Towards a multi robotic construction system by Katya Bryskina

Towards a Multi-Robotic Construction System Using clay for construction with a team of small cooperative robots

Architectural Association School of Architecture Master of Architecture, Emergent Technologies and Design 2015-2017

ÂŠ Architectural Association, 2017 36 Bedford Square, London WC1B 3ES

Towards a Multi-Robotic Construction System Using Clay for Construction with a Team of Small Cooperative Robots

M.Arch. Candidates

Ekaterina Bryskina JosĂŠ M. Cherem

Course Directors

Michael Weinstock George Jeronimidis

Studio Master

Evan Greenberg

Studio Tutor

Elif Erdine

Course Tutor

Manja van de Worp

Acknowledgments We would like to express our most sincere gratitude to Michael Weinstock and George Jeronimidis for their continuous support and guidance throughout the course of the dissertation. We would also like to express our gratitude to the studio tutors and external collaborators for their constructive criticism and generous advice and to our fellow students for sharing with us your valuable insight. Finally, we would like to acknowledge the constant support and continuous encouragement from our friends and family, this work wouldnâ&#x20AC;&#x2122;t have been possible without you.

Abstract Robotic construction processes can provide high levels of customization while reducing project costs, time and embodied energy. Therefore, such processes have the potential of ushering the production of architecture into the new paradigm of mass customization. Significant limitations of current robotic construction technologies include the need of either large gantry systems or of highly sophisticated materials in order to build structures at an architectural scale. This research aims to avoid such limitations by introducing a layer-by-layer, additive manufacturing, multi-robotic construction method which uses clay as a building material, thus allowing for the construction of large structures with a team of relatively small cooperative robots. The first step towards this highly ambitious goal is to identify the various fields of research that must come together into an integrated system. Material research, robotic system design, device synthesis and integration, and robotic material manipulation are some of the main topics which are encompassed within the research. In addition, climate-specific passive building strategies are extracted from a study on clay vernacular architectures and are used to inform the proposed design solutions.

Table of Contents

0.0 Introduction 0.1 Mass Customization 0.2 Automated Construction 0.3 Research Proposal

12 14 16

1.0 Domain 1.1 Case Studies 1.2 Multi-Robot Systems 1.3 Material Selection 1.4 Clay in Architecture

20 36 42 50

2.0 Methods

1.1 Funicular Form-Finding 1.2 Finite Element Analysis 1.3 Parametric Robot Control 1.4 Robotic Prototyping 1.5 Computer Vision 1.6 Goal-Based Vector Field Pathfinding

58 58 59 59 60 61

3.0 Research Development 3.1 Construction Method 3.2 Multi-Robot System Design 3.3 Primary Deposition Strategy 3.4 Support Material Deposition Strategy 3.5 Robotic Prototyping - Primary and Supports 3.6 Slicing 3.7 Secondary Deposition Strategy 3.8 Robotic Prototyping - Secondary Deposition 3.9 Devices

64 70 76 82 88 104 106 116 122

4.0 Design Development 4.1 Site - Case Study 4.2 Clustering Strategy 4.3 Building Morphologies 4.4 Selective Indirect Porosity 4.5 Second Stage Deposition 4.6 Design Proposal

136 138 140 144 146 148

5.0 Conclusions 5.1 Construction Method 5.2 Deposition Strategies 5.3 Multi-Robot System Design 5.4 Devices 5.5 Design Development

156 157 157 158 158

6.0 References 6.1 Image References 6.2 Text References

162 168

0.0

Introduction

0.1 0.2 0.3

Mass Customization Automated Construction Research Proposal

12 14 16

0.1 Mass Customization Fig. 1 Mass production of social housing in Mexico City

The construction industry is currently facing many challenges including low labor efficiency, high accident rates, and a vanishing skilled workforce which has led to insufficient and difficult control of the construction site. In addition to this, the building sector is one of the biggest energy consumers and carbon emitters. [1][2] Throughout the twentieth century, attempts at tackling some of these issues have focused on the mass-production of large-scale housing developments, which are in most cases made up of large amounts of identical houses and have therefore failed to meet the needs of individuals. In the past two decades, industries which were previously facing similar problems have started to transcend the paradigm of mass-production into a new paradigm: mass customization. Taking advantage of a new automation approach generally known as rapid prototyping or 3D printing, mass customization aims at combining the flexibility and personalization of custom-made with the low unit costs of mass production. Several rapid prototyping methods have been developed and successfully implemented in a large variety of domains such as the automotive, aerospace and healthcare industries amongst many others but have failed to make such radical transformations in the building sector, mainly due to material and scaling constrains.

Introduction

Towards a Multi-Robotic Construction System

0.2 Automated Construction Fig. 2 Comparison between traditional and robotic construction methods in terms of flexibility and embodied energy.

Introduction

Today, the effective use of automation is one of the greatest opportunities, as well as one of the greatest challenges, facing the construction industry and has therefore been the main subject of interest for many researchers on the field. This has led to the design and development of a variety of robotic construction processes that aim at providing high levels of customization while reducing project costs, time and embodied energy. The different strategies that have been developed can be divided in two main categories: factory printing, which usually involves an on-site assembly process of the printed parts, and on-site printing. They can then be further subdivided into those which use a gantry system and those which use mobile-robots. [3] Gantry based approaches are currently the most successful in terms of achieved scale and material feasibility for construction but are limited by the need to build a gantry at least as big as the parts it can print which is labor intensive and time consuming. The main limitation of current proposals for mobile-robot based approaches relies on the need of highly sophisticated materials which are not appropriate for the construction of inhabitable spaces.

Conventional

cost

Prefab (modular)

Prefab (manufactured) Robotic Construction Emergency

architectural flexibility

Embodied Energy

CO2 Emissions 7.00E+05

2.00E+04

0.00E+00

Traditional Robotic Construction*

Towards a Multi-Robotic Construction System

0.3 Research Proposal This research proposes a layer-by-layer additive manufacturing (AM) multi-robotic construction method which uses clay as the main building material. The proposed method uses the granular support material as a ramp through which the robots can access the top layer of the printed structure in order to print over it the subsequent layer. Although large amounts of support material are required for this method, once the printed structure has cured the supports are removed and reused for other structures, therefore generating no material waste. This method makes it possible to build large clay structures with a team of relatively small cooperative mobile robots. The proposed robotic units are designed from a synthesis of off-the-shelf devices which are currently widely available. In addition, each unit is allocated with a specific task in order for them to be kept as simple as possible. One of the main challenges that must be addressed is the method through which multiple robots can communicate with each other in order to cooperate towards achieving a common goal. This research presents an evaluation of possible coordination protocols and proposes the design of a weakly centralized multi-robot system (MRS). In such a system, the global awareness is centralized on an unmanned aerial vehicle (UAV) equipped with an infrared sensor, taking advantage of its privileged vantage point in order to provide the ground-based units with information regarding their position relative to each other and to the building plot. Local awareness is distributed amongst the ground-based unitâ&#x20AC;&#x2122;s on-board sensing capabilities which enable them to modify their locomotion routines for on-the-go error correction. The proposed construction method is composed of three deposition strategies that when combined can provide a wide variety of architectural solutions to specific contexts. The primary and secondary deposition strategies, which deal with the extrusion of clay, are tested through a deterministic, or top-down, approach in which their toolpaths are defined explicitly to be executed by a robot equipped with a clay extruding end effector. On the other hand, the proposed support material deposition strategy relies on a stochastic, or bottom-up, approach in which stigmergic communication is used to define the locomotion routines of the corresponding robotic units without the need for explicitly defined tool-paths. Finally, the proposed strategies are integrated into the design of a context specific settlement in which a study of vernacular architectures is used to inform the development of passive bio-climatic design solutions. Construction metrics related to material quantification and active printing times for the proposed design are extracted and used to evaluate its feasibility.

Introduction

Towards a Multi-Robotic Construction System

1.0

Domain

1.1 1.2 1.3 1.4

Case Studies Multi-Robot Systems Material Selection Clay in Architecture

20 36 42 50

1.1 Case Studies

Overview Today, the effective use of automation is one of the greatest opportunities, as well as one of the greatest challenges, facing the construction industry and has therefore been the main subject of interest for many researchers on the field. This has led to the design and development of a variety of robotic construction processes that aim at providing high levels of customization while reducing project costs, time and embodied energy. Significant limitations of current robotic construction, additive manufacturing technologies include the need of either large gantry systems or of highly sophisticated materials in order to build structures at an architectural scale. Some selected projects which have made contributions towards the field of robotic construction are briefly described and evaluated.

Domain

Amalgamma

Solar Sinter

Woven Clay

Additive Manufacturing

3D structures from digital files. Successive layers of material are deposited according to specific toolpaths. Minibuilders

Level of Comunication and Coordination

Material Sophistication

Scale of the outcome is limited by material performance.

The scale of the outcome is limited by the size of the tool or gantry. W.A.S.P.

Deterministic Approach

Stochastic Approach

Top-Down logic High degree of control and error reduction.

Bottom-Up logic Responsive and addaptive error control. D-Shape

M.R.F.S.F.S.

Termes

Integrated Approach

Freeform

Top-Down control of large structures. Bottom-Up material manipulation for responsive and addaptive error control ICD/ITKE Research Pavilion 2014-15

Towards a Multi-Robotic Construction System

1.1.1 Amalgamma Wonderlab - UCL, The Bartlett School of Architecture 2014-2015

Fig. Concrete extrusion end-effector mounted on an robotic arm.

Overview

Fig.

Evaluation

Large scale prototype of a concrete column.

Using concrete opens the possibility to create objects at an architectural scale. ranular supports allow for greater morphological freedom even when working with a slow curing material such as concrete or clay. sing a translucent material as support creates objects with interesting visual effects. The size of the product is currently limited to the size of the robotic arm.

Domain

Amalgamma proposes a new additive manufacturing method which combines two existing concrete 3d printing tecniques extrusion printing and powder printing. Concrete is extruded layer-by-layer over a bed of granular material which works as supports, allowing for a higher printing resolution as well as for large overhangs which wouldnâ&#x20AC;&#x2122;t be possible with traditional contouring tecniques. [1]

1.1.2 ICD/ITKE Research Pavilion 2014-15 Inst. for Computational Design (Prof. Menges) Inst. of Building Structures & Structural Design (Prof. Knippers) Overview

Fig. 3

This project demonstrates the architectural potential of a novel building method inspired by the underwater nest construction of the water spider. Through a novel robotic fabrication process an initially flexible pneumatic formwork is gradually stiffened by reinforcing it with carbon fibers from the inside. The resulting lightweight fiber composite shell forms a pavilion with unique architectural qualities, while at the same time being a highly material-efficient structure.â&#x20AC;&#x2122;

Exterior view of the pavilion during the fabrication stage.

Evaluation

Fig.

The project successfully demonstrates the possibility of developing an in-situ robotic construction process. The initial part of the design process consists on generating the shell geometry and main fiber bundle locations using a computational form finding method informed by fabrication constraints and structural simulation. Subsequently, during the construction process, an embedded sensor system allows for constant feedback between the actual production conditions and the digital generation of robot control codes. This means that the robot can adapt to the changing stiffness of the pneumatic formwork during the fiber placement process. This integration of a deterministic and a stochastic design approach is particularly relevant.

Diving Bell Water Spider (Agyroneda Aquatica) reinforcing an air bubble from the inside.

Fig. yber- hysical fibre lacement process.

Towards a Multi-Robotic Construction System

1.1.3 Minibuilders Institute for Advanced Architecture of Catalonia (IAAC), 2014

Fig. 6

Overview

Foundation robot (topright)

Fig.

Minibuilders consists of a heterogeneous multi-robot system composed by three types of robots (foundation, gripper and vacuum . ach robot has a different function which contributes to the creation of large scale structures made of a fast curing synthetic paste. The foundation robot uses a line following photo-sensor to print the first layers of the structure which the gripper robot clamps into to continue printing the subsequent layers. acuum robots are then placed on the structure to print extra shells that provide greater structural performance.

Grip robot (top-left)

Evaluation

Fig. Vacuum robot (bottom-left)

Fig. 9 To reinforce the shell, vacuum robots are attached onto the surface to print an additional layer and to smooth it.

Domain

One of the main limitations of the system is the material which needs to cure almost immediately since each printed layer is used to support the gripper robot for the consecutive layers. This means that working with slow curing materials such as concrete or clay is not possible. Another important limitation is the need for human interaction to place the robots on the structure which reduces the possibility of fully autonomous building. n the other hand, using mobile robots makes it possible to print large structures using small robots and eliminates the need for any site preparation before construction. Communication between robots was not developed.

1.1.4 Solar Sinter Markus Larsson, 2011

Overview

Evaluation

This research looks towards the vast potential offered by solar energy and naturally abundant materials such as silica sand in combination with new technologies such as 3D printing. Silica sand solidifies as glass during the cooling process after having reached its melting point. This process is known as sintering and it was defined as the main logic for the development of Solar-Sinter.

The use of natural, renewable materials has significant advantages in terms of both ecology and economy. The combination of an unlimited source of silica (in the form of quartz) and solar energy has a huge potential to be used for construction. The same material in two different stages is used for printing and support material, similar to a selective laser sintering SLS 3D printer. This allows the process to avoid any material waste. The large size of the devise and its restricted mobility are important limitations in terms of a bigger scale application.

Solar-sinter has two photovoltaic panels that produce electricity to charge a battery which provides power to the motors. The heat required for the sintering process comes from a Fresnel lens that focuses sunlight into a powerful beam. sun-tracking devise moves the lens in x and y directions, while rotating the machine towards the sun during the day. t the same time, two motors move a box with sand (the printing bed) according to the path of the predefined geometry. nother platform lowers the sand box when a layer is finished and allows for a layer of fresh sand to be loaded and flattened at the focal point. After the printing is completed, the structure stays inside to cool down slowly before it will be dug out.

Fig. 10 The focal point of the lens directs on the center of the printing bed where the geometry is being printed

Fig. 11 â&#x20AC;&#x153;Solar Sinterâ&#x20AC;? fully autonomous set up in the desert.

Towards a Multi-Robotic Construction System

1.1.5 Woven clay Harvard Graduate School, 2013

Fig.12 Assembly logic

Fig.13 The clay extruder was developed as the end-effector for a 6-axis industrial robotic arm

Fig. 14 The woven clay facade panels with different light permeability were produced using the 3D printing technique and assembled together

Domain

Overview

Evaluation

This project focuses on a material investigation of clay in relationship with robotic manufacturing processes. arvard SD Design obotics roup uses clay coil extrusion with a 6-axis industrial robotic arm and clay extruder to create a variety of lattice patterning effects. The weaving technique was introduced to incorporate both assembly logics and performance qualities. ultiple facade components with different patterns and light permeability were produced and assembled together.

The research proposes an off-site fabrication process of architectural elements which have to be assembled onsite. The size of the panels is limited by the lattice patterning along the surface of the firing kilns printing bed . For industrial purposes, this limitation can be scaled up to a certain degree, but robotic arm mobility limits the process to a certain size as well. In addition, prefabrication of the printing beds adds a lot of complexity to the process.

1.1.6 Termes Self-organizing systems research group, Harvard, 2011

Overview

Evaluation

T S is a hardware system that is an important step toward the goal of automated construction by swarms of robots. The system comprises a mobile robot and specialized passive building blocks; the robot can autonomously manipulate the blocks, build structures with them, and manoeuvre on these structures as well as in unstructured environments.

This approach allows for non-specialized users such as designers to interface with a swarm of robots at the more explicit swarm scale rather than at the agent level, in which the emergent behaviour is implicit in the local rules of interaction. s a result, small simple robots can build structure significantly larger than the size of the robot and if one robot fails other will complete the task. Termes can work just with a single type of prefabricated blocks that limits a design possibilities, but the decentralized control algorithm can be applied to variety of fabrication and construction robotic processes.

To illustrate the robotâ&#x20AC;&#x2122;s ability to perform complex tasks, it is demonstrated autonomously building a ten-block structure significantly larger than itself. Further on, a decentralized control algorithm is presented in which the user input is limited to a description of a desired structure. The control algorithm then converts this high-level description into low-level instructions for multiple simultaneously active robots, which proceed to autonomously build the user-specified structure.

Fig. 15 Snapshots in the process of autonomously building a tenblock structure. The robot collects blocks from the docking station at the left, where new blocks are added by hand as construction proceeds.

Fig. 16 Custom designed robots and construction blocks.

Influenced by termites, the social insects from which this project takes its name, the robot is designed with a philosophy of simplicity: it needs to perform only a few basic tasks, has relatively few sensors and actuators (10 and 3 respectively , and responds only to local conditions. obots act independently, responding as necessary to the presence of others but each carrying out its own tasks and capable of building the entire structure alone. .

Towards a Multi-Robotic Construction System

1.1.7 Mobile Robotic Fabrication System for Filament Structures ITECH M.Sc 2015 Maria Yablonina - ICD: Prof. A. Menges, E. Baharlou, M. Prado, T. Schwinn Overview Fig. System proposal: one robot per plane. Each robot is enabled with a mechanism that allows to pass the bobbin from one machine to the other. Robots are capable of attaching the thread to re-defined anchor oints.

This project proposes a semi-autonomous multi-robot system capable of distributing fiber filament using any horizontal or vertical surface as a support for new structures. nlike larger industrial robots, these ones are not limited by position or reach which allows them to build structures that are much larger than themselves. This mobile robotic system can potentially take robotic fabrication processes away from production halls and into urban fabrication sites.

Evaluation This system has the potential to scale up by employing materials which are more suitable for construction such as steel wire or carbon fiber. ne of the main limitations of this approach is the need for previously positioned anchor points which the robotic units can use to place the filament material which reduces the geometrical flexibility as well as the systems autonomy. In addition, a suction mechanism is used to allow the robots to climb walls which requires them to be connected to a compressor and to an energy source throughout the entire construction process. Communication between robots was not explored but could further enhance the system.

Fig. Physical model capable of withstanding the weight of a human.

Domain

Towards a Multi-Robotic Construction System

1.1.8 From Concept to Implementation Case-Study: Contour Crafting Dr. Khoshnevis, University of Southern California 1998 - Ongoing 1.1.8.1 Setting the Stage Fig. Schematic design of the extrusion assembly with top and side trowels.

The initial phase of a research project consists on identifying an existing gap in the field of research. In , Dr. hoshnevis identified a lack of automation in the construction industry and pointed out many of the problems which this industry is facing and which could be solved through automation. These included high project costs, low labor efficiency, high at-site accident rates, vanishing skilled workforce, and poor control of construction projects. e then acknowledged some of the reasons for which existing automation technologies such as rapid prototyping which were already being applied in various manufacturing industries were not being applied for construction. Some of this limitations were the inability of current layering fabrication methods to deliver a wide variety of materials applicable to construction as well as the severe constraints brought on by the low rates of material deposition which made such technologies attractive only for small scale fabrication of industrial parts.

Fig. Residential Building Construction using Contour Crafting

Material feed barrel

Nozzle

Side trowel control mechanism

Top trowel Side trowel

1.1.8.2 Introducing a New Approach n initial conceptual schema of the proposed novel technology Contour Crafting is presented as part of the same research paper. Contour Crafting consists of a layered fabrication technology capable of creating smooth and accurate planar free-form surfaces by combining computer control and ancient tools such as trowels, blades, sculpturing knives, and putty knives. Some of the potential benefits of Contour Crafting, such as better surface quality, higher fabrication speed, and a wider choice of materials are pointed out. schematic design of the fabrication tool as well as possible applications for it are presented.

Domain

1.1.8.3 Devices: Schematic Design In a follow-up paper from , some interesting challenges of automated construction are pointed out and a schematic design for possible solutions are presented. The integration of utility conduits within the wall, imbedding of modular mesh reinforcement, tiling of floors and walls, and painting are some of the challenges that are discussed. Schematic designs for the devices include the necessary mechanisms required to perform the different actions but do not get into the specific characteristics of the selected mechanisms such as assembly, cabling, and power supply.

Fig. Schematic design for an automated tiling mechanism.

Fig. Schematic design for an automated plumbing installation mechanism

Fig. 3 CC in operation and representative 2.5D and 3D shapes and arts filled ith concrete.

Towards a Multi-Robotic Construction System

1.1.8.4 Revisiting Conceptual Schema Fig. Schematic Design of full scale nozzle assembly.

nder a new grant from the ational Science Foundation, the development of new nozzle assemblies capable of fabricating at a full architectural scale begin to take place. new schematic design for such an assembly is proposed.

1.1.8.5 Exploration of Robotic Alternatives Fig. Conceptual proposal of multi mobile-robot construction system.

Domain

The main limitations of the proposed system, which are a large amount of required site preparation and the need for a gantry system larger than the printed structure, are pointed out and a new approach which involves the coordinated action of multiple mobile robots is proposed as a possible solution. Some of the advantages of such a system, which include ease of transportation and setup, the possibility of having various robots working on different parts of the same structure concurrently, and an unlimited construction footprint are discussed.

Fig.

1.1.8.6 Existing Technology Integration In some cases, technologies that are necessary or that could be helpful for the system have been previously developed for other uses. In such cases, it is possible to integrate these technologies by adapting them to the specific project needs. Contour Crafting proposes the integration of the IST oboCrane system to aid with the positioning of beams for flat roof constructions. sing a oboCrane to carry a material tank for roof material delivery is also considered.

Proposed implementation of NIST RoboCrane system for Contour Crafting.

1.1.8.7 Implementation comparison between the construction of a concrete wall using traditional methods and Contour Crafting is presented in order to make apparent the advantages of the proposed method, mainly, itâ&#x20AC;&#x2122;s simplicity and lack of material waste. Some of the limitations of the system are also discussed, principally the inferior sheathing physical properties compared to traditional formwork systems. This is solved by limiting the pour rate to less than five inches per hour 3cm hour , thus reducing the lateral pressure and eliminating the need for ridge formwork materials.

Fig.

Reinforcement

Wales Studs Ties Brace

Concrete form (Sheating)

Schematic of conventional formwork system (left) and Contour Crafting (right) for vertical concrete wall.

Form tie

Sheathing

Fig. Construction of a full scale wall with internal form ties.

Towards a Multi-Robotic Construction System

1.1.9 Mega-Scale Additive Manufacturing: Current State Overview In the past decade, a variety of methods for printing structures at an architectural scale through additive manufacturing have been devised by different companies and research teams. The different strategies can be divided in two main categories factory printing, which usually involves an on-site assembly process of the printed parts, and on-site printing. This can be further subdivided into those which use a gantry system (on-site or at a factory) and those which use mobile-robots on-site .

1.1.9.1 D-shape Factory gantry-based Fig. Two meter tall â&#x20AC;&#x153;radiolariaâ&#x20AC;? inspired structure built using the d-shape printer.

Invented by nrico Dini, the d-shape printer uses a process similar to that of Selective Laser Sintering SLS 3D printers but rather than using a laser to synthesize the powder support material, which would require excessive amounts of energy to scale up, it uses selective liquid binding to create structures or parts of structures of up to 6m x 6m x 6m which are then trucked to site. It originally used synthetic binders such as epoxy and polyurethane but has recently transitioned into organic binders to produce more environmentally friendly structures. The structure takes around hours to dry, after which the granular support material must be removed to reveal the solid sandstone-like structure within. ecause of the support material, this method provides greater architectural freedom but it also requires a large amount of material to work, even if the support material can be reused for future prints. nother drawback is the labor intensive period of support material removal. 3

1.1.9.2 Worldâ&#x20AC;&#x2122;s Advanced Saving Project (WASP) Factory and on-site gantry-based Fig. 3 Full scale on-site construction using clay with a gantry system.

Domain

S uses a delta gantry system to print large scale structures using concrete and clay layer-by-layer extrusion. xperimentation began within a factory setting to produce construction components such as concrete beams and has progressed to an on-site gantry system capable of extruding a clay and straw mixture to produce mud huts which utilize local materials in order to provide long lasting structures with low environmental impact. The main limitation of the system relies on the large structure that has to be built for the printer, which in itself defines the maximum size of the printed part.

1.1.9.3 Freeform Project Factory gantry-based The freeform project, developed by a research team at the Loughborough niversity in Leicestershire consists of a gantry-based concrete printer capable of creating construction components. The main advantage of this system is the use of a foam-based support material that is deposited strategically to support overhangs and that is removed after the printing process is complete. This provides greater design flexibility without the need for using supports everywhere as in powder-bed printing methods.

Fig. 3 Double curvature concrete â&#x20AC;&#x153;slabâ&#x20AC;? printed with concrete over foam supports.

1.1.9.4 Digital Construction Platform: A Compound Arm Approach (DCP) On-site single mobile-robot DC is an in-progress research project being developed at the assachusetts Institute of Technology IT that consists of a -axis hydraulic mobile boom arm ltec mounted on a fully mobile truck with a reach diameter of over feet and attached to a -axis robotic arm . The system uses the large boom arm for gross positioning and the small robotic arm for fine positioning. ne of the main advantages of this system relies on the wide variety of end-effectors that can be attached to the arm. y attaching a sensor, it is able to generate volumetric scanning of physical geometry and environmental conditions, such as radiation, soil stability, temperature, and chemical mapping . It is also possible to attach fabrication tools such as a mill, a gripper a welding tool or an extruder thus providing real-time digital sensing, on-the-fly performance-based design, and onsite construction . s a fist case study implementation, researchers at IT have used the DC for large-scale printing of quick cure polyurethane foam to produce doubly curved geometries without the need for any support material. [16]

Fig. 3 Foam form-work being printed by a robotic arm which will eventually be cast with concrete.

Towards a Multi-Robotic Construction System

1.2 Multi-Robot Systems

Fig. ulti-robot system taxonomy.

Overview ulti-robot systems S currently play an important role in many areas such as explorations in hazardous environments, military missions in extreme conditions, and industrial applications for repetitive processes, amongst others. hen considering an on-site additive manufacturing process at an architectural scale, S present a number of advantages over the single robot plus gantry system approach which has been tested and implemented in the past decade such as D-shape and Contour Crafting 3 . Some of the most significant advantages include ease of transportation and setup, the possibility of having various robots working on different parts of the same structure concurrently, and an unlimited construction footprint. To further understand the different types of multi-robot systems, their advantages and their limitations, a taxonomy centered on cooperative capabilities will be discussed.

1.2.1 Taxonomy Cooperation Level

Cooperative

Knowledge Level

Organization Level

Domain

Unaware

Aware

Coordination Level

Strongly Coordinated

Strongly Centralized

Weakly Centralized

Not Coordinated

ot Cooperative -

Weakly Coordinated

Distributed

Fig. Cooperation between robotic agents is used to solve a task that could not be solved by a single robot.

Cooperation S is said to be cooperative when several robots operate together to perform a common global task. Cooperation is used when the task cannot be achieved by a single robot or when its execution can be improved by using more than one robot in order to obtain higher performances. obotic agents operating in the same environment but that do not share a common objective are said to be not cooperative.

Knowledge The second level of the explored taxonomy, knowledge level, deals with the amount of knowledge that each robot has about the presence of other robots within the system. S is said to possess awareness when a robot has knowledge about the existence of the other members of the system. hen a S is unaware, robots perform their tasks as if they were the only robots present within the system. Cooperation is still possible within an unaware S, although it is considered the weakest form of cooperation.

Towards a Multi-Robotic Construction System

Coordination Fig. 3 Organizational possibilities for multi-robot systems.

There are various ways through which cooperation between robots can be achieved. The level of coordination is related to the mechanism which is used to achieve cooperation. S is said to be coordinated when the actions performed by each robot take into account the actions performed by other robots within the system in such a way that the whole becomes a coherent, high performance operation. hile strongly coordinated systems rely on a system of signals by which a robot exerts its influence over the behavior of another robot, weakly coordinated systems do not depend on a protocol and are therefore more capable of dealing with failures in communication. This also means that weakly coordinated systems are less suited for dynamic environments and complex goals since they lack many of the organizational capabilities offered by a coordination protocol. The main advantage of a not coordinated S relies in its less complex design which makes it less prone to fault, although it is not suited for tasks which require high levels of organization.

Organization In S, organization refers to method through which the decision system works within the system and is divided between centralized and distributed approaches. S is said to have a centralized organization when there is a robotic agent that is in charge of organizing the work performed by the other robots. This agent, often referred to as the leader, is responsible for the decisional process of the whole team. It is also possible for a centralized system to have a hierarchical structure in which a robot operating under the control of a leader is also a leader of a sub-team within the same system. Centralized systems can be further classified into strongly and weakly centralized. Strong centralization is when the role of the leader is assigned at the beginning of the mission and is kept until completion. In weakly centralized systems, the role of the leader is assigned dynamically throughout the mission in order to respond to changes in the environment or to the failure of the current leader. hile centralization makes task assignment between team members simpler, it has the disadvantage of strongly relying on communication which if it fails, it results in the failure of the entire system. Such systems also lack robustness and the ability to respond to dynamic environments, therefore they

Centralized Organization

Hierarchical Organization

Team Leader

Sub-Leader

Domain

are mostly employed when dealing with a small amount of robots in environments which are well structured such as factories and laboratories. In such settings, centralized systems have advantages such as efficiency and runtime flexibility . Decentralized systems do not have a specified leader, therefore each robot executes its own control scheme autonomously . xamples of such systems can be found in nature, more specifically in social insect such as termites, ants and bees. In such cases, each member of the colony relies only on local sensing and are capable of integrating simple individual activities into complex, highly coordinated systems without requiring any global supervision . The main advantage to a completely decentralized system is in its robustness, or the ability of the system to cope with partial failures and to respond to changing environments on the go. nother important advantage is in terms of system scalability, where it is possible to increase or decrease the amount of robots without having to modify the systemâ&#x20AC;&#x2122;s control scheme or having the risk of overloading a coordinating agent . n the other hand, it becomes significantly more complex to achieve coordination between distributed agents.

Distributed Organization

Communication Different types of communication in S are distinguished by the method through which robots exchange information, and are divided into two main categories, direct and indirect communication. Direct communication relies on on-board hardware devices to send signals that can be understood by the other members of the team. This method of communication is the easiest way to exchange information but often becomes a critical point of failure for the system due to noise or hardware failure. Indirect communication uses stigmergy to communicate between team members. In robotics, stigmergy is when a robot alters the environment in such a way that affects the sensory input of another robot, thus altering its behavior . lthough using indirect communication makes the system more robust by not relying in communication devices, it also implies a more complex S design since each member of the team must be able to interpret changes in its surrounding environment.

Fig. Indirect communication through stigmergy in ant colonies.

1: Ant finds a source of food Nest

Food Source

2: Releases pheromones on its way back to the nest. Pheromone Trail

3: Other ants follow the pheromones to reach the food source.

Towards a Multi-Robotic Construction System

System Composition Fig. Comparison between a homogeneous swarm of one-thousand Kilobots (left) and a heterogeneous MRS composed of three types of robots (right).

Domain

S can be further distinguished by their composition, or whether they are homogeneous or heterogeneous. omogeneous systems are those which are composed by robots that are all exactly the same, both in hardware and in control software. The robustness of such a system comes from the fact that every member of the team is capable of performing the same task, therefore the failure of any member can easily be compensated by another member of the team, thus ensuring fault tolerance. omogeneous systems are usually employed in swarm approaches in which a large distributed team executes a set of repetitive actions and in which time is not a critical resource. Since the completion of the task usually relies on some mathematical convergence, the main challenge comes in defining the correct set of rules to ensure the achievement of the task in hand. eterogeneous systems are those in which members of the team have a difference either in hardware of in the control software. y not relying on the fact that all robots must be the same, it becomes easier to modify the system composition in order to better adapt to a changing environment, thus ensuring adaptability without giving up fault tolerance. The main drawback to heterogeneous systems is the added complexity in the design of multiple control software as well as in the design of the different robotic agents.

Towards a Multi-Robotic Construction System

1.3 Material Selection

Overview arious parameters must be taken into consideration in order to select a construction material that will enable and enhance a robotic construction method. atural granular materials, because of their world-wide availability, allow for the design of a construction method that uses locally available materials while still allowing it to perform in a variety of geographical contexts. In addition, most natural granular materials are recyclable, biodegradable, fireproof, and durable. nother advantage of using granular materials for a robotic construction process is their ability to be handled in small quantities while at the same time enabling the possibility to construct large non-discrete elements through a process of solidification. Solidifying granular materials into small discrete objects that can then be assembled i.e. bricks is another possibility. The main limitations of traditional construction methods with granular materials are the high labor intensity that they require and the lack of geometrical flexibility that they provide, both of which could be solved through a robotic construction process.

Domain

Fig. 1 Large dickite plates in sandstone, Cretaceous, West of Shetland Dimensions: ~130 Âľm wide

Towards a Multi-Robotic Construction System

There are three methods through which a granular material can be solidified, each with its specific potentials and limitations

1.3.1 Crystallization Crystallization is a process that consists in dissolving a substance and the depositing of suspended particles which creates liquid bridges between them and solidifies the substance. This process is used in some of the most common building techniques with earth such as Cob, ammed arth, attle and Daub, udbricks, Compressed arth locks and others. ll of these techniques use natural materials such as sand, clay, water and fibrous or organic material sticks, straw and or manure for reinforcement. The main advantage of crystallization is that with certain materials, such as clay, only water is needed for solidification to occur. The main limitation is in terms of the relatively low structural performance which leads to a need for massive construction elements. n example of a large scale additive manufacturing processes which uses crystallization is S chapter . . .

1.3.2 Sintering Sintering is the process of forming large particles, lumps, or masses through heating or pressure without melting it to the point of liquefaction. During the sintering process in the brick manufacturing process, stable initial raw materials transform into complex compounds at high temperatures. 3 This process is mostly used in the fabrication of clay bricks, 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 cooling time. For example, fired-clay bricks that are fabricated on a higher temperature will provide the highest strength and significantly improve physical properties 3 . Sintering is the process through which Selective Laser Sintering SLS 3D printers solidify powder materials to create solid objects. The main advantage of this process is the high structural performance that granular materials can achieve. The main limitation is the high amount of energy required.

1.3.3 Liquid binder nother way in which granular materials can be solidified is through the application of a liquid binder to achieve granule consolidation. There is a wide variety of natural and synthetic liquid binders available, and the result of the chemical reaction can perform remarkably different depending on the selected granular material and binder. This solidification process is mostly used for soil stabilization. ne of its main advantages is the ability to achieve differentiation by the selective application of the binder. Its main limitation is the increased material sophistication. n example of a large scale additive manufacturing processes which uses liquid binders is D-Shape chapter . . .

Domain

Fig. 2 Large scale additive manufacturing process with unfired clay which gets crystalized and solidified when mixed with water.

Fig. 3 Selective Laser Sintering SLS 3D printer in which powdered material is solidified layer-by-layer through a heat sintering process.

Fig. 4 Large scale D-Shape printer in action. ranular material gets solidified layer-by-layer through the selective deposition of a liquid binder.

Towards a Multi-Robotic Construction System

Fig. 5

decision must be taken regarding the assembly logic that the proposed construction system will follow. Two options are considered in the context of the research and their potentials and limitations are evaluated.

Assembly logic.

Assembly logic

Discrete

Non-discrete

Fabrication + Assembly

Fabrication = Assembly

- Adding complexity at fabrication level

Domain

- Adding complexity at assembly level - All construction processes are possible onsite by robotic system

1.3.4 Discrete assembly logic

1.3.5 Non-discrete assembly logic

discrete assembly logic is divided into two steps. The first step is the fabrication of discrete elements bricks, panels, frames, etc. which can be all identical, composed by families of variations, or all unique, and can be fabricated either off-site or on-site. Identical elements are better suited for bottom-up approaches since they are less restrictive. nique elements are mostly employed in top-down approaches in which complex geometries are rationalized and discretized. The second step consist on the on-site assembly of the elements. The main limitation of employing a discrete assembly logic for a robotic construction method is the added complexity gained by separating fabrication and assembly, although in some cases the assembly process can become relatively simple since it consists only on the correct positioning of prefabricated elements.

Non-discrete assembly logics are those in which fabrication and assembly are replaced by a single material deposition process. lthough the process might be considerably more complex than the assembly of pre-made elements, by eliminating the fabrication process it becomes considerably easier to integrate the entire construction process into an automated system. The devices used for non-discrete assembly strategies should be designed specifically for the selected material and deposition strategy.

Fig. 6 Flight Assembled Architecture (2011-2012) by Gramazio & ohler is the first architect ral installation assembled by flying robots” and an example of discrete assembly logic.

Fig. 7 The project “Dune” (20072008) by Magnus Larsson. An example of a non-discrete assemble logic, where Bacillus Pasteurii bacteria was used to solidify the dune’s surface.

Towards a Multi-Robotic Construction System

1.3.6 Conclusions Clay is selected as a main building material because it is recyclable, biodegradable, fireproof, durable and available world-wide. In addition, it can easily be solidified through a process of crystallization by simply mixing it with water and allowing it to cure naturally. Furthermore, a non-discrete assembly logic is selected because it allows for an easier integration of an entire construction process into an automated system by eliminating the need for an added process of fabrication and on-site assembly. The following chapter looks at ways in which clay has been used as a construction material to provide passive bio-climatic design solutions.

Domain

Towards a Multi-Robotic Construction System

1.4 Clay In Architecture

Fig. 1 A map of climatic regions in which at least 60% of vernacular architectures contain clay.

Fig. 2 Percentage of observed dwellings which contain earth as a wall building material in individual climatic regions.

Fig. 3 Percentage of observed dwellings which contain earth as a roof building material in individual climatic regions.

Overview arth is one of the most common building materials used on our planet. pproximately of the population of developing countries, the majority of rural populations, and at least of urban populations live in earth homesâ&#x20AC;&#x2122;. Furthermore, earth is an abundant, natural and recyclable resource, which makes it a perfectly adequate material to respond to todayâ&#x20AC;&#x2122;s necessity of reducing energy consumption in the building sector. Despite the huge potential of earth as a construction material, there are certain limitations which have prevented it from being widely adopted as a solution for contemporary architecture. Its low mechanical and tensile resistance as well as the traditional methods in which it is used, impose a limit in terms of design flexibility. Furthermore, in developed societies in which human labor is very costly, the traditionally intensive labor requirements of working with earth imply elevated construction costs. In addition to this, a lack of specific legal context for earth construction has hindered its establishment as a common building material.

Climatic Regions with high incidence of vernacular earthen architectures Climatic Regions with low or no incidence of vernacular earthen architectures

Observed Vernacular Wall Constructions with Earth 100%

60%

0% Tr et qu or

at a

l ca

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tit e

e in

um id

ap C

t er

rra

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M oa

lti

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ve O

Observed Vernacular Roof Constructions with Earth 100%

60%

qu l ia

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Domain

oa tC

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Building Envelopes: Massive or Lightweight uilding envelopes can generally be divided into two categories massive and lightweight. Since the scope of this project focuses on clay as a building material, the research and analysis of vernacular architectures will be centered on massive envelopes made from earth or mud. Such architectures have the ability to store and radiate heat, and can reduce infiltration by creating a tight envelope, which is why they are the most common vernacular dwellings in cold climates. owever, with the proper thickness a massive envelope has the ability to reverse the temperature extremes of desert climates inside a dwelling by transferring the heat that is absorbed during the day into the structure at night and doing the opposite during the night. In order to take advantage of dry desert winds, massive dwellings in desert climates will often have loose infiltration that can allow wind to go through the envelope while still protecting the interior from direct solar radiation. Traditional engineering solutions such as stone arches and corbelled domes are included to provide massive roofs, although thatch roofs are also seen in many massive vernacular buildings.

Massive

Fig. 4 Observed wall mass types in percentage of dwellings in individual climatic regions.

Fig. 5 Variation of outdoor and indoor temperatures for a 460mm earth wall during the hottest periods of the year 2012.

Lightweight

Mass in Walls

100% -

60% -

Tr et

tit

er t

de ic

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tin

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Indoor Temperature

Temperature C

s part of a research from which aimed to demonstrate the bioclimatic performance of earthen structures in real conditions, a demonstrative earth building was constructed and its hygrothermal performance was monitored for two consecutive years. It is clear from their analysis of the gathered data that earthen walls are successful in reducing internal temperature fluctuations even when the external temperature fluctuates between hot and cold extremes Fig. . This can be attributed to the high thermal inertia of the walls which is a result of their massive thickness mm . From this study it was also concluded that the optimum thickness of earthen walls is equal to mm since it enables to achieve the optimum values of thermal inertia, with a significant impact on the damping factor and on the thermal lag. It ensures a reduction of the fluctuations of the outdoor temperature and a limitation of the risk of overheating the building.

Outdoor Temperature

Time

Towards a Multi-Robotic Construction System

1.4.1 Vernacular Architecture Bio-Climatic Performance

Overview ernacular architectures have evolved around the globe through long periods of trial and error by local builders who possess specific knowledge about the environment which they inhabit. Therefore, such architectures showcase valuable examples of climate-specific passive building technologies which could inform modern buildings. ecause of the intrinsic relation between vernacular architectures and their environment, design solutions vary widely with the worlds spectrum of climate, terrain and culture, but are always looking at improving the energy performance of buildings at a low cost and with local materials.

Domain

Ceiling structure

Fig. 6

Vaulted ceilings are a very common feature of vernacular dwellings. In hot and humid climates, vaulted ceilings play an important role in cooling by allowing hot air to gather above occupants and cool air to rest near the floor. n cold climates it is ass med that a lted ceilings ere sed in order to allo for the stratification of smo e from the o en fire its.

Cross section of a single Tholos dome from northern Syria. Its height allows for the stratification of hot air.

Fig. 7

oom structure Most vernacular dwellings are composed of single room structures. In warm climates, single rooms facilitate the construction of tall vaulted ceilings which allow for air stratification hile in cold climates single rooms are ic er to arm ith a fire it. For these reasons When connecting multiple rooms, in most cases each room has an independent vault.

Cross section of a double Tholos dome from northern Syria with a projection of the required height if the domes were combined into one.

Towards a Multi-Robotic Construction System

Fig. 8

Infiltration

Diagram showing the wind tower effect and cooling through evaporation.

Air exchange is a key element used to control the interior temperature of vernacular dwellings. In cold climates, it is important to keep the heat inside of the dwelling, therefore virtually no openings are found except for a hole in the roof to allow smoke to escape. In hot climates, loose infiltration allo s for nat ral entilation hich hel s reduce the internal temperature of the structure. In places with infrequent wind and high humidity, natural ventilation is achieved by bringing cool air up from shaded areas under the dwellings. The close proximity between houses also helps to reduce the temperature by enhancing shading.

Fig. 9 Pit House Cross Section

Domain

elationship to ground Fully or partially subterranean vernacular dwellings take advantage of the steady temperature of the earth as a method to red ce tem erat re fl ct ations inside of the dwellings. This is seen only in places with extreme climates, both cold and hot. In temperate and tropical environments, all vernacular dwellings are situated either at ground level or above the ground.

Wind

Shading

Fig. 10

Overhangs in vernacular architectures are mostly used for shading walls and the ground around dwellings as well as for protection from water. In climates with high diurnal temperature ranges, where massive walls are common, eaves were not used. In cold climates, eaves were used to protect the structure from rain and snow. In some cases, such as in Nepal, roof overhangs are only used on rammed-earth and adobe brick buildings as a way to protect the walls from heavy rains. The position of homes relative to each other also plays an important role in shading. In cases where massive walls are used for solar gain, vernacular structures are rarely positioned to shade each other. On the other hand, lightweight structures in hot climates tend to be places close to each other as a method for cooling their structure with shade.

Large overhangs provide shading to the walls while the stilt structure allows for cold wind to flo nder it.

Windows

Fig. 11

Since glazing was not widely available until the 19th century, large windows are very uncommon in vernacular architecture worldwide. In most traditional dwellings, doors are used to bring in light and air. In the few cases where windows are present, glazing is replaced by shutters hich can decrease infiltration as ell as solar gain. n warm climates, window â&#x20AC;&#x153;grillsâ&#x20AC;? are used as an alternative to gla ing since they can allo air and light to infiltrate the structure while preventing direct solar gain and visual access to the buildingâ&#x20AC;&#x2122;s interior.

Mashrabiyya: Traditional Arabic wood latticework

Towards a Multi-Robotic Construction System

2.0

Methods

2.1 2.2 2.3 2.4 2.5 2.6

Funicular Form-Finding Finite Element Analysis Parametric Robot Control Robotic Prototyping Computer Vision oal- ased ector Field athfinding

58 58 59 59 60 61

2.1 Funicular Form-Finding

Form-finding is the process through which a structureâ&#x20AC;&#x2122;s geometry is defined by the relationship between force and form. Funicular structures are those which achieve a state of equilibrium by adopting a form which corresponds to the applied loads. angaroo, a live physics engine that works within the rasshopper environment, is used to generate geometries that respond to the mechanical properties of un-fired clay in order to design structures which are more stable as well as more material efficient.

2.2 Finite Element Analysis (FEA)

F is a computational method through which an object with specific material properties can be analyzed in order to understand how it will be affected by applied stresses. aramba, aF plug-in for rasshopper, is used to extract data about the distribution of strains for specific geometries. This data is then used to differentiate the structure in terms of material distribution.

Methods

2.3 Parametric Robot Control

To transition from design into fabrication it is necessary to convert geometries into tool-paths that can be understood by the fabrication unit, in this case a -3 industrial robotic arm. C, a parametric robot control tool that works within the rasshopper environment is used to generate the robot program and to ensure through digital simulations that there are no collisions or unreachable points. Thanks to the parametric nature of the software, it is possible to continuously change variables such as material refill points, slicing distance and end-effector dimensions and to easily visualize how these changes affect the robot program.

2.4 Robotic Prototyping

aterial prototypes are constructed using a -3 industrial robotic arm equipped with a pneumatic clay extruding end-effector. These prototypes give us valuable information regarding the proposed construction method such as the performance of different granular materials as supports, the ideal ratios between clay, water and fibers to achieve the correct consistency for clay extrusion, as well as the relationship between air pressure, printing speed and material consistency. Information regarding curing times and layer separation was also extracted from this prototypes.

Towards a Multi-Robotic Construction System

2.5 Computer Vision

Computer vision deals with the extraction of digital images from the real world which are automatically processed and analyzed in order to produce useful information. inect infrared camera is used for the extraction of three dimensional spatial and topographical data that is then processed and analyzed to produce a vector field which can be used by robotic agents to navigate through space while achieving specific goals.

Methods

oal

ased ector Field Path nding

Goal

Generate Heatmap Determines the path-distance between the goal and every tile or node in the map.

5 Goal

Goal

Generate Vector Field Designates the direction from each node to the neighboring node closest to the goal.

Goal

Navigate Towards Goal Every particle finds the vector closest to itself and moves in that direction and magnitude. This is a recursive process.

oal-based vector field pathfinding is a grid-based approach in which rather than calculating the path to the goal for every pathfinder or agent, it calculates the path from the goal to every node in the graph. This is particularly helpful when working with a very large number of agents since the bulk of the computation is in generating the vector field, after which the amount of agents does not scale up computation time linearly. There are three basic steps to goal-based vector field pathfinding which are illustrated in the above image.

Towards a Multi-Robotic Construction System

3.0 Research Development

3.1 3.2 3.3 3.4 3.5 3.6 3.7 3.8 3.9

Construction Method Multi-Robot System Design Primary Deposition Strategy Support Material Deposition Strategy Robotic Prototyping -Primary and Support Material Deposition Slicing Secondary Deposition Strategy Robotic Prototyping -Secondary Deposition Devices

64 70 76 82 88 104 106 116 122

3.1 Construction Method

Fig.1 Integrated design logic diagram Set of devices

Site

High level of communication

Environmental data

Material properties

Multi-robot system

Material system

Construction method

3.1.1 Integrated Design Logic Today, robotic construction methods have the great potential to push the field of architecture to a new era and change the way in which architects design. [1] To realize its potential it is important to develop in parallel a construction method, the set of devices that are required to perform it and the parameters which define the design. In addition, everything must be informed by the specific material properties that drive the investigation. The construction of a design process becomes as meaningful as the resulting architectural proposal. [1]

3.1.2 Construction Method This research proposes a layer-by-layer additive manufacturing (AM) multi-robotic construction method, which uses clay as the main building material. Due to the long curing time of clay, dry granular support material is used throughout the deposition process in order to provide greater geometrical flexibility. ne of the main challenges of using ground based mobile robots for the construction of large-scale structures relies on the question of how to allow the robots to gain height. The proposed method uses the granular support material as a ramp through which the robots can access the top layer of the printed structure in order to print over it the subsequent layer. The inclination of the heap is defined by the angle of repose of the selected granular material, which can range from 150 to 450 degrees and can vary depending on the building site. Although large amounts of support material are required for this method, once the printed structure has cured the supports are removed and reused for other structures, therefore generating no material waste. This method makes it possible to build large clay structures with a team of relatively small cooperative mobile robots.

Research Development

Fig. 2 Construction process Mobile Devices

Support material Printed structure Support material ramp

Fig. 3 Diagrammatic section of the construction method

x x angle of repose angle of repose max. climbing angle

Towards a Multi-Robotic Construction System

3.1.3 Support Material Distribution Different geometries require different amounts and positioning of granular material in order to provide support and avoid deformations during the curing process. The combined support heaps from multiple neighboring structures generate a continuous surface with various peaks and valleys which are defined by the spatial relationship between structures.

Plan

Section

Falsework

Contained falsework

x Contained + free falsework x angle of repose angle of repose max. climbing angle

+ Geometry with opening

Contained + free falsework x

Research Development

angle of repose

Fig. 4 Support material distribution for the column

Fig. 5 Support material distribution for the dome

Towards a Multi-Robotic Construction System

3.1.4 Deposition Sequence The deposition sequence logic is composed of two main stages that enable the system to provide a wide range of special qualities. The method aims at taking advantage of the large amount of support material that is required at the different stages of the construction process while at the same time increasing the design possibilities. nce the initial geometries are completed, their connected support heaps work as a falsework over which a second printing sequence is executed. The positioning of the initial structures in relation to each other as well as the support materialâ&#x20AC;&#x2122;s angle of repose define the geometry of the printed surface. Different deposition strategies are designed and implemented for each stage of the construction process that will be further described in chapter 3.3.

First stage deposition Second stage deposition Angle of repose Support material Minimum Height x angle of repose

Research Development

Fig. 6 Deposition sequence for two columns

Towards a Multi-Robotic Construction System

3.2 Multi-Robot System Design

The end-goal of this project is to design a system composed of multiple medium scale robots capable of building structures at an architectural scale. The initial step towards this highly ambitious goal is to determine the properties of such a system.

Fig. 1

3.2.1 System Composition

Proposed heterogeneous multi-robot system which includes a paste deposition rover (top-left), a support material dispensing rover (top-right), a stationary unit for material preparation (bottom-left) and an UAV equipped with an infrared sensor (bottom-right).

Research Development

The first decision that must be taken for the design of the MRS is in terms of its composition. Since a construction process usually requires a variety of tasks being executed simultaneously, a heterogeneous composition is better suited since it allows us to design different robots with properties and capabilities which directly relate to their specific tasks without having to integrate all of them into a single robot. By doing so, individual robotic units are kept as simple as possible. This also allows us to define team compositions related to the specific task at hand.

Fig. 2

3.2.2 Cooperation and Awareness

Multiple rovers work together towards the same goal.

Since the size of the desired outcome is significantly larger than the size of an individual robot, the system must be cooperative so that multiple robots can work together towards the same goal and accomplish it in a reasonable amount of time. To allow for many robots to work together towards the same goal, the actions of each robot must take into account the actions that are being performed by the rest of the team, therefore each member of the system must possess knowledge about the existence of the other robots, which means the MRS must be aware.

Fig. 3

3.2.3 Coordination In terms of coordination, a strongly coordinated system, in which communication between agents relies on a system of signals, is preferred since it is better suited for dealing with dynamic environments such as a construction site. Some aspects of weak coordination could be helpful for dealing with â&#x20AC;&#x153;on the goâ&#x20AC;? error correction, in which an agentâ&#x20AC;&#x2122;s on-board local sensing can make modifications to its coordination protocol for simple tasks such as collision avoidance with other agents or with unexpected obstructions.

An example of on-board sensing in which a light sensor is used to identify the material over which the rover is situated. Material State Detection

Towards a Multi-Robotic Construction System

Fig. 4

3.2.4 Organization

Comparison between global and local awareness.

Fig. 5

3.2.5 Communication

Stigmergic communication in which the 3D scan of a support heap generated by the UAV’s infrared sensor is used to define the ro er s locomotion routines.

The MRS should be capable of following precise instructions in a setting outside of a controlled environment in order to build user specified structures. Since the desired outcome is predefined rather than emergent, a distributed system, because of its lack of control, is not desirable. n the other hand, working on a dynamic site in which it is important for the system to be able to respond and adapt to changes means that a strongly centralized system is not the desired approach either. A combination of both approaches, referred to as weakly centralized systems could provide the high level of control required as well as the ability to respond to local conditions.

Research Development

In terms of communication, both direct and indirect methods can potentially be integrated into a combined strategy in which direct communication is used for the precise execution of the coordination protocol while indirect, stigmergic communication can be used for local modifications of the protocol for error correction. odifications to the environment which can be used for stigmergic communication might include, but are not limited to, the deposition of both building and support material.

UAV’s global awareness used for the coordination between rovers.

Rovers local on-board sensing used for “on the go” error correction.

Fig. 6

3.2.6 Robotic Motion Planning In robotics, motion planning is the process of breaking down a desired movement task into discrete motions. A great number of solutions have been developed in the past two decades for the problem of robotic motion planning, each of them with their specific advantages and limitations. For relatively low-dimensional problems such as the one we are dealing with, gridbased algorithms can provide solutions quickly, although they are not always optimal.

Grid-Based Approach

Discretization of a 3D space into a 2D grid with obstructions.

Fig. 7

Grid-based approaches consist on the overlaying of a grid on the configuration space. t each point on the grid, the robot is allowed to move to adjacent grid points as long as they are not part of an obstruction. By doing this, the set of actions required to reach a goal are discretized and search algorithms can then be used to find a viable path. The resolution of the overlaid grid is an important factor that must be defined taking into account that coarser grids will make the search faster but less precise. It is possible to use a grid that is coarser the further it is from the goal and becomes finer as it approaches it fig. , that way you can have more precision where it matters and faster computation where precision is not essential. It is also important to consider that since grid-based approaches produce paths whose changes in direction are constrained to multiples of a given base angle, the paths produced are very often suboptimal. This is often solved through the use of â&#x20AC;&#x153;any-angle path planning algorithmsâ&#x20AC;?, in which, as the name states, paths are not constrained to the grid edges although in most cases, grid edges are used to propagate information in order to speed up the search. [1]

Grid-based approach with differential grid resolution.

Towards a Multi-Robotic Construction System

Fig. 8

3.2.7 Cloud Robotics

he fi e elements of clo d robotics.

Cloud robotics is a field of robotics that attempts to invoke cloud technologies such as cloud computing, cloud storage, and other Internet technologies centered on the benefits of converged infrastructure and shared services for robotics.” [2] When designing a relatively small mobile robot, its total weight must be kept as low as possible in order to increase its payload capacity, which will determine the amount of material that it can transport for deposition. As the rover’s on-board computation and storage increase, so does their size and weight, therefore a trade-off must be made between the robot’s on-board computing capabilities, or “intelligence”, and its mobility and operation time. A possible solution to this can be found in Cloud Computing which gives each robotic unit access to a cluster of computers with the required computing power to perform the tasks of many robots simultaneously. Cloud storage, another feature of cloud robotics, allows for all of the data that is compiled by the multi-robot system’s sensory network to be stored on external remote server farms with shared memory and processors. This keeps the robotic performance safe from crashing and

Cloud Computing

Big Data

pen-Source

The Five Elements of Cloud Robotics

n-demand human guidance and error

Collective Robot Learning

loosing the data. For example, when an needs to be recharged and replaced by another one, all data is available to it on the cloud. In addition, robotics concerns error modes, where the robot cannot determine what to do” [3] and if the system gets stuck it will be reported to a user through the Cloud.

Fig. 9 Device-user integration through the implementation of cloud robotics.

Research Development

Towards a Multi-Robotic Construction System

3.3 Primary Deposition Strategy

Fig. 1

3.3.1 Massive Extrusion

Transition from a linear extruded element to a massive extrusion.

ne of the most significant bio-climatic properties of earthen architecture, the ability to delay the transfer of heat into the interior, is mainly due to the massive nature of its walls. Clay extrusion can range in diameter from a few millimeters for small object which require a high printing resolution up to several centimeters for industrial purposes, for which large amounts of energy are necessary to power the enormous extruders. Considering clay extrusion in the context of this project, in which medium sized rovers must be able to carry and power an extruder, the diameter of the extrusion is limited to a range of around five to ten centimeters. In order to build structures at an architectural scale that are able to provide comfortable spaces in climates with extreme daily temperature fluctuations, it is necessary to think of a deposition strategy which allows for the design of architectural elements with varying thicknesses. As already mentioned in chapter 1.4, the optimal thickness of clay walls to ensure a reduction of temperature fluctuations is said to be millimeters according to a study on the bioclimatic performance of unfired clay bricks in construction.

extrusion length per container = container volume ยน (d/2)^2

Research Development

Wall Thickness

d = extrusion diameter

3.3.2 Wall Thickness Differentiation

Fig. 2

ernacular earthen architectures, although highly adapted to their climatic context, lack the possibility to achieve differentiation within the same structure, at a local scale, which can be seen in the high degree of symmetry of such structures. This is mainly due to the manual nature of traditional building techniques as well as the need for highly robust structures that are capable of withstanding a lot more forces than the ones they are subjected to. This leads to structures that respond only to the most crucial aspects of their environment (temperature fluctuations while ignoring other aspects which could provide a higher level of comfort light, wind). When designing for a robotic additive manufacturing process, as opposed to traditional building techniques, differentiation at a local scale becomes possible and therefore the design possibilities become significantly wider.

Wall thickness differentiation enabled by the deposition strategy.

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Fig. 3 Linear displacement mechanism which makes it possible to execute the deposition strategy with a rover.

3.3.3 Massive Extrusion: Rover sing a rover for extrusion processes usually limits the extrusion toolpath to the dimensions of the rover, since the toolpaths are defined exclusively by the roverâ&#x20AC;&#x2122;s locomotion and passing over recently deposited material must be avoided. In order to avoid this limitation and enable the deposition of massive elements, a device is added to the rover which allows the extruder nozzle to move linearly independent from the roverâ&#x20AC;&#x2122;s locomotion routine. This also simplifies the roverâ&#x20AC;&#x2122;s path and allows for local deposition differentiation.

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3.3.4 Rover Extrusion Sequence

Fig. 4

The printing sequence coordinates the roverâ&#x20AC;&#x2122;s locomotion and the extruders linear displacement in order to execute the printing of massive elements.

Rover: Halt xtruder Linear Displacement + Extrude

Rover: Move Forward xtruder Extrude

Rover: Halt xtruder Linear Displacement + Extrude

Rover extrusion sequence.

Rover: Move Forward xtruder Extrude

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3.3.5 Geometry Generation Funicular form-finding is used to generate geometries which will take advantage of the mechanical properties of unfired clay. The varying shell thickness is informed by an analysis of material utilization which is then used to define the slicing and toolpath generation.

efine Bo ndary

Differential thickness based on displacement analysis

efinin

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oolpaths

Generate Surface nic lar or findin

Geometry slicing

Final Geometry

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3.4 Support Material Deposition Strategy

The support material deposition strategy consists on the layer-by-layer construction of a granular material falsework. It is executed in parallel with the primary deposition to provide it with temporary supports and prevent the structure from deforming during the curing process, thus increasing the morphological possibilities. There is a wide variety of natural granular materials that could potentially be used such as dry clay, sand, gravel and salt between others. ne of the main requirements is that it is available on-site in order to reduce the carbon footprint. In addition, the selected granular material will have an effect on the surface finish of the structure, since some of it will become bonded to the hardened clay structure. Curing time might also vary depending on the selection. Granular materials have different angles of repose that range between 150 and 450. The angle of repose of the selected granular material has to be taken into account to calculate the support material distribution for specific geometries, as well as to be able to quantify the amount of material needed prior to construction. ther key factors that have to be taken into consideration are particles size and compaction of the selected granular material, since they will define the size of the opening on the deposition device in order to calibrate it to the required deposition speed. To calculate the roverâ&#x20AC;&#x2122;s recharge sequence, the volume of each support layer has to be divided by the volume of material which a single rover can carry determined by its maximum payload capacity) multiplied by the number of available Powder Rovers. For optimal construction speed, the relation between number of Powder Rovers and number of Paste Rovers should be calibrated taking into account the volume relation in each layer between clay and support material as well as rover deposition speeds so that both tasks can be executed in the same amount of time in each layer.

Fig. 1 Angle of repose table for granular materials

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Type of Granular Materials

Angle of Repose

1.Sand (Dry) 2.Sand (Damp) 3.Sand (Dry and compact) 4.Gravel .Sand- ravel mix 6.Clay(Dry) .Clay Damp

25 to 35 30 to 40 35 to 45 40 to 45 25 to 35 30 35 to 45

Number of recharcge operations

v layer

vcontainer X

Amount of Powder Rovers

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3. .1

oal

ased ector Field Path nding

An initial proof of concept of the communication strategy is tested using a Kinect v.2 sensor to generate a height map of the built area, which is then used to identify the areas where more support material is needed. The generated height map is then discretized into rectangular cells, each with a “heat value” indicating the minimum number of cells between itself and the closest area where supports are needed. The optimal cell size for path smoothness is equal to the rover’s dimensions but it must be taken into account that computation time increases as cell size decreases, which means that optimal cell size for path execution time, including the time it will take to compute and update the vector field, might be larger than the rover’s dimensions. The next step is to place a vector from the center of each cell to its neighboring cell with the smallest heat value . nce the vector field is generated, any number of rovers can use it to find their way to their closest goal and deposit supports over it. s more supports are deposited, the height map and consequently the vector field get updated on the go until the entire layer is complete.

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3D scan of support pile

2D heat map

current goal

Discretized work space and goal identification Variations of discretization resolution

Multiple Goal Vector Field

Goal-based vector field

Modified heat map

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d t

Diameter 25mm Gravel 5ml

3.4.2 Material Tests ravel granules with an average diameter of mm were used in tests , and 3. Its angle of repose was observed to be between 40 and 45 degrees. The material was deposited manually at three different speeds in order to calculate the relationship between deposition speed, layer height and path length. The nozzle diameter was kept at a constant 25 mm, which allowed for gravel to flow easily through it. The same test was performed with sand, but due to its dampness, the particles agglomerated at the nozzle and got stuck. In order to prevent this from happening and to widen the range of possible support materials, a vibration mechanism is proposed as a part of the Powder Rover.

Sand (Damp) Height: 60 mm Volume:

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Gravel (5mm) Height: 40 mm Volume:

Test 1 Test 2 Test 3

Time

Distance

Speed

10 sec 10 sec 14 sec

0.41 m 0.82 m 2.24 m

0.041 m/s 0.082 m/s 0.224 m/s

Test 1

Height: 50 mm

Distance: 410 mm

Width: 150 mm

Distance: 820 mm

Width: 190 mm

Test 2

Height: 30 mm

Test 3

Speed

Height 5: mm

Distance: 2240 mm

Width: 380 mm

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3.5 Robotic Prototyping Primary and Support Material Deposition

Overview The aim of the experiments is to test the proposed primary deposition strategy in parallel with the support material performance in order to extract data related to material performance and device calibration. n industrial kr-3 -axis robotic arm equipped with a pneumatic clay extruding end-effector is used to perform the deposition. Two tests were performed for the continuous path deposition of predefined geometries and two different support materials were tested.

3.5.1 Test 1 The mixture ratios and deposition speed were calibrated during the process. The moisture content was gradually reduced to initial C of air-drying clay mixture which provided a suitable viscosity for extrusion. s a next step, some layers were printed without support material to test ensure that the extrudate keeps the coil shape and that the layers stay bonded after the drying process. The optimal robot speed for the material mixture was defined as . m s. fterwards, the toolpath of the geometry was executed layer by layer. Clay was extruded robotically and support material was deposited manually in parallel.

Fig. 1 First sample was printed to calibrate the speed of the deposition and to test that the mixture keeps the coil shape.

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Robotic Setup: ase

mm x

Fig. 2 mm x

ox mm x mm rinting area mm x

Go to start point of the segment

Process pseudocode

mm Start extruding

Mixture: ir-drying clay with nylon reinforcing fibers additional moisture content

of xecute toolpath

Support material: Polystyrene Beads (Styrofoam)

Stop extruding

The box is used to prevent support material dispersal in the robotic cell.

End-effector:

Go to the recharge position

neumatic extruder Nozzle diameter: 10 mm [ pause ] recharge the extruder

Fig. 3 The column was generated as an initial geometry for testing. Fig. 4 Pneumatic extruder was used as an end-effector during the deposition process.

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Fig. 5 Simulation of tool path execution with the industrial robotic arm KUKA KR-30.

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Fig. 6 After the curing process is completed, support material has to be removed.

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3.5.2 Test 1 - Observations fter completing the experiment, an analysis of the achievements and failures is discussed in order to improve the process for the future experimentation. The clay mixture performed well in terms of layer bonding and had enough plasticity to flow under pressure. oisture content will be slightly reduced for further experiments to try to reduce the curing time. Polystyrene Beads were selected as a support material in order to reduce the weight of the large volume of material required for supports. Due to the lightness of the material, it failed to provide enough support to the printed structure which was therefore dramatically deformed after only a few layers. For the next experiment, a different granular material has to be tested. During the printing process, clay shrinkage and coil deformation have to be taken into account and should inform the geometry slicing. For this initial test, the height of each layer was assumed to be equal to the diameter of the extrusion but due to the slow curing nature of clay, the base layers became deformed as the printing progressed. This produced a height discrepancy between the nozzle and the structure which resulted in inaccurate printing. This test was performed using only continuous paths, but the future intension is to work with discontinuous paths as well in order to increase the geometrical possibilities. To be able to do this, it is important to be able to stop the extrusion immediately for the transfer between path segments. sing a screw extruder rather than a pneumatic one could be a potential solution to this problem since it provides a higher level of control. Another solution to this while still working with a pneumatic extruder could be the introduction of one or two solenoid valves connected to the robotâ&#x20AC;&#x2122;s i o to have control over the pressure that is injected to the extruder.

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Fig. The part of the column that was printed during Test 1 after the drying process.

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Fig. 8 Simulation of column tool path execution with the industrial robotic arm KUKA KR-30.

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Fig. 9 Deposition process of the column. Active printing time was 18 min.

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Fig. 10 Column deposition process.

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Fig. 11 Front view of the column that was printed during Test 2 after the support material was removed.

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Fig. 12 Simulation of dome tool path execution with the industrial robotic arm KUKA KR-30.

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Fig. 13 Deposition process of the dome. Active printing time was 24 min.

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Fig. 14 Dome deposition process.

Fig. 15 Top view of the dome after the deposition process was complied.

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Fig. 16 Front view of the dome that was printed during the Test 2 after the support material was removed.

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3.5.3 Test 2 - Observations Two geometries, a dome and a column, composed of continuous tool-paths were tested. The height of each layer was defined at mm with a nozzle diameter of mm. The discrepancy between layer height and nozzle diameter was introduced to respond to the deformation of clay during the printing process as well as to enhance the bonding between layers. In the final layers of the printed dome, a separation between the tip of the nozzle and the layer below was again observed and produced a printing failure. Possible solutions to this problem that could be implemented for further tests are discussed in the following chapter (3.3.4). Rock salt, the selected granular support material, performed correctly as it kept the structures from deforming during the printing and curing processes.

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3.6 Slicing

3.6.1 Non-Uniform Slicing In additive manufacturing, slicing is the process through which a solid geometry is converted into a series of planar horizontal slices which are then converted into machine instructions, or â&#x20AC;&#x153;g-codesâ&#x20AC;?. There is a wide variety of available slicing algorithms, but since most of them are designed for high resolution 3D printers in which layer heights range in the microns and the materials being used have almost immediate curing times, it is not necessary to consider layer deformations. Therefore, uniform slicing algorithms, those in which every layer has the same height are the most commonly used. In the case of this project, layer heights range in the centimeters and curing time in the hours, therefore it is important to consider layer deformations and to create a non-uniform slicing algorithm that accounts for them.

Slicing Planes

Solid Geometry

Layer Height

Uniform Slicing

Non-Uniform Slicing

3.6.2 Layer deformation Due to the slow curing nature of clay, the base layers become deformed by the weight of the layers that are printed above them. This means that as the printing progresses, the deformations increase. If a uniform slicing method is used, as the deformations increase, the printing nozzle becomes increasingly separated from the layer below which brings problems such as inaccurate printing and less bonding between layers.

Printing Nozzle Height Discrepancy First Printed Layer

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Deformed Layer

3.6.3 Dynamic Slicing Traditional slicing algorithms start by converting a solid geometry into all of the layers that conform it before starting fabrication. An alternative that could potentially solve the issue of layer deformation is to design a slicing method that works in parallel with the fabrication process by generating a single slice, printing its corresponding layer, generating a height map of the printed layer and using that data to generate the following slice. This becomes a recursive process that stops once the entire geometry has been fabricated.

d d

First slice defined by extruder diameter.

Printed layer deformation.

Scanning of printed layer.

Subsequent slice defined by extruder d iameter minus material deformation.

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3.7 Secondary Deposition Strategy Fig. 1 Secondary deposition pattern

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The secondary deposition strategy which uses the support heaps from the primary printing as falsework is used to create connections with a multi-layer envelope and provide different amounts of shading between the structures. The goal is to take full advantage of the large amount of support material that is used for the primary deposition throughout all of the construction stages. This strategy is applied once the support heap is completed and an infrared sensor is used to generate a digital model of it that is then used to generate the tool paths.

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3.7.1 Deep Deposition Method In order to be able to print subsequent layers without deforming the previously printed ones, a deep deposition method is devised which allows rovers to print inside of the support heap by vertically levelling the extruder. The first layer is printed within the support pile, where the depth of the extruder is defined by the diameter of the extrusion multiplied by the amount of layers that will conform the envelope. For every successive layer, the depth of the extruder is reduced an amount equal to the diameter of the extruder. The nozzle of the extruder has a tip with a diagonal cut which helps by displacing the support material directly in front of the extrusion in order to prevent the extrusion from deforming during the deposition process.

3.7.2 Manual Test The deposition method was tested manually to prove that it is possible to deposit clay within the support material heap. lso, it was crucial to define the limitations and possibilities for the robotic deposition in the future. Due to the lack of precision inherent to a manual deposition approach, the support material, in this case gravel, was deposited one layer at a time. Four layers were deposited in a regular grid configuration. The result of this experiment shows that a deep deposition method can be achieved. ost of the layers were properly bonded to each other once the curing process was complete and the few cases in which layer separation was observed can probably be attributed to the lack of precision that would be solved with a robotic deposition approach.

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Deep Deposition

Manual Test

Nozzle Section

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3.7.3 Infrared Sensor Kinect V2 Fig. 2 Infrared sensor Kinect V2

Infrared sensor inect was used to compute a height map of a support heap. The points from the height map which were higher than 0 were selected to generate the actual building area. After this, the geometry and toolpaths for the secondary deposition were generated. This test was used as an initial proof of concept for computer vision application which in the future would be performed with an .

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Fig. 3 Scanning process and secondary deposition geometry generation

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Layer 1

Layer 2

Path 1 Path 2 Path 3 Path 4 Path 5 Path 6

Layer 3

“Paste Rover” paths Rover size 0

90 Layer 4

Multi-layer envelope

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Layer 4

Multi-layer envelope

3.7.4 Multi-Layer Envelope Equal Density Pattern

The mesh pattern, which is generated taking into account the roverâ&#x20AC;&#x2122;s dimensions and the extruderâ&#x20AC;&#x2122;s mobility, has the ability to differentiate its density based on nodal displacement analysis, where areas submitted to higher strains have a higher density in order to improve the structural performance. Multiple layers are superimposed in order to increase the depth of the structure and to better regulate the amount of direct light. In addition, the mesh pattern allows for the infiltration of wind and larger openings can be created in the envelope to let direct light in required areas.

Density Differenciation

In order to avoid vertical alignment between path connections from the superimposed meshes, the axis of each layer is rotated in relation to the layer below. The system has a high degree of flexibility during the deposition process since the paths can be applied and adjusted to any heap geometry.

Path Connections

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Fig. 4 Simulation of the secondary deposition tool path execution with multiple robots colaborating

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3.8 Robotic Prototyping Secondary Deposition

3.8.1 Test 1 s a next step, a multi-layer mesh pattern was generated to be tested through a robotic deposition process using an industrial robotic arm. A tool path consisting of four layers was executed inside a container filled up with rock salt as a support material. The diameter of the nozzle was mm and the height of each layer was defined as mm in order to increase the bonding between layers. fter executing the robotic deposition, the result shows that due to the large discrepancy between nozzle diameter and layer height the extruded material got deformed to the point of filling up the mesh openings which is something that should be re-calibrated for future prints. Another observation is that due to the printed material being fully enclosed by support material, the curing process had a dramatic increase in time which should be taken into account in the future. possible solution might come from experimenting with different support materials that could enhance the curing process by allowing more air through or by absorbing moisture from the printed clay mixture.

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Fig. 1 Deep deposition process of the four layer mesh pattern

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3.8.2 Test 2 The goal of the experiment was to test the secondary deposition method in combination with the proposed computer vision approach. Two previously printed elements, a dome and a column, were placed on the printing bed and their corresponding support heaps were formed manually in between them. After this, the heap was scanned with infrared sensor inect . . and the tool paths for the multi-layer envelope were generated. During the execution of the tool path, a number of unexpected collisions occurred between the end effector nozzle and the previously printed structures. This was probably caused by scanning inaccuracies due to the high amount of noise and lack of sufficient detail inherent to todayâ&#x20AC;&#x2122;s consumer 3D cameras such as the inect.

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Fig. 2 Robotic Setup

First stage deposition

Second stage deposition - Pattern generationH

Infrared Sensor

enerated

eight- ap

eight - Map

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Fig. 3 Simulation of the secondary deposition tool path execution with the industrial robotic arm KUKA KR-30.

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3.8.3 Test 2 - Observations ultiple trials to modify and execute the tool path were performed but the desired result was not achieved. Further research on the subject of enhancing coarse 3D depth maps from compact sensors such as the inect could be informed by some already existing promising solutions which combine the captured depth map with surface normals obtained from polarization cues [1], from photometric stereo [2], or from shape-from-shading [3]. It is also important to consider that for the real-world application in which a must perform the scanning of large support heaps in the context of a construction site, a dynamic scanning approach in which multiple captures are combined into a single height map would have to be developed.

Fig. 4 A. Depth from Microsoft Kinect B. hree Photos sing a Polarizer C. Polarization Enhanced Depth

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3.4 Devices Conceptual Schema

Overview The introduction of robotics for in-situ construction processes has been an ongoing research topic since the early 1980s. [1] The general aim is to achieve fully automated construction scenarios and bring intelligent, service-oriented and distributed manufacturing systems [1] into architecture. There are a variety of technical aspects and economic challenges that have to be addressed for the application of such innovative processes. At the same time, computational design has progressed much faster than construction techniques and can therefore help to push the investigation of robotic processes. Devices which are currently available from different areas can be adopted and synthesized for construction purposes. The proposed construction process is divided into a number of steps that are represented by a sequence of actions that have to be performed by specific robotic units. Locomotion, suction, mixing and deposition processes are specified as the main functions. s a result, a robotic program was defined for different types of robots which is based on the construction methodâ&#x20AC;&#x2122;s requirements and the specific material properties of clay. set of devices which are widely available are synthesized into the conceptual design of the robotic units.

Fig. 1 Task Distribution Building plot

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Building plot

Support material

Paste Rover

Powder Rover

Station Unit

Functions: Mixing Clay Deposition

Functions: Suction Support Material Deposition

Functions: Water Extraction Material Processing Rover Recharging

Fig. 2 Construction process

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3.4.1 Paste Rover The aste

overâ&#x20AC;&#x2122;s main device is a paste extruder for layer-by-layer material deposition.

neumatic extruders are the most commonly employed for additive manufacturing processes which are gantry based, mainly due to the simplicity of their design. The main limitation of such extruders when considering their application for a relatively small mobile robot, is that they rely on an air compressor to generate thrust which increases the weight and the energy consumption of the robotic units and therefore limits the amount of material that they can carry. possible solution can be found in infinite screw extruders which are widely employed for material mixing and continuous extrusion operations in a wide variety of industrial applications such as polymer processing, rubber production, food production amongst others. Apart from eliminating the need for a compressor, such extrusion systems provide other advantages such as continuous material recharging without the need for disassembly and higher control over material flow rate which can be controlled through the speed of the screw. oth single and twin screw extruders could potentially be implemented within a mobile robot. nother device that must be integrated into the aste overâ&#x20AC;&#x2122;s design is a linear displacement mechanism which enables the extrusion of massive elements see chapter 3.3. as well as a vertical leveling device for deep deposition (see chapter 3.3.5), both of which can be assembled from off-the-shelf components such as stepper motors and chain drives.

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Extruder Leveling the Extruder Base

400 mm

Leveling Device 400 mm

Sliding Mechanism Chain Extruder

Stepper Motor

Water

Pre-Mixed Paste

Water

Clay + Additives

Helical Gear Acryllic Container Archimidean Screw

Spraying water to increase bonding by preventing the extrusion from drying

Pneumatic Extruder

Mixed in Nozzle Nozzle

Single screw extruder

Twin screw extruder

Multiple Screw Extruder

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3.4.2 Powder Rover Powder Rover is the device in charge of gathering granular material from the site (or from the Station nit and depositing it at the building plot to create a falsework. This device requires a suction feature with certain level of filtration as well as a vibration mechanism to enhance the deposition of granular material. The suction mechanism is based on a Dyson Cyclone Dust Collector which uses a fan to provide suction. In addition, a vibration device is introduced in order to keep finer particles in a loose state during the deposition process and avoid them from getting compacted and stuck inside the container. The vibration mechanism is based on an Eccentric Rotating Mass vibration motor which provides higher deposition control by calibrating the vibration frequency to specific granular materials. Granular materials with bigger particles can be deposited through gravity and, in this case, the vibration device can be turned off to save energy. Device parameters such as opening size, deposition speed and vibration frequency must all be calibrated to the selected granular material.

3.4.3 On-Board Sensing As previously mentioned in chapters 3.2.3 and 3.2.4, a weakly centralized system which combines aspects of centralized and distributed systems is proposed. lthough the systemâ&#x20AC;&#x2122;s global awareness is centralized in an with a privileged vantage point, local awareness is distributed throughout the ground-based robots for on-the-go error correction. The roverâ&#x20AC;&#x2122;s proposed on-board sensing consists on a range-finder either laser or ultrasonic for collision avoidance with other rovers or unpredicted obstructions, a light sensor for material state detection and an inclination sensor for boundary detection.

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Suction

Hose

utput Filter

entilation Fan Container Motor Power supply

ibration mechanism Sliding mechanism Deposition Intake port Leveling device Granular material

n- oard Sensing

Photo Sensor

Material State Detection

Tilt Sensor

Boundary Detection

ltrasonic ange Finder

Collision Avoidance

Printed Structure bstacle over

bstacle

Construction Area Angle of Repose Area

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3.4.4 Station Unit Station nit for material preparation is proposed in order to reduce the size and complexity of the mobile units (Powder and Paste Rovers) and increase the quality of the material preparation process. This device is manually filled up with dry clay and natural reinforcement material such as fibers or lime which are all mixed with water that can be extracted using an industrial air dehumidifier or added manually when needed. In addition, solar panels and a battery are proposed for the production and storage of energy to power the device. Adding a station robot increases the complexity of the system in terms of robotic interaction, but also increases the quality of the construction process.

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3.4.5 Flying Robot Flying obot, or , is a key member of the proposed multi-robot system in which the global awareness of the entire system is centralized. The main function of the flying robot is to estimate the parameters of an upcoming task on the ground by computing height maps with the use of an on-board infrared sensor. [3] These parameters are then used to compute paths which are translated into rover instructions. There are two methods that are proposed through which the Flying Robot can communicate with the ground based rovers, direct and indirect chapter 3. . . The relationship between battery life and charging time for the selected must be studied, since it will determine the amount of backup units that the system must have.

Fig. 3 Mavic Pro is one of the latest UAV models that are available on the market.

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3.4.6 Building Materials and Energy Sourcing Autonomy of the multi-robot system is a central aspect and one of the most challenging areas of investigation. The two main challenges regarding autonomy are energy and material sourcing. Some possible solutions to these challenges are discussed below.

3.4.6.1 Solar-Powered Robots possible solution for the robotâ&#x20AC;&#x2122;s energy source is to integrate into their design a solar panel and an energy management system with a smart host microcontroller. [9] This introduces the construction of a solar tracking mechanism aimed at increasing the roverâ&#x20AC;&#x2122;s power regardless of its mobility. [4] This solar-powered system requires a pack of dual batteries for each robot with the aim of completing the process of charging a battery independently while the other battery provides all the energy consumed by the robotic device. ne battery functions as a primary source and another one as a backup battery. When the charge of one battery is fully consumed, the controller automatically switches to the other battery with a relay for robot functioning. [5] This enables the system to have continuous performance throughout the construction process.

3. . .2 Air Deh midi er Device At any given time, the atmosphere contains 3400 trillion gallons of water vapor, which would be enough to cover the entire arth in inch of water. This creates an opportunity to extract water from humid ambient air for the proposed construction process. n air dehumidifier is a device that can be used to provide the required amount of water for clay crystallization. The device is based on the principle of cooling the air below its dew point to remove its moisture. 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 storing container. [8] Solar energy can be used to provide power for the dehumidifier units. The amount of energy needs to be calculated according to the amount of water that needs to be produced for the construction. The best measurement in this case is the efficiency of the machine sometimes called its energy factor), which is how much water it removes divided by how much power it uses, measured in liters (or pints) per kilowatt hour (L/kWh). [8] The main limitation of such a device is that it requires for the relative humidity to remain above 50% for effective functioning.

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Fig. 4 DSolar robot is powered by solar panels and developed by LEGO Mindstorms NXT and Dexter Industries.

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4.0 Design Development

4.1 4.2 4.3 4.4 4.5 4.6

Site Case Study Clustering Strategy Building Morphologies Selective Indirect Porosity Second Stage Deposition Design Proposal

136 138 140 144 146 148

4.0 Design Development The section illustrates the design possibilities of the described construction method.

Overview Up to this point, the construction method, deposition strategies and geometry generation were described and tested. The goal of the design stage is to integrate the developed strategies and to show the design possibilities of the method applied to a specific context. s a part of the design proposal, a possible site was defined in a context in which clay is currently being used as the main building material, but the construction process and spatial qualities can be improved through automation. The intension is to propose a comprehensive settlement design which enables the possibility of constant growth. A clustering strategy is introduced and the cluster development strategy is subdivided into a set of steps which aims to provide a pedestrian network and semi-public spaces. At the same time, the secondary deposition strategy is applied to generate semi-shaded spaces and spaces with open sky views. Also, variations of building morphologies are discussed. In addition, ventilation and light penetration design strategies are introduced and applied to specific building units. Finally, construction metrics for the designed cluster are extracted to unfold the relationship between the various parameters that make up the construction method, including amount of rovers, construction time, refill points and amount of required material.

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4.1 Site Case study Centre-Est Region, Burkina Faso

Fig. 1 Gando is a village in Burkina Faso, in the Centre-Est Region, the Boulgou province and the Department of Tenkodogo. Population is about 2500 residents.

Fig. 2 Geographical location of the site.

This landlocked region in west Africa was selected as a case study site for the possible implementation of the proposed robotic construction method for various reasons. With a seventy percent rural population, geographical and infrastructural isolation make it essential to use local materials for construction, which is one of the reasons for which clay soil is the most common building material. Daily temperature extremes during the winter and high summer precipitations have made protection from heat and rain a priority, this has led to solutions in which proper lighting and ventilation are traded off. In addition, because of the high labour intensity of traditional clay vault construction, most settlements have opted for simpler solutions such as flat sheet metal roofs which provide very little insulation and do not allow for the dissipation of hot air. With no access to electricity, passive bio-climatic solutions are necessary to ensure comfort within the dwellings as well as in open public spaces. Communities in this region are organized in clusters which are configured by family sub-clusters. This organization creates public and semi-public open spaces throughout the settlements, but since they lack protection from the sun and rain, most activities must happen indoors, or when available, under the shade of a tree.

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50 °C

Fig. 3

40 °C

Climate diagrams of average temperatures and precipitation at Centre-Est Region, Burkina Faso.

30 °C 20 °C 10 °C

JanF

eb MarA pr MayJ un JulA

Mean daily max.H

ot Days

Mean daily min.C

old Nights

ug SepO ct NovD ec

100mm 75mm 50mm 25mm 0mm

JanF

eb MarA pr MayJ un JulA

ug SepO ct NovD ec

Precipitation

Fig. 4 Aggregation pattern of Gando village.

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4.2 Clustering Strategy

10m

5m 3m

Aggregation pattern

1. An aggregation strategy based on clusters and sub clusters is proposed which allows for a range of morphological variations while ensuring the creation of public and semi-public spaces.

Morphological Variations Empty cells

2. Connections between sub-clusters are ensured by selecting certain building plots which are to remain empty throughout the building aggregation process.

Three different cell sizes are defined, where two of them are for building units and the largest one is assigned for open spaces. The open spaces play an important role in the organization of the building units, where all units are placed around them. As a result, this logic creates a spatial distribution system that has the potential for continuous growth through the addition of new clusters.

The First Set of Columns

3. The first set of columns is placed in each empty cell of the pattern to provide support for the secondary deposition envelope and to ensure that a habitable height is maintained throughout the structure.

138 Design Development

Connections between Clusters

4. Once the unit aggregation is completed, connections between clusters are identified.

Pedestrian Network

5. A pedestrian network which creates connections between units is defined.

The Second Set of Columns

. fter the openings are defined, a second set of columns is placed to provide the required support for secondary deposition structure. In addition, they create semi-private open spaces and ensure that a habitable height is maintained throughout the structure.

Openings

. s a next step, openings in the secondary deposition structure are proposed. The aim is to provide the public spaces with protection from the sun as well as to allow for the central spaces to have open sky views and increased light penetration. In addition, the openings help to navigate through clusters by providing visual references between them.

Surface of Secondary Deposition Stage

. s a final step, the support material around each element of the system is calculated which provides the surface for the secondary deposition. The openings are projected on the surface to define the boundaries which generate the multi-layer envelope.

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4.3 Building Morphologies

Morphological variation is created by differentiating the amount and direction of circular cells that make up each building type. There are a variety of possibilities for different size dwelling units (single units and multiple units) and public units, where educational and commercial activities can take place. Multiple dwelling units can be partitioned to increase the population density. The programmatic requirements of each cluster define the arrangement of units within it. Funicular form-finding is employed to generate the shell morphologies from the varying plan configurations. uilding height ranges between . m and . m and the openings range between 2, 1m and 2, 8 m in height. Shell thickness, which is informed by utilization analysis ranges between 0.1 m and 0.4 m for each unit. Finally, the amount of clay necessary for the construction of each unit was quantified.

140 Design Development

Building Morphologies Dwelling Units

Unit 1 Unit area: 30.77 m 2 Amount of clay: 3 .3 m

Unit 2 Unit area: 2 54.04 m Amount of clay: 3 . m3

Unit 3 Unit area: 2 40.1 m Amount of clay: . m3

Unit 4 Unit area: 2 . m Amount of clay: 3 . m

Unit 5 Unit area: 2 86.51 m Amount of clay: . m3

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Building Morphologies Multiple Dwelling Units

Unit 6 Unit area: 2 72.58 m Amount of clay: 3 3. m

Unit 7 Unit area: 2 . m Amount of clay: . m3

Unit 8 Unit area: 2 11 . m Amount of clay: . m3

Unit 9 Unit area: 2 184.14 m Amount of clay: 3 . m

Unit 10 Unit area: 2 1 . m Amount of clay: 3 . m

142 Design Development

Building Morphologies Public Units: Educational and Commercial

Unit 11 Unit area: 2 72.78 m Amount of clay: 3 . m

Unit 12 Unit area: 2 11 . m Amount of clay: 3 . m

Unit 13 Unit area: 2 151.78 m Amount of clay: 3 . m

Unit 14 Unit area: 2 184.4 m Amount of clay: 3 10.45 m

Unit 15 Unit area: 2 . m Amount of clay: 3 111.26 m

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4.4 Selective Indirect Porosity

ir exchange is a key element for designing structures that can passively regulate their interior temperature. In warm climates, where it is desirable to allow infiltration of air and light while preventing direct solar gain as well as visual access to the building interior, it is preferable for openings to be indirect to the surface normal. y selectively decreasing the thickness of the wall and inverting the side of the modification in consecutive layers, it is possible to generate indirect openings throughout the structure. Support material is used in order to allow for bridging over the opening without the clay deforming during the curing process. From a structural point of view, it is desirable to have less openings at the base of the structure, where all of the loads concentrate, and to increase the amount of openings at the top layers of the structure, thus reducing their weight. From a bio-climatic perspective, it is also beneficial to increase the amount of openings at the top of the structure in order to allow for the stratification of hot air. Since support material must be deposited within the wall at every opening, the question of how to remove it once the curing process is complete becomes of importance. A branching pattern is proposed as a way of gradually increasing the amount of openings as the structure progresses upwards while at the same time maintaining continuous vertical connections between all of the openings. This allows us to define a number of support extraction points at the base of the structure, where the branching pattern starts, from which the supports of every opening can be removed.

Support material allows for bridging.

Size of opening defined by change in wall thickness.

Bridges work as eaves to prevent direct solar radiation. Bridge thickness defined by layer repetition.

144 Design Development

Selective Indirect Porosity is Infrormed by Utilization Analysis

Geometry with Selective Indirect Porosity

Branching pattern increases the amount of openings at the top while mantaining vertical connections between them.

Support material extraction point.

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4.5 Second Stage Deposition Mesh Differentiation

Fig. 5 Nodal displacement analysis of the second stage deposition pattern is used to differentiate the mesh by increasing the pattern density in the areas of highest displacement.

Single Cluster with Support Material

Multi-layer Envelope

Second Stage Deposition

146 Design Development

Equal Density Distribution

Layer Rotation and Superposition

Nodal Displacement Analysis

Density Differentiation

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4.6 Design Proposal

Fig. 6 Plan view of the cluster (Primary deposition units)

The proposed design shows the aggregation of multiple dwelling and commercial units, which are integrated with open public and semi-public spaces by the second stage printing pattern. The two sets of columns provide support to the multi-layer envelope and the openings in it. In addition, they maintain a habitable height under the secondary deposition and help to subdivide the space into public and semi-public spaces.

Fig. 7 Plan view of the cluster with multi-layer envelope (Second stage deposition)

01 m5

148 Design Development

10m

Section A-A

Section B-B

Section C-C

10m

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Fig. 8 Axonometric view of the cluster with multi-layer envelope (Second stage deposition)

150 Design Development

Fig. Axonometric view of the cluster with multi-layer envelope (Second stage deposition)

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4.6.1 Construction Metrics

Construction metrics are extracted for the proposed cluster design in order to unfold the relationship between the multiple variables that make up the construction method. Modifying one of the variables will have an effect on all of the rest. Understanding these relationships is crucial for the calibration of the whole systemâ&#x20AC;&#x2122;s performance. Printing time for the primary deposition sequence is determined by the tool path length divided by the amount of rovers in the team, taking into account the speed at which they can extrude. This printing time is then used to inform the speed at which support material must be deposited in order to be able to execute both tasks in parallel. lthough active printing time can be calculated, material recharge times, which are related to the material container sizes and the location of the stationary units must also be taken into account. A further subdivision of the construction sequence into local sub-clusters could reduce the large amount of support material needed.

152 Design Development

Covered Area

m 3. m 3

Amount of Clay Number of Layers

Total Toolpath Length 3

2413 m

Number of Toolpaths per Layer

Number of Refill Points per paste Rover

Printing Time

6 hrs.

Amount of Support Material

m 3 50

Powder Rovers Powder Rovers Container

. m 3

Number of Refill Points Printing Time Deposition Speed

42.7 hrs. .

33 m 3 sec

Units

8 72

Columns uilding Area Total Toolpath Length

3m 230 788 m

Amount of Clay

3m 3 25

Paste Rovers Paste Rovers Container Number of Refill Points Diameter Printing Time Speed

m 3 283 50 mm

42.7 hrs. 0.06 m/sec

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5.0

Conclusions

5.1 5.2 5.3 5.4 5.5

Construction Method Deposition Strategies Multi-Robot System Design Devices Design Development

156 157 157 158 158

Multiple strategies are proposed for the development of the described construction method. In addition, a variety of tests are performed to provide proofs of concept regarding specific aspects of the method. Through this approach, an understanding is gained of the further work that is required to go from a conceptual stage to the actual implementation of the proposed system.

5.1 Construction Method The proposed construction method opens the opportunity to create a variety of geometrical possibilities using soft curing materials such as clay. In addition, the use of granular materials as temporary supports enables small ground-based mobile robots to gain height and build structures larger than themselves. At the same time, it allows for the on-site production of structures with an unlimited footprint and variable thicknesses while generating no material waste. At the current stage of development, the possibility of printing complex geometries that are limited in scale by the robotâ&#x20AC;&#x2122;s reach is demonstrated through the use of an industrial robotic arm and provides a proof of concept of the construction method at a desktop scale. The described multi-robot construction method has a high level of flexibility in terms of possible applications. This method forms a complex organization of relatively simple devices that are assembled together to perform a construction process. This gives an opportunity to develop a system that is based on the latest technologies for a new construction process. As a result, the system gained a lot of complexity in terms of hardware and software requirements for which it was not possible to test it as whole at the current stage.

156 Conclusions

5.2 Deposition Strategies Printing times for the proposed deposition strategies were found to be relatively fast, but the curing process has to be further evaluated in relation to various parameters. A systematic study has to be performed through a variety of material tests in order to better understand the different variables that affect curing time. This can help to more precisely quantify the time when support material can be removed without producing layer deformations. Also, the hygroscopicity of different granular materials has to be further investigated to find preferable support solutions which could enhance the curing process. The Deep Deposition Method has a great potential, but a variety of problems were faced during the experimentation stage for which further investigation is needed in order to improve the quality of the deposition. Also, pattern exploration in terms of structural and environmental performance has to be further integrated. ne of the possible solutions could be the introduction of weaving and interlocking of the printed layers, making use of the three dimensional printing space generated by the support heap in order to improve bonding between layers and the global systemâ&#x20AC;&#x2122;s performance. To further develop the construction sequence, a strategy for the re-deposition of support material from previously printed structures to be used for new ones must be developed. In addition, the amount of available support material in a specific site should inform the subdivision of the construction sequence into steps which can be accomplished with the available resources.

5.3 Multi-Robot System Design Defining the characteristics that a multi-robot system should have in relation to the proposed construction method is only the first step towards the actual implementation of such a system, for which a collective effort from specialists across a variety of fields is required. ne of the greatest challenges that must be addressed is the development of a computer vision strategy which integrates consumer-available sensing hardware such as the Kinect v2 with custom software capable of performing the various tasks that are required. Some of these tasks include: locating the available robotic units and differentiating them by type (Paste, Powder, Station), generating accurate height maps of the building plot by combining multiple partial scans, defining specific instructions based on the produced height maps without intervention from a human user, amongst others. In addition, the sensing capabilities should be centralized in a Flying Robot (UAV), while the computation, which would very likely exceed the computing capabilities of current consumer available UAVs should be externalized, making use of the new field of Cloud obotics. Another important aspect of the proposed MRS that must be further developed is the communication between robotic units. global map of the building site, generated by the â&#x20AC;&#x2122;s centralized awareness, should include topographical and positional information and should be accessible by every ground based unit in order for them to define their immediate goals based on the available information. In addition, individual rovers should be able to over-write their control protocol using data gathered from their on-board sensors for on-the-go error correction. Each one of this seemingly simple tasks will require the combined knowledge and expertise from the fields of mechatronics and software engineering in order to reach a level of implementation.

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5.4 Devices The aim of the devices chapter (3.4) was to propose a synthesis of widely available devices related to the specific tasks required to execute the construction process. This provides an initial proof that such a system can be accomplished with existing technologies. A variety of technical aspects were lacking in the research which should be addressed. Component specifications and the connection schematics between them have to be designed with a high level of detail to progress from the conceptual stage to the actual prototyping and implementation of the different robotic units. Such a task can be very time-consuming and it requires a high level of technical knowledge on the field of mechatronics. The amount of energy and water that is required by the system has to be quantified. The amount has to be extracted in relation to the constructionâ&#x20AC;&#x2122;s volume, as this data will define the size and amount of ir-Dehumidifier and Solar anels units. lso, the amount of Station nits has to be defined in relationship to the size of the construction and aste and owder overâ&#x20AC;&#x2122;s deposition speed.

5.5 Design Developement The intension of the design development is to integrate the proposed strategies into a site-specific design solution and through this, to evaluate the feasibility of the construction process in terms of required robotic units, amount of material and active printing times. A site in which the proposed construction method could potentially be applied was selected taking into account factors such as the availability of clay, climatic conditions which are appropriate for clay architectures, and a social scenario which calls for new design solutions for the improvement of the populations quality of life. The economic viability of the project was not considered during the site selection process although it is important to consider that economic factors would be the main drivers for the initial stage of implementation of such a project, and it would take a very long time until such advancements in construction can be introduced in the places where they are most needed. In terms of design, an aggregation strategy which is informed by the specific climatic conditions of the selected site should be introduced. Computational tools for environmental analysis could further inform the design process at a variety of scales, from the development of individual units, their aggregation into clusters and for the Secondary Deposition. Also, the basic set of shells that were generated can be significantly improved for a specifically defined program. much higher level of detailing has to be developed to achieve a design proposal that is suitable for living.

158 Conclusions

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6.0

References

6.1 6.2

Image References Text References

162 168

6.1 Image References

0.0 Introduction Fig. 1 Mass production of social housing in Mexico City Torres, Y. (2004) Construcción de viviendas cayó 9.7% en 2013. Available at: http://eleconomista.com.mx/ sistema-financiero construccion-viviendas-cayo-97-2013 (Accessed: 25 January 2017). Fig. 2 Comparison between traditional and robotic construction methods in terms of flexibility and embodied energy. Khoshnevis, B., Kwon, H. and Bukkapatnam, S., 2004. Automated Construction using Contour Crafting. In IIE Annual Conference. Proceedings, Houston, TX, USA.

builders. Available at: https://iaac.net/research-projects/ large-scale-3d-printing/minibuilders/ (Accessed: 18 January 2017). Fig. 9 To reinforce the shell, vacuum robots are attached onto the surface to print an additional layer and to smooth it. Jin, S., Maggs, S., Sadan, D. and Nan, C. (2015) Minibuilders. Available at: https://iaac.net/research-projects/ large-scale-3d-printing/minibuilders/ (Accessed: 18 January 2017). Fig. 10 The focal point of the lens directs on the center of the printing bed where the geometry is being printed. Kayser, M., 2011. Solar Sinter Project. Markus Kayser.

1.1 Case Studies Fig. 1 Concrete extrusion end-effector mounted on a robotic arm. Camilleri, F., Doukhi, N., Lopez Rodriguez, A. and Strukov, R. (2015) Amalgamma. Available at: https://www. amalgamma.org (Accessed: 18 January 2017). Fig. 2 Large scale prototype of a concrete column. Camilleri, F., Doukhi, N., Lopez Rodriguez, A. and Strukov, R. (2015) Amalgamma. Available at: https://www. amalgamma.org (Accessed: 18 January 2017). Fig. 3 Exterior view of the pavilion during the fabrication stage. Doerstelmann, Moritz, et al. “ICD/ITKE Research Pavilion 2014–15: Fibre Placement on a Pneumatic Body Based on a Water Spider Web.” Architectural Design 85.5 (2015): 60-65. Fig. 4 Diving Bell Water Spider (Agyroneda Aquatica) reinforcing an air bubble from the inside. Doerstelmann, Moritz, et al. “ICD/ITKE Research Pavilion 2014–15: Fibre Placement on a Pneumatic Body Based on a Water Spider Web.” Architectural Design 85.5 (2015): 60-65. Fig. Cyber-physical fibre placement process. Doerstelmann, Moritz, et al. “ICD/ITKE Research Pavilion 2014–15: Fibre Placement on a Pneumatic Body Based on a Water Spider Web.” Architectural Design 85.5 (2015): 60-65. Fig. 6 Foundation robot (top-right) Jin, S., Maggs, S., Sadan, D. and Nan, C. (2015) Minibuilders. Available at: https://iaac.net/research-projects/ large-scale-3d-printing/minibuilders/ (Accessed: 18 January 2017). Fig. 7 Grip robot (top-left) Jin, S., Maggs, S., Sadan, D. and Nan, C. (2015) Minibuilders. Available at: https://iaac.net/research-projects/ large-scale-3d-printing/minibuilders/ (Accessed: 18 January 2017). Fig.8 Vacuum robot (bottom-left) Jin, S., Maggs, S., Sadan, D. and Nan, C. (2015) Mini-

162 References

Fig. 11 “Solar Sinter” fully autonomous set up in the desert. Kayser, M., 2011. Solar Sinter Project. Markus Kayser. Fig.12 Assembly logic. Friedman, J., Kim, H. and Mesa, O., 2014. Experiments in Additive Clay Depositions. In Robotic Fabrication in Architecture, Art and Design 2014 (pp. 261-272). Springer International Publishing. Fig.13 The clay extruder was developed as the end-effector for a 6-axis industrial robotic arm. Friedman, J., Kim, H. and Mesa, O., 2014. Experiments in Additive Clay Depositions. In Robotic Fabrication in Architecture, Art and Design 2014 (pp. 261-272). Springer International Publishing. Fig. 14 The woven clay facade panels with different light permeability were produced with using the 3D printing technique and assembled together. Friedman, J., Kim, H. and Mesa, O., 2014. Experiments in Additive Clay Depositions. In Robotic Fabrication in Architecture, Art and Design 2014 (pp. 261-272). Springer International Publishing. Fig. 15 Snapshots in the process of autonomously building a ten-block structure. The robot collects blocks from the docking station at the left, where new blocks are added by hand as construction proceeds. Petersen, K., Nagpal, R. and Werfel, J., 2011. Termes: An autonomous robotic system for three-dimensional collective construction. Proc. Robotics: Science & Systems VII Fig. 16 Custom designed robots and construction blocks. Petersen, K., Nagpal, R. and Werfel, J., 2011. Termes: An autonomous robotic system for three-dimensional collective construction. Proc. Robotics: Science & Systems VII Fig. 17 System proposal: one robot per plane. Each robot is enabled with a mechanism that allows to pass the bobbin from one machine to the other. Robots are capable of attaching the thread to pre-defined anchor points. Yablonina, M. (2015) ITECH M.Sc 2015: Mobile robot-

ic fabrication system for filament structures. vailable at: http://icd.uni-stuttgart.de/?p=15699 (Accessed: 18 January 2017

Mega-scale fabrication by contour crafting. International Journal of Industrial and Systems Engineering, 1(3), pp.301-320.

Fig. 18 Physical model capable of withstanding the weight of a human. Yablonina, M. (2015) ITECH M.Sc 2015: Mobile robotic fabrication system for filament structures. vailable at: http://icd.uni-stuttgart.de/?p=15699 (Accessed: 18 January 2017

Fig. 28 Construction of a full scale wall with internal form ties. Khoshnevis, B., Hwang, D., Yao, K.T. and Yeh, Z., 2006. Mega-scale fabrication by contour crafting. International Journal of Industrial and Systems Engineering, 1(3), pp.301-320.

Fig. 19 Schematic design of the extrusion assembly with top and side trowels. Khoshnevis, B. and Dutton, R., 1998. Innovative rapid prototyping process makes large sized, smooth surfaced complex shapes in a wide variety of materials. Materials Technology, 13(2), pp.53-56.

Fig. 29 Two-meter-tall “radiolaria” inspired structure built using the d-shape printer. D-Shape. 2015. “The Technology.” Monolite UK. http:// www.d-shape.com/tecnologia.htm.

Fig. 20 Residential Building Construction using Contour Crafting Khoshnevis, B. and Dutton, R., 1998. Innovative rapid prototyping process makes large sized, smooth surfaced complex shapes in a wide variety of materials. Materials Technology, 13(2), pp.53-56. Fig. 21 Schematic design for an automated tiling mechanism. Khoshnevis, B., Kwon, H. and Bukkapatnam, S., 2004. Automated Construction using Contour Crafting. In IIE Annual Conference. Proceedings, Houston, TX, USA. Fig. 22 Schematic design for an automated plumbing installation mechanism. Khoshnevis, B., Kwon, H. and Bukkapatnam, S., 2004. Automated Construction using Contour Crafting. In IIE Annual Conference. Proceedings, Houston, TX, USA. Fig. 23 CC in operation and representative 2.5D and 3D shapes and parts filled with concrete. Khoshnevis, B., Kwon, H. and Bukkapatnam, S., 2004. Automated Construction using Contour Crafting. In IIE Annual Conference. Proceedings, Houston, TX, USA. Fig. 24 Schematic Design of full scale nozzle assembly. Khoshnevis, B., Kwon, H. and Bukkapatnam, S., 2004. Automated Construction using Contour Crafting. In IIE Annual Conference. Proceedings, Houston, TX, USA. Fig. 25 Conceptual proposal of multi mobile-robot construction system. Khoshnevis, B., Kwon, H. and Bukkapatnam, S., 2004. Automated Construction using Contour Crafting. In IIE Annual Conference. Proceedings, Houston, TX, USA. Fig. 26 Proposed implementation of NIST RoboCrane system for Contour Crafting. Albus, J., Bostelman, R. and Dagalakis, N., 1992. The NIST robocrane. Journal of Robotics System, 10(5). Fig. 27 Schematic of conventional formwork system (left) and Contour Crafting (right) for vertical concrete wall. Khoshnevis, B., Hwang, D., Yao, K.T. and Yeh, Z., 2006.

Fig. 30 Full scale on-site construction using clay with a gantry system. orld’s dvanced Saving roject. . bout s WASProject.” WASP. http://www.wasproject.it/w/en/ wasp/. Fig. 31 Double curvature concrete “slab” printed with concrete over foam supports. eating, S. and xman, . , Immaterial obotic Fabrication’. roceedings of ob rch obotic Fabrication in Architecture, Art and Design. Fig. 32 Foam form-work being printed by a robotic arm which will eventually be cast with concrete. Buswell, Richard, and Simon Austin. 2015. “Freeform Construction: Partners.” Loughborough University. http:// www.freeformconstruction.com/partners.php. 1.2 Multi Robot Systems Fig. 1 Multi-robot system taxonomy. Redrawn from: Iocchi, L., Nardi, D. and Salerno, M., 2000, August. Reactivity and deliberation: a survey on multi-robot systems. In Workshop on Balancing Reactivity and Social Deliberation in Multi-Agent Systems (pp. 9-32). Springer Berlin Heidelberg. Fig. 2 Cooperation between robotic agents is used to solve a task that could not be solved by a single robot. edrawn from athews, ., Christensen, .L., ’ rady, R. and Dorigo, M., 2012, October. Spatially targeted communication and self-assembly. In 2012 IEEE/RSJ International Conference on Intelligent Robots and Systems (pp. 2678-2679). IEEE. Fig. 3 Organizational possibilities for multi-robot systems. Fig. 4 Indirect communication through stigmergy in ant colonies. Fig. 5 Comparison between a homogeneous swarm of one-thousand Kilobots (left) and a heterogeneous MRS composed of three types of robots (right). Rubenstein, M., Ahler, C. and Nagpal, R., 2012, May. Ki-

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lobot: A low cost scalable robot system for collective behaviors. In Robotics and Automation (ICRA), 2012 IEEE International Conference on (pp. 3293-3298). IEEE.

earth as a wall building material in individual climatic regions. Data from: Z.J. Zhai, J.M. Previtali / Energy and Buildings 42 (2010) 357–365

1.3 Material Selection Fig. 1 Large dickite plates in sandstone, Cretaceous, West of Shetland. Dimensions: ~130 µm wide velyne Delbos, ames utton Institute. Images of Clay rchive’ of the ineralogical Society of reat ritain Ireland and The Clay Minerals Society. Fig. 2 Large scale additive manufacturing process with unfired clay which gets crystalized and solidified when mixed with water. orld’s dvanced Saving roject. . bout s WASProject.” WASP. http://www.wasproject.it/w/en/ wasp/. Fig. 3 Selective Laser Sintering (SLS) 3D printer in which powdered material is solidified layer-by-layer through a heat sintering process. Marketing, O. (2016) Additive manufacturing - what is (AM). Available at: http://www.optomec.com/additive-manufacturing/ (Accessed: 19 January 2017). Fig. 4 Large scale D-Shape printer in action. Granular material gets solidified layer-by-layer through the selective deposition of a liquid binder. D-Shape. 2015. “The Technology.” Monolite UK. http:// www.d-shape.com/tecnologia.htm. Fig. 5 Assembly logic Fig. 6 Flight Assembled Architecture (2011-2012) byramazio ohler is the first architectural installation assembled by flying robots and an example of discrete assembly logic. Augugliaro, F., Lupashin, S., Hamer, M., Male, C., Hehn, M., Mueller, M.W., Willmann, J.S., Gramazio, F., Kohler, . and D’ ndrea, ., . The flight assembled architecture installation Cooperative construction with flying machines. IEEE Control Systems, 34(4), pp.46-64.

164 References

Fig. 3 Percentage of observed dwellings which contain earth as a roof building material in individual climatic regions. Redrawn from: Z.J. Zhai, J.M. Previtali / Energy and Buildings 42 (2010) 357–365

Fig. 4 Observed wall mass types in percentage of dwellings in individual climatic regions. Data from: Z.J. Zhai, J.M. Previtali / Energy and Buildings 42 (2010) 357–365 Fig. 5 Variation of outdoor and indoor temperatures for a 460mm earth wall during the hottest periods of the year 2012. Redrawn from: Z.J. Zhai, J.M. Previtali / Energy and Buildings 42 (2010) 357–365 Fig. 6 Cross section of a single Tholos dome from northern Syria. Redrawn from: Meca, S., 2009. Earthen domes and habitats. Villages of Northern Syria. Edizioni ETS. Pisa, 20(4). Fig. 7 Cross section of a double Tholos dome from northern Syria. Redrawn from: Meca, S., 2009. Earthen domes and habitats. Villages of Northern Syria. Edizioni ETS. Pisa, 20(4). Fig. 8 Diagram showing the wind tower effect and cooling through evaporation. edrawn from ohnson’s rcticle Fig. 9 Pit House Cross Section edrawn from archeologist ames Teit’s drawing from the 1980s. Original image from American Museum of Natural History

Fig. 7 The project “Dune” (2007-2008) by Magnus Larsson (img.). An example of a non-discrete assemble logic, where Bacillus Pasteurii bacteria was used to solidify the dune’s surface. Larsson, M. (2008) Magnuslarsson.Com. Available at: http://www.magnuslarsson.com/architecture/dune.asp (Accessed: 22 January 2017).

Fig. 10 Large overhangs provide shading to the walls while the stilt structure allows for cold wind to flow under it. Redrawn from History, C.M. of (no date) Civilization.Ca - mystery of the maya. Available at: http://www.historymuseum.ca/cmc/exhibitions/civil/maya/mmp05eng.shtml (Accessed: 19 January 2017).

1.4 Clay in Architecture Fig. 1 A map of climatic regions in which at least 60% of vernacular architectures contain clay. Climatic divisions from: R. de Dear, Developing an Adaptive Model of Thermal Comfort and Preference, ASHRAE RP-884, March 1997.

Fig. 11 Mashrabiyya: Traditional Arabic wood latticework. Limited, A. (2012) Stock photo - aged interleaved wooden window (Mashrabiya) and a built-in couch. Available at: http://www.alamy.com/stock-photo-agedinterleaved-wooden-window-mashrabiya-and-a-built-incouch-93653936.html (Accessed: 19 January 2017).

Fig. 2 Percentage of observed dwellings which contain

3.1 Construction Method

Fig. 4 Rover extrusion sequence. Fig.1 Integrated design logic diagram 3.4 Support-Material Deposition Strategy Fig. 2 Construction process Fig. 3 Diagrammatic section of the construction method Fig. 4 Support material distribution for the column

Fig.1 Angle of repose table for granular materials DEPTH OF FOOTINGS - FOUNDATIONS (2012) Available at: http://www.abuildersengineer.com/2012/11/ depth-of-footings-foundations.html (Accessed: 2 November 2016).

Fig. 5 Support material distribution for the dome Fig. 6 Deposition sequence for two columns 3.2 Multi-Robot System Design Fig. 1 Proposed heterogeneous multi-robot system which includes a paste deposition rover (top-left), a support material dispensing rover (top-right), a stationary unit for material preparation (bottom-left) and an UAV equipped with an infrared sensor (bottom-right). Fig. 2 Multiple rovers work together towards the same goal. Fig. 3 An example of on-board sensing in which a light sensor is used to identify the material over which the rover is situated. Fig. 4 Comparison between global and local awareness.

3.5 Robotic Prototyping - Primary Deposition & Support Material Deposition Fig. 1 First sample was printed to calibrate the speed of the deposition and to test that the mixture keeps the coil shape. Fig. 2 Process pseudocode Fig. 3 The column was generated as an initial geometry for testing. Fig.4 Pneumatic extruder was used as an end-effector during the deposition process. Fig. 6 After the curing process is complied, support material has to be removed. Fig. 7 The part of the column that was printed during the Test 1 after the drying process.

Fig. 5 Stigmergic communication in which the 3D scan of a support heap generated by the ’s infrared sensor is used to define the rover’s locomotion routines.

Fig. 8 Simulation of column tool path execution with the industrial robotic arm KUKA KR-30

Fig. 6 Discretization of a 3D space into a 2D grid with obstructions.

Fig. 9 Deposition process of the column. Active printing time was 18 min.

Fig. 7 Grid-based approach with differential grid resolution.

Fig. 10 Column deposition process.

Fig. The five elements of cloud robotics. Goldberg, K. (2014) Robots with their heads in the clouds – aspen ideas. Available at: https://medium. com/aspen-ideas/robots-with-their-heads-in-the-cloudse88ac44def8a#.57xo0e596 (Accessed: 6 December 2016). Fig. 9 Device-user integration through the implementation of cloud robotics. 3.3 Primary Deposition Strategy Fig. 1 Transition from a linear extruded element to a massive extrusion. Fig. 2 Wall thickness differentiation enabled by the deposition strategy. Fig. 3 Linear displacement mechanism which makes it possible to execute the deposition strategy with a rover.

Fig. 11 Front view of the column that was printed during the Test 2 after the support material was removed. Fig. 12 Simulation of dome tool path execution with the industrial robotic arm KUKA KR-30. Fig. 13 Deposition process of the dome. Active printing time was 24 min. Fig. 14 Dome deposition process. Fig. 15 Top view of the dome after the deposition process was complied. Fig. 16 Front view of the dome that was printed during the Test 2 after the support material was removed. 3.7 Secondary Deposition Strategy Fig. 1 Secondary deposition pattern Fig. 2 Infrared sensor Kinect V.2

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Fig. 4 Aggregation pattern of Gando village. Fig. 3 Scanning process and secondary deposition geometry generation Fig.4 Simulation of the secondary deposition tool path execution with the multi-robot collaboration. 3.8 Robotic Prototyping â&#x20AC;&#x201C; Secondary Deposition

Fig. 6 Plan View of the Cluster (Primary Deposition Unites)

Fig. 1 Deep deposition process of the 4 layer mesh pattern

Fig. 7 Plan View of the Cluster with Multi-Layer Envelope (Second Stage Deposition)

Fig. 2 Robotic Setup

Fig. 8 Axonometric View of the Cluster with Multi-Layer Envelope (Second Stage Deposition)

Fig. 3 Simulation of the secondary deposition tool path execution with the industrial robotic arm KUKA KR-30. Fig. 4 A. Depth from Microsoft Kinect; B. Three Photos using a Polarizer; C. Polarization Enhanced Depth 3.9 Devices - Conceptual Schema Fig. 1 Task Distribution Fig. 2 Construction process Fig. 3 Mavic Pro is one of the latest UAV models that are available on the market. Reserved, D.A.R. (2017) Buy Mavic pro | DJI store. Available at: http://store.dji.com/product/mavic-pro?gclid=CjwKEAiA8JbEBRCz2szzhqrx7H8SJAC6FjXXIXM4mBqX4Udrp6w4Unu5twLdMjl7TSf_KS3JN13V6hoCFvbw_wcB#/?_k=r0rvyz (Accessed: 23 January 2017). Fig. 4 DSolar robot is powered by solar panels and developed by LEGO Mindstorms NXT and Dexter Industries. DSolar â&#x20AC;&#x201C; tandem solar panels (2010) Available at: https://www.dexterindustries.com/dsolar-tandem-solar-panels/ (Accessed: 23 January 2017). 4.0 Design Development Fig.1 Gando is a village in Burkina Faso, in the Centre-Est Region, the Boulgou province and the Department of Tenkodogo. Population is about 2500 residents. File: Gando village.jpg - Wikimedia commons (2000) Available at: https://commons.wikimedia.org/wiki/ File:Gando_village.jpg (Accessed: 18 January 2017). Fig.2 Geographical location of the site. Fig. 3 Climate diagrams of average temperatures and precipitation at Centre-Est Region, Burkina Faso. Forecast (2006) Tenkodogo. Available at: https://www. meteoblue.com/en/weather/forecast/modelclimate/tenkodogo_burkina-faso_2354675 (Accessed: 18 January 2017).

166 References

Fig. 5 Nodal displacement analysis of the second stage deposition pattern is used to differentiate the mesh by increasing the pattern density in the areas of highest displacement.

Fig. 9 Axonometric View of the Cluster with Multi-Layer Envelope (Second Stage Deposition)

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6.2 Text References

0.0 Introduction [1] Khoshnevis, B., 2004. Automated construction by contour crafting—related robotics and information technologies. Automation in construction, 13(1), pp.5-19. [2] Zuo, J., Read, B., Pullen, S. and Shi, Q., 2012. Achieving carbon neutrality in commercial building developments–Perceptions of the construction industry. Habitat International, 36(2), pp.278-286. [3] Kreiger, M.A., MacAllister, B.A., Wilhoit, J.M. and Case, M.P., 2015. The current state of 3D printing for use in construction. In The Proceedings of the 2015 Conference on Autonomous and Robotic Construction of Infrastructure. Ames. Iowa (pp. 149-158). 1.1 Case Studies [1] Camilleri, F., Doukhi, N., Lopez Rodriguez, A. and Strukov, R. (2015) Amalgamma. Available at: https:// www.amalgamma.org (Accessed: 18 January 2017). [2] Doerstelmann, Moritz, et al. “ICD/ITKE Research Pavilion 2014–15: Fibre Placement on a Pneumatic Body Based on a Water Spider Web.” Architectural Design 85.5 (2015): 60-65.

[11] Khoshnevis, B., Hwang, D., Yao, K.T. and Yeh, Z., 2006. Mega-scale fabrication by contour crafting. International Journal of Industrial and Systems Engineering, 1(3), pp.301-320. [12] Kreiger, M.A., MacAllister, B.A., Wilhoit, J.M. and Case, M.P., 2015. The current state of 3D printing for use in construction. In The Proceedings of the 2015 Conference on Autonomous and Robotic Construction of Infrastructure. Ames. Iowa (pp. 149-158). [13] D-Shape. 2015. “The Technology.” Monolite UK. http://www.d-shape.com/tecnologia.htm. [14] World’s Advanced Saving Project. 2015. “About Us - WASProject.” WASP. http://www.wasproject.it/w/en/ wasp/. [15] Keating, S. and Oxman, N. 2012, ‘Immaterial Robotic Fabrication’. Proceedings of RobArch: Robotic Fabrication in Architecture, Art and Design. [16] Keating, S., Spielberg, N.A., Klein, J. and Oxman, N., 2014. Digital Construction Platform: A Compound Arm Approach.

[3] Jin, S., Maggs, S., Sadan, D. and Nan, C. (2015) Minibuilders. Available at: https://iaac.net/research-projects/large-scale-3d-printing/minibuilders/ (Accessed: 18 January 2017).

[17] “Small Robots Printing Big Structures.” 2015. Minibuilders. http://iaac.net/printingrobots/.

[4] Kayser, M., 2011. Solar Sinter Project. Markus Kayser.

[18] Buswell, Richard, and Simon Austin. 2015. “Freeform Construction: Partners.” Loughborough University. http://www.freeformconstruction.com/partners. php.

[5] Friedman, J., Kim, H. and Mesa, O., 2014. Experiments in Additive Clay Depositions. In Robotic Fabrication in Architecture, Art and Design 2014 (pp. 261-272). Springer International Publishing. [6] Petersen, K., Nagpal, R. and Werfel, J., 2011. Termes: An autonomous robotic system for three-dimensional collective construction. Proc. Robotics: Science & Systems VII. [7] Yablonina, M. (2015) ITECH M.Sc 2015: Mobile robotic fabrication system for filament str ct res. ailable at: http://icd.uni-stuttgart.de/?p=15699 (Accessed: 18 January 2017 [8] Khoshnevis, B. and Dutton, R., 1998. Innovative rapid prototyping process makes large sized, smooth surfaced complex shapes in a wide variety of materials. Materials Technology, 13(2), pp.53-56. [9] Khoshnevis, B., Kwon, H. and Bukkapatnam, S., 2004. Automated Construction using Contour Crafting. In IIE Annual Conference. Proceedings, Houston, TX, USA.

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95.’Human Robot Interaction and Cooperative Robots’, Proceedings. 1995 IEEE/RSJ International Conference on (Vol. 1, pp. 226-234). IEEE. [6] Werfel, J., Petersen, K. and Nagpal, R., 2014. Designing collective behavior in a termite-inspired robot construction team. Science, 343(6172), pp.754-758. [7] Bonabeau, E., Dorigo, M., Theraulaz, G., 1999, arm ntelligence From at ral to rtificial ystems [8] Holland, O. and Melhuish, C., 1999. Stigmergy, self-organization, and sorting in collective robotics. rtificial life .1 . 1.3 Granular Materials 1 om ressi e strength of extr ded nfired clay masonry units, A. Heath MS, PhD, P. Walker BSc, PhD, MIEAust, CPEng, C. Fourie MSc and M. Lawrence MA, MSc, PhD, 2009

cost paths. IEEE transactions on Systems Science and Cybernetics, 4(2), pp.100-107. [2] Bensoussan, A. and Bensoussan, J. (eds.) (2016) Comparative handbook: Robotic technologies law. Belgium: Larcier. [3] Goldberg, K. (2014) Robots with their heads in the clouds – aspen ideas. Available at: https://medium. com/aspen-ideas/robots-with-their-heads-in-the-cloudse88ac44def8a#.57xo0e596 (Accessed: 6 December 2016). 3.3 Primary Deposition Strategy [1] El Fgaier, F., Lafhaj, Z., Brachelet, F., Antczak, E. and Chapiseau, C., 2015. Thermal performance of nfired clay bric s sed in constr ction in the north of France: Case study. Case Studies in Construction Materials, 3, pp.102-111. 3.8 Robotic Prototyping – Deep Deposition

[2] Oxford (2016) ‘Sinter’, in Oxford Dictionary. Available at htt s en.oxforddictionaries.com definition sinter (Accessed: 10 October 2016). [3] Effect of the Change of Firing Temperature on Microstructure and Physical Properties of Clay Bricks from Beruas (Malaysia) I. Johari1 , S. Said1 , B. Hisham1 , A. Bakar1 , Z. A. Ahmad2* 1 School of Civil Engineering, University Sains Malaysia, Penang, Malaysia 2 School of Material and Mineral Resources Engineering, University Sains Malaysia, Malaysi [4] Direct observations of liquid binder–particle interactions: the role of wetting behavior in agglomerate growth, S.J.R Simons, R.J Fairbrother, Powder technologies, Pages 44–58, 2000 1.4 Clay in Architecture [1] Houben, H. and Guillaud, H., 1994. Earth construction: a comprehensive guide. Intermediate Technology Publications. [2] El Fgaier, F., Lafhaj, Z., Brachelet, F., Antczak, E. and Chapiseau, C., 2015. Thermal performance of nfired clay bric s sed in constr ction in the north of France: Case study. Case Studies in Construction Materials, 3, pp.102-111.

[1] Kadambi, A., Taamazyan, V., Shi, B. and Raskar, R., 2015. Polarized 3D: High-quality depth sensing with polarization cues. In Proceedings of the IEEE International Conference on Computer Vision (pp. 3370-3378). [2] C. Wu, M. Zollhofer, M. Nießner, M. Stamminger, S. Izadi, and ¨ C. Theobalt. Real-time shading-based refinement for cons mer de th [3] D. Nehab, S. Rusinkiewicz, J. Davis, and R. Ramamoorthi. ffi- ciently combining ositions and normals for precise 3d geometry. SIGGRAPH, 2005. 3.9 Devices [1]. Schwartz, T., Andraos, S., Nelson, J., Knapp, C. and Arnold, B., 2016. Towards On-site Collaborative Robotics. In Robotic Fabrication in Architecture, Art and Design 2016 (pp. 388-397). Springer International Publishing. [2]. Dyson, James. “Vacuum cleaning appliances.” U.S. Patent 4,373,228, issued February 15, 1983. [3]. Kohlgrüber, K., Bierdel, M. and Kohlgruber, K. (2007) Co-rotating twin-screw extruders: Fundamentals, technology, and applications. Bethesda, MD, United States: Hanser Gardner Publications, United States.

3.1 Construction Method 1 xman . ro oyo . eating . Peters B. and Tsai, E., 2014. Towards robotic swarm printing. Architectural Design, 84(3), pp.108-115. 3.2 Multi-Robot System Design [1] Hart, P.E., Nilsson, N.J. and Raphael, B., 1968. A formal basis for the heuristic determination of minimum

[4]. Sanguino, T.D.J.M. and 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. [5]. Reddy, M.H. and Kumar, G.P., 2014. Intelligent Battery Management System for Semi Autonomous Solared Power Vehicle.

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[6]. Pontious, K., Weidner, B., Guerin, N., Dates, A., Pierrakos, O. and Altaii, K., 2016, April. Design of an atmospheric water generator: Harvesting water out of thin air. In 2016 IEEE Systems and Information Engineering Design Symposium (SIEDS) (pp. 6-11). IEEE. ) . hris oodford 16 o do deh midifiers work? Available at: http://www.explainthatstuff.com/deh midifier.html ccessed 1 e tember 16 . [8]. Engel, D.R. and Clasby Jr, M.E., Engel Daniel R and Clasby Jr Matthew E, 1993. Apparatus and method for extracting potable water from atmosphere. U.S. Patent 5,259,203.

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