外文翻译中英文翻译电力绞车的控制.docx

外文翻译中英文翻译电力绞车的控制.docx

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外文翻译中英文翻译电力绞车的控制

外文翻译、中英文翻译——电力绞车的控制

英文原文

ElectricalWinchControls

byTomYoung

Theformofmotorcontrolweallknowbestisthesimplemanualstationwithupanddownpushbuttons.Whilethesestationsmaystillbetheperfectchoiceforcertainapplications，adizzyingarrayofmoresophisticatedcontrolsisalsoavailable.Thisarticleaddressesthebasicelectricalrequirementsofthemotorsanduserinterfaceissuesyouwillneedtoaddressbeforespcifying，buildingorbuyingwinchcontrols.

beginwith，themanualcontrolstationsshouldbeofthehold-to-runtype，sothatifyoutakeyourfingeroffofthebuttonthewinchstops.Additionally，everycontrolstationneedsanemergencystopE-stopthatkillsallpowertothewinch，notjustthecontrolcircuit.Thinkaboutit―ifthewinchisn’tstoppingwhenitshould，youreallyneedafailsafewaytokillthelinepower.It’salsoagreatideatohaveakeyoperatedswitchoncontrolstations，especiallywhereaccesstothestationsisnotcontrolled.

Safeoperationbyauthorizedpersonnelmustbeconsideredwhendesigningeventhesimplestmanualcontrols.

ControllingFixedSpeedMotors

Theactualcontrollingdeviceforafixedspeedwinchisathreephasereversingstarter.ThemotorisreversedbysimplyswitchingthephasesequencefromABCtoCBA.Thisisaccomplishedbytwothree-polecontactors，interlocked，sotheycan’tbothbeclosedatthesametime.TheNECrequiresbothoverloadandshortcircuitprotection.Toprotectthemotorfromoverheatingduetomechanicaloverloadsathermaloverloadrelayisbuiltintothestarter.Thishasbi-metallicstripsthatmatchtheheatingpatternofthemotorandtripscontactswhentheyoverheat.Alternatively，athermistorcanbemountedinthemotorwindingtomonitorthemotortemperature.Shortcircuitprotectionisgenerallyprovidedbyfusesratedforusewithmotors.

Aseparatelinecontactorshouldbeprovidedaheadofthereversingcontactorforredundancy.Thiscontactoriscontrolledbythesafetycircuits:

E-stopandovertravel　limits.

Thisbringsustolimitswitches.Whenyougettothenormalendoftravellimitthewinchstopsandyoucanonlymoveitintheoppositedirectionawayfromthelimit.Therealsoneedstobeanovertravellimitincase，duetoanelectricalormechanicalproblem，thewinchrunspastthenormallimit.Ifyouhitanovertravellimitthelinecontactoropenssothereisnowaytodriveoffof

thelimits.Ifthisoccurs，acompetenttechnicianneedstofixtheproblemthatresultedinhittingtheovertravellimit.Then，youcanoverridetheovertravelsusingthespringreturntoggleswitchinsidethestarter―asopposedtousingjumpersorhandshootingthecontactors.

VariableSpeedRequirements

Ofcourse，thesimplefixedspeedstartergetsreplacedwithavariablespeeddrive.Here’swherethingsstarttogetinteresting!

Attheveryleastyouneedtoaddaspeedpottothecontrolstation.Ajoystickisabetteroperatorinterface，asitgivesyouamoreintuitivecontrolofthemovingpiece.

Unfortunately，youcan’tjustorderanyoldvariablespeeddrivefromyourlocalsupplierandexpectittoraiseandlowerequipmentsafelyandreliablyoverkidsonstage.Mostvariablespeeddriveswon’t，astheyaren’tdesignedforlifting.Thedriveneedstobesetupsothattorqueisdevelopedatthemotorbeforethebrakeisreleased，andwhenstoppingthebrakeissetbeforetorqueistakenaway.

FormanyyearsDCmotorsanddrivesprovidedapopularsolutionastheyallowedforgoodtorqueatallspeeds.ThelargeDCmotorsrequiredformostwinchesareexpensive，costingmanytimeswhatacomparableACmotorcosts.However，theearlyACdriveswerenotveryuseful，astheyhadaverylimitedspeedrangeandproducedlowtorqueatlowspeeds.Morerecently，astheACdrivesimproved，thelowcostandplentifulavailabilityofACmotorsresultedinatransitiontoACdrives.

TherearetwofamiliesofvariablespeedACdrives.Variablefrequencyinvertersarewellknownandreadilyavailable.ThesedrivesconvertACtoDC，thenconvertit

backtoACwithadifferentfrequency.Ifthedriveproduces30Hz，anormal60Hzmotorwillrunathalfspeed.Intheorythisisgreat，butinrealitythereareacoupleofproblems.First，atypical60Hzmotorgetsconfusedatalinefrequencybelow2or3Hz，andstartstocogjerkandsputter，orjuststops.Thislimitsyoutoaspeedrangeofaslowas20:

1―hardlysuitableforsubtleeffectsonstage!

Second，manylowercostinvertersarealsoincapableofprovidingfulltorqueatlowspeeds.Employingsuchdrivescanresultinjerkymoves，oracompletefailuretoliftthepiece―exactlywhatyoudon’twanttoseewhenyouaretryingtostartsmoothlyliftingascenicelement.Someofthenewerinvertersareclosedloopobtainfeedbackfromthemotortoprovidemoreaccuratespeedcontrolandwillworkquitewell.

TheotherfamilyofACdrivesisfluxvectordrives.Theseunitsrequireanencodermountedonthemotorshaftallowingthedrivetopreciselymonitortherotationofthearmature.Aprocessordeterminestheexactvectorofmagneticfluxthusfluxvectordriverequiredtorotatethearmaturethenextfewdegreesatagivenspeed.Thesedrivesallowaninfinitespeedrange，asyoucanactuallyproducefulltorqueatzerospeed.Theprecisespeedandpositioncontrolofferedbythesedrivesmakethemafavoriteinhighperformanceapplications.

PLC-basedcontrolsprovidesystemstatusaswellascontroloptions.ThisscreengivetheoperatorfullaccesstoCarnegieHall’sninestagefloorlifts.

PLCBasedSystems

APLCisaprogrammablelogiccontroller.Firstdevelopedtoreplacetherelaybasedindustrialcontrolsystemsofthe’50sand’60s，thesecontrolsareathomeinrugged，industrialenvironments.ThesearemodularsystemswithagreatvarietyofI/Omodulesallowingsemi-customhardwareconfigurationstobeassembledeasilyatareasonableprice.Theseincludepositioncontrolmodules，counters，A/DandD/Aconvertersandallsortsofsolidstateorhardcontactclosureoutputs.ThegreatvarietyofI/OcomponentsandthemodularnatureofthePLCmakethisaneffectivewaytobuildcustomandsemi-customcontrolsystems.

ThegreatestdrawbacktoPLCsystemsisthelackofreallygreatdisplaystotellyouwhattheyaredoingortohelpyouprogramthem.Monochromeandmediumresolutioncolordisplaysarethenorm，astheprimaryuseforthesecomponentsinonafactoryfloor.

OneofthefirstmajorPLCsystemsusedinalargeentertainmentvenueisthecomplexliftandwagonsystemattheoriginalMGMGrandnowBally’sinLasVegas.SeveralmanufacturersofferstandardPLC-basedsystemsandahostofsemi-customacousticbanner，shell，andliftcontrolsystemsisalsoavailable.TheabilitytobuildcustomsystemsfromstandardbuildingblocksisthegreateststrengthofPLC-basedcontrols.

HighEndControllers

Themostsophisticatedriggingcontrollersgowellbeyondspeed，time，andpositioncontrol.Theyincludetheabilitytowritecomplexcues，recordprofiledmoves，andmanagemultiplecuesrunningatonce.

Manyofthelargeroperahousesaremovingtowardpointhoistsystems，wherethereisaseparatewinchforeachliftlinetheriggingequivalentofdimmerpercircuit.Whenmultiplewinchesareusedtocarryasinglepiece，thewinchesmustbeperfectlysynchronized，ortheloadcanshiftsothatanindividualwinchcanbecomedangerouslyoverloaded.Thecontrolsystemmustbeabletokeepselectedwinchesinsynchorprovidearapid，coordinatedstopifawinchisunabletostayinsynchwiththeothers.Withatypicaltopspeedofofeachother240fpmandarequirementtokeepthewincheswithina1/8〃，youhavelessthanthreemillisecondstorecognizeaproblem，attempttocorrecttheerrantwinch’sspeed，determinethatyou’vefailedandinitiateacoordinatedstopofallthewinchesinthegroup.Thistakesalotofcomputing，fastI/O，andwell-writtensoftware.

Therearetwoverydifferentapproachestolargeriggingcontrolsystems.Originally，asingleconsolewasused，withtheusualproblemofwhereitshouldbelocatedfortheoperator’soptimumview.Unfortunatelythiscanchangenotonlyfromshowtoshow，butalsofromonecuetothenext.Thisdilemmahasbeenpartiallyaddressedbyusingvideocamerasatdifferentlocationsinconjunctionwith3Dscreengraphicsthatallowtheoperatortoviewtheexpectedriggingmotionthreedimensionallyfromanyviewpoint.Thisallowstheoperatortoviewtheonscreenmovementoftheriggingfromaviewpointthatmatcheshisactualviewofthestage，ortheactualviewofaclosedcircuitcamera.Forcomplexmoveswithinter-relatedpiecesthismakesthecontrolandunderstandingofwhatishappeningmuchsimpler.

Theotherapproachisadistributedsystem，withseveralportableconsoles.Thisallowsdifferentoperatorstocontroldifferentaspectsoftherigging，inthesamemannerwehavedonewithmanualsets.AdramaticexampleofthisapproachisusedbytheRoyalOperaatCoventGarden，wheretherearetenconsolescontrollingatotalof240motors.Eachconsolehasfiveplaybacks，andissetupsothateachmotorisassignedtoasingleconsole.Oneoperatorandconsolecouldcontroleverything，butfrequentlyoneconsolemayberunningstagelifts，anothertheonstagerigging，andathirdisbeingusedbackstagetomovestoreddrops.

Cutting-edgeportableconsolesallowmultipleoperatorstocontroltheactionfromthebestvantagepointsandprovide3Ddisplays.

ReprintedfromPROTOCOL，theJournaloftheEntertainmentServicesandTechnologyAssociationFall2003issue.?

2003ESTA.

Conclusion

Thetremendousvarietyofriggingcontrolsystemscurrentlyavailablerangesfromthepushbutton