带式输送机驱动方式比较机械毕业设计外文翻译

带式输送机驱动方式比较--机械毕业设计外文翻译AComparisonofDriveStartingMechanismsforAggregateBeltConveyorsAbstractThepurposeofthispaperistodescribethetorque/speedcharacteristics，duringstartingconditions，ofthemostcommondrivesusedonbeltconveyorstoday.RequirementsofaBeltConveyorDriveAbeltconveyorisconsideredtobeaconstanttorquedevice.Inotherwords，therequireddrivingtorqueisapproximatelyconstantatvaryingspeedsseefigurel.otherapplications，suchasapumpdrive，havevariabletorquerequirementsseefigure2.However，toincreasethespeedofaconveyoradditionaltorquemustbeaddeduntilthedesiredspeedisobtained.Newton’sSecondLawofMotiongovernsthisrelationship.Themoststraightforwardexamplewouldbeaconstantaccelerationtorqueseefigure3.Inrealitytheaccelerationtorqueisrarelyconstant.However，staticcalculationmodelsasoutlinedintheConveyorEquipmentManufacturersAssociationhandbookCEMAmakethisassumption.Whenusingstaticmodelstheaverageaccelerationtorqueisestimatedovertheentireaccelerationtimeandassumedtobelinear.Dynamicmodels，whicharebeyondthescopeofthispaper，allowaccelerationtorquevaluestovaryinmagnitudeduringtheaccelerationordecelerationPeriod.Itshouldbenotedthat，givenaconstantload，alargeraccelerationtorqueresultsinafasteraccelerationtimeandalsohigherPeakbelttensions.Conversely，asmalleraccelerationtorqueresultsinalongerstarttimeandsmallerPeakbelttensions.Across-The-LineACMotorStartTechnicallythisisthesimplesttypeofdriveusedonabeltconveyor.InthisdrivetypeanACsquirrelcageinductionmotorisstartedbysimplythrowingthecontactorandenergizingthemotor.Theresultingoutputtorque，assumingthatratedvoltageismaintained，isstrictlyafunctionofthemotordesign.NEMAhasProvideddesignstandardsthatdefinetheoutputtorquecharacteristicsofthemostcommonlyused3Phasemotorsuptoapproximately250hpfigure4.Insizeslargerthan250hpmanufacturersgenerallyusetheNEMAdesigncodesinarelativemanneri.e.，NEMAChasagreaterlockedrotortorquethanaNEMABmotor.ThemostcriticallocationsontheACmotorspeed/torquecurvehavebeennamedfordefinitionpurposes.Thesecommonnamesareprovidedinfigure5.Themostrigorousmethodofdeterminingaverageaccelerationtorque，forstaticcalculations，istobreakthecurveintoseveralverticalsections，thensumtheindividualareasunderthecurveandfinallydividebythenumberofsections.Themorecommonwayistoapplythefollowingsimplifiedequation:Thesestaticapproximationmethodsworkformostbeltconveyorsbutcangetthedesignerintotroublefromtimetotime，especiallyonlongand/orsteepand/orfastconveyors.Oneitemthatneedstobeexaminedisbreakawaytorque.Justbecausethedriveprovidesenoughaveragetorquetoacceleratetheloaddoesn’tmeanthatitprovidesenoughtorquetobreakitawayfromzerospeedandgetitmoving.CEMAdefinesbreakawaytorqueastwicethetorquerequiredtoovercomethetotalfrictionplusthetorquerequiredtolifttheloadvertically.LockedrotortorqueLRTneedstobegreaterthanbreakawaytorque!AgoodstaticProgrammakesthischeck.Inadditiontoexaminingtheeffectthataveragetorquehasontheconveyorcomponentsthebeltdesignerneedstodeterminetheeffectofpeaktorque.ItisnotuncommonforthebreakdowntorqueBDTofaNEMACmotortobegreaterthan2.5timesfullloadtorqueFLT.GenerallythebeltingandPulleymanufacturersallowatransientoverloadof1.5timesfullloadoperatingload.Anacross-the-linestartcaneasilycausetensionstoexceedtheseimums.Thesehigherthannormalloadscanbedesignedintotheconveyoriftheyareknownupfront.Consideringonlyaveragestartingtorquecancausetheconveyordesignertoundersizethetake-upweight.Itisnotuncommonforconveyorswithacross-the-linestarterstoexperienceintermittentdriveslip.ThisgenerallyhappenswhenPeaktorqueBDTisinputbythedriveandthetake-uphasbeensizedforaveragetorquebutnotpeaktorque.Theresultcanbedevastating.Whenthedrivepulleyslipsduringthiscondition，thetensionontheTlandT2sideshighandlowofthedrivePulleytriestoequalize.Thiscansubjectalowtensionbendortake-uppulley，justbehindthedrivepulley，totensionsthatapproachTltension.ThesePulleysarerarely，ifever，designedforthisloadconditionandtheresultislowtensionPulleyfailure.Thisconditioniseasilydemonstratedwithdynamicanalysis.AnothercommonProblemwithacross-the-linestartsiscausedbyvoltagedipsduringstarting.Ifthepowerdistributionsystemisnotstiffenoughtohandlethehugeinrushcurrentsofanacross-the-1inestart，thestartingtorqueofthemotorscanbereducedtoaPointthattheconveyorwillnotstart.ThisisduetothefactthattheoutputtorqueofanACsquirrelcageinductionmotorisreducedbythesquareoftheappliedvoltage.Inotherwords，avoltagedropof10%wouldequatetoatorquereductionof19%.ReducedVoltageStartingThereducedvoltagestartingofanACsquirrelcageinductionmotorisdonefortwobasicreasons:1.ToreducetheinrushcurrentthatnaturallyoccurswhenamotorisStartedacross-the-1ine.Atypicalcurrent/speedgraphisshowninfigure6.Itisnotuncommonfortheinrushcurrenttobe6timesormorethanitisatfullloadtorque.Asstatedabovehighinrushcurrentscausethevoltageinapowerdistributionsystemtosag.Thecostofelectricalpowerdistributionequipmentcanbecomeveryhighifitneedstobedesignedtohandlethehighinrushcurrents.2.ToreducePeakmotortorqueduringstartingconditions，whichsubsequentlyincreasesaccelerationtime.ByreducingthePeaktorquestheconveyorcomponentscanbedesignedforlowertensionloads.Thisprimarilyincludesbelting，Pulleysandexternalsupportstructure.Thiscanresultinsignificantcostsavings.TwocommontypesofreducedvoltagestartersaretheCurrentLimitingandtheConstantTorquedevices.Graphsareincludedabovefigures7through8thatdepictthesamemotor/conveyorapplicationwithanAcross-The-Line，alimitdCurren,andaconstantTorquestart.Afterstudyingthegraphsitbecomesapparentthatthebestuseofthelimitedtorquestartistoprotectthepowerdistributionsystemfromhighinrushcurrents.TheconstanttorquestartreducesthehightorquePeaksandProtectstheconveyor’smechanicalcomponents.InbothcasestheStarttimeisincreasedbecausetheoverallmagnitudeofacceleratingtorqueisreduced.However，neithermethodwillmakeiteasiertostarta“hard-to-startconveyor.”Correctingahardstartingconveyorisnotareasontouseareducedvoltagestarter!翻译带式输送机驱动方式比较摘要本文的目的是描述最常见的机用输送皮带起动扭矩/转速特性带被认为是一个恒转矩装置换句话说所需驱动力矩大约是速度在不断变化见图1其他应用如泵有可变扭矩要求见2。但是,增加的速度输送额外的扭矩必须加上之前的速度获得牛顿第二运动定律规这种关系最简单的例子是一个恒定加速度力矩见3。现实的加速度转矩很少常数不过输送设备制造协会手册在静态计算模型这一假设当使用静态模型的平均加速度转矩估计整个加速时间,并假定为线性动态模型超出了本文件的范围在加速或减速允许加速度扭矩值不一应当指出,由于恒载荷大扭矩加速更快的加速时间也带的紧反过来说一个较小的加速度转矩一个较长的启动时间和较小的带张紧峰值在技术上这是带式输送机采用最简单的一种动了交流驱动鼠笼式异步电动机是由简单的电机假定额定电压,输出矩纯粹是电机设计的NEMA美国提供的设计标准确定输出扭矩特性,最常用的三相电机大约250马力图4。功率大于250马力厂商普遍使用NEMA美国设计规范一个相对的方式即NEMA电机比NEMA电