Implementation of subdivision algorithm of single spectral line for grating signal

Abstract

In order to improve the subdivision number and tracking speed of grating Moiré fringe signals in the grating displacement measurement system based on charge coupled device (CCD), the first harmonic phase value of signals was obtained with a discrete Fourier transform (DFT) single spectral line algorithm according to the feature that the period of grating Moiré fringe signals collected by CCD would not change with the running speed. The inverse tangent of first harmonic spectral line plural was calculated with the coordinate rotation digital computer (CORDIC) algorithm to obtain the phase values of Moiré fringe signals at any moment. In addition, the magnitude and direction of displacement were attained through the fringe movement phase difference of two consecutive moments, and all the algorithms were realized with FPGA. The ModelSim simulated results show that the DFT and CORDIC modules will only delay 22 clock cycles to output the results. The proposed method has such characteristics as high subdivision number, fast calculation speed and simple implementation. The present research provides the reference for solving the decline of tracking speed resulted from the improvement of subdivision number of Moiré fringe in grating precision displacement measurement.