Color monitor for printing presses

Abstract

Method for signaling the coloring state when the operating state changes in printing presses (1) with a control computer (5), comprising the following process steps: Specifying a target color density (DV) Soll ) for a print job and saving the setting in the control computer (5), calculating an actual color density (DV Ist ) based on the current state in operation of the printing press (1) by the control computer (5), comparing actual color density (DV Ist ) and target color density (DV) Soll ) in the control computer (5) and output of a first signal by the control computer (5) when the actual color density (DV Ist ) in a tolerance band stored in the control computer (5) around the target color density (DV) Soll ) is lying around.

Description

[0001] The present invention relates to a method for signaling the coloring state when the operating state changes in printing presses with a control computer.

[0002] In offset printing presses, changes to machine parameters such as printing speed, temperature, and humidity affect the ink application on the substrate and thus the print quality. Since the printed materials should correspond as closely as possible to the original artwork, these deviations must be compensated for. To ensure the printer knows when the printed materials are close enough to the original to be sold as prints, they must take so-called proof sheets from sheet-fed presses and measure them with a colorimeter. The colorimeter readings are then usually compared with the digital data of the original artwork, and any deviations are identified and corrected by adjusting the color control.However, this approach has the disadvantage that waste paper may be produced until the printing materials are measured using the colorimeter, which then cannot be sold.

[0003] In printing presses with short inking units, especially anilox inking units, the problem persists that there are no inking zones with inking zone sliders in the inking units to individually regulate the ink dosage in each printing unit. With anilox inking units, ink dosage can therefore be controlled almost exclusively via the printing speed and the temperature of the inking unit. While changes in printing speed can be made quickly, changes in temperature are slow, as temperature control is inherently a sluggish system. Furthermore, printing speed is usually unsuitable as a control parameter, since printers, especially for larger print runs, want to set the printing speed as high as possible to produce many prints in a short time.

[0004] A method for adjusting the transfer of printing ink using a short inking unit is described in German patent DE 10 2004 044 215 B4. This method involves temperature control via the outer surface of the anilox roller in the inking unit. This temperature control influences the viscosity and flow of the printing ink. The temperature is adjusted according to the printing speed, allowing the ink to be correctly adjusted to different printing speeds using the temperature control device. However, this process is very slow due to the inertness of the temperature control mechanism.

[0005] The use of color measuring devices to control print quality is known from patents US 7,884,926 B2, US 7,894,065 B2 and US 7,515,267 B2.

[0006] The object of the present invention is to provide a method which signals to the printer that the printing materials meet at least a certain predetermined quality standard and can be sold.

[0007] According to the invention, this problem is solved by claim 1. Advantageous embodiments of the invention can be found in the dependent claims and the drawings. The present invention is particularly suitable for use in offset printing presses with short inking units. In principle, however, it can also be used in all offset printing presses equipped with a control computer. In the method according to the invention, a corresponding target color density is specified to the control computer for a new print job based on the printing template and stored in the control computer. Furthermore, the control computer is able to calculate or at least estimate the current actual color density and thus the current coloration based on the current operating state of the printing press and by taking into account influencing factors such as printing speed, temperature, humidity, ink, and substrate.This calculated actual color density is then compared with the target color density stored in the control computer. The control computer then issues an initial signal if the calculated actual color density falls within a tolerance band around the target color density stored in the control computer. This tolerance band can, for example, encompass the barely permissible color deviations, ensuring that the printed materials are still marketable when this initial signal is issued. In this case, the printer does not need to measure the printed materials with a colorimeter to determine if the print quality is marketable. Instead, the printer can use the initial signal to determine when and if the printed materials are marketable. Furthermore, this initial signal can be continuously updated, keeping the printer constantly informed about the marketability of their printed materials.

[0008] In a first embodiment of the invention, a second signal is output by the control computer when the actual color density lies outside a tolerance band around the target color density. This second signal indicates to the printer that the printing materials are not saleable and must be disposed of as waste paper. Together with the first signal, the printer thus receives continuous information as to whether the printing materials are saleable or waste paper.

[0009] In a further embodiment of the invention, a third signal is output by the control computer when the actual color density matches the target color density. In this case, the color of the printing template and the substrate match exactly, and the best possible print quality is produced. For particularly high quality requirements and high-value print jobs, this exact match may be required by the customer; the printer can then directly verify this quality using the third signal.

[0010] Advantageously, the signals are transmitted to a display device, and each output signal is assigned a different representation, particularly a display color, on the display device. In this case, the three signals are displayed on the screen of the printing press control, for example, in different colors such as green for best print quality, orange for marketable print quality, and red for waste paper. This display is continuously updated, allowing the printer to visually determine the current print quality at any given time.

[0011] Advantageously, the system allows different tolerance bands to be selected via the display device and entered using an operating device, particularly a keyboard. In this case, the printer can define the quality limits for acceptable product quality based on the print jobs and customer requirements. A printing company that exclusively prints elaborate packaging that must meet high quality standards can set lower tolerance limits than, for example, printing companies that exclusively produce advertising flyers, where even print materials with larger color deviations can still be sold. The tolerance bands can be entered and selected, for example, as percentage values ​​via the control computer's keyboard or a touchscreen. Tolerance limits can be entered both above and below the optimal color target value, for example...-3% downwards and +5% upwards. In this way, every printer and print shop can individually define the range for acceptable print quality for their printing presses, specific to each job and based on their own requirements. It is also possible to select different tolerance bands, which are then reapplied for each print job. The tolerance bands can be displayed on the display device in different colors around the target value.

[0012] In one embodiment of the invention, the control computer is connected to a colorimeter, and characteristic curves for controlling the printing press are recorded and stored using the colorimeter and the control computer. These characteristic curves are recorded as a function of various parameters such as temperature, printing speed, substrate, and ink, so that the characteristics of the machine, the substrates, and the ink are recorded once, as is done, for example, by the printing press manufacturer, and then stored. During operation of the printing press, the control computer selects the appropriate characteristic curves based on the parameters entered or detected by a sensor, or recalculates them if necessary, for example, by interpolating known characteristic curves with slightly differing parameters.These calculated characteristic curves can also be saved in the control computer for future use.

[0013] In a particularly advantageous embodiment of the invention, the display surface is a touchscreen, and the first signal is yellow, the second red, and the third green. This representation essentially corresponds to a traffic light with the colors red, yellow / orange, and green. Green indicates that optimal print quality with the best possible match to the print template is present, while yellow / orange indicates that although slight deviations from optimal print quality exist, these remain within the specified tolerance ranges, and the printed materials are therefore saleable. Red indicates that the print quality is so poor that the printed materials can no longer be sold and must instead be disposed of as waste paper.In this way, a printer can be continuously informed, visually and in an easily understandable manner, about the print quality it is currently producing.

[0014] The present invention is described and explained in more detail below with reference to several figures. These show: Fig. 1 a sheet-fed printing press with short inking units and a display of the current print quality, Fig. 2 the fundamental relationship between color density and temperature, Fig. 3a a change in printing speed from 8,000 to 15,000 printed sheets, Fig. 3b the course of the target temperature required by the change in printing speed and the course of the actual temperature and Fig. 3c the course of the target color density, the actual color density and the tolerance bands.

[0015] In Fig. Figure 1 shows a sheet-fed printing press 1 with two printing units 3 and 4. The two printing units 3 and 4 are identical in design and each has a plate cylinder 11 and 12, which carries the printing plate, a blanket cylinder 13 and 20, and impression cylinders 10 and 19. Both printing units 3 and 4 are supplied with ink via short inking units 16 and 17. Sheet-shaped substrates 22 are taken from the feeder stack 8 in the feeder 2 and transferred to the first printing unit 3 by means of the feeder table 9. The first ink separation is applied in the first printing unit 3 between the blanket cylinder 20 and the impression cylinder 19. The printed sheets 22 are then transferred to the second printing unit 4 by means of a transport cylinder 14, where the second ink separation is applied. A delivery unit 6 is located at the output of the second printing unit 4, which places the substrates 22 onto the delivery stack 7.

[0016] Since printing press 1 is equipped with so-called short inking units 16, 17, the color output can essentially only be controlled via the printing speed V and the temperature T in the inking units 16, 17. This control is achieved via the control computer 5, which controls all components of printing press 1 via a communication link 18 and a data bus. The control computer 5 also has a screen 15, which is a touchscreen and displays the current operating status of printing press 1. Furthermore, the operator of printing press 1 can input data and control the printing press 1 via the screen 15. The screen 15 is designed to continuously display the current print quality produced by printing press 1 in the form of a traffic light system with the colors red (R), orange (O), and green (G).Red means that the printing materials 22 currently produced by printing press 1 are not saleable and must be sorted out as waste paper. Orange means that printing materials 22 deviate from the optimal coloring state but are within the tolerance ranges specified by the printer and can still be sold. Green indicates that the optimal coloring state has been reached and there is virtually no deviation between printing material 22 and the printing template.

[0017] A colorimeter 21 can also be connected to the control computer 5, which can be used to measure the substrates 22. In this way, the print quality on the substrates 22 can be additionally checked by measuring color values. The colorimeter 21 can also be used to record characteristic curves for controlling the printing press 1 as a function of parameters such as paper, ink, printing speed V, and temperature T, and to save these curves in the control computer 5. This recording of characteristic curves can be carried out at the manufacturer's premises before the printing press 1 is delivered.

[0018] In Fig. Figure 2 illustrates the relationship between color density (DV) and temperature (T). This relationship is not entirely linear and must be considered when setting the color density. The color density depends on the color of the original print, and the values ​​of a digitally stored print file can be converted into corresponding color density values ​​(DV) using the control computer 5. The computer 5 then calculates the appropriate temperature (T) at which the specified color density values ​​(DV) are achieved, based on the printing speed (V) and other parameters such as the substrate and ink. These specified color density values ​​are then referred to as the target color density values ​​(DV). Soll referred to as, while the current color density values ​​are called actual color density values ​​DV. Ist These are designated. When the display unit 15 shows the green signal G, the actual color density values ​​DV are correct. Ist and color density target values ​​DV Soll agree.

[0019] In Fig. Figure 3a shows a change in printing speed V in sheets per hour plotted against time in seconds. It can be seen that at time S = 20 seconds, the printing speed increases rapidly from 8,000 sheets per hour to 15,000 sheets per hour. This increase in printing speed V results in a change in the color of the printed sheets 22, as the color is dependent on the printing speed V.

[0020] In Fig. 3b is, firstly, the course of the target temperature T. Soll drawn in, and secondly the course of the actual temperature T Ist To achieve the desired DV coloration Soll To achieve this, the target temperature T must be reached. Soll can be achieved. However, it can be seen that, particularly during and shortly after the change in pressure speed, the actual temperature T Ist significantly deviates from the target temperature T SollThis deviates because temperature control is a slow process and the temperature T in the short inking units 16, 17 cannot change quickly or even abruptly. However, this results in the difference between the target temperature T and the actual temperature increasing over a certain period. Soll , which is necessary to achieve the specified color, and the actual temperature T Ist is very large and thus the target color density DV Soll This goal cannot be achieved. This means that waste paper will be produced for a certain period of time.

[0021] In Fig. 3c shows the progression of the color density DV, where the target color density DV Soll is shown and is based on the actual temperature T Ist Actual color density calculated by control computer 5 DV Ist is shown. The actual color density DV Ist This corresponds to the estimated color density actually present on printing sheet 22. Furthermore, in Fig. 3c Tolerance bands around the target color density DV Soll The diagram shows the upper limit labeled dDV+ and the lower limit labeled dDV-. As long as the target color density DV Soll If the color density falls outside the two tolerance limits dDV- and dDV+, waste paper is produced and the indicator light on display device 15 illuminates red. Upon reaching the lower limit dDV-, the indicator light on display device 15 changes to orange, signaling to the printer that the printed sheets 22 produced from this point onward are ready for sale. If the actual color density DV Soll the target color density DV Soll When the optimal print quality is reached at time s=140 sec., the traffic light on the display device 15 switches to green, signaling to the printer that the optimal print quality has now been achieved.

[0022] The control computer 5 thus calculates the appropriate temperature T depending on the desired printing speed V. Soll, which are necessary to achieve the desired color density DV Soll This is necessary. At the same time, the control computer 5 calculates the actual color density DV based on the determined or estimated actual values ​​of temperature and printing speed. Ist and represents the deviation from the specified target color density DV Soll fixed. Depending on the extent of these deviations, the corresponding print quality is then displayed on the display device 15 in the image of the traffic light. In this way, the printer can be kept constantly informed about the print quality it is producing and can decide whether the currently produced substrates meet its requirements. To record the actual temperature T IstEach of the inking units 16 and 17 can be equipped with a temperature sensor, which, for example, transmits the temperature of the anilox rollers to the control computer 5. In addition to changes in printing speed, other processes such as the duration of a printing interruption, a temperature increase caused by the printer, or changes resulting from a print job change can also be taken into account. This data can be entered into the control computer 5 by the printer or recorded by sensors during operation of the printing press 1. The tolerance bands dDV- and dDV+ in Fig. 3c are not fixed, but can be entered or selected by the printer via the surface of screen 15, so that the printer can always define quality requirements for the current print job and thus different tolerance bands. Reference symbol list 1 sheet-fed printing press 2 investors 3 Printing unit 4 Printing unit 5 control computers 6 outriggers 7 cantilever stacks 8 investor stacks 9 Investor table 10 counter-pressure cylinders 11 plate cylinders 12 plate cylinders 13 rubber blanket cylinders 14 transport cylinders 15" screen 16 Short inking unit 17 Short inking unit 18 Communication link 19 counter-pressure cylinders 20 rubber blanket cylinders 21 Colorimeter 22 printed sheets DV Ist Color density actual value DV Soll Color density target value Temperature V Printing speed

Claims

[1] Method for signaling the coloring state when the operating state changes in printing presses (1) with a control computer (5), comprising the following process steps: Specifying a target color density (DV) Soll ) for a print job and saving the setting in the control computer (5), calculating an actual color density (DV Ist ) based on the current state in operation of the printing press (1) by the control computer (5), comparing actual color density (DV Ist ) and target color density (DV) Soll ) in the control computer (5) and output of a first signal by the control computer (5) when the actual color density (DV Ist ) in a tolerance band stored in the control computer (5) around the target color density (DV) Soll ) is lying around. [2] Method according to claim 1, characterized by , Output of a second signal by the control computer (5) when the actual color density (DV) Ist) outside a tolerance band around the target color density (DV) Soll ) lies. [3] Method according to claim 1 or 2, characterized by , Output of a third signal by the control computer (5) when the actual color density (DV) Ist ) with the target color density (DV) Soll ) matches. [4] Method according to any one of the preceding claims, characterized by , that the signals are transmitted to a display device (15) and that each output signal on the display device (15) is assigned a different representation, in particular a display color. [5] Method according to any one of the preceding claims, characterized by , that the control computer (5) is supplied with the operating states temperature (T) in the inking unit (16,17) and printing speed (V). [6] Method according to any one of the preceding claims, characterized by, that process-specific actual states such as the properties of printing ink or substrate (22) are supplied to the control computer (5). [7] Method according to any one of the preceding claims, characterized by , that different tolerance bands can be selected via a display device (15) and entered via an operating device, in particular a keyboard. [8] Method according to claim 7, characterized by , that each tolerance band is assigned a different display color on the display device (15). [9] Method according to any one of the preceding claims, characterized by , that the control computer (5) is connected to a color measuring device (21) and that characteristic curves for controlling the printing press (1) are recorded and stored using the color measuring device (21) and the control computer (5). [10] Method according to any one of claims 4 to 9, characterized by, that the display device (15) is a touchscreen and that the first signal is assigned to the color yellow, the second signal to the color red and the third signal to the color green.

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