PD control with on-line gravity compensation for robots with flexible links

A proportional-derivative (PD) control with online gravity compensation is proposed for regulation tasks of robot manipulators with flexible links. The control law is an extension of a previous PD control with constant gravity compensation at the desired configuration. It is based on a gravity-biased modification of the desired link deflection and requires measuring only position and velocity on the joint side. Global asymptotic stability of the control law at the desired robot configuration is proven via Lyapunov argument and La Salle's Theorem. Simulation tests on a two-link arm are carried out in order to compare performance of the new scheme with respect to the case of constant gravity compensation and results on the advantages of the on-line compensation are shown.