| 摘要 |
A speed reducer has a crankshaft to be rotated in conjunction with a drive unit. First through third eccentric portions are provided on the crankshaft. First through third externally-toothed gears are adapted to be moved respectively in conjunction with the first through third eccentric portions. Pin teeth are disposed along an inner periphery of a case to allow each of the first, second and third externally-toothed gears to be in meshing engagement therewith. An output shaft unit is adapted to be rotated in conjunction with the first, second and third externally-toothed gears. The first, second and third eccentric portions are arranged with a given phase difference in a rotation direction of the crankshaft with respect to each other. Each of the first, second and third externally-toothed gears is in meshing engagement with less than half of the plurality of pin teeth.
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