Patent ID: 8867964

Claim:
A rotary body unit comprising: a first rotary body configured to rotate about a central axis by a drive force input from an external source and having a first outer peripheral surface, the first rotary body having a radius that is a distance from the central axis of the first rotary body to the first outer peripheral surface; a second rotary body having a second outer peripheral surface contacting the first outer peripheral surface of the first rotary body, a friction being generated between the first outer peripheral surface and the second outer peripheral surface when the first rotary body rotates, the second rotary body being configured to rotate about a central axis of the second rotary body by following a rotation of the first rotary body through the friction, the second rotary body having a radius that is a distance from the central axis of the second rotary body to the second outer peripheral surface; a first gear configured to rotate together with the first rotary body; and a second gear configured to rotate together with the second rotary body and directly, meshingly engaged with the first gear, the first gear having a first pitch circle defined by meshing engagement with the second gear, the second gear having a second pitch circle defined by the meshing engagement with the first gear, wherein a radius of the first pitch circle is smaller than the radius of the first rotary body, and a radius of the second pitch circle is larger than the radius of the second rotary body.