ThecompanySeverstalcompletedthesuccessfulintroductionofnewin-lineplate-straighteningmachines(PSMs)onits2800and5000millsinAugust20031,2,3.Themaindesignfeaturesofthemachinesareasfollows:eachmachineisequippedwithhydraulichold-downmechanisms(toimprovethedynamicsandaccuracyofthemachineadjustmentsandmorereliablymaintainaconstantgap)；themachineshavemechanismstoindividuallyadjusteachworkrollerwiththeaidofhydrauliccylinders(thisbroadenstherangeofstraighteningregimesthatcanberealizedbyprovidingameasureofcontroloverthechangeinthecurvatureoftheplate)；eachworkrollerisprovidedwithitsownadjustabledrive(toeliminaterigidkinematicconstraintsbetweenthespindles)；thesystemofrollersofthePSMisenclosedincassettes(tofacilitaterepairsandreducerollerreplacementcosts)；thePSMhasasystemthatcanbeusedtoadjustthemachinefromanine-rollerstraighteningschemetoafive-rollerschemeinwhichthedistancebetweentherollersisdoubled(thisisdonetowidentherangeofplatethick-nessesthatthemachinecanaccomodate).Thus,thenewstraighteningmachineisasophisticatedmulti-functionsystemofmechanismsthatincludesawiderangeofhydraulicallyandelectricallydrivencomponentscontrolledbydigitalandanalogsignals.TheentirecomplexofPSMmechanismscanbedividedintotwofunctionalgroups:themaingroup,whichincludesthemechanismsthatpartici-patedirectlyinthestraighteningoperation(thehold-downmechanisms,themechanismsthatindividuallyadjusttherollers,themechanismsthatadjustthecomponentsfordifferentstraighteningregimes,themechanismthatmovesthetoprollerofthefeeder,andthemaindrive)；theauxiliarygroup(whichincludesthecassettereplacementmechanism,thespindle-lock-ingmechanism,andtheequipmentthatcoolsthesystemofrollers).AlthoughthePSMhasalargenumberofmechanisms,theuseofmodernhydraulicandelectricdriveshasmadeitpossibletoalmostcompletelyautomatethemainandauxiliaryoperationsperformedonthePSMandtheunitsthatoperatewithit.Describedbelowarethefeaturesandtheautomaticcontrolsystemsforthemostimportantmechanismsoftheplate-straighteningmachine.Theoperatingregimesofthosemechanismsarealsodiscussed.Thehydraulichold-downmechanisms(HHMs)ofthesheet-straighteningmachinefunctionintwomainregimes:theadjustmentregime；theregimeinwhichthespecifiedpositionsaremaintained.Therearecertainrequirementsforthecontrolsystemandcertainefficiencycriteriaforeachregime.Intheadjustmentregime,thecontrolsystemforthehydraulichold-downmechanismsmustdothefollowing:synchronizethemovementsofthehydrauliccylindersandkeeptheangulardeeflectionwithinprescribedlimits；maximizespeedinadjustingthemachineforanewplatesize；maintainahighdegreeofaccuracyinpositioningthemechanisms；Metallurgist,Vol.48,Nos.78,2004AUTOMATINGTHECONTROLOFMODERNEQUIPMENTFORSTRAIGHTENINGFLAT-ROLLEDPRODUCTSYu.N.Belobrov,V.G.Smirnov,A.I.Titarenko,V.A.Perekhodchenko,andI.L.SinelnikovUDC621.982NovokramatorskMachinePlantAO.TranslatedfromMetallurg,No.8,pp.5156,August,2004.406Thecontrolsystemhasthefollowingrequirementswhenoperatinginthemaintenanceregime:stabilizethecoordinatesofthetopcassetteandthetoprollerofthefeederwithahighdegreeofaccuracy；minimizethetimeneededtoreturntheequipmenttotheprescribedcoordinateswhendeviationsoccur(suchasduetotheforceexertedbyaplatebeingstraightened).Needforsynchronization.Experienceinoperatingtheplate-straighteningmachineinplateshopNo.3atSeverstalhasshownthatthemostproblematicfactorinadjustingthemachineisthenonuniformityoftheforcesappliedtothehydrauliccylinders.ThisnonuniformityisduetotheasymmetricdistributionofthemassesofthemovingpartsofthePSM(inpar-ticular,theeffectoftheweightofthespindleassembly).Displacementofthe“hydrauliczeropoint”relativetothe“electri-calzeropoint”intheservovalvesisalsoacontributingfactor.*Thelatterreasonismoresignificant,thesmallerthevolumeofthehydrauliccylinder.Thus,theHHMofthetoprollerofthefeederisthemostsensitivetodriftofthezeropoint.Therearealsootherfactorsthataffectthedynamism,simultaneousness,andsynchronismoftheoperationofthehold-downmechanisms:differentiationofthefrictionalforcesonpartsofthehydrauliccylindersduetodifferentcombinationsofdevia-tionsinthedimensionsofthematedparts,despitethenarrowtolerances；differencesinthe“springing”characteristicsandtheindicescharacterizingtheinertiaofthehydraulicsupplychan-nels(duetodifferencesinthelengthsofthepipesleadingfromtheservovalvestothehydrauliccylinders).Thus,sincethePSMisnotequippedwithdevicestomechanicallysynchronizetheoperationofthecylinders,thetransmissionofsignalsofthesameamplitudetotheinputsoftheservovalvesinevitablyresultsinaspeeddifferencethatcanseriouslydamagethemechanisms.Tominimizeandeliminatetheeffectsoftheabove-mentionedfactors,wedevelopedanalgorithmforelectricalsyn-chronizationofthehold-downmechanisms.TheHHMofthetopcassette,composedoffourhold-downcylindersandfourbalancingcylinders,isdesignedtoensuremobileadjustmentofthemachinetosettherequiredsizeofstraighteninggap(inaccordancewiththethicknessoftheplate)andmaintainthatgapwithaspecifiedaccuracyinthepresenceandabsenceofaloadonthehousingsfromthestraighteningforce.Thehydraulicsystemofthehold-downmechanismisdesignedinsuchawaythatonlyonechamberofthehydrauliccylindersisusedastheworkingchamber.Thesecondchamberisalwaysconnectedtothedischargechannel.Thetopcassetteisloweredwhenthebalancingforcesareovercomebythehold-downcylinders.Thecassetteisraisedonlybytheactionofthebalancingcylinders.Thisarrangementhasmadeitpossibletoeliminategapsinthepositioningoftheequipment.407Fig.1.Blockdiagramofthecontrolsystemofthehydrauliccylinder.*Thehydrauliczeropointisthepositionthattheslidevalveoccupieswhenitcoversthedeliveryanddischargemains.Theelectricalzeropointisthecontrolsignalthatshouldmovethevalvetothehydrauliczeropoint.Thesepointsshouldide-allycoincide,butinactualservovalveswithzerooverlapthereisalwaysacertainamountofdisplacementthatresultsinleakageofthehydraulicfluid.TheHHMofthetoprollerofthefeederconsistsoftwohydrauliccylinders.Hydraulicfluidisfedintotheplungerchamberwhentherolleristobeloweredandisfedintotherodchamberwhenitistoberaised.ControlPrinciples.Individualcircuitshavebeenprovided(Fig.1)tocontrolthehydrauliccylindersofthehold-downmechanisms.Thecontrolsignal(Xctl)senttotheinputoftheservovalveisformedbyaproportional-integral(PI)con-troller(toimprovethesensitivityofthesystem,wechosetousevalveswith“zero”overlap).Thesignalsenttotheinputofthecontroller(theerrorsignalXerr)isformedasthedifferencebetweenthecontrol-pointsignalforposition(Xcpt)andthefeedbacksignal(Xf.b).Thelattersignalisreceivedfromthelineardisplacementgage(G)ofthegivenhydrauliccylinder.ThegagesoftheHHMforthetopcassettearebuiltintothebalancinghydrauliccylinders(HCs).Thecylindersareinstalledinsuchawaythattheirmovementscanbeconsideredtobeequaltothedisplacementsofthecorrespondingcylin-derrods,withallowanceforcertaincoefficients.ThegagesintheHHMforthetoprollerofthefeederareincorporateddirectlyintothehold-downcylinders.Theintegralpartofthecontrollerisactivatedonlyduringthefinaladjustmentstageandduringstabilizationoftheprescribedcoordinate.Whenthedisplacementsexceedacertainthresholdvalue,thefunctionsofthePIcontrolleraretakenoverbyaproportional(P)controllerwiththetransferfunctionW(s)=k.Thus,Xctl(t)=kXerr(t).Whentherearesignificantdifferencesbetweenthedisplacementsoftheworkingrollers,thedifference(error)betweenthecontrolpointandthefeedbacksignalfromthelineardisplacementgagereachesvaluesgreatenoughsothattheoutputsignalwhichcontrolstheoperationoftheservovalvereachesthesaturationzone.Inthiscase,furtherregu-lationofthedisplacementrateand,thussynchronizationofthemovementsofthecylindersbecomesimpossibleaslongastheerrorexceedsthevalueatwhichXctlisgreaterthantheboundaryvalueforthesaturationzone(Xsat).Thelimit-ingerrorthelargesterrorforwhichXctldoesnotreachsaturationisinverselyproportionaltothegainofthecon-trollerk:XerrXsat/k.SolvingthegivenproblembydecreasingkleadstoalossofspeedintheadjustmentofthePSMandadecreaseincontrolaccuracyduringthestraighteningoperation.Thus,tokeepthecontrolsignalfromreachingthesaturationzonewhentherearesubstantialdisplacements,thesystemwasdesignedsothattheinputofthecontrollerisfednottheactualrequiredvalue(Xrq)butanincrement(DX)ofamagnitudesuchthattheconditionkDXXsatissatisfied.ThecontrolpointisincreasedbytheamountDXafterthepositionofthecylinderhasbeenchangedbytheamountcorrespondingtotheincre-menthavingthelargestlagrelativetothecylindersdirectionofmotion.Theadjustmentofthecontrolpointiscontinueduntilthedifferencebetweentherequiredvalueandtheactualpositionofthemechanismbecomeslessthantheincrement:XrqXf.bDX.ThentheinputofthecontrollerisfedthevalueXcpt,whichisequaltotherequiredadjustment:Xcpt=Xrq.Theadjustmentisthuscompleted.Useoftheprincipleofasteppedincreaseinthecontrolpointmakesitpossiblesynchronizethemovementsofthecylindersandsetthecontrolpointwithahighdegreeofaccuracyforalmostanyidealrepetitionfactor.MechanismsforIndividualAdjustmentoftheWorkingRollers.Theplate-straighteningmachineisdesignedsothateachworkingrollercanbemovedvertically,whichisdonebymeansofahydrauliccylinderactinginconcertwithaV-beltdrive.Thecylindersaresuppliedwithpowerfromservovalvesoperatedwithproportionalcontrol.Alineardisplacementgageisbuiltintoeachcylindertoobtainafeedbacksignalonthepositionoftheroller.Sincethesegagesareactuallytransmitinginformationonthepositionofthecylinderrodsratherthantheworkingrollersthemselves,thefollowingconversionisperformedtoobtaintherollerscoordinates:Xrol=kredXf.b,wherekredisthegearratioofthedrive；Xf.bisthepositionofthecylinderrodmeasuredbythelineardisplacementtrans-ducers.Thus,apositionfeedbackcircuitisprovidedtocontrolthepositionofeachworkingroller.Figure1presentsadia-gramofoneofthecircuits.ThecontrolsignalsaregeneratedbymeansofthePIcontrollere,whichhasmadeitpossibletoachieveahighdegreeofaccuracyinadjustingthesystemwithoutsacrificingspeed.408Theindividualdriveoftherollers.Theabove-describeddesignisbasedontheuseofindividualacdriveswithmotorsofdifferentpowersfedfromfrequencyconverters.Eachindividualdriveoffersthefollowingadvantagesoveragroupdrive:greaterreliabilitythankstotheabsenceofadditionalloadsonthecomponentsofthemechanismsduetodiffer-encesbetweenthelinearvelocitiesoftheworkingrollersandthespeedoftheplate；thepossibilitythatthemachinecouldcontinuetooperateifoneorevenseveraldrivesmalfunction；inthiscase,thecorrespondingrollerswouldberemovedfromthestraighteningzone；thepossibilitythatthelinearvelocitiesoftherollerscouldbeindividuallycorrectedinaccordancewiththeactualspeedoftheplate；suchacorrectioncouldbemadeeitherasapreliminarymeasure(onthebasisofmeasuredandcalculatedvalues)orduringthestraighteningoperation(onthebasisofthedataobtainedfromthefrequencycon-verters,whichemployartificialintelligence).Themaindriveofthestraighteningmachinerotatesninestraighteningrollersandtwohousingrollers.Thisdrivemustbehighlyreliableinoperation,sincethefactthatthePSMisinstalledinthemilllinemeansthatsizableproductionlossescanbeincurredifthedrivefailstoworkproperlyevenforashortperiodoftime.Therequirementsthatmustbesatisfiedbythedrivearedeterminedbytheoperationalanddesignfeaturesofthemachineasawhole:theplatebeingstraightenedmustcreatearigidkinematiccouplingbetweenthestraighteningrollers,therollersofthehousing,andtheadjacentsectionsoftherollerconveyors；theplateshouldundergoelongationduringthestraighteningoperationasaresultofplasticdeformation,withtheincrementsinlengthbeingdifferentoneachworkingrollerduetothedifferentiationofthebendingradii；thissit-uationleadstoanonuniformincreaseinthespeedoftheplateasitmovestowardtheendofthePSM；itmustbepossibletouseworkingrollersofdifferentdiameters(thisbeingdone,forexample,duetononuniformwearorregrinding)；theloadsontherollersshouldbedifferentiatedinaccordancewiththechosenstraighteningregime；reversestraighteningshouldbepossible.Inlightoftheabovefactorsandtheactualoperatingregimesoftheplate-straighteningmachinebeingdiscussedhere,thefollowingrequirementscanbeestablishedfortheelectricdrive:regulationofspeedwithinbroadlimits,includingstartupofthemotorsunderload；operationinthereverseregime；arigidcharacteristicw=(M)；highdegreeofaccuracyinmaintainingtheprescribedspeed；fullysynchronousoperation.Theelementbase.Thedriveoftherollerswasbuiltwiththeuseofasynchronousthree-phasemotor