科研之友
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摘要
The moire patterns formed by two overlapping circular gratings with slightly different periods were used for 2-D (in-plane) displacement measurement in a recently published paper. In this work, the application of the moire patterns formed by such gratings is extended to 3-D displacement measurement. The 3-D measurement is based on the principle that the moire pattern changes when the viewing direction is changed in the presence of out-of-plane displacement (z-component) between the two grating planes. Two different methods for the out-of-plane displacement measurement are proposed. The first method uses a single viewing direction (SVD) normal to the grating plane and co-axial with the circular grating. In this method, the moire fringes move outwards for increasing z-displacement. This movement is represented by an offset shift in the polar transformed moire fringes. The second method uses multiple viewing directions (MVD) whereby the moire pattern changes when the viewing direction is shifted from the normal viewing direction to the off-normal viewing direction. The offset shift in the polar transformed moire fringes in the SVD method and the absolute difference in the in-plane displacements extracted from successive moire patterns in the MVD method were used to determine the z-displacement quantitatively. Experimental results show that the z-displacement component can be determined from both the SVD and MVD methods. However, the MVD method gives better accuracy and precision with an absolute mean error of 0.0533 +/- 0.009 mm at 95% confidence compared to the SVD method which has an absolute mean error of 0.218 +/- 0.065 mm.
- 出版日期2012-6
