A. M. Beard
D. W. Schubert
Barry Controls, 40 Guest St., Brighton, MA 02135
A. H. von Flotow
Hood Technol. Corp., Hood River, OR 97031
Active control in the presence of resonant structural dynamics is challenging since such dynamics are both uncertain and easy to destabilize. This is particularly true when broadband control is required. Active vibration isolation is plagued by such difficulties. In spite of much development work, few systems are in service and these remain very sensitive to structural resonances. For each such system, the control logic is fine-tuned during installation. When the system's environment changes (sometimes only slightly), unstable behavior is common. This presentation describes basic options in passive/active vibration isolation and highlights mechanical architectures which make robust active control possible. Simple theoretical arguments are supported with experimental evidence. The presentation concludes with a detailed description of a recently developed system which is based upon one such mechanical architecture; Barry Controls' STACIS-2000. This system uses seismic motion sensors (geophones) and piezo-ceramic stack actuators to create feedback-stabilized ``artificial bedrock.'' Vibration-sensitive payloads are mounted to these stiff, quiet points. The system delivers the isolation performance of a well-damped 0.3-Hz passive mount and the stiffness (to inertial space) of a 25-Hz mount. The system is robust to the dynamics of both the vibration source and the receiver.