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