A manipulator-assisted multiple UAV landing system for USV subject to disturbance

As human activities in the ocean become increasingly frequent, the cooperative system of unmanned surface vehicles (USVs) and unmanned aerial vehicles (UAVs) has played a more important role in marine exploration and monitoring. However, marine waves significantly disturb the USV motion, which makes it difficult for a UAV to land accurately. An oversized landing platform is usually necessary to guarantee safety during the landing process, which limits the number of UAVs that can be carried. This paper proposes a manipulator-assisted landing system, which is capable of landing multiple UAVs without increasing the USV's size. The proposed system can capture the hovering UAVs, and place them on landing platforms accurately. To address the disturbance caused by the base motion, a robust nonlinear model predictive controller (MPC) based on an adaptive estimator is designed for the onboard manipulator. The working strategy of the system is designed to plan the motion of each device. The manipulator controller has been validated through simulations and indoor experiments. Field experiments show that the proposed system is capable of catching and placing the UAVs when the disturbed USV roll range is approximately six degrees.