Winding – tensioning – or guiding – Tension control or brake – Supply controlled
Reexamination Certificate
1999-04-29
2001-02-27
Jillions, John M. (Department: 3653)
Winding, tensioning, or guiding
Tension control or brake
Supply controlled
C226S034000
Reexamination Certificate
active
06193184
ABSTRACT:
The present invention relates to a method and a system for controlling a material web, preferably of paper or plastic and in particular in connection with the packaging of products such as edible ice products, whereby at least one web is guided in an S-configuration over a set of guiding rollers in order to achieve a stabilized web tension.
In connection with a continuous advancing of a paper web—from unreeling to working or handling—in, for example, packaging machines for flow packing it is known to regulate the tension of the web in order to ensure a well defined longitudinal folding of the web, yet also to avoid that the guiding edges used for such a folding exhibit a cutting effect or even cause a rupture of the web, while a stabilized tension of the web also contributes to ensuring a desired uniformity of the final products.
For the folding it is important that the paper web is drawn over the folding edges with a sufficient tension to ensure that a longitudinal folding will take place, but without the tension being so high that the web is ruptured as a consequence of the folding edges being turned into cutting edges. Likewise it is important that the web be held correctly positioned in the lateral direction relative to the folding edges in order to ensure the desired folding profile relative to imprint details on the wrapping web.
The paper web is advanced in being pulled through the packaging line from the outer end of the web, by suitable advancing means such as draw rollers.
The tension in the web occurs by virtue of the web being pulled outwardly from a tension adjustment system, in which it is exposed to a controllable friction, based on a current detection of the web tension. In the adjustment system the web is guided about a synchronously rotating friction roller with an adjustable deflection angle, the web as paid out from this roller being guided about a delivery roller in the form of a dancing roller, the position of which is controllable for adjustment of the said deflection angle of the web. When the friction roller is driven with a peripheral speed corresponding to the moving speed of the web, a well defined frictional engagement is established between the web and the roller surface, given by the particular friction coefficient, the deflection angle and the pressure of the web against the roller surface. If for some reason a rising or falling web tension occurs, such a change may be return adjusted by causing the dancing roller to change its position for changing the said deflection angle of the web for a corresponding decreasing or increasing of the web friction against the roller, until the tension is detected to be normal.
In principle, all this functions well in practice, but the requirement of both a web tension detector and a moving system for the said dancing roller is a complication, and another problem is that in general the web tension has to be relatively high, higher than optimally desirable.
There is an associated, different problem, viz. with respect to the correct positioning of the web in the transverse direction. It is well known that in connection with the advancing of web materials via guiding rollers it is almost impossible to effect a lateral adjustment by mechanical abutment means in case of small changes of the web direction at the intake end, so it is required, moreover, to use detection means for detecting lateral displacements of the web and, controlled thereby, means for compensation adjustment of a roller for achieving an accurate lateral positioning of the paid out web, this being a significant additional and expensive complication. The problem is due to the fact that in case of a noticeable friction between a web material and a support surface therefor it is not possible to subject the web to an effective lateral displacement just by applying pressure to a side edge of the web, viz. when the web itself is not sufficiently stiff to be able to transfer the required pressure to the whole width of the web for overcoming the said friction-with the support surface.
In plural lane packaging systems, more webs are moved in parallel through the packing machine, such that packing can be effected in a plurality of lanes for increasing the overall capacity of the system. These webs, which are advanced with the same speed, are handled by common friction and pay-out rollers and are also moved through a common tension adjustment station. Thus, the handling of the webs in plural lane systems is not particularly complicated due to the additional webs. However, problems may arise in case of production disturbances imparting changes in the tension of the single webs, and besides, the plural lane system is limited to the handling of the same products in all the packaging lanes.
On this background, it is the purpose of the invention to provide a method and an associated system for adjusting the tension of a paper or sheet web to a relatively low tension level. Moreover, it is desired to provide a method and a system that will be well suited for individual control of the webs in plural lane packing machines.
Basically, the invention is characterized in that the friction roller in the web tension adjustment station is driven with a peripheral speed which is substantially higher than the advancing speed of the web, such that a sliding friction is established between the web and the friction roller.
With the invention, an entirely novel principle for the adjustment of the tension in a paper or sheet web has been provided.
Inasfar as the friction roller is driven with a noticeably higher speed, the web will be subjected to an “auxiliary drive” due to the friction, but now it is no longer the static friction, but a considerably lower dynamical friction by the provoked marked sliding between the elements. Accordingly, a drop in tension in the paid out web will occur across the friction roller, compared to the tension at the intake side, resulting in a decreased tension in the web as advanced through the folding tools, whereby the risk of damaging the web by these tools will be lowered considerably.
Moreover, the sliding engagement will condition a self adjusting effect with respect to the web tension, such that the adjustment system will not have to include special sensor or controlling units. Should the web tension decrease, the web will be pulled against the friction roller with a lower force, whereby the sliding friction and therewith the auxiliary drive effect of the friction roller will decrease. For a lower auxiliary drive effect of the friction roller, the said tension reducing effect on the web will also be decreased, whereby the original tension in the web will be reestablished automatically. Correspondingly, the auxiliary drive will be strengthened if the web tension tends to rise, this primarily referring to the tension in the web stretch between the web supply reel and the adjustment system, as the web is unreeled. Thus, the pulling off of the web will be effected with an increasing force, but in such a manner that the increased tension will not be transferred to the web length delivered from the adjustment system.
Thus, with a system according to the invention it is not a requirement to be able to change the deflection angle about the friction roller in order to adjust the web tension. The pay-out roller arranged in connection with the friction roller, need not be dynamically movably arranged, although it will of course still be an option that it could be arranged as a dancing roller in order to still enable a change of the deflection angle. However, it should be position adjustable, viz. to a correct position relative to the actual friction coefficient.
The disclosed principle of the invention is also well suited for use in a plural lane packaging machine, where more webs are advanced in parallel, inasfar as the tension of the single webs as handled by common friction and pay-out rollers is individually self adjusting, implying allowable variations of the material structure and thickness etc. of the paper webs, without this affecting the qual
Jillions John M.
Nixon & Peabody LLP
Safran David S.
Tetra Pak Hoyer A/S
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