Adaptive Predefined-Time Output-Feedback Control of Uncertain Nonlinear Systems with Dead-Zone Actuation via Fractional-Power Feedback

This paper investigates adaptive predefined-time and prescribed-accuracy output-feedback control for integer-order strict-feedback nonlinear systems subject to asymmetric dead-zone actuation and unavailable states. Although the controlled plant is integer order, the proposed feedback mechanism employs complementary noninteger powers below and above unity. The resulting dynamic fractional-power feedback loop assigns the convergence-time bound through a single time parameter while maintaining a prescribed residual tracking band. Instead of requiring the exact inverse of the actuator characteristic, the asymmetric dead zone is decomposed into a sign-dependent positive gain and a bounded offset that are incorporated directly into the control recursion. A neural state observer reconstructs the unavailable states, radial basis function neural networks approximate the unknown nonlinearities, and command-filtered backstepping avoids the repeated differentiation of virtual controls. Lyapunov analysis proves that all closed-loop signals remain bounded and that the tracking error enters the prescribed accuracy set within the predefined-time bound. Simulations involving a benchmark nonlinear plant and a single-link manipulator demonstrate the effectiveness of the fractional-power feedback, state-estimation, and dead-zone compensation mechanisms.