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Modern control systems
Automatica. Vol. 18, No. 2, pp. 251-252, 1982 Printed in Great Britain.
0005-1098/821020251-02503.0010 Pergamon Press Ltd. International Federation of Automatic Control
Book Review Modern Control Systems* 3rd edn by R. C. Dorf
Reviewer: C. RICHARD JOHNSON, JR. School of Electrical Engineering, Cornell University, Ithaca, NY 14853, U.S.A.
without the ability to warn the reader that it only holds for stable systems, since the concept of stability has not yet been introduced. This same topic of steady-state error also illustrates the shallowness of the concise readable presentation, since only the unity feedback case is used to define the concepts of type and error constants. As noted in Johnson (1980) such a restriction can be misleading, but is quite common in other introductory texts. This lack of depth has proved dissappointing to some students and falsely reassuring to others. One criticism of earlier editions of this text universally made by undergraduate students is the inadequate number of simple exercises useful for mastering the analysis and design techniques introduced by the text. In fact the overwhelming practical details in most problem statements, intended to assure the student of the relevance of even the most fundamental concepts, have been frequently criticized as obscuring the tools to be acquired. The penchant for involved, seemingly real examples and problems and the absence of more rote exercises has been retained by the current edition. I was first introduced to Dorf's text as a broad, readable, alternate presentation of control analysis and design useful as a complement to more detailed, occasionally overburdening texts. Doff has retained this readability of earlier editions. However, the concomittant shallowness of the presentation remains the major shortcoming of the text. The eleventh chapter entitled digital control systems is an example of this strategy. Over a quarter of this chapter extols the power of the digital computer as a control device complete with enticing pictures of a microcomputer breadboard, an elaborate computer control room, and robots such as R2-D2 and C-3PO from Star Wars, while very little indication as to the design of sampled-data control systems is given. Given the same space, a chapter on sensor and actuator technology may have been more successful and would have distinguished this edition from its competitors. Though this third edition retains the readability of earlier editions and will probably retain much of their popularity, ] would only recommend this text for students wanting a single glimpse at control analysis and design; not for those students considering embarking on further study into this area.
Modern Control Systems by Richard C. Dorf is an undeniably popular text for an introduction to control systems at the undergraduate level. The first two editions have been widely adopted. The third edition, which is the subject of this review, was published in 1980. However, despite the use of the accolade 'modern' in the title and the statement in the preface to the third edition that a 'real attempt' was made to provide a 'modern' selection of topics and the addition of a perfunctory chapter on 'digital control systems', the book focuses more on classical rather than modern control concepts. In fact the basis of modern control, the state variable description, is relegated to Chapter 9 after chapters on mathematical models (devoted to the more classical staples of transfer functions and block diagrams), the characteristics of feedback, performance evaluation, stability, root locus, Bode plots, and Nyquist plots. This ordering was retained from the second edition. A more 'modern' perspective could have been provided by the major surgery required to merge the state variable concepts into the chapter on mathematical models, which is a clearly appropriate but perhaps pedagogically nontraditional approach. A concise summary of the chapters in this third edition is provided by another recent review (Walker, 1981), so the remainder of this review will focus on some major and minor characteristics that may be construed as either detractions or attractions of this text. The failure to simultaneously blend the modern and classical approaches to control systems analysis and design, as already mentioned, is the first criticism. Segments of the research community have been promoting such a combination. For example, consider Bryson (1979) and Doyle and Stein (1981). Each approach, i.e. classical and modern, has its strengths and weaknesses both in practice and in pedagogy; but future generations of control engineers may be left with the incorrect impression by this text that these two approaches are separate and unequal. Another disturbing characteristic is the devotion of only one chapter, the tenth in eleven (less than 60 of nearly 500 pages), to control design. As noted on p. 360, examples in earlier chapters 'illustrated' various design techniques but were not intended to provide comprehensive design guidelines. About a quarter of Chapter 10 is devoted to introducing the modern approaches of optimal control and state variable feedback. The remainder focuses primarily on the frequency response or singularity placement improvements of classical lead-lag concepts. In section 10.10 optimal control is given a more thorough introduction than state variable feedback in Section 10.11. A reversal of this presentation would blend more nicely with the singularity relocation aspects of lead-lag compensation. Another example of questionable ordering of topics is the development of steady-state error concepts in Sections 3.5 and 4.4 prior to the discussion of stability in Chapter 5. In Sections 3.5 and 4.4 the final value theorem is invoked
REFERENCES Bryson, Jr., A. E. (1979). Some connections between modern and classical control concepts. J. Dynamic Systems, Measurement, and Control, !@1,91. Doyle, J. C. and G. Stein (1981). Multivariable feedback design: concepts for a classical/modern synthesis. IEEE Trans Aut. Control, AC-2~, 4. Johnson, Jr., C. R. (1980). On the presentation of error coefficients in introductory control theory. Int. J. of Elec. Engng Educ., 17, 257. Walker, B. K. (1981). Review of modern control systems, 3rd edition. Control Systems Magazine, 1, 18.
About the reviewer C. Richard Johnson, Jr. was born in Macon, Georgia, on 27 May 1950. He received the B.E.E. degree from the Georgia Institute of Technology in 1973, and the M.S.E.E. degree
*Modern Control Systems, 3rd edn, by R. C. Doff is published by Addison-Wesley, Reading, MA. 493 pp. 251
2S2
Book Review
from Stanford University in 1975. He received his Ph.D. in electrical engineering from Stanford University in 1977. For the 1972-1973 academic year, he received a scholarship for study at the Technische Universit~t, Hannover, Germany. In 1977 Dr Johnson joined the Department of Electrical Engineering of Virginia Polytechnic Institute and State
University in Blackshurg, Virginia as an assistant professor. In 1981 he joined the faculty of the School of Electrical Engineering at Cornell University in Ithaca, New York as an associate professor. He currently teaches and conducts research in the areas of adaptive parameter estimation and control theory.
0005-1098/821020251-02503.0010 Pergamon Press Ltd. International Federation of Automatic Control
Book Review Modern Control Systems* 3rd edn by R. C. Dorf
Reviewer: C. RICHARD JOHNSON, JR. School of Electrical Engineering, Cornell University, Ithaca, NY 14853, U.S.A.
without the ability to warn the reader that it only holds for stable systems, since the concept of stability has not yet been introduced. This same topic of steady-state error also illustrates the shallowness of the concise readable presentation, since only the unity feedback case is used to define the concepts of type and error constants. As noted in Johnson (1980) such a restriction can be misleading, but is quite common in other introductory texts. This lack of depth has proved dissappointing to some students and falsely reassuring to others. One criticism of earlier editions of this text universally made by undergraduate students is the inadequate number of simple exercises useful for mastering the analysis and design techniques introduced by the text. In fact the overwhelming practical details in most problem statements, intended to assure the student of the relevance of even the most fundamental concepts, have been frequently criticized as obscuring the tools to be acquired. The penchant for involved, seemingly real examples and problems and the absence of more rote exercises has been retained by the current edition. I was first introduced to Dorf's text as a broad, readable, alternate presentation of control analysis and design useful as a complement to more detailed, occasionally overburdening texts. Doff has retained this readability of earlier editions. However, the concomittant shallowness of the presentation remains the major shortcoming of the text. The eleventh chapter entitled digital control systems is an example of this strategy. Over a quarter of this chapter extols the power of the digital computer as a control device complete with enticing pictures of a microcomputer breadboard, an elaborate computer control room, and robots such as R2-D2 and C-3PO from Star Wars, while very little indication as to the design of sampled-data control systems is given. Given the same space, a chapter on sensor and actuator technology may have been more successful and would have distinguished this edition from its competitors. Though this third edition retains the readability of earlier editions and will probably retain much of their popularity, ] would only recommend this text for students wanting a single glimpse at control analysis and design; not for those students considering embarking on further study into this area.
Modern Control Systems by Richard C. Dorf is an undeniably popular text for an introduction to control systems at the undergraduate level. The first two editions have been widely adopted. The third edition, which is the subject of this review, was published in 1980. However, despite the use of the accolade 'modern' in the title and the statement in the preface to the third edition that a 'real attempt' was made to provide a 'modern' selection of topics and the addition of a perfunctory chapter on 'digital control systems', the book focuses more on classical rather than modern control concepts. In fact the basis of modern control, the state variable description, is relegated to Chapter 9 after chapters on mathematical models (devoted to the more classical staples of transfer functions and block diagrams), the characteristics of feedback, performance evaluation, stability, root locus, Bode plots, and Nyquist plots. This ordering was retained from the second edition. A more 'modern' perspective could have been provided by the major surgery required to merge the state variable concepts into the chapter on mathematical models, which is a clearly appropriate but perhaps pedagogically nontraditional approach. A concise summary of the chapters in this third edition is provided by another recent review (Walker, 1981), so the remainder of this review will focus on some major and minor characteristics that may be construed as either detractions or attractions of this text. The failure to simultaneously blend the modern and classical approaches to control systems analysis and design, as already mentioned, is the first criticism. Segments of the research community have been promoting such a combination. For example, consider Bryson (1979) and Doyle and Stein (1981). Each approach, i.e. classical and modern, has its strengths and weaknesses both in practice and in pedagogy; but future generations of control engineers may be left with the incorrect impression by this text that these two approaches are separate and unequal. Another disturbing characteristic is the devotion of only one chapter, the tenth in eleven (less than 60 of nearly 500 pages), to control design. As noted on p. 360, examples in earlier chapters 'illustrated' various design techniques but were not intended to provide comprehensive design guidelines. About a quarter of Chapter 10 is devoted to introducing the modern approaches of optimal control and state variable feedback. The remainder focuses primarily on the frequency response or singularity placement improvements of classical lead-lag concepts. In section 10.10 optimal control is given a more thorough introduction than state variable feedback in Section 10.11. A reversal of this presentation would blend more nicely with the singularity relocation aspects of lead-lag compensation. Another example of questionable ordering of topics is the development of steady-state error concepts in Sections 3.5 and 4.4 prior to the discussion of stability in Chapter 5. In Sections 3.5 and 4.4 the final value theorem is invoked
REFERENCES Bryson, Jr., A. E. (1979). Some connections between modern and classical control concepts. J. Dynamic Systems, Measurement, and Control, !@1,91. Doyle, J. C. and G. Stein (1981). Multivariable feedback design: concepts for a classical/modern synthesis. IEEE Trans Aut. Control, AC-2~, 4. Johnson, Jr., C. R. (1980). On the presentation of error coefficients in introductory control theory. Int. J. of Elec. Engng Educ., 17, 257. Walker, B. K. (1981). Review of modern control systems, 3rd edition. Control Systems Magazine, 1, 18.
About the reviewer C. Richard Johnson, Jr. was born in Macon, Georgia, on 27 May 1950. He received the B.E.E. degree from the Georgia Institute of Technology in 1973, and the M.S.E.E. degree
*Modern Control Systems, 3rd edn, by R. C. Doff is published by Addison-Wesley, Reading, MA. 493 pp. 251
2S2
Book Review
from Stanford University in 1975. He received his Ph.D. in electrical engineering from Stanford University in 1977. For the 1972-1973 academic year, he received a scholarship for study at the Technische Universit~t, Hannover, Germany. In 1977 Dr Johnson joined the Department of Electrical Engineering of Virginia Polytechnic Institute and State
University in Blackshurg, Virginia as an assistant professor. In 1981 he joined the faculty of the School of Electrical Engineering at Cornell University in Ithaca, New York as an associate professor. He currently teaches and conducts research in the areas of adaptive parameter estimation and control theory.