Motion control systems with H∞ positive joint torque feedback

Positive joint torque feedback (JTF) can compensate the detrimental effects of load torques on position tracking performance. However, with (real world) nonideal torque sources, simple unity gain positive torque feedback can actually deteriorate the performance, or even result in instability. In this work, a new H-infinity joint torque feedback approach is proposed which takes into account the actuator's finite bandwidth dynamics, and minimizes the system's sensitivity to load torque disturbances and load dynamics. We also address implementation issues such as the development of a hydraulic dynamometer testbed for measurement of the disturbance sensitivity and of an innovative method for identifying the actuator dynamics. Experiment results with our experimental direct-drive motor demonstrate that the additional H-infinity positive torque feedback remarkably improves the disturbance attenuation and load decoupling properties of a simple PID motion controller. The optimal torque feedback also reduces the tracking error when dealing with a dynamic load while, unlike the conventional unity joint torque feedback, maintaining robust stability.