EP0488910B1 - Method and apparatus for regulating the water-ink balance on a printing plate of an offset printing machine - Google Patents

Method and apparatus for regulating the water-ink balance on a printing plate of an offset printing machine Download PDF

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Publication number
EP0488910B1
EP0488910B1 EP91420415A EP91420415A EP0488910B1 EP 0488910 B1 EP0488910 B1 EP 0488910B1 EP 91420415 A EP91420415 A EP 91420415A EP 91420415 A EP91420415 A EP 91420415A EP 0488910 B1 EP0488910 B1 EP 0488910B1
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Prior art keywords
offset plate
water
area
offset
focal plane
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German (de)
French (fr)
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EP0488910A1 (en
Inventor
Laurent Balducci
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ASSOCIATION DE GESTION DE L'ECOLE FRANCAISE DE PAPETERIE ET DE L'IMPRIMERIE
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ASSOCIATION DE GESTION DE L'ECOLE FRANCAISE DE PAPETERIE ET DE L'IMPRIMERIE
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    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B41—PRINTING; LINING MACHINES; TYPEWRITERS; STAMPS
    • B41F—PRINTING MACHINES OR PRESSES
    • B41F33/00—Indicating, counting, warning, control or safety devices
    • B41F33/0063—Devices for measuring the thickness of liquid films on rollers or cylinders
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B41—PRINTING; LINING MACHINES; TYPEWRITERS; STAMPS
    • B41F—PRINTING MACHINES OR PRESSES
    • B41F33/00—Indicating, counting, warning, control or safety devices
    • B41F33/0054—Devices for controlling dampening
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y10—TECHNICAL SUBJECTS COVERED BY FORMER USPC
    • Y10S—TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y10S101/00—Printing
    • Y10S101/45—Sensor for ink or dampening fluid thickness or density

Definitions

  • the present invention relates to offset machines and in particular the methods of inking and wetting the offset plate.
  • Figure 1 shows a simplified example of the mechanism of an offset machine.
  • a plate cylinder 1 on which an offset plate 2 is mounted first comes into contact with wetting rollers 3a and 3b and then with ink rollers 4a and 4b.
  • the ink on the plate 2 is then transferred to a cylinder 5 called a blanket.
  • the blanket 5 is in contact with a printing cylinder 6. Paper 7 passing between the cylinders 5 and 6 is printed by the ink present on the blanket 5.
  • the surface of the offset plate 2 is formed in such a way that, when inking, the ink only deposits on desired areas of the plate to constitute an image.
  • FIG. 2 represents a magnification of a section of the offset plate 2.
  • a resin film has been deposited on the rough surface 20 of the plate 2 and then etched according to the image to be reproduced, leaving resin dots 21 of variable dimensions and zones 22 devoid of resin.
  • density the ratio of the surface of the points 21 on the surface of the zones 22.
  • the coverage rate by the ink varies, that is to say that the ink more or less covers the points 21, the water occupying the remaining area.
  • the problem posed is to move as little as possible from the water-ink balance which corresponds to the ideal state where the ink would exactly cover the points 21, in other words, where the coverage rate would be equal to density.
  • the respective amounts of water and ink must be between certain limits, namely an upper limit where the ink would overflow the points 21 during transfer to the blanket 5 and a lower limit where the the water in zones 22 would not entirely cover the ridges of the roughness of surface 20. If the lower limit is not respected, the ink also adheres to zones 22 and the offset plate must be cleaned.
  • control bars which are printed at the same time as each image. These control bars have several screened areas at different point sizes and at different ideal coverage rates. These control bars are examined visually or with optical densitometers on the printed sheet to determine whether to readjust the wetting and inking settings.
  • the document FR-A-2 556 283 (under priority of patent applications of the United States of America No. 560 837 of December 13, 1983 and No. 618 252 of June 7, 1984) describes a system for measuring the average quantity of water present on a moving ink roller.
  • the roller is illuminated at a non-normal incidence and the reflected light is collected by several optical sensors.
  • the signals delivered by these sensors are then processed to obtain an indication of the average amount of water on the roller.
  • a drawback of this system is that no indication of the coverage rate is obtained on the offset plate, which, as we have seen above, is essential for detecting the water-ink balance.
  • Another drawback is linked to the illumination of the roller under a different incidence from normal, which causes intensity fluctuations at the level of the sensors linked to surface and eccentricity defects of the roller.
  • German patent application 36 11 645 describes a system for providing an indication of the water-ink ratio. For this, it includes a non-coherent light source illuminating the offset plate and two sensors collecting the re-emitted light, one corresponding to water and the other to ink. The lighting and reception angles are separate, so that the sensors do not receive the reflected light.
  • An object of the present invention is to continuously provide an indication of the water-ink balance.
  • Another object of the invention is to overcome the problems of surface defects and eccentricity.
  • a method for monitoring the water-ink balance in an offset machine which includes an offset plate fixed to a cylinder, the method comprising the following steps: lighting under normal incidence, with a coherent light source, a predetermined area of the moving offset plate, the density of which is known; collecting in the focal plane of a converging optical system a part of the re-emitted light perpendicular to the plane of the illuminated area; and measuring the light intensity in at least one area of the focal plane.
  • the light intensity is measured around the axis of the converging optical system.
  • the light intensity is also measured in at least one zone remote from the axis of the converging optical system.
  • the predetermined area is a regularly screened area.
  • the predetermined area is illuminated in synchronism with the movement of the offset plate.
  • the present invention also provides a device for regulating the water-ink balance in an offset machine comprising an offset plate fixed to a cylinder, and a system for wetting and inking this plate, the device comprising: a coherent light source illuminating under normal incidence a predetermined area of the moving offset plate; a measurement cell comprising a sensor placed in the axis and in the focal plane of a converging optical system, which collects a fraction of the re-emitted light perpendicular to said zone; a servo system taking into account the signal delivered by the sensor to adjust the wetting and / or inking of the offset plate.
  • At least a second sensor is placed in the focal plane of the converging optical system off the axis, and means are provided for acting on the servo system to determine a minimum wetting at from the signal of this second sensor.
  • FIG. 3 represents a device according to the present invention which makes it possible to provide an indication of the water-ink balance.
  • the device has been adapted on a conventional offset machine, for example that of FIG. 1.
  • a coherent light source 30, such as a laser provides a beam which is reflected on a mirror 31 to project, normally on its surface, a light spot on the moving offset plate 2.
  • a converging lens 32 whose axis is normal to the plate 2, supports the mirror 31 and collects the light re-emitted by the illuminated area of the plate.
  • Two sensors 33 and 34 are placed in the focal plane of the lens 32, the sensor 33 being in the axis of the lens.
  • Illuminating the plate 2 normally and collecting the re-emitted light in the normal direction makes the device practically insensitive to surface and centering defects of the cylinder 1.
  • the above system is activated at specific times when the light source 30 illuminates a predetermined area 35 of the plate 2, the characteristics of which are known, in particular the density.
  • This predetermined area is, for example, one of the screened areas of a control bar printed at the same time as each image.
  • This particular arrangement and the use of a coherent light source make it possible to obtain in the focal plane of the lens 32 the Fourier transform of the re-emitted wave from the zone 35. It turns out that the average value of this Fourier transform, which is a light intensity measured by the sensor 33, varies in the opposite direction with respect to the variations in the coverage rate of the area 35. As we know the density of this area, we also know the water balance - ink that it should present.
  • the device according to the present invention can be adapted to any offset machine and be associated with a servo system easy to perform by those skilled in the art, which makes it possible to act on the wetting and / or inking settings.
  • the present invention is susceptible to various variations and modifications.
  • to collect the light re-emitted around an axis normal to the illuminated area instead of using a lens, it is possible to use any other convergent light-collecting optical system and to place detectors in the focal plane of this optical system.

Abstract

The present invention relates to a method for monitoring the water/ink balance in an offset printing machine comprising an offset plate (2) fastened to a cylinder (1), the method involving the following steps: illuminating a predetermined zone (35) of the moving offset plate (2), the density of which is known, at normal incidence with a coherent-light source (30); collecting in the focal plane of a convergent lens (32) some of the light reemitted about an axis normal to the plane of the illuminated zone (35); and measuring the light intensity in at least one zone of the focal plane. <IMAGE>

Description

La présente invention concerne les machines offset et en particulier les procédés d'encrage et de mouillage de la plaque offset.The present invention relates to offset machines and in particular the methods of inking and wetting the offset plate.

Avant d'aborder les problèmes que l'invention vise à résoudre, on va brièvement décrire le fonctionnement d'une machine offset.Before tackling the problems that the invention aims to solve, we will briefly describe the operation of an offset machine.

La figure 1 représente un exemple simplifié du mécanisme d'une machine offset. Un cylindre porte-plaque 1 sur lequel est monté une plaque offset 2, entre d'abord en contact avec des rouleaux de mouillage 3a et 3b puis avec des rouleaux encreurs 4a et 4b. L'encre se trouvant sur la plaque 2 est alors transférée sur un cylindre 5 appelé blanchet. Le blanchet 5 est en contact avec un cylindre d'impression 6. Du papier 7 passant entre les cylindres 5 et 6 est imprimé par l'encre présente sur le blanchet 5.Figure 1 shows a simplified example of the mechanism of an offset machine. A plate cylinder 1 on which an offset plate 2 is mounted, first comes into contact with wetting rollers 3a and 3b and then with ink rollers 4a and 4b. The ink on the plate 2 is then transferred to a cylinder 5 called a blanket. The blanket 5 is in contact with a printing cylinder 6. Paper 7 passing between the cylinders 5 and 6 is printed by the ink present on the blanket 5.

La surface de la plaque offset 2 est constituée de telle manière que, lors de l'encrage, l'encre vient seulement se déposer sur des zones voulues de la plaque pour constituer une image.The surface of the offset plate 2 is formed in such a way that, when inking, the ink only deposits on desired areas of the plate to constitute an image.

La figure 2 représente un grossissement d'une coupe de la plaque offset 2. Un film de résine a été déposé sur la surface rugueuse 20 de la plaque 2 puis gravé en fonction de l'image à reproduire en laissant des points de résine 21 de dimensions variables et des zones 22 dépourvues de résine. On appelera densité le rapport de la surface des points 21 sur la surface des zones 22. Lors du mouillage par les rouleaux 3, la rugosité de la surface 20 capte l'eau qui est en plus repoussée par les points 21 qui sont hydrophobes. Ensuite, lors de l'encrage par les rouleaux 4, l'encre qui est grasse et donc hydrophobe, vient se déposer essentiellement sur les points 21 qui sont de plus oléophiles.FIG. 2 represents a magnification of a section of the offset plate 2. A resin film has been deposited on the rough surface 20 of the plate 2 and then etched according to the image to be reproduced, leaving resin dots 21 of variable dimensions and zones 22 devoid of resin. We will call density the ratio of the surface of the points 21 on the surface of the zones 22. When wetting by the rollers 3, the roughness of the surface 20 captures the water which is more repelled by the points 21 which are hydrophobic. Then, during inking by the rollers 4, the ink, which is oily and therefore hydrophobic, is deposited essentially on the points 21 which are more oleophilic.

Selon les quantités respectives d'eau et d'encre déposées sur la plaque 2, le taux de couverture par l'encre varie, c'est-à-dire que l'encre recouvre plus ou moins les points 21, l'eau occupant la surface restante. Ainsi, le problème posé est de s'éloigner le moins possible de l'équilibre eau-encre qui correspond à l'état idéal où l'encre recouvrirait exactement les points 21, en d'autres termes , où le taux de couverture serait égal à la densité.According to the respective quantities of water and ink deposited on the plate 2, the coverage rate by the ink varies, that is to say that the ink more or less covers the points 21, the water occupying the remaining area. Thus, the problem posed is to move as little as possible from the water-ink balance which corresponds to the ideal state where the ink would exactly cover the points 21, in other words, where the coverage rate would be equal to density.

Pour que le fonctionnement soit correct, les quantités respectives d'eau et d'encre doivent être comprises entre des limites déterminées à savoir une limite supérieure où l'encre déborderait des points 21 lors du transfert sur le blanchet 5 et une limite inférieure où l'eau dans les zones 22 ne recouvrirait pas entièrement les crêtes de la rugosité de la surface 20. Si la limite inférieure n'est pas respectée, l'encre vient aussi adhérer dans les zones 22 et il faut nettoyer la plaque offset.For correct functioning, the respective amounts of water and ink must be between certain limits, namely an upper limit where the ink would overflow the points 21 during transfer to the blanket 5 and a lower limit where the the water in zones 22 would not entirely cover the ridges of the roughness of surface 20. If the lower limit is not respected, the ink also adheres to zones 22 and the offset plate must be cleaned.

Dans des machines offset classiques, l'équilibre eau-encre est obtenu par des réglages manuels séparés du mouillage et de l'encrage. L'effet de ces réglages est éventuellement contrôlé à l'aide d'une barre de contrôle qui est imprimée en même temps que chaque image. Ces barres de contrôle comportent plusieurs zones tramées à différentes tailles de points et à différents taux de couverture idéaux. Ces barres de contrôle sont examinées à l'oeil ou avec des densitomètres optiques sur la feuille imprimée pour déterminer s'il faut réajuster les réglages de mouillage et d'encrage.In conventional offset machines, the water-ink balance is obtained by manual adjustments separate from wetting and inking. The effect of these settings is optionally controlled using a control bar which is printed at the same time as each image. These control bars have several screened areas at different point sizes and at different ideal coverage rates. These control bars are examined visually or with optical densitometers on the printed sheet to determine whether to readjust the wetting and inking settings.

Le document FR-A-2 556 283 (sous priorité des demandes de brevet des Etats-Unis d'Amérique N° 560 837 du 13 décembre 1983 et N° 618 252 du 7 juin 1984) décrit un système de mesure de la quantité moyenne d'eau présente sur un rouleau encreur en mouvement. Le rouleau est éclairé sous une incidence non normale et la lumière réfléchie est recueillie par plusieurs capteurs optiques. Les signaux délivrés par ces capteurs sont ensuite traités pour obtenir une indication de la quantité moyenne d'eau sur le rouleau. Un inconvénient de ce système est qu'on n'obtient pas d'indication du taux de couverture sur la plaque offset, qui, comme nous l'avons vu précédemment, est primordiale pour détecter l'équilibre eau-encre. Un autre inconvénient est lié à l'éclairement du rouleau sous une incidence différente de la normale, ce qui provoque des fluctuations d'intensité au niveau des capteurs liées aux défauts de surface et d'excentration du rouleau.The document FR-A-2 556 283 (under priority of patent applications of the United States of America No. 560 837 of December 13, 1983 and No. 618 252 of June 7, 1984) describes a system for measuring the average quantity of water present on a moving ink roller. The roller is illuminated at a non-normal incidence and the reflected light is collected by several optical sensors. The signals delivered by these sensors are then processed to obtain an indication of the average amount of water on the roller. A drawback of this system is that no indication of the coverage rate is obtained on the offset plate, which, as we have seen above, is essential for detecting the water-ink balance. Another drawback is linked to the illumination of the roller under a different incidence from normal, which causes intensity fluctuations at the level of the sensors linked to surface and eccentricity defects of the roller.

La demande de brevet allemand 36 11 645 décrit un système permettant de fournir une indication du rapport eau-encre. Pour cela, il comprend une source lumineuse non-cohérente éclairant la plaque offset et deux capteurs recueillant la lumière réémise, l'un correspondant à l'eau et l'autre à l'encre. Les angles d'éclairage et de réception sont distincts, de manière que les capteurs ne reçoivent pas la lumière réfléchie.German patent application 36 11 645 describes a system for providing an indication of the water-ink ratio. For this, it includes a non-coherent light source illuminating the offset plate and two sensors collecting the re-emitted light, one corresponding to water and the other to ink. The lighting and reception angles are separate, so that the sensors do not receive the reflected light.

Un objet de la présente invention est de fournir en continu une indication sur l'équilibre eau-encre.An object of the present invention is to continuously provide an indication of the water-ink balance.

Un autre objet de l'invention est de s'affranchir des problèmes de défauts de surface et d'excentration.Another object of the invention is to overcome the problems of surface defects and eccentricity.

Ces objets ainsi que d'autres de la présente invention sont atteints avec un procédé pour surveiller l'équilibre eau-encre dans une machine offset qui comprend une plaque offset fixée sur un cylindre, le procédé comprenant les étapes suivantes : éclairer sous incidence normale, avec une source de lumière cohérente, une zone prédéterminée de la plaque offset en mouvement, dont on connaît la densité ; recueillir dans le plan focal d'un système optique convergent une partie de la lumière réémise perpendiculairement au plan de la zone éclairée ; et mesurer l'intensité lumineuse en au moins une zone du plan focal.These and other objects of the present invention are achieved with a method for monitoring the water-ink balance in an offset machine which includes an offset plate fixed to a cylinder, the method comprising the following steps: lighting under normal incidence, with a coherent light source, a predetermined area of the moving offset plate, the density of which is known; collecting in the focal plane of a converging optical system a part of the re-emitted light perpendicular to the plane of the illuminated area; and measuring the light intensity in at least one area of the focal plane.

Selon un mode de réalisation de la présente invention, l'intensité lumineuse est mesurée autour de l'axe du système optique convergent.According to an embodiment of the present invention, the light intensity is measured around the axis of the converging optical system.

Selon un mode de réalisation de la présente invention, l'intensité lumineuse est en outre mesurée dans au moins une zone éloignée de l'axe du système optique convergent.According to an embodiment of the present invention, the light intensity is also measured in at least one zone remote from the axis of the converging optical system.

Selon un mode de réalisation de la présente invention, la zone prédéterminée est une zone régulièrement tramée.According to an embodiment of the present invention, the predetermined area is a regularly screened area.

Selon un mode de réalisation de la présente invention, la zone prédéterminée est éclairéé en synchronisme avec le mouvement de la plaque offset.According to an embodiment of the present invention, the predetermined area is illuminated in synchronism with the movement of the offset plate.

Pour mettre en oeuvre ce procédé, la présente invention prévoit aussi un dispositif de régulation de l'équilibre eau-encre dans une machine offset comprenant une plaque offset fixée sur un cylindre, et un système de mouillage et d'encrage de cette plaque, le dispositif comprenant : une source de lumière cohérente éclairant sous incidence normale une zone prédéterminée de la plaque offset en mouvement ; une cellule de mesure comprenant un capteur placé dans l'axe et dans le plan focal d'un système optique convergent, qui recueille une fraction de la lumière réémise perpendiculairement à ladite zone ; un système d'asservissement prenant en compte le signal délivré par le capteur pour régler le mouillage et/ou l'encrage de la plaque offset.To implement this method, the present invention also provides a device for regulating the water-ink balance in an offset machine comprising an offset plate fixed to a cylinder, and a system for wetting and inking this plate, the device comprising: a coherent light source illuminating under normal incidence a predetermined area of the moving offset plate; a measurement cell comprising a sensor placed in the axis and in the focal plane of a converging optical system, which collects a fraction of the re-emitted light perpendicular to said zone; a servo system taking into account the signal delivered by the sensor to adjust the wetting and / or inking of the offset plate.

Selon un mode de réalisation de la présente invention, au moins un deuxième capteur est placé dans le plan focal du système optique convergent hors de l'axe, et des moyens sont prévus pour agir sur le système d'asservissement pour déterminer un mouillage minimal à partir du signal de ce deuxième capteur.According to an embodiment of the present invention, at least a second sensor is placed in the focal plane of the converging optical system off the axis, and means are provided for acting on the servo system to determine a minimum wetting at from the signal of this second sensor.

Ces objets, caractéristiques et avantages ainsi que d'autres de la présente invention seront exposés plus en détail dans la description suivante de modes de réalisation particuliers faite en relation avec les figures jointes parmi lesquelles :

  • les figures 1 et 2, précédemment décrites, illustrent l'état de la technique ; et
  • la figure 3 représente un mode de réalisation de la présente invention.
These objects, characteristics and advantages as well as others of the present invention will be explained in more detail in the following description of particular embodiments made in relation to the attached figures, among which:
  • Figures 1 and 2, previously described, illustrate the state of the art; and
  • Figure 3 shows an embodiment of the present invention.

Dans les figures, des mêmes références représentent des mêmes éléments.In the figures, the same references represent the same elements.

La figure 3 représente un dispositif selon la présente invention qui permet de fournir une indication sur l'équilibre eau-encre. Le dispositif a été adapté sur une machine offset classique, par exemple celle de la figure 1. Une source de lumière cohérente 30, telle qu'un laser, fournit un faisceau qui se réfléchit sur un miroir 31 pour projeter, normalement à sa surface, une tache lumineuse sur la plaque offset 2 en mouvement. Une lentille convergente 32 dont l'axe est normal à la plaque 2, supporte le miroir 31 et recueille la lumière réémise par la zone éclairée de la plaque. Deux capteurs 33 et 34 sont placés dans le plan focal de la lentille 32, le capteur 33 étant dans l'axe de la lentille.FIG. 3 represents a device according to the present invention which makes it possible to provide an indication of the water-ink balance. The device has been adapted on a conventional offset machine, for example that of FIG. 1. A coherent light source 30, such as a laser, provides a beam which is reflected on a mirror 31 to project, normally on its surface, a light spot on the moving offset plate 2. A converging lens 32 whose axis is normal to the plate 2, supports the mirror 31 and collects the light re-emitted by the illuminated area of the plate. Two sensors 33 and 34 are placed in the focal plane of the lens 32, the sensor 33 being in the axis of the lens.

Le fait d'éclairer la plaque 2 normalement et de recueillir la lumière réémise dans la direction normale rend le dispositif pratiquement insensible aux défauts de surface et de centrage du cylindre 1.Illuminating the plate 2 normally and collecting the re-emitted light in the normal direction makes the device practically insensitive to surface and centering defects of the cylinder 1.

Le système ci-dessus est activé à des moments précis quand la source de lumière 30 éclaire une zone prédéterminée 35 de la plaque 2, dont on connaît les caractéristiques, notamment la densité. Cette zone prédéterminée est, par exemple, une des zones tramées d'une barre de contrôle imprimée en même temps que chaque image.The above system is activated at specific times when the light source 30 illuminates a predetermined area 35 of the plate 2, the characteristics of which are known, in particular the density. This predetermined area is, for example, one of the screened areas of a control bar printed at the same time as each image.

Cette disposition particulière et l'utilisation d'une source de lumière cohérente permettent d'obtenir dans le plan focal de la lentille 32 la transformée de Fourier de l'onde réémise à partir de la zone 35. Il s'avère que la valeur moyenne de cette transformée de Fourier, qui est une intensité lumineuse mesurée par le capteur 33, varie en sens inverse par rapport aux variations du taux de couverture de la zone 35. Comme on connaît la densité de cette zone, on connaît aussi l'équilibre eau-encre qu'elle devrait présenter.This particular arrangement and the use of a coherent light source make it possible to obtain in the focal plane of the lens 32 the Fourier transform of the re-emitted wave from the zone 35. It turns out that the average value of this Fourier transform, which is a light intensity measured by the sensor 33, varies in the opposite direction with respect to the variations in the coverage rate of the area 35. As we know the density of this area, we also know the water balance - ink that it should present.

Ainsi, en considérant une zone 35 déterminée qui reflète les conditions d'ensemble, on peut corriger les réglages de mouillage et/ou d'encrage dans un système d'asservissement 38 pour maintenir l'équilibre eau-encre d'ensemble de la manière suivante. On forme la différence I-I₀entre le signal I délivré par le capteur 33 et un signal de référence I₀ qui correspondrait au signal délivré par le capteur dans le cas où on aurait l'équilibre eau-encre dans la zone 35. On agit ensuite sur le mouillage et/ou l'encrage, par exemple, proportionnellement respectivement à I₀-I et à I-I₀ pour réduire, et idéalement annuler, la différence I-I₀.Thus, by considering a determined zone 35 which reflects the overall conditions, it is possible to correct the settings for wetting and / or inking in a servo system 38 to maintain the overall water-ink balance in the manner next. We form the difference I-I₀between the signal I delivered by the sensor 33 and a reference signal I₀ which would correspond to the signal delivered by the sensor in the case where there is water-ink balance in zone 35. We then act on wetting and / or inking, for example, proportionally respectively to I₀-I and to I-I₀ to reduce, and ideally cancel, the difference I-I₀.

Dans une couronne du plan focal de la lentille 32 éloignée de l'axe de la lentille, on constate la présence de taches lumineuses secondaires qui représentent la caractéristique d'avoir une intensité qui varie brusquement quand la quantité d'eau déposée sur la plaque offset 2 dans la zone considérée 35 atteint la limite inférieure, c'est-à-dire, en se référant à nouveau à la figure 2, que, lors du mouillage, l'eau déposée sur la plaque offset ne recouvre pas entièrement les crêtes de la rugosité de la surface 20. Ainsi, grâce à un capteur 34 mesurant cette intensité secondaire, on peut aussi contrôler si on se trouve au-dessus de la limite inférieure. Cette information peut aussi être avantageusement exploitée par le système d'asservissement 38 pour corriger les réglages de mouillage.In a ring of the focal plane of the lens 32 remote from the axis of the lens, there is the presence of secondary light spots which represent the characteristic of having an intensity which varies suddenly when the amount of water deposited on the offset plate 2 in the zone under consideration 35 reaches the lower limit, that is to say again with reference to FIG. 2, that, during wetting, the water deposited on the offset plate does not entirely cover the ridges of the roughness of the surface 20. Thus, thanks to a sensor 34 measuring this secondary intensity, it is also possible to check whether one is above the lower limit. This information can also be advantageously used by the servo system 38 to correct the wetting settings.

Le dispositif selon la présente invention peut s'adapter à toute machine offset et être associé à un système d'asservissement facile à réaliser par l'homme du métier, qui permet d'agir sur les réglages de mouillage et/ou d'encrage.The device according to the present invention can be adapted to any offset machine and be associated with a servo system easy to perform by those skilled in the art, which makes it possible to act on the wetting and / or inking settings.

L'homme de l'art notera que la présente invention est susceptible de diverses variantes et modifications. Par exemple, pour recueillir la lumière réémise autour d'un axe normal à la zone éclairée, au lieu d'utiliser une lentille on pourra utiliser tout autre système optique convergent collecteur de lumière et placer des détecteurs dans le plan focal de ce système optique. On peut aussi envisager de multiplier le nombre de dispositifs pour surveiller les évolutions de plusieurs zones tramées différentes pour améliorer la stabilité du procédé. On peut aussi envisager de polariser la source lumineuse et d'analyser la lumière sous des conditions de polarisation croisée pour augmenter la sensibilité.Those skilled in the art will appreciate that the present invention is susceptible to various variations and modifications. For example, to collect the light re-emitted around an axis normal to the illuminated area, instead of using a lens, it is possible to use any other convergent light-collecting optical system and to place detectors in the focal plane of this optical system. We can also consider increasing the number of devices to monitor the progress of several different screened areas to improve the stability of the process. One can also consider polarizing the light source and analyzing the light under cross-polarization conditions to increase the sensitivity.

Claims (7)

  1. A method for controlling the water-ink equilibrium in an offset machine including an offset plate (2) fixed on a cylinder (1) comprising the following steps:
    - illuminating under normal incidence, with a coherent light source (30), a predetermined area (35) of said offset plate (2) in motion, the density of which is known;
    - collecting in the focal plane of a convergent optical system (32) a portion of the light reemitted perpendicularly to the plane of said illuminated area (35); and
    - measuring the light intensity in at least one area of the focal plane.
  2. A method according to claim 1, wherein the light intensity is measured around the axis of the convergent optical system.
  3. A method according to claim 2, wherein said light intensity is moreover measured in at least one area distant from the axis of the convergent optical system.
  4. A method according to claim 1, wherein said predetermined area (35) is a regularly screened area.
  5. A method according to claim 1, wherein said predetermined area (35) is illuminated in synchronism with the motion of the offset plate.
  6. A device for regulating the water-ink equilibrium in an offset machine comprising an offset plate (2) fixed on a cylinder (1), and a system for wetting and inking said plate, comprising:
    - a coherent light source (30) illuminating under a normal incidence said predetermined area (35) of said offset plate (2) in motion;
    - a measuring cell comprising a sensor (33) placed in the axis and in the focal plane of said convergent optical system (32), which collects a fraction of the light reemitted perpendicularly to said area (35);
    - a servo-control system (38) sensitive to the signal provided by said sensor (33) for adjusting the wetting and/or inking of said offset plate (2).
  7. A device according to claim 6, comprising at least a second sensor placed distant from the axis in the focal plane of said convergent optical system (32), and means for acting on the servo-control system for determining a minimal wetting from the signal of said second sensor.
EP91420415A 1990-11-30 1991-11-22 Method and apparatus for regulating the water-ink balance on a printing plate of an offset printing machine Expired - Lifetime EP0488910B1 (en)

Applications Claiming Priority (2)

Application Number Priority Date Filing Date Title
FR9015385 1990-11-30
FR9015385A FR2669855B1 (en) 1990-11-30 1990-11-30 METHOD AND DEVICE FOR REGULATING THE WATER-INK BALANCE ON AN OFFSET MACHINE PLATE.

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EP0488910A1 EP0488910A1 (en) 1992-06-03
EP0488910B1 true EP0488910B1 (en) 1995-10-18

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EP (1) EP0488910B1 (en)
JP (1) JPH0691857A (en)
AT (1) ATE129192T1 (en)
CA (1) CA2056171A1 (en)
DE (1) DE69113957T2 (en)
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AUPQ611200A0 (en) * 2000-03-09 2000-03-30 Commonwealth Scientific And Industrial Research Organisation Determination of change in thickness of dampening solution on offset printing rollers
SE0003840L (en) * 2000-10-23 2002-04-24 Baldwin Jimek Ab Method and apparatus for detecting toning in a printing press
UA64588A (en) * 2003-07-01 2004-02-16 Pavlo Valentynovych Kandaurov Method for monitoring the layer of fountain solution on printing plate
US6796227B1 (en) 2003-08-18 2004-09-28 Quad Tech Lithographic press dampening control system
DE102008000031B4 (en) * 2008-01-10 2014-07-10 Koenig & Bauer Aktiengesellschaft Method for controlling an arrangement of printing forms arranged on forming cylinders of a printing machine
EP2380741A1 (en) * 2010-04-23 2011-10-26 GVT GmbH Method and device for measuring the thickness of a dampening solution or ink emulsion layer in offset printing

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Publication number Priority date Publication date Assignee Title
DE2214721B1 (en) * 1972-03-25 1973-06-14 Heidelberger Druckmaschinen Ag, 6900 Heidelberg PROCESS AND DEVICE FOR AUTOMATIC ADJUSTMENT OF FLUCTUATIONS IN THE PAINT AND MOISTURE FLUID ON OFFSET MACHINES
US3981238A (en) * 1972-09-27 1976-09-21 European Rotogravure Association Method and apparatus for determining doctor blade position in a rotogravure process
IT1033240B (en) * 1974-03-14 1979-07-10 Grapho Metronic Gmbh & Co HUMIDIFIER IN AN OFFSET PRINTER MACHINE WITH A DEVICE FOR ADJUSTING THE QUANTITY OF WATER ON THE PLATE
EP0126613B1 (en) * 1983-05-17 1989-09-20 Sumitomo Heavy Industries, Ltd Method of an apparatus for measuring dampening water for printing machine
US4677298A (en) * 1983-12-13 1987-06-30 Kollmorgen Technologies Corporation Method of monitoring ink-water balance on a lithographic printing press
DE3611645A1 (en) * 1986-04-07 1987-10-08 Grapho Metronic Gmbh & Co Method and device for regulating the proportions of ink and damping medium in a layer of emulsion on the printing plate of an offset printing machine
DE3732934A1 (en) * 1987-09-30 1989-04-20 Heidelberger Druckmasch Ag SENSOR DEVICE

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FR2669855A1 (en) 1992-06-05
ES2082170T3 (en) 1996-03-16
CA2056171A1 (en) 1992-05-31
EP0488910A1 (en) 1992-06-03
US5249036A (en) 1993-09-28
DE69113957T2 (en) 1996-05-15
ATE129192T1 (en) 1995-11-15
JPH0691857A (en) 1994-04-05
DE69113957D1 (en) 1995-11-23
FR2669855B1 (en) 1995-07-13

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