GB2030077A - Photocomposition of text and pictures - Google Patents

Photocomposition of text and pictures Download PDF

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Publication number
GB2030077A
GB2030077A GB7913582A GB7913582A GB2030077A GB 2030077 A GB2030077 A GB 2030077A GB 7913582 A GB7913582 A GB 7913582A GB 7913582 A GB7913582 A GB 7913582A GB 2030077 A GB2030077 A GB 2030077A
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GB
United Kingdom
Prior art keywords
printing surface
light spot
light
modulator
printing
Prior art date
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Granted
Application number
GB7913582A
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GB2030077B (en
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EERO BYCKLING
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EERO BYCKLING
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Publication date
Application filed by EERO BYCKLING filed Critical EERO BYCKLING
Publication of GB2030077A publication Critical patent/GB2030077A/en
Application granted granted Critical
Publication of GB2030077B publication Critical patent/GB2030077B/en
Expired legal-status Critical Current

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Classifications

    • G—PHYSICS
    • G02—OPTICS
    • G02B—OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
    • G02B26/00—Optical devices or arrangements for the control of light using movable or deformable optical elements
    • G02B26/08—Optical devices or arrangements for the control of light using movable or deformable optical elements for controlling the direction of light
    • G02B26/10—Scanning systems
    • G02B26/101—Scanning systems with both horizontal and vertical deflecting means, e.g. raster or XY scanners
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B41—PRINTING; LINING MACHINES; TYPEWRITERS; STAMPS
    • B41J—TYPEWRITERS; SELECTIVE PRINTING MECHANISMS, i.e. MECHANISMS PRINTING OTHERWISE THAN FROM A FORME; CORRECTION OF TYPOGRAPHICAL ERRORS
    • B41J2/00—Typewriters or selective printing mechanisms characterised by the printing or marking process for which they are designed
    • B41J2/435—Typewriters or selective printing mechanisms characterised by the printing or marking process for which they are designed characterised by selective application of radiation to a printing material or impression-transfer material
    • B41J2/47—Typewriters or selective printing mechanisms characterised by the printing or marking process for which they are designed characterised by selective application of radiation to a printing material or impression-transfer material using the combination of scanning and modulation of light
    • G—PHYSICS
    • G06—COMPUTING; CALCULATING OR COUNTING
    • G06K—GRAPHICAL DATA READING; PRESENTATION OF DATA; RECORD CARRIERS; HANDLING RECORD CARRIERS
    • G06K15/00—Arrangements for producing a permanent visual presentation of the output data, e.g. computer output printers
    • G06K15/02—Arrangements for producing a permanent visual presentation of the output data, e.g. computer output printers using printers
    • G06K15/12—Arrangements for producing a permanent visual presentation of the output data, e.g. computer output printers using printers by photographic printing, e.g. by laser printers
    • G06K15/1204—Arrangements for producing a permanent visual presentation of the output data, e.g. computer output printers using printers by photographic printing, e.g. by laser printers involving the fast moving of an optical beam in the main scanning direction
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04N—PICTORIAL COMMUNICATION, e.g. TELEVISION
    • H04N1/00—Scanning, transmission or reproduction of documents or the like, e.g. facsimile transmission; Details thereof
    • H04N1/04—Scanning arrangements, i.e. arrangements for the displacement of active reading or reproducing elements relative to the original or reproducing medium, or vice versa
    • H04N1/113—Scanning arrangements, i.e. arrangements for the displacement of active reading or reproducing elements relative to the original or reproducing medium, or vice versa using oscillating or rotating mirrors
    • H04N1/1135—Scanning arrangements, i.e. arrangements for the displacement of active reading or reproducing elements relative to the original or reproducing medium, or vice versa using oscillating or rotating mirrors for the main-scan only
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04N—PICTORIAL COMMUNICATION, e.g. TELEVISION
    • H04N1/00—Scanning, transmission or reproduction of documents or the like, e.g. facsimile transmission; Details thereof
    • H04N1/04—Scanning arrangements, i.e. arrangements for the displacement of active reading or reproducing elements relative to the original or reproducing medium, or vice versa
    • H04N1/10—Scanning arrangements, i.e. arrangements for the displacement of active reading or reproducing elements relative to the original or reproducing medium, or vice versa using flat picture-bearing surfaces
    • H04N1/1008—Scanning arrangements, i.e. arrangements for the displacement of active reading or reproducing elements relative to the original or reproducing medium, or vice versa using flat picture-bearing surfaces with sub-scanning by translatory movement of the picture-bearing surface
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04N—PICTORIAL COMMUNICATION, e.g. TELEVISION
    • H04N2201/00—Indexing scheme relating to scanning, transmission or reproduction of documents or the like, and to details thereof
    • H04N2201/04—Scanning arrangements
    • H04N2201/0402—Arrangements not specific to a particular one of the scanning methods covered by groups H04N1/04 - H04N1/207
    • H04N2201/0426—Scanning an image in a series of contiguous zones

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  • Physics & Mathematics (AREA)
  • Engineering & Computer Science (AREA)
  • General Physics & Mathematics (AREA)
  • Optics & Photonics (AREA)
  • Multimedia (AREA)
  • Signal Processing (AREA)
  • General Engineering & Computer Science (AREA)
  • Theoretical Computer Science (AREA)
  • Facsimile Scanning Arrangements (AREA)

Abstract

The device consists of a laser light source, a modulator, a deflector, and a mirror, to produce a light spot, optical components to guide and focus the light beam on a photosensitive surface, and means to move the light beam and surface relative to each other. The combination of the movement of the mirror and the movement of the surface together cause the motion of the light spot in a certain diraction on the printing surface and the deflector causes a faster motion perpendicular to the above mentioned motion so that an unmodulated light spot would expose on the surface a stripe consisting of parallel lines. The part of text or figures intended in the area of one stripe is written by modulating the light using the modulator. <IMAGE>

Description

SPECIFICATION A device for writing text and pictures on a photosensitive surface in the production of printing plates This invention is concerned with a device which modulates, deflects and focuses laser light on an image surface in order to transform text and pictorial material in the form of electronic signal into the form of images on the printing plate by exposing a photosensitive surface of removing a film from the surface. The generation of the letters, characters, portions of letters and characters, pictures or picture elements is accomplished by deflecting the light spot on the image surface in the horizontal direction with respect to the printed page and simultaneously deflecting it at a faster rate in the vertical direction with respect to the printed page.Thus a stripe consisting of vertical strokes is generated and the portions of the characters and pictures which fall inside the stripe can be written by modulating the light with a modulator. The total material intended on the printing plate is generated by covering the area of the plate with adjoining stripes containing text and picture material.
In the printing process, printing plates are used in which height variations of the surface or the adhesion properties of the surface with respect to ink are controlled to obtain the required printing properties.
In this field, methods are known to produce plates for printing by exposing the surface by a camera or exposing through film in contact printing. Further, devices are known in which a laser beam is deflected across the image surface in the manner of a television raster and simultaneous modulation of the signal will write the material on the surface. To obtain sufficient quality, the resolution of the image must be high, which means that the number of picture elements must be large enough, which implies that the information content of the image is large. This sets requirements for the memory capacity and data handling capacity of the control computer which are difficult to fulfill in practice. Additionally, the number of the TV-raster lines will be large.To obtain a sufficiently short writing time for the whole printed page, a fast deflection mechanism is required, which has been technically hard to implement.
As a result of this invention, a device has been created in which letters and other characters, the raster points of pictures, and other picture elements are composed only while the image is being written on the image surface.
This means that the characters can be stored in the control computer in alphanumeric form and the pictures in raster point form. This coding decreases the information content strongly. Further, because the light spot moving in the horizontal direction is simultaneously deflected more rapidly in the vertical direction, one writes a wide horizontal stripe instead of a narrow line. If the total time for writing a complete page is fixed, the horizontal scanning frequency in this technique is considerably smaller than in TV-scanning, which simplifies its implementation mechanically.
The invention is applicable to writing text and pictures directly on printing plates or cylinders but it can be used without modification also to write on photosensitive film or paper. These are then used to transfer the material to a printing plate or they are used for proof reading.
The invention will be studied in more detail in the accompanying drawing which shows one embodiment of the device according to the invention.
The device has been constructed in the laboratory in the form shown in the figure.
The laser (Laser) is a 9W argon ion laser which emits a collimated beam of light having the wavelength 488nm. The light beam then propagates through a set of optical and electro-optical elements. First, the prisms P1 and P2 are used to direct the beam into a proper direction. After going through the lens L1, the beam enters the acousto-optic modulator Mod.. The Modulator is used to modulate the the intensity of the light, specifically to turn the beam on and off. This is accomplished by letting the light travel through a transparent medium into which one can generate an ultrasound wave. If there is no ultrasound present, the light beam travels straight through. In the presence of ultrasound of correct frequency, e.g. 110 MHz, and correct amplitude, the beam is deflected by Bragg diffraction.The speed of switching depends on the diameter of the light beam in the acousto-optic modulator. To decrease the rise and fall times of the modulator, the light beam, which has the diameter 2mm when emitted by the laser, is focused into a narrower beam by the lens L1.
The diameter of the beam in the modulator must, however, not be too small to avoid damage to the acousto-optic material. In the constructed device, the beam diameter inside the modulator was 0.2mm, which resulted in the rise time 40ns. The knife edge K1 is used to cut off the non-diffracted beam after the modulator, and let pass the diffracted beam, The pair of lenses L2 and L3 are needed to expand the beam into a larger diameter. The size of the light spot on the image surface depends on aberrations and on diffraction.
The diffraction limited spot size is inversely proportional to the beam diameter. In the device, the diameter of the beam after L3 was required to be 1 8mm, and therefore the focal lengths of the lenses L2 and L3 were chosen to be 9.5mm and 95mm. If the quality of the beam after the lens 3 is not sufficiently good, one can also put a small pinhole into the focus point of the lenses L2 and L3 to act as a spatial filter. The mirrors M1, M2, and M3 are only to direct the beam into a required direction.
The cylindrical lenses C1 and C2 and the acousto-optic deflector Defl. form a system to generate the fast vertical deflection of the light spot on the image surface. The acoustooptic deflector consists of transparent material through which the light beam travels. On the surface of the acousto-optic material there is a generator of acoustic waves. The frequency and amplitude of the ultrasound traversing the acousto-optic material can be adjusted. When the light wave meets the acoustic wave it is diffracted according to Bragg diffraction. The angle of diffraction depends on the frequency of the acoustic wave. Thus by varying the frequency one can direct the light beam into required direction. In the device, when the frequency is changed from 50MHz to 90MHz, the angle of direction changes by 5 mrad.In an acousto-optic deflector the aperture is usually rectangular. To obtain sufficient resolution, the aperture must be large enough in the direction in which the acoustic wave travels.
In the direction perpendicular to this direction the aperture must be small in order that the ultrasound field seen by the light beam be homogeneous enough. In the device, the aperture for the light beam was 38mm X 2mm. In order to get the beam into this aperture, it is compressed in one dimension by the cylindrical lens C1. This had focal length 600mm and focused the light beam into a narrow line into the deflector. The cylindrical lens C2 is used to change the beam back into a collimated beam with rotationally symmetric cross section. The resolution of the deflector was 1 30 resolution elements and the maximum frequency of vertical scanning 30kHz.
The pair of positive lenses L4 and L5 has three different tasks. It is a telescope with magnification 2 and thus it multiples the deflection angle of the vertical deflector by 2.
This is required to get large enough vertical deflection of the light spot on the image surface. Secondly, the telescope provides a focus point at which the undiffracted part of the beam can be cut off with the knife edge K2. Finally, the telescope images the aperture of the acousto-optic deflector onto the input pupil of the lens L6.
The horizontal deflection of the light spot is provided by the mirror M4 which is rotated by means of the galvanometer Galv.. When the mirror turns an angle, the beam is deflected by an angle twice that. The peak-to-peak turning angle of mirror was 25Q. The resonance frequency of the galvanometer was 83Hz. In the new technique, the galvanometer will oscillate, creating a constant velocity movement for the spot on the image surface. The frequency on oscillation is 3Hz.
In a TV scanning technique the frequency would be 400Hz which is very difficult to obtain with conventional galvanometer scanners. The galvanometer was provided with a capacitive position sensor which has a linearity of 0.15% and a repeatability of 1 arc second, and which is used to control the velocity of the scan and the position of the light spot. The size of the mirror M4 is determined by the size of the beam, and it was 26mm X 26mm.
The lens L6 focuses the beam, into a small spot in the image surface. In order to be able to use planar printing plates, the lens must focus the beam on a plane, that is, the lens must be a field flattening lens. The spot size is determined by diffraction and by lens aberrations, in addition to possible effects due to deteoriation of the beam quality before the projection lens L6. Diffraction effects require large enough aperture, in this case 22mm.
Coupled with aberrations, the resulting spot size was 40cm. The focal of the lens was 407mm. Because the horizontal scan angle was 50 , the length of the horizontal scan is 420mm, or equal to the width of a newspaper page. The vertical deflection angle was 10 mrad after multiplication in the telescope, and this gives the length 4mm of the vertical scan for the spot. Characters that are smaller than this can thus be generated inside one stripe; otherwise they are composed of parts of this height. Linearity of the written text in the horizontal direction can be controlled by a proper design of the lens. However, this can not be done with respect to the effect that the length of the vertical deflection, for a given deflection angle in the acousto-optic element, grows as the horizontal deflection increases.
This must be compensated for electronically in the drive circuit of the acousto-optic deflector.
The printing plate or similar light sensitive surface is placed on a moving carriage. This can be translated in the vertical direction by a mechanism which also takes care of accurate positioning of the carriage. Actually, a high accuracy is not needed in the mechanism of the device because any positioning errors in the vertical direction can be compensated for electronically by means of the fast vertical deflection system. It suffices to have a detecting system which determines the position of light spot with respect to the moving carriage.
The device operates so that the light spot, focused by the lens on the image surface, is moved by the mirror M4 in the horizontal direction with respect to the printed page, and simultaneously the deflector Defl. deflects the spot in the vertical direction with respect to the printed page. The latter movement is shorter and faster than the former. Without modulation the device thus writes short parallel vertical lines which together generate a wide horizontal stripe. In the surface area thus formed, one can write arbitrary text or picture material by modulating the light beam. When one complete stripe is written, the image surface is moved a distance equal to the width of the stripe, and the next stripe is written in the same manner.
If a character is located complete inside one stripe, the information which determines its geometric shape is needed only during the time that the light spot is inside the rectangle defined by the size of the character. The geometric data needs to be stored in a fast memory only while the character is being written. In this respect, the method differs from TV scanning technique, in which the data for a complete horizontal string of characters must be available in a fast storage. In the new technique, raster pictures can be generated in the same way as characters.
Characters of large size or line drawings are generated by recalling from a memory that portion of the geometric form which falls inside the stripe.
If one stripe consists of N resolution elements in the vertical direction, which are generated during one vertical stroke, it follows that the velocity of the mirror for horizontal deflection will be smaller by a factor N compared to TV scanning technique, assuming the same resolution and total writing time in the two cases.
The rotation of the mirror M4 is accomplished by a galvanometer as an oscillating movement or by a rotating polygon mirror which rotates around an axis. This motion is not needed if the image surface is moved mechanically also in the horizontal direction.
This is convenient in particular if the printing surface is cylindrical, in which case it is rotated around its axis. In this situation the advantage compared to the TV scanning technique is particularly great, because the rotation rate of the cylinder is smaller by the factor N in the new technique compared to the TV scanning technique.
Instead of moving the image surface in the vertical direction mechanically, it is possible to move the optics of the system in the vertical direction with respect to the image surface.
A major advantage of the invention is that when the system is implemented in practice, the required speeds and magnitudes of the deflections can be economically and advantageously achieved with existing components: a fast small vertical deflection with acousto-optic deflector, a slower large horizontal deflection with a mirror, and the slowest large vertical motion mechanically.
In one practical experiment a device was built and studied in which the width of the printing plate is 41 Omm, the vertical deflection created by an acousto-optic deflector is 4mm and the number of resolution elements in this interval is 160, the total height of the printing plate is 580mm and the size of the light spot on the image surface is 25 to 1 501lem. The total amount of information on one newspaper page corresponding to TV scanning with 23zm resolution is 300 Mbits.
In alphanumeric form the amount of information is 300 kbits for text and 4 Mbits for pictures.

Claims (5)

1. A device for writing text and pictures on an image surface in the production of a printing surface, such as printing plate, a printing cylinder, a photosensitive film, or a paper, comprising: -a laser light source for emitting a light beam, optical means for directing and focusing the light beam onto the image surface, -a modulator for modulating the light beam, -horizontal deflection means, vertical deflection means, -mechanical means for moving the printing surface in a reciprocating manner, the movement of the horizontal deflection means and the movement of the printing surface, in combination, causing the light spot to move in a certain direction on the printing surface, and the vertical deflecting means causing a motion of the light spot perpendicular to and faster than the first mentioned motion such that an unmodulated light spot exposes on the printing surface stripes consisting of parallel lines, such that when the light beam is modulated, it can be used to write characters of arbitrary shape on the printing surface when the printing plate is moved to cover its total area by adjoining stripes.
2. A device as claimed in Claim 1, wherein the printing surface is stationary while writing a stripe and the horizontal deflection means comprises a rotatable mirror.
3. A device as claimed in Claim 1, wherein the horizontal deflection means comprises a fixed mirror and the printing surface moves with respect to the light spot in a direction perpendicular to the direction in which the light spot deflected by the vertical deflecting means.
4. A device as claimed in Claim 1, wherein the vertical deflection means comprises an acousto-optic deflector and the modulator comprises an acousto-optic modulator.
5. A device as claimed in Claim 1, further comprising an electronic circuit for driving the modulator and containing the control signal of the written character essentially only during writing of the character.
GB7913582A 1978-09-08 1979-04-19 Photocomposition of text and pictures Expired GB2030077B (en)

Applications Claiming Priority (1)

Application Number Priority Date Filing Date Title
FI782753A FI782753A (en) 1978-09-08 1978-09-08 ANORDINATION FOER SKRIVNING AV TEXT OCH BILDER MED LASER PAO EN BILDYTA VID FRAMSTAELLNING AV TRYCKPLATTOR

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Publication Number Publication Date
GB2030077A true GB2030077A (en) 1980-04-02
GB2030077B GB2030077B (en) 1983-01-12

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GB7913582A Expired GB2030077B (en) 1978-09-08 1979-04-19 Photocomposition of text and pictures

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GB (1) GB2030077B (en)

Cited By (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
GB2253112A (en) * 1990-12-24 1992-08-26 Ms Servizi Informatici Electronic apparatus for the laser imprinting of screen-process printing stencils and the like
EP0723204A1 (en) * 1995-01-17 1996-07-24 Agfa-Gevaert N.V. A method and apparatus for obtaining a lithographic plate

Cited By (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
GB2253112A (en) * 1990-12-24 1992-08-26 Ms Servizi Informatici Electronic apparatus for the laser imprinting of screen-process printing stencils and the like
GB2253112B (en) * 1990-12-24 1994-09-21 Ms Servizi Informatici Electronic apparatus for the laser imprinting of screen-process printing stencils and the like
EP0723204A1 (en) * 1995-01-17 1996-07-24 Agfa-Gevaert N.V. A method and apparatus for obtaining a lithographic plate

Also Published As

Publication number Publication date
FI782753A (en) 1980-03-09
GB2030077B (en) 1983-01-12

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Date Code Title Description
PCNP Patent ceased through non-payment of renewal fee

Effective date: 19930419