Patent ID: 8840513

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 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 installed in the circular cam, is disposed 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 mounted with a ring member of a circular ring shape, is inserted in a through hole formed in the revolving gear, and is in contact with the through hole through the ring member; and a second rotational shaft which is disposed on the central axis of the ring gear, is connected to the penetration pin, and outputs a rotation of the second rotational shaft according to the rotation of the revolving gear, wherein the ring member is mounted to the penetration pin through an elastic member, wherein the elastic member is one of a plurality of elastic members and is of a hollow circular pipe shape, and the ring member is mounted to the penetration pin through the plurality of elastic members, the plurality of elastic members being held in respective retaining grooves around the penetration pin.