Active Control Of Flexible Structures

A complete solution for problems of vibration control in structures that may be subject to a broadband primary vibration field, this book addresses the following steps: experimental identification of the dynamic model of the structure; optimal placement of sensors and actuators; formulation of control constraints in terms of controller frequency response shape; controller design and simulation; and controller implementation and rapid prototyping. The identification procedure is a gray-box approach tailored to the estimation of modal parameters of large-scale flexible structures. The actuator/sensor placement algorithm maximizes a modal controllability index improving the effectiveness of the control. Considering limitations of sensors and actuators, the controller is chosen as a stable, band-pass MIMO system resulting from the closed-form solution of a robust control problem. Experimental results on an aeronautical stiffened skin panel are presented using rapid-prototyping hardware.

My objective in writing this book was to cross the bridge between the structural dynamics and control communities, while providing an overview of the potential of SMART materials for sensing and actuating purposes in active vibration c- trol. I wanted to keep it relatively simple and focused on systems which worked. This resulted in the following: (i) I restricted the text to fundamental concepts and left aside most advanced ones (i.e. robust control) whose usefulness had not yet clearly been established for the application at hand. (ii) I promoted the use of collocated actuator/sensor pairs whose potential, I thought, was strongly underestimated by the control community. (iii) I emphasized control laws with guaranteed stability for active damping (the wide-ranging applications of the IFF are particularly impressive). (iv) I tried to explain why an accurate pred- tion of the transmission zeros (usually called anti-resonances by the structural dynamicists) is so important in evaluating the performance of a control system. (v) I emphasized the fact that the open-loop zeros are more difficult to predict than the poles, and that they could be strongly influenced by the model trun- tion (high frequency dynamics) or by local effects (such as membrane strains in piezoelectric shells), especially for nearly collocated distributed actuator/sensor pairs; this effect alone explains many disappointments in active control systems.

With Active Control of Structures, two global pioneers present the state-of-the-art in the theory, design and application of active vibration control. As the demand for high performance structural systems increases, so will the demand for information and innovation in structural vibration control; this book provides an effective treatise of the subject that will meet this requirement. The authors introduce active vibration control through the use of smart materials and structures, semi-active control devices and a variety of feedback options; they then discuss topics including methods and devices in civil structures, modal analysis, active control of high-rise buildings and bridge towers, active tendon control of cable structures, and active and semi-active isolation in mechanical structures. Active Control of Structures: Discusses new types of vibration control methods and devices, including the newly developed reduced-order physical modelling method for structural control; Introduces triple high-rise buildings connected by active control bridges as devised by Professor Seto; Offers a design strategy from modelling to controller design for flexible structures; Makes prolific use of practical examples and figures to describe the topics and technology in an intelligible manner.

Flexible structures arise in significant important areas of application, such as robotics, large space structures, and antenna control. Difficulties related to sensing and identification hamper control of such systems. These problems require collaboration between mathematicians and engineers. To promote such collaboration, the Fields Institute sponsored a three-day workshop entitled ``Problems in Sensing, Identification, and Control of Flexible Structures'' in June 1992. This volume contains papers presented at the workshop. Topics range from theoretical research on the well-posedness of systems, to experimental implementations of various controllers. A number of controller design techniques are discussed and compared, and there are several papers on modelling the complex dynamics of flexible structures. This book is a useful resource to control theorists, engineers, and mathematicians interested in this important field of research.

This textbook is an introduction to the dynamics of active structures and to the feedback control of lightly damped flexible structures; the emphasis is placed on basic issues and simple control strategies that work. Now in its fourth edition, more chapters have been added, and comments and feedback from readers have been taken into account, while at the same time the unique premise of bridging the gap between structure and control has remained. Many examples, covering a broad field of applications from bridges to satellites and telescopes, and problems bring the subject to life and take the audience from theory to practice. The book has 19 chapters dealing with some concepts in structural dynamics; electromagnetic and piezoelectric transducers; piezoelectric beam, plate and truss; passive damping with piezoelectric transducers; collocated versus non-collocated control; active damping with collocated systems; vibration isolation; state space approach; analysis and synthesis in the frequency domain; optimal control; controllability and observability; stability; applications; tendon control of cable structures; active control of deformable mirrors for Adaptive Optics and large earth-based and space telescopes; and semi-active control. The book concludes with an exhaustive bibliography and index. This book is intended for structural engineers who want to acquire some background in vibration control, and for control engineers who are dealing with flexible structures. It can be used as a textbook for a graduate course on vibration control or active structures. A solutions manual is available through the publisher to teachers using this book as a textbook.

This book presents iterative learning control (ILC) to address practical issues of flexible structures. It is divided into four parts: Part I provides a general introduction to ILC and flexible structures, while Part II proposes various types of ILC for simple flexible structures to address issues such as vibration, input saturation, input dead-zone, input backlash, external disturbances, and trajectory tracking. It also includes simple partial differential equations to deal with the common problems of flexible structures. Part III discusses the design of ILC for flexible micro aerial vehicles and two-link manipulators, and lastly, Part IV offers a summary of the topics covered. Unlike most of the literature on ILC, which focuses on ordinary differential equation systems, this book explores distributed parameter systems, which are comparatively less stabilized through ILC.Including a comprehensive introduction to ILC of flexible structures, it also examines novel approaches used in ILC to address input constraints and disturbance rejection. This book is intended for researchers, graduate students and engineers in various fields, such as flexible structures, external disturbances, nonlinear inputs and tracking control.

I was introduced to structural control by Raphael Haftka and Bill Hallauer during a one year stay at the Aerospace and Ocean Engineering department of Virginia Tech., during the academic year 1985-1986. At that time, there was a tremendous interest in large space structures in the USA, mainly because of the Strategic Defense Initiative and the space station program. Most of the work was theoretical or numerical, but Bill Hallauer was one of the few experimen talists trying to implement control systems which worked on actual structures. When I returned to Belgium, I was appointed at the chair of Mechanical Engi neering and Robotics at ULB, and I decided to start some basic vibration control experiments on my own. A little later, smart materials became widely available and offered completely new possibilities, particularly for precision structures, but also brought new difficulties due to the strong coupling in their constitutive equations, which requires a complete reformulation of the classical modelling techniques such as finite elements. We started in this new field with the sup port of the national and regional governments, the European Space Agency, and some bilateral collaborations with European aerospace companies. Our Active Structures Laboratory was inaugurated in October 1995.