Design, Optimization, and Compensation of a High-Precision Single-Excitation Absolute Capacitance Angular Encoder up to ±4$^{\prime\prime}$

Abstract

This paper presents a single-excitation absolute capacitive rotary encoder that is small in size, lightweight, robust, and highly precise. The encoder consists of two plates: a rotor and a stator. The rotor consists of a planar coupling ring, a petal-form sensitive electrode, and a rough sensitive electrode, whereas the stator consists of a planar excitation ring and eight groups of collection electrodes. First, the two sensitive electrodes together with the eight sets of collection electrodes encode the angular position into amplitude-modulated signals, which are read out by a single-excitation electronic system. High-precision absolute position information is obtained by using the combination of 36 petal-form sensitive electrodes and a rough sensitive electrode. Then, a linear programming method is used to optimize the critical dimensions of the encoder within a limited area to achieve a miniaturized design. Finally, a harmonic frequency compensation method is used to reduce repeatable and periodical measurement errors, which are caused by manufacturing, circuit, and installation errors. A prototype is fabricated and tested on a high-precision testing turntable. The measurement results show that the resolution is 0.00015° and the accuracy over the full absolute range is 0.0022°, indicating that the encoder has considerable potential for use in high-precision applications.