| 摘要 |
PROBLEM TO BE SOLVED: To simplify the structure and adjustment of an optical system in a size measuring apparatus using an optical scale. SOLUTION: In a structure for creating a two-phase signal with a phase shifted byπ/2 from the optical scale comprised of one movable grating and two fixed gratings, the moving grating or the fixed gratings are made of a liquid crystal element. By changing a liquid crystal drive voltage, the optical intensity distributions of the gratings are reversed. While a stylus is moving, a standard tow-phase signal with a phase shifted byπ/2 is outputted, and counter operation is perform to detect the distance of movement of the integral multiple of one pitch length of the gratings. While the stylus is halted, a reference two-phase signal with an inversed phase from that of the standard two- phase signal is outputted with the standard two-phase signal, and the phases of the signals are detected from the relation of intensity of four-phase signals to detect the distance of movement of the length of one pitch of the gratings or less.
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