Practical stabilization of nonlinear plants with uncertain input and output nonlinearities

This paper addresses the stabilization problem of "sandwich systems", i.e. intrin- sically nonlinear and uncertain SIMO plants containing simultaneoulsy either backlash and dead zone in the actuator and dead zones in sensors. The proposed controllers, based on sliding mode control, have been shown to achieve state (hence output) boundedness. The rationale followed in control design consists in ensuring the achievement of a sliding motion which, in turn, guarantees the attraction of the state vector towards a boundary layer, whose maximum width depends on the uncertainty on output measurements caused by the presence of unknown deadzones in sensors. Furthermore, the control laws have been designed as to simultaneously guarantee also the avoidance of actuator nonlineari- ties, ensuring that the ’forbidden region’ of dead zones and backlash are never entered, even in the presence of uncertainties. Simulation results show the effectiveness of the proposed controllers.