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，theyalesimplertomainta