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

Abstract

The humidity control system for the band of material passing through a printing machine includes photoelectric detectors (10,20) detecting the position of a mark on the left and a mark on the right of the material. This allows determination of the size of the print produced by the first station (11), whilst further marks allows determination of the size of the print produced by the second station (12). The detectors are connected to an electronic processing circuit (30) which determines the difference between the printing sizes. In the event of three being a significant difference in the sizes controls (52,54) are automatically used to drying and / or use of water vapour at each station to correct the humidity and consequently the difference in size.

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...

AI Technical Summary

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

Images