Rotation measuring mechanism, sheet conveyance apparatus, original reading apparatus, and image forming apparatus

A rotation measuring apparatus, 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 axially 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.

A sheet conveyance apparatus comprising:

• a roller pair formed of two conveyance rollers, one fixed and one movable linearly in a direction perpendicular to an axis of the movable conveyance roller, rotating while contacting each other, thereby forming a conveyance nip;
• a sheet conveyance unit to convey a sheet of recording media by rotation of the two conveyance rollers;
• and
• a rotation measuring mechanism to measure a rotation amount of the conveyance roller that is movable in a direction perpendicular to a rotation axis and pressing against the other of the two conveyance rollers, the rotation measuring mechanism configured to measure a displacement amount of the movable conveyance roller in the direction perpendicular to the rotation axis in addition to the rotation amount so that rotation of the movable conveyance roller is detected and displacement of the movable conveyance roller in the direction perpendicular to the axis of the rotary member is detected.