Theory and design of CNC systems

Computer Numerical Control (CNC) controllers are high value-added products counting for over 30% of the price of machine tools. The development of CNC technology depends on the integration of technologies from many different industries, and requires strategic long-term support. "Theory and Design of CNC Systems" covers the elements of control, the design of control systems, and modern open-architecture control systems. Topics covered include Numerical Control Kernel (NCK) design of CNC, Programmable Logic Control (PLC), and the Man-Machine Interface (MMI), as well as the major modules for the development of conversational programming methods. The concepts and primary elements of STEP-NC are also introduced. A collaboration of several authors with considerable experience in CNC development, education, and research, this highly focused textbook on the principles and development technologies of CNC controllers can also be used as a guide for those working on CNC development in industry.

Author Notes

Suk-Hwan Suh is a professor within the School of Industrial Engineering at POSTECH.nbsp;Henbsp;has beennbsp;a project analyst for the Hyundai Motor Company and worked in various universities in the USA, France and Australia. His research interests are unbiquitous manufacturing and management for extended product life cycle; international standard information technology global cooperation & conformance; and e-manufacturing for STEP-NC, intelligent shop floor, MES, ERP.

Seong-Kyoon Kang currently works for K&S International Patents in Seoul.

Dae-Hyuk Chung is based in Changwon, Korea, working for Doosan Infracore, Ltd.

Dr Ian Stroud is first assistant at the Laboratoire des outils Informatiques por la Conception et la Production en mécanique at the Ecole Polytechnique Federal de Lausanne.

Abbreviations	p. xvii
Part I Principles and NCK Design of CNC Systems
1 Introduction to NC Systems	p. 3
1.1 Introduction	p. 3
1.2 The History of NC and NC Machine Tools	p. 6
1.3 CNC Driving System Components	p. 8
1.3.1 Driving Motor and Sensor	p. 9
1.3.2 Linear Movement Guide	p. 15
1.3.3 Coupling	p. 16
1.4 CNC Control Loop	p. 17
1.4.1 Semi-closed Loop	p. 18
1.4.2 Closed Loop	p. 18
1.4.3 Hybrid Loop	p. 19
1.4.4 Open Loop	p. 19
1.5 The Components of the CNC system	p. 19
1.5.1 MMI Function	p. 22
1.5.2 NCK Function	p. 23
1.5.3 PLC Function	p. 25
1.5.4 Real-time Control System	p. 28
1.6 The Progress Direction of the CNC System	p. 29
1.7 Summary	p. 31
2 Interpreter	p. 33
2.1 Introduction	p. 33
2.2 Part Program	p. 34
2.2.1 Program Structure	p. 35
2.2.2 Main Programs and Subprograms	p. 39
2.3 Main CNC System Functions	p. 40
2.3.1 Coordinate Systems	p. 40
2.3.2 Interpolation Functions	p. 42
2.3.3 Feed Function	p. 48
2.3.4 Tools and Tool Functions	p. 50
2.3.5 Spindle Functions	p. 53
2.3.6 Fixed-cycle Function	p. 53
2.3.7 Skip Function	p. 56
2.3.8 Program Verification	p. 56
2.3.9 Advanced Functions	p. 57
2.4 G&M-code Interpreter	p. 62
2.5 Summary	p. 66
3 Interpolator	p. 69
3.1 Introduction	p. 69
3.2 Hardware Interpolator	p. 70
3.2.1 Hardware Interpolation DDA	p. 71
3.2.2 DDA Interpolation	p. 73
3.3 Software Interpolator	p. 75
3.3.1 Software Interpolation Methods	p. 78
3.3.2 Sampled-Data Interpolation	p. 86
3.4 Fine Interpolation	p. 96
3.5 NURBS Interpolation	p. 98
3.5.1 NURBS Equation Form	p. 99
3.5.2 NURBS Geometric Characteristics	p. 100
3.5.3 NURBS Interpolation Algorithm	p. 101
3.6 Summary	p. 106
4 Acceleration and Deceleration	p. 107
4.1 Introduction	p. 107
4.2 Acc/Dec Control After Interpolation	p. 108
4.2.1 Acc/Dec Control by Digital Filter	p. 109
4.2.2 Acc/Dec Control by Digital Circuit	p. 112
4.2.3 Acc/Dec Control Machining Errors	p. 121
4.2.4 Block Overlap in ADCAI	p. 126
4.3 Acc/Dec Control Before Interpolation	p. 128
4.3.1 Speed-profile Generation	p. 129
4.3.2 Block Overlap Control	p. 132
4.3.3 Corner Speed of Two Blocks Connected by an Acute Angle	p. 142
4.3.4 Corner Speed Considering Speed Difference of Each Axis	p. 144
4.4 Look Ahead	p. 145
4.4.1 Look-Ahead Algorithm	p. 147
4.4.2 Simulation Results	p. 152
4.5 Summary	p. 155
5 PID Control System	p. 157
5.1 Introduction	p. 157
5.2 The Servo Controller	p. 158
5.3 Servo Control for Positioning	p. 160
5.4 Position Control	p. 161
5.4.1 PID Controller	p. 162
5.4.2 PID Gain Tuning	p. 166
5.4.3 Feedforward Control	p. 171
5.5 Analysis of the Following Error	p. 179
5.5.1 The Following Error of the Feedback Controller	p. 179
5.5.2 The Following Error of the Feedforward Controller	p. 182
5.5.3 Comparison of Following Errors	p. 183
5.6 Summary	p. 185
6 Numerical Control Kernel	p. 187
6.1 Introduction	p. 187
6.2 Architecture of ACDAI-type NCK	p. 187
6.2.1 Implementation of the Interpolator	p. 188
6.2.2 Implementation of the Rough Interpolator	p. 193
6.2.3 Implementation of an Acc/Dec Controller	p. 199
6.2.4 Implementation of Fine Interpolator	p. 203
6.2.5 Implementation of the Position Controller	p. 208
6.3 Architecture of an ADCBI-type NCK	p. 211
6.3.1 Implementation of the Look-Ahead Module	p. 213
6.3.2 Implementation of an Acc/Dec Controller	p. 215
6.3.3 Implementation of the Rough Interpolator	p. 222
6.3.4 The Mapping Module	p. 225
6.4 Summary	p. 226
Part II Open-architectural Soft CNC Systems
7 Programmable Logic Control	p. 229
7.1 Introduction	p. 229
7.2 PLC Elements	p. 230
7.3 PLC Programming	p. 234
7.4 Machine Tool PLC Programming	p. 235
7.5 PLC System Functions	p. 240
7.5.1 Software Model and Communication Model	p. 242
7.5.2 Programming Model	p. 244
7.5.3 User Programming Languages	p. 245
7.6 Soft PLC	p. 247
7.7 PLC Configuration Elements	p. 248
7.7.1 PLC System Functions	p. 249
7.7.2 Executor Programming Sequence	p. 253
7.7.3 Executor Implementation Example	p. 254
7.8 Summary	p. 268
8 Man-Machine Interface	p. 271
8.1 MMI Function	p. 271
8.1.1 Area for Status Display	p. 271
8.1.2 Area for Data Input	p. 273
8.1.3 Area for MPG Handling	p. 273
8.1.4 Area for Machine Operation	p. 273
8.2 Structure of the MMI System	p. 275
8.3 CNC Programming	p. 278
8.3.1 The Sequence of Part Programming	p. 278
8.3.2 Manual Part Programming	p. 279
8.3.3 Automatic Part Programming	p. 280
8.4 Mazatrol Conversational System	p. 289
8.4.1 Turning Conversational System	p. 289
8.4.2 Programming Procedure	p. 292
8.5 Conversational Programming System Design	p. 294
8.5.1 Main Sequence for Design	p. 294
8.5.2 Key Design Factors	p. 296
8.6 Development of the Machining Cycle	p. 305
8.6.1 Turning Fixed Cycle	p. 305
8.6.2 Turning Cycle for Arbitrary Shape	p. 306
8.6.3 Corner Machining Cycle	p. 310
8.6.4 Drilling Sequence	p. 312
8.7 Summary	p. 314
9 CNC Architecture Design	p. 315
9.1 Introduction	p. 315
9.2 Operating Systems	p. 317
9.3 Real-time Programming	p. 319
9.4 Structure of a Real-time OS	p. 321
9.5 Process Management	p. 323
9.5.1 Process Creation and Termination	p. 324
9.5.2 Process State Transition	p. 324
9.5.3 Process Scheduling	p. 325
9.6 Process Synchronization	p. 330
9.6.1 Semaphores	p. 330
9.6.2 Using Semaphores	p. 331
9.6.3 Events and Signals	p. 331
9.7 Resources	p. 334
9.7.1 System Resources	p. 334
9.7.2 Mutual Exclusion	p. 335
9.7.3 Deadlock	p. 336
9.8 Inter-process Communication	p. 337
9.8.1 Shared Memory	p. 337
9.8.2 Message System	p. 338
9.9 Key Performance Indices	p. 340
9.9.1 Task Switching Time	p. 340
9.9.2 Context Switching Time	p. 341
9.9.3 Semaphore Shuffling Time	p. 341
9.9.4 Task Dispatch Latency Time	p. 341
9.10 Hardware and Operating Systems	p. 344
9.10.1 Architecture of Multi-processing Hardware	p. 344
9.10.2 Operating System Configuration	p. 347
9.10.3 CNC System Architecture	p. 348
9.11 Summary	p. 350
10 Design of PC-NC and Open CNC	p. 353
10.1 Introduction	p. 353
10.2 Design of Software Architecture	p. 356
10.2.1 CNC System Modeling	p. 356
10.3 Design of Soft-NC System	p. 359
10.3.1 Design of Task Module	p. 359
10.3.2 Design of the System Kernel	p. 361
10.3.3 PLC Program Scanning and Scheduling	p. 362
10.3.4 Task Synchronization Mechanism	p. 365
10.3.5 Inter-Task Communication	p. 369
10.4 Motion Control System Programming Example	p. 376
10.4.1 Design of System Architecture	p. 377
10.4.2 Creating Tasks	p. 378
10.4.3 Task Synchronization	p. 378
10.4.4 Task Priority	p. 381
10.4.5 Inter-Task Communication	p. 381
10.4.6 Create Event Service	p. 384
10.5 Open-CNC Systems	p. 387
10.5.1 Closed-type CNC Systems	p. 387
10.5.2 Open CNC Systems	p. 389
10.6 Summary	p. 393
11 STEP-NC System	p. 395
11.1 Introduction	p. 395
11.2 Background of STEP-NC	p. 397
11.2.1 Problems with G&M Codes	p. 397
11.2.2 Historical Background	p. 398
11.3 STEP-NC: A New CNC Interface Based on STEP	p. 399
11.3.1 Contents	p. 399
11.3.2 Relationship Between STEP and STEP-NC	p. 399
11.3.3 Objectives and Impacts	p. 401
11.4 STEP-NC Data Model	p. 402
11.4.1 Part 1: Overview and Fundamental Principles	p. 403
11.4.2 Part 10: General Process Data	p. 405
11.4.3 Part 11: Process Data for Milling	p. 407
11.4.4 Part 12: Process Data for Turning	p. 407
11.4.5 Tools for Milling and Turning	p. 408
11.5 Part Programming	p. 410
11.5.1 Part Programming for the Milling Operation	p. 411
11.5.2 Part Programming for the Turning Operation	p. 414
11.6 STEP-CNC System	p. 415
11.6.1 Types of STEP-CNC	p. 417
11.6.2 Intelligent STEP-CNC Systems	p. 418
11.7 Worldwide Research and Development	p. 422
11.7.1 WZL-Aachen University (Germany)	p. 422
11.7.2 ISW-University of Stuttgart (Germany)	p. 424
11.7.3 POSTECH (South Korea)	p. 425
11.7.4 Ecole Polytechnic Federale of Lausanne (Switzerland)	p. 426
11.7.5 University of Bath (UK)	p. 427
11.7.6 NIST (USA)	p. 427
11.8 Future Prospects	p. 428
A Turning and Milling G-code System	p. 431
A.1 Turning	p. 431
A.2 Milling	p. 434
A.3 Classification of G-code Groups	p. 437
Bibliography	p. 439
Index	p. 447

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Table of Contents