Force control of direct-drive robot

This paper deals with a torque-position hybrid control of direct-drive robot. The tested robot has three-degrees-of-freedom and each joint has a direct-drive AC motor with a high resolution encoder. A direct-drive of each link realizes high precision task because no transmission exists between the shaft of the motor and the link. On the contrary, the interactive forces give significant effects to the joint motion as the equivalent gear ratio is unity. It is essential to reduce these interactive terms in realization of direct-drive robot. Here, a disturbance observer which estimates a disturbance torque is applied to a motion control system, and an acceleration-based torque controller is realized in the force task.