Method for operating a printing press supply system

Abstract

Method for operating a system comprising a printing press (14) and a supply unit (15) for a device (3) of the printing press (14) with a fluid, wherein the fluid is conveyed to the device (3) by means of a supply pump (12) of the supply unit (15) and away from the device (3) by means of a return pump (13) of the supply unit (15), a fluid level is monitored by means of a sensor (4), and wherein, depending on the results of the level monitoring, the return pump (13) is controlled such that the level is brought to an optimal value and substantially maintained at the latter, and wherein, from the magnitude of a level difference by which the fluid level drops in a certain period of time, and this period of time, the current consumption of the fluid is automatically calculated and a new setpoint for the delivery rate or speed of the return pump (13) is determined.

Description

[0001] The present invention relates to a method for operating a system comprising a printing press and a supply device for supplying a device of the printing press with a fluid, and arose against the following background: Sheetfed offset printing presses have coating units to which the coating is supplied by a coating supply unit. The coating is pumped from a storage drum by the coating supply unit. The coating supply unit and the storage drum are housed in a cabinet next to the printing press. The supply unit comprises two pumps: a feed pump that pumps the coating to the coating unit, and a return pump that pumps the coating back into the drum. A chambered doctor blade of the coating unit can be connected to the feed pump, and the return pump can be connected to a collection tray located below the chambered doctor blade. The collection tray serves to catch the unprinted coating that escapes from the chambered doctor blade and flows into the tray as a free jet.

[0002] These design constraints result in the following problems: If too much paint accumulates in the drip tray, it overflows. This results in contamination of the printing press and downtime for cleaning. The problem of a drip tray overflowing in a paint shop is addressed in EP 0 841 162 B1. This document proposes preventing overflow by switching off the feed pump.

[0003] If, on the other hand, there is too little paint in the open-topped collection tray, the return pump also draws in ambient air, which causes the circulating paint to foam and leads to pressure problems. The problem of unwanted air intake by the return pump is mentioned in EP 0 958 920 A1. In the system described therein, the return pump is indeed connected directly to the chambered doctor blade, but an anilox roller associated with the chambered doctor blade causes air to enter the chambered doctor blade.

[0004] Further prior art is provided by DE 41 16 989 A1, which describes a system in which paint is pumped out of a trough. In a specific operating mode of the system, the liquid level in the trough decreases slowly, with the pump being briefly switched off when the liquid level reaches a minimum level mark. During operation, paint is continuously drawn from the trough by wetting a roller. The trough is therefore not a collection trough, but a reservoir for a dipping roller.

[0005] The invention is based on the objective of providing a method for operating a system of the type mentioned above, whereby safe operation is ensured. In particular, the method should prevent ambient air from being drawn in by the supply device and prevent the fluid from overflowing.

[0006] This problem is solved by a method with the features of claim 1. In the inventive method for operating a system comprising a printing press and a supply device for supplying a device of the printing press with a fluid, the fluid is conveyed to the device by means of a supply pump of the supply device and away from the device by means of a return pump of the supply device, the fluid level is monitored by means of a sensor, and depending on the results of the level monitoring, the return pump is controlled such that the level is brought to an optimal value and is substantially maintained at this value.

[0007] In the method according to the invention, the fill level control is essentially carried out solely by means of the return pump.

[0008] Several further developments of the inventive method are possible. For example, the fill level in a trough can be designed such that sufficient fluid is always available for the return pump, thus preventing unwanted air contamination in the fluid drawn in by the return pump. A level sensor arranged in or above the trough can monitor a minimum fill level and a "good" range. The signals from the level sensor, as well as the delivery data from the feed pump and the return pump, can be made available to a machine control system of the printing press. When the corresponding signal is reached, the machine control system acts on the return pump, causing it to deliver more or less fluid.In the control loop formed by the return pump, the main influencing parameters should be taken into account. These parameters are determined by the fluid flow rate set by the supply pump and by the machine speed of the printing press. A defined fluid level can be achieved based on these main influencing parameters. By controlling the speed of the return pump, the defined fluid level can be established in a receiving tray, and this level can be maintained using data from the supply unit and the machine operating data. The fluid level in the tray can be detected using a level sensor. The tray can be a storage tray containing a dipping roller, or preferably a collection tray located beneath a chambered doctor blade.

[0009] The dependent claims describe further advantageous embodiments of the method according to the invention. In one embodiment, the fill level is automatically reduced from a permissible minimum value to the optimal value by temporarily lowering the delivery rate of the return pump. In another embodiment, the fill level is reduced to the permissible minimum value before the start of pressure operation by keeping the return pump stationary while the fluid is pumped by the supply pump. In the method according to the invention and the two embodiments described above, the delivery rate of the supply pump can remain unchanged. In yet another embodiment, the fill level is automatically reduced from a permissible maximum value to the optimal value during pressure operation by temporarily increasing the delivery rate of the return pump.Here too, the delivery rate of the feed pump can remain unchanged. In a further embodiment, the fluid is stored in a container and pumped from the container to the device by means of the feed pump. The device can include a collection tray from which the fluid is pumped into the container by means of the return pump. The fill level, which is brought to the optimal value by the method according to the invention and essentially maintained at this value, can be formed in the collection tray. The fluid is preferably a printing ink or a varnish or a similar coating liquid for coating a preferably arc-shaped substrate. According to a further embodiment, the device is a metering device.

[0010] The invention also includes a supply device configured for carrying out the method according to the invention or one of its further developments. Likewise, the invention includes a printing press configured for carrying out the method according to the invention or one of its further developments. Furthermore, the invention includes a system comprising the aforementioned supply device and the aforementioned printing press. This system may include a control unit programmed to carry out the method according to the invention or one of its further developments.

[0011] Further constructively and functionally advantageous developments of the invention will result from the following description of a preferred embodiment and the accompanying drawing.

[0012] This shows: Fig. 1 a system comprising a printing press and a supply unit and Fig. 2. A program flowchart for controlling the system. Fig. 1.

[0013] In Fig. Figure 1 shows a printing press 14 and a supply unit 15 in detail. The supply unit 15 serves to supply the printing press 14 with a printable fluid, e.g., ink or varnish. The fluid is stored in a container 9 and circulates through a pipe system 16. The supply unit 15 comprises a feed pump 12 with a drive motor 8 and a return pump 13 with a drive motor 7. The pumps 12 and 13 are volumetric pumps, and the drive motors 7 and 8 are electric motors. The pumps 12 and 13 are integrated into the pipe system 16 and circulate the fluid within it. The drive motors 7 and 8 are controlled by an electronic control unit 6.

[0014] The printing press 14 comprises a roller 2 to which a metering device 3 is attached. The roller 2 is an anilox roller and the metering device 3 is a chambered doctor blade. The metering device 3 rests against the roller 2 to supply it with the fluid. A collection tray 1 is arranged below the metering device 3, which collects the fluid flowing freely from an outlet of the metering device 3. The outlet is formed by a throttle valve 11, which is adjustable to regulate the fluid's outflow resistance.

[0015] The fluid pressure in a chamber of the metering device 3 is monitored by a sensor 10. The sensor 10 is integrated into the piping system 16 between an inlet of the metering device 3 and the feed pump 12. The fluid flows into the chamber of the metering device 3 through the inlet. The feed pump 12 supplies the metering device 3 with the fluid from the container 9. The return pump 13 is connected to an outlet of the collection tray 1 and pumps the fluid back from the latter into the container 9. The sensor 10 signals its measured values ​​to an electronic machine control 5 of the printing press 14. The machine control 5 and the device control 6 are interconnected, so that, based on the measured values ​​of the sensor 10, the delivery rate or speed of the feed pump 12 is regulated to maintain a constant fluid pressure in the chamber of the metering device 3.

[0016] The fluid collected in the drip tray 1 forms a level within the drip tray 1 that, under pressure, can vary between a maximum fill level A and a minimum fill level B. A sensor 4 is positioned above the drip tray 1 to monitor the fill level. This sensor operates without contact and signals its measured values ​​to the machine control 5.

[0017] The system shown basically works as follows: Before pressure is applied, the collection tray 1 must be filled with fluid up to the minimum fill level B before the return pump 13 is activated. The minimum fill level B ensures that the return pump 13 does not draw in air, which could lead to complications. Such complications would include, for example, foaming of the fluid and insufficient filling of the grid recesses (cells or grooves) of the roller 2 with the fluid. If the return pump 13 were activated before the minimum fill level B is reached, there would be a risk of drawing in a certain amount of air through the outlet of the collection tray 1.

[0018] In pressure operation, both pumps 12 and 13 are running, and the fluid level in the collection tray 1 can fall. Based on the extent of the fluid level drop over a given time, and this time period, the current fluid consumption is automatically calculated, and a new setpoint for the flow rate or speed of the return pump 13 is determined. As soon as the fluid level reaches the minimum level B due to its drop, the flow rate or speed of the return pump 13 is reduced. However, the flow rate or speed of the return pump 13 is not initially reduced to the previously calculated new setpoint, but rather to an automatically calculated intermediate value. This intermediate value is slightly lower than the new setpoint, resulting in the level in the collection tray 1 rising to an optimal level, which lies approximately midway between the maximum level A and the minimum level B.The flow rate or speed is held at the intermediate value for an automatically calculated period of time and only then increased from the intermediate value to the new target value, so that at the optimal fill level an equilibrium is maintained between the fluid volume flowing into the collection tray 1 and the fluid volume pumped out of it.

[0019] By changing the operating parameters of the printing press 14, e.g., the printing speed, the fluid level can increase until the maximum fill level A is reached. Once the maximum fill level A is reached, the level is automatically reduced back to the optimal fill level.

[0020] Fig.Figure 2 shows the flowchart of a program according to which the device controller 6 controls the supply unit 15. Reference numbers 17 to 32 denote process and program steps. Step 17 is the start step. In step 19, sensor 4 checks whether the level in the collection tray 1 is too high. If the level is not too high, the return pump 13 is kept stationary in step 18. However, if the level is too high in step 19, i.e., the minimum level B is reached before pressure is applied, an initial speed value for the return pump 13 is calculated in step 21. This calculation takes into account a target speed value for the supply pump 12, as specified in step 22.

[0021] In step 23, it is checked whether a change in the setpoint speed of the supply pump 12 exceeds the set filter limits. If so, a new initial speed value for the return pump 13 is calculated in step 24. However, if the change in the setpoint speed of the supply pump 12 remains within the filter limits, step 25 checks whether the fill level in the collection tray 1 is lower than a so-called "good range." The good range can also be referred to as the optimal fill level.

[0022] If the result of the test in step 25 is "Yes", a target value for the speed of the return pump 13 is calculated in step 26 by subtracting a calculated change value from the previously valid value. According to step 27, this results in an increase in the fill level by the amount of fluid corresponding to the so-called OK range. This raises the fill level back to the optimal level. If, on the other hand, the result of the test in step 25 is "No", then step 28 checks whether the fill level is higher than the OK range. In other words, it checks whether the current fill level in the collection tray 1 is above the optimal fill level.

[0023] If the latter is true, in step 29 the target value of the speed of the return pump 13 is corrected by adding a calculated change value to the previously valid value. As a result, according to step 30, the fill level is reduced by the amount of fluid corresponding to the OK range.

[0024] Step 31 checks whether the control should be switched off. If control is to continue, i.e., not be suspended, a new change value for the setpoint speed of the return pump 13 is calculated in step 20. However, if the control is to be switched off in step 31, the program is stopped in step 32. Reference symbol list 1 drip tray 2 rollers 3 Dosing device 4 Sensor 5 Machine control 6 Device control 7 Drive motor 8 Drive motor 9 containers 10 Sensor 11 Throttle valve 12 Flow pump 13 Return pump 14 printing press 15 Power supply unit 16 piping system Steps 17-32 A maximum fill level B minimum fill level

Claims

[1] Method for operating a system comprising a printing press (14) and a (15) for supplying a device (3) of the printing press (14) with a fluid, wherein the fluid is conveyed to the device (3) by means of a feed pump (12) of the supply device (15) and away from the device (3) by means of a return pump (13) of the supply device (15), a fluid level is monitored by means of a sensor (4), and wherein, depending on the results of the level monitoring, the return pump (13) is controlled such that the level is brought to an optimal value and is substantially maintained at the latter, and wherein, from the magnitude of a level difference by which the fluid level drops in a certain period of time, and this period of time, the current consumption of the fluid is automatically calculated and a new setpoint for the delivery rate or speed of the return pump (13) is determined. [2] Method according to claim 1, wherein the fill level is automatically brought from a permissible minimum value (B) to the optimal value by temporarily reducing the delivery rate of the return pump (13). [3] Method according to claim 2, wherein the fill level is brought to the permissible minimum value before the start of pressure operation by keeping the return pump (13) stationary while the fluid is pumped by means of the supply pump (12). [4] Method according to any one of claims 1 to 3, wherein the delivery rate of the feed pump (12) is maintained unchanged. [5] Method according to any one of claims 1 to 4, wherein the fill level during pressure operation is automatically brought from a permissible maximum value to the optimal value by temporarily increasing the delivery rate of the return pump (13). [6] Method according to claim 5, wherein the delivery rate of the feed pump (12) is maintained unchanged. [7] Method according to any one of claims 1 to 6, wherein the fluid is stored in a container (9) and is pumped from the container (9) to the device (3) by means of the feed pump (12), and wherein the device (3) comprises a collection tray (1) from which the fluid is pumped into the container (9) by means of the return pump (13). [8] Method according to claim 7, wherein the fill level is formed in the collection tray (1). [9] Method according to any one of claims 1 to 8 wherein the fluid is a printing ink or a varnish. [10] Method according to any one of claims 1 to 9, wherein the device (3) is a metering device. [11] Supply device (15) designed to carry out the method according to any one of claims 1 to 10. [12] Printing machine (14) designed to carry out the method according to any one of claims 1 to 10. [13] System comprising a supply device (15) according to claim 11 and a printing press (14) according to claim 12. [14] System according to claim 13, wherein this comprises a controller (6) programmed to carry out the method according to any one of claims 1 to 10.

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