EP0393365B1 - Method and device for supplying damping liquid in an offset printing machine - Google Patents

Description

The invention relates to a method for determining the dampening solution guidance of an offset printing machine, wherein the printing plate is inked with ink while accepting the ink (toning) of areas which are actually color-free in the production process, and then a defined dampening solution supply is carried out.

From the practice of printing technology, a method for determining the dampening solution guidance on an offset printing machine is known, in which the printer manually adjusts the dipping roller and the metering roller of the dampening unit to one another such that initially there is only a relatively low contact pressure between these rollers. The amount of dampening solution conveyed by the dipping roller is transferred via the metering roller and a dampening roller to the surface of an offset printing plate mounted on a plate cylinder. Due to the low contact pressure, the dampening solution delivery is relatively large. This is also visually visible; the rubber immersion roller receives a glossy film of moisture. Based on this presetting, the printer then makes the basic setting for the amount of dampening solution by adjusting the dipping roller and the dosing roller to each other by increasing the pressure so that a more even film builds up on the dosing roller while observing the dipping roller. The shiny dampening solution layer described above changes into a matt appearance. Depending on the individual capabilities of the printer, the described procedure ensures that the immersion roller and metering roller are largely parallel. If this setting is found, then, if the color distribution is uneven, the Print format width may set problems during production. This creates an excess of dampening solution on the side where less dampening solution is required, which may lead to the build-up of an unstable emulsion. On the other hand, if the dampening solution supply is insufficient, coloring of areas which are actually free of color in the production run can be noticeable. This coloring is called "toning".

From the Fogra Symposium "Offset Moisture in Research and Practice" (Munich, November 17 and 18, 1986), it is from a lecture by Dr.-Ing. Burkhardt Wirz known to measure the dampening solution film on a printing plate, to change this dampening solution film in such a way that slight lubrication occurs and to regulate the supply of ink and water according to this determined target value by measuring the thickness of the dampening solution film and this thickness certain color-water ratio is assigned. This ratio is set by detouring the determination of the thickness of the dampening solution film and assigning it to the determined target value. The setpoint assignment must be carried out again for each printing plate, since the optimal ink-water ratio is not uniform for different printing plates. The printer must therefore always carry out new calibrations by changing the setpoint value, both when changing the printing plate and when changing other boundary conditions or a certain course of the tent.

In contrast, the invention has for its object to provide a determination of the dampening solution guidance of an offset printing press, in which the dampening solution requirement can be carried out by a direct detection of the inflow or freewheeling of the printing plate, even without the supply of a printing medium.

The object is achieved according to the invention in a method of the type mentioned at the outset, by means of a defined dampening solution supply until the areas which are actually color-free have no color, the dampening solution supply being such that the toning areas are approximately uniformly color-free over the format or subject width and the Setting the dampening solution guidance at this time is used as a measure for the dampening solution guidance to be set.

The dampening solution requirement is recorded by directly recording the inflow or overflow of the non-printing areas on the printing plate, which can also take place without the addition of a printing medium. It is expedient to capture depending on the subject across the format or subject width, so that problem-free printing is ensured.

The printing plate is inked with ink while accepting ink (toning) of areas that are actually color-free during production, and then a defined dampening solution supply or enlargement of the dampening solution supply is carried out while recording the ink removal process of the toning surfaces, which is used as a measure for the dampening solution guidance to be set becomes. Accordingly, the moisture film on the rollers of the dampening unit is no longer observed — as in the prior art — when determining the dampening solution setting values, but rather the transition behavior of a colored printing plate is considered when dampening solution is applied to it. For this purpose, the offset printing plate is first allowed to "run in" old color, preferably with a defined quantity of ink. This is a coloring of the printing plate, in which normally color-free areas also take on color during the production process. This feed process is carried out with little or no dampening solution supply. Then follows a defined dampening solution supply or an enlargement of the dampening solution supply to a defined value while recording the ink removal process that occurs as a result of the previously toning surfaces. Depending on how large the amount of dampening solution supplied and its distribution over the width of the printing format, the offset printing plate will "run free", ie the toned areas will lose their color again depending on the dampening solution supply. The manner of this ink removal process is a measure of the dampening solution guidance to be set. If, for example, in the case of a dampening solution supply which does not correspond to the subject, only one offset printing plate side edge is free, while toned areas are retained on the other side, this is an indication that for the existing printing process the dampening solution setting is not yet correct. Here, however, the direction is clearly shown how to achieve an optimal dampening solution setting, because the one-sided lack of free running of the printing plate shows that the amount of dampening solution must be increased on this side. The intensity and timely recording of the ink removal process allows detailed conclusions about the dampening solution guide, so that adequate to the subject and color guide can be found in a quick and easy manner, an optimal dampening solution setting, which is accordingly based on consumption, so that in the subsequent production a Waste toning or the formation of an unstable emulsion - which hinders the application of paint - is not to be feared.

In order to be able to supply dampening solution in accordance with the requirements for printing plates with an uneven ink distribution across the printing format width, the defined dampening solution addition is carried out as a function of the subject.

When the offset printing plate is freewheeling, it can be done in such a way that the toning surfaces become approximately uniformly color-free over the format width. This means that during the freewheeling process the dampening solution supply is adjusted over the width of the printing format in such a way that all toning surfaces are subject to an even decrease in color. This leads to the dampening solution setting being sought at the end of the freewheeling process.

When carrying out the method according to the invention, the detection of the color decrease by the printer, i. H. that is done by visual observation. However, the individual capabilities of the printer are then incorporated. Alternatively, however, it is also possible for the color decrease to be detected by optical sensors. Accordingly, automatic adjustment of the dampening solution guidance is possible if the data recorded by the sensors are used to adjust the dampening system.

According to a preferred development of the invention it is provided that the control of the ink take-off is carried out in a peripheral zone of the printing plate clamped on a printing cylinder. In particular, this check of the ink take-off takes place - taking into account the direction of rotation of the plate cylinder - at the two upstream areas of the subject. Particularly good and meaningful results are achieved if the ink removal is checked in an area between the start of the printing plate and the beginning of the subject. This area is particularly predestined for the measurement, because here the dampening roller comes into contact with each revolution after passing through the longitudinal groove (channel) of the plate cylinder, which is used to fasten the pressure plate, so that parameter changes can be recognized here as early as possible. This sampling point is also the area from which any lubrication that may occur originates. This refers to the smearing of color from the printing area to the color-free area during the printing process.

The color removal is preferably checked periodically, in particular with each plate cylinder revolution.

The process according to the invention is distinguished by the special feature that the dampening solution setting can be carried out before the actual printing process. The Accordingly, the printing plate can run in and run free without the addition of a printing medium (for example paper), so that the production of waste is largely restricted.

To adjust the dampening solution guidance, the amount of dampening solution and its distribution over the printing format width are preferably made by adjusting the speed of the immersion roller and / or adjusting the pressure between the immersion roller and metering roller. Depending on the speed of the dipping roller, the dampening solution flow rate can be metered via the roller differential speed. The greater the pressure between the rollers mentioned, the thinner the fountain solution film conveyed. The dampening solution distribution can be varied over the width of the printing format by the inclination of the dipping roller and the metering roller.

It can also be done in such a way that the sensors also determine the layer thickness of the dampening solution. Accordingly, the sensors perform a double function in that they detect the toning of areas which are actually color-free before and at the beginning of the printing process, and furthermore, for example, to adjust the dampening solution guidance. B. in the time-sharing process- determine the dampening solution supply with regard to the layer thickness. According to a development of the invention, the sensation of the toning state is not limited to the period before the printing process, but can also take place in the printing phase, so that corresponding interventions in the dampening solution management can also be carried out during this time. This considerably reduces the risk of lubrication. Furthermore, the dual function of the sensors can also be used during the production printing process, ie the sensors can continuously determine the dampening solution layer thickness and accordingly represent, for example, the actual value transmitter for a dampening solution control circuit.

The invention further relates to a method for determining the dampening solution guidance of an offset printing machine, in which dampening solution is applied to the printing plate, and then the inking plate is colored while increasing the ink supply until a color acceptance (toning) of areas which are colorless in the production process takes place and the dampening solution is guided in such a way that the color-free areas tone uniformly over the width of the subject, the setting of the dampening solution guide being recorded on the printing plate at the time when the ink begins to be taken and used as a measure of the dampening agent guide to be set. This method represents a variant of the method mentioned at the outset, in that it is not the free running of the printing plate with ink that is used as a measure of the dampening solution guidance to be set, but rather the supply process of the areas which are actually ink-free. This inflow depends on the amount of dampening solution present at the same time. If this is not matched to the subject of the printing plate used, an uneven supply of ink will occur, for example, which gives conclusions about the correction to be made to the dampening solution supply. Both the type of inflow and the time required for this represent essential information.

To carry out the method according to the invention, a device for guiding the dampening solution of an offset printing machine is preferably provided, with a sensor device optically scanning the outer surface of a printing plate clamped on a plate cylinder, which provides an output signal influencing the dampening solution supply quantity to a dampening roller arrangement, which includes an immersion roller and one this has interacting metering roller, wherein at least two sensors spaced apart from one another in the printing format width direction, a toning of sensors of the printing plate which are color-free in the continuous printing process are provided and an actuating device with an actuator and a control device enables inclination of the axes of the plunger roller and metering roller lying in one plane, which due to the data recorded by the sensors controls the actuators in such a way that the appropriate amount of subject-specific dampening solution required for the respective pressure is transferred to the surface of the offset printing plate via a corresponding pressure between the immersion roller and the metering roller. Due to the arrangement of the sensors according to the invention, processes which develop asymmetrically over the printing format width can be recognized immediately. Such processes are counteracted by appropriately inclining the dipping roller and metering roller relative to one another.

From DE-OS 31 05 020 a device for applying a fluid is known, in which a fluid wedge formed between a roller arrangement is sensed. DE-AS 24 12 234 discloses a device for measuring a dampening solution layer thickness, in which a sensor determines the amount of dampening solution on the printing plate and controls the dipping roller speed as a function thereof. DE-OS 15 36 450 relates to a device for applying a dampening liquid, in which the axes of co-operating rollers can be set at an angle to one another by adjusting a roller bearing. Japanese Patent Laid-Open No. 63-162243 relates to the determination of the dampening solution layer thickness on the surface of a printing plate by means of a sensor which controls the speed of the dip roller.

An adjusting device with an electric one is preferred at each end region of the dipping or metering roller Actuator provided. Each actuator has a position sensor which is connected to an electrical control device, preferably a microprocessor, which controls the associated actuator and to which the sensors are connected. Potentiometers are used as position sensors. The arrangement is designed such that the sensors preferably monitor the area between the start of the printing plate and the beginning of the subject, since changes in the process parameters are detected as early as possible. According to a development of the invention, an optical sensor row is provided with a plurality (more than two) of sensors, which are preferably evenly spaced from one another and monitor the inking state of the printing plate. This enables the peripheral surface of the offset printing plate to be monitored virtually in zones.

The device according to the invention is explained in more detail using an exemplary embodiment.

Fig. 1

eine schematische Ansicht eines Feuchtwerks einer Offset-Druckmaschine mit Sensor- und Stelleinrichtung,

Fig. 2

einen Querschnitt durch den Plattenzylinder der Anordnung gemäß der Fig. 1 in schematischer Darstellung und

Fig. 3

ein Blockdiagramm.

Show it:

Fig. 1

1 shows a schematic view of a dampening unit of an offset printing press with sensor and actuating device,

Fig. 2

a cross section through the plate cylinder of the arrangement of FIG. 1 in a schematic representation and

Fig. 3

a block diagram.

Figure 1 shows schematically the structure of a dampening unit 1 of an offset printing machine, not shown. The dampening unit 1 has an immersion roller 2, which dips with a circumferential region into a container 3 'containing dampening solution. The dipping roller 2 works with a metering roller 3 together, which in turn rests against a dampening roller 4, which cooperates with a plate cylinder 5, on the lateral surface of which an offset printing plate 6, not shown, is clamped. The outer surface of the offset printing plate 6 is scanned by an optical sensor device 7, which is formed by two sensors 8 spaced apart from one another in the printing format width direction. The sensors 8 are arranged such that they lie approximately in the longitudinal edge region of the pressure plate 6 on both sides. The lines 8 connect the sensors 8 to a control device 10, which is preferably designed as a microprocessor. The control device 10 is connected to the machine control 11 of the offset printing press.

An actuating device 14, which is only indicated schematically, is provided at each end region 12 or 13 of immersion roller 2 or metering roller 3. Each actuating device 14 has an electric actuator 15, which is connected to a position sensor 16. Each position sensor 16 is preferably designed as a potentiometer 17, which is connected via a line 18 to the control device 10 and forms a component of the latter.

The constructive means, not shown here, of each actuating device 14 make it possible to adjust the immersion roller 2 and metering roller 3 in the direction of the respective double arrow 19 towards or away from one another. Accordingly, the rollers 2 and 3 can be inclined relative to one another by changing the contact pressure, but their axes 20 and 21 remain lying in one plane. The actuators 15 are controlled via lines 22 connected to the control device 10.

The arrangement is now designed according to the invention so that, depending on the data recorded by the sensors 8 Control device 10 controls the actuators 15 in such a way that the appropriate amount of subject-dependent dampening solution required for the respective pressure is transferred to the surface of the offset printing plate 6 by means of a corresponding pressure between the dipping roller 2 and the metering roller 3. For this purpose, the axes 20 and 21 and / or the above-described inclination of the axes 20 and 21 can be shifted in parallel. An inclined position means that in one side area of the rollers there is a greater pressing pressure than in the other side area. The potentiometers 17 report the respective position of the actuators 15 to the control device 10.

The detailed process control of the device according to FIG. 1 is explained in more detail below:
According to the invention, an optimal dampening solution guide should be adequate for the subject and color guide, the dampening solution supply values being determined before the actual printing process begins. For this purpose, the printing plate 6 is colored with ink by an inking unit not shown in the figures. The procedure is such that color-free areas take on color in the production process. This process is called "toning" in the technical language. Due to the ink acceptance of areas that are inherently ink-free, the printing plate 6 is "tapped". This process can take place without the addition of dampening solution or else with a low dampening solution supply.

According to the invention, the procedure is now such that after the offset printing plate 6 has closed, a defined fountain solution supply or the enlargement of the fountain solution supply to a defined value is carried out, so that the color of the toned areas is reduced. The process of this ink removal is carried out by the sensors 8 detected. The data determined in this way are processed in the control device 10 and represent a measure of the dampening solution guidance to be set. The dampening quantity is adjusted by adjusting the pressure between the immersion roller 2 and the metering roller 3, in particular also with the axes 20 and 21 of these rollers 2 and 3 inclined relative to each other. For this purpose, the control device 10 controls the actuators 15 accordingly via the lines 22. A corresponding position message is sent to the control device 10 via the potentiometer 17 and the lines 18.

According to the invention, in the present method, the lateral surface of the offset printing plate 6 is checked in a peripheral zone 23 (FIG. 2), which includes the area between the plate start 24 and the beginning of the subject 25. In other words: The optical scanning by the sensors 8 takes place - taking into account the direction of rotation of the plate cylinder 5, which is represented in FIG. 2 by the arrow 26 - following the longitudinal groove 27 of the plate cylinder 5 which serves to fasten the printing plate. The area up to Experience shows that subject 25 is most likely to undergo a change, since smearing or the like can be detected here as early as possible. As a result, the changes that occur as a result of the ink removal process will also occur in this area at an early stage.

The above is to be clarified in more detail using an example: It is assumed that the subject of the printing plate 6 used requires an uneven color distribution, e.g. B. needs half more Color than the other. If a uniform dampening solution film is now supplied via the printing format broad side, an excess of dampening solution will occur on the side that requires less dampening solution without using the method according to the invention. According to the invention, however, the already recognized tendency excess dampening solution will lead to a faster freewheeling of the offset printing plate 6 on the corresponding side, which is determined by the associated sensor 8. This leads to a corresponding difference signal at the two sensors 8, as a result of which the immersion roller 2 and metering roller 3 are set obliquely with respect to one another in such a way that the offset printing plate 6 is freewheeling symmetrically. This leads to a sujet-dependent, consumption-dependent, full-width adjustment of the rollers, so that the dampening solution guidance is optimally determined.

The functional sequence is explained again with reference to the block diagram in FIG. 3: A rotary angle sensor 28 assigned to the plate cylinder 5 interacts with the sensor 8 in such a way that the surface of the offset printing plate 6 is queried in the area 23 described above. The sensor 8 monitors in itself color-free areas of the printing plate 6 with regard to an ink acceptance (toning). If a toning process occurs, the associated actuator 15 is controlled via the control device 10 such that the dampening solution supply in the section assigned to the sensor 8 is increased by changing the pressing force between the immersion roller 2 and the metering roller 3 or the relative inclination of these rollers to one another. The respective actuator position is detected by the potentiometer 17 and can be displayed on a display 29.

Since each end region 12 or 13 of immersion roller 2 or metering roller 3 is assigned an actuating device 14 in FIG. 3 the individual components are duplicated. The dashed connecting line between the blocks "Tonen" makes it clear that the data originating from the sensors 8 can be compared with one another to generate a differential control signal.

According to another embodiment, the method according to the invention for determining the dampening solution guidance of an offset printing press can also be carried out in such a way that a preferably small amount of dampening solution is first applied to the printing plate and then ink is supplied over the printing format width, depending on the subject, in such a way that ink-free in the production process Apply color to areas. The toning process thus established is detected by the sensors 8 and used as a measure of the dampening solution guidance to be corrected. The manner in which the offset printing plate 6 tilts with ink thus forms the information for the dampening solution supply to be carried out.

The use of the methods and devices according to the invention is not limited to the period before the actual printing process, but can also be used during the ongoing printing process to monitor and correct the dampening solution guidance. In addition, it is possible to use the sensors 8 for a double function by optically measuring the layer thickness of the dampening solution outside of the monitoring region 23 and accordingly forming an actual value for the dampening solution control.

Claims (20)

1. Method of determining the damping fluid conduction of an offset printing machine, a colouring of the printing plate with ink being performed with ink acceptance (scumming) of areas which are in fact ink-free in the production printing process and subsequently a defined feeding of damping fluid taking place until the in fact ink-free areas have no ink, the feeding of the damping fluid taking place in such a way that the areas which are scummed become ink-free more or less uniformly over the width of the format or subject and the setting of the damping fluid conduction being used at this point in time as a measure of the damping fluid conduction to be set.
2. Method according to Claim 1, characterized in that the feeding of the damping fluid takes place in dependence on the subject in a monitored manner over the width of the format or the subject.
3. Method according to one or more of the preceding claims, characterized in that the determination of the ink acceptance takes place by observation.
4. Method according to one or more of the preceding claims, characterized in that the determination of the ink acceptance is performed by optical sensors (8).
5. Method according to one or more of the preceding claims, characterized in that the monitoring of the ink acceptance is performed in a peripheral zone (23) of the printing plate (6) mounted on an impression cylinder (5).
6. Method according to one or more of the preceding claims, characterized in that the monitoring of the ink acceptance is performed at the border regions between subject and border of the printing plate.
7. Method according to one or more of the preceding claims, characterized in that the monitoring of the ink acceptance is performed in a region (peripheral zone 23) between beginning of the printing (24) and beginning of the subject (25).
8. Method according to one or more of the preceding claims, characterized in that the monitoring of the ink acceptance is performed periodically, preferably with each revolution of the plate cylinder.
9. Method according to one or more of the preceding claims, characterized by determination of the damping fluid setting without the feeding of a pressure medium.
10. Method according to one or more of the preceding claims, characterized in that the rate of feeding the damping fluid and its distribution over the width of the printing format takes place by setting the rotational speed of the dipping roller and/or setting the pressure acting between dipping roller (2) and metering roller (3) of the damping unit (1) and/or relative skewing of dipping roller (2) and metering roller (3) with respect to each other.
11. Method according to one or more of the preceding claims, characterized in that a defined amount of ink and ink distribution over the width of the printing format or width of the subject is used for the scumming operation.
12. Method according to one or more of the preceding claims, characterized in that the sensors (8) are additionally used for determining the layer thickness of the damping fluid.
13. Method according to one or more of the preceding claims, characterized in that a sensing for scumming states is performed during the production printing process.
14. Method of determining the damping fluid conduction of an offset printing machine, in which damping fluid is applied to the printing plate and then, by increasing the feeding of ink, a colouring of the printing plate takes place until an ink acceptance (scumming) of areas which are in fact ink-free in the production printing process takes place, and the damping fluid conduction takes place in such a way that the in fact ink-free areas scum uniformly over the width of the subject, the setting of the damping fluid conduction being determined at the point in time of the beginning of the ink acceptance on the printing plate and used as a measure of the damping fluid conduction to be set.
15. Apparatus for the damping fluid conduction of an offset printing machine, for carrying out the method according to one or more of the preceding Claims 1-14, having a sensor device (7) which optically scans the lateral surface of a printing plate (6) mounted on a plate cylinder and delivers an output signal, influencing the rate of feeding the damping fluid, to a damping unit roller arrangement which has a dipping roller (2) and a metering roller (3) interacting with the latter, characterized by at least two sensors (8), which are spaced apart from each other in the direction of the width of the printing format and monitor any scumming of areas of the printing plate (6) which are in fact ink-free in the production printing process, and an actuating device (14), which effects a skewing of the coplanar axes (20, 21) of dipping roller (2) and metering roller (3) and has actuators (15) and a control device (10), which drives the actuators (15) on the basis of the data determined by the sensors (8) in such a way that the subject-dependent, optimum amount of damping fluid required for the respective print is transferred to the surface of the offset printing plate (6) by means of an appropriate pressure acting between dipping roller (2) and metering roller (3).
16. Apparatus according to Claim 15, characterized in that the actuating device (14) has an electrical actuator (15) respectively at each end region (12, 13) of the dipping roller (2) and the metering roller (3).
17. Apparatus according to one or more of the preceding Claims 15, 16, characterized in that each actuator (15) has a position feeler (16), which is connected to an electrical control device (10) which drives the associated actuator (15) and on which the sensors (8) are connected.
18. Apparatus according to one or more of the preceding Claims 15-17, characterized in that the position feeler (16) is a potentiometer (17).
19. Apparatus according to one or more of the preceding Claims 15-18, characterized in that the sensors (8) monitor the region (23) between the beginning of the printing plate (24) and the beginning of the subject (25).
20. Apparatus according to one or more of the preceding Claims 15-19, characterized by a row of optical sensors having a plurality of sensors (8) which are preferably spaced uniformly apart from one another and monitor the colouring state of the printing plate (6).

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