Discrete-time variable structure controller with a decoupled disturbance compensator and its application to a CNC servomechanism

This paper develops a new approach in regulation and tracking, combining a disturbance compensator with a controller, both of which are formulated in the discrete-time domain using the variable structure concept. For single-input single-output, linear time-invariant systems, an algorithm for exactly decoupling the disturbance estimation dynamics from the sliding mode dynamics is developed. This allows the two dynamic modes to be tuned separately. It is shown that the developed approach preserves the robustness properties of the sliding mode and asymptotically achieves zero tracking error, in the presence of external disturbances and parametric uncertainties. Both computer simulation results and experimental results using a CNC milling machine are used to demonstrate those properties of the proposed method in both regulation and tracking.