Disturbance attenuation and load decoupling with H∞ positive joint torque feedback

Positive joint torque feedback 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. An H^∞ joint torque feedback is proposed which takes the dynamics and uncertainty of the actuator into account and minimizes the system´s sensitivity to load torques. In our experimental direct-drive system, the H^∞ positive torque feedback inner loop drastically improved the disturbance attenuation (25 dB) and load decoupling properties of a simple PID position controller