The invention relates to a web guiding device for guiding a material web, in particular a film web, and a device for processing a material web, in particular a film web.
During the processing of material webs, such as for example film webs or paper webs, in an embossing device, printing devices or the like, the material webs are as a rule provided on reels, unwound for processing, guided to the processing position via deflection rollers and sometimes then wound up again.
If, when a new reel is provided, the material web is drawn in obliquely or asymmetrically, different tensile forces act on opposite edge areas of the material web, which can lead to creasing, folding or tearing of the material web.
However, in some cases, an asymmetrical, i.e. oblique drawing-in of a material web can also be desirable, for example in order to guarantee that an edge area of the material web is under high material tension—and therefore smooth—in order in particular to make possible a reliable reading of register marks or the like.
Irrespective of whether an asymmetrical drawing-in of the material web takes place in a targeted or undesired manner, it is necessary to correct such an asymmetry again as early as possible in order to avoid the above-named defects.
It is known to use web guide rollers with integrated differential gear to compensate for an oblique drawing-in. A detection of an oblique drawing-in and an active correction of the web guidance by active adjusting means, for example pneumatic, hydraulic or electric adjusting cylinders or the like, are also known. Such devices are however complex, expensive to buy and susceptible to faults.
Furthermore, to compensate for symmetrical web tensions, as can also occur when the web is drawn in straight, for example because of an out-of-roundness of the reel, so-called dancer rollers are known. Under varying tensile stress of the web, these swing perpendicular to the direction of extension thereof and thus again compensate for the tensile stress. However, they are not suitable for compensating for an oblique drawing-in.