Controller structure for plants with combined saturation and stiction

A compensation strategy for plants that suffer from both stiction and saturation in the input is proposed. This strategy exploits a principle established previously by the authors referred to as the “saturation equivalence.” This approach shows that, for systems affected by a certain class of nonlinearities and saturation at the actuator, the addition of a right inverse of the nonlinearity, in series with the plant, results in a saturation. This article shows that a stiction model belongs to this class of nonlinearities and that it can be compensated using the method of “saturation equivalence” by implementing a right inverse for an approximate stiction model. Then, the resulting saturation can be treated by traditional methods, such as anti-windup or model predictive control. Results are demonstrated in a case study plant via simulation.