DECELERATING MECHANISM

PURPOSE:To secure a high reduction gear ratio, by setting a roller at a circumferential bisection position between an inside member and a thin outside member, while fitting the outside member in the inner circumference of a housing. CONSTITUTION:A roller 23 is set up at a circumferential bisection position between an inside member 21 and a thin outside member 22, and this outside member 22 is deformed into an oval, while the outside member 22 is fitted in the inner circumference of a housing 3, making a contact point between the outside member 22 and the housing 3 into the partial rolling contact between two points P. With this constitution, it comes to the following equation that a reduction gear ratio R=alphaX(d-D)/D (alpha; revolution ratio of the rotor to shaft rotation, d; ID size of the housing, D; OD size of an outer ring) whereby revolution of the point P is yet more reduced as far as alpha than that in case of an input shaft and, what is more, since deceleration by a difference between the ID size of the housing 3 and the OD size of the outer ring operates in a multiplicative manner, a high reduction gear ratio can be secured.