Magnetic Actuators and Sensors E-Book

John R. Brauer

• Herausgeber: John Wiley & Sons
• Kategorie: Fachliteratur
• Sprache: Englisch

Seitenzahl: 480

Veröffentlichungsjahr: 2014

Beschreibung

A fully updated, easy-to-read guide on magnetic actuators and sensors The Second Edition of this must-have book for today's engineers includes the latest updates and advances in the field of magnetic actuators and sensors. Magnetic Actuators and Sensors emphasizes computer-aided design techniques--especially magnetic finite element analysis; offers many new sections on topics ranging from magnetic separators to spin valve sensors; and features numerous worked calculations, illustrations, and real-life applications. To aid readers in building solid, fundamental, theoretical background and design know-how, the book provides in-depth coverage in four parts: PART I: MAGNETICS * Introduction * Basic Electromagnetics * Reluctance Method * Finite-Element Method * Magnetic Force * Other Magnetic Performance Parameters PART II: ACTUATORS * Magnetic Actuators Operated by Direct Current * Magnetic Actuators Operated by Alternating Current * Magnetic Actuator Transient Operation PART III: SENSORS * Hall Effect and Magnetoresistive Sensors * Other Magnetic Sensors PART IV: SYSTEMS * Coil Design and Temperature Calculations * Electromagnetic Compatibility * Electromechanical Finite Elements * Electromechanical Analysis Using Systems Models * Coupled Electrohydraulic Analysis Using Systems Models With access to a support website containing downloadable software data files (including MATLAB® data files) for verifying design techniques and analytical methods, Magnetic Actuators and Sensors, Second Edition is an exemplary learning tool for practicing engineers and engineering students involved in the design and application of magnetic actuators and sensors.

Leseprobe

Contents

Cover

IEEE Press

Title Page

Copyright

Preface

Preface to the First Edition

List of 66 Examples

Part I: Magnetics

Chapter 1: Introduction

1.1 OVERVIEW OF MAGNETIC ACTUATORS

1.2 OVERVIEW OF MAGNETIC SENSORS

1.3 ACTUATORS AND SENSORS IN MOTION CONTROL SYSTEMS

1.4 MAGNETIC ACTUATORS AND SENSORS IN MECHATRONICS

REFERENCES

Chapter 2: Basic Electromagnetics

2.1 VECTORS

2.2 AMPERE'S LAW

2.3 MAGNETIC MATERIALS

2.4 FARADAY'S LAW

2.5 POTENTIALS

2.6 MAXWELL'S EQUATIONS

PROBLEMS

REFERENCES

Chapter 3: Reluctance Method

3.1 SIMPLIFYING AMPERE'S LAW

3.2 APPLICATIONS

3.3 FRINGING FLUX

3.4 COMPLEX RELUCTANCE

3.5 LIMITATIONS

PROBLEMS

REFERENCES

Chapter 4: Finite-Element Method

4.1 ENERGY CONSERVATION AND FUNCTIONAL MINIMIZATION

4.2 TRIANGULAR ELEMENTS FOR MAGNETOSTATICS

4.3 MATRIX EQUATION

4.4 FINITE-ELEMENT MODELS

PROBLEMS

REFERENCES

Chapter 5: Magnetic Force

5.1 MAGNETIC FLUX LINE PLOTS

5.2 MAGNETIC ENERGY

5.3 MAGNETIC FORCE ON STEEL

5.4 MAGNETIC PRESSURE ON STEEL

5.5 LORENTZ FORCE

5.6 PERMANENT MAGNETS

5.7 MAGNETIC TORQUE

5.8 MAGNETIC VOLUME FORCES ON PERMEABLE PARTICLES

PROBLEMS

REFERENCES

Chapter 6: Other Magnetic Performance Parameters

6.1 MAGNETIC FLUX AND FLUX LINKAGE

6.2 INDUCTANCE

6.3 CAPACITANCE

6.4 IMPEDANCE

PROBLEMS

REFERENCES

Part II: Actuators

Chapter 7: Magnetic Actuators Operated by DC

7.1 SOLENOID ACTUATORS

7.2 VOICE COIL ACTUATORS

7.3 OTHER ACTUATORS USING COILS AND PERMANENT MAGNETS

7.4 PROPORTIONAL ACTUATORS

7.5 ROTARY ACTUATORS

7.6 MAGNETIC BEARINGS AND COUPLINGS

7.7 MAGNETIC SEPARATORS

PROBLEMS

REFERENCES

Chapter 8: Magnetic Actuators Operated by AC

8.1 SKIN DEPTH

8.2 POWER LOSSES IN STEEL

8.3 FORCE PULSATIONS

8.4 CUTS IN STEEL

PROBLEMS

REFERENCES

Chapter 9: Magnetic Actuator Transient Operation

9.1 BASIC TIMELINE

9.2 SIZE, FORCE, AND ACCELERATION

9.3 LINEAR MAGNETIC DIFFUSION TIMES

9.4 NONLINEAR MAGNETIC INFUSION TIMES

9.5 NONLINEAR MAGNETIC EFFUSION TIME

9.6 PULSE RESPONSE OF NONLINEAR STEEL

PROBLEMS

REFERENCES

Part III: Sensors

Chapter 10: Hall Effect and Magnetoresistive Sensors

10.1 SIMPLE HALL VOLTAGE EQUATION

10.2 HALL EFFECT CONDUCTIVITY TENSOR

10.3 FINITE-ELEMENT COMPUTATION OF HALL FIELDS

10.4 HALL SENSORS FOR POSITION OR CURRENT

10.5 MAGNETORESISTANCE

10.6 MAGNETORESISTIVE HEADS FOR HARD DISK DRIVES

10.7 GIANT MAGNETORESISTIVE SPIN VALVE SENSORS

PROBLEMS

REFERENCES

Chapter 11: Other Magnetic Sensors

11.1 SPEED SENSORS BASED ON FARADAY'S LAW

11.2 INDUCTIVE RECORDING HEADS

11.3 PROXIMITY SENSORS USING IMPEDANCE

11.4 LINEAR VARIABLE DIFFERENTIAL TRANSFORMERS

11.5 MAGNETOSTRICTIVE SENSORS

11.6 FLUXGATE SENSORS

11.7 CHATTOCK COIL FIELD AND CURRENT SENSOR

11.8 SQUID MAGNETOMETERS

11.9 MAGNETOIMPEDANCE AND MINIATURE SENSORS

11.10 MEMS SENSORS

PROBLEMS

REFERENCES

Part IV: Systems

Chapter 12: Coil Design and Temperature Calculations

12.1 WIRE SIZE DETERMINATION FOR DC CURRENTS

12.2 COIL TIME CONSTANT AND IMPEDANCE

12.3 SKIN EFFECTS AND PROXIMITY EFFECTS FOR AC CURRENTS

12.4 FINITE-ELEMENT COMPUTATION OF TEMPERATURES

PROBLEMS

REFERENCES

Chapter 13: Electromagnetic Compatibility

13.1 SIGNAL-TO-NOISE RATIO

13.2 SHIELDS AND APERTURES

13.3 TEST CHAMBERS

PROBLEMS

REFERENCES

Chapter 14: Electromechanical Finite Elements

14.1 ELECTROMAGNETIC FINITE-ELEMENT MATRIX EQUATION

14.2 0D AND 1D FINITE ELEMENTS FOR COUPLING ELECTRIC CIRCUITS

14.3 STRUCTURAL FINITE-ELEMENT MATRIX EQUATION

14.4 FORCE AND MOTION COMPUTATION BY TIME STEPPING

14.5 TYPICAL ELECTROMECHANICAL APPLICATIONS

PROBLEMS

REFERENCES

Chapter 15: Electromechanical Analysis Using Systems Models

15.1 ELECTRIC CIRCUIT MODELS OF MAGNETIC DEVICES

15.2 VHDL–AMS/SIMPLORER MODELS

15.3 MATLAB/SIMULINK MODELS

15.4 INCLUDING EDDY CURRENT DIFFUSION USING A RESISTOR

15.5 MAGNETIC ACTUATOR SYSTEMS FOR 2D PLANAR MOTION

15.6 OPTIMIZING MAGNETIC ACTUATOR SYSTEMS

PROBLEMS

REFERENCES

Chapter 16: Coupled Electrohydraulic Analysis Using Systems Models

16.1 COMPARING HYDRAULICS AND MAGNETICS

16.2 HYDRAULIC BASICS AND ELECTRICAL ANALOGIES

16.3 MODELING HYDRAULIC CIRCUITS IN SPICE

16.4 ELECTROHYDRAULIC MODELS IN SPICE AND SIMPLORER

16.5 HYDRAULIC VALVES AND CYLINDERS IN SYSTEMS MODELS

16.6 MAGNETIC DIFFUSION RESISTOR IN ELECTROHYDRAULIC MODELS

16.7 OPTIMIZATION OF AN ELECTROHYDRAULIC SYSTEM

16.8 MAGNETIC ACTUATORS FOR DIGITAL HYDRAULICS

PROBLEMS

REFERENCES

Appendix A: Symbols, Dimensions, and Units

Appendix B: Nonlinear B–H Curves

Appendix C: Final Answers for Odd-Numbered Problems

Index

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IEEE Press Editorial Board

John Anderson, Editor in Chief

Linda Shafer          Saeid Nahavandi      George Zobrist

George W. Arnold     Om P. Malik               Tariq Samad

Ekram Hossain      Mary Lanzerotti      Dmitry Goldgof

Kenneth Moore, Director of IEEE Book and Information Services (BIS)

Technical Reviewers

Mark Solveson, ANSYS Corporation

Mark A. Juds, Eaton Corporation

Yogeshwarsing Calleecharan, Ph.D.

Copyright © 2014 by The Institute of Electrical and Electronics Engineers, Inc.

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Library of Congress Cataloging-in-Publication Data:

Brauer, John R., 1943–  Magnetic actuators and sensors / John R. Brauer. – Second edition.   pages cm  ISBN 978-1-118-50525-0 (hardback) 1. Actuators. 2. Detectors. I. Title.  TJ223.A25B73 2013  621.34–dc23

2013018187

PREFACE

Since the publication of this book 7 years ago, I have received hundreds of emails from dozens of readers. I would like to thank all of you for your feedback. Your thoughtful questions, helpful suggestions, and many minor corrections have encouraged me to undertake an improved second edition.

Another important reason for a second edition is that considerable progress has been made over the past 7 years in the analysis and design of magnetic actuators and sensors. Accordingly, this edition has a number of added sections to cover new material. Other changes over the past 7 years include the availability of software products. While the free version of Maxwell software (Maxwell SV, a subset of Maxwell version 9) can no longer be downloaded, the Maxwell files used in both the editions still function in the commercial Maxwell version 16 now sold by ANSYS, Inc. Two free magnetic finite-element software products currently available are mentioned in Chapter 4.

Additions for the second edition are summarized here. In Part I, Chapter 1 has a new section on mechatronics and added figures. Chapter 2 adds magnetization and magnetization curve material. Chapter 3 has a new large figure comparing various types of circuits. Chapter 4 updates available finite-element software. Chapter 5 has new material on Halbach magnets, and a new section on magnetic volume forces on permeable particles.

In Part II, Chapter 7 has two new sections, one on magnetic bearings and one on magnetic separators. Chapter 9 has its Section 9.3 greatly expanded to begin with Maxwell's equations. It also has a new large section added on magnetic infusion and effusion.

In Part III, Chapter 10 has a new figure on the range of magnetic field magnitudes, new material on encoders and current sensors, and a new section on GMR spin valve sensors. Chapter 11 has four new sections: Chattock coils, SQUID magnetometers, magnetoimpedance and miniature sensors, and MEMS sensors.

In Part IV, Chapter 14 clarifies both its electromagnetic and mechanical sections, and it ends with new material on reciprocating linear actuators. Chapter 15 has a new frequency domain analysis, a new section on actuators for 2D planar motion, and a new final section containing two detailed examples of optimization of magnetic actuators and systems. Chapter 16 adds new sections on optimizing an electrohydraulic system and on digital hydraulic valves. Finally, Appendix A has been expanded and new Appendices B and C have been added. Files for all examples in this book now appear at http://booksupport.wiley.com.

I thank all of my colleagues over many decades for their friendship and help, and I would like to especially thank the following for their contributions to this second edition. Mark Juds has contributed material including the B–H data of Appendix B. Mark Solveson is the first author of the design optimization studies added to Chapters 15 and 16. The reviewers of both editions made many helpful suggestions which I have endeavored to fulfill. Also I would like to thank my wife, Susan, for again reading aloud every word of this edition and suggesting changes for clarity. Finally, this year marks the 100th anniversary of the birth of my mother, Elizabeth, who taught me many good things including her love of books. I hope this book helps the next generation of engineers.

JOHN R. BRAUER

[email protected]; http://johnrbrauer.com

Fish Creek, Wisconsin

PREFACE TO THE FIRST EDITION

This book is written for practicing engineers and engineering students involved with the design or application of magnetic actuators and sensors. The reader should have completed at least one basic course in electrical engineering and/or mechanical engineering. This book is suitable for engineering college juniors, seniors, and graduate students.

IEEE societies whose members will be interested in this book include the Magnetics Society, Computer Society, Power Engineering Society, Industry Applications Society, and Control System Society. Readers of the IEEE/ASME Transactions on Mechatronics, sponsored by the IEEE Industrial Electronics Society, may also want to read this book. Many members of the Society of Automotive Engineers (SAE) might also be very interested in this book because the magnetic devices discussed here are commonly used in automobiles and aircraft.

This book is a suitable text for upper-level engineering undergraduates or graduate students in courses with titles such as “Actuators and Sensors” or “Mechatronics.” It can also serve as a supplementary text for courses such as “Electromagnetic Fields,” “Electromechanical Energy Conversion,” or “Feedback Control Systems.” It is also appropriate as a reference book for “Senior Projects” in electrical and mechanical engineering. Its basic material has been used in a 16-hour seminar for industry that I have taught many times at the Milwaukee School of Engineering. More than twice as many class hours, however, will be required to thoroughly cover the contents of this book.

The chapters on magnetic actuators are intended to replace a venerable book by Herbert C. Roters, Electromagnetic Devices, published by John Wiley & Sons in 1941. Over the decades since 1941, many technological revolutions have occurred. Perhaps, the most wide-ranging revolution has been the rise of the modern computer. The computer not only uses magnetic actuators and sensors in its disk drives and external interfaces but also enables new ways of analyzing and designing magnetic devices. Hence this book includes the latest computer-aided engineering methods from the most recently published technical papers. The latest software tools are used, especially the electromagnetic finite-element software package Maxwell SV, which are available to students at no charge from Ansoft Corporation, for which I am a part-time consultant. Other software tools used include SPICE, MATLAB, and Simplorer. Simplorer SV, the student version, is also available to students free of charge from Ansoft Corporation. If desired, the reader can work the computational examples and problems with other available software packages, which should yield similar results. To download Maxwell SV and Simplorer SV along with their example files, please visit the website for this book:

ftp://ftp.wiley.com/public/sci_tech_med/magnetic_actuators/

This book is divided into four parts, each containing several chapters. Part I, on magnetics, begins with an introductory chapter defining magnetic actuators and sensors and why they are important. The second chapter is a review of basic electromagnetics, needed because magnetic fields are the key to understanding magnetic actuators and sensors. Chapter 3 is on the reluctance method, a way to approximately calculate magnetic fields by hand. Chapter 4 covers the finite-element method, which calculates magnetic fields very accurately via the computer. Magnetic force is a required output of magnetic actuators and is discussed in Chapter 5, and other magnetic performance parameters are the subject of Chapter 6.

Part II is on actuators. Chapter 7 discusses direct current (DC) actuators, while Chapter 8 deals with alternating current (AC) actuators. The last chapter devoted strictly to magnetic actuators is Chapter 9, on their transient operation.

Part III of the book is on sensors. Chapter 10 describes in detail the Hall effect and magnetoresistance, and applies these principles to sensing position. Chapter 11 covers many other types of magnetic sensors. However, types of sensors involving quantum effects are not included, because quantum theory is beyond the scope of this book.

Part IV of the book, on systems, covers many system aspects common to both magnetic actuators and sensors. Chapter 12 presents coil design and temperature calculations. Electromagnetic compatibility issues common to sensors and actuators are discussed in Chapter 13. Electromechanical performance is analyzed in Chapter 14 using coupled finite elements, while Chapter 15 uses electromechanical system software. Finally, Chapter 16 shows the advantages of electrohydraulic systems that incorporate magnetic actuators and/or sensors. Many examples are presented throughout the book because my teaching experience has shown that they are vital to learning. The examples that are numbered are simple enough to be fully described, solved, and repeated by the reader. In addition, problems at the end of the chapters enable the reader to progress beyond the solved examples.

I would like to thank the many engineers whom I have known for making this book possible. Starting with my father, Robert C. Brauer PE, it has been my great pleasure to work with you for many decades. I thank my wife, Susan McCord Brauer, for her encouragement and advice on writing. Thanks also go to the reviewers of this book for their many excellent suggestions. All of you have taught me many things. This book is my attempt to summarize some of what I have learned and to pass it on.

JOHN R. BRAUER

[email protected]

Fish Creek, Wisconsin

January 2006

LIST OF 66 EXAMPLES

2.1Gradient Calculations2.2Divergence and Curl of a Vector2.3Ampere’s Law at a Point and Along a Closed Path2.4Magnetic Flux Density in Various Materials Surrounding a Wire2.5Induced Voltage and Current2.6Fields from Potentials2.7Displacement Current in a Capacitor3.1Reluctance Method for “C” Steel Path with Airgap3.2Reluctance Method for Sensor with Variable Airgap4.1Matrix Equation for Two Finite Elements4.2Finite-Element Analysis of the “C” Steel Path with Airgap of Example 3.15.1Relation Between A and B for 2D Planar Problem5.2Flux Line Plot of the “C” Steel Path with Airgap of Examples 3.1 and 4.25.3Force on One Pole of the “C” Steel Path with Airgap of Examples 3.1, 4.2, and 5.25.4Force between Two Permanent Magnets6.1Finding Flux in Example 5.3 using Maxwell6.2Finding Force Given Flux Linkage Versus Current and Position6.3Finding an Inductance Matrix using Maxwell6.4Finding Capacitance using Maxwell6.5Finding an Impedance Matrix using Maxwell7.1Fluxes and Forces on Clapper Armature Solenoid of Planar Geometry7.2Fluxes and Forces on Clapper Armature Solenoid of Axisymmetric Geometry7.3Fluxes and Forces on Planar Plunger Armature Solenoid7.4Fluxes and Forces on Axisymmetric Plunger Armature Solenoid7.5Force of Voice Coil Actuator7.6Separator Using a Steel Wire7.7Force Density of a Permanent Magnet Separator on a Biomolecular Microplate8.1AC Flux Linkage and Equivalent Circuits of Solenoid of Example 7.1 with a Solid Steel Clapper8.2Fluxes and Forces on Axisymmetric Plunger Armature Solenoid of Example 7.4 with Added Shading Ring8.3Loss and Reluctance of a Cylindrical Pole with Added Radial Slots9.1Magnetic Diffusion into Linear Steel Slab During Turnon and Turnoff9.2Magnetic Infusion in Nonlinear Rectangular Inductor9.3Magnetic Infusion in Nonlinear Bessho Plunger Actuator9.4Magnetic Effusion in Nonlinear Rectangular Inductor9.5Magnetic Effusion in Nonlinear Bessho Plunger9.6Flux Rise and Fall in Conducting Slabs9.7Flux Rise and Fall in a Conducting Cylinder10.1Simple Hall Equation Applied to Semiconducting Bar10.2Hall Voltage Computed for Wide 2D Semiconductor Bar of Example 10.110.3Hall Voltage Computed for More Narrow 2D Semiconductor Bar10.4Effect of Finite Hall Electrodes on Current Flow10.5Hall Voltage Computed for Wide 3D Semiconductor Bar with Finite Hall Electrodes10.6Hall Voltage Computed for Narrower 3D Semiconductor Bar with Finite Hall Electrodes10.7Hall Sensor Output for Toothed Wheel of Example 3.211.1Speed Sensor Output for Toothed Wheel of Example 3.211.2Writing and Reading with an Inductive Head11.3Impedance of Proximity Sensor for Two Target Positions11.4Simple LVDT12.1Simple DC Coil Design at a Given Temperature12.2Skin Effect in an Isolated Conductor12.3Skin and Proximity Effects in Stator Coil with Clapper12.4Steady Thermal Conduction Computation Using Analogy to Electrostatics13.1Cylindrical Shield without and with an Aperture13.2Characteristic Impedance of Triplate14.1Constant Permeability Transformer with Impedance Loading its Secondary14.2Nonlinear Transformer Waveforms with Impedance Loading its Secondary15.1SPICE LR Model of Axisymmetric Clapper Actuator15.2Including a Speed Voltage in Example 15.115.3Simplorer VHDL–AMS Voltage Step Response of Solenoid15.4Step Response Times and Overshoot of Linear Voice Coil15.5Frequency Response of Linear Voice Coil Actuator15.6RE for Inductor of Example 9.215.7Simplorer Model of Inductor of Example 9.2 with Input Step Current and RE16.1SPICE Model of Hydraulic Circuit with Linear (Laminar) Orifices16.2SPICE Model of Hydraulic Circuit with Linear and Nonlinear (Turbulent) Orifices16.3SPICE Model of Switched Hydraulic Circuit with Hydraulic Capacitance

PART I

MAGNETICS

CHAPTER 1

Introduction

Magnetic actuators and sensors use magnetic fields to produce and sense motion. Magnetic actuators enable applied electric voltage or current signals to move objects. To sense the motion with an electric signal produced by magnetic fields, magnetic sensors are often used.

Since computers have inputs and outputs that are electrical signals, magnetic actuators and sensors are ideal for computer control of motion. Hence magnetic actuators and sensors are increasing in popularity. Motion control that was in the past accomplished by manual command is now increasingly carried out by computers with magnetic sensors as their input interface and magnetic actuators as their output interface.

Both magnetic actuators and magnetic sensors are energy conversion devices, using the energy stored in static, transient, or low frequency magnetic fields. This book is focused on these magnetic devices, not on devices using electric fields or high frequency electromagnetic fields.

1.1 OVERVIEW OF MAGNETIC ACTUATORS

Figure 1.1 is a block diagram of a magnetic actuator. Input electrical energy in the form of voltage and current is converted to magnetic energy. The magnetic energy creates a magnetic force, which produces mechanical motion over a limited range, typically along a straight line but sometimes rotating over an arc. Thus magnetic actuators convert input electrical energy into output mechanical energy. As mentioned in the caption of Figure 1.1, the blocks are often nonlinear (output not proportional to input), as will be discussed later in this book.

Figure 1.1 Block diagram of a magnetic actuator. The blocks are not necessarily linear. Both the magnetic circuit block and the force factor block are often nonlinear. The force factor block often produces a force proportional to the square of the magnetic field.

Typical magnetic actuators include the following.

Contactors, circuit breakers, and relays to control electric motors and circuits.Switchgear and relays for electric power transmission and distribution.Head positioners for computer disk drives.Loudspeakers.Fuel injectors in engines of automobiles, trucks, and locomotives.Electrohydraulic valves in airplanes, tractors, robots, automobiles, and other mobile or stationary equipment.Biomedical prosthetic devices for artificial hearts, limbs, ears, and other organs.Magnetic separators that produce forces on magnetic objects large and small, including particles smaller than a micron targeted within the human body for tumors, etc.

Since magnetic actuators produce motion over a limited range, other electromechanical energy converters with large ranges of motion are not discussed in this book. Thus electric motors that produce multiple 360° rotations are not covered here. However, “step motors” which produce only a few degrees of rotary motion are classified as magnetic actuators and are included in this book.

1.2 OVERVIEW OF MAGNETIC SENSORS

A magnetic sensor has the block diagram shown in Figure 1.2. Compared to a magnetic actuator, the energy flow is different, and the amount of energy is often much smaller. The main input is now a mechanical parameter such as position or velocity, although electrical and/or magnetic input energy is usually needed as well. Input energy is converted to magnetic field energy. The output of a magnetic sensor is an electrical signal. In many cases the signal is a voltage with very little current, and thus the output electrical energy is often very small.

Figure 1.2 Block diagram of a magnetic sensor. The blocks are not necessarily linear.

Magnetic devices that output large amounts of electrical energy are not normally classified as sensors. Hence typical generators and alternators are not discussed in this book.

Typical magnetic sensors include the following.

Proximity sensors to determine presence and location of conducting objects for factory automation, bomb or weapon detection, and petroleum exploration.Microphones that sense air motion (sound waves).Linear variable differential transformers to determine object position.Velocity sensors for antilock brakes and stability control in automobiles.Hall effect position or velocity sensors.Magnetoresistive position or field sensors.

Design of magnetic actuators and sensors involves analysis of their magnetic fields. The actuator or sensor should have geometry and materials that utilize magnetic fields to produce maximum output for minimum size and cost.

1.3 ACTUATORS AND SENSORS IN MOTION CONTROL SYSTEMS

Motion control systems can use nonmagnetic actuators and/or nonmagnetic sensors. For example, electric field devices called piezoelectrics are sometimes used as sensors instead of magnetic sensors. Other nonmagnetic sensors include global positioning system (GPS) sensors that use high frequency electromagnetic fields, radio frequency identification (RFID) tags, and optical sensors such as television cameras. Nonmagnetic actuators and sensors are not discussed in this book.

An example of a motion control system that uses both a magnetic actuator and a magnetic sensor is the computer disk drive head assembly shown in Figure 1.3. The head assembly is a magnetic sensor that senses (“reads”) not only the computer data magnetically recorded on the hard disk, but also the position (track) on the disk. To position the heads at various radii on the disk, a magnetic actuator called a voice coil actuator is used.

Figure 1.3 Typical computer disk drive head assembly. The actuator coil is the rounded triangle in the upper left. The four heads are all moved inward and outward toward the spindle hub by the magnetic force and torque on the actuator coil. Portions of the actuator and all magnetic disks are removed to allow the coil and heads to be seen.

Often the best way to control motion is to use a feedback control system as shown in Figure 1.4. Its block diagram contains both an actuator and a sensor. The sensor may be a magnetic sensor measuring position or velocity, while the actuator may be a magnetic actuator producing a magnetic force. It is found that accurate control requires an accurate sensor. Control systems books widely used by electrical and mechanical engineers describe how to analyze and design such control systems [1–4]. The system design requires mathematical models of both actuators and sensors, which will be discussed throughout this book.

Figure 1.4 Basic feedback control system which may use both a magnetic actuator and a magnetic sensor.

Another example of a magnetic actuator and a magnetic sensor is shown in Figure 1.5. It shows a tubular magnetic actuator and a magnetic Hall effect sensor packaged together to produce and sense motion along a straight line. This linear motion is accomplished without any gears or chains, thus enabling long maintenance-free life with low friction. Associated electronic controls enable precise motion control.

Figure 1.5 Magnetic actuator with built-in magnetic sensor, producing straight-line motion along its axis. Figure courtesy of Dunkermotoren Linear Systems.

1.4 MAGNETIC ACTUATORS AND SENSORS IN MECHATRONICS

The word “mechatronics” is a blend of the words mechanics and electronics [5]. Mechatronic systems contain both mechanical components and electronics with controlling software. To enable the electronics to control mechanical motion, electromechanical devices are used, often containing magnetic actuators and sensors, as shown in Figures 1.1–1.5.

Figure 1.6 depicts mechatronics as made up of four major overlapping systems [6]. The mechanical systems are controlled by electrical/electronic systems, computer systems, and control systems–-all working together. Note all four major systems have overlaps; one overlap area is called electromechanical systems. Magnetic actuators and sensors are important components of electromechanical systems.

Figure 1.6 Venn diagram showing major engineering areas in mechatronics and how they relate to magnetic actuators and sensors.

Figure 1.6 is actually a simplified picture of the overlapping and multidisciplinary or “multiphysics” nature of mechatronics. This book also deals with additional overlaps not explicitly indicated in Figure 1.6, for example, the use of computer software to analyze and design magnetic actuators and sensors. To understand mechatronic systems containing magnetic actuators and sensors, this book is ordered in parts devoted to Magnetics, then Actuators, then Sensors, and finally to the resulting Systems.

REFERENCES

1. Dorf RC, Bishop RH. Modern Control Systems, 9th ed. Upper Saddle River, NJ: Prentice-Hall Inc.; 2001.

2. Dorsey J. Continuous and Discrete Control Systems, New York: McGraw-Hill; 2002.

3. Phillips CL, Harbor RD. Feedback Control Systems, 4th ed. Upper Saddle River, NJ: Prentice-Hall Inc.; 2000.

4. Lumkes JH Jr. Control Strategies for Dynamic Systems, New York: Marcel Dekker, Inc.; 2002.

5. Cetinkunt S. Mechatronics, Hoboken, NJ: John Wiley & Sons, Inc.; 2007.

6. Kevan T. Mechatronics primer: Reinventing machine design, Desktop Engineering, February, 2009. pp. 14–16.

CHAPTER 2

Basic Electromagnetics

Study of magnetic fields provides an explanation of how magnetic actuators and sensors work. Hence this chapter presents the basic principles of electromagnetics, a subject that includes magnetic fields.

In reviewing electromagnetic theory, this chapter also introduces various parameters and their symbols. The symbols and notations used in this chapter will be used throughout the book, and most are also listed in Appendix A along with their units.

2.1 VECTORS

Magnetic fields are vectors, and thus it is useful to review mathematical operations involving vectors. A vector is defined here as a parameter having both magnitude and direction. Thus it differs from a scalar, which has only magnitude (and no direction). In this book, vectors are indicated by bold type, and scalars are indicated by italic non-bold type.

To define direction, rectangular coordinates are often used. Also called Cartesian coordinates, the position and direction are specified in terms of , and . This book denotes the three rectangular direction unit vectors as , and ; they all have magnitude equal to one.