AxeBot机器人全方位自主移动机器人的机械设计毕业论文外文翻译.docx

AxeBot机器人全方位自主移动机器人的机械设计毕业论文外文翻译.docx

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AxeBot机器人全方位自主移动机器人的机械设计毕业论文外文翻译

AxeBotRobot:

TheMechanicalDesignforanAutonomousOmnidirectionalMobileRobot

TiagoP.doNascimento,AugustoLoureirodaCosta,CristianeCorreaPaimPost-graduationPrograminElectricalEngineering

UniversidadeFederaldaBahia

Salvador,Bahia,Brasil

tiagopn@ieee.org,augusto.loureiro@ufba.br,cpaim@ufba.br

Abstract

TheAxeBotrobot’smechanicaldesign,afullyautonomousmobilerobot,fortheRoboCupSmallSizeLeague,ispresentedinthispaper.TheAxeBotrobotusesthreeomnidirectionalwheelsformovementandisequippedbyashootingdeviceforshootingtheballindifferentdirections.OncetheAxeBotrobotisafullyautonomousmobilerobotallthesensors,engines,servos,batteries,andthecomputersystem,mustbeembeddedon.Theprojectcanbeseparatedinfourdifferentparts:

thechassisdesign,thewheeldesign,theshootingdevicedesignandtheoverallassemblywhichmakesashelldesignpossibletocoverthewholerobot.TheAxeBotmechanicaldesignbringsupanewchassisconceptforthreewheelsomnidirectionalrobot,alsopresentanewshootingdevice,andfinallypresentAxeBotsprototypeassembly.

1.Introduction

TheRoboCupInitiativeisaninternationalresearchgroupwhoseaimsaretopromotethefieldsofRoboticsandArtificialIntelligence.Astandardchallenge,asoccermatchperformedbyautonomousrobotteams,wasproposedin1996[1].Initiallywiththreedifferentleagues2D:

RobotSoccerSimulationleague,SmallSizeRobotleague,andMiddleSizeRobotleague.Nowadaystheseleagueshavebeenincreasedupto:

Four-LeggedLeague,HumanoidLeague,MiddleSizeLeague,RoboCupJuniorSoccer,SmallSizeLeague,SoccerSimulation,StandardRobotLeague.Also,anotherchallenge,theRoboCupRescuewasproposedin1999toshowthattheresultfromtherobotsoccerresearchcouldbedirectlyappliedonarealworldproblemlikeadisasterrescuemadebyrobots.Throughtheintegrationoftechnologyandadvancedcomputeralgorithms,thegoalofRoboCupistobuildateamofhumanoidrobotsthatcanbeatthecurrentWorldCupchampionsbytheyear2050.

TheAxeBotusesthreeomnidirectionalwheels,positionedonacirclewithanangleof120oamongeachwheel,tomoveindifferentdirections.ThreeMaxxonA-22motorsareusedtodrivetheomnidirectionalwheels,onemotorperwheel.ThesemotorsarecontrolledbytwoBrainstemMoto1.0andacascadecontrollermadetocontroltherobottrajectory[2][3].TheAxeBotalsoholdsashootingdevicetokicktheballindifferentdirections,aVisionSystemwithaCMUCamPlusandGP202Infra-redsensor[4],aembeddedComputerSystembasedonStrongArm,calledStarGateKitandaIEEE802.11wirelessnetworkcard.ThisworkpresentsthemechanicalprojecttoenclosetheseequipmentsintoanfullyautonomousomnidirectionalrobotcalledAxeBot.ThecompleteAxeBotdynamicsandkinematicsmodelcanbefoundin[5],thismodelwasusedtospecifysomemechanicalparameter,likethewheeldiameter.

2.TheChassis

Thechassisoftherobotistheframetowhichallothercomponentscanbeattached,directlyorindirectly.Thereforethechassismustbestrongenoughtocarrytheweightofallpartswhentherobotisinrestoinmovement.Thechassishastowithstandtheforcesonit,causedbytheaccelerationoftherobotaswell.Anotherimportantrequirementofthechassisisthatitfixesallcomponentsinastiffway,sothattherewillbesmallrelativedisplacementsofthecomponentswithintherobot,duringaccelerationanddeceleration.Thisisparticularimportantforthethreedrivingmotors,whicharepositionedonthegroundplanewithanangleof120obetweeneachmotor.Theperformanceofthecontroloftherobotisdependentonapreciseandstiffplacementofthemotors[6].Thechassishastobestrongenoughalsotowithstandacollisionoftherobot

againstthewalloragainstanotherrobot,withthehighestpossibleimpactvelocitythatcanoccur.Finallythechassishastobebuiltwiththesmallestamountofmaterial.Atfirsttoreducethecosts,andtominimizethetotalweightoftherobot.Lessweightrequireslesspowertoaccelerate.Sowiththesamemotors,lessweightgivesyoumoreacceleration.Thisisofcourseonlytrue,whenallthepowergeneratedbythemotorscanbetransferred,viathewheels,totheground.Inotherwords,thewheelsmusthaveenoughtractionthattherewillbenoslipbetweenthewheelsandtheground[7].

2.1.Material

Fiberglasswasusedtobuildthechassis.Thischoiceispurelyfinancial,becausethematerialisnotexpensive（althoughitisstrong）andthereisnoneedtohireaprofessionalconstructor.Thebuildingofallthechassis（sixintotal）canbedonebytheteammembersthemselves.Onlythemouldshavetobebuiltbyaprofessional.Theupperandlowerchassiscanbemadeusingonemouldthatcanbeadjustedtoproducethedifferentchassis.

2.2.Design

Theprimarygoalofthedesignisthefixationofthemotorsinthedesiredpositions.Thereforeagroundplatewith3slotsforthemotorsismodeled.Atthefrontsideeachmotorcanbeattachedtothechassis.Attherimofthegroundplateanedgeisattachedtogivethechassismoretorsionstiffness.Thisedgecanalsobeusedforattachingothercomponentsoftherobot,likethecoveringshell.Alsothereisacutouttocreatespacefortheshootingdeviceoftherobot.Insection5thedesignofthisdevicewillbediscussed.Howevernofinaldesignwillbepresentedandthereforewestickwiththisassumptionthattheshootingdeviceneedsthesecutouts.Alledgesarerounded,becausethiswillmaketheconstructionoftheeasierpart.Thefinalpart,thelowerchassis,isshowninthefigurebelow.ThispartismodeledinSolidEdge.Togetastifferandstrongerchassis,asecondchassispart,theupperchassis,ismodeled.Thisisalmostanexactcopyofthefirstpart,onlynowthereare3cutoutsthatprovidemorespaceforplacingthecomponentsoftherobot.Thesecutoutsalsosavesomematerialandthereforeweight.ThebothpartsareThissandwichconstructiongivesthewholechassismorestiffness,andsothetotalthicknessofboththechassiscanprobablybelowerthanusingonechassispart.

Figure1:

Lowerchassis

Figure2:

Upperandlowerchassisattachedtoeachother

2.3.Chassismould

Tobuildtheseparts,amouldwasmade.Thisisjustanegativeoftheactualrobotparts.Infigure3themouldoftheupperchassis.Tochangethismouldinthemouldforthelowerchassis,wherethegroundplatedoesnothaveholes,theindicatedpieces（withwhitestripes）andthenotindicatedleftpiece（symmetrictothemostrightpart）shouldbelowered4mm.Fortheupperandlowerchassis,thebasismouldisexactlythesame.Onlypieceoneandtwoaredifferentforthetwochassis,themotorpieceandtheshootingsystempiecearethesame.

Figure3:

Chassismould

3.Wheels

TheAxeBotrobotisequippedwiththreewheelspositionedonacirclewithanangleof120°amongattachedtoeachotherasshowninthepicturebelow.eachwheel.ThesewheelshavetoenabletheomnidirectionalityoftheAxeBotrobot.Thismeansthatthewheelshavetobeabletolettherobotmaketwotranslationalmovements（inxandy-direction,seefigure4）withoutrotatingtherobotarounditsz-axis（theaxisperpendiculartotheyandx-axis,thatisrotationinfigure4）.Thewheelshavealsotoenablearotationofthetotalrobotaroundthez-axis.

Figure4:

AxeBotwheelspositions

Nevertheless,thewheelshavetobeassmallandlightaspossibletominimizeweightandmomentofinertiabutstillremainusableandmanageable.ThewheelsarebasedonanexistingdesignofanomnidirectionalwheelfromtheCornellRobot2003[8].Figure5showsanexplodedviewthefinalversionofawheel.Thetwoshellsareconnectedtoeachotherbyscrewsandholdeverypartontherightplace.Thehubisalsoattachedtotheshellsbyscrews.Thehubismountedontheoutputaxleofamotorbyascrewtotransfertherotationaloutputofamotortothewheel.Theringsoftherollersareincontactwiththefloor.Arollercanrotatearounditsrolleraxle.

Asmentionedabove,thewheelhastoenabletwotranslations（xandy,seefigure4）withoutrotatingarounditsz-axis.Thewholewheelensuresonetranslationbyrotatingaroundtheoutputshaftofthemotorswhiletherollersensuretheothertranslation.Combiningthesetranslationsonaproperwayarobotcanmoveanywhereinaplaneormakearotation.

3.1.Ring

Theringistheonlypartofthewheelthatisincontactwiththefloor.Notethatawheelcanalsobeincontactwiththefloorbytworings.Toobtainmaximumgrip（noslip）theCornellRobot2003teamfirstdevelopedrollerswithoutrings.Therollershadsharpedgestocutintothecarpetofthefootballfieldformaximumgrip.Thishoweverruinedthecarpetandrubberringswereaddedinthedesigntoobtainmaximumgripwithoutruiningthecarpet.Theringsarecircularwithacircularprofile.

Figure5:

Explodedviewofthewheel

ThereforetherubberringsarealsousedfortheAxeBot2006.Rubberringscanbeboughtinseveralsizesandsincetheyarehighlyelasticitwasn’tdifficulttofindaringofarightsize.Sincetherearemorethanone‘rightsizes’andthegeometryoftheringisthatsimple,notechnicaldrawingoftheringwasmade.

3.2.Roller

Thegeometryoftherollersmaynotrestricttherotationoftherollerandshouldenabletheplacementoftherubberring,withouttheringfallingoff.Thiscanbeeasilyobtained（seedrawings）.Theonlyproblemisfrictionwiththeiraxlesandwiththeshells.

Thegeometryoftherollerscaninfluencethefriction