This application is a National Stage under 35 U.S.C. § 371 of International Application No. PCT/EP2019/025460, filed Dec. 18, 2019, which claims priority to International Application No. PCT/162019/052602, filed on Mar. 29, 2019, and European Patent Application No. 18020647.6, filed on Dec. 20, 2018, the contents of all of which are incorporated by reference in their entirety.
This invention relates to an inking system for a printing machine. In particular, it relates to a system for delivering precise amounts of ink to the printing machine.
A printing machine is composed of several printing units; each printing unit is printing one colour on a substrate. The combination of colours results in the coloured printed pattern. Modern machines offer an inline quality control system that verifies the quality of the printed material and feeds back the result to the printing units. The quality control may take place at the end of the printing process, or after each unit. In this context of quality control, the reaction time between the detection of a quality issue and its resolution is important. A printing unit may solve a quality issue by modifying a printing parameter, like for example, the printing pressure, the ink temperature, the ink composition, the pattern alignment, etc. To be reactive on parameters involving ink composition or ink temperature, modern printing units tend to minimise the amount of ink used in the ink buffer in direct contact with the printing apparatus. The ink buffer may be, for example, an ink pan, a reservoir with a double doctor blade or an inking nip between the printing and the inking cylinder. To handle a small inking buffer or to regulate an ink mixture a precise inking dispensing system is needed.
The current invention discloses an ink dispensing system that uses air pressure to control the dispensing of ink. The dispensing system comprises a first chamber for holding ink under pressure. A pressure source delivers air to the chamber to adjust the pressure in the chamber. A first ink channel connects the output of the chamber to an output of the ink dispensing system. The pressure in the chamber is used as a parameter to control the flow (or equivalently the amount) of ink coming out of the chamber and out of the dispensing system. A control system monitors the flow of ink dispensed by the system to regulate the pressure delivered to the chamber, thereby adjusting the flow of ink.
The sensor may be a flow sensor and/or a sensor that measures a level (and thereby—optionally—a volume of ink by knowing the container shape and size). When using a flow sensor, the sensor is placed on the ink channel. Flow is the most convenient (direct/fast reacting) value to regulate, and thus the flow sensor is the preferred solution. When using a level sensor, it may be placed inside the chamber or after the system output (to measure the level of ink delivered). The volume/amount of ink (delivered at the output or remaining in the chamber) is obtained using the level sensor or can be computed by integrating over time the readings of a flow sensor. The flow of ink is obtained by using the flow sensor or can be computed by deriving over time the readings of a level sensor.
Controlling the flow of ink using pressure allows for very precise control of the flow. By regulating the flow, the system continuously dispenses ink, even if it can stop and restart the flow. Using pressure also allows for very precise control of the level of ink (in the inking buffer), since the level is the result of the accumulation of a flow of ink.
Advantageously, to regulate the composition of the ink at the output, the system comprises a second chamber to hold ink under pressure. The composition of ink in the second chamber is meant to be different from the one in the first chamber. Ink coming out of the second chamber is transported via a second ink channel. The second ink channel flows into the first ink channel at a junction point. The resulting ink mixture is processed with a mixer to obtain a homogeneous mixture. Additionally, the dispensing unit either comprises a second pressure source (which is part of the second ink channel) or comprises a mixing valve at the junction to control the relative amount of ink mixed from each channel. As a result, the dispensing system can control the total flow of ink at the output of the dispensing system, as well as the relative flow of ink stemming from the first and second chamber respectively thereby controlling the ink composition.
In the configuration using the second pressure source, the second pressure source delivers air to the second chamber to adjust the chamber pressure. The system further comprises a second sensor to measure the flow of ink coming out of the second chamber (before the junction point with the first channel). Preferably, the first sensor is configured to measure the flow of ink stemming from the first chamber (in other words, it is preferably placed on the first ink channel before the mixing point).
In the configuration using the mixing valve, the first pressure source may be connected to the first and the second chamber.
The pressure source used here are configured to set a controllable pressure value. In other words, the pressure at the output of the pressure source may be set to (virtually) any value between two pressure boundaries.
Advantageously, to refill the chamber(s), an ink reservoir may be attached to each chamber. The ink reservoir, thanks to a pump, can refill the chamber with ink without having to depressurise the chamber, and thus without having to interrupt the printing process. The ink reservoir is at kept at ambient pressure to allow for a convenient refill. Optionally, an anti-return valve is placed between the ink reservoir and the ink chamber to prevent ink from flowing back to the reservoir when the pump is idle.
The invention is also about a printing unit integrating the dispensing system that controls the ink composition. The dispensing system is well adapted for a printing unit type that uses a fixed cliché, i.e. a gravure, flexographic or offset printing unit, each unit printing a single colour channel. An optical sensor is used at the output of the unit to measure an optical parameter on the printed medium (for example the optical density, the brightness or the spectrum of a colour patch). When the measurement does not match a specified value, the control system changes the relative mixture of ink to reach or approach the specified value. Please note that the (absolute) composition of the ink in each channel does not need to be known. The absolute mixing proportion of the inks needs not to be known either. The dispensing system needs only to be able to vary (and to keep stable) the relative proportion of the ink stemming from each chamber, and vary (and to keep stable) the total flow of ink.
The invention is about dispensing precise amounts of ink, optionally with an adjustable composition when using two or more ink chambers. It is particularly well suited for inking systems with a very small ink buffer between the output of the dispensing system and the printed medium. In particular, in said inking system, there is no recirculation of ink between the ink buffer and the ink chamber. In particular, there is no return channel from the ink buffer to the ink chamber or to the ink refill reservoir.
Embodiments of the present invention are illustrated by way of example in the accompanying drawings in which reference numbers indicate the same or similar elements and in which;
Please note that any pressure source disclosed and claimed in this document may be a source of pressurised air with constant pressure connected to controllable air valve (for example a proportional valve), or may be a pump. The controllable air valve delivers a (settable) fraction of the pressure present in the source of pressurised air. Also, when mentioning two pressure sources, it may refer to a single source of pressurised air with two controllable air valves.
The pressure sources 4,24 in this document deliver air under pressure. By air we mean any gas—but preferably air—that does not interfere with the ink quality (it could be CO2).
The chambers inlet 12 and outlet 13 (of any exemplary chamber in this document) are preferably positioned and configured such that the air entering the chamber pushes the ink through the outlet 13, without creating bubbles or any other artefacts. Advantageously, the outlet is positioned such that the chamber can be emptied by the air under pressure. For example, to achieve this characteristic, the inlet 12 may be positioned on the top of the chamber 2 and the outlet on the bottom of the chamber 2.
Please note that to obtain a reactive system, the path length between the junction point 17 of the ink channels and the output of the dispensing system should be kept as short as possible. Thus, the output of the dispensing system may be the output of the mixer. Also, the mixer can be a passive device, or an active one where an element (for example a rotating helix, a rotating element or an oscillating body) actioned by a motor mixes the ink inside the mixer.
The first and second chambers are supposed to be filled with inks having different characteristics for regulating the ink composition. For example, the first chamber 2 may be filled with ink having a pigment concentration below specification, while the second chamber 22 may be filled with ink having a pigment concentration above specification. By controlling the ink proportion (for example by acting on the mixing valve 11), the system 1 can dispense ink with an adjustable density. This adjustment capability allows the ink dispensing system 1 to compensate for printing instabilities caused by environmental parameters, like temperature or humidity, or due to the wearing of the printing hardware. To do that, the printing machine (or printing unit) that integrates the dispensing system must have a sensor that monitors the quality of the print and feeds back the measurement. The measurement is compared to the desired value to adjust the composition and/or the amount of the dispensed ink.
The control system used to control any embodiments of the invention takes as input the reading of the sensors and a piece of information from the quality control system of the printing machine/unit. Said piece of information can be the measurement of an optical sensor that reads the printed substrate (along with its desired value), or a more abstract piece of information instructing the system to change the ink characteristics in a certain way, or to augment or reduce the ink flow dispensed by the system 1. The control system outputs control signals to the pressure sources 4,24 and/or to the mixing valve, thereby controlling the total amount of ink dispensed by the system 1 and, if applicable, the composition of the ink dispensed.
The examples that are suited for controlling the ink composition in this document can be extended to embodiments using any number of chambers (greater than two). This would allow controlling more than one parameter of the ink composition, for example by affecting the hue and the density of the dispensed ink.
Please note that when this document mentions an example of a dispensing system, it means an exemplary embodiment of a dispensing system according to the invention.
Please note that to regulate the composition of ink to obtain a target value, it is sufficient to be able to modify the relative amount of ink in the ink mixture without measuring the absolute values. For example, the system does not need to know that the ink mixture of the example in
Please note that the first ink channel 3 connects the output of the chamber 2 to the output of the dispensing system 14, while the second ink channel 23 connects the output of chamber 22 to the junction 17. Thus, after the junction 17, the first ink channel 3 may contain ink from several ink chambers.
The output 14 of the dispensing system may be a single output, as depicted in the Figures, or it might be multiple: a set of connections, preferably having the same length, may connect the output of the mixer to several outputs 14 of the dispensing system. In this way, the dispensed ink can be distributed over a larger area or along a line.
In practice, the pressure used in the chambers ranges typically between 1 and 2 bars, for example, 1.5 bar. They could, however, range from 0.1 to 3 bars.
Please note that pressure is used to push the ink out of the system 1. The dispensing system is usually dispensing ink continuously, but may also be stopped and restarted when needed. Given the volumes of air/ink under pressure involved in the system, the frequency of this stop and restart process is several orders of magnitude slower than the ones used in ink jet printing, where the ink dispensed is used to create a pattern.
The volume of the chamber 2,22 is dimensioned so that, when using the printing unit at full speed, full width and at 100% ink coverage, the chamber is designed to consume its ink content in 5 to 10 minutes. This is the time needed for an operator to switch an empty ink reservoir 7,27 with a new—full—one without interrupting the printing process. In our implementation, a chamber 2,22 contains three litres of ink. Alternatively, the chamber 2,22 may contain between two and five litres of ink. In any case, the capacity of an ink chamber is larger than 0.1 litres. Please note that instead of switching a reservoir 7,27 with a new, full one, the operator may simply refill the reservoir with new ink.
By fixed cliché, we mean a picture that is the same for the whole duration of the printing job (in contrast to digital printing where the pictures may change from page to page).
Please note that when the dispensing system is running, the ink follows a path from upstream to downstream.
Number | Date | Country | Kind |
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18020647 | Dec 2018 | EP | regional |
Filing Document | Filing Date | Country | Kind |
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PCT/EP2019/025460 | 12/18/2019 | WO |
Publishing Document | Publishing Date | Country | Kind |
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WO2020/126084 | 6/25/2020 | WO | A |
Number | Name | Date | Kind |
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8708439 | Ihme | Apr 2014 | B2 |
20010011512 | Koehler | Aug 2001 | A1 |
20160096360 | Zetzl | Apr 2016 | A1 |
Number | Date | Country |
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101939167 | Jan 2011 | CN |
103358681 | Oct 2013 | CN |
103448363 | Dec 2013 | CN |
107531056 | Jan 2018 | CN |
1362701 | Nov 2003 | EP |
0068018 | Nov 2000 | WO |
2009071133 | Jun 2009 | WO |
2013159777 | Oct 2013 | WO |
2017174219 | Oct 2017 | WO |
Entry |
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International Search Report and Written Opinion issued on Apr. 3, 2020 in International Patent Application No. PCT/EP2019/025460 (10 pages, in English). |
Cheng Guangyao et al., “Three-dimensional surface color spray painting technology”, pp. 9-13, Cultural Development Press, published Jul. 31, 2018. |
Chinese Search Report in corresponding Chinese Application No. 2019800916822, dated Feb. 17, 2023. |
Number | Date | Country | |
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20220080721 A1 | Mar 2022 | US |
Number | Date | Country | |
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Parent | PCT/IB2019/052602 | Mar 2019 | US |
Child | 17415629 | US |