Robotics Final Assignment

Robotics & Automation

Assignment : Analysis and design of a robot system

Vazguene AKOPIAN 10006669

Module Number : CE00453-7

Contents

Introduction...............................................................................................................................3

Section 1

1.1 Study of the Puma 560 robot kinematics...........................................................3

1.2 Creation of a three link robot.............................................................................5

Section 2

2.1 The Task..............................................................................................................9

2.2 The Workspace.................................................................................................10

2.3 The Robot.........................................................................................................11

2.4 The Sensors.......................................................................................................12

2.5 The Gripper.......................................................................................................14

2.6 The Safety.........................................................................................................16

2.7 Approximate cost and payback........................................................................17

Conclusion...............................................................................................................................17

List of figuresFigure 1 : Joint angles positions

Figure 2 : Velocity of each joint

Figure 3 : Robot specifications

Figure 4 : DH Matrix

Figure 5 : Three link created robot

Figure 6 : Results of the forward kinematics on MATLAB

Figure 7 : Rotation component into RPY

Figure 8 : Schematic of the robot-cashier system

Figure 9 : STÄUBLI TX60

Figure 10 : CamCube 3.0 by PMD

Figure 11 : Torquemeter SCAIME DR1

Figure 12 : Gripper METAL WORKS Series P9-32

Figure 13 : Design of the pinch of the gripper

Vazguene AKOPIAN10006669 2 Module : CE00453-7

Introduction

In this report we will treat some aspects of the manipulation and the creation of robots. The

first section will explain the simulation of a robot with MATLAB and the robotic toolbox, the

study of its kinematics and the design of a three link robot with DH matrices. In the second

part we will see the design and requirements of a robot-cashier system.

Section 1

1. 1 Study of the Puma 560 robot kinematics

First of all is the creation of the point B which will be the final position of the robot. Its

coordinates are x = 0.211, y = 0.851, z = 0.010. Now that we have this point we can use the

'ikine' function (inverse kinematics) to obtain the joint angles in the final position :

clear all;puma560;%drivebot(p560) P=transl(0.211,0.851,0.010);% movement of the arm to coordinatesPointB=ikine(p560,P)% inverse kinematics to get the joint angles

The joint angles obtained are : 16.8637 28.2835 -14.1317 -75.3982 -14.1518 71.1009.

To get position and velocity graphs we calculate the trajectory of the robot with the function

'jtraj' which needs the initial and final coordinates, the total time and the sampling rate.


This is the code to obtain position and velocity graphs :

P=transl(0.211,0.851,0.010);% movement of the arm to coordinatesPointB=ikine(p560,P)% inverse kinematics to get the joint angles %%t=[0:0.125:7]' % total time and sampling rate (in sec)start=[0 0 0 0 0 0];% initial position : all joint angle at 0stop=PointB;% final position [p v]=jtraj(start,stop,t);%calculation of the trajectory to the point Bsubplot(6,1,1);plot(t,p(:,1))% position graphs subplot(6,1,2);plot(t,p(:,2))subplot(6,1,3);plot(t,p(:,3))subplot(6,1,4);plot(t,p(:,4))subplot(6,1,5);plot(t,p(:,5))subplot(6,1,6);plot(t,p(:,6))figure; subplot(6,1,1);plot(t,v(:,1))% velocity graphs subplot(6,1,2);plot(t,v(:,2))subplot(6,1,3);plot(t,v(:,3))subplot(6,1,4);plot(t,v(:,4))subplot(6,1,5);plot(t,v(:,5))subplot(6,1,6);plot(t,v(:,6))

From this code we get two figures, the position graph :

Figure 1 : Joint angles positions


And the velocity graph as well :

Figure 2 : Velocity of each joint

1.2 Creation of a three link robot

First steps of the creation of a robot is to define its dimensions and rotation axes :

Figure 3 : Robot specifications

a = 300mm

b = 200mm

c = 80mm

1,2,3 : the rotation axis of the joints is z


The DH matrix permits to describe the mobility of the robot, its "freedom". It is composed of

four parameters (a, α, θ, d) that we have chosen before :

α a θ d

0 300 θ1 0

0 200 θ2 0

0 80 θ3 0

Figure 4 : DH Matrix

The following program permits to give to our robot the decided dimensions in this DH

matrix. The command 'link' permits to write each line separately, then they are put together

in the matrix 'R' which is used to simulate the robot.

clear all; l1=link([0 300 0 0]); l2=link([0 200 0 0]);l3=link([0 80 0 0]);R{1}=l1;R{2}=l2;R{3}=l3;S=robot(R)drivebot(S)

Figure 5 : Three link created robot


Now that we have set up the dimensions, we must choose the angles to use in the forward

kinematics. We get :

θ1 = 90° = 1.570 rad

θ2 = 60° = 1.047 rad

θ3 = 90° = 1.570 rad

The following code allows to give to our robot the angles of its joints and to perform the

forward kinematics with 'fkine'.

angle=[1.570 1.047 1.570]T=fkine(S,angle)

The result of this command shows the coordinates of the final point :

Figure 6 : Results of the forward kinematics on MATLAB

By using 'tr2rpy' we can get the values of the roll, the pitch and the yaw the end point. The

results are shown below :

roll = 0

pitch = 0

yaw = -2.0962


To verify these results we do some manual calculation using the rotation and translation

matrices applied to this case. For this robot we only need the rotation about Z and

translation along X matrices to calculate the forward kinematics. We replace with our values

of angles and lengths and after the multiplication of the three rotations by the three

translations we obtain these results :

-0.5 0.86 0 -213.2

-0.86 -0.5 0 331.2

0 0 1 0

0 0 0 1

The slight differences between the results are due to approximations done in previous steps

of the calculation.

To calculate the roll, pitch and yaw we will use the formulas below :

Figure 7 : Rotation component into RPY

As our r31, r32 and r33 equal to 0, X and Y equal to 0 and we find Z = -2.0974. The difference

of 0.0012 is due to previous approximation.

The manual calculation and MATLAB give almost the same results.


Section 2

2.1 The Task

The goal of the robot from this case study is to replace a human cashier in the supermarkets.

The customer arrives and lays his items on the first conveyer (the slow one). The items go

then to a faster conveyer which will split the items from each other. Inside the Plexiglas

shield (level 0), the 3D camera placed on the top of the system (level 2) will see the items

arriving in the workspace. The conveyer will stop when an item arrives at the laser sensors

and, guided by the camera, the robot arm will take the closest item on the conveyer.

The robot will bring the item above the barcode readers and turn the item until it receives

the signal that the item has been scanned.

Once the price recorded, the arm will put the item in the hole on the last conveyer (level -1),

which will bring it to the customer, on the weighing machine. The arm will repeat the

operation while items are coming on the conveyors.

The customer will have plastic bags available on one side of the system. He will have 2

seconds to take an item and put it back on the weighing machine, inside the bag. If this

operation takes too long, the customer will hear the message to put the item back on the

weighing machine, the robot will stop and a red light high placed on the system will switch

on, attracting the attention of security guards.

Once the client has paid his items he can leave and the next customer can put his own items

on the first conveyer.


2.2 The Workspace

Figure 8 : Schematic of the robot-cashier system

The robot has to work in the same workspace as the human operator did before, so more

than the Plexiglas box, one bumper pole one each side of the arm will stop it if , in case of a

problem, the arm decides to go behind its workstation. Besides, these bumpers are an

additional security for the worker, in case he has to penetrate inside the Plexiglas fence

through the gate.

Also there is the possibility to put another cashier robot in the other side, next to this one to

optimise place.


2.3 The Robot

The arm that seemed the most adapted to this situation is the industrial robot arm STÄUBLI

TX60.

Figure 9 : STÄUBLI TX60

This arm has six degrees of freedom which assures an excellent mobility. The robot is quiet

compact so a small work-envelope fits. Also, it is waterproof and it benefits a total dust

protection.

The payload of this arm is 3.5 kg with a maximum of 9 kg. To this we must add the weight of

the gripper and the pinch, so approximately 1.5 kg which gives us 2 kg to 7.5 kg for the

payload of the robot, which is enough for supermarket items.

The reach at wrist of this arm is 670 mm, but once the gripper and the pinch (gripper's

fingers) added the reach becomes 940 mm.


2.4 The Sensors

The most important detector of this system is the Time Of Flight (TOF) 3D Camera.

Figure 10 : CamCube 3.0 by PMD

This camera will see and analyse the size of each item. It is wide-angle so it sees everything

from the arrival of the items on the conveyor to the arm robot placing the item after

scanning on the last conveyor. This camera gives directions to the robot arm in all its

movements.

On each side of the camera there is a matrix of infrared light which spreads in the area and

the camera gets the light when it returns and calculates the distance from the time that the

light needed to come back.


The second sensor to be used in this case is the torque meter.

Figure 11 : Torquemeter SCAIME DR1

The torque meter will detect if something opposes resistance on the arm's motor in two

cases :

when the gripper grabs an item from the conveyer it must not be cashed by the

robot, so the torque meter will detect this and stop the motor

if something goes wrong and the arm touches one of the bumper poles, to avoid any

mechanical damage the sensor will also stop the motor.

Also, there is the possibility to add a slip detector to improve the robot's abilities if

necessary.


2.5 The Gripper

For this kind of task the robot-cashier has to grab every kind of objects, of every size, every

shape so choosing an angular gripper was the only thing left.

Figure 12 : Gripper METAL WORKS Series P9-32

The METAL WORKS Series P9-32 has a jaw opening angle adjustable up to 180°, so it can

grab objects of any size. The clamping force at 20 mm from the jaw pivot is 180 N so it can

lift even big bottles or beer packs.


Then we had to find a pinch that could be versatile enough to fit to all items of a

supermarket. Is this system does not exist yet we had design the fingers of the grip.

Figure 13 : Design of the pinch of the gripper

This kind of design can grab big items like a bottle, a box of cereal with the wide inside part,

and small items with the hole in the middle of the end of the fingers for cylindrical items, or

between the end of fingers for any other shape. To benefit lightness and strength the pinch

will made in aluminium.


2.6 The Safety

In a supermarket the customer stays very close to the cashier so we had to secure the

workplace of the robot without loss of place and with 100% safety guarantee for the

customer. The whole workplace of the robot is secured with a Plexiglas fence accessible only

through a service door. If an employee has to enter into the security fence, the fact of

opening the door will automatically stop the robot. Moreover to guarantee the safety of the

employee one bumper pole is fixed in the ground to create a guardrail in case of

uncontrolled movements of the arm.

Two emergency buttons have been installed : one at the end of the first conveyer and

another one next to the weighing machine at the end of the process.

The 3D camera's angle is wide enough to see the whole process, so it will be able to detect if

a human hand comes inside the workplace of the robot and shut down the arm before it

hurts anyone.

The entire part of the supermarket will be monitored by a team of human operatives who

will ensure that everything is working safely and intervene if anything goes wrong.


2.7 Approximate cost and payback period

The calculation of the cost or the payback of this system includes every part's price :

the arm

the gripper and the pinch

the 3D camera and the torque meter

the Plexiglas fence

the secured door of the fence

the three conveyers

the emergency buttons

the bumper poles

the weighing machine

the installation costs

The price of all these parts must be compared to the cost per year of a cashier : his salary,

the cost of an employee to the company, any other spending that the company has to do

related to the employee.

To get the payback period we have to divide the total price of the robot system by the total

cost of a cashier employee per year.

The approximate cost is the sum of the elements listed above.

Conclusion

Through this assignment we saw how to manipulate and understand a robot on MATLAB

with the Robotic Toolbox, the possibilities of this software. We also learned a lot about how

to design an entire robot system and how to apply it in the real world, the aspects of the

conception that have to be treated and all the questions that have to be answered.


Robotics Final Assignment

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