Theory and Application of Sampling Moire Method

Sampling moire method is a newly developed moire method using an image processor for a grating pattern to measure shape or displacement or strain distributions. A grating pattern on an object is recorded by a digital camera. Though the digitized image shows the grating, a moire fringe pattern appears by thinning-out the pixels, i.e., sampling the image with a larger pitch than the pixel pitch. If the sampling pitch is changed, the moire pattern is changed very much. If the phase of the sampling is changed, the phase of the moire pattern is changed. The phase analysis of moire pattern provides accurate result of displacement of the grating. If the number of the phase-shifted moire patterns i.e. the number of pixels for a pitch of grating is larger, the resolution of phase analysis becomes more accurate but the spatial resolution becomes worse. Since the sampling moire method is useful to analyze the phases of a moire fringe and a grating from one image of a grating pattern, it is possible to analyze dynamic deformation accurately. In this paper, the theory of the sampling moire method is introduced and some applications of the sampling moire method to displacement measurement of a beam, and shape and strain measurement of a rubber structure are shown.