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.