Abstruct-This paper describes recent results in applying robust control techniques to achieve vibration suppression of an active precision truss structure. The active structure incorporates piezoelectric members which serve as both structural and actuation elements. The problem considered is multiple-input, multiple-output with non-collocated actuators and sensors. Several characterizations of uncertainty are studied and the resulting controllers are compared experimentally. One characterization uses a novel approach involving eigenvalue perturbation descriptions.

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The effectiveness of viscous elements in introducing damping in a structure is a function of several variables, including their number, their location in the structure, and their physical properties. This paper addresses the questions of the placement of these elements and the selection of their physical parameters via optimization techniques. The paper investigates various metrics to define these optimization problems, and compares the damping profiles that are obtained. Both discrete and continuous optimization problems are formulated and solved, corresponding, respectively, to the problems of placement of damping elements and to the tuning of their parameters. Particular emphasis is placed on techniques to make feasible the large scale problems resulting from the optimization formulations. Numerical results involving a lightly damped testbed structure are presented.

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