Patent ID: 7995212

Claim:
An optical displacement measuring device comprising: a diffraction grating configured to move relatively in a direction parallel to a grating vector as to a coherent beam to be irradiated to diffract said coherent beam; a light emitting unit configured to emit said coherent beam; an irradiated light receiving optical system configured to divide said coherent beam emitted from said light emitting unit into two coherent beams, irradiate each of said two coherent beams on said diffraction grating to generate two one-time diffracted beams, and cause two two-time diffracted beams to be generated by diffracting said two one-time beams through said diffraction grating to interfere with each other; a reflecting optical system configured to irradiate each of said two one-time diffracted beams on said diffraction grating; and a light receiving unit configured to receive an interference beam obtained by causing said two two-time diffracted beams to interfere with each other by said irradiated light receiving optical system to detect an interference signal; wherein said irradiated light receiving optical system includes a first imaging element configured to condense said coherent beam emitted from said light emitting unit, and a second imaging element configured to image said two two-time diffracted beams diffracted at said diffraction grating; and wherein said reflecting optical system includes a third imaging element between one reflector and said diffraction grating, said third imaging element configured to irradiate one of said two one-time diffracted beams on said diffraction grating, and a fourth imaging element between the other reflector and said diffraction grating, said fourth imaging element configured to irradiate the other of said two one-time diffracted beams on said diffraction grating; and wherein said third imaging element and said fourth imaging element have the same focal length, said diffraction grating is disposed in one focal position of said third imaging element and said fourth imaging element, and one of said reflectors is disposed in the other focal position of said third imaging element, and the other of said reflectors is disposed in the other focal position of said fourth imaging element.