Fundamental Aspects of Structure Control

Abstract

Within the last decade control problems of flexible systems have attracted increasingly more interest and importance. By now, the well-known problems associated with computational difficulties, spillover, parameter uncertainties, robustness, high-dimensionality, actuator/sensor numbers and locations have been addressed by numerous investigators [1–4]. According to the way controls are designed, control techniques have been classified such as coupled-control (CC) and Independent Modal-Space Control (IMSC) and comparisons have been made regarding their advantages and disadvantages [5]. Mostly linear state feedback approaches dominated the field by utilizing pole-allocation techniques and linear optimal control theory, although output feedback schemes also appeared rather frequently. The highlight of the difficulties has been the control and observation spillover phenomena which invited a host of approaches to eliminate or minimize their effects. Almost across the board, whatever the control technique, the emphasis in controlling structural systems has been on control theories and approaches and on how the principles of these theories could be applied properly to the structural system. However, an important point has been and is being overlooked: it is that the controlled system, being a structurally dynamic system, does constitute a separate branch of science which has a particular discipline in its own right with its deep-rooted foundation in the ages-old “Principles of Mechanics.” In controlling such a physical system, which requires interdisciplinary attention, it is imperative to make sure not only how the principles of control theory are applied properly but also how the principles of mechanics are to be paid due respect and not violated by the control approach.