Tuning of dynamic feedback control for nonlinear mechanical systems

Mechanical systems are often only equipped with position measurement encoders and obtain the velocity signal by differentiation. However, differentiation largely amplifies noise. In this paper we look at dynamic feedback control of Euler-Lagrange mechanical systems. Dynamic feedback is often used to avoid velocity measurements in the control feedback. In the Euler-Lagrange literature it is shown that the dynamic extension realizes an approximate differentiator, justifying its application. We show in this paper that the dynamic extension used in the Euler-Lagrange literature actually realizes a lead-compensator, proving that a lead-compensator can also globally asymptotically stabilize a nonlinear mechanical systems. Furthermore, based on the lead-compensator structure it is then possible to offer a frequency approach to tune the controller gains.