WO1992002368A1 - Gravure d'un element d'impression - Google Patents

Gravure d'un element d'impression Download PDF

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Publication number
WO1992002368A1
WO1992002368A1 PCT/GB1991/001333 GB9101333W WO9202368A1 WO 1992002368 A1 WO1992002368 A1 WO 1992002368A1 GB 9101333 W GB9101333 W GB 9101333W WO 9202368 A1 WO9202368 A1 WO 9202368A1
Authority
WO
WIPO (PCT)
Prior art keywords
engraving
printing member
region
calibration pattern
screen
Prior art date
Application number
PCT/GB1991/001333
Other languages
English (en)
Inventor
Peter Martin Zollman
Original Assignee
Zed Instruments Limited
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by Zed Instruments Limited filed Critical Zed Instruments Limited
Publication of WO1992002368A1 publication Critical patent/WO1992002368A1/fr

Links

Classifications

    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B41—PRINTING; LINING MACHINES; TYPEWRITERS; STAMPS
    • B41C—PROCESSES FOR THE MANUFACTURE OR REPRODUCTION OF PRINTING SURFACES
    • B41C1/00—Forme preparation
    • B41C1/02—Engraving; Heads therefor
    • B41C1/04—Engraving; Heads therefor using heads controlled by an electric information signal
    • B41C1/05—Heat-generating engraving heads, e.g. laser beam, electron beam

Definitions

  • the present invention relates to a method and apparatus for engraving printing members such as rotary screens.
  • EP-A-0320137 discloses one example of an engraving machine used for preparing a rotary printing screen.
  • a laser engraving head traverses the screen with the laser turned on to ablate the lacquer from regions of the screen that are required to transmit ink.
  • the control data for the engraving head is primarily determined by the characteristics of the pattern, often made of dots, which is required on the screen.
  • the appropriate control parameters for the engraving head to produce a desired output will also depend upon the characteristics of the lacquer, the ink to be used in printing, the nature of the substrate and the performance characteristics of the engraving and printing machines.
  • the engraving parameters such as the timing and duration of the pulses from the laser, should be adjusted to reflect these variables.
  • a method of engraving a printing member using a digitally controlled engraving head is characterised by generating a predetermined calibration pattern on a region of the printing member away from the main printing region of the printing member, illuminating the printing member in the region of the calibration pattern, detecting light from the region of the calibration pattern, comparing the total light intensity with an expected value, and modifying engraving parameters for the main printing region of the printing member in accordance with the results of the comparison.
  • the present invention provides a method of engraving having a control loop which effectively compensates for many of the variables discussed above.
  • a value can be determined which, in the example of a perforated nickel sleeve, will correspond directly to the total area of open perforations.
  • an error value is derived which is then used to correct the control parameters as the main portion of the screen is engraved. This correction may be effected by manual intervention of the operator to set particular control parameters, but preferably is carried out automatically and more preferably as part of a closed control loop.
  • a source of light and a light detector may be arranged on the same side of the printing member, and the light detected after scattering or reflection from the calibration pattern.
  • the printing member is a perforated, hollow, cylindrical screen and the light illuminating the calibration pattern is transmitted from one side of the screen and detected on the other side of the screen.
  • the light detector is optically restricted to minimise sensitivity to ambient illumination.
  • the screen may be supported on a mandrel extending along the length of the screen, but preferably the screen is supported without a mandrel by end ring assemblies positioned at either end and the light source or light sensor inside the printing screen is positioned between the end-ring assemblies.
  • the calibration pattern includes regions corresponding to 0% and 100% transmission and these regions are used to calibrate the light source and detector.
  • the calibration pattern includes lines having a predetermined mark-space ratio.
  • the engraving parameters modified in accordance with the result of the comparison include one or more of the laser intensity and the delay in turning the laser on and in turning the laser off.
  • an engraving machine for preparing printing members comprises an engraving head, means for generating a predetermined calibration pattern for engraving by the head on a region of the printing member away from a main printing region, a light source for illuminating the printing member in the region of the calibration pattern, a light sensor for detecting light from the region of the calibration pattern, means for comparing the total light intensity with an expected value, and means for modifying engraving parameters for the main portion of the printing member in accordance with the results of the comparison.
  • the light sensor is optically restricted so that it only accepts light over a small range of solid angle. The use of an optically restricted sensor also minimises sensitivity to ambient illumination.
  • Figure 1 is a schematic cross-sectional view of an engraving apparatus
  • Figure 2 is a longitudinal section through the engraving apparatus of Figure 1;
  • Figure 3 shows three alternative calibration patterns
  • Figure 4 shows a further alternative calibration pattern
  • Figure 5 is a block diagram showing schematically the control system for the apparatus of Figure 1;
  • Figure 6 is a sectional view of an alternative embodiment
  • Figure 7 is a schematic view of one example of the 0 arrangement of the light source and light sensor of the engraving apparatus.
  • a printing screen 1 comprising a hollow perforated 5 nickel sleeve is mounted and supported by a mandrel 2 in a laser engraving machine.
  • the screen 1 is supported towards its ends by end ring assemblies 3.
  • a rotary drive is applied to the mandrel 2 to turn the screen 1 about its longitudinal axis.
  • the laser engraving head is turned ON to ablate lacquer from those regions of the screen 1 where ink transmissive areas are required. The image of the required
  • the arrangement of the engraving head and the screen, and the mechanical and control mechanisms associated wi*h the movement of the engraving head relative to the screen, are conventional in nature and generally similar to that described in the present applicant's above cited European application.
  • the engraving head 6 is mounted on a carriage which is moved progressively from one end of the screen to the other as the screen is rotated.
  • t ' -ee calibration patterns are shown in Figure 3, which t ⁇ ws from top to bottom patterns for regular half-tone, horizontal lines and vertical lines respectively.
  • the calibration pattern may include a plurality of thin lines having a known predetermined mark-space ratio.
  • the data for generating the calibration patterns is stored in the control computer 8 and is output to the laser engraving head at the start of the engraving of each screen, irrespective of the nature of the image subsequently to be engraved in the main printing region of the screen.
  • a light source and light detector are then used to compare a parameter dependent on the total area of open cells with an expected predetermined value, also programmed in the computer 8 and on this basis a control signal to modify the engraving parameters is derived.
  • the support mandrel 2 extends along the length of the screen.
  • a light source 5 is mounted in a recess 9.
  • the source 5 is mounted so as to be held stationary as the mandrel 2 rotates and is positioned so as to clear the portion 10 of the mandrel bridging the recess 9.
  • the light source 5 directs light onto the screen 1 in the region of the calibration pattern.
  • Light passing through the screen is detected by a sensor 4 mounted on the outside of the screen 1 opposite the light source 5.
  • a mask may be provided between the source 5 and sensor 4 to ensure that the sensor 4 only receives light from a known precisely determined area.
  • the light source 5 includes optics 19 to collimate the light.
  • the light then enters a beam expander 17 before transmission to the screen 1 so that only a fixed area of the screen is illuminated independent of its exact position between the illumination source 5 and the sensor 4.
  • a focusing lens 18 is shown situated on the opposite side of the screen 1 to concentrate the transmitted light onto the light sensor 4.
  • the light sensor 4 may be optically restricted so that it only accepts light over a small range of solid angle. This also minimises sensitivity to ambient illumination.
  • the sensor 4 may be a conventional photo-electric cell arranged to produce an output proportional to the intensity of light falling on it across its entire surface.
  • the light source 5 need not be chosen to be blocked by the screen lacquer. Light transmitted by the lacquer is deflected because the surfaces of the lacquer film are not parallel. Once light is deflected from its original direction it cannot reach the sensor 4.
  • the light source 5 illuminates different regions of the calibration pattern and the intensity of light reaching the sensor 4 varies according to the total area of open cells.
  • the output from the sensor 4 provides a parameter dependent on the total open area of a region of the calibration pattern.
  • a separate determination is made for each of the steps of the step wedge. This produces a series of parameters corresponding to different intensities.
  • a corresponding series of expected values is stored in the computer. Comparison of the measured and expected values produces an error signal which is used in the computer 8 to modify the data sent to the engraving head as it moves further along the screen to engrave the image in the main printing portion of that screen.
  • the control data for the laser may be modified to increase the amplitude of the laser and/or to increase the duration of each pulse of the laser.
  • This first correction in particular is appropriate when the calibration pattern includes thin lines and it is found that the mark-space ratio for circumferential lines is lower than expected. Increasing the duration of the laser pulse is appropriate where the mark-space ratio in the horizontal direction is too low.
  • the error coefficient derived by comparison of the predetermined and measures values may be used in a closed loop control system, with a measured correction being applied to the engraving parameters supplied to the laser, calculated in accordance with the magnitude of the error i.e. an iterative control system.
  • an open loop control system may be used.
  • the achieved results are interpolated and possibly extrapolated to produce a response curve.
  • the inverse of this curve is applied to the engraving signal to achieve the required transmission.
  • the present invention is applicable to many different screen types.
  • it may be used for engraving galvano screens in which acid resistant lacquer is ablated by the laser from a solid copper or nickel surface.
  • both the light source and sensor are arranged on the same side of the screen when the measurement made on the basis of the different reflectivities of the ablated and non-ablated cells.
  • the light source 5 and sensor 4 are incorporated in an engraving machine generally similar to the type described in EP-A-0320137. This machine includes a laser 11, an engraving head 12 mounted on a movable carriage 13 and end ring assemblies 14.
  • this machine Rather than using a solid support mandrel this machine relies upon the end ring assemblies 14 at each end of the screen being driven in synchronism by motor 15.
  • a movable support ring 16 tracks with the engraving head 12 to support the screen 1 locally. In this case, since there is free space inside the screen immediately adjacent the end rings the mounting of the light source is considerably simplified.
  • the source and sensor can be fitted and serviced when the mandrel is stationary, avoiding the need for an axial opening to provide access.

Landscapes

  • Engineering & Computer Science (AREA)
  • Physics & Mathematics (AREA)
  • Optics & Photonics (AREA)
  • Plasma & Fusion (AREA)
  • Manufacturing & Machinery (AREA)
  • Manufacture Or Reproduction Of Printing Formes (AREA)

Abstract

Procédé de gravure d'un élément d'impression (1) utilisant une tête de gravure à commande numérique (6, 12) qui comprend la création d'un modèle de dimensionnement prédéterminé sur une région de l'élément d'impression (1) située à distance de la région d'impression principale de l'élément d'impression (1), l'éclairage de l'élément d'impression sur la région du modèle de dimensionnement, la détection de la lumière provenant de la région du modèle de dimensionnement, la comparaison de l'intensité lumineuse totale avec une valeur souhaitée et la modification automatique des paramètres de gravure laser pour la région d'impression principale de l'élément d'impression (1) en fonction des résultats de la comparaison.
PCT/GB1991/001333 1990-08-06 1991-08-05 Gravure d'un element d'impression WO1992002368A1 (fr)

Applications Claiming Priority (2)

Application Number Priority Date Filing Date Title
GB9017190.1 1990-08-06
GB909017190A GB9017190D0 (en) 1990-08-06 1990-08-06 Printing member engraving

Publications (1)

Publication Number Publication Date
WO1992002368A1 true WO1992002368A1 (fr) 1992-02-20

Family

ID=10680219

Family Applications (1)

Application Number Title Priority Date Filing Date
PCT/GB1991/001333 WO1992002368A1 (fr) 1990-08-06 1991-08-05 Gravure d'un element d'impression

Country Status (4)

Country Link
EP (1) EP0542787A1 (fr)
JP (1) JPH05509265A (fr)
GB (1) GB9017190D0 (fr)
WO (1) WO1992002368A1 (fr)

Cited By (7)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
EP0591559A1 (fr) * 1992-09-28 1994-04-13 Schablonentechnik Kufstein Aktiengesellschaft Méthode et appareillage de gravage de cylindres imprimeurs
EP0641649A1 (fr) * 1993-09-04 1995-03-08 Kissel & Wolf GmbH Procédé pour éliminer un revêtement stencil sur formes pour l'impression sérigraphique et dispositif pour la mise en oeuvre de ce procédé
EP0884582A1 (fr) * 1997-06-10 1998-12-16 Bayer Corporation Fluorimètre pour mesurer la densité de points en demi-teintes
DE10215694A1 (de) * 2002-04-10 2003-10-23 Heidelberger Druckmasch Ag Verfahren und Herstellen einer Druckform
EP1637929A1 (fr) * 2004-09-15 2006-03-22 Agfa Corporation Méthode et système pour établir des échelles d'exposition pour des appareils d'imagerie par faisceau laser
WO2006045128A1 (fr) * 2004-10-28 2006-05-04 Oesterreichische Banknoten- Und Sicherheitsdruck Gmbh Dispositif pour graver des plaques d'impression
US8168917B2 (en) * 2006-05-30 2012-05-01 Caterpillar Inc. System and method for laser-encoding information on hydraulic rods

Citations (6)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
DE2344233A1 (de) * 1972-09-09 1974-03-21 Newton Horwood Ltd Druckplatte und verfahren zu ihrer herstellung
GB2069292A (en) * 1980-02-11 1981-08-19 Exxon Research Engineering Co Internal test method and apparatus for facsimile transceiver
EP0144188A2 (fr) * 1983-12-07 1985-06-12 Xerox Corporation Système pour la correction en densité d'une copie
US4839722A (en) * 1987-10-30 1989-06-13 Colorocs Corporation Method and apparatus for providing improved color correction in a subtrative color printing system
EP0320137A1 (fr) * 1987-11-25 1989-06-14 Zed Instruments Limited Appareil pour la gravure au laser pour la fabrication d'écrans sérigraphiques cylindriques
WO1990006234A1 (fr) * 1988-11-28 1990-06-14 Stork Screens B.V. Procede et dispositif permettant de former un modele de reserve sur un objet cylindrique et cylindre metallique attaque obtenu avec un tel modele de reserve

Patent Citations (6)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
DE2344233A1 (de) * 1972-09-09 1974-03-21 Newton Horwood Ltd Druckplatte und verfahren zu ihrer herstellung
GB2069292A (en) * 1980-02-11 1981-08-19 Exxon Research Engineering Co Internal test method and apparatus for facsimile transceiver
EP0144188A2 (fr) * 1983-12-07 1985-06-12 Xerox Corporation Système pour la correction en densité d'une copie
US4839722A (en) * 1987-10-30 1989-06-13 Colorocs Corporation Method and apparatus for providing improved color correction in a subtrative color printing system
EP0320137A1 (fr) * 1987-11-25 1989-06-14 Zed Instruments Limited Appareil pour la gravure au laser pour la fabrication d'écrans sérigraphiques cylindriques
WO1990006234A1 (fr) * 1988-11-28 1990-06-14 Stork Screens B.V. Procede et dispositif permettant de former un modele de reserve sur un objet cylindrique et cylindre metallique attaque obtenu avec un tel modele de reserve

Non-Patent Citations (1)

* Cited by examiner, † Cited by third party
Title
Klischograph, no. 2, 1969, U. Gast: "Können Laserstrahlen die Druckformenherstellung beschleunigen", pages 8-12, see page 10, paragraph 2 *

Cited By (10)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
EP0591559A1 (fr) * 1992-09-28 1994-04-13 Schablonentechnik Kufstein Aktiengesellschaft Méthode et appareillage de gravage de cylindres imprimeurs
US5378509A (en) * 1992-09-28 1995-01-03 Schablonentechnik Kufstein Ges. M.B.H. Method for etching round templates
EP0641649A1 (fr) * 1993-09-04 1995-03-08 Kissel & Wolf GmbH Procédé pour éliminer un revêtement stencil sur formes pour l'impression sérigraphique et dispositif pour la mise en oeuvre de ce procédé
US6024020A (en) * 1996-08-21 2000-02-15 Agfa Corporation Fluorescence dot area meter for measuring the halftone dot area on a printing plate
EP0884582A1 (fr) * 1997-06-10 1998-12-16 Bayer Corporation Fluorimètre pour mesurer la densité de points en demi-teintes
DE10215694A1 (de) * 2002-04-10 2003-10-23 Heidelberger Druckmasch Ag Verfahren und Herstellen einer Druckform
EP1637929A1 (fr) * 2004-09-15 2006-03-22 Agfa Corporation Méthode et système pour établir des échelles d'exposition pour des appareils d'imagerie par faisceau laser
WO2006045128A1 (fr) * 2004-10-28 2006-05-04 Oesterreichische Banknoten- Und Sicherheitsdruck Gmbh Dispositif pour graver des plaques d'impression
AT501045B1 (de) * 2004-10-28 2006-06-15 Oesterreichische Banknoten U S Vorrichtung zum gravieren
US8168917B2 (en) * 2006-05-30 2012-05-01 Caterpillar Inc. System and method for laser-encoding information on hydraulic rods

Also Published As

Publication number Publication date
EP0542787A1 (fr) 1993-05-26
JPH05509265A (ja) 1993-12-22
GB9017190D0 (en) 1990-09-19

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