Patent ID: 7300393

Claim:
An automatic tool changer for a machine tool, including a speed reducer for reducing a rotational speed of a driving force for turning a plurality of tools to be changed, said speed reducer comprising: a driving plate to which the driving force is inputted, provided rotatably and having a ball-driving groove; a holder provided fixedly on a base of the speed reducer and having guide holes for respectively holding and guiding a plurality of balls movably in a radial direction with respect to an axis perpendicular to a face of the holder by restricting circumferential motion of the plurality of balls; and a driven plate to which a tool-holding device for detachably holding the plurality of tools is fixed, provided rotatably and having a ball-driven groove, said driving plate, said holder and said driven plate being coaxially arranged such that the balls respectively held by the guide holes of said holder are engaged with the ball-driving groove of said driving plate and the ball-driven groove of said driven plate, thereby said driven plate is rotated by the driving force inputted to said driving plate, wherein the ball-driven groove of said driven plate is defined by a continuous curved line having a plurality of cycles along a circumference of the driven plate, and the ball-driving groove of said driving plate is defined by a continuous curved line obtained by enlarging two or more cycles of the ball-driven groove in an angular direction by an amount corresponding to a set speed ratio for the speed reducer.