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毕业设计论文外文文献翻译光信息科学与技术光电目标位置和速度测量系统中英文对照
Electro-opticaltargetsystemforpositionandspeedmeasurement
Abstract
Thispaperintroducesanelectro-opticaltargetsystem(EOTS)coveringthespeedrangefromsubsonictosupersonic.Thismicrocomputer-basedsystemhasanovelstructureandshowsthecapabilityofpreciselydetectingthepositionaswellasthevelocityofsmallcaliberprojectilesinrealtime.AprototypeEOTSwhosetargetareais1m2hasbeenconstructedandtested.Aspeedaccuracyofbetterthan0.3%wasachieved.Apositionaccuracy,mainlydependentonthespacingbetweenphotodiodesinEOTS,ofbetterthan1mmonatargetareaof1m2wasalsoaccomplished.
Keywords:
Externalballistics,Nocontactmeasurement,Electro-opticaltechniques,Positionmeasurement,Speedmeasurement
1Introduction
Thespeedandpositionmeasurementsofprojectilesaretwoimportantitemsinballisticresearch.Todeterminetheseparameterspreciselyoneneedsanaccuratemeasuringsystem.Aconventionalmethod,namelythehangingup(andtakingdown)oftargetdiscs[l],thoughaccurateinpositionmeasuring,istimeconsuming.Ashot-positionindicator(SPI),describedinReference2,canmeasurethepositionofahighspeedprojectilebyacousticmeasurement.However,theSPIdoesnotprovidethespeedinformation;neitherdoestheconventionalmethod.Besides,theSPIisusedwithinthelimitsofsupersonicprojectiles.
Tomeasurethespeedandpositionofprojectilesrapidlyandsimultaneously,differentelectro-opticalbasedsystemshavebeenproposed3-5].Thesesystemshavetheabilitytocoverthespeedrangefromsubsonictosupersonic.Onesystem,calledthetargetmeasurementsystem(TMS)[3],usesverticalandhorizontalbanksoflightsourcestoformtwoperpendicularlightgridsthatconstructthetargetarea.Anothersystem,calledtheelectro-opticalprojectileanalyzer[4],usesthesameprincipleasTMS,butsimplifieslightsourceswithfiberopticsbundlesandasinglelightsourceineachlightgrid.Theothersystem,calledtheelectronicyawscreen(EYS)[5],usesasolidstatelaserthatiscollimatedanddirectedtoaone-dimensionalbeamexpandersystemtoformafan-shapedlightscreen.Thislightscreenthenisreflectedbyamirrortoconstructaportionofthetargetarea.Thelightscreenismoreprecisethanthelightgridbecausethereisnodeadzoneinthetargetareaaswiththelightgridsystem.
Fromtheaspectofspeedandpositionmeasurement,wetakeadvantageoftheabovesystemsandproposeanovelsystem;theelectro-opticaltargetsystem(EOTS)[6].Weuseacylindricalmirrorthatreflectstheincidentlaserbeamintoa90ºfan-shapedlightscreen.Twosuchlightscreensconstructatwo-dimensionalpositioningsystem.Weevenproposeabentcylindricalmirrortogeneratea90ºlightscreenwithafewdegreesextendedinadirectionnormaltothelightscreentoreducethesensitivitytovibrations.
AprototypeEOTS,whosetargetareais1m2andmeasuredspeedrangeisfrom50m/sto1200m/s,hasbeenconstructedandtested.Aspeedrangeofupto5000m/scanalsobeexpectedaccordingtothesimulationresultsfromtheelectroniccircuitusingPSpice[7].Finally,anine-pointtestingresultfroma0.38in.pistolisshowninthispaper.Theresultshowsthatthestandarddeviationofpositionaccuracyislessthan1mm.
2BasicprincipleofEOTS
Fig.1showstheopticalconfigurationofEOTS.AlaserbeamfromaHe-Nelaserisdirectedontoacylindricalmirror.Thereflectedlaserbeamscreateafan-shapedlightscreenandaredirectedontophotodiodesthatareneatlyarrangedintoanL-shapedphotodiodearray.EOTSusestwolasersources,twocylindricalmirrorsandtwophotodiodearrays,whicharearrangedontheoppositesidesoftheEOTSbodytoformtwofan-shapedlightscreens.Eachlightscreeniscombinedwithitsownsignalprocessingcircuittoconstructanopticalgate.Althoughthereisadistancebetweenthetwoparallellightscreens,viewedfromadistancepoint,thesefanbeamsintersectinaregionofspacecalledthetargetarea(Fig.2).Aprojectilecanbemeasuredonlyifittravelsthroughthistargetarea.
Fig.1OpticalconfigurationofEOTS
Fig.3showstheshotpositionoftheprojectileiscalculated.Thetargetarea,fortheconvenienceofillustration,isasquareofdimensionDoneachside.ThenumberofphotodiodesontheL-shapedphotodiodearrayis2N.Eachphotodiodeisnumberedinorder,asshowninthefigure.Forillustrationclarity,onlythephotodiodearrayandthecylindricalmirrorofthefirstopticalgateareshown.Theprojectileisconsideredtobeincidentnormallytothefirstandtothesecondopticalgateinsequence.Whentheprojectileblocksthelightscreens,therespectivephotodiodeswillbeactivatedbythedisturbance.Inthefirstopticalgate,thelaserbeamfromthecylindricalmirrortoeachphotodiodemakesauniqueanglewiththey-axis.Thisangleismeasuredcounter-clockwisefromtheaxis.Theanglewithrespecttoaphotodiode,numberedn,canbecalculatedas
(1)
and
(2)
Ifcertainphotodiodes,numberedfromjtok,areactivatedbyprojectiles,thentheshot-positionangleδ1,isgivenby
(3)
Fig.2Intersectionsofthetwolightscreensinthetargetarea
Similarly,theshot-positionangleofthesecondopticalgateδ2,measuredclockwisefromtheminusy-axis,isdecided.Afterthetwoangleshavebeenmeasured,the
Fig.3Illustrationofshot-positioncalculation
shotpositionoftheprojectileisdeducedinCartesiancoordinatesas
(4)
and
(5)
IfSisthedistancebetweenthetwolightscreens,thentheaveragespeedvfortheprojectilepassingthroughthedistanceSisgivenby
(6)
whereTisthetimeintervalfortheprojectiletopassthroughdistanceS.
3ConfigurationofEOTS
3.1OpticalsystemofEOTS
WeuseaHe-Nelaserdirectedontoacylindricalmirrortocreatealightscreen.Therelationamongthelaserbeamdiameterd,thecylindricalmirrordiameterwandthebeamexpandingangleφisshowninFig.4.Thisrelationcanbecalculatedas
(7)
Tocreatealightscreenofwhichφequals90º,theratioofwtodis2.8.BecausetheHe-NelaserbeamhasGaussiandistributionandeachphotodiodeonthephotodiodearrayhasadifferentdistancetothecylindricalmirror,thereceivedlaserpowerateachphotodiodeisnotconstant.ThiswillinfluencethespeedaccuracyofEOTS(seeFig.6andSection4.1).
3.2Analoguecircuitry
EOTShas2Nanaloguechannelsineachofitstwoopticalgates.Everyanaloguechannelhasthesamestructure.Eachanaloguechannelcontainsaphotodiode,alinearamplifier,aband-passfilterandacomparator.Thelinearamplifieramplifiesthesignalcomingfromthephotodiode.Theband-passfilterfiltersnoisessuchas
Fig.4Laserbeamdirectsonacylindricalmirror
bugsflyingthroughthelightscreenandflickerofotherlightsourcesnearby.ThecomparatorcomparestheoutputV0,comingfromthefilterwithathresholdvoltageVTH.IfV0ishigherthanVTH,thenthecomparatorwillactivateaflip-flop(FF)tochangethestate.
3.3Digitalcircuitry
Fig.5istheblockdiagramofthedigitalsignalprocessingcircuit.InputcomingfromtheanaloguechannelisfedtoarelativeFF.Whentheprojectileblocksthelightscreenofthefirstopticalgate,thestate-changedFFswillmaketheoutputoftheNANDgateU1changestate.TheU1locksallFFsofthefirstopticalgatetoprotectgenuineprojectiledatafromtheinfluenceofshockwavesbehindtheprojectile,andstartsthecounterU5thatoperatesataclockfrequencyof10MHz.Astheprojectileblocksthelightscreenofthesecondopticalgate,thecircuitofthesecondopticalgatefunctionsasthecircuitofthefirstopticalgatedid,butstopsthecounter.Moreover,theNANDgateU2passesaninterruptsignal(INT)tothecentralprocessingunit(CPU)whileU5isbeingstopped.TheCPUthenrecognizestheinterruptrequest,pickstheprojectiledataup,andresetsU5andallFFsforthenextshot,insequence.InFig.5,thecounterrelatesthetimeintervalTineqn.6.Besides,everyphotodiodeisassignedaspecificFFandeveryFFisgivenarelativeaddress.Therefore,theCPUwillbeabletoidentifywhichphotodiodegeneratesthesignal,todecidetheimpactpositionofeqns.1-5,andtocalculatethespeedoftheprojectile.
Fig.5Blockdiagramofdigitalsignalprocessingcircuit
4AccuracyofEOTS
4.1Accuracyofspeedmeasurement
Theaccuracyofprojectilevelocitymeasurementwithsky-screenshasbeendeducedbyHartwig[8]as
(8)
whereparameterswerethesameaseqn.6used.Δv,ΔSandΔTarevaluesofmaximumerrorinv,SandT,respectively.InEOTS,photodiodesaredirectedbynonuniformopticalpower,asdescribedinSection3.1,whichimpliesthatdifferentanaloguechannelswillhavedifferentresponsetimes,asthoughtheyareactivatedinthesameway.Fig.6describesthetypicalinputandoutputwaveformsofananaloguechannelwhenaprojectilepassesthroughthelightscreen.Thedottedlineisthe
Fig.6Typicalinputandoutputwaveformofanaloguechannel
responseoftheweakeropticalinputwithrespecttothesolidline.InthisFigure,theopticalpowerdensitydirectedontothephotodiodeisconsideredtobeconstantalongthex-axis.Referringtothesolidline,theprojectiletouchesthelightscreenatT1andentirelyblockslaserbeamsatT2;theactivatedphotodiodecurrentIDdropsfromIDHtoIDL.TheoutputvoltageV0oftheanaloguechannelthenrisestoasaturationvoltageVsat.ThecounterisnottriggereduntilV0islargerthanVTH.TheintervalfromT1tothetimethatV0equalsVTHiscalledtheresponsetimetrFromFig.6,wecanrealisethatadifferentinputpowerv