Patent ID: 8100807

Claim:
A reduction gear transmission comprising: a first reduction gear unit having a first input shaft that rotates in accordance with a rotation of an output shaft of a motor, a first external gear that revolves orbitally around an axis line of the first input shaft in accordance with a rotation of the first input shaft, a first internal gear meshing with the first external gear and having a number of teeth differing from a number of teeth of the first external gear, and a first output shaft that rotates around an axis line of the first internal gear; and a second reduction gear unit having a crankshaft that rotates in accordance with a rotation of the first output shaft, an eccentric cam that revolves orbitally around an axis line of the crankshaft in accordance with a rotation of the crankshaft, a second external gear engaging with the eccentric cam and having a through hole at a center of the second external gear, a cylindrical member passing through the through hole of the second external gear, a second internal gear meshing with the second external gear and having a number of teeth differing from a number of teeth of the second external gear, and a second output shaft rotating around an axis line of the second internal gear, wherein the first reduction gear unit is positioned between an extensional plane that continues from an outer circumferential surface of the second reduction gear unit and an extensional plane that continues from an inner circumferential surface of the cylindrical member.