Tip position tracking of flexible-link manipulators based on online robust trajectory modification

This paper presents a composite controller for tip position tracking of flexible link manipulators. In this regard, an inner/outer control structure is proposed. Opposed to previous conducted researches in this area, the desired reference trajectory is robustly modified (online) to minimize the tracking error of the tip utilizing the outer controller. The outer trajectory modifier is a μ synthesis based controller which modifies the reference trajectory of the inner loop in the uncertain situations. In the inner control loop a Lyapunov Redesign Feedback Linearization (LRFL) approach is applied to alleviate the degrading effects of uncertainties and nonlinearities presented in the dynamics of the flexible link. In the inner control loop, a conventional redefined output namely "close to the tip" is considered to avoid the difficulties associated with non-minimum phase behavior of the main output (tip). In conventional control strategies this choice leads to undesirable oscillations in tip. These oscillations are considerably minimized applying the outer trajectory modifier. Simulation results performed on a single-link flexible manipulator (with the parameters of an experimental setup) are presented to illustrate the significant improvements of performance over the conventional methods.