DevelopmentHistory
In1976,theBritishMonaCompanyappliedlaserscanningtechnologytothephototypesettingmachine,andmadetheLasercomptypelaserphototypesettingmachine.
Modernlaserphototypesettingmachinesareequippedwithamicrocomputer.TheoperatorsitsinfrontofaChinesecharacterterminal.Likeatypewriter,anelectroniccomputereditingandtypesettingsystemisusedtoinputmanuscriptsintothecomputer.Thecontentofthemanuscriptisconvertedintodotmatrixinformationbythecomputer,andthedotmatrixinformationisusedtocontroltheacousto-opticmodulator,sothatthediffractedlightpassesthroughthebeamexpanderandisreflectedbythepolyhedralmirror.Theobjectivelensfocusesonthephotosensitivefilmtohaveacertainsize.Lightspot.
Wheneverthepolyhedralmirrorturnsoveroneside,arowofdotmatrixinformationisscannedandexposedonthephotosensitivefilm.Withthecontinuousmovementofthephotosensitivefilmandthecontinuousrotationofthepolyhedralmirror,theline-by-linedotmatrixinformationexposedonthephotosensitivefilmformsthetypesettingofthetext.Thistypeoftypesettingiscommonlyknownasfilm.Thenusefilmtomakeaplateandprint.
Productfeatures
Laserimagesetterisakindofequipmentdevelopedinthe1970s.Thelaserimagesetterisequippedwithaglassfontlibrary.Usingthemainlensoftheimagesetterwithdifferentfocallengths,thecharactersontheglasstemplatecanbeenlargedorreduced,andmorethan20kindsofcharactersofdifferentsizescanbephotographedandimagedonthephotosensitiveplate.
Productclassification
Therearefourmaintypesofimagesetters:outerdrumtype,winchtype,innerdrumtypeandvirtualdrumtype.Imagesettersofdifferentstructuresaredifferentinperformanceparametersandoperation.
Externaldrumimagesetters
Theworkingmethodofexternaldrumimagesettersissimilartothatoftraditionalelectricextensions,recordingfilmTheoutercircumferenceattachedtothedrumrotateswiththedrum,andonelineisrecordedeverytimeitrotates.Atthesametime,thelaserheadmoveshorizontallyforoneline,andthenthenextlineisrecorded.Theadvantagesofthistypeofimagesetterarethattherecordingaccuracyandregistrationaccuracyarehigh,thestructureissimple,theworkisstable,andtherecordingformatcanbemadelarge.
Thedisadvantageoftheexternaldrumtypeimagesetteristhatitisinconvenienttooperateandhasalowdegreeofautomation.Itusuallyrequiresmanualfilmloadingandunloading,andmanualloadingandunloadingmustbeperformedinadarkroom.Largeformatimagesettershavealargerecordingdrum,whichrequiresanairextractionsystemandafilmfixingdevice.Thelargertherecordingdrum,thegreatertheinertiaduringrotation,andtherotationspeedwillbelimited.Therecordingspeedislower,andthenumberoflaserbeamsmustbeincreased.Toincreasetherecordingspeed.Therefore,thistypeofimagesetterisrarelyused.
However,theouterdrumstructureisverysuitablefordirectplatemakingmachines,becausedirectplatemakingisasingleplate,notacontinuousfilm,theplatesizeisfixed,andthedirectplatecanbeoperatedinthebrightroom,whichpartiallyoffsetsItsshortcomings,coupledwiththeshortopticalpathofthisstructure,easytocontrol,lowlaserloss,canusemultiplelaserstospeeduptheexposure.Inaddition,theoutercylinderstructureissimpletohandlethedustduringplatemaking,andtheplateloadingmethodisthesameastheplateloadingmethodoftheprintingmachine,soitcanachievehighprecision.Withtheimprovementofthedesignlevel,thedegreeofautomationwillcontinuetoincrease,soitisconsideredtobethebestdirectplatemakingmachinestructure.
Innerdrumimagesetter
Alsoknownasinnerdrumimagesetter,itisconsideredtobethebesttypeofimagesetterinthestructure,almostAllhigh-endimagesettersusethisstructure.Thisstructurehasthecharacteristicsofhighrecordingaccuracy,largeformat,highdegreeofautomation,easyoperation,andfastspeed,butthepriceismoreexpensivethanthefirsttwotypesofimagesetters.
Theworkingmethodoftheinnerdrumtypeimagesetteristoplacetherecordingfilmontheinnercircumferenceofthedrum.Thedrumandthefilmarenotmovedbutarescannedandrecordedbythelaserbeam,sothereisnoerrorcausedbyunevenfilmtravel.Thelaserbeamislocatedonthecentralaxisofthedrum,andthelasercanrotatearoundthecentralaxis,recording1lineperrevolution,whilethelasermoves1lineintheaxialdirection.Itcanbeseenthattherecordingbeamofthisstructurehasthesamedistancefromanypointonthefilm.Therefore,thelightspotisnotdeformed,andtheproblemofreducedrecordingaccuracycausedbyunstablefilmtransmissioncanbeeffectivelyavoided,whichisthereasonforitsveryhighrepeataccuracy.Ontheotherhand,becausethedrumdoesnotmove,thebeamisdeflectedbytherotationoftheprism.Theprismisverylightandthemomentofinertiaissmall,sotherotationspeedcanbeveryhighandtherecordingspeedisalsoveryfast.
Theinnerdrumtypeimagesetteralsousescontinuousfilm,soitiseasytooperate.Butitsrecordinglengthislimitedtotherangeofthedrumcircumference(usuallylimitedtohalfofthecircumference),anditcannotrecordinfinitelylonglayoutslikeacapstan-typeimagesetter.
Capstanimagesetters
Theworkingprincipleofcapstanimagesetters:Thefilmisdrivenbyseveralfrictiondriverollers,usually3rollersAnd5-rollstructure.Whilethefilmisbeingdriven,thelaserrecordsthegraphicinformationonthefilm,sothemovingspeedandexposurespeedofthefilmmustbestrictlyconsistent.Thelaserlightsourceofthecapstantypeimagesetterisfixed,andthedeflectionoftheexposurelightisrealizedbytherotationofthegalvanometerorprism.
Thefeatureofthistypeofimagesetteristhatthestructureandoperationareverysimple,thepriceisalsorelativelycheap,itcanusecontinuousfilm,andthecontinuousrecordinglengthisunlimited.Thedisadvantageisthattherecordingaccuracyandregistrationaccuracyareslightlylower,andoneunitisonlylimitedtoquartoorlessformatimagesetters.Thewinchtypeimagesetterisamid-rangeimagesetter,andbecauseofitsmoderateprice,itisthemostusedtypeofimagesetter.
Therearetwomainreasonswhytheaccuracyofthecapstantypeimagesetterisnothigh:oneisduetounevenfilmtravelorslippage,especiallywhentheimagesetterisusedforacertainperiodoftime,thefeedrollerisagingorToodirty,itiseasiertocausetheregistrationaccuracytodrop;secondly,itiscausedbythestructureitself.Thefilmrecordingismovedbythefilminonedirection,andthelightisdeflectedbytherotationoftheprismintheotherdirection.Theprismrotatesonecircletorecordoneorseverallines.Ifthelaserspotiscircular,thelaserisperpendiculartothemiddleofthefilm,andthespotcanbeguaranteedtobecircular;whileonbothsidesofthefilm,thelaserisnolongerperpendiculartothefilm,andtheshapeofthespotwillbedeformed.Itbecomesanovalshape,whichaffectstherecordingaccuracy.Therefore,thegreaterthedeflectionangleofthelaserbeam,thegreaterthedistancebetweenthelaserbeamandthecenterandthetwosidesofthefilm,andthegreaterthedistortionofthespot.Inordertosolvethisproblem,itisnecessarytoincreasethedistancebetweentheprismandthefilm,reducethedeflectionangle,andlimittherecordingformat.Thisisthereasonwhythecapstan-typeimagesettercannotbetoolarge.
Virtaldrumimagesetters
Thestructureofthevirtualdrumimagesettersissimilartothatoftheinnerdrumimagesetters.Thedifferenceisthatitusesthefilmtodirectlyringonthetwosupportrings,andthefilmisusedasthedrum,soitiscalledthevirtualdrum.
Performanceparameters
Themainperformanceparametersofthelaserimagesetterare:recordingaccuracy(recordingresolution),repeatability(registererror),format,recordingspeedandlaserwavelength,etc.,Amongthem,recordingaccuracyandrepeataccuracyarethetwomostimportantindicatorstomeasuretheperformanceofimagesetters,andtheyarealsothestandardforclassifyingimagesetters.
Recordingaccuracy
Therecordingaccuracyreferstothenumberoflightspotsthattheimagesettercanrecordinaunitlength,thatis,therecordingresolution,usuallymeasuredinperinchItisexpressedindots(dpi)ordotspercentimeter(dpc).Thehighertherecordingresolution,thesmallerthesizeofthelaserspot,andthehigherthedensityofthespot.Becausethedotsoftheprintedimageareformedbymanylaserbeams,thesmallerthelaserspot,themoredotswillbeformedunderthesamenumberofscreenlines,andthemoregrayscalechangesintheimagecanbeformed.,Makethedotsizesmallerundertheconditionofensuringthenumberofgraylevels,thatis,getahighernumberofscreenlines.Withintherangeofaprintingdot,everytimealaserdotexposureisincreasedordecreased,thesizeoftheprintingdotchangesbyonelevel,whichconstitutesagraylevelofdifferentshades.Therefore,themorelaserspotsthatmakeupthedots,themoregraylevelsareproduced.Thecameracanproduceupto256graylevelsinthisway,thatis,aprintingdotiscomposedof16×16laserdots.
Repeataccuracy
Repeataccuracyreferstotheaccuracyofthepositionoftheimageoneachcolorplate,whichisrequiredforcolorprinting,usuallythefirstcolorTheerrorcalculationoftheoverlapbetweentheplateandthelastcolorplate.Monochromeprintsdonotrequireoverprinting,sotheregistrationaccuracyisnothigh,butforcolorprinting,theregistrationaccuracyisaveryimportantparameter.Iftheoverprintingaccuracyisnotenough,therewillbemisalignmentbetweenthevariouscolorsoftheprintedproduct,whitespacebetweenthecolorblocks,andghostinginsmallfonts.Therefore,therepeataccuracyoftheimagetypesetteriscrucialforcolorprintingplates.important.
Format
Phototypesettingmachineshavevariousformatwidths,generallyincludingpositiveeight-opening,largeeight-opening,positivefour-opening,largefour-opening,andevenfolioandForfull-openformat,generalimagesetterscanuseseveraldifferentformatsoffilmwithinthemaximumformattoadapttodifferentformatrequirementsandachievethepurposeofsavingfilm.Therecordingaccuracyandrepeatabilityoftheimagesetterhasagreatrelationshipwiththeformat.Thelargertheformat,thehighertheaccuracyrequirements,andthemoredifficultitistomanufacture,sothepricewillriseexponentially.
Generally,imagesetterswithinnerandouterrollerstructurescanachievehighrecordingaccuracy,becausethedistancefromthelasertothefilmisalwaysthesame.However,thelaserbeamoftheimagesetterwithacapstanstructureisscannedbytheprismdeflectedbeaminthehorizontaldirection,sothedistancebetweenthelaserbeamandthemiddleandbothendsofthefilmisdifferent.Thelargertheformat,thegreaterthedeflectionangleofthelaserscanning,andthedistancebetweenthelaserbeamandthemiddleofthefilmThegreaterthedistancebetweenthetwoends,thegreaterthenonlineardistortion,andthereforethegreatertheerror.Therefore,itisgenerallyrestrictedthatthephototypesettingformatofthecapstan-typeimagesettercannotexceedfouropen,anditisalsonecessarytotrytoreducethedeflectionangleofthelaserbeamasmuchaspossibletoreducethedeformationofthelightspot.
Phototypesettingspeed
Thephototypesettingspeedisusuallymeasuredbythefilmtravelspeedwhenrecordingwith1200dpiresolution.Thenewtypeofimagesettercanreachaveryfastspeed,butthisisnottheonlyfactorthatdeterminesthespeedofthefilm,becauseitisalsolimitedbytheRIPspeed.Thetimeusedtooutputalayoutshouldbeequaltothesumofthetimeusedtotransmitdatathroughthenetwork,thetimeusedbyRIPtointerpretthelayout,andthetimeusedbytheimagesettertorecord.Therefore,thephototypesettingspeedonlyaffectstherecordingtime.
Laserwavelength
Thecommonlyusedlasersforimagesettersarehelium-neonlasers,withawavelengthof633nm,redsemiconductorlasers,withawavelengthof650nmor670nm,infraredsemiconductorsLaser,thelaseris780nminfraredlight.Thewavelengthofthelaserdeterminesthetypeoffilmused,andeventhepriceofthefilmused.Forexample,thedomesticammonia-neonlaserphototypesettingfilmisthecheapest,almostalltextphototypesusethiskindoffilm,whiletheinfraredphototypesettingfilmisexpensiveandusedless.