This paper focuses on the challenge of autonomous landing of unmanned aerial vehicles (UAVs) on unknown moving unmanned ground vehicles (UGVs) in GPS-denied environments. We present a newly integrated UWB-Vision framework for autonomous approach and landing of UAVs in GPS-Denied environments. Our framework combines ultra-wideband (UWB) relative localization and Apriltag localization techniques. UWB technology is utilized to measure the relative distance between the UAV and UGV, while the inertial measurement unit (IMU) estimates the target's displacement for precise and real-time position estimation. In addition, Apriltag positioning is integrated into the framework to enhance landing accuracy. Experimental results validate the effectiveness and correctness of our proposed approach. This research contributes to the advancement of autonomous UAV landing in GPS-denied environments.

This paper presents a novel incremental sliding mode control scheme to address the attitude-tracking issue in both the helicopter and airplane modes of an electric vertical takeoff and landing vehicle, guaranteeing the stabilization of the attitude-tracking error within a predefined time. Firstly, an incremental model of the vehicle’s attitude control system with external disturbances is established. The high-order terms of the incremental model and instantaneous perturbations are retained as lumped terms rather than directly discarding them to ensure the accuracy of the incremental model. Then, a novel nonsingular sliding surface is developed. Once the ideal sliding motion is established, the states on the sliding surface will converge to the equilibrium point within a predefined time. Furthermore, a predefined-time incremental sliding mode controller is developed by using sliding mode control and incremental control techniques. It effectively reduces the reliance on the model information and attenuates the effects of external disturbances. The predefined-time stability of the entire controlled system is rigorously proven using Lyapunov theory. Finally, numerical simulation examples verify the effectiveness of the proposed control scheme.