MEASUREMENT OF 2-DIMENSIONAL DISPLACEMENT USING 2-D ZERO-REFERENCE MARKS

Several 2-D displacement sensing methods are reviewed. As to the cross diffraction grating,there is no absolute zero-reference. In regards to the optical fiber method, the output signal is affected greatly by the quality of the reflecting surface and it is hard to get high resolution. Considering the concentric-circle gratings, the displacement can only be gained with complicated calculating of the experiment data. Compared with the advantages and limitations of the methods above, a novel 2-D zero-reference mark is especially proposed and demonstrated. This kind of mark has an absolute zero-reference when used in pair, and the experimental result is simple to dispose. By superimposing a pair of specially coded 2-D marks, the correct alignment position of the two marks can be detected by the maximum output of the sharp intensity peak. And each slope of the peak is of good linearity which can be used to achieve high resolution in positioning and alignment in two dimensions. Design and fabrication of such 2-D zero-reference marks are introduced in detail. The experiment results are agreed with the theoretical ones.