光栅信号单谱线细分算法实现

Implementation of subdivision algorithm of single spectral line for grating signal

在基于电荷耦合器件(CCD)的光栅位移测量系统中,为提高光栅莫尔条纹信号的细分数和跟踪速度,根据CCD采集的光栅莫尔条纹信号周期不随运行速度变化的特点,利用离散傅里叶变换(DFT)单谱线算法来获得信号一次谐波的相位值.采用坐标旋转数字计算机(CORDIC)算法对一次谐波谱线的复数求出反正切,获得莫尔条纹信号在任意时刻的相位值,再通过两次相邻时刻的条纹移动相位差值获得位移的大小和方向,全部算法采用FPGA实现.ModelSim仿真结果表明,DFT模块和CORDIC模块共延迟22个时钟周期即可输出结果.此方法具有细分数高、运算速度快、实现简单等特点,为解决光栅精密位移测量中由于莫尔条纹细分数提高而导致跟踪速度下降的问题提供了参考.

In order to improve the subdivision number and tracking speed of grating Moir6 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 Moir6 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 Moir6 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 DFF 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 Moir6 fringe in grating precision displacement measurement.