Abstract
A method for controlling the inking in a printing press includes compensation of an ink requirement in an inking unit and/or compensation of a dampening solution requirement in a dampening unit of the printing press in the event of a change in the printing speed. The printing speed profile or machine state prevailing before the instant of the change in the printing speed is taken into consideration in the compensation of the metering of ink or dampening solution.
Claims
1. A method for controlling inking in a printing press, the method comprising the following steps: compensating metering of at least one of ink in an inking unit or dampening solution in a dampening unit of the printing press upon a change in printing speed; and taking a printing speed profile including all changes in the printing speed before an instant of the change in the printing speed or a machine state prevailing before the instant of the change in the printing speed into consideration in the compensation of metering of at least one of the ink or the dampening solution.
2. The method according to claim 1, which further comprises selecting the machine state as either a stable continuous printing phase, a start-up after washing a rubber blanket, a start-up without washing the rubber blanket or a print job change.
3. The method according to claim 1, which further comprises, if there is too much ink in the inking unit, carrying out the compensation of the ink metering in a delayed manner upon an increase in the printing speed, but carrying out the compensation of the dampening solution metering immediately.
4. The method according to claim 1, which further comprises, if there is too little ink in the inking unit, carrying out the compensation of the ink metering immediately upon an increase in the printing speed, but carrying out the compensation of the dampening solution metering in a delayed manner.
5. The method according to claim 3, which further comprises carrying out the delay proportionally to a speed difference.
6. The method according to claim 4, which further comprises carrying out the delay proportionally to a speed difference.
7. The method according to claim 1, which further comprises carrying out the compensation of the ink metering in a delayed manner and carrying out the compensation of the dampening solution metering immediately in a printing press having a blanket cylinder with a rubber blanket, during a start-up of the printing press without washing the rubber blanket on the blanket cylinder or upon a print job change at a lower continuous printing speed than in a preceding print job.
Description
BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING
(1) FIG. 1 is a diagrammatic, longitudinal-sectional view of a sheet-fed offset printing press having a control computer which is programmed according to the invention;
(2) FIG. 2 is a flow chart showing an overview of decision criteria of the control computer during selection of a suitable speed compensation of ink and dampening solution;
(3) FIG. 3 is a flow chart showing a speed compensation during a change in the printing speed in a stable continuous printing phase;
(4) FIG. 4 is a flow chart showing a speed compensation during ink input as a function of a continuous printing speed of a current print job in comparison with a speed during ink input;
(5) FIG. 5 is a flow chart showing a speed compensation during start-up of the printing press after washing of a rubber blanket;
(6) FIG. 6 is a flow chart showing a speed compensation during start-up of the printing press without washing of the rubber blanket;
(7) FIG. 7 is a flow chart showing a speed compensation during a print job change as a function of the continuous printing speed of the current print job in comparison with that of a preceding print job; and
(8) FIG. 8 is a diagram showing a relationship of printing speed compensation for overdriving inking after washing of the rubber blanket to printing speed difference.
DETAILED DESCRIPTION OF THE INVENTION
(9) Referring now to the figures of the drawings in detail and first, particularly, to FIG. 1 thereof, there is seen a printing press 1 which has two printing units 3, 4, each having a respective inking unit 16, 17 and dampening unit 18, 19. The inking units 16, 17 serve for ink metering and have electric actuating motors which are connected to a control computer 5 of the printing press 1. The ink which is metered in the inking units 16, 17 can be dampened by way of the dampening units 18, 19. The dampening solution metering in the dampening units 18, 19 can also be controlled by the control computer 5. The metered and dampened ink is first of all transferred onto plate cylinders 11, 12 carrying printing plates in the printing units 3, 4, and from there onto blanket cylinders 13, 26. From there, a printing image is then transferred in a press nip between the blanket cylinders 13, 26 and impression cylinders 10, 28 onto printing sheets 9 which are situated in the printing press 1. The printing materials or sheets 9 are transferred between the two printing units 3, 4 through the use of a transport cylinder 14. Required new printing sheets 9 are raised up from a feed stack 8 in a feeder 2 through the use of a suction apparatus and are fed to the first printing unit 3 over a suction belt table. Following the second printing unit 4, the finished printing materials 9 are transferred to gripper chains in a delivery 6 and are deposited on a delivery stack 7.
(10) The control computer 5 of the printing press 1 is connected over communications links 22 to all of the electric adjusting motors of the printing press 1, in order to be able to perform the desired adjusting operations. In particular, the control computer 5 can adjust individual inking zones in the inking units 16, 17 in order to meter the ink. Moreover, a display screen 15 is connected to the control computer 5. The operating state of the printing press 1 is shown on the display screen 15 and inputs of the operating staff are possible through the display screen 15. Furthermore, an external color measuring instrument 20 is connected to the control computer 5 through a communications link 22. The color of finished printed sheets 9 which are deposited in the delivery stack 7 can be measured by way of the external color measuring instrument 20. To this end, the printed sheets 9 have to be removed from the delivery stack 7 by the operating staff and have to be placed under the color measuring instrument 20. Furthermore, the printing press 1 has an inline color measuring device 21 at the outlet or exit of the second printing unit 4, which can likewise measure the color of the printed sheets 9. The produced printed sheets 9 can have their color measured continuously by way of the inline color measuring device 21, with the result that color measured values can be transmitted continuously to the control computer 5 by the inline color measuring instrument 21. In the control computer 5, the color measured values which are detected in this way are compared with a setpoint coloring S which is predefined by the operating staff and is dependent on the respective print job and the associated printing original. The setpoint coloring S serves as a target value for a corresponding ink presetting characteristic curve in the inking units 16, 17 of the printing press 1.
(11) FIG. 2 depicts decision criteria for the control computer 5 which detects the machine state and the change in the printing speed. First of all, the control computer 5 determines whether or not a change in the printing speed is carried out. If this is not the case, nothing is changed about the ink and dampening solution metering. If, however, the control computer 5 has determined a change in the printing speed, the machine state is retrieved. By way of example, but not exclusively, five machine states which the control computer 5 retrieves through sensors or a running printing program of the printing press 1 are shown in FIG. 2. If a change in the printing speed takes place in a stable continuous printing phase, a speed compensation 1 is performed. If the printing press 1 is currently situated in an ink input phase, a printing speed compensation 2 is performed. During start-up of the printing press 1, after washing the rubber blanket (RB) on the blanket cylinder 13, 26, a speed compensation 3 takes place. If the printing press 1 is started up without washing of the rubber blanket on the blanket cylinder 13, 26, a speed compensation 4 takes place. If there is a print job change, a speed compensation 5 is performed. These five speed compensations are shown in the following FIGS. 3 to 7.
(12) FIG. 3 depicts the speed compensation 1 which is performed during a change in the printing speed in the stable continuous printing phase. In the stable continuous printing phase, the printing unit 3, 4 is situated in a stationary stable state. If, however, the printing speed is increased, more ink and dampening solution have to be supplied. Since, however, the increase in the dampening solution metering is discernible much more rapidly than the increase in the ink metering, the dampening solution metering is initiated subsequently in a delayed manner, in order to prevent a reduction in the ink density on the printing material 9. In the case of a reduction in the printing speed, however, a distinction has to be made as to whether a new stable state is aimed for or the printing press 1 is stopped. If the printing press 1 is to be stopped, the compensations of ink and dampening solution take place immediately. Otherwise, the procedure is as in the case of an increase in the printing speed.
(13) In FIG. 4, a speed compensation takes place during the ink input. In this machine state, the printing unit 3, 4 is not situated as a rule in a stationary stable state. The ink input usually takes place at a different speed than at a continuous printing speed. The speeds of the ink input and continuous printing therefore have to be taken into consideration in this case. If the ink input speed S II is lower than the continuous printing speed S Continuous Printing, the ink has to be compensated immediately and dampening solution metering has to be compensated in a delayed manner, in order to achieve equalization as rapidly as possible. If, however, the ink input speed S II is greater than the continuous printing speed S Continuous Printing, this leads to an excessive supply of ink, and ink and dampening solution are compensated immediately.
(14) A further machine state illustrated in FIG. 5 is the start-up of the printing press 1 after washing of the rubber blanket on the blanket cylinder 13, 26. In this case, that ink quantity which corresponds to the continuous printing state is situated in the printing unit 3, 4. Since, however, the resistance of the printing unit 3, 4 as a rule rises at higher printing speeds, the ink quantity is too great for the starting speed. However, the corresponding ink quantities are missing at the start on the rubber blankets of the blanket cylinders 13, 26. The first printed sheets 9 are therefore usually underinked, for which reason ink and dampening solution are compensated immediately, in order to avoid such underinking.
(15) FIG. 6 illustrates speed compensation during start-up of the printing press 1 without washing of the rubber blanket on the blanket cylinder 13, 26. That ink quantity which corresponds to the continuous printing state is also situated in the printing unit 3, 4 in this case. Since, however, the rubber blanket is not washed, ink is still situated correspondingly on the rubber blanket. Since the resistance of the printing unit 3, 4 as a rule rises at higher speeds, the ink quantity is too great for the starting speed. In this case, this leads to clear overinking of the first sheets 9. In order to avoid such overinking, the dampening solution is compensated immediately and the ink metering is initiated subsequently in a delayed manner.
(16) FIG. 7 shows the speed compensation after the print job change. In this case, the state is similar to after an ink input. The printing unit 3, 4 is not situated as a rule in a stationary stable state. The most important influencing parameter in this case is the printing speed of the preceding print job S PR. If this printing speed S PR is greater than that of the following job S Continuous Printing, the ink quantity in the inking unit is too great; if it is lower, the ink quantity is too small. In the first case, the ink is therefore compensated in a delayed manner and the dampening solution is compensated immediately, in order to dissipate the excessive ink quantity. In the second case, the ink is compensated immediately and the dampening solution metering is compensated in a delayed manner, in order to obtain correspondingly more ink in the inking unit 16, 17.
(17) FIG. 8 shows the start-up behavior of the printing press 1 during restarting of the printing press after washing of the rubber blanket. In this case, the printing speed difference (ds), that is to say the speed difference between the starting sheet and the continuous printing speed S Continuous Printing, is plotted on the x axis, and the difference in the ink density which results from the overinking during restarting after washing of the rubber blanket, is plotted on the y axis. The greater the printing speed difference, the greater the difference in the ink density.
