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1、Chapter2MechanismandMachineOneofthefundamentalconcernsindesigningamachineisitsmechanismforachievingadesiredmotion.Thetaskofreconstructiondesignoflostancientmachinesismainlythedesignofmechanisms.Thischapterpre-sentsthedefinitionsofmechanismsandmachines,
2、thecharacteristicsofmechanicalmembersandjoints,thedefinitionsofkinematiclinkchains,theconceptofconstrainedmotion,theidentificationofthetopologicalstructureofmechanisms,andtheprocessofmechanismandmachinedesign[1,2].2.1DefinitionsAmechanismisanassemblyof
3、mechanicalmembersconnectedbyjoints,andthesemembersaresoformedandconnectedsuchthattheytransmitconstrainedmotionsbymovinguponeachother.Four-barlinkagesusedinvariousapplicationsfortransmittingmotionsaretypicalexamplesofmechanisms.Figure2.1(a)showsafour-ba
4、rlinkageforguidinganauto-mobilehood,andFigure2.1(b)showsafour-barlinkage,namedinancientChinathejiechi,fordrawingparallellines.(a)(b)Figure2.1Applicationsoffour-barlinkages1920Chapter2MechanismandMachineAmachineisapieceofequipment,mechanicalinnature,des
5、ignedforproducinganeffectiveworkoutputorforconservingmechanicalenergy.Ingeneral,itconsistsofoneormoremechanisms,hasacertaintypeofpowerinput,andhasanadequatecontrolsysteminordertoserveaspecialpurposeorperformaspecialfunction.Typicalmachinesareworkingma-
6、chineswhichconvertmechanicalenergytoeffectiveworkoutputs,suchasmachinetools,forklifts,generators,andcompressors.Figure2.2showsamodernverticalmachiningcenteranditsautomatictoolchanger.Primemoverslikeinternalcombustionengines,steamengines,turbines,andele
7、ctricalmotorsarealsomachineswhichtransformotherformsofenergy(suchaswind,heat,water,electricity,andsoon)tomechanicalenergyasthedrivingpowerofworkingmachines.Figure2.3showsajet-enginetur-bineforacommercialaircraft.Machinesshouldhavesuitablecontrollingdev
8、ices,suchashumanpowercontrol,hydrauliccontrol,pneumaticcontrol,electricalcontrol,electroniccontrol,andcomputercontrolforeffectivelyproducingtherequiredmotionandwork.Figure2.4showsahand-operatedpaddlemachineusedinancientChina[3].Itisamac
