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外文翻译---液压与气压系统.doc

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外文翻译---液压与气压系统.doc

HydraulicSystemThereareonlythreebasicmethodsoftransmittingpowerElectrical,mechanical.andfluidpower.Mostapplicationsactuallyuseacombinationofthethreemethodstoobtainthemostefficientoverallsystem.Toproperlydeterminewhichprinciplemethodtouse。itisimportanttoknowthesalientfeaturesofeachtype.Forexample,fluidsystemscalltransmitpowermoreeconomicallyOvergreaterdistancesthanCanmechanicaltypes.However。fluidsystemsarerestrictedtoshorterdistancesthanareelectricalsystems.Hydraulicpowertransmissionsystemaleconcernedwiththegeneration,modulation,andcontrolofpressureandflowand,andingeneralsuchsystemsinclude1.Pumpswhichconvertavailablepowerfromtheprimemovertohydraulicpowerattheactuator.2.Valveswhichcontrolthedirectionofpumpflow,thelevelofpowerproduced,andtheamountoffluid一一flowtotheactuators.Thepowerlevelisdeterminedbycontrollingboththeflowandpressurelevel.3.ActuatorswhichconverthydraulicpowertousablemechanicalpowerOutputatthepointrequired.4.Themedium,whichisaliquid,providesrigidtransmissionandcontrolaswellas1ubricationofcomponents,sealinginvalves.andcoolingofthesystem.5.Connectorswhichlinkthevarioussystemcomponents,providepowerconductorsforthefluidunderpressure,andfluidflowreturntotankreservoir..6、Fluidstorageandconditioningequipmentwhichensuresufficientqualityandquantityaswellascoolingofthefluid.7、pneumaticssystemsrequiredalubricatortoinject。averyfinemistofoilintotheairdischargingfromthepressureregulator.ThispreventswearofthecloselyfittingmovingpartsofpneumaticHydraulicsystemsaleusedinindustrialapplicationssuchasstampingpresses,steelmills,andgeneralmanufacturing,agriculturalmachines,miningindustry,aviation,spacetechnology,deepseaexploration,transportation,marinetechnology,andoffshoregasandpetroleumexploration.Inshort,veryfewpeoplegetthroughadayoftheir1iveswithoutsomehowbenefitingfromthetechnologyofhydraulics2.Theprincipleofelectricaldischargemachiningalsocalledelectroisorsparkerosionmachining,isbasedontheerosionofmetalsbysparkdischarges.Weknowthatwhentwocurrentconductinwiresareallowedtotoucheachother,anarcisproduced.Ifwelookcloselyatthepointofcontactbetweenthetwowires,wenotethatasmallportionofthemetalhasbeenerodedaway,leavingasmallcrater.ThebasicEDMsystemconsistsofashapetoolandtheworkpiece,connectedtoadcpowersupplyandplacedinadielectricfluidthisisoneofthemostwidelyusedmachiningprocesses,particularlyfordiesinkingoperationswhenthepotentialdifferencebetweenthetoolandtheworkpieceissufficientlyhigh,atransientsparkdischargesthroughthefluid,removingaverysmallamountofmetalfromtheworkpiecesurface.Thecapacitordischargeisrepeatedatratesofbetween50,withvoltagesusuallyrangingbetween50vand380vandcurrentsfrom0.1Ato500A.Mechanicalcontrolincludescamsandgovernors.Althoughtheyhavebeenusedforthecontrolofverycomplexmachines,tobecosteffectively,todaytheyareusedforsimpleandfixedcycletaskcontrol.Someautomatedmachines,suchasscrewmachines,stillusecambasedcontrol.Mechanicalcontrolisdifficulttomanufactureandissubjecttowear.Pneumaticcontrolisstillverypopularforcertainapplications.Itusescompressedair,valves,andswitchstoconstructsimplecontrollogic,butiseasilyslow.Becausestandardcompaonentsareusedtoconstructthelogic,itiseasiertobuildthanamechanicalcontrol.Pneumaticcontrolpartsaresubjecttowear.Asdoesamechanicalcontrol,anelectromechanicalcontrolusesswitches,relays,timescounters,andsoon,toconstructlogic,itisfasterandmoreflexible.Thecontrollersusingelectromechanicalcontrolarecalledrelaydevices.Thevaluesintheexpresstherelativetooldistancefromthehomeposition.Thisdistanceisshownintherelativeorincrementalcoordinates,UandW.whenreadingthevaluesinthenotpossibletoknowdirectlyhowfarthetoolisfromthepartorigin.Justhowfaritisfromthehomeposition.mountedonexhaustportsofairvalvesandactuatorstoreducenoiseandpreventoperatingpersonnelfrompossibleinjuryresultingnotonlyfromexposuretonoisebutalsofromhighspeedairborneparticles.Thesignofthecoordinatesiszeroornegativebecausethetoolcannotmovefartherthanthemachineorigin.thusatpresent,thevaluesarezerosothetoolisatthehomeposition.Thevaluesinthearenormallyusedwhensettingupthetoolsinordertofindtherealtooldistancesfromthepartorigin.Thevaluesintheabsolutepositionexpresstheabsolutetooldistancefromthepartorigin.Thisdistanceisshowninshowninabsolutecoordinates,xandz.thesignmaybepositiveornegative,dependingonthequadrantsinwhichthetoolismoving.becauseofthecompressibilityofair,itisimpossibletoobtainprecisecontrolledactuatorvelocitieswithpneumaticsystems.also,precisepositioningcontrolisnotobtainable.Whilepneumaticpressuresarequitesofaristogood.Thisisanimportantpieceofinformationfortheoperatorwhenmaching,sinceanyvalueintheabsolutepositionisdirectlyrelatedtothepart.ThesecretofhydraulicsystemsSUCCESSandwidespreaduseisitsversatilityandmanageability.Fluidpowerisnothinderedbythegeometryoperationswhenthepotentialdifferencebetweenthetoolandtheworkpieceissufficientlyhigh,atransientsparkdischargesthroughthefluid,removingaverysmallamountofmetalfromtheworkpieceofthemachineasistheeaseinmechanicalsystems.Also,powercanbetransmittedinalmostlimitlessquantitiesbecausefluidsystemsarenotsolimitedbythephysical1imitationsofmaterialsasaretheelectricalsystems.Forexample,theperformanceofanelectromagnetislimitedbyThesaturationlimitofsteel.Ontheotherhand,thepowerlimitoffluidsystemsis1imitedonlybythestrengthcapacityofthematerial.Intheexpresstherelativetooldistancefromthehomeposition.Thisdistanceisshownintherelativeorincrementalcoordinates,UandW.whenreadingthevaluesinthenotpossibletoknowdirectlyhowfarthetoolisfromthepartorigin.Justhowfaritisfromthehomeposition.Thesignofthecoordinatesiszeroornegativebecausethetoolcannotmovefartherthanthemachineorigin.thusatpresent,thevaluesarezerosothetoolisatthehomeposition.Thevaluesinthearenormallyusedwhensettingupthetoolsinordertofindtherealtooldistancesfromthepartorigin.Industryisgoingtodependmoreandmoreonautomationinordertoincreaseproductivity.Thisincludesremoteanddirectcontrolofproductionoperations,manufacturingprocesses。andmaterialshandling.Fluidpoweristhemuscleofautomationbecauseofadvantagesinthefollowingfourmajorcategories.1.Easeandaccuracyofcontr01.BytheuseofSimpleleversandpushbuttons,theoperatorofafluidpowersystemCallreadilystart,stop,speeduporslowdown,andpositionforceswhichprovideanydesiredhorsepowerWithtolerancesaspreciseasonetenthousandthOfaninch.Fig.131showsafluidpowersystemwhichallowsallaircraftpilottoraiseandlowerhislandinggear.Whenthepilotmovesasmallcontr01valveinonedirection,oilunderpressureflowstooneendofthecylindertolowerthelandinggear.Toretractthelandinggear,thepilotmovesthevalveleverintheoppositedirection,a110wlng0iltoflowintotheotherendofthecylinder.2.Multiplicationofforce.Afluidpowersystemwithoutusingcumbersomegears,pulleys,andleversCanmultiplyforcesSimplyandefficientlyfromafractionofanouncetoseveralhundredtonsofoutput.3.Constantforceortorque.Onlyfluidpowersystemsarecapableofprovidingconstantforceortorqueregardlessofspeedchanges.Thisisaccomplishedwhethertheworkoutputmovesafewinchesperhour,severalhundredinchesperminute,afewrevolutionsperhour.orthousandsofrevolutionsperminute.4.Simplicity,safety,economy.general,fluidpowersystemsusefewermovingpartsthancomparablemechanicalorelectricalsystems.Thus,theyalesimplertomaintainandoperate.This,inturn,maximizessafety,compactness,andreliability.Forexample,anewpowersteeringcontr01designedhasmadeallotherkindsofpowersystemsobsoleteonmanyoffhighwayvehicles.TheSteeringunitconsistsofamanuallyoperateddirectionalcontrolvalveandmeterinasinglebody.transportation,marinetechnology,andoffshoregasandpetroleumexploration.Inshort,veryfewpeoplegetthroughadayoftheir1iveswithoutsomehowbenefitingfromthetechnologyofhydraulics2.Becausethesteeringunitisfullyfluid1inked,mechanicallinkages,universaljoints。bearings,reductiongears,etc.areeliminated.Thisprovidesasimple,compactsystem.Inaddition,verylittleinputtorqueisrequiredtoproducethecontrolneededforthetoughestapplications.Thisisimportantwhere1imitationsofcontrolspacerequireasmallsteeringwheelanditbecomesnecessarytoreduceoperatorfatigue.

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