Output-feedback global tracking control of robot manipulators with flexible joints

We present a controller for flexible-joint robots without link velocity measurement. Our main result consists in a simple controller of the type proportional-derivative plus feedforward and a series of cascaded filters; the control design is reminiscent of classical backstepping control. To avoid the assumption that link velocities, accelerations and jerks are measured, we use approximate differentiation. The originality of our work lays in establishing uniform global asymptotic stability for the closed-loop system.