EP1666252A2 - Device and method for adjusting the printing image in a flexographic printing machine - Google Patents

Abstract

The method involves moving a part of rollers (3, 7, 8) by actuating drives (M1-M4) commonly and independent of each other such that the rollers involved in a printing process are engaged with each other. A measuring process is executed by a camera (K), and consecutive intensity values of light are recorded by the camera, where the light is reflected by sections of a print image (10). The intensity values are fed to a control and regulating unit (13), and a signal is produced by the control and regulating unit depending on the measured intensity values for the drives of the part of the rollers. An independent claim is also included for a rotary printing machine comprising a camera for executing a measuring process.

Description

The invention relates to a device and a method according to the preamble of claims 1 and 17.

It should be noted that there is a need to adjust the print image by optimizing the relative position of the rollers involved in the inking and printing process in all areas of the rotary printing. Thus, in gravure printing machines, the position of the impression roller is set to the pressure roller. In flexographic printing machines, the impression cylinder, the pressure roller and the anilox roller must be adjusted to each other.

Therefore, flexographic printing machines are known, which are equipped with a pressure roller and an anilox roller, which are movable on at least one console of the printing press frame. These two rollers can be employed by their own actuators both independently of each other and together to the impression cylinder on which the printing material is applied.

Thus, DE 29 41 521 A1 and DE 37 42 129 A1 show printing presses in which the bearing blocks of the pressure cylinder carrying carriage guided in carriage guides of the inking unit of the printing press frame and provided with its own spindle drives and in which the carriage of the printing cylinder with further slide guides for the bearing blocks of the inking or anilox rollers carrying carriage are provided, which in turn have their own spindle drives.

From DE 40 01 735 A 1, a flexographic printing machine is known, in which the carriage carrying the pressure roller and carrying the Farbauftrags- or anilox rollers carried in a common carriage guide the inking unit of the printing press and are moved together and individually by spindle drives.

In rotary printing machines of this known type, the adjustment of the printed image in a known manner can be done as follows. An electronic control device is provided which can access data entered into a memory device. The data relate to the travel between the pressure roller and the counterpressure roller, taking into account the geometrical dimensions of the machine and the diameter of the rollers. This control device then sets the relative roller positions, so that it should be ensured that all parts of the printed image are transmitted.
However, the various rollers, printing plates and the materials to be printed and all other parts involved geometric tolerances, so often an additional Beistellvorgang is necessary.
This loading operation is performed by the print engine operator, who adjusts the roll positions while observing the print image.
This type of adjustment of the printed image ensures that a very good printed image is obtained against each other with the least amount of pressure applied to the rollers involved in the printing process. However, this type of adjustment of the printed image is cumbersome, requires a lot of time and waste and is also disadvantageous in that it depends on the subjective assessment of the printing press operator by visual inspection.

The object of the invention is therefore to provide a device or a method of the type described, which allow automatic adjustment of the printed image to the desired optimum quality.

According to the invention, this object is achieved in a device or a method of the type specified in that at least one of the printed image on the substrate web detecting camera is provided which successively recorded intensity values of light, which is reflected at least by image portions of the printed image, an electronic control device supplies. This control device evaluates these intensity values in such a way that these intensity values are checked, and determines from the recorded intensity values the optimum roll positions and thus controls the positioning motors automatically.

One goal may be to image the printed image without loss of area on the substrate.

It is advantageous if the course of the intensity values are evaluated. Until or how the change of the intensity values has a certain course, which represents an optimal pressure. Then the Anstellvorgang can be terminated or at least interrupted.

In another embodiment, the intensity values of the light of selected spectral ranges, ie wavelengths, can be recorded.

In a further embodiment, it is provided to compare the values of the light intensity with a target image stored in a memory. The addition process is terminated when or as long as the best match between the measurement and the target image exists.

It is advantageous if a control program is provided, to which the geometrical dimensions of the rollers involved in the printing and inking process are known and which optionally (for example in the case of long travel ranges, or after a roll change) provisionally adjusts the position of these rollers by signals to the actuators.

However, the method according to the invention also works if there is no additional control program.

In an advantageous embodiment of the invention it is provided that in the memory unit, the digitized Söllform the printed image is stored.

This desired shape is then (possibly in the control device) compared with the respective recorded print image. The control device then generates actuating signals for the actuators moving the rollers until the comparison yields the best match between the recorded print image and its stored desired form.

Another embodiment of the invention does not require a stored in a memory digitized desired form. In this further embodiment, use is made of the fact that the intensity of the reflected light of different sections of the printed image as a function of the relative roller position has a characteristic course.

Thus, the intensity of the reflected light does not change unless contact is made between all the rollers involved in the printing or inking process. When the contact is made, the ink transfer to the substrate begins and the intensity of the reflected light changes relatively strongly until an optimum color transfer value is achieved. A further approximation of the rollers then leads only to a smaller change in the intensity of the reflected light.

In the region in which the intensity change flattened, an optimum between ink transfer and contact pressure of the rollers is usually achieved against each other. A further mutual approach of the rollers then only builds up pressure, which can lead to damage to the rollers, roller bearings, printing plates, materials to be printed, etc.

For this reason, it is advantageous to disassemble the recorded print image into different sections, or at the same time to take it with a camera which records a plurality of image sections.
In the evaluation of the image sections, the mentioned course of the light intensity is recorded for the individual image sections.
Only when a sufficient number of image sections have a certain selected intensity profile, the mutual approach of the rollers to each other is terminated. With high demands on print quality this will be the case if the change in the intensity of all image sections decreases or has already decreased. This ensures that a good ink transfer takes place on all sections of the printed image.

An improvement of this embodiment can be achieved if there is a difference between the intensity values of the printed substrate and the intensity values of the unprinted substrate. The difference values obtained are referred to below as contrast values. They can be used in a similar way as the intensity values.

As a further advantageous measure, the use of at least one color camera is recommended, so that light of selected wavelength ranges can be recorded. This measure is suitable both to facilitate the comparison with a stored digitized desired shape of the printed image and to perform the course of the light intensity or the contrast values in an improved form. Commercially available cameras of modern design usually have as photosensitive elements semiconductor devices that are sensitive to light of certain wavelengths, which is due to the photoelectric effect and its applications in the semiconductor field. It is expedient for a camera in this way to be able to assign electrical output values to color intensity values of several colors (eg red, yellow, blue). These values are then made accessible to a control and control unit.

In this way, the color intensity profile of different colors or even the entire spectrum of a printed image or even the sections of a printed image can be recorded. The measured values are then used in the manner already described in order to set the suitable position of the pressure rollers. Also for the individual colors can be done in the manner already described a contrast formation.

Light intensity values can also be converted into coordinate systems suitable for further evaluation. The same goes for the course Contrast values. These values derived in the last analysis from intensity values and color values (wavelength / frequency) also have a characteristic course as a function of the relative position of the rollers and can be used in the manner already described.

Particularly advantageous is the use of the method according to the invention in flexographic printing, since in this case the thickness of the stitches has to be considered additionally. In addition, their adhesive tapes and other elements involved may have different thickness tolerances, so that it may happen that in a gentle, slightly touching employment not all parts of the plates produce printed images and only partial images arise. Therefore, the deviation between the above-mentioned geometric target value and the actual positions of the rollers involved in the printing process in the flexographic printing is particularly large.

As a camera, a digital camera is expediently used, which supplies digitized images of the recorded print images.

For multiple printing units, the setting can be made separately for each printing unit.

Furthermore, a separate adjustment of the actuators for producing the parallelism of the various rollers may be provided if, due to an inclination of a roller over the length thereof different pressures result. When flexographic printing would z. B. provide a separate adjustability of the actuators one side of the inking unit or the inking units, especially to ensure the parallelism of pressure and impression cylinder.
A measuring operation in the sense of this application is the observation of the course of the intensity or contrast values, while the rollers involved in the printing process are adjusted to one another. If only one camera is used, it is possible to sequentially set several inking units of a machine, that is to perform a measuring operation during the setting of an inking unit.

However, it is also possible to perform only one measuring operation on the printing material, which has already undergone several inking units, during the setting of these inking units of a machine. This procedure leads to further time savings. This procedure may also be possible when using only one camera.

As soon as the settings or settings are reached that give the best match between the recorded print images and the target shape, the values can be stored in a memory. The same naturally also applies to those setting values which result from the other setting methods according to the invention.

In this way, these setting values can be found quickly, for example after a print interruption and after a shutdown of the printing cylinder.

In a further embodiment of the invention, it is provided that at least one suppression takes place between at least two rollers during the addition process of the rollers involved in the printing process.

It is advantageous here if the contact pressure which prevails between the rollers involved in the suppression, lowered again and the suppression is canceled. Furthermore, it can be provided that the rollers, after the contact pressure has been lowered, are again set against each other, wherein the contact pressure increases again.

Fig. 1

schematisch eine Flexodruckmaschine mit nur einem Druckwerk, bei der eine elektronische Steuereinrichtung die Einregelung der Druckwalze die beste Druckqualität ermöglicht, und

Fig. 2

A bis C die schematisch die Abfolge der Anstellung von Rasterwalze und Druckwalze einer Flexodruckmaschine relativ zueinander und deren gemeinsame Anstellung an den Gegendruckzylinder

Fig. 3

schematisch die Unterteilung des Druckbildes in Abschnitte

Fig. 4

schematisch den Verlauf der Kontrastwerte eines Bildabschnitts als Funktion der relativen Walzenposition.

Embodiments of the invention are explained below with reference to the drawings. In this show

Fig. 1

schematically a flexographic printing press with only one printing unit, in which an electronic control device enables the adjustment of the pressure roller, the best print quality, and

Fig. 2

A to C schematically show the sequence of employment of Anilox roller and pressure roller of a flexographic printing machine relative to each other and their joint employment of the impression cylinder

Fig. 3

schematically the subdivision of the printed image into sections

Fig. 4

schematically shows the course of the contrast values of an image section as a function of the relative roller position.

In a printing machine frame, of which only the side parts 1 and 2 are shown schematically, a counter-pressure roller 3 provided with a drive is mounted in the usual way. The side parts 1, 2 carry a printing unit console 4, on the guides in not shown, the bearing blocks 5 and 6 of a pressure roller 7 and an anilox roller 8 slidably guided in the direction of the double arrows A and B. The mutually arranged bearing blocks 5, 6 are movable by individually controllable servo motors M1 to M4, in such a way that each roller 7, 8 can be moved by itself and both in a fixed position to each other are moved together.

The printing machine frame 1, 2 is provided with further Farbwerkskunsolen not shown, on which in a corresponding manner printing and anilox rollers 8 are moved, with only the single impression roller 3 is provided for all printing cylinder.

The flexographic printing machine according to the invention can in principle be configured in the same way from its mechanical construction as the flexographic printing machines described in DE 29 41 521 A1, DE 37 42 129 A1 and DE 40 01 735 A1.

The anilox roller 8 is provided with a conventional inking device, which preferably consists of a known ink chamber doctor blade.

The pressure roller 7 is provided with printing on the web 17 clichés 9. In this case, a diamond pattern, which is easy in the figure is to be represented, imprinted. By hired to the platen roller 3 pressure roller 7, the running on the platen 3 in the direction of arrows C and D paper web 17 is printed with a printed image 10, which is shown for the sake of simplicity in the form of squares. This print image 10 is recorded in the detection area 11 by the camera K, which feeds successively recorded images via the line 12 to the computer-equipped control unit 13. In the control unit 13 data are entered via a special input device 14, which relate to the diameter of the pressure roller 7 and the thickness of the worn therefrom 9 clichés.

Via another input unit 15, for example in the form of data stored on a CD, the desired shape of the printed image 10 to be printed is entered into the control and regulation unit 13. In the control and regulation unit 13, for example, in one embodiment, the printed images taken by the camera K are compared with the desired form of the printed image entered via the input unit 15, and the control and regulating unit 13 sends signals to an adjusting device 16 via lines according to the signals generated by the control unit 13, the servo motors M1 to M4 of the printing and anilox roller 7, 8 controls.

Once the pressure roller 7 has been adjusted to a position that produces the best quality printed images, the settings are stored in a memory of the control unit, so that, if necessary, the optimal position of the printing and anilox rollers 7, 8 can be found again ,

In the exemplary embodiments illustrated in FIG. 2 it is shown in which manner or sequence the three rollers involved in a flexographic printing machine can be set against one another. In other printing processes, such as gravure printing, a representation of the relative roll position setting is not necessary because only two rolls are involved in gravure printing in the printing process.

FIG. 2 is constructed in matrix form. The columns denoted by the capital letters A to C contain exemplary embodiments, while the lines denoted by the small letters a to e designate method steps of the individual exemplary embodiments. The printing material, which runs during printing between the pressure 7 and counter-pressure roller 6 and which is assigned the reference numeral 17 in Figure 1, is not shown in Figure 2. The individual movement of a roller 7, 8 is represented by an arrow within a roller, while an arrow passing through both rollers indicates the mutual movement of the roller packet without a change in the relative position of the rollers relative to one another.
In particular, in the description of Figure 2, the term "overpress" is often used. Therefore, it should be noted at this point that by "overpressing" is meant a pitching or pressing of the rollers which goes beyond the exact geometrical dimensions thereof. By this measure, it is ensured that between the "overpressed" rollers or between the substrate, which is printed between over-pressed rollers, and one of these rollers takes place in any case a full-surface ink transfer. The "distance" by which it must be "overdriven" or the pressure that is necessary for this varies from printing process to printing process from millimeter fractions to millimeters. It is clear that in most printing processes flexible rollers, substrates or other flexible additional elements are used, which increase this distance. In this context, the clichés of flexographic printing or gravure impression are mentioned as examples.
However, it is also worth mentioning that cylinders made of steel can usually be overpowered by simple means, which goes beyond the ovality of their mantle surface. This is the case in particular if the cylinders have rubberized lateral surfaces. Therefore, the mentioned overpressing can be used in various printing processes.

In the first embodiment A of Figure 2 is the line a - as in the other embodiments also - the initial state in which the three rollers involved, 7, 8 are not yet employed against each other.

In method step A b, the pressure roller 7 is set against the counter-pressure roller 6 and over-pressed in the manner already described above. The individual movement of the pressure roller 7 is represented by the arrow. This ensures that all zones of the plate (when colored) transfer color to the substrate. In the process step A b, however, there is still no contact and thus no ink transfer to the pressure roller 7 and the substrate.
The next step c of the embodiment A is in approaching the anilox roller 8 to the platen 7 until all pixels on the substrate can be seen. This circumstance is verified in the manner already described with the help of at least one camera.
Since a permanent suppression of the in step b to each other set rollers 3 and 7 is undesirable, now carried out the process steps A d and A e.
The process step A d shows how the two rollers 7 and 8 are moved away from the counter-pressure roller, wherein the set relative position between the anilox roller 8 and the pressure roller 7 is maintained.
As part of the process step A e, the two rollers are moved back to the counter-pressure roller until all pixels are again present on the substrate, which is verified again with the help of the camera. The process is completed, the print image optimized and the actual production process can begin.

Also in the second embodiment B, the line a is the initial state, in which the three rollers involved, 7, 8 are not yet employed against each other.
In process step B b, the anilox roller 8 is made against the pressure roller 7 and suppressed in the manner already described above. This ensures that all zones of the cliché are completely colored.
The next step c of the embodiment B is in approaching the package of anilox roller 8 and pressure roller 7 to the platen roller 3 to all pixels on the substrate can be seen.

This circumstance is verified in the manner already described with the help of at least one camera.
Since a permanent suppression of the rollers 7 and 8, which are set to one another in method step b, is undesirable, method steps B d and B e are now carried out.
The process step B d shows how the roller 8 is moved away from the pressure roller 7, whereby the set relative position between the pressure roller 7 and the counter-pressure roller 3 is maintained.
As part of the process step B e, the two rollers are again brought together until again all pixels are present on the substrate, which is verified again with the help of the camera. The process is completed, the print image optimized and the actual production process can begin.
In the third embodiment C, the pressure roller 7 and the anilox roller 8 are made common to the counter-pressure roller 3 wherein all three rollers involved 3, 7, 8 are suppressed from each other.
In the exemplary embodiment C1, the pair of rollers consisting of printing roller 7 and anilox roller 8 are then driven together by the counterpressure roller, whereby the suppression between the rollers of the roller pair remains.
In process step C1 d, the roller pair is adjusted to the counterpressure roller until all image elements are transferred to the printing material.
In step C1 e, the anilox roller 8 is moved away from the pressure roller, there is at least no complete color transfer instead.
The retraction of the anilox roller 8 to the pressure roller 7 shown in the method step C1 f takes place again until the printed image is imaged without loss of area.

The embodiment of FIG. 2 C 2 differs in steps c to e of the embodiment of FIG. 2 C 1, characterized in that in step c, the anilox roller 8 of the employee in the over-pressed position on the platen roller 7 pressure roller from its over-pressed position relative is moved to the pressure roller in the direction of the arrow. Subsequently, the anilox roller 8 in step d in their optimal employment of the pressure roller brought and in steps e and f, the common departure of pressure roller and anilox roll from the platen roller and the hiring done by the control unit in a form to the platen, which ensures that the printed image is imaged without loss of area.

FIG. 3 schematically illustrates the manner in which the printed image 10 contained in the rectangle 20 can be decomposed into various sections 18. For illustrative reasons, it was omitted to sketch the print image itself. In practice, it is possible to decompose a printed image 10 into thousands of sections 18.
FIG. 4 shows the contrast profile K _{i of} the sections 18a and 18b, which is plotted as a function of the position of the rollers relative to each other. The resulting characteristics 19 a and 19 b are assigned to the sections 18 a and 18 b. It immediately becomes clear that both characteristics are largely the same shape. However, the fact that both characteristics have almost identical maxima is due to the fact that the contrast values were normalized in this embodiment. Such standardization may be performed, for example, with respect to average values of multiple sections 18.
The course of the two characteristic curves is offset relative to the roll position, since the rolls involved in the printing process, clichés, etc., as already mentioned several tolerances, which in this case cause the portion 18 a "earlier" is completely printed, as the portion 18 b , In the present embodiment, the portion 18a is already completely printed when the area 21a of the characteristic 19a is reached. Both sections 19 a, b are printed when the portion 21 b of the curve 19 b is reached.
Similarly, when the nip section 21 n is reached, where n is a selected number of image sections, the setting operation of the printing rollers can be terminated.
However, the fact that the regions 21 of the characteristic curves 19 lie behind the second inflection point of the characteristic curves 19 in the exemplary embodiment shown does not mean that this always has to be the case. Rather, the characteristics shown on several areas, the course so It is characteristic that an evaluation device can easily recognize when the characteristic curves 19 of a selected number of image sections 18 has reached such a range. The definition of this range is therefore a measure that depends on a number of parameters (print quality to be achieved, substrate, printing process, etc.) and can be performed as needed.
The consideration of the characteristics of Figure 4 also facilitates the understanding that all devices and methods of the invention also work when the rollers involved in the printing process are initially suppressed against each other and then traversed the rollers from each other (the mechanical contact remains).
In this case, the observer would first see the region of the characteristic curves shown on the right in FIG. 4, in which there is relative color saturation on the printing material 17 and the slope of the characteristic curves is low.
In this case, the disengagement of the rollers would have to be stopped if, with a number m of sections 18, the assigned areas 21 of the characteristic curves 19 had been left off and the contrast values in these areas began to decrease more.
This variant of the invention, in which the setting of the roll positions by a shutdown of the rolls is achieved and carried out as long as the image is reproduced without undesirable loss of area, is covered by the main claims.

The computation steps necessary for the various mathematical operations for carrying out the illustrated exemplary embodiment and the computation steps for carrying out the other exemplary embodiments contained in the description and the claims can be carried out in an evaluation and arithmetic unit. This can also be contained in the control unit 13. LIST OF REFERENCE NUMBERS 1 Printing machine frame 2 Printing machine frame 3 Backing roll 4 Printing unit console 5 bearing block 6 bearing block 7 platen 8th anilox roller 9 cliche 10 print image 11 detection range 12 management 13 Control unit 14 input device 15 input unit 16 setting device 17 paper web 18 Sections of the printed image 19 Contrast curve / curve 20 rectangle 21 Range of the characteristic K camera M1 actuator M2 actuator M3 actuator M4 actuator

Claims (16)

Method for adjusting the printed image of a rotary printing press by adjusting the relative position of the rollers (3, 7, 8) involved in the ink transfer,
wherein at least .A Part of these rollers (7, 8) by their own actuators (M1 to M4) both together and independently from each other against each other movable, so that the rollers involved in the printing process (3, 7, 8) are adjustable against each other,
characterized, that measuring operations are carried out with at least one camera (K) in which intensity values of the light, which is reflected at least from image sections of the printed image, are successively recorded, - That the intensity values are fed to a control unit, and - That the control unit generates signals due to the measured intensity values for the actuators of at least part of the rollers involved in the printing and inking process. Method according to claim 1,
characterized, - That the control unit generates as long as signals for the actuators of at least part of the rollers involved in the printing and inking process, - until or how the recorded intensity values have or have exhibited a certain course. Method according to one of the preceding claims,
characterized in that
Light of selected wavelength ranges is recorded. Method according to one of the preceding claims,
characterized in that - That the control unit generates as long as signals for the actuators of at least part of the rollers involved in the printing and inking process, - Until or as the comparison of the intensity values with the desired shape of the printed image, which is stored in a memory unit, the best match results. Method according to one of the preceding claims,
characterized, - That the intensity of the reflected light of different portions (18) of the printed image (10) on the intensity of the unprinted substrate (17) reflected light is subtracted, and - that an evaluation or arithmetic unit (13) sets these difference or contrast values (k _i ) of sections of the print image in relation to the relative roll positions, whereby a similar printing process-typical intensity profile or contrast value profile (19) can be observed for different sections of the print image, and - That the control unit (13) as long as for actuators (M1, M2, M3, M4) of the rollers involved in the printing or inking process (3, 7, 8) generates signals until a predetermined proportion of the different sections (18) the print image a certain intensity curve or contrast value course (19) has or has exhibited. Method according to one of the preceding claims,
characterized,
in that the recording of the printed image (10) or at least parts thereof (10) is provided with at least one color camera (K) for recording. Method according to one of the preceding claims,
characterized, - That the light intensity curve or the course of the contrast values of at least one color from a computing unit in relation to the roll positions is set, and - That the control unit (13) as long as for actuators (M1, M2, M3, M4) of the rollers involved in the printing or inking process (3, 7, 8) generates signals until a predetermined proportion of the different sections of the printed image ( 10) has or has exhibited a specific color intensity profile (19). Method according to one of the preceding claims,
characterized, that the light intensity values or contrast values (19) of several colors are recorded by the control unit, and that a computing unit converts these values into another coordinate system which is based on coordinates derived from the light intensity values or contrast values (19), and - that at least a selection of these coordinates is set in relation to the relative roll positions, and - That the control unit (13) as long as for actuators (M1, M2, M3, M4) of the rollers involved in the printing or inking process (3, 7, 8) generates signals until a predetermined proportion of the different sections (18) of the printed image (10) has or has exhibited a specific coordinate course. Method according to one of the preceding claims,
characterized,
in that the values (k _i ) derived from the light or color intensity of the reflected light of the printed image are normalized. Method according to one of the preceding claims,
characterized,
that of the light or color intensity of the reflected light of the printed image derived values (k _i) are pressed against the position of the rolls involved in the printing or inking process (3, 7, 8) plotted and visualized on a console or a display. Method according to one of claims 1 to 9,
characterized,
In the case of several printing units, the setting for each printing unit takes place on the basis of separate measuring processes. Method according to one of claims 1 to 9,
characterized,
that the setting of several printing units takes place due to a measuring process. Method according to one of the preceding claims,
characterized,
in that the geometrical settings of the rollers (3, 7, 8) with respect to each other, in which the best match between the recorded print image (10) and the desired form of the printed image was determined,
and / or until a predetermined proportion of the different sections (3, 7, 8) of the printed image has or has exhibited a specific intensity or contrast profile,
be stored in a memory. Rotary printing machine, in which the setting of their printed image by the Adjustment of the relative position of the rollers involved in the ink transfer (3, 7, 8) is vornehmbar,
in which at least a part of these rollers (7, 8) can be moved relative to one another by their own actuating drives (M1 to M4) both together and independently of one another, so that the rollers (3, 7, 8) involved in the printing process can be set against each other,
characterized,
in that at least one camera (K) is provided with which measuring operations can be carried out in which intensity values of light reflected at least from image sections of the printed image can be received successively,
is provided that a control and regulating unit, wherein the recorded intensity values can be fed,
that the control and regulating unit (13) is adapted to generate (7, 8 3) signals based on the measured intensity values for the actuators of at least some of the rolls involved in the printing and inking process. Rotary printing machine according to the preceding claim,
characterized in that
with the camera different spectral ranges of the reflected light can be received. Rotary printing machine according to the preceding claim,
characterized by
in that the actuators are equipped with a separate adjusting device for producing the parallelism of rollers (3, 7, 8) involved in the printing process.

Images