THE MICROPROCESSOR AND COMPUTER-AIDED DESIGN AND MANUFACTURE by Suneel Kumar Khurmi, B.Sc.(Eng), A.C.G.I. September 1982 A thesis submitted for the degree of Doctor of Philosophy of the University of London and for the Diploma of Membership of the Imperial College. Department of Mechanical Engineering Imperial College of Science and Technology University of London - 2 - ABSTRACT The thesis describes the design, implementation and application of software for a low cost microcomputer based Computer-Aided Design and Computer-Aided Manufacture (CAD/CAM) system. The CAD workstation consists of a Motorola 68B09 8-bit microcomputer, a floppy disc, a Hewlett-Packard graphics ^ VDU, a printer and a plotter. The Numerical Control system consists of a hierarchical multi-microcomputer control system on a retrofitted Student Colchester lathe and a Bridgeport milling machine. t The CAD and NC part-programming software consists of several packages which assist the operator through the conceptual realms of product design and manufacture. They assist in the storage of the geometrical and technological information associated with the product, geometrical t editing, draughting, design analysis, cutter path derivation, NC simulation and part program generation. These packages are executed sequentially to produce 2/2^ dimensional NC part programs for a variety of machine tools, for example the Colchester and Bridgeport machines. Most of the packages are modular and have been developed in * , the high level language Pascal to maintain system modularity, flexibility and expandability. - 3 - ABSTRACT The thesis is subdivided into four main sections. The first section introduces the reader to microprocessors, CAD, CAM and the implications associated with CAD/CAM integration. The second section describes the importance of the selection and usage of microcomputer languages and operating systems in conjunction with CAD/CAM hardware. The selection is supplemented by the proposals of an ideal CAD workstation and a CNC system. A detailed description of the software packages and their capability is presented in the third section with two detailed examples illustrating the use of the system. The first illustrates a turned component and the second a pocket milled component. Finally, in the fourth section, a comparison between the CAD/CAM system described and those commercially available is presented. The advantages and limitations of the current system are discussed with particular reference to development into a commercial system. ft ft ACKNOWLEDGEMENTS The author wishes to acknowledge the guidance and support of his supervisor Dr. C.B.Besant. He also wishes to acknowledge the assistance and guidance of his fellow collegues. In particular Dr. H.A.Pak for his help in the writing of some of the early software used in this work, S.Ahmad, O.Alankus, D.Dalzell, L.Daneshmend, D.Etela, T.Jin, G.Kartsounis, C.Lui, F.Maali, S.Premi and N.Zarimpas for their useful criticisms at various stages of the project. This project was sponsored by Science and Engineering Research Council. Finally, thanks are also due to his parents and other members of the family for their moral and financial support. - 5 - NOTATION A/D Analogue to digital ft Baud Baud rate (bits/second) Bit One binary digit Bus Media for interconnection betwee Byte Eight bits ft CAD Computer-aided design CAM Computer-aided manufacture CLDATA Cutter location data 41 CMC Computer numerical control CPDR Cutter path derivate CPU Central processor unit ft CR Carriage return - CRT Cathode ray tube DB Database ft D/A Digital to analogue DBMS Database management system DOS Disc operating system DNC Direct numerical control ECL Emitter coupled logic EPROM Erasable programmable read only i FMS Flexible manufacturing system ft IC Integrated circuit IEEE Institute of Electrical and Elec I/O Input/Output 3 ft K Kilo (10 ) LSI Large scale integration M Mega (10**) MCU Machine control unit NOTATION Million instructions per second Machine tool Machine tool interpreter languag Numerical control -9 Nano seconds (10 sec) Original equipment manufacturer Printed circuit board Part program generate package Random access memory Read only memory Transistor-transistor logic Voltage controlled oscillator Visual display unit Very large scale integration micro (10 - 7 - CONTENTS ABSTRACT 1 a ACKNOWLEDGEMENTS 3 NOTATION 4 Chapter 1 : INTRODUCTION 11 m 1.1 Introduction to the integrated circuit and the microcomputer. 11 1.2 Impact of the IC in the manufacturing industry. 12 1.3 Evolution of Computer-Aided Design (CAD) and 21 Computer-Aided Manufacture (CAM). Chapter 2 : COMPUTER-AIDED DESIGN (CAD) 28 2.1 Conventional manual design techniques. 29 * 2.2 Computers in mechanical design. 32 2.3 Advantages of CAD. 38 2.4 Social implications of CAD. 40 » Chapter 3 : COMPUTER-AIDED MANUFACTURE (CAM) 41 3.1 Computer-Aided Manufacture. 41 3.2 Numerical Control in CAM. 46 a 3.3 NC Computer management. 49 3.4 Computer Numerical Control (CNC). 50 3.5 Direct Numerical Control (DNC). 53 3.6 Microcomputers as an aid in part programming. 54 * 3.7 Use of microprocessors in CAM and NC hardware. 56 Chapter 4 : CAD/CAM INTEGRATION 60 ft 4.1 CAD-CAM data link. 61 4.2 Hardware and software savings in integrated microprocessor 66 based CAD/CAM systems. 4.3 Implications of CAD/CAM integration. 69 CONTENTS Chapter 5 : CHOICE AND USE OF MICROCOMPUTER LANGUAGE S70 5.1 Selection of software development tools. 71 5.2 Influencing factors in choosing low and high level microcomputer 73 languages for CAD/CAM applications. 5.3 Structure of the high level language PASCAL. 76 5.4 The precedence of a microcomputer's operating system. 81 Chapter 6 : PROPOSALS AND ARCHITECTURE OF THE MICROCOMPUTER BASED CAD I CAM WORKSTATION 82 6.1 Proposal for a CAD/CAM workstation. .82 6.2 Proposal for a NC system. 96 6.3 Description of the current M6809 based CAD/CAM system. 106 6.3.1 The CAD/CAM workstation. 106 6.3.2 The operating system. 113 6.3.3 The NC turning system. 115 6.3.4 The NC milling system. 120 Chapter 7 : DESCRIPTION OF THE WORKSTATION'S SOFTWARE 123 7.1 Software hierarchy. 123 7.2 The CREATE package. 128 7.3 The EDIT package. • 146 7.4 The DISPLAY package. 149 7.5 The PLOTTER package. 172 7.6 The DESIGN Analysis package. 175 7.7 The Turning Cutter Path Derivate TCPDR package. 180 7.8 The Milling Cutter Path Derivate MCPDR package. ' 194 7.9 The Part Program Generate PPGP package. 216 7.10 Machine Tool Interpreter Language (MTIL) and CAM. 217 - 9 - CONTENTS Chapter 8 : THE USE OF THE SYSTEM TO CAD/CAM 220 APPLICATIONS 8.1 An example of a turned component. 220 8.2 An example of a milled component. 241 Chapter 9 : EVALUATION AND ECONOMIC ASPECTS OF THE 249 CAD/CAM SYSTEM 9.1 Evaluation of the geometrical repertoire of the current system. 249 9.2 Arithmetic precision of the current system. 255 9.3 Data processing for the current system. 259 9.4 Comparison of the machine tool control codes output by the 261 current system with those of APT and COMPACT. 9.5 Analysis of the MCPDR package with reference to the GNC, 262 Polysurf and Surfset packages. 9.6 Diagnostics and program debugging. 264 9.7 Economic aspects associated with NC and the current system. 266 Chapter 10 : CONCLUSIONS, DISCUSSION AND SUGGESTIONS 271 FOR FUTURE WORK 10.1 Conclusions and discussion. 271 10.2 Suggestions for future work. 274 REFERENCES 280 4 • 4 CONTENTS APPENDICES A : CREATE package command repertoire. B : Primitives' database organisation. C : CREATE & EDIT packages' error messages. D : DISPLAY package command repertoire. E : PLOTTER package command repertoire. F : Varignon's theorem. G : Moment of inertia of composite bodies. H : Determination of the centroid of composite bodies. I : Description of the TCLDATA and MCLDATA files. J : TCPDR and MCPDR packages' command repertoire. K : PPGP package's command repertoire. L : Paper presented at CAD82 conference. M : Paper presented at MICAD82 conference. CHAPTER 1 INTRODUCTION 1.1 Introduction to the integrated circuit and the microcomputer The ever diminishing size and cost of microelectronic devices has brought about two technological achievements. Firstly, in the integration of two technologies - Computer- Aided Design and Computer-Aided Manufacture into unified CAD/CAM systems, whereby a design is developed and the manufacturing process controlled from start to finish with a single system. And secondly, in the feasibility of low cost CAD/CAM systems on an economic scale which can be related to small sized manufacturing industries. Though still in their infancy the 1980s are well on course to become the decade of the silicon chip, Fig. 1.1. During the next few years microelectronics will develop rapidly from being a source of intense popular interest to emerge as a pervasive force with a direct impact on an everwidening area of our daily lives. One of the controversial aspects of the new technology is the effect that it will have on employment. It is clear that the displacement of labour will involve not only the man on the shop floor but line management as well. Furthermore, computers can probably come out with much better programs for optimum cash flow strategies, payroll and so on, and therefore some middle-line management will be obviated as well. - 12 - 10 Components/Chip 1M / RAM O / / / / 10 256K q ' RAM . ' 64K rQ 32 Bit 105 H RAM ji-processor 16K RAM 16 Bit ji-processor 104 H 8 Bit ji-processor 10 h Calculator Chip 10 2 J io h l -« Subcircuit Circuit System o.i 1960 '65 '70 75 80 '85 FIG. 1.1 PROGRESS IN MICROELECTRONIC INTEGRATION - 13 - INTRODUCTION The potential applications of the new technology are m almost limitless, from the washing machine to the fully automated shop floor to the most sophisticated space research developments, such as the NASA space shuttle.