II1'I3RID POSITION/FORCE CONTROL

WONG KLAN ANN

Universiti Malaysia Sarawak 1999TJ

211 W872

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BORANG PENYERAHAN TESIS

Judul: Hybrid Position/Force Control

SI? SI PI; NGA. IIAN: 1996/97

Saya Wong Kian Ann(HURUF BESAR)

mengaku membenarkan tesis ini disimpan di Pusat Khidmat Maklumat Akademik, Universiti Malaysia Sarawak dengan syarat-syaral kegunaan seperti herikut:

I .

Hakmilik kertas projek adalah di hawah nama penulis melainkan penulisan sehagai projck hersama dan dihiayai oleh UNIMAS, hakmiliknya adalah kepunyaan UNIMAS.

2. Naskhah salinan di dalam hentuk kertas atau mikro hanya holch dihuat dengan kehenaran hertulis daripada penulis.

3. Pusat Khidmat Maklumat Akademik. UNIMAS dihenarkan membuat salinan untuk pengajian mereka. 4. Kertas projek hanya holeh diterhitkan dengan kehenaran penulis. Bayaran royalti adalah mengikut kadar

yang dipersetujui kelak. 5. * Saya memhenarkan/tidak memhenarkan Perpustakaan membuat salinan kertas prgjek ini sebagai bahan

pertukaran di antara institusi pengajian tinggi. 6. ** Sila tandakan ( J )

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Alanwl Irlap:

SULIT

TERHAD

TIDAK TERHAD

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(TAN I) NG E: NULIS) (TANDATANGAN PENYELIA)

6, Jalan Pangsan 3,

Seksen 27/12 C,

Shah Alam, Selangor.Nama Pcayclia

Tarikh: 21 -11 -1998 Tarikh: 21-11-1998

CATATANkY

Potonk yang lidak bcrkcnaan.

. lika Kcrtus I'rojck ini SULIT atau TF. KHAU, sila lampirkan surat daripada pihak bcrkuasa/ orl; unisasi Ixrkcnaan dcnl; an mcnycrtakan sckali tempoh kcrtas projck. Ini pcrlu dikelaskan schauai Slll. l'1' atuu "I'IiKHAU.

(Mengandungi maklumat yang herdarjah keselamatan atau kepentingan Malaysia seperti yang termaktuh di dalam AKTA RAHSIA RASMI 1972).

(Mengandungi maklumat TERHAD yang telah ditentukan oleh organisasi/ hadan di mana penyclidikan dijalankan).

Mr. Andrew Ragai Henry Rigit

Approval Sheet

This project report attached hereto, entitle "Hybrid Position/Force Control" prepared

and submitted by WONG KIAN ANN in partial fulfilment of the requirements for

the degree of Bachelor of Engineering with honours in Mechanical Engineering and

Manufacturing Systems is hereby accepted.

Date:(Dr. Ha How Ung Head ProgrammeMechanical Engineering & Manufacturing Systems Faculty cif' Engineering Universiti Malaysia Sarawak

Pusat Khidmat Maklumat Akadlrrik UN[VERSITI MALAYSIA SARAit-, -XK

P. KHIDMAT MAKLUMAT UNIMAS

�III"0000078250

HYBRID POSITION/FORCE CONTROL

WONG KIAN ANN

Tesis Dikemukakan Kepada Fakulti Kejuruteraan, Universiti Malaysia Sarawak

Sebagai Memenuhi Sebahagian daripada Syarat penganugerahan Sarjana Muda Kejuruteraan

Dengan Kepujian (Kejuruteraan Mekanikal dan Sistem Pembuatan) Januari 1999

(

Dedicate to my beloved family.

My life will not be completed without them.

II

Acknowledgement

This project will not be successfully completed without the help from all parties.

The author would like to thank those parties that made a difference: Dr. Ha How

Ung, Head Programme of Mechanical Engineering and Manufacturing Systems, who

offered constant encouragement; Mr. Andrew R. H. Rigit, project supervisor, his

suggestions and criticisms of this project had a significant influence in the way the

material is presented in this report; Pass Group members, who contributed funds at a

critical juncture. Besides, the author would like to thank a very special friend,

Belinda Lip for her helpful comments and suggestions especially in the grammar

mistakes. Finally, the author would also like to thank his family especially K. B.

Wong, eldest brother, for his support and love. K. B. Wong died before this report

was completed. He will be missed by the author and those who were fortunate to

know him.

Abstract

This project report presents a hybrid control scheme controlling the joint position and

Cartesian contact force of a robot manipulator with inner computed-torque

feedforward loop. The control scheme consists of two controllers: the proportional

plus derivative position controller and the proportional plus velocity force controller.

The controllers are designed based on the model reference control and orthogonal

force/position constraints under the assumption of constant desired forces and slowly

time-varying motion. Simulations studies performed on a 6 degree of freedom

PUMA 560 robot model are presented.

IV

Abstrak

Laporan project ini mempersemhahkan sejenis teknik kawalan gabungan yang

hertujuan mengawal gerakan tangan robot. Sistem kawalan ini terdiri daripada sistem

kawalan kedudukan rujukan sendi dan sistem kawalan daya sentuhan rujukan

Kartesian dengan hantuan loop suap-depan dalaman tork-berkomputcran. Sistem

kawalan ini mempunyai dua sub-sistem iaiatu: pengawal kedudukan jenis berkadaran

campur pemhezean; dan pengawal daya jenis berkadaran campur halaju. Kedua-dua

sub-sistem ini direkacipta berdasarkan konsep kawalan rujukan permodelan dan sifat

ketentangan daya dan kedudukan herorthogonal dengan angapan bahawa daya ialah

tetap dan gerakan adalah perlahan herhanding dengan masa. Simulasi komputer

dijalankan dengan hantuan model robot jenis PUMA 560 yang mempunyai enam

darjah gerakan bebas.

V

Puy at Khidmat t'N Makfumat Akademik iVERSITI MA[. AYSIA SARAWAK

Table of Contents

Dedication

Acknowledgement

Abstract

Abstrak

Table of Contents

List of Table

List of Algorithm

List of Figure

Chapter 1 Introduction

1.1 Robotics Technology

1.2 Today's Robot Application in Manufacturing

. 1.2. I Material Handling

1.2.2 Welding

1.2.3 Spray Painting/Coating

1.2.4 Packaging and Palletising

1.2.5 Water Jet Cutting

1.3 Future Robot Applications

1.4 Stiffness and Compliance

1.5 Project Objectives

Chapter 2 Theoretical Modelling

2.1 Object Location 2.1.1 Cartesian Co-ordinates

11. 2 Three Dimensional Translation and Orientation

Page

ii

III

iv

V

vi

IX

IX

X

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3

4

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13

13

14

16

17

17

18

18

vi

2.2 Manipulator Kinematics 21

2.2. 1 Link Description 22

2.2.2 Forward Kinematics Equation 25

2.2.3 Manipulator Jacobian 27

2.3 Manipulator Rigid-Body Dynamics 29

2.3. 1 Joint Velocities of a Robot Manipulator 31

2.3.2 Kinetic Energy of a Robot Manipulator 35

2.3.3 Potential Energy of a Robot Manipulator 37

2.3.4 Motion Equation of a Manipulator 37

2.3.5 Cartesian Space Dynamic Formulation 39

2.4 PUMA 560 Model 41

2.4.1 Kinematics Model 41

2.4.2 Dynamics Model 47

Chapter 3 Force Control 3.1 Robot Control Technology

3.2 Force and Torque Sensing

3.2. 1 Elements of a Wrist Force Sensor

3.3 Natural and Artificial Constraints

3.4 Hybrid Position/Force Control

3.4. 1 Position Control Along a Single Degree-of-freedom

3.4.2 Force Control Along a Single Degree-of-freedom

3.4.3 Hybrid Position/Force Control Scheme

Chapter 4 Results and Discussions

4.1 Methodologies

4.2 Control Gains Tuning

4.2. 1 Position Gains Tuning

4.2.2 Force Gains Tuning

49

49

53

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54

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61

65

70

70

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73

77

vii

4.3 Results 77

4.3. 1 Result 1: Tracking a Trajectory in Free Space 78

4.3.2 Result 2: Exerting a Force While in Contact with the

Environment 84

Chapter 5 Conclusions and Recommendations

Appendix A PUMA 560 Robot Parameters

Appendix B Result 1 Setting File

Appendix C Simulation File

Appendix D Result 2 Setting File

References

88

89

90

91

93

94

viii

List of Table

Page

Table 1.1 Tasks that the robots can do today and may be able to do in the

future. 15

Table 3.1 ABB robots performance. (Source: ABB Flexible Automation) 51

Table 4.1 The values of Kp, and Kpd for each joint position controller. 76

Table 4.2 The results of the transient analysis. 80

List of Algorithm

Algorithm 2.1 The link co-ordinate system assignment [111. 26

IX

List of Figure

Page

Figure 1.1 ABB robot in material handling task. (Source: ABB Flexible

Automation) 4

Figure 1.2 Spot welding. (Source: ABB Flexible Automation) 6

Figure 1.3 Master-slave arc welding. (Source: ABB Flexible

Automation) 8

Figure 1.4 TR 5002. (Source: Aßß Flexible Automation) 9

Figure 1.5 Large working envelope. (Source: ABB Flexible

Automation) I 1

Figure 1.6 IRB 4400L10. (Source: ABB Flexible Automation) 12

Figure 2.1 Co-ordinate frame showing position directions of axes 19

according to the right-hand rule.

Figure 2.2 D-H notation of link co-ordinate system and its parameters. (Source: Robotics Toolbox Manual) 24

Figure 2.3 A point 'r; in link i. 33

Figure 2.4 Six degree of freedom PUMA 560 robot. 43

Figure 2.5 PUMA 560 link co-ordinate transformation matrices. 46

Figure 3.1 Wrist force sensor. 55

Figure 3.2 Manipulator in contact with the environment. 57

Figure 3.3 Mechanical model of a DC torque motor connected through

gearing to an inertial load. 60

Figure 3.4 A position control system for the single joint link. 62

Figure 3.5 Force and torque constraints for a single link rod. 63

Figure 3.6 A practical force control system for a single joint link. 66

Figure 3.7 Hybrid position/force control block diagram. 49

Figure 4.1 Robot/environment model used in the simulations. 72

Figure 4.2 Joint position step response. 79

Figure 4.3 The Cartesian co-ordinate for the trajectory. 82

Figure 4.4 Joint position for the trajectory. 83

X

Figure 4.5 The force step response. 86

Figure 4.6 Unstable initial contact force. 87

XI

Chapter 1

Introduction

This chapter describes briefly the active research fields in robotics technology. The

study of today's robot applications and future robot applications are compared. From

there, it is possible to identify the importance of implementing active compliant

motion robot controller to improve its accuracy and stability. Finally, the project

objectives are provided as a context for the detailed analysis of robot force control in

subsequent chapters.

1.1 Robotics Technology

The word 'robot' was first coined by the Czechoslovakian playwright Karel

Capek which means forced labour or serf [ 11. Since in our childhood we saw

robot cartoons and movies all around of us. In our mind, we often think of

robot as a human like machine that is able to move, talk, fight and even fly!

However, robot has a totally different meaning in the engineering world

especially in the industrial field. The Robot Institute of America has defined

robot as [21:

A programmable, multifunctional manipulator designed to move

material, parts, tools, or specialised devices through various

programmed motions for the performance of a variety of tasks.

I

From the above definition, a machine can he called a robot when it is able to

reprogram and do multifunctional manufacturing task. However, this

definition restricts robots to industrial applications only.

The study of robots is called `robotics'. The term was coined and first used by

the Russian born America scientist and writer Isaac Asimov [3]. When

discussing about robotic systems, there are plenty of different areas that could

be studied. Below are some major robotics field commonly see in reference

books, magazines and research journals:

1. Robot Mechanism Design - This area mostly discuss some issues

involving the design of the robot such as size, weight, speed and load

capability. Mobile robot has been a hot topic in recent researches [7].

2. Control of Robot - A controller is needed to control the robot according

to task specification. The issues involved in this field include stability,

accuracy, and reliability of the robot control system such as PID, CTM,

adaptive control, force control and etc. [4]. The present robot control

researches arc being in artificial intelligence, neural networks and fuzzy

systems.

3. Programming of Robot - To control the robot, the robot has to be taught

how to do the job. This lead to the development of robotics programming

language such as VAL from Unimation, AR-BASIC from American

Cimflex, and AML developed by IBM. The latest trend in robot

2

programming is Off-Line Programming Systems (OLP). OLP is defined as

a robot programming language which has been sufficiently extended,

generally by means of computer graphics, that the development of robot

programs can take place without access to the robot itself [5].

4. Robot Application - In this field, the study is concentrated in industrial

applications such as spot welding, spray painting, cutting, material

handling, and assembly. The future trends will be in flexible

manufacturing applications, bio-medical applications and multi-robot

systems.

1.2 Today's Robot Applications in Manufacturing

For more detail investigations of the today's industrial robot applications in

manufacturing, ABB robots were taken as a case study. ABB (Asian Brown

Boveri) is one of the leading industrial robot manufacturers in the world. First

ABB robot was introduced in 1974. ABB robots have been applied to various

industrial applications including:

I. Material Handling 4. Packaging and Palletising

2. Welding 5. Water Jet Cutting

3. Spray Painting/Coating

1.2.1 Material Handling

For material handling task, the robot needs to move to a prescribed location,

grasps an object, moves to a second prescribed location, and release the object

3

(see Figure I. 1). ABB robots are being actively applied in foundry industry

for the needs of flexibility, capability, and precision in handling both delicate

and heavy parts. One of the reasons robots used in foundry industry is to

reduce the hazards (heat, noise, fumes, and dust) exposure to the workers.

When using robots for foundry environment, some protections have to he

made including anti-rust coat on all unpainted parts; all bearings, joints and

cable-contacts are sealed; anti-dust strip above the controller cabinets' door.

1.2.2 Welding

Welding is a process that joints metals by fusing them. Spot welding and arc

welding are two major welding techniques that robots have been successfully

used. There are over 20,000 ABB robots installed in the body shops of the

world's leading car manufacturers.

1. Spot welding - Spot welding is a process in which two sheet metal parts

are fused together at localised points by passing a large electric current

through the parts where the weld is to be made. The electric current results

in sufficient heat in the contact area to fuse the two metal parts, hence

producing the weld. ABB robot - IRB 6400 has been specially design for

spot welding applications (see Figure 1.2). IRB 6400 robots have several

advanced capabilities including:

" Reweld and process-error routines.

" Multi-tasking functionality.

" High load offset capability.

4

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Figure 1.1 ABB robot in material handling task. (Source: ABB Flexible

Automation. )

5

Figure 1.2 Spot welding. (Source: ABB Flexible Automation. )

6

2. Arc welding - Arc welding is a continuous welding process. The process

uses an electrode in the form of a rod or wire of metal to supply the high

electric current (100 to 300 A) needed for establishing the arc. The arc

between the welding rod and the metal parts to be joined produces

temperatures that are sufficiently high to form a pool of molten metal to

fuse the two pieces together.

One of the advanced functions for ABB robots in arc welding is Master-

Slave application (see Figure 1.3). Master-slave means two ABB robots

can weld on the same workpiece while it is moving in a positioner. One

robot is the master, and the second robot, the slave, moves and welds in

time with the master robot. Besides, one robot can be used as a six-axis

positioner, holding and moving the workpiece while a second robot welds

the workpiece. The positioner robot can pick-up and unloads workpieces.

1.2.3 Spray Painting/Coating

Because of the health hazards such as fumes and mist in the air, noise from

nozzle, fire hazards and potential cancer hazards to human, the use of

industrial robots has developed as an alternative means of performing spray

painting/coating operations. ABB robot - TR 5002 has been specially design

for painting operation (see Figure 1.4). TR 5002 is able to perform enhanced

path accuracy and uniform speed through corners, which give an even film,

build on the painted surface.

7

Figure 1.3 ylaster-slave arc welding. (Source: ABB Flexible Automation. )

Figure 1.4 TR 5002. (Source: ABB Flexible Automation. )

9

Besides, TR 5002 has a large working envelope shown in Figure 1.5.

ABB robot - IRB 4400LIO has been specially developed for sealing

application illustrated in Figure 1.6. IRB 440OLIO able to perform several

sealing processes involved:

I. Stone-ship coating. 3. Body-side coating.

2. Sealing. 4. Air blasting.

1.2.4 Packaging and Palletising

Frequent changes in packaging style and shape have become a key factor in

marketing consumer goods. A robot-based packaging line gives the flexibility

and reliability to meet these challenges. Operator safety, space and cost

savings are some principal features that can be gained in robotised packaging

applications, compared with dedicated packaging systems.

ABB robot - IRB 640 has been design specially to suit the palletising

operations. It is able to carry a payload up to 160 kg and having a high

productivity up to 1,200 cycles per hour. Bellow is some palletising operations

that can be done by IRB 640:

1. End-of-the-line palletising.

2. Middle-of-the-line palletising.

3. Complex-end-of-the-line palletising.

4. Palletising/depalletising station.

10