Improving the fault tolerance of multi-robot networks through a combined control law strategy

Applications based on groups of self-organized mobile robots and - more generically - agents are becoming pervasive in communication, monitoring, traffic and transportation systems. Their advantage is the possibility of providing services without the existence of a previously defined infrastructure and with a high degree of autonomy. On the other hand, physical agents, in general, are prone to failures, adding uncertainty and unpredictability in the environments in which they operate. Therefore, a robust topology regarding failures is an imperative requirement. In this paper, we show that mechanisms based solely on connectivity maintenance are not enough to obtain a sufficiently resilient network, and a robustness-oriented approach is necessary. Thus, we propose a local combined control law that aims at maintaining the overall network connectivity while improving the network robustness via actions that reduce vulnerability to failures that might lead to network disconnection. The combined control law performance was validated from two perspectives: as a reactive and as a proactive mechanism. As a reactive mechanism, it was able to accommodate ongoing failures and postpone or avoid network fragmentation. As a proactive mechanism, the network topology was able to evolve from a potentially vulnerable topology w.r.t. failures to a more robust one

A Decentralized Control Strategy for Resilient Connectivity Maintenance in Multi-robot Systems Subject to Failures

A Decentralized Control Strategy for Resilient Connectivity Maintenance in Multi-robot Systems Subject to Failure

Toward efficient adaptive ad-hoc multi-robot network topologies

The availability of robust and power-efficient robotic devices boosts their use in a wide range of applications, most of them unfeasible in the recent past due to environmental restrictions or because they are hazardous to humans. Nowadays, robots can support or perform missions of search and rescue, exploration, surveillance, and reconnaissance, or provide a communication infrastructure to clients when there is no network infrastructure available. In general, these applications require efficient and multi-objective teamwork. Hence, successful control and coordination of a group of wireless-networked robots relies on effective inter-robot communication. In this sense, this work proposes a model that aims at providing more efficient network topologies addressing the issues of connectivity maintenance, collision avoidance, robustness to failure and area coverage improvement. The model performance was experimentally validated considering fault-free and fault-prone scenarios. Results demonstrated the feasibility of having simultaneous controls acting to achieve more resilient networks able to enhancing their sensing area while avoiding collision and maintaining the network connectivity with regard to fault-free scenarios

Improving robustness in multi-robot networks

This paper addresses the topological robustness of robot networks under failures; a subject often neglected in the literature. Robots are likely to fail due to several causes, which may lead to a poorly connected or a fragmented network. Our purpose is to discuss how to design resilient robot networks. For that, we first demonstrate the problem analyzing the results from a protocol to simulate failures of both central and random (w.r.t. topology) robots. Then, we propose mechanisms for detecting the probability of a robot being in a fragile local configuration and for improving its local robustness. The procedures rely solely on local information: each robot estimates its probability of being in a harmful configuration based on the positions of its neighbors. Such probability is estimated as the number of paths connecting a robot to its 2-hop neighbors by the number of paths existing in the subgraph encompassing its 1-hop and 2-hop neighborhoods. For reversing an adverse configuration, robots change their position to an average position towards their 2-hop neighbors with fewer alternative paths. The results showed that the proposed mechanism is efficient for detecting fragile topological configurations and for improving the overall network robustness

Robust connectivity maintenance for fallible robots

Multi-robot systems are promising tools for many hazardous real-world problems. In particular, the practical application of swarm robotics was identified as one of the grand challenges of the next decade. As swarms enter the real world, they have to deal with the inevitable problems of hardware, software, and communication failure, especially for long-term deployments. Communication is a key element for effective collaboration, and the ability of robots to communicate is expressed by the swarm’s connectivity. In this paper, we analyze a set of techniques to assess, control, and enforce connectivity in the context of fallible robots. Past research has addressed the issue of connectivity but, for the most part, without making system reliability a constitutional part of the model. We introduce a controller for connectivity maintenance in the presence of faults and discuss the optimization of its parameters and performance. We validate our approach in simulation and via physical robot experiments