CA1127543A - Laser platemaking device - Google Patents
Laser platemaking deviceInfo
- Publication number
- CA1127543A CA1127543A CA336,340A CA336340A CA1127543A CA 1127543 A CA1127543 A CA 1127543A CA 336340 A CA336340 A CA 336340A CA 1127543 A CA1127543 A CA 1127543A
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- Canada
- Prior art keywords
- laser
- output
- modulator
- plate material
- input
- Prior art date
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Abstract
Abstract of the Disclosure A laser platemaking device for use primarily in printing comprises a system for synchronous scanning of an original and a plate material, an optoelectronic reader and a halftone pulse transducer, both optically associated with the synchronous scanning system and connected to an electronic circuit for generating a sequence of signals to control the laser beam parameters, which permits a line and a dot pattern to be produ-ced on the plate material within a single process cycle and inclu-des a dot and a line channel connected in parallel, a dot-line switch for automatic switchover of the line and dot channels, and a unit for registering the boundaries of halftone images, kinematically linked with the synchronous scanning system and generating commands to the dot-line switch, the laser platema-king device also comprising a laser-optical system for forming images on the surface of the plate material using a laser modulator.
Description
~~ ICE
l'hc prese~t inv~ntion rela-tes to ~he art of plate .maL.-ng or ~p~oduction~ ænd more particularly to laser devices ior mal.<ing plates used in all main printing processes - le~e_-~,ress~ offset~ pho-togravure and screen stencillng7 and ~pli-cable in printing and publishing7 including printing ol ~rt~o-~and lettering on manufactured products~ e.g. glassg and h~^ldicraft ar~tic es~
Q.t present~ the overwhelming majority of presswork, such as books, newspapers and magazines, involves letterpress ~r.d offset printing. The difference betv~een letterpress and ofl-set printing lies in the specific features of printing plates.
Printing plates, or t~peforms, ~or letterpress printing are essentially heavy and bulky castings involving complex loundry, electropla-ting, photochemical and photoprinting pro-cesses and equipme~t, as well as trueing. ~his renders printing expensive 9 time-, labor- and material-consuming.
Offs~t plates are much simpler, lighter and cheaper.
~hey are essentially thin metal, plastic or paper plates with a special coa~ing on which the image to be duplicated is form-ed. In of~set printing9 the most complex, expensive and time-consuming factor is the process o~ platemaking. ~o this end, multiple phototransfer of images is used, which necessi-tates photoprinting and photochemical e~uipment, a large amount of chemicals and various ~terials, including precious ones (sil-ver).
~ herefore 9 extensive research is under way, aimed at deve-.
~127543-- 2 --1G?ing simpler tcc~icues Ior of I set plate making~ A -c~-v ?ro-isins t~elld is applic~tion of laser beams. The maaor acv~-l-ta-ges oi lase-~ beæms include the capaci-ty for e~tremcly ;~igh concentra-tion of energy ~ith-n a small volume~ easy anc in-s~ aneous control of the laser energ~ in space and in -~im~.
This permits effective use oC laser be~ns for precision pro-ccssing oL all materials, both metal and nonmetallic.
It is of particular advan-tage to work non-me-tals; ~hich requires relatively cornpact and inexpensive lasers. ~his is hy one of the earliest developments after the advent of la-sers involved their application in printing.
Kno~n in the art is a system t'~aser Graph" intended for makin~ letterpress typeforms based on a plastic rather than metal. Used as the form material is a polyethyleneterephthalate film coated with a thin layer of metal.
The prior art system comprises -two self-contained laser devices - a scanning scriber and an etching unit. The form material is secured in the scanning scriber where used as the original is a high-quality newspaper page copy prepared by conventional methods. The original is read out by ~e~ns of a focused helium-neon laser beam. ~he laser beam reflected from the original and carrying information on the image is sensed b~ an optical reader, amplified and used for modula-tion of the beam of an argon laser which simultaneously scans the form material. ~he focused beam of the 15-W argon laser evapo-rates the me~allic coating of the form plate in the nonprinting areas ~nd leaves vhe coa~ing in the printing areas~ vneLeby L`or;!in~ -m~-~allic prin-ving areas and transferrin~ the ima~ -c-.
the ori~inal to the typeiorm surLace in facsimile. The type~ O~l~..^~
is then positioned in the e-tching unit in which the nonr)~ vin~
a~ea are recessed vo a required dep-th with -the aid oi a 400~
C2 laser be&rl17 as a result of evaporation of the plastic base.
The ~tyeform proàuced within six minutes is ~hen used fo~^
runnin~ the newspaper. The use of the prior art system has made it possible to substantially cut down the platemakin~ cycle but the high cost of this system restric-ts its application.
Also known is another system "~aserite" intended for ex-posure of plates with the aid of an argon laser. Its appli-cation is effective in automatic con-trol systems of publishing houses with transmission of page images via communication lines from the publishing to the printing house. The paste-up prepared in -the publishing house is sent via a communication link to the printing Aouse in which it is sensed by the re-ceiver unit of the system with simultaneous exposure on a photofilm which is subsequently used for platema'~ing by con-ventional photomechanical techniques.
Another known laser platemaking device "~og~" is built around a solid-state YAG laser and makes an offset plate and a transparency at the same time. r~he form material is a plasvic-coated substrate. r~he laser beam fuses the plastic to the substrats everywhere except the nonprinting areas. After processing, the plastic is separated from the substrate and ~1~75~3 L, lay be used as a tr~nsparency~ while the subsura---e Wit^l the '-`u_c~ printirlg areas serves as the printing plate. ~ere s only one exis-~in~ unit oi the device and its capacity is ~ GW.
Yet ano~her device9 closest in concept to the one p~oposed herein~ comprises a system of simultaneous scanni.lg of the color copy &nd the plate material, including an electric drive rota-ting a cylinder scanning system. The la~tter com~rises -two cJlinders rnoun-ted on a common sha~-t. The copy~ e.g. a color transparency9 is placed on one cylinder9 while the ot~er accommo-dates a photosensitive film.
This device also com~rises an optoelectronic reader asso-cia-ted with a synchronous scanning unit, and a halftone puls0 transducer.
- Other components of the above laser device include an electronic circuit connected to the optoelectronic reader and producing a sequence o~ signals for controlling laser beam parameters as well as driving a correc-tor, a comparator asso-ciated with a shaper coupled to the hal~tone pulse transducer~
an analog-to-digital converter, a control computer, and output amplifiers.
In addition9 the laser device comprises a laser-optical system ~or image formation~ which includes a laser, optical modulators whose inputs are connected to the output amplifiers, and optical units for directing laser beams to the sc~ned sur~'ace and focusing -them thereon.
'~he photosensi~ive film becomes a color-separating trans-parency after laser and photochemical processing. ~he color
l'hc prese~t inv~ntion rela-tes to ~he art of plate .maL.-ng or ~p~oduction~ ænd more particularly to laser devices ior mal.<ing plates used in all main printing processes - le~e_-~,ress~ offset~ pho-togravure and screen stencillng7 and ~pli-cable in printing and publishing7 including printing ol ~rt~o-~and lettering on manufactured products~ e.g. glassg and h~^ldicraft ar~tic es~
Q.t present~ the overwhelming majority of presswork, such as books, newspapers and magazines, involves letterpress ~r.d offset printing. The difference betv~een letterpress and ofl-set printing lies in the specific features of printing plates.
Printing plates, or t~peforms, ~or letterpress printing are essentially heavy and bulky castings involving complex loundry, electropla-ting, photochemical and photoprinting pro-cesses and equipme~t, as well as trueing. ~his renders printing expensive 9 time-, labor- and material-consuming.
Offs~t plates are much simpler, lighter and cheaper.
~hey are essentially thin metal, plastic or paper plates with a special coa~ing on which the image to be duplicated is form-ed. In of~set printing9 the most complex, expensive and time-consuming factor is the process o~ platemaking. ~o this end, multiple phototransfer of images is used, which necessi-tates photoprinting and photochemical e~uipment, a large amount of chemicals and various ~terials, including precious ones (sil-ver).
~ herefore 9 extensive research is under way, aimed at deve-.
~127543-- 2 --1G?ing simpler tcc~icues Ior of I set plate making~ A -c~-v ?ro-isins t~elld is applic~tion of laser beams. The maaor acv~-l-ta-ges oi lase-~ beæms include the capaci-ty for e~tremcly ;~igh concentra-tion of energy ~ith-n a small volume~ easy anc in-s~ aneous control of the laser energ~ in space and in -~im~.
This permits effective use oC laser be~ns for precision pro-ccssing oL all materials, both metal and nonmetallic.
It is of particular advan-tage to work non-me-tals; ~hich requires relatively cornpact and inexpensive lasers. ~his is hy one of the earliest developments after the advent of la-sers involved their application in printing.
Kno~n in the art is a system t'~aser Graph" intended for makin~ letterpress typeforms based on a plastic rather than metal. Used as the form material is a polyethyleneterephthalate film coated with a thin layer of metal.
The prior art system comprises -two self-contained laser devices - a scanning scriber and an etching unit. The form material is secured in the scanning scriber where used as the original is a high-quality newspaper page copy prepared by conventional methods. The original is read out by ~e~ns of a focused helium-neon laser beam. ~he laser beam reflected from the original and carrying information on the image is sensed b~ an optical reader, amplified and used for modula-tion of the beam of an argon laser which simultaneously scans the form material. ~he focused beam of the 15-W argon laser evapo-rates the me~allic coating of the form plate in the nonprinting areas ~nd leaves vhe coa~ing in the printing areas~ vneLeby L`or;!in~ -m~-~allic prin-ving areas and transferrin~ the ima~ -c-.
the ori~inal to the typeiorm surLace in facsimile. The type~ O~l~..^~
is then positioned in the e-tching unit in which the nonr)~ vin~
a~ea are recessed vo a required dep-th with -the aid oi a 400~
C2 laser be&rl17 as a result of evaporation of the plastic base.
The ~tyeform proàuced within six minutes is ~hen used fo~^
runnin~ the newspaper. The use of the prior art system has made it possible to substantially cut down the platemakin~ cycle but the high cost of this system restric-ts its application.
Also known is another system "~aserite" intended for ex-posure of plates with the aid of an argon laser. Its appli-cation is effective in automatic con-trol systems of publishing houses with transmission of page images via communication lines from the publishing to the printing house. The paste-up prepared in -the publishing house is sent via a communication link to the printing Aouse in which it is sensed by the re-ceiver unit of the system with simultaneous exposure on a photofilm which is subsequently used for platema'~ing by con-ventional photomechanical techniques.
Another known laser platemaking device "~og~" is built around a solid-state YAG laser and makes an offset plate and a transparency at the same time. r~he form material is a plasvic-coated substrate. r~he laser beam fuses the plastic to the substrats everywhere except the nonprinting areas. After processing, the plastic is separated from the substrate and ~1~75~3 L, lay be used as a tr~nsparency~ while the subsura---e Wit^l the '-`u_c~ printirlg areas serves as the printing plate. ~ere s only one exis-~in~ unit oi the device and its capacity is ~ GW.
Yet ano~her device9 closest in concept to the one p~oposed herein~ comprises a system of simultaneous scanni.lg of the color copy &nd the plate material, including an electric drive rota-ting a cylinder scanning system. The la~tter com~rises -two cJlinders rnoun-ted on a common sha~-t. The copy~ e.g. a color transparency9 is placed on one cylinder9 while the ot~er accommo-dates a photosensitive film.
This device also com~rises an optoelectronic reader asso-cia-ted with a synchronous scanning unit, and a halftone puls0 transducer.
- Other components of the above laser device include an electronic circuit connected to the optoelectronic reader and producing a sequence o~ signals for controlling laser beam parameters as well as driving a correc-tor, a comparator asso-ciated with a shaper coupled to the hal~tone pulse transducer~
an analog-to-digital converter, a control computer, and output amplifiers.
In addition9 the laser device comprises a laser-optical system ~or image formation~ which includes a laser, optical modulators whose inputs are connected to the output amplifiers, and optical units for directing laser beams to the sc~ned sur~'ace and focusing -them thereon.
'~he photosensi~ive film becomes a color-separating trans-parency after laser and photochemical processing. ~he color
2~S~3 separator is intended IOr lorming continuous-tone imaOes ~ ch, wl.eIl tr-~ns~it-ted uxing ~he printing process~ are broken up invo ao-ts wi-th dirnensions proportional to the op-tical densi~vy o the -transmitted portions of the original. This process is l~nowJn as ~the halftone process or screening and the patte n of the resulting i~age is known as dot pattern.
'i'he dot pat-tern must have a precise orientation of t.ie screen elements. ~~~n trans~nission of a black-and-white con~inuous---tone image, the screen elements are oriented at an angle of 45'~, while in color printing the screen elements of each color are oriented at different angles, e.g. 15, 30 and 45 to the generatrix of the cylinder.
For screening of continuous-tone images, in the prior art laser device provision is made for generation of a sequence of half-tone pulses matched in coordinates and time with the sur-faces of the copy and plate material.
'~he halftone pulses are generated by the halftone pulse transducer which senses the sequence of contrast lines cut in the surface of one of the cylinders. ~he line-by-line read-out of the copy is perI`ormed by the optoelectronic reader which produces an analog signal proportional to the optical densit~ in the read-out area of the copy.
'~he sequence of halftone pulses and the analog pulse are fed into the electronic circuit. '~he halftone pulses are applied to the shaper which converts the bell-shaped waveform o~ the pulses, generated b~ the halftone pulse transducer, to a required square waveform. '~he analog signal is appli-~ 127543 ~, ed -to t`ne correc-tGr with the aid of which it is conditiGned so as bO correc-l- ior im~erfections of the copy and to provide for such a co~bination of printing Lnk colors as to reproduce color images with hignest fidelity. ~rom the correc~or the analog signal proceeds to the co~parator also receivirg the sequence of halftone pulses from the shaper. Co~parison o~
both signals results in a sequence of halftone pulses at the comparator output; whose wid-th is proportional to the optical density of the copy a-t the moment of passage of a pulse. These pulses are referred to as data halftone pulses. '~hey are ap-plied to the analog-to-digital converter and further to the address register OL the computer. '~he coded information on the image of the copy is fed from the address register to a storage of the computer. The latter receives data determining the desired shape of the screen elements, in this case diamond shape. In accordance with the data~ the storage generates a sequence of pulses whose number and width depends on the opti-cal density of the copy in the read-out portion of the copy, the size of said portion depen~ing, in turn, on the selected screen ruling. '~he selected sequence of pulses is applied ~o the output register of ~he computer, then to the operational control unit of the latter, which also receives a synchronizing sequence of halftone pulses, definin~ a cycle of putting out pulse trains to the group of parallel-connected output ampli-fier. '~rains of amplified pulses are applied therefrom to the electronic inputs of the optical modulators controlling ~12~S~L3 the intensity of the laser-optical systern channels. ~^is syste~
includes an argon laser. It operates at a wavelength oi abou-t ~.5 m crons~ a-t ~vl~ch tL^le sensi-tivity of -the filrn is m~imu~.
To e~ose -the photosensitive film at a linear scanning speed of several meters per second, a laser beam power oi several tens of milliwatts is suificient. '~herefore~ normal operation of the prior art multichannel laser device is ensured at a laser beam power of several wat-ts. Such a laser beam is directea toward a plurality of optical semitransparent cells spli-tting the beam among five channels. Each channel includes an optical ~odulator, an analyzer, a focusing lens and an opti-cal wedge for fine adjustment of the intensity of the laser channels, equalizing the laser beam power in all channel.
~ he controlled laser channels simultaneously write a group of lines on the photomaterial, at instants preset by the half-tone pulse transducer, the lines forming screen elements of a predetermined shape and an area determined by the optical density of the read-out portion of the copy, which permits re-production on the photosensitive film of continuous-tone imag-es of the desired quality.
A specific feature of the prior art devices is making of a photographic transparency from which a printing plate is sub-sequently produced by conventional photomechanical techniques.
Used as originals in the prior art devices are high-quali-ty copies produced by conventional letterpress or offset pro-cesses.
~lZ75~3 cGnsider now -the currentlJ e~ployed -technique of m~king G fset plates. r'he prinved rl~atter to be reproduced is no~rrally divided into gro~ps: uy~ev/ritten text9 captions~ graphical art-wor~, ~nd con-t~nuous-tone illustra-tions (photographs). T~ te~t ard captions are com2osed thcn sent for s-tripping-in or pas-ting--up. Ini~iall~, the first la~out is prepared. ~fter ~pp-~oval by ~he eclitor, the layout is disassembled. ~he line im~es are reasse~bled, arAd the -tone illustrations undergo an additional operation - screening. As a result, a mock-up is prepared which is essentiall~ the final copy to be duplicated. ~rom this rnock--up a transparency is made to scale. ~hereafter, a photosensitive layer is applied on the plate material. ~he latter is exposed to the transparency9 and the resulting image is then tanned and retouched. ~he finished printing plate goes to the printing machine for a run.
As can be inferred from the above description o~ prior art devices and techniques of offset printing, all of the des-cribed laser platemaking systems and devices perform only one of the above-mentioned operations. ~he use of prior art laser devices speeds up individual operations but fails to improve the platemaking procedure as a whole.
Argon or helium-neon lasers used in the known devices feature a low efficiency. Highly promising are C02 lasers 100 times as efficient as the former two. However, the known pumped C02 lasers are cumbersome and hard to operate, while sealed C02 lasers are not reliable because of the lack of ~27543 _ 9 _ high-quality optical materials.
It is an object of the plesent invention to provide a plavemak~ng device which will improve the platemaking process by producinO a line and a do-t pa-ttern within a single cycle.
Another object of the invention is to provide a plateilla'.~ing device which will simplify -the platema~l~ing procedure throu~n elirnination of all photographic and photochemical processes.
Still another object of the invention is to subst&ntially cut down the platemaking cycle time.
Yet ano-ther object of the invention is to enhance the re-liability of the laser device by using a sealed C02 laser with a novel polarizing element design.
~ hese objects are attained by that, in a laser platemaking device comprising a system of synchronous scanning of an original and a plate material; an optoelectronic reader and a halftone pulse transducer, both optically associated with the synchro-nous scanning system; an electronic circuit for generating a se~uence of signals to control the laser beam parameters, coupled to the optoelectronic reader and to the halftone pulse transducer and including a corrector connected to the opto-electronic reader; a comparator whose first input is connected to the output of the corrector, a shaper having its input connected to the output of the halftone pulse transducer whose input is electrically associated with the output of the shaper and having its output connected to a second input of the comparator; and a laser-optical system for forming images on ` ~Z17S~3 bhe su~f`ace OL the plate material, including a laser, an Opbi-cal modula-tor OQtiCally associated wi-th the laser and having its input connected to an output amplifier, a rotating mirror arlanged between the laser and the optical modulator, &nd an op-tical unit for directing the laser beam to and focusin.O it on the scanned surface of the plate material, arranged between the opticel modulator and the plate material, according to -the invention, the electronic circuit also comprises a parallel arrangement including a line channel for con-trolling the laser be~m in reproducing line images and a dot channel for controlling the laser beam in reproducing half-tone images, a dot-line switch for automatic switchover of the line and dot channels, having its ~`irst and second inputs connected to the output of the ; line and dot channels~and a unit for registering the boundary of halftone images and producing a command to the dot-line switch, kinematically associated with the synchronous sc~nning system~ the output of the halftone image boundary registering unit being connected to a third input of the dot-line switch whose output is cornected to the input of the output amplifier9 and the function of the optical modulator being performed by a laser modulator.
It is advisable that the laser platemaking device comprise a series a~rangement including a synchronous scanning system step sensor optically associated with the synchronous scanning system, a plate material step counter, a~d.a step generator having its output connected to the first input of the comparator9 .
7~3 a phase-chan~ing s~ivch, and a phase-snif-t circuit having its input cornbined with a iirst inpu-t of the phase-changinOr switch and co~nected ~o the output of the shaper and hav~lg its out-put connected vo a second input of the phase-changing switch whose third in~ju-t is connected -to a second output of the plate material step counter, coupled to a second in?ut of the step generator, the output of the phase-changing switcn being connec-ted to the input of a synchronized sawtooth generator.
ri'he phase-shif`t circuit should preferably be an inverter.
~ t is expedient that the laser comprise an optical cavity formed by an output mirror, a fully reflecting spherical mirror and a polarizing element, the polarizing element being essenti-ally a fully reflecting flat mirror having its working surface arranged at an angle of 45 i15 to the optical axis of the laser, -the plane of i~ncidence of the laser beam on the fully reflecting flat mirror of the optical cavity and the plane of incidence of the laser beam on the rotating mirror coinciding with the plane of incidence of the laser beam on the laser modulator, and the transmittance of the output mirror of the optical cavity exceeding 50~0.
To obtain a dot and a line pattern on the plate ma-terial within a single step without distortion, the laser beam from the exit of the laser modulator should preferably be directed at an angle of 3 to 6 to a line forming a right angle with the surface of the plate material at the point of contact bet-ween the laser beam and the plate material surface.
~LlZ~'5~L3 - 12 _ The laser modula-tor shGuld preferably be an electrooptic nlGdulato~.
It is also pref'erable tha-t the laser modulator be an aCOUSbO--optic one.
'~he proposed laser pla-temaking device will permi~ eliminat-ing complex and time-consuming steps from the platemaking pro-cess. The process cycle time is reduced by approximatel~ Gne order of magnitude. The use of the device in printing houses will permit reducing equipment, floor space and personnel re-quirements.
~ he invention will now be described in greater detail with reference to a specific embodiment thereof, taken in conjunction with the accompanying dra-.vings, wherein:
~ ig. 1 is a flow chart of offset printing using a laser platemaking device according to the invention;
Fig. 2 is a schematic of a laser platemaking device accord-ing to the invention;
Fig. 3 is a schematic of the sealed C02 laser, according to the invention;
Fig. 4 are time diagrams illustrating formation of a dot pattern, according to the invention;
Fig. 5 shows highlight (~) and shadow (T) details of a real dot pattern, according to the invention.
The proposed laser platemaking device can be used in the making of, for example, offset plates within a single process cycle from a simplest copy including text, line and unscreened tone images.
~127S43 -- '1,3 --A platemakLn;r cycle comr~rises the following steps:
readout OI the copy; formation of the final image and repro-duction thereof on the surlace of a prin-ting plate which does not re~uire additional processing before bein~ put into print.
Referri.-lg novi to Fig. 1 7 a manuscript 1 and captions 2 are sent, for example, to co~posing machines 3, while illustrations 4 are scaled by rneans of a scaling unit 5. ~he type matter com-posed of` the manuscript 2 and captions 2, as well as the scaled illustrations 4, are delivered to a layout table 6 where they are inte~rated into a mock-up with all the necessary columns, heads, inserts, line and unscreened tone illustrations. ~hey are pasted on a paper (film) base and/or placed on a laser platemaking device 7. ~rom the resulting paste-up, the laser device 7 makes a printing plate with automatic screening of tone images, which is then run on printing machines 8 with-out any additional processing.
The laser platemaking device comprises a system for synchro-nous scanning of an original and a plate material, including an electric drive 9 (~ig. 2) whose shaft ~0 carries working cylinders 11 and 12. Attached to -the cylinder 11 is the original 13 and contras-t lines 14 are cut therein, while the cylinder 12 accommodates the plate material 15.
~ he laser device also comprises an~optoelectronic reader 16 optically associated with the synchronous scanning system, a halftone pulse transducer 17, and an electronic circuit in-s~
-tended for generation of a sequence of signals to control the laser bea~ par~neters, which circuit includes a corrector 18 whose inpu-t 19 is connected -~o the output of the optoelectronic reader 16, a synchronized sawtooth generator 20, and a compa-rator 21 whose input 22 is connected to the output o~ the correc-tor 18 and whose input 23 is connected to the output of the syn-chronized sawtooth generator 20. The corrector 18 and compara--tor 21 form a dot eh~nnel controlling the laser beam in repro-ducing halftone images.
~ he electronic circuit also includes a compara-tor 24 whose input 25 is connected to the output of the optoelectronic read-er 16. ~he comparator 24 represents a line channel control-ling the laser beam in reproducing line images.
Additionally, the electronic circuit comprising a shaper 26 whose input 27 is connected to the output of the halftone pulse transducer 17 and a dot-line switch 28 ensuring automatic switchover of the line and dot channels and permitting a line and a dot pattern to be obtained on the plate material 15 within a single process cycle, inputs 29 and 30 of the switch being connected to the outputs of the dot and line channels, respecti-vely.
~ he electronic circuit ~urther includes a unit 31 for re-gistering the boundaries of halftone images, producing commands to the dot-line switch 28 and incorporating a program cylinder 32 mounted on the shaft 10 and an optoeIectronic sensor 33 opti-cally associated with contrast patches 34 on the cylinder 32.
11~7S~3 The ou-tpu-t of the optoelec-tronic sensor ~ is connected to an input ~5 o~` the dot-line switch 28.
~ inally, the electronic circuit compris~s an output ampli-fier 36 built a:.ound, for example, a transistor 37. ~he collec-tor circuit of the transistor 37 includes a resistor 38 having one of its terminals connec~ed to a power supply ~9. '~he base of the transistor 37 is connected to the outpùt of the dot-line switch 28.
The laser platemaking device also comprises a laser-optical system ~or forming an image on the surface of the plate material 15, including a laser 40 with a power supply 41 which is a sta-bilized current source, a laser modulator 42 optically associated via a rotating mirror 43 with the laser 40, and an optical unit 44 for directing the laser beam to and ~ocusing it on the scpnned surface of the plate material 15. Connected to an input 45 of the laser modulator 42 is the output of the amplifier 36.
The laser modulator 42 may be an electrooptic or acousto-optic one.
~ he laser platemaking device additionally comprises a se-ries circuit including a synchronous scanning system step sensor 46 optically associated, for example, with a contrast line 47 on the working cylinder 12, a plate material step coun~er 48, and a step generator 49 having its output connected to the input 22 of the comparator 21.
~ inally, the laser platemaking device comprises a phase-~1;27~43 cn~nging switch 50 and a phase-shiIt circuit 51 whose i~put 52 is combined with an inpu-t 53 of the phase-changing swi~ch 50 and connected to the output of the shaper 26. The output of the phase-shift circuit 51 is connected to an input 54 of the phase-changing switch 50 whose input 55 is connected to a second output of the counter 48, coupled to an input 56 of the step generator 49. The ou~put of the phase-changing switch 50 is connected to an input 57 of the synchronized sawtooth ~enera-tor 20.
The phase-shift circuit 51 may essentially be an inverter.
Fig. 3 is a schematic presentation of the laser 40.
A gas-discha~ge-tube 58 accommodates an anode 59, a cathode 60, and a polarizing element which is essentially a fully reflecting flat rnirror 61 whose working surface is arr~nged at an angle of 45 +15 to the optical axis 62 of the laser.
The latter also includes a fully reflecting spherical mirror 63 and an output mirror 64 forming, together with the fully reflecting flat mirror 61, the optical cavity of the laser 40.
'~he laser platemaking device operates as follows. The electric drive 9 (~ig. 2) rotates the shaft 10 with the work-ing cylinders 11 and 12 rigidly mounted thereon. The infor-mation from the mock-up 13, including text, line and unscreened tone images (photographs), is read out line by line by the op-toelectronic reader 16 moved along the working cylinder 11 by an independent step motor (not shown). The output of the opto-electronic reader 16 is an analog electric signal proportional .
1~'7543 to -the optical density of the read-out portion of the original 1~.
The ~nalog ~ignal from the output of the optoelectronic reader 16 is applied to two channels: the line and dot channels.
The signal arriving at the line channel reaches the compara-tor 24 with a controlled threshold voltage. By setting an appro-pria-te level of the thresho:Ld voltage, one can selectivel~
read out the line portion o~ the original 13, eliminating paste smudges, image borders and tone differences.
The conditioned analog signal is applied from the output of -the comparator 2~ to the input 30 of the dot-line switch 28.
'~he signal applied to the dot channel reaches the correc-tor 18 to eliminate the effect of imperfections of the tone images of the original 13 on the plate quality, then arrives at the input 22 of the switch 21, and, finally, at the input 29 of the dot-line switch 28.
At the same time, a sequence of contrast lines 14 is sensed by the halftone pulse transducer 17 which produces a sequence of pulses matched, in coordinates and time, with the surface of the working cylinders 11 and 12. The halftone pulses are equal in number to the screen elements on the plate material 15, determining the ruling of the dot pattern of the halftone image.
~ he sequence of halftone pulses is applied to the input 27 of the shaper 26, then to the phase-changing switch 50 and to the phase-shift circuit 51.
~ rom the output of the phase-changing switch 50,-the sequence of halftone pulses proceeds to the synchronized s~wtooth genera-~or 20 a~d Iurther to the comparator 21.
Comparison o~ sawtooth pulses 65 (~ig. 4) with the analog signal 66 used as the threshold level results in that the com-parator 21 ~Fig. 2) produces a sequence o~ data halftone puls-es whose width is proportional to the optical density o~ the read-out portiorl of the original 13. Information from the line and dot channels is fed to the dot-line switch 28 with the aid of which the line or dot channel is automatically connected to the output amplifier 36. The command initiating the switchover of these channels arrives from the unit 31 for registering the boundaries of hal~tone images. Secured on the program cylinder 32 of this unit 31 are the contrast patches 34 whose position and shape correspond to those of tone images on the original 13.
~ he edges of the contrast patches 34 are read out by the optoelectronic sensor 33 producing a pulse corresponding to crossing of a tone image boundary, which is applied to the switch 28 and, serving as a control pulse, switches over the line and dot channels. The unit 31 can also be used for trans-mitting parts of the original 13 in different modes, e.g.
negative, positive, or color. The unit 31 may also serve for selective scaling of parts of the original 13.
On the plate material 15, the image is reproduced by means of a laser beam ~ocused thereon with the aid of the optical unit 44. ~he latter is actuated by a step motor (not shown).
The beam is generated by the laser 40 which is essentially a sealed C02 laser operating at a wavelength of ~0.6 microns and ensuring a beam power of about 30 W in CW generation. With the aid of the rotating mirror 43 tha beam is directed to the :
laser modulator 42 controlling the beam intensity and-further to the optical unit 4L~. ~he laser beam intensity is varied by changing uh~ parameters of the electric signal applied to the laser modulauor 42.
'~he image formed on the plate material 15 within a cycle reproduces the original 13, including text, line and unscreened tone images (photographs).
In order to reproduce,for example, the text from the original 13, the unit 31 generates a command which arrives at the input 35 of the switch 28. ~he amplifier ~6 becomes coupled to the line ch~nnel, and the input of the amplifier 36 receives an ana-log signal proportional to the optical density of the read-out portion of the original 13. A signal appears at the output of the amplifier 36, controlling the laser beam intensity via the laser modulator 42.
The modulated laser beam is focused with the air of the optical unit 44 on the surface of the plate material 15, fo~n-ing a spot 40 microns in diameter. ~he laser beam diameter and the stroke of the optical unit 44 are selected such as to repro-duce a line having a minimum width of 0.1 mm without any distor-tion. For distortion-free reproduction of sùch a line it has to be scanned during at least three revolutions of the working cylinders 11 and 12. ~his is why the ruling of the reproduced plate is selected equal to 300 l/cm~ Thus, the text and line images from the original 13 are reproduced in facs;m;le.
Following a respective command from the unit 31, the dot channel becomes connected to the amplifier 36, and its input ~lZ7543 -- 20 _ receives a se~uence of data half`tone pulses. The output of ~he amplifier 36 is a signal controlling the laser beam intensity with the aid of the laser modulator 42.
The dot pattern of halftone images is also formed by a com-bination of lines written by the laser beam on the plate ma-terial 15. ~hese lines, however, are not a facsimile copy of the images on the original 13.
'lhe screen elements are formed artificially by consecutive writting of lines. Therewith, the width of screen elements is determined by the number of lines, while their height is defi-ned by the width of the data halftone pulses arriving from the output amplifier 36 and controlling the laser modulator 42. ~he dimensions of screen elements determine the ruling of the dot pattern of the halftone image. Therefore, in the proposed laser platemaking device, the ruling is varied by changing the number of lines in screen elements and by changing the spacing between the contrast lines 14 on the working cylinder 11, read out by the transducer 17.
The formation of screen elements with a ruling of, for example, 4f~ l/c~ is illustrated in Fig. 4. Consider first the formation of a dot pattern in reproduction of grey tones (Fig. 4A). ~he desired wave~orm of the control data halftone pulses is shaped at the output of the comparator 21 (Fig. 2).
Its input 23 receives a sequence of sawtooth pulses 65 (Fig.4A) whose freguency is preset by the halftone pulse transducer 17 ~Fig. 2) which ties these pulses, in coordinates and time, with ~1:27~
the surface oY the rigidly linked working cylinders 11 ~nd 12.
The phase of these pul~es is maintained constant during the ti~e period it takes for the line sequence of screen elements to be written over their entire width. In accordance with the selected ruling of 300 l/cm~ the full width of the screen ele-ments with the ruling, equal to 40 l/cm, which varies along the diagonal of the image outline, will be written during five revo-lutions of the working cylinders 11 and 12.
~ he diagrams corresponding to five revolutions of the working cylinders 11 and 12 are labeled aI, aII, aIII, aIV and aV(~ig. 4), where I,II,III,IV and V stand for numbers of revo-lutions of the cylinders 11 and 12 (Fig. 2).
"a" stands for a group of revolutions of the cylinders 11 and 12, during which a screen element is formed. Subsequent groups of revolutions, during which next screen elements are formed, are designated "b" and "c" (Fig. 4).
The combination of a sawtooth signal with a staircase wavefor~, labeled I, II, III, IV or V, is maintained throughout a complete revolution of the cylinder 12 (~ig. 2).
~ he revolutions are counted by the stroke counter 48, which receives a pulse per reYolutio~ o~ the cylinder 12 from the sensor 46. After five revolutions a pulse is produced at the output of the counter 48, applied to the input 55 of the phase-changing switch 50. ~ollowing this signal, applied from the output of the phase-changing switch 50 to the input 57 of the generator 20 is a sequence of hal~tone pulses shi~ted by ~.~2~5~;~
half a period with respect -to the hal~tone pulses correspon~ing to tne previous group o~ revolutions of the cylinders 11 and 12, arriving at the input 54 of the phase-changing switch 50 from the output of the phase-shift circuit 51. As a result of opera-tion of the phase-changing switch 50, the phase of the data hal~tone pulses is shifted b~ half a period of repetition of these pulses, and the laser beam starts writing the next line sequence of screen elements, beginning with the sixth revolu-tion of the working cylinder 12.
Fig. 4A represents diagrams of screen elements corresponding to these revolutions of the working cylinder 12, labeled bI,bII, bIII,bI~ and bV. After ten revolutions of the cylinder 12 (Fig.2), the phase of the halftone pulses is in the same way changed to the initial state and, beginning with the eleventh revolution of the working cylinder 12, the laser beam will write a third sequence of screen elements cI,cII cIII cIV and cv (~i 4) then the process repeats itself.
In reproduction of black-and-white images, the screen ele-ments must form an angle of 45 to the generatrix of the cylin-der 12 (~ig. 2). ~o this end, the halftone pulse phase deter-mined by the phase-shift circuit 51 is shifted through 180, in which case a simple inverter can be used as the circuit 51.
The sequence of sawtooth pulses arriving at the input of the comparator 21 is compared with the reference voltage which is an analog signal coming from the corrector 18. In reproduction of "grey" tones, the magnitude of the analog signal 66' (~ig.4A) is selected equal to half the amplitude of the sawtooth pulses 65.
7~3 '~o produce screen elements of triangular-tr~pezoidal shape ensuring a higher quality halftone image, a staircase voltage is added to the analog signal at the input o~ the comparator 21.
~his voltage is produced by the generator 49 by way of incremen-tal addition o~ a fixed voltage from the counter 48 to the pre-vious voltage value. A~ter five revol~tions (at a ruling of 40 l/cm), the total voltage is zeroized following a command from the counter 48, then the process repeats itself. As a result of such addition, the analog signal 66 (Fig. 4) derived at the input 22 (Fig. 2) of the comparator 21 also has a perio-dical staircase waveform.
~ he addition of sawtooth pulses 65 to the analog staircase signal 66 permits a sequence of pulses to be produced at the output of the comparator 21 (Fig. 2), whose width changes, at the same tonality of the hal~tone image determined by the points of intersection of the compared signals, with each revolution of the working cylinders 11 and ~. During the first revolution, the longest lines are written, while during the fifth revolution, the shortest.
The use of the proposed laser device at varying tonality of the original image involves changes not only in the length of lines within a sequence of screen elements but also in their number.For example, in reproducing a light grey tone (Fig. 4B), only two lines are written during revolutions I and II of the working cylinders 11 and 12 within a screen element. In reprodu-cing the lightest tone (Fig. 4C), only one short line is written 75~3 during revolution I, while in the case of the darkest tone (Fig. 4D) breaks of minimum length remain on the last line written duringr revolution V.
An example of a real dot pattern produced on a printin~
plate is shown in Fig. 5~, T at 16x magnification. The screen elemen-ts have a triangular-trape~oidal shape, the minimum dimen-sion of a screen element in the highlight portion being about 20 microns (Fig. 5~) and in the shadow portion, 50 microns (Fig. 5T).
~ he laser beam is contrlled with the aid of the laser modu-lator in case it is linearly polarized; therefore, the laser 40 in t~e ~roposed device provlde~ for linear polarization of the beam.
~ he laser platemaking device makes it possible to produce plates directly without intermediate steps. ~o this end, the plate processing beam must be powerful enough.
The process of making an offset plate at a linear writing speed of, for example, 200 m/min ensuring high efficiency of the proposed device is practically realized using a sealed C02 laser which ensures a linearly polarized beam having a power of 30 W in single-mode operation. ~his laser is the most econo-mic and easiest in operation and in manufacture~
~ he least reliable component in currently used C02 lasers is the optical element used for linear polarization of the beam.
Used as this element is an optically polished plate of ~aCl or .~L2~;43 -- 25 _ KCl arranged at the Brewstar angle to the optical axis o the laser and bo~ded to the end of the gas-discharge tube, serving at the same time as part of the vacuum envelope of the gas-dis-charge tube~ l'his joint cannot be made by soldering or welding because of the properties of the materials involved, while known adhesives evolve a complex mixture of gases with the result that the working gas mixture of the C02 laser deteriorates within a short period of time, and the laser may fail at any time.
~ o enhance the reliability of the C02 laser, used as the polarizing element is a fully reflecting flat metal mirror 61 (Fig. 3) forming part of the optical cavity of the laser 40.
~he working surface of the mirror 61 is set at an angle of 45 $ 15 to the optical axis 62 of the laser 40. At the same time, the design of the laser-optical system ensures propaga-tion of the laser beam in a single plane, i.e. the plane of incidence of the laser beam on the fully reflecting flat mirror 61 of the optical cavity and that on the rotating mirror 43 (Fig. 2) coincide with the plane of incidence of the laser beam on the laser modulator 42.
The degree of beam polarization is determined not only by the properties of the polarizing element but also by the number of reflections of the laser beam in the optical cavity of the laser 40 (Fig. 3), which, in turn, depends on the refleçtion coefficient of the output mirror 64. To increase the degree of beam polarization, the number of reflections of the laser beam must be increased. At a reflection coefficient of the out-put mirror 64 equal to 35~o~ the degree of linear polarization of the laser beam, ensured by the inclined fully reflecting fla-t mirror 61, equals 95~o~ which is not adequate for quality repro-duction of the image by the laser beam. At a reflection coeffi-cient of the output mirror 64 exceeding 50%, the degree of pola-rization su~passes the value of 98% necessary for proper opera-tion of the laser modulator 42.
~ he plate material 15 (Fig. 2) processed by the laser beam reflects a greater or lesser part of the beam. The reflected beam returns, in this case, to the optical cavity of the laser 40, whereby the properties of the beam generated by the laser 40 are impaired - the power level becomes unstable and the polari~ation is distorted.
; ~o eliminate this uncontrollable effect, one should direct the beam from the e~it of the laser modulator 42 at an angle of 3 to 6 to a line forming a right angle with the surface of the plate material 15 at the point of contact of the laser beam therewith.
Thus, the proposed laser device makes it possible to produce printing plates (preferably offset ones) oontaining halftone and line images~ as well as enables complex and time-consuming steps to be eliminated from the platemaking process.
~ ith proper selection of plate materials, the proposed laser device can be used for making plates applicable in other printing processes as well - letterpress, photogravure, and sten-ciling. The device of the present invention can also be used as an output device in automatic systems employed in publishing houses for aata transmission through communication links.
'i'he dot pat-tern must have a precise orientation of t.ie screen elements. ~~~n trans~nission of a black-and-white con~inuous---tone image, the screen elements are oriented at an angle of 45'~, while in color printing the screen elements of each color are oriented at different angles, e.g. 15, 30 and 45 to the generatrix of the cylinder.
For screening of continuous-tone images, in the prior art laser device provision is made for generation of a sequence of half-tone pulses matched in coordinates and time with the sur-faces of the copy and plate material.
'~he halftone pulses are generated by the halftone pulse transducer which senses the sequence of contrast lines cut in the surface of one of the cylinders. ~he line-by-line read-out of the copy is perI`ormed by the optoelectronic reader which produces an analog signal proportional to the optical densit~ in the read-out area of the copy.
'~he sequence of halftone pulses and the analog pulse are fed into the electronic circuit. '~he halftone pulses are applied to the shaper which converts the bell-shaped waveform o~ the pulses, generated b~ the halftone pulse transducer, to a required square waveform. '~he analog signal is appli-~ 127543 ~, ed -to t`ne correc-tGr with the aid of which it is conditiGned so as bO correc-l- ior im~erfections of the copy and to provide for such a co~bination of printing Lnk colors as to reproduce color images with hignest fidelity. ~rom the correc~or the analog signal proceeds to the co~parator also receivirg the sequence of halftone pulses from the shaper. Co~parison o~
both signals results in a sequence of halftone pulses at the comparator output; whose wid-th is proportional to the optical density of the copy a-t the moment of passage of a pulse. These pulses are referred to as data halftone pulses. '~hey are ap-plied to the analog-to-digital converter and further to the address register OL the computer. '~he coded information on the image of the copy is fed from the address register to a storage of the computer. The latter receives data determining the desired shape of the screen elements, in this case diamond shape. In accordance with the data~ the storage generates a sequence of pulses whose number and width depends on the opti-cal density of the copy in the read-out portion of the copy, the size of said portion depen~ing, in turn, on the selected screen ruling. '~he selected sequence of pulses is applied ~o the output register of ~he computer, then to the operational control unit of the latter, which also receives a synchronizing sequence of halftone pulses, definin~ a cycle of putting out pulse trains to the group of parallel-connected output ampli-fier. '~rains of amplified pulses are applied therefrom to the electronic inputs of the optical modulators controlling ~12~S~L3 the intensity of the laser-optical systern channels. ~^is syste~
includes an argon laser. It operates at a wavelength oi abou-t ~.5 m crons~ a-t ~vl~ch tL^le sensi-tivity of -the filrn is m~imu~.
To e~ose -the photosensitive film at a linear scanning speed of several meters per second, a laser beam power oi several tens of milliwatts is suificient. '~herefore~ normal operation of the prior art multichannel laser device is ensured at a laser beam power of several wat-ts. Such a laser beam is directea toward a plurality of optical semitransparent cells spli-tting the beam among five channels. Each channel includes an optical ~odulator, an analyzer, a focusing lens and an opti-cal wedge for fine adjustment of the intensity of the laser channels, equalizing the laser beam power in all channel.
~ he controlled laser channels simultaneously write a group of lines on the photomaterial, at instants preset by the half-tone pulse transducer, the lines forming screen elements of a predetermined shape and an area determined by the optical density of the read-out portion of the copy, which permits re-production on the photosensitive film of continuous-tone imag-es of the desired quality.
A specific feature of the prior art devices is making of a photographic transparency from which a printing plate is sub-sequently produced by conventional photomechanical techniques.
Used as originals in the prior art devices are high-quali-ty copies produced by conventional letterpress or offset pro-cesses.
~lZ75~3 cGnsider now -the currentlJ e~ployed -technique of m~king G fset plates. r'he prinved rl~atter to be reproduced is no~rrally divided into gro~ps: uy~ev/ritten text9 captions~ graphical art-wor~, ~nd con-t~nuous-tone illustra-tions (photographs). T~ te~t ard captions are com2osed thcn sent for s-tripping-in or pas-ting--up. Ini~iall~, the first la~out is prepared. ~fter ~pp-~oval by ~he eclitor, the layout is disassembled. ~he line im~es are reasse~bled, arAd the -tone illustrations undergo an additional operation - screening. As a result, a mock-up is prepared which is essentiall~ the final copy to be duplicated. ~rom this rnock--up a transparency is made to scale. ~hereafter, a photosensitive layer is applied on the plate material. ~he latter is exposed to the transparency9 and the resulting image is then tanned and retouched. ~he finished printing plate goes to the printing machine for a run.
As can be inferred from the above description o~ prior art devices and techniques of offset printing, all of the des-cribed laser platemaking systems and devices perform only one of the above-mentioned operations. ~he use of prior art laser devices speeds up individual operations but fails to improve the platemaking procedure as a whole.
Argon or helium-neon lasers used in the known devices feature a low efficiency. Highly promising are C02 lasers 100 times as efficient as the former two. However, the known pumped C02 lasers are cumbersome and hard to operate, while sealed C02 lasers are not reliable because of the lack of ~27543 _ 9 _ high-quality optical materials.
It is an object of the plesent invention to provide a plavemak~ng device which will improve the platemaking process by producinO a line and a do-t pa-ttern within a single cycle.
Another object of the invention is to provide a plateilla'.~ing device which will simplify -the platema~l~ing procedure throu~n elirnination of all photographic and photochemical processes.
Still another object of the invention is to subst&ntially cut down the platemaking cycle time.
Yet ano-ther object of the invention is to enhance the re-liability of the laser device by using a sealed C02 laser with a novel polarizing element design.
~ hese objects are attained by that, in a laser platemaking device comprising a system of synchronous scanning of an original and a plate material; an optoelectronic reader and a halftone pulse transducer, both optically associated with the synchro-nous scanning system; an electronic circuit for generating a se~uence of signals to control the laser beam parameters, coupled to the optoelectronic reader and to the halftone pulse transducer and including a corrector connected to the opto-electronic reader; a comparator whose first input is connected to the output of the corrector, a shaper having its input connected to the output of the halftone pulse transducer whose input is electrically associated with the output of the shaper and having its output connected to a second input of the comparator; and a laser-optical system for forming images on ` ~Z17S~3 bhe su~f`ace OL the plate material, including a laser, an Opbi-cal modula-tor OQtiCally associated wi-th the laser and having its input connected to an output amplifier, a rotating mirror arlanged between the laser and the optical modulator, &nd an op-tical unit for directing the laser beam to and focusin.O it on the scanned surface of the plate material, arranged between the opticel modulator and the plate material, according to -the invention, the electronic circuit also comprises a parallel arrangement including a line channel for con-trolling the laser be~m in reproducing line images and a dot channel for controlling the laser beam in reproducing half-tone images, a dot-line switch for automatic switchover of the line and dot channels, having its ~`irst and second inputs connected to the output of the ; line and dot channels~and a unit for registering the boundary of halftone images and producing a command to the dot-line switch, kinematically associated with the synchronous sc~nning system~ the output of the halftone image boundary registering unit being connected to a third input of the dot-line switch whose output is cornected to the input of the output amplifier9 and the function of the optical modulator being performed by a laser modulator.
It is advisable that the laser platemaking device comprise a series a~rangement including a synchronous scanning system step sensor optically associated with the synchronous scanning system, a plate material step counter, a~d.a step generator having its output connected to the first input of the comparator9 .
7~3 a phase-chan~ing s~ivch, and a phase-snif-t circuit having its input cornbined with a iirst inpu-t of the phase-changinOr switch and co~nected ~o the output of the shaper and hav~lg its out-put connected vo a second input of the phase-changing switch whose third in~ju-t is connected -to a second output of the plate material step counter, coupled to a second in?ut of the step generator, the output of the phase-changing switcn being connec-ted to the input of a synchronized sawtooth generator.
ri'he phase-shif`t circuit should preferably be an inverter.
~ t is expedient that the laser comprise an optical cavity formed by an output mirror, a fully reflecting spherical mirror and a polarizing element, the polarizing element being essenti-ally a fully reflecting flat mirror having its working surface arranged at an angle of 45 i15 to the optical axis of the laser, -the plane of i~ncidence of the laser beam on the fully reflecting flat mirror of the optical cavity and the plane of incidence of the laser beam on the rotating mirror coinciding with the plane of incidence of the laser beam on the laser modulator, and the transmittance of the output mirror of the optical cavity exceeding 50~0.
To obtain a dot and a line pattern on the plate ma-terial within a single step without distortion, the laser beam from the exit of the laser modulator should preferably be directed at an angle of 3 to 6 to a line forming a right angle with the surface of the plate material at the point of contact bet-ween the laser beam and the plate material surface.
~LlZ~'5~L3 - 12 _ The laser modula-tor shGuld preferably be an electrooptic nlGdulato~.
It is also pref'erable tha-t the laser modulator be an aCOUSbO--optic one.
'~he proposed laser pla-temaking device will permi~ eliminat-ing complex and time-consuming steps from the platemaking pro-cess. The process cycle time is reduced by approximatel~ Gne order of magnitude. The use of the device in printing houses will permit reducing equipment, floor space and personnel re-quirements.
~ he invention will now be described in greater detail with reference to a specific embodiment thereof, taken in conjunction with the accompanying dra-.vings, wherein:
~ ig. 1 is a flow chart of offset printing using a laser platemaking device according to the invention;
Fig. 2 is a schematic of a laser platemaking device accord-ing to the invention;
Fig. 3 is a schematic of the sealed C02 laser, according to the invention;
Fig. 4 are time diagrams illustrating formation of a dot pattern, according to the invention;
Fig. 5 shows highlight (~) and shadow (T) details of a real dot pattern, according to the invention.
The proposed laser platemaking device can be used in the making of, for example, offset plates within a single process cycle from a simplest copy including text, line and unscreened tone images.
~127S43 -- '1,3 --A platemakLn;r cycle comr~rises the following steps:
readout OI the copy; formation of the final image and repro-duction thereof on the surlace of a prin-ting plate which does not re~uire additional processing before bein~ put into print.
Referri.-lg novi to Fig. 1 7 a manuscript 1 and captions 2 are sent, for example, to co~posing machines 3, while illustrations 4 are scaled by rneans of a scaling unit 5. ~he type matter com-posed of` the manuscript 2 and captions 2, as well as the scaled illustrations 4, are delivered to a layout table 6 where they are inte~rated into a mock-up with all the necessary columns, heads, inserts, line and unscreened tone illustrations. ~hey are pasted on a paper (film) base and/or placed on a laser platemaking device 7. ~rom the resulting paste-up, the laser device 7 makes a printing plate with automatic screening of tone images, which is then run on printing machines 8 with-out any additional processing.
The laser platemaking device comprises a system for synchro-nous scanning of an original and a plate material, including an electric drive 9 (~ig. 2) whose shaft ~0 carries working cylinders 11 and 12. Attached to -the cylinder 11 is the original 13 and contras-t lines 14 are cut therein, while the cylinder 12 accommodates the plate material 15.
~ he laser device also comprises an~optoelectronic reader 16 optically associated with the synchronous scanning system, a halftone pulse transducer 17, and an electronic circuit in-s~
-tended for generation of a sequence of signals to control the laser bea~ par~neters, which circuit includes a corrector 18 whose inpu-t 19 is connected -~o the output of the optoelectronic reader 16, a synchronized sawtooth generator 20, and a compa-rator 21 whose input 22 is connected to the output o~ the correc-tor 18 and whose input 23 is connected to the output of the syn-chronized sawtooth generator 20. The corrector 18 and compara--tor 21 form a dot eh~nnel controlling the laser beam in repro-ducing halftone images.
~ he electronic circuit also includes a compara-tor 24 whose input 25 is connected to the output of the optoelectronic read-er 16. ~he comparator 24 represents a line channel control-ling the laser beam in reproducing line images.
Additionally, the electronic circuit comprising a shaper 26 whose input 27 is connected to the output of the halftone pulse transducer 17 and a dot-line switch 28 ensuring automatic switchover of the line and dot channels and permitting a line and a dot pattern to be obtained on the plate material 15 within a single process cycle, inputs 29 and 30 of the switch being connected to the outputs of the dot and line channels, respecti-vely.
~ he electronic circuit ~urther includes a unit 31 for re-gistering the boundaries of halftone images, producing commands to the dot-line switch 28 and incorporating a program cylinder 32 mounted on the shaft 10 and an optoeIectronic sensor 33 opti-cally associated with contrast patches 34 on the cylinder 32.
11~7S~3 The ou-tpu-t of the optoelec-tronic sensor ~ is connected to an input ~5 o~` the dot-line switch 28.
~ inally, the electronic circuit compris~s an output ampli-fier 36 built a:.ound, for example, a transistor 37. ~he collec-tor circuit of the transistor 37 includes a resistor 38 having one of its terminals connec~ed to a power supply ~9. '~he base of the transistor 37 is connected to the outpùt of the dot-line switch 28.
The laser platemaking device also comprises a laser-optical system ~or forming an image on the surface of the plate material 15, including a laser 40 with a power supply 41 which is a sta-bilized current source, a laser modulator 42 optically associated via a rotating mirror 43 with the laser 40, and an optical unit 44 for directing the laser beam to and ~ocusing it on the scpnned surface of the plate material 15. Connected to an input 45 of the laser modulator 42 is the output of the amplifier 36.
The laser modulator 42 may be an electrooptic or acousto-optic one.
~ he laser platemaking device additionally comprises a se-ries circuit including a synchronous scanning system step sensor 46 optically associated, for example, with a contrast line 47 on the working cylinder 12, a plate material step coun~er 48, and a step generator 49 having its output connected to the input 22 of the comparator 21.
~ inally, the laser platemaking device comprises a phase-~1;27~43 cn~nging switch 50 and a phase-shiIt circuit 51 whose i~put 52 is combined with an inpu-t 53 of the phase-changing swi~ch 50 and connected to the output of the shaper 26. The output of the phase-shift circuit 51 is connected to an input 54 of the phase-changing switch 50 whose input 55 is connected to a second output of the counter 48, coupled to an input 56 of the step generator 49. The ou~put of the phase-changing switch 50 is connected to an input 57 of the synchronized sawtooth ~enera-tor 20.
The phase-shift circuit 51 may essentially be an inverter.
Fig. 3 is a schematic presentation of the laser 40.
A gas-discha~ge-tube 58 accommodates an anode 59, a cathode 60, and a polarizing element which is essentially a fully reflecting flat rnirror 61 whose working surface is arr~nged at an angle of 45 +15 to the optical axis 62 of the laser.
The latter also includes a fully reflecting spherical mirror 63 and an output mirror 64 forming, together with the fully reflecting flat mirror 61, the optical cavity of the laser 40.
'~he laser platemaking device operates as follows. The electric drive 9 (~ig. 2) rotates the shaft 10 with the work-ing cylinders 11 and 12 rigidly mounted thereon. The infor-mation from the mock-up 13, including text, line and unscreened tone images (photographs), is read out line by line by the op-toelectronic reader 16 moved along the working cylinder 11 by an independent step motor (not shown). The output of the opto-electronic reader 16 is an analog electric signal proportional .
1~'7543 to -the optical density of the read-out portion of the original 1~.
The ~nalog ~ignal from the output of the optoelectronic reader 16 is applied to two channels: the line and dot channels.
The signal arriving at the line channel reaches the compara-tor 24 with a controlled threshold voltage. By setting an appro-pria-te level of the thresho:Ld voltage, one can selectivel~
read out the line portion o~ the original 13, eliminating paste smudges, image borders and tone differences.
The conditioned analog signal is applied from the output of -the comparator 2~ to the input 30 of the dot-line switch 28.
'~he signal applied to the dot channel reaches the correc-tor 18 to eliminate the effect of imperfections of the tone images of the original 13 on the plate quality, then arrives at the input 22 of the switch 21, and, finally, at the input 29 of the dot-line switch 28.
At the same time, a sequence of contrast lines 14 is sensed by the halftone pulse transducer 17 which produces a sequence of pulses matched, in coordinates and time, with the surface of the working cylinders 11 and 12. The halftone pulses are equal in number to the screen elements on the plate material 15, determining the ruling of the dot pattern of the halftone image.
~ he sequence of halftone pulses is applied to the input 27 of the shaper 26, then to the phase-changing switch 50 and to the phase-shift circuit 51.
~ rom the output of the phase-changing switch 50,-the sequence of halftone pulses proceeds to the synchronized s~wtooth genera-~or 20 a~d Iurther to the comparator 21.
Comparison o~ sawtooth pulses 65 (~ig. 4) with the analog signal 66 used as the threshold level results in that the com-parator 21 ~Fig. 2) produces a sequence o~ data halftone puls-es whose width is proportional to the optical density o~ the read-out portiorl of the original 13. Information from the line and dot channels is fed to the dot-line switch 28 with the aid of which the line or dot channel is automatically connected to the output amplifier 36. The command initiating the switchover of these channels arrives from the unit 31 for registering the boundaries of hal~tone images. Secured on the program cylinder 32 of this unit 31 are the contrast patches 34 whose position and shape correspond to those of tone images on the original 13.
~ he edges of the contrast patches 34 are read out by the optoelectronic sensor 33 producing a pulse corresponding to crossing of a tone image boundary, which is applied to the switch 28 and, serving as a control pulse, switches over the line and dot channels. The unit 31 can also be used for trans-mitting parts of the original 13 in different modes, e.g.
negative, positive, or color. The unit 31 may also serve for selective scaling of parts of the original 13.
On the plate material 15, the image is reproduced by means of a laser beam ~ocused thereon with the aid of the optical unit 44. ~he latter is actuated by a step motor (not shown).
The beam is generated by the laser 40 which is essentially a sealed C02 laser operating at a wavelength of ~0.6 microns and ensuring a beam power of about 30 W in CW generation. With the aid of the rotating mirror 43 tha beam is directed to the :
laser modulator 42 controlling the beam intensity and-further to the optical unit 4L~. ~he laser beam intensity is varied by changing uh~ parameters of the electric signal applied to the laser modulauor 42.
'~he image formed on the plate material 15 within a cycle reproduces the original 13, including text, line and unscreened tone images (photographs).
In order to reproduce,for example, the text from the original 13, the unit 31 generates a command which arrives at the input 35 of the switch 28. ~he amplifier ~6 becomes coupled to the line ch~nnel, and the input of the amplifier 36 receives an ana-log signal proportional to the optical density of the read-out portion of the original 13. A signal appears at the output of the amplifier 36, controlling the laser beam intensity via the laser modulator 42.
The modulated laser beam is focused with the air of the optical unit 44 on the surface of the plate material 15, fo~n-ing a spot 40 microns in diameter. ~he laser beam diameter and the stroke of the optical unit 44 are selected such as to repro-duce a line having a minimum width of 0.1 mm without any distor-tion. For distortion-free reproduction of sùch a line it has to be scanned during at least three revolutions of the working cylinders 11 and 12. ~his is why the ruling of the reproduced plate is selected equal to 300 l/cm~ Thus, the text and line images from the original 13 are reproduced in facs;m;le.
Following a respective command from the unit 31, the dot channel becomes connected to the amplifier 36, and its input ~lZ7543 -- 20 _ receives a se~uence of data half`tone pulses. The output of ~he amplifier 36 is a signal controlling the laser beam intensity with the aid of the laser modulator 42.
The dot pattern of halftone images is also formed by a com-bination of lines written by the laser beam on the plate ma-terial 15. ~hese lines, however, are not a facsimile copy of the images on the original 13.
'lhe screen elements are formed artificially by consecutive writting of lines. Therewith, the width of screen elements is determined by the number of lines, while their height is defi-ned by the width of the data halftone pulses arriving from the output amplifier 36 and controlling the laser modulator 42. ~he dimensions of screen elements determine the ruling of the dot pattern of the halftone image. Therefore, in the proposed laser platemaking device, the ruling is varied by changing the number of lines in screen elements and by changing the spacing between the contrast lines 14 on the working cylinder 11, read out by the transducer 17.
The formation of screen elements with a ruling of, for example, 4f~ l/c~ is illustrated in Fig. 4. Consider first the formation of a dot pattern in reproduction of grey tones (Fig. 4A). ~he desired wave~orm of the control data halftone pulses is shaped at the output of the comparator 21 (Fig. 2).
Its input 23 receives a sequence of sawtooth pulses 65 (Fig.4A) whose freguency is preset by the halftone pulse transducer 17 ~Fig. 2) which ties these pulses, in coordinates and time, with ~1:27~
the surface oY the rigidly linked working cylinders 11 ~nd 12.
The phase of these pul~es is maintained constant during the ti~e period it takes for the line sequence of screen elements to be written over their entire width. In accordance with the selected ruling of 300 l/cm~ the full width of the screen ele-ments with the ruling, equal to 40 l/cm, which varies along the diagonal of the image outline, will be written during five revo-lutions of the working cylinders 11 and 12.
~ he diagrams corresponding to five revolutions of the working cylinders 11 and 12 are labeled aI, aII, aIII, aIV and aV(~ig. 4), where I,II,III,IV and V stand for numbers of revo-lutions of the cylinders 11 and 12 (Fig. 2).
"a" stands for a group of revolutions of the cylinders 11 and 12, during which a screen element is formed. Subsequent groups of revolutions, during which next screen elements are formed, are designated "b" and "c" (Fig. 4).
The combination of a sawtooth signal with a staircase wavefor~, labeled I, II, III, IV or V, is maintained throughout a complete revolution of the cylinder 12 (~ig. 2).
~ he revolutions are counted by the stroke counter 48, which receives a pulse per reYolutio~ o~ the cylinder 12 from the sensor 46. After five revolutions a pulse is produced at the output of the counter 48, applied to the input 55 of the phase-changing switch 50. ~ollowing this signal, applied from the output of the phase-changing switch 50 to the input 57 of the generator 20 is a sequence of hal~tone pulses shi~ted by ~.~2~5~;~
half a period with respect -to the hal~tone pulses correspon~ing to tne previous group o~ revolutions of the cylinders 11 and 12, arriving at the input 54 of the phase-changing switch 50 from the output of the phase-shift circuit 51. As a result of opera-tion of the phase-changing switch 50, the phase of the data hal~tone pulses is shifted b~ half a period of repetition of these pulses, and the laser beam starts writing the next line sequence of screen elements, beginning with the sixth revolu-tion of the working cylinder 12.
Fig. 4A represents diagrams of screen elements corresponding to these revolutions of the working cylinder 12, labeled bI,bII, bIII,bI~ and bV. After ten revolutions of the cylinder 12 (Fig.2), the phase of the halftone pulses is in the same way changed to the initial state and, beginning with the eleventh revolution of the working cylinder 12, the laser beam will write a third sequence of screen elements cI,cII cIII cIV and cv (~i 4) then the process repeats itself.
In reproduction of black-and-white images, the screen ele-ments must form an angle of 45 to the generatrix of the cylin-der 12 (~ig. 2). ~o this end, the halftone pulse phase deter-mined by the phase-shift circuit 51 is shifted through 180, in which case a simple inverter can be used as the circuit 51.
The sequence of sawtooth pulses arriving at the input of the comparator 21 is compared with the reference voltage which is an analog signal coming from the corrector 18. In reproduction of "grey" tones, the magnitude of the analog signal 66' (~ig.4A) is selected equal to half the amplitude of the sawtooth pulses 65.
7~3 '~o produce screen elements of triangular-tr~pezoidal shape ensuring a higher quality halftone image, a staircase voltage is added to the analog signal at the input o~ the comparator 21.
~his voltage is produced by the generator 49 by way of incremen-tal addition o~ a fixed voltage from the counter 48 to the pre-vious voltage value. A~ter five revol~tions (at a ruling of 40 l/cm), the total voltage is zeroized following a command from the counter 48, then the process repeats itself. As a result of such addition, the analog signal 66 (Fig. 4) derived at the input 22 (Fig. 2) of the comparator 21 also has a perio-dical staircase waveform.
~ he addition of sawtooth pulses 65 to the analog staircase signal 66 permits a sequence of pulses to be produced at the output of the comparator 21 (Fig. 2), whose width changes, at the same tonality of the hal~tone image determined by the points of intersection of the compared signals, with each revolution of the working cylinders 11 and ~. During the first revolution, the longest lines are written, while during the fifth revolution, the shortest.
The use of the proposed laser device at varying tonality of the original image involves changes not only in the length of lines within a sequence of screen elements but also in their number.For example, in reproducing a light grey tone (Fig. 4B), only two lines are written during revolutions I and II of the working cylinders 11 and 12 within a screen element. In reprodu-cing the lightest tone (Fig. 4C), only one short line is written 75~3 during revolution I, while in the case of the darkest tone (Fig. 4D) breaks of minimum length remain on the last line written duringr revolution V.
An example of a real dot pattern produced on a printin~
plate is shown in Fig. 5~, T at 16x magnification. The screen elemen-ts have a triangular-trape~oidal shape, the minimum dimen-sion of a screen element in the highlight portion being about 20 microns (Fig. 5~) and in the shadow portion, 50 microns (Fig. 5T).
~ he laser beam is contrlled with the aid of the laser modu-lator in case it is linearly polarized; therefore, the laser 40 in t~e ~roposed device provlde~ for linear polarization of the beam.
~ he laser platemaking device makes it possible to produce plates directly without intermediate steps. ~o this end, the plate processing beam must be powerful enough.
The process of making an offset plate at a linear writing speed of, for example, 200 m/min ensuring high efficiency of the proposed device is practically realized using a sealed C02 laser which ensures a linearly polarized beam having a power of 30 W in single-mode operation. ~his laser is the most econo-mic and easiest in operation and in manufacture~
~ he least reliable component in currently used C02 lasers is the optical element used for linear polarization of the beam.
Used as this element is an optically polished plate of ~aCl or .~L2~;43 -- 25 _ KCl arranged at the Brewstar angle to the optical axis o the laser and bo~ded to the end of the gas-discharge tube, serving at the same time as part of the vacuum envelope of the gas-dis-charge tube~ l'his joint cannot be made by soldering or welding because of the properties of the materials involved, while known adhesives evolve a complex mixture of gases with the result that the working gas mixture of the C02 laser deteriorates within a short period of time, and the laser may fail at any time.
~ o enhance the reliability of the C02 laser, used as the polarizing element is a fully reflecting flat metal mirror 61 (Fig. 3) forming part of the optical cavity of the laser 40.
~he working surface of the mirror 61 is set at an angle of 45 $ 15 to the optical axis 62 of the laser 40. At the same time, the design of the laser-optical system ensures propaga-tion of the laser beam in a single plane, i.e. the plane of incidence of the laser beam on the fully reflecting flat mirror 61 of the optical cavity and that on the rotating mirror 43 (Fig. 2) coincide with the plane of incidence of the laser beam on the laser modulator 42.
The degree of beam polarization is determined not only by the properties of the polarizing element but also by the number of reflections of the laser beam in the optical cavity of the laser 40 (Fig. 3), which, in turn, depends on the refleçtion coefficient of the output mirror 64. To increase the degree of beam polarization, the number of reflections of the laser beam must be increased. At a reflection coefficient of the out-put mirror 64 equal to 35~o~ the degree of linear polarization of the laser beam, ensured by the inclined fully reflecting fla-t mirror 61, equals 95~o~ which is not adequate for quality repro-duction of the image by the laser beam. At a reflection coeffi-cient of the output mirror 64 exceeding 50%, the degree of pola-rization su~passes the value of 98% necessary for proper opera-tion of the laser modulator 42.
~ he plate material 15 (Fig. 2) processed by the laser beam reflects a greater or lesser part of the beam. The reflected beam returns, in this case, to the optical cavity of the laser 40, whereby the properties of the beam generated by the laser 40 are impaired - the power level becomes unstable and the polari~ation is distorted.
; ~o eliminate this uncontrollable effect, one should direct the beam from the e~it of the laser modulator 42 at an angle of 3 to 6 to a line forming a right angle with the surface of the plate material 15 at the point of contact of the laser beam therewith.
Thus, the proposed laser device makes it possible to produce printing plates (preferably offset ones) oontaining halftone and line images~ as well as enables complex and time-consuming steps to be eliminated from the platemaking process.
~ ith proper selection of plate materials, the proposed laser device can be used for making plates applicable in other printing processes as well - letterpress, photogravure, and sten-ciling. The device of the present invention can also be used as an output device in automatic systems employed in publishing houses for aata transmission through communication links.
Claims (19)
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:
1. A laser device for making printing plates on a plate material from an original comprising: a system for synchronous scanning of said original and plate material; an optoelectronic reader optically associated with said synchronous scanning sys-tem; a halftone pulse transducer optically associated with said synchronous scanning system; an electronic circuit intended for generating a sequence of signals to control the laser beam parameters, connected to said optoelectronic reader and to said halftone pulse transducer, said electronic circuit comprising:
a corrector having an input and an output, said input being con-nected to said optoelectronic reader; a comparator having inputs and an output, the first one of said inputs being connected to said output of said corrector; a shaper having an input and an output, said input being connected to said halftone pulse trans-ducer; a synchronized sawtooth generator having an input and an output, said output being connected to the second one of said inputs of said comparator and said input being electri-cally associated with said output of said shaper; an output am-plifier having an input and an output; a line channel controlling the laser beam in reproducing line parts of the original; a dot channel controlling the laser beam in reproducing halftone parts of the original, said line and dot channels, being connec-ted in parallel; a dot-line switch automatically switching over said line and dot channels, having inputs and an output, the first and second ones of said inputs being connected to said line and dot channels; a unit for registering the boundaries of halftone parts of the original, kinematically linked with said synchronous scanning system, generating commands to said dot-line switch and having an output, said output being connected to the third one of said inputs of said dot-line switch; said output of said dot-line switch being connected to said input of said output amplifier; said laser platemaking device also comprising: a laser-optical system for forming images on the surface of said plate material, comprising: a laser; a laser modulator optically associated with said laser and having an input, said input being connected to said output of said output amplifier; an optical unit for directing the laser beam to and focussing it on the scanned surface of said plate material, arranged between said laser modulator and plate material; a deflecting mirror arranged between said laser and laser modu-lator.
a corrector having an input and an output, said input being con-nected to said optoelectronic reader; a comparator having inputs and an output, the first one of said inputs being connected to said output of said corrector; a shaper having an input and an output, said input being connected to said halftone pulse trans-ducer; a synchronized sawtooth generator having an input and an output, said output being connected to the second one of said inputs of said comparator and said input being electri-cally associated with said output of said shaper; an output am-plifier having an input and an output; a line channel controlling the laser beam in reproducing line parts of the original; a dot channel controlling the laser beam in reproducing halftone parts of the original, said line and dot channels, being connec-ted in parallel; a dot-line switch automatically switching over said line and dot channels, having inputs and an output, the first and second ones of said inputs being connected to said line and dot channels; a unit for registering the boundaries of halftone parts of the original, kinematically linked with said synchronous scanning system, generating commands to said dot-line switch and having an output, said output being connected to the third one of said inputs of said dot-line switch; said output of said dot-line switch being connected to said input of said output amplifier; said laser platemaking device also comprising: a laser-optical system for forming images on the surface of said plate material, comprising: a laser; a laser modulator optically associated with said laser and having an input, said input being connected to said output of said output amplifier; an optical unit for directing the laser beam to and focussing it on the scanned surface of said plate material, arranged between said laser modulator and plate material; a deflecting mirror arranged between said laser and laser modu-lator.
2. A laser device as claimed in claim 1 comprising:
a synchronous scanning system step sensor optically associated with said synchronous scanning system; a plate material step counter having an input and outputs; a step generator having an input and an output, said output being connected to said first input of said comparator; said synchronous scanning system step sensor, plate material step counter and step generator being connected in series; a phase-changing switch having inputs and an output; a phase-shift circuit having an input and an output, said input being combined with the first one of said inputs of said phase-changing switch and connected to said output of said shaper, and said output being connected to the second one of said inputs of said phase-changing switch; the third one of said inputs of said phase-changing switch being connected to the second one of said outputs of said plate material step counter, coupled to said input of said step generator; said output of said phase-changing switch being connected to said input of said synchronized sawtooth generator.
a synchronous scanning system step sensor optically associated with said synchronous scanning system; a plate material step counter having an input and outputs; a step generator having an input and an output, said output being connected to said first input of said comparator; said synchronous scanning system step sensor, plate material step counter and step generator being connected in series; a phase-changing switch having inputs and an output; a phase-shift circuit having an input and an output, said input being combined with the first one of said inputs of said phase-changing switch and connected to said output of said shaper, and said output being connected to the second one of said inputs of said phase-changing switch; the third one of said inputs of said phase-changing switch being connected to the second one of said outputs of said plate material step counter, coupled to said input of said step generator; said output of said phase-changing switch being connected to said input of said synchronized sawtooth generator.
3. A laser device as claimed in claim 1, comprising:
an optical cavity of said laser, including an output mirror, a fully reflecting spherical mirror and a polarizing element;
said polarizing element being essentially a fully reflecting flat mirror, the working surface whereof is inclined at an angle of 45 ? 15° to the optical axis of said laser; the plane of inci-dence of the laser beam on said fully reflecting flat mirror of said optical cavity and the plane of incidence of the laser beam on said deflecting mirror coinciding with the plane of incidence of the laser beam on said laser modulator; the coefficient of reflection of said output mirror of said optical cavity of said laser exceeding 50%.
an optical cavity of said laser, including an output mirror, a fully reflecting spherical mirror and a polarizing element;
said polarizing element being essentially a fully reflecting flat mirror, the working surface whereof is inclined at an angle of 45 ? 15° to the optical axis of said laser; the plane of inci-dence of the laser beam on said fully reflecting flat mirror of said optical cavity and the plane of incidence of the laser beam on said deflecting mirror coinciding with the plane of incidence of the laser beam on said laser modulator; the coefficient of reflection of said output mirror of said optical cavity of said laser exceeding 50%.
4. A laser device as claimed in claim 1, wherein, in order to produce a dot and a line pattern on said plate material within a single process cycle without distortions, the laser beam from the exit of said laser modulator is directed at an angle of 3 to 6° to a line forming a right angle with the sur-face of said plate material at the point of contact between the laser beam and the surface of said plate material.
5. A laser device as claimed in claim 1, wherein an electrooptic modulator is used as said laser modulator.
6. A laser device as claimed in claim 1, wherein an acousto-optic modulator is used as said laser modulator.
7. A laser device as claimed in claim 2, wherein an inverter is used as said phase-shift circuit.
8. A laser device as claimed in claim 2, comprising:
an optical cavity of said laser, including an output mirror, a fully reflecting spherical mirror and a polarizing element; said polarizing element being essentially a fully reflecting flat mirror, the working surface whereof is inclined at an angle of 45 ? 15° to the optical axis of said laser; the plane of inci-dence of the laser beam on said fully reflecting flat mirror of said optical cavity and the plane of incidence of the laser beam on said rotating mirror coinciding with the plane of incidence of the laser beam on said laser modulator; the coefficient of reflection of said output mirror of said optical cavity of said laser exceeding 50%.
an optical cavity of said laser, including an output mirror, a fully reflecting spherical mirror and a polarizing element; said polarizing element being essentially a fully reflecting flat mirror, the working surface whereof is inclined at an angle of 45 ? 15° to the optical axis of said laser; the plane of inci-dence of the laser beam on said fully reflecting flat mirror of said optical cavity and the plane of incidence of the laser beam on said rotating mirror coinciding with the plane of incidence of the laser beam on said laser modulator; the coefficient of reflection of said output mirror of said optical cavity of said laser exceeding 50%.
9. A laser device as claimed in claim 2, wherein, in order to produce a dot and a line pattern on said plate material within a single process cycle without distortion, the laser beam from the exit of said laser modulator is directed at an angle of 3 to 6° to a line forming a right angle with the sur-face of said plate material at the point of contact between the laser beam and the surface of said plate material.
10. A laser device as claimed in claim 2, wherein an electrooptic modulator is used as said laser modulator.
11. A laser device as claimed in claim 2, wherein an acousto-optic modulator is used as said laser modulator.
12. A laser device as claimed in claim 3, wherein, in order to produce a dot and line pattern on said plate material within a single process cycle without distortions, the laser beam from the exit of said laser modulator is directed at an angle of 3 to 6° to a line forming a right angle with the sur-face of said plate material at the point of contact between the laser beam and the surface of said plate material.
13. A laser device as claimed in claim 3, wherein an electrooptic modulator is used as said laser modulator.
14. A laser device as claimed in claim 3, wherein an acousto-optic modulator is used as said laser modulator.
15. A laser device as claimed in claim 4, wherein an electrooptic modulator is used as said laser modulator.
16. A laser device as claimed in claim 4, wherein an acousto-optic modulator is used as said laser modulator.
17. A laser device as claimed in claim 7, wherein, in order to produce a dot and a line pattern on said plate material within a single process cycle without distortions, the laser beam from the exit of said laser modulator is directed at an angle of 3 to 6° to a line forming a right angle with the sur-face of said plate material at the point of contact between the laser beam and the surface of said plate material.
18. A laser device as claimed in claim 7, wherein an electrooptic modulator is used as said laser modulator.
19. A laser device as claimed in claim 7, wherein an acousto-optic modulator is used as said laser modulator.
Priority Applications (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CA336,340A CA1127543A (en) | 1979-09-26 | 1979-09-26 | Laser platemaking device |
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CA336,340A CA1127543A (en) | 1979-09-26 | 1979-09-26 | Laser platemaking device |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1127543A true CA1127543A (en) | 1982-07-13 |
Family
ID=4115213
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA336,340A Expired CA1127543A (en) | 1979-09-26 | 1979-09-26 | Laser platemaking device |
Country Status (1)
| Country | Link |
|---|---|
| CA (1) | CA1127543A (en) |
-
1979
- 1979-09-26 CA CA336,340A patent/CA1127543A/en not_active Expired
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