Phase subdivision of absolute coding grating in displacement measurement

A phase subdivision of absolute coding grating is proposed to improve the resolution and precision of displacement measurement. The used grating consists of multiple code channel grating of Gray code, and the basic code channel is high frequency Rochi grating. Fourier analysis method is adopted to extract the phase value of grating in decoding, and the wrapped phase distribution of basic code channel is obtained by Fourier transform, filtering, and inverse Fourier transform, then the unwrapped phase distribution could be recovered using the phase order information of Gray code. High resolution of phase subdivision can be achieved via linear fitting of phase distribution. Analysis of the basic principle and the subdivision of the phase to improve the resolution of displacement measurement have also been described in this paper. Experimental results show that the resolution and precision of absolute coding grating is enhanced greatly after phase subdivision and calibration.