机械专业外文翻译(中英文翻译)

第1页外文翻译英文原文BeltConveyingSystemsDevelopmentofdrivingsystemAmongthemethodsofmaterialconveyingemployed，beltconveyorsplayaveryimportantpartinthereliablecarryingofmaterialoverlongdistancesatcompetitivecost．Conveyorsystemshavebecomelargerandmorecomplexanddrivesystemshavealsobeengoingthroughaprocessofevolutionandwillcontinuetodoso．Nowadays，biggerbeltsrequiremorepowerandhavebroughttheneedforlargerindividualdrivesaswellasmultipledrivessuchas3drivesof750kWforonebelt(thisisthecasefortheconveyordrivesinChengzhuangMine)．Theabilitytocontroldriveaccelerationtorqueiscriticaltobeltconveyors’performance．Anefficientdrivesystemshouldbeabletoprovidesmooth，softstartswhilemaintainingbelttensionswithinthespecifiedsafelimits．Forloadsharingonmultipledrives．torqueandspeedcontrolarealsoimportantconsiderationsinthedrivesystem’sdesign.Duetotheadvancesinconveyordrivecontroltechnology，atpresentmanymorereliable．Cost-effectiveandperformance-drivenconveyordrivesystemscoveringawiderangeofpowerareavailableforcustomers’choices[1].1Analysisonconveyordrivetechnologies1．1DirectdrivesFull-voltagestarters．Withafull-voltagestarterdesign，theconveyorheadshaftisdirect-coupledtothemotorthroughthegeardrive．Directfull-voltagestartersareadequateforrelativelylow-power,simple-profileconveyors．Withdirectfu11-voltagestarters．nocontrolisprovidedforvariousconveyorloadsand．dependingontheratiobetweenfu11-andno-1oadpowerrequirements，emptystartingtimescanbethreeorfourtimesfasterthanfullload．Themaintenance-freestartingsystemissimple，low-costandveryreliable．However,theycannotcontrolstartingtorqueandmaximumstalltorque；therefore．theyare第2页limitedtothelow-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’srotatingarmatureis第3页connectedexternally．ThemostcommontechnologyforcontrollingDCdrivesisaSCRdevice．whichallowsforcontinualvariable-speedoperation．TheDCdrivesystemismechanicallysimple,butcanincludecomplexcustom-designedelectronicstomonitorandcontrolthecompletesystem．Thissystemoptionisexpensiveincomparisontoothersoft-startsystems．butitisareliable,cost-effectivedriveinapplicationsinwhichtorque,1oadsharingandvariablespeedareprimaryconsiderations．DCmotorsgenerallyareusedwithhigher-powerconveyors，includingcomplexprofileconveyorswithmultiple-drivesystems，boostertrippersystemsneedingbelttensioncontrolandconveyorsrequiringawidevariable-speedrange．1．2HydrokineticcouplingHydrokineticcouplings，commonlyreferredtoasfluidcouplings．arecomposedofthreebasicelements;thedrivenimpeller,whichactsasacentrifugalpump；thedrivinghydraulicturbineknownastherunnerandacasingthatenclosesthetwopowercomponents．Hydraulicfluidispumpedfromthedrivenimpellertothedrivingrunner,producingtorqueatthedrivenshaft．Becausecirculatinghydraulicfluidproducesthetorqueandspeed，nomechanicalconnectionisrequiredbetweenthedrivinganddrivenshafts．Thepowerproducedbythiscouplingisbasedonthecirculatedfluid’samountanddensityandthetorqueinproportiontoinputspeed．Becausethepumpingactionwithinthefluidcouplingdependsoncentrifugalforces．theoutputspeedislessthantheinputspeed．Referredtoasslip．thisnormallyisbetweenl%and3%．Basichydrokineticcouplingsareavailableinconfigura