Patent ID: 8759747

Claim:
A rotary encoder comprising: a rotary member which includes a cylindrical surface on which a plurality of marks are arranged in a circumferential direction, and configured to be rotated around an axis of the cylindrical surface; a light source configured to emit a light toward the cylindrical surface; a detector including a plurality of photoelectric conversion elements, and configured to detect marks of the plurality of marks with the light emitted from the light source; and a signal processor configured to obtain a rotation angle of the rotary member based on an output from the detector, wherein the detector is configured to output periodic signals with a plurality of periods, corresponding to the marks of the plurality of marks, and being uneven due to a geometrical layout of the light source, the cylindrical surface, and the detector, and the signal processor is configured to obtain the rotation angle based on the output periodic signals and a reference periodic signal with the uneven plurality of periods and with a reference phase.