FI121610B - A method for diagnosing the printing process - Google Patents

Description

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Background of the Invention

The invention relates to a method for diagnosing a printing process. In particular, the invention relates to the detection of a track maintenance need, wherein the track maintenance need is determined from the transverse profile of the machine direction tension of the web.

The invention also relates to a method of aligning a web of a web printing process in which at least one pressure sensitive sensor is mounted on or below the surface of the roll in at least one roll. Preferably, said pressure sensitive sensor measures the position of the edge of the web, preferably at each end independently.

The invention also relates to a computer program, in which data obtained from the method according to the invention are input and which controls the automatic maintenance and / or adjustment of the printing process 15.

There is no known method for a printing press to measure, for example, the dirt of a printing press roll or track, and to determine the need for cleaning and maintenance due to the dirt. Nor is it possible to measure track flutter.

Offset printing is the most widely used printing method today.

o 20 In offset printing technology, the heavy and non-heavy surface are at the same level, so that ^ can also be referred to as the flat printing method. The printing element (printing plate) is a flat surface and does not distinguish clearly between raised points c (j) (embossing method) or recesses (gravure printing method).

| The flat weight method is based on the ratio of fat to water, i.e.

^ 25 that they reject each other, o δ 00 o o

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The offset printing process is based on the fact that fat (color) and water repel each other. The surface of the printing plate is exposed in the plate printer such that the areas to be printed become greasy, but water-resistant. Non-printed areas favor water but repel oily color. Because the ink is 5 greasy, it only adheres to the color receiving sites.

In an offset printing process, the image to be printed does not move directly from the printing plate to the paper, but first inversely to the surface of the rubber cylinder and then to the paper. This also gives rise to the term 'offset', because in this printing technique 10, the blank (printing plate) to be printed never touches the printing medium (paper) directly, but from the printing plate, the blank is transferred to the rubber fabric of the printing unit. Paper is too hard and would quickly break the surface of the platen.

15 Printing Event In an offset printing process, the wetting rollers dampen the surface of the printing plate and at the same time the color rolls apply color to the printing plate, whereby the wetting water adheres to non-printing surfaces and printing ink areas. The ink then moves from the printing plate to the rubber cylinder and the paper passes between the rubber cylinder and the counter cylinder, whereby the ink is transferred to the printing paper.

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Offset printing can be done on rotary printing or sheet printing. Rotary printing machines use continuous paper from the roll of paper between printing rolls as printing paper, which is cut into side sheets only at the end of printing 0. Rotary printing is a printing method faster than sheet printing, which is why it is used when printing volumes are larger.

i C \ l cm Gravure printing is a printing technique using gravure printing.

c In gravure printing, the weight of the printing surface is below the unpressurized surface Q_ ^. The ink is transferred to the printing material from the recesses of the printing surface, o 30 where the method is named. In offset printing, as in oo §, offset plates are not used as printing surfaces to be mounted around the cylinder, but instead

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The copper-plated cylinders are drilled each time with the engraving diamond. In addition to high printing speed and accurate printing quality, gravure printing has the advantage that relatively inexpensive mechanical supercalendered paper can be used.

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Also gravure printing machines are generally web printing machines (i.e. rotary printing machines), i.e. machines whose printing material comes from a roll. In the printing process, the gravure printing cylinder is first colored with liquid ink, whereby the screen cup on the surface of the cylinder is filled. Immediately after coloring, a thin steel scraper, 10, or blade, removes excess color from the base areas between the raster cups. The material to be printed passes between the press roll and the gravure cylinder, whereby the ink is transferred from the raster cups to the material being printed with a high compression force. After printing, the printing material passes through a dryer which evaporates the solvent from the ink and dries the ink.

15 Traditionally, the operator rotates the printing press and monitors the behavior of the web. If there is a problem in some area, then some of the printing press will be left alone in the automation system and new problems may arise at unattended process points. No solution based on measurements is known in the prior art. So far, operators have made visual observations.

20 The track position sensors currently known and used in the printing press environment are based on machine vision. The disadvantages of these are track distortions due to contamination of the machine vision. In this case, the adjustment system ^ incorrectly adjusts the alignment of the track, which causes color alignment problems.

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cv 25 Brief Description of the Invention

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It is an object of the invention to solve the above problems. The object of the invention is achieved by the method of independent claims 1 and 8.

Preferred embodiments of the invention are set forth in the dependent claims.

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Preferably, the invention employs measuring methods of the type described in WO 2006/075055, WO 2006/075056 and Fl 113466 B (METSO PAPER, INC.).

To measure the position of the paper web edge, as well as the tension profile and profile differences between certain process steps, can be measured using iRoll technology (METSO PAPER, INC.) Or similar techniques. Preferably, but not necessarily, the invention uses a piezo-film. An EMF film, which is an electrically permanently charged cellular plastic film that functions in the same way as a piezoelectric sensor, can also be used. The voltage signal produced by the EMF film depends on the pressure change across the 10 elements so that each element of the element produces an equal change in output voltage as the pressure changes. Thus, the short-term voltage measured by the high-impedance amplifier is integral to the entire sensor pressure. The sensor acts as a dynamic sensor, it does not give a constant result in long-term compression, but the DC component 15 acting over the sensor changes as a result of leakage currents. Because of this, the sensor will only work when it experiences pressure changes. The solution of the invention can also be implemented with another sensor, for example a resistive pressure sensitive film, a piezoelectric PVDF film (polyvinylidene fluoride film) or a PLL film (piezo-pyroluminescent film).

Preferably, the pressure sensor used to measure the tension profile used in the method of the invention is either a movable film surface pressure sensor mounted on a roll surface or a 0 fixed roll containing a membrane pressure sensor mounted at some point in the printing process.

δ cv cv The web tension is measured in the iRoll measurement in the machine direction, that is, in the longitudinal direction of the web cv 25. If the transducer is mounted transversely, 1 measurement result is obtained over the entire web width. Hereby a transverse profile of the longitudinal tension of the web is obtained. In practice, the track tension 2 is never completely uniform over the entire track width, o 00 o o cv 5

Diagnostic condition of a printing press based on a pressure sensitive sensor, preferably a film, is based on the sensitivity of the film to detect variations. In the measurement program, these appear in the form of vibrations at a given frequency or distortion of the shape of the tension profiles from a prior known or learned basic profile.

The method according to the invention can be used as a diagnostic tool for the purity and maintenance of a printing press. As the roller contaminates, the roller diameter changes, resulting in an abnormal shape of the tension profile of the web. This shape may, for example, take the form of a systematic skew in the profile. Measurement based on a pressure sensitive membrane is also sensitive enough to detect fluttering on the track or deterioration of the roller bearings. Resting may be due to low track tension or excitation from the frame through the roll (s).

In the method according to the invention, one or more iRoll rolls or rolls of a similar technology are mounted on the printing press. The signal from the roller can be monitored by long-term data acquisition. When the roll is clean, a certain "normal" profile, the basic profile, is obtained from the paper. When the roll is dirty, a distorted profile is obtained which does not correlate with changes in the paper profile. Preferably, the long-term change or the difference between the long-term trend after the unwinding 20 measurement or the measurement data from the paper mill and the weight unit after the roll is compared. These profile differences are calculated using two or more measurements. Permissible deviation limits are set for the differential signal, which indicates the need for cleaning of the printing press rolls or other maintenance needs.

cv 25 i cv By using the method of the invention, the printing machine is easier to clean, and there is no need for unnecessary cleaning or maintenance on the track

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procedures, but are performed as needed based on the diagnostic signal °.

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In another preferred embodiment of the invention, a pressure-sensitive transducer, preferably a weight-sensitive diaphragm, is mounted on the tension measuring roller or one or more other rolls to provide information on where the edge of the web is located. This information can be used for positioning the web, as the method of the invention meets the requirements for printing inks by the printing press. In a preferred embodiment, edge positioning is performed based on tension profile measurement.

In the method of the invention, a pressure sensitive sensor is mounted on one or more rolls of the printing press. One or more sensors shall be mounted on the roll so that the position of the edge of the track is independently obtained at both ends. This information is utilized to adjust the web's lateral alignment and to optimize ink alignment. Preferably, but not necessarily, the invention employs the measurement methods disclosed in F113466B (METSO PAPER, INC.).

One or more pieces of pressure-sensitive film are mounted on the roll or under the coating to accurately measure the position of the track edge. These rolls are present in the printing press in at least one, preferably several, or even in number according to the number of weight units 20.

Compared to the state of the art, i.e. machine vision, the technique of the invention, like machine vision, does not get dirty or disturbed by paper dust floating in the air or similar impurities. In addition, web edge detection can be combined, for example, with tension profile measurements with the same cv 25 automation system, whereby adjustment can be easily automated.

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w Using a weight-sensitive sensor to align the edge of the paper web provides good results

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£ the exact edge alignment values required for the ink alignment section to succeed in reducing the amount of waste material.

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The prior art measuring and control system, which significantly improves the state of the art, provides new opportunities for applying pressure sensitive sensor technology in a printing press environment.

BRIEF DESCRIPTION OF THE DRAWINGS FIGURE 1 shows a tension profile of a unit of weight from a dirty roll before and after a unit of weight.

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for determining the need for maintenance of a printing process wherein the need for servicing of a track is determined from a transverse profile of the machine direction tension of the web. Preferably, the measured transverse tension profile is compared to a known base tension profile, the deviation and / or profile difference between the base tension profile and the measured tension profile is analyzed, and the weighting process is adjusted based on the tension profile deviation and or profile difference.

Preferably, the base tension profile according to the invention is a tension profile obtained from a paper mill on a roll of paper, a base tension profile based on data previously collected from the same roll, or a tension profile obtained from another process point in the printing process, such as

According to one embodiment of the invention, the profile difference is 0 outside the deviation limits set for the maintenance need, δ ^ Preferably, the maintenance need can also be detected when the measured tension profile does not correlate with said basic tension profile, when there is vibration or

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learning about the basic profile.

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The maintenance need determined by the method of the invention is preferably roll cleaning, cylinder grinding, coating renewal and / or roll bearing repair.

The invention also relates to a method for aligning the web 5 of a web printing process in which at least one pressure sensitive sensor is mounted on or below the surface of the roll in at least one roll. Preferably, said pressure sensitive sensor measures the position of the edge of the web, preferably at each end independently.

On the basis of the information obtained by the method according to the invention, the lateral alignment of the web is preferably adjusted, whereby the alignment of the printing inks and / or the alignment of the sub-colors, folding and cutting can be advantageously optimized.

Figure 1 shows the tension profile before and after the printing unit with the roll covered with ink. Graph 1 illustrates the tension profile before the unit of weight, and graph 2 represents the tension profile graph after the unit of weight.

The invention also relates to a computer program into which data obtained from tension profile measurements and tension profile deviations and / or profile differences are fed to a program, whereby the program controls the adjustments and maintenance of the printing process.

It will be obvious to a person skilled in the art that as technology advances, the basic idea 20 of the invention can be implemented in many different ways. The invention and its embodiments are thus not limited to the examples described above, but may vary within the scope of the claims, δ ™ EXAMPLE 1

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A A fixed (JPY) iRoll roll was used to measure the tension profile of the printing process

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^ 25 before and after the unit of weight. Figure 1 shows a tension profile graph,

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£ with profile shape before and after the unit of weight, o δ 00 o o

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At the time of measuring the tension profiles, when the latter roll was covered with ink, the tension profiles differed as shown in Fig. 1. The skew of the stress profile was the opposite.

5 After cleaning this ink layer, which is up to 1mm thick, the tension profile after the printing unit turned in the same way as it did before the printing unit. Thus, after cleaning the roll, the removal of ink accumulated on the roll surface affected the roll diameter so much that the tension profile turned in a different direction. The ink accumulated on the roll surface clearly affects the tension profile. It can also be inferred from this that the cleanability of 10 printing presses is runnable.

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Claims (8)

1. A method for determining the service need in a printing process characterized in that the service requirements of the rollers are determined on the basis of the transverse profile of the gap measured in the machine direction based on the gap. A method according to claim 1, characterized by comparing the measured transverse voltage profile with a known basic voltage profile, analyzing the deviation and / or the difference in profile between the basic voltage profile and the measured voltage profile, and adjusting the printing process on the basis of the deviation and / or profile difference. 3. A method according to claim 2, characterized in that the base voltage profile 15 is a voltage profile for the paper roll taken by the paper mill, the basic voltage profile is based on data previously collected from the same roller, or the basic voltage profile is a voltage profile obtained from another printing process phase. , for example, a voltage profile obtained from measurement after the roll-off. 20 A method according to any of the preceding claims, characterized in that said profile difference is outside the deviation limits set for the service requirement. o cm 25 5. A method according to any of the preceding claims, characterized in that in Y said profile difference on the basis of which it is ascertained that the need for maintenance is dependent on the measured voltage profile, which does not correlate g with said basic voltage profile, the heating occurring on a certain fre frequency in the voltage profile and / or a skew in the shape of the voltage profile, δ δ which differs from the previously known or obtained basic profile. oo o o CM A method according to any of the preceding claims, characterized in that said service requirements are cleaning of the roller, grinding of the cylinder, removal of the coating and / or repair of the roller's bearings. 7. A method according to any of the preceding claims, characterized in that the sub-process and / or the adjustment of the printing process and / or the printing apparatus are carried out by hand or with an automation system. A computer program in which the information obtained by the method 10 according to claim 1 is entered and which controls the adjustment according to claim 7. o δ CVJ CM CM CM X CC CL O δ oo o o CM