@article {Hunt2020b,
	title = {The Bayesian Superorganism: Collective Probability Estimation in Swarm Systems},
	journal = {Artificial Life Conference Proceedings},
	volume = {32},
	year = {2020},
	note = {doi: 10.1162/isal_a_00247},
	month = {7},
	pages = {315-323},
	publisher = {MIT Press},
	abstract = {Superorganisms such as social insect colonies are very successful relative to their non-social counterparts. Powerful emergent information processing capabilities would seem to contribute to the abundance of such ?swarm? systems, as they effectively explore and exploit their environment collectively. We develop a Bayesian model of collective information processing in a decision-making task: choosing a nest site (a ?multi-armed bandit? problem). House-hunting Temnothorax ants are adept at discovering and choosing the best available nest site for their colony: we propose that this is possible via rapid, decentralized estimation of the probability that each choice is best. Viewed this way, their behavioral algorithm can be understood as a statistical method that anticipates recent advances in mathematics. Our nest finding model incorporates insights from approximate Bayesian computation as a model of colony-level behavior; and particle filtering as a model of Temnothorax ?tandem running?. Our framework suggests that the mechanisms of complex collective behavior can sometimes be explained as a spatial enactment of Bayesian inference. It facilitates the generation of quantitative hypotheses regarding individual and collective movement behaviors when collective decisions must be made. It also points to the potential for bioinspired statistical techniques. Finally, it suggests simple mechanisms for collective decision-making in engineered systems, such as robot swarms.},
	doi = {10.1162/isal_a_00247},
	url = {https://www.mitpressjournals.org/doi/abs/10.1162/isal_a_00247},
	author = {Edmund R Hunt and Nigel R Franks and Roland J Baddeley}
}
@conference {377,
	title = {Adding Heuristics to Conflict-Based Search for Multi-Agent Pathfinding},
	booktitle = {International Conference on Automated Planning and Scheduling (ICAPS)},
	year = {2018},
	author = {Ariel Felner and Jiaoyang Li and Eli Boyarski and Hang Ma and Liron Cohen and T. K. Satish Kumar and Sven Keonig}
}
@conference {375,
	title = {Multi-Agent Path Finding with Deadlines},
	booktitle = {International Joint Conference on Artificial Intelligence (IJCAI)},
	year = {2018},
	keywords = {conference},
	author = {Hang Ma and Glenn Wagner and Ariel Felner and Jiaoyang Li and T. K. Satish Kumar and Sven Koenig}
}
@conference {376,
	title = {Multi-Agent Path Finding with Deadlines: Preliminary Results},
	booktitle = {International Conference on Autonomous Agents and Multiagent Systems (AAMAS)},
	year = {2018},
	author = {Hang Ma and Glenn Wagner and Ariel Felner and Jiaoyang Li and T. K. Satish Kumar and Sven Koenig}
}
@conference {418,
	title = {A Search-Based Approach to Solve Pursuit-Evasion Games with Limited Visibility in Polygonal Environments},
	booktitle = {International Conference on Autonomous \& Multiagent Systems (AAMAS)},
	year = {2018},
	url = {http://dl.acm.org/citation.cfm?id=3237383.323795},
	author = {Quattrini Li, Alberto and Raffaele Fioratto and Francesco Amigoni and Volkan Isler}
}
@conference {302,
	title = {A Geometric Approach for the Cooperative Two-Pursuer One-Evader Differential Game},
	booktitle = {20th IFAC World Congress},
	year = {2017},
	doi = {10.1016/j.ifacol.2017.08.2366},
	url = {https://www.sciencedirect.com/science/article/pii/S240589631733183X},
	author = {Eloy Garcia and Zachariah E. Fuchs and Dejan Milutinovi{\'c} and David W. Casbeer and Meir Pachter}
}
@article {370,
	title = {Multirobot Systems [TC Spotlight]},
	journal = {IEEE Robotics \& Automation Magazine},
	volume = {24},
	year = {2017},
	month = {Jan-06-2017},
	pages = {12 - 16},
	issn = {1070-9932},
	doi = {10.1109/MRA.2017.2691138},
	url = {http://ieeexplore.ieee.org/document/7947267/http://xplorestaging.ieee.org/ielx7/100/7947233/07947267.pdf?arnumber=7947267},
	author = {Ayanian, Nora and Fitch, Robert and Franchi, Antonio and Sabattini, Lorenzo}
}
@conference {142,
	title = {Decentralized Motion Control for Cooperative Manipulation with a Team of Networked Mobile Manipulators},
	booktitle = {2016 IEEE Int. Conf. on Robotics and Automation},
	year = {2016},
	month = {05/2016},
	address = {Stockholm, Sweden},
	keywords = {Calibration of ground robots, Motion control of multiple robots},
	author = {Antonio Petitti and Antonio Franchi and Donato Di Paola and Alessandro Rizzo}
}
@article {132,
	title = {Decentralized Multi-Robot Encirclement of a 3D Target with Guaranteed Collision Avoidance},
	journal = {Autonomous Robots},
	volume = {40},
	year = {2016},
	month = {02/2016},
	pages = {245-265},
	abstract = {We present a control framework for achieving encirclement of a target moving in 3D using a multi-robot system. Three variations of a basic control strategy are proposed for different versions of the encirclement problem, and their effectiveness is formally established. An extension ensuring maintenance of a safe inter-robot distance is also discussed. The proposed framework is fully decentralized and only requires local communication among robots; in particular, each robot locally estimates all the relevant global quantities. We validate the proposed strategy through simulations on kinematic point robots and quadrotor UAVs, as well as experiments on differential-drive wheeled mobile robots.},
	keywords = {Motion control of multiple robots},
	author = {Antonio Franchi and Paolo Stegagno and Giuseppe Oriolo}
}
@article {195,
	title = {Ad Hoc Communication in Teams of Mobile Robots using Zigbee Technology},
	journal = {Computer Applications in Engineering Education},
	volume = {23},
	year = {2015},
	month = {Sep.},
	pages = {733-745},
	author = {Fernandes, A. and Couceiro, M. and Portugal, D. and Santos, J. M. and Rocha, R. P.}
}
@article {97,
	title = {Decentralized rigidity maintenance control with range measurements for multi-robot systems},
	journal = {International Journal of Robotics Research},
	volume = {34},
	year = {2015},
	month = {01/2015},
	pages = {128},
	chapter = {105},
	abstract = {This work proposes a fully decentralized strategy for maintaining the formation rigidity of a multi-robot system using only range measurements, while still allowing the graph topology to change freely over time. In this direction, a first contribution of this work is an extension of rigidity theory to weighted frameworks and the rigidity eigenvalue, which when positive ensures the infinitesimal rigidity of the framework. We then propose a distributed algorithm for estimating a common relative position reference frame amongst a team of robots with only range measurements in addition to one agent endowed with the capability of measuring the bearing to two other agents. This first estimation step is embedded into a subsequent distributed algorithm for estimating the rigidity eigenvalue associated with the weighted framework. The estimate of the rigidity eigenvalue is finally used to generate a local control action for each agent that both maintains the rigidity property and enforces additional constraints such as collision avoidance and sensing/communication range limits and occlusions. As an additional feature of our approach, the communication and sensing links among the robots are also left free to change over time while preserving rigidity of the whole framework. The proposed scheme is then experimentally validated with a robotic testbed consisting of six quadrotor unmanned aerial vehicles operating in a cluttered environment. },
	keywords = {Decentralized control, distributed algorithm, distributed estimation, graph rigidity, multi-robot},
	doi = {10.1177/0278364914546173},
	url = {http://ijr.sagepub.com/content/34/1/105},
	author = {Daniel Zelazo and Antonio Franchi and Heinrich H. B{\"u}lthoff and Paolo Robuffo Giordano}
}
@article {196,
	title = {Understanding the Communication Complexity of the Robotic Darwinian PSO},
	journal = {Robotica},
	volume = {33},
	year = {2015},
	month = {Jan.},
	pages = {157-180},
	author = {Couceiro, M.S. and Fernandes, A. and Rocha, R. P. and Ferreira, N.M.F.}
}
@article {201,
	title = {Benchmark of Swarm Robotics Distributed Techniques in a Search Task},
	journal = {Robotics and Autonomous Systems},
	volume = {62},
	year = {2014},
	month = {Feb.},
	pages = {200-213},
	author = {Couceiro, M.S. and Vargas, P. A. and Rocha, R. P. and Ferreira, N. M. F.}
}
@article {199,
	title = {Benchmark of Swarm Robotics Distributed Techniques in a Search Task},
	journal = {Robotica},
	volume = {32},
	year = {2014},
	month = {Oct.},
	pages = {1017-1038},
	author = {Couceiro MS and Portugal, D and Rocha, RP and Ferreira, NMF}
}
@article {200,
	title = {Darwinian Swarm Exploration under Communication Constraints: Initial Deployment and Fault-Tolerance Assessment},
	journal = {Robotics and Autonomous Systems},
	volume = {62},
	year = {2014},
	month = {Apr.},
	pages = {528-544},
	author = {Couceiro, M.S. and Figueiredo, C.M. and Rocha, R.P. and Ferreira, N.M.F.}
}
@conference {143,
	title = {The Flying Hand: a Formation of UAVs for Cooperative Aerial Tele-Manipulation},
	booktitle = {2014 IEEE Int. Conf. on Robotics and Automation},
	year = {2014},
	month = {05/2014},
	address = {Hong Kong, China},
	abstract = {The flying hand is a robotic hand consisting of a swarm of UAVs able to grasp an object where each UAV contributes to the grasping task with a single contact point at the tooltip. The swarm of robots is teleoperated by a human hand whose fingertip motions are tracked, e.g., using an RGB-D camera. We solve the kinematic dissimilarity of this unique master-slave system using a multi-layered approach that includes: a hand interpreter that translates the fingertip motion in a desired motion for the object to be manipulated; a mapping algorithm that transforms the desired object motions into a suitable set of virtual points deviating from the planned contact points; a compliant force control for the case of quadrotor UAVs that allows to use them as indirect 3D force effectors. Visual feedback is also used as sensory substitution technique to provide a hint on the internal forces exerted on the object. We validate the approach with several human-in-the-loop simulations including the full physical model of the object, contact points and UAVs.},
	keywords = {Aerial Physical Interaction, Aerial Robotics, Bilateral Shared Control of Mobile Robots, Motion control of multiple robots},
	author = {Guido Gioioso and Antonio Franchi and Gionata Salvietti and Stefano Scheggi and Domenico Prattichizzo}
}
@article {197,
	title = {Mechanism and Convergence Analysis of a Multi-Robot Swarm Approach Based on Natural Selection},
	journal = {Journal of Intelligent and Robotic Systems},
	volume = {76},
	year = {2014},
	month = {Nov.},
	pages = {353-381},
	author = {Couceiro, M S and Martins, F M and Rocha, R P and Ferreira, N M F}
}
@conference {144,
	title = {Multi-Target Visual Tracking with UAVs},
	booktitle = {2014 IEEE/RSJ Int. Conf. on Intelligent Robots and Systems},
	year = {2014},
	month = {09/2014},
	address = {Chicago, IL},
	abstract = {We study the problem of tracking mobile targets using a team of aerial robots. Each robot carries a camera to detect targets moving on the ground. The overall goal is to plan for the trajectories of the robots in order to track the most number of targets, and accurately estimate the target locations using the images. The two objectives can conflict since a robot may fly to a higher altitude and potentially cover a larger number of targets at the expense of accuracy. We start by showing that k >= 3 robots may not be able to track all n targets while maintaining a constant factor approximation of the optimal quality of tracking at all times. Next, we study the problem of choosing robot trajectories to maximize either the number of targets tracked or the quality of tracking. We formulate this problem as the weighted version of a combinatorial optimization problem known as the Maximum Group Coverage (MGC) problem. A greedy algorithm yields a 1/2 approximation for the weighted MGC problem. Finally, we evaluate the algorithm and the sensing model through simulations and preliminary experiments.},
	author = {Pratap Tokekar and Volkan Isler and Antonio Franchi}
}
@article {136,
	title = {Mutual Localization in Multi-Robot Systems using Anonymous Relative Measurements},
	journal = {The International Journal of Robotics Research},
	volume = {32},
	year = {2013},
	month = {09/2013},
	pages = {1303-1322},
	abstract = {We propose a decentralized method to perform mutual localization in multi-robot systems using anonymous relative measurements, i.e., measurements that do not include the identity of the measured robot. This is a challenging and practically relevant operating scenario that has received little attention in the literature. Our mutual localization algorithm includes two main components: a probabilistic multiple registration stage, which provides all data associations that are consistent with the relative robot measurements and the current belief, and a dynamic filtering stage, which incorporates odometric data into the estimation process. The design of the proposed method proceeds from a detailed formal analysis of the implications of anonymity on the mutual localization problem. Experimental results on a team of differential-drive robots illustrate the effectiveness of the approach, and in particular its robustness against false positives and negatives that may affect the robot measurement process. We also provide an experimental comparison that shows how the proposed method outperforms more classical approaches that may be designed building on existing techniques. The source code of the proposed method is available within the MLAM ROS stack.},
	keywords = {Localization of ground robots},
	author = {Antonio Franchi and Giuseppe Oriolo and Paolo Stegagno}
}
@article {137,
	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},
	author = {Paolo Robuffo Giordano and Antonio Franchi and Cristian Secchi and Heinrich H. B{\"u}lthoff}
}
@article {203,
	title = {A PSO Multi-Robot Exploration Approach Over Unreliable MANETs},
	journal = {Advanced Robotics},
	volume = {27},
	year = {2013},
	pages = {1221-1234},
	author = {M.S. Couceiro and R. P. Rocha and N.M.F. Ferreira}
}
@conference {43,
	title = {RMASBench: Benchmarking Dynamic Multi-Agent Coordination in Urban Search and Rescue},
	booktitle = {Proc. of the 12th Int. Conf. on Autonomous Agents and Multiagent Systems (AAMAS 2013)},
	year = {2013},
	abstract = {We propose RMASBench, a new benchmarking tool based on the RoboCup Rescue Agent simulation system, to easily compare coordination approaches in a dynamic rescue scenario. In particular, we offer simple interfaces to plug-in coordination algorithms without the need for implementing and tuning low-level agents behaviors. Moreover, we add to the realism of the simulation by providing a large scale crowd simulator, which exploits GPUs parallel architecture, to simulate the behavior of thousands of agents in real time. Finally, we focus on a specific coordination problem where fire fighters must combat fires and prevent them from spreading across the city. We formalize this problem as a Distributed Constraint Optimization Problem and we compare two state-of-the art solution techniques: DSA and MaxSum. We perform an extensive empirical evaluation of such techniques considering several standard measures for performance (e.g. damages to buildings) and coordination overhead (e.g., message exchanged and non concurrent constraint checks). Our results provide interesting insights on limitations and benefits of DSA and MaxSum in our rescue scenario and demonstrate that RMASBench offers powerful tools to compare coordination algorithms in a dynamic environment.},
	keywords = {agent coordination, agent simulation, DCOP, performance metrics},
	isbn = {978-1-4503-1993-5},
	url = {http://dl.acm.org/citation.cfm?id=2484920.2485139},
	author = {A. Kleiner and A. Farinelli and S. Ramchurn and B. Shi and F. Maffioletti and R. Reffato}
}
@article {138,
	title = {Semi-Autonomous Haptic Teleoperation Control Architecture of Multiple Unmanned Aerial Vehicles},
	journal = {IEEE/ASME Transaction on Mechatronics, Focused Section on Aerospace Mechatronics},
	volume = {18},
	year = {2013},
	month = {08/2013},
	pages = {1334-1345},
	abstract = {We propose a novel semi-autonomous haptic teleoperation control architecture for multiple unmanned aerial vehicles (UAVs), consisting of three control layers: 1) UAV control layer, where each UAV is abstracted by, and is controlled to follow the trajectory of, its own kinematic Cartesian virtual point (VP); 2) VP control layer, which modulates each VP{\textquoteright}s motion according to the teleoperation commands and local artificial potentials (for VP-VP/VP-obstacle collision avoidance and VP-VP connectivity preservation); and 3) teleoperation layer, through which a single remote human user can command all (or some) of the VPs{\textquoteright} velocity while haptically perceiving the state of all (or some) of the UAVs and obstacles. Master-passivity/slave-stability and some asymptotic performance measures are proved. Experimental results using four custom-built quadrotor-type UAVs are also presented to illustrate the theory.},
	keywords = {Bilateral Shared Control of Mobile Robots, Motion control of multiple robots, UAV hardware platforms},
	author = {Dongjun Lee and Antonio Franchi and Hyoung Il Son and Heinrich H. B{\"u}lthoff and Paolo Robuffo Giordano}
}
@conference {146,
	title = {3D Mutual Localization with Anonymous Bearing Measurements},
	booktitle = {2012 IEEE Int. Conf. on Robotics and Automation},
	year = {2012},
	month = {05/2012},
	address = {St. Paul, MN},
	abstract = {We present a decentralized algorithm for estimating mutual 3-D poses in a group of mobile robots, such as a team of UAVs. Our algorithm uses bearing measurements reconstructed, e.g., by a visual sensor, and inertial measurements coming from the robot IMU. Since identification of a specific robot in a group would require visual tagging and may be cumbersome in practice, we simply assume that the bear- ing measurements are anonymous. The proposed localization method is a non-trivial extension of our previous algorithm for the 2-D case, and exhibits similar performance and robustness. An experimental validation of the algorithm has been performed using quadrotor UAVs.},
	keywords = {Distributed algorithms, Estimation, Localization, Localization of aerial robots, Multi-robot systems},
	author = {Marco Cognetti and Paolo Stegagno and Antonio Franchi and Giuseppe Oriolo and Heinrich H. B{\"u}lthoff}
}
@article {141,
	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},
	author = {Antonio Franchi and Cristian Secchi and Hyoung Il Son and Heinrich H. B{\"u}lthoff and Paolo Robuffo Giordano}
}
@article {134,
	title = {On Cooperative Patrolling: Optimal Trajectories, Complexity Analysis, and Approximation Algorithms},
	journal = {IEEE Transaction on Robotics},
	volume = {28},
	year = {2012},
	month = {06/2012},
	pages = {592-606},
	abstract = {The subject of this work 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 we 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.},
	keywords = {Coverage, Distributed algorithms, Multi-robot systems, Patrolling / Surveillance},
	url = {http://ieeexplore.ieee.org/xpls/abs_all.jsp?arnumber=6122514},
	author = {Fabio Pasqualetti and Antonio Franchi and Francesco Bullo}
}
@article {135,
	title = {Distributed Pursuit-Evasion without Mapping and Global Localization via Local Frontiers},
	journal = {Autonomous Robots},
	volume = {32},
	year = {2012},
	month = {01/2012},
	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.},
	keywords = {Coverage, Distributed algorithms, Multi-robot systems, Pursuit-evasion / Clearing},
	url = {http://www.springerlink.com/content/a02pr41790ll754w/},
	author = {Joseph W. Durham and Antonio Franchi and Francesco Bullo}
}
@article {205,
	title = {A Fuzzified Systematic Adjustment of the Robotic Darwinian PSO},
	journal = {Robotics and Autonomous Systems},
	volume = {60},
	year = {2012},
	month = {Dec.},
	pages = {1625-1639},
	author = {Couceiro, M. S. and Machado, J. A. T. and Rocha, R. P. and Ferreira, N. M. F.}
}
@article {206,
	title = {Introducing the Fractional Order Darwinian Particle Swarm Optimization},
	journal = {Signal, Image and Video Processing, Special Issue on Fractional Signals and Systems},
	volume = {6},
	year = {2012},
	month = {Sep.},
	pages = {343-350},
	author = {Couceiro, M. S. and Rocha, R. P. and Ferreira, N. M. and Machado, J. T.}
}
@article {207,
	title = {A Low-Cost Educational Platform for Swarm Robotics},
	journal = {Journal of Robots, Education and Art},
	volume = {1},
	year = {2012},
	month = {Feb.},
	pages = {1-15},
	author = {Couceiro, M. S. and Figueiredo, C. M. and Luz, J. M. and Ferreira, N. M. and Rocha, R. P.}
}
@article {35,
	title = {Modeling and Control of UAV Bearing-Formations with Bilateral High-Level Steering},
	journal = {The International Journal of Robotics Research, Special Issue on 3D Exploration, Mapping, and Surveillance},
	volume = {31},
	year = {2012},
	month = {10/2012},
	pages = {1504-1525},
	abstract = {In this paper we address the problem of controlling the motion of a group of 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 to impose 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 {\textquoteleft}human-in-the-loop{\textquoteright} 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.},
	keywords = {Bilateral Shared Control of Mobile Robots, Decentralized control, Force feedback, Formation control, Haptics, Motion control of multiple robots, Multi-robot systems, Teleoperation},
	author = {Antonio Franchi and Carlo Masone and Volker Grabe and Markus Ryll and Heinrich H. B{\"u}lthoff and Paolo Robuffo Giordano}
}
@conference {98,
	title = {Rigidity Maintenance Control for Multi-Robot Systems},
	booktitle = {2012 Robotics: Science and Systems Conference},
	year = {2012},
	month = {07/2012},
	address = {Sydney, Australia},
	abstract = {Rigidity of formations in multi-robot systems is important for formation control, localization, and sensor fusion. This work proposes a rigidity maintenance gradient controller for a multi-agent robot team. To develop such a controller, we first provide an alternative characterization of the rigidity matrix and use that to introduce the novel concept of the rigidity eigenvalue. We provide a necessary and sufficient condition relating the positivity of the rigidity eigenvalue to the rigidity of the formation. The rigidity maintenance controller is based on the gradient of the rigidity eigenvalue with respect to each robot position. This gradient has a naturally distributed structure, and is thus amenable to a distributed implementation. Additional requirements such as obstacle and inter-agent collision avoidance, as well as typical constraints such as limited sensing/communication ranges and line-of-sight occlusions, are also explicitly considered. Finally, we present a simulation with a group of seven quadrotor UAVs to demonstrate and validate the theoretical results.},
	keywords = {Decentralized control, Formation control, Motion control of multiple robots, Multi-robot systems, Rigidity mainenance},
	author = {Daniel Zelazo and Antonio Franchi and Frank Allg{\"o}wer and Heinrich H. B{\"u}lthoff and Paolo Robuffo Giordano}
}
@article {139,
	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},
	author = {Antonio Franchi and Cristian Secchi and Markus Ryll and Heinrich H. B{\"u}lthoff and Paolo Robuffo Giordano}
}
@conference {46,
	title = {The SHERPA project: smart collaboration between humans and ground-aerial robots for improving rescuing activities in alpine environments},
	booktitle = {Proc. of the IEEE Int. Workshop on Safety, Security and Rescue Robotics (SSRR)},
	year = {2012},
	address = {College Station, US},
	abstract = {The goal of the paper is to present the foreseen research activity of the European project {\textquoteleft}{\textquoteleft}SHERPA{\textquoteright}{\textquoteright} whose activities will start officially on February 1th 2013. The goal of SHERPA is to develop a mixed ground and aerial robotic platform to support search and rescue activities in a real-world hostile environment, like the alpine scenario that is specifically targeted in the project. Looking into the technological platform and the alpine rescuing scenario, we plan to address a number of research topics about cognition and control. What makes the project potentially very rich from a scientific viewpoint is the heterogeneity and the capabilities to be owned by the different actors of the SHERPA system: the human rescuer is the {\textquoteleft}{\textquoteleft}busy genius{\textquoteright}{\textquoteright}, working in team with the ground vehicle, as the {\textquoteleft}{\textquoteleft}intelligent donkey{\textquoteright}{\textquoteright}, and with the aerial platforms, i.e. the {\textquoteleft}{\textquoteleft}trained wasps{\textquoteright}{\textquoteright} and {\textquoteleft}{\textquoteleft}patrolling hawks{\textquoteright}{\textquoteright}. Indeed, the research activity focuses on how the {\textquoteleft}{\textquoteleft}busy genius{\textquoteright}{\textquoteright} and the {\textquoteleft}{\textquoteleft}SHERPA animals{\textquoteright}{\textquoteright} interact and collaborate with each other, with their own features and capabilities, toward the achievement of a common goal.},
	keywords = {alpine environments, autonomous aerial vehicles, busy genius, Cognitive Systems, European project, Ground and Aerial Robotics, ground-aerial robots, human rescuer, intelligent donkey, patrolling hawks, real-world hostile environment, rescuing activities, Robust Control, Search and Rescue, search and rescue activities, SHERPA project, smart collaboration, telerobotics, trained wasps},
	doi = {10.1109/SSRR.2012.6523905},
	author = {Marconi, L. and Melchiorri, C. and Beetz, M. and Pangercic, D. and Siegwart, R. and Leutenegger, S. and Carloni, R. and Stramigioli, S. and Bruyninckx, H. and Doherty, P. and Kleiner, A. and Lippiello, V. and Finzi, A. and Siciliano, B. and Sala, A. and Tomatis, N.}
}
@conference {145,
	title = {Mutual Localization using Anonymous Bearing Measurements},
	booktitle = {2011 IEEE/RSJ Int. Conf. on Intelligent Robots and Systems},
	year = {2011},
	month = {09/2011},
	address = {San Francisco, CA},
	abstract = {This paper addresses the problem of mutual localization in multi-robot systems in presence of anonymous (i.e., without the identity information) bearing-only measurements. The solution of this problem is relevant for the design and implementation of any decentralized multi-robot algorithm/control. A novel algorithm for probabilistic multiple registration of these measurements is presented, where no global localization, distances, or identity are used. With respect to more conventional solutions that could be conceived on the basis of the current literature, our method is theoretically suitable for tasks requiring frequent, many-to-many encounters among agents (e.g., formation control, cooperative exploration, multiple-view environment sensing). An extensive experimental study validates our method and compares it with the fullinformative case of bearing plus-distance measurements. The results show that the proposed localization system exhibits an accuracy commensurate to our previous method [1] which uses bearing-plus-distance information.},
	keywords = {Distributed algorithms, Estimation, Localization, Multi-robot systems},
	author = {Paolo Stegagno and Marco Cognetti and Antonio Franchi and Giuseppe Oriolo}
}
@article {140,
	title = {The Sensor-based Random Graph Method for Cooperative Robot Exploration},
	journal = {IEEE/ASME Transaction on Mechatronics},
	volume = {14},
	year = {2009},
	month = {04/2009},
	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 which automatically realizes a trade-off 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.},
	keywords = {Coverage, Distributed algorithms, Exploration, Multi-robot systems},
	author = {Antonio Franchi and Luigi Freda and Giuseppe Oriolo and Marilena Vendittelli}
}
