• Enforcing network connectivity in robot team missions

D Tardioli, AR Mosteo, L Riazuelo, JL Villarroel, L Montano

The International Journal of Robotics Research 29 (4), 460-480

The growing interest in robot teams for surveillance or rescue missions entails new technological challenges. Robots have to move to complete their tasks while maintaining communication among them-selves and with their human operators, in many cases without the aid of a communication infrastructure. Guaranteeing connectivity en-ables robots to explicitly exchange information needed in collaborative task execution, and allows operators to monitor or manuallycontrol any robot at all times. Network paths should be multi-hop,so as not to unnecessarily restrict the team’s range. In this workwe contribute a complete system which integrates three research as-pects, usually studied separately, to achieve these characteristics: amulti-robot cooperative motion control technique based on a virtualspring–damper model which prevents communication network splits,a task allocation algorithm that takes advantage of network link in-formation in order to ensure autonomous mission completion, and anetwork layer which works over wireless 802.11 devices, capable ofsustaining hard real-time traffic and changing topologies. Link quality among peers is the key metric used to cooperatively move the ro-bots and maintain uninterrupted connectivity, and the basis for novel ideas presented in each subsystem.Simulations and experimental re-sults with real robots are presented and discussed.

• Enforcing network connectivity in robot team missions

D Tardioli, AR Mosteo, L Riazuelo, JL Villarroel, L Montano

The International Journal of Robotics Research 29 (4), 460-480

Ad-hoc networks usually support best-effort traffic and occasionally some kind of quality of service (QoS). However, there are some applications, which generally involve cooperative control, with hard real-time traffic requirements where strict deadlines must be met. To meet deadlines, the communication network has to support the timely delivery of inter-task messages. This is the case, for example, of applications involving cooperative robot teams, such as those used for rescue tasks in hostile environments, emergencies or disaster recovery, where a wired backbone is in-feasible or economically unviable. In this paper, we present RT-WMP, a novel protocol that allows wireless real-time traffic in relatively small mobile ad-hoc networks using the low-cost commercial 802.11 technology. The protocol is based on a token-passing approach and message exchange is priority based. Moreover, support for frequent topology changes is provided through the sharing of a matrix that describes link quality amongst the members of the network.

• Pound: A multi-master ROS node for reducing delay and jitter in wireless multi-robot networks

D Tardioli, R Parasuraman, P Ögren

Robotics and Autonomous Systems 111, 73-87

The Robot Operating System (ROS) is a popular and widely used software framework for building robotics systems. With the growth of its popularity, it has started to be used in multi-robot systems as well. However, the TCP connections that the platform relies on for connecting the so-called ROS nodes presents several issues regarding limited-bandwidth, delays, and jitter, when used in wireless multi-hop networks. In this paper, we present a thorough analysis of the problem and propose a new ROS node called Pound to improve the wireless communication performance by reducing delay and jitter in data exchanges, especially in multi-hop networks. Pound allows the use of multiple ROS masters (roscores), features data compression, and importantly, introduces a priority scheme that allows favoring more important flows over less important ones. We compare Pound to the state-of-the-art solutions through extensive experiments and show that it performs equally well, or better in all the test cases, including a control-over-network example.

• Signal-based deployment planning for robot teams in tunnel-like fading environments

C Rizzo, D Tardioli, D Sicignano, L Riazuelo, JL Villarroel, L Montano

The International Journal of Robotics Research 32 (12), 1381-1397

Deploying a multi-robot team in confined environments poses multiple challenges that involve task and motion planning, localization and mapping, safe navigation, coordination of robots and also communications among all of them. In recent years, increasing attention has been paid to these challenges by the robotics community, but many problems remain unresolved. In this paper we address a technique for planning the deployment of a robot team in so-called fading environments, such as tunnels or galleries, where signal propagation presents specific characteristics. In order to maintain constant connectivity and high signal quality in the communication network formed by the robots and the base station, the robot deployment is driven by real-time signal measurements. First, an analysis of the signal propagation to obtain the general characteristic parameters of the signals in this kind of environment is carried out. Second, a technique which uses these parameters to drive the deployment is developed. A general strategy for this kind of environment in which the signals exhibit similar behavior is implemented. A complete system involving all of the above-mentioned robotics tasks has been developed. Finally, the system has been evaluated by means of simulation and in a real scenario.

• Robot teams for intervention in confined and structured environments

D Tardioli, D Sicignano, L Riazuelo, A Romeo, JL Villarroel, L Montano

Journal of Field Robotics 33 (6), 765-801

Safety, security, and rescue robotics can be extremely useful in emergency scenarios such as mining accidents or tunnel collapses where robot teams can be used to carry out cooperative exploration, intervention, or logistic missions. Deploying a multirobot team in such confined environments poses multiple challenges that involve task planning, motion planning, localization and mapping, safe navigation, coordination, and communications among all the robots. To complete their mission, robots have to be able to move in the environment with full autonomy while at the same time maintaining communication among themselves and with their human operators to accomplish team collaboration. Guaranteeing connectivity enables robots to explicitly exchange information needed in the execution of collaborative tasks and allows operators to monitor and teleoperate the robots and receive information about the environment. In this work, we present a system that integrates several research aspects to achieve a real exploration exercise in a tunnel using a robot team. These aspects are as follows: deployment planning, semantic feature recognition, multirobot navigation, localization, map building, and real-time communications. Two experimental scenarios have been used for the assessment of the system. The first is the Spanish Santa Marta mine, a large mazelike environment selected for its complexity for all the tasks involved. The second is the Spanish-French Somport tunnel, an old railway between Spain and France through the Central Pyrenees, used to carry out the real-world experiments. The latter is a simpler scenario, but it serves to highlight the real communication issues.

• Ground robotics in tunnels: Keys and lessons learned after 10 years of research and experiments

D Tardioli, L Riazuelo, D Sicignano, C Rizzo, F Lera, JL Villarroel, L Montano

Journal of Field Robotics 36 (6), 1074-1101

The work reported in this article describes the research advances and the lessons learned by the Robotics, Perception and Real-Time group over a decade of research in the field of ground robotics in confined environments. This study has primarily focused on localization, navigation, and communications in tunnel-like environments. As will be discussed, this type of environment presents several special characteristics that often make well-established techniques fail. The aim is to share, in an open way, the experience, errors, and successes of this group with the robotics community so that those that work in such environments can avoid (some of) the errors made. At the very least, these findings can be readily taken into account when designing a solution, without needing to sift through the technical details found in the papers cited within this text.