Flexible-Fixed-Time-Performance-Based Adaptive Tracking Control for Unmanned Helicopter With Input Saturation

This article proposes an adaptive tracking control strategy for a 6-DOF unmanned helicopter with external disturbances and input saturation, which is able to guarantee the flexible fixed-time prescribed performance. Different from the majority of prescribed performance control methods with input saturation, which neglect the conflict between input and performance constraints, the strategy offered achieves a trade-off by introducing a flexible fixed-time prescribed performance function. Besides, the desired tracking signals are temporarily adjusted during the saturation phase to enhance the feasibility of the tracking task. A hyperbolic tangent function is utilized to tackle the problem of saturated input. To compensate for the composite disturbances that involve external disturbances and the estimation error of the hyperbolic tangent function, a parameter adaptive estimation method is adopted to approximate its upper bound. Combining with the backstepping technology, the trajectory tracking controller is investigated to guarantee that tracking errors meet the prescribed performance within fixed time. Comparative simulations illustrate the effectiveness and merits of the proposed control scheme.