AxeBot機(jī)器人：全方位自主移動(dòng)機(jī)器人的機(jī)械設(shè)計(jì)畢業(yè)論文外文翻譯

1、AxeBotRobot:TheMechanicalDesignforanAutonomousOmnidirectionalMobileRobotTiagoP.doNascimento,AugustoLoureirodaCosta,CristianeCorreaPaimPost-graduationPrograminElectricalEngineeringUniversidadeFederaldaBahiaSalvador,Bahia,B,augusto.loureiroufba.br,cpaimufba.brAbstractTheAxeBotrobot

2、?smechanicaldesign,afullyautonomousmobilerobot,fortheRoboCupSmallSizeLeague,ispresentedinthispaper.TheAxeBotrobotusesthreeomnidirectionalwheelsformovementandisequippedbyashootingdeviceforshootingtheballindifferentdirections.OncetheAxeBotrobotisafullyautonomousmobilerobotallthesensors,engines,servos,

3、batteries,andthecomputersystem,mustbeembeddedon.Theprojectcanbeseparatedinfourdifferentparts:thechassisdesign,thewheeldesign,theshootingdevicedesignandtheoverallassemblywhichmakesashelldesignpossibletocoverthewholerobot.TheAxeBotmechanicaldesignbringsupanewchassisconceptforthreewheelsomnidirectional

4、robot,alsopresentanewshootingdevice,andfinallypresentAxeBotsprototypeassembly.1. IntroductionTheRoboCupInitiativeisaninternationalresearchgroupwhoseaimsaretopromotethefieldsofRoboticsandArtificialIntelligence.Astandardchallenge,asoccermatchperformedbyautonomousrobotteams,wasproposedin19961.Initially

5、withthreedifferentleagues2D:RobotSoccerSimulationleague,SmallSizeRobotleague,andMiddleSizeRobotleague.Nowadaystheseleagueshavebeenincreasedupto:Four-LeggedLeague,HumanoidLeague,MiddleSizeLeague,RoboCupJuniorSoccer,SmallSizeLeague,SoccerSimulation,StandardRobotLeague.Also,anotherchallenge,theRoboCupR

6、escuewasproposedin1999toshowthattheresultfromtherobotsoccerresearchcouldbedirectlyappliedonarealworldproblemlikeadisasterrescuemadebyrobots.Throughtheintegrationoftechnologyandadvancedcomputeralgorithms,thegoalofRoboCupistobuildateamofhumanoidrobotsthatcanbeatthecurrentWorldCupchampionsbytheyear2050

7、.TheAxeBotusesthreeomnidirectionalwheels,positionedonacirclewithanangleof120oamongeachwheel,tomoveindifferentdirections.ThreeMaxxonA-22motorsareusedtodrivetheomnidirectionalwheels,onemotorperwheel.ThesemotorsarecontrolledbytwoBrainstemMoto1.0andacascadecontrollermadetocontroltherobottrajectory23.The

8、AxeBotalsoholdsashootingdevicetokicktheballindifferentdirections,aVisionSystemwithaCMUCamPlusandGP202Infra-redsensor4,aembeddedComputerSystembasedonStrongArm,calledStarGateKitandaIEEE802.11wirelessnetworkcard.Thisworkpresentsthemechanicalprojecttoenclosetheseequipmentsintoanfullyautonomousomnidirect

9、ionalrobotcalledAxeBot.ThecompleteAxeBotdynamicsandkinematicsmodelcanbefoundin5,thismodelwasusedtospecifysomemechanicalparameter,likethewheeldiameter.2. TheChassisThechassisoftherobotistheframetowhichallothercomponentscanbeattached,directlyorindirectly.Thereforethechassismustbestrongenoughtocarrythe

10、weightofallpartswhentherobotisinrestoinmovement.Thechassishastowithstandtheforcesonit,causedbytheaccelerationoftherobotaswell.Anotherimportantrequirementofthechassisisthatitfixesallcomponentsinastiffway,sothattherewillbesmallrelativedisplacementsofthecomponentswithintherobot,duringaccelerationanddec

11、eleration.Thisisparticularimportantforthethreedrivingmotors,whicharepositionedonthegroundplanewithanangleof120obetweeneachmotor.Theperformanceofthecontroloftherobotisdependentonapreciseandstiffplacementofthemotors6.Thechassishastobestrongenoughalsotowithstandacollisionoftherobotagainstthewalloragain

12、stanotherrobot,withthehighestpossibleimpactvelocitythatcanoccur.Finallythechassishastobebuiltwiththesmallestamountofmaterial.Atfirsttoreducethecosts,andtominimizethetotalweightoftherobot.Lessweightrequireslesspowertoaccelerate.Sowiththesamemotors,lessweightgivesyoumoreacceleration.Thisisofcourseonly

13、true,whenallthepowergeneratedbythemotorscanbetransferred,viathewheels,totheground.Inotherwords,thewheelsmusthaveenoughtractionthattherewillbenoslipbetweenthewheelsandtheground7.2.1. MaterialFiberglasswasusedtobuildthechassis.Thischoiceispurelyfinancial,becausethematerialisnotexpensive(althoughitisst

14、rong)andthereisnoneedtohireaprofessionalconstructor.Thebuildingofallthechassis(sixintotal)canbedonebytheteammembersthemselves.Onlythemouldshavetobebuiltbyaprofessional.Theupperandlowerchassiscanbemadeusingonemouldthatcanbeadjustedtoproducethedifferentchassis.2.2. DesignTheprimarygoalofthedesignisthe

15、fixationofthemotorsinthedesiredpositions.Thereforeagroundplatewith3slotsforthemotorsismodeled.Atthefrontsideeachmotorcanbeattachedtothechassis.Attherimofthegroundplateanedgeisattachedtogivethechassismoretorsionstiffness.Thisedgecanalsobeusedforattachingothercomponentsoftherobot,likethecoveringshell.

16、Alsothereisacutouttocreatespacefortheshootingdeviceoftherobot.Insection5thedesignofthisdevicewillbediscussed.Howevernofinaldesignwillbepresentedandthereforewestickwiththisassumptionthattheshootingdeviceneedsthesecutouts.Alledgesarerounded,becausethiswillmaketheconstructionoftheeasierpart.Thefinalpar

17、t,thelowerchassis,isshowninthefigurebelow.ThispartismodeledinSolidEdge.Togetastifferandstrongerchassis,asecondchassispart,theupperchassis,ismodeled.Thisisalmostanexactcopyofthefirstpart,onlynowthereare3cutoutsthatprovidemorespaceforplacingthecomponentsoftherobot.Thesecutoutsalsosavesomematerialandth

18、ereforeweight.ThebothpartsareThissandwichconstructiongivesthewholechassismorestiffness,andsothetotalthicknessofboththechassiscanprobablybelowerthanusingonechassispart.Figure1:LowerchassisFigure2:UpperandlowerchassisattachedtoeachotherChassismouldTobuildtheseparts,amouldwasmade.Thisisjustanegativeoft

19、heactualrobotparts.Infigure3themouldoftheupperchassis.Tochangethismouldinthemouldforthelowerchassis,wherethegroundplatedoesnothaveholes,theindicatedpieces(withwhitestripes)andthenotindicatedleftpiece(symmetrictothemostrightpart)shouldbelowered4mm.Fortheupperandlowerchassis,thebasismouldisexactlythes

20、ame.Onlypieceoneandtwoaredifferentforthetwochassis,themotorpieceandtheshootingsystempiecearethesame.Figure3:Chassismould3. WheelsTheAxeBotrobotisequippedwiththreewheelspositionedonacirclewithanangleof120°amongattachedtoeachotherasshowninthepicturebelow.eachwheel.Thesewheelshavetoenabletheomnidi

21、rectionalityoftheAxeBotrobot.Thismeansthatthewheelshavetobeabletolettherobotmaketwotranslationalmovements(inxandy-direction,seefigure4)withoutrotatingtherobotarounditsz-axis(theaxisperpendiculartotheyandx-axis,thatisrotationinfigure4).Thewheelshavealsotoenablearotationofthetotalrobotaroundthez-axis.

22、Figure4:AxeBotwheelspositionsNevertheless,thewheelshavetobeassmallandlightaspossibletominimizeweightandmomentofinertiabutstillremainusableandmanageable.ThewheelsarebasedonanexistingdesignofanomnidirectionalwheelfromtheCornellRobot20038.Figure5showsanexplodedviewthefinalversionofawheel.Thetwoshellsar

23、econnectedtoeachotherbyscrewsandholdeverypartontherightplace.Thehubisalsoattachedtotheshellsbyscrews.Thehubismountedontheoutputaxleofamotorbyascrewtotransfertherotationaloutputofamotortothewheel.Theringsoftherollersareincontactwiththefloor.Arollercanrotatearounditsrolleraxle.Asmentionedabove,thewhee

24、lhastoenabletwotranslations(xandy,seefigure4)withoutrotatingarounditsz-axis.Thewholewheelensuresonetranslationbyrotatingaroundtheoutputshaftofthemotorswhiletherollersensuretheothertranslation.Combiningthesetranslationsonaproperwayarobotcanmoveanywhereinaplaneormakearotation.3.1.RingTheringistheonlyp

25、artofthewheelthatisincontactwiththefloor.Notethatawheelcanalsobeincontactwiththefloorbytworings.Toobtainmaximumgrip(noslip)theCornellRobot2003teamfirstdevelopedrollerswithoutrings.Therollershadsharpedgestocutintothecarpetofthefootballfieldformaximumgrip.Thishoweverruinedthecarpetandrubberringsweread

26、dedinthedesigntoobtainmaximumgripwithoutruiningthecarpet.Theringsarecircularwithacircularprofile.Figure5:ExplodedviewofthewheelThereforetherubberringsarealsousedfortheAxeBot2006.Rubberringscanbeboughtinseveralsizesandsincetheyarehighlyelasticitwasn?tdifficulttofindaringofarightsize.Sincetherearemore

27、thanone,rightsizes?andthegeometryoftheringisthatsimple,notechnicaldrawingoftheringwasmade.3.2.RollerThegeometryoftherollersmaynotrestricttherotationoftherollerandshouldenabletheplacementoftherubberring,withouttheringfallingoff.Thiscanbeeasilyobtained(seedrawings).Theonlyproblemisfrictionwiththeiraxl

28、esandwiththeshells.Thegeometryoftherollerscaninfluencethefrictionwiththeshellsandthefrictionwithitsrolleraxle.Tominimizethepossibilityofwearonthecontactareabetweentherollerandtherolleraxle,thiscontactareashouldbeasbigaspossible.Whenthetorqueofthemotoristransferredthrougharollertotheground(drivingthe

29、robot),therollerthatisonthegroundispressedagainsttheshells.Itwilloccuroftenthat,inthissituation,thedesireddrivingdirectionalsorequiresarotationoftheroller(thenthesummationofthetwotranslationalmovementswillresultsinthedesireddrivingdirection).Therotatingrolleris,inthissituation,pressedagainsttheshell

30、swhich,insomecases,canresultinwearoftherollerandortheshells.Thisdependsonthematerialoftheroller,thematerialoftheshell,themagnitudeoftheforcewhichpressesthesurfacesoneachother(inthiscaseitisthetorqueofthemotor)andthegeometryofbothcontactsurfaces.Onlythematerialsandgeometrycanbechoseninthedesignproces

31、softhewheels.Asmallcontactarearesultsinlowfrictionbutpossiblewearofoneofthetwosurfacesandthoughmaterialshavetobeusedtoavoidwear.Alargecontactareawillnotcausewearbutwillresultinalargefrictionforce.Anoptimumforthecontactareaandthematerialshastobefound.Thegeometryhastobemachinablealso.Problemsthatareme

32、ntionedabovedidnotoccurwiththedesignoftherollersoftheCornellRobot2003.ThereforethesamegeometryfortherollersisusedfortheAxeBot.TheCornellRobot2003teamdesignedawheelwith15rollersthatworkedverywell.Thereforealso15rollersareusedineachwheeloftheAxeBot2006.TheprototypesofthewheelsoftheCornellRobot2003firs

33、thadDelrinrollerstominimizefrictionandweight.Delrinisakindofplasticwhichisusedwithmovingcontactsurfacesbecauseofitslowfrictioncoefficientswithothermaterials.AfterafewtestwiththeprototyperobotitbecameclearthattheDelrin-rollerseasilybrokewithacollision.ThereforetheCornellRobot2003wasequippedwithalumin

34、umrollers.Thesewerestrongenoughtowithstandcollisionsandaluminumhasalowdensity(comparedtoothermetals).However,duringotherprototypetestsoftheCornellRobot2003teamsomealuminumresiduebuiltuponthesteelrollersaxles.TheCornellRobot2003didnotencounterproblemsduetothewearingofthealuminumrollers,buttooptimizet

35、hedesignoftheAxeBotwheelsthisproblemwassolved.Toavoidwearingofthealuminumrollersothermaterialfortheaxlescanbeusedortherollerscanbemadeofatoughermaterial.AfterafewcalculationsitbecameclearthatrolleraxlesofDelrin(toreducethefriction)arestrongenough(seethesectionabouttheaxles),butitisnotpossibletoprodu

36、cethinbarsofDelrin.Thereforesteelaxlesareused,thesamematerialastherolleraxlesoftheCornellRobot2003.Sotoavoidwearoftherollersamorethoughmaterialthanaluminumhastobeusedfortherollers.Steelismorethoughandaneasilyobtainableandcheapmaterial.Adisadvantageofsteelcomparedtoaluminumisitshigherdensity.Thiswill

37、increasethemomentoftheinertiawhich,costs?moretorqueofthemotor.Thetotalmomentofinertiaofawheelwithsteelrollersis1.3910-4kgm2and和emomentofinertiaofawheelwithaluminumrollersis1.3010-4kgm2.Usingsteelrollersinsteadofaluminumrollerswouldincreasethemomentofinertiaby7thisincreaseisneglectablesmallandsteelro

38、llerscanbeused.Concerningfriction,usingsteelrollersandsteelaxlesisalsobetterthanusingaluminumrollersandsteelaxlessincethefriction-coefficientbetweensteelandsteelislowerthanthatbetweensteelandaluminum.Alubricantcanalsobeusedtoevenmorereducefriction.3.3. RolleraxleAsmentionedabove,theuseofDelrinforthe

39、rolleraxleswasinvestigatedsinceitwouldreducethewearofthealuminumrollers.InastaticsituationwascalculatedwhetherDelrinaxlesof2.4mmdiameterwouldbestrongenough.Thiswasalsodoneinadynamicalsituation(droppingtherobotonthefloorandlandingononeroller),butwithoutusingaFiniteElementMethodthisdidnotresultinreali

40、sticresults.Whenthetotalweightof3.5kgofoneAxeBot2006wouldcompletelybeononerolleraxlethiswouldresultinashearstressintheaxle.Inthissituationtheshearstresscanbecalculatedbydividingtheforceontheaxle(duetotheweightoftheAxeBot)bytheareaoftheshearplane.Theareaoftheshearplaneisofcoursetheareaofacirclewithar

41、adiussimilartotheradiusoftheaxles.NotethattheweightoftheAxeBothastobedividedbytwosincetherearetwoshearplanesinoneaxle.Themagnitudeoftheshearstresswouldbe3.8MPa.Delrinstartstoplasticallydeforminduetoshearataround44MPa.Statically,Delrinaxleswouldbestrongenough.However,thiscalculationwasnotnecessaryitb

42、ecameclearthatitisnotpossibletoproduceDelrinbarsof2.5mm(diameter).Thereforesteelaxleswillbeused(aluminumaxleswouldresultinmorefriction).Toreducefriction,theaxleswerecoatedwithalubricantlikecarbon.Lubricantslikecarbonareeasilyavailable.TheCornellrobotteam2003documentationdoesnotmentionproblemsofwearo

43、ftheirpolycarbonateshellsduetotheirsteelrolleraxles.Asonecanbereadfurtherdownthissection,theshellsoftheAxeBotwheelswillbemadeofaluminumorpolycarbonate.Thecoefficientoffrictionbetweenaluminum(shells)andsteel(axles)andbetweenpolycarbonate(shells)andsteel(axles)areofequalsizes(about0.45-).Also,thegeome

44、tryofthewheelsoftheCornellrobotandtheAxeBotarealmostthesame.Thereforeitismostlikelythatwearingduetofrictionwillnotbeaproblemwithsteelrolleraxlesandpolycarbonateoraluminumshells.Productiontheaxlescaneasilybemadeoutofasteelbar.Dependingontheavailablediametersofsteelbars,thediameteroftheaxlescouldbeadj

45、usted.Theedgesoftheaxlesareroundedtoavoidsharpcorners.HubThehubconnectsthewheeltotheaxleofthemotor.AM2-boltcanbeusedforthispurpose,theholeinthehubwherethisboltwillbeplacedisdimensioned1.5mmindiametersoscrewthreadcanbemadetofitintheM2-bolt.ThehubisconnectedtotheshellsbythreeM3-screws.Correspondinghol

46、esof2.5mmwillbemadeinthehubandtheshells.Thegeometryofthehubcanbechangedtofacilitatetheproductionprocess.Thehubcanbemadeoutofaluminumorpolycarbonate,bothlightmaterials.Toinvestigatetheoption(andprice)ofinjectionmouldingthehuboutofpolycarbonateasketchofadesignforamouldhasbeenmade.3.4. ShellsAlmostthea

47、llgeometryoftheshellsoftheCornellRobot2003isused.Onlylittlechangesintheslotsfortherollersoftheaxleshavebeenmadetofacilitatetheproductionprocessoftheshells.Inthesectionabouttheproductionoftheshellsadifferentdesignfortheslotsoftheaxlesispresentedtomaketheproductionoftheshellseasily.Theshellscanbemadeo

48、utofaluminumorathough,lightplasticlikepolycarbonate.TheCornellRobothadshellsofpolycarbonate.Thebestmachinablematerialispreferred,andtheoneusedontheAxeBot?sshell.Whenusingaplasticthatcanbeinjectionmolded,moldshavebeendesignedtocheckthepricesofinjectionmoulding.4. ShootingDeviceThisdesignconsistsofave

49、rticalarm(thekickarm),thatcanswingaroundanaxlewhichisfixedtotherobot.Thismovementwillbeactuatedbyoneofthetwoservos,thekickingservo,thatisalsofixedtotherobot.Theotherservo,thedirectionalservo,isattachedtothebottomofthekickarm(theservosocket).Apendulum-likesystemisformed,soalargemassisconcentratedinth

50、elowerpartofarotatingarm.Thekickingservohasakickingplateattachedtoitwhichcanrotateandtherebymakesitpossibletoshootindifferentdirections.Thekickingplatecanbepositionedveryaccuratelysinceservosaredesignedforthesekindsoftasks.Thekickingplateisalsoconnectedtotheservosocket.Thereforethecollisionforcebetw

51、eentheballandthekickingplatewillbeguidedtoanddividedbythesetwoconnectionpoints.Therewillbelessbendinginthekickingplatethenwithoneconnectionpointandsmallerreactionforceswillactontheconnectionpoints.Figure6:TheAxeBotshootingdevice5. ShellandAxeBotAssemblyTheshellisthecoverofthetotalrobot.Itwillbemadef

52、romfiberglassaswell,forthesamereasonsasstatedinthesectionaboutthechassis.Inthefigurebelowthedesignoftheshellisshown.Therearecutoutstomakeroomforthewheelsaswellasfortheshootingdevice.Thediameteroftheshellis178mm.Becausethemaximumallowablediameteris180mm,amarginof2mmiscreated.Ontopoftheshellavisionsys

53、temwillbemounted.Forthesakeofcompactnessoftherobottheheightshouldbeassmallaspossible,withallthepartsfittingin.Thismouldcanbebuiltwiththesimplemillingmachinethatisavailable.Toassembletherobotthemostimportantdemandistoobtainatotalcentreofgravitythathasthelowestpossiblepositionintherobot.Thiswillgiveth

54、erobotpositivedrivingabilities.Anotherdemandisofcoursethatallthepartsfitinthemaximumheightof150mm.Tocheckthis,allthepartsoftherobothavebeenmodeledinSolidEdge.Infigure7anexplodedviewofthetotalrobotassemblyisshown.Therobotconsistsofanupperandlowerchassis.Threemotorswiththreeomnidirectionalwheelsareatt

55、achedtoit.Onthebottomoftherobot,thetwobatterypacksareplaced,becausethesepartshavethelargestmass.Thethreemotorprocessorsareattachedtotwogeneralprocessors.Alsotheoverallprocessorwiththedata-transfer-unitisassembled.Thelatterpartsareassembledinawaythatismostcompact.Withthisassemblyitispossibleforallpar

56、tstofitinashellwithheightof100mm.Amodelfortheshelloftherobotisdesigned.Alsoamolttoproducethesepartsismodeled.Itispossibletoproducethismodelbyusingthemillingmachinethatisavailableattheuniversity.Theassemblyofalltheparts,excepttheshootingdevice,showsthatashellheightof100mmispossible.Figure7:Explodedvi

57、ewofthetotalrobotassemblyFigure8:Totalrobotassembly6. ConclusionTheAxeBotmechanicaldesign,afullyautonomousmobilerobot,fortheRoboCupSmallSizeLeague,waspresentedinthispaper.ThismechanicaldesignbringsupanewconceptofchassisforthreewheelsomnidirectionalmobileforRoboCupF-180league,thatcanbebuilteasilyandc

58、heap.AlsoaneweffectuatormobilerobotdesignforRoboCupF-180leagueispresentedhere.Thisneweffectuatorallowsthemobilerobottoshoottheballindifferentdirections,insteadofjustshootaheadliketheothershootingdevices.Finallythemechanicalprojectpresentedhereenclosesallpart,sensor,actuators,effectuator,computersyst

59、ems,wheels,chassisandcovershellintotheAxeBotprototype.TheAxeBotrobotwasconceptforacademicalproposes,usingtherobotsoccerasalaboratorytoresearchinAutonomousMobileRobots,ArtificialIntelligenceandrelatedareas.Lookingforward,inafewmonths,fourmoreAxeBotsareexpectedtobebuiltlikethetwoinfigure9.TheserobotswillformtheMecaTeamF-180,andheightof100mmispossible.willsupportourresearchintomulti-robotsystems,asitcanbeseeninfigure9bel