Piezoelectric polymer actuators for active vibration isolation in space applications

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 passiv e vibration damping down to sub-Hertz frequencies while allowing the isolat ed experiment to follow the near-de bias motion of the spacecraft. The actu ator is currently optimized for the vibration level of the Space Shuttle an d assembled from a pair of bimorphs in a leaf-spring configuration. Changin g the size and number of sheets used in construction can vary electromechan ical properties. Passive damping has been demonstrated in one and two-dimen sional tests. For large (greater than a few kilograms) suspended masses, th e system is underdamped and relative velocity feedback must be used to remo ve the resonance. Real-time control of the resonance frequency is achieved by controlling the voltage applied to the actuator with feedback from a dis placement sensor. A folded pendulum seismic monitoring device was adapted f or use as a one-dimensional low frequency test platform and has obtained ac curate measurements of the effective spring constant and damping coefficien t. Single-degree-of-freedom active feedback testing is also being conducted using this device. Two-dimensional (three-degree-of-freedom) passive dampi ng tests were conducted on NASA's KC-135 Reduced Gravity Platform in March 1998.