Browsing by Author "Bohannan, G"

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Piezoelectric polymer actuators for active vibration isolation in space applications
(1999) Bohannan, G; Schmidt, V. Hugo; Brandt, Dan; Mooibroek, M
A lightweight actuator for active vibration isolation in space applications is being developed to replace the heavy electromagnetic systems now in use. The actuator has a low effective spring constant that provides for passive vibration damping down to sub-Hertz frequencies while allowing the isolated experiment to follow the near-dc bias motion of the spacecraft. The actuator is currently optimized for the vibration level of the Space Shuttle and assembled from a pair of bimorphs in a leaf-spring configuration. Changing the size and number of sheets used in construction can vary electromechanical properties. Passive damping has been demonstrated in one and two-dimensional tests. For large (greater than a few kilograms) suspended masses, the system is underdamped and relative velocity feedback must be used to remove the resonance. Real-time control of the resonance frequency is achieved by controlling the voltage applied to the actuator with feedback from a displacement sensor. A folded pendulum seismic monitoring device was adapted for use as a one-dimensional low frequency test platform and has obtained accurate measurements of the effective spring constant and damping coefficient. Single-degree-of-freedom active feedback testing is also being conducted using this device. Two-dimensional (three-degree-of-freedom) passive damping tests were conducted on NASA's KC-135 Reduced Gravity Platform in March 1998.