Load Sensitivity Analysis and Adaptive Control of a Direct-Drive Arm

Direct-drive arms have excellent features including no backlash, small friction, and high mechanical stiffness. The drive system, however, is sensitive to the change in system parameters; When the arm grasps an object, for example, dynamic responses become significantly different. In this paper, we analyze the sensitivity of the direct-drive arm to the change of inertial loads at its endpoint. Then, an adaptive control scheme on the basis of the sensitivity analysis is presented. The method is implemented on a 3 d.o.f. direct-drive arm and experiments of trajectory control demonstrate the effectiveness of the method.