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Method of Precise Auto Tool Setting for Micro Milling

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Method of Precise Auto Tool Setting for Micro Milling

    Method of Precise Auto Tool Setting for

    Micro Milling

    TransTianjinUniv201117:284287

    DOI101007/sl2209011-16398

    MethodofPreciseAutoToolSettingforMicroMilling*

    ZHAOMeng(赵孟),HENing(何宁),

    (CollegeofMechanicalEngineering,NanjingUniversity

    LILiang(李亮),HUANGXunbin(黄逊彬)

    ofAeronauticsandAstronautics,Nanjing210016,China)

    ?TianjinUniversityandSpringerVerlagBerlinHeidelberg2011

    Abstract:Basedonmicroscopeandimageprocessing,anewmethodofautotoolsettingformicromillingwaspre

    sented.FirstlyarealtimeimageoftooksettingareawasobtainedbymicroscopeandCCDcamera,thenimageproc

    essingwascarriedoutonthisimageandthegapbetweenthetoolandworkpiecewascalculated.Thegapmeasure

    mentwassenttomotioncontrollingcardtomakethetoolapproachtothesurfaceofworkpiece.Thesestepswere

    repeateduntilthegapiszerowhichmeansthattoolsettingwasfinished.Moreover,areliabilityverificationtestwas

    conducted.Resultsindicatedthattheprecisionoftoolsettingissatisfactory. Keywords:micromilling;too[setting;imageprocessing

    Ofallkindsofmicromanufacturingmethods,micro

    millingisatraditiona1.efficientandeconomica1way.But

    inmicromilling,thediameteroftoolsisusuallyvery

    smal1(0.050.5mm),sotoolsettingmustbeprecise

    enoughtoensuremanufacturingaccuracy.

    Therearemanywaysoftoolsetting.Thetrycutting toolsettingmethodisusedwhenprecisionisnothigh, usuallylowerthan0.1ran1.sothemethoddoesnotmeet thedemandsofmicrotoo1setting.Lasertoo1setting equipmentissuperiorbutcostly.Therefore,inthispaper, anewmethodoftoolsettingbasedonmicroscopeandim

    ageprocessingispresented,andasoftwareispro

    granmaedtomaketheprocessoftoolsexingautomatic[,. 1Toolsettingprincipleandequipment

    ThetoolsettingequipmentincludesCCDmicro

    scope(magnification0.677),imageacquisitionsys

    tern.LED1ightandaself-mademicromillingmachine. Theself-mademicromillingmachinewasmadein2005 itsperf0rmanceisshowninTab.1,andtheequipmentis showninFig.1whiledoingtoolsetting.

    Tab.1Performancesofmicromillingmachine

    Fig.1Pictureoftoolsettingequipment

    Thetoolsettingprincipleisbasedonimageprocess

    ing.MicroscopeandCCDareusedtoobtaintheimageof toolsettingarea,thenthegapbetweenthetoolandwork- piececanbecalculatedwiththeaidofimageprocessing. Theresultissenttothemotioncontrollingcardofmicro millingmachinetomakethetoolapproachtoworkpiece. Fig.2istheschematicdiagramoftoolsetting. Accepteddate:20110520.

    *SupportedbyNationalNaturalScienceFoundationofChina(No.50935003)

    ZHAOMeng,bornin1985,male,doctoratestudent. CorrespondencetoZttAOMeng,E-mail:zhaomeng@nuaaedu.cn? MachiIle

    Pontrt>I

I

    ling

    MicromilIing

    Image

    a?tl1sI1nn

    Fig.2Schematicdiagramoftoolsetting 2Imageprocessingflow

    ZHA0Mengetni:MethodofPreciseAutoToolSettingforMicroMilling

    2.1Gray.scaletransformation

    Tofacilitateimageprocessingandimprovethe computingspeed,the24bitimagefromtheimageacqui

    sitioncardisfirstconvertedto8.bitgrayscalebefore

    imageprocessing.Themostcommonlyusedgraycon

    versionmethodisexpressedas

    Grayscale=0.30R+0.59G+0.11B(1)

    whereR,GandBrepresentred,greenandbluecompo

    nentvaluesineachpixe1.Fig.3(a)andFig.3(e)arethe grayimagesottheexperiment.

    2.2Mid.valuefiltering

    Thisexperimentchoosesthemethodofmid.value filteringtoremovenoise.andtheresultisgood.Themid.

    valuefilteringmethodisexpressedas (a)

    (e)

    Fig.3Imageprocessing((a),(b)

    processingforzaxistoolsetting

    (b)

    (,)=??f(m+i,,z+)(2)7f=1,=1

    wheretheselectedareaisa3×3matrix,(m.)isthe

    centerofthismatrix.Fig.3(b)andFig.3(f)showthe

imagesaftermid.valuefilteringJ.

    2.3Binarymorphologicalimageprocessing (1)zaxistoolsetting

    Fig.3(c)showsthatbinaryimagestillhassome noise,especiallyontheedgeofthetool,ithasagreat impactonthemeasurementofthegapdistance.Simple binarymorphologicalimageprocessingisusedtosmooth theburr.Fig.3(d)showstheimageaftermorphological imageprocessingwithoutanynoise.

    (2)xandyaxestoolsetting

    TheimageprocessingforxandYaxestoolsettingis similartothatforzaxis,andtheimageaftermorphologi

    calimageprocessingisshowninFig.3(h).

    (c)

    (f)

    (d)

    (h)

    (c)and(d)aregrayimage,mid-valuefilteringimage.binaryimageandbinaryimageaftermor

    phologicalimage

    (e),(f),(g)and(h)aresimilarbutforxandyaxestoolsetting) 2.4Gapmeasurementandcalibration

    Gapmeasurementisthecoreofthesystem.Calibra

    tionisdividedintocameracalibrationandsystemcali

    bration.Systemcalibrationusesconversionfactorbe. tweenthesystemandtheactualphysicalsize. (1)zaxistoolsetting

    Fig.4showstoolsettingpictures.Fig.4(a)showsa distanceof70gmabovetheworkpiece.Toobtainthe calibrationfactor,commandsaresenttothemotioncon

    trollingcardsmanuallyandthetoolmovesdownward

    f0r10gmeachtime(4timestotally).Fig.4(e,showsa distanceof30gmabovetheworkpiece.Thedistance betweenthetooIanditsshadowiseasytobecalculated fromtheimage,anditis2timesofthegapdistance,soa formulaforzaxiscalibrationissetup.

    (2)xandyaxestoolsetting

    ForthereisnoshadowinxandYaxestoolsetting, thedataplaneischangedintoanedgeofagroove.How- ever,thecalibrationprincipleissimilar,sothewayof calibrationforzaxisisalsofitforxandaxes.Tab.2 showstherelationshipbetweentheactualdistanceofgap andpixels.

    Theempiricalformulacanbeformulatedinthissys

    tem:

    az=0.51pm/pixel,axy=1.86gm/pixel(3)

    

    285

    Ill_

    Tramac#on,~ofTianjinUniversityVo1.|7No4201i (a)70pm(bj60pm(c)50gm(d)40pm(e)30pm

    (g)8Opm(h)

    Fig.4Actualdistanceofgap

    Tab.2Actualdistanceandpixels

    60gm(i)40"m

    (Thetoolusedinthetestis500um)

    2.5Toolsettingsoftware

    Accordingtotheabovecalibrationandtoo1setting areaimage.thedistancebetweenthetoolandworkpiece cadbecalculated.Thenthedistancewillbesenttothe machinemotioncontrollingcardtomakethetoolmovea

    correspondingdistance.Thesestepswillberepeateduntil thedistancecalculatedbysoftwareiS0,whichmeansthat thetoo1settingiSfinished.Atoolsettingsoftwareinclud

    ingfunctionmodulesofrealtimeimageacquisition, im

    ageprocessing,gapmeasurementcalculationandcorn- municationtomachinemotioncardiSprogrammed.and afterinitializingtheparameters,onlyoneclickonthe button"start"wil1orderthe

    automatically.Thegraphical

    softwareisshowninFig.5.

    2.6Errorcontrol

    equipmenttodotoolsetting

    userinterface(GUI)ofthis

    Thereexisttoolmanufacturingerrorandspindlero

    Fig.5GUIoftoolsettingsoftware

    zaxistoolsetting,withtherotatingofspindle.10pic

    turesindifferentpositionsbutofthesameheightofZ axisaretakentocalculatetheminimalgapdistanceto avoiderror,andthatcanalsoavoiderrorcausedbyspin

    dierotatingerrorinxandvaxestoo1setting. Afterbinarymorphologicalimageprocessing,pixel lOSSiSinevitable.Thiswil1reducesystemaccuracy. However.theprofileoftooljSblurrywithoutthisstep. 3Reliabilityverificationtest

    Areliabilitytestwasconductedtoverifythetool settingprecision,andthestepsareasfollows. Step1Adataplanewasmilledbya3mmend

    mil1.

    Step2Theq53mmendmillwaschangedintoa

    450.5mmendmill,thentoolsettingwasconductedwith machinedplaneasreferenceplane.Whentoolsettingwas done,agroovewasmilledwithZaxisdepthof15gm. tatingerror,tiltoftooltopsurfacemightbelargerthan2 gmor5gm,whichcaninduceerrorsintoolsetting.Soinwas

    286

    Step3AfterStep2,asurfacemappingmicroscope usedtomeasurethedepthofthegroove.Fig.6(a) ZHA0Menget:MethodofPreciseAutoToolSettingforMicroMilling andFig.6(b)showthemicroimageofthegrooveand3D reconstruction,andfromFig.6(c)thedepthofthegroove canbederived.whichis9.53gm.

    Step4Agroupoftestsweredonewiththedepthof 15pm,20gm,25pm,30gmand35lam,andthegap

    distanceanderrorareshowninFig.7.

    (a)Microimageofgroove

    (b)3Dreconstructionofgroove

    Itisalsonoticedthatinzaxistoolsetting,ifthesur

    faceofworkpieceisnotshining(surfaceisunreflecting, likeSi),systemaccuracyisnotsohigh.However,the mostcommonlyusedmaterialsareshining,suchasA1, Cu,steel,ceramicsandglass.Thisisalimitationofthe method.

    4Conclusions

    (1)Anewmethodformicrotoolsettingbasedoil microscopeandimageprocessingwasputt0rward? (2)Imageprocessingincludesgrayscaletransfor

    mation,mid.valuefiltering,binarymorphologicalimage

processingandgapmeasurement.Andaforrnulaofcali

    brationfromcameracalibrationtosystemcalibrationwas setuptocalculatetherealgaDdistance.

    (3)Asoftwareincludingfunctionmodulesofreal- timeimageacquisition,imageprocessing,gmeasure.

    mentcalculationandcommunicationwithmachinemo

    tioncontrollingcardwasprogrammedtomakethetool settingprocessautomaticallyandtheoperationsimple. (4)Areliabilityverificationtestwasconducted, whichindicatesthattheprecisionoftoolsettingis6_7gm.

    References

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    Fig.7Gapdistanceandtoolsettingerror

    Themicromillingmachineusedinthetestshasa highprecisioninzaxis(resolution1gm),andthetiltof zaxisislessthan1Hm,soaftertheadditionofthema

    chineerrortothetoolsettingsystemerror,theprecision ofthistoolsettingmethodis67gm.

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