US Patent 9314934 Gravity-counterbalanced robot arm

An arm assembly for use in a robot to provide gravity counterbalancing of the robot arms. The arm assembly includes an arm and a drive assembly. The arm assembly includes a differential interconnecting the drive assembly with the arm link. The differential is attached to a torso-side or upper end of the arm link, and the differential is adapted to provide gravity counterbalancing for the predefined mass of the arm link. A pair of half counterweights are provided and arranged to each move in one degree of freedom and to provide two equal counterweights to the differential's two inputs such as input gears, pulleys, or the like. The drive assembly includes two motors that are grounded. In some embodiments, both the motors and the counterweights are spaced apart from the robot's shoulder, i.e., spaced apart from the differential near the robot's pelvis or low in the torso.