《凸轮机构讲义》PPT课件

Chapter4.CamsandItsDesign,SunZhihongZhsun67792580,Todaystopics,Characteristicsofcammechanisms凸轮机构的特点Classificationandapplicationofcammechanisms凸轮机构的分类及应用Thefollowersmotiontype从动件的运动形式,Whatisacammechanism?Asystem/mechanismthatusesacam(凸轮)andafollower(从动件)tocreateaspecificmotion.Inmostcases,thecamismerelyaflatpieceofmetalthathasanunusualshapeorprofile(轮廓).Thecamisattachedtoashaft(轴)whichenableittobeturnedbyapplyingaturningactiontotheshaft.Asthecamrotates,itistheprofileorshapeofthecamthatcausesthefollowertomoveinaparticularway.Themovementofthefolloweristhentransmitted(传递)toanothermechanismoranotherpartofthemechanism.,AdvantagesofcammechanismsSimpleandcompact(简单、紧凑)thereonlythreelinks,cam(凸轮),follower(从动件),frame(机架).Sometimes,thereisaroller(滚子).Thefollowercanpreciselyrealizeanytypemotion.ExampleDisadvantagesofcammechanismsHigherpair(高副),linecontactorpointcontact(线或点接触)Canttransfer(传递)largepower.FunctionContinuousturningmotiontranslating(往复移动)oroscillating(摆动)motion.Example,Applicationofcammechanism,Camshaft（凸轮轴）ofanEngineincorporatingaRockerArm（摆臂）:Thediagramshownrightisatypicalcamandfollowersystemthatcouldbeusedinanengine.Thissystemincorporatesarockerarm.Inthiscasethemotionthatthecamimpartsonthefolloweristranslatedtothevalvethroughapushrodandtherockerarm.,Dobby多臂提花机,作者：潘存云教授,绕线机构,Yarnwindingmachine(绕线机),作者：潘存云教授,送料机构,Feedingmechanism送料机构,FeederofAutomaticMachineTools自动机床的进刀机构,园柱凸轮回转滚子带动推杆往复摆动刀架的进刀和退刀,机床进给机构,录音机卷带机构,织机开口机构,Classificationofcammechanism凸轮机构的分类,Bythecamshape(按凸轮形状分)Bythefollowershape(按从动件类型分)Bythefollowersmotiontype(按从动件运动形式分)Bythemannerofkeepingthecamandthefollowerincontact(按从动件与凸轮的锁合方式分),Edge,plateorfacecams盘状凸轮,Translatingcams移动凸轮,Cylindricalordrumcams圆柱凸轮,BythefollowerendsshapeKnife-edgefollower尖顶从动件,Theendofthefollowerisverysharp(nearlyapoint)ThecontactbetweenthecamandthefollowerisapointThefolloweriseasytobeworn.Itsrarelyused.,作者：潘存云教授,BythefollowerendsshapeDiskcamwithrollerfollower滚子从动件,Theendofthefollowerisaroller)LinecontactThefrictioncoefficientisverysmall(slidingfriction).Thistypeofrolleriswidelyused.,作者：潘存云教授,BythefollowerendsshapeDiskcamwithflatfollower平底从动件,ThefollowerendshapeisaflatplanThepressureangleofthemechanismalwaysis0,soitcantransmitlargepower.Butitisdifficulttodesignandmanufacture.,BythefollowersmotiontypeOscillatingfollower摆动从动件,BythefollowersmotiontypeTranslatingfollower移动从动件,4.BythemannerofkeepingthecamandfollowerincontactForce-closedcammechanism(力锁合),WithanexternaldownwardforceVs,Withoutanexternaldownwardforce,弹簧力锁合(springforceclosed),优点：只需要设计适当的轮廓曲线，从动件便可获得任意的运动规律，且结构简单、紧凑、设计方便。,缺点：线接触，容易磨损。,槽道凸轮Groovedcam,等径凸轮Constantradiuscam,r1+r2=const,优点：只需要设计适当的轮廓曲线，从动件便可获得任意的运动规律，且结构简单、紧凑、设计方便。,缺点：线接触，容易磨损。,等宽凸轮(constantwidthcam),等宽凸轮,优点：只需要设计适当的轮廓曲线，从动件便可获得任意的运动规律，且结构简单、紧凑、设计方便。,缺点：线接触，容易磨损。,共轭凸轮(Conjugatecam),主回凸轮,优点：只需要设计适当的轮廓曲线，从动件便可获得任意的运动规律，且结构简单、紧凑、设计方便。,缺点：线接触，容易磨损。,设计凸轮机构时的主要任务:1)Selectionofthecamtype选择凸轮类型,而根据工作要求选定推杆运动规律，是设计凸轮轮廓曲线的前提。,2)Selectionofthefollowersmotiontype选择从动件形式,3)Decisionofthestructuredimension设计结构尺寸,4)Designingthecamprofile设计凸轮轮廓,Thefollowersmotiontype从动件的运动规律,凸轮机构设计的基本任务:1)根据工作要求选定凸轮机构的形式;,名词术语：,一、推杆的常用运动规律,基圆、,推程运动角、,基圆半径、,推程、,远休止角、,回程运动角、,回程、,近休止角、,行程。一个循环,而根据工作要求选定推杆运动规律，是设计凸轮轮廓曲线的前提。,2)推杆运动规律;,3)合理确定结构尺寸;,4)设计轮廓曲线。,Thefollowersmotiontype从动件的运动规律,Flowersmotion:theflowersdisplacement(位移)S,velocityvandaccelerationaduringrise(升程)andreturn(回程):,S=S()v=v()a=a(),Thefollowersmotiontype从动件的运动规律,Uniformvelocity(等速运动规律)ConstantAccelerationMotion(等加速等减速运动规律)SimpleHarmonicMotion(简谐运动规律/余弦加速度运动规律)Combinedmotion(组合运动规律),Thefollowersmotiontype从动件的运动规律,Uniformvelocity(等速运动规律),Rigidshock刚性冲击,推程运动方程：sh/0,vh/0,v-h/0,a0,a0,回程运动方程：sh(1-/0),从动件作等速运动时，其位移线图为一过原点的倾斜直线。速度线图为一条水平直线，V0的大小为位移线图中倾斜直线的斜率。加速度为零。,此种运动规律只适用于低速运动的场合.,Constantacceleration/decelerationmotion(等加速等减速运动),减速段推程运动方程为：,sh-2h(0)2/20,v-4h(0-)/20,a-4h2/20,加速段推程运动方程为：,s2h2/20,v4h/20,a4h2/20,这种运动规律只适用于中速运动场合.,SimpleHarmonicMotion(余弦加速度),推程：sh1-cos(/0)/2,vhsin(/0)/20,a2h2cos(/0)/220,回程：sh1cos(/0)/2,v-hsin(/0)/20,a-2h2cos(/0)/220,在起始和终止处理论上a为有限值，产生柔性冲击。,Selectionoffollowermotion,1.机器的工作过程只要求凸轮转过一角度0时，推杆完成一行程h(直动推杆)或(摆动推杆)，对运动规律并无严格要求。则应选择直线或圆弧等易加工曲线作为凸轮的轮廓曲线。如夹紧凸轮。,2.机器的工作过程对推杆运动有要求，则应严格按工作要求的运动规律来设计凸轮廓线。如刀架进给凸轮。,Selectionoffollowermotion,理由：,amax,动量mv,若机构突然被卡住，