Tracking control of a harmonic drive actuator with sliding-mode disturbance observers

This paper describes the tracking control of a harmonic drive actuator that features flexible transmission with significant torque ripples. The plant is modeled as a flexible-joint mechanism, and a design approach superior to the conventional integrator backstepping design is demonstrated to obtain a nominal controller. To deal with the torque ripples, internal model principle-based sliding-mode disturbance observers (IMP-SDOBs) are designed by incorporating the disturbance model into the SDOB design. Experimental studies on a harmonic drive actuator equipped with a torque sensor are conducted, demonstrating the feasibility of the proposed controller/observer structure.