机器人原文.docx

机器人原文.docx

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机器人原文

WHISKERBASEDMOBILEROBOTNAVIGATION

DavidJungandAlexanderZelinsky

IntelligentRoboticsLaboratory

ComputerScienceDepartment,UniversityofWollongong

Wollongong,NSW2500,Australia.

djung@cs.uow.edu.au

1.INTRODUCTION

Oneoftherequirementsofourresearch,andacommonrequirementforanautonomousmobilerobots,istheabilitytonavigatecompetentlyinanunstructuredenvironment.Thisproblemhasreceivedmuchresearchattentionintheroboticscommunity.Amajordifficultyisthattherearetwocompetingaspectstonavigation.Arobotmustbeabletoreactveryquicklytoitsenvironmenttopreventcollisionswithstaticanddynamicobstacles.Also,inordertoachieveusefulpurposivenavigationarobotmustuseamap-likerepresentationofitsenvironment.Thisimpliessomesortoflimitedcognition（asdefinedby[McFarland91]）.Theformerimpliesminimalprocessingtomeetthereal-timerequirements,whilethelaterrequiresmoreprocessingthancantypicallybeachievedforreal-timeresponse.Thebasiccontroldesignapproachescanbebroadlydividedintofourtypes.Thesearedefinedby[Mataric92a]andwebrieflyreiteratethemandtheirshortcomingshere.Thepurelyreactiveapproachesuseamappingfromsensorsetstoassociatedactions;asetofrules[Brooks87].Theplanner-basedstrategiesoriginatedwiththesymbolicAIcommunityandemployasense-plan-actcycle.Theplanstageusescognitivetechniquestoreasonaboutasymbolicworldmodel.

Therealsoexisthybridsystemswhichemployreactivecomponentsbeneathplanner-basedsystemstoprovidethebenefitsofboth.Anotherapproachisbehaviour-based,whichusesasetofinteractingdistributedconcurrentbehaviours,eachofwhichmayincorporatememoryandlearningofenvironmentrepresentations.

Figure1-YamabicoRobotwithWhiskers

Thepurelyreactiveapproachachievesrobustrealtimeperformance,butthetasksthatcanbeachievedarelimitedbecauseofthelackofanycognition.Theplanningapproachsuffersfromanumberofproblemsincludingslowinteractionwiththeenvironmentduetoslowprocessing,theframeproblemandthesymbolgroundingproblem.Thehybridapproachesattempttomarrytwoincompatiblephilosophiesandstillsufferfrommanyoftheproblemsoftheplanningapproaches.Formoredepthontheseproblemsreferto[Pfeifer95].Thebehaviour-basedapproachhasthepotentialofreal-timeresponseandcognitivisticprocessinginauniformmanner.

Aspartofourongoingresearchintocooperativeheterogeneousmulti-robotsystems,describedbelow,werequirepurposivenavigationandhighspeedwallfollowingatcloserange,upto1m/secat30mm.Thisimmediatelyprecludestheuseofpurelyreactiveorplannerbasedarchitectures.Henceweareadoptingthebehaviour-basedapproach.Alsowehavedevelopedanovelwhiskersensortailoredtoourtask.

Theremainderofthispaperdescribesboththewhiskersensorandthenavigationsystembasedonthewhiskerwehavedeveloped.Thefollowingsectiondescribesourcooperativemulti-robotresearchprojectforwhichthewhiskerbasednavigationwasdeveloped.Section2describesourwhiskersensorsandhowtheyrelatetoexistingwhiskers.Thesectionalsodescribeshowthewhiskersareusedtodetect‘natural’landmarksinthelaboratoryenvironment.Section3detailstechniquesforwhiskerbasedwallfollowingandfinallythelasttwosectionsdiscussthegeneralarchitectureandspecificorganisationofbehaviourunitsusedtoaccomplishwhiskerbasednavigation.

1.1TheContext

Thissectionbrieflydescribestherobotsandtheresearchintocooperationbetweenmultiplerobotsforwhichthewhiskerbasednavigationwasdeveloped.Theaimoftheresearchistoassesstheeffectonperformanceofchangingsomeparametersofthecooperationtechniqueemployed.Thecontextoftheassessmentisaspecificcooperativetaskperformedbyour‘Yamabico’autonomousmobilerobots[Yuta91],oneofwhichispicturedinFigure1.ThetaskwehavechosenisfortwoYamabicorobotstocleanourlaboratoryfloor.Eachhasdifferenttoolssuchthatneithercanaccomplishthetaskalone.Onerobotisequippedwithavacuumcleanerandtheotherwithasweepforsweepingclosetowalls,asisexplainedbelow.Formoreinformationonthecooperationaspectrefertoourpreviouspublication[Jung96].

Therobotseachhavetwowheelscontrolledusingshaftencoderfeedback,andfourultrasonicrangesensors,onefacingeachcompassdirectionrelativetotherobot.Therobotsalsohavethreeprocessorcardsconnectedviaabus,twoMotorola68000’swhichmanagethemainapplicationprogramandthefourultrasonicsensorsandoneINMOST805forthelocomotioncontrol.

Oneoftherobots,thevacuum,hasavacuumcleanercapableofbeingcontrolledviasoftware.It’staskistovacuumpilesoflitterfromthelaboratoryfloor.Itcannotvacuumclosetowallsorfurniture.ItalsohasaCCDcameramountedontopwhichsendsvideosignalsviaavideotransmittertoourvisionsystem.

TheMEPtrackingvisionsystemwasdevelopedbyFujitsuR&DJapan.Itisdesignedforreal-timetrackingofmultipleobjectsinblackandwhiteframesofNTSCvideo.Thehardwareconsistsofatrackingmodulewhichcantrackupto72objectsatframerate（30Hz）.AprocessorcardrunningtheVxWorksoperatingsystemexecutestheapplicationprogramandcontrolsthevisioncardviaaVME-bus.Thetrackingofobjectsisbasedonsimple88or1616templatecomparisonusingcrosscorrelationwhichisbasedontheblock-matchingsystemdevelopedbyInoue’sLaboratoryatUniversityofTokyo[Inoue85].

ThevisionsystemisconnectedviaethernettoourhostUNIXworkstationwhichhasaserialconnectiontoaradiomodem.Therobotalsohasaradiomodemandusingthenetworkingsoftwarewedevelopedthevisualmotorpathiscomplete.Thevisionsystemallowsitto‘see’pilesoflitter,butnotfineparticlesscatteredoverthefloor.

Figure2-Thevisionsystemsegmentingthe

imageintoregionsoffloorcarpetandobstacle.

Thevisionsystem’smatchingcapabilityhasalsobeenusedtoimplementarobustcollisionavoidancebehaviour[Zelinsky95b]forthevacuum.Figure2showstheviewfromtherobot,wheretheimagehasbeendividedintoacoursegrid.Eachsquareinthegridisclassifiedbasedonhowwellitmatchesagainstatemplateofthelaboratorycarpet.Thereisaseparatecarpettemplateforeachrowinthegridtoallowforthetexturescalingasthecarpetbecomesfartherawaytowardsthetopoftheimage.Foreachelementofthegrid,thevisionsystemgivesadistortionvaluewhichindicatestheconfidenceofthematchbetweenthecarpettemplateandtheimage.Nextthemainprogramthresholdsthedistortiontoclassifythegridelementaseithercarpetornon-carpet.Thevisualbehaviourforcollisionavoidancemapstheimagespaceintothefloorandphysicallydirectstherobottoavoidareasthatwerenotmatchedascarpet.Althoughthismatchingprocesscontainsnoise,sincetheclassificationisre-evaluatedatframeratearobustcollisionavoidancebehaviourresults.

Theotherrobot,thesweep,hasabrushtoolthatisdraggedoverthefloortosweepdistributedlitterintolargerpilesforthevacuumtopickup.Therobotisrequiredtosweepveryclosetowallswerethevacuumcannotreach.Thiswillrequirebasiccompetenceatnavigatingaroundourclutteredlaboratory,includingobstacleavoidance,andtheabilitytofollowalongwallscloselyathighspeed.Thiscannotbeachievedusingexistingwhiskers,asisshowninthesectiontofollow.

2.WHISKERS

Torealisethesweepingtasktherobotrequiredsensorstoreliablyfollowwallsatcloserangeandhighspeedandsimultaneouslyavoidobstacles.Therobotwasinitiallyequippedwithfourultrasonicrangesensorsasshownbelow.

Figure3-Schematiclayoutofsensors

Theultrasonicrangesensorsprovednottoberobustforwallfollowingbecausetheyoftengiveincorrectdistancereadingsforspecularsurfacesthatareinclinedwithrespecttotherobot.Inadditionthesensorswehavecannotmeasuredistancesunderthe5cmwerequireforclosefollowing.Infraredsensorswereconsidered,butaretypicallydifficulttomakerobustforawidevarietyofsurfacematerialtypesandcolours.

Nextweconsideredcontactsensors,suchaswhiskers.Mostcontactsensorsfortactilesensinginuseonrobotstodatecanbedividedintotwotypes.Thosewhichmeasurestrainandthosethatmeasuredeformation.Mosttactilesensorsthatmeasurethestrainareusedinsystemswithmanipulators.Forareviewsee[Nicholls89]and[Fearing90].Activewhiskersensorsthatmeasurestrainforrecoveringobjectshapehavealsobeenreported,forexampleby[Russell85],buttheseareprohibitivelyexpensivefortheuseofmanyonasmallinexpensivemobilerobotandprovidemoreinformationthanwerequire.Ofthetactilesensorsthatmeasuredeformation,onecommontypeistheskinlikesensors,thattypicallyarecomprisedofanarrayofsimplesensorsformeasuringdeformationataparticularpoint.Theseareusuallyexpensiveandmeasuredeformationsonlyoverasmallrange.Thephysicalsensorsusedmaybeoptical,magnetic,resistive,pneumaticorevenultrasonic,forexample[Russell90].Anothercommontypeofsensorformeasuringdeformationisthemechanicalwhisker.Thistypeofwhisker,asisinuseonmobilerobotstodate,providesonlybinarydeformationinformation;thatis,contact/non-contactinformation（referto[Everett88],[Russell90]forexamples）.Acommonandcheapdesigninvolvesmountingpianowiresuchthatdeformationcontactsitwithaconductingplatehencemakingacircuitasshownbelow.

Figure4-Abinarywhisker1

Forwallfollowingtheinformationrequiredforcontrolof