PRINTING SYSTEM

Abstract

A printing system (10) is provided for printing on a material, comprising an ink formulation module (12) comprising at least one ink reservoir (14) and an ink adjustment system (16), a printing unit (18) for applying ink to the material, a sensor module (22) comprising at least one probe (24) for generating color measurement data, and a control module (25) being connected to the ink formulation module (12), the sensor module (22) and the printing unit (18). The color measurement data comprises at least one ink color value of the ink before being applied on the material by the printing unit (18). The control module (25) is configured to receive the color measurement data from the sensor module (22) and to transmit an ink adjustment request to the ink formulation module (12), wherein the ink formulation module (12) is configured to adjust the ink composition of the ink in the at least one ink reservoir (14) based on the ink adjustment request.

Claims

1. A printing system for printing on a material, the printing system comprising: an ink formulation module comprising at least one ink reservoir and an ink adjustment system, a printing unit for applying ink to the material, a sensor module comprising at least one probe for generating color measurement data, and a control module being connected to the ink formulation module, the sensor module, and the printing unit, wherein the color measurement data comprises at least one ink color value of the ink before being applied on the material by the printing unit, wherein the control module is configured to receive the color measurement data from the sensor module and to transmit an ink adjustment request to the ink formulation module, and wherein the ink formulation module is configured to adjust an ink composition of the ink in the at least one ink reservoir based on the ink adjustment request.

2. The printing system according to claim 1, wherein the control module comprises a computer-based module for mathematical calculation of the ink adjustment configured to create the ink adjustment request.

3. The printing system according to claim 1, wherein the control module is configured to create a database comprising the color measurement data and the ink adjustment request is calculated based on the data stored in the database.

4. The printing system according to claim 1, wherein the control module is configured to provide a quality parameter, in particular an actual E value, for characterizing the quality of the printing process and for creating an ink reformulation request.

5. The printing system according to claim 1, wherein the control module is a cloud-based module.

6. The printing system according to claim 1, wherein the sensor module comprises a probe assigned to the at least one ink reservoir, a probe assigned to an ink supply line connecting the ink formulation module with the printing unit and/or a probe assigned to a printing cylinder of the printing unit, especially an anilox roll of the printing unit.

7. The printing system according to claim 1, wherein the at least one probe is an optical sensing probe and the color measurement data comprises a remission spectrum of the ink, especially wherein the color measurement data further comprises measurement data of the color spaces XYZ, xyY, L*a*b*, L*u*v* and/or uvL*.

8. The printing system according to claim 1, wherein the probe has a transparent cap.

9. The printing system according to claim 6, wherein the ink supply line comprises a measurement section which comprises a vision panel.

10. The printing system according to claim 1, wherein the sensor module comprises a probe for each of the inks used in the printing system.

11. The printing system according to claim 1, wherein the ink adjustment system comprises an auxiliary ink reservoir and a solvent reservoir.

12. The printing system according to claim 1, wherein the control module is configured to further receive at least one ink color value of the ink after being applied on the material by the printing unit, especially before and/or after being dried on the material.

13. The printing system according to claim 1, wherein the control module is configured to further receive unit parameters describing the printing unit.

14. The printing system according to claim 1, wherein the printing system comprises a display connected to the control module and which is adapted to display the color measurement data.

Description

[0057] Further advantages and features will become apparent from the following description of the invention and from the appended Figures which show non-limiting exemplary embodiments of the invention and in which:

[0058] FIG. 1 shows a schematic representation of a first embodiment of the printing system according to the invention;

[0059] FIG. 2 shows selected parts of the printing system of FIG. 1;

[0060] FIG. 3 shows selected parts of a second embodiment of the printing system according to the invention;

[0061] FIG. 4 shows selected parts of a third embodiment of the printing system according to the invention; and

[0062] FIG. 5 shows selected parts of a fourth embodiment of the printing system according to the invention.

[0063] In FIG. 1, a first embodiment of the printing system 10 according to the invention is shown schematically.

[0064] The printing system 10 comprises an ink formulation module 12 with four ink reservoirs 14 to provide four inks for four-color printing, preferably in the CMYK color model. However, the printing system 10 could also have less or more than four ink reservoirs 14, e.g. eight ink reservoirs for eight-color printing.

[0065] The ink formulation module 12 further comprises an ink adjustment system 16 configured to adjust the ink formulation in each of the ink reservoirs 14.

[0066] The ink reservoirs 14 of the ink formulation module 12 are connected to a printing unit 18 by ink supply lines 20, wherein each ink reservoir 14 is associated to one of the ink supply lines 20.

[0067] The printing unit 18 is used to print the ink provided by the ink formulation module 12 on a material, e.g. on paper, cardboard or foil. It is to be understood that FIG. 1 is only illustrative in nature and that the printing unit 18 comprises several components as known in the art. E.g., the printing unit 18 is a flexographic printing unit or an intaglio-printing unit.

[0068] The printing system 10 further has a sensor module 22 which comprises four probes 24, wherein each of the probes 24 is associated to one of the ink supply lines 20. The probes 24 are connected by fiber optic cables to the sensor module 22.

[0069] The probes 24 are configured to provide color measurement data of the ink in the associated ink supply line 20 to the sensor module 22, wherein the color measurement data comprises at least one ink color value. Accordingly, the color measurement data comprises information about the inks before they are applied on the material in the printing unit 18.

[0070] The sensor module 22 is further connected to a control module 25 by means of a programmable logic controller 26. However, the sensor module 22 could also be directly connected to the control module 25.

[0071] The connections between the sensor module 22, the control module 25 and the programmable logic controller 26 are established by an Ethernet connection or by a wireless connection.

[0072] Preferably, the control module 25 is a cloud-based module.

[0073] The control module 25 comprises an ink adjustment module 28 and a computer-based module 30 for mathematical calculation of the ink adjustment which are configured to provide an ink adjustment request based on the color measurement data received from the sensor module 22. The computer-based module 30 uses a machine learning algorithm to create the ink adjustment request.

[0074] The control module 25 is connected to the ink formulation module 12 by means of the programmable logic controller 26 and is configured to transmit the ink adjustment request to the ink formulation module 12.

[0075] Based on the ink adjustment request, the ink adjustment system 16 adjusts at least one of the inks in the ink reservoirs 14.

[0076] Additionally, the printing system 10 shown in FIG. 1 comprises an inline measurement module 32 for providing ink color values of the ink in a wet state after being applied on the material by the printing unit 18 and/or to provide unit parameters describing the printing unit 18. The unit parameters can in principle also be supplied by the printing unit 18 itself.

[0077] Further, the printing system 10 comprises a control station 34 for providing ink color values of the dry ink after application on the material.

[0078] The inline measurement module 32 and the control station 34 are connected to the control module 25 and configured to transmit the ink color values and/or unit parameters to the control module 25.

[0079] In FIG. 2, selected parts of the printing system 10 are shown in more detail.

[0080] In FIG. 2, only one of the ink reservoirs 14 is shown for simplification. The ink reservoir 14 is e.g. an ink bucket. The ink bucket e.g. has a volume in the range of from 20 to 40 L, especially with a volume of 30 L. Of course, the ink bucket could have any volume suitable for the printing system 10 at hand.

[0081] The ink in the ink reservoir 14 is transferred by a first pump 36 to the ink supply line 20 associated to the ink reservoir 14. To homogenize the flow speed of the ink in the ink supply line 20, a damper 38 is arranged downstream of the first pump 36 in the ink supply line 20. Further, a temperature unit 40 for temperature adjustment of the ink and a viscosity control unit 42 for adjusting the viscosity of the ink are arranged downstream of the damper 38 in the ink supply line 20.

[0082] The ink supply line 20 comprises a measurement section 44 in which the probe 24 extends into the ink supply line 20. The probe 24 is an optical sensing probe adapted to measure a remission spectrum of the ink flowing through the ink supply line 20. The probe 24 is impermeable for ink to prevent damages to the probe due to interaction with the ink.

[0083] Of course, FIG. 2 is illustrative in nature, only. The probe 24 and the measurement section 44 can be located at any position which allows reliable measurement of the ink. E.g., the position of the probe 24 and the measurement section 44 can be chosen such to minimize deviations in the temperature of the ink.

[0084] In the embodiment shown in FIG. 2, the probe 24 comprises an integrated light source for producing D.sub.50 light. In principle, any standard illuminant could be used, e.g. D.sub.65 light.

[0085] The D.sub.50 light is emitted into the ink to obtain the remission spectrum of the ink by the probe 24 from which information about the ink in the colorspace XYZ, xyY, L*a*b*, L*u*v* and/or uvt* can be calculated.

[0086] As schematically shown in FIG. 2, the probe 24 is aligned perpendicular to the flow direction of the ink within the ink supply line 20. This arrangement can prevent the formation of air bubbles in front of the probe 24.

[0087] The probe 24 is adapted to transmit the remission spectrum of the ink as color measurement data to the sensor module 22 by a fiber optic cable.

[0088] The color measurement data is then transmitted to the control module 25 by means of the programmable logic controller 26.

[0089] As explained before, the control module 25 generates an ink adjustment request based on the color measurement data.

[0090] The ink adjustment request is generated based on an actual E value, i.e. based on the Euclidean distance in color space between the target ink color and the ink color corresponding to the color measurement data, as defined e.g. in DIN EN ISO 11664-4 or DIN EN ISO 11664-6.

[0091] However, further information can be taken into account when generating the ink adjustment request, e.g. the ink density. Additionally, unit parameters and/or ink color values of the ink after being applied on the material and submitted by the inline measurement module 32 and/or the control station 34 can use for generating the ink adjustment request.

[0092] To further optimize this process, the ink adjustment module 28 can build up a database in which all parameters usable for generating the ink adjustment request are stored and can be taken into account in subsequent iterations of optimizing the ink composition and/or for generating the ink adjustment process in future printing processes.

[0093] The database can especially be assessed by the computer-based module 30 to automatically find an optimal ink adjustment request without any manual adjustment of personnel.

[0094] The ink adjustment request is then transmitted to the ink adjustment system 16 of the ink formulation module 12.

[0095] The ink adjustment system 16 comprises an auxiliary ink reservoir 46 and a solvent reservoir 48. By means of a second pump 50, ink from the auxiliary ink reservoir 46 and/or solvent from the solvent reservoir 48 can be pumped into the ink reservoir 14 to adjust the ink stored in the ink reservoir 14.

[0096] The auxiliary ink reservoir 46 typically has a volume much lower than the volume of the ink reservoir 14, e.g. a volume in the range of from 1 to 10 L, especially a volume of 5 L.

[0097] With other words, the ink adjustment request received from the control module provides the ink adjustment system 16 with the information which amount of ink and/or solvent must be applied to the ink reservoir 14 to optimize the ink composition in the ink reservoir 14.

[0098] Accordingly, the printing system 10 allows to automatically adjust the ink composition based on information of the liquid ink in an easy way, thereby reducing waste and downtime of the printing system 10 and providing a consistent high quality print.

[0099] In FIG. 3, a second embodiment of the printing system 10 is shown schematically. The second embodiment essentially corresponds to the first embodiment so that only differences between the first and the second embodiment will be discussed in the following. Identical and functionally identical components are provided with the same reference signs.

[0100] In the second embodiment, the probe 24 is arranged outside of the ink supply line 20 close to the measurement section 44. Further, the probe 24 does not have an integrated light source, but an additional light source 52 is provided by the sensor module 22, wherein the probe 24 and the additional light source 52 are arranged at an angle relative to each other. In the shown embodiment, the angle is in the range of 10 to 35, for example 20.

[0101] The measurement section 44 further comprises a vision panel 47 which is transparent at least for the wavelengths of the light provided by the light source 52 and of the remission spectrum of the ink flowing through the measurement section 44 of the ink supply line 20. E.g., the vision panel 47 is out of borosilicate glass.

[0102] In this embodiment, the probe 24 does not have direct contact with the ink. Accordingly, there is no risk that ink accumulates on the probe 24 and the probe 24 does need to be impermeable for the ink so that cheaper probes 24 can be used. Further, no additional turbulences are generated in the flowing ink, as there is no interaction with the probe 24.

[0103] Further, the sensor module 22 comprises a calibration device 53. The calibration device 53 is movable as indicated by the double-arrow P in FIG. 2. Accordingly, the calibration device 53 can be moved to a position for calibration of the probe 24.

[0104] In FIG. 4, a third embodiment of the printing system 10 is shown schematically. The third embodiment essentially corresponds to the first and second embodiment so that only differences will be discussed in the following. Identical and functionally identical components are provided with the same reference signs.

[0105] In the third embodiment, the probe 24 is arranged within the ink reservoir 14 and has an integrated light source.

[0106] More specifically, in FIG. 4 it can be seen that the ink reservoir 14 is an ink bucket 54 closed by a lid 56. A stirrer 58 extends through the lid 56 and is used to homogenize the ink provided in the ink bucket 54 by stirring.

[0107] Similar to the stirrer 58, the probe 24 extends through the lid 56 into the ink.

[0108] In this embodiment, the probe 24 could also comprise a means for detection of the ink level in the ink reservoir 14, e.g. a capacity sensor, an infrasound sensor, a microwave sensor and/or a sensor for measuring the hydrostatic pressure. The additional means for detection of the ink level could also be separate from the probe 24.

[0109] In FIG. 5, a fourth embodiment of the printing system 10 is shown schematically. The fourth embodiment essentially corresponds to the above described embodiments so that only differences will be discussed in the following. Identical and functionally identical components are provided with the same reference signs.

[0110] In the fourth embodiment, the probe 24 is associated to the printing unit 18. Specifically, the probe 24 is arranged next to an anilox roll 60 of the printing unit 18. Ink is supplied on the anilox roll 60 by means of a chamber doctor blade 62 as known in the art.

[0111] Accordingly, in the fourth embodiment, the probe 24 collects color measurement data of the ink while the ink is provided in gravures of the anilox roll 60 but before the ink is transferred from the anilox roll 60 to a printing plate mounted on a plate cylinder 62 and accordingly before the ink is supplied from the plate cylinder 62 on the material provided on an impression cylinder 64.

[0112] It should be clear that the printing system 10 could also comprise a multitude of probes 24, preferably arranged at different parts of the printing system 10. While this increases the complexity and the cost of the printing system 10, such an embodiment further increases the amount of information about the printing system 10 taken into account by the control module 25 when generating the ink adjustment request, thereby increasing the chance of successfully find an optimal ink formulation without any intervention of personnel.