Identification and Control of Mechanical Systems

5R17. Identification and Control of Mechanical Systems. - Jer-Nan Juang (Struct Dyn Branch, NASA Langley Res Center, Hampton VA 23665) and Minh Q Phan (Thayer Sch of Eng, Dartmouth Col, Hanover NH). Cambridge UP, Cambridge, UK. 2001. 334 pp. ISBN 0-521-78355-0. $80.00.Reviewed by L Dewell (Adv Tech Center, Lockheed Martin Space Syst, 1111 Lockheed Martin Way, Sunnyvale CA 94089).This textbook presents the concepts and results of modern, multivariable control theory, with a particular focus on its application to mechanical systems. The book is tailored to an audience which is not familiar with multivariable systems analysis, including linear algebra, linear system theory, etc. It is suitable as a textbook for an advanced undergraduate course in linear systems theory and modern control. In the opinion of this reviewer, it is ideally suited as a textbook for practicing engineers from fields other than dynamics and control, who, through self-study or in a group, wish to gain an understanding of the underpinnings of modern control systems. The authors suggest that the book is also appropriate for graduate study, but it seems to lack the technical depth for study at the graduate level. The book begins with three chapters dealing with the theory of ordinary differential equations, linear algebra, and the derivation of equations of motion. The next two chapters extend the treatment of dynamic systems to the field of structural dynamics through a treatment of the finite element method and the vibration of beams. Subsequent chapters variously present the concepts of modern control. Chapter 6 discusses stability augmentation of structural dynamic systems through position, rate, or acceleration feedback; Chapters 8 and 9 discusses the general problem of regulation and tracking using full-state and output feedback. Finally, the book concludes with two chapters dealing with advanced topics of system identification and predictive control. Several chapters of this book are excellent, self-contained treatments of subjects which have previously been dispersed in various textbooks on control and linear systems theory. For example, Chapter 2 is one of the best summaries of linear algebra for control systems engineers that this reviewer has seen in a textbook. Chapters 5 and 6 are an outstanding introduction to the problems of flexible structures and their control. Finally, the treatment of system identification in Chapter 10 brings out the essential features of recent results in the field in a manner which is manageable to the uninitiated. This book is particularly strong in its presentation of flexible structure control. The authors do an excellent job of illustrating stability augmentation of a flexible-body system using so-called virtual passive controllers. In particular, the authors show that the damping of a structural dynamic system cannot be augmented by position sensors alone, if the controller structure is limited to static controllers. However, with dynamic controllers obeying a second-order form, damping can be augmented to any desired degree using only position feedback. In addition, the authors make a conscious effort to present many of the results while staying within the second-order form which is so familiar to structural dynamicists, in addition to showing the results in the first-order, state-space form. Although this choice carries a certain burden of additional analysis and discussion, it serves the structural dynamics community well. The authors' choice of arrangement of the chapters was sometimes difficult to understand. It seemed to this reviewer that Chapters 4 and 5 were written independently, without mutual comparison for overlapping material. In fact, it occurred to this reviewer that the finite element method of Chapter 4 should have appeared as a final section to Chapter 5. Chapter 7 seemed out of place in the second half of the book, being a basic treatment of state-space systems. It would have been more appropriate if this material appeared near the beginning of the text. Despite some reservations about organization or presentation, which are inevitably subjective to some extent, this reviewer found the book enjoyable and easy to read. The treatment of pole-placement using the singular-value decomposition was interesting and well worth the study. It was particularly pleasant to examine the examples, as the authors carefully chose examples which were just complex enough to illustrate the point at hand, while not being so involved as to muddy the water with other concepts or considerations. In summary, Identification and Control of Mechanical Systems seems to be an excellent vehicle for the study of modern control by advanced undergraduate students, and particularly for practicing engineers in structural dynamics who wish to bridge the technical gap between dynamics and control.