Patent ID: 8826718

Claim:
An angle detection apparatus comprising: a grating disk supported by a rotation axis; at least three detectors equidistantly positioned opposite a front surface of the grating disk in a circumferential direction of the grating disk; and an eccentricity amount estimator configured to cause each of the detectors to: detect a rotation angle of the grating disk rotated by a reference angle from a predetermined initial position; measure an angle error at each of the at least three detectors from a difference between the rotation angle and the reference angle; acquire a tangential vector by rotating by 90° a directional vector of each of the at least three detectors relative to a rotational center of the rotation axis; and calculate an eccentricity vector whose inner product with the tangential vector is the angle error, wherein in the calculation of the eccentricity vector; the eccentricity vector is calculated a plurality of times with respect to different reference angles rotated from the predetermined initial position; a detector center is determined from a plurality of calculated eccentricity vectors; and the eccentricity vector of the rotational center of the rotation axis relative to the detector center is calculated from one of an initial eccentricity vector from the detector center to the predetermined initial position and the eccentricity vector.