Rotation transmitting device

A rotation transmitting device which has a rotation input shaft disposed in a first space, a rotation output shaft disposed in a second space, a flexible meshing gear drive for transmitting a rotational motion introduced via the rotation input shaft into a side of the rotation output shaft, wherein the flexible meshing gear drive has a circular rigid internal gear, a flexible external gear and a wave generator for flexing the flexible external gear radially to mesh it partially with the rigid internal gear and for shifting meshing portions circumferentially, and wherein the wave generator is connected with the rotation input shaft, the rigid internal gear is connected with the rotation output shaft, and the flexible external gear is used as a partition wall for air-tightly partitioning the first and second spaces:

• comprising
• a bearing mechanism for rotatably supporting the rotation output shaft, a magnetic fluid as lubricant for lubricating portions to be lubricated in the bearing mechanism, and a magnetic circuit for generating a magnetic force to retain the magnetic fluid on the portions to be lubricated;
• wherein the bearing mechanism has first and second roller bearings for rotatable supporting the rotation output shaft, and a first spacer which is inserted between outer races of the first and second roller bearings to maintain the gap between the roller bearings to be constant,
• the first spacer has a magnet member magnetized along an axial line direction of the rotation transmitting device, a first spacer piece inserted between the magnet member and the outer race of the first roller bearing, and a second spacer piece inserted between the magnet member and the outer race of the second roller bearing,
• the first and second roller bearings, and at least a portion of the rotation output shaft supported by the first and second roller bearings are made of a magnetic material, and
• the magnetic circuit is formed along a route starting from the first spacer piece, passing through the rotation output shaft and the second roller bearing, and returning to the first spacer piece.