Hierarchical task-based formation control and collision avoidance of UAVs in finite time

This work addresses the problem of distributedly controlling the position of a group of Unmanned Aerial Vehicles (UAVs), that are considered as holonomic three-dimensional agents, to achieve a desired formation while collisions are avoided. We propose a generic control scheme computed by the adaptive convex combination of two control laws dealing with two, possibly conflicting, tasks, which are formation control and obstacle avoidance. The main contributions of the paper are threefold: First, the whole proposed scheme is distributed by nature, since the formation control is formulated as a consensus problem of virtual agents and the collision avoidance strategy is reactive, valid for unknown environments. Second, two control protocols are proposed to guarantee convergence to the desired formation in finite or predefined time; in the last case, the formation is achieved in a constant time independently of the initial UAVs positions. And finally, the control scheme generates continuous control signals in spite of activation and deactivation of the obstacle avoidance task, and stability is proved even in the transition of tasks. The effectiveness of the proposed approach is shown through realistic simulations and real experiments for a group of quadrotors. (c) 2021 European Control Association. Published by Elsevier Ltd. All rights reserved.