Patent ID: 8684877

Claim:
A gear transmission having an internal gear and an external gear meshing with each other, one of the internal gear and the external gear being eccentrically rotatable relative to the other, the gear transmission comprising: a crankshaft having an end fixed to a first gear, the crankshaft being configured to eccentrically rotate one of the internal gear and the external gear; a two-stage gear having a center gear, which meshes with the first gear, and an outer-toothed ring gear, which is disposed coaxially with the center gear and surrounds the first gear; and a second gear meshing with the outer-toothed ring gear, the second gear being configured to transmit torque from a motor to the two-stage gear; wherein the two-stage gear is configured such that a range where an outer teeth portion of the center gear is formed and a range where an outer teeth portion of the outer-toothed ring gear is formed are each at least partially disposed in a common plane that is perpendicular to a rotational axis of the gear transmission.