Ink printing apparatuses can be used for single or multicolor printing of a printing substrate web, for example a belt shaped recording medium made of the most varied materials (for example paper). The design of such ink printing apparatuses is known, see for example EPO 788882 B1. Ink printing apparatuses that operate according to the drop-on-demand (DoD) principle have a print head or multiple print heads with nozzles comprising ink channels, the activators of which nozzles—controlled by a printer controller—excite ink droplets in the direction of the printing substrate web, which ink droplets are deflected onto the printing substrate web in order to apply printing dots there for a print image. The activators can generate ink droplets thermally (bubble jet) or piezoelectrically.
In the printing of a printing substrate web it is sometimes necessary to halt the printing substrate web during the printing operation in a pause function, for example in order to monitor the register quality after printing a print job, or to correct problems in the post-processing of the printing substrate web. After running up the printing substrate web again, print image disruptions can then occur at those web segments that were located directly under the printing nozzle after activation of the pause function. Due to the relatively large transfer printing zone in ink printing apparatuses (for example inkjet printing systems), in particular in color printing, the print image disruptions that occur due to the pause cause a correspondingly large amount of spoilage. The occurring print image defects include print image distortions or color register errors. The causes for these are the swelling or shrinking of the printing substrate web during the pause and, connected with this, the position shifts of the printing substrate web below the printing heads.
These problems are explained using
In
Upon triggering the pause function, the following effects on the printing substrate web 3 are thus to be considered:
It is an object to specify a method in which, after triggering a pause function, the unwanted influences of the temperature and the environment air on the printing substrate web (and therefore on the print image) are minimized, in particular after ending a printing pause.
In a method to execute a pause function of an ink printing system wherein a printing substrate web is printed with a printing unit with print bars having print heads, a real value of a web tension of the printing substrate web is measured with a web tension sensor. In a printing operation the real value of the web tension is regulated to a predetermined desired operating value of the web tension. With triggering of the pause function, the web tension is further regulated by modifying the desired value of the web tension so that the printing substrate web assumes a position at the print heads after an end of the pause function that it had before a beginning of the pause function. After the end of the pause function, the real value of the web tension is regulated again to the desired operating value of the web tension.
For the purposes of promoting an understanding of the principles of the invention, reference will now be made to a preferred exemplary embodiment/best mode illustrated in the drawings and specific language will be used to describe the same. It will nevertheless be understood that no limitation of the scope of the invention is thereby intended, and such alterations and further modifications in the illustrated embodiment and such further applications of the principles of the invention as illustrated as would normally occur to one skilled in the art to which the invention relates are included.
According to the exemplary embodiment, a real value of web tension of the printing substrate web is measured with a web tension sensor, and the real value of the web tension is regulated to a predetermined desired value of the web tension (called a desired operating value in the following) of the printing substrate web. This regulation of the web tension of the printing substrate web also takes place during a printing pause. With triggering of the pause function, the desired value of the web tension of the printing substrate web is altered, starting from the desired operating value, so that after the end of the pause the printing substrate web assumes the position at the print heads that it had assumed before the beginning of the pause. After the end of the pause, the real value of the web tension of the printing substrate web is regulated to the desired operating value of the web tension again.
If a swelling of the printing substrate web occurs during the printing pause, the desired value of the web tension decreases after triggering the pause function. Conversely, the desired value of the web tension increases after triggering the pause function if a shrinking of the printing substrate web occurs during the printing pause.
An advantage of the method according to the exemplary embodiment lies in that, after ending the pause, a web segment of the printing substrate web that was situated under the print heads before the pause lies below the printing unit. This result is achieved solely with the printer controller used to regulate the web tension of the printing substrate web, such that no additional components are required.
The exemplary embodiment is shown in drawing figures.
According to
In the exemplary embodiment, the real value of the web tension, measured by the web tension sensor 10, is now related to the second servo amplifier SV 2 to which the desired value of the web tension is also supplied. The regulator 13 comprised in the second servo amplifier SV 2 now regulates the real value of the web tension to its desired value. This desired value is the predetermined desired operating value matched to the printing operation. For example, if the real value of the web tension is too low, the take-off roller 9 is accelerated until the desired value of the web tension of the printing substrate web 3 is achieved. The same accordingly applies if the real value of the web tension is too high; here the rotation speed of the take-off roller 9 is reduced until the desired value of the web tension has appeared.
In the exemplary embodiment, the drive roller 7 is the master drive; the take-off roller 9 follows the driver roller 7 in slave operation. However, the take-off roller 9 can also be used as a master driver, the drive roller 7 can operate in slave operation, and the regulator for the web tension can be arranged in the first servo amplifier SV1.
If the printing operation transitions into a pause, the initially illustrated problems occur. For example, the printing substrate web 3 can swell during the pause if it is exposed to moisture, or it can shrink if it is exposed to heat.
In both cases, during the pause the printing substrate web 3 is moved with the result that, after the end of the pause, the position of the printing substrate web 3 relative to the print heads 5 has changed in comparison to the position of the printing substrate web 3 before the pause. The result is that the print dots generated by print heads 5 that print the printing substrate web 3 after the pause are shifted relative to the desired position of these print dots, such that print image errors occur.
In order to avoid these print image errors, according to the exemplary embodiment the desired value of the web tension (at the drive unit that regulates the web tension) is changed at the beginning of the pause, starting from the desired operating position, so that the position of the printing substrate web 3 under the print heads 5 after the end of the pause corresponds to their position before the beginning of the pause.
In the first case (swelling of the printing substrate web 3), the desired value of the web tension is decreased by such an amount from the desired operating value (starting at the beginning of the pause), and the regulator 13 is affected, so that the position of the printing substrate web 3 coincides after the end of the pause with the position of the printing substrate web 3 that existed before the beginning of the pause. The extension of the printing substrate web 3 that was generated by the swelling then does not lead to a shift of the position of the printing substrate web 3 after the end of the pause. The take-off roller 9 tensions the printing substrate web 3 such that the extension due to the swelling is compensated after the course of the pause. An example of this case can be learned from
A comparable result can then be achieved if, in the first case, the desired value of the web tension of the printing substrate web 3 is increased before triggering the pause and the desired value of the web tension is set at the desired operating value during the pause.
The same accordingly applies to the second case. Here, before triggering the pause the desired value of the web tension of the printing substrate web 3 is decreased and, during the pause, the desired value of the web tension is set to the desired operating value.
The dependency of the length change of a printing substrate web 3 on the humidity or on the temperature per type of printing substrate web 3 is known or—in the case of operation—can be determined via measurement per printing apparatus and type of the printing substrate web, and the desired values of the web tension can be associated with these measurement values. These desired values can then be stored in the control circuit RS and, depending on the type of printing substrate web 3 that is used in the printing operation, can be supplied as a desired value of the web tension to (for example) the regulator 13 of the take-off roller 9 upon triggering of the pause function.
Although a preferred exemplary embodiment is shown and described in detail in the drawings and in the preceding specification, it should be viewed as purely exemplary and not as limiting the invention. It is noted that only preferred exemplary embodiment is shown and described, and all variations and modifications that presently or in the future lie within the protective scope of the invention should be protected.
Number | Date | Country | Kind |
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10 2011 054 693 | Oct 2011 | DE | national |
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