@article {2013l-RobFraSecBue,
	title = {A Passivity-Based Decentralized Strategy for Generalized Connectivity Maintenance},
	journal = {The International Journal of Robotics Research},
	volume = {32},
	year = {2013},
	month = {03/2013},
	pages = { 299-323},
	abstract = {The design of decentralized controllers coping with the typical constraints on the inter-robot sensing/communication capabilities represents a promising direction in multi-robot research thanks to the inherent scalability and fault tolerance of these approaches. In these cases, connectivity of the underlying interaction graph plays a fundamental role: it represents a necessary condition for allowing a group or robots achieving a common task by resorting to only local information. Goal of this paper is to present a novel decentralized strategy able to enforce connectivity maintenance for a group of robots in a flexible way, that is, by granting large freedom to the group internal configuration so as to allow establishment/deletion of interaction links at anytime as long as global connectivity is preserved. A peculiar feature of our approach is that we are able to embed into a unique connectivity preserving action a large number of constraints and requirements for the group: (i) presence of specific inter-robot sensing/communication models, (ii) group requirements such as formation control, and (iii) individual requirements such as collision avoidance. This is achieved by defining a suitable global potential function of the second smallest eigenvalue λ2 of the graph Laplacian, and by computing, in a decentralized way, a gradient-like controller built on top of this potential. Simulation results obtained with a group of quadorotor UAVs and UGVs, and experimental results obtained with four quadrotor UAVs, are finally presented to thoroughly illustrate the features of our approach on a concrete case study.},
	keywords = {Bilateral Shared Control of Mobile Robots, Connectivity maintenance, Motion control of multiple robots},
	attachments = {https://homepages.laas.fr/afranchi/robotics/sites/default/files/2013l-RobFraSecBue-preprint.pdf , https://homepages.laas.fr/afranchi/robotics/sites/default/files/IJRRConn_MM_1_LQ.mp4},
	author = {Paolo Robuffo Giordano and Antonio Franchi and Cristian Secchi and Heinrich H. B{\"u}lthoff}
}
@conference {2012b-SecFraBueRob,
	title = {Bilateral Teleoperation of a Group of UAVs with Communication Delays and Switching Topology},
	booktitle = {2012 IEEE Int. Conf. on Robotics and Automation},
	year = {2012},
	month = {05/2012},
	address = {St. Paul, MN},
	abstract = {In this paper, we present a passivity-based decentralized approach for bilaterally teleoperating a group of UAVs composing the slave side of the teleoperation system. In particular, we explicitly consider the presence of time delays, both among the master and slave, and within UAVs composing the group. Our focus is on analyzing suitable (passive) strategies that allow a stable teloperation of the group despite presence of delays, while still ensuring high flexibility to the group topology (e.g., possibility to autonomously split or join during the motion). The performance and soundness of the approach is validated by means of human/hardware-in-the-loop simulations (HHIL).},
	keywords = {Bilateral Shared Control of Mobile Robots, Decentralized control, Distributed algorithms, Force feedback, Motion control of multiple robots, Multi-robot systems, Teleoperation},
	attachments = {https://homepages.laas.fr/afranchi/robotics/sites/default/files/2012d-SecFraBueRob.pdf , https://homepages.laas.fr/afranchi/robotics/sites/default/files/2012d-SecFraBueRob.mp4},
	author = {Cristian Secchi and Antonio Franchi and Heinrich H. B{\"u}lthoff and Paolo Robuffo Giordano}
}
@article {2012e-FraSecSonBueRob,
	title = {Bilateral Teleoperation of Groups of Mobile Robots with Time-Varying Topology},
	journal = {IEEE Transaction on Robotics},
	volume = {28},
	year = {2012},
	month = {10/2012},
	pages = {1019	-1033},
	abstract = {In this paper, a novel decentralized control strategy for bilaterally teleoperating heterogeneous groups of mobile robots from different domains (aerial, ground, marine and under- water) is proposed. By using a decentralized control architecture, the group of robots, treated as the slave-side, is made able to navigate in a cluttered environment while avoiding obstacles, inter-robot collisions and following the human motion commands. Simultaneously, the human operator acting on the master side is provided with a suitable force feedback informative of the group response and of the interaction with the surrounding environment. Using passivity based techniques, we allow the behavior of the group to be as flexible as possible with arbitrary split and join events (e.g., due to inter-robot visibility/packet losses or specific task requirements) while guaranteeing the stability of the system. We provide a rigorous analysis of the system stability and steady-state characteristics, and validate performance through human/hardware-in-the-tloop simulations by considering a heterogeneous fleet of UAVs and UGVs as case study. Finally, we also provide an experimental validation with 4 quadrotor UAV},
	keywords = {Bilateral Shared Control of Mobile Robots, Decentralized control, Distributed algorithms, Force feedback, Haptics, Motion control of multiple robots, Multi-robot systems, Teleoperation},
	attachments = {https://homepages.laas.fr/afranchi/robotics/sites/default/files/2012e-FraSecSonBueRob.pdf},
	author = {Antonio Franchi and Cristian Secchi and Hyoung Il Son and Heinrich H. B{\"u}lthoff and Paolo Robuffo Giordano}
}
@article {2012f-FraSecRylBueRob,
	title = {Shared Control: Balancing Autonomy and Human Assistance with a Group of Quadrotor UAVs.},
	journal = {IEEE Robotics and Automation Magazine, Special Issue on Aerial Robotics and the Quadrotor Platform},
	volume = {19},
	year = {2012},
	month = {09/2012},
	pages = {57-68},
	abstract = {In this paper, we present a complete control framework and associated experimental testbed for the bilateral shared control of a group of quadrotor UAVs. This control architecture is applicable to any task and allows to integrate: i) a decentralized topological motion control (responsible for the mutual interactions in the UAV formation), ii) a human assistance module (allowing human intervention, whenever needed, on some aspects of the UAV group behavior), and iii) a force-feedback possibility (increasing the telepresence of the human assistants by providing suitable haptic cues informative of the UAV behavior). 
We will show, as worked-out case studies, how to specialize the topological motion controller to the relevant cases of constant, unconstrained and connected group topologies, and how to let a human operator intervening at the level of single UAVs or of the whole group dynamics.
A detailed description of the experimental testbed is also provided with emphasis on the quadrotor UAV hardware and software architectures. Finally, the versatility of the proposed framework is demonstrated by means of experiments with real UAVs. Although quadrotors are used as actual robotic platforms, the proposed framework can be straightforwardly extended to many different kinds of UAVs with similar motion characteristics.},
	keywords = {Bilateral Shared Control of Mobile Robots, Decentralized control, Force feedback, Formation control, Haptics, Middleware for robotics, Motion control of multiple robots, Multi-robot systems, UAV hardware platforms},
	attachments = {https://homepages.laas.fr/afranchi/robotics/sites/default/files/2012f-FraSecRylBueRob-preprint.pdf},
	author = {Antonio Franchi and Cristian Secchi and Markus Ryll and Heinrich H. B{\"u}lthoff and Paolo Robuffo Giordano}
}
@conference {2011k-RobFraSecBue,
	title = {Experiments of Passivity-Based Bilateral Aerial Teleoperation of a Group of UAVs with Decentralized Velocity Synchronization},
	booktitle = {2011 IEEE/RSJ Int. Conf. on Intelligent Robots and Systems},
	year = {2011},
	month = {09/2011},
	pages = {163-170},
	address = {San Francisco, CA},
	abstract = {In this paper, we present an experimental validation of a novel decentralized passivity-based control strategy for teleoperating a group of Unmanned Aerial Vehicles (UAVs): the slave side, consisting of the UAVs, is endowed with large group autonomy by allowing time-varying topology and interrobot/obstacle collision avoidance. The master side, represented by a human operator, controls the group motion and receives suitable force feedback cues informing her/him about the remote slave motion status. Passivity theory is exploited for guaranteeing stability of the slave side and of the overall teleoperation channel. Results of experiments involving the use of 4 quadcopters are reported and discussed, confirming the soundness of the paper theoretical claims.},
	keywords = {Bilateral Shared Control of Mobile Robots, Decentralized control, Distributed algorithms, Force feedback, Haptics, Motion control of multiple robots, Multi-robot systems, Teleoperation},
	attachments = {https://homepages.laas.fr/afranchi/robotics/sites/default/files/2011k-RobFraSecBue-preprint.pdf , https://homepages.laas.fr/afranchi/robotics/sites/default/files/2011k-RobFraSecBue.mp4},
	author = {Paolo Robuffo Giordano and Antonio Franchi and Cristian Secchi and Heinrich H. B{\"u}lthoff}
}
@conference {2011a-FraRobSecSonBue,
	title = {A Passivity-Based Decentralized Approach for the Bilateral Teleoperation of a Group of UAVs with Switching Topology},
	booktitle = {2011 IEEE Int. Conf. on Robotics and Automation},
	year = {2011},
	month = {05/2011},
	pages = {898-905},
	address = {Shanghai, China},
	abstract = {In this paper, a novel distributed control strategy for teleoperating a fleet of Unmanned Aerial Vehicles (UAVs) is proposed. Using passivity based techniques, we allow the behavior of the UAVs to be as flexible as possible with arbitrary split and join decisions while guaranteeing stability of the system. Furthermore, the overall teleoperation system is also made passive and, therefore, characterized by a stable behavior both in free motion and when interacting with unknown {passive} obstacles. The performance of the system is validated through semi-experiments.},
	keywords = {Bilateral Shared Control of Mobile Robots, Decentralized control, Distributed algorithms, Force feedback, Haptics, Motion control of multiple robots, Multi-robot systems, Teleoperation},
	attachments = {https://homepages.laas.fr/afranchi/robotics/sites/default/files/2011a-FraRobSecSonBue-preprint.pdf , https://homepages.laas.fr/afranchi/robotics/sites/default/files/2011a-FraRobSecSonBue-low_qlty.mp4},
	author = {Antonio Franchi and Paolo Robuffo Giordano and Cristian Secchi and Hyoung Il Son and Heinrich H. B{\"u}lthoff}
}
