| 摘要 |
PROBLEM TO BE SOLVED: To reduce the number of parts in a grid interference type displacement measuring device. SOLUTION: A stationary grid 40 and a displacement grid 42 are disposed on an optical path between a coherent light source 10 and a photodetecting element 44, and a grid pitch P1 of the stationary grid 40 and the grid pitch P2 of the displacement grid 42 are made different. Light from the coherent light source 10 is divided into a diffracted light and transmitted light by the stationary grid 40. The diffracting light is diffracted by the displacement grid 42, and further transmitted through the stationary grid 40 to enter the photodetecting element 44. The transmitted light is diffracted by the displacement grid 42 and further diffracted by the stationary grid 40 to enter the photodetecting element 44. Since the stationary grid 40 and the displacement grid 42 are different in grid pitch, two luminous fluxes entering the photodetecting element 44 are superposed at an angle to generate an interference fringe. The interference fringe is detected by the photodetecting element 44 to measure the displacement.
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