An inverse dynamics sliding control technique for flexible multi-link manipulators

In this paper, a control strategy based on nonlinear inversion is considered that results in small tip-position tracking errors while maintaining robust closed-loop performance for a class of multi-link structurally flexible manipulators. This is achieved by defining new outputs near the end points of the arms as well as by augmenting the nominal control inputs by terms that ensure stable operation of the closed loop system in the presence of considerable parametric uncertainties. Motivated by the concept of a sliding surface in variable structure control (VSC) a robust control term is developed to drive the nonlinear plant´s error dynamics onto a sliding surface. The discontinuous functions normally used in classical VSC are replaced by saturation nonlinearities at the outset. This also facilitates analysis by the standard Lyapunov techniques. The controller performance is demonstrated by simulation on a two-link flexible manipulator with a considerable amount of parametric uncertainty