电梯毕业设计外文翻译--电梯安全.doc -- 5 元

ELEVATORSAFETYGIVETHEMINERABRAKEABSTRACTOverafiveyearperiod,therewereatleast18documentedcasesofascendingelevatorsstrikingtheoverhead.Insomecases,theaccidentsresultedinseriousinjuriesorfatalities.Theseaccidentsoccurredoncounterweightedelevatorsasaresultofelectrical,mechanical,andstructuralfailures.Elevatorcarsarefittedwithsafetiesthatgriptheguiderailsandstopafallingcarhowever,thesedevicesdonotprovideprotectionintheupwarddirection.Rulesandregulationsapplyingtoelevatorsafetyhavecomeunderreviewinresponsetotheseaccidents.Somegoverningauthoritieshavealreadyrevisedtheirregulationstorequireascendingcaroverspeedprotection.Thispaperwilldiscussbasicelevatordesign,hazards,regulations,andemergencybrakingsystemsdesignedtoprovideascendingcaroverspeedprotection.Inaddition,acasestudyreportonapneumaticropebrakesysteminstalledandtestedonamineelevatorwillbediscussed.INTRODUCTIONElevatorsincorporateseveralsafetyfeaturestopreventthecarfromcrashingintothebottomoftheshaft.Safetiesinstalledonthecarcanpreventthistypeofaccidentfromoccurringwhenthemachinebrakefailsorthewireropessuspendingthecarbreak.However,theinherentdesignofthesafetiesrendertheminoperativeintheascendingdirection.Intheupwarddirection,themachinebrakeisrequiredtostopthecageIrvhenanemergencyconditionoccurs.Undernormaloperation,themachinebrakeservesonlyasaparkingbrakedtoholdthecageatrest.However,whenanemergencyconditionisdetected,modernelevatorcontrolsystemdesignsrelysolelyonthemachinebraketostopthecar.IntheUnitedStatesminingindustry,theaccidenthistoryhasproventhatthisisnotthebestcontrolstrategy2,3.Theseaccidentsoccurredwhentheretardingeffortofthedrivemotorwasdefeatedwhenthemechanicalbrakeswereinoperative.Thisallowedthecounterweighttofalltothebottomoftheshaft,causingthecartooverspeedandstriketheheadframe.Thehighspeedelevatorcrashesintotheoverheadstructurecausedextensivemechanicaldamageandpotentiallyfatalinjuries.ELEVATORDESIGNAbasicunderstandingofelevatoroperationisrequiredinordertoassessthesafetyhazardspresentanddeterminetheaccidentpreventmethodsavailable.Figure1showsacompleteviewofamineelevator.Fig.1MicoElevatorInatypicalelevator,theearisraisedandloeredbysixtoeightmotor–drivenwireropesthatareattachedtothetopofthecaratoneend,travelaroundapairofsheaves,andareagainattachedtoacounterweightattheotherend.Thecounterweightaddsacceleratingforcewhentheelevatorcarisascendingandprovidesaretardingeffortwhenthecarisdescendingsothatlessmotorhorsepowerisrequired.Thecounterweightisacollectionofmetalweightsthatisequaltotheweightofthecarcontainingabout45ofitsratedload.AsetofchainsareloopedfromthebottomofthecounterweighttotheundersideofthecartohelpmaintainbalancebyoffsettingtheweightofthesuspensionropesGuiderailsthatrunthelengthoftheshaftkeepthecarandcounterweightfromswayingSUSPENSIONriCPCSortwistingduringtheirtravel.Rollersareattachedtothecarandthecounterweighttoprovidesmoothtravelalongtheguiderails.Thetractiontoraiseandlowerthecarcomesfromthefrictionofthewireropesagainstthegroovedsheaves.Themainsheaveisdrivenbyanelectricmotor.MotorgeneratorMGsetstypicallyprovidetodcpowerforthedrivemotor.Newersystemsuseastaticdrivecontrol.Theelevatorcontrolsvarythemotorsspeedbasedonasetoffeedbacksignalsthatindicatethecarspositionintheshaftway.Asthecarapproachesitsdestination,aswitchnearthelandingsignalsthecontrolstostopthecaratfloorlevel.Additionalshaftwaylimitswitchesareinstalledtomonitorovertravelconditions.Theworstfearoflitanypassengersisthattheelevatorwillgooutofcontrolandfallthroughspaceuntilitsmashesintothebottomoftheshaft.Thereareseveralsafetyfeaturesinmodernelevatorstopreventthisfromoccurring.Thefirstisthehighstrengthwireropesthemselves.Each0.625indiameterextrahighstrengthwireropecansupport32,000lb,orabouttwicetheaverageweightofamineelevatorfilledwith20passengers.Forsafetyssakeandtoreducewear,eachcarhassixtoeightofthesecables.Inaddition,elevatorshavebuffersinstalledattheshaftbottomthatcanstopthecarwithoutkillingitspassengersiftheyarestruckatthenormalspeedoftheelevatorAspreviouslydiscussed,modernelevatorshaveseveralspeedcontrolfeatures.Iftheydonotwork,thecontrolswilldisconnectthemotorandapplythemachinebrake.Finally,theelevatoritselfisequippedwithsafetiesmountedunderneaththecar.Ifthecarsurpassestheratedspeedby15to25,thegovernorwilltrip,andthesafetieswillgriptheguiderailsandstopthecar.Thiswastheinventionthatmadeelevatortransportationacceptableforthegeneralpublic.SAFETYHAZARDSAhistoricalperspectiveofelevatordevelopmentcanaccountfortodaysproblemswithelevatorsafetyrulesandregulations4.Inthebeginningofmodernelevatorhistory,itwasrealizedthatalthoughtherewereseveralfactorsofsafetyinthesuspensionropedesign,thequalityofconstructionandperiodicinspectioncouldnotbeassured.Therefore,theelevatorcarwasequippedwithreliablestandbysafetiesthatwouldstopthecarsafelyifthesuspensionropesfailed.In1853,Elisha.Otis,aNewYorkmechanic,designedanddemonstratedaninstantaneoussafetycapableofsafelystoppingafree–fallingcar.Thisaddressedthehazardshowninfigure2.Lateron,itwasrealizedthatpassengersmaybeinjuredwhenthecaroverspeedsinthedowndirectionwithsuspensionropesintact,asshowninfigure3.Topreventthishazard,anoverspeedgovernorwithgraduallyappliedsafetieswasdeveloped.Itdetectedtheoverpeelingconditionandactivatedthesafeties.