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英文原文ElectricalWinchControlsbyTomYoungTheformofmotorcontrolweallknowbestisthesimplemanualstationwithupanddownpushbuttons.Whilethesestationsmaystillbetheperfectchoiceforcertainapplications，adizzyingarrayofmoresophisticatedcontrolsisalsoavailable.Thisarticleaddressesthebasicelectricalrequirementsofthemotorsanduserinterfaceissuesyouwillneedtoaddressbeforespcifying，buildingorbuyingwinchcontrols.beginwith，themanualcontrolstationsshouldbeofthehold-to-runtype，sothatifyoutakeyourfingeroffofthebuttonthewinchstops.Additionally，everycontrolstationneedsanemergencystop(E-stop)thatkillsallpowertothewinch，notjustthecontrolcircuit.Thinkaboutit—ifthewinchisn’tstoppingwhenitshould，youreallyneedafailsafewaytokillthelinepower.It’salsoagreatideatohaveakeyoperatedswitchoncontrolstations，especiallywhereaccesstothestationsisnotcontrolled.Safeoperationbyauthorizedpersonnelmustbeconsideredwhendesigningeventhesimplestmanualcontrols.ControllingFixedSpeedMotorsTheactualcontrollingdeviceforafixedspeedwinchisathreephasereversingstarter.ThemotorisreversedbysimplyswitchingthephasesequencefromABCtoCBA.Thisisaccomplishedbytwothree-polecontactors，interlocked，sotheycan’tbothbeclosedatthesametime.TheNECrequiresbothoverloadandshortcircuitprotection.Toprotectthemotorfromoverheatingduetomechanicaloverloadsathermaloverloadrelayisbuiltintothestarter.Thishasbi-metallicstripsthatmatchtheheatingpatternofthemotorandtripscontactswhentheyoverheat.Alternatively，athermistorcanbemountedinthemotorwindingtomonitorthemotortemperature.Shortcircuitprotectionisgenerallyprovidedbyfusesratedforusewithmotors.Aseparatelinecontactorshouldbeprovidedaheadofthereversingcontactorforredundancy.Thiscontactoriscontrolledbythesafetycircuits:E-stopandovertravellimits.Thisbringsustolimitswitches.Whenyougettothenormalendoftravellimitthewinchstopsandyoucanonlymoveitintheoppositedirection(awayfromthelimit).Therealsoneedstobeanovertravellimitincase，duetoanelectricalormechanicalproblem，thewinchrunspastthenormallimit.Ifyouhitanovertravellimitthelinecontactoropenssothereisnowaytodriveoffofthelimits.Ifthisoccurs，acompetenttechnicianneedstofixtheproblemthatresultedinhittingtheovertravellimit.Then，youcanoverridetheovertravelsusingthespringreturntoggleswitchinsidethestarter—asopposedtousingjumpersorhandshootingthecontactors.VariableSpeedRequirementsOfcourse，thesimplefixedspeedstartergetsreplacedwithavariablespeeddrive.Here’swherethingsstarttogetinteresting!Attheveryleastyouneedtoaddaspeedpottothecontrolstation.Ajoystickisabetteroperatorinterface，asitgivesyouamoreintuitivecontrolofthemovingpiece.Unfortunately，youcan’tjustorderanyoldvariablespeeddrivefromyourlocalsupplierandexpectittoraiseandlowerequipmentsafelyandreliablyoverkidsonstage.Mostvariablespeeddriveswon’t，astheyaren’tdesignedforlifting.Thedriveneedstobesetupsothattorqueisdevelopedatthemotorbeforethebrakeisreleased，and(whenstopping)thebrakeissetbeforetorqueistakenaway.FormanyyearsDCmotorsanddrivesprovidedapopularsolutionastheyallowedforgoodtorqueatallspeeds.ThelargeDCmotorsrequiredformostwinchesareexpensive，costingmanytimeswhatacomparableACmotorcosts.However，theearlyACdriveswerenotveryuseful，astheyhadaverylimitedspeedrangeandproducedlowtorqueatlowspeeds.Morerecently，astheACdrivesimproved，thelowcostandplentifulavailabilityofACmotorsresultedinatransitiontoACdrives.TherearetwofamiliesofvariablespeedACdrives.Variablefrequencyinvertersarewellknownandreadilyavailable.ThesedrivesconvertACtoDC，thenconvertitbacktoACwithadifferentfrequency.Ifthedriveproduces30Hz，anormal60Hzmotorwillrunathalfspeed.Intheorythisisgreat，butinrealitythereareacoupleofproblems.First，atypical60Hzmotorgetsconfusedatalinefrequencybelow2or3Hz，andstartstocog(jerkandsputter)，orjuststops.Thislimitsyoutoaspeedrangeofaslowas20:1—hardlysuitableforsubtleeffectsonstage!Second，manylowercostinvertersarealsoincapableofprovidingfulltorqueatlowspeeds.Employingsuchdrivescanresultinjerkymoves，oracompletefailuretoliftthepiece—exactlywhatyoudon’twanttoseewhenyouaretryingtostartsmoothlyliftingascenicelement.Someofthenewerinvertersareclosedloop(obtainfeedbackfromthemotortoprovidemoreaccuratespeedcontrol)andwillworkquitewell.TheotherfamilyofACdrivesisfluxvectordrives.Theseunitsrequireanencodermountedonthemotorshaftallowingthedrivetopreciselymonitortherotationofthearmature.Aprocessordeterminestheexactvectorofmagneticflux(thusfluxvectordrive)requiredtorotatethearmaturethenextfewdegreesatagivenspeed.Thesedrivesallowaninfinitespeedrange，asyoucanactuallyproducefulltorqueatzerospeed.Theprecisespeedandpositioncontrolofferedbythesedrivesmakethemafavoriteinhighperformanceapplications.PLC-basedcontrolsprovidesystemstatusaswellascontroloptions.ThisscreengivetheoperatorfullaccesstoCarnegieHall’sninestagefloorlifts.PLCBasedSystemsAPLCisaprogrammablelogiccontroller.Firstdevelopedtoreplacetherelaybasedindustrialcontrolsystemsofthe’50sand’60s，thesecontrolsareathomeinrugged，industrialenvironments.ThesearemodularsystemswithagreatvarietyofI/Omodulesallowingsemi-customhardwareconfigurationstobeassembledeasily