A High-Accuracy Capacitive Absolute Time-Grating Linear Displacement Sensor Based on a Multi-Stage Composite Method

Abstract

In this paper, an absolute time-grating displacement sensor with high accuracy and high resolution is proposed, where primary, secondary, and tertiary stage capacitor arrays with M, N, and N -1 measurement periods, respectively, are combined by a multi-stage composite method that applies the four orthogonal traveling wave signals output by the primary-stage as the excitation signals of the secondary and tertiary stages. Combining the primary and secondary stages yields sensor A, with M + N measurement periods. Similarly, sensor B, composed of the primary and tertiary stages, has M + N -1 measurement periods. Sensor A is used as the fine measurement component, and the phase difference between sensors A and B is used as the coarse measurement component. Absolute positioning is realized in a similar manner to a Vernier caliper measurement. The output signal of each stage includes odd harmonics, such that the measurement error of each stage contains the fourth harmonic. This is retained in the synthesis stage by the multi-stage composite method. Experimental results for a prototype sensor yield an absolute positioning error of ±200 nm over a measurement range of 200 mm. Depending on the multi-stage composite method, the measurement accuracy and resolution of the same size time-grating are improved, and the connection of the input and output are focused on a stationary component. This compact and convenient sensor has wider application prospects for machine tools and automatic machine systems.