Papers by Frederico Santos
Interest on using mobile autonomous agents has been growing, recently, due to their capacity to c... more Interest on using mobile autonomous agents has been growing, recently, due to their capacity to cooperate for diverse purposes, from rescue to demining and security. In many of these applications the environments are inherently unstructured and dynamic, requiring substantial computation resources for gathering enough sensory input data to allow a safe navigation and interaction with the environment. As with humans, who depend heavily on vision for these purposes, mobile robots employ vision frequently as the primary source of input data when operating in such environments. However, vision-based algorithms are seldom developed with reactive and real-time concerns, exhibiting large variations in the execution time and leading to occasional periods of black-out or vacant input data. This paper addresses this problem in the scope of the CAMBADA robotic soccer team developed at the University of Aveiro, Portugal. It presents an evolution from a monolithic to a modular architecture for the vision system that improves its reactivity. With the proposed architecture it is possible to track different objects with different rates without losing any frames.
Interest on using mobile autonomous agents has been growing, recently, due to their capacity to c... more Interest on using mobile autonomous agents has been growing, recently, due to their capacity to cooperate for diverse purposes, from rescue to demining and security. Such cooperation typically requires the exchange of state data that is time sensitive and thus, applications should be aware of temporal data coherency. In order to provide such information a real-time communications protocol must be used to prevent unbounded latency of message delivery. This is, however, not a trivial task when using wireless links because of their poor reliability properties, exhibiting high bit error rates, omissions and inconsistencies. This paper describes such a communication protocol that adapts itself to the current conditions of the medium attempting to deliver an adequate timeliness while using the least bandwidth. The protocol operates over IEEE 802.11 networks in both managed and ad-hoc modes and it is fully distributed. It has been developed within the framework of the CAMBADA project at the University of Aveiro, Portugal, which aims at developing a robotic soccer team. This paper describes the protocol and presents some preliminary experimental results.
Wireless communication became pervasive in many application domains, either to interconnect piece... more Wireless communication became pervasive in many application domains, either to interconnect pieces of equipment, such as computer peripherals and mobile devices, or to facilitate the installation and operation of distributed systems in general, e.g., wireless LANs, or even to allow distributed systems to extend seamlessly over fixed or mobile hosts, such as industrial plants with mobile robots. In this paper we focus on the latter case, particularly on the communication system for a set of mobile robots that must cooperate in real-time to achieve a common goal. The communication is based on IEEE802.11, complemented with an overlay transmission control that reduces collisions among the robotic team. For efficiency in bandwidth usage, the protocol relies on broadcasts but these are known to be unreliable. Therefore, we carried out experiments to determine the effectiveness of using broadcasts instead of unicasts in the presence of spurious traffic. The results show that broadcasts are indeed more effective than unicasts even for relatively high spurious loads. However, this behavior was not verified when the spurious load had a very high level of burstiness, causing a noticeable degradation of broadcasts reliability.
... Serão descritos ao longo do artigo alguns aspectos importantes, tanto na construção do hardwa... more ... Serão descritos ao longo do artigo alguns aspectos importantes, tanto na construção do hardware, como do desenvolvimento do software. É dada especial atenção ao cálculo daposição global e regresso ao ponto de partida, sem informação prévia. ...
Interest on using mobile autonomous agents has been growing, recently, due to their capacity to c... more Interest on using mobile autonomous agents has been growing, recently, due to their capacity to cooperate for diverse purposes, from rescue to demining and security. However, such cooperation requires the exchange of state data that is time sensitive while achieving timeliness with RF communication is intrinsically difficult due to the openess of the medium. This paper describes a communication layer that improves the timeliness of periodic data exchanges among the team reducing the chances of lost packets caused by collisions between team members. In particular, the paper extends a previous proposal for an adaptive TDMA protocol with new self-configuration capabilities according to the current number of active team members. This feature further reduces the likelyhood of collisions within the team. Several experimental results with an actual system implementation show the effectiveness of the proposed solution.
Interest on using mobile autonomous agents has been growing, recently, due to their capacity to c... more Interest on using mobile autonomous agents has been growing, recently, due to their capacity to cooperate for diverse purposes, from rescue to demining and security. However, such cooperation requires the exchange of state data that is time sensitive and thus, applications should be aware of data temporal coherency. In this paper we describe the architecture of the agents that constitute the CAMBADA (Cooperative Autonomous Mobile roBots with Advanced Distributed Architecture) robotic soccer team developed at the University of Aveiro, Portugal. This architecture is built around a real-time database that is partially replicated in all team members and contains both local and remote state variables. The temporal coherency of the data is enforced by an adequate management system that refreshes each database item transparently at a rate specified by the application. The application software accesses the state variables of all agents with local operations, only, delivering both value and temporal coherency.
The RoboCup Middle-Size League robotic soccer competitions pose a real cooperation problem for te... more The RoboCup Middle-Size League robotic soccer competitions pose a real cooperation problem for teams of mobile autonomous robots. In the current state-of-practice cooperation is essential to overcome the opponent team and thus a wireless communication protocol and associated middleware are now fundamental components in the multi-robots system architecture. Nevertheless, the wireless communication has relatively low reliability and limited bandwidth. Since it is shared by both teams, it is a fundamental resource that must be used parsimoniously. Curiously, to the best of our knowledge, no previous study on the effective use of the wireless medium in actual game situations was done. In this paper we show how current teams use the wireless medium and we propose a set of best practices towards a more efficient utilization. Then, we present a communication protocol and middleware that follow such best practices and have been successfully used by one particular MSL team in the past four years.
ABSTRACT Cooperating mobile autonomous robots have been generating a growing interest in fields s... more ABSTRACT Cooperating mobile autonomous robots have been generating a growing interest in fields such as rescue, demining and security. These applications require a real time middleware and wireless communication protocol that can effecient and timely support the fusion of the distributed perception and the development of coordinated behaviors. This paper proposes an affordable middleware, based on low-cost and open-source COTS technologies, which relies on a real-time database partially replicated in all team members, containing both local and remote state variables, in a distributed shared memory style. This provides seamless access to the complete team state, with fast non-blocking local operations. The remote data is updated autonomously in the background by a WiFi-based wireless communication protocol, at an adequate refresh rate. The software infrastruture is complemented with a task manager that provides scheduling and synchronization services to the application processes on top of the Linux operating system. Such infrastructure has been successfully used for four years in one RoboCup middle-size soccer team, and it has proved to be dependable in the presence of uncontrolled spurious traffic in the communication channel, using an adaptive technique to synchronizating the robots in the team and reconfiguring the communications dynamically and automatically according to the number of currently active team members.
Resumo -Este artigo descreve um sistema de localização de baixo custo para pequenos robôs autónom... more Resumo -Este artigo descreve um sistema de localização de baixo custo para pequenos robôs autónomos e móveis. Este sistema foi desenvolvido para aplicação no robô Bulldozer IV, vencedor do concurso Micro-Rato 2001. O sistema combina informação azimutal absoluta com informação odométrica relativa e permite ao robô, após atingir uma zona a lvo no interior de um labirinto desconhecido, regressar ao ponto de partida. No caso particular do desempenho no concurso, refira-se que este robô foi capaz, por duas vezes, de voltar à posição de partida e parar a menos de 20cm de distância desta após percorrer um trajecto com aproximadamente 25 metros de comprimento por entre vários obstáculos estáticos e dinâmicos. Este artigo apresenta uma breve discussão sobre as técnicas comummente usadas para percepção de localização em robôs móveis e autónomos. Seguidamente, é descrito o funcionamento do sistema de localização desenvolvido e a sua integração no sistema de navegação do robô Bulldozer IV. São ainda apresentados resultados experimentais que permitem caracterizar o desempenho do sistema de navegação em termos de distância final entre o ponto de paragem e o ponto de partida.
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Papers by Frederico Santos