US Patent 8482242 Rotary drive device

A first angle-detecting unit outputs a first rotation angle according to the rotation angle of a rotation shaft of a servo motor. A second angle-detecting unit outputs a second rotation angle according to a rotation angle of a rotation shaft of a reduction gear. A torque calculation unit calculates the torque acting on the rotation shaft of the reduction gear according to the angle difference between the first rotation angle and the second rotation angle. An angle-control unit generates a torque reference value according to the difference between the angle reference value and the second rotation angle. A torque control unit generates a current reference value according to the difference between the torque reference value and the torque.