Patent ID: 8478561

Claim:
A rotation measuring mechanism, comprising: a rotary member; a detection target mounted coaxially on the rotary member and rotating with the rotary member and linearly movable in a direction perpendicular to an axis of the rotary member; a detector to detect the detection target, provided opposite the detection target, that outputs one cycle of a sine wave at each rotation of the detection target, and changes an amplitude of the output sine wave in accordance with displacement of the detection target together with the rotary member in a direction perpendicular to the axis of the rotary member so that rotation of the detection target is detected and displacement of the detection target in the direction perpendicular to the axis of the rotary member is detected; and a processor configured to calculate a rotation amount of the rotary member based on the detection target sine wave and the displacement amount of the rotary member in the direction perpendicular to the axis of the rotary member based on the amount of change in the amplitude of the sine wave produced by the detector.