Alejandro R. Mosteo

Enforcing Network Connectivity in Robot Team Missions

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 themselves and with their human operators, in many cases without the aid of a communication infrastructure. Guaranteeing connectivity enables robots to explicitly exchange information needed in collaborative task execution, and allows operators to monitor or manually control any robot at all times. Network paths should be multi-hop, so as not to unnecessarily restrict the team’s range. In this work we contribute a complete system which integrates three research aspects, usually studied separately, to achieve these characteristics: a multi-robot cooperative motion control technique based on a virtual spring—damper model which prevents communication network splits, a task allocation algorithm that takes advantage of network link information in order to ensure autonomous mission completion, and a network layer which works over wireless 802.11 devices, capable of sustaining hard real-time traffic and changing topologies. Link quality among peers is the key metric used to cooperatively move the robots and maintain uninterrupted connectivity, and the basis for novel ideas presented in each subsystem. Simulations and experimental results with real robots are presented and discussed.

Comparative experiments on optimization criteria and algorithms for auction based multi-robot task allocation

Auction based techniques are a highly successful tool used for multi-robot task allocation. However, theoretical performance and a proper taxonomy of optimization objectives have remained scarce until recent studies. Implementations from different authors have not been compared in common grounds and in light of these recent findings. In this paper we address this lack of comparative experimentation, providing simulation results on a large real life based scenario and in random worlds. Two intuitive optimization objectives, minimum total resource usage and minimum total time, are evaluated in object searching missions. A method for flexible tailoring of the bidding rules is presented and new insight is gained on the effect of using hybrid criteria for the optimization objective.

Guaranteed-Performance Multi-robot Routing under Limited Communication Range

A common assumption made in multi-robot research is that robots operate in a fully networked environment, where any two robots can communicate reliably at any time. However, in real-world missions over large geographical areas robots have a limited communication range and signal propagation conditions may be unpredictable due to obstacles or interferences. In such cases, communication limitations must be taken explicitly into account. In this paper, we present a multirobot routing algorithmfor dense environments under limited communication range. We focus on the aspect of careful mission planning in order to guarantee continuous connectivity and mission completeness, while offering a guarantee on performance under a variety of team objectives. The proposed algorithms are demonstrated in a large-scale domain using realistic simulations on the Player/Stage platform.

Efficient multi-robot formations using distributed optimization

This paper studies the problem of multi-robot formations by means of distributed optimization. In order to reach a desired configuration, robots can adjust two elements, the set of desired positions and the particular role of each robot within the formation. Although the two problems, positions and assignment, have been deeply studied separately, there are few solutions that consider both of them together. The main contribution of this paper is a distributed algorithm that computes the optimal solution for both parameters simultaneously, accompanied by proof that the set of optimal positions is independent of the assignment of the team of robots to those positions. This demonstration also allows us to compute the optimal positions by means of a standard distributed averaging method. In order to solve the assignment problem, we consider an existing distributed simplex algorithm and propose a modification that takes into account the variations in costs generated by the averaging algorithm. The whole method is provably correct to achieve the optimal solution.

Concurrent tree traversals for improved mission performance under limited communication range

In previous work we presented a multi-robot strategy for routing missions in large scenarios where network connectivity must be explicitly preserved. This strategy is founded on the traversal of path trees in such a way that connectivity to a static control center is always maintained, while ensuring that any target that is reachable by a chain consisting of all robots is eventually visited. In this work we improve the strategy performance by extending its sequential one-task-at-a-time execution approach with concurrent execution of tasks. We demonstrate that the general problem is NP-hard and offer several heuristic approaches to tackle it. We study the improvements that these heuristics can offer in regard to several important variables like network range and clustering of targets, and finally compare their performance over the optimal solutions for small problem instances. In summary, we offer a complete characterization of the new concurrent capabilities of the CONNECTTREE strategy.

Optimal role and position assignment in multi-robot freely reachable formations

Abstract Many multi-robot problems require the achievement of formations as part of the overall mission. This work considers a scenario in which unlabeled homogeneous robots must adopt a given formation pattern buildable anywhere in the environment. This involves finding the relative pose of the formation in regard to the initial robot positions, understood as a translation and a rotation; and the optimal assignment of the role of each robot within the formation. This paper provides an optimal solution for the combined parameters of translation, rotation and assignment that minimizes total displacement. To achieve this objective we first formally prove that the three decision variables are separable. Since computing the optimal assignment without accounting for the rotation is a computationally expensive problem, we propose an algorithm that efficiently computes the optimal roles together with the rotation. The algorithm is provably correct and finds the optimal solution in finite time. A distributed implementation is also discussed. Simulation results characterize the complexity of our solution and demonstrate its effectiveness.

A Practical Mobile Robotics Engineering Course Using LEGO Mindstorms

Mobile robotics and autonomous systems are subjects of increasing interest in the curricula of engineering studies, being application domains of growing importance in leading research and industry trends. In order to fulfill this demand, we have designed a robotics course for students from different engineering degrees and backgrounds. The course includes basic ideas from main topics in mobile robotics, with an important practical component. During the course, each student team is provided with a LEGO Mindstorms kit to freely build a robot and develop several modules demonstrating the specific competences being taught. Complete integration of all modules is the last step towards participation in a final obstacle-race competition, which has been shown to be a very successful and motivating activity for the students. This paper summarizes the course content, goals and methodology and details the results obtained in the student contest performed in the recent years.

SANCTA: an Aada 2005 general-purpose architecture for mobile robotics research

We present SANCTA, a flexible control architecture for multirobot teams. It is fully written in Ada 2005, except for the reuse of some C libraries. In this paper we highlight the architectural elements of our implementation and also present our experiences using the cuttingedge 2005 implementation from GNAT, through its GPL 2005 and 2006 iterations. We expect to exemplify the kind of advantages and challenges that developers can find in using the new Ada 2005 features. Since this architecture makes use of a wide range of Ada capabilities, from low level hardware interaction to graphical user interfaces, we believe it is a good example of a successful mid-size project using Ada 2005 in academy.

Visual data association in narrow-bandwidth networks

The performance of any cooperative task that involves two or more robots will be determined by their capacity to recognize common information of the environment. Vision sensors are very effective for this particular goal, but the cost of transmitting the visual information represents a real issue, even more if communication must be performed in narrow bandwidth networks and/or over a multi-hop path. Visual vocabularies provide a dimensionality reduction that has been effectively used in computer vision to reduce the computational load of performing searches in large volumes of data. In this paper we propose to exploit the same technique to decrease the volume of information that is exchanged in the network. This way, robots do not need to send the full descriptors associated to the features they observe, but only the word indices of the corresponding features in the vocabulary. Experiments with a wide variety of vocabularies are used to evaluate the quality of the association given by the algorithm. Finally, real experiments in a wireless network with a limited bandwidth are reported, showing the advantages of the proposed method compared to the communication of full images or feature descriptors.

RxAda: An Ada implementation of the ReactiveX API

The ReactiveX API, also known as the Reactive Extensions in the .NET world, is a recently popularized reactive programming framework for asynchronous, event-based, multi-threaded programming. Presented by its proponents as a solid tool for applications requiring a simple yet powerful approach to event-driven systems, it has seen favorable adoption in many popular languages. Although Ada has been long-favored by powerful tasking capabilities that reduce the need for additional multi-threading support, the reactive approach has properties that are well-suited to the safety and maintainability culture predominant in the Ada world, such as complexity reduction, race-condition and deadlock avoidance, and enhanced maintainability by means of concise and well-defined information flows. This work presents the design for a ReactiveX Ada implementation that aims to balance desirable library properties such as compile-time checks, reasonable user-required generic instantiations, and a shallow learning curve for both library clients and maintainers. The Ada programmer can henceforth benefit from the abundant documentation existing for the language-agnostic ReactiveX approach without stepping out of the Ada tool chain.