Patent ID: 7435945

Claim:
A photoelectric encoder comprising: a main scale including a main scale grating having a main scale grating pitch p 1 ; a light receiving portion with an index grating pattern having an index grating pitch p 2 and a light receiving element, the light receiving portion capable of moving relative to the main scale, the light receiving portion configured to detect a bright/dark pattern comprising an image of the main scale grating; and a lens element having a focal length f, an effective plane of the lens element located at a distance B from a plane of the index grating pattern, the lens element disposed between the main scale and the light receiving portion during operation, with the effective plane of the lens element located at a distance A from a plane of the main scale grating during operation, wherein the photoelectric encoder is configured such that during operation: light from the main scale grating is input to the lens element and output from the lens element; the light output from the lens element forms the bright/dark pattern comprising an image of the main scale grating focused proximate to the plane of the index grating pattern; and the lens element is positioned relative to the main scale grating such that a distance ratio (B/A) is nominally equal to a pitch ratio (p 2 /p 1 ), whereby the image of the main scale grating focused proximate to the plane of the index grating pattern has a magnified grating pitch that is nominally equal to the index grating pitch p 2 .