外文翻译---液压与气压系统.doc -- 5 元

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．