A ROBUST DELAY-COMPENSATION TECHNIQUE BASED ON MEMORY

This paper addresses the effects of time delay on actively isolated st ructures subjected to support excitation. A force proportional to the absolute velocity of the base of the isolated structure applied at the base of the structure (co-located active damping) is the control sche me considered. The actuating mechanisms have some non-zero time respon se. Consequently, if no compensation is provided, the performance of t he system is worse than that of the ideal delay-free controller. The d ynamics of the controller-actuator system is modelled by a delay opera tor on the feedback signal. Time delays producing instability of the c ontrolled structure are investigated, and the effect of time delay on the mean square acceleration of the structure subjected to stationary random excitation is assessed. A delay-compensation technique that req uires memory of past control actions is proposed and compared with a c ommonly used compensation technique. By using simple numerical example s, it is shown that the proposed delay-compensation strategy improves the performance of the system significantly. The technique is extended to other models of the actuator dynamics and modified to provide robu stness to small parameter uncertainties.