@article {Guo2021,
	title = {Semantic Histogram Based Graph Matching for Real-Time Multi-Robot Global Localization in Large Scale Environment},
	journal = {IEEE Robotics and Automation Letters},
	volume = {6},
	year = {2021},
	pages = {8349{\textendash}8356},
	publisher = {IEEE},
	abstract = {The core problem of visual multi-robot simultaneous localization and mapping (MR-SLAM) is how to efficiently and accurately perform multi-robot global localization (MR-GL). The difficulties are two-fold. The first is the difficulty of global localization for significant viewpoint difference. Appearance-based localization methods tend to fail under large viewpoint changes. Recently, semantic graphs have been utilized to overcome the viewpoint variation problem. However, the methods are highly time-consuming, especially in large-scale environments. This leads to the second difficulty, which is how to perform real-time global localization. In this letter, we propose a semantic histogram based graph matching method that is robust to viewpoint variation and can achieve real-time global localization. Based on that, we develop a system that can accurately and efficiently perform MR-GL for both homogeneous and heterogeneous robots. The experimental results show that our approach is about 30 times faster than Random Walk based semantic descriptors. Moreover, it achieves an accuracy of 95\% for global localization, while the accuracy of the state-of-the-art method is 85\%.},
	keywords = {Global localization, Histograms, large viewpoint difference, Location awareness, multi-robot map merging, Real-time systems, semantic SLAM, Semantics, Simultaneous localization and mapping, Three-dimensional displays, Visualization},
	issn = {2377-3774},
	doi = {10.1109/LRA.2021.3058935},
	author = {Xiyue Guo and Junjie Hu and Junfeng Chen and Fuqin Deng and Tin Lun Lam}
}
@conference {365,
	title = {Intelligent Robotic IoT System (IRIS)Testbed},
	booktitle = {2018 IEEE/RSJ International Conference on Intelligent Robots and Systems (IROS)2018 IEEE/RSJ International Conference on Intelligent Robots and Systems (IROS)},
	year = {2018},
	publisher = {IEEE},
	organization = {IEEE},
	address = {Madrid},
	doi = {10.1109/IROS.2018.8593636},
	url = {https://ieeexplore.ieee.org/document/8593636/http://xplorestaging.ieee.org/ielx7/8574473/8593358/08593636.pdf?arnumber=8593636},
	author = {Tran, Jason A. and Ghosh, Pradipta and Gu, Yutong and Kim, Richard and D{\textquoteright}Souza, Daniel and Ayanian, Nora and Krishnamachari, Bhaskar}
}
@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 {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 {215,
	title = {A Multirobot System for Distributed Area Coverage and Signal Searching in Large Outdoor Scenarios},
	journal = {Journal of Field Robotics},
	year = {2015},
	pages = {n/a{\textendash}n/a},
	issn = {1556-4967},
	doi = {10.1002/rob.21636},
	url = {http://dx.doi.org/10.1002/rob.21636},
	author = {Garz{\'o}n, Mario and Valente, Jo{\~a}o and Rold{\'a}n, Juan Jes{\'u}s and Cancar, Leandro and Barrientos, Antonio and Del Cerro, Jaime}
}
@article {148,
	title = {Occlusion-Based Cooperative Transport with a Swarm of Miniature Mobile Robots},
	journal = {IEEE Transactions on Robotics},
	volume = {31},
	year = {2015},
	pages = {307{\textendash}321},
	keywords = {cooperation without communication, cooperative transport, e-puck, occlusion, swarm robotics},
	doi = {10.1109/TRO.2015.2400731},
	author = {Chen, Jianing and Gauci, Melvin and Li, Wei and Kolling, A. and Gross, Roderich}
}
@article {167,
	title = {A semantically-informed multirobot system for exploration of relevant areas in search and rescue settings},
	journal = {Autonomous Robots},
	year = {2015},
	pages = {1{\textendash}17},
	abstract = {Coordinated multirobot exploration involves autonomous discovering and mapping of the features of initially unknown environments by using multiple robots. Autonomously exploring mobile robots are usually driven, both in selecting locations to visit and in assigning them to robots, by knowledge of the already explored portions of the environment, often represented in a metric map. In the literature, some works addressed the use of semantic knowledge in exploration, which, embedded in a semantic map, associates spatial concepts (like {\textquoteleft}rooms{\textquoteright} and {\textquoteleft}corridors{\textquoteright}) with metric entities, showing its effectiveness in improving the total area explored by robots. In this paper, we build on these results and propose a system that exploits semantic information to push robots to explore relevant areas of initially unknown environments, according to a priori information provided by human users. Discovery of relevant areas is significant in some search and rescue settings, in which human rescuers can instruct robots to search for victims in specific areas, for example in cubicles if a disaster happened in an office building during working hours. We propose to speed up the exploration of specific areas by using semantic information both to select locations to visit and to determine the number of robots to allocate to those locations. In this way, for example, more robots could be assigned to a candidate location in a corridor, so the attached rooms can be explored faster. We tested our semantic-based multirobot exploration system within a reliable robot simulator and we evaluated its performance in realistic search and rescue indoor settings with respect to state-of-the-art approaches.},
	keywords = {Coordinated multirobot exploration, Search and Rescue, Semantic map},
	issn = {1573-7527},
	doi = {10.1007/s10514-015-9480-x},
	url = {http://dx.doi.org/10.1007/s10514-015-9480-x},
	author = {Quattrini~Li, Alberto and Cipolleschi, Riccardo and Giusto, Michele and Amigoni, Francesco}
}
@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}
}
@conference {GargPersistent2014,
	title = {Persistent Monitoring of Stochastic Spatio-temporal Phenomena with a Small Team of Robots},
	booktitle = {Robotics: Science and Systems},
	year = {2014},
	month = {Jul},
	address = {Berkeley, CA},
	author = {Sahil Garg and Nora Ayanian}
}
@article {147,
	title = {Self-Organized Aggregation without Computation},
	journal = {The International Journal of Robotics Research},
	volume = {33},
	year = {2014},
	pages = {1145-1161},
	keywords = {aggregation, minimal information processing, rendezvous, swarm robotics},
	doi = {10.1177/0278364914525244},
	author = {Gauci, Melvin and Chen, Jianing and Li, Wei and Dodd, Tony J. and Gross, Roderich}
}
@article {216,
	title = {An Aerial-Ground Robotic System for Navigation and Obstacle Mapping in Large Outdoor Areas},
	journal = {Sensors},
	volume = {13},
	year = {2013},
	pages = {1247},
	abstract = {There are many outdoor robotic applications where a robot must reach a goal position or explore an area without previous knowledge of the environment around it. Additionally, other applications (like path planning) require the use of known maps or previous information of the environment. This work presents a system composed by a terrestrial and an aerial robot that cooperate and share sensor information in order to address those requirements. The ground robot is able to navigate in an unknown large environment aided by visual feedback from a camera on board the aerial robot. At the same time, the obstacles are mapped in real-time by putting together the information from the camera and the positioning system of the ground robot. A set of experiments were carried out with the purpose of verifying the system applicability. The experiments were performed in a simulation environment and outdoor with a medium-sized ground robot and a mini quad-rotor. The proposed robotic system shows outstanding results in simultaneous navigation and mapping applications in large outdoor environments.},
	issn = {1424-8220},
	doi = {10.3390/s130101247},
	url = {http://www.mdpi.com/1424-8220/13/1/1247},
	author = {Garz{\'o}n, Mario and Valente, Jo{\~a}o and Zapata, David and Barrientos, Antonio}
}
@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}
}
@conference {336,
	title = {Semantically-Informed Coordinated Multirobot Exploration of Relevant Areas in Search and Rescue Settings},
	booktitle = {Proceedings of the 6th European Conference on Mobile Robots (ECMR)},
	year = {2013},
	abstract = {Coordinated multirobot exploration involves autonomous discovering of unknown features in environments by using multiple robots. Autonomously exploring mobile robots are driven by knowledge of the already explored portions of the environment, usually represented in a metric map. In the literature, some works addressed the use of semantic knowledge in exploration, which, embedded in a semantic map, associates spatial concepts (like {\textquoteleft}rooms{\textquoteright} and {\textquoteleft}corridors{\textquoteright}) with metric entities, showing its effectiveness to improve total explored area. In this paper, we build on these results and propose a system that exploits semantic information to push robots to explore areas that are relevant, according to a priori information provided by human users. We tested our semantic-based multirobot exploration system in a reliable robot simulator and evaluated its performance in realistic search and rescue settings with respect to state-of-the-art approaches.},
	doi = {10.1109/ECMR.2013.6698845},
	author = {Riccardo Cipolleschi and Michele Giusto and Quattrini~Li, Alberto and Francesco Amigoni}
}
@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}
}
@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 {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}
}
@inbook {217,
	title = {Computational Science and Its Applications - ICCSA 2011: International Conference, Santander, Spain, June 20-23, 2011. Proceedings, Part III},
	year = {2011},
	pages = {58{\textendash}73},
	publisher = {Springer Berlin Heidelberg},
	organization = {Springer Berlin Heidelberg},
	chapter = {Multi-robot Visual Coverage Path Planning: Geometrical Metamorphosis of the Workspace through Raster Graphics Based Approaches},
	address = {Berlin, Heidelberg},
	isbn = {978-3-642-21931-3},
	doi = {10.1007/978-3-642-21931-3_5},
	url = {http://dx.doi.org/10.1007/978-3-642-21931-3_5},
	author = {Valente, Jo{\~a}o and Barrientos, Antonio and Del Cerro, Jaime and Rossi, Claudio and Colorado, Julian and Sanz, David and Garz{\'o}n, Mario},
	editor = {Murgante, Beniamino and Gervasi, Osvaldo and Iglesias, Andr{\'e}s and Taniar, David and Apduhan, Bernady O.}
}
@inbook {182,
	title = {A Distributed Multi-robot Cooperation Framework for Real Time Task Achievement},
	booktitle = {Distributed Autonomous Robotic Systems 7},
	year = {2006},
	pages = {187-196},
	publisher = {Springer},
	organization = {Springer},
	isbn = {978-4-431-35878-7},
	doi = {10.1007/4-431-35881-1_19},
	url = {http://dx.doi.org/10.1007/4-431-35881-1_19},
	author = {Sanem Sariel and Tucker Balch},
	editor = {Gini, Maria and Voyles, Richard}
}
@inbook {183,
	title = {Empirical Evaluation of Auction-Based Coordination of AUVs in a Realistic Simulated Mine Countermeasure Task},
	booktitle = {Distributed Autonomous Robotic Systems 7},
	year = {2006},
	pages = {197-206},
	publisher = {Springer},
	organization = {Springer},
	isbn = {978-4-431-35878-7},
	doi = {10.1007/4-431-35881-1_19},
	url = {http://dx.doi.org/10.1007/4-431-35881-1_19},
	author = {Sanem Sariel and Tucker Balch and Jason Stack},
	editor = {Gini, Maria and Voyles, Richard}
}
