Method and device for controlling humidity of belt-shape material in pringting machine

Abstract

The invention relates to a method and device for controlling the humidity of strip materials in a color printing press. By measuring the width of a mark printed at one station and the width of a mark printed at the next station; measuring the random occurrence between two printings. The width difference of The correction signal acts on each dryer at the lower station of the printing press. This results in better alignment accuracy of one color on top of another and shorter negative feedback time.

Description

technical field [0001] The present invention relates to a method and combination for controlling the moisture content of web material such as paper or cardboard in a color printing press having a plurality of stations in which subsequent primaries are printed on top of previous primaries in each printing. Background technique [0002] Such printing presses generally have means to control the transverse and / or longitudinal alignment of the print. Such devices are generally based on one or several photocells or other sensors for detecting the position of adjacent printed characters and / or additional printed characters on the blank space of each station. The computer receives the signal from the sensor to determine the error of the longitudinal and transverse alignment marks, and gives a correction signal to move the compensation roller and the printing roller to correct the alignment marks. [0003] Thanks to such an alignment control device, it is possible to superimpose som...

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Problems solved by technology

[0008] We immediately see that, contrary to the assertions of US Patent 4,798,136, the system described is not a substitute for the means of controlling longitudinal orientation and lateral orientation operated by printed logos

In fact, there are reasons for disturbing the positioning, such as the unevenness of the paper tape due to the lateral deviation, the change of the elastic coefficient due to the longitudinal deviation, the change of the traction pull, the inertia and friction of the return roller, etc., which require correction of a The relative position of a typographical element to another typographical element, for which the above system cannot do anything

[0009] In addition, it also involves correcting for variations in print width, and in practice it has been proven that such a device is completely incapable of guaranteeing very precise print alignment at the edges of wide paper strips traveling at high speeds

And the width of the paper web can never be kept strictly constant on all conveyor rollers

while the inherent inhomogeneity makes it difficult to correct for

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