Patent ID: 6635863
Filing Date: 2003-10-21
Classification: G01D

Abstract:
An optical encoder, comprising:a main scale having first optical gratings formed thereon with angular pitch P along a measurement axis, said measurement axis describing a circular arc; a detection head having photodetective device arrays which are formed thereon and serve as second optical gratings, said detection head being arranged opposing to said main scale and relatively movable along said measurement axis to detect relative displacement between said main scale and said detection head, wherein said second optical gratings are arranged with distance pitch P on a straight line and the photodetective device arrays are arranged with a phase difference of (2n+1)P/4 (n: an integer); and an aperture for defining said photodetective device arrays so that an effective photodetective surface of said photodetective device arrays have sizes of a track width larger at the center and smaller at peripheries.