Patent ID: 8710426
Filing Date: 2014-04-29
Classification: G01D

Abstract:
1. An encoder comprising: a light modulation section that is configured to modulate a wavelength of light emitted from a light source section; an optical member that is configured to split the light into four light beams; a moving member that has a diffraction grating at an incidence plane and is configured to move in at least one direction, the incidence plane having a first region and a second region, the first region into which a first light beam having a relatively short optical path length and a third light beam having a relatively long optical path length are entered, the second region into which a second beam having a relatively short optical path length and a fourth beam having a relatively long optical path length are entered, entering axes of the first and third beams into the incidence plane having a symmetrical relationship with respect to a direction, entering axes of the second and fourth beams into the incidence plane having a symmetrical relationship with respect to the direction, entering axes of the first and second beams into the incidence plane having a symmetrical relationship with respect to the direction; and two light receiving sections that receive a first interfering light and a second interfering light respectively, the first interfering light being formed by an interference of the first and third light beams at the diffraction grating, the second interfering light being formed by an interference of the second and fourth light beams at the diffraction grating, wherein the split light enters into the moving member such that an interference fringe of the first interfering light and an interference fringe of the second interfering light move in mutually opposite directions on the moving member, based on the modulation by the light modulation section.