翻譯部分英文原文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