Built-in Capacitive Displacement Sensor with Long Full-Scale Range for Electrostatic Microactuators

Abstract

This paper describes a built-in capacitive displacement sensor for microactuators. The sensor with long full-scale range is developed for electrostatic microactuators that have a large out-of-plane motion range. A carrier wave with a frequency of 24 MHz is utilized to measure the capacitance between the moving electrode and the sensing electrode of the actuator. The zero method, wherein an additional feedback signal cancels the received signal at the sensing electrode, is applied. The method prevents the fluctuation of the displacement signal caused by the high driving voltage for the electrostatic actuator. The validity of the sensor is demonstrated by using a large-size actuator prior to applying the sensor to an actual microactuator. The acquired full-scale range, sensing band, resolution and linearity were respectively 4.5 mm, from DC to 30 kHz, 60 μm on average, and ±2.5%FS.