Second Order Sliding Mode Hybrid Control for Constrained Manipulators with Friction

This paper deals with the hybrid position/force control of constrained manipulators subjected to uncertainties and disturbances of various nature, including Coulomb friction. The proposed solution is based on sliding-mode control theory, which has been shown to be highly effective in counteracting uncertainties and disturbances for some classes of uncertain nonlinear systems. Specific drawbacks presented by the classical sliding mode techniques are the chattering phenomenon and the algebraic coupling between constraint forces and possibly discontinuous control signals. Both these problems are addressed in the paper by exploiting the robustness properties of second-order sliding-mode control algorithms. A specific algorithm of this kind, recently developed by the authors, is proved to be effective also when the dynamic equation of the system includes discontinuous disturbances.