Harmonic drive apparatus

Claim 1

A harmonic drive apparatus comprising: a circular spline which has internal spline teeth and which is rotatable around a rotational axis; a flexible cylindrical flexspline which is concentrically disposed within the circular spline and which has external spline teeth, the number of flexspline external teeth being less than the number of internal teeth of the circular spline; a wave generator disposed within the flexspline for flexing the flexspline in the radial direction thereof so as to locally engage the flexspline external teeth with the internal teeth of the circular spline; and a multi-row ball bearing flexible in the radial direction thereof disposed between the wave generator and the flexspline, said bearing including balls equally spaced along the circumferential direction of the wave generator in at least two circumferential lines surrounding said wave generator inside said flexspline, the circumferential lines being separated from one another in the axial direction of the wave generator, and means for increasing the frequency of torque fluctuation of the apparatus when said generator is rotated, said means including means, flexible in the radial direction of said bearing, for retaining the balls in each of the circumferential lines offset from the balls in at least one other of the circumferential lines with respect to the circumferential direction of the wave generator.