A Compact and High-Precision Capacitive Absolute Angular Displacement Sensor

The present work proposes a compact capacitive absolute angular displacement sensor design that adopts a stator and rotor configuration with a double capacitive ring structure, where the outer ring is composed of n measurement periods that function as a fine measurement component, providing high precision measurements. The inner ring is composed of a single measurement period that functions as a coarse measurement component, thereby providing an absolute position measurement. High measurement accuracy is obtained by adopting single-row excitation electrodes with induction electrodes that adopt a differential sensing structure to eliminate common-mode interference. In addition to the double-ring structure, the compact size of the proposed sensor is facilitated by integrating the electrodes of the stator and rotor and the peripheral circuits required for their respective signal processing using printed circuit board technology. A prototype of the proposed sensor is fabricated with outer and inner radii, and aggregate thickness dimensions of 30 mm, 7 mm, and less than 10 mm, respectively. The sensor design is optimized accordingly by increasing the radial interval between the outer and inner rings and adding shielding. Finally, the experimental results show that the optimized sensor design achieves a precision of $12^{\prime \prime }$ and resolution of $0.31^{\prime \prime }$ over the full measurement range of 0° to 360°. As such, the proposed sensor design is demonstrated to realize the small mechanical dimensions suffered by absolute angular displacement sensors. Accordingly, the relatively low cost and low power consumption of the proposed sensor have excellent potential for a wide variety of applications.