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In this paper, an adaptive prescribed performance control method is presented for a class of uncertain strict feedback nonaffine nonlinear systems with the coupling effect of time-varying delays, dead-zone input, and unknown control directions. Owing to the universal approximation property, fuzzy logic systems are used to approximate the uncertain terms in the system. Since there is no systematic approach to determine the required upper bounds of errors in control systems, the prior selection of control parameters to have a satisfactory performance is somehow impossible. Therefore, the prescribed performance technique as a solution is applied in this study to bring satisfactory performance indices to the system such as overshoot and steady state performance within a predetermined bound. Dynamic surface control strategy is also introduced to the proposed control scheme to address the "explosion of complexity" behavior existing in conventional backstepping methods. To ease the control design, the mean-value theorem is utilized to transform the nonaffine system into the affine one. Moreover, with the help of this theorem, the unknown dead-zone nonlinearity is separated into the linear and nonlinear disturbance-like bounded term. The proposed method relaxes a prior knowledge of control direction by employing Nussbaum-type functions, and the effect of time-varying delays are compensated by constructing the proper Lyapunov-Krasovskii functions. The proposed controller guarantees that all the closed-loop signals are semiglobally uniformly ultimately bounded and the error evolves within the decaying prescribed bounds. In the end, in order to demonstrate the superiority of this method, simulation examples are given. KEYWORDS adaptive fuzzy control, dead-zone nonlinearity, dynamic surface control, nonaffine systems, prescribed performance, time-varying delays 1134

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In many control engineering applications, it is impossible or expensive to measure all the states of the dynamical system and only the system output is available for controller design. In this study, a new dynamic output feedback control algorithm is proposed to stabilize the unstable periodic orbit of chaotic spinning disks with incomplete state information. The proposed control structure is based on the T‐S fuzzy systems. This investigation also introduces a new design procedure to satisfy a constraint on the T‐S fuzzy dynamic output feedback control signal. This procedure is independent of the exact value of initial states. Finally, computer simulations are accomplished to illustrate the performance of the proposed control algorithm. © 2015 Wiley Periodicals, Inc. Complexity 21: 148–159, 2016