A Multivector Variable Area Type Capacitive Angular Displacement Encoder Based on a Rotating Electric Field and Improvement of Its Demodulation Method

Abstract

The problems of the traditional type grating angular displacement encoder make it difficult to balance the measurement performance of miniaturization, high precision and high resolution, and the ability to resist vibration and shock is poor. In this article, a multivector variable-area capacitive angular displacement encoder based on a rotating electric field is proposed. Based on the principle of constructing a rotating electric field, a three-layer transmissive sensing structure with upper and lower layers of electrode plates and a modulation rotor as the middle layer is proposed and designed. A single-channel signal is used as the input excitation signal of the capacitive sensor to avoid the problem of mismatching multiple input signals. A pair of quadrature signals reflecting the spatial angle information is obtained through electric field demodulation and differential processing. The phase demodulation method based on the time scale is further adopted to improve the precision of demodulation. Simulations and experiments show that the sensor has a diameter of 50 mm, a thickness of 5 mm, a resolution of <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$0.81''$ </tex-math></inline-formula> , an accuracy of <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$2.5''$ </tex-math></inline-formula> , and a maximum nonlinear error of <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$40''$ </tex-math></inline-formula> . The design is verified to be feasible, which provides a new solution for capacitive angular position sensor design.