Chapter4ForceAnalysisofPlanarMechanism1.ContentsofForceAnalysis1)Knowingtheexternalappliedloads,calculatetheconstraintforceswhichoccurinpairs.Constraintforcescanbeusedtodesignkinematicpairs.2)Knowingtheresistanceactingondrivenlink,calculatetheforcesactingondrivinglink,orknowingthedrivingforce,calculatetheresistanceactingondrivenlink.3)Theforceanalysisisthetheoreticalfoundationtocalculatetheefficiency.4)Makeuseoftheforceanalysis,wecandesignsomeselflockingmechanism.4.1Introduction2.MethodsofForceAnalysis

Therearetwogeneralmethodsofperformingacompleteforceanalysis：Graphicalforceanalysis&Analyticalforceanalysis.1.InertiaForcesFig.4-1Inertiaforceandinertiatorqueintoresultantforce(連桿的慣性力與慣性力矩的合成)4.2ForceAnalysisIncludingInertiaForcesinMechanisms

Fig4-1ashowsaslidercrankmechanism.Becauseoftheconstrainedmotionofthemechanism,accelerations,suchasas2,α2oftheindividuallink2andaC3oftheslider3,maybedeterminedfirst,thentheinertiaforcesFi2andtorqueMs2actingonthelink2canbecalculatedrespectively.2.KinetostaticAnalysisofPlanarMechanism(1)Kinetostaticanalysisofplanarmechanismbygraphicalmethod

Example4-1Fig4-2ashowsaconventionalshapermechanisminwhichtheangularvelocityofthecrankandalldimensionsoflinksareknown.SupposetheweightoftheramisG5,resistanceactingontheramisFr,andinertiaforceactingontheramisFi5.Theotherweightsandinertiaforcesneednottobeconsidered.DeterminetheinputtorqueMbactingonthedrivinglinkandtheconstraintforcesinpairs.Fig.4-2Graphicalforceanalysisofsharper(牛頭刨床的動態(tài)靜力分析)Fig.4-3Analyticalforceanalysis(動態(tài)靜力分析的解析法)

Example4-2Fig4-3showsaslidercrankmechanismusedinalotofmachines,suchasinternalcombustionengineandreciprocatingcompressors.Allthedimensionsoflinks,angularpositionofthecrankandangularvelocityofthecrankareknown.Thekinematicanalysisisfirstperformedalso.

(2)Kinetostaticanalysisofplanarmechanismbyanalyticalmethod1.FrictioninKinematicPairs(1)FrictioninslidingpairsThefrictioninslidingpairscanbedividedintoplanesurfacefrictionandVsurfacefriction.

4.3ForceAnalysisIncludingFrictioninMechanismsFig.4-4Frictionontheplane

surface(平面中的摩擦)1)Frictiononplanesurface.Aslider1isrestonasmoothplanesurface2whichishorizontal.Supposethattheslider1isslidingrelativetothesurface2totherightataconstantvelocityv12actedbyadrivingforceFwhichisinclinedatanangleαtothenormal,asshowninFig4-4.2)Frictiononinclinedplanesurface.AblockofweightGrestingonaplaneinclinedatanangleαtothehorizontalisactedonbyahorizontalforceFdwhichtendstomovethebodyuptheplanewithauniformvelocityv12.ThisisshowninFig4-5a.Fig.4-5Frictionontheinclinedplanesurface(斜面摩擦)3)FrictiononVplanesurface.IftheblockshowninFig4-6aischangedintoaVblockwithaincludedangle2θshowninFig4-6b,anditsweightisG,therearetwonormalreactionforcesN21,andfromFig4-6c,Fig.4-6FrictiononV-planesurface(槽面摩擦)(2)FrictioninturningpairsThebearingsareusedextensivelyastuningpairsinmachinery,andtheycanbedividedintojournalbearingandthrustbearing.1)Frictioninjournalbearing.Whenashaftrestsinthebearing,theverticalloadGactsthroughtheaxisoftheshaft.ThenormalreactionN21ofthebearingactsinlinewithGintheverticallyupwarddirectionshowninFig4-7a.

Fig.4-7Frictioninajournalbearing(徑向軸承中的摩擦)2)Frictioninthrustbearing.Whenarotatingshaftissubjectedtoanaxialload,thethrustistakenbyacollarbearing,orthrustbearing.Fig4-8ashowsathrustbearingactedbyanaxialloadG.Fig.4-8Frictioninathrustbearing(推力軸承的摩擦)（3）FrictioninhelicalpairsAccordingtothetoothshape,thescrewcanbedividedintosquarethreadsandVthreads.Asquarethreadscrewisusedtotransmitpower,andVthreadedscrewisusedtofastenanelementtoanother.Fig.4-9Frictioninsquarethread(矩形螺紋的摩擦)Fig4-9ashowsasquarethreadedscrew;itmaybethoughtofsimplyasaninclinedplaneorwedgewrappedaroundacylinder.Fig.4-10FrictioninV-thread(三角形螺紋的摩擦)Fig4-10ashowsaVthread;itsthreadangleis2β,andtheanglebetweentheVfacesofthethreadis2θ.Fig4-10bshowsatrianglewhichisthedevelopmentofahelixofdiameterdandleadl.2.ForceAnalysisIncludingFrictionExample4-3Fig4-11showsaslidercrankmechanisminwhichresistantforceFrisappliedtothepiston4.Thecrank1isrotatingintheclockwisedirection;thedimensionsoflinksandthefrictionalcoefficientofpairsareknown.Determinetheconstraintforcesinpairsandtheinputtorque.

Fig.4-11Forceanalysisconsideringthefrictioninaslider-cranklinkage

(考慮摩擦的曲柄滑塊機(jī)構(gòu)力分析)Example4-4Fig4-12ashowsacammechanismwithanoscillatingfollowerinwhichresistantforceFrisappliedtothefolloweratpointF.Thecam1isrotatinginthecounterclockwisedirection;thedimensionsofthemechanismandthefrictionalcoefficientofpairsareknown.Determinetheconstraintforcesinpairsandtheinputtorque.

Fig.4-12Forceanalysisconsideringthefrictioninacammechanism

(考慮摩擦的凸輪機(jī)構(gòu)的力分析)1.SelflockinginKinematicPairs4.4FrictionandDesignofSelflockingMechanismsTherearetwoforcesinakinematicpairwhichisusedtoconnecttwolinks;theoneisdrivingforceandtheotherisfrictionforcewhichresiststhemotionofthelink.Ifthedrivingforceactinginapairisinfinite,andthelinkisnotmovable,itiscalledasselflockingofapair.Foraslidingpair,appliedresultantforceactswithinthefrictionalangleofabody,theselflockingwilloccurintheslidingpair.Forarotatingpair,appliedresultantforceactswithinthefrictionalcircleofabody,theselflockingwilloccurintheturningpair.2.SelflockingMechanisms(1)Travelofamechanism

1)Positivetravelofamechanism.AdrivingforceactsonthedriverAshowninFig4-13;theworkisdonebytheresistantforceactingonthedrivenlinkB.Thistravelispositivetravel.Fig.4-13Travelofmechanism

(機(jī)構(gòu)的行程)(2)SelflockingmechanismIfthenegativetravelofamechanismisinselflocking,itiscalledasselflockingmechanism.Selflockingmechanismcanbeusedwidelyinmechanicalengineering.2)Negativetravelofamechanism.IftaketheresistantasadrivingforceanditactsonthelinkB,andtheoriginaldrivinglink,suchasA,becomesadrivenlink,thistravelisnegativetravel.3.DesignofSelflockingMechanismsExample4-5Fig4-14showsawedgeexpellermechanismwhichisusedtocompressabody4withloadedFrbyapplyingahorizontalforceFtothewedge2.Ifthecoefficientoffrictionofthecontactsurfacesareallthesameandknown,analyzetheconditionofselflockingofthewedges.

Fig.4-14Analysisofself-lockingmechanism(自鎖機(jī)構(gòu)的分析)Fig.4-15Designofself-lockingmechanism(自鎖機(jī)構(gòu)的設(shè)計(jì))Example4-6DesignaneccentricdiscclampershowninFig4-15,inwhichthelink1isaneccentricdisc,body2isaworkpiecewhichwillbeclamped.Aftertheworkpiecehasbeenclamped,theforceFactedonthehandlemustberemoved.Andthentheworkpiecewhichhasbeenclampedcannotbeloosed.Determinethepositionofthepivotoftheeccentricdisc.

Chapter5SynthesisofPlanarLinkages1.TheCharacteristicsofPlanarLinkages1)Alinkagehasasimplestructureanditiseasytomanufacture,soithasalowcost.2)Thepressureinalowerpairwithsurfacecontactislower,sothelinkagehasalargeloadcapacity.3)Alinkagecanachievevariousmotionsbydesigningitsdimensionsofthelinks.4)Alinkagecantransmitmotionwithinalongdistance.5)Itisdifficulttoperformprecisionmotion;thisisadisadvantageoflinkages.5.1CharacteristicsandTypesofPlanarLinkagesFig.5-1Typesoffour-barlinkages(鉸鏈四桿機(jī)構(gòu)的類型)2.TypesofPlanarLinkagesFig.5-2Typesoffour-barlinkageswithaslidingpair(含有一個(gè)移動副的四桿機(jī)構(gòu)類型)(1)CrankrockerlinkageIfafourbarlinkageshowninFig5-1aisdesignedsothatlink1canrotatecontinuouslywhilelink3onlyoscillatesthroughanangle,itiscalledacrankrockerlinkage.(2)DoublecranklinkageBothlink2andlink4inFig5-1bcanrotatecontinuouslyrelativetotheframe1;thislinkageiscalledadoublecranklinkage.(3)DoublerockerlinkageBothlink2andlink4inFig5-1ccannotrotatecompletelyrelativetotheframe3;thislinkageiscalledadoublerockerlinkage.(4)ParallelcrankfourbarlinkageIfinafourbarlinkage,twooppositelinksareparallelandequalinlength,asshowninFig5-1d,cranks2and4alwayshavethesameangularvelocity.Thismechanismiscalledaparallelcrankfourbarlinkage.Itiswidelyused,suchasinthecouplingoflocomotivewheels,inpantograph,etc.(5)IsoscelestrapeziumlinkageIftworockersofadoublerockerlinkageareequalinlength,seetheFig5-1e,thislinkageiscalledanisoscelestrapeziumlinkage;itcanbeusedinthesteeringmechanisminautomobiles.(6)SlidercranklinkageThislinkageisshowninFig5-2a,inwhichsidelink1isacrank,andtheothersidelink3isaslider.TurningpairsAandBarefullturningpairs,andCisoscillatingturningpair.(7)RotatingguidebarlinkageIfboththesidelink2andsidelink4canrotatecompletely,thislinkageiscalledarotatingguidebarlinkageshowninFig5-2b,inwhichthecouplerbecomesasliderinshape.(8)RockingblocklinkageThecrankrotatescompletelywhiletheblockonlyoscillatesaboutitspivotcenterC,thislinkageiscalledrockblocklinkageshowninFig5-2c.Itiswidelyusedinhydrauliccylindermechanism.(9)SlidingguidebarlinkageIftheguidelink4reciprocatesalongtheaxisofthefixedblock,andtheothersidelink2oscillatesaboutthepivotC,thelinkageiscalledaslidingguidebarlinkageshowninFig5-2d.Itcanbeusedinsomewaterpumps.(10)RockingguidebarlinkageIfthelink2canrotatesaboutpivotBcompletely,andthelink4oscillatesaboutthepivotAshowninFig5-2e,thislinkageiscalledarockingguidebarlinkage.Itisusedinmachinetoolssuchasshapers.(11)DoubleslidercranklinkageInafourbarlinkage,iftwosidelinks1and3becomesliderswhicharereciprocatingalongeachaxisofcrossframe,andthetwopairsofthesamekindareadjacent,itisknownasadoubleslidercranklinkageshowninFig5-3a.Thislinkagecandrawellipses.(12)DoublerotatingblocklinkageIftwoslidersarerotatingcompletelyabouttheirpivotsAandBrelativetotheframe2,thislinkageiscalledadoublerotatingblockmechanismshowninFig5-3b.ItcanalsobecalledOldhamlinkage,anditisusedtoconnecttwoshaftshavingparallelmisalignment.(13)SinelinkageThislinkagecanalsobecalledaScotchyokelinkage,inwhichthecrank2rotatesaboutitspivot.Acompletely,andlink4reciprocatesinthefixedlink1toproduceasimpleharmonicmotion.ItisshowninFig5-3c.

(14)TangentlinkageInatangentmechanism,thesidelink2oscillatesaboutitspivotA,theotherlink4reciprocatesalongitsaxis,andthelink3isasliderinshape.ItisalsocalledtheRapsonsslidelinkage.Thedisplacementoflink4hasatangentmotion.Fig.5-3Typesoffour-barlinkageswithtwoslidingpairs

(含有兩個(gè)移動副的四桿機(jī)構(gòu)類型)3.EvolutionandMutationofPlanarLinkages(1)InversionofafourbarlinkageDifferentmechanismscanbeobtainedbyfixingdifferentlinksofamechanism.Thisisknownasinversion.Theprincipleisthattherelativemotionbetweenlinksofafourbarlinkagedoesnotchangeindifferentinversion.

Fig.5-4Evolutionfromturningpairtoslidingpair(轉(zhuǎn)動副向移動副的演化)(2)ConvertingaturningpairintoaslidingpairIftheradiusofthepinDisincreasedtoalengthoflDC,andtherocker3ismadeasliderwithacurvewhichradiusislDC,thenthismechanismbecomesacurveslidercrankmechanismshowninFig5-4b.IfthelDCweremadeinfiniteinlength,thenpointCwouldhaverectilinearmotionandlink3couldbereplacedbyaslider,asshowninFig5-4c.Fig.5-5Eccentricdiskmechanism(偏心盤機(jī)構(gòu))(3)ExpansionofpinsizeinaturningpairIfweincreasethesizeofthecrankpinBshowninFig5-5auntilitislargerthanthelengthofthecrank,thisenlargedcrankpiniscalledaneccentricdiskandcanbeusedtoreplacethecrankshowninFig5-5a.ThecrankconsistsofacirculardiskwithcenterB,whichispivotedoffcenteratAtotheframe.Thediskrotatesinsidetheringendofcoupler2.4.ApplicationsofPlanarLinkages(1)ApplicationsoflinkagesconsistedofturningpairsFig5-6aisajawcrusher.Itconsistsofacrankrockerlinkage.Theconnectingrodisthemovingjawusedtocrushtherocks.ItskinematicdiagramisshowninFig5-6b.Fig5-6cshowsadoughmixingmachine;itconsistsofacrankrockerlinkagealso.Fig.5-6Applicationsofcrank-rockerlinkage(曲柄搖桿機(jī)構(gòu)的應(yīng)用)

1—eccentricdisk(偏心盤)2—beltwheel(帶輪)3—movingjaw(動鄂)4—movingjawboard(動鄂板)

5—fixedjawboard(靜鄂板)6—rocker(擺桿)7—spring(彈簧)Fig.5-7Applicationsofdouble-rockerlinkage(雙搖桿機(jī)構(gòu)的應(yīng)用)Fig5-7ashowsacranewhichisusedinports.Itconsistsofadoublerockerlinkage.ThepointEoncouplercanmovealongastraightline.ornearlyalongastraightline,thereforetheliftedbodymaymovesteadilyalongthispath.Fig.5-8Applicationsofdouble-cranklinkage(雙曲柄機(jī)構(gòu)的應(yīng)用)Fig5-8ashowsainertiavibratingscreen.Itisadoublecranklinkage,andisalsocalledadraglinklinkage.IfthedriverACrotatescounterclockwisewithconstantangularvelocity,theslidermakesaslowstrokeandreturnswithaquickstroke.Theinertiaforcescancausevibrationofthescreentoperformseparationofthematerials.Fig5-8bshowsaparalleldoublecranklinkageusedinthecoupleroflocomotivewheels,andFig5-8cshowsahydraulicliftwithtwosetsofparalleldoublecranklinkages.(2)ApplicationsofslidercranklinkageSlidercranklinkagesareusedwidelyinvariousmulticylinderengines.Fig5-9aisaVenginewitheightcylinders.Thisengineconsistsofeightslidercranklinkages.Fig5-9bshowsashearingmachine.Itconsistsofoneslidercranklinkage.Fig.5-9Applicationsofslider-cranklinkage(曲柄滑塊機(jī)構(gòu)的應(yīng)用)(3)ApplicationofcranksliderquickreturnlinkageFig5-10aisashaper;itconsistsofgearmechanismandslidingguidebarlinkage.Fig5-10bisashapertoo;itconsistsofrotatingguidebarlinkage.Fig.5-10Applicationsrockingguide-barlinkageandrotatingguide-barlinkage

(擺動導(dǎo)桿機(jī)構(gòu)和轉(zhuǎn)動導(dǎo)桿機(jī)構(gòu))Fig.5-11Applicationsofslidingguide-barlinkageandrocking-blocklinkage

(移動導(dǎo)桿機(jī)構(gòu)和曲柄搖塊機(jī)構(gòu)的應(yīng)用)

1—handle(手柄)2—link(連桿)3—cylinder(簡體)4—plunger(活塞)Fig5-11ashowsahandpump,inwhichlink4ismadeintheformofacylinderandaplungerfixedtothelink3reciprocatesinit；itconsistsofslidingguidebarlinkage.Fig5-11bshowsaselfloadingtruck,inwhicharockingblocklinkageisusedtoperformselfloadingwork.

(4)ApplicationoffourbarlinkageswithtwoslidingpairsFig5-12ashowsanellipticaltrammelinwhichthefixedlink1isintheformofguidesforsliders2and4.Fig5-12bshowsanOldhamscoupling,anditconsistsofadoublerotatingblocklinkageshowninFig5-3b.Fig5-12cshowsamechanismwhichisusedtodrivetheneedleofasewingmachine;itisasinelinkage.Fig.5-12Applicationsoffour-barlinkageswithtwoslidingpairs(含有兩個(gè)移動副機(jī)構(gòu)的應(yīng)用)1.GrashofCriteria5.2FundamentalFeaturesofFourbarLinkagesFig.5-13Grashoflaw(曲柄存在條件)Fig5-13showsafourbarlinkageABCD,andifthelinkABcanrotatethroughafullrevolutionwithanangularvelocityωclockwise,itmustpassthroughthepositionsAB1andAB2.Thelink1whichcanrotatethroughafullrevolutionmustbetheshortestlink;thesumofthelengthofshortestlinkandthelongestlink(theremustbealongestlinkamongb,c,d)cannotbegreaterthanthesumoftheremainingtwolinks.

TheGrashofcriteriacanbestatedasfollowing:

1)Alinkage,inwhichthesumofthelengthoftheshortestandlongestlinksislessthanthesumofthelengthoftheothertwolinks,musthaveacrank.2)Thecrankmustbetheshortestlink.2.QuickreturnMotion

Whenthecrankrotatesthroughafullrevolutionwithanangularvelocityωclockwise,andtherockeronlyoscillatesthroughanangleψ,thecrankandcouplerwillformastraightlineateachextremeposition.Fig-14showsacrankrockerlinkageinthetwoextremepositionsofthedrivenlink.Fig.5-14Quick-returncharacteristics(急回特性)3.PressureAngleandTransmissionAngleFig.5-15Transmissionangleandpressureangle(傳動角和壓力角)Thepressureangleαistheacuteanglebetweenthedirectionofthestaticforcetransferredthroughthecouplerandtheabsolutevelocityoftheoutputlinkattheconnectedpoint,suchasatC.Sincethecouplerisatwoforcelink,thedirectionofthestaticforceofthecouplerisalongthelineofitspinjoints.

TheacuteangleγbetweenthecouplerandoutputlinkisknownastransmissionangleshowninFig5-15.Noticethatinthiscase,α+γ=90.Fig.5-16Transmissionangleinaslider-cranklinkage(曲柄滑塊機(jī)構(gòu)的傳動角)ThetransmissionangleinaslidercranklinkageisshowninFig5-16.4.DeadPointFig5-17showsacrankrockerlinkage.Whenthecrankrotatescompletely,thereisnodangerofthelinkagelocking,becausethetransmissionanglecannotbezeroatanypositions.However,iftherockerbecomesadrivinglink,thecrankisadrivenlink,andthentherockermovestotheextremepositionDC1andDC2,thetransmissionanglesbecomezero,thelinkagelockingwilloccur.Wecallthesepositionsasdeadpointsortogglepositions.Therockerwillthenhavetobedriventogetthelinkageoutofthetoggleposition.Fig.5-17Deadpoints(死點(diǎn))Fig.5-18Overcomedeadpointbyusingflywheel

(利用飛輪克服死點(diǎn))

1—flywheel(飛輪)2—crankshaft(曲軸)

3—camshaft(凸輪軸)4—valve(氣門)

5—piston(活塞)6—connectlink(連桿)Fig5-18showsasinglecylinderenginewithfourstrokecycle.Theflywheelcancarrythepistonthroughtheenginesexhauststroke,intakestrokeandcompressionstroke.Fig5-19isadrivingmechanismofthelocomotivewheels;thephaseangleofthecranksis90°.Ifoneofthemisatthedeadposition,theothercanbedriveneasily.Fig.5-19Overcomedeadpointsbyusingdifferentphase(錯(cuò)位排列克服死點(diǎn))Fig.5-20Self-lockingclamp(自鎖夾具)Fig5-20showsaclampingdevice,inwhichafterasmallforceFappliedonthecouplerhasbeenremoved,thereactionforceoftheclampedworkpiecetothelinkABcannotdrivethelinkagetomoveatall.Wecanalsodesignmanydevicesusingthedeadpointposition.1.Introduction（1）MotiongenerationFig5-21ashowsaoverturningdeviceusedinacastingworkshop.ThisdeviceisdesignedtoguidethesandboxwhichisfixedtothecouplerintwopositionsB1C1andB2C2.Fig5-21bshowsaspeedchangedevicewhichiscontrolledbyhand.Itisdesignedtoactualizetheinputandoutputlinksthroughthethreepositions.

（2）PathgenerationAcoupleristhemostinterestinglinkinamechanism.5.3SynthesisofFourbarLinkagesFig.5-21Problemsofsynthesisofafour-barlinkage1(四桿機(jī)構(gòu)設(shè)計(jì)基本問題1)Fig5-22ashowsafourbarlinkagewhichisontheextremepositions,andfromthisfigurewehave:a=（AC1－AC2）/2Thisformulaforcalculatingthelengthofthecrankisveryusefultodesignafourbarlinkage.

Fig.5-22Problemsofsynthesisoffour-barlinkages2(四桿機(jī)構(gòu)設(shè)計(jì)基本問題2)Fig.5-23Guidingabodythroughtwocouplerpositions(按連桿的兩個(gè)位置設(shè)計(jì)四桿機(jī)構(gòu))1)Twoprescribedlinkpositions.Fig5-23ashowstwopositionsofacouplerBC.Itisdesiredtodesignamechanismwhichwillcarrythelinkthroughthesetwopositions.(1)DesignofafourbarmechanismforspecifiedcouplerpositionsGuidingabodythroughtwoorthreelinkpositionsareoftenusedtodesignafourbarlinkage.2.GraphicalSynthesisofFourbarLinkage

2)Threeprescribedlinkpositions.Theprocedureissimilartotheaboveprocesses(Fig5-24).Fig.5-24Guidingabodythroughthreecouplerpositions(按連桿的三個(gè)位置設(shè)計(jì)四桿機(jī)構(gòu))Fig.5-25Guidingabodythroughanumberoflinkplanepositions

(按連桿平面位置設(shè)計(jì)四桿機(jī)構(gòu))3)Twoorthreeprescribedpositionsofthecouplerplane.ThreeprescribedpositionsofacouplerplaneareshowninFig5-25.

Fig.5-26Principleofinversion(反轉(zhuǎn)法的原理)（2）Designofafourbarlinkageforcorrelatedangularpositionsofinputandoutputlinks1)Inversionmethod.Fig5-26showsafourbarlinkage;themotionoftheinputlinkABfromtheφ1toφ2causesamotionoftheoutputlinkDCfromψ1toψ2.Fig.5-27Coordinationofthepositionsoftheinputandoutputlinks

(按兩連架桿的三組對應(yīng)位置設(shè)計(jì)四桿機(jī)構(gòu))2)Threeprescribedangularpositionsoftheinputandoutputlinks.Fig5-27illustratesaprobleminwhichitisdesiredtodeterminethedimensionsofalinkageinwhichtheoutputlinkistooccupythreeangularpositionsψ1,ψ2andψ3correspondingtothethreegivenpositionsφ1,φ2andφ3oftheinputlink.

（3）DesignofafourbarlinkageforquickreturnmotionSomeexternalworkisbeingdonebythelinkageontheforwardstroke,andthereturnstrokeneedstobeaccomplishedasrapidlyaspossiblesothatamaximumtimewillbeavailableforworkingstroke.1)Crankrockerlinkage.SynthesizingacrankrockerlinkageforspecifiedvalueofK,thelengthofrockerDCandtheangleψbetweenthetwoextremepositionsoftherockerareknown.TheproceduresareinFig5-28.

Fig.5-28Synthesisofacrank-rocker

linkageforagivenK(已知K設(shè)計(jì)

曲柄搖桿機(jī)構(gòu))Fig.5-29Synthesisofaslider-crank

linkageforagivenK(已知K值設(shè)計(jì)

曲柄滑塊機(jī)構(gòu))2)Slidercranklinkage.

Fig.5-30Synthesisofaguide-bar

linkageforagivenK

(已知K值設(shè)計(jì)導(dǎo)桿機(jī)構(gòu))3)Guidebarmechanism.Fig.5-31Couplercurve(連桿曲線)（4）DesignofafourbarlinkageforspecifiedtracingpathCouplercurvescanbecapableofapproximatingstraightlinesandlargecirclearcswithremotecenters,sotheyarequiteusefulpathmotionsformachinedesign.Fig5-31showsafourbarlinkage,inwhichthepointFonthecouplercangenerateaclosepath.3.AnalyticalSynthesisofFourbarLinkage(1)DesignofafourbarlinkageforspecifiedcouplerpositionsFig5-32showsthreepositionsofacouplerBCinwhichthecoordinatesofthepointBandCareshowninFig5-32.Itisdesiredtodesignamechanismwhichwillcarrythelinkthroughthesepositionsbyusinganalyticalmethod.

Fig.5-32Guidingabodythroughanumberoflinkpositions(按連桿的對應(yīng)位置設(shè)計(jì)四桿機(jī)構(gòu))Fig.5-33Coordinationofthepositionsoftheinputandoutputlinks(按連架桿的對應(yīng)位置設(shè)計(jì)四桿機(jī)構(gòu))(2)DesignofafourbarlinkageforcorrelatedpositionsofinputandoutputlinksUsuallythelengthsofthelinkABandtheframeADaregivenbyadesigner.

（3）DesignofafourbarlinkageforquickreturnmotionFig5-34showsafourbarlinkageintheextremepositions.

Fig.5-34Synthesisofafour-barlinkage

foragivenK(已知K設(shè)計(jì)四桿機(jī)構(gòu))（4）DesignofafourbarlinkageforcouplercurveAfourbarlinkageABCDwithacouplerpointPisshowninFig5-35.ThepositionofpointPonthecouplermaybelocatedbylengthofe,fandangleγshowninFig5-35.

Fig.5-35Designofafour-barlinkagefor

couplercurve(按連桿曲線設(shè)計(jì)四桿機(jī)構(gòu))Chapter6DesignofCamMechanisms1.CompositionandCharacteristicsofCamMechanisms6.1IntroductionFig.6-1Cammechanisms(盤形凸輪機(jī)構(gòu))Acammechanismconsistsofcam,followerandframe,anditbelongstothecategoryofhigherpairmechanism.Fig6-1showstwokindsofcammechanisms，inwhichFig6-1ashowsadiskcamwithatranslatingfollower,andFig6-1bshowsadiskcamwithanoscillatingfollower.Cammechanismiswidelyusedinautomaticmachines,internalcombustionengines,machinetools,printingmachines,andsoon.Comparedtolinkages,camsareeasierdesignedtogiveaspecificoutputmotion.Camsalsohaveasimplestructureandreliableperformance.2.TypesofCamMechanisms(1)Typesofcams

(2)

Typesoffollowershapes

（Fig6-4）

(3)

Typesoffollowermotion

（Fig6-4、Fig6-5）

(4)

Typesofmotionconstraints

Disccam（Fig6-1）

Translatingcam（Fig6-2）

Spatialcam（Fig6-3）Knifeedgefollower

Rollerfollower

Flatfacedfollower

SphericalfacedfollowerReciprocatingfollowerOscillatingfollowerForceclosure（Fig6-6）Formclosure（Fig6-7）Fig.6-2Translatingcammechanisms(移動凸輪機(jī)構(gòu))Fig.6-3Spatialcammechanisms(空間凸輪機(jī)構(gòu))Fig.6-4Followertypes(從動件的分類)Fig.6-5Disccamwithradialfollower

(直動從動件盤形凸輪機(jī)構(gòu))Fig.6-6Force-closedcammechanism

(力封閉凸輪機(jī)構(gòu))Fig.6-7Form-closedcammechanism(形封閉式凸輪機(jī)構(gòu))3.CamsTerminology1)Camprofile

2)Basiccircle

3)Tracepoint

4)Pitchcurveofthecam

5)Primecircle

6)Pressureangle

7)Risetravel

8)Returntravel

9)Stroke

10)Angleofascent

11)Angleofdescent

12)Angledweltatthehighestposition

13)Angledweltatthelowestposition14)Camangle

15)FollowerdisplacementFig.6-8Nomenclaturesofcammechanism(凸輪機(jī)構(gòu)名詞術(shù)語)

1—follower(從動件)2—pressureangle(壓力角)3—tracepoint(軌跡點(diǎn))

4—pitchcurve(理論廓線)5—camprofile(凸輪實(shí)際廓線)

6—primecircle(理論廓線基圓)7—basecircle(實(shí)際廓線基圓)Fig.6-9Camangleandfollowerdisplacement(凸輪轉(zhuǎn)角與從動件的位移)Fig.6-10Motionofthefollower(凸輪機(jī)構(gòu)運(yùn)動循環(huán)圖)1.BasicTypesofFollowerMotions(1)Polynomialmotions

6.2BasicTypesofFollowerMotionandDesign1)ConstantvelocitymotionFig.6-11Constant-velocitycurve

(等速運(yùn)動規(guī)律)2)ConstantaccelerationanddecelerationmotionFig.6-12Constantaccelerationanddeceleration

curve(等加速等減速運(yùn)動規(guī)律)3）The3-4-5polynomialmotionFig.6-133-4-5polynomialcurve

(五次多項(xiàng)式運(yùn)動規(guī)律)(2)TrigonometricmotionsThemotionsoftrigonometricformaresimpleharmonicmotionwhichhasacosineaccelerationcurveandcycloidmotionwhichhasasineaccelerationcurve.1)Simpleharmonicmotion

Fig.6-14Simpleharmonicmotion(簡諧運(yùn)動)Fig.6-15Cosineacceleration

curve(余弦運(yùn)動規(guī)律)2)CycloidmotionFig.6-17Sineaccelerationcurve(正弦運(yùn)動規(guī)律)Fig.6-16Cycloi