US Patent 7051610 Ball-worm transmission

A ball-worm transmission is provided which replaces the sliding friction of the classic worm mechanism with the rolling friction of spherical balls. The ball-worm transmission assembly includes a worm which defines a recirculation path, and a gear coupled to the worm via a plurality of spherical balls. The gear includes a plurality of teeth each having a thickness in a central plane of the gear and a lesser thickness towards both sides of the gear, so that a gap is defined between the teeth is larger towards both sides of the gear than in the central plane of the gear.