电梯毕业设计 外文翻译Word文件下载.docx
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电梯毕业设计 外文翻译Word文件下载.docx
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hazards,regulations,andemergencybrakingsystemsdesignedtoprovideascendingcar
overspeedprotection.Inaddition,acase-studyreportonapneumaticropebrakesystem
installedandtestedonamineelevatorwillbediscussed.
INTRODUCTION
Elevatorsincorporateseveralsafetyfeaturestopreventthecarfromcrashingintothe
bottomoftheshaft.Safetiesinstalledonthecarcanpreventthistypeofaccidentfrom
occurringwhenthemachinebrakefailsorthewireropessuspendingthecarbreak.
However,theinherentdesignofthesafetiesrendertheminoperativeintheascending
direction.
Intheupwarddirection,themachinebrakeisrequiredtostopthecageIrvhenan
emergencyconditionoccurs.Undernormaloperation,themachinebrakeservesonlyasa
parkingbrakedtoholdthecageatrest.However,whenanemergencyconditionisdetected,
modernelevatorcontrolsystemdesignsrelysolelyonthemachinebraketostopthecar.
IntheUnitedStatesminingindustry,theaccidenthistoryhasproventhatthisisnotthe
bestcontrolstrategy[2],[3].Theseaccidentsoccurredwhentheretardingeffortofthedrive
motorwasdefeatedwhenthemechanicalbrakeswereinoperative.Thisallowedthe
counterweighttofalltothebottomoftheshaft,causingthecartooverspeedandstrikethe
headframe.Thehigh-speedelevatorcrashesintotheoverheadstructurecausedextensive
mechanicaldamageandpotentiallyfatalinjuries.
ELEVATORDESIGN
Abasicunderstandingofelevatoroperationisrequiredinordertoassessthesafety
hazardspresentanddeterminetheaccidentpreventmethodsavailable.Figure1showsa
completeviewofamineelevator.
Fig.1MicoElevator
drivenwireropes–Inatypicalelevator,theearisraisedandloeredbysixtoeightmotorthatareattachedtothetopofthecaratoneend,travelaroundapairofsheaves,andareagain
attachedtoacounterweightattheotherend.
Thecounterweightaddsacceleratingforcewhentheelevatorcarisascendingand
providesaretardingeffortwhenthecarisdescendingsothatlessmotorhorsepoweris
required.Thecounterweightisacollectionofmetalweightsthatisequaltotheweightofthe
carcontainingabout45%ofitsratedload.Asetofchainsareloopedfromthebottomofthe
counterweighttotheundersideofthecartohelpmaintainbalancebyoffsettingthe
weightofthesuspensionropes
Guiderailsthatrunthelengthoftheshaftkeepthecarandcounterweightfromswaying
ortwistingduringtheirtravel.Rollersareattachedtothecarandthecounterweighttoprovide
smoothtravelalongtheguiderails.
Thetractiontoraiseandlowerthecarcomesfromthefrictionofthewireropesagainst
thegroovedsheaves.Themainsheaveisdrivenbyanelectricmotor.
Motor-generator(M-G)setstypicallypro-videtodcpowerforthedrivemotor.Newer
systemsuseastaticdrivecontrol.Theelevatorcontrolsvarythemotor'
sspeedbasedonaset
offeedbacksignalsthatindicatethecar'
spositionintheshaftway.Asthecarapproachesits
destination,aswitchnearthelandingsignalsthecontrolstostopthecaratfloorlevel.
Additionalshaftwaylimitswitchesareinstalledtomonitorovertravelconditions.
Theworstfearof'
litanypassengersisthattheelevatorwillgooutofcontrolandfall
throughspaceuntilitsmashesintothebottomoftheshaft.Thereareseveralsafetyfeaturesin
modernelevatorstopreventthisfromoccurring.Thefirstisthehigh-strengthwireropes
themselves.Each0.625-in-diameterextra-high-strengthwireropecansupport32,000lb,or
abouttwicetheaverageweightofamineelevatorfilledwith20passengers.Forsafety'
s
sakeandtoreducewear,eachcarhassixtoeightofthesecables.Inaddition,elevatorshave
buffersinstalledattheshaftbottomthatcanstopthecarwithoutkillingitspassengersifthey
arestruckatthenormalspeedoftheelevator
Aspreviouslydiscussed,modernelevatorshaveseveralspeedcontrolfeatures.Ifthey
donotwork,thecontrolswilldisconnectthemotorandapplythemachinebrake.Finally,the
elevatoritselfisequippedwithsafetiesmountedunderneaththecar.Ifthecarsurpassesthe
ratedspeedby15to25%,thegovernorwilltrip,andthesafetieswillgriptheguiderailsand
stopthecar.Thiswastheinventionthatmadeelevatortransportationacceptableforthe
generalpublic.
SAFETYHAZARDS
Ahistoricalperspectiveofelevatordevelopmentcanaccountfortoday'
sproblems
withelevatorsafetyrulesandregulations[4].Inthebeginningofmodernelevatorhistory,it
wasrealizedthatalthoughtherewereseveralfactorsofsafetyinthesuspensionropedesign,
thequalityofconstructionandperiodicinspectioncouldnotbeassured.Therefore,the
elevatorcarwasequippedwithreliablestandby'
safetiesthatwouldstopthecarsafelyifthe
suspensionropesfailed.In1853,Elisha.Otis,aNewYorkmechanic,designedand
demonstratedaninstantaneoussafetycapableofsafelystoppingafree–fallingcar.This
addressedthehazardshowninfigure2.
Lateron,itwasrealizedthatpassengersmaybeinjuredwhenthecaroverspeedsinthe
downdirectionwithsuspensionropesintact,asshowninfigure3.Topreventthishazard,an
o-verspeedgovernorwithgraduallyappliedsafetieswasdeveloped.Itdetectedtheover
peelingconditionandactivatedthesafeties.
Furthermore,itwasnoticedthatfrequentapplicationofsafeties
asafetysystem.Therefore,andoncausedmechanicalstresstheelevatorstructure
governoroverspeedswitchwasinstalledthatwouldtrytostopthecarbymachinebrake
beforethesafetiesactivated.Theswitchwasausefulideabecauseitcouldalsoinitiate
stoppinginthecaseofoverspeedingintheupdirectionaswell.
Theproblemstartedinthe1920'
swhentheAmericanElevatorSafetyCodewas
developed.Thewritersmostlikelylookedatthetechnologythatwasavailableatthattime
andsubsequentlyrequireditonallelevatorscoveredbytheCode.
Thewritersweresoconcentratedondescribingthedesignoftherequireddevicesthat
theyforgottoacknowledgethehazardsthatthedevicesareguardingagainstandtheelevator
componentsthatmayfail
andcausethehazards.Theydidnotconsiderthefactthatfor90%oftheelevatortrips,
theelevatorispartiallyloaded(i.e.lessthan45%ofratedload)[5].Therefore,ifabrake
failureoccurs,theelevatorwilloverspeedandcrashintheupdirectionasshowninfigure4
.
Fig.4CaroverspeedUP
Untilrecently,elevatorsafetysystemshavenotdifferedsignificantlyfromtheearly
1900'
sdesigns.Theproblemarisesbecauserulernakingcommitteesandregulatory
authoritiesarereluctanttorequirenewsafeguardswhenthetechnologyhasnotbeenfully
developed.Conversely,theelevatormanufacturingindustrycannotjustifytheproduct
developmentexpenseforanewsafetydevicewithlittlemarketability.Thisproblemwillbe
addressedinthefollowingsections
RULESANDREGULATIONS
Severalrulemakingcommitteesandgovernmentsafetyauthoritieshaveaddressedthe
deficienciesintheexistingelevatorregulationsandhaveproposedrevisionstotheelevator
safetycodes.
ThereportfromtheAmericanSocietyofMechanicalEngineers-A17Mechanical
DesignCommitteeonCarsascendingintothebuildingoverhead,-datedSeptember1987,
containedthetypesoffailuresthatcouldresultinelevatorsacceleratingintooverhead
structureandananalysisofthepossiblesolutions.Inaddition,aproposaltotheA17.1
CommitteeforanewcodeRule205.6wasintroducedasfollows:
Rule205.6(Preventionofoverspeedingcarfromstrikingtheoverheadstructure'
):
Alltractionelevatorsshallbeprovidedwithameanstopreventanascendingcarfrom
strikingtheoverheadstructure.Thisrneansshallconformtothefollowingrequirements:
1.Priortothetimewhenthecounterweightstrikesitsbuffer,itshallreducethespeedof
thecartothespeedforwhichthecounterweightbufferisdesigned.
2.Itshallnotdevelopanaverageretardationofthecarinexcessof32.2ft/s2(9.81m/s2)
duringthestoppingphase.
3.1tshallbeamechanicalmeansindependentofthedrivingmachinebrake.
4.1tshallpreventoverspeedingoftheelevatorsystemthroughthecontrolofoneor
moreofthefollowing
a.counterweight
b.car
c.suspensionorcompensatingropesystem.
Thisproposedruleiscurrentlyundercommitteereview,andconsiderationhasbeen
giventorequiringprotectiontopreventthecarfromleavingthelandingwiththedoors
openedorunlocked.
PennsylvaniaBureauofDeepMineSafety
AnascendingelevatorcaraccidentoccurredatawesternPennsylvaniacoalmineon
February4,1987andcausedextensivestructuraldamageanddisabledtheelevatorfortwo
months.Followingthisaccident,the
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