Patent ID: 6166817
Filing Date: 2000-12-26
Classification: G01D

Abstract:
An optical displacement measurement system comprising:a diffraction grating adapted to be irradiated with a coherent beam of light and move in directions parallel to a grating vector relative to the coherent beam for diffracting the coherent beam;light emitting means for emitting the coherent beam of light;an irradiation optical system for dividing the coherent beam of light emitted from said light emitting means into two coherent beams of light and irradiating said diffraction grating with each of the two coherent beams;a reflection optical system for reflecting each of a first pair of diffracted beams obtained from said coherent beams through diffraction by said diffraction grating and irradiating said diffraction grating with each of said first pair of diffracted beams;an interference optical system for causing each of a second pair of diffracted beams obtained by diffracting each of said first pair of diffracted beams to interfere with each other;light receiving means for receiving the second pair of diffracted beams interfering with each other and detecting an interference signal therefrom;position detecting means for determining a phase difference of said second pair of diffracted beams from the interference signal detected by said light receiving means and detecting a position of the diffraction grating having been relatively moved;said irradiation optical system having first focussing means for focussing the two coherent beams irradiating the diffraction grating on a grating plane of the diffraction grating; andsaid reflection optical system having reflecting means and second focussing means, said second focussing means collimating said each of said first pair of diffracted beams, and said reflecting means being positioned perpendicular to the light beams collimated by said second focussing means and reflecting the light beams backward so that the reflected beams trace a same optical path followed after being diffracted by the diffraction grating and then enter said second focussing means causing the focussed beams to focus at a same spot where the beams are diffracted.