This paper addresses the control of hydraulically driven manipulators with friction compensation. A cascade control strategy combined with a friction observer based on the Lugre friction model and including stiction effects is used and the convergence properties of the closed loop system are established using the Lyapunov method. This controller design and analysis are the new contributions of the paper. The theoretical analysis resulted in practical rules to tune the controller gains in order to guarantee its stability and the convergence of all the tracking errors, including the friction observer errors. An experimental implementation outlines the controller design details and illustrates the main features of the proposed strategy.

Keywords:hydraulically driven manipulators, cascade control, friction compensation, lyapunov based design