| Summary: | This work addresses fuzzy adaptive tracking control of uncertain nonlinear systems with unknown control gain signs. Nussbaum functions are used to eliminate the effect of unknown control directions (i.e. unknown control gain signs). In order to make tracking errors approach a predefined neighborhood, two controllers are developed by the aid of fuzzy adaptive prescribed performance control (PPC) technique. The controlled system is transformed to an equivalent one by using appropriate transformation function. Under the proposed tracking controllers without accurate initial errors, the boundedness of all involved variables is guaranteed. Moreover, the tracking errors can remain within the small prescribed performance bounds (PPBs). Finally, simulation results show the effectiveness of the proposed methods.
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