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Aerial Co-Manipulation With Cables: The Role of Internal Force for Equilibria, Stability, and Passivity, IEEE Robotics and Automation Letters ( Volume: 3, Issue: 3, July 2018 )

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This letter considers the cooperative manipulation of a cable-suspended load with two generic aerial robots without the need of explicit communication. The role of the internal force for the asymptotic stability of the beam position-and-attitude equilibria is analyzed in depth. Using a nonlinear Lyapunov-based approach, we prove that if a nonzero internal force is chosen, then the asymptotic stabilization of any desired beam attitude can be achieved with a decentralized and communicationless master-slave admittance controller. If, conversely, a zero internal force is chosen, as done in the majority of the state-of-the-art algorithms, the attitude of the beam is not controllable without communication. Furthermore, we formally proof the output-strictly passivity of the system with respect to an energy-like storage function and a certain input-output pair. This proves the stability and the robustness of the method during motion and in nonideal. The theoretical findings are validated through extensive simulations.