光学精密工程

　　　　　　　　　　OpticsandPrecisionEngineering　　　　　　　　

2005年10月　　　　Oct.2005

ArticleID　10042924X(2005)0520570205

第13卷　第5期

　光学精密工程

Vol.13　No.5

Experimentalresearchandanalysis

ofthree2fingermicro2tweezers

HUANGWen2hao,XINGHao

(DepartmentofPrecisionMachineryandPrecisionInstrument,UniversityofScienceandTechnologyofChina,HeFei230027,China)

Abstract:Anewtypeofthree2fingermicro2tweezerdrivenbyelectro2staticforcewasdevelopedforstablemanipulationandassemblyofmicrodevices.Thewholesystemconsistsofmicro2tweezersandaspeciallydesignedhighfrequencyACpowersupply.Thefreeendofthefingersclosesandopenswiththeincreaseanddecreaseofthevoltage.Thetweezerscangraspandmanipulatemicroobjectsatsizefrom30～100μm.Aquantitativesimulationmethodbasedonboundarxel2ementmethod(BEM)andequationofenergyconservationisintroducedtoanalyzethenon2linearofthetweezerclosure.Thesimulationresultsagreewellwiththeexperimentaldata.

Keywords:three2fingermicro2tweezer;particulation;manipulation,opening,grasping

1　Introduction

　　With2ro2me2chanicalM),grasping,manipu2latingandofmicroobjectsarequitefascinating.Newtoolsforthesepurposeshavebeendevelopedrapidly.However,mostoftheseresearchesarefocusedontwo2fingermicro2tweezers[1～3].Thestabilityandapplicationoftwo2fingermicro2tweezersinmanipulationandassemblyareverylimitedingraspingsphere,co2lumnarorcomplicatedmicroobjects[4].Inordertograspparticlesmoresteadily,carbonfibersareusedtocreatethethreefingersofmicro2tweezers,whichisdrivenbyapowersupplywithahighfrequencyalternativepotential.Inthispaper,themanufactureprocessofthethree2fingermicro2tweezersandthedesignconsidera2tionsofthepowersupplywillbeintroduced.

ulatingofmicroobjectsatsizefrom30

～100μmarepresented.Inordertoexplainthenon2linearclosureprocess,asimulationmethodbasedonahybridmethodofboundaryelementmethod(BEM)[5]andequationofenergyconser2vationwillbediscussed.Theresultsshowthatthemethodisveryeffective.

2　Three2fingermicrotweezers

2.1　Fabricationofthree2fingermicro2tweezers

Themostimportantchallengesinthemanu2factureofthethree2fingermicro2tweezersarehowtodividethethreefingerssymmetricallyinspaceandhowtoapplytheelectrostaticforcestoobtainthesymmetricalmovementsofthefin2gers.Here,carbonfibersandopticalfibersareusedtomakethethree2fingermicro2tweezers.Withremarkablepropertiesinmechanicsande

2

　　Receiveddate:2005203216;Reviseddate:2005206227.

　　Foundationitem:NationalnaturalsciencefoundationofChina(No.50275140;No.50335050)

No.5HUANGWen2hao,etal:Experimentalresearchandanalysisofthree2fingermicro2

tweezers571

lectricalconductionthecarbonfiberissuitableforelectromechanicaldevicesinmicroscale.

quallybiasedbetweenthetwosides(Arm1inthisillustration),i.e.V12=V13≠V23.Atsuchelectricalpotential,non2symmetricalmovementsofthethreefingersareexpectedifDCvoltageisadopted.However,byusingACvoltage,thebiasvoltagebetweeneverytwofingersisrota2ting.Ifthefrequencyisfastenough,wecana2chievethesymmetricalmovementsoffingersto2wardthegeometricalcenter.ThefrequencyofACvoltageisselectedbyusingavaluewhichisfarawayfromtheresonancefrequency(ω1=1.5kHz,ω1=9.8kHz)ofthefingers.Wechoose20kHzasthefrequencyofthepowersupply.2.2　Experiment

Wecarriedouttheexperimentofthethreefingersclosing,graspingandulatingthemicroobjectundertt,twasinvestigatedbytotheelectrodes.Withtheofpeakvoltagevalue,everytwofin2gersofthethreegotclosertoeachothersimul2taneouslyandcouldreturntotheiroriginalposi2tionswiththevoltageremoved.Wefoundthateveryfingerofthemicro2tweezershadanelasticresponsebeforeclosed.Asthevoltage(V0)in2creasedto162V,thefingersofthetweezersclosedsuddenly.

Fig.4showstheclosure

processofthemicro2tweezers.Duringthevolt2ageincreasingthevibrationwasnotobservedwithintheopticalmicroscoperesolution

limit.

μm,Threecarbonfibers,withadiameterof5wereattachedindividuallyinthejointgapbe2tweeneachtwoofthethreetightlytiedopticalfibers,whosediameteris125μm,andthisprocesscouldensurethethreefingerstobepar2allelandsymmetricalinspace.Freeendsofthecarbonfibersactasthefingersandtheotherendsarefixedontheelectrodes,respectively.TheelectrodesareformedbythreeAufilmsde2positedonaslide.Withalltheseprocedures,wegotthethree2fingermicro2tweezers.Fig.1istheschematicillustrationofthethree2fingermicro2tweezers.Thelengthofthefingersis2.0mm;thedistancebetweeneachtwoofthefingersis108μm.Fig.2showstheopticalmicrographoftheactualthree2fingermicro2

tweezers.

Fig.1　Schematicillustrationofthethree2fingermi2

cro2

tweezers

Fig.2　Opticalmicrographofthethree2fingermi2

cro2tweezers

Inordertocloseandopenthethreefingerstogether,apowersupplywithanalternativehighfrequencywasdesignedandthewaveformisshowninFig.3(a).FromFig.3(b),ateachtimeposition(t0),onlyoneofthefingerise2

Fig.3(a)Waveformofvoltageusedtodrivethethree2fin2

germicro2tweezers.

572

　　　　　OpticsandPrecisionEngineering　　　Vol.13

stableandrepeatableintheexperiment.

3　Simulationmethod

　　Thefingersofthemicro2tweezerscouldbeconsideredasasystemofthreeisolatedconduc2

3(b)Illustrationofvoltageoneachfingerattimet0

.

torsembeddedinauniformvacuumdielectricmedium.Theprocessofthethreefingersclosingisalsoregardedastheelasticenergytobalancewiththeelectrostaticenergy.Andtheelasticen2ergyis

Gelas

4=

2

L

2dx,5x2

(1)

whereyisthedisplacementxposition,ristheradiusofthe,lengthofthe,Esthe

Fig.4　Opticalmicrographsofthethree2fingermicro2

tweezersat0,80,140,162

V

ththevoltagein2,thedistributedforcesonthefingermaybeassumedasuniformforces.Fromthechargedensitydiscusseda2bove,theelectrostaticenergyis

2

CV=-QV,

22

Gelec=-(2)

Becausethechargesonlydistributeonthefingersurface,anexteriorregionismoreeffi2

Fig.5　Micrographoftheprocessofmanipulating

thepolymerball

cient.SincethedirectBEMneedstodefineafarfieldboundary,indirectBEMformulationisap2pliedhere,inwhichonlythesurfaceofthecon2ductorsneedstobediscretized.FortheLaplaceequation,theindirectBEMformulationis

Thethree2fingermicro2tweezerscouldgraspparticlesatsizefrom30μmto100μm.Fig.5showstheprocessofmanipulatingapolymerballwhosediameterisabout50μm.Inthisexperi2

ment,weusethenon2conductiveobjects.How2ever,webelievethatwecanalsograspconduc2tivethingsifaninsulatefilmiscoveredonthefingers.InFig.5,Ashowsthetweezersap2proachingtheball;Bisthemicrographofgrasp2ingtheball;C～Dshowthemovementoftheball;fromtheFwecanseethattheballhasbeenputdown.Wefoundthemanipulationwas

ui=

∫

Γ

3

uσdΓ,

(3)

whereuiisthepotentialatipoint,σisthesourcedensity,whosephysicsmeaningisthedifferencebetweenthedifferentialofinteriorandexteriorpotential

No.5HUANGWen2hao,etal:Experimentalresearchandanalysisofthree2fingermicro

2tweezers573

α,i=-n

3

3

(4)

　　Theultimatecalculatedresultis171V,whichisveryclosetotheexperimentresult162V.Andthesimulatedprocessisfamiliarwiththeexperimentverymuch.Whenthedis2placementofthetipisabout2/3totheorigindisplacement,thethreefingersareclosed.Fig.6isthedisplacementofonefingertipcomparedwiththeexperimentdata.

uisGreenfunction,uisthepotentialati

pointgeneratedbythechargeatjpointin2D.

3

u=

()ln,πR2

(5)

WiththeenlargementofR,u3→∞,wecanintroduceaconstantD,whichislargee2nough,toensureu→aconstant,whentheboundaryisdiscretetoNconstantelements.

N

4　Conclusions

　　Wehaveproposedanappropriatestructure

ofthree2fingermicro2tweezers.Thetweezersaresuitableforgraspingandmanipulatingmicroob2jectsatsizeof30～100μm.Afeasiblesimula2tionmethodisdiscussed.Alttherearesomedeficienciesinprocesses,thet2tweezersis

ui=

j=1

σu∑∫

j

3

Γi

dΓ+D,(6)

FortheentireNdistributedboundaries,thereareNequations,butN+1unknownquali2ty.SoanadditionalequationbasedonthefeatureofinductivechargesisintΓ

,(7)

Equation(6)and(7)maybesolvedforαonthesurfaceatacertainu.Thentheforcesactingonthefingerscanbecalculated.

Here,thesmalldeformationassumptionisusedforcomputingthedeformedshapeofthefingers.First,asmallvoltageisappliedonthefingersontheinitialposition.Thechargedensi2tyonthesurfaceiscalculatedbyBEMunderthiscondition.Thedeformationcanbeachievedbytheequationofelectrostaticenergyandelasticenergy.Andtheachieveddeformationreplacedtheinitialpositionabove.Thentheiteratemeth2odcanbeusedcontinuously.

Fig.6　Displacementofonefingertipwiththepotential

applied

5　Acknowledgement

　　Itisacknowledgedthattheresearchissup2portedbytheKeyProjectofNationalNaturalScienceFoundationofChina.(No.50275140,No.50335050)

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HUANGWen2haoiscurrentlyaprofessorinDepartmentofPrecisionMachineryandPrecisionInstrumentationatUniver2sityofScienceandTechnologyofChina.Hisresearchinterestincludenanometrology,two2photonmicro2fabrication,mi2cromanipulation,etc.Tel:[1**********]372;E2mail:[email protected]

XINGHaoiscurrentlyagraduatestudentinDepartmentofPrecisionMachineryandPrecisionInstrumentation,UniversityofScienceandTechnologyofChina.Tel:[1**********]415;E2mail:[email protected]