Patent ID: 7553249

Claim:
A speed reducer comprising: a crankshaft adapted to be rotated in conjunction with a drive unit; a first eccentric portion provided on said crankshaft; a second eccentric portion provided on said crankshaft; a third eccentric portion provided on said crankshaft; a first externally-toothed gear adapted to be moved in conjunction with said first eccentric portion; a second externally-toothed gear adapted to be moved in conjunction with said second eccentric portion; a third externally-toothed gear adapted to be moved in conjunction with said third eccentric portion; a plurality of pin teeth disposed along an inner periphery of a case to allow each of said first, second and third externally-toothed gears to be in meshing engagement therewith; and an output shaft unit adapted to be rotated in conjunction with said first, second and third externally-toothed gears, wherein said first, second and third eccentric portions are arranged with a given phase difference in a rotation direction of said crankshaft with respect to each other, wherein each of said first, second and third externally-toothed gears is in meshing engagement with less than half of said plurality of pin teeth.