毕业设计电梯外文翻译Word格式文档下载.docx

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Overafive-yearperiod,therewereatleast18documentedcasesofascendingelevatorsstrikingtheoverhead.Insomecases,theaccidentsresultedinseriousinjuriesorfatalities.Theseaccidentsoccurredoncounterweightedelevatorsasaresultofelectrical,mechanical,andstructuralfailures.Elevatorcarsarefittedwithsafetiesthatgriptheguiderailsandstopafallingcar;

however,thesedevicesdonotprovideprotectionintheuowarddirection.

Rulesandregulatioinsapplyingtoelevatorsafetyhavecomeunderreviewinresponsetotheseaccidents.Somegoverningauthoritieshavealreadyrevisedtheirregulationstorequireascendingcaroverspeedprotection.thispaperwilldiscussbasicelevatondesign,hazard,regulation,andemergencybrakingsystemsdesignedtoprovideascendingcaroverspeedprotection.Inaddition,acase-studyreportonapneumaticropebrakesysteminstalledandtestedonamineelevatorwillbediscussed.

INTRODUCTION

Elevatorsincorporateseveralsafetyfeaturestopreventthecarfromcrashingintothebottomoftheshaft.safetiesinstalledonthecarcanpreventthistypeofaccidentformoccurringwhenthemachinebrakefailsorthewireropessuspendingthecarbreak.However,theinherentdesignofthesafetiesrendertheminoperativeintheascendingdirection.

Intheupwarddirection,themachinebrakeisrequiredtostopthecagewhenanemergencyconditionoccurs.Undernormaloperation,themachinebrakeservesonlyasaparkingbrakedtoholdthecageatrest.However,whenanemergencyconditionisdetected,modernelevatorcontrolsystemdesignsrelysolelyonthemachinebraketostopthecar.

IntheUnitedStatesminingindustry,theaccidenthistoryhasproventhatthisisnotthebestcontrolstrategy[2],[3].Theseaccidentsoccurredwhentheretardingeffortofthedrivemotorwasdefeatedwhenthemechanicalbrakewereinoperative.Thisallowedthecounterweighttofalltothebottomoftheshaft,causingthecartooverspeedandstriketheheadframe.Thehigh-speedelevatorcrashesintotheoverheadstructurecausedextensivemechanicaldamageandpotentiallyfatalinjuries.

ELEVATORDESIGN

Abasicunderstandingofelevatoroprationisrequiredinordertoassessthesafetyhazardspresentanddeterminetheaccidentpreventmethodsavailable.Figure1showsacompleteviewofamineelevator.

Inatypicalelevator,thecarisraisedandloweredbysixtoeightmotor-drivenwireropesthatareattachedtothetopofthecaratoneend,travelaroundapairofsheaves,andareagainattachedtoacounterweightattheotherend.

Thecounterweightaddsacceleratingforcewhentheelevatorcarisascendingandprovidesaretardingeffortwhenthecarisdescendingsothatlessmotorhorsepowerisrequired.Thecounterweightisacollectionofmetalweightsthatisequaltotheweigheofthecarcontainingabout45%ofitsratedload.Asetofchainsareloopedfromthebottomofthecounterweighttotheundersideofthecartohelpmaintainbalancebyoffsettingtheweightofthesuspensionropes.

Guiderailsthatrunthelengthoftheshaftkeepthecarandcounterweightfromswayingortwistingduringtheirtravel.Rollersareattachedtothecarandthecounterweighttoprovidesmoothtravelalongtheguiderails

Thetractiontorasieandlowerthecarcomesfromthefrictionofthewireropeagainstthegroovedsheaves.Themainsheaveisdrivenbyanelectricmotor.

Mostelevatorsuseadirectcurrentmotorbecauseitsspeedcanbepreciselycontrolledtoallowsmoothaccelerationanddeceleration.Motor-generator（M-G）setstypicallyprovidetodopowerforthedrivemotor.Newersystemsuseastaticdrivecontrol.Theelevatorcontrolsvarythemotor’sspeedbasedonasetoffeedbacksignalsthatindicatethecar’spositionintheshaftway.Asthecarapproachesitsdestination,aswitchnearthelandingsignalsthecontrolstostopthecaratfloorlevel.Additionalshaftwaylimitswitchesareinstalledtomonitorovertravelconditions.

Theworstfearofmanypassengersisthattheelevatorwillgooutofcontrolandfallthroughspaceuntilitsmashesintothebottomoftheshaft.Thereareseveralsafetyfeatureinmodernelevatorstopreventthisfromoccurring.

Thefirstisthehigh-strengthwireropesthemselves.Each0.625-in-diameterextra-high-strengthwireropecansupport32,0001b,orabouttwicetheaverageweightofamineelevatorfilledwith20passengers.Forsafety’ssakeandtoreducewear,eachcarhassixtoeightofthesecables.Inaddition,elevatorshavebuffersintstalledattheshaftbottomthatcanstopthecarwithoutkillingitspassengersiftheyarestruckatthenormalspeedoftheelevator.

Aspreviouslydiscussed,modernelevatorshaveseveralspeedcontrolfeatures.Iftheydonotwork,thecontrolswilldisconnectthemotorandapplythemachinebrake.Finally,theelevatoritselfisequippedwithsafetiesmountedunderneaththecar.Ifthecarsurpassestheratedspeedby15to16%,thegovernorwilltrip,andthesafetieswillgriptheguiderailsandstopthecar.Thiswastheinventionthatmadeelevatortransportationacceptableforthegeneralpublic.

SAFETYHAZARDS

Ahistoricalperspectiveofelevatordevelopmentcanaccountfortoday’sproblemswithelevatorsafetyrulesandregulations[4].Inthebeginningofmodernelevatorhistory,itwasrealizedthatalthoughtherewereseveralfactorsofsafetyinthesuspensionropedesign,thequalityofconstructionandperiodicinspectioncouldnotbeassured.Therefore,theelevatorcaiwasequippedwithreliablestandby”safeties”thatwouldstopthecarsafelyifthesuspensionropefailed.In1853,ElishaOtis,aNewYorkmechanic,desingnedanddemonstratedaninstantaneoussafetycapableofsafelystoppingafree-fallingcar.Thisaddressedthehazardshowninfigure2.

Lateron,itwasrealizedthatpassengersmaybeinjuredwhenthecaroverspeedsinthedowndirectionwithsuspensionropesintact,asshowninfigure3.Topreventthishazard,anoverspeedgovernorwithgraduallyappliedsafetieswasdeveloped.Itdetectedtheoverspeedingconditionandactivatedthesafeties.

Furthermore,itwasnoticedthatfrequentapplicationofsafetiescausedmechanicalstressontheelevatorstructureandsafetysystem.Therefore,agovernoroverspeedswitchwasinstalledthatwouldtrytostopthecarbymachinebrakebeforethesafetiesactivated.Theswitchwasausefulideabecauseitcouldalsoinitiatestoppinginthecaseofoverspeedingintheupdirectionaswell.

Theproblemstartedinthe1920’swhentheAmericanElevatorSafetyCodewasdeveloped.ThewritersmostlikelylooledatthetechnologythatwasavailableatthattimeandsubsequentlyrequireditonallelevatorscoveredbytheCode.

Thewritersweresoconcentratedondescribingthedesignoftherequireddevicesthattheyforgottoacknowledgethehazards’thatthedevicesareguardingagainstandtheelevatorcomponentsthatmayfailandcausethehazards.Theydidnotconsiderthefactthatfor90%oftheelevatortrips,theelevatorispartiallyloaded（i.e.lessthan45%ofratedload）[5].Therefore,ifabrakefailureoccurs,theelevatorwilloverspeedandcrashintheupdirectionasshowninfigure4.

Untilrecently,elevatorsafetysystemshavenotdifferedsignificantlyfromtheearly1990’sdesigns.Theproblemarisesbecauserulemakingcommitteesandregulatoryauthoritiesarereluctanttorequirenewsafeguardswhenthetechnologyhasnotbeenfullydeveloped.Conversely,theelevatormanufacturingindustrycannotjustifytheproductdevelopmentexpenseforanewsafetydevicewithlittlemarketability.Thisproblemwillbeaddressedinthefollowingsections.

RULESANDREGULATIONS

Severalrulemakingcommitteesandgovernmentsafetyauthoritieshaveaddressedthedeficienciesintheexistingelevatorregulationsandhaveproposedrevisionstotheelevatorsafetycodes.

Thereport-formtheAmericanSocietyofMechanicalEngineers-A17MechanicalDesignCommitteeon“Carsascendingintothebuildingoverhead”-datedSeptember1987,containedthetypeoffailuresthatcouldresultinelevatorsacceleratingintooverheadstructureandananalysisofthepossiblesolutions.Inaddition,aproposaltotheA17.1CommitteeforanewcodeRule205.6wasintroducedasfollows:

R205.6（“Preventionofoverspeedingcarfromstrikingtheoverheadstructure”）:

Alltractionelevarorsshallbeprovidedwithameanstopreventanascendingcarfromstrikingtheoverheadstructure.Thismeansshallconformtothefollowingrequirements:

1.Priortothetimewhenthecounterweighestrikesitsbuffer,itshallreducethespeedofthecartothespeedforwhichthecounterweightbufferisdesigned.

2.Itshallnotdevelopanaverageretardationofthecarinexcessof32.2ft/s2（9.81m/s2）duringthestoppingphase.

3.Itshallbeamechanicalmeansindependentofthedrivingmachinebrake.

4.Itshallpreventoverspeedingoftheelevatorsystemthroughthecontrolofoneormoreofthefollowing:

a.counterweight

b.car

c.suspensionorcompensatingropesystem.

Thisproposedruleiscurrentlyundercommitteereview,andcondiderationhasbeengiventorequiringprotectiontopreventthecarfromleavingthelandingwiththedoorsopenedorunlocked.

PennsyIvaniaBureauofDeepMineSafety

AnascendingelevatorcaraccidentoccurredatawesternPennsylvaniacoalmineonFebruary4,1987andcausedextensivestructuraldamageanddisabletheelevatorfortwomonths.Followingthisaccident,thePennsylvaniaBureauofDeepMineSafetyestablishedanadvisorycommitteetodeterminethesedevicesthatareavailableoprovideascendingcaroverspeedprotectionfornewandexistingmineelevatorinstallations.

Thefollowingfourpreotectivemethodsweredeterminedtobefeasiblebase