Vision-based quadrotor rapid landing control with an uncooperative platform: an alternating predictive observer approach

The challenge of allowing a quadrotor to land quickly on an unknown moving platform using visual cues is addressed. A position-based visual servoing (PBVS) framework is designed that utilises the relative position data captured by the onboard camera to ensure a successful landing. The inherent limitation imposed by the camera's low sampling rate, which hampers the update and transfer rate of control commands, is mitigated by introducing an alternating predictive observer (APO). This observer inputs rapid actual or virtual position information into the control system. Actual relative positions are used for observer design when available from the camera, whereas virtual relative positions, predicted by the quadrotor model, are used when direct sampling is unattainable. This approach enables a process that alternates between prediction and observation, allowing for the design of a sampled-data controller that updates at a fast rate, commensurate with the APO. The robustness of the proposed PBVS-APO controller is exhibited, requiring no prior knowledge of the platform's dynamics. Validation through numerical simulations and experiments confirms the high control bandwidth and the rapid landing efficacy of the control strategy.