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1、Chapter9IntroductionofScrews,HooksCouplingsandIntermittentMechanismsFig9-1ashowsascrewmechanismwhichconsistsofscrew1,nut2andframe3,inwhichthepairsA,BandCarescrewpair,turningpairandprismaticpairrespectively.Supposetheleadofscrewisl,andwhenthescrewrotatesanangl
2、e,thedistancemovedbythenutisasfollows:Fig.9-1 Screwmechanisms(螺旋机构)1—Screw(螺杆)2—Nut(螺母)3—Frame(机架)A—Screwpair(螺旋副)B—Turningpair(转动副)C—Slidingpair(移动副)D—Screwpair(螺旋副)9.1ScrewMechanismsFig.9-2 Rollerscrewmechanism(滚珠丝杠传动机构)Accordingtothefrictionpropertybetween
3、thethreadandnut,thescrewscanbeclassifiedasslidingscrewsandrollingscrews.Squarethreadandacmethreadareusedtoscrewsbywhichpoweristobetransmitted.Fig9-2showsarollingscrewinwhichrollersarelocatedbetweenthethreadsofthescrewandnut.Itiscalledasarollerscrewmechanismwhi
4、chhashighefficiencyandlonglifeanditisusedwidelyasapowerscrew.Fig.9-3 Singleuniversaljoint(单万向联轴器)9.2UniversalJoints1.SingleUniversalJointFig9-3ashowsasingleuniversaljointwhichconsistsofthedrivingyoke,drivenyokeandcrosspiecewhichconnectsthetwoyokes.Theaxesofth
5、edrivingshaftanddrivenshaftintersectatpointOwhichistherotatingcenterofthecrosspiece,andtheacuteanglebetweenthetwoshaftsisdenotedasα.Althoughbothshaftsmustcompletearevolutioninthesamelengthoftime,theangularvelocityratiooftheshaftsisnotaconstantduringtherevoluti
6、on,butvariesasafunctionoftheanglesαandφ1.AsshaftsIandⅡrotate,thepointAandBdescribetwocirclesshowninFig9-3b.2.DoubleUniversalJointsTohavethesameangularvelocitiesoftheinputshaftⅠandoutputshaftⅡ,thefollowingconditionsmustbesatisfied.1)ThedrivingshaftⅠ,drivenshaf
7、tⅡandtheintermediateshaftⅢmustlieinthesameplane.2)Thetwoyokesoftheintermediateshaftmustlieinthesameplane.3)Theanglebetweenthedrivingshaftandintermediateshaftmustbeequaltotheanglebetweenthedrivenshaftandtheintermediateshaft.Fig.9-4 Doubleuniversaljoints(双万向联
8、轴器)9.3RatchetMechanismsFig9-5showsaratchetmechanismwhichconsistsofdrivingrock1,ratchetwheel3,pawls2、4andspring5.Asthedrivingrock1ismadetooscillatecounterclockwiseaboutthecenterofth
