Control of a Direct-Drive Arm

A direct-drive arm is a mechanical arm in which the shafts of articulated joints are directly coupled to the rotors of motors with high torque. Since the arm does not contain transmission mechanisms between the motors and their loads, the drive system has no backlash, small friction, and high mechanical stiffness, all of which are desirable for fast, accurate, and versatile robots. First, the prototype robot is described, and basic feedback controllers for single-link drive systems are designed. Second, feedforward compensation is discussed. This compensation significantly reduces the effect of interactions among multiple joints and nonlinear forces. The experiments showed the excellent performance of the direct-drive arm in terms of speed and accuracy.