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Design Examples and Design Problems (DP)

CHAPTER 1 PAGE Example Example Example Example Example Example Example CDP1.1 DP1.1 DP1.2 DP1.3 DPI .4 DPI .5 DP1.6 DPI.7 DP1.8

Hybrid Fuel Vehicles Wind Power Embedded Computers Smart Grid Control Systems Rotating Disk Speed Control Insulin Delivery Control System Disk Drive Read System Traction Drive Motor Control Automobile Noise Control Automobile Cruise Control Dairy Farm Automation Welder Control Automobile Traction Control Hubble Telescope Vibration Nanorobotics in Medicine Human Transportation Vehicle

CHAPTER 2 Example Example Example Example Example Example Example CDP2.1 DP2.1 DP2.2 DP2.3 DP2.4 DP2.5

Photovoltaic Generators Fluid Flow Modeling Electric Traction Motor Control Mechanical Accelerometer Laboratory Robot Low-Pass Filter Disk Drive Read System Traction Drive Motor Control Selection of Transfer Functions Television Beam Circuit Transfer Function Determination Op Amp Differentiating Circuit Grandfather Clock Pendulum

CHAPTER 3 Example

Example Example CDP3.1 DP3.1 DP3.2

DP3.3 DP3.4 DP3.5

Modeling the Orientation of a Space Station Printer Belt Drive Disk Drive Read System Traction Drive Motor Control Shock Absorber for Motorcycle Diagonal Matrix Differential Equation Aircraft Arresting Gear Bungi Jumping System State Variable Feedback

CHAPTER 4 Example

Example Example Example CDP4.1 DP4.1 DP4.2

English Channel Boring Machines Mars Rover Vehicle Blood Pressure Control Disk Drive Read System Traction Drive Motor Control Speed Control System Airplane Roll Angle Control

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DP43 DP4.4 DP4.5 DP4.6 DP4.7 DP4.8

Velocity Control System Laser Eye Surgery Pulse Generating Op Amp Hydrobot Unmanned Underwater Vehicles Mobile Remote-Controlled Video Camera

297 297 298 298 298

299

CHAPTER 5 Example Example

Example CDP5.1 DP5.1 DP5.2 DP5.3 DP5.4 DP5.5

DP5.6 DP5.7 DP5.8

Hubble Telescope Pointing Attitude Control of an Airplane Disk Drive Read System Traction Drive Motor Control Jet Fighter Roll Angle Control Welding Arm Position Control Automobile Active Suspension Satellite Orientation Control Deburring Robot for Machined Parts DC Motor Position Control Three-Dimensional Cam Spray Paint Robot

CHAPTER 6 Example Example Example CDP6.1 DP6.1 DP6.2 DP6.3 DP6.4 DP6.5 DP6.6 DP6.7 DP6.8

Tracked Vehicle Turning Robot-Controlled Motorcycle Disk Drive Read System Traction Drive Motor Control Automobile Ignition Control Mars Guided Vehicle Control Parameter Selection Space Shuttle Rocket Traffic Control System State Variable Feedback Inner and Outer Loop Control PD Controller Design

CHAPTER 7 Example Example Example Example Example CDP7.1 DP7.1 DP7.2 DP7.3 DP7.4 DP7.5 DP7.6 DP7.7 DP7.8 DP7.9

Wind Turbine Speed Control Laser Manipulator Control Robot Control System Automobile Velocity Control Disk Drive Read System Traction Drive Motor Control Pitch Rate Aircraft Control Helicopter Velocity Control Mars Rover Remotely Controlled Welder High-Performance Jet Aircraft Control of Walking Motion Mobile Robot with Vision OP Amp Control System Robot Arm Elbow Joint Actuator

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DP7.10 Four-Wheel-Steered Automobile 546 DP7.11 Pilot Crane Control 547 DP7.12 Planetary Rover Vehicle 547 DP7.13 Roll Angle Aircraft Autopilot 548 DP7.14 PD Control of a Marginally

Stable Process 548

CHAPTER 8 Example Maximum Power Pointing

Example Example Example CDP8.1 DP8.1 DP8.2

DP8.3

DP8.4 DP8.5 DP8.6 DP8.7

Tracking Engraving Machine Control Control of a Six-Legged Robot Disk Drive Read System Traction Drive Motor Control Automobile Steering System Autonomous Planetary Explorer-Ambler Vial Position Control Under a Dispenser Automatic Anesthesia Control Black Box Control State Variable System Design PID Controller Design

CHAPTER 9 Example Example

Example Example CDP9.1 DP9.1

DP9.2 DP9.3 DP9.4 DP9.5 DP9.6 DP9.7 DP9.8 DP9.9 DP9.10 DP9.11

PID Control of Wind Turbines Remotely Controlled Reconnaissance Vehicle Hot Ingot Robot Control Disk Drive Read System Traction Drive Motor Control Mobile Robot for Toxic Waste Cleanup Control of a Flexible Arm Blood Pressure Regulator Robot Tennis Player Electrohydraulic Actuator Steel Strip-Rolling Mill Lunar Vehicle Control High-Speed Steel-Rolling Mill Two-Tank Temperature Control State Variable Feedback Control Nuclear Reactor Control

CHAPTER 10 Example Example Example Example CDP10.1 DPI 0.1 DPI 0.2

DPI 0.3 DP 10.4 DP10.5 DPI 0.6

Rotor Winder Control System The X-Y Plotter Milling Machine Control System Disk Drive Read System Traction Drive Motor Control Two Cooperating Robots Heading Control of a Bi-Wing Aircraft Mast Flight System High-Speed Train Tilt Control Tape Transport Speed Control Automobile Engine Control

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DPI 0.7 DP10.8 DP10.9 DP10.10 DP10.11

Aircraft Roll Angle Control Windmill Radiometer Control with Time Delay Loop Shaping Polymerase Chain Reaction Control

828 828 829 830

830

CHAPTER 11 Example Example Example CDP11.1 DP11.1 DPI 1.2 DPI 1.3 DP11.4 DP11.5 DP 11.6 DPI 1.7

Automatic Test System Diesel Electric Locomotive Disk Drive Read System Traction Drive Motor Control Levitation of a Steel Ball Automobile Carburetor State Variable Compensation Helicopter Control Manufacturing of Paper Coupled-Drive Control Tracking a Reference Input

CHAPTER 12 Example Example Example Example

Example Example CDP12.1 DP12.1 DP12.2 DP12.3 DP12.4 DP12.5 DPI 2.6

DP12.7 DP12.8

DP12.9 DP12.10 DP12.11 DP12.12 DP 12.13

Aircraft Autopilot Space Telescope Control Robust Bobbin Drive Ultra-Precision Diamond Turning Machine Digital Audio Tape Controller Disk Drive Read System Traction Drive Motor Control Turntable Position Control Robust Parameter Design Dexterous Hand Master Microscope Control Microscope Control Artificial Control of Leg Articulation Elevator Position Control Electric Ventricular Assist Device Space Robot Control Solar Panel Pointing Control Magnetically Levitated Train Mars Guided Vehicle Control Benchmark Mass-Spring

CHAPTER 13 Example Example Example CDP13.1 DP13.1 DP13.2

Worktable Motion Control Fly-by-wire Aircraft Control Disk Drive Read System Traction Drive Motor Control Temperature Control System Disk Drive Read-Write Head-

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Positioning System 1034 DP13.3 Vehicle Traction Control 1034 DP13.4 Machine-Tool System 1035 DPI3.5 Polymer Extruder Control 1035 DPI 3.6 Sampled-Data System 1035

Modern Control Systems TWELFTH EDITION

Richard C. Dorf University of California, Davis

Robert H. Bishop Marquette University

Prentice Hall

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Copyright 2011,2008,2005,2001 by Pearson Education, Inc., Upper Saddle River, New Jersey 07458. All rights reserved. Manufactured in the United States of America. This publication is protected by Copyright and permis-sions should be obtained from the publisher prior to any prohibited reproduction, storage in a retrieval system, or transmission in any form or by any means, electronic, mechanical, photocopying, recording, or likewise. To obtain permission(s) to use materials from this work, please submit a written request to Pearson Higher Education, Permissions Department, 1 Lake Street, Upper Saddle River, NJ 07458. The author and publisher of this book have used their best efforts in preparing this book. These efforts include the development, research, and testing of the theories and programs to determine their effectiveness. The author and publisher make no warranty of any kind, expressed or implied, with regard to these programs or the documentation contained in this book. The author and publisher shall not be liable in any event for incidental or consequential damages in connection with, or arising out of, the furnishing, performance, or use of these programs.

Library of Congress Cataloging-in-Publication Data Dorf, Richard C.

Modern control systems / Richard C. Dorf, Robert H. Bishop. 12th ed. p. cm.

ISBN-13:978-0-13-602458-3 ISBN-10:0-13-602458-0

1. Feedback control systems. I. Bishop, Robert H. II. Title. TJ216.D67 2010 629.83-dc22 2010015651

Prentice Hall is an imprint of

10 9 8 7 6 5 4 3 2 1

ISBN-13:978-0-13-602458-3 www.pearsonhighered.com ISBN-10: 0-13-602458-0

http://www.pearsonhighered.com

Of the greater teachers when they are gone, their students will say: we did it ourselves.

Dedicated to

Lynda Ferrera Bishop

and

Joy MacDonald Dorf

In grateful appreciation

Contents Preface xi About the Authors xxii

CHAPTER 1 Introduction to Control Systems 1 1.1 Introduction 2 1.2 Brief History of Automatic Control 5 1.3 Examples of Control Systems 10 1.4 Engineering Design 17 1.5 Control System Design 18 1.6 Mechatronic Systems 21 1.7 Green Engineering 25 1.8 The Future Evolution of Control Systems 27 1.9 Design Examples 28 1.10 Sequential Design Example: Disk Drive Read System 32 1.11 Summary 34

Skills Check 35 Exercises 37 Problems 39 Advanced Problems 44 Design Problems 46 Terms and Concepts 48

CHAPTER 2 Mathematical Models of Systems 49 2.1 Introduction 50 2.2 Differential Equations of Physical Systems 50 2.3 Linear Approximations of Physical Systems 55 2.4 The Laplace Transform 58 2.5 The Transfer Function of Linear Systems 65 2.6 Block Diagram Models 79 2.7 Signal-Flow Graph Models 84 2.8 Design Examples 90 2.9 The Simulation of Systems Using Control Design Software 113 2.10 Sequential Design Example: Disk Drive Read System 128 2.11 Summary 130

Skills Check 131 Exercises 135 Problems 141 Advanced Problems 153 Design Problems 155 Computer Problems 157 Terms and Concepts 159

CHAPTER 3 State Variable Models 161 3.1 Introduction 162 3.2 The State Variables of a Dynamic System 162

VI Contents

3.3 The State Differential Equation 166 3.4 Signal-Flow Graph and Block Diagram Models 171 3.5 Alternative Signal-Flow Graph and Block Diagram Models 182 3.6 The Transfer Function from the State Equation 187 3.7 The Time Response and the State Transition Matrix 189 3.8 Design Examples 193 3.9 Analysis of State Variable Models Using Control Design Software 206 3.10 Sequential Design Example: Disk Drive Read System 209 3.11 Summary 213


CHAPTER 4 Feedback Control System Characteristics 234 4.1 Introduction 235 4.2 Error Signal Analysis 237 4.3 Sensitivity of Control Systems to Parameter Variations 239 4.4 Disturbance Signals in a Feedback Control System 242 4.5 Control of the Transient Response 247 4.6 Steady-State Error 250 4.7 The Cost of Feedback 253 4.8 Design Examples 254 4.9 Control System Characteristics Using Control Design

Software 268 4.10 Sequential Design Example: Disk Drive Read System 273 4.11 Summary 277


CHAPTER 5 The Performance of Feedback Control Systems 304 5.1 Introduction 305 5.2 Test Input Signals 305 5.3 Performance of Second-Order Systems 308 5.4 Effects of a Third Pole and a Zero on the Second-Order System

Response 314 5.5 The 5-Plane Root Location and the Transient Response 320 5.6 The Steady-State Error of Feedback Control Systems 322 5.7 Performance Indices 330 5.8 The Simplification of Linear Systems 339 5.9 Design Examples 342 5.10 System Performance Using Control Design Software 356 5.11 Sequential Design Example: Disk Drive Read System 360

Contents vii

5.12 Summary 364 Skills Check 364 Exercises 368 Problems 371 Advanced Problems 377 Design Problems 379 Computer Problems 382 Terms and Concepts 384

CHAPTER 6 The Stability of Linear Feedback Systems 386 6.1 The Concept of Stability 387 6.2 The Routh-Hurwitz Stability Criterion 391 6.3 The Relative Stability of Feedback Control Systems 399 6.4 The Stability of State Variable Systems 401 6.5 Design Examples 404 6.6 System Stability Using Control Design Software 413 6.7 Sequential Design Example: Disk Drive Read System 421 6.8 Summary 424


CHAPTER The Root Locus Method 443 7.1 Introduction 444 7.2 The Root Locus Concept 444 7.3 The Root Locus Procedure 449 7.4 Parameter Design by the Root Locus Method 467 7.5 Sensitivity and the Root Locus 473 7.6 PID Controllers 480 7.7 Negative Gain Root Locus 492 7.8 Design Examples 496 7.9 The Root Locus Using Control Design Software 510 7.10 Sequential Design Example: Disk Drive Read System 516 7.11 Summary 518


CHAPTER 8 Frequency Response Methods 553 8.1 Introduction 554 8.2 Frequency Response Plots 556 8.3 Frequency Response Measurements 577 8.4 Performance Specifications in the Frequency Domain 579 8.5 Log Magnitude and Phase Diagrams 582 8.6 Design Examples 583

viii Contents

8.7 Frequency Response Methods Using Control Design Software 596 8.8 Sequential Design Example: Disk Drive Read System 602 8.9 Summary 603


CHAPTER 9 Stability in the Frequency Domain 634 9.1 Introduction 635 9.2 Mapping Contours in the s-Plane 636 9.3 The Nyquist Criterion 642 9.4 Relative Stability and the Nyquist Criterion 653 9.5 Time-Domain Performance Criteria in the Frequency Domain 661 9.6 System Bandwidth 668 9.7 The Stability of Control Systems with Time Delays 668 9.8 Design Examples 673 9.9 PID Controllers in the Frequency Domain 691 9.10 Stability in the Frequency Domain Using Control Design Software 692 9.11 Sequential Design Example: Disk Drive Read System 700 9.12 Summary 703


CHAPTER 1 0 The Design of Feedback Control Systems 743 10.1 Introduction 744 10.2 Approaches to System Design 745 10.3 Cascade Compensation Networks 747 10.4 Phase-Lead Design Using the Bode Diagram 751 10.5 Phase-Lead Design Using the Root Locus 757 10.6 System Design Using Integration Networks 764 10.7 Phase-Lag Design Using the Root Locus 767 10.8 Phase-Lag Design Using the Bode Diagram 772 10.9 Design on the Bode Diagram Using Analytical Methods 776 10.10 Systems with a Prefilter 778 10.11 Design for Deadbeat Response 781 10.12 Design Examples 783 10.13 System Design Using Control Design Software 796 10.14 Sequential Design Example: Disk Drive Read System 802 10.15 Summary 804


Contents ix

CHAPTER 11 The Design of State Variable Feedback Systems 834 11.1 Introduction 835 11.2 Controllability and Observability 835 11.3 Full-State Feedback Control Design 841 11.4 Observer Design 847 11.5 Integrated Full-State Feedback and Observer 851 11.6 Reference Inputs 857 11.7 Optimal Control Systems 859 11.8 Internal Model Design 869 11.9 Design Examples 873 11.10 State Variable Design Using Control Design Software 882 11.11 Sequential Design Example: Disk Drive Read System 888 11.12 Summary 890


CHAPTER 1 2 Robust Control Systems 910 12.1 Introduction 911 12.2 Robust Control Systems and System Sensitivity 912 12.3 Analysis of Robustness 916 12.4 Systems with Uncertain Parameters 918 12.5 The Design of Robust Control Systems 920 12.6 The Design of Robust PID-Controlled Systems 926 12.7 The Robust Internal Model Control System 932 12.8 Design Examples 935 12.9 The Pseudo-Quantitative Feedback System 952 12.10 Robust Control Systems Using Control Design Software 953 12.11 Sequential Design Example: Disk Drive Read System 958 12.12 Summary 960


CHAPTER 1 3 Digital Control Systems 984 13.1 Introduction 985 13.2 Digital Computer Control System Applications 985 13.3 Sampled-Data Systems 987 13.4 The z-Transform 990 13.5 Closed-Loop Feedback Sampled-Data Systems 995

X Contents

13.6 Performance of a Sampled-Data, Second-Order System 999 13.7 Closed-Loop Systems with Digital Computer Compensation 1001 13.8 The Root Locus of Digital Control Systems 1004 13.9 Implementation of Digital Controllers 1008 13.10 Design Examples 1009 13.11 Digital Control Systems Using Control Design Software 1018 13.12 Sequential Design Example: Disk Drive Read System 1023 13.13 Summary 1025


APPENDIX A MATLAB Basics 1038

References 1056

Index 1071

4 ^ WEBRESOURCES

APPENDIX B

APPENDIX C

APPENDIX D

APPENDIX E

APPENDIX F

APPENDIX G

APPENDIX H

APPENDIX 1

MathScript RT Module Basics

Symbols, Units, and Conversion Factors

Laplace Transform Pairs

An Introduction to Matrix Algebra

Decibel Conversion

Complex Numbers

z-Transform Pairs Preface

Discrete-Time Evaluation of the Time Response

Preface

MODERN CONTROL SYSTEMSTHE BOOK

Global issues such as climate change, clean water, sustainability, waste management, emissions reduction, and minimizing raw material and energy use have caused many engineers to re-think existing approaches to engineering design. One outcome of the evolving design strategy is to consider green engineering.The goal of green engi-neering is to design products that minimize pollution, reduce the risk to human health, and improve the environment. Applying the principles of green engineering highlights the power of feedback control systems as an enabling technology.

To reduce greenhouse gases and minimize pollution, it is necessary to improve both the quality and quantity of our environmental monitoring systems. One exam-ple is to use wireless measurements on mobile sensing platforms to measure the external environment. Another example is to monitor the quality of the delivered power to measure leading and lagging power, voltage variations, and waveform har-monics. Many green engineering systems and components require careful monitor-ing of current and voltages. For example, current transformers are used in various capacities for measuring and monitoring current within the power grid network of interconnected systems used to deliver electricity. Sensors are key components of any feedback control system because the measurements provide the required infor-mation as to the state of the system so the control system can take the appropriate action.

The role of control systems in green engineering will continue to expand as the global issues facing us require ever increasing levels of automation and precision. In the book, we present key examples from green engineering such as wind turbine control and modeling of a photovoltaic generator for feedback control to achieve maximum power delivery as the sunlight varies over time.

The wind and sun are important sources of renewable energy around the world. Wind energy conversion to electric power is achieved by wind energy turbines con-nected to electric generators. The intermittency characteristic of the wind makes smart grid development essential to bring the energy to the power grid when it is available and to provide energy from other sources when the wind dies down or is disrupted. A smart grid can be viewed as a system comprised of hardware and soft-ware that routes power more reliably and efficiently to homes, businesses, schools, and other users of power in the presence of intermittency and other disturbances. The irregular character of wind direction and power also results in the need for reli-able, steady electric energy by using control systems on the wind turbines them-selves. The goal of these control devices is to reduce the effects of wind intermittency and the effect of wind direction change. Energy storage systems are also critical technologies for green engineering. We seek energy storage systems that are renewable, such as fuel cells. Active control can be a key element of effective renewable energy storage systems as well.

xi

xii Preface

Control engineering is an exciting and a challenging field. By its very nature, con-trol engineering is a multidisciplinary subject, and it has taken its place as a core course in the engineering curriculum. It is reasonable to expect different approaches to mastering and practicing the art of control engineering. Since the subject has a strong mathematical foundation, we might approach it from a strictly theoretical point of view, emphasizing theorems and proofs. On the other hand, since the ulti-mate objective is to implement controllers in real systems, we might take an ad hoc approach relying only on intuition and hands-on experience when designing feed-back control systems. Our approach is to present a control engineering methodology that, while based on mathematical fundamentals, stresses physical system modeling and practical control system designs with realistic system specifications.

We believe that the most important and productive approach to learning is for each of us to rediscover and re-create anew the answers and methods of the past. Thus, the ideal is to present the student with a series of problems and questions and point to some of the answers that have been obtained over the past decades. The traditional methodto confront the student not with the problem but with the fin-ished solutionis to deprive the student of all excitement, to shut off the creative impulse, to reduce the adventure of humankind to a dusty heap of theorems. The issue, then, is to present some of the unanswered and important problems that we continue to confront, for it may be asserted that what we have truly learned and understood, we discovered ourselves.

The purpose of this book is to present the structure of feedback control theory and to provide a sequence of exciting discoveries as we proceed through the text and problems. If this book is able to assist the student in discovering feedback con-trol system theory and practice, it will have succeeded.

WHAT'S NEW IN THIS EDITION

This latest edition of Modern Control Systems incorporates the following key updates:

A new section in Chapter 1 on green engineering. The role of control systems in green engineering will continue to expand as global environmental challenges require ever increasing levels of automation and precision.

New design problems in key chapters that illustrate control design to support green engineering applications, such as smart grids, environmental monitoring, wind power and solar power generation.

Q A new section in each chapter entitled "Skills Check" that allows students to test their knowledge of the basic principles. Answers are provided at the end of each chapter for immediate feedback.

A new section on the negative gain root locus.

A new section on PID tuning methods with emphasis on manual tuning and Ziegler-Nichols tuning methods.

Over 20% of the problems updated or newly added. With the twelfth edition we now have a total of over 1000 end-of-chapter exercises, problems, advanced problems, design problems, and computer problems. Instructors will have no difficulty finding different problems to assign semester after semester.

Video solutions of representative homework problems are available on the companion website: www.pearsonhighered.com/dorf.

http://www.pearsonhighered.com/dorf

Preface x i i i

THE AUDIENCE

This text is designed for an introductory undergraduate course in control systems for engineering students. There is very little demarcation between aerospace, chemical, electrical, industrial, and mechanical engineering in control system practice; there-fore, this text is written without any conscious bias toward one discipline. Thus, it is hoped that this book will be equally useful for all engineering disciplines and, per-haps, will assist in illustrating the utility of control engineering. The numerous prob-lems and examples represent all fields, and the examples of the sociological, biological, ecological, and economic control systems are intended to provide the reader with an awareness of the general applicability of control theory to many facets of life. We believe that exposing students of one discipline to examples and problems from other disciplines will provide them with the ability to see beyond their own field of study. Many students pursue careers in engineering fields other than their own. For example, many electrical and mechanical engineers find them-selves in the aerospace industry working alongside aerospace engineers. We hope this introduction to control engineering will give students a broader understanding of control system design and analysis.

In its first eleven editions, Modern Control Systems has been used in senior-level courses for engineering students at more than 400 colleges and universities. It also has been used in courses for engineering graduate students with no previous back-ground in control engineering.

THE TWELFTH EDITION

A companion website is available to students and faculty using the twelfth edition. The website contains all the m-files in the book, Laplace and z-transform tables, written materials on matrix algebra and complex numbers, symbols, units, and con-version factors, and an introduction to the LabVIEW MathScript RT Module. An icon will appear in the book margin whenever there is additional related mate-rial on the website. The companion website also includes video solutions of repre-sentative homework problems and a complete Pearson eText. The MCS website address is www.pearsonhighered.com/dorf.

With the twelfth edition, we continue to evolve the design emphasis that his-torically has characterized Modern Control Systems. Using the real-world engi-neering problems associated with designing a controller for a disk drive read system, we present the Sequential Design Example (identified by an arrow icon in the text), which is considered sequentially in each chapter using the methods and concepts in that chapter. Disk drives are used in computers of all sizes and they represent an important application of control engineering. Various aspects of the design of controllers for the disk drive read system are considered in each chapter. For example, in Chapter 1 we identify the control goals, identify the variables to be controlled, write the control specifications, and establish the preliminary sys-tem configuration for the disk drive. Then, in Chapter 2, we obtain models of the


Preface

process, sensors, and actuators. In the remaining chapters, we continue the design process, stressing the main points of the chapters.

In the same spirit as the Sequential Design Example, we present a design prob-lem that we call the Continuous Design Problem (identified by an arrow icon in the text) to give students the opportunity to build upon a design problem from chapter to chapter. High-precision machinery places stringent demands on table slide sys-tems. In the Continuous Design Problem, students apply the techniques and tools presented in each chapter to the development of a design solution that meets the specified requirements.

The computer-aided design and analysis component of the book continues to evolve and improve. The end-of-chapter computer problem set is identified by the graphical icon in the text. Also, many of the solutions to various components of the Sequential Design Example utilize m-files with corresponding scripts included in the figures.

A new feature of the twelfth edition is a Skills Check section at the end of each chapter. The section is noted with a check mark icon. In each Skills Check section, we provide three sets of problems to test your knowledge of the chapter material. This includes True of False, Multiple Choice, and Word Match problems. To obtain

Preface XV

direct feedback, you can check your answers with the answer key provided at the conclusion of the end-of-chapter problems.

PEDAGOGY

The book is organized around the concepts of control system theory as they have been developed in the frequency and time domains. An attempt has been made to make the selection of topics, as well as the systems discussed in the examples and problems, modern in the best sense. Therefore, this book includes discussions on robust control systems and system sensitivity, state variable models, controllability and observability, computer control systems, internal model control, robust PID con-trollers, and computer-aided design and analysis, to name a few. However, the classi-cal topics of control theory that have proved to be so very useful in practice have been retained and expanded.

Building Basic Principles: From Classical to Modern. Our goal is to present a clear exposition of the basic principles of frequency- and time-domain design techniques. The classical methods of control engineering are thoroughly covered: Laplace trans-forms and transfer functions; root locus design; Routh-Hurwitz stability analysis; frequency response methods, including Bode, Nyquist, and Nichols; steady-state error for standard test signals; second-order system approximations; and phase and gain margin and bandwidth. In addition, coverage of the state variable method is significant. Fundamental notions of controllability and observability for state vari-able models are discussed. Full state feedback design with Ackermann's formula for pole placement is presented, along with a discussion on the limitations of state vari-able feedback. Observers are introduced as a means to provide state estimates when the complete state is not measured.

Upon this strong foundation of basic principles, the book provides many oppor-tunities to explore topics beyond the traditional. Advances in robust control theory are introduced in Chapter 12. The implementation of digital computer control sys-tems is discussed in Chapter 13. Each chapter (but the first) introduces the student to the notion of computer-aided design and analysis. The book concludes with an extensive references section, divided by chapter, to guide the student to further sources of information on control engineering.

Progressive Development of Problem-Solving Skills. Reading the chapters, attending lectures and taking notes, and working through the illustrated examples are all part of the learning process. But the real test comes at the end of the chapter with the prob-lems. The book takes the issue of problem solving seriously. In each chapter, there are five problem types:

Exercises

Problems

Q Advanced Problems

Q Design Problems

Q Computer Problems

Preface

For example, the problem set for The Root Locus Method, Chapter 7 (see page 443) includes 28 exercises, 39 problems, 14 advanced problems, 14 design problems, and 10 computer-based problems. The exercises permit the students to readily uti-lize the concepts and methods introduced in each chapter by solving relatively straightforward exercises before attempting the more complex problems. Answers to one-third of the exercises are provided. The problems require an extension of the concepts of the chapter to new situations. The advanced problems represent prob-lems of increasing complexity. The design problems emphasize the design task; the computer-based problems give the student practice with problem solving using computers. In total, the book contains more than 1000 problems. The abundance of problems of increasing complexity gives students confidence in their problem-solving ability as they work their way from the exercises to the design and computer-based problems. An instructor's manual, available to all adopters of the text for course use, contains complete solutions to all end-of-chapter problems.

A set of m-files, the Modem Control Systems Toolbox, has been developed by the authors to supplement the text. The m-files contain the scripts from each com-puter-based example in the text. You may retrieve the m-files from the companion website: www.pearsonhighered.com/dorf.

Design Emphasis without Compromising Basic Principles. The all-important topic of design of real-world, complex control systems is a major theme throughout the text. Emphasis on design for real-world applications addresses interest in design by ABET and industry.

The design process consists of seven main building blocks that we arrange into three groups:

1. Establishment of goals and variables to be controlled, and definition of specifications (metrics) against which to measure performance

2. System definition and modeling 3. Control system design and integrated system simulation and analysis

In each chapter of this book, we highlight the connection between the design process and the main topics of that chapter. The objective is to demonstrate differ-ent aspects of the design process through illustrative examples. Various aspects of the control system design process are illustrated in detail in the following examples:

Q smart grids (Section 1.9, page 28)

Q photovoltaic generators (Section 2.8, page 91) a space station orientation modeling (Section 3.8. page 193) Q blood pressure control during anesthesia (Section 4.8, page 259) Q attitude control of an airplane (Section 5.9, page 346)

Q robot-controlled motorcycle (Section 6.5, page 406)

wind turbine rotor speed control (Section 7.8, page 497) Q maximum power pointing tracking (Section 8.6, page 583) Q PID control of wind turbines (Section 9.8, page 674) Q milling machine control system (Section 10.12, page 790)


Preface xvii

Topics emphasized in this example

Shading indicates the topics that are emphasized in each chapter. Some chapters will have many shaded blocks, and other chapters will emphasize just one or two topics.

Establish the control goals

Identify the variables to be controlled

Write the specifications

In this column remarks relate the design topics on the left to specific sections, figures, equations, and tables in the example.

(1) Establishment of goals, variables to be controlled, and specifications.

1 Obtain a model of the process, the

actuator, and the sensor

~r Describe a controller and select key

parameters to be adjusted

\ ' Optimize the parameters and

analyze the performance

1

(2) System definition and modeling.

(3) Control system design, simulation, and analysis.

If the performance does not meet the specifications, then iterate the configuration.

If the performance meets the specifications, then finalize the design.

diesel electric locomotive control (Section 11.9, page 876)

digital audio tape controller (Section 12.8, page 943)

Q manufacturing worktable control (Section 13.10, page 1009)

Each chapter includes a section to assist students in utilizing computer-aided design and analysis concepts and in reworking many of the design examples. In Chapter 5, the Sequential Design Example: Disk Drive Read System is analyzed using computer-based methods. An m-file script that can be used to analyze the design is presented in Figure 5.47, p. 362. In general, each script is annotated with comment boxes that highlight important aspects of the script. The accompanying output of the script (generally a graph) also contains comment boxes pointing out significant ele-ments. The scripts can also be utilized with modifications as the foundation for solv-ing other related problems.

XViii Preface

IVet-JU, * t=[0:0.01:1]; nc=[Ka*5];dc=[1]; sysc=tf(nc,dc); ng-[1];dg-[1 20 0]; sysg-tf(ng.dg); sys1=series(sysc,sysg); ] sys=TeedbacK(sysi, pj); f * y=step(sys,t); J

plot(t,y), grid xlabeI(Time (s)') ylabelCy(ty)

Select Ka.

Compute the closed-loop

transfer function.

(a)

1.2

1

0.8

0.6

0.4

0.2

0 0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1

Time (s)

(b)

Learning Enhancement. Each chapter begins with a chapter preview describing the topics the student can expect to encounter. The chapters conclude with an end-of-chapter summary, skills check, as well as terms and concepts. These sec-tions reinforce the important concepts introduced in the chapter and serve as a reference for later use.

A second color is used to add emphasis when needed and to make the graphs and figures easier to interpret. Design Problem 4.4, page 297, asks the student to de-termine the value of K of the controller so that the response, denoted by Y(s), to a step change in the position, denoted by R(s), is satisfactory and the effect of the dis-turbance, denoted by Td(s)> is minimized.The associated Figure DP4.4, p. 298, assists the student with (a) visualizing the problem and (b) taking the next step to develop the transfer function model and to complete the design.

Ka = 60.

Ka = 30.

Preface xix

Control ler

Argon laser

Laser 1

systemjl |

Fiber optics * IlidLJJI

Patient

Ophthalmologist

R(s) position

Controller

(a)

W

,- +

Camera and laser

.v(.v + 1 )(s + 4) -+Ks)

(b)

THE ORGANIZATION

Chapter 1 Introduction to Control Systems. Chapter 1 provides an introduction to the basic history of control theory and practice. The purpose of this chapter is to describe the general approach to designing and building a control system.

Chapter 2 Mathematical Models of Systems. Mathematical models of physical sys-tems in input-output or transfer function form are developed in Chapter 2. A wide range of systems (including mechanical, electrical, and fluid) are considered.

Chapter 3 State Variable Models. Mathematical models of systems in state vari-able form are developed in Chapter 3. Using matrix methods, the transient response of control systems and the performance of these systems are examined.

Chapter 4 Feedback Control System Characteristics. The characteristics of feed-back control systems are described in Chapter 4. The advantages of feedback are discussed, and the concept of the system error signal is introduced.

XX Preface

Chapter 5 The Performance of Feedback Control Systems. In Chapter 5, the per-formance of control systems is examined. The performance of a control system is correlated with the s-plane location of the poles and zeros of the transfer function of the system.

Chapter 6 The Stability of Linear Feedback Systems. The stability of feedback sys-tems is investigated in Chapter 6. The relationship of system stability to the charac-teristic equation of the system transfer function is studied. The Routh-Hurwitz stability criterion is introduced.

Chapter 7 The Root Locus Method. Chapter 7 deals with the motion of the roots of the characteristic equation in the s-plane as one or two parameters are varied. The locus of roots in the s-plane is determined by a graphical method. We also introduce the popular PID controller and the Ziegler-Nichols PID tuning method.

Chapter 8 Frequency Response Methods. In Chapter 8, a steady-state sinusoid input signal is utilized to examine the steady-state response of the system as the fre-quency of the sinusoid is varied. The development of the frequency response plot, called the Bode plot, is considered.

Chapter 9 Stability in the Frequency Domain. System stability utilizing frequency response methods is investigated in Chapter 9. Relative stability and the Nyquist criterion are discussed.

Chapter 10 The Design of Feedback Control Systems. Several approaches to designing and compensating a control system are described and developed in Chapter 10. Various candidates for service as compensators are presented and it is shown how they help to achieve improved performance.

Chapter 11 The Design of State Variable Feedback Systems. The main topic of Chapter 11 is the design of control systems using state variable models. Full-state feedback design and observer design methods based on pole placement are dis-cussed. Tests for controllability and observability are presented, and the concept of an internal model design is discussed.

Chapter 12 Robust Control Systems. Chapter 12 deals with the design of highly accurate control systems in the presence of significant uncertainty. Five methods for robust design are discussed, including root locus, frequency response, ITAE meth-ods for robust PID controllers, internal models, and pseudo-quantitative feedback.

Chapter 13 Digital Control Systems. Methods for describing and analyzing the performance of computer control systems are described in Chapter 13. The stability and performance of sampled-data systems are discussed.

Appendix A MATLAB Basics

Preface XXI

ACKNOWLEDGMENTS

We wish to express our sincere appreciation to the following individuals who have assisted us with the development of this twelfth edition, as well as all previous edi-tions: Mahmoud A. Abdallah, Central Sate University (OH); John N. Chiasson, Uni-versity of Pittsburgh; Samy El-Sawah, California State Polytechnic University, Pomona; Peter J. Gorder, Kansas State University; Duane Hanselman, University of Maine; Ashok Iyer, University of Nevada, Las Vegas; Leslie R. Koval, University of Missouri-Rolla; L. G. Kraft, University of New Hampshire; Thomas Kurfess, Geor-gia Institute of Technology; Julio C Mandojana, Mankato State University; Luigi Mariani, University of Padova; Jure Medanic, University of Illinois at Urbana-Champaign; Eduardo A. Misawa, Oklahoma State University; Medhat M. Morcos, Kansas State University; Mark Nagurka, Marquette University; D. Subbaram Naidu, Idaho State University; Ron Perez, University of Wisconsin-Milwaukee; Carla Schwartz, The MathWorks, Inc.; Murat Tanyel, Dordt College; Hal Tharp, University of Arizona; John Valasek, Texas A & M University; Paul P. Wang, Duke University; and Ravi Warrier, GMI Engineering and Management Institute.

OPEN LINES OF COMMUNICATION

The authors would like to establish a line of communication with the users of Modern Control Systems. We encourage all readers to send comments and sugges-tions for this and future editions. By doing this, we can keep you informed of any general-interest news regarding the textbook and pass along comments of other users.

Keep in touch!

Richard C. Dorf Robert H. Bishop

[email protected] rhbishop @ marquette.edu

mailto:[email protected]://marquette.edu

About the Authors

Richard C. Dorf is a Professor of Electrical and Computer Engineering at the Uni-versity of California, Davis. Known as an instructor who is highly concerned with the discipline of electrical engineering and its application to social and economic needs, Professor Dorf has written and edited several successful engineering text-books and handbooks, including the best selling Engineering Handbook, second edition and the third edition of the Electrical Engineering Handbook. Professor Dorf is also co-author of Technology Ventures, a leading textbook on technology entrepreneurship. Professor Dorf is a Fellow of the IEEE and a Fellow of the ASEE. He is active in the fields of control system design and robotics. Dr. Dorf holds a patent for the PIDA controller.

Robert H. Bishop is the OPUS Dean of Engineering at Marquette University. Prior to coming to Marquette University, he was a Professor of Aerospace Engineering and Engineering Mechanics at The University of Texas at Austin for 20 years where he held the Joe J. King Professorship and was a Distinguished Teaching Professor. Professor Bishop started his engineering career as a member of the tech-nical staff at the MIT Charles Stark Draper Laboratory. He authors the well-known textbook for teaching graphical programming entitled Learning with LabVIEW and is also the editor-in-chief of the Mechatronics Handbook. A talented educator, Pro-fessor Bishop has been recognized with numerous teaching awards including the coveted Lockheed Martin Tactical Aircraft Systems Award for Excellence in Engi-neering Teaching. He also received the John Leland Atwood Award by the Ameri-can Society of Engineering Educators (ASEE) and the American Institute of Aeronautics and Astronautics (AIAA) that is given periodically to "a leader who has made lasting and significant contributions to aerospace engineering education." He is a Fellow of the AIAA, a Fellow of the American Astronautical Society (AAS), and active in ASEE and in the Institute of Electrical and Electronics Engineers (IEEE).

xxii

C HAPTE R Introduction to Control 1 Systems 1.1

1.2

1.3

1.4

1.5

1.6

1.7

1.8

1.9

1.10

1.11

Introduction 2

Brief History of Automatic Control 5

Examples of Control Systems 10

Engineering Design 17

Control System Design 18

Mechatronic Systems 21

Green Engineering 25

The Future Evolution of Control Systems 27

Design Examples 28

Sequential Design Example: Disk Drive Read System 32

Summary 34

PREVIEW

In this chapter, we discuss open- and closed-loop feedback control systems. A con-trol system consists of interconnected components to achieve a desired purpose. We examine examples of control systems through the course of history. These early sys-tems incorporated many of the same ideas of feedback that are employed in modern manufacturing processes, alternative energy, complex hybrid automobiles, and so-phisticated robots. A design process is presented that encompasses the establish-ment of goals and variables to be controlled, definition of specifications, system definition, modeling, and analysis. The iterative nature of design allows us to handle the design gap effectively while accomplishing necessary trade-offs in complexity, performance, and cost. Finally, we introduce the Sequential Design Example: Disk Drive Read System. This example will be considered sequentially in each chapter of this book. It represents a very important and practical control system design problem while simultaneously serving as a useful learning tool.

DESIRED OUTCOMES

Upon completion of Chapter 1, students should:

Possess a basic understanding of control system engineering and be able to offer some illustrative examples and their relationship to key contemporary issues.

Q Be able to recount a brief history of control systems and their role in society.

Be capable of discussing the future of controls in the context of their evolution-ary pathways.

G Recognize the elements of control system design and possess an appreciation of controls in the context of engineering design.

1

2 Chapter 1 Introduction to Control Systems

1.1 INTRODUCTION

Engineering is concerned with understanding and controlling the materials and forces of nature for the benefit of humankind. Control system engineers are con-cerned with understanding and controlling segments of their environment, often called systems, to provide useful economic products for society. The twin goals of understanding and controlling are complementary because effective systems con-trol requires that the systems be understood and modeled. Furthermore, control en-gineering must often consider the control of poorly understood systems such as chemical process systems. The present challenge to control engineers is the model-ing and control of modern, complex, interrelated systems such as traffic control sys-tems, chemical processes, and robotic systems. Simultaneously, the fortunate engineer has the opportunity to control many useful and interesting industrial au-tomation systems. Perhaps the most characteristic quality of control engineering is the opportunity to control machines and industrial and economic processes for the benefit of society.

Control engineering is based on the foundations of feedback theory and linear system analysis, and it integrates the concepts of network theory and communica-tion theory. Therefore control engineering is not limited to any engineering disci-pline but is equally applicable to aeronautical, chemical, mechanical, environmental, civil, and electrical engineering. For example, a control system often includes elec-trical, mechanical, and chemical components. Furthermore, as the understanding of the dynamics of business, social, and political systems increases, the ability to control these systems will also increase.

A control system is an interconnection of components forming a system configu-ration that will provide a desired system response. The basis for analysis of a system is the foundation provided by linear system theory, which assumes a cause-effect re-lationship for the components of a system. Therefore a component or process to be controlled can be represented by a block, as shown in Figure 1.1. The input-output relationship represents the cause-and-effect relationship of the process, which in turn represents a processing of the input signal to provide an output signal variable, often with a power amplification. An open-loop control system uses a controller and an ac-tuator to obtain the desired response, as shown in Figure 1.2. An open-loop system is a system without feedback.

An open-loop control system utilizes an actuating device to control the process directly without using feedback.

FIGURE 1.1 Process to be controlled.

Input Process Output

FIGURE 1.2 Open-loop control system (without feedback).

Desired output response

Controller Actuator Process Output

Section 1.1 Introduction 3

FIGURE 1.3 Closed-loop feedback control system (with feedback).

Desired output response

Controller Actuator Process

Measurement output Sensor

Actual output

Feedback

In contrast to an open-loop control system, a closed-loop control system utilizes an additional measure of the actual output to compare the actual output with the desired output response. The measure of the output is called the feedback signal. A simple closed-loop feedback control system is shown in Figure 1.3. A feedback con-trol system is a control system that tends to maintain a prescribed relationship of one system variable to another by comparing functions of these variables and using the difference as a means of control. With an accurate sensor, the measured output is a good approximation of the actual output of the system.

A feedback control system often uses a function of a prescribed relationship be-tween the output and reference input to control the process. Often the difference between the output of the process under control and the reference input is amplified and used to control the process so that the difference is continually reduced. In gen-eral, the difference between the desired output and the actual output is equal to the error, which is then adjusted by the controller. The output of the controller causes the actuator to modulate the process in order to reduce the error. The sequence is such, for instance, that if a ship is heading incorrectly to the right, the rudder is actuated to direct the ship to the left. The system shown in Figure 1.3 is a negative feedback con-trol system, because the output is subtracted from the input and the difference is used as the input signal to the controller. The feedback concept has been the founda-tion for control system analysis and design.

A closed-loop control system uses a measurement of the output and feedback of this signal to compare it with the desired output (reference or command).

As we will discuss in Chapter 4, closed-loop control has many advantages over open-loop control including the ability to reject external disturbances and improve measurement noise attenuation. We incorporate the disturbances and measurement noise in the block diagram as external inputs, as illustrated in Figure 1.4. External disturbances and measurement noise are inevitable in real-world applications and must be addressed in practical control system designs.

FIGURE 1.4 Closed-loop feedback system with external disturbances and

noise.

Desired output ^ response A

- Error Controller

Disturbance

Mea surcmcnt o utput

Actuator Process

Feedback

^ Actual output

K Measurement - + noise

4 Chapter 1 Introduction to Control Systems

Desired output response Controller #2 ( " }

Error Controller #1 Actuator Process

Measurement output Sensor #1

I

Feedback

Measurement output Sensor #2

Actual output

Feedback

FIGURE 1.5 Multiloop feedback system with an inner loop and an outer loop.

The feedback systems in Figures 1.3 and 1.4 are single-loop feedback systems. Many feedback control systems contain more than one feedback loop. A common multi-loop feedback control system is illustrated in Figure 1.5 with an inner loop and an outer loop. In this scenario, the inner loop has a controller and a sensor and the outer loop has a controller and sensor. Other varieties of multiloop feedback sys-tems are considered throughout the book as they represent more practical situa-tions found in real-world applications. However, we use the single-loop feedback system for learning about the benefits of feedback control systems since the out-comes readily extend to multiloop systems.

Due to the increasing complexity of the system under control and the interest in achieving optimum performance, the importance of control system engineering has grown in the past decade. Furthermore, as the systems become more complex, the in-terrelationship of many controlled variables must be considered in the control scheme. A block diagram depicting a multivariable control system is shown in Figure 1.6.

A common example of an open-loop control system is a microwave oven set to operate for a fixed time. An example of a closed-loop control system is a person steering an automobile (assuming his or her eyes are open) by looking at the auto's location on the road and making the appropriate adjustments.

The introduction of feedback enables us to control a desired output and can im-prove accuracy, but it requires attention to the issue of stability of response.

Desired output

response Comparison

4 L 1 i i L

Error

Controller

N /leasure ment output

Actuator

Sensor

Process

Fcedbac k.

Actual output

FIGURE 1.6 Multivariable control system.

Section 1.2 Brief History of Automatic Control

1.2 BRIEF HISTORY OF AUTOMATIC CONTROL

5

The use of feedback to control a system has a fascinating history. The first applications of feedback control appeared in the development of float regulator mechanisms in Greece in the period 300 to 1 B.C. [1, 2.31 The water clock of Ktesibios used a float regulator (refer to Problem PI.11). An oil lamp devised by Philon in approximately 250 B.C. used a float regulator in an oil lamp for maintaining a constant level of fuel oil. Heron of Alexandria, who lived in the first century A.D., published a book entitled Pneumatics, which outlined several forms of water-level mechanisms using float regulators [1].

The first feedback system to be invented in modern Europe was the tempera-ture regulator of Cornelis Drebbel (1572-1633) of Holland [1]. Dennis Papin (1647-1712) invented the first pressure regulator for steam boilers in 1681. Papin's pressure regulator was a form of safety regulator similar to a pressure-cooker valve.

The first automatic feedback controller used in an industrial process is generally agreed to be James Watt's flyball governor, developed in 1769 for controlling the speed of a steam engine [1.2]. The all-mechanical device, shown in Figure 1.7, mea-sured the speed of the output shaft and utilized the movement of the flyball to con-trol the steam valve and therefore the amount of steam entering the engine. As depicted in Figure 1.7, the governor shaft axis is connected via mechanical linkages and beveled gears to the output shaft of the steam engine. As the steam engine out-put shaft speed increases, the ball weights rise and move away from the shaft axis and through mechanical linkages the steam valve closes and the engine slows down.

The first historical feedback system, claimed by Russia, is the water-level float regulator said to have been invented by I. Polzunov in 1765 [4]. The level regulator system is shown in Figure l.S.The float detects the water level and controls the valve that covers the water inlet in the boiler.

The next century was characterized by the development of automatic control systems through intuition and invention. Efforts to increase the accuracy of the

FIGURE 1.7 Watt's flyball governor.

Shaft axis

Mewl ball

Measured Boiler

Output shaft

Engine

6

FIGURE 1.8 Water-level float regulator.

Chapter 1 Introduction to Control Systems

Water

Float

Valvt

control system led to slower attenuation of the transient oscillations and even to unstable systems. It then became imperative to develop a theory of automatic con-trol. In 1868, J. C. Maxwell formulated a mathematical theory related to control theory using a differential equation model of a governor [5]. Maxwell's study was concerned with the effect various system parameters had on the system perfor-mance. During the same period, I. A. Vyshnegradskii formulated a mathematical theory of regulators [6].

Prior to World War II, control theory and practice developed differently in the United States and western Europe than in Russia and eastern Europe. The main im-petus for the use of feedback in the United States was the development of the tele-phone system and electronic feedback amplifiers by Bode, Nyquist, and Black at Bell Telephone Laboratories [7-10,12].

Harold S. Black graduated from Worcester Polytechnic Institute in 1921 and joined Bell Laboratories of American Telegraph and Telephone (AT&T). In 1921, the major task confronting Bell Laboratories was the improvement of the telephone system and the design of improved signal amplifiers. Black was assigned the task of linearizing, stabilizing, and improving the amplifiers that were used in tandem to carry conversations over distances of several thousand miles.

Black reports [8]:

Then came the morning of Tuesday, August 2,1927, when the concept of the negative feedback amplifier came to me in a flash while I was crossing the Hudson River on the Lackawanna Ferry, on my way to work. For more than 50 years I have pondered how and why the idea came, and I can't say any more today than I could that morning. All I know is that after several years of hard work on the problem, I suddenly realized that if I fed the amplifier output back to the input, in reverse phase, and kept the device from oscillating (singing, as we called it then), 1 would have exactly what I wanted: a means of canceling out the distortion in the output. I opened my morning newspaper and on a page of The New York Times I sketched a simple canonical diagram of a negative feed-back amplifier plus the equations for the amplification with feedback. I signed the sketch, and 20 minutes later, when I reached the laboratory at 463 West Street, it was witnessed, understood, and signed by the late Earl C. Blessing.

I envisioned this circuit as leading to extremely linear amplifiers (40 to 50 dB of negative feedback), but an important question is: How did I know I could avoid

Section 1.2 Brief History of Automatic Control 7

self-oscillations over very wide frequency bands when many people doubted such cir-cuits would be stable? My confidence stemmed from work that I had done two years earlier on certain novel oscillator circuits and three years earlier in designing the termi-nal circuits, including the filters, and developing the mathematics for a carrier telephone system for short toll circuits.

The frequency domain was used primarily to describe the operation of the feed-back amplifiers in terms of bandwidth and other frequency variables. In contrast, the eminent mathematicians and applied mechanicians in the former Soviet Union inspired and dominated the field of control theory. Therefore, the Russian theory tended to utilize a time-domain formulation using differential equations.

The control of an industrial process (manufacturing, production, and so on) by automatic rather than manual means is often called automation. Automation is prevalent in the chemical, electric power, paper, automobile, and steel industries, among others. The concept of automation is central to our industrial society. Auto-matic machines are used to increase the production of a plant per worker in order to offset rising wages and inflationary costs. Thus industries are concerned with the productivity per worker of their plants. Productivity is defined as the ratio of physi-cal output to physical input [26]. In this case, we are referring to labor productivity, which is real output per hour of work.

The transformation of the U.S. labor force in the country's brief history follows the progressive mechanization of work that attended the evolution of the agrarian republic into an industrial world power. In 1820, more than 70 percent of the labor force worked on the farm. By 1900, less than 40 percent were engaged in agriculture. Today, less than 5 percent works in agriculture [15].

In 1925, some 588,000 peopleabout 1.3 percent of the nation's labor force were needed to mine 520 million tons of bituminous coal and lignite, almost all of it from underground. By 1980, production was up to 774 million tons, but the work force had been reduced to 208,000. Furthermore, only 136,000 of that number were employed in underground mining operations. The highly mechanized and highly productive surface mines, with just 72,000 workers, produced 482 million tons, or 62 percent of the total [27].

A large impetus to the theory and practice of automatic control occurred during World War II when it became necessary to design and construct automatic airplane piloting, gun-positioning systems, radar antenna control systems, and other military systems based on the feedback control approach. The complexity and expected per-formance of these military systems necessitated an extension of the available con-trol techniques and fostered interest in control systems and the development of new insights and methods. Prior to 1940, for most cases, the design of control systems was an art involving a trial-and-error approach. During the 1940s, mathematical and an-alytical methods increased in number and utility, and control engineering became an engineering discipline in its own right [10-12].

Another example of the discovery of an engineering solution to a control system problem was the creation of a gun director by David B. Parkinson of Bell Telephone Laboratories. In the spring of 1940, Parkinson was a 29-year-old engineer intent on improving the automatic level recorder, an instrument that used strip-chart paper to plot the record of a voltage. A critical component was a small potentiometer used to control the pen of the recorder through an actuator.


Parkinson had a dream about an antiaircraft gun that was successfully felling airplanes. Parkinson described the situation [13]:

After three or four shots one of the men in the crew smiled at me and beckoned me to come closer to the gun. When I drew near he pointed to the exposed end of the left trunnion. Mounted there was the control potentiometer of my level recorder!

The next morning Parkinson realized the significance of his dream:

If my potentiometer could control the pen on the recorder, something similar could, with suitable engineering, control an antiaircraft gun.

After considerable effort, an engineering model was delivered for testing to the U.S. Army on December 1, 1941. Production models were available by early 1943, and eventually 300() gun controllers were delivered. Input to the controller was pro-vided by radar, and the gun was aimed by taking the data of the airplane's present position and calculating the target's future position.

Frequency-domain techniques continued to dominate the field of control follow-ing World War II with the increased use of the Laplace transform and the complex fre-quency plane. During the 1950s, the emphasis in control engineering theory was on the development and use of the s-plane methods and, particularly, the root locus ap-proach. Furthermore, during the 1980s, the use of digital computers for control com-ponents became routine. The technology of these new control elements to perform accurate and rapid calculations was formerly unavailable to control engineers. There are now over 400,000 digital process control computers installed in the United States [14, 27]. These computers are employed especially for process control systems in which many variables are measured and controlled simultaneously by the computer.

With the advent of Sputnik and the space age, another new impetus was imparted to control engineering. It became necessary to design complex, highly accurate control systems for missiles and space probes. Furthermore, the necessity to minimize the weight of satellites and to control them very accurately has spawned the important field of optimal control. Due to these requirements, the time-domain methods devel-oped by Liapunov, Minorsky, and others have been met with great interest in the last two decades. Recent theories of optimal control developed by L. S. Pontryagin in the former Soviet Union and R. Bellman in the United States, as well as recent studies of robust systems, have contributed to the interest in time-domain methods. It now is clear that control engineering must consider both the time-domain and the frequency-domain approaches simultaneously in the analysis and design of control systems.

A notable recent advance with worldwide impact is the U.S. space-based ra-dionavigation system known as the Global Positioning System or GPS [82-85]. In the distant past, various strategies and sensors were developed to keep explorers on the oceans from getting lost, including following coastlines, using compasses to point north, and sextants to measure the angles of stars, the moon, and the sun above the horizon. The early explorers were able to estimate latitude accurately, but not longi-tude. It was not until the 1700s with the development of the chronometer that, when used with the sextant, the longitude could be estimated. Radio-based navigation sys-tems began to appear in the early twentieth century and were used in World War II. With the advent of Sputnik and the space age, it became known that radio signals from satellites could be used to navigate on the ground by observing the Doppler shift of the received radio signals. Research and development culminated in the

Section 1.2 Brief History of Automatic Control 9

1990s with 24 navigation satellites (known as the GPS) that solved the fundamental problem that explorers faced for centuries by providing a dependable mechanism to pinpoint the current location. Freely available on a continuous worldwide basis, GPS provides very reliable location and time information anytime, day or night, anywhere in the world. Using GPS as a sensor to provide position (and velocity) in-formation is a mainstay of active control systems for transportation systems in the air, on the ground, and on the oceans. The GPS assists relief and emergency workers to save lives, and helps us with our everyday activities including the control of power grids, banking, farming, surveying, and many other tasks.

A selected history of control system development is summarized in Table 1.1.

Table 1.1 Selected Historical Developments of Control Systems 1769 James Watt's steam engine and governor developed. The Watt steam engine

is often used to mark the beginning of the Industrial Revolution in Great Britain. During the Industrial Revolution, great strides were made in the development of mechanization, a technology preceding automation.

1800 Eli Whitney's concept of interchangeable parts manufacturing demonstrated in the production of muskets. Whitney's development is often considered to be the beginning of mass production.

1868 J. C. Maxwell formulates a mathematical model for a governor control of a steam engine.

1913 Henry Ford's mechanized assembly machine introduced for automobile production.

1927 H. S. Black conceives of the negative feedback amplifier and H. W. Bode analyzes feedback amplifiers.

1932 H. Nyquist develops a method for analyzing the stability of systems. 1941 Creation of first antiaircraft gun with active control. 1952 Numerical control (NC) developed at Massachusetts Institute of Technology

for control of machine-tool axes. 1954 George Devol develops "programmed article transfer," considered to be the

first industrial robot design. 1957 Sputnik launches the space age leading, in time, to miniaturization of

computers and advances in automatic control theory. 1960 First Unimate robot introduced, based on Devol's designs. Unimate

installed in 1961 for tending die-casting machines. 1970 State-variable models and optimal control developed. 1980 Robust control system design widely studied. 1983 Introduction of the personal computer (and control design software soon

thereafter) brought the tools of design to the engineer's desktop. 1990 Export-oriented manufacturing companies emphasize automation. 1994 Feedback control widely used in automobiles. Reliable, robust systems

demanded in manufacturing. 1995 The Global Positioning System (GPS) was operational providing positioning,

navigation, and timing services worldwide. 1997 First ever autonomous rover vehicle, known as Sojourner, explores the

Martian surface. 1998-2003 Advances in micro- and nanotechnology. First intelligent micromachines

are developed and functioning nanomachines are created. 2007 The Orbital Express mission performed the first autonomous space

rendezvous and docking.

1 0 Chapter 1 Introduction to Control Systems

1.3 EXAMPLES OF CONTROL SYSTEMS

Control engineering is concerned with the analysis and design of goal-oriented sys-tems. Therefore the mechanization of goal-oriented policies has grown into a hierarchy of goal-oriented control systems. Modern control theory is concerned with systems that have self-organizing, adaptive, robust, learning, and optimum qualities.

Feedback control is a fundamental fact of modern industry and society. Driving an automobile is a pleasant task when the auto responds rapidly to the driver's com-mands. Many cars have power steering and brakes, which utilize hydraulic ampli-fiers for amplification of the force to the brakes or the steering wheel. A simple block diagram of an automobile steering control system is shown in Figure 1.9(a).

Desired course

of travel o Error Driver Steeri ng mechiinism Automobile

Measurement, visual and tactile

Actual + course

of travel

(a)

SL' \ Desired direction

Actual ~~ of travel direction of travel

(b)

FIGURE 1.9 (a) Automobile steering control system, (b) The driver uses the difference between the actual and the desired direction of travel to generate a controlled adjustment of the steering wheel, (c) Typical direction-of-travel response.

Desired direction of travel Actual direction of travel

Section 1.3 Examples of Control Systems 11

The desired course is compared with a measurement of the actual course in order to generate a measure of the error, as shown in Figure 1.9(b). This measurement is ob-tained by visual and tactile (body movement) feedback, as provided by the feel of the steering wheel by the hand (sensor). This feedback system is a familiar version of the steering control system in an ocean liner or the flight controls in a large air-plane. A typical dircction-of-travel response is shown in Figure 1.9(c).

A basic, manually controlled closed-loop system for regulating the level of fluid in a tank is shown in Figure 1.10. The input is a reference level of fluid that the op-erator is instructed to maintain. (This reference is memorized by the operator.) The power amplifier is the operator, and the sensor is visual. The operator compares the actual level with the desired level and opens or closes the valve (actuator), adjusting the fluid flow out. to maintain the desired level.

Other familiar control systems have the same basic elements as the system shown in Figure 1.3. A refrigerator has a temperature setting or desired temperature, a thermostat to measure the actual temperature and the error, and a compressor motor for power amplification. Other examples in the home are the oven, furnace, and water heater. In industry, there are many examples, including speed controls; process temperature and pressure controls; and position, thickness, composition, and quality controls [14,17,18].

In its modern usage, automation can be defined as a technology that uses pro-grammed commands to operate a given process, combined with feedback of infor-mation to determine that the commands have been properly executed. Automation is often used for processes that were previously operated by humans. When auto-mated, the process can operate without human assistance or interference. In fact, most automated systems are capable of performing their functions with greater ac-curacy and precision, and in less time, than humans are able to do. A semiautomated process is one that incorporates both humans and robots. For instance, many auto-mobile assembly line operations require cooperation between a human operator and an intelligent robot.

Feedback control systems are used extensively in industrial applications. Thou-sands of industrial and laboratory robots are currently in use. Manipulators can pick up objects weighing hundreds of pounds and position them with an accuracy of one-tenth of an inch or better [28]. Automatic handling equipment for home, school, and industry is particularly useful for hazardous, repetitious, dull, or simple tasks.

Fluid input

FIGURE 1.10 A manual control system for regulating the level of fluid in a tank by adjusting fne output valve. The operator views the level of fluid through a port in the side of the tank. Valve ' Fluid output


Machines that automatically load and unload, cut, weld, or cast are used by industry to obtain accuracy, safety, economy, and productivity [14,27,28,38]. The use of com-puters integrated with machines that perform tasks like a human worker has been foreseen by several authors. In his famous 1923 play, entitled R.U.R. [48], Karel Capek called artificial workers robots, deriving the word from the Czech noun roboia, meaning "work."

A robot is a computer-controlled machine and involves technology closely asso-ciated with automation. Industrial robotics can be defined as a particular field of automation in which the automated machine (that is, the robot) is designed to sub-stitute for human labor [18, 27, 33]. Thus robots possess certain humanlike charac-teristics. Today, the most common humanlike characteristic is a mechanical manipulator that is patterned somewhat after the human arm and wrist. Some de-vices even have anthropomorphic mechanisms, including what we might recognize as mechanical arms, wrists, and hands [14, 27,28]. An example of an anthropomor-phic robot is shown in Figure 1.11. We recognize that the automatic machine is well suited to some tasks, as noted in Table 1.2, and that other tasks are best carried out by humans.

Another very important application of control technology is in the control of the modern automobile [19, 20]. Control systems for suspension, steering, and engine control have been introduced. Many new autos have a four-wheel-steering system, as well as an antiskid control system.

FIGURE 1.11 The Honda P3 humanoid robot. P3 walks, climbs stairs, and turns corners. Photo courtesy of American Honda Motor, Inc.


Table 1.2 Task Difficulty: Human Versus Automatic Machine

Tasks Difficult for a Machine Tasks Difficult for a Human

Inspect seedlings in a nursery. Drive a vehicle through rugged terrain. Identify the most expensive jewels on a tray of jewels.

Inspect a system in a hot, toxic environment.

Repetitively assemble a clock. Land an airliner at night, in bad weather.

A three-axis control system for inspecting individual semiconductor wafers is shown in Figure 1.12. This system uses a specific motor to drive each axis to the de-sired position in the x-y-z-axis, respectively. The goal is to achieve smooth, accurate movement in each axis. This control system is an important one for the semiconductor manufacturing industry.

There has been considerable discussion recently concerning the gap between practice and theory in control engineering. However, it is natural that theory pre-cedes the applications in many fields of control engineering. Nonetheless, it is inter-esting to note that in the electric power industry, the largest industry in the United States, the gap is relatively insignificant. The electric power industry is primarily

v-axis motor

FIGURE 1.12 A three-axis control system for inspecting individual semiconductor wafers with a highly sensitive camera.


interested in energy conversion, control, and distribution. It is critical that computer control be increasingly applied to the power industry in order to improve the effi-cient use of energy resources. Also, the control of power plants for minimum waste emission has become increasingly important. The modern, large-capacity plants, which exceed several hundred megawatts, require automatic control systems that account for the interrelationship of the process variables and optimum power pro-duction. It is common to have 90 or more manipulated variables under coordinated control. A simplified model showing several of the important control variables of a large boiler-generator system is shown in Figure 1.13. This is an example of the im-portance of measuring many variables, such as pressure and oxygen, to provide in-formation to the computer for control calculations.

The electric power industry has used the modern aspects of control engineering for significant and interesting applications. It appears that in the process industry, the factor that maintains the applications gap is the lack of instrumentation to mea-sure all the important process variables, including the quality and composition of the product. As these instruments become available, the applications of modern control theory to industrial systems should increase measurably.

Another important industry, the metallurgical industry, has had considerable suc-cess in automatically controlling its processes. In fact, in many cases, the control theory is being fully implemented. For example, a hot-strip steel mill, which involves a $100-million investment, is controlled for temperature, strip width, thickness, and quality.

Rapidly rising energy costs coupled with threats of energy curtailment are result-ing in new efforts for efficient automatic energy management. Computer controls are used to control energy use in industry and to stabilize and connect loads evenly to gain fuel economy.

FIGURE 1.13 Coordinated control system for a boiler-generator.

Feed Valve

Feed , ^ - / Q v water v*^

Fuel

Air

Valve

Valve

Boiler


There has been considerable interest recently in applying the feedback control concepts to automatic warehousing and inventory control. Furthermore, automatic control of agricultural systems (farms) is receiving increased interest. Automatically controlled silos and tractors have been developed and tested. Automatic control of wind turbine generators, solar heating and cooling, and automobile engine perfor-mance are important modern examples [20,21].

Also, there have been many applications of control system theory to biomedical experimentation, diagnosis, prosthetics, and biological control systems [22, 23, 48]. The control systems under consideration range from the cellular level to the central nervous system and include temperature regulation and neurological, respiratory, and cardiovascular control. Most physiological control systems are closed-loop sys-tems. However, we find not one controller but rather control loop within control loop, forming a hierarchy of systems. The modeling of the structure of biological processes confronts the analyst with a high-order model and a complex structure. Prosthetic devices that aid the 46 million handicapped individuals in the United States are designed to provide automatically controlled aids to the disabled [22,27,39]. The robotic hand shown in Figure 1.14 belongs to Obrero, a humanoid robot devel-oped at MIT that is capable of sensitive manipulation. The Obrero robot is respon-sive to the properties of the object it holds and does not rely on vision as the main sensor. The hand has position and force control of the fingers employing very sensi-tive tactile sensors and series elastic actuators in its joints.

Finally, it has become interesting and valuable to attempt to model the feedback processes prevalent in the social, economic, and political spheres. This approach is undeveloped at present but appears to have a reasonable future. Society, of course, is composed of many feedback systems and regulatory bodies, such as the Federal Reserve Board, which are controllers exerting the forces on society necessary to main-tain a desired output. A simple lumped model of the national income feedback con-trol system is shown in Figure 1.15. This type of model helps the analyst to understand the effects of government controlgranted its existenceand the dynamic effects of

(a) Computer-aided drawing (Courtesy of Eduaido Torres-Jara). (b) The Obrero robotic hand (Photo by Iuliu Vasilescu).

FIGURE 1.14 The Obrero robot is responsive to the properties of the object it holds and does not rely on vision as the main sensor but as a complement. Obrero is part of the Humanoid Robotics Group at the MIT Computer Science and Artificial Intelligence Laboratory.


Private business investment

FIGURE 1.15 A feedback control system model of the national income.

Desired + national K^_/" income

Government Government

spending

Measurement

Business production

National

Consumer spending

Consumers

Tax collections

government spending. Of course, many other loops not shown also exist, since, theo-retically, government spending cannot exceed the tax collected without generating a deficit, which is itself a control loop containing the Internal Revenue Service and the Congress. In a socialist country, the loop due to consumers is de-emphasized and gov-ernment control is emphasized. In that case, the measurement block must be accu-rate and must respond rapidly; both are very difficult characteristics to realize from a bureaucratic system. This type of political or social feedback model, while usually nonrigorous, does impart information and understanding.

The ongoing area of research and development of unmanned aerial vehicles (UAVs) is full of potential for the application of control systems. An example of a UAV is shown in Figure 1.16. UAVs are unmanned but are usually controlled by ground operators. Typically they do not operate autonomously and their inability to provide the level of safety of a manned plane keeps them from flying freely in the commercial airspace. One significant challenge is to develop control systems that will avoid in-air collisions. Ultimately, the goal is to employ the UAV autonomously in such applications as aerial photography to assist in disaster mitigation, survey

FIGURE 1.16 An unmanned aerial vehicle. (Used with permission. Credit: DARPA.)

Section 1.4 Engineering Design 17

work to assist in construction projects, crop monitoring, and continuous weather monitoring. In a military setting, UAVs can perform intelligence, surveilUmce, and reconnaissance missions [74]. Smart unmanned aircraft will require significant deployment of advanced control systems throughout the airframe.

1.4 ENGINEERING DESIGN

Engineering design is the central task of the engineer. It is a complex process in which both creativity and analysis play major roles.

Design is the process of conceiving or inventing the forms, parts, and details of a system to achieve a specified purpose.

Design activity can be thought of as planning for the emergence of a particu-lar product or system. Design is an innovative act whereby the engineer creatively uses knowledge and materials to specify the shape, function, and material content of a system. The design steps are (1) to determine a need arising from the values of various groups, covering the spectrum from public policy makers to the con-sumer; (2) t

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