EP1839854A1 - Method and device for the optimal position adjustment in a rotary flexographic printing machine comprising several printing groups - Google Patents

Abstract

The method involves calculating a relative position of a thrust bearing (1) and a printing cylinder (2) from diameter values, and imprinting of printing marks (5-8) with different and well known nominal tonal values. Adjustment of the relative position between the thrust bearing and the printing cylinder and between the printing cylinder and an impression cylinder (3) is determined. The adjustment of relative position between the thrust bearing and the printing cylinder is realized to determine an adjustment value corresponding to the impression cylinder. An independent claim is also included for a device for optimally adjustment of a supply in a rotary flexographic printing machine.

Description

The invention relates to a method and a device for optimum adjustment of the provision in a multiple printing units having rotary flexographic printing machine according to claim 1 or claim 9.

The job-oriented setting of the roll group in a flexographic printing press, which at least the relative positioning of the plate cylinder to the inking roller (also called anilox roller / Aniloxwalze) whose task is to color the plate with ink and the positioning of the plate cylinder to the printing cylinder, which carries the substrate comprises , is associated with considerable consumption of material and time. Usually, this is done today so that calculated from the known geometric dimensions and positions of the inking roller, the forme cylinder, the material and the printing cylinder, a relative positioning of all participating cylinders to each other and this is then set. If a particular pressure between the two pairings is used as the basis for the calculation, this results in a setting in which, as a result of this pressing, color is also transported in both pairings and thus pressure is created. Such motorized presetting systems can be found today in all modern machines.

However, it is unavoidable that specific production tolerances of the elements involved, different elastic properties, in particular the structure of the printing plate, variations in material thickness in the printing material, ink transfer properties, etc., have an effect on the print result achieved.

Therefore, there is still the task with each print job to set the machine so that a quality-appropriate Pressure arises and in particular the printing form is not subjected to unnecessary wear, which reduces the life of the mold and their replacement represents a significant cost factor.

If, therefore, a first adjustment is made for a print job in accordance with the geometric data, then this requires an additional correction in order to be able to produce optimum conditions.

This correction is usually still done by hand by the printer, for example, the pressure initially reduced until the pressure is no longer takes place and then again delivered so far - the pressure is increased - until a pressure just can be reached again. He observes the result of his actions visually directly on the printing line. This procedure is performed successively for both cylinder pairings and each printing unit on the running machine. Optionally, the printer also uses a video link observing device which takes an image of the printed result and reproduces it on a screen.

In the EP 1 249 346 a method and a device is described, which transmit the procedure shown here directly into an automatic process and thus saves the individual Verstellhandlungen by being performed by engines.

Although this described method is an improvement, it still has a number of disadvantages. There is done analogously to the procedure of the printer by means of a known camera-based inspection system in an interactive manner a sequence of adjustments of the pressure in the cylinder pairings and observed in their effect on the printed image respectively. This is always checked in at least two consecutive pictures, if the Print shows fewer or more elements than the previous image. Depending on the result, it is then decided whether the pressure is increased or decreased. If no change occurs, the goal is reached and concluded on a completeness of the pressure. From the completeness of the pressure is then closed in a manner not described in detail on the appropriate pressure in the respective pairings. The disadvantage of this is, first, that this procedure must be performed individually and sequentially for each color and thus a considerable amount of material is consumed despite the automation of the processes, secondly in the parked or non-printing printing units, the ink on the anilox roll or the forme cylinder can dry and leads to an additional washing effort. Thirdly, this method can not take into account how a reproduction of tonal values in the image really takes place, so that as a rule this must be left to the printer in further subsequent setting steps. Not to be neglected is the high capital expenditure, which represents the use of a full-surface inspection system for image acquisition and evaluation.

The invention is therefore an object of the invention to provide a method and apparatus for optimal adjustment of the provision in a plurality of printing units having rotary flexographic printing machine, which make it possible with relatively simple technical means and little effort a reduction of waste and a requirement of the printing process to achieve better adapted control or control results.

The solution of this object is achieved by the features of claim 1 and claim 9.

The dependent claims have advantageous developments of the method and the device according to the invention to the content.

An example of the device according to the invention for explaining the procedure according to the invention is explained in more detail below with reference to the drawing.

If, in addition to the printed image constituting the actual printed product, additional marks are placed, these can be arranged in such a way that marks printed by a printing unit find a space spatially separated from the marks printed from another printing group (for example, side by side or one behind the other or in a block ) and thus in one print marks from all printing units are included at the same time. This eliminates the otherwise necessary for distinguishing the pressure in the just not needed printing units and the color does not dry.

For color-accurate image reproduction, it is of considerable importance that the reproduction of tone values in the individual colors takes place correctly, especially in autotypical four-color printing. In particular, this is also determined to a considerable extent by the pressing, so that it is advantageous, instead of the simple yes / no criterion of completeness of a print, to use the criterion of a correct tonal value reproduced by the printing characteristic (10, Figure 1 - Tonwert im Pressure FD _G depending on the nominal value FD _N on the mold). If, for each color, a plurality of stamps, each with a different tonal value known in its shape on the mold, are printed, it can be concluded by measuring the dot increments on the printed stamps on the properties of the tonal reproduction in the print.

This approach also avoids the dilemma of having to create or record a master who represents them for an assessment of completeness. In a printing company, a predetermined dot gain for the printing process is known and a goal for a quality-appropriate printing. According to the invention, therefore, the target tonal characteristic and the nominal solid density are used as a criterion for the selection of a suitable pressure.

For this purpose, for example, in four process steps, starting from the calculated original setting of the pressure, this between the anilox roller 1 and forme cylinder 2 and / or forme cylinder 2 and counter-pressure cylinder 3 is varied and the pressure characteristic is determined in each case. It is then selected that pressure in which the pressure characteristic of the target characteristic comes closest. For this it is not necessary to reduce the pressure to such an extent that the pressure in the printing unit is suspended. Rather, it is sufficient to have achieved a minimum pressure at which the characteristic comes close to the nominal tonal characteristic. Thus, for example, the printing of 3 marks with a coverage of 30%, 50% and 75% provides sufficiently good information on the characteristic curve that allows the selection of the correct pressing. In the case of a plurality of tonal characteristic curves, the adjustment of the rollers is preferably carried out on the basis of the characteristic curves which come closest to the desired tonal characteristic 17. In a case where two characteristics are located approximately equidistant or close to the target Tonwertkennlie 17, a setting is made according to an average value. This further has the advantage that one does not have to add an empirical amount of pressure, starting from the exposure of the pressure (or a no longer occurring increase in elements), but can actually select a value that has already been realized.

In addition to the described measurements on halftone marker fields, a full-tone field is also printed. This solid field then makes it possible to make a statement about the layer thickness which has been applied to the printed substrate by the coloring unit from a relation between pigment concentration per area and optical density conventionally used in densitometry and, in particular, whether the optical density provided for the printed product during printing is available. Such specifications are known, for example, by in-house standards or else generally accepted standards or predetermined as predetermined target values. At the same time it can be concluded from a sufficient homogeneity of the ink application on a solid surface on the correct pressure pressure between the cylinder pairs. For example, if the pressure is too high, so-called squeezing edges are produced; if the pressure is too low, the pressure is "flaky".

The determination of the correct pressure is now carried out so that, starting from the computationally determined pressure, two to three further pressure settings are predetermined, for example X + 50 μm, X-50 μm and X-100 μm, in which the pressure characteristic is determined on one print copy or is measured on several printed copies for the purpose of averaging. Already in the production of a printing form, a certain printing characteristic, namely the typical of the machine with which a product is to be printed, has been taken into account as known. Now, this expected characteristic curve is compared with the recorded characteristic curves and the pressure between the impression cylinder and the pressure cylinder, which comes closest to this characteristic, is set. Thereafter, the pressure between cliché and anilox roller is varied in the same way and the pressure is used, in which the characteristic corresponds to the specifications and further the full tone brand with its properties comes closest to the specifications.

To measure the color density on the solid tone or halftone fields, methods and devices are used, as used, for example, in known in-line density measuring devices in offset printing. Such measuring heads consist, for example, of a reflectance measuring head, which has a geometry 0 ° / 45 °, 45 ° / 0 °, between the optical axis of the illumination and that of a measured value recording device, is equipped with a plurality of optical filters which are selected such that all the measured colors have the highest possible influence on the colors used or correspond to customary standards and have a device for synchronizing the moment of the measurement with the printed product. Equally, for example, the optical principle can be reversed to the effect that the illumination takes place in selected spectral ranges and the detection then takes place without a color filter or else a combination of both.

An example of a possible procedure according to the invention is described below:

A first pressure within a pair of cylinders is set, for example, the computationally determined pressure +50 microns.

The measured color density values described above are now registered by the full-tone and half-tone measurement fields, and from this the print characteristic is constructed. Thereafter, the pressure in a cylinder pairing is reduced by a fixed value and again generates a pressure curve for the new pressing. In the next steps, this procedure is repeated, so that a set of pressure characteristics is produced, one characteristic belonging to one pressing setting at a time. In addition, that characteristic is inserted, which presupposes in the production of the printing form as a characteristic curve for the printing press has been. Now, a change in the second press pairing is performed, which is traversed according to a same pattern. At the same time, the full-tone field is always measured, for which a nominal solid density may also be assumed to be known.

At the end, the pairing setting is selected, which comes closest to both the required setpoint density parameters and the required pressure curve.

None of the aforementioned procedures requires a complete shutdown of the pressure or the absence of self-printing elements.

When measured using a densitometric probe, it provides both color density and optical area coverage values, which are preferably calculated using the well-known Morey-Davis equation. A measuring head can detect several consecutive mark fields even with a pass under the sensor, so that the number of copies required for the measurement is further reduced.

Instead of the stepwise change in the pressure, a further advantageous embodiment of the invention is that the adjustment of the pressure between the cylinder pairings takes place continuously between two defined limits, and from the knowledge of the time course and the path length between the press contact and the position of the sensor associated with each measurement the correct pressure.

Alternatively, the acquisition of color density and optical area coverage can also be done by a camera providing illumination geometry similar to the described 0/45 and 45/0 arrangements, respectively. On In this way, it is equally possible to detect several measuring fields within one format and it is not necessary to install a separate measuring device in the machine. Although normal RGB cameras have no filter suitable for measuring a color density, this can be exploited in favor of a rapid mode of operation, as described, for example, by Künzli, Noser, Loger and Murad (EMPA, St. Gallen 1993).

In order to adapt to the conditions in a machine or the printing form, it may be useful to arrange the corresponding measuring fields over the width of the print several times. It can thus light deviations from the parallelism or the flatness of the cylinders / forms involved registered and compensated by mediation.

The single FIGURE of the drawing shows a schematically greatly simplified representation of a device according to the invention for optimum adjustment of the provision in a plurality of printing units 9 having rotary flexographic printing machine, wherein only a printing unit 9 is shown schematically very simplified representatively for all printing units.

The printing unit 9 has an anilox roller 1 with a diameter D ₁ . Further, the printing unit 9 has a forme cylinder 2 with a diameter D ₂ , which cooperates with the anilox roller 1 and with respect to this over a displacement V _{1 is} adjustable in order to adjust the pressure between the anilox roller 1 and the forme cylinder 2 can.

Furthermore, the printing unit 9 has a counter-pressure cylinder 3 with a diameter D ₃ , which interacts with the forme cylinder 2 for guiding a material web 4 to be printed. The relative position between the forme cylinder 2 and the impression cylinder 3 can be adjusted along a displacement V ₂ .

The device according to the invention also has a control unit 16, which is provided with a computing unit 15. Further, an adjusting unit 13 for adjusting the relative position between the anilox roller 1 and the forme cylinder 2 and the forme cylinder 2 and the impression cylinder 3 is provided. The control unit 13 is in signal communication with the control unit 16 for exchanging position and status information.

The device furthermore has a color-selective sensor 14, which is in signal communication with the arithmetic unit 15 and the control unit 16 for exchanging measured data and control information for measuring value acquisition.

As the figure further clarifies, a series of print marks 5, 6, 7 and 8 is printed on the material web 4 by the printing unit 9 in the example case. Here, the mark 8 represents a full tone mark.

The color-selective sensor 14, which is always arranged in the web running direction L behind the printing units 9 to be adjusted by the method according to the invention, detects the print marks 5 to 8 for a plurality of Verstellschritten between the anilox roller 1 and the forme cylinder 2 according to the predetermined adjustment V ₁ and the forme cylinder 2 and the impression cylinder 2 corresponding to the adjustment V ₂ . The measurement result is forwarded to the arithmetic unit 15 in each case.

In this, actual tone values FD _{G are} calculated from the reflectance values resulting from the color-selective detection for each of the print marks 5 to 8. Furthermore, a pressure characteristic curve 10 is generated from the calculated actual tone values FD _G , which the calculated actual tone values FD _G over known Nominal tonal values FD _N of print marks 5 to 8 (diagram A).

Further, pressure characteristic curves 11 are created, wherein each set in the recording of a characteristic relative position change between the anilox roller 1 and the forme cylinder 2 and the forme cylinder 2 and the impression cylinder 3 represents the share parameters.

In the diagram also specified for the printing process and taken into account in the printing plate manufacturing target Tonwerkkennlinie 17 is entered and this is compared in the arithmetic unit 15 with the determined pressure characteristic family 11 (diagram B).

In a further method step, the detected solid densities D _{G of} the full-tone mark 8 are evaluated as a function of the relative positions of the cylinders, which results in further characteristics DG _1/2 DG _2/3 , as can be seen from the figure (diagram C).

The measured or calculated full tone densities D _{G of} the full tone mark 8 are compared with a nominal solid density D _N , which is predetermined for the printing process and is taken into account in the printing plate production.

Finally, the adjustment of the relative position between the anilox roller 1 and the forme cylinder 2 and the forme cylinder 2 and the impression cylinder 3 is determined and adjusted by the actuator 13, in which the Tonwerk characteristic of the desired Tonwertkennlinie 17 and the Volltondichte the desired Volltondichte D _N comes closest.

Although this does not appear in detail from the schematically simplified representation of the figures, it is According to the invention, it is possible for the color-selective sensor 14 to be arranged on a traverse above the material web 4 so that it can be moved by a motor to the respective measuring position.

Furthermore, it is possible that one color-selective sensor 14 is arranged on the left and the right side of the material web 4.

As possible training variants for the color-selective sensor 14, a per se known color density measuring device or a video camera are conceivable.

Furthermore, as a further embodiment of the color-selective sensor 14, a sensor line arranged in the web running direction can be used, which consists of elements arranged one after the other with different spectral sensitivity.

As an alternative, a sensor line arranged in the web running direction can be used as a color-selective sensor, in which a filter with a different spectral characteristic is connected upstream in successive measurements.

definitions Shade:

Measure (in%) for the proportion of a property within a surface that has only the two properties "0" and "1" (in the present case, the properties are usually properties of an optical nature).

Nenntonwert:

The nominal tone value is the tone value assigned to a surface as a property by definition.

Dot gain:

As the dot gain caused by a process step, the difference of the tone value after the process is referred to the tone value before the process. In the present case, this designates the difference between the tone value after the print and the nominal tone value 12.

full tone:

Brand with 100% area coverage (reference marks).

Color selective detection:

Remission measurement, which determines how much light is returned from a mark in a given spectral range.

Target tone:

The tonal value that a surface should have as a result of a machining process.

Tonwertkennlinie:

A curve in which the nominal tone values are plotted on one axis of an x, y coordinate system and those assigned to the same surface on the other axis. For example, one typical approach to printing is to plot the nominal tone values on one side and actual tones after passing through a machining process on the other axis.

Target Tonwertkennlinie:

A tone characteristic that plots nominal tone levels on one axis and nominal pitches on the other.

Target solid density:

A given full-tone density value that has to be achieved.

LIST OF REFERENCE NUMBERS

1

anilox roller

2

form cylinder

3

Impression cylinder

4

Web / print web

5-8

print marks

9

printing unit

10

Pressure characteristic curve

11

Pressure characteristic curves

12

Tone curve without dot gain

17

Target Tonwerkennlinie

V ₁

Adjustment between 1 and 2

V ₂

Adjustment between 2 and 3

FD _G

Actual tone

FD _N

Nominal tone

D _N

Target solid density

D _G

Measured or calculated solid density

Claims (15)

Method for optimal adjustment of the provision in a multiple printing units (9) having rotary flexographic printing machine by adjusting the relative positions between an anilox roller (1) and a forme cylinder (2) and the forme cylinder (2) and a printed material web (4), with the following method steps : Calculation of a relative position of anilox roller (1) and forme cylinder (2) from their known diameter values (D1, D2) and the relative position of forme cylinder (2) and the impression cylinder (3) leading the material web (4) from their known diameters (D2, D2) D3) and the thickness (d) and the type of material web (4), - Printing of print marks (5 to 8) with different and known nominal tonal values (FD _N ) at different locations of the web (4) by each printing unit (9), all printing units (9) simultaneously printing and each one of a Printing unit (9) printed print marks represents a full-tone mark (8), - Color-selective detection of the print marks (5 to 8) for a plurality of adjustment steps in a predetermined sequence and within predetermined adjustment ranges (V1, V2) of the pairing anilox roller (1) / forme cylinder (2) or forme cylinder (2) / impression cylinder (3) with material web (4), - calculating actual tone values (FD _G ) from reflectance values resulting from the color-selective detection for each of the print marks (5 to 8) and setting up a pressure characteristic curve (10) from the calculated actual tone values (FD _G ) which calculate the calculated actual values Levels (FD _G ) above the known nominal tonal values (FD _N ) of the print marks (5 to 8), - Creating pressure characteristic sets (11) from the calculated pressure characteristic curves (10), wherein each set during the recording of a characteristic relative position change of two cylinders (1, 2 or 2, 3) of a pairing represents the share parameter, Comparing the ascertained printing characteristic family (11) with a nominal tone value characteristic (17) predetermined for the printing process and taken into account in the printing plate production, Detecting or calculating full tone densities (D _G ) of the solid marks (8) and applying solid density curves (D _{G1 / 2,} D _{G2 / 3} ) over the set relative positions between anilox roller (1) and forme cylinder (2) or forme cylinder ( 2) and impression cylinder (3), Comparing the measured or calculated solid density (D _G ) of the full tone mark (8) with a desired solid density (D _N ), which is predetermined for the printing process and is taken into account in the printing plate production, - Determining the setting of the relative position between the anilox roller (1) and the forme cylinder (2) and the forme cylinder (2) and the impression cylinder (3), taking into account the desired Tonwertkennlinie (17) nearest Tonwertkennlinie (12), and where the solid density (D) is closest to the desired solid density (D _N ), - Carrying out the adjustment of the relative positions between the anilox roller (1) and the forme cylinder (2) or the forme cylinder (2) and the impression cylinder (3) in accordance with the set values thus determined. The method of claim 1, wherein in addition to the target Volltondichte (D _N ) nor the homogeneity or uniformity of the Volltonmarke (8) by measuring at different locations on the Volltonmarke (8) is detected on the Volltonmarke (8) and only the setting as is assessed in which the homogeneity does not fall below a certain degree of homogeneity. The method of claim 1 or 2, wherein for a customer order a job-specific desired Tonwertkennlinie (17) is used. The method according to claim 1, wherein the settings for the cylinder positioning are calculated by a computer unit (15) from a plurality of the desired tone value characteristic (17) at the next coming characteristic curves (10) and transmitted to an actuator (13). Method according to one of claims 1 to 4, wherein at several points of the material web (4) print marks are arranged and scanned. The method of claim 5, wherein the marks are located respectively at the left and right edges of the web (4) and are scanned there. Method according to Claim 6, wherein a parallel position in the respective cylinder pairing is set there by the values determined for the respective side of the material web (4) and transferred to the control unit (16). Method for optimally adjusting the provision in a rotary flexographic printing machine having a plurality of printing units (9) by adjusting the relative positions between an anilox roller (1) and a forme cylinder (2) a forme cylinder (2) and the forme cylinder (2) and a printed material web (4), with the following process steps: Calculation of a relative position of anilox roller (1) and forme cylinder (2) from their known diameter values (D1, D2) and the relative position of forme cylinder (2) and the impression cylinder (3) leading the material web (4) from their known diameters (D2, D2) D3) and the thickness (d) and the type of material web (4), - Printing of print marks (5 to 8) with different and known nominal tonal values (FD _N ) at different locations of the web (4) by each printing unit (9), all printing units (9) simultaneously printing and each one of a Printing unit (9) printed print marks represents a full-tone mark (8), - Color-selective detection of the print marks (5 to 8) for a plurality of adjustment steps in a predetermined sequence and within predetermined adjustment ranges (V1, V2) of the pairing anilox roller (1) / forme cylinder (2) or forme cylinder (2) / impression cylinder (3) with material web (4), - calculating actual tone values (FD _G ) from reflectance values resulting from the color-selective detection for each of the print marks (5 to 8) and setting up a pressure characteristic curve (10) from the calculated actual tone values (FD _G ) which calculate the calculated actual values Plots tone values (FD _G ) above the known nominal tone values (FD _N ) of the print marks (5 to 8), - Creating pressure characteristic sets (11) from the calculated pressure characteristic curves (10), wherein the respectively set when recording a characteristic relative position change of two Cylinders (1, 2 or 2, 3) of a pairing represents the share parameter, Comparing the ascertained printing characteristic family (11) with a nominal tone value characteristic (17) predetermined for the printing process and taken into account in the printing plate production, Detecting or calculating homogeneities of the solid ink marks (8) and applying corresponding characteristic curves over the adjusted relative positions of anilox roller (1) and forme cylinder (2) or forme cylinder (2) and impression cylinder (3), Comparing the measured or calculated homogeneities of the full tone mark (8) with a desired homogeneity, which is predetermined for the printing process and is taken into account in the printing plate production, - Determining the setting of the relative position between the anilox roller (1) and the forme cylinder (2) and the forme cylinder (2) and the impression cylinder (3), taking into account the desired Tonwertkennlinie (17) nearest Tonwertkennlinie (12), and in which the homogeneity of the desired homogeneity comes closest - Carrying out the adjustment of the relative positions between the anilox roller (1) and the forme cylinder (2) or the forme cylinder (2) and the impression cylinder (3) in accordance with the set values thus determined. Device for optimal adjustment of the provision in a multiple printing units (9) having rotary flexographic printing machine by adjusting the relative positions between an anilox roller (1) and a forme cylinder (2) and the forme cylinder (2) and one of a counter-pressure cylinder (3) guided to be printed Material web (4) with the following components: - With a control unit (16) having a computing unit (15), - With an adjusting unit (13) for adjusting the relative position between the anilox roller (1) and forme cylinder (2) and forme cylinder (2) and impression cylinder (3), which is in signal communication with the control unit (16) for the exchange of position and status information and - With a color-selective sensor (14), which communicates with the arithmetic unit (15) and the control unit (16) for the exchange of measurement data and control information for data acquisition in signal communication. Apparatus according to claim 9, wherein the color-selective sensor (14) is moved on a traverse under the control of the motor to the measuring position. Apparatus according to claim 9 or 10, wherein each color-selective sensor (14) is arranged on the left and the right side of the printing web. Device according to one of Claims 9 to 11, wherein a color density measuring device known per se is used as the color-selective sensor (14). Device according to one of Claims 9 to 11, wherein a video camera is used as color-selective sensor (14). Device according to one of claims 9 to 11, wherein as a color-selective sensor (14) arranged in the web running direction sensor line is used, which consists of successively arranged elements with different spectral sensitivity. Device according to one of claims 9 to 11, wherein as the color-selective sensor (14) arranged in the web running direction sensor line is used, which is preceded by a filter with different spectral characteristics in successive measurements.

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