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翻译部分英文原文BeltConveyingSystemsDevelopmentofdrivingsystemAmongthemethodsofmaterialconveyingemployed,beltconveyorsplayaveryimportantpartinthereliablecarryingofmaterialoverlongdistancesatcompetitivecostConveyorsystemshavebecomelargerandmorecomplexanddrivesystemshavealsobeengoingthroughaprocessofevolutionandwillcontinuetodosoNowadays,biggerbeltsrequiremorepowerandhavebroughttheneedforlargerindividualdrivesaswellasmultipledrivessuchas3drivesof750kWforonebelt(thisisthecasefortheconveyordrivesinChengzhuangMine)TheabilitytocontroldriveaccelerationtorqueiscriticaltobeltconveyorsperformanceAnefficientdrivesystemshouldbeabletoprovidesmooth,softstartswhilemaintainingbelttensionswithinthespecifiedsafelimitsForloadsharingonmultipledrivestorqueandspeedcontrolarealsoimportantconsiderationsinthedrivesystemsdesign.Duetotheadvancesinconveyordrivecontroltechnology,atpresentmanymorereliableCost-effectiveandperformance-drivenconveyordrivesystemscoveringawiderangeofpowerareavailableforcustomerschoices1.1Analysisonconveyordrivetechnologies11DirectdrivesFull-voltagestartersWithafull-voltagestarterdesign,theconveyorheadshaftisdirect-coupledtothemotorthroughthegeardriveDirectfull-voltagestartersareadequateforrelativelylow-power,simple-profileconveyorsWithdirectfu11-voltagestartersnocontrolisprovidedforvariousconveyorloadsanddependingontheratiobetweenfu11-andno-1oadpowerrequirements,emptystartingtimescanbethreeorfourtimesfasterthanfullloadThemaintenance-freestartingsystemissimple,low-costandveryreliableHowever,theycannotcontrolstartingtorqueandmaximumstalltorque;thereforetheyarelimitedtothelow-power,simple-profileconveyorbeltdrivesReduced-voltagestartersAsconveyorpowerrequirementsincrease,controllingtheappliedmotortorqueduringtheaccelerationperiodbecomesincreasinglyimportantBecausemotortorque1safunctionofvoltage,motorvoltagemustbecontrolledThiscanbeachievedthroughreduced-voltagestartersbyemployingasiliconcontrolledrectifier(SCR)AcommonstartingmethodwithSCRreduced-voltagestartersistoapplylowvoltageinitiallytotakeupconveyorbeltslackandthentoapplyatimedlinearrampuptofullvoltageandbeltspeedHowever,thisstartingmethodwillnotproduceconstantconveyorbeltaccelerationWhenaccelerationiscompletetheSCRs,whichcontroltheappliedvoltagetotheelectricmotorarelockedinfullconduction,providingfu11-linevoltagetothemotorMotorswithhighertorqueandpulluptorque,canprovidebetterstartingtorquewhencombinedwiththeSCRstarters,whichareavailableinsizesupto750KWWoundrotorinductionmotorsWoundrotorinductionmotorsareconnecteddirectlytothedrivesystemreducerandareamodifiedconfigurationofastandardACinductionmotorByinsertingresistanceinserieswiththemotorsrotorwindingsthemodifiedmotorcontrolsystemcontrolsmotortorqueForconveyorstarting,resistanceisplacedinserieswiththerotorforlowinitialtorqueAstheconveyoraccelerates,theresistanceisreducedslowlytomaintainaconstantaccelerationtorqueOnmultiple-drivesystemsanexternalslipresistormaybeleftinserieswiththerotorwindingstoaidinloadsharingThemotorsystemshavearelativelysimpledesignHowever,thecontrolsystemsforthesecanbehighlycomplex,becausetheyarebasedoncomputercontroloftheresistanceswitchingToday,themajorityofcontrolsystemsarecustomdesignedtomeetaconveyorsystemsparticularspecificationsWoundrotormotorsareappropriateforsystemsrequiringmorethan400kWDCmotorDCmotorsavailablefromafractionofthousandsofkW,aredesignedtodeliverconstanttorquebelowbasespeedandconstantkWabovebasespeedtothemaximumallowablerevolutionsperminute(r/min)withthemajorityofconveyordrives,aDCshuntwoundmotorisusedWhereinthemotorsrotatingarmatureisconnectedexternallyThemostcommontechnologyforcontrollingDCdrivesisaSCRdevicewhichallowsforcontinualvariable-speedoperationTheDCdrivesystemismechanicallysimple,butcanincludecomplexcustom-designedelectronicstomonitorandcontrolthecompletesystemThissystemoptionisexpensiveincomparisontoothersoft-startsystemsbutitisareliable,cost-effectivedriveinapplicationsinwhichtorque,1oadsharingandvariablespeedareprimaryconsiderationsDCmotorsgenerallyareusedwithhigher-powerconveyors,includingcomplexprofileconveyorswithmultiple-drivesystems,boostertrippersystemsneedingbelttensioncontrolandconveyorsrequiringawidevariable-speedrange12HydrokineticcouplingHydrokineticcouplings,commonlyreferredtoasfluidcouplingsarecomposedofthreebasicelements;thedrivenimpeller,whichactsasacentrifugalpump;thedrivinghydraulicturbineknownastherunnerandacasingthatenclosesthetwopowercomponentsHydraulicfluidispumpedfromthedrivenimpellertothedrivingrunner,producingtorqueatthedrivenshaftBecausecirculatinghydraulicfluidproducesthetorqueandspeed,nomechanicalconnectionisrequiredbetweenthedrivinganddrivenshaftsThepowerproducedbythiscouplingisbasedonthecirculatedfluidsamountanddensityandthetorqueinproportiontoinputspeedBecausethepumpingactionwithinthefluidcouplingdependsoncentrifugalforcestheoutputspeedislessthantheinputspeedReferredtoasslipthisnormallyisbetweenl%and3%BasichydrokineticcouplingsareavailableinconfigurationsfromfractionaltoseveralthousandkWFixed-fillfluidcouplingsFixed-fillfluidcouplingsarethemostcommonlyusedsoft-startdevicesforconveyorswithsimplerbeltprofilesandlimitedconvex/concavesectionsTheyarerelativelysimple,1ow-cost,reliable,maintenancefreedevicesthatprovideexcellentsoftstartingresultstothemajorityofbeltconveyorsinusetodayVariable-filldraincouplingsDrainable-fluidcouplingsworkonthesameprincipleasfixed-fillcouplingsThecouplingsimpellersaremountedontheACmotorandtherunnersonthedrivenreducerhigh-speedshaftHousingmountedtothedrivebaseenclosestheworkingcircuitThecouplingsrotatingcasingcontainsbleed-offorificesthatcontinuallyallowfluidtoexittheworkingcircuitintoaseparatehydraulicreservoirOilfromthereservoirispumpedthroughaheatexchangertoasolenoid-operatedhydraulicvalvethatcontrolsthefilling
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