Patent ID: 8549947

Claim:
A ball speed reducer ( 20 ) comprising: a worm wheel ( 30 ) including a plurality of recesses ( 32 ) formed in an outer peripheral surface thereof; magnets ( 34 ) that are contained in the recesses ( 32 ); balls ( 36 ) made of a magnetic material, the balls ( 36 ) being partially contained in the recesses ( 32 ), and the balls ( 36 ) being attracted and held by the magnets ( 34 ); and a worm gear ( 22 ) including a spiral groove ( 26 ) formed in an outer peripheral surface thereof, the spiral groove ( 26 ) receiving surfaces of the balls ( 36 ), and the worm gear ( 22 ) being rotationally driven by driving means, wherein each of the recesses ( 32 ) includes a container section ( 32 A) for containing a corresponding one of the magnets ( 34 ) and a spherical section ( 32 B) for receiving a corresponding one of the balls ( 36 ), and wherein each of the recesses ( 32 ) is configured so that a space ( 38 ) is formed between a corresponding one of the magnets ( 34 ) and a corresponding one of the balls ( 36 ) when the magnet ( 34 ) is contained in the container section ( 32 A) and the ball ( 36 ) is received in the spherical section ( 32 B).