Patent ID: 7391010

Claim:
A photoelectric encoder comprising: a light-emitting device; and a plurality of light-receiving devices arranged in one direction in a region that light from the light-emitting device can reach, for detecting an amount of movement of a moving object, the moving object alternately having in a common pitch a light-on portion that produces a state in which light is incident from the light-emitting device to the light-receiving devices and a light-off portion that produces a state in which the light is not incident from the light-emitting device to the light-receiving devices, wherein the plurality of light-receiving devices have same dimensions and comprise a first group of four light-receiving devices which are arranged in the one direction in a second pitch such that phases of the four light-receiving devices in the first group are different from each other by 45° in a light-on portion width and a second group of four light-receiving devices which are arranged in a third pitch such that phases of the four light-receiving devices in the second group are different from each other by 45° in a light-off portion width, the second group of four light-receiving devices corresponding with the first group of four light-receiving devices; and a comparing section which respectively obtains first, second, third and fourth differential signals by taking a difference between outputs of light-receiving device pairs, each light-receiving device pair having a first light-receiving device from the first group of light-receiving devices and a second light-receiving device from the second group of light-receiving devices, of which phases of the paired outputs are different from each other by 180°; a first logical operating section which takes an exclusive-OR of logical values expressed by the first and second differential signals that have phases different from each other by 90°; and a second logical operating section which takes an exclusive-OR of logical values expressed by the third and fourth differential signals that have phases different from each other by 90°, wherein the comparing section comprises a plurality of amplifiers corresponding to the respective light-receiving device pairs, the plurality of amplifiers are arranged in the one direction along an array constructed of the plurality of light-receiving devices, and a center position of the array constructed of the plurality of light-receiving devices and a center position of an array constructed of the plurality of amplifiers coincide with each other in the one direction.