Application of adaptive trusses to vibration isolation in flexible structures

This dissertation presents techniques for using adaptive trusses for active vibration isolation in flexible structures. Passive methods have been used almost exclusively in the past for vibration isolation, although in the more recent literature active techniques have been proposed in an attempt to achieve greater isolation performance. Most of the active techniques, however, require either detailed knowledge of the system or of the disturbance to be isolated. This work focuses on techniques in which knowledge of the disturbance is minimal, and in some cases, knowledge of the system is not necessary. Two new active vibration isolation methods are presented which are based on feedback of transmitted forces in the system. The methods include force feedback through a high gain, and state feedback using the LQR method with disturbance modelling. A third method which has been demonstrated in the literature, force feedback through a classical compensator, is also presented for comparison. For the purpose of discussion, each of the methods is applied to a system which includes a single active mount. The methods are then applied analytically to an adaptive truss, which essentially contains multiple mounts, to demonstrate multi-degree-of-freedom active vibration isolation. It is shown that force feedback provides two-way isolation, and its effects are independent of the type of active mount used (whether it is a force- or displacement-commanded mount). The most promising technique proves to be the simplest, the high-gain feedback method. This technique is a stable, model-free method of vibration isolation which places no restrictions on the type of system disturbance, other than that it must be within the actuator’s bandwidth. The high-gain approach is applied experimentally and shown to agree with the simulated results.