Patent ID: 7147582

Claim:
A power transmission device comprising: an input shaft; an output shaft; a plurality of internally meshing planetary gear mechanisms, each including an external gear and an internal gear having external teeth and internal teeth a difference in a number of teeth between which is slight; wherein at least two of the plurality of internally meshing planetary gear mechanisms are disposed in parallel on a path of power transmission and the at least two of the plurality of internally meshing planetary gear mechanisms are different from each other in power transmission characteristics, wherein for the at least two of the plurality of internally meshing planetary gear mechanisms to be disposed in parallel on a path of power transmission, a plurality of power-transmissible routes through which power can be transmitted must exist between shared members, wherein factors of the mutually different power transmission characteristics of the two internally meshing planetary gear mechanisms include at least one of rotational resistance, rigidity, and backlash of a rotation system in each mechanism.