机械专业外文翻译(中英文翻译) (1)Word文档下载推荐.doc

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英文原文

BeltConveyingSystemsDevelopmentofdrivingsystem

Amongthemethodsofmaterialconveyingemployed，beltconveyorsplayaveryimportantpartinthereliablecarryingofmaterialoverlongdistancesatcompetitivecost．Conveyorsystemshavebecomelargerandmorecomplexanddrivesystemshavealsobeengoingthroughaprocessofevolutionandwillcontinuetodoso．Nowadays，biggerbeltsrequiremorepowerandhavebroughttheneedforlargerindividualdrivesaswellasmultipledrivessuchas3drivesof750kWforonebelt（thisisthecasefortheconveyordrivesinChengzhuangMine）．Theabilitytocontroldriveaccelerationtorqueiscriticaltobeltconveyors’performance．Anefficientdrivesystemshouldbeabletoprovidesmooth，softstartswhilemaintainingbelttensionswithinthespecifiedsafelimits．Forloadsharingonmultipledrives．torqueandspeedcontrolarealsoimportantconsiderationsinthedrivesystem’sdesign.Duetotheadvancesinconveyordrivecontroltechnology，atpresentmanymorereliable．Cost-effectiveandperformance-drivenconveyordrivesystemscoveringawiderangeofpowerareavailableforcustomers’choices[1].

1Analysisonconveyordrivetechnologies

1．1Directdrives

Full-voltagestarters．Withafull-voltagestarterdesign，theconveyorheadshaftisdirect-coupledtothemotorthroughthegeardrive．Directfull-voltagestartersareadequateforrelativelylow-power,simple-profileconveyors．Withdirectfu11-voltagestarters．nocontrolisprovidedforvariousconveyorloadsand．dependingontheratiobetweenfu11-andno-1oadpowerrequirements，emptystartingtimescanbethreeorfourtimesfasterthanfullload．Themaintenance-freestartingsystemissimple，low-costandveryreliable．However,theycannotcontrolstartingtorqueandmaximumstalltorque；

therefore．theyarelimitedtothelow-power,simple-profileconveyorbeltdrives．

Reduced-voltagestarters．Asconveyorpowerrequirementsincrease，controllingtheappliedmotortorqueduringtheaccelerationperiodbecomesincreasinglyimportant．Becausemotortorque1safunctionofvoltage，motorvoltagemustbecontrolled．Thiscanbeachievedthroughreduced-voltagestartersbyemployingasiliconcontrolledrectifier（SCR）．AcommonstartingmethodwithSCRreduced-voltagestartersistoapplylowvoltageinitiallytotakeupconveyorbeltslack．andthentoapplyatimedlinearrampuptofullvoltageandbeltspeed．However,thisstartingmethodwillnotproduceconstantconveyorbeltacceleration．Whenaccelerationiscomplete．theSCRs,whichcontroltheappliedvoltagetotheelectricmotor．arelockedinfullconduction,providingfu11-linevoltagetothemotor．Motorswithhighertorqueandpull—uptorque，canprovidebetterstartingtorquewhencombinedwiththeSCRstarters,whichareavailableinsizesupto750KW．

Woundrotorinductionmotors．WoundrotorinductionmotorsareconnecteddirectlytothedrivesystemreducerandareamodifiedconfigurationofastandardACinductionmotor．Byinsertingresistanceinserieswiththemotor’srotorwindings．themodifiedmotorcontrolsystemcontrolsmotortorque．Forconveyorstarting，resistanceisplacedinserieswiththerotorforlowinitialtorque．Astheconveyoraccelerates，theresistanceisreducedslowlytomaintainaconstantaccelerationtorque．Onmultiple-drivesystems．anexternalslipresistormaybeleftinserieswiththerotorwindingstoaidinloadsharing．Themotorsystemshavearelativelysimpledesign．However,thecontrolsystemsforthesecanbehighlycomplex，becausetheyarebasedoncomputercontroloftheresistanceswitching．Today，themajorityofcontrolsystemsarecustomdesignedtomeetaconveyorsystem’sparticularspecifications．Woundrotormotorsareappropriateforsystemsrequiringmorethan400kW．

DCmotor．DCmotors．availablefromafractionofthousandsofkW，aredesignedtodeliverconstanttorquebelowbasespeedandconstantkWabovebasespeedtothemaximumallowablerevolutionsperminute（r/min）．withthemajorityofconveyordrives,aDCshuntwoundmotorisused．Whereinthemotor’srotatingarmatureisconnectedexternally．ThemostcommontechnologyforcontrollingDCdrivesisaSCRdevice．whichallowsforcontinualvariable-speedoperation．TheDCdrivesystemismechanicallysimple,butcanincludecomplexcustom-designedelectronicstomonitorandcontrolthecompletesystem．Thissystemoptionisexpensiveincomparisontoothersoft-startsystems．butitisareliable,cost-effectivedriveinapplicationsinwhichtorque,1oadsharingandvariablespeedareprimaryconsiderations．DCmotorsgenerallyareusedwithhigher-powerconveyors，includingcomplexprofileconveyorswithmultiple-drivesystems，boostertrippersystemsneedingbelttensioncontrolandconveyorsrequiringawidevariable-speedrange．

1．2Hydrokineticcoupling

Hydrokineticcouplings，commonlyreferredtoasfluidcouplings．arecomposedofthreebasicelements;

thedrivenimpeller,whichactsasacentrifugalpump；

thedrivinghydraulicturbineknownastherunnerandacasingthatenclosesthetwopowercomponents．Hydraulicfluidispumpedfromthedrivenimpellertothedrivingrunner,producingtorqueatthedrivenshaft．Becausecirculatinghydraulicfluidproducesthetorqueandspeed，nomechanicalconnectionisrequiredbetweenthedrivinganddrivenshafts．Thepowerproducedbythiscouplingisbasedonthecirculatedfluid’samountanddensityandthetorqueinproportiontoinputspeed．Becausethepumpingactionwithinthefluidcouplingdependsoncentrifugalforces．theoutputspeedislessthantheinputspeed．Referredtoasslip．thisnormallyisbetweenl%and3%．BasichydrokineticcouplingsareavailableinconfigurationsfromfractionaltoseveralthousandkW．

Fixed-fillfluidcouplings．Fixed-fillfluidcouplingsarethemostcommonlyusedsoft-startdevicesforconveyorswithsimplerbeltprofilesandlimitedconvex/concavesections．Theyarerelativelysimple,1ow-cost,reliable,maintenancefreedevicesthatprovideexcellentsoftstartingresultstothemajorityofbeltconveyorsinusetoday．

Variable-filldraincouplings．Drainable-fluidcouplingsworkonthesameprincipleasfixed-fillcouplings．Thecoupling’simpellersaremountedontheACmotorandtherunnersonthedrivenreducerhigh-speedshaft．Housingmountedtothedrivebaseenclosestheworkingcircuit．Thecoupling’srotatingcasingcontainsbleed-offorificesthatcontinuallyallowfluidtoexittheworkingcircuitintoaseparatehydraulicreservoir．Oilfromthereservoirispumpedthroughaheatexchangertoasolenoid-operatedhydraulicvalvethatcontrolsthefillingofthefluidcoupling．Tocontrolthestartingtorqueofasingle-driveconveyorsystem，theACmotorcurrentmustbemonitoredtoprovidefeedbacktothesolenoidcontrolvalve．Variablefilldraincouplingsareusedinmediumtohigh-kWconveyorsystemsandareavailableinsizesuptothousandsofkW．Thedrivescanbemechanicallycomplexanddependingonthecontrolparameters．thesystemcanbeelectronicallyintricate．Thedrivesystemcostismediumtohigh,dependinguponsizespecified．

Hydrokineticscoopcontroldrive．Thescoopcontrolfluidcouplingconsistsofthethreestandardfluidcouplingcomponents：

adrivenimpeller,adrivingrunnerandacasingthatenclosestheworkingcircuit．Thecasingisfittedwithfixedorificesthatbleedapredeterminedamountoffluidintoareservoir．Whenthescooptubeisfullyextendedintothereservoir,thecouplingisl00percentfilled．Thescooptube,extendingoutsidethefluidcoupling，ispositionedusinganelectricactuatortoengagethetubefromthefullyretractedtothefullyengagedposition．Thiscontrolprovidesreasonablysmoothaccelerationrates．tobutthecomputer-basedcontrolsystemisverycomplex．Scoopcontrolcouplingsareappliedonconveyorsrequiringsingleormultipledrivesfroml50kWto750kW.

1．3Variable-frequencycontrol（VFC）

Variablefrequencycontrolisalsooneofthedirectdrivemethods．Theemphasizingdiscussionaboutithereisbecausethatithassouniquecharacteristicandsogoodperformancecomparedwithotherdrivingmethodsforbeltconveyor．VFCdevicesProvidevariablefrequencyandvoltagetotheinductionmotor,resultinginanexcellentstartingtorqueandaccelerationrateforbeltconveyordrives．VFCdrives．availablefromfractionaltoseveralthousand（kW）,areelectroniccontrollersthatrectifyAClinepowertoDCand，throughaninverter,convertDCbacktoACwithfrequencyandvoltagecontro1．VFCdrivesadoptvectorcontrolordirecttorquecontrol（DTC）technology，andcanadoptdifferentoperatingspeedsaccordingtodifferentloads．VFCdrivescanmakestartingorstallingaccordingtoanygivenS-curves．realizingtheautomatictrackforstartingorstallingcurves．VFCdrivesprovideexcellentspeedandtorquecontrolforstartingconveyorbelts．andcanalsobedesignedtoprovideloadsharingformultipledrives．easilyVFCcontrollersarefrequentlyinstalledonlower-poweredconveyordrives，butwhenusedattherangeofmedium-highvoltageinthepast．thestructureofVFCcontrollersbecomesverycomplicatedduetothelimitationofvoltageratingofpowersemiconductordevices，thecombinationofmedium-highvoltagedrivesandvariablespeedisoftensolvedwithlow-voltageinvertersusingstep-uptransformerattheoutput，orwithmultiplelow-voltageinvertersconnectedinseries．Three-levelvoltage-fedPWMconvertersystemsarerecentlyshowingincreasingpopularityformulti-megawattindustrialdriveapplicationsbecauseofeasyvoltagesharingbetweentheseriesdevicesandimprovedharmonicqualityattheoutputcomparedtotwo-levelconvertersystemsWithsimpleseriesconnectionofdevices．ThiskindofVFCsystemwiththree750kW/2．3kVinverters