Patent ID: 6407815
Filing Date: 2002-06-18
Classification: G01D

Abstract:
An optical displacement measurement system comprising:a diffraction grating arranged for movement in directions parallel to a grating vector thereof; light emitting means for emitting a coherent beam of light; an irradiation optical system for dividing the coherent beam of light emitted from the light emitting means into two coherent beams of light for converting the two coherent beams of light into two converging beams of light, and for irradiating the two converging beams of light on the surface of the diffraction grating to form a first spot thereon; light receiving means; an interference optical system for causing the two diffracted beams of light obtained from the diffraction grating to interfere with each other forming two interfering diffracted beams of light, for converting the two interfering diffracted beams of light into two converging beams of light, and for irradiating the two converging beams of light on the light receiving means to form a second spot thereon; and position detecting means for determining a phase difference of the two diffracted beams of light from an interference signal produced by the light receiving means and detecting a relative position of the diffraction grating, wherein the diffraction grating is positioned substantially where the first beam spot has a minimum diameter and where an optical path difference between the beams of light forming the first beam spot has a minimum diameter, and the light receiving means is positioned substantially where the second beam spot has a minimum diameter and where an optical path difference between the beams of light forming the second beam spot has a minimum diameter.