Control of linear dampers for large space structures

Abstract

This paper addresses the problem of designing a control system for a linear proof-mass damper (actuator) for large space structures. Initially, a linear control law is developed for a self-contained damper. The linear control law shows that although adequate damping can be achieved at high frequencies, very little damping can be obtained at frequencies of 1 Hz or less, because stops must be set to limit the motion of the proof mass. To improve the actuator performance at low frequencies, this paper considers the limiting performance method and its application to control problems. In a preliminary study, the optimal response is calculated for a single-degreeof-freedom model of a cantilever beam controlled by a proof-mass damper using a limiting-performance/minimum-time formulation. It is shown that considerable damping can be achieved at low frequencies. Also, parameter identification is used to find a suboptimal feedback control law based on the limiting performance characteristics. There is an important difference in the way that the last two methods handle elastic impacts between the proof mass and the stops. The limiting-performance-method solution brings the relative motion to rest before impact occurs by applying the appropriate forces. However, in the suboptimal case, the proof mass can strike the stops since the dynamics of elastic impact are modeled.