Patent ID: 8517878

Claim:
A planetary gear mechanism comprising: a first member having a first internally toothed gear formed on an inner circumferential surface thereof; a second member that has a second internally toothed gear formed on an inner circumferential surface thereof, and is rotatable relative to the first member about an axis of input and output shafts; an oscillating member that is formed in an annular shape, and includes a first externally toothed gear that is formed on an outer circumferential surface thereof to be able to mesh with the first internally toothed gear, and a second externally toothed gear that is formed on the outer circumferential surface to be able to mesh with the second internally toothed gear, such that the number of teeth of the first externally toothed gear is smaller than the number of teeth of the first internally toothed gear, and the number of teeth of the second externally toothed gear is smaller than the number of teeth of the second internally toothed gear, the oscillating member being formed so as to oscillate relative to the first member and the second member, so that only a circumferential portion of the first externally toothed gear meshes with the first internally toothed gear, and only a circumferential portion of the second externally toothed gear meshes with the second internally toothed gear; and a third member including an eccentric portion having an outer circumferential surface whose center is displaced from the axis of the input and output shafts, said eccentric portion supporting an inner circumferential surface of the oscillating member and rotating about the axis of the input and output shafts so as to oscillate the oscillating member, or being rotated about the axis of the input and output shafts due to oscillation of the oscillating member, wherein driving force is applied to the third member to oscillate and rotate the oscillating member, and move a circumferential position at which the first externally toothed gear and the first internally toothed gear mesh with each other, and a circumferential position at which the second externally toothed gear and the second internally toothed gear mesh with each other, so that the driving force is delivered at a reduced speed to at least one of the first member and the second member, or driving force is applied to at least one of the first member and the second member so as to move a circumferential position at which the first externally toothed gear and the first internally toothed gear mesh with each other, and a circumferential position at which the second externally toothed gear and the second internally toothed gear mesh with each other, and oscillate and rotate the oscillating member, so that the driving force is delivered at an increased speed to the third member; a part of the second member is inserted in a central portion of the third member; and a second support bearing is disposed between the third member and said part of the second member inserted in the third member.