X–Y pedestal: partial quasi-linearization and cascade-based global output feedback tracking control

Abstract

This paper addresses the problem of output (angular position) feedback tracking control of two-degree-of-freedom X-Y pedestal systems. Both the velocity observer and the controller are based on a partial quasi-linearized model for the X-Y pedestal system. The two-dimensional velocity observer is uniformly globally exponentially convergent and does not require a priori upper-bound knowledge of the velocity magnitude. An important feature of the proposed observer is that it constructs a uniform global stable output feedback tracking controller with any domain of initial tracking errors and initial estimation errors. The proof of the main results is based on the well-established theorems for cascaded nonlinear timevarying systems. Due to uniform asymptotic stability of the observer and the output feedback controller, numerical simulations show their robust performance in the face of bounded additive perturbations on both input and output.