Patent ID: 7723671
Filing Date: 2010-05-25
Classification: G01D

Abstract:
1. An encoder, comprising: a scale for measurement on which a pattern arranged along a predetermined direction is formed; a beam-splitting optical system that splits an incident illumination light at least into a first light that is irradiated to the scale for measurement and a second light that includes information on an irradiation position of the first light on the scale for measurement; a photoreceiver for the second light that receives the second light; a detection device that detects the information on the irradiation position of the first light on the scale for measurement based on a light-receiving result of the photoreceiver for the second light; a photoreceiver for the first light that receives an interference light of the first light via the scale for measurement; a scale for detection of which a positional relation with the beam-splitting optical system is fixed and to which the second light is irradiated; and a modulator that modulates the first light in an arrangement direction of the first pattern, and also modulates the second light in an arrangement direction of the second pattern, wherein the scale for measurement is displaced relative to the beam-splitting optical system, the photoreceiver for the second light receives a light via the scale for detection, the detection device computes the relative displacement of the scale for measurement based on a light-receiving result of the photoreceiver for the first light and a light-receiving result of the photoreceiver for the second light, the scale for measurement has a first pattern arranged in a direction in which the scale for measurement is displaced, the scale for detection has a second pattern arranged along an arrangement direction of the first pattern, and the beam-splitting optical system has: a beam-splitting element that splits the illumination light into two lights, and an optical member that makes the two lights interfere with each other on the scale for measurement and on the scale for detection, wherein the first light is a light that is obtained by part of the two respective lights interfering on the scale for measurement, and the second light is a light that is obtained by part of the two respective lights interfering on the scale for detection.