Robust practical stabilization of nonlinear uncertain plants with input and output nonsmooth nonlinearities

This paper addresses the stabilization problem of "sandwich systems," i.e., intrinsically nonlinear and uncertain single-input-multiple output (SIMO) plants containing simultaneously either backlash or 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 toward a boundary layer, whose maximum width depends on the uncertainty in output measurements caused by the presence of unknown dead zones in sensors. Furthermore, the control laws have been designed as to simultaneously guarantee also the avoidance of actuator nonlinearities, ensuring that the "forbidden region" of dead zone and backlash are never entered, even in the presence of uncertainties. The proposed schemes do not require inversion of nonlinearity. Simulation results show the effectiveness of the proposed controllers.