Piezoelectric polymer actuators for vibration suppression

Abstract

We have designed and built piezoelectric polymer actuators in a 'bellows' configuration and have used them in a near-zero-g environment vibrations suppression apparatus. The actuator is based on poly(vinylidene fluoride) (PVDF) sheets produced by AMP and electroded to our specifications. The actuator consists of two bimorphs, each with a double-bend precurvature, glued together at their ends so that the actuator has its thickest air gap at the middle. Each bimorph consists of two sheets glued together. Each sheet is electroded completely on the outside (ground) side, and has three electrode areas on the other side. If the electrode on the middle half is positive, and on the outer two quarters are negative, the bimorph curvature and the actuator length increase; with opposite polarities they decrease. In the vibration isolation application, the box to be isolated has actuators mounted between it and its surrounding enclosure on the vibrating vehicle. Feedback control is provided to change actuator length to compensate for vehicle motions and vibrations. This feedback is provided by accelerometers and by laser diode position sensors. The inherent softness of the actuator provides good passive damping of higher frequencies. So far, a one-dimensional test of the system has been made using a mass on a 'folded pendulum' as a 'weightless' (no restoring force for small displacements) load. Also, a two- dimensional version was flown on NASA's KC-135, which provided 25-second near-zero-g intervals during parabolic flight segments. Our goal is three-dimensional isolation for space vehicle applications.