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1、Chapter5SynthesisofPlanarLinkages1.TheCharacteristicsofPlanarLinkages1)Alinkagehasasimplestructureanditiseasytomanufacture,soithasalowcost.2)Thepressureinalowerpairwithsurfacecontactislower,sothelinkagehasalargeloadcapacity.3)Alinkagecanachievevariousmotionsbydesigningitsdim
2、ensionsofthelinks.4)Alinkagecantransmitmotionwithinalongdistance.5)Itisdifficulttoperformprecisionmotion;thisisadisadvantageoflinkages.5.1CharacteristicsandTypesofPlanarLinkagesFig.5-1 Typesoffour-barlinkages(铰链四杆机构的类型)2.TypesofPlanarLinkagesFig.5-2 Typesoffour-barlinkageswi
3、thaslidingpair(含有一个移动副的四杆机构类型)(1)CrankrockerlinkageIfafourbarlinkageshowninFig5-1aisdesignedsothatlink1canrotatecontinuouslywhilelink3onlyoscillatesthroughanangle,itiscalledacrankrockerlinkage.(2)DoublecranklinkageBothlink2andlink4inFig5-1bcanrotatecontinuouslyrelativetothefr
4、ame1;thislinkageiscalledadoublecranklinkage.(3)DoublerockerlinkageBothlink2andlink4inFig5-1ccannotrotatecompletelyrelativetotheframe3;thislinkageiscalledadoublerockerlinkage.(4)ParallelcrankfourbarlinkageIfinafourbarlinkage,twooppositelinksareparallelandequalinlength,asshown
5、inFig5-1d,cranks2and4alwayshavethesameangularvelocity.Thismechanismiscalledaparallelcrankfourbarlinkage.Itiswidelyused,suchasinthecouplingoflocomotivewheels,inpantograph,etc.(5)IsoscelestrapeziumlinkageIftworockersofadoublerockerlinkageareequalinlength,seetheFig5-1e,thislinka
6、geiscalledanisoscelestrapeziumlinkage;itcanbeusedinthesteeringmechanisminautomobiles.(6)SlidercranklinkageThislinkageisshowninFig5-2a,inwhichsidelink1isacrank,andtheothersidelink3isaslider.TurningpairsAandBarefullturningpairs,andCisoscillatingturningpair.(7)Rotatingguidebarli
7、nkageIfboththesidelink2andsidelink4canrotatecompletely,thislinkageiscalledarotatingguidebarlinkageshowninFig5-2b,inwhichthecouplerbecomesasliderinshape.(8)RockingblocklinkageThecrankrotatescompletelywhiletheblockonlyoscillatesaboutitspivotcenterC,thislinkageiscalledrockblockl
8、inkageshowninFig5-2c.Itiswidelyusedinhydrauliccylindermechani
