EP3715125B1 - Machine stoppage - Google Patents

Description

The present invention deals with a method for controlling the color of a printing press after a machine standstill.

The invention lies in the technical field of offset printing.

When a printing press has come to a standstill, it often takes several sheets to restart the printing press before the production speed is reached again. During this time, the print color achieved changes despite the color settings remaining the same, since the amount of color in the inking unit and the color supply are not in a state of equilibrium for the changing printing speed.

In the case of inline color control, there is therefore usually a wait until the production speed has been reached and only then are measurements of the print color achieved again carried out for the color control. Even shortly after the production speed has been reached, however, a stable state is usually not reached, since the "wrong amount" of ink, i.e. usually too much, was printed during the run-up. This leads to a longer waiting time, especially when there are target value changes in the machine status, before the target value changes can be readjusted accordingly by the color control. During this time, sheets with a different print color are produced, which in most cases can be regarded as waste and thus impair the performance of the printing press. This becomes particularly problematic if new target color values result at the same time as or as a result of the machine downtime. In this case, the suspension of the inline color control until the production speed has been reached leads to a particularly high level of waste.

• Warten bis Fortdruckgeschindigkeit erreicht ist
• (Modellbasierte) Prädiktion des stabilen Druckbogens
• Farbregelung nach Prädiktion

The state of the art on this problem can be summarized in the following points:

• Wait until the print speed is reached
• (Model-based) prediction of the stable sheet
• Color control based on prediction

Disadvantage of this known procedure is the relatively long passive time after machine start-up. This usually applies to around 50 sheets. However, since the actual color control can only regulate the new target values after the production speed has been reached, especially with new color target values, the result is a significantly higher waste volume of 50 sheets + X.

This is from the prior art from the German patent application DE 10 2008 04 14 30 A1 a method for color control of an offset printing machine is known, in which, as part of the inline color control, the measured values of the respective printing colors determined by means of an image detection system are evaluated as implausible, the color control is suspended. The measured values for the individual ink zones of the inking units are determined and checked for plausibility. If this no longer agrees with the specified values, this is communicated to the user of the printing press and the color control for these color zones is suspended. If the user has then managed to correct the underlying error and the image acquisition system again delivers plausible measured values for the individual color zones, the color control is resumed. However, the method presented here is not designed with regard to the problems of color control after a machine downtime, and is therefore not set for the specific problems of color control after a machine downtime, which is associated with corresponding waste sheets. The desired reduction in waste after restarting a printing press after a machine standstill is therefore not possible with this method.

Furthermore, from the EP 0 228 347 A1 a method for ink application control in a printing machine is known, whereby to improve the color management control of an offset printing machine, color measuring fields provided on the printed sheet are evaluated colorimetrically by spectral measurement, with spectral remissions being used for matching the color or color coordinates being calculated therefrom and with corresponding target remissions or target color coordinates are compared, the resulting color distances being used to control the color control, and the spectral remissions being converted into filter color densities for the production run stabilization, and the color control being carried out conventionally on the basis of these color densities.

The object of the present invention is therefore to disclose an improved method for ink control in a printing press, which noticeably reduces waste in a printing press when it is started up after a machine standstill.

This problem is solved by a method according to claim 1, namely a method for controlling the color of a printing press using a computer, with the computer carrying out a first inline color control mode for color control, which regulates desired color target values, the first inline color control mode during a start of the printing press is subjected to a machine standstill and is only activated again after a desired production speed has been reached, with the computer executing a second, separate color control mode while the printing press is starting up until the desired production speed is reached, which achieves the desired color target values by controlling the ink quantity required for this in the relevant inking units realized, wherein the first inline color control mode implements a closed control loop, while the second color control mode represents an open control loop, the closed control loop of the first inline color control mode a Rü feedback in the form of a color measurement including evaluation of color measurement values by the computer to achieve the desired color target values, the color measurement is carried out using an inline camera system, which is installed after the last printing unit of the printing press, and the open control circuit of the second color control mode controls the for the required color quantity into the inking units without feedback in the form of a color measurement including evaluation of color measurement values by the computer.

The core of the method according to the invention is therefore to reduce the problem of the color control to be suspended until the normal production speed is reached and thus the production of waste by carrying out a substitute color control during this period, which, unlike the color control, is no longer based on a completely closed control circuit with incoming measured values that are evaluated, but directly introduces the ink quantities required for the desired ink target values into the relevant inking units. The result is that there is no closed control circuit and therefore no validation of the color control carried out in the individual printing units by checking by means of measurement obviously not as good as that of full closed loop color control. Nevertheless, with the method according to the invention, the desired desired color values are approached much more quickly than if no color regulation or color control is carried out at all during the time the printing press is being run up after the machine has been at a standstill. Therefore, with this approach, the amount of waste that accumulates during the start-up of the printing press can be noticeably reduced, and the task set according to the invention can thus be solved accordingly.

Advantageous and therefore preferred developments of the method result from the associated subclaims and from the description with the associated drawings.

A preferred further development of the method according to the invention is that the printing machine is an offset printing machine and the quantities of ink are transported into the inking unit directly via the ink zones of the inking units of the offset printing machine. The process is primarily intended for an offset printing press, with the transport of the required quantities of ink into the inking unit being implemented directly via the ink zones of the individual inking units. Alternatively, of course, it can also be used in an Anicolor machine without ink zones, even if the efficiency of the process is reduced.

According to the invention, it is provided that the first inline color control mode implements a closed control loop, while the second color control mode represents an open control loop. The inline color control has feedback in the form of measured values that are provided by a color measurement system that is inline in the printing press. A closed control loop is thus implemented via this feedback. Since this is not reasonably possible for the reasons already mentioned during the start-up of the printing press, this feedback is missing during the substitute color control during the period of the start-up of the printing press. This then represents an open control loop.

According to the invention, the closed control loop of the first inline color control mode has feedback in the form of a color measurement including evaluation of measured color values by the computer in order to achieve the desired target color values.

The feedback in the form of the color measurement already mentioned is evaluated by the computer, which implements the closed control circuit, and used to adjust the desired setpoint.

According to the invention, the color measurement is carried out using an inline camera system, which is installed after the last printing unit of the printing press. The Inline image acquisition system is realized by means of a camera system, which is attached after the last printing unit of the printing press. In most cases, inline image acquisition or camera systems are already present in many printing presses in order to carry out a corresponding image inspection for quality control of the printed products produced. Depending on the structure of the inline camera system, they are also ideal for using inline color measurement.

According to the invention, the open control loop of the second color control mode controls the amount of color required for the desired desired color values in the inking units without feedback in the form of a color measurement including evaluation of measured color values by the computer. In the method of color control according to the invention, which is used during the time the printing press is being started up after the machine has stopped, feedback in the form of color measurement has to be dispensed with. Here, an open control circuit is implemented by means of direct control of the relevant inking units to introduce the necessary ink quantities to achieve the desired ink target values. As already mentioned, this is less precise than a closed control loop with feedback in the form of measured values for the color measurement, but it is still significantly better than a completely deactivated color control, as is currently carried out in the prior art.

A further preferred development of the method according to the invention is that the computer checks whether new desired color values are available when the printing press is started after the machine has stopped and only in this case carries out the color control until the desired continuous printing speed is reached. The presence of new color target values after the machine downtime is on the one hand the main application for the method according to the invention, since in the event that no new color target values are available, the extent of waste produced is lower and thus also the Reduced need for dedicated color control during press start-up. The use of the method according to the invention after a machine standstill is therefore mainly necessary and must be carried out if new desired color values are available. The computer should therefore check this and only carry out the color control according to the invention if new desired color values are available.

A further preferred development of the method according to the invention is that when the printing press is started after the standstill, the computer checks the plausibility of the last available measured values of the color measurement in addition to checking for new color target values and only carries out the color control until the desired production speed is reached if the measured values are valid . In addition to checking whether new color target values are available for the print job to be carried out, it can also make sense to validate the last available measured values, which were generated via the color control with a closed control loop up to the machine standstill, and only if plausible measured values are available perform the inventive method with the color control. The reason for this is that when the method according to the invention is carried out without appropriate feedback, one has to rely on the fact that the color control method carried out before the machine stopped was still working within the target parameters. A quasi-blind setting of new target color values in the individual color values without feedback to a color control system that is completely out of step would not be recommended.

A further preferred development of the method according to the invention is that the computer, during the start of the printing press after a machine standstill until the desired production speed is reached, also implements desired setpoint values for humidity and/or temperature control by switching off the respective inline control by direct control. The method according to the invention can be used not only for color control, but also for any humidity and temperature controls in the printing press used. Therefore, after a machine standstill, the respective humidity control and / or Temperature control can be implemented by direct control until the desired production speed is reached. Of course, this presupposes that the actual control loops for humidity and/or temperature control cannot be used during the start of the printing press either. Otherwise, it is of course more obvious to fall back on their closed control loops with appropriate feedback.

The invention as such and constructively and/or functionally advantageous developments of the invention are described in more detail below with reference to the associated drawings using at least one preferred exemplary embodiment. In the drawings, corresponding elements are given the same reference numbers.

Figur 1:

ein Beispiel eines verwendeten Bilderfassungssystems in einer Offset-Druckmaschine

Figur 2:

den schematischen Ablauf des Verfahrens

The drawings show:

Figure 1:

an example of an image acquisition system used in an offset printing machine

Figure 2:

the schematic sequence of the procedure

figure 1 shows an example of an image acquisition system 2, which is used for color measurement of the color control of an offset printing press. It consists of at least one image sensor 5, usually in the form of a camera system 5, which is integrated into the offset printing machine 4. The at least one camera 5 records the print images generated by the printing machine 4 and sends the data to a computer 3, 6 for evaluation. This computer 3, 6 can be its own separate computer 6, for example one or more specialized image processing computers 6, or it can be identical to the control computer 3 of the offset printing press 4. At least the control computer 3 of the offset printing machine 4 has a display 7 on which the results of the image inspection are shown to the user 1.

figure 2 shows the process flow. The inline color control in the form of a first color control mode 8 runs by default in normal operation Offset printing machine 4. If the machine stops, this color control 8 is interrupted by the control computer 3 of the offset printing machine 4. The computer 3 then checks whether new desired color values 12 are present together with the machine downtime. If this is the case, the computer 3 initiates a separate color control 9 in the form of a second color control mode 9 by tracking the quantities of color required for this in the relevant inking units. If no new desired color values 12 are available, as in the prior art, there is a wait until the continuous printing speed 10 is reached again. The color values set in the inking units before the actual color control 8 is interrupted are usually sufficient to avoid excessive waste until the color control 8 is restarted. In principle, it is of course also possible to use the second color control mode 9 without any new desired color values 12 being present. Here it depends on the individual case. Since there is no control with feedback 8 by measured color values 11 in the second color control mode 9, the new desired color values 12 are of course not achieved immediately by means of the second color control mode 9. However, as soon as the actual color control 8 starts again under computer control after the continuous printing speed 10 of the offset printing press 4 has been reached, it can adjust the new color target values 12 much more quickly than would be possible in the prior art without a second color control mode 9 . This reduces the amount of waste produced considerably.

In a further preferred embodiment variant, the computer 3 also checks the validity of the last stored color measurement values 11 of the actual color regulation 8 in addition to the presence of new desired color values 12 . Both values 11, 12 are taken into account accordingly. The last measured values 11 stored indicate how well the desired color target values 12 were adjusted before the machine stopped, or whether the color control method 8 was still working within the target parameters. The second color control mode 9 is carried out accordingly only if they are valid and new desired color values 12 are present. The advantage of this variant is that both variables 11, 12 are taken into account. In addition, the statics are tracked immediately, the dynamics are carried out via a time-dependent control. Since the status of the dynamics can only be estimated with difficulty, only the dynamics of the setpoint change are taken into account Restarting the offset printing press 4 is taken into account. This prevents the color control 8 from overshooting.

The same approach of direct control of the relevant actuators in the offset printing press 4 until the desired target values 12 are reached can also be implemented for humidity and/or temperature control if the respective inline control is also switched off there until the respective production speed 10 is reached occurs.

reference list

1

user

2

image capture system

3

control computer

4

printing press

5

Camera system / image sensor

6

image processing computer

7

screen

8th

first (inline) color control mode

9

second color control mode

10

production speed

11

color readings

12

color target values

Claims (5)

1. Method of controlling colours in a printing press (4) by means of a computer (3), wherein the computer (3) implements a first inline colour control mode (8) for colour control purposes to attain desired target colour values (12),

   wherein the first inline colour control mode (8) is stopped while the printing press (4) is started after a standstill of the machine and not reactivated until a desired printing speed (10) has been reached,

   wherein the computer (3) implements a second separate colour control mode (9) during the start of the printing press (4) until the desired printing speed (10) is reached, said second ink control mode (9) attaining the desired target colour values (12) by introducing an amount of ink required for this purpose to the inking units in question,

   wherein the first inline colour control mode (8) implements a closed control loop whereas the second colour control mode (9) represents an open control loop,

   said closed control loop of the first inline colour control mode (8) including feedback in the form of colour measurements and analysis of measured colour values (11) by the computer (3) to attain the desired target colour values (12),

   wherein the colour measurements are taken by means of an inline camera system (5) disposed downstream of the last printing unit of the printing press (4), and wherein the open control loop of the second colour control mode (9) implements the introduction of the amount of ink required for the desired target colour values (12) into the inking units without feedback in the form of colour measurements and analysis of measured colour values (11) by the computer (3).
2. Method according to claim 1,
   characterized
   in that the printing press (4) is an offset printing press (4) and in that the transport of the amounts of ink into the inking unit is implemented directly via the ink keys of the inking units of the offset printing press (4).
3. Method according to any one of the preceding claims,
   characterized
   in that when the printing press (4) is started after the machine standstill the computer (3) checks whether there are new target colour values (12) and only implements the second colour control mode (9) until the desired printing speed (10) is reached if this is the case.
4. Method according to any one of the preceding claims,
   characterized
   in that when the printing machine (4) is started after the standstill, in addition to checking for new colour target values (12), the computer (3) checks the last available measured colour values (11) of the colour measurement for plausibility and only implements the second ink control mode (9) until the desired printing speed (10) is reached if the measured colour values (11) are valid.
5. Method according to any one of the preceding claims,
   characterized
   in that during the start of the printing machine (4) after a machine standstill up until the desired printing speed is reached, the computer (3) implements desired target values for dampening solution control and temperature control by means of direct actuation while switching off the respective inline control.

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