Global adaptive output feedback controllers with application to nonlinear friction compensation

In this paper we consider a class of nonlinear systems in which a set of constant parameters is unknown and some state variables are not available for measurement. For such systems we provide a constructive procedure for the solution of the global adaptive tracking problem with dynamic partial state feedback. We illustrate an application of the control strategy to the adaptive nonlinear friction compensation of a DC motor servomechanism. We improve previous results in two directions: we allow for a subset of the unmeasurable states to enter in the system nonlinearly; we consider systems which are linearly parametrized with respect to a set of unknown constant parameters.