Global Output-Feedback Tracking for Planar Nonlinear Systems with Unknown Control Coefficients

This paper considers the problem of global practical tracking by output-feedback for a class of planar nonlinear systems with unknown control coefficients. Compared with the closely related works, the key point of the paper is that it is only required the sign information but not the upper and lower bounds of unknown control coefficients are known a prior. Motivated by our recent works, by combining the methods of universal control and dead zone with backstepping technique, and skillfully constructing a new Lyapunov function, we design a new adaptive tracking controller with the suitable design parameters which guarantees that the resulting closed-loop system state is globally hounded while the tracking error belongs to a prescribed arbitrarily small interval of the origin after a unite time. A numerical example is given to illustrate the effectiveness of the theoretical results.