Saturation and stiction control based on the saturation equivalence principle

What is it about?

When a hard nonlinearity, like stiction, is present in a system, if an inverse of the nonlinearity can be constructed, then its effects can be completely compensated. When, saturation is also present, the combination of the inverse nonlinearity, the saturation, and the nonlinearity itself, are equivalent to a saturation, which can then be compensated by standard saturation controllers. This principle, first described by the authors and known as the saturation equivalence principle, is validated for the stiction nonlinearity.

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Why is it important?

In the literature, saturation and stiction are considered individually, and beyond the authors own work, there has not been an attempt at compensation of their combined effects. The control scheme that is proposed in this paper, implies that simple saturation compensation techniques can be used in plants that exhibit complex nonlinear behaviours belonging to a certain class of nonlinearities. This is established by the saturation equivalence principle, which has been previously demonstrated for backlash and deadzone by the authors.