Patent ID: 8651992

Claim:
A speed reducer comprising: a ring gear which is formed with a plurality of gear teeth on the inner circumference thereof; a revolving gear which is disposed inside the ring gear, is formed with a plurality of gear teeth on the outer circumference thereof and is engaged with the ring gear; a circular cam which is disposed to be able to rotate with respect to the revolving gear in a central position of the revolving gear; a first rotational shaft which is vertically installed in the circular cam on the central axis of the ring gear, and rotates the circular cam around the central axis to revolve the revolving gear around the central axis; a penetration pin which is inserted in a through hole formed in the revolving gear; a second rotational shaft which is disposed on the central axis of the ring gear, is connected to the penetration pin, and outputs its rotation according to the rotation of the revolving gear; and an elastic member which has a shape of a circular ring, is mounted to either an inner circumferential surface of the through hole or an outer circumferential surface of the penetration pin, and is formed so that an inner diameter of the circular ring is able to move with respect to an outer diameter of the circular ring.