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外文翻译--设计和开发一个竞争低成本四自由度机器人手臂 英文版.pdf

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外文翻译--设计和开发一个竞争低成本四自由度机器人手臂 英文版.pdf

ModernMechanicalEngineering,2011,1,4755doi10.4236/mme.2011.12007PublishedOnlineNovember2011http//www.SciRP.org/journal/mmeCopyright©2011SciRes.MMEDesignandDevelopmentofaCompetitiveLowCostRobotArmwithFourDegreesofFreedomAshrafElfasakhany1,2,EduardoYanez2,KarenBaylon2,RicardoSalgado21DepartmentofMechanicalEngineering,FacultyofEngineering,TaifUniversity,AlHaweiah,SaudiArabia2TecnológicodeMonterrey,CampusCiudadJuárez,CiudadJuarez,MexicoEmailashr12000yahoo.comReceivedOctober19,2011revisedNovember7,2011acceptedNovember15,2011AbstractThemainfocusofthisworkwastodesign,developandimplementationofcompetitivelyrobotarmwithenhancedcontrolandstumpycost.Therobotarmwasdesignedwithfourdegreesoffreedomandtalentedtoaccomplishaccuratelysimpletasks,suchaslightmaterialhandling,whichwillbeintegratedintoamobileplatformthatservesasanassistantforindustrialworkforce.Therobotarmisequippedwithseveralservomotorswhichdolinksbetweenarmsandperformarmmovements.Theservomotorsincludeencodersothatnocontrollerwasimplemented.TocontroltherobotweusedLabview,whichperformsinversekinematiccalculationsandcommunicatestheproperanglesseriallytoamicrocontrollerthatdrivestheservomotorswiththecapabilityofmodifyingposition,speedandacceleration.Testingandvalidationoftherobotarmwascarriedoutandresultsshowsthatitworkproperly.KeywordsRobotArm,LowCost,Design,Validation,FourDegreesofFreedom,ServoMotors,ArduinoRobotControl,LabviewRobotControl1.IntroductionThetermroboticsispracticallydefinedasthestudy,designanduseofrobotsystemsformanufacturing1.Robotsaregenerallyusedtoperformunsafe,hazardous,highlyrepetitive,andunpleasanttasks.Theyhavemanydifferentfunctionssuchasmaterialhandling,assembly,arcwelding,resistancewelding,machinetoolloadandunloadfunctions,painting,spraying,etc.Therearemainlytwodifferentkindsofrobotsaservicerobotandanindustrialrobotic.Servicerobotisarobotthatoperatessemiorfullyautonomouslytoperformservicesusefultothewellbeingofhumansandequipment,excludingmanufacturingoperations2.Industrialrobot,ontheotherhand,isofficiallydefinedbyISOasanautomaticallycontrolledandmultipurposemanipulatorprogrammableinthreeormoreaxis1.Industrialrobotsaredesignedtomovematerial,parts,tools,orspecializeddevicesthroughvariableprogrammedmotionstoperformavarietyoftasks.Anindustrialrobotsystemincludesnotonlyindustrialrobotsbutalsoanydevicesand/orsensorsrequiredfortherobottoperformitstasksaswellassequencingormonitoringcommunicationinterfaces.In2007theworldmarketgrewby3withapproximately114,000newinstalledindustrialrobots.Attheendof2007therewerearoundonemillionindustrialrobotsinuse,comparedwithanestimated50,000servicerobotsforindustrialuse3.Duetoincreaseusingofindustrialrobotarms,anevolutiontothattopicbegantryingtoimitatehumanmovementsinadetailmode.ForexampleagroupofstudentsinKoreamadeadesignofinnovationsthatroboticarmtakeaccountofdancinghand,weightlifting,Chinesecalligraphywritingandcolorclassification4.AnothergroupofengineersatUSAdevelopeightdegreesoffreedomrobotarm.Thisrobotisabletograspmanyobjectswithalotofshapesfromapentoaballandsimulatingalsothehandofhumanbeing5.Inspace,theSpaceShuttleRemoteManipulatorSystem,knownasSSRMSorCanadarm,anditssuccessorisexampleofmultidegreeoffreedomrobotarmsthathavebeenusedtoperformavarietyoftaskssuchasinspectionsofthespaceshuttleusingaspeciallydeployedboomwithcamerasandsensorsattachedattheendeffectorandsatellitedeploymentandretrievalmanoeuvresfromthecargobayofthespaceshuttle6.InMexico,Scientistsareontracktodesignanddevelopmanyrobotarms,andtheMexicangovernmentA.ELFASAKHANYETAL.48estimatesthatinMexicothereareabout11,000roboticarmsusedindifferentindustrialapplications.However,theexpertsthinkthattheapogeeoftherobotarmsisnotonlyofhigherquality,butalsoaccurately,repeatability,andstumpycost.Mostrobotsaresetupforanoperationbytheteachandrepeattechnique.Inthismode,atrainedoperatorprogrammertypicallyusesaportablecontroldeviceateachpendanttoteacharobotitstaskmanually.Robotspeedsduringtheseprogrammingsessionsareslow.Thepresentworkispartofatwophaseproject,whichrequiresamobilerobottobeabletotransportthetoolsfromthestorageroomtotheindustrialcell.Inthisphaseintheproject,whichcarriedoutatMonterreyUniversityofTechnology,Mexico,themainfocuswastodesign,developmentandimplementationofanindustrialroboticarmwithstumpycost,accurateandsuperiorcontrol.Thisrobotarmwasdesignedwithfourdegreesoffreedomandtalentedtoaccomplishsimpletasks,suchaslightmaterialhandling,whichwillbeintegratedintoamobileplatformthatservesasanassistantforindustrialworkforce.2.MechanicalDesignThemechanicaldesignoftherobotarmisbasedonarobotmanipulatorwithsimilarfunctionstoahumanarm68.Thelinksofsuchamanipulatorareconnectedbyjointsallowingrotationalmotionandthelinksofthemanipulatorisconsideredtoformakinematicchain.Thebusinessendofthekinematicchainofthemanipulatoriscalledtheendeffectororendofarmtoolinganditisanalogoustothehumanhand.Figure1showstheFreeBodyDiagramformechanicaldesignoftheroboticarm.Asshown,theendeffectorisnotincludedinthedesignbecauseacommerciallyavailablegripperisused.ThisisbecausethattheendeffectorisoneofthemostcomplexFigure1.Freebodydiagramoftherobotarm.partsofthesystemand,inturn,itismucheasierandeconomicaltouseacommercialonethanbuildit.Figure2showstheworkregionoftheroboticarm.Thisisthetypicalworkspaceofarobotarmwithfourdegreeoffreedom4DOF.Themechanicaldesignwaslimitedto4DOFmainlybecausethatsuchadesignallowsmostofthenecessarymovementsandkeepsthecostsandthecomplexityoftherobotcompetitively.Accordingly,rotationalmotionofthejointsisrestrictedwhererotationisdonearoundtwoaxisintheshoulderandaroundonlyoneintheelbowandthewrist,seeFigure1.Therobotarmjointsaretypicallyactuatedbyelectricalmotors.Theservomotorswerechosen,sincetheyincludeencoderswhichautomaticallyprovidefeedbacktothemotorsandadjustthepositionaccordingly.However,thedisadvantageofthesemotorsisthatrotationrangeislessthan180˚span,whichgreatlydecreasestheregionreachedbythearmandthepossiblepositions9.Thequalificationsofservomotorswereselectedbasedonthemaximumtorquerequiredbythestructureandpossibleloads.Inthecurrentstudy,thematerialusedforthestructurewasacrylic.Figure3showstheforcediagramusedforloadcalculations.Thecalculationswerecarriedoutonlyforthejointsthathavethelargestloads,sincetheotherjointswouldhavethesamemotor,i.e.themotorcanmovethelinkswithoutproblems.Thecalculationsconsideredtheweightofthemotors,about50grams,exceptfortheweightofmotoratjointB,sinceitiscarriedoutbylinkBA.Figure4showstheforcediagramonlinkCB,whichcontainsthejointsBandCwiththehighestloadcarrythelinksDCandEDandthecalculationsarecarriedoutasfollows.Figure2.Workregionoftheroboticarm.Copyright©2011SciRes.MME49A.ELFASAKHANYETAL.Figure3.Forcediagramofrobotarm.Figure4.ForcediagramoflinkCB.ThevaluesusedforthetorquecalculationsWd0.011kgweightoflinkDEWc0.030kgweightoflinkCDWb0.030kgweightoflinkCBL1kgloadCmDm0.050kgweightofmotorLBC0.14mlengthoflinkBCLCD0.14mlengthoflinkCDLDE0.05mlengthoflinkDEPerformingthesumofforcesintheYaxis,usingtheloadsasshowninFigure4,andsolvingforCYandCB,seeEquations14.Similarly,performingthesumofmomentsaroundpointC,Equation5,andpointB,Equation6,toobtainthetorqueinCandB,Equations7and8,respectively.gydmcmYFLWDWCC0121.141kg9.8ms11.18NYC20ydmcmBBFLWDWCWgC321.171kg9.8ms11.4758NBC4220cCDDEcDCDCDDEmCDcWLLMWLLLLDLM52202DEBBCCDDEDBCCDCDmBCCDcBCBCmBCBBLMLLLLWLLLDLLWLLCLWM61.968Nm278.6ozincM73.554Nm503.38ozinBM8Theservomotorthatwasselected,basedonthecalculations,istheHextronikHX12K,whichhasatorqueof280oz/in.Thismotorwasrecommendedbecauseitismuchcheaperthananyothermotorwithsamespecifications.SinceweneedmoretorqueatjointB,seeEquation8,weusedtwomotorsatpointBtocomplywiththetorquerequirementshowever,onemotorisenoughfortheotherjoints.UsingtwomotorsatjointBismuchcheaperthanusingonebigmotorwith560oz/in.Otherrelevantcharacteristicsofthemotors,whichcanbeshowninFigure5,arethattheycanturn60degreesin130millisecondsandtheyhaveaweightof47.9gramseach.Oncetheinitialdimensionsfortherobotarmandthemotorweredefined,thedesignwerecarriedoutusingtheSolidWorksplatformdesignshouldcarefullytakeintoaccountthethicknessoftheacrylicsheetandthewaythatthepieceswouldbeattachedtoeachother.Theacrylicsheetusedtomaketherobotis1/8thicknessandFigure5.Servomotor.Copyright©2011SciRes.MMEA.ELFASAKHANYETAL.50thatthinsheetwaschosenbecauseiteasierformachiningandlessweightwithagoodresistance.Duringdesign,wefacedsomedifficultiesduetothewayofjoiningthinacrylicpartsstrongly.Itwasneededtoolstoburnandjointheacrylicpartsandthatwerentavailableandtheteamconsideredthatamechanicaljunctionbasedonscrewsandnutswouldbemuchstrongthanotheralternatives,suchasglueforexample.Inordertoaccomplishthis,asmallfeaturewasdesignedwhichallowedtofastentheboltswiththenutswithouthavingtoscrewinthethinacryliclayer.TheresultofthisprocesswasthetridimensionaldesignshowninFigure6.Byendofdesign,eachpartwasprintedinfullscaleincardboardpaperandthenweverifiedallthedimensionsandtheinterfacesoftheassembly.Inturn,webuiltthefirstprototypeoftherobotarm.Next,partsoftherobotarmweremachinedfromtheacrylicsheetusingacircularsawandDermaltools.Thedetailingonthepartswasdoneinaprofessionalworkshopsincethepartsofrobotarmweretoosmallanditisnotaneasyforaccomplishingsuchsmallandaccuratecuts.Duringassemblingtherobotpartswiththemotors,fewproblemspopup.Therewerecriticalpointsthatdidnotresistthefasteningand,inturn,maybreakdownhence,reinforcementsinthesepointswereconsidered.ThefinalresultoftherobotarmisshowninFigure7.3.RobotArmInverseKinematicsTovalidatetherightpositioningoftheroboticarm,inversekinematicscalculationsarecarriedout.SuchcalculationsareusedtoobtaintheangleofeachmotorfromFigure6.Robotarm3Dmodel.Figure7.Robotarmcompleteassembly.apositiongivenbyusingtheCartesiancoordinatesystem,asshowninFigure8.EachmotorwillhaveaspecificfunctionthemotorlocatedintheAunionpositionsthefinalelementintheyaxis,themotorsBandCpositionsthefinalelementinthexandzaxis.Theproblemwassimplifiedbyusingthexzplane,asshowninFigure9.Inwhichthefollowingknownvaluesweredefined9LABtheforearmlength.LBCthearmlength.zthepositioninthezaxis.xthepositioninthexaxis.ythepositionintheyaxis.Usingtrigonometryrelations,asshowninFigure9,themotoranglesθ2andθ1areobtained,asseeninEquations9and10.2222180arcCos2LABLBCxzLABLBC29222122arcTanarcCos2zLABLBCxxLABxz2100arcTanyx11ThemotorBisgoingtouseθ1andthemotorCisgoingtouseθ2.TheangleforthemotorAiscalculatedasCopyright©2011SciRes.MME

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