Passivity-Based Control Improvement of Single-Link Flexible Manipulators by a Two-Degree-of-Freedom PID Motor Controller

A new approach to a previous passivity-based control scheme of single-link flexible manipulators is presented herein. Such previous scheme achieves precise positioning of the link tip by combining a position angular control of the motor (inner loop) with a link vibration damping (outer loop), which can be designed independently by decoupling joint and link dynamics with a linear strain feedback. Although, precise positioning can be achieved under large tip payload changes, the used inner loop cannot eliminate the steady-state position error due to the nonlinearities present in the motor. The contribution presented in this work consists of using a two-degree of freedom PID motor controller to solve this problem, eliminating thus the steady-state error while also improving the settling time of the angular position. Simulation and experimental results are carried out to illustrate these improvements.