Patent ID: 7145130

Claim:
A rotation detecting device comprising: a non-rotating internal gear concentrically arranged with a rotation center of a rotary body; a planetary gear that meshes with the internal gear and that rotates and revolves on an inner circumference of the internal gear as the rotary body rotates; a rotation transmitting member that is concentrically arranged with the rotation center of the rotary body and that rotates on its own axis by the rotation of the planetary gear; an output medium provided in the rotation transmitting member; a rotation angle detecting unit arranged to face the output medium for detecting a rotation angle of one or more full rotations of the rotary body; and a rotor having a code disc anchored to the rotor; the rotor having an eccentric shaft formed in the rotor; the rotation center of the rotor coinciding with a rotation center of the rotary body; the rotary body being anchored to a central opening of the rotor; and the eccentric shaft of the rotor is attached to a central opening of a planetary gear so that the planetary gear meshes with the non-rotating internal gear.