Analysis, planning and control for cooperative transportation of tethered multi-rotor UAVs

The calculation of available wrench set of tethered multi-rotor UAVs is more challenging than that of the traditional cable-driven parallel robots (CDPRs) with fixed anchor points, due to the bounded thrust, motion acceleration and external disturbance acting on multi-rotor unmanned aerial vehicles (UAVs). To our best knowledge, this is the first work to investigate the dynamic available wrench set. We define an index called capacity margin to evaluate the robustness of the quasi-static motion for different system configurations and to represent the available maximum acceleration of the payload. Moreover, the feasible trajectories of multi-rotor UAVs are optimized using a tension distribution algorithm to accomplish the manipulation of the payload. Without the need of centralized ground control station, payload states and UAVs' velocity information, a decentralized output feedback control based on fixed-time extended state observer (ESO) is developed for the group of multi-rotor UAVs. The rigorous proof of stability of the closed-loop system is conducted. Finally, numerical simulations and comparative experiments are demonstrated to validate the proposed tension distribution algorithm and control strategy.