A new method of moire contouring, absolute shadow moire contouring by rotating a grating, is described in this paper. In the shadow moire system, the period of the grating is varied by rotating the grating, so that the phase of the moire pattern is changed as well. By selecting suitable rotation angles, four images at different positions of the grating are acquired to obtain the absolute distance from the object to the grating. The theoretical analysis is presented for the method and some experiments have been done to verify the theoretical analysis. The results show that the method is fast and very accurate. The measurable range is directly proportional to the period of the grating and inversely proportional to the angles to which the grating is rotated.
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