A DISTRIBUTED MICROPROCESSOR CONTROL

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1 A DISTRIBUTED MICROPROCESSOR CONTROL SYSTEM FOR AN INDUSTRIAL ROBOT, \ Raad by F. Rafauli. B. Eng. A Thesis Submitted to the School of Gr?duate Studies ~, in Partial Fulfilment of the Requirements for the Degree... Master of Engineering McMaster University June 198:1

2 ,, MASTER OF ENGINEERING (.1981) Electrical and Computer Engineering McMASTER UNIVERSITY Hamilton, Ontario TITLE: A Distributed Microprocessor Control System for an Industrial Robot AUTHOR: Raad F. ~fauli, B.Eng. (McMaster University) SUPERVISORS: Dr. N. K. Sinha, Department of Electrical and Computer Enginee:ring Dr. J. TlustYt Department of Mechanical Engineering NUMBER OF PAGES: ix, 81, Appendices A-D (60), References (2) ;. ". \ if i'

3 / ABSTRACT Complex automation systems, such as industrial robots, require. a computer-based control system for the effective utilizatio~ of the \ advanced technology. A state~of-the-art was studied and presented in this thesis. A distributed computer control system for a modified Unimate 2000 robot, is presented. The l6-bi~ Intel 8086 microprocessor was used as the master computer, and the 8-bit Intel 8748 micrgprocessor as, the slave processor. The system is effective and the experimental results agree with the simulation... iii

4 ( ACKNOWLEDGEMENTS The author wishes to express his sincere thanks to his supervisors, Dr. N. K. Sinha and Dr. J. Tlusty for their support and."~ guidance throughout the course of this work. Also, many shanks to Dr. R. Kit~i and Mr. P. Yo~g for their time spent in constructive discussions. Finally, a special thank you to my two brothers for their financial support, and to my wife for her moral support. ~, ~. f iv

5 TABLE OF CONTENTS, Page CHAPTER 1 - THE INDUSTR~ ROBOT 1.1 Introduction 1.2 Major Coordinate System Cartesian Work Envelope Cylindrical Work Envelope \ Spherical Work Envelope Articulated Work Envelope Power Sources " 1.4 The Control Non-Servo Controlled Servo Controlled Manipulator Path 1.5 Command Generation ) Programming the Robot Cartesian Interpolation Joiht Interpolation C~bic Spline InterpOlation Constant Acceleration, Constant Velo~ity Algorithm On-Line Programming Off-Line Programming Programming Languages v

6 Page CRAPTE~ 2 THE CONTROL SXSTEM P 2.1 Introduction 2.2 System Architecture ~ 2.3,Detailed System Functional Description ~5 \ The Master Cpmputer The Slave Processors The Manual Controller The Interlock Signals The Mechanical Range Limltations and the Safety Features 2.4 Position Control System CHAPTER 3 - HARDWARE-CONSIDERAT!ON, 3~1 The West-Amp Servo Amplifier 3.2 The Electro Craft Servo Amplifier 3.3 The Electro Craft Servo Motors 3.4 The Position Feedback Transducer 3.5 The Master Computer a.6 The Servo Cards ( Control Board Select Digital Data, Input Digital Data Output and Transfer Acknowledge Synchronizations Analog Signal Generations System Protection and Manual/Computer Select The Positional Feedback The Central Processor Unit (CPU) vi

7 Page CHAPTER 3 (continued) 3.7 The Manual Controller 62 CHAPTER 4 - SOFTWARE CONSIDERATION 69 CHAPTER,5 - CONCLUSION 80. APPENDIX A - PLM/86 PROGRAM LISTING APPENDIX B - ASM48 PR9GRAM LISTING APPENDIX C - SCHEMATIC DIAGRAMS APPENDIX D - isbc86!l2a MON;TOR COMMANDS REFERENCES / vii

8 LIST OF FIGURES Figure ' Major Robot Coordinate Systems Manipulator Path Control Quadratic Interpolation of Joint Position Single-Axis Point-to-Point Motion Using A Single Cubic Spline F~nction Single-Axis Point-to-Point Motion Using Cubic Spline.FunctionsJ Single-Axis Po~t-To-Point Motion Using A Single Trapezoidal V~locity Profile Single-Axis Point-to-Point Motion Using A Triangular. Velocity' Profile Velocity Profile for Three Joints Motion Single-Axis Path Control Motion Using A Trapezoidal.Vero~ity Profile Page Constant Velocity fo~ Off-Line Programming , The Five Axes of Motion of the Unimate 2000 Robot The Distributed Microprocessor Control Syste~ Closed-Loop Servo System Computer Within the Positional L90P Photograph of the Velocity Profile Approximate Model for One-Joint of the Robot The Root-Locus for the Positional Servo System Common Bus Configuration 47 viii

9 ). ;.' Figure Page 3.2 Control Board Enable Signal Generation Functional Block Diagram of the Servo Card Control Board Select Signal Generation Digital Data Input Digital Data Output and Transfer Acknowledge Synchronizing Signals Byte Parallel Loading of the DAC Digital to Analog Converter, Bipolar Operation Computer/Manual Select and System Protection 57 '3.11 The Positional Feedback 59 t The CPU Interface on the Servo C~d Velocity, Acceleration Control j 3.14 Command Velocity Generation 63 ~, 3.15 Generated Command Controller Miscellaneous Functions Generation System's Software Organization Plot of the Fortran Simulation for one Joint of the Robot Control Program Flowchart II! I I!- ix

10 CHAPTER 1 THE INDUSTRIAL ROBOT 1.1 Introduction All industrial ro~ots inclu~ three basic elements: an articulated arm, controls and power source. The arm moves in up to six differen~ axes. Three are provided by the arm itself which may rotate in an arc around its base and reaches up ~ do~ vertically and in and out horizontally. As many as three other motions are added at the wrist which allows the hand or gripper attached to it to rotate, and move in vertical and horizontal planes. These articulations enable the arm to move to some predetermined point in space, work on an object, and then return to the original position or to a sequence of other points in sp~e. The pattern of movements depe~ds on the need of the job and the programming capacity of the controls. \ /,J 1.2 The Major Coordinate Systems for Industrial Robots / The point in space accessible to a robot depends on its designed work ~nvelope. There are four basic design categories: Cartesian, cylindrical, spherical, and articulated, that carve out slightly different geometric work areas in space, as shown in Figure

11 2 I'., CAR.TESW (3 Translative Coords.) B) CYLINDRICAL (1 Rotary. 2 Trans.) C) SPHERICAL (2 Rotary. 1 Trans.) D) ARTICULATED I (3 Ro tary Co-o1::ds.) }tour MAJOR ROBOT COORDINATE SYSTEMS Figut. 1.1 ~jor Robot Coordinatb S1't~ " I t

12 The Cartesian work. envelope is created when the horizontal robot arm is attached to a vertical column and mov~s ur and down and in and out in relation to this column. The column itself is mounted on a third linear axis which moves in two directions. These three m&vements combine to gen~rate a work e~velope in the shape of a three dimensional rectangle. \ \ The cylindrical work envelope is created when the horizontal arm is at~ached to a vertical carriage and moves up and down and in - '"',. and out in relation to this carriage. The carriage itself is mounted on a pedesthl which rotates. These three movements combine to generate a work ehvelope that is a portion of a cylin In a 8pheri~al work envelope, the robot is mounted on a~base somewhere near its midpoint so that it can tilt up and down and in and around its support point. combine to generate a work, The arm extends horizontally. ~ envelope that is a portion of These motions a sphere In an artic~ated work envelope, the arm is attached to a pedestal.th~t rotates. The arm itself is jointed, adding a kind of elbow movement ',to the articulations. Thus, as the arm rotates and reaches in the Worizontal and verti~al planes, it generates a portion of a sphere in space and as the elbow bends, it enables the robot arm to come in ~lose to the base. The jointed action enlarges the work area accessible to 'the robot.

13 4 1.3 Power Sources Power is delivered to robots by hy~raulic, pneumatic, or electic motors. Most robot makers have gone the hydraulic route, which is espec~ally good where heavy loads are involved. Electric motors have the advantage of being less noisy, cleaner, more accurate, and may be less expensive. Pneumatically activated robots take advantage of the co~ressed air supply that is commonly available. 1.4 The Controls n When classified according to the type control,robots fall into two general categories:, The non-servo are iess flexible than the servo controlled, but are also less expensive and very accurate. In this type of robot, each joint moves between two end points that are determined by mechanical stops. When hydraulic or pneumatic power is delivered to the joints, the motors drive the joint until it reaches a mechanical stop. A limit switch then signals the power off until ~he program calls for another move. The valves then open and again deliver fluid to the joints. / In these robots, c~ntrolled acceleration and deceleration 1 require special designs. The number of different positions to which the robot can go in sequence is limited ~ The servo controlled robots can do many things the simpler

14 5 ones can't. They can be programmed to do a more complex sequence of tasks and can have controlled velocity, acceleration, and deceleration. A servo c~trolled robot has encoders, potentiometers, rel ~- solvers or other feedback devices at each of the joints. These devices feed position signals back to the controller which compares them with the commanded position. The controller then sends correction signal~ to the hydraulic or electric motors at the joint. This thesis will consider the servo controlled robots only Manipulator Path Consider a manipulator consisting of an arm, the end ~~hich is its wrist, and an end-effector, which may be a hand or a tool. The end-effector, is usually attached directly to the wrist. The threedimensional path of the end-effector of a manipulator is described by two variables. [lj 1) End-effector position: The position of a point fixed v in the end-effector in & reference cartesian coordinate system. 2) End-effector orientation: The orientation of a cartesian that ector posi- coordinate system attached to the h the system's origin coincides with the end-e tion. The above definition of end-effector position ~nd ). orientation is based on attaching a cartesian reference frame to the end-effector. The word "state" is used to represent both position and orientation of

15 - 6 an end-effector. position servo. There are two common ways to control an industrial robot with (a) For material handling jobs, a point-to-point control is sufficient where the joints may start moving at the same time but don't all necessarily finish moving at the same time under program control. When this ~s the case, the end-effector assumes various states as it moves between the two end points and the shape of the path is not predictable. Figure 1.2a shows three trained endeffector positions, A through C, in three dimensions and illustrates the path travelled by the end-effectot between these positions. Point-to-point movements are fast and the shape of the path is irrelevant.,,but the start and end points are important. AD I \ I \, (4) Point-Co-point (b) Int~rpolaced Scraight- (c) Incerpolated Straight- Segment Path Segment Pach with Smooth Transitions Detveen Segments Figure L 2. Pach Cont:

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Introduction to robotics. Md. Ferdous Alam, Lecturer, MEE, SUST

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