Patent ID: 7394062

Claim:
An optical encoder for detecting relative movement of a scale unit and light projection unit, comprising: a scale unit; a light projection unit for projecting a light beam onto said scale unit; a diffraction grating portion formed on said scale unit and irradiated with said light beam; a reference position detection portion formed on said scale unit and irradiated with said light beam; a first sensor for generating an incremental signal using said light beam reflected by or transmitted through said diffraction grating portion; a second sensor for generating a reference position signal using said light beam reflected by or transmitted through said reference position detection portion immediately after being reflected by or transmitted through said diffraction grating portion, wherein when one of said incremental signal and said reference position signal is generated using a transmitted light component of said light beam, the other of said incremental signal and said reference position signal is generated using a reflected light component of said light beam, and wherein said reference position detection portion is a lens.