Robust Perfect Tracking Control With Discrete Sliding Mode Controller

The closed-loop transfer function of a plant controlled with a classical feedback controller, depends on the dynamics of the plant. Since most feedforward tracking controllers are designed based on this closed-loop transfer function, they are not robust against plant model uncertainties. Sliding-mode controllers have the property that when the system is on the switching line, the closed-loop behavior is independent of the plant dynamics. As a result, it can be expected that a feedforward control design based on this closed-loop behavior is robust against plant model uncertainties. This paper studies this feedforward robustness issue in detail and verifies the results on an experimental test setup: a stage driven by a linear motor. An integrated procedure is proposed in designing the closed-loop discrete-time sliding mode controller using the reaching law method.