Landing a UAV on Static or Moving Platforms Using a Formation Controller

Landing an unmanned aerial vehicle (UAV) on static or mobile platforms (such as an unmanned ground vehicle-UGV) is challenging since the UAV should hover exactly over the platform. This article presents a solution to this problem based on the virtual structure control paradigm. The problem is addressed as the control of a heterogeneous formation of a UGV and a UAV, with the UAV landing on or taking off from the UGV. The formation is characterized as a three-dimensional straight line linking the two vehicles, which start navigating cooperatively, keeping a desired formation shape (the desired straight line). Subsequently, the structure is changed to make the UAV hover above the UGV, to land on it. Then, the distance between the vehicles is gradually reduced to a suitable altitude, and the UAV drops on the UGV. The UAV can then takeoff, if required, either resuming the formation structure or flying independently of the UGV, and land back on the UGV after finishing the mission, if required. The stability of the control structure proposed to guide the vehicles during the cooperative navigation and landing is proven, based on the theory of Lyapunov, and its effectiveness is checked through experimental results.