A dual-loop robust controller for DC electro-mechanical servo system

In order to further improve the tracking performances of the conventional disturbance observer (DOB)-based control schemes, a dual-loop robust control scheme is proposed for DC electro-mechanical servo system. The outer-loop sliding mode controller (SMC) is designed in order to deal with the impacts from the remainder equivalent disturbances, which is due to the inadequate estimation of the inner-loop DOB. Meanwhile, the existence of DOB can reduce the switching gain of SMC law, which can suppress the high-frequency chattering of control input to a certain extent. Moreover, an approximate differential method is employed in order to reliably acquire the differential information in a noisy environment. From the experiment results on a DC motor servo system, it is presented that the proposed dual-loop control scheme can effectively improve the tracking performances with respect to higher tracking accuracy and stronger system robustness against external disturbances and parameter perturbations, compared with the traditional DOB+PD control scheme.