Patent ID: 8562474

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 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; a sliding member which has a hollow circular tube shape, is engaged with the outer circumference of the penetration pin to be able to slide thereon, and has a shape which becomes thin toward its one end; and a biasing member which biases the sliding member in a direction where the shape becomes thin to be in contact with the inner circumference of the through hole, wherein the inner circumference of the through hole of the revolving gear has a shape which becomes narrow toward its one end.