INVERSION-BASED SLIDING CONTROL OF A FLEXIBLE-LINK MANIPULATOR

In this paper a control strategy based on nonlinear inversion is consi dered for a class of multi-link, structurally flexible manipulators to achieve small tip-position tracking errors while maintaining robust c losed-loop performance. This is accomplished by defining new outputs n ear the end points of the arms. Motivated by the concept of a sliding surface in variable structure control (VSC), a robustifying term is de veloped to drive the nonlinear plant's error dynamics onto a sliding s urface. On this surface the error dynamics are guaranteed to be indepe ndent of parametric uncertainties. In order to avoid over-excitation o f higher frequency flexural modes due to control chattering, the disco ntinuous functions normally used in classical VSC are replaced by satu ration nonlinearities at the outset. This also facilitates analysis by the standard Lyapunov techniques. The controller performance is demon strated by simulation on a two-link manipulator with the second link f lexible and with considerable parametric uncertainty. In the absence o f the sliding controller, the inversion-based controller results in in stability when subjected to parametric uncertainty.