Variable-Structure Disturbance Observers for Harmonic Drive Actuators

This paper presents the design of a high-order variable-structure disturbance observer (VSDO) that yields asymptotic estimation of unknown disturbances described by polynomial functions of time with arbitrary degrees. In comparison with conventional VSDO, the high-order VSDO requires a small switching gain for ensuring the existence of a sliding mode, thus diminishing the chattering phenomenon further. Two high-order VSDOs were implemented to simultaneously observing the motor-side and the load-side disturbances in a harmonic drive actuator. Experimental results show that the compensation provided by the high-order VSDOs effectively deals with the disturbances due to harmonic drive gearing.