Patent ID: 8382629

Claim:
A reduction gear transmission comprising: a motor gear fixed to an output shaft of a motor; an intermediate shaft extending parallel to the output shaft of the motor; a first gear fixed to the intermediate shaft and meshing with the motor gear; a second gear fixed to the intermediate shaft; an input shaft extending parallel to the output shaft of the motor and having a through hole formed along an axis line of the input shaft, wherein the input shaft has an input gear meshing with the second gear and eccentrically rotates an eccentric rotation member in accordance with the rotation of the input gear; an external gear having a center through hole formed at a center position of the external gear, the external gear engaging with the eccentric rotation member, wherein the external gear revolves orbitally around the axis line of the input shaft when the input shaft rotates; an internal gear having a number of teeth differing from a number of teeth of the external gear, and the internal gear surrounding the external gear while the teeth of the internal gear are meshing with the external gear, and the internal gear allowing the orbital revolution of the external gear, wherein: when viewed from the axis line of the input shaft, the motor gear and the first gear mesh at a position which is offset from a straight line formed by connecting an axis line of the intermediate shaft and the axis line of the input shaft, and the output shaft of the motor and the intermediate shaft are arranged within an inner diameter of the internal gear; and a crankshaft that extends parallel to the input shaft and has a fourth gear; wherein: the input shaft has on an outer face of the input shaft a third gear meshing with the fourth gear, a second through hole which is offset from the center through hole of the external gear is formed on the external gear, the crankshaft, which comprises the eccentric rotation member, passes through the second through hole, and the eccentric rotation member is formed on the crankshaft and engages with the external gear inside the second through hole.