Time-Varying Control Barrier Function for Safe and Precise Landing of a UAV on a Moving Target

In this article, we present a control barrier func- tion (CBF)-based control strategy for safe and precise landing of an unmanned aerial vehicle (UAV) on a moving target. The CBF is time-varying, as it depends on the velocity of the landing platform and captures three crucial safety constraints: (a) collision avoidance with the landing platform, (b) precise vertical descent on a narrow landing platform, and (c) ground clearance throughout the landing maneuver. The proposed CBF’s parameters can be adjusted to set the desired width and height of the descending cone. A quadratic program- based CBF safety filter is designed, which takes a nominal position tracking control input and yields a minimally invasive control input that enforces the safety constraints throughout the landing maneuver. The controller’s feasibility is analyzed and its performance is validated through multiple experiments using a quadrotor UAV and an unmanned ground vehicle.