Patent ID: 7145131

Claim:
An absolute encoder comprising: a rotation axis; a rotating plate attached to the rotation axis, having a first opening and a second opening formed in a prescribed positional relation to the first opening; a photodetector that has a photosensitive area in which a plurality of pixels are two-dimensionally arrayed, is provided so as to face one side of the rotating plate, and is able to obtain light intensity profiles in a first direction and a second direction in the two-dimensional array, respectively; light supplying means that is provided so as to face the photosensitive area of the photodetector with the first opening and second opening of the rotating plate placed therebetween and supplies measuring light for measuring an angle; and angle calculating means for calculating an absolute value of the rotating angle of the rotation axis based on a correlation between a first detected position and a second detected position where the measuring light components passed through the first opening and second opening of the rotating plate are respectively detected by the photosensitive area of the photodetector, wherein, in said photodetector, one pixel is composed of a plurality of photosensitive portions outputting an electric current responsive to the intensity of respective incident light components being disposed on the same plane adjacent to each other; photosensitive portions at one side of a plurality of photosensitive portions composing corresponding respective pixels are electrically connected to each other over a plurality of pixels arrayed in the first direction; and photosensitive portions at the other side of a plurality of photosensitive portions composing corresponding respective pixels are electrically connected to each other over a plurality of pixels arrayed in the second direction.