外文翻译---液压与气压系统.doc
HydraulicSystemThereareonlythreebasicmethodsoftransmittingpower:Electrical,mechanicalandfluidpowerMostapplicationsactuallyuseacombinationofthethreemethodstoobtainthemostefficientoverallsystemToproperlydeterminewhichprinciplemethodtouse。itisimportanttoknowthesalientfeaturesofeachtypeForexample,fluidsystemscalltransmitpowermoreeconomicallyOvergreaterdistancesthanCanmechanicaltypesHowever。fluidsystemsarerestrictedtoshorterdistancesthanareelectricalsystemsHydraulicpowertransmissionsystemaleconcernedwiththegeneration,modulation,andcontrolofpressureandflowand,andingeneralsuchsystemsinclude:1Pumpswhichconvertavailablepowerfromtheprimemovertohydraulicpowerattheactuator2Valveswhichcontrolthedirectionofpump-flow,thelevelofpowerproduced,andtheamountoffluid一一flowtotheactuatorsThepowerlevelisdeterminedbycontrollingboththeflowandpressurelevel3ActuatorswhichconverthydraulicpowertousablemechanicalpowerOutputatthepointrequired4Themedium,whichisaliquid,providesrigidtransmissionandcontrolaswellas1ubricationofcomponents,sealinginvalvesandcoolingofthesystem5Connectorswhichlinkthevarioussystemcomponents,providepowerconductorsforthefluidunderpressure,andfluidflowreturntotank(reservoir)6、Fluidstorageandconditioningequipmentwhichensuresufficientqualityandquantityaswellascoolingofthefluid7、pneumaticssystemsrequiredalubricatortoinject。averyfinemistofoilintotheairdischargingfromthepressureregulatorThispreventswearofthecloselyfittingmovingpartsofpneumaticHydraulicsystemsaleusedinindustrialapplicationssuchasstampingpresses,steelmills,andgeneralmanufacturing,agriculturalmachines,miningindustry,aviation,spacetechnology,deepseaexploration,transportation,marinetechnology,andoffshoregasandpetroleumexplorationInshort,veryfewpeoplegetthroughadayoftheir1iveswithoutsomehowbenefitingfromthetechnologyofhydraulics2Theprincipleofelectrical-dischargemachiningalsocalledelectroisorspark-erosionmachining,isbasedontheerosionofmetalsbysparkdischarges.Weknowthatwhentwocurrent-conductinwiresareallowedtotoucheachother,anarcisproduced.Ifwelookcloselyatthepointofcontactbetweenthetwowires,wenotethatasmallportionofthemetalhasbeenerodedaway,leavingasmallcrater.ThebasicEDMsystemconsistsofashapetoolandtheworkpiece,connectedtoadcpowersupplyandplacedinadielectricfluidthisisoneofthemostwidelyusedmachiningprocesses,particularlyfordie-sinkingoperationswhenthepotentialdifferencebetweenthetoolandtheworkpieceissufficientlyhigh,atransientsparkdischargesthroughthefluid,removingaverysmallamountofmetalfromtheworkpiecesurface.Thecapacitordischargeisrepeatedatratesofbetween50,withvoltagesusuallyrangingbetween50vand380vandcurrentsfrom0.1Ato500A.Mechanicalcontrolincludescamsandgovernors.Althoughtheyhavebeenusedforthecontrolofverycomplexmachines,tobecosteffectively,todaytheyareusedforsimpleandfixed-cycletaskcontrol.Someautomatedmachines,suchasscrewmachines,stillusecam-basedcontrol.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,itisimpossibletoobtainprecisecontrolledactuatorvelocitieswithpneumaticsystemsalso,precisepositioningcontrolisnotobtainableWhilepneumaticpressuresarequitesofaristogood.Thisisanimportantpieceofinformationfortheoperatorwhenmaching,sinceanyvalueintheabsolutepositionisdirectlyrelatedtothepart.ThesecretofhydraulicsystemsSUCCESSandwidespreaduseisitsversatilityandmanageabilityFluidpowerisnothinderedbythegeometryoperationswhenthepotentialdifferencebetweenthetoolandtheworkpieceissufficientlyhigh,atransientsparkdischargesthroughthefluid,removingaverysmallamountofmetalfromtheworkpieceofthemachineasistheeaseinmechanicalsystemsAlso,powercanbetransmittedinalmostlimitlessquantitiesbecausefluidsystemsarenotsolimitedbythephysical1imitationsofmaterialsasaretheelectricalsystemsForexample,theperformanceofanelectromagnetislimitedbyThesaturationlimitofsteelOntheotherhand,thepowerlimitoffluidsystemsis1imitedonlybythestrengthcapacityofthematerialIntheexpresstherelativetooldistancefromthehomeposition.Thisdistanceisshownintherelativeorincrementalcoordinates,UandW.whenreadingthevaluesinthenotpossibletoknowdirectlyhowfarthetoolisfromthepartorigin.Justhowfaritisfromthehomeposition.Thesignofthecoordinatesiszeroornegativebecausethetoolcannotmovefartherthanthemachineorigin.thusatpresent,thevaluesarezerosothetoolisatthehomeposition.Thevaluesinthearenormallyusedwhensettingupthetoolsinordertofindtherealtooldistancesfromthepartorigin.IndustryisgoingtodependmoreandmoreonautomationinordertoincreaseproductivityThisincludesremoteanddirectcontrolofproductionoperations,manufacturingprocesses。andmaterialshandlingFluidpoweristhemuscleofautomationbecauseofadvantagesinthefollowingfourmajorcategories1Easeandaccuracyofcontr01BytheuseofSimpleleversandpushbuttons,theoperatorofafluidpowersystemCallreadilystart,stop,speeduporslowdown,andpositionforceswhichprovideanydesiredhorsepowerWithtolerancesaspreciseasonetenthousandthOfaninchFig131showsafluidpowersystemwhichallowsallaircraftpilottoraiseandlowerhislandinggearWhenthepilotmovesasmallcontr01valveinonedirection,oilunderpressureflowstooneendofthecylindertolowerthelandinggearToretractthelandinggear,thepilotmovesthevalveleverintheoppositedirection,a110wlng0iltoflowintotheotherendofthecylinder2MultiplicationofforceAfluidpowersystem(withoutusingcumbersomegears,pulleys,andlevers)CanmultiplyforcesSimplyandefficientlyfromafractionofanouncetoseveralhundredtonsofoutput3ConstantforceortorqueOnlyfluidpowersystemsarecapableofprovidingconstantforceortorqueregardlessofspeedchangesThisisaccomplishedwhethertheworkoutputmovesafewinchesperhour,severalhundredinchesperminute,afewrevolutionsperhourorthousandsofrevolutionsperminute4Simplicity,safety,economygeneral,fluidpowersystemsusefewermovingpartsthancomparablemechanicalorelectricalsystemsThus,theyalesimplertomaintainandoperateThis,inturn,maximizessafety,compactness,andreliabilityForexample,anewpowersteeringcontr01designedhasmadeallotherkindsofpowersystemsobsoleteonmanyoffhighwayvehiclesTheSteeringunitconsistsofamanuallyoperateddirectionalcontrolvalveandmeterinasinglebodytransportation,marinetechnology,andoffshoregasandpetroleumexplorationInshort,veryfewpeoplegetthroughadayoftheir1iveswithoutsomehowbenefitingfromthetechnologyofhydraulics2Becausethesteeringunitisfullyfluid1inked,mechanicallinkages,universaljoints。bearings,reductiongears,etcareeliminatedThisprovidesasimple,compactsystemInaddition,verylittleinputtorqueisrequiredtoproducethecontrolneededforthetoughestapplicationsThisisimportantwhere1imitationsofcontrolspacerequireasmallsteeringwheelanditbecomesnecessarytoreduceoperatorfatigue