| 摘要 |
PURPOSE:To prevent a detection error due to the mismatching between the border parts of respective position detection parts from occurring by setting a range which is twice as large as the minimum position detection width of a high-order position detection part as the detection range of a low-order position detection part. CONSTITUTION:Binary code patterns 11a-11f consisting of a linear Fresnel belt plate are formed on a code plate 3. Further, slanting slit groups 12a and 12b consisting of many slits formed slantingly crossing the moving direction of the code plate 3 are formed at pitch twice as large as the minimum position detection width of detection by the patterns 11a-11f. Laser light 1 is projected on them through a collimator lens 2 and then when a transmitted diffraction image meets corresponding to slits of the mask 4, it is detected by corresponding photodetecting elements of a photodetector 5. Then the position detection is performed at the border part of both position detection parts according to whether or not mutual overlapping digits between primary and secondary detection data are different, thereby eliminating a detection error completely.
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