Table Of ContentScientific Methods in Mobile Robotics
Ulrich Nehmzow
Scientific Methods in
Mobile Robotics
Quantitative Analysis of Agent Behaviour
With116Figures
123
UlrichNehmzow,DiplIng,PhD,CEng,MIEE
DepartmentofComputerScience
UniversityofEssex
ColchesterCO43SQ
UnitedKingdom
BritishLibraryCataloguinginPublicationData
Nehmzow,Ulrich,1961-
Scientificmethodsinmobilerobotics:quantitative
analysisofagentbehaviour.-(Springerseriesinadvanced
manufacturing)
1.Mobilerobots2.Robots-Dynamics-Simulationmethods
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DedicatedtotheRobotMODICgroup:
SteveBillings,TheocharisKyriacou,RobertoIglesiasRodr´ıguez,
KeithWalkerandHugoVieiraNeto,
anditssupportteam:
ClaudiaandHenriettaNehmzow,
MariaKyriacou,MicheleVieiraandMaxineWalker
Foreword
Mobilerobotsarewidelyappliedinarangeofapplicationsfromtransportation,
surveillancethroughtohealthcare.Inalltheseapplicationsitisclearlyimportant
to be able to analyse and control the performance of the mobile robot and it is
thereforesurprisingthatformalisedmethodstoachievethisarenotreadilyavail-
able. This book introduces methods and procedures from statistics, dynamical
systemstheory,andsystemidentificationthatcanbeappliedtoaddresstheseim-
portantproblems.Thecoreobjectiveistotrytoexplaintheinteractionbetween
therobot,thetaskandtheenvironmentinatransparentmannersuchthatsystem
characteristicscanbeanalysed,controllerscanbedesigned,andbehaviourscan
be replicated in a systematic and structured manner. This aim of constructing a
formalised approach for task-achieving mobile robots represents a refreshingly
newapproachtothiscomplexsetofproblems.
Dr Nehmzow has done an outstanding job of constructing and describing a
unifiedframework,whichclearlysetsoutthecrucialissuesforthedevelopment
of a theory for mobile robots. Thanks to the careful organisation of the topics
andaclearexposition,thisbookprovidesanexcellentintroductiontosomenew
directionsinthissubjectarea.DrNehmzow’sbookrepresentsamajordeparture
from the traditional treatment of mobile robots, and provides a refreshing new
lookatsomelong-standingproblems.Iamsurethatthisisjustthebeginningof
an exciting new phase in this subject area. This book provides a very readable
account of the concepts involved; it should have a broad appeal, and will I am
sureprovideavaluablereferenceformanyyearstocome.
SABillings
Sheffield,May2005
vii
Preface
This book is about scientific method in the investigation of behaviour, where
“behaviour”standsforthebehaviourofany“behaving”agent,beitlivingbeing
ormachine.Itthereforealsocoverstheanalysisofrobotbehaviour,butisnotre-
strictedtothat.Thematerialdiscussedinthisbookhasbeenequallysuccessfully
presentedtobiologistsandroboticistsalike!
“Scientificmethod”herestandsfortheprinciplesandproceduresforthesys-
tematic pursuit of knowledge [MerriamWebster,2005], and encompasses the
followingaspects:
• Recognitionandformulationofaproblem
• Experimental procedure, consisting of experimental design, procedure for
observation,collectionofdataandinterpretation
• Theformulationandtestingofhypotheses
The hypothesis put forward in this book is that behaviour — mainly mo-
tion—canbedescribedandanalysedquantitatively,andthatthesequantitative
descriptions can be used to support principled investigation, replication and in-
dependentverificationofexperiments.
Thisbookitselfisanexperiment.Besidesanalysingthebehaviourofagents,
itinvestigatesthequestionofhowreadyweare,asacommunityofroboticsprac-
titioners,toextendthepracticesofroboticsresearchtoincludeexactdescriptions
of robot behaviour, to make testable predictions about it, and to include inde-
pendent replication and verification of experimental results in our repertoire of
standardprocedures.
Ienjoyeddevelopingthematerialpresentedinthisbookverymuch.Itopened
up a new way of doing robotics, led to animated, stimulating and fruitful dis-
cussion, and new research (the “Robot Java” presented in Section 6.7 is one
example of this). Investigating ways of interpreting experimental results quan-
titatively led to completely new experimental methods in our lab. For example,
insteadofsimplydevelopingaself-chargingrobot,say,wewouldtrytofindthe
ix
x Preface
baseline,the“standard”withwhichtocompareourresults.Thismeantthatpub-
lications would no longer only contain the description of a particular result (an
existence proof), but also its quantitative comparison with an established base-
line,acceptedbythecommunity.
The responses so far to these arguments have been truly surprising! There
seems to be little middle ground; the topic of employing scientific methods in
robotics appears to divide the community into two distinct camps. We had re-
sponses across the whole spectrum: on the one hand, one of the most reputable
journalsinroboticsevendeniedpeerreviewtoapaperontaskidentificationand
rejected it without review, and in one seminar the audience literally fell asleep!
On the other hand, the same talk given two days later resulted in the request to
stay an extra night to “discuss the topic further tomorrow” (and this was after
two hours of discussion); the universities of Palermo, Santiago de Compostela
and the Memorial University Newfoundland requested “Scientific Methods in
Robotics”asanextramuralcourse,changedthetimetablesforalltheirrobotics
studentsandexaminedthemontheguestlectures!
I am encouraged by these responses, because they show that the topic of
scientific methods in mobilerobotics is notbland and arbitrary,but either ared
herringoranimportantextensiontoourdiscipline.Thepurposeofthisbookis
to find out which, and to encourage scientific discussion on this topic that is a
principledandsystematicengagementwiththeargumentpresented.Ifyouenjoy
agoodargument,Ihopeyouwillenjoythisone!
Acknowledgements
Science is never done in isolation, but crucially depends on external input. “As
iron sharpens iron, so one man sharpens another” (Prov. 27,17), and this book
provesthispoint.Imayhavewrittenit,buttheexperimentsandresultspresented
here are the result of collaboration with colleagues all over the world. Many of
them have become friends through this collaboration, and I am grateful for all
thesupportandfeedbackIreceived.
Most of the experiments discussed in this book were conducted at the Uni-
versityofEssex,whereournewroboticsresearchlaboratoryprovidedexcellent
facilitiestoconducttheresearchpresentedinthisbook.Ibenefitedgreatlyfrom
the discussions with everyone in the Analytical and Cognitive Robotics Group
at Essex — Theo Kyriacou, Hugo Vieira Neto, Libor Spacek, John Ford and
DongbingGu,tonamebutafew—aswellaswithmycolleagueJeffReynolds.
MuchofthisbookwasactuallywrittenwhilevisitingPhillipMcKerrow’sgroup
at the University of Wollongong; I appreciate their support, and the sabbatical
Preface xi
granted by Essex University. And talking of sabbaticals, Keith Walker (Point
LomaNazareneUniversity,SanDiego)andRobertoIglesiasRodriguez(Dept.of
ElectronicsandComputerScienceattheUniversityofSantiagodeCompostela)
made important contributions during their sabbaticals at Essex. I am also in-
debtedtomanycolleaguesfromotherdisciplines,notablythelifesciences,who
commented on the applicability of methods proposed in this book to biology,
psychology etc. I am especially grateful for the support I received from Wolf-
gang and Roswitha Wiltschko and their group at the J.W. Goethe University in
Frankfurt.
The RobotMODIC project, which forms the backbone of work discussed in
this book, would not have happened without the help and commitment of my
colleagueandfriendSteveBillingsattheUniversityofSheffield,thecommitted
workbymycolleagueandfriendTheoKyriacou,andthesupportbytheBritish
EngineeringandPhysicalSciencesResearchCouncil.Ibenefitedgreatlyfromall
this scientific, technical, financial and moral support, and thank my colleagues
andsponsors.
Finally,IthankallmyfamilyinGermanyfortheirfaithful,kindandgenerous
supportandlove.MywifeClaudia,aswithbook#1,wasaconstructivehelpall
alongtheway,andHenriettawasajoytobe“criticised”by.Thankyouall!
As before, I have written this book with Johann Sebastian Bach’s motto
“SDG”firmlyinmind.
UlrichNehmzow
Colchester,Essex,October2005
Contents
1 ABriefIntroductiontoMobileRobotics ..................... 1
1.1 ThisBookisnotaboutMobileRobotics..................... 1
1.2 WhatisMobileRobotics? ................................ 1
1.3 TheEmergenceofBehaviour.............................. 5
1.4 ExamplesofResearchIssuesinAutonomousMobileRobotics .. 7
1.5 Summary .............................................. 9
2 IntroductiontoScientificMethodsinMobileRobotics .......... 11
2.1 Introduction............................................ 11
2.2 Motivation:AnalyticalRobotics ........................... 13
2.3 Robot-EnvironmentInteractionasComputation .............. 15
2.4 ATheoryofRobot-EnvironmentInteraction ................. 16
2.5 RobotEngineeringvsRobotScience........................ 18
2.6 ScientificMethodandAutonomousMobileRobotics .......... 19
2.7 ToolsUsedinthisBook .................................. 27
2.8 Summary:TheContrastBetween
ExperimentalMobileRoboticsandScientificMobileRobotics .. 28
3 StatisticalToolsforDescribingExperimentalData............. 29
3.1 Introduction............................................ 29
3.2 TheNormalDistribution ................................. 30
3.3 ParametricMethodstoCompareSamples.................... 33
3.4 Non-ParametricMethodstoCompareSamples ............... 43
3.5 TestingforRandomnessinaSequence ...................... 55
3.6 ParametricTestsforaTrend(CorrelationAnalysis) ........... 57
3.7 Non-ParametricTestsforaTrend .......................... 65
3.8 AnalysingCategoricalData ............................... 69
3.9 PrincipalComponentAnalysis............................. 80
xiii
xiv Contents
4 DynamicalSystemsTheoryandAgentBehaviour.............. 85
4.1 Introduction............................................ 85
4.2 DynamicalSystemsTheory ............................... 85
4.3 Describing(Robot)BehaviourQuantitativelyThroughPhase
SpaceAnalysis ......................................... 95
4.4 SensitivitytoInitialConditions:TheLyapunovExponent ......100
4.5 Aperiodicity:TheDimensionofAttractors...................116
4.6 Summary ..............................................119
5 AnalysisofAgentBehaviour—CaseStudies ................. 121
5.1 AnalysingtheMovementofaRandom-WalkMobileRobot.....121
5.2 “ChaosWalker”.........................................126
5.3 AnalysingtheFlightPathsofCarrierPigeons ................133
6 ComputerModellingofRobot-EnvironmentInteraction ........ 139
6.1 Introduction............................................139
6.2 SomePracticalConsiderationsRegardingRobotModelling.....141
6.3 CaseStudy:ModelAcquisitionUsingArtificialNeuralNetworks143
6.4 LinearPolynomialModelsandLinearRecurrenceRelations ....150
6.5 NARMAXModelling....................................155
6.6 AccurateSimulation:EnvironmentIdentification..............156
6.7 TaskIdentification.......................................173
6.8 SensorIdentification .....................................184
6.9 WhenAreTwoBehaviourstheSame? ......................185
6.10 Conclusion.............................................193
7 Conclusion............................................. 195
7.1 Motivation .............................................195
7.2 QuantitativeDescriptionsofRobot-EnvironmentInteraction ....196
7.3 ATheoryofRobot-EnvironmentInteraction .................197
7.4 Outlook:TowardsAnalyticalRobotics ......................199
References................................................. 201
Index..................................................... 205
