Design and development of 2 r 2 dof force controlled robot

DESIGN AND DEVELOPMENT OF 2-R 2-DOF FORCE CONTROLLED ROBOT Kemparaju C R 1, Chetan Kumar D S2,Ronald Reagon R3 1,2,3

Assistant Professor, Department of Mechanical Engineering, New Horizon College of Engineering, Outer Ring Road, Bengaluru-560103.

Abstract: Social changes have directly affected the demand for quality products and services which is evident from greater demand for manufactured products of superior quality at a more economical price. To meet this demand of customers, sophisticated controls and equipments have been developed in all sectors adopting newer technology in association with integrating different technologies. In line with integration a revolutionary change has taken place in the field of robotics whereon robots are developed to attain higher accuracy in speed position and force control. Thus force controlled robotic arm is used to guide an operator to move in designated path accurately without actually deviating from the path. It can be used in various production areas like welding, gluing, Sequential tightening of bolts etc. The major use of these kinds of robotic arms is that we can achieve the same degree of accuracy, precision and quality produced by a skilled worker from an unskilled worker. Thus reducing unemployment in developing countries which have huge unemployment rates that too in a very less cost.

Keywords: Robot, Degrees of Freedom, Accuracy, Precision I. INTRODUCTION Robotics is a branch of technology that deals with design, construction, operation and application of robots, as well as computer systems for their control, sensory feedback, and information processing.

These technologies deal with automated machines that can take the place of humans in dangerous environments or manufacturing processes, or resemble humans in appearance, behavior, and or cognition. Many of today’s robots are inspired by nature contributing to the field of bio-inspired robotics.

The concept of creating machines that can operate autonomously dates back to classical times, but research into the functionality and potential uses of robots did not grow substantially until the 20 th century. Throughout history, robotics has been often seen to mimic human behavior, and often manage tasks in a similar fashion, Today, robotics is a rapidly growing field, as technological advances continue; research, design and building. New robot serves various practical purposes, whether domestically, commercially or militarily. Many robots do jobs that are hazardous people such as diffusing bombs, mines and exploring ship wrecks.

II. LITRETURE REVIEW Jinno M and Takahashina M implemented the theoretical concept of force control to that of production areas like Grinding, Chamfering and Polishing in the year 1995. To facilitate easier operations they developed task oriented robot language and force control for following edges of work pieces. They also developed tool moment control method, a skip function and round function to cope up with work piece difference James E Bobrow and Brian W McDonell suggested that Pneumatic actuators used in force control robot is as good as that of electric actuators, in the year 1998. The control approach which they used was the triangular form of coupled rigid body and air flow dynamics to establish path tracking. In

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addition they developed a hybrid position /force controlled algorithm. They also suggested that the tip force on robot can be controlled without need of expensive force and torque sensors.

Rajesh Kumar, Puneet Gupta and Peter Berkelman in the year 2000 reviewed the use of force control robot in assistive Micro surgical operation wherein fine manipulation tasks requiring human judgment, sensory integration and hand eye coordination was the need of hour. They also reviewed the stable force control law.

III. ROBOT CONFIGURATION Robots can take many physical forms and there is no absolute “best” configuration, the best will depend on the particular application as different configurations have different advantages which make them more suitable for certain tasks. Physical and geometric configurations are not only consideration n choice of robot for task, others include  Reach  Working Volume or Envelope  Payload capacity  Accuracy  Repeatability  Maneuverability  Speed of Operation  Form of motion  Sensing devices These entire factors combine together to formulate the final design of the robot called its configuration. The configuration determines to a large extent the tasks to which the robot is best suited.

There are seven basic industrial robot design configuration  Cartesian or Rectangular  Cylindrical  Revolute or articulated  Polar or spherical Cartesian or Rectangular Configuration The Cartesian Configuration provides for three linear axis of movement at the right angles to each other. The modes of movement are similar to those on a milling machine, providing movement in X, Y and Z axis. It can also be called Rectangular configuration as it is the working range sweeps a rectangular volume.

O

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Advantages  Easily programmed and controlled movements  Good accuracy  Simple control system  Fast operation  Inherent stiff structure  Large payload capacity  Structural simplicity, giving good reliability Applications Areas where linear movements of high accuracy are needed Ex; Manipulation of components through apertures i.e furnace doors and machine openings The Cylindrical Configuration combines both vertical and horizontal linear movements, with rotary movement in the horizontal plane about the vertical axis.

T

Advantages  Easily programmed and controlled movements.  Good accuracy.  Simple control system.  Fast operation.  Good access to front and sides.  Structural simplicity, giving good reliability.

Applications Applications include small circular manufacturing cells or loading and unloading operations servicing conveyor type systems.

Revolute or Articulated Configuration The Revolute configuration comprises a number of rigid arms connected by rotary joints, rotary moment at the base is also provided. Since all movements are by angular rotation of the joints complex calculations are often needed to move the arm in straight lines.

R

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Advantages  Extremely good maneuverability  Ability to reach over obstructions  Easy front , side , rear and overhead access  Large reach for small floor area  Fast movements due to rotary joints Applications Spot and Arc welding, adhesive placing Polar or Spherical Configuration This combine’s rotational movement in both the horizontal and vertical planes with a linear in or out movement of the arm. It is sometimes referred to as Gun Turret configuration.

Advantages  Easily controlled and programmed movements  Fast operation  Large payload capacity  Accuracy and Repeatability at long reaches Applications Suited to lifting and shifting operations and to reach horizontal and inclined tunnels IV. ROBOT MOTIONS The robots movement can be divided into two general categories: arm and body motions, and wrist motions. The individual joint motions associated with these two categories are sometimes referred to by the term ―degrees of freedom, and a typical industrial robot is equipped with 4 to 6 degrees of freedom. The robot motions are accomplished by means of powered joints. Connecting the various manipulator joints together are rigid members that are called links. The joints used in the design of industrial robots typically involve a relative motion of the adjoining links that is either linear or rotational. Linear joints involve a sliding or translational motion of the connecting links. This motion can be achieved in a number of ways (e.g., by a piston, a telescoping mechanism, and relative motion along a linear track or rail).

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There are at least three types of rotating joint that can be distinguished in robot manipulators. The three types are shown in figure.  Vertical traverse: This is the capability to move the wrist up or down to provide the desired vertical attitude.  Radial traverse: This involves the extension or retraction (in or out movement) of the arm from the vertical center of the robot.  Rotational traverse: This is the rotation of the arm about the vertical axis.

V. KINEMATICS OF ROBOTIC ARM Robot arm kinematics deals with analytical study of the geometry of the motion of a robot arm with respect to a fixed reference coordinate system as a function of time without regard to the forces or moments that cause the motion.

Thus, it deals with the analytical description of the spatial displacement of the robot as a function of time, in particular the relation between the joint variable space and the position and orientation of the end effectors of a robot arm.

Vector and matrix algebra are utilized to develop a systematic and generalized approach to describe and represent the location of the links of a robot arm with respect to a fixed reference frame. Since the link of a robot arm may rotate and/or translate with respect to a reference co-ordinate frame a body attached co-ordinate frame will be established along the joint axis for each link FORWARD OR DIRECT KINEMATICS For the forward or direct kinematics the inputs are the joint angles vectors and the link parameters.

The output of the problem is the orientation and the position of the tool or the end effectors.

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Y

L1 & L2 =link lengths in mm θ1 & θ2 =Angles made by the links in degree X & đ?‘Œ= position of the end effectors From the figure, by trigonometry X = L1 cosθ1 + L2 cos(θ1 + θ2 ) Y = L1 sinθ1 + L2 sin(θ1 + θ2 ) Writing in the matrix from, cosθ1 cos(θ1 + θ2 ) L1 X [ ]=[ ][ ] sinθ1 sin(θ1 + θ2 ) L2 Y The output of the matrix are X & đ?‘Œ which are the position of the end effector.By giving the values of the joint angles and length of the link, we can calculate the position of the end effectors.

INVERSE KINEMATICS In certain situation it is possible to know the position and orientation of the objects placed in the workplace or envelope and it is desired to know the joint vectors given the link parameters of the robots. In such situation the inverse kinematics in used.

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In many cases it is more important to be able to derive the joint angles given the end-of-arm position in world space. The typical situation to move its end of arm to a point in space defined by the point’s co-ordinates .for the two link manipulator we have developed, there are two possible configuration for reaching the point (X,Y)as show in fig‌there are several strategy available to select the appropriate configuration, one of the approach is that employed in the control system Unimate PUMA robot. In the PUMA’s control language VAL, there is a set of commands called ABOVE and BELOW that determines whether the elbow is to make an angle đ?œƒ2 that is greater than or less than zero.

Y

X L1 & L2 =Link lengths in mm. θ1 & θ2 =Angles made by the links in degree.

X & đ?‘Œ= Position of the end effectors.

R = Resultant in mm. Îą =Angle made by the resultant. Îą = tan−1

Y X

R=√X 2 + Y 2

up

Temp

cos(Îą − θ1 ) = (L21 + R2 − L22 )/2L1 R Temp θ1 = cos −1 [(L21 + R2 − L22 )/2L1 R]

θ1 =Îą + θ1 Temp θ1down =Îą − θ1 up up up θ2 =cos −1 [(X − L1 ∗ cos θ1 )/ L2 ] − θ1 θdown =cos −1 [(X − L1 ∗ cos θ1down )/ L2 ] − θ1down 2 Where, up up θ1 & θ2 = Elbow ABOVE configuration θ1down & θdown =Elbow BELOW configuration 2 Where the elbow ABOVE and BELOW configuration gives the two pairs of angles, In order to reach the given end effector’s position, two angles are to be chosen i.e., one from the ABOVE configuration and one from the BELOW configuration.

Knowing the link lengths and arm position (X, Y) in work space, we can easily calculate the joint angles.

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VI. DESIGN The complete design of our robotic arm is done using SOLIDWORKS 2015 modeling software.

DESIGN ITERATION 1 This was basically a conceptual design wherein we tried to design the robotic arm similar to that of SCARA configuration as shown in the figure, we modeled the parts and assembled because we felt that it would be comfortable for the operator to work on.

Inference: After the concept design of the SCARA type configuration robot we actually saw that the drive train was getting longer than actual link itself, hence it became clear that this design though being good had to tweaked a little in order to make it aesthetically good.

DESIGN ITERATION 2 It was also a conceptual design but with a slight improvement that is instead of placing the drive train over the link vertically we mounted the drive train onto the links horizontally inside the link itself.

VII. CONCLUSIONS In modern era, where both quality and time plays a highly important role. This importance led to development of robots, although the advent of robots increased precision, accuracy, quality and decreased the lead time by a large extent, it eliminated the human labor from shop floor thus causing unemployment in both developed as well as developing countries.

This major drawback can be negated by using force controlled robotic arm which guides an operator to move in designated path accurately without actually allowing him to deviate from the path. It can be used in various production areas like welding, gluing, Sequential tightening of bolts etc. The major use of these kinds of robotic arms is that we can achieve the same degree of accuracy, precision and quality produced by a skilled worker from an unskilled worker. Thus reducing unemployment in developing countries which have huge unemployment rates that too in 1/10 th of cost of actual automation.

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