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This paper describes the configuration and measured performance of an hybrid, active-passive vibration isolation mount designed to mitigate vibratory disturbances on sensitive spacecraft instruments. The device, called the Active Vibration Canceler (AVC), consists of a passive isolation stage using composite leaf springs faced with shape-memory metal sheet material to provide load-adaptive damping, and an active, force-canceling stage using a motion-amplified electrostrictive stack actuator to augment attenuation of transmitted vibrations in the 10-120 Hz band. The paper discusses the features of the AVC design and active control architecture, and presents results of experiments characterizing the broadband performance of the device. Performance measurements show that the AVC provides up to 40 dB attenuation of base disturbances at 100 Hz, and that the electrostrictive active stage provides in excess of 10 dB attenuation over the passive isolator in the range 10-100 Hz. The measurements indicate that hybrid devices of this type can be effective in reducing transmitted vibrations to sensitive instruments, and that the incorporation of active elements can significantly enhance attenuation of broadband vibrations in isolation applications.

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SUMMARYIn this paper we extend the Lanczos algorithm for the dynamic analysis of structures' to systems with general matrix coefficients. The equations of dynamic equilibrium are first transformed to a system of first order differential equations. Then the unsymmetric Lanczos method is used to generate two sets of vectors. These vectors are used in a method of weighted residuals to reduce the equations of motion to a small unsymmetric tridiagonal system.The algorithm is further simplified for systems of equations with symmetric matrices. By appropriate choice of the starting vectors we obtain an implementation of the Lanczos method that is remarkably close to that in Reference 7, but generalized to the case with indefinite matrix coefficients. This simplification eliminates one of the sets of vectors generated by the unsymmetric Lanczos method and results in a symmetric tridiagonal, but indefinite, system. We identify the difficulties that may arise when this implementation is applied to problems with symmetric indefinite matrices such as vibration of structures with velocity feedback control forces which lead to symmetric damping matrices.This approach is used to evaluate the vibration response of a damped beam problem and a space mast structure with symmetric damping matrix arising from velocity feedback control forces. In both problems, accurate solutions were obtained with as few as 20 Lanczos vectors.