techniques within the industrialisation movement, from which machines and robots have arisen to essential tools for human activities, a series of data and considerations aimed at underlining issues and criticality have been collected and investigated within the contemporary construction industry. A sector that, on the wave of an increasing demand of housing realities and a pure interest in economical growth, developed for a long time without taking in account side-effects and externalities of such activities, concerning manpower, environment and energy consumption. Current state of construction industry amounts to a transition threshold in which technologies directly coming from the manufacturing realm are slowly and constantly suggesting alternative methodologies for fabrication, production and assembly of structural infrastructures. Precision, repeatability and adaptability typically involved in warehouse production are employed in applications in which outdoor and on-site complications are faced through the utilisation of computer numerically controlled means and advanced production processes. The awareness of the costs related with workmen injuries and with the modification of natural ecosystems, as well as all other consequences of overengineered construction methods, have been moving interests towards robotic system to be employed on-site for substituting or helping in dangerous and complicated tasks. The field of robotic is increasingly assuming importance in modern construction, as it already did in the field of manufacture. But where controlled settings normally involve large and complex machines, on-site operations are not easily controllable given the amount of unexpected events and adverse agents, such as weather conditions and human complications. In order to get closer to a solution, collaborative biological creature have been questioned and their construction skills taken as inspiration for designing systems that can rely on a large amount of small robotic units and in which scalability becomes fundamental aim. Control of such systems can be centralised or decentralised, according to the amount of information with which agents are provided during the process. Decentralisation requests more time for development of its internal logics, while centralisation has the advantage of directly inputting instructions without the need of translating them into sets of simple and local rules. Additive manufacturing has been here intended as the essential mean for employing traditional construction material within contemporary construction paradigms. Earth, soil and minerals in form of granules and viscous pastes have been experimented towards their integration in extrusion techniques and robotic application, trying to follow logics that maintain advantages and benefits traditionally considered in ancient construction techniques. For this reason, natural air drying processes have been employed in order to provide crystallisation of soil particles - in particular clay, loam and sand - within the attempt of determining low consumption of material and energy and low emission of harmful gases in the atmosphere, goals also supported by the reduction of transportation needs and the removal of energy expensive processing of raw material.

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Within these considerations, computational processes have been employed for exploring and conceiving designs able to perform structural and environmental functions while facilitating their automated construction process. Digital models have been generated for visualisation and analysis of performances and algorithms have been executed for generating multiple scenarios of application of the system. In particular, evolutionary and multi-objective optimisation have been here employed, rather than for obtaining the highest performances configuration, for producing a simplified catalogue of options in which input parameters and constants are retrieved from empirical analysis as well as scientific literature. The establishment of a fitness landscape composed by several versions of the same methodology represents a useful tool for controlling how variations in construction tools influence the final design as well as how designers and constructors may interpret and execute the process, allowing for clear planning and management of available resources. In regard to the material employed, earth, with its components, is considered a composite material, meaning that internal composition highly influences physical properties of outcome of the construction process. Small variations in amount and quality of loam, sand, clay and water need to be empirically evaluated and compared with desired results, in a process that is also strongly related with environmental conditions. From material manipulation executed, major criticalities arose from manual mixing of particles with water, as well as partial evaporation of water during operations. This, together with viscosity concerns, shows how main contribute to the quality of the manufactured objects is the homogeneity of water absorption and soil particles compaction, whose processes are likely dependent on nature and disposition of support material as well as difference in composition between support and extrusion material. Producing an artefact with clay would request the utilisation of clay itself as support material, while objects made of a mixture of clay and loam would need similar composition to be used as support material, showing how water displacement modes during drying process is needed to be as uniform as possible, avoiding changes in medium and allowing for consistent evaporation of all the water that does not intervene in sinterization processes. For addressing robotic deposition of material, a small tracked ground rover based on an Arduino microcontroller has been purchased and assembled. The unit is controlled by uploading code into its motherboard specifying for both motors direction and speed of rotation. Two modalities of exploration have been considered, both of them trying to graphically deduce location of speed variation. The first one, requesting much more calculation for being used, consisted in developing a continuous path along which both motors would have continuously functioned varying velocity - but not direction. Within computation of the path, visual scripting showed lack of efficiency if not coupled with complex mathematics. The result of this test presented the additional duty of calculating time duration for each speed variation, a task that is not as simple as supposed and that include advanced robotics argumentations. As a response to this situation, a second modality has been developed as made

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of multiple segment that approximate the intended path. This intermittent or discontinuous solution permits to program the unit for the execution of a certain path without having to compute small variation in velocity of the motors throughout path development. As a matter of fact, the path is here composed by segment spaced out by points in which the rover employs both motors spinning in opposite direction for rotating on itself towards the direction of the successive segment to describe. In this case, higher resolution of the path is achievable by increasing the amount of segment composing the trajectory or scaling the trajectory up while maintaining the same size of robot employed. The intermittent configuration has the advantage of not requesting complex calculation while still being effective for path planning purposes and task execution. The code uploaded for the description of sample path showed how even simple digital and robotic tool can be successfully controlled and employed for robotic applications of limited complexity. On the other side, the unit used in this exploration clearly presented several problems in hardware configuration and stability, forcing the user to continuously adjust cable and wires as well as track parallelism for a correct locomotion. The construction logic behind this research is based on additive manufacturing paradigms and takes inspiration by fabrication and construction technologies that are currently evolving from 3d printing instances and methods. As usually occurs in this field, three-dimensional materialisation of an object presents, within all others issue, the challenge of gaining height while avoiding collapse of the structure being built. The method here speculated sees the utilisation of support material as filler of all the voids left within the built volume, in the attempt of rendering the process independent from gravitational forces influence. As a consequence, in each layer material in form of dry granules is deposited around extrusions for generating a continuous, compression resistant and flat surface to be employed as base for the successive layer. At the end of process and after air drying, support material, still dry and uncemented, is removed for revealing the solid geometry manufactured. Depending on nature of material used, further operations of cleaning and finishing are requested. Within these premises, examined by tests and prototypes on a small scale, analogous methods are hypothesized for medium and large scale construction. Here, with the employment of ground rovers for collection and deposition of material and aerial robots for control of operations and data gathering, collaboration between constructing agents is considered the solution for such complex operations. Ground units have been thought as divided into categories, each of them manipulating specific phases of material, and considered essential tool for challenging scaling processes. Support material is therefore not only a way of avoiding collapse but especially a mean for allowing units to climb over already deposited material and accessing higher level of the structure to build. Consequently, considering maximum slope coverable by selected or designed robot motors, the construction process needs to be supported by free space around the structure to materialise for allowing deposition of support material to be climbed.

244

Evolutionary optimisation tools have been then employed for understanding how variation in thickness of extrusion, available funds and time, as well as robotic units power are related to material and energy consumption and desired performances. Such tools are of fundamental importance for tracing a map of dependencies between variables and objectives that otherwise would be almost impossible to follow in virtue of the complexity of the system. The algorithm outlined for this scope is clearly not exhaustive enough for being directly applied to real construction operations, being based on several theoretical assumptions and being rooted in multiple and sometimes not homogeneous analysis of such technologies and methods. In particular, limited attention has been dedicated to electronic and energy sciences besides the attribution of plausible values for machines power descending from current instances of mobile robots design. Similarly, relationship between variation in material load and its effects on units performance are expressed through direct proportionality, assuming that more material to displace signifies the necessity of heavier units, therefore needing more power to execute dislocation tasks, and that bigger units tend to request more money for being produced and controlled. In addition, arguments about tasks for material collection and support material deposition have not been deepened due to the amount of variables to be computed for obtaining plausible and indicative results. Complete parametrisation of construction method, though of great interest for this research, has been intentionally avoided. Proposed patterns and material disposition are of such digital complexity to render this process incredibly heavy in terms of computer processing, therefore two outcome instances of the construction method - with extrusion of 10 and 30 cm in diameter - are selected and tested and compared for occlusion and shading, radiation, rainflow analysis and texture. The results of these operations need to be commented in the light of how the algorithm from which they originated has been structured and set. Self-shading analysis on structure with thick walls, not so differently from experience, suggest that the denser the mesh of the structure, the larger is the contribution of the extrusions to light protection, while occlusion test on single layer structure shows how, not so directly deducible, larger meshes can constitute a better solution for increasing protection by penetration of solar rays into the structure, likely attributable to larger amount of shading performed by the thicker elements. Similarly, though maximum radiation is equal for both variations, total radiation per square meter is higher for thinner meshes, where contributes of direct radiation is higher than those of indirect radiation. Rainflow analysis, not really accounting for difference in disposition of particles within their starting position, gives similar results of protection for both instances, not completely justifying employment of more material only for protection from atmospheric agents.

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Further developments

246

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Further development of this research are to be identified in three different areas: material deposition techniques, nature of robotic agents and consideration upon construction logic employed. Material deposition has been here developed through the utilisation of mechanical and pneumatic tools for extruding soil, while deposition of linear elements has been executed manually. Successively, automated distribution of dry granular material will be investigated through the design and testing of ejector pumps able to dislocate granules through the employment of air or gravity, as well as moderate modifications will be applied to the designed extruder for viscous materials. At the same time, different granular materials to be used as support during the process will be examined in order to potentially reducing effort and energy for cleaning and finishing phases of the structure and better controlling moisture displacement during drying process. For this reason, granular materials that are less hygroscopic than loam and clay - for instance, sand - or that are completely non-hygroscopic - like light expanded clay aggregate - will be tested in compression and ease of distribution during operations. As previously mentioned, sample ground robot used have showed evident fragility and lack of reliability in execution of tasks, especially when tested on rough terrains and in uncontrolled settings. From here the necessity of designing and producing units that are able to withstand longer period of usage, as well as to dispose of larger amount of power for displacing material and tools by themselves while granting integrity between coded instruction and hardware responsiveness. On the other hand, though of simple management and comprehension, the Arduino based interface is limited in complexity and does not allow for data control during process, rendering data input and path execution as two separate phases. Therefore, specifically designed control interface will be tested or conceived through the utilisation of programming languages with higher stability, possibilities of intervention on mounted software - possible candidates are the complex C++ as well as the more intuitive Python - and real-time control of the process. Concerning the construction logic, multiple are the areas to explore. Initially, on-site availability of material needs to be addressed in terms of location and storage, understanding if distributed storage of resources in correspondence of each rover can increase efficiency and resilience of the process or if centralised collection of material at precharged and defined refill station to be intermittently reached by the units are able to simplify the design of the hardware involved and to reduce operational costs. Then, cooperation rules between robots have to be developed for precise evaluation of needed amount of rover in each category for available time as well as for desired design outcome. Eventually, large scale prototyping will be performed through utilisation of a contained number of produced robotic units for each category in uncontrolled setting, looking at cooperation in material deposition and removal of support material, while trying to plot an exhaustive report upon correlation between variables and parameters for the tested multi-robotic construction system.

248

From top left clockwise. Light expanded clay aggregate to be employed as support material.

MATERIAL DEPOSITION

Non-hygroscopic support material

Granular material ejector pump

Diagram of centrifugal pump for liquids and solids. Differential drive simulator in Processing by Artica Creative Computing. Cooperation in ants for generating a bridge.

ROBOTIC AGENTS

Ground rover custom design

Development of control interface

Draft of mechanical dislocation system composed by a stepper motor, sprocket and threaded rod. Assembling of differential drive tracked rover.

CONSTRUCTION LOGIC

Material collection and refill

Multi-robotic construction system for unfired soil masonry

Cooperative behaviour

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Map of contribution

250

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E. B ABSTRACT INTRODUCTION // Industrialisation and machines // Construction industry issues // Resources scarcity and availability // Environmental emissions // Earth construction DOMAIN EARTH AND LOAM // Granular materials // Soil mineralogy // Soil phases // Hygroscopic properties // Construction techniques ROBOTIC FABRICATION // Automation and manufacture // Prefabricated masonry // Selective laser sintering // Solar sinter // Industrial extrusion // Woven clay MOBILE ROBOTS // Robustness, scalability and flexibility // Collaborative behaviour in natural systems // Termes // Spatially targeted communication ROBOTIC CONSTRUCTION // On-site automation // GHG emissions // Site safety // Prior art overview // Vertical slip forming // D-Shape // Big Delta WASPS // Rock print // Minibuilders SITE SELECTION METHODS // Control and Dataflow // Parametric Form-finding // Structural Analysis (FEA) // Environmental Analysis // Multi-objective optimization // Cellular Automata (CA) // Agent Based Modeling (ABM) // Physical computing // Material tests

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J. M. C. F. M. M.

E. B.

J. M. C. F. M. M.

RESEARCH DEVELOPMENT MATERIAL EXPLORATION // Manual forming_Water absorption // Casting_Layers cohesion // Direct extrusion_Overlapping // Direct extrusion_Spanning // Direct extrusion_Masonry // Hydrostatic extrusion_Pneumatic tool // Hydrostatic extrusion_Clay // Hydrostatic extrusion_Clay > Loam > Sand // Hydrostatic extrusion_Loam > Clay > Sand // Hydrostatic extrusion_CNC technologies ROBOT CONTROL // Centralized control // Decentralized control // Robotic unit hardware // Path processing // Differential drive kinematics // Path planning // Linear and angular velocity // Continuous path // Discontinuous path CONSTRUCTION STRATEGY // Material manipulation // Soil crystallization // Layering logic // Construction process // Autonomy // Fitness landscape generation // Time/Mass/Cost Projection // Porosity/Energy/Mass Projection DESIGN DEVELOPMENT // Linear component // Components aggregation // Structural analysis // Environmental strategy // Occlusion and radiation analysis // Rainflow analysis // Section resolution and texture CONCLUSIONS FURTHER DEVELOPMENTS

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