Patent ID: 6759647
Filing Date: 2004-07-06
Classification: G01D

Abstract:
A projection encoder which has a light source, reflecting gratings having a prescribed shape and arranged at a constant pitch, transmission gratings having a prescribed shape and arranged at a constant pitch, and photodetectors for receiving a reflected light image that is emitted by the light source, transmitted by the transmission gratings, and reflected by the reflecting gratings, with at least the relative movement position of the reflecting gratings and transmission gratings being detected based on a detection signal obtained from the photodetectors, the projection encoder comprising:a reflecting grating plate on which the reflecting gratings are formed; a substrate on which the transmission gratings and photodetectors are formed; and a home position detection mechanism for detecting the home position of the reflecting grating plate and the substrate; said home position detection mechanism comprising: a reflecting grating region designed for detecting the home position and formed on the reflecting grating plate; and a photodetector area designed for detecting the home position and formed on the substrate; wherein nonreflecting gratings and reflecting gratings of constant width are arranged in accordance with an M-series arrangement pattern in the reflecting grating region for detecting the home position; Z-phase photodetectors and Zâ€²-phase photodetectors of constant width for obtaining Z-phase signals and Zâ€²-phase signals differing in phase are arranged in accordance with the M-series arrangement pattern in the photodetector region for detecting the home position; and a positional relation of the reflecting grating region for detecting the home position and the photodetector region for detecting the home position is set in a manner such that the reflected light image reflected by the reflecting grating region for detecting the home position can be received in the photodetector region for detecting the home position.