A High-Precision Absolute Angular-Displacement Capacitive Sensor Using Three-Stage Time-Grating in Conjunction With a Remodulation Scheme

This paper presents a novel absolute angular-displacement capacitive sensor developed by combining three incremental angular-displacement time-grating capacitive sensors according to a developed three-stage remodulation scheme. In the multistage remodulation scheme, the output signals of the first-stage induction electrodes with N measurement periods provide the input signals of the second- and third-stage excitation electrodes. This novel scheme provides a fine measurement component in the second stage with 2N measurement periods, and a coarse measurement component in the third stage with a measurement period corresponding to a single 360° revolution of the sensor. This effective doubling in the periodicity of the second-stage sensor achieves higher resolution and measurement accuracy than that achieved by standard devices of an equivalent size fabricated under an equivalent precision, while the single period of the third-stage sensor achieves an absolute positioning capability. As a result, their combination facilitates the measurement of absolute angular positions with high accuracy and resolution. A prototype sensor with a diameter of 57 mm was fabricated using standard printed circuit board technology, and the signal-processing components of the sensor were integrated on the back of the stator. Experimental results demonstrate an achievable measurement accuracy of ±25" over a full 360° range.