A differential capacitance to voltage converter for electrostatic levitation applications

This paper presents the design and performance of a high-performance position sensor dedicated to a three-axis electrostatic levitation system. The position measurement is based on differential capacitance sensors and capacitance to voltage converters (CVCs), and aims at detecting the motion of a spherical rotor suspended nearly in the center of the electrode cavity. The CVC proposed is mainly composed of an ac capacitive bridge and a phase-sensitive detector (PSD), is capable of detecting capacitance changes from dc up to at least 20 kHz, and is able to decouple the position of a levitated rotor moving along three orthogonal axes. The major error sources and their effects on the accuracy of the displacement sensing are also discussed. The experimental results show that the resolution of the proposed position sensor is a few nanometer in the 0-20 kHz bandwidth and the 20 mum range. The position is digitized with a high-speed A/D converter to feed the control laws of an electrostatically levitated system. (C) 2002 Elsevier Science B.V. All rights reserved.