Patent ID: 8403794

Claim:
A decelerator, decelerating the rotation of an input shaft and transmitting the decelerated rotation to an output shaft, comprising: an eccentric part, provided on the input shaft and comprising a first and second eccentric part which are arranged so as to neutralize the centrifugal force due to the eccentric motion to each other; a revolution member, rotatably retained in the eccentric part and making a revolution motion in accordance with the rotation of the input shaft around its rotation axis, the revolution member further comprising a first revolution member, rotatably retained in the first eccentric part; and a second revolution member, rotatably retained in the second eccentric part and having the same outer periphery shape as the first revolution member; an outer periphery engagement part, engaging with the outer periphery of the revolution member to generate the rotation motion of the revolution member; a motion conversion mechanism, converting the rotation motion of the revolution member to the rotation motion around the rotation axis of input shaft and transmitting it to the output shaft; a counter weight, attached to the input shaft so as to cancel the imbalance inertia moment generated due to the revolution motion of the revolution member, the counterweight further comprising a first counter weight and a second counter weight, which are attached to the input shaft on both sides of the first and second eccentric parts to shift the phases of the first and second counter weights by 180 degrees from the first and second eccentric parts respectively in order to cancel the imbalance inertia couple generated by the rotations of the first and second revolution members.