机械外文翻译调直机的反馈方法.docx

机械外文翻译调直机的反馈方法.docx

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机械外文翻译调直机的反馈方法

AClosedLoopFeedbackMethodforaManualBar

Straightener

RobertJ.Miklosovic,ZhiqiangGao

DepartmentofElectricalandComputerEngineering

ClevelandStateUniversity

Cleveland,Ohio,USA

Abstract—Automationofauniquemanuallycontrolledindustrialbarstraightenerisproposed.Acontinuous-timeclosedloopmodelisconstructedinSimulinkforanevent-drivenprocessthroughtheuseofasynchronoustimers.ThesystemissimulatedwithlinearandnonlinearPDcontrollers.Anonlinearfilter,calledthetrackingdifferentiator,isintroducedasanalternativetoalinearapproximatemeansofprovidingaccuratederivativefeedbackinthepresenceofnoise.Inbothcases,thenonlineartechniquesoutperformedtheirlinearcounterpartswhileretainingtuningsimplicity.

I.BACKGROUND

Precisionstraighteningofacylindricalmetalbarislargelybasedontheabilitytopreciselymeasureitsgeometry.Afewfundamentalmeasurementsandhoweachinfluencesthetolerancespecificationonstraightnessshouldfirstbeunderstood.Methodsformeasuringroundnessandstraightnessarecoveredtolaythegroundworkfortheproblemformulation.ThebasicoperationofthemachineisoutlinedinSectionII,anditsfundamentallimitationsandneedforautomationarediscussed.SectionIIIaddressesthetaskofclosingtheloopthroughblockdiagramsandtheroleofnewhardwareintheprocess.SectionIVcontainsdescriptionsofalloftheblocksthataremodeledinSimulink.ThelinearandnonlinearcontrollerdesignsarediscussedinSectionV,thesystemissimulatedinSectionVI,andconcludingremarksaremadeinSectionVII.

A.MeasuringRoundness

Roundnessisaquantityderivedfromcomparingtheshapeofacross-sectionalareaatonedistinctpointalongacylinder’slengthagainstacircle.Aroundmetalbarthatisarbitrarilylongwithrespecttoitsdiameterhastobecheckedforroundnessinmanylocationslengthwiseandaveragedtoinsureoverallconsistency.RoundnessisapproximatedbyrotatingtheworkpieceonerevolutioninaVeeblockwhilemeasuringthesurfacewithanindicator.Takingthedifferencebetweentheminimumandmaximumindicatorreadingsinthiscaseisreferredtoasthetotalindicatorreading（TIR）[1].

B.MeasuringStraightness

Straightnessisaquantityderivedfromcomparingtheaxialcenterlineofaspecificsectionofacylinder’slengthagainstastraightline.AsimplemethodforapproximatingstraightnessisbyrotatingthebaronerevolutionbetweentwoVeeblocksthatareafixeddistance（d）apart,whilemeasuringinthecenterwithanindicator.Thedistancethattheaxialcenterlineofthepartdeviatesfromatheoreticallystraightcenterlinedirectlybelowtheindicatorequalstheextenttowhichthepartisbowed,orwarped,overlengthd.Themaximumandminimumindicatorreadings（IXandIN）arephysicallyrepresentedinFig.

1.Fromthis,TIRisderivedas:

TIR=IX–IN=（R+|Bow|）-（R–|Bow|）=2*|Bow|

（1）

Deviationsinroundness,outsidediameter（OD）size,andfinishcanadverselyaffectthemeasurement.

Figure1.Max.andmin.indicatorreadingsofabowedpart

C.Straightening

Thestraighteningprocess,whichcanbebrokenintosteps,simplyinvolvescorrectinganyerrorwhilecheckingforstraightness.First,thepartismeasuredforstraightness.Then,itisrotatedsothatthebowisoriented180degreesawayfromtheVeeblockswiththemaximumindicatorreadingfacingupwards.Finally,acounter-bendingforcereplacestheindicatorandstraightenstheworkpieceagainsttheVeeblocks.

II.MACHINEOPERATION

Thestraightenertobeautomatedusesanon-contactultrasonicsensorinplaceoftheindicatorandrollersinplaceoftheVeeblocksinanefforttominimizecontactwear.Thepartslowlyspiralsthroughthemachine.Theindicatorreadingbecomesacontinuoussinusoidatthesensor’soutput,havingapeak-to-peakvalueequaltotheTIReachrevolution.TIRissampledfromthesensoroutputandcalculatedeachrevolution,makingthesampleperiodofonerevolutiontheminimumtimebetweenconsecutivebends（YSP）.TIRistheplantoutput（Y）tobecontrolled.Whenthepartisstraightened,themachinestopsrotationwiththebowfacingupwards,butthepartcontinuestofeedlengthwisewhileanaircylindercounterbendsthepartoveraperiodoftime.Thisbendtime（BT）isthecontrolvariable（U）.Fig.2illustratesthisoperation.

Figure2.Thestraightenertobeautomated

A.ProcessLimitations

Thereareaspectsoftheprocessthatcanlimitthecontroller’sperformanceandslowitdownbyextendingYSP.Eachisobservedandtakenintoconsiderationwhenproducing

anaccuratesimulationmodel:

1.TheultrasonicsensorintroducesRFInoiseintoits.Theuseofafeedbackfilterisessential.

2.Aroughpartsurfacefinishaddsdistortiontothesensoroutput.

3.Anout-of-roundpartsuperimposesharmonicsonthesensoroutputsinusoid,placingaboundontheminimumsteadystateerrorthatisachievable.

4.Inconsistentmaterialdensityproducesfalsemeasurements.Themeasuredfocallengthofa

transducerisdependentonthedensityofthematerialthatisbeingmeasured[2].Theunitcannotmeasureaccuratelyinthepresenceofatime-variantmaterialdensity（i.e.hardspots）.Althoughunavoidable,itcanbedetected,sinceTIRchangesmonotonically.

5.AninconsistentODcausesverticalshiftsinthesensoroutput.AdifferentialTIRmeasurementcancelstheseaffects.

6.Atwistedpartconditionisdetectedwhentheangularpositionofthemaximumindicatorreadingslowlymoveswitheachrevolution.Thisconditioniscreatedwhenthepartisnotstraightenedatthepreciseangularlocationandoccursbecauseofthequantizationaffectofthedigitalreadoutusedbytheoperator.Thenewcontrollerwilluseacontinuoussignalandthepartcanbestraightened30to45degreesaheadofthetwistwhenencountered.

B.TheNeedforAutomation

Replacementoftheoperatorwithelectronichardwareisbeneficialinseveralways.Thecostoftheelectronicsismuchlessthantheongoinghourlywageandscheduleofanoperator.Thelimitationsassociatedwiththedigitalreadoutareeliminated,whichhelpsthemachinetostraightenfasterwithmoreprecision.Theprocesscanbedrasticallyspeduptoproducemore.Thoughtheminimumsampletimeisonerevolution,itdoesnotneedtobeslowenoughforhumancomprehension.AProgrammableLogicController（PLC）canmakeseveralcalculationsandtesttheresultagainstasetofrulesmanytimesfasterthanahumanbeing.

C.ResearchMethodology

Thefocusissplitbetweenmodelingandcontroldesign,sincethisisanewcontrolproblem.Theprocessismanuallycontrolledratherthanbeingstrictlymanualinoperation,meaningthemachineneedsonlyanewcontroller.Thereisnoneedforacompletemechanicaloverhaul,sothebestmethodofstraighteningisnotresearched.Typicalofasmallcompany,timeandmoneyarelimited.GaoandHuang[3]presentedanewerror-basedcontroldesignframeworkincludingsuchinnovationsasanonlineartrackingdifferentiatorandanonlinearproportional-integral-derivative（NPID）controlmethod.Thesemethodsprovetobepowerfulandsimpletotune,whichmakethemidealforuseinanindustrialenvironment.

III.ACLOSEDLOOPSOLUTION

Thetaskofautomationcanbeginoncetheprocessiswelldefined.Astraightforwardsystemblockdiagramisdeveloped,andeachblockismodeledinSimulink.Aspectsofthehardwareconfigurationarecarefullyconsidered.

A.FromOpenLooptoClosedLoop

Theopenloopmulti-input-multi-output（MIMO）blockdiagram,inFig.3,representsthemanuallycontrolledprocess.TheoperatorcalculatesTIRandmonitorstheangularposition（􀀀P）ofthebowwitheachrevolution.WhenYapproachesaspecifiedlimit,theoperatorsetsBTproportionaltoYandits

rate,andthenpushesabutton（BP）tostraightenthepart.ThebendtimercreatesapulsetriggeredbyBPthatcounter-bendsthepartforBTminutes.Thiseventforcestheparttohaveaspecificrateforaperiodoftime.Aftertheevent,theparttakesonanewrateandtheprocessperpetuates.Therefore,Y’isa

piece-wisecontinuousfunctionoftime.Theoperator’sinvolvementintheprocessisrepresentedasablockinFig.4.

Figure3.Openloopblockdiagram

Figure4.Operatorblock

Rearrangingtheblocksandbreakingeachfunctiondownintosmallermore-manageableblocksreducestherepresentationtoausableclosedloop,single-input-singleoutput（SISO）form.Fig.5showshowaSISOplantisobtainedbycombiningtheprocesswiththetaskofsamplingtheTIR,sinceitcanbeconsistentlycomputed.

Figure5.SISOplantblock

Theplanthasavariable-widthpulseastheinput（U）andthesampledTIR（Y）astheoutputtobecontrolled.Theincomingchangingpositionoftheworkpieceismodeledasanunknownratedisturbance（D）.TheclosedloopSISOblockdiagramisshowninFig.6.

Figure6.Closedloopblockdiagram

B.HardwareConfiguration

DepictedinFig.7,anencoderandaPLCaretheonlyhardwareneededforautomation.Theencoderfeedstheangularpositionofthepartbacktothecontroller,andthePLChandlesallofclosedloopfunctionsoutsideoftheprocess.

Figure7.Hardwareconfiguration

Fig.8depictsthehardwarelayoutforplantdataacquisitionduringmanualoperation.ThePLCisalsousedtocalibrateastripchartrecorder,showninFig.9,whichsimplifiescalibrationfortheoperatorandremovesroomforerrorduringdataacquisition.UsingthePLCforbothdataacquisitionand

controlkeepscostslower.

Figure8.Openloopdataacquisitionconfiguration

Figure9.Chartrecordersettingsfora.006”TIRsignal

IV.MODELING

SimulationmodelinginvolvestheconstructionofSi