A Textbook of Robotics 2: Structure, Control and Operation

266 Pages·1984·8.232 MB·English

by  Moshe Shoham (auth.)

A Textbook of Robotics 2
Structure, Control and
Operation
A Textbook of Robotics 2
Structure, Control and
Operation
Moshe Shoham
Copyright ~ 1984 by Eshed Robotec (1982) Limited.
Softcover reprint of the hardcover 1s t edition 1984
All rights reserved.
British Library Cataloguing in Publication Data
Shoham, Moshe
A textbook of robotics.
2: Structure, control and operation
1. Robots, Industrial
I. Title
629.8'92 TSI91.H
ISBN-13: 978-1-4615-9890-9 e-ISBN-13: 978-1-4615-9888-6
DOl: 10.1007/978-1-4615-9888-6
Table of Contents
CHAPTER ONE
COMPONENTS OF ROBOTIC SYSTEMS 1
General 1
Mechanical Arm 5
End Effector 7
Robot Motors 10
Computer (Controller) 11
Sensors 12
CHAPTER TWO
THE MECHANICAL ARM 15
Introduction 15
Mechanical Arm Structure 16
Classifying Robots 26
Cartesian Robots 27
Cylindrical Robots 30
Spherical Robots 33
Horizontal Articulated Robots 34
Vertical Articulated Robots 35
Structural Characteristics of Robots 36
Mechanical Rigidity 40
Effects of Structure on Control 40
Effects of Structure on Work Envelope
and Work Volume 46
Cartesian Robot Work Volume 48
Cylindrical Robot Work Volume 48
Spherical Robot Work Volume 50
Horizontal Articulated Robot Work Volume 51
Vertical Articulated Robot Work Volume 53
Robot Work Volumes: Comparison 55
Work Volume in Theory and Practice 55
i
Advantages and Disadvantages of Various
Kinematic Structures: Summary 56
Open and Closed Kinematic Structures 58
Wrist Joints 61
CHAPTER THREE
FUNDAMENTAL CONCEPTS OF CONTROL 63
Control Systems 63
Open-Loop Control 66
Closed-Loop Control 68
Negative and Positive Feedback 73
Control System Errors and Stability 76
Transient and Steady State Response 76
Stabilization and Servo Systems 81
Loading Error 84
Controller Types 85
Proportional Control 85
Integral Control 88
Proportional-Integral Control 89
Differential Control 90
Proportional-Differential Control 91
Proportional-Integral-Differential Control 92
CHAPTER FOUR
ELECTRICAL DRIVE CU1roNENTS 93
DC Servo MOtors 93
DC MOtor Structure 95
The MOtor as a Generator 97
Opposite EMF in DC MOtors 98
Classifying DC MOtors by Excitation Type 101
Linear Regulation of Rate of Revolution in
DC Servo MOtors 105
Pulse Width MOdulation Control lOB
Stepping MOtors III
Stepping MOtor Controllers 116
Stepping MOtor Structure 118
Stepping Motors: Summary 121
Considerations in the Use of Stepping Versus
DC Servo MOtors 122
ii
Advantage of DC Motors 122
Disadvantage of DC Servo Motors 122
Advantage of Stepping Motors 123
Disadvantage of Stepping Motors 123
CHAPTER FIVE
HYDRAULIC DRIVE SYSTEMS 125
Properties of Hydraulic Fluids 126
Analogies between Hydraulic and Electrical
Parameters 129
Principle of the Hydraulic Amplifier 129
Reduction of Pressure Using a
Venturi Tube 130
Cy linders 132
Cylinder Structure 132
Piston Motion 134
Piston Rate of Motion 135
Selecting the Appropriate Cylinder 136
Power Sources 137
Gear Pump Structure and Principles
of Operation 137
Radial Hydraulic Motors 138
~~~ 1~
Directional Control Valves 140
Regulating Valves 144
Electrohydraulic Servo Valves 144
Servo Valve Structure and Principles
of Operation 144
CHAPTER SIX
FEEDBACK DEVICES 147
Potentiometers 147
Optical Encoders 151
Resolution 152
Range 153
Absolute Position Encoder 153
Incremental Position Encoder 156
Computing the Resolution of Incremental
Position Encoders 159
iii
Measuring Rates of Revolution Using
Incremental Position Encoders 160
Increasing the Resolution of Incremental
Position Encoders 161
DC Tachometers (Tachogenerators) 162
CHAPTER SEVEN
DRIVE AND CONTROL SYSTEMS: AN APPRAISAL 167
Automatic Drilling Process: Computerized
Control System for One Axis 168
Operating Description 169
Automatic Command for Filling Containers with
a Constant Powder Volume 172
Computer-Controlled System for Hydraulic Cylinder
Position and Velocity Control 176
System Description and Component Functions 178
System Characteristics 178
Description of Operation 179
Hydraulic Cartesian Robot with Three Degrees of
Freedom 183
CHAPTER EIGHT
ROBaI' PATH OONI'ROL 187
What is Path Control? 187
Point-to-Point Control 188
Point-to-Point Control: Summary 199
Continuous Path Control 200
Continuous Path Control Computations 201
Joint Coordinate System 202
World Coordinate System 202
Tool Coordinate System 204
Conversions within Systems 205
Extracting Joint Variable Values for
Robots with Two Degrees of Freedom 207
Extracting Joint Variable Values for
Robots with Three Degrees of Freedom 210
Continuous Path Control in Practice 213
iv
CHAPTER NINE
A CASE STUDY 217
Defining the Task 217
Can this Robot Perform this Task? 220
Do the Robot's Degrees of Freedom Enable it
to Carry out the Task? 221
Can the Robot Motors Move the Arm and
the Payload? 221
Is the Accuracy Achieved by the Robot Suitable
to the Accuracy Requirements of the Task? 224
Operation of L11e Robot Components during Execution
of the Assigned Task 229
Will the Motor Stop at that Point? 234
What kind of Controller is Used in this Control
System? 236
GLOSSARY ~1
INDEX 257
v
Chapter One
Components of Robotic
Systems
GENERAL
A human being observing a robot in action may feel that
it is so independent that no one can predict its
actions. Obviously, this is not the case. Robots are
designed to carry out, with great precision, any
programs we design for them. In fact, robots resemble
humans, at times, in their ability to carry out
extremely complicated activities. These activities are
sometimes so complex that people who are unfamiliar
with the principles of robot operation may find it
difficult to understand the system.
To simplify this problem, we will now ''break down" the
robot into its component parts, explain the structure
and operation of each component, and describe the
1
Structure, Control and Operation
integration of all these components into a single
system.
Examining a robot in action, we note that the activity
of the robot arm is composed of two main sub
activities:
* Motion of the robot arm from one point to another,
through a series of intermediate points.
* Actuation*, at certain of these points, of an
end effector attached to the end of the
robot arm.
This rather simplistic description, in fact, may also
be used to describe the activity of the human arm.
The description of arm activity given above presents
that activity as it appears to the observer. In
practice, however, the activity results from the
combined operation of motors, control circuits, a
computer, and additional components. In fact, the main
problem affecting robot technology is
communication and coordination between the various
robot subsystems.
Before describing the subsystems making up the robot
system, we will briefly compare man and robot as
systems. This comparison is shown in Figure 1-1.
We can ask two questions concerning this illustration:
* What part of the system moves the arm?
In man, the arm is moved by muscles; in robots,
by motors.
* Technical terms will be under lined on their first
occurrence and defined, either explicitly or in
context. For future reference, all technical terms
are accumulated in a glossary at the end of the
book.
2