Trajectory Generation for Quadrotors Air Parallel Docking With Time-Varying Avoidance Constraints

Abstract

The Self-Reconfiguring Flight Structure (SRFS), consisting of quadrotor Unmanned Aerial Vehicle (UAV) units, is more functional, but still in its infancy because docking efficiency and security are hardly guaranteed. To obtain SRFS by docking, it is important to generate a safe and efficient trajectory for each quadrotor. This letter presents a Legendre pseudospectral method with time-varying avoidance constraints for generating docking trajectories. Firstly, all quadrotors are integrated into an optimization framework, which generates parallel docking flight trajectories for quadrotors and ensures that all trajectories are globally optimal. Then, because the avoidance constraints with constant avoidance distance only guarantee position safety of quadrotors at discrete points, the strategy of time-varying avoidance constraints is proposed to ensure that the trajectories interpolated by the Lagrangian interpolation basis functions are safe everywhere. Simulation experiments show that our method can generate high-quality and safe trajectories for quadrotors performing parallel docking task. Finally, real-world experiments verify that the docking task of multiple quadrotors can be accomplished in a completely parallel manner, thus reducing the number of steps in the docking process.