This paper is devoted to the global practical tracking by output-feedback for a class of uncertain nonlinear systems with only the tracking error measurable. Different from the closely related works, the systems have unmeasured states dependent growth with unknown constant rate, and the reference signal, as well as its first order derivative, has unknown bound. Mainly because of these, the tracking problem can hardly be solved by straightforwardly extending the existing results. In the paper, motivated by the related stabilization results, and flexibly using the ideas of universal control and dead zone, an adaptive output-feedback controller is designed to make the tracking error prescribed arbitrarily small after a finite time while keeping all the states of the closed-loop system bounded. A numerical example demonstrates the effectiveness of the theoretical results.

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This paper deals with the global practical tracking problem by output-feedback for a class of uncertain cascade systems with zero-dynamics and unmeasured states dependent growth. The systems investigated are substantially different from the closely related works, and have zero-dynamics, unknown growth rate, and unknown time-varying control coefficients. This makes the problem much more difficult to solve. Motivated by the authors' recent works, this paper proposes a new adaptive control scheme to achieve the global practical tracking. It is shown that the designed controller guarantees that the state of the resulting closed-loop system is globally bounded and the tracking error converges to a prescribed arbitrarily small neighborhood of the origin after a finite time. This is achieved by combining the methods of universal control and dead zone with backstepping technique, and using the framework of performance analysis in the closely related works. A numerical example demonstrates the effectiveness of the theoretical results.

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This paper is the further investigation of work of Yan and Liu, 2011, and considers the global practical tracking problem by output feedback for a class of uncertain nonlinear systems with not only unmeasured states dependent growth but also time-varying time delay. Compared with the closely related works, the remarkableness of the paper is that the time-varying time delay and unmeasurable states are permitted in the system nonlinear growth. Motivated by the related tracking results and flexibly using the ideas and techniques of universal control and dead zone, an adaptive output-feedback tracking controller is explicitly designed with the help of a new Lyapunov-Krasovskii functional, to make the tracking error prescribed arbitrarily small after a finite time while keeping all the closed-loop signals bounded. A numerical example demonstrates the effectiveness of the results.

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