Patent ID: 7597643

Claim:
An eccentrically-orbital gear device, comprising: an internal gear; an external gear placed inside the internal gear; an input shaft having a first input-side eccentric part which is inserted in a central hole formed in the external gear such that the first input-side eccentric part is rotatable around its center line; and a crankshaft rotatably supported by a device main body, the crankshaft having a first crank-side eccentric part which is engageable with the external gear with an eccentricity equal to that of the first input-side eccentric part, the external gear producing eccentrically-orbital motion while being meshed with the internal gear and being inhibited by the crankshaft from rotating, wherein the input shaft has a second input-side eccentric part whose eccentricity is larger than that of the first input-side eccentric part, the second input-side eccentric part is provided with a driving member for driving the crankshaft such that the driving member is rotatable around a center line of the second input-side eccentric part, and the crankshaft has a second crank-side eccentric part which has an eccentricity equal to that of the second input-side eccentric part and which is engageable with the driving member.