Arbitrarily small damping allows global output feedback tracking of a class of Euler-Lagrange systems

This paper proposes a new analysis technique called "ISS regulator approach" to show that a simple causal PD controller plus feedforward using only position measurements solves the global output feedback tracking control problem of robot manipulators with arbitrarily small damping. To this end, we first show that a causal PD regulator leads to a global input-to-state stable system with respect to a bounded input disturbance. Then, using this fact we prove that the addition of a feedforward compensation renders the overall error system uniformly globally asymptotically stable. In addition, we present a possible extension of the proposed method to other classes of Euler-Lagrange systems.