Active Stiffener Actuators for High-Precision Shape Control of Circular Plate Structure

Abstract

Spaced-based adaptive optic systems have gained considerable attention within the past couple of decades. Achieving the increasingly stringent performance requirements for these systems is greatly hindered by strict weight restrictions, size limitations, and subjected hostile environments. There has been considerable attention in lightweight adaptive optics, where piezoelectric sheet actuators are directly attached on the back of optical mirrors to achieve a high-precision surface shape with minimum additional weight. In recent studies, it was discovered that the performance of the system could be further improved if the piezoelectric sheet actuator were decoupled in direction, meaning that the actuation in one of the two directions is eliminated. To realize the decoupling effect, the concept of utilizing the active stiffener for high-precision shape control is proposed and investigated in the study. The active stiffener is a stiffener-piezoceramic actuator pair that consists of an passive insert (stiffener) placed between the host structure and the active piezoelectric actuator. The basic premise is that the insert (stiffener) will reduce the action transmitted in one direction while allowing adequate action to transmit in the orthogonal direction. In this research, analytical and experimental efforts are carried out to examine the effect of the active stiffener actuators for shape control of circular plate structures. Analysis is performed on two large flexible circular plate structures, one having the direct attached actuators and the other utilizing the active stiffener actuators. It is shown that more reductions in the surface error can be achieved with the active stiffeners, as compared to systems with the direct attached actuators. It is illustrated that the direct attached actuators generate more localized deformation in the structure, whereas the decoupling capability of the active stiffener reduces the undesired localized deformation considerably. The experimental results verify the analytical predictions and clearly demonstrate the performance improvement of the active stiffener concept over the direct attached actuator.