Vibration control of a microactuator for servo application by active damping

Abstract

When using a microactuator for servo applications that require high position accuracy and fast response, one of the typical issues is the microactuator's large amplitude resonance. This resonance occurs because most microactuators use springs to support their moving masses, combined with little damping effects that are due mainly to the viscosity of the air. To solve this problem, we propose the use of a capacitive position sensing method, combined with a high aspect ratio, highly area-efficient, and high structural-height microactuator that can obtain a large capacitance change for a given stroke. This combination does not require a very complex or difficult implementation such as an on-chip preamplifier or a sophisticated filter. A microactuator was manufactured and combined with a relatively simple capacitive sensing circuit made of discrete components such as a spectrum analyzer and amplifier. Even with this relatively crude setup, we were able to obtain a high quality capacitive position signal. The controller was designed and the active damping control loop was successfully closed. The performance was measured by experiment, and demonstrated that the active damping was extremely effective in suppressing oscillations caused by external force disturbances, and in settling to the new position for a step input.