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Method for Measuring Velocity of Warhead Fragments Based on Photoelectric Detection

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Method for Measuring Velocity of Warhead Fragments Based on Photoelectric Detection

    Method for Measuring Velocity of Warhead

    Fragments Based on Photoelectric

    Detection

    JOURNAL0FCHINAORDNANCE

    MethodforMeasuringVelocityofWarheadFragments

    BasedonPh0t0electricDetection

    NIJinping(4K晋平),YANGLei(杨雷)

    SchoolofOptoelectronicalEngineering,Xi'anTechnologicialUniversity,Xi'an710032,China

    Abstract:Formeasuringvelocityandimpactingpositionofsinglefragmentofwarhead,anoncontactmeasuringmethod

    isproposed,inwhichasixlightscreenarray,apositionindicator,amulti

    channelchronographandacomputerareused.

    Theprincipleofmeasurementisdescribed.Thekeydeviceofthesystemisalightscreenarraysensorwhichconsistsofsix

    lightscreensallocatedwithcertaingeometricalparameters.Whenthefragmentfliesthroughthelightscreenarray,the

    timeofpassingthrougheachofthescreensisrecordedbythemulti

    channelchronograph.Accordingt.

    othetimedataand

    thegeometricalparametersofthearray,thevelocityvectorandthelocationofthefragmentcanbecalculatedimmediate

    ly.Thepresentedmethodcanbeusedtolocatethefragmentandtomeasuretherealvelocityonitsflyingdirection.Itcan

    alsobeusedtomeasurethevelocityofafragmentswarlTlafterthesystemisengineeredfurther.

KeyWords:instrumentandmetertechnique;fragment;direction;position;velocitymeasure

    ment;lightscreen;trajec

    tory

    CLCNumber:TJ810.6DocumentCode:AArticleID:1673002X(2007)04027506

    Introduction

    Forevaluatingandcheckingtheperformanceofa missileoraprojectileinaweaponsystem,thekinetic energy(orvelocity)impactingonthegroundofthe warheadfragmentsisavitalfactortobedetermined. Accuratemeasurementofthevelocityoffragmentsis animportantprojectinthefieldofendballistictrajec

    tory[

    .

    Comparedwithordinaryprojectiles,thesize ofwarheadfragmentsissmallandtheamountof themislarge.Thereforetheinductioncoilusedinve

    locitymeasurementisunabletodetectsignalsfrom thefragments.Althoughtheskyscreensandlight screenshaveenoughsensibilitytosenseanddetectthe fragment,neithercanbedirectlyusedThisisbe

    cause,accordingtotheprincipleofmeasuringvelocity withzoneblockmeasuringsystem,thereisabigdif

    ferencebetweentheresultofmeasurementandrea1 valuewhiletherealtrajectoryisunparalleltotheas

    sumedtrajectory[3..Insomecases,itisimpossibleto letthefragment'sflyfollowthedesignedpath.To thelargesensitiveareaofthesensors(skyscreensor 1ightscreens),theconditionismoreserious.Atthe timeofexplosion,therearelargenumbersoffrag

    mentsandhighlyintensivedistributioninaround

    areanearthecenterandthemeasuredenvironmentis disturbedbyexplosiveflame,sandydust,shockwave andfragmentpowder.Allofaboveresultinthefact thatitisconsiderabledifficultytomeasuretheveloci

    tyofafragment[.

    Highspeedphotographandzrayphotograph

    technologyareanothermethodstomeasurefrag

    ments[

    .Theyrecordtheimageoffragmentsinreal timeandtherealvelocityofafragmentcanbefigured outbyanalyzingtheimages.However,suchkindof methodisdifficulttodistinguishtheindividua1ofa swarmoffragmentsinthedynamicexplosionandthe hugeerroroccurswhenthefragmentflyingalonga largeangletoanassumedtrajectory.Moreover,un

    dertheconditionsofhightemperature,highpres

    Reeeived20070510

    SponsoredbyFoundationofDepartmentEducationofShaanxiProvinceofChina(o3JC31)a

    ndKeyLabFoundationinNanjingUniversityofSci enceandTechnology(51453010103SX0201) BiographiesNIJinping(1965),professor,dorctor,jpni@263.net;YANGLei(1975(),lecturer,master,xaityang@126.corn

    ?--——

    —— 275?--

    jouRNALOFCHINAORDNANCE,2007,Vo1.3,No.4 sure,andhighintensityofshock,thequalityofthe filmnegativeofzrayispoor,theimageisblurryand haslowratioofsignaltonoise(SNR).Theerror

causedbyreadinginmanualisinevitable.Inaddi

    tion,themethodshavethedefectsofhighcost,bad environment,anddifficultdisposa1.Asaresult,al

    mostnooneusethehighspeedphotographandzray

    photographinthefieldoffragmentmeasurement. Nowadays,themethodtomeasurethefragment isusingmostlythecombshapedtargetwhichworks

    incontactmannerundertheconditionofstill——explo.

    sion.Inthismethod,still,theflyingangleconsider

    ablyaffectsontheprecisionofmeasurement.A methodusingfour..1ight-screentoconstructageomet.

    ricalarraywasproposedbysomeresearchers[.

    It

    couldmeasurethevelocityandimpactingpositionof projectiles.However,itstrictlydemandstheprojec

    tiletogothroughthemeasuringplaneinperpendicu

    larmanner.Otherwise,thereisbigerrorbetweenre

    alvalueandthemeasuredresult.Becauseofthelarge distributionofprojectilesorfragments,allabove methodsareincapableofmeetingtherequirementof thefragmentmeasurement.

    Itseemsthatfewdevelopedmethodstomeasure warheadfragmentinnon-contactmannerwerere.

    ported[1,3,5,8-9].Inthispaper,basedontheprinci

    pleofmeasurementwithdoublesensors,aspecialar

    raywithmultiplelightscreensisproposed.Thearray iscomposedofsixlightscreens.Amongthem,four

    1ighscreenisusedtomeasurethecoordinatesinhori

    zontal(zaxis)andvertical(Yaxis)directionsre

    spectively,andtwolightscreenscanbeshared.As

    theprojectilesorfragmentsgothroughallofsixlight screens,theimpactingpositionandthevelocityof themcanbeobtainedwithouttheconstraintthatthe flyingpathhastobeparalleltotheassumedtrajecto

    ry.Itisrealizedthattheproposedmethodworksin noncontactmarlnPr.

    1CompositionandPrincipleof

    MeasuringSystem

    1.1CompositionofMeasuringSystem

    Themeasuringsystemconsistsofasixlight

    screenarray,apositionindicator,amultichannel

    chronographandacomputer.Fig.1depictsitscorn

    position.Thesixlightscreenarrayiscomposedofsix lightscreenstodetectthesignalfromfragment. Whenthefragmentgoesthroughanyoneofthesix lightscreens,apulsesignalisgenerated.Weassume thesensitivescreenisanidealplaningeometryand thethicknessoftheplaneiszerointheoreticanalysis. Thatmeansnosoonerhadthefragmenttouchedthe planethanthesignalwouldbeproduced.InFig.1, G1,G2,,andG6standforsixlightscreensre

    spectively.Thepositionindicatorthatismadefrom paperboardorwoodveneerislocatedbehindthear

    ray.Itmustbestrongenoughnottobespiltbythe explosiveshockwhilethefragmentwouldmakeahole onit.Themultichannelchronographisusedto

    recordthetimebetweensignalsproducedbysixlight screens.Finally,thetimedadaaretransmittedtoa computertobeprocessed.Theflyingparametersof fragmentssuchasvelocity

ordinatesarecalculatedby

    0

    

    

    vectorandthepositionco

    thespecialsoftware.

    Fig.1Compositionofameasuringsystem

    Formeasuring,thearrayisplacedonapoint apartfromthecenterofstillexplosionlocation.Then

    thecomputerisconnectedtothearrayandlocatedfar enoughfromthestillexplosioncenter.Thefragments explodedflydivergentlyalongaglobulardirection. Thereforetherearealimitednumberoffragmentson aspecificpointapartfromthecenter[.

    AssumeN

    fragmentsareflyingthroughthearray,the6xN pulsesareproducedbysixlightscreensrespectively. EachlightscreenmayproducelikelyNpulsesignals. ---——

    276---——

NIJin.ping.eta1.|MethodforMeasuringVelocityo}WarheadFragmentsBasedonPhotoele

    ctricDetection

    Themultichannelchronographrecordthetime,that isindicatedbyt1(i),t2(i),t3(i),t4(i),t5(i), t6(i),wherei=1,2,,Narecorrespondingtime

    sequencesforithfragment.Notethatseveralcompli

    catedcasesshouldbeconsideredtoanalysisthetime sequences.Caseone:morethanonefragmentmaygo throughsimultaneouslyoneofsixlightscreenssothat

    thescreengeneratesonlyonesigna1.Casetwo:some fragmentsmaygothroughjustpartofallsixlight screenssothatthetimesequenceswil1beinvalidfor measurementforthe1ackofremaindersigna1pro

    ducedbythescreenswithwhichthefragmentdoes notgothrough.Therefore,thenumberofpulsesig

    nalsrecordedbythemultichannelchronographin

    eachchanne1maybedifferent.A11ofthetimese

    quencescanbe1istedinTable1.

    Table1Pulsetimesequences

    InTable1,1,2,,6maybeidenticalor

    differenteachother.EveryrowinTable1indicates theonechannelofthechronograph,buteverycol

    umndoesnotindicatedeterminatelythetimese

    quencesproducedbythesamefragment.Thenature numberineveryiteminthetableisonlyindicativeof thereachingsequencesofpulseinranking. 1.2PrincipleofMeasurement

    Theschematicstructureofthesix--light-screen

    arrayisshowninFig.2.Forillustrationclarity,an idealplaneingeometryisusedtoindicatethereal lightscreen.InFig.2,GIstandsforthelightscreen depictedasaplaneOABC.Similarly,theplaneDE

    FGstandsforthelightscreenG2,theplaneAODE standsforthelightscreenG3,theplaneJFGKstands forthelightscreenG4,theplaneFOCEstandsfor thelightscreenG5andtheplaneIGDJstandsforthe lightscreenG6.Fig.3showstheprojectionsof3D

    structureontheplanesofxOzandyOzrespectively.

TheplanesofxOzandv0arerelatedwiththeco

    ordinatesofzandy,respectively.G1isparallelto G2.Thesetwolightscreensconstitutefirstmeasur

    ingvelocitysystem.G3isparalleltoG4,whichcon

    stitutesecondmeasuringvelocitysystem.Gsisparal

    leltoG6,whichconstitutesthirdmeasuringvelocity

    system.

    G

    G.

    G

    /

    (a)Positionsofscreensrelativeto

    /

    O2

    (b)Positionsofscreensrelativetoy

    Fig.2Schematicstructureofarrayswithsixlightscreens (a)ProjectionsofscreensrelativetoonaplanexOz (b)ProjectionsofscreensrelativetoYonaplaneyOa Fig.3Projectionsofscreensontwoperpendicularplanes LetG1beadatumplane(referencedplane), then,theanglebetweenplanesG1andGsisog,and ?--——

    277?--——

    JOURNALOFCHINAORDNANCE,2007,Vo1.3,No.4 theanglebetweenplanesGlandG3is.Theline

    01O2thatisorthogonaltoplaneGlisanassumed trajectoryoffragments.Assumethattl,2,3,4,

    5,t6arethemomentswhenthefragmentflies

throughG1,G2,,G6,respectivelyandthemo

    mentt1isstartingpointoftime(Itsvalueiszero.), hence,thethreemeasuringvelocitysystemscanmea

    surethreetimesdatarl,z-2andz-3,respectively Whentheflyingdirectionofafragmentisparal

    leltotheplanexOz,thevelocityoffragmentcanbe calculatedunderthefollowingassumptions.Theve

    locityofafragmentis,andthevelocitybetween twolightscreensisinvariable(theattenuationofve

    locityissosmallthatwecanneglectit).Thedistance offirstmeasuringvelocitysystemisSlandS3isthe distanceofthirdmeasuringvelocitysystem.O1O2is

    theassumedtrajectorythatisperpendiculartothe planeG1.Twocasesmayoccurincalculationas showninFig.4.

    io

    (a)

    D/lO

    (b)

    G

    G

    G2

    G

    Fig.4SchematicplottrajectoryparalleltoplanexOz 1)Whenarealflyingdirectionisparallelto 01O2,thevelocitiesmeasuredbythefirstandthird velocitymeasuringsystemsareasfollows

    Sl

    1.

    '1

S

    v3=_COSO/'

    (1)

    (2)

    where1isthevelocitymeasuredbythefirstmeasur

    ing-velocitysystem,v3isthevelocitymeasuredby thirdmeasuringvelocitysystem,r1isthetimeperi

    odwhenthefragmentfliesthroughGIandG2,z-3is thetimeperiodwhenthefragmentfliesthroughG5 andG6.Itiseasytounderstandthatv3isnotthere

    alvelocityofthefragment.

    2)Whentheflyingdirectionhasanangleawith aplane2,thevelocitiesmeasuredbytwomeasur

    ing-velocitysystemsaredepictedasfollows.As showninFig.4(b),theline0i0istherealtrajec

    toryofthefragment.yshouldsatisfythecondition of(.<y<.),whereisdeterminedaccording tothepositionoffireandmustguaranteethefrag

    mentflyingthroughallsixlightscreens.isnega

    tivewhentherealtrajectorylocatesontheleftsideof 0102.Then

    ,

    1:

    S1

    ,(3)

    '1

    :

    S3

    ,(4)

    where

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