Transmission apparatus with reduced frictional force

A transmission apparatus comprising a circular spline, a flexspline, and a wave generator and having an elliptic cam having major and minor axes and an input shaft connected to said wave generator, and a wave generator bearing which is arranged around said cam and in which a plurality of balls are interposed between inner and outer races, wherein

• said wave generator bearing comprises a ring-shaped retainer having a plurality of pockets for holding said balls which roll between said inner and outer races to be in contact with said inner and outer races and to be separated from each other in a circumferential direction;
• each of said pockets of said retainer has a pocket inner surface forming a narrow opening portion at the inner race side and forming, at the outer race side, a wide opening portion having a larger size than said narrow opening portion at the inner race side;
• and
• said pocket inner surface has a first contour line curved in a palne perpendicular to an axis of said wave generator, whereby
• the balls at minor axis positons of said cam are in contact with the narrow opening portion of said pocket, and the surface of the balls at major axis positions of asid cam engage the pocket inner surface in an area containing a substantially central portion of said first contour line, said substantially central portion being substantially midway between said wide opening portion and said narrow opening portion.