Robust servo-system based on two-degree-of-freedom control with sliding mode

A robust servo system, based on a combination of linear robust control and sliding mode control is proposed. This new control system can be said to be a nonlinear system (sliding mode control system) which has a inner loop of linear control (two-degree-of-freedom control). Due to this inner loop of linear control, a disturbance is strongly suppressed but not completely. Then, the outer loop of sliding mode control eliminates this disturbance suppression error. In this paper, a linear robust-servo design of two-degree-of-freedom control system is shown. Sliding mode control is applied to this system and the disturbance suppression characteristics are discussed. Through simulations and experiments, it is proved that the introduction of nonlinear control (sliding mode) drastically improves the disturbance suppression characteristics of a linear system (two-degree-of-freedom control)