@Article{ RobuffoGiordanoFSB2012,
title = {A Passivity-Based Decentralized Strategy for Generalized Connectivity Maintenance},
journal = {International Journal of Robotics Research},
year = {2013},
month = {3},
volume = {32},
number = {3},
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 to achieve a common task by resorting to only local information. The 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) the 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 quadrotor unmanned aerial vehicles (UAVs) and unmanned ground vehicles, and experimental results obtained with four quadrotor UAVs, are finally presented to thoroughly illustrate the features of our approach on a concrete case study.},
file_url = {fileadmin/user_upload/files/publications/2013/2013l-RobFraSecBue-preprint.pdf},
web_url = {http://ijr.sagepub.com/content/32/3/299.full.pdf+html},
state = {published},
DOI = {10.1177/0278364912469671},
author = {Robuffo Giordano P{robu_pa}{Department Human Perception, Cognition and Action}, Franchi A{antonio}{Department Human Perception, Cognition and Action}, Secchi C and B\"ulthoff HH{hhb}{Department Human Perception, Cognition and Action}}
}

@Article{ FranchiSSBR2012,
title = {Bilateral Teleoperation of Groups of Mobile Robots with Time-Varying Topology},
journal = {IEEE Transaction on Robotics},
year = {2012},
month = {10},
volume = {28},
number = {5},
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 underwater) is proposed. By using a decentralized control architecture, the group of robots, which is treated as the slave side, is made able to navigate in a cluttered environment while avoiding obstacles, interrobot 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 interrobot 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-loop simulations by considering a heterogeneous fleet of unmanned aerial vehicles (UAVs) and unmanned ground vehicles as a case study. Finally, we also provide an experimental validation with four quadrotor UAVs.},
file_url = {fileadmin/user_upload/files/publications/2012/2012e-FraSecSonBueRob.pdf},
web_url = {http://ieeexplore.ieee.org/xpl/articleDetails.jsp?arnumber=6199993},
state = {published},
DOI = {10.1109/TRO.2012.2196304},
author = {Franchi A{antonio}{Department Human Perception, Cognition and Action}, Secchi C, Son HI{chakurt}{Department Human Perception, Cognition and Action}, B\"ulthoff HH{hhb}{Department Human Perception, Cognition and Action} and Robuffo Giordano P{robu_pa}{Department Human Perception, Cognition and Action}}
}

@Article{ FranchiMGRBR2012,
title = {Modeling and Control of UAV Bearing-Formations with Bilateral High-Level Steering},
journal = {International Journal of Robotics Research},
year = {2012},
month = {10},
volume = {31},
number = {12},
pages = {1504-1525},
abstract = {In this paper we address the problem of controlling the motion of a group of unmanned aerial vehicles (UAVs) bound to keep a formation defined in terms of only relative angles (i.e. a bearing formation). This problem can naturally arise within the context of several multi-robot applications such as, e.g. exploration, coverage, and surveillance. First, we introduce and thoroughly analyze the concept and properties of bearing formations, and provide a class of minimally linear sets of bearings sufficient to uniquely define such formations. We then propose a bearing-only formation controller requiring only bearing measurements, converging almost globally, and maintaining bounded inter-agent distances despite the lack of direct metric information.

The controller still leaves the possibility of imposing group motions tangent to the current bearing formation. These can be either autonomously chosen by the robots because of any additional task (e.g. exploration), or exploited by an assisting human co-operator. For this latter ‘human-in-the-loop’ case, we propose a multi-master/multi-slave bilateral shared control system providing the co-operator with some suitable force cues informative of the UAV performance. The proposed theoretical framework is extensively validated by means of simulations and experiments with quadrotor UAVs equipped with onboard cameras. Practical limitations, e.g. limited field-of-view, are also considered.},
file_url = {fileadmin/user_upload/files/publications/2012/2012q-FraMasGraRylBueRob-preprint.pdf},
web_url = {http://ijr.sagepub.com/content/early/2012/10/05/0278364912462493.full.pdf+html},
state = {published},
DOI = {10.1177/0278364912462493},
author = {Franchi A{antonio}{Department Human Perception, Cognition and Action}, Masone C{masone}{Department Human Perception, Cognition and Action}, Grabe V{vgrabe}{Department Human Perception, Cognition and Action}, Ryll M{maryll}{Department Human Perception, Cognition and Action}, B\"ulthoff HH{hhb}{Department Human Perception, Cognition and Action} and Robuffo Giordano P{robu_pa}{Department Human Perception, Cognition and Action}}
}

@Article{ FranchiSRBR2012,
title = {Shared Control: Balancing Autonomy and Human Assistance with a Group of Quadrotor UAVs},
journal = {IEEE Robotics & Automation Magazine},
year = {2012},
month = {9},
volume = {19},
number = {3},
pages = {57-68},
abstract = {Robustness and flexibility constitute the main advantages of multiple-robot systems with respect to single-robot ones as per the recent literature. The use of multiple unmanned aerial vehicles (UAVs) combines these benefits with the agility and pervasiveness of aerial platforms [1], [2]. The degree of autonomy of the multi-UAV system should be tuned according to the specificities of the situation under consideration. For regular missions, fully autonomous UAV systems are often appropriate, but, in general, the use of semiautonomous groups of UAVs, supervised or partially controlled by one or more human operators, is the only viable solution to deal with the complexity and unpredictability of real-world scenarios as in, e.g., the case of search and rescue missions or exploration of large/cluttered environments [3]. In addition, the human presence is also mandatory for taking the responsibility of critical decisions in high-risk situations [4].},
file_url = {fileadmin/user_upload/files/publications/2012/2012f-FraSecRylBueRob-preprint_01.pdf},
web_url = {http://ieeexplore.ieee.org/xpl/articleDetails.jsp?tp=&arnumber=6290692&contentType=Journals+%26+Magazines&sortType%3Dasc_p_Sequence%26filter%3DAND%28p_IS_Number%3A6299141%29},
state = {published},
DOI = {10.1109/MRA.2012.2205625},
author = {Franchi A{antonio}{Department Human Perception, Cognition and Action}, Secchi C, Ryll M{maryll}{Department Human Perception, Cognition and Action}, B\"ulthoff HH{hhb}{Department Human Perception, Cognition and Action} and Robuffo Giordano P{robu_pa}{Department Human Perception, Cognition and Action}}
}

@Article{ PasqualettiFB2011,
title = {On Cooperative Patrolling: Optimal Trajectories, Complexity Analysis, and Approximation Algorithms},
journal = {IEEE Transaction on Robotics},
year = {2012},
month = {6},
volume = {28},
number = {3},
pages = {592-606},
abstract = {The subject of this paper is the patrolling of an environment with the aid of a team of autonomous agents. We consider both the design of open-loop trajectories with optimal properties and of distributed control laws converging to optimal trajectories. As performance criteria, the refresh time and the latency are considered, i.e., respectively, time gap between any two visits of the same region and the time necessary to inform every agent about an event occurred in the environment. We associate a graph with the environment, and we study separately the case of a chain, tree, and cyclic graph. For the case of chain graph, we first describe a minimum refresh time and latency team trajectory and propose a polynomial time algorithm for its computation. Then, we describe a distributed procedure that steers the robots toward an optimal trajectory. For the case of tree graph, a polynomial time algorithm is developed for the minimum refresh time problem, under the technical assumption of a constant number of robots involved in the patrolling task. Finally, we show that the design of a minimum refresh time trajectory for a cyclic graph is NP-hard, and we develop a constant factor approximation algorithm.},
file_url = {fileadmin/user_upload/files/publications/2012/2010f-FraPasBul-preprint.pdf},
web_url = {http://ieeexplore.ieee.org/xpl/articleDetails.jsp?arnumber=6122514},
state = {published},
DOI = {10.1109/TRO.2011.2179580},
author = {Pasqualetti F, Franchi A{antonio}{Department Human Perception, Cognition and Action} and Bullo F}
}

@Article{ DurhamFB2011,
title = {Distributed pursuit-evasion without mapping or global localization via local frontiers},
journal = {Autonomous Robots},
year = {2012},
month = {1},
volume = {32},
number = {1},
pages = {81-95},
abstract = {This paper addresses a visibility-based pursuit-evasion problem in which a team of mobile robots with limited sensing and communication capabilities must coordinate to detect any evaders in an unknown, multiply-connected planar environment. Our distributed algorithm to guarantee evader detection is built around maintaining complete coverage of the frontier between cleared and contaminated regions while expanding the cleared region. We detail a novel distributed method for storing and updating this frontier without building a map of the environment or requiring global localization. We demonstrate the functionality of the algorithm through simulations in realistic environments and through hardware experiments. We also compare Monte Carlo results for our algorithm to the theoretical optimum area cleared as a function of the number of robots available.},
file_url = {fileadmin/user_upload/files/publications/2012/2011c-DurFraBul-preprint.pdf},
web_url = {http://www.springerlink.com/content/a02pr41790ll754w/fulltext.pdf},
state = {published},
DOI = {10.1007/s10514-011-9260-1},
author = {Durham JW, Franchi A{antonio}{Department Human Perception, Cognition and Action} and Bullo F}
}

@Article{ 6416,
title = {The sensor-based random graph method for cooperative robot exploration},
journal = {IEEE/ASME Transactions on Mechatronics},
year = {2009},
month = {4},
volume = {14},
number = {2},
pages = {163-175},
abstract = {We present a decentralized cooperative exploration strategy for a team of mobile robots equipped with range finders. A roadmap of the explored area, with the associate safe region, is built in the form of a sensor-based random graph (SRG). This is expanded by the robots by using a randomized local planner that automatically realizes a tradeoff between information gain and navigation cost. The nodes of the SRG represent view configurations that have been visited by at least one robot, and are connected by arcs that represent safe paths. These paths have been actually traveled by the robots or added to the SRG to improve its connectivity. Decentralized cooperation and coordination mechanisms are used so as to guarantee exploration efficiency and avoid conflicts. Simulations and experiments are presented to show the performance of the proposed technique.},
file_url = {fileadmin/user_upload/files/publications/2009b-FFOV.pdf},
web_url = {http://antoniofranchi.com/robotics/?q=node/47},
state = {published},
DOI = {10.1109/TMECH.2009.2013617},
author = {Franchi A{antonio}, Freda L, Oriolo G and Vendittelli M}
}