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This work studies how parametric uncertainties affect the cooperative manipulation of a cable-suspended beam-shaped load by means of two aerial robots not explicitly communicating with each other. In particular, the work sheds light on the impact of the uncertain knowledge of the model parameters available to an established communication-less force-based controller. First, we find the closed-loop equilibrium configurations in the presence of the aforementioned uncertainties, and then we study their stability. Hence, we show the fundamental role played in the robustness of the load attitude control by the internal force induced in the manipulated object by non-vertical cables. Furthermore, we formally study the sensitivity of the attitude error to such parametric variations, and we provide a method to act on the load position error in the presence of the uncertainties. Eventually, we validate the results through an extensive set of numerical tests in a realistic simulation environment including underactuated aerial vehicles and sagging-prone cables, and through hardware experiments.

International audience; Abstract This work introduces the G-Fly-Crane, a proof-of-concept aerial multi-robot system designed to demonstrate the advantage of using multiple aerial robots as a valuable tool for novel construction techniques, not requiring the use of heavy engines and costly infrastructures. We experimentally demonstrate its capability to perform pick-and-place and manipulation tasks in a construction scenario, with an increased payload capacity and dexterity compared to the single robot case. The system is composed of three aerial robots connected to a platform by three pairs of cables. The platform is equipped with a gripper, enabling the grasping of objects. The paper describes in detail the hardware and software architecture of our prototype and explains the implemented control methods. A shared control strategy incorporates the human operator in the control loop, thus increasing the overall system reliability when performing complex tasks. The paper also discusses the next steps required to bring this technology from indoor laboratory conditions to real-world applications.

Technological developments have exponentially been increasing during the last century, with an evident peak in the last few decades. The recent need for the development of an increasingly technological world, with a look at aerospace, calls for wider deployment of robots that must coordinate with each other to achieve specific and more and more complex tasks. Therefore, during the last decade, control of multi-agent systems has gained a significant amount of attention due to the great variety of its applications, including transportation and full-pose object manipulations.One of the earliest successful demonstrations for aerial cooperative manipulation is the cable-suspended transportation and manipulation by multiple quadrotors or helicopters. Following this line, this thesis attempts to first provide a contribution in the modelling, design and control perspective of multi-robot aerial manipulators which are capable of transporting and manipulating objects in real scenarios taking into account and compensating for the variety of model and dynamical uncertainties which may arise.A reasonable range of useful applications can benefit from such approaches: structure assembly in the construction field, contact-based inspection in refineries and bridges, transportation and harvesting in agriculture, removing untreated human waste in environmental cleanup.However, motion control strategies, alone, illustrate their inadequacies with respect to uncertainties and errors which may arise as a result of interactions with the external environment and/or with humans. Therefore, the second main contribution of this thesis has been to conceive control approaches which could be adopted in interacting with the environment on one hand and collaborating with humans on the other hand., Les développements technologiques ont augmenté de façon exponentielle au cours du siècle dernier, avec un pic évident au cours des dernières décennies. Le besoin récent de développement d'un monde de plus en plus technologique, avec un regard tourné vers le domaine aérospatial, appelle un déploiement plus large de robots qui doivent se coordonner entre eux pour réaliser des tâches spécifiques et de plus en plus complexes. Par conséquent, au cours de la dernière décennie, le contrôle des systèmes multi-agents a attiré une attention considérable en raison de la grande variété de ses applications, y compris le transport et les manipulations d'objets.L'une des premières démonstrations réussies de manipulation coopérative aérienne est le transport et la manipulation par câble suspendu par plusieurs quadrotors ou hélicoptères. Suivant cette ligne, cette thèse tente, d'abord, d'apporter une contribution dans la perspective de modélisation, de conception et de contrôle de manipulateurs aériens multi-robots capables de transporter et de manipuler des objets à 6 degrés de liberté dans des scénarios réels prenant en compte et compensant pour la variété des incertitudes de modèle et dynamiques qui peuvent survenir.Une gamme raisonnable d'applications utiles peut bénéficier de telles approches : assemblage de structures dans le domaine de la construction, inspection par contact dans les raffineries et les ponts, transport et récolte dans l'agriculture, élimination des déchets humains non traités dans le cadre du nettoyage de l'environnement.Cependant, les stratégies de contrôle de mouvement, à elles seules, illustrent leurs insuffisances vis-à-vis des incertitudes et des erreurs qui peuvent survenir à la suite d'interactions avec l'environnement extérieur et/ou avec l'homme. Par conséquent, la deuxième contribution principale de cette thèse a été de concevoir des approches de contrôle qui pourraient être adoptées en interaction avec l'environnement d'une part et en collaboration avec l'homme d'autre part.

The Fly-Crane is a multi-robot aerial manipulator system composed of three aerial vehicles towed to a platform by means of six cables. This paper presents a method to estimate the mass and the position of the center of mass of a loaded platform (i.e. the Fly-Crane platform including a transported load). The precise knowledge of these parameters allows to sensibly minimize the total effort exerted during a full-pose manipulation task The estimation is based on the measure of the forces applied by the aerial vehicles to the platform in different static configurations. We demonstrate that only two different configurations are sufficient to estimate the inertial parameters. Far-from-ideal numerical simulations show the effectiveness of the estimation method. Once the parameters are estimated, we show the enhancement of the system performances by minimizing the total exerted effort. The validity of the proposed algorithm in non-ideal conditions is presented through simulations based on the Gazebo simulator.