Patent ID: 7064842

Claim:
An optical displacement sensor for measuring a displacement of a scale, wherein the scale is movable in a predetermined direction and includes a diffraction grating which has a predetermined period in a direction of the predetermined direction, said optical displacement sensor comprising: a surface emitting laser light source for emitting a light beam to the diffraction grating such that a principal axis of the light beam is perpendicular to the direction of the predetermined direction and inclines at a predetermined angle relative to a line perpendicular to a surface of the diffraction grating within a plane perpendicular to the direction of the predetermined direction; and a photosensor for detecting a specific portion of a diffraction interference pattern which is generated by interaction of the light beam and the diffraction grating, wherein the photosensor comprises a plurality of light detecting areas arranged at intervals of approximately np1(z1+z2)/z1 in a spatial period direction of the diffraction grating on the scale; where: z1 is an optical distance along the principal axis of the light beam from a beam emitting surface of the surface emitting laser light source to a scale surface where the diffraction grating is formed; z2 is an optical distance along the principal axis of the light beam from the scale surface to the photosensor; p1 is a spatial period of the diffraction grating; and n is a natural number; wherein z1=z2 and the surface emitting laser light source and the photosensor are arranged on a same side of the scale; and wherein the scale surface where the diffraction grating is formed is parallel to a light receiving surface of the photosensor.