EP0092743A1 - Method and device for printing webs - Google Patents

Abstract

A color printing arrangement has a series of printing stations in each of which a different color is imprinted upon predetermined regions of a travelling band to form color images. A device for measuring the width of the band by sensing the edges thereof is located immediately upstream of each printing station. The width of the band at the first printing station is compared with the width at each of the following printing stations. As long as the widths at the latter printing stations are the same as that at the first printing station, the band is allowed to continue travelling unchanged. However, when the width of the band at a printing station downstream of the first printing station differs from the width at the first printing station, the band is operated upon to return the width to its original value. The reason is that a departure from the original width of the band causes the predetermined regions which are to be imprinted to be moved out of alignment with the printing devices in the printing stations. By returning the width to its original value, the alignment of the predetermined regions is restored.

Description

The invention relates to a method for printing on print carriers in multi-color printing, in which at least two colors are printed one above the other to produce a desired mixed color, with a control which directs the print carrier into a register.

In the so-called longitudinal register control, a print mark is printed on a print carrier by a printing unit. Another stamp is printed by a second printing unit. These two marks are printed on tracks that are closely adjacent to each other. There are therefore two scanning tracks, each of which is continuously illuminated by a small point of light. The light reflected by the print carrier is picked up by a photocell. If a print mark passes under the light point, the intensity of the reflected light changes. The photocell converts this change in light intensity into an electrical pulse. Since the two adjacent brands are scanned, two impulses arise. These two impulses must be amplified in an electronic arrangement in a form suitable for measurement and control purposes.

The time difference of the two pulses measured at the output of the electronic arrangement controls an electrical current. The current strength depends on the size of the time difference. If the two print marks are far apart, the time difference between the two pulses is large and, accordingly, the output current. This output current controls a regi stermotor that adjusts a printing cylinder stored in the printing unit. The pressure cylinder is adjusted according to a predefined time difference between the two pulses controlled by the brands. If there is a large time difference, the pressure cylinder is adjusted by a large amount. It is also possible to run the register motor forwards or backwards depending on the appearance of the two marks.

With the so-called page register control, the print carrier is aligned with regard to its lateral position in the print line. For this purpose, in addition to the marks extending in the longitudinal direction of the print carrier for the alignment of the print carrier in the longitudinal direction, marks which are at an angle to the feed direction are also printed on the print carrier. As a rule, these marks run at an angle of 45 ° to the feed direction of the print medium. Via a corresponding electronic circuit, the pair of marks, which consists of the marks extending in the longitudinal direction of the print carrier and a respectively assigned mark in an inclined position, generate two electrical control pulses, one of which serves to regulate the longitudinal register and the other to regulate the side register of the print carrier. The longitudinal register control takes place in the manner already described, while the side register control acts on a paper roller via a register motor, with the aid of which the printing medium is guided to one side or the other.

Controlling the print carrier in this way has significant disadvantages. When creating the artwork, the marks must be aligned with the entire image. The assembled position of the marks in relation to the picture can only be achieved within the scope of technical possibilities relative accuracy. Another disadvantage is that in the control of printed marks it is assumed that the position of the mark with respect to the image to be printed always remains the same, so that when the mark is aligned, the image is also aligned with a specific printing unit. This assumption neglects the fact that the print medium stretches across its entire surface in various ways, for example depending on the area coverage of the image.

In fact, a brand cannot represent the different circumstances of a printed carrier. Despite a precise alignment of the brand with respect to the printing unit, it is not certain that the surfaces to be printed are also aligned accordingly.

A further disadvantage can be seen in the fact that the conventional methods only act on the printing medium in a secondary manner, for example by aligning the position of the printing cylinders in accordance with the course of the printing path or by controlling paper guide rollers in such a way that the printing medium rolls on them is steered into the desired position below the printing unit. Here remains uncertain whether the path of the print carrier changes according to the adjustment of the paper guide roller or the printing cylinder. depending on the elasticity behavior of the print carrier, it is conceivable that it expands in an undesired other direction despite a tension applied, for example, by a paper printing roller. One consequence of this unintentional stretching is, for example, that the colors of different printing units are not printed one above the other as intended, but side by side. The observer sees lines of several colors next to each other that do not merge as desired into a mixed color.

The disadvantages described above, which result from the control of the printing medium with respect to the printing units via the marks printed on the printing medium, show that the marks are at most inclined to position the cylinders among one another in a register. In contrast, they are not able to represent an aid for carrying out a method by means of which an image printed on the printing medium can be aligned with respect to the printing unit.

It is therefore an object of the present invention to improve the method of the type mentioned in the introduction in such a way that different primary colors are printed directly over one another in a fitting manner.

This object is achieved according to the invention in that the print carrier is controlled in accordance with at least one parameter directly taken from it and acts directly on the print carrier in the sense of a predetermined influencing of this parameter.

This eliminates the hitherto usual detour via the control of the print carrier according to the brands printed on it. Rather, it is ensured that the entire printing medium is preserved in its dimension in the passage through all printing units. Different expansion behavior with regard to both the positive and the negative expansion (shrinkage) of the print carrier over its entire surface no longer plays a role, since the parameter once selected is representative of the entire surface of the print carrier.

By keeping this parameter constant, it is ensured that the entire area of the print carrier remains constant. In addition, for the purpose of keeping the dimensions of the printing medium constant, this is acted upon directly, so that the detour via an adjustment of guide rollers or of printing cylinders is saved. They therefore now need a drive that keeps the cylinders in register. The direct impact on the print carrier not only ensures its dimensional stability, it is also technically relatively easy to implement and works independently of subjective influences such as e.g. B. the manual accuracy during assembly. In the case of a print carrier web, its width is preferably chosen as the parameter to be measured and thus kept constant.

In conventional printing presses it was customary to scan the marks and to change the position of mechanical parts within the printing press in accordance with the time differences between two successive marks so that the position of the paper web could be influenced thereby.

In such a printing press, the time differences between successive brands must be determined precisely. In accordance with these time differences of marks passing by a photocell, system parts must be controlled in such a way that a predetermined time difference of the marks passing by is neither exceeded nor fallen short of. In this way, criteria are used for the control of the system parts, which are not decisive for the registration accuracy.

It is therefore an object of the present invention to provide a device for printing on print carriers in multi-color printing, which prints at least two colors from one printing unit to produce a desired mixed color, and which is provided with a control unit which directs the printing medium into a printing line of a respective printing unit, To improve so that the steering of the print medium is done with relatively simple and cheap means so that different primary colors are printed directly on top of each other in a fitting manner.

This object is achieved in that at least one scanner measuring a selected parameter of the print carrier is provided in front of each printing unit printing a specific color, and the scanner is connected to a control device which compares the measured values of the first scanner with the measured values of all subsequent scanners, which is connected to is connected in a regulating manner to an actuator influencing the parameter of the pressure carrier.

With this device it is possible to act directly on the print carrier in order to keep its dimensions constant. An action on moving forward. directional parts are not necessary. As a result, the entire device becomes flexible and follows the control signals emanating from the control device quickly and relatively without inertia. These act directly on the printing medium, so that this is kept so largely constant with regard to its overall dimensions by keeping a representative parameter constant that care is taken to ensure that the subsequent printing units each print the contours specified by the preceding printing units with their color, so that the desired printing impression is created. The device therefore works more accurately, faster and with less effort than the conventional devices.

Further details of the invention will become apparent from the following detailed description and the accompanying drawings, in which a preferred embodiment of the inventive device is shown.

• Figur 1 Eine schematische Darstellung einer Vorrichtung in Draufsicht und
• Figur 2 eine schematische Darstellung einer Vorrichtung in Seitenansicht.

The drawings show:

• Figure 1 is a schematic representation of a device in plan view and
• Figure 2 is a schematic representation of a device in side view.

The method according to the invention can expediently be carried out using a device of the type shown in the figures. This device essentially consists of an unwind 1, three printing units 2, 3, 4 and a reeling 5. A printing medium 6 extends from the unwinding 1 through the printing units 2, 3, 4 to the reeling 5. It is from the unwinding 1 , which can be a supply roll, unrolled, conveyed through the printing units 2, 3, 4 and rolled up on the reel 5 for further processing. The print carrier 6 has a predetermined width 7, which represents a parameter that is binding for the entire dimensions of the print carrier 6.

The width 7 of the print carrier 6 is measured at an inlet 9, at which the print carrier 6 runs into the first of the three printing units 2, 3, 4 arranged one behind the other. Suitable measuring means for measuring the width 7 are provided at this inlet 9. These measuring means can be, for example, photoelectric scanners 10, 11, with the aid of which the width 7 of the print carrier 6 is scanned. Each of the two scanners 10, 11 receives a pulse from a side edge 12, 13 of the print carrier 6 assigned to it. The respectively recorded impulse They are fed via a line 14 into a control device 15, which evaluates the pulses in the sense of calculating the width 7.

In the first printing unit 2, the printing medium 6 is printed with a first basic color. This first basic color can also serve as a first final color for a representation to be colored accordingly. However, it is also possible to mix this first printing ink with further colors which are printed, for example, by the subsequent printing units 3, 4 on the first color which has been printed on the printing medium 6 by the printing unit 2.

For the purpose of this mixture, the printing medium 6 must run into the second printing unit 3 in such a way that the second printing unit 3 with the second color contained therein directly overprints the contours 16 printed in the first basic color by the first printing unit 2. In order to be able to control this exact assignment of the contour 16 to a register of the printing unit 3 which imprints the second color, care is taken that the dimensions of the printing medium 6 entering the printing unit 3 are the same as those which have already been determined at the inlet 9. If the dimensions of the print carrier 6 are identical, it can also be assumed that the contours 16 have exactly maintained their position with respect to the print carrier 6. With a corresponding alignment of the printing unit 3 with respect to the printing medium 6, the register of the printing unit 3 directly hits the contours 16 printed by the printing unit 2.

In order to be able to maintain this identity of the printing medium 6 in the area of the printing unit 3, the width 7 of the printing medium 6 is measured by means of two scanners 18, 19 at an inlet 17 of the printing unit 3 corresponding to the inlet 9. The pulses picked up by the scanners 18, 19 are conducted via a line 20 into the control device 15, in which the measured values of the scanners 10, 11 are already stored. The control device 15 compares the values measured at the inlet 9 with those that were measured at the inlet 17. If the width at both inlets 9, 17 is the same, care is taken that the printing unit 3 overprints the contours 16 to be overprinted, which were produced by the printing unit 2, as desired. If, however, the two measured values from the inlet 9 on the one hand and from the inlet 17 on the other hand differ from one another, the control device 15 calculates the corresponding difference and converts it into a correspondingly large control pulse, the size of which corresponds to the calculated difference.

A heater 21 is provided in the printing unit 2, which can be designed, for example, as an electric heater and is connected to a power source 22. The current source 22 is connected to the heater 21 via a line 23. In this line 23 there is a variable resistor 24, by means of which the heat emitted by the heater 21 can be regulated. The control resistor 24 is connected to the control device 15 via a control line 25. The control device 15 controls the control resistor 24 with the aid of the control pulse it emits. Instead of an electric heater, any energy source, for. B. gas, Hot water or steam can be used and controlled using appropriate control options.

As soon as the scanner 18, 19 determine a width 7 of the print carrier 6, which differs significantly from the width measured at the inlet 9, it can be concluded from this difference that the expansion of the print carrier 6 on the between the inlet 9 and the inlet 17 lying route has changed significantly. The change in this elongation results with a constant tension acting on the pressure carrier 6 in that the dimensions of the pressure carrier 6 have changed considerably on the route lying between the inlets 9, 17. Stretching can be reduced to the original size by removing moisture from the print carrier 6 by drying it with the aid of the heater 21. With a correspondingly large deviation, a correspondingly large amount of heat must be emitted by the heater 21 in order to be able to carry out the drying process to the desired extent. If there is a small deviation in width, it is sufficient to specify a smaller amount of heat in order to be able to reduce the elongation to the original dimension. The regulation of the expansion or shrinkage carried out with the aid of the heater 21 is very precise, so that it can be expected that the pressure carrier 6 at the inlet 17 has been returned to the same width that it already had at the inlet 9.

In the second printing unit 3, the contour 16 is overprinted with a second color, which also represents a first basic color outside the contour 16. The printing unit 3 provides the printing medium 6 with a new contour 26 in this way. Parts of this contour 26 have reached their final coloring at the outlet of the printing unit 3.

They appear either in the base color printed by printing unit 3 or in a mixed color which is composed of the two colors of printing units 2 and 3. Other parts of the contour 26, on the other hand, are printed with a third color by the printing unit 4, so that at the outlet 27 there is a contour 28 on the printing medium 6, in which, on the one hand, mixed colors from the basic color applied by the printing unit 4 and those from the preceding printing units 2, Find 3 printed colors and on the other hand a basic color applied by the printing unit 4. The commander 28 can therefore have a total of three primary colors.

For the creation of this mixed color, it is necessary that the contour 26 is controlled so precisely in the last printing unit 4 that its register prints the color contained in it directly on the contour 26, insofar as mixed colors are to be produced. As a result, the print carrier 6 must be controlled exactly under the printing unit Z, as it has already been controlled under the printing unit 3. For this purpose, scanners 30, 31 are provided at an inlet 29 of the print carrier 6 into the printing unit Z and are connected to the control device 15 via a line 32. These scanners 30, 31 scan the width 7 of the print carrier 6. The rule over line 32 Device 15 delivered measured value is compared with the measured value of the scanner 10, 11, which is stored in the control device 15. If the measured values match, the contour 28 runs exactly under the register of the printing unit 4, so that the color printed by them immediately reaches the desired locations on the contour 26. If the measured values of the scanner 30, 31 on the one hand and the scanner 10, 11 on the other hand differ, the control device 15 emits a control pulse.

In the conveying direction of the print carrier 6 there is a drying chamber 33 in front of the scanners 30, 31, through which the print carrier 6 runs on its way between the printing units 3, 4. This drying chamber 33 is flowed through by dry air, which is generated by a fan 34, which can be driven by a motor 35. The blower 34 is connected to the drying chamber 33 via an intake port 36. Intake area 36 opens into drying chamber 33 in the area of a suction side 37. Opposite suction side 37 is a pressure side 38, which is connected to a pressure nozzle 39. This pressure port 39 opens into the ambient air, which is sucked through the pressure port 39 into the drying chamber 33. The air stream sucked in through the pressure port 39 sweeps over the pressure carrier 6 on its way towards the suction side 37 and extracts the moisture from it, the removal of which is necessary in order to return the pressure carrier 6 to the same degree that it already had at the inlet 9.

The return of the stretch depends on the amount of air drawn through the drying chamber 33. This can be regulated with the aid of the speed of the fan 34. The speed control of the Ge blown 34 is possible with the help of a built-in gear between the motor 35 and the fan 34. However, it is also possible to use a motor 35 whose speed can be regulated. Its power supply 40 can be controlled by the control pulse emitted by the control device 15, for example via a control resistor 41. It is also conceivable to regulate the heating provided in the drying chamber 33 with regard to the heat it emits.

The print carrier 6 is unrolled from the unwind 1. Its width is determined at the inlet 9 into the printing unit. In the area of the printing unit 2, the printing medium 6 is printed with the contour 16. The width of the print carrier 6 is measured by the scanners 18, 19 at the inlet 17 into the printing unit 3. The measured values recorded by these scanners 18, 19 are compared with the measured values recorded at the inlet 9 in the control device 15. If the width 7 coincides, the print carrier 6 runs unchanged under the printing unit 3 and is printed there again, so that a new contour 26 appears behind the printing unit 3 in the direction in which the print carrier 6 runs. If the measured values differ, the width 7 at the inlet 17 of the printing unit 3 is corrected so that it corresponds to the width 7 at the inlet 9. For this purpose, a heater 21 can be provided in the printing unit 2, with the aid of the heat given off by this, the expansion of the printing medium 6 is reduced to the level at the inlet 9.

The width of the print carrier 6 corrected in this way is scanned again at the inlet 29 into the printing unit 4 by scanners 30, 31 and compared with the corresponding measured values that were recorded at the inlet 9 in the control device 15 chen. If the measured values match, the print carrier 6 runs unchanged into the printing unit 4. If the measured value recorded by the scanners 30, 31 differs from that which was recorded at the inlet 9, a control pulse is generated in the control device 15, which controls the motor 35 with respect to its speed and the heating of the air conveyed by the fan 34. The air heated in this way is passed through the drying chamber 33 through which the pressure carrier 6 passes. As a result, so much moisture is withdrawn from the pressure carrier 6 that it is returned to the stretch that it had at the inlet 9. As a result, the print carrier 6 at the inlet 29 has the same dimensions as at the inlet 9, so that the contour 26 corresponds exactly to the register of the printing unit 4.

At the output 27 of the printing unit 4, the contour 28 appears, of which individual parts have been newly created in the printing unit 4, while other parts have overprinted the contours 16, 26. The carrier 6 printed in this way is rolled up onto the reel 5.

The device according to the invention is expediently provided exclusively with either heaters or drying chambers. Drying using the heated air proves to be the most sensible.

The scanning and detection of the width 7 can be carried out in any technically simple and effective manner which is suitable for generating control pulses. The type of scanning and detection is not important. Instead of the width 7, other parameters can also be used to determine the elongation of the pressure carrier 6. However, these parameters should be functionally related to the expansion of the print carrier 6. In particular, moisture is also considered as a parameter.

Claims (21)

1. A method for printing on print media in multi-color printing, in which at least two colors are printed one above the other to produce a desired mixed color, with a control directing the print media into a register, characterized in that the print media (6) corresponds to at least one directly removed from it Parameter is controlled and acted directly on the print carrier (6) in the sense of a predetermined influence on this parameter. 2. The method according to claim 1, characterized in that is acted on the pressure carriers (6) in the sense of keeping the parameter constant. 3. The method according to claim 1 and 2, characterized in that the width of the printing medium (6) is kept constant. 4. The method according to claim 1 to 3, characterized in that the width (7) of the printing medium (6) at the inlet (9) in the first printing unit (2) measured, further width measurements at the inlets (17, 29) in further printing units (3, 4) and the results of which are compared with the first width measurement, any width differences that may occur are determined and the printing medium (6) is returned to its originally measured width (7) by compensating for width differences. 5. The method according to claim 1 to 4, characterized in that the width (7) of the print carrier (6) at its unwind (1) festge from a supply roll is set and a coarse adjustment of scanners (10, 11; 18, 19; 30, 31) is carried out in accordance with the width (7) determined in this way, with which the width (7 ) of the pressure carrier (6) entering this is determined. 6. The method according to claim 1 to 5, characterized in that the width (7) of the pressure carrier (6) is kept constant by influencing its degree of expansion. 7. The method according to claim 1 to 6, characterized in that the degree of expansion of the pressure carrier (6) is kept constant by influencing the elasticity. 8. The method according to claim 1 to 6, characterized in that the degree of expansion of the pressure carrier (6) is kept constant by influencing the tension. 9. The method according to claim 1 to 8, characterized in that the degree of expansion of the pressure carrier (6) is influenced by its degree of dryness. 10. The method according to claim 1 to 9, characterized in that the drying of the printing medium (6) is carried out by increasing its temperature. 11. The method according to claim 1 to 9, characterized in that the drying of the printing medium (6) is carried out with air. 12. The method according to claim 1 to 11, characterized in that the drying of the printing medium (6) is carried out with heated air. 13. Device for printing on print carriers in multi-color printing, which prints at least two colors from one printing unit to produce a desired mixed color one above the other and which is provided with a control which guides the printing medium in a printing line of a respective printing unit according to the method according to claims 1 to 13, characterized in that at least one scanner (10, 11; 18, 19; 30, 31) measuring a selected parameter of the print carrier (6) is provided in front of each printing unit (2, 3, 4) and the scanner (10 , 11; 18, 19; 30, 31) are connected to a control device (15) which compares the measured values of the first scanner (10, 11) with the measured values of all subsequent scanners (18, '19; 30, 31) and which is connected to a the control element influencing the parameter of the pressure carrier (6) is connected in a regulating manner. 14. The apparatus according to claim 13, characterized in that the scanner (10, 11; 18, 19; 30, 31) are designed as measuring devices for measuring the width (7) of the print carrier (6). 15. The apparatus of claim 13 and 14, characterized in that the scanner (10, 11; 18, 19; 30, 31) are designed as measuring devices for measuring the moisture of the pressure medium (6). 16. The apparatus according to claim 13 to 15, characterized in that the actuator is connected to a heater (21) heating the pressure carrier (6). 17. The apparatus according to claim 13 to 15, characterized in that the actuator is designed as a fan control for controlling an air flow. 18. The apparatus according to claim 17, characterized in that the actuator is designed for controlling an amount of air. 19. The apparatus according to claim 17, characterized in that the actuator is designed to control a flow rate. 20. The apparatus of claim 13 to 19, characterized in that the actuator is connected to the heating of a drying chamber (33) and is designed as a fan control of the air stream flowing through the drying chamber (33). 21. The apparatus according to claim 13 to 20, characterized in that behind a roll (1) of the pressure carrier (6) from a supply roll one-the width (7) of the pressure carrier (6) measuring scanner (10, 11) is provided, which is connected to the scanners (18, 19; 30, 31) assigned to the other printing units (2, 3, 4) for making rough settings.

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