Robust torque control of harmonic drive under constrained-motion

A harmonic drive is a compact, light-weight and high-ratio torque transmission device which has almost zero backlash. Its unique performance features captures the attention of designers in many industrial applications, especially in robotics. However, the torque control of harmonic drive systems is still a challenging problem for researchers. In this paper the torque control of an harmonic drive system for constrained motion is examined in detail. A nominal model for the system is obtained from experimental frequency responses of the system, and the deviation of the system from the model is encapsulated by multiplicative uncertainty. A robust torque controller is designed using this information in an H_∞-framework, and implemented on two different setups. It is illustrated that the performance features of the closed-loop system is exceptionally good, both in time and frequency domains