Patent ID: 8303458

Claim:
An automatic speed reduction ratio switching apparatus for automatically switching a speed reduction ratio between an input shaft connected to a rotary drive source and an output shaft connected to an actuating member, comprising: a sun gear connected to the input shaft; a carrier connected to the output shaft; a planetary gear mounted rotatably in the carrier and meshed with the sun gear; an internal gear meshed with the planetary gear and which is capable of displacement in axial directions; a thrust force generating mechanism that generates a thrust force between the internal gear and the planetary gear; a rotation regulating mechanism that regulates rotational movement of the internal gear when the internal gear is displaced in at least one of the axial directions; and a slide resistance member arranged between the internal gear and the carrier for regulating movement in the axial directions of the internal gear, and for enabling displacement of the internal gear in the axial directions when the thrust force is applied at or above a predetermined value, the slide resistance member comprising only a packing member without a viscous resistance medium, wherein the planetary gear revolves instead of rotate due to a static frictional force between the packing member and an inner circumferential surface of an outer member of the internal gear when a rotation having a low load is transmitted to the input shaft.