An infinite-order integral disturbance observer for improved estimation of periodic disturbances in motion control systems

ABSTRACT In this paper, a disturbance observer is devised for motion control systems suffering unknown periodic disturbances. In the proposed scheme, the structure of a so-called integral disturbance observer is utilized for its error-feedback form, and the repetitive learning control theory is applied to the observer design, constituting an infinite-order integral disturbance observer to obtain an enhanced estimation of a periodic disturbance. A comparative study of different disturbance observers is performed, and experimental results are reported, practically showing the effectiveness of the proposed scheme.