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Laser phototypesetting



Introduction

Theimagesetterconvertstheimagesandtextproducedinthecomputerfromelectricalsignalsintoopticalsignals,andthelaserbeamscansonthesilversaltfilm-exposure,Makethefilmgeneratelatentimage,completethewholeprocessoflaserphototypesettingafterfilmdevelopingmachinedeveloping,fixing,washinganddrying.

Accordingtotheneedsofusers,theimagesetterisinstalledwithdifferentworkingsoftware.Theimagesettercanautomaticallyscantheinputcolorgraphicsandtextsaccordingtotheprintingrequirementstoscanoutfourfilmswithsmallblackandwhitedots.Itiscalledhangingscreenandcolorseparationtomeettheneedsofusersinoffsetprinting,usingred,cyan,yellow,andblackinkstosuperimposeandprintcolors.

Thetechnologyofusingacomputertocontrollaserequipmentforphotographictypesettingisoneoftheelectronicphototypesettingtechnologies.Laserphototypesettingequipmentisasophisticatedandadvancedoutputdevice.Throughlaserphototypesetting,high-qualitybooks,newspapersandmagazinescanbeobtained,whichisakeyoutputdeviceincomputer-aidedpublishing.Theelectronicphototypesettingsystemwiththelaserimagesetterastheoutputmachineiscalledthelaserphototypesettingsystem.ChinasuccessfullydevelopedacomputerlaserChinesecharactereditingandtypesettingsystemin1985.

Classification

Laserimagesetterisdividedintoinnerdrumtypeandouterdrumtypeaccordingtotheinstallationpositionofthelaserhead.

Thestructureoftheimagesetterinwhichthelaserheadisinstalledintherotatingdrumiscalledtheinnerdrumtype.Thephotosensitivefilmisclampedonthedruminthemachine,andthephotosensitivefilmofthefilmfacesinwardandtowardthedirectionoflaseremission.MostoftheproductsofcompaniessuchasJapanScreenareofthistype.Thisstructurehashighprecisionandhighcost.

Theimagesetterstructureinwhichthelaserheadisinstalledoutsidetherotatingdrumiscalledtheouterdrumtype.Thephotosensitivefilmisclampedonthedruminsidethemachine,andthephotosensitivefilmofthefilmfacesoutwards,facingthedirectionoflaseremission.ManyoftheimagesettersproducedbyHangzhou'sphototypesettingmachinefactoriesaremostlyofthistype,andthecostofthisstructureislower.

Thereisadevicethatintegratestheinputimageandtextwiththecolorseparationoutputfilm:theelectroniccolorseparationmachine,whichalsobelongstothelaserphototypesettingwork.Thiskindofequipmenthashighprecisionandlargevolume.

LaserphototypesettingtechnologywaspromotedinChinainthelate1980swiththeappearanceofChinesecharacterinputprograms.ThefirsttousethistechnologywasanewspaperwithalargeamountofChinesecharactertypesetting.WiththepopularizationofChinesecharacterinputmethods,traditionaltypesettingandprintinghavebasicallydisappeared.Thedigitalphotoandtextinputmethodsupportstherapidproductionandarrangementofgraphicsandtextonthecomputer,andthelaserphototypesettingtechnologyenablesthegraphicsandtextinthecomputertobegeneratedonfilm,providingafilmforprinting,whichgreatlyshortenstheproductioncycle,Improvethespeedofrespondingtoinformation.

Principle

Textorimageiscomposedofdotmatrix(ieblackandwhitedots)andstoredinthecomputerindigitalform.Whenthelaserscansonthefilm,thedigitalsignalcontrolsthelaserbeamorTurnitonorofftoexposetheimage.

Thehelium-neonlasertubeemitsalaserbeam,whichisemittedfromtheapertureonthesafetyfilterthroughthemodulator.Whenthemachinecoverisopened,thesafetyfilterisautomaticallyinsertedintotheopticalpath.Inordertoreasonablylimitthesizeoftheopticalsystem,aprismisusedtoreversethebeamby180°.Thelightbeamisreflectedfromtheprismandpassesthroughthelightintensityconverterandtheopticalaxisdriftcorrectionlens.Thelightbeampassesthroughthesecond180°reverseprismandthenentersthebeamexpander.Theexpandedlightbeamhitsthe45°inclinedreflector,rotatesdown90°,andthenhitstheeight-sidedrotatingmirror.Theanglebetweeneachofitssmallreflectorsandthe45°reflectorisalso45°,anditsfunctionistoturnthelightbeamby90°.Thelightbeamisfocusedbythefocusinglensandthenhitsthefilm.Wheneverthesmallmirrorreflectsthelaserbeam,alaserbeamsweepsacrossthefilm.Therefore,everytimetheeight-sidedrotatingmirrorrotates,thereareeightscanlinesonthefilm.Whenthelasertypesettingmachineworks,thetypesettingcontentinformationisfirstsenttothebufferregisterinpreparationforsendingittothemodulator.Thisinformationisexpressedintheformof"0"and"1",andthemodulatorusesthisinformationtocontroltheonandoffofthelightbeamintheopticalsystem.Eachlineoftextiscomposedofsomelaserscanlines,andeachscanlineiscomposedofsomeblackandwhitedots.Aftertheinformationinonebufferregisterisusedup,theotherbufferregisterisfilledwiththeinformationofthesubsequenttext.Inthisway,informationiscontinuouslysenttothemodulator.

Components

Laserimagesetteriscomposedoflaser,modulator,lightintensityconverter,opticalaxisdriftcorrectionlens,beamexpanderandoctagonalmirror.

Laser

Itisatubefilledwithhelium-neongas.Oneendofthetubeisatotalreflectionmirror,andtheotherendisareflectorwithaslighttransmittance.Heliumatomsemitmanyelectronsafterbeingexcitedbyradiofrequencypower.Theseelectronscollidewithneonatomsandtheneonatomsalsobecomeexcited.Theexcitedneonatomthencollideswiththeheliumatom.Theenergyconversionproducedduringthecollisioncausesthehelium-neonatomicgastoemitlight.Thelightisreflectedbackandforthbetweenthetwomirrorsofthelasertubetoimproveitscoherenceandparallelism,andfinallyoutputfromthemirrorwithaslighttransmittance.Theadvantageofthehelium-neonlasertubeisthatthebeamparallelismisgood,anditsmonochromaticityisalsoverygood,andtheopticalsystemisnolongerneededtoeliminatechromaticaberration.

Modulator

Anopticalswitchthatcontrolstheonandoffofthelightbeamintheopticalsystemaccordingtotheprincipleoflightrefraction.Thelightmodulatoronthelasertypesettingmachineusesapieceofacousto-opticcrystalmaterial.Whenthemodulatoristurnedoff,thelaserbeampassesdirectlythroughthecrystal;andwhenthemodulatorisworking,theRFpowersourcecausestheacousto-opticcrystaltogenerateapressurewave.Thischangeinthecrystalcausesthebeamtodiffract(thatis,morethanonerefractedlightisoutput).Apreciselightmodulatorcanenhancethefirst-orderdiffractedlight.Itissuchastrengthenedbeamthatemergesfromtheopticalsystem.

Lightintensityconverter

Itchangestheintensityofthelaserbeambyadjustingitspositiontoadapttovariousoutputrequirements.Ithas9workingpositionsintotal.Bit0isatransparentdiaphragmwithnofiltereffect,andbits1to8aretheworkingpositionsoftheintensityfilter.Thelargerthepositionnumber,themorethelightintensityattenuates.

Opticalaxisdriftcorrectionlens

Duetotheinfluenceofvariousfactorssuchastemperature,thebeammaydriftoffthecorrectpath.Thedriftcorrectionlensisusedtoeliminatethisdriftdeviation.

Beamexpander

Usedtoexpandthebeamdiameter.

Eight-sidedrotatingmirror

Itisapyramidwitheightsmallmirrors,rotatingclockwiseataspeedof3000rpm.The45°reflectorreflectsthebeamoutputfromthebeamexpandertothesmallreflectoroftheeight-sidedrotatingmirror.Wheneverthesmallmirrorrotatestoacertainposition,thelightbeamisreflectedtothehorizontalscanningplane,thatis,itsweepsacrossthefilm.Thefilmfeedamountcorrespondingtoeachsmallmirroris0.0254mm.Adisc-shapedgratingisinstalledontheaxisoftheeight-sidedrotatingmirror.Itisaroundplexiglassplatewith3000linesengravedonthesurface.Whentheeight-sidedrotatingmirrorrotates,thecomputertracksthescanningprocess,andthecontrolsignalisprovidedbythephotocellalignedwiththegratingline.

Directplatemaking

Uselaserbeamtoexposeandimageonphotosensitiveplate,afterprocessing,itisdirectlyprintedonoffsetprintingrotarypress.Thistechnologyiscalledlaserdirectplatemaking.Thelaserimagesetterwiththisfunctioniscalledthefifth-generationimagesetter.

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