Composite control of direct-drive robots

The present trend toward the development of gearless robots aims to eliminate mechanical complexity where possible. Consistent with this objective is the increasing use of brushless motors as joint actuators. These electronically commutated motors do have the required characteristic of high torque at low-speed, but pose a challenge for accurate torque control at the joints. It is shown that by coordinating the feedback linearization design of the mechanical link dynamics with that of the electrical motor dynamics, greater control accuracy can be achieved. The feedback linearization is applied to a reduced-order model which accounts for the electrical dynamics with an asymptotic approximation of the integral manifold. A first-order correction to the current commands of joint actuators improves the torque tracking accuracy of the robot