EP1216833B1 - Method for regulating the ink-fountain solution balance in a rotary offset printing machine - Google Patents

Abstract

A method for regulating the ink-to-wetting agent equilibrium in a rotary offset printing machine, the wetting agent quantity being determined especially using the signals of a sensor which measures the light reflectance of an area on the printing form of the rotary printing machine that is wetted by a wetting agent. The method includes: presetting the wetting agent quantity supplied to the printing form, calibrating the wetting agent quantity supplied at an ink quantity that is essentially kept constant, adjusting the wetting agent quantity to a wetting agent quantity setpoint value that is characteristic for the specific print job, increasing or decreasing the ink quantity from an ink quantity setpoint value to an ink quantity target value that is desirable for the printing job to be processed, and a corresponding increasing or decreasing of the wetting agent quantity setpoint value in the same direction to a wetting agent quantity target value, and regulating the supplied wetting agent quantity in a closed control loop as a function of the wetting agent quantity target value.

Description

The invention relates to a method for controlling the ink-to-dampening solution equilibrium in a rotary offset printing machine, wherein the amount of dampening solution is determined in particular by means of the signals of a sensor which determines the light reflectivity of a moistened wetted area on a printing form of the rotary printing press.

If in an offset printing press, that is to say, for example, in a sheet-fed offset printing press or in a web-fed rotary offset printing machine, too little fountain solution is supplied to the printing plates, then the areas of the printing plate which can be used for the respective print job to produce the four primary colors black, yellow, Cyan and magenta composite printed image should generally be colorless, accept color. This caused by a lack of fountain solution occurrence of color in the inherently color-free areas of the printing forme is referred to in the printing technology as lubrication, and the supplied dampening solution amount, hereafter called dampening, in which just does not occur lubrication, or in the lubrication just starts, is also called the lubrication limit.

Furthermore, it is necessary for an optimum printing result that the so-called color-to-dampening solution balance in the offset process is maintained, so that forms a required for the printing process optimum emulsion of dampening solution and ink on the printing plates.

From DE 44 36 582 C2 it is known to regulate the dampening solution quantity for a printing forme of a current offset rotary printing machine, whereby a number of measured values are recorded several times at a change of the dampening solution quantity at a certain angle of rotation of the printing form, of the measured values their respective scattering value is calculated, difference amounts of the scattering values are formed when exceeding one of the difference amounts over a predetermined difference value, the lubrication limit is determined and then the dampening solution quantity for the production pressure is increased by a predetermined amount and is guided such that the measured values remain constant on average. The document gives no suggestion to combine the humidity control in combination with a change in the ink guide, in particular a color control, by which the amount of color in the printing, inked areas of a printing plate during the continuous printing operation is controlled or regulated.

Furthermore, from DE-OS 29 31 579 a device for zonal regulation of dampening solution guide is known in which the actuators for the zonewise color metering - also called ink fountain keys - are coupled with zonal corresponding, the ink fountain key associated actuators for dampening solution guide. The coupling takes place here in a mechanical manner via a mechanical control gear. The font gives no indication to calibrate the amount of fountain solution at substantially constant amount of ink.

Accordingly, it is an object of the present invention to provide a method for controlling the ink to fountain solution balance in a rotary offset printing machine, with which the optimum emulsion of ink and fountain solution can be adjusted after a short time and with a high reproducibility.

This object is achieved by the features of claim 1.

Further features of the invention are contained in the subclaims.

According to the inventive method for controlling the color-to-dampening solution balance in a rotary offset printing machine, which is preferably realized by a corresponding control and regulation software in a known Druckmaschinensteuerungs- and -regelseinrichtung, which is supplied to a printing plate or printing form dampening solution using the signals of a sensor which preferably has the light reflectivity of a Wetting agent wetted, preferably non-printing area, determined on the printing plate. For this purpose, the sensor can, for example, detect the reflected light of a laser which is directed in the normal direction or at an angle to the non-printing area of the printing form, and generate a sensor signal which is a measure of the light as a function of the detected light intensity Reflectivity of the printing plate, which in turn depends on the amount of fountain solution in the area. According to the invention, the printing for the respective print job to be supplied dampening solution is preset, which can be done for example in a known manner by entanglement or a variation of the contact pressure between dampening agent rollers in the dampening unit of the printing press, or in any other known manner. The default of the printing forme supplied dampening solution amount and / or the printing form supplied ink quantity in the default setting is preferably carried out at standstill of the printing press, or in creep operation thereof, whereby the waste of waste is reduced in an advantageous manner.

The presetting of the dampening solution quantity is preferably carried out on the basis of a preset signal value which corresponds to the signal value of the sensor for the dampening solution target value which was determined by the sensor during a preceding print job. The dampening solution target quantity of the previous print job, or the signal value of the sensor assigned to it, which essentially corresponds to the optimum amount of dampening solution for the preceding job, can be stored in a memory, for example. This results in the advantage that a pre-adjustment of the dampening solution can be brought about in a simple manner by increasing the dampening solution amount until the signal value measured by the sensor corresponds to the stored signal value.

Similarly, it is possible to pre-adjust the amount of dampening solution based on a calculated preset signal value, preferably from the signal values of the sensor for the dampening solution target values during two or three several previous print jobs is determined by averaging. It is assumed here that the fountain solution target values of the preceding print jobs essentially correspond to the optimum fountain solution quantity for the set color quantity which has led to an optimum color dampening emulsion in the preceding print jobs. Averaging reduces the influence of signal values of the sensor, which were measured at a non-optimal setting of the color to dampening solution balance in the previous print jobs and stored to form the average value.

In order to ensure that the printing press is operated with an excess of dampening solution when it is started up, it may be provided that the preset signal value is multiplied by a factor preferably preselectable by the machine operator, or a preferably preselectable value is added thereto. By over-moistening when booting the printing presses waste accumulation is advantageously reduced to an acceptable print quality and reduces the risk of penetration or high migration of paper fibers or other contaminants of the substrate due to the stickiness of the ink in the printing unit or even in the dampening unit ,

Following the presetting of the amount of fountain solution supplied, the amount of dampening solution is shut down, for example, by reducing the speed of the scoop roller or reducing the Verschränkungswinkels between the scoop roller and its associated dampening dosing roller, or in another known manner with the printing presses until the signal of The sensor passes a minimum in the area of the lubrication limit and rises again to calibrate the amount of dampening solution. The signal of the sensor in the minimum, which can be determined even more accurately by further known mathematical methods, is preferably stored in a memory of an associated control device.

Following this, the dampening solution quantity is increased again starting from the stored value until the signal from the sensor has a value which corresponds to one Dampening agent quantity default value corresponds. For example, the dampening solution setpoint may be determined by multiplying the signal value of the sensor at the minimum by a predetermined factor and may, for example, be in the range of 14% above the signal value of the sensor at the minimum.

In the same way, it is conceivable that to the signal value of the sensor at the minimum of a preferably predetermined by the printing press operator and variable value is added, which is preferably determined empirically, or is determined by taking into account the color area coverage of the printing form. The predefined factor or the value added to the dampening solution quantity default value are preferably likewise preselectable by the machine operator. This has the advantage that the optimum dampening solution quantity default value can be easily changed by the printer if the color-to-dampening agent balance deviates from a customary default value, for example by selecting another dampening solution additive or by choosing another printing ink.

The predetermined factor or value added to the fountain solution setpoint is preferably determined based on the signal values of the sensor determined at the dampening solution target values for the previous one or more of the preceding print jobs, and preferably stored in a memory of the printing press ,

Preferably, after the amount of dampening solution has been increased by adjusting an associated actuator, for example by increasing the speed of the dampening solution scoop roller or by increasing the angle of attack between a scoop roller and a metering roller applied thereto, until the signal of the sensor corresponds to the signal for the dampening solution quantity default value, the amount of dampening solution is adjusted in a preferably closed control loop to this dampening solution quantity default value. For this purpose, for example, a suitably designed control circuit may be used, for example a PID controller, which is preferably is also implemented in software in the (central) Druckmaschinensteuerungs- and - control device.

If the amount of ink supplied to the printing plate in one or more of the inking zones is increased or decreased from a pre-set ink amount value to a desired ink amount target value subsequent to reaching the fountain solution pre-set value, such as manually by the printer after inspection of the ink first printed copies, or can be done automatically by the machine control in the case of an automatic ink quantity control or - so according to the invention, the dampening solution default value is increased in a corresponding manner and in the same direction to a dampening target.

According to a further embodiment of the invention, increasing or decreasing the dampening solution target value takes place substantially simultaneously with increasing or decreasing the amount of ink to the new target color amount, resulting in a very fast regulation, by which the amount of waste accumulated further reduce. In the same way, however, it may also be provided that the dampening solution quantity target value is increased or decreased only after a preferably predefinable time period after the time at which the ink quantity target value was set by the ink zone control or regulation. In this type of tracking of dampening solution target value, there is the advantage that when controlling the amount of ink in the individual ink zones, the combined ink quantity control and dampening solution amount is less sensitive to oversteer and against vibration.

According to a preferred embodiment of the invention, the value by which the fountain solution target value is increased or decreased is determined by means of stored or calculated signal values of the sensor associated with a respective increase or decrease of the ink quantity target value. The stored signal values of the sensor are preferably determined on an empirical basis and together with the associated values for an increase or decrease in the Color set target value stored in a memory of the printing press, such as a map, as a parameter or parameterized curves.

According to the preferred embodiment of the invention, the ink amount target value is changed in a closed loop, for which the ink coverage or color density on the printing plate or on the substrate according to a known from the prior art method, for example, densitometrically or colorimetrically determined by a corresponding sensor.

According to a further embodiment, the amount of dampening solution supplied is controlled in a closed loop depending on the dampening target value in a narrow range around the dampening solution target value such that oscillation of the dampening solution amount measured by the sensor is reduced by the dampening solution target becomes. In this case, further parameters, such as, for example, the temperature of the dampening solution, the printing plate and / or the speed of the printing press, may be included in the control process by the control device in order to obtain a reliable control of the dampening solution quantity.

The invention will be described below with reference to the drawings with reference to an exemplary embodiment.

Fig. 1

ein Flussdiagramm über die beim erfindungsgemäßen Verfahren ablaufenden Verfahrensschritte,

Fig. 2

den zeitlichen Verlauf der zugeführten Feuchtmittelmenge und den zugehörigen Verlauf des Sensorsignals während der Voreinstellung und des Kalibrierungsvorgangs und beim Erhöhen der zugeführten Feuchtmittelmenge auf den Feuchtmittelmengen-Vorgabewert,

Fig. 3

den Signalverlauf in Abhängigkeit von der zugeführten Feuchtmittelmenge mit dem eingezeichneten Regelbereich für die Feuchtmittelmenge um den Feuchtmittelmengen-Vorgabewert herum und den zugehörigen Sensorsignalen und

Fig. 4

den Verlauf des Sensorsignals in Abhängigkeit von der zugeführten Feuchtmittelmenge nach einer Erhöhung bzw. einer Erniedrigung der zugeführten Feuchtmittelmenge auf einen erhöhten oder erniedrigten Feuchtmittelmengen-Zielwert nach einer entsprechenden Erhöhung oder Erniedrigung der Farbmenge vom Farbmengen-Vorgabewert auf einen neuen Farbmengen-Zielwert.

In the drawings show:

Fig. 1

a flowchart of the process steps in the process according to the invention,

Fig. 2

the time profile of the amount of dampening solution supplied and the associated course of the sensor signal during the presetting and the calibration process and when increasing the amount of dampening solution supplied to the dampening solution quantity default value,

Fig. 3

the waveform as a function of the amount of fountain solution supplied with the drawn control range for the dampening solution to the fountain solution set value around and the associated sensor signals and

Fig. 4

the course of the sensor signal as a function of the amount of dampening solution supplied after an increase or a decrease in the amount of dampening solution supplied to an increased or decreased dampening solution target value after a corresponding increase or decrease in the amount of color from the color set default value to a new color quantity target value.

As shown in FIG. 1, in a first method step 1, the dampening solution quantity supplied to the printing form is set to a dampening solution presetting value V ₀ when the printing press is stationary. The presetting is carried out - as shown in FIG. 2 - on the basis of a preset signal value S ₀ measured by a sensor, which is not shown, to which the supplied dampening solution quantity is preferably increased during standstill or during creeping operation of the printing press. In order to ensure overhydration during calibration of the dampening solution quantity in the subsequent method step 2, the supplied fountain solution quantity is then increased during the creeping operation of the printing machine until the preset signal value of the sensor has increased by a value ΔS to a higher preset signal value S ₁ .

In the subsequent method step 2, as shown in FIGS. 1 and 2, a calibration of the supplied amount of fountain solution is carried out at essentially constant ink quantity. For this purpose, the amount of dampening solution at a time t ₀ (see the lower half of FIG. 2) of the value corresponding to the preset signal value S ₁ for the dampening solution amount until the signal S of the sensor a minimum at the _Run through V _min . The associated value S _{min of} the sensor signal S at the minimum is stored and used as the base value or reference value for the further control and regulation processes of the fountain solution quantity and / or the ink quantity.

In the method step denoted by the reference numeral 3 in FIG. 1, the dampening solution quantity is subsequently adjusted to a preset dampening agent preset value V _default for the respective print job, which can be effected by the dampening solution quantity V continuously returning after passing through the minimum V _min is increased until the signal value S of the sensor reaches the default signal value S _default .

As shown in FIG. 3, the amount of dampening solution is then controlled by the dampening solution quantity default value V _default by means of the signals S of the sensor in such a way - the control preferably takes place in a closed loop - that the dampening solution amount V in the in Fig. 3 hatched drawn area 10 is located, in which an optimum for the printing color-to-dampening emulsion is obtained. The amount of ink is set to a substantially constant color set default value F _default , which is determined, for example, as a function of the ink coverage on the printing form for the associated color on the basis of prepress data. The color quantity default value F _default is expressed in FIG. 3 in that the sensor signal S is a function of the color _{specification} value F _default .

In a next process step 4 (FIG. 1), the ink quantity is increased from the ink quantity default value F _default to a desired ink quantity target value F _{target +} for the print job to be processed or lowered to a lower ink quantity target value F _target , which is shown in FIG. 4 by the two waveforms S (F _{target +} ) and S (F _target ) lying to the right and left of the waveform S (F _default ) is expressed.

As can also be seen in FIG. 4, when the amount of ink is increased from the ink quantity default value F, the _{specification is set} to a higher ink quantity target value F _{target +} the Dampening agent amount also increased to a higher dampening solution target value V _{target +} , which is expressed by the shifted in the direction of arrow 12 curve for the signal S of the sensor.

In a corresponding manner, the supplied dampening solution quantity V is lowered from the dampening solution quantity default value V _target to a lower dampening solution target value V _target if the amount of ink is lowered in accordance with arrow 14 from the ink quantity default value F _default to the lower ink quantity target value F _target . The various curves of the family of curves for the signal curve S with an increase or decrease in the amount of ink, of which only three curves are shown by way of example in FIG. 4, are advantageously stored in a characteristic field as parameters in the preferred embodiment of the invention, so that the to the signal values associated fountain solution quantities can be assigned by reading the parameters. In the same way, however, it is likewise conceivable for the values of the sensor signal S dependent on the amount of ink F and the amount of fountain solution V to be stored as parameterized curves in a memory of the control and regulating device, by means of which the associated signal values S or dampening agent quantities are calculated depending on what size is currently known and which is needed.

Following this, in a fifth method step, the supplied fountain solution quantity V is regulated in a closed control loop as a function of the dampening solution target value V _target , V _{target +} , which advantageously depends on the signal values for the respective dampening solution target values V _target and V _{target +} within the optimum range for the respective color-to-dampening emulsion 10 (see FIG. 3) takes place, which latter is indicated only schematically in Fig. 4.

LIST OF REFERENCE NUMBERS

V

supplied amount of fountain solution

V ₀

Dampening solution quantity at preset signal value

V _default

Moisturizing agent quantity target value-

V _min

Dampening agent quantities at the lubrication limit

V _goal

Dampening agent target value

.DELTA.s

Value is increased by the preset signal value

S

Sensor signal

S ₀

Preset signal value

S ₁

Preset signal value

S _min

Value of the sensor signal at the minimum

S _default

Value of the sensor signal at the dampening solution quantity default value

t

Time

t ₀

Start time at which calibration is started

F _default

F _{target +}

increased color quantity default value

F _target

reduced color quantity default value

1

first process step

2

second process step

3

third process step

4

fourth process step

5

fifth process step

10

Range of optimum color-to-dampening emulsion

12

arrow

14

arrow

Claims (19)

1. Method for controlling the ink/moisturising agent balance in a rotation offset print machine, whereby the moisturising agent quantity especially is determined by means of the signals from a sensor which determines the light reflection capability of an area wetted with the moisturising agent on a print cylinder of the rotation print machine, with the following method steps:

   - pre-adjustment of the moisturising agent quantity to be added to the print cylinder;

   - calibration of the added moisturising agent quantity by means of a substantially consistent ink quantity;

   - adjustment of moisturising agent quantity to a pre-determined moisturising agent quantity value characteristic for the relevant print application; characterised by:

   - the increasing or lowering of the ink quantity from a pre-determined ink quantity value to a desired ink quantity target value for the print application to be processed, and a corresponding increasing or lowering of the pre-determined moisturising agent quantity value in the same direction to a moisturising agent quantity target value; as well as

   - controlling of the added moisturising agent quantity within a closed control cycle depending on the moisturising agent quantity target value.
2. Method according to Claim 1, characterised in that the increasing or lowering of the pre-determined moisturising agent quantity is carried out simultaneously with the increasing or lowering of the ink quantity to the desired ink quantity target value.
3. Method according to Claim 1 or 2, characterised in that the value by which the pre-determined moisturising agent quantity is increased or lowered is determined with the aid of stored or calculated signal values from the sensor, which are allocated to a relevant increase or lowering of the ink quantity target value.
4. Method according to Claim 3, characterised in that the stored signal values from the sensor are determined on an imperial basis and stored together with the associated values for an increasing or lowering of the ink quantity target value in a storage facility in the print machine.
5. Method according to Claim 1, characterised in that the pre-adjustment of the moisturising agent quantity and/or ink quantity supplied to the print cylinder is carried out when the print machine is standing still.
6. Method according to Claim 1, characterised in that the pre-adjustment of the moisturising agent quantity is carried out on the basis of a pre-adjustment signal value which equals the signal value of the sensor for the moisturising agent quantity target value during the preceding print application.
7. Method according to Claim 1, characterised in that the pre-adjustment of the moisturising agent quantity is carried out on the basis of a calculated pre-adjustment signal value, which is determined with the aid of the signal values from the sensor for the moisturising agent quantity target values during two or more preceding print applications by means of median value calculation.
8. Method according to Claim 7, characterised in that the pre-adjustment signal value is multiplied with a factor that can be chosen by the machine operator or increased by a pre-selectable value to ensure an overmoistening during the start-up of the print machine.
9. Method according to one of the Claims 6 to 8, characterised in that the signal value or the signal values from the sensor for the moisturising agent quantity value(s) is/are determined during the slow operation or during the continuous print operation of the print machine.
10. Method according to one of the preceding Claims, characterised in that the moisturising agent quantity supplied for calibration is reduced until the signal from the sensor exceeds a minimum.
11. Method according to Claim 10, characterised in that the pre-determined moisturising agent quantity is determined by multiplying the signal value of the sensor at the minimum with a pre-determined factor for adjusting the moisturising agent quantity, and in that the supplied moisturising agent quantity is increased following the exceeding of the minimum until the signal from the sensor reached a value which equals the pre-determined moisturising agent value.
12. Method according to Claim 10, characterised in that the pre-determined moisturising agent quantity is determined by adding a pre-determined value to the signal value from the sensor at the minimum, and in that the supplied moisturising agent quantity is increased following the exceeding of the minimum until the signal from the sensor reaches a value that equals the pre-determined moisturising agent value.
13. Method according to Claim 11 or 12, characterised in that the pre-determined factor or the value that is to be added to the pre-determined moisturising medium quantity can be pre-determined by the machine operator, and in that the supplied moisturising medium quantity is increased following the exceeding of the minimum until the signal from the sensor reaches a value that equals the pre-determined moisturising medium quantity value.
14. Method according to Claim 11 or 12, characterised in that the pre-determined factor or the value added to the pre-determined moisturising medium quantity value is determined on the basis of signal values from the sensor equalling the moisturising medium target values for preceding print applications, and in that the same is stored in a storage facility of the print machine.
15. Method according to one of the preceding Claims, characterised in that the increasing or lowering of the ink quantity to the ink quantity target value is carried out in a closed control cycle by means of one or more additional ink sensors.
16. Method according to Claim 15, characterised in that the ink sensors detect the ink density on the print cylinder or the material to be printed onto in a colorimetric or densitometric way.
17. Method according to one of the preceding Claims, characterised in that the ink quantity supplied to the print cylinder is adjusted to the pre-determined ink quantity value prior to calibration.
18. Method according to one of the preceding Claims, characterised in that the calibration is carried out prior to accelerating the print machine to operating speed.
19. Method according to one of the preceding Claims, characterised in that the control of the supplied moisturising medium quantity occurs in a closed control cycle depending on the moisturising medium quantity target value in the way that a variance of the measured moisturising medium quantity around the moisturising medium quantity target value is reduced.

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