Dynamic active impedance for vibration suppression of Large Space Structures

This paper approaches the control of Large Space Structures (LSS) by modulating the impedance of a joint to obtain desired vibration suppression. The suppression of several vibration modes cannot be done efficiently with a constant gain control system, i.e. a constant joint impedance. A dynamic active impedance controller is required and is proposed herein for this purpose. The method is applied to a flexible beam which is modelled by the Euler-Bernoulli equation. The experimental set-up and its operation can emulate a typical slew maneuver about a fixed axis. The boundary conditions for the beam in this case are defined for a servomotor at one end and a free condition at the other end. The beam parameters are experimentally identified for the first three modes of vibration. Active impedances are determined separately for the rigid mode and the first three modes of vibration using a pole placement method. The four different active impedances are realized using gain scheduling while transitions between gains follow a cubic polynomial of time. Preliminary experiments establish the minimum duration for each transition from one active impedance to another in suppressing beam vibrations. (Author)