Experimental results on neural network-based control strategies for flexible-link manipulators

The problem of controlling a nonminimum phase nonlinear system with application to tip position control of a flexible-link manipulator is considered. An output re-definition strategy is developed which is applicable to a class of open-loop stable nonlinear systems whose input-output maps contain nonlinear terms from output and linear terms from input. No a priori knowledge about the nonlinearities of the system is required. The output re-definition scheme is based on first identifying the nonlinearities of the system using neural networks and then modifying the system zero dynamics. A stable/anti-stable factorization is performed on the zero dynamics of the system. The new output is re-defined using the neural identifier and the stable part of the zero dynamics. A controller is then designed based on the new output whose zero dynamics are stable and can be inverted. For the flexible-link manipulator case, the controller is composed of a stabilizing joint PD controller and an output re-definition tracking controller. Experimental and simulation results are presented to show the effectiveness of the proposed control scheme as compared to both linear and nonlinear conventional controllers