Research on the Measurement of Displacement based on Grating Reticle Image

A new method is present to get movement displacement directly when applying grating reticle to AC servo driving control system to carry on high precise orientation for the micro-objects. Adjusting the optical path until grating reticle image can be gathered clearly by vidicon. After analyzing and processing the grating reticle image collected by vidicon, the mapping coefficient can be accurately calculated between grid width and pixels. Comparing the fore-and-aft two grating reticle images after the worktable moved. The phase difference of two images can be figured out by phase difference ratio arithmetic based on Lissajous figures. Accordingly the actual displacement of the worktable can be calculated by the mapping coefficient. The experiments show that this method can implement sub-pixel measurement easily and rapidly in micro electronics manufacture. Keywords-displacement measurement; grating; image processing; Lissajous figure; AC servo motor