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railwayconsiststhefieldtoinherentlyandotherscomputervisionguidance5,6.ThesetruckshavebettervisibilityfordriversbuttheyarenotfundamentalsolutionstoovercomeMechanismandMachineTheory4520101892–1896ContentslistsavailableatScienceDirectMechanismandMachineTheorytheshortagesofthegeneralmaststructures,andtheproblemofhighselfweighthasnotbeencrackedcompletelyeither.Inordertoimprovethedrivingcomfortandsafetyforthedriversandtoreduceenergyconsumption,thispaperfocusesontheinnovativedesignoftheliftingmechanismforforklifttrucks.Aspatialmultilinkliftguidancemechanismisproposed,andthenanewkindofliftingmechanismbasedonitispresented.Thismechanismnotonlyexpandsthevisionfieldofthedriverbutalsoreducesthewholeweightofthevehicle.2.PropositionofaliftguidancemechanismExpandingthedriversvisionhasalwayschangingtheformsofthemast2,3,whileAsiswellknown,aplanarRRRopenchaSupposethattwosuchplanarRRRlinkagesRRRopenchainlinkagesareconnectedwith⁎Correspondingauthor.Fax861062788308.Emailaddressjingshanzhaomail.tsinghua.edu.cn0094114X/–seefrontmatter©2010ElsevierLtd.doi10.1016/j.mechmachtheory.2010.08.002beenanimportantresearchproject.Somekindsoftruckshaveimprovedvisibilityviautilizethevisualguidancemethodsofmobilecameraspacemanipulation4orcomponentswillbadlyaffectthedriversbetweenpedestriansandtrucksaredueanimportantroleinsupportingtheloadsenoughanditsselfweighthastobeincreasedtheunnecessarywasteofenergy.stations,warehouses,portsandfactoriesforloading,unloadingandconveying.Aofachassisandaworkdevicewhichcanbetiltedandliftedvertically.followingmajordisadvantages.First,themastsystemcomposedofseverallargeofvisionbecauseitlocatesinfrontofthedriver.Manyaccidentsinvolvingcollisionsbadvisibilitiesoftheforklifttrucks1,2.Inaddition,themastsystemplaysguidingtheforkframetoliftvertically.Soitsstrengthandstiffnessmustbehigh.Theweightoftherearequilibratorisincreasedasaresult,whichsurelyimproves1.IntroductionForklifttrucksareusuallyusedatgeneralweightbalancedforklifttruckHowever,thegeneralforkliftshaveShortcommunicationInnovativedesignoftheliftingmechanismsforforklifttrucksJianYiWang,JingShanZhao⁎,FuLeiChu,ZhiJingFengDepartmentofPrecisionInstrumentsandMechanology,TsinghuaUniversity,Beijing100084,PRChinaarticleinfoabstractArticlehistoryReceived17June2010Receivedinrevisedform3August2010Accepted4August2010Availableonline1September2010Forklifttruckisoneofthemostimportanttoolsinlogistics.However,thegeneralmastsystemofaforklifttrucknotonlyrestrainsthedriversvision,butalsoincreasesthewholeweightofatruckanddecreasesthefueleconomy.Therefore,thispaperfocusesontheinnovativedesignofanewliftingmechanismforforklifttruck.Firstly,aspatialmultilinkliftguidancemechanismisproposed.Andthen,undertheconstraintsofthismechanism,themobilityoftheforkandforkframeisinvestigatedintheory.Lastly,anewliftingmechanismbasedonitispresentedandcomputersimulationisusedtodemonstratethefeasibilityofmotion.Thismultilinkliftingmechanismtakesadvantageofflexiblecabledriveandrigidbodyguidance,whichnotonlyprovidestheoperatorwithawiderfieldofvisionbutalsoreducestheequilibrateweightofavehicleandthereforeimprovesthefueleconomy.©2010ElsevierLtd.Allrightsreserved.KeywordsForklifttruckSpatialmultilinkmechanismRigidbodyguidanceFlexibledrivingmethodjournalhomepagewww.elsevier.com/locate/mechmtinlinkagethatconsistsofthreerevolutepairsandtwolinksgeneratesplanarmotions.areplacedintwoplaneswithacertainnonzerosubtendedangle.TheendsofthetwoasamerigidbodythroughrevolutepairsshowninFig.1.Link1isthebaseandrigidJ.S.Zhao.Allrightsreserved.1893J.Y.Wangetal./MechanismandMachineTheory4520101892–1896body4isconnectedwiththebasethroughtwoparallelRRRkinematicchains,ABCandDEF.Itiseasytofindthat,thesetwokinematicchainsarebothplanarRRRkinematiclinkages.Thereforethetrackofrigidbody4mustbeparalleltobothofplaneαandplaneβ.Thatis,rigidbody4canonlymakeafreetranslationparalleltotheintersectionline,mn,ofthetwoplanes.Asaresult,thetrackofrigidbody4isastraightline.SlidercrankmechanismisacommonmechanismthatappliesRRRopenchainstructure.ItiswidelyusedandexamplesofitsFig.1.Spatialmultilinkstructure.applicationsareeasilyfoundingasolineanddieselengines7.However,intheapplicationsofslidercrankmechanism,deadpointspossiblyleadtoactuatingfailure.Inordertoimprovethestabilityandavoidthedeadpoints,thispaperreplacestheRRRkinematicchainswithRPRkinematicchains,whicharecomposedoftworevolutepairsandoneprismaticpairandcanalsoonlygenerateplanarmotionswithoutdeadpoints.SupposethetwoverticalplanesthatthesupportblocksandtheirRPRkinematicchainslocatedaresymmetricalwithrespecttothelongitudinalsymmetricalplaneofthevehicle.AsisshowninFig.2,thesubtendedanglebetweenthetwoplanesisdenotedbyθ0∘bθb180∘.TwoRPRkinematicchainsareplacedinthetwoplanes,respectively.EveryRPRkinematicchainincludestworevolutepairsandoneprismaticpair,aconnectingrodandaslideway.Theconnectingrodandtheslidewayareconnectedthroughaprismaticpair.TheforkframehastwoextrudedrevolutepairsconnectedwiththeendsofthetwoRPRkinematicchains.Asisdiscussedabove,insuchaspatialmultilinkstructure,thetrackoftheforkframeisinastraightline.Inaddition,onecanimprovethestrengthandstiffnessbyaddinganothersimilarkinematicchainineachverticalplane,inwhichthesupportblockslocated,toconnecttheforkframeandthetruckchassis.Meanwhile,theupperandlowerkinematicchainsareconnectedbyconstraintrods.Asthetrackoftheupperandlowerkinematicchainsareparallel,theconstraintrodsprovideredundantrestraintsandimprovethestiffnessandstabilityoftheliftguidancemechanismandtheloadcarryingcapacity8.Nowthekinematicprinciplesofthespatialmultilinkliftguidancemechanismcanbeanalyzedintheory.InordertoinvestigatethedegreeoffreedomDoFoftheforkframe,onecanestablishaCartesiancoordinatesystem,wherexoyplaneistheplanedeterminedbytheaxesofrevolutepairsAandD,theoriginofcoordinatesystemistheintersectionpointofaxesofAandD,xaxisistheaxisofrevolutepairA.ThecoordinatesystemisshowninFig.3.AssumethatthesubtendedangleoftheaxesofrevolutepairDandrevolutepairAisdenotedbyφ0obφb180o,thedistancefromrevolutepairsAandDtotheoriginofcoordinatesystemareequalanddenotedbya.ThecoordinatesofAandDarea00ðÞandacosφasinφ0ðÞ,respectively.Inaddition,thecoordinatesofCandFcanbeexpressedasayCzCðÞandxFyFzF,individually.Itisnotdifficulttofindthat,theaxesofrevolutepairsAandCareparallel,andsoaretheaxesofrevolutepairsDandF.s1100ðÞTdenotesthedirectionvectoroftheaxesofrevolutepairsAandC,s2cosφsinφ0ðÞTdenotestheunitdirectionvectoroftheaxesofrevolutepairsDandF,s30yCzCðÞTdenotesthedirectionvectorofprismaticpairBands4xF−bcosφyF−bsinφzFTdenotesthedirectionvectorofprismaticpairE.Accordingtothescrewtheory9,theterminalconstraintscrewmatrixofakinematicchaincanbeobtainedbysolvingthereciprocalscrewequationTEτ0ð1ÞwhereτThetheterminalFig.2.Anewliftguidancemechanism.1fork2forkframe3extrudedrevolutepair4connectingrod5constraintrod6slideway7supportblock.1894J.Y.Wangetal./MechanismandMachineTheory4520101892–1896000001inaccordancewithEq.1,onecanobtaintheterminalconstraintscrewmatrixcomposedofasetofbasescrewsofconstraintscrewsystem.τABC1000000000102435Tð3Þ1000zC−yCTherefore,isakinematicscrewmatrixandistheterminalconstraintscrew.kinematicscrewmatrixofakinematicchain,ABC,canbeexpressedasABCABC½C1381000000000yCzC2435Tð2ÞFig.3.Cartesiancoordinatesystem.Itproves1895J.Y.Wangetal./MechanismandMachineTheory4520101892–1896Undertheconstraintsoftheliftguidancemechanism,theforkframecanbeliftedupanddownperpendiculartotheground.3.ImplementThissimulateAswhileisshownoftheworks,InraisedmechanisperpendicuThisCabledriveweightrequiremMeanwhilthiskindthembecomesCF000001ðÞTð6ÞthattheforkframehasonlyoneDoFalongzdirection,i.e.,thetrackoftheforkframeisrestrictedtoastraightline.AccordingtoEq.1,solongas0∘bφb180∘,thekinematicscrewmatrixoftheframeCFcanbesolelyobtainedτCFτABCτDEFC2C3ð5ÞConsequently,theterminalconstraintscrewmatrixonCFcanbeexpressedasτDEFcosφsinφ0000000sinφ−cosφ000000145ð4ÞSimilarly,theterminalconstraintscrewmatrixofkinematicchainDEFisobtained23TFig.4.Implementationofthenewliftingmechanismandcomputersimulations.1forkframe2frontpulley3frontsupportingrods4backsupportingrods5cables6backpulley.ationofanewliftingmechanismsectionwillpresentanewliftingmechanismforforklifttruckbasedontheliftguidancemechanismproposedaboveanditsmotioninacomputer.isdiscussedabove,theliftguidancemechanismrestrainsthetrackoftheforkframeinastraightline.Inordertoliftgoodsnotaffectingthedriversfieldofvision,onecanusewindlassandsoftsteelcablestolifttheforkandforkframe.ThestructureinFig.4a.Onecansetawindlassattherearoftheforklifttruckandplacessomepulleysandsupportingrodsonthetopcab.Oneendofeachcableisconnectedwiththeforkframeandtheotherendisfixedtothewindlass.Whenthewindlassthecableswillliftordroptheforkframe.ordertoverifywhetherthiskindofforklifttruckcanachievethedesiredmovements,especiallyinsuretheforkframetobevertically,Pro/engineersoftwareisutilizedtosimulateitsmotion.Fig.4a,bandcshowdifferentpositionswhenthemliftstheforkandforkframeup.Fromthesimulationonefindsthatthetrackoftheforkandforkframeisastraightlinelartotheground.Inaddition,withoutthemastsystem,thedriverhasabettervisionforwardsandbackwards.kindofliftingmechanismconsistsoftheflexiblecabledriveandrigidbodyguidancewithbetterstructuralperformances.nmanipulatorshavebeenwidelyinvestigatedinapplicationsfortheiruniqueadvantagessuchaslowinertia,lightandsoon10.Itisnotdifficulttofindthattheweightofgoodsissupportedmostlybythecables.Therefore,theentforstrengthandstiffnessoftheliftguidancemechanismislower,andtheweightofitcanbedecreasedasaresult.e,comparedwithcomponentsofthegeneralforklifttrucks,suchascylinder,chains,chainwheelsandthemastsystem,ofliftingmechanismutilizeswindlass,cablesandseveralconnectingrods.Theirweightislowerandthegravitycenterofmovesbackwards.Consequently,theweightofrearequilibratorisgreatlydecreasedandthewholeweightofthetruckmuchlower.Sotheproposedforklifttruckreducesenergyconsumptionandimprovesthefueleconomyofthevehicle.
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