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CONTROLO 2006 7th PORTUGUESE CONFERENCE ON AUTOMATIC CONTROL

Instituto Superior Técnico Lisboa, Portugal

September 11-13, 2006

FINAL PROGRAM AND

BOOK OF ABSTRACTS

Organized by

COPYRIGHT

The material presented at CONTROLO’2006 remains the copyright of the respective authors. By submitting it to the Conference, authors have given APCA permission to be included in the Proceedings in CD-ROM format.

Proceedings published by APCA - Associação Portuguesa de Controlo Automático (Portuguese Society of Automatic Control) and IST - Instituto Superior Técnico.

ISBN978-972-97025-2-5

Contents

Organizing Committee ............................................................................ 1

International Program Committee.............................................................. 3

Reviewers List ........................................................................................ 4

Welcome to CONTROLO’2006.................................................................... 5

Invited Plenary Lectures........................................................................... 7

Tutorial Session .................................................................................... 15

Program at a Glance.............................................................................. 21

Technical Program................................................................................. 27

Book of Abstracts

Monday Sessions (MA, MP)............................................................. 37 Tuesday Sessions (TA, TP) ............................................................. 49 Wednesday Sessions (WA, WP)....................................................... 60

Author’s Index...................................................................................... 69

1

CONTROLO’2006 7th Portuguese Conference on Automatic Control Instituto Superior Técnico

Lisboa, Portugal September 11-13, 2006

GENERAL CHAIR: Miguel Ayala Botto, Instituto Superior Técnico/IDMEC, Portugal

CHAIRS OF THE IPC: Chair: Michel Verhaegen, Delft Center for Systems and Control/TU-Delft, The Netherlands Vice-chair: João Miranda Lemos, Instituto Superior Técnico/INESC-ID, Portugal

LOCAL ORGANIZING COMMITTEE: Miguel Ayala Botto, Instituto Superior Técnico/IDMEC, Portugal João Miranda Lemos, Instituto Superior Técnico/INESC-ID, Portugal José Sá da Costa, Instituto Superior Técnico/IDMEC, Portugal Maria Isabel Ribeiro, Instituto Superior Técnico/ISR, Portugal João M.C. Sousa, Instituto Superior Técnico/IDMEC, Portugal Carlos Cardeira, Instituto Superior Técnico/IDMEC, Portugal José Santos-Victor, Instituto Superior Técnico/ISR, Portugal

ORGANIZERS: Associação Portuguesa de Controlo Automático Instituto Superior Técnico

FINANCIAL AND ADMINISTRATIVE SUPPORTERS:

Associação Portuguesa de Controlo Automático (APCA) Instituto Superior Técnico (IST)

Instituto de Engenharia Mecânica (IDMEC) Instituto de Sistemas e Robótica (ISR) Instituto de Engenharia de Sistemas e Computadores (INESC-ID) Fundação para a Ciência e Tecnologia (FCT) Fundação Calouste Gulbenkian (FCG) Reitoria da Universidade Técnica de Lisboa (UTL) Rede Eléctrica Nacional (REN) Metropolitano de Lisboa Banco Espírito Santo (BES) Ordem dos Engenheiros Revista Robótica

3

INTERNATIONAL PROGRAM COMMITTEE

Chair: Michel Verhaegen, Delft Center for Systems and Control/TU-Delft, The Netherlands Vice-chair: João Miranda Lemos, Instituto Superior Técnico/INESC-ID, Portugal

MembersJanos Abonyi University of Veszprém HungaryPedro Albertos Universidad Politècnica de València SpainFrank Allgöwer University of Stuttgart GermanyDerek Atherton University of Sussex UKRobert Babuska Technical University of Delft HollandLuís Baptista ENIDH PortugalEstela Bicho Universidade do Minho PortugalJosé Boaventura Universidade Trás-os-Montes e Alto Douro PortugalEduardo Camacho Universidad de Sevilla SpainRaja Chatila LAAS/CNRS FranceAnna Costa University of São Paulo BrazilCarlos Couto Universidade do Minho PortugalClaudio de Persis Università di Roma ItalyBart de Schutter Technical University of Delft HollandGeorgi Dimirovski Dogus University Turkey TurkeyAntónio Dourado Correia Universidade de Coimbra PortugalHermínio Duarte Ramos Universidade Nova de Lisboa PortugalGuy Dumont University of British Columbia CanadaJorge Ferreira Universidade de Aveiro PortugalSebastião Feyo de Azevedo Universidade do Porto PortugalJoão Figueiredo Universidade de Évora PortugalJosé Fellipe de Souza Universidade da Beira Interior PortugalToshio Fukuda Nagoya University JapanLuís Gomes Universidade Nova de Lisboa PortugalTore Hägglund Lund Institute of Technology SwedenJoão Hespanha University of California, Santa Barbara USAGiovanni Indiveri University of Leece ItalyAlberto Isidori Washington University USARolf Johansson Lund Institute of Technology SwedenKrzysztof Kozlowski Poznan University of Technology PolandPedro Lima Instituto Superior Técnico PortugalFernando Lobo Pereira Universidade do Porto PortugalPaulo Lopes dos Santos Universidade do Porto PortugalDavid Lowe Aston University UKZoubir Mammeri IRIT - Toulouse FranceJorge Martins de Carvalho Universidade do Porto PortugalTeresa Mendonça FC da Universidade do Porto PortugalEdoardo Mosca Università di Firenze ItalyAlexandre Mota Universidade de Aveiro PortugalRui Neves da Silva Universidade Nova de Lisboa PortugalHenk Nijmeijer University of Eindhoven HollandUrbano Nunes Universidade de Coimbra PortugalAntónio Pascoal Instituto Superior Técnico PortugalNorberto Pires Universidade de Coimbra PortugalCésar Prada Universidad de Valladolid SpainMaria João Rendas I3S/CNRS FrancePierre Rouchon École de Mines de Paris FranceAntónio Ruano Universidade do Algarve PortugalFrancisco Rubio Universidad de Sevilla SpainAntonio Sala Universidad Politècnica de València SpainMiguel Salichs Universidad Carlos III de Madrid SpainRicardo Sanz Universidad Politécnica de Madrid SpainJurek Sasiadek Carleton University CanadaRiccardo Scattolini Politecnico de Milano ItalyJacquelien Scherpen Technical University of Delft HollandRodolphe Sepulchre Université de Liège BelgiumBruno Siciliano Università degli Studi di Napoli Federico II ItalyFátima Silva Leite Universidade de Coimbra PortugalJonas Sjöberg Chalmers University of Technology SwedenMarcel Staroswiecki Université des Sciences et Technologies de Lille FrancePaulo Tabuada University of Notre Dame USAJosé Tenreiro Machado Instituto Superior de Engenharia do Porto PortugalJean-Pierre Thomesse LORIA - Nancy FranceOsman Tokhi University of Sheffield UKAníbal Traça de Almeida Universidade de Coimbra PortugalJosé Valente de Oliveira Universidade do Algarve PortugalTon van den Boom Technical University of Delft HollandSiep Weiland Eindhoven University of Technology Holland

4

LIST OF REVIEWERS

Arnaldo Abrantes Fernando Fontes Maria do Rosário PinhoAntónio Pedro Aguiar Toshio Fukuda Norberto Pires Pedro Albertos Francisco Garcia César Prada Frank Allgöwer Alexander Gegov Mário Ramalho Luis Almeida Luís Gomes Luís RatoMaria Margarida Amorim Ferreira Paulo Gonçalves João Reis Plamen Angelov Maria da Graça Ruano Maria João Rendas Derek Atherton Tore Hägglund Maria Isabel Ribeiro Miguel Ayala Botto João Hespanha Romualdo Luis Ribera Salcedo José Raúl Azinheira Knut Hupper Luis Rodrigues Robert Babuska Giovanni Indiveri Anabela Rodrigues Luís Baptista Rolf Johansson António Ruano Ramiro Barbosa Uzay Kaymak Francisco RubioPedro Beirão Krzysztof Kozlowski Thomas Runkler Alberto Bemporad Paulo Leitão José Sá da Costa Alexandre Bernardino Arie Leizarowitz Antonio SalaEstela Bicho Francisco Lemos Miguel SalichsCarlos Bispo Pedro Lima Jorge Salvador Marques José Boaventura Xavier Litrico Manuel Fernando dos Santos SilvaJosé Borges Fernando Lobo Pereira José Santos-Victor Kouamana Bousson Paulo Lopes dos Santos Helena SarmentoPaulo Branco David Lowe Jurek Sasiadek Luis Brito Palma Maria Paula Macedo Rocha Riccardo ScattoliniJoão Calado Zoubir Mammeri Jacquelien Scherpen Rogério Caldas Pinto Silvério Marques Christian SchmidPedro Caldas Pinto Jorge Martins Rodolphe Sepulchre Eugénio Campos Ferreira Jorge Martins de Carvalho José Luís Sequeira Carlos Cardeira Mário Mendes João Sequeira José Cardoso de Menezes Luís Mendonça Mário SerafimJosé Cardoso Igreja Teresa Feio Mendonça Paulo Shirley Adolfo Cartaxo João Miranda Lemos Bruno Siciliano Maria Teresa Carvalho Hugo Alonso Monteiro Carlos SilvaJoão Paulo Carvalho Gustavo Monteiro da Silva Fátima Silva LeiteLuigi Chisci Filipe Morais Miguel Silva Alessandro Chiuso António Moreira Carlos SilvestreQ.P. Chu Edoardo Mosca Carlota SimõesFernando Coito José Paulo Moura Oliveira Jonas Sjöberg Luís Correia Alexandra Moutinho Filomena Soares Anna Costa J.A. Mulder Paulo de Sousa Gil João da Costa Sousa David Naso José Filippe de SouzaBertinho Costa Rui Neves da Silva Marcel Staroswiecki Bart de Schutter Henk Nijmeijer Paulo Tabuada Georgi Dimirovski Urbano Nunes José Tenreiro Machado Sebastian Dormido Catarina Nunes Delfim Torres António Dourado Correia Paulo Oliveira José Valente de Oliveira Hermínio Duarte Ramos Manuel Ortigeira Duarte Valério Guy Dumont Rainer Palm Ton van den Boom Edgar Fernandes António Pascoal Michel Verhaegen Jorge Ferreira Teresa Perdicoúlis Susana VieiraVítor M. Ferreira dos Santos Carlos Pereira Rui Vilela Dionísio Sebastião Feyo de Azevedo Claudio de Persis Blas Vinagre Hugo Fialho Magalhães Luís Pina Alexander Zaslavski João Figueiredo Carla Pinheiro

A MULTI-AGENT SYSTEM WITHDISTRIBUTED COORDINATION FORCONTROLLING A SINGLE ROBOT

Bianca Innocenti 1 Beatriz Lopez 1 Joaquim Salvi

Institute of Informatics and ApplicationsUniversity of Girona

Abstract: The demand of sophisticated robotic capabilities is bringing researchersto propose hybrid control architectures based on multi-agent systems, in orderto provide mechanisms to distribute, coordinate, adapt and extend the controlsystem of the robots. This paper presents a multi-agent architecture developed tocontrol a single mobile robot. Unlike others, the presented architecture distributescoordination among agents; they negotiate in order to take control of the conflictingresources of the robot. Some agents have been implemented and tested in a mobilerobot, the Pioneer 2DX of ActivMedia Robotics.

Keywords: Robotics and automation, multi-agent systems

1. INTRODUCTION

The demand of sophisticated robotic capabilitiesis bringing together research from traditionallyemphasized low-level sensing and control taskwith research concerned with high-level cognitivefunctions that enable robots to reason, act andperceive in changing, incompletely known, andunpredictable environments in a robust manner.On designing low-level and high-level capabilities,most robot architectures found in the literaturerely on hybrid approaches that usually have threemain layers: the reactive, the intermediate andthe deliberative layers. Commonly, reactive layercontains a set of behaviors that are combined inorder to give a rapid response over unexpectedevents while planning a task, or a mission, ora path is executed independently in the delib-erative level. The intermediate layer bridges thegap between the symbolic (deliberative) and thesignals (reactive) levels of abstraction. Works as

1 This work was partially supported by the Spanish MECProject TIN2004-06354-C02-02 and by the DURSI Au-tomation Engineering and Distributed Systems, 00296.

(Bryson, 2001) have proved the benefits of thesearchitectures.

Advances in Multi-Agent Systems (MAS) haveinspired researchers to go one abstract level fur-ther in implementing the architectures, in whichmodules are replaced by agents. The differentlayers can provide alternative actions at a giventime (go, stop); even at the same layer severalagents can suggest different actions (go, avoidobstacles). So the key issue in MAS is the co-ordination mechanism that are used to choosethe most relevant action to take at a particu-lar time according to the possible set of actionsprovided by the different agents. Most of the de-veloped MAS architectures are built to controla multi-robot system (Hu and Gu, 2000; Spearset al., 2004; Dorigo and et Al., 2004), but thereare several developments to control a single robot(Busquets et al., 2003; Giorgini et al., 2002; Nevesand Oliveira, 1997a).

One of the major issues in robot control architec-tures is the formulation of effective mechanismsfor the coordination of the conflicting agents with

the aim of showing a rational and coherent globalbehavior. There are two main classes of behaviorcoordination mechanisms: arbitration and com-mand fusion mechanisms (see (Pirjanian, 1999)).The former selects one behavior from a groupof competing ones, and give to it the ultimatecontrol of the robot until next selection cycle. Thelatter combines recommendations from multiplebehaviors to form a control action that representstheir consensus (all the behaviors simultaneouslycontribute to the control).

Unlike other architectures, ours distributes coor-dination that is performed as a negotiation amongagents. Our approach gives flexibility to the ar-chitecture being easier to add agents to the com-munity and to distribute the system in differentcomputers. Some agents of the architecture havebeen implemented in an ad-hoc MAS platformand tested in a mobile robot, the Pioneer 2DXof ActivMedia Robotics. The ultimate goal of ourresearch is to deploy our architecture in roboticassistance for elderly people (Pollack et al., 2002),tour/museum guiding (Jensen et al., 2005), orchildren with autism (Dautenhahn et al., 2005).All of them are complex applications that are achallenge for the current robot’s architectures.

This paper is organized as follows. Next Sectiondescribes the proposed architecture. Section 3presents the coordination mechanisms used tocoordinate the agents. The implementation of thearchitecture and some experimental results arepresented in Section 4. Finally, conclusions andfuture work are drawn in Section 5.

2. MAS ARCHITECTURE

The proposed architecture is shown in Figure1. Agents can be grouped in perception, behav-ioral, deliberative and actuator agents. Perceptionagents obtain information about the environmentand about the internal conditions of the robot;behavioral agents carry out specific actions, asavoiding obstacles; deliberative agents implementscomplex tasks as planning; and actuator agentsare in charge of controlling the linear and angularspeed of the robot interacting directly with mo-tors.

There is a perception agent per each sensorpresent on the robot. These agents extract in-formation about the environment and the robot.They process and transmit the information whenrequired, in an appropriate way to the otheragents in the community. Particularly, perceptionagents are the following: the encoder agent, thesonar agent and the battery sensor agent. Firstly,the encoder agent is responsible for getting theposition and heading of the robot in local coor-dinates, related to a frame attached to the center

Fig. 1. MAS Architecture as well as the informa-tion flow among them. Dotted lines denotethat only one agent at the time communicateswith the robot agent.

of mass of the robot and translate them to globalcoordinates, on an earth fixed frame. Secondly,the sonar agent is in charge of creating a localmap to locate obstacles based on the reading ofthe ultrasonic sensors. It has to find the obstaclesin the path of the robot and update the mapwhen the robot is moving. And finally, the batterysensor agent obtains the battery charge from therobot. The robot should recharge when batteryvoltage is 10V because they can be permanentlydamaged, so this agent senses this value at givenfrequency, that increases as the value tends to10V.

There is a behavioral agent per each basic behav-ior to perform. Based on the information receivedfrom perception agents, they calculate the linearand angular speed the robot should have in orderto achieve the desired action. As they cannotuse the same resource at the same time, somecoordination must be done. Instead of centraliz-ing the behavior selection in a coordinator agentthat selects the winning action (as for example,in (Busquets et al., 2003)), behavioral agents ne-gotiate to take control (see section 3.1). Behav-ioral agents are the following: the goto agent,the avoid agent, the battery charger agent andthe goThrough agent. Firstly, the goto agent isresponsible for driving the robot to the targetposition, based on the information provided bythe encoder agent. This agent calculates the lin-ear and the angular speeds that should have therobot in order to arrive to the desired position.It does not consider obstacles in the path nor itcalculates a trajectory. Secondly, the avoid agentmust avoid the obstacles that could be in thepath to the target. It asks the sonar agent for theclosest obstacle point and calculates the suitablelinear and angular speeds for not colliding withthe object. Thirdly, the battery charger agent,based on the information given by battery sen-

sor agent, analyzes when it is necessary to go tothe recharger point. It sends an alarm to taskplanning agent when the battery level goes under10.4 V, indicating that reaching the rechargerpoint is essential and asking the path planningagent to calculate the optimal trajectory to thispoint. And finally, the goThrough agent, basedon the information provided by the localizationand the sonar agents, calculates the linear andthe angular speeds of the robot in order to drivethe robot through narrow places like doors. Unlikegoto agent, it considers the distances to obstaclesto drive the robot among them.

There is a deliberative agent for each complextask to perform. These agents receive informationfrom perception agents, behavioral agents andother deliberative agents. Their roles vary frompath planning to task planning. These agentsare: the localization agent, the path planningagent, the task planning agent and the clientagent. The localization agent must localize therobot in the global map. It receives informationfrom the sonar agent and the encoder agent andfinds the robot’s location. The path planningagent is responsible for the calculation of a freeof non-moving obstacles trajectory to the goal.Based on the information given by the localizationagent, the task planning or the battery chargeragents it finds the path to the target. The taskplanning agent, based on the information providedby the client and the localization agents, plans thesequence of tasks to reach the goal. And finally,the client agent is the user interface that allowsgiving goals to the architecture. The user can senda goal task to the architecture through the clientagent.

There is an actuator agent per each possible ro-bot’s actuator. In the current Pioneer configura-tion only one agent is needed in spite the factthat there are two motors in the robot. Thereis an on-board micro-controller that controls themotors and the rest of the circuitry, that is notrecommended to bypass. This microprocessor onlyaccepts one client connected at a time, therefore isnot possible to communicate the micro-controllerto the rest of the agents in the architecture. Thisis why the robot agent must be defined. It com-municates, each 100 ms, with the robot micro-controller and gets the actual position and sonarreadings of the robot. Then it sends this informa-tion to the encoder agent and to the sonar agentrespectively, when asked for. It also sends to themicro-controller, the desired angular and linearspeeds.

The role of the actuator agent has been reducedmerely to an interface between the robot and thewhole architecture, due to the robot constraintsmentioned above.

3. COORDINATION MECHANISMS

There are several architectures built as multi-agent systems to control a single robot. The MASproposed by (Neves and Oliveira, 1997a) has twokind of agents at the reactive level: elementaryagents (EA) that have basic abilities, and high-level agents (HA) responsible for the integrationand coordination of several elementary agents.Each HA agents implements a different coordina-tion mechanisms according to the complex behav-ior to obtain. Thus, there are HA that select theresult of the EA who has a higher value and thereare HA that execute the intersection of every pro-posed EA’s outputs (Neves and Oliveira, 1997b).Each HA centralizes the selection of the desiredaction and there is only one HA activated at atime.

(Busquets et al., 2003) presents an architecturethat differs from typical hybrid ones in that all thecomponents of the architecture coordinate amongthem obtaining a non hierarchical structure. Theway they coordinate is based in a specific agentthat determines which action must be carried out.Each agent sends a bid, that represents the ur-gency on having a service engaged, to the coordi-nation agent who choose the action correspondingto the highest bid. Thus, this architecture uses anarbitration mechanism to coordinate the behav-iors.

In (Giorgini et al., 2002) the definition of theMAS system control architecture is based on theorganization theory and the strategic alliances. Inthis work, the MAS is considered as an organi-zation and the robot architecture is designed as ajoint of specialized social entities that interact andcooperate among each other in order to achievecommon or private goals. The structure of theorganization defines the social roles of variouscomponents, their responsibilities for tasks andgoals, the way in which the resources are allocatedand the strategies that must be adopted. Thisstructure defines how to coordinate the activitiesof various actors and how they depend on eachother. There is no negotiation to decide upon theaction to perform, but all is predefined.

Our approach differs from the previous ones inthat neither a centralized nor a predefined coor-dination is used, but is based on a peer-to-peernegotiation as explained in the following section.

3.1 Coordination among agents

As stated, coordination among agents is necessarywhen there are several agents trying to use thesame resource at a given time. In our architecture,these conflicts can arise among the avoid, the gotoand the goThrough agents when trying to send

a) Conflicting actions among avoid, b) Conflicting actions between batterygoto and goThrough agents charger and task planning agents

Fig. 2. Need of agent coordination.

conflicting actions to the robot agent and betweenthe battery charger and the task planning agentswhen demanding a trajectory to the path planningagent, as shown in figure 2. Here, circles representthe agents, and the arrows, the communicationflow between two agents.

A possible solution to this problem is to definea central coordinator agent that imposes a deci-sion among the conflicting agents based on someknowledge. However, we believe that such central-ized coordination mechanism can be a bottleneckwhen dealing with architectures with a lot ofagents. Conversely, we think that a distributedcoordination approach can be more appropriatedto deal with them. Particularly we propose a ne-gotiation mechanism based on agent’s utilities.

Each agent computes a normalized utility value(between [0,1]). For example, the utility functionof the goto agent, pGoto, is based on the dis-tance left to goal position (dl) in millimeters, asexpressed by equation 1:

pGoto = α ∗ dl + β (1)

being:

α =pmax − pmin

uL − uHβ =

uL ∗ pmin − uH ∗ pmax

uL − uH(2)

where pmax and pmin are the maximum and min-imum values respectively of the pGoto parameter,and uL and uH are the distance thresholds.

Figure 3 shows the shape of pGoto as well asthe parameters used to calculate α and β. Pmin

and pmax allow the modification of the overallimportance of the behavior, while with uL and uH

are set according to the relevance of the behavior.pGoto varies among pmin ≤ pGoto ≤ pmax.

The other agents in the architecture computestheir utility value in a similar way. In order tosolve conflicting decisions, the utility value is usedto obtain the control over the resources. Thisutility value is sent to the other agents in conflictin order to negotiate the best action. Thus, theagent who has a higher value of utility wins

Fig. 3. Utility parameter of goto agent.

the decision. This agent is getting the controlregarding to the conflicting activity. For example,suppose that the goto agent has a utility valueof 0.5, the goThrough agent of 0.3 and the avoidagent of 0.7; being 0.7 the higher value, the avoidagent takes the control of the situation, and it isthe only one that sends speeds to the robot agent.

To reduce communication among agents using thisdecentralized approach, the agent who has thecontrol, broadcasts its utility value. If there is noresponse, meaning that it has the highest value,the agent uses the resource. On the other hand,if there is an agent with a higher utility value, itinforms the rest about this situation, indicatingthat it is going to use the resource.

Figure 4 shows the communication diagram forthe conflicting action described in figure 2-a). Theparameters of the message refers to the emitteragent and to the receiver agent, as for exam-ple, send(goto, avoid, utility) means that the gotoagent sends its utility value to the avoid agent.The client agent starts the process sending thedesired goal position to the goto agent. Then thegoto agent asks the encoder agent for the currentposition of the robot. On the other hand, theavoid agent asks the sonar agent for the coor-dinates of the nearest obstacle. Both sonar andencoder agents asks the robot agent for the sensorsinformation, and they respond to the avoid andthe goto agents respectively. Then, the goto agentcalculates the utility value and sends this value tothe avoid agent. If the goto’s utility is the highest(case A) in Figure 4) then it sends the desired

Fig. 4. Communication diagram.

speeds to the robot agent. Otherwise, that is, theavoid’s utility is the highest, then the goto agentremains listening the avoid’s utility until its utilitygoes over the avoid’s value. It is the avoid agentwho has the robot’s control (case B) in Figure 4).

4. EXPERIMENTAL RESULTS

In order to develop the architecture, an ad-hocMAS platform has been developed using C++for Linux OS. The decision of building an ad-hocplatform stands on the fact that all the existingcommercial multi-agent platforms cannot operatein real-time and most of them have an agent (e.g.the facilitator in Open Agent Architecture) thatcentralizes all the communication, becoming thebottleneck of the whole architecture.

Some agents have been implemented: the encoder,the sonar, the goto, the avoid, the robot andthe client agents. Several experiments have beencarried out with our architecture in a Pioneer2DX (a detailed description of the robot andits dynamic model can be found in (Innocentiet al., 2004)). To communicate the robot withthe agents, the commercial library ARIA fromActivMedia is used.

In the experiments, a goal position is introducedin the MAS architecture, and the goto and theavoid agents must drive the robot to it withoutcolliding. For example, in the experiment depictedin Figure 5 the robot must move in a hallwaythat has an square column of 0.5 meters. Theinitial position of the robot respect to globalframe is (x, y,Θ)i = (1, 0.5, 0), the goal positionis (x, y,Θ) = (5, 0.6, 0) and the column is locatedat 1.1 m from the robot. The trajectory describedby the robot is shown in Figure 5.

It can be seen in Figure 5 the moment wheneach agent takes control of the robot. First, theobstacle is detected and the avoid agent sends theappropriate linear and angular speeds in orderto avoid the column. When the obstacle is no

0 1 2 3 4 5 60

0.2

0.4

0.6

0.8

1

1.2

1.4

1.6

1.8

2

x[m]

y[m

]

Avoid

Goto

Avoid

Goto

AvoidGoto

Fig. 5. Trajectory of the robot until goal position.

more detected, the utility value of the avoid agentdecreases under the utility value of the goto agent,and the latter takes the robot’s control. As thisagent drives the robot to the goal position, thecolumn is again detected and the utility value ofthe avoid agent increases over the utility value ofthe goto agent, and this agent controls the robotagain. Both agents take alternatively the controlof the robot until the goal position is reached. Theexperiment shows how the negotiation protocolis valid when dealing with the robot movementwhile maintaining an adequate responsiveness tothe obstacles found in the path.

It can be observed that there is only one agentacting at a time. This causes non smooth tra-jectories to be obtained due to the change ofbehaviors. Smoothen trajectories can be achievedby other methods, as for example see (Gerkey etal., 2002),(Saffiotti, 1997), however they requirea centralized action coordinator. How to improvetrajectory smoothness by maintaining a distrib-uted coordination mechanisms is being consideredat the moment.

5. CONCLUSIONS

In order to tackle the robotics goal of developingcompletely autonomous robots capable of modi-fying their performance in complex and changingenvironments, a multi-agent architecture to con-trol a single robot has been proposed. The archi-tecture does not present any hierarchical organi-zation of behaviors (reactive over deliberative) asmost previous proposals, and it performs a nego-tiation process among the agents with conflictingresources to distribute coordination. Some agentshave been implemented and some encouragingresults have been obtained.

By definition, MAS let designers to deploy thewhole system in an abstract way, defining at thebeginning of the process the relations, protocolsand communication mechanisms among them,and allowing the addition or deletion of agents on

the system without having to modify the wholecommunity. Conversely, in systems designed asmodules, the addition or deletion of a particularsubsystem causes that all the rest of the modulesmay be reprogrammed.

In addition, a MAS architecture can be run indifferent computers if needed, strengthening thecomputational properties of the system. If newagents are added to the system, providing richerand more complex behaviors, their execution canbe distributed in different computers. As a con-sequence, complex behaviors could be achievedwithout significant computational cost but prob-ably with some communication throughput cost.Recent works as (Soh and Tsatsoulis, November,2005), in which a MAS approach has been proveduseful for real-time robotics, makes us believe thatwe are working in the right direction.

Future work includes the comparison of our dis-tributed coordination mechanism with the previ-ous approaches, in order to validate our experi-ments.

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Pollack, M., S. Engberg, J.T. Matthews, Sebas-tian Thrun, L. Brown, D. Colbry, C. Orosz,B. Peintner, S. Ramakrishnan, J. Dunbar-Jacob, C. McCarthy, Michael Montemerlo,Joelle Pineau and Nicholas Roy (2002). Pearl:A mobile robotic assistant for the elderly.Workshop on Automation as Caregiver: theRole of Intelligent Technology in Elder Care(AAAI).

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69

Author’s Index

Abdelkarim,Souissi.......................................... MA-7:2 Afonso,José A. ................................................. TP-5:8 Afonso,Paulo................................................... MP-8:4 Aguiar,António Pedro ...................................... MA-4:1Ailon,Amit ........................................................ MA-8:3Akgunduz,Ali ................................................... WA-4:2 Ako, Steve....................................................... WP-2:1 Alawneh,Fawzat A.M. ..................................... WA-3:3 Aleixo,José Carlos ........................................... TP-3:1 Almeida,Heitor.................................................. TP-5:8 Almeida,Luis ................................................... MP-8:1 ......................................................................... TP-1:1 Almeida,T......................................................... TP-5:4 Alonso,Hugo .................................................... TA-8:1 Alves,Carlos .................................................... MP-6:3 Alves,Paula ..................................................... MP-6:3 Aracil,Javier .................................................... WP-2:2 Athans,Michael.................................................... TT:1 Atherton,Derek P............................................. MA-5:2 Ayala Botto,Miguel .......................................... MA-1:3 .........................................................................WA-1:1 ........................................................................ WA-5:1 ........................................................................ WA-5:3 ........................................................................ WA-7:1 Azevedo,José Luís.......................................... MP-8:1 ........................................................................ MP-8:4 Azevedo-Perdicoúlis,Teresa Paula .................. TA-1:2 Azinheira,José Raúl ........................................ WA-6:1Bahrami,Mohsen ............................................. WA-6:3 Balaguer,Pedro ............................................... MA-5:1 Baptista,Luis Filipe ........................................... TA-3:1 ........................................................................ WP-1:3 Batista,Pedro Tiago Martins............................ MA-4:2 Becerra,Victor ................................................. MA-2:3 Beirão,Pedro .................................................... TP-4:1 Bemporad,Alberto ............................................ PL-2:1 Ben Yamin,Rabin ............................................ MA-6:2 Berducat,Michel .............................................. WA-3:2 Berenguel,Manuel ........................................... MP-4:2Bicho,Estela .................................................... MA-8:1 Blot,Joel .......................................................... MP-5:2 Boaventura Cunha,José................................... TA-2:2 ........................................................................ WP-2:3 Bobál,Vladimír................................................. MA-6:1 ......................................................................... TP-5:7 Bóia,Nuno Filipe............................................... TA-3:1 Bondia,Jorge.................................................... TA-7:1 Borges,José .................................................... MA-1:3 ........................................................................ WA-1:1 Brás,Isabel ...................................................... MP-1:3 Caetano,Marco António Leonel....................... WA-1:3 Calado,João.................................................... MA-2:3........................................................................ MP-2:3 Caldas Pinto,João ............................................ TP-5:5Caldas Pinto,Pedro .......................................... TA-2:1 Calderón,Antonio J.......................................... MP-7:4 Canarias,Daniel............................................... WA-3:1 Cano,Ramon................................................... WP-2:2 Canudas-de-Wit,Carlos................................... WP-2:2 Carapito,Ana ................................................... MP-1:3 Cardeira,Carlos ............................................... MP-8:4 Cardoso,Alberto Lebre .................................... MP-2:2Cardoso,F. ....................................................... TP-5:4 Carrondo,Manuel ............................................ MP-6:3

Carvalhal,Paulo................................................ TP-5:8 Carvalho-Ostertag,Joana ................................ MP-1:2 Chotai,Arun ..................................................... WP-2:1 Christo,Camilo ................................................. TP-5:5 Coelho,Ezequiel T............................................ TP-5:8 Coelho,João Paulo.......................................... WP-2:3 Conceição,André Scolari................................ TP-5:10 ........................................................................ WP-4:1 Costa,Bertinho Andrade................................... TP-5:4 ........................................................................ WA-6:2 Costa,Lino A. ................................................... TA-2:3 Costa,Paulo .................................................... WP-1:1 ........................................................................ WP-4:1 Costa,Paulo J................................................. TP-5:10 Costa e Silva,Eliana Oliveira........................... MA-8:1 Cruz,António José Gonçalves.......................... TP-5:2 Cunha, Manuel Bernardo ................................ MP-8:1 ........................................................................ MP-8:4 Dediós,Luis Sánchez ...................................... MP-6:1Denis,Bruno ..................................................... TP-1:2Díaz,Ediberto Vásquez ................................... MA-1:1 Dlapa,Marek.................................................... MA-6:3Dourado,António ............................................. MP-2:2 ......................................................................... TA-4:2 Duarte,Belmiro ................................................ MA-2:2 Ebrahimi,Behrouz............................................ WA-6:3 Erlhagen,Wolfram ........................................... MA-8:1 Fazelinia,Hassan ............................................ WA-4:2 Fernandes,Joana Lis....................................... WA-8:1 Ferreira,Ana Patrícia ....................................... MP-6:2 Ferreira,Eugénio Campos ............................... MP-6:4 Ferreira,H......................................................... TP-5:4 Ferreira,Jorge .................................................. TP-5:9 Ferreira,Manuel J. ............................................ TA-6:2 . ........................................................................ TP-5:8 Ferreira,Ricardo .............................................. WA-2:2 Feyo de Azevedo,Sebastião ........................... MP-6:1 Fiacchini,Mirco ................................................ WP-2:2 Figueiredo,João .............................................. WA-3:1 ........................................................................ WA-7:1 Filipescu,Adrian .............................................. WP-4:3 Filipovic,Vojislav Z............................................ TP-2:2 Fiuza,José Miguel ........................................... WA-6:2Fleming,Peter................................................... PL-4:1 Fonseca,Pedro................................................ MP-8:1 Fontes,Fernando A.C.C. ................................. MA-3:3Fornés,José .................................................... MP-4:2 Francisco,Mario............................................... WA-3:3 Fredriksson,Jonas............................................ TP-5:6 Freitas,Francisco Teixeira............................... WP-1:2 Freitas,P........................................................... TP-5:4 Fuertes,Josep M. ............................................. TP-1:1 Gabel,Thomas ................................................ MP-8:2Gaivão,José Pedro.......................................... WA-1:2 Georgieva,Petia .............................................. MP-6:1 Germano,J. ...................................................... TP-5:4 Gil,Rodrigo Bernardo ....................................... TA-4:3 Giordano,Roberto Campos .............................. TP-5:2 Glizer,Valery Y. ............................................... MP-5:3 Gomes-Mota,João........................................... MP-4:1 Gonçalves,José .............................................. WP-1:1 Gonçalves,Paulo Sequeira............................... TP-5:5 Goncharova,Elena ........................................... TP-3:3 Guerra,Manuel ................................................ WA-2:1 Guzmán,J. Luis ............................................... MP-4:2 Habbi,Ahcène ................................................. MA-7:3 Hacene,Rezine ............................................... MA-7:2

70

Author’s Index

Hafner,Roland................................................. MP-8:2 Hardt,Denise Cabral Cardoso ......................... WA-1:3 Hattori,Satomi .................................................. TA-3:2 Henriques,Jorge Oliveira.................................. TA-4:2 Hering,Pavel .................................................... TP-2:3 Hernandez,Roberto......................................... MP-7:3 Herzallah,Randa ............................................. MP-3:1 ......................................................................... TP-2:1 Hespanha,João Pedro .................................... MA-4:1Horla,Dariusz ................................................... TA-7:2 Hüper,Knut ....................................................... TA-1:1Innocenti,Bianca............................................... TP-1:3 Inverno,José ................................................... WA-8:1 Jalowicki,Slawomir ........................................... TP-5:1 Jank,Gerhard ................................................... TA-1:2 Jelicic,Zoran D. ............................................... WA-8:2 Johnson,Jeffrey............................................... MP-8:3 Kase,Wataru ................................................... MA-5:3 Khadir,Mohamed Tarek................................... WP-2:3 Khan,Mohammed Ali....................................... MP-5:1 ........................................................................ MP-5:4 Khoo,Ivan........................................................ MA-2:3 Kim,Youngwoo................................................ MA-4:3 Klaassens,Ben ................................................ MA-8:2 Koko,Jonas ..................................................... WA-3:2Komatsu,Tadashi ............................................. TA-3:2 Kowalczyk,Wojciech........................................ WA-4:3 Kozák,Stefan................................................... MA-7:1 Kozlowski,Krzysztof ........................................ WA-4:3 Kraetzschmar,Gerhard.................................... MP-8:3 Král,Ladislav ................................................... MP-3:2 Królikowski,Andrzej .......................................... TA-7:2 Kruijper,Margreta ............................................ WP-2:1 Kubalcík,Marek ............................................... MA-6:1 ......................................................................... TP-5:3 Lages,Walter Fetter.......................................... TA-3:3 Lange,Sascha ................................................. MP-8:2Larsen,Lars Finn .............................................. TA-4:1 Lau,Nuno ........................................................ MP-8:1Lauer,Martin .................................................... MP-8:2 Leão,Celina P................................................... TA-2:3 Leite,Fátima Silva............................................. TA-1:1 ......................................................................... TA-1:3 Leizarowitz,Arie................................................ TA-5:1 Lemos,João Miranda....................................... MA-2:1 ........................................................................ MP-1:1 ......................................................................... TP-4:2 ......................................................................... TP-5:4 ........................................................................ WA-6:2 Lesage,Jean-Jacques ...................................... TP-1:2 Lima,José........................................................ WP-1:1 Lima,Pedro...................................................... MP-8:4 ........................................................................ WA-4:1 Lima,Teresa Pedroso de.................................. TP-3:1 Lopes,João Almeida........................................ MP-6:2 Lopes,Sofia ..................................................... MA-3:3Lopes dos Santos, Paulo ................................ MA-1:2López,Beatriz ................................................... TP-1:3 Lourenço,João Miguel..................................... MP-1:1 Lowe,David ..................................................... MP-3:1 ......................................................................... TP-2:1 Lykina,Valeriya................................................. TA-5:2 Maca,Miroslav .................................................. TP-5:3 Machado,Fernando Jorge ............................... WA-7:2

Machado,José.................................................. TP-1:2 Madrid,Angel P. de.......................................... MP-7:3 Magalhães,António Pessoa ............................ WP-1:2 Magalhães,Hugo.............................................. TP-4:2 Mañoso,Carolina............................................. MP-7:3 Manuelli,Claudia .............................................. TA-8:2 Manzi,João Teotônio....................................... WA-8:3 Martinet,Philippe ............................................. WA-3:2 Martins,Jorge M. .............................................. TA-3:1 ......................................................................... TA-6:3 Martins de Carvalho,Jorge Leite ..................... MA-1:2 Matheus,Justo Elias ......................................... TA-4:2 Matsuzaki,Sinya.............................................. MA-4:3 Mendes,Mário ................................................. MP-2:3 Mendonça,Luís ............................................... MP-2:1 Mendonça,Teresa ............................................ TA-8:1 ......................................................................... TP-4:2 ........................................................................ WA-1:2 Menezes,José Cardoso de ............................. MP-6:2Mitra,Tapan..................................................... MP-5:4Monje,Concepción A. ...................................... MP-7:1 Moraga,César de Prada.................................. MA-1:1 Moreira,António Paulo.................................... TP-5:10 ........................................................................ WP-1:1 ........................................................................ WP-4:1 Mosca,Edoardo................................................ TA-8:2 Moutinho,Alexandra ........................................ WA-6:1 Mutoh,Yasuhiko .............................................. MA-5:3 Narikiyo,Tatsuo ............................................... MA-4:3 Nidamarthi,Srinivas .......................................... TP-5:1Nogueira,Dora.................................................. TA-4:2 Nogueira,Nuno Filipe ...................................... WA-7:2Novais,José ..................................................... TA-4:3 Novák,Jakub .................................................... TP-5:7 Nucci,Edson Romano ...................................... TP-5:2 Nunes,Catarina ................................................ TP-4:2 Nunes,Urbano................................................. WP-4:3 Oberle,Hans Joachim...................................... MA-3:2 Oliveira,Mónica ................................................ TP-5:9 Oliveira,Nuno .................................................. WA-8:1 Oliveira,Paulo Jorge........................................ MA-4:2 Oliveira,Paulo Moura....................................... WP-2:3 ......................................................................... TA-2:2 Oliveira,Rui ..................................................... MP-6:3 Oliveira,Vinícius Menezes de........................... TA-3:3 Ortega,Manuel Gil ............................................ TP-4:3 Ostertag,Eric ................................................... MP-1:2 Ovseevich,Alexander J. ................................... TP-3:3 Pahliani,Abdolkarim ........................................ WA-4:1 Paiva,Sérgio.................................................... WA-8:3 Paris,Alexandre N. ........................................... TA-6:3......................................................................... TP-5:5 Paulusová,Jana .............................................. MA-7:1 Pereira,Artur.................................................... MP-8:1 Pereira,Fernando Lobo .................................... TP-3:2 Pereira,Wagner Coelho.................................... TA-8:3 Petrovacki,Nebojsa ......................................... WA-8:2 Pickenhain,Sabine ........................................... TA-5:2 Piedade,M.S. ................................................... TP-5:4Pina,Luis Miguel.............................................. WA-5:3 Pinheiro,Carla ................................................. WA-8:1 Pinho,Maria do Rosário................................... MA-3:1 Pinto,Raquel ................................................... WP-3:1 Pires,Eduardo José Solteiro............................. TA-2:2 Piron,Emmanuel ............................................. WA-3:2 Polderman,Jan Willem .................................... WP-3:1Prieto,Alberto .................................................. WP-2:2

71

Author’s Index

Príncipe,José C................................................ PL-1:1Prokop,Roman ................................................ MA-6:3 Ramôa Ribeiro,Fernando................................ WA-8:1 Ramos,José Arquel......................................... MA-1:2 Rasmussen,Henrik........................................... TA-4:1 Reis,João ......................................................... TA-6:1 Riedmiller,Martin ............................................. MP-8:2 Rijo,Manuel ..................................................... WA-3:1 Rocha,Isabel ................................................... MP-6:4 Rocha,Paula ................................................... MP-1:3 ......................................................................... TA-8:1 ......................................................................... TP-3:1 ........................................................................ WA-1:2 ........................................................................ WP-3:1 Rocha,Vitor José.............................................. TA-4:3 Rodrigues,Luis ................................................ WA-4:2 ........................................................................ WA-5:2 Rodrigues,Rui Carreira .................................... TA-1:3 Romanenko,Andrey ........................................ MA-2:2 Romero,Miguel................................................ MP-7:3 Rosenblueth,Javier ......................................... MA-3:1Roshanian,Jafar .............................................. WA-6:3 Ruano,António Eduardo................................... TA-8:3 Ruano,Maria Graça.......................................... TA-8:3 Rubio,Alberto ................................................... TP-4:3 Rubio,Francisco R........................................... MP-4:2. ........................................................................ TP-4:3 . ....................................................................... WP-2:2 Runkler,Thomas A. .......................................... TA-2:1 Sá da Costa,José............................................ MP-2:1 ........................................................................ MP-2:3 ........................................................................ MP-7:2 ......................................................................... TA-3:1 ......................................................................... TA-6:1 ......................................................................... TA-6:3 ......................................................................... TP-4:1 ........................................................................ WA-5:1 Sahli,K.............................................................. TP-5:6 Sala,Antonio..................................................... TA-7:1 Salvi,Joaquim................................................... TP-1:3 Samadi,Behzad............................................... WA-5:2 Sandín,Roberto ............................................... WA-3:3 Santos,Cristina Peixoto.................................... TA-6:2 ......................................................................... TP-5:8 ........................................................................ WP-4:2 Santos,Elsa..................................................... WA-1:2 Santos,Maria Antónia....................................... TA-4:2 Santos,Max Mauro ........................................... TP-1:1 Santos,Valérie dos .......................................... WA-7:3Santos,Vitor .................................................... MP-8:4 Santos-Victor, José .......................................... PL-6:1Schilling,Klaus.................................................. PL-5:1 Serrador,Gabirel.............................................. WP-1:3 Shaban,Essam M............................................ WP-2:1 Shaked,Uri ...................................................... MA-6:2 Shirley,Paulo Oconnor .................................... MA-2:1 Sidi Ammi,Moulay Rchid ................................. WA-2:3 ........................................................................ WP-3:2 Silva,Carlos ..................................................... WP-1:3 Silva,Geraldo Nunes ........................................ TP-3:2 Silva,Leonardo Bione ...................................... WA-6:2Silva,Luís F. ..................................................... TP-5:8 Silva,Miguel Pedro .......................................... WA-5:1Silva,Pedro Abrantes ...................................... WA-7:1

Silva,Pedro Miguel .......................................... MA-2:3 Silva,Rosineide Gomes.................................... TP-5:2 Silvestre,Carlos Jorge ..................................... MA-4:2Šimandl,Miroslav............................................. MP-3:2......................................................................... TP-2:3 Sjöberg,Jonas .................................................. TP-5:6 Sklar,Elizabeth ................................................ MP-8:3 Soares,Filomena O. ......................................... TA-2:3 Solea,Razvan.................................................. WP-4:3 Sousa,João M.C. ............................................ MP-2:1 . ........................................................................ TA-2:1 . ........................................................................ TP-5:5 Sousa,L............................................................ TP-5:4 Souza,V.R........................................................ TP-5:2 Taylor,Charles James ..................................... WP-2:1 Teixeira,Ana.................................................... MP-6:3 Teixeira,César Alexandre................................. TA-8:3 Tenreiro Machado,José António ...................... TA-2:2 Thybo,Claus..................................................... TA-4:1Torres,Delfim .................................................. WA-2:3 Touré,Youssoufi .............................................. WA-7:3 Vale,Alberto .................................................... MP-4:1 Valério,Duarte ................................................. MP-7:2 ......................................................................... TP-4:1 van den Boom,Ton.......................................... MA-8:2van der Noll,Erik.............................................. MA-8:2Vega,Pastora .................................................. WA-3:3 Verdult,Vincent................................................ MA-1:3 ........................................................................ WA-1:1 Verhaegen,Michel ........................................... MA-1:3......................................................................... PL-3:1 ........................................................................ WA-1:1 Veryha,Yauheni ............................................... TP-5:1 Vigário,Bruno Teixeira..................................... WP-1:2Viguria,Antidio................................................. WP-2:2 Vilanova,Ramon.............................................. MA-5:1 Vinagre,Blas M................................................ MP-7:1 . ....................................................................... MP-7:4 Virin,Teddy...................................................... WA-3:2 Vivas,Carlos..................................................... TP-4:3 Vojtesek,Jiri...................................................... TP-5:7 Wagner,Marcus................................................ TA-5:2 Xavier,João ..................................................... WA-2:2 Yaesh,Isaac .................................................... MA-6:2Yoneyama,Takashi ......................................... WA-1:3Zaslavski,Alexander J. .................................... MP-5:1 .......................................................................... TA-5:1 . ........................................................................ TA-5:3 Zelmat,Mimoun ............................................... MA-7:3 Zhiltsova,Tatiana.............................................. TP-5:9