H∞-based robust torque control of harmonic drive systems under free- and constrained-motion applications

In this paper the torque control of a harmonic drive system for constrained-motion and free-motion applications is examined in detail. A nominal model for the system is obtained in each case from experimental frequency responses of the system, and the deviation of the system from the model is encapsulated by a multiplicative uncertainty. Robust torque controllers are designed using these information in an H_∞ -framework, and implemented on two different setups. From time and frequency domain experiments, it is shown that the closed-loop system retains robust stability, while improving the tracking performance exceptionally well