Patent ID: 8666261

Claim:
A photoelectric encoder comprising: a scale having an incremental track formed with reflection gratings at equal intervals along a length measurement direction; a detector which displaces relative to the scale; a reflection origin mark formed in at least one place of the incremental track, provided on the scale; alight application section provided in the detector for applying light to the incremental track; a pair of origin signal reception sections provided in the detector and placed symmetrically with respect to the light application section in the length measurement direction; and a signal processing section having an origin signal processing section configured to find a differential signal of output from the pair of origin signal reception sections by light reflected on the origin mark, configured to generate an origin detection signal corresponding to a position of the origin mark, and configured to output an origin signal, wherein the origin signal processing section is adapted to provide the maximum value of the signal level output from the origin signal reception sections by side lobe light occurring as reflected on the origin mark as a stipulated value, provide an effective area of origin detection between the first position at which output of one of the origin signal reception sections for outputting a larger signal level than the stipulated value earlier than the relative displacement becomes a larger signal level than the stipulated value and the first position at which output of the other origin signal reception section exceeds the stipulated value and then becomes a smaller signal level than the stipulated value, and generate the origin detection signal in the effective area.