FI94779C - Method and apparatus for controlling the variation of the transverse stress of a web - Google Patents

Description

94779

Method and apparatus for adjusting the transverse variation of web tension Förfarande och anordning för regiering av Variationen päden tvämktade spänningen av en bana 5

The invention relates to a method for adjusting the transverse variation 10 of the web tension, in which method the transverse variation of the web tension is measured.

The invention also relates to a device for adjusting the transverse variation of the web tension, which device comprises a measuring device for measuring the transverse variation of the web tension.

With regard to the prior art, reference is made to Finnish patent 80,522, which discloses a method and apparatus for measuring the tension of a moving web. In this known method, the tension of the web is measured indirectly by measuring the pressure of an air mattress formed near the web, having a measuring strip at least partially curved in the direction of travel of the web, and a moving mattress proportional to the web tension. When the pressure is measured at several points on a straight line approximately perpendicular to the direction of travel of the web, the transverse variation of the web tension is measured.

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Finnish patent 85,524 discloses a method for producing uniform paper and a drying section of a paper machine intended for the application of the method. In this known solution i, a measuring technique according to FI patent 80 522 is used to control the paper machine to measure the transverse variation of the web tension. Based on the measurement result 30, the structure of the paper web is influenced in such a way that a uniform tension as well as a uniform moisture is achieved in the paper web.

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With regard to the prior art, reference is further made to WO 91/03600, which discloses a method of operating a paper machine to provide a constant tension as well as a constant thickness in a paper web. In the solution, the tension of the paper web is measured by the so-called by means of a roll with a fragmentary roll structure, and in addition to this, a measurement of the thickness of the paper web is performed.

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The transverse variation of the paper web tension causes a number of problems, which makes it particularly important to control the transverse variation of the paper web tension. With slitters, local variations in the tension of the paper web cause runnability problems because the loose points in the free web cause flutter, 10 creases on the rollers and blades. In addition, the blades may have web breaks or the formation of bellows, i.e. bends. The overtight points of the web, in turn, easily cause web breaks.

In winding the paper web, local variations in the tension of the paper web cause the rolls 15 to vary in tightness, i.e., both loose rolls and tight rollers are formed. Similarly, there are defect problems in a single roll, such as crepe wrinkles and local side throw, and so on.

In coating machines, local variations in web tension cause a poor tension profile of 20, which increases the lateral displacement of the web. As a result, web edge cutters may have breaks. The local variation of the web tension impairs the application and increases the possibility of the tongue in the application.

Problems in coating machines due to local variations in paper tension also occur in paper machines, as, for example, in paper web drying, local variations in web tension increase wrinkles due to flutter and bagging, and • particularly tight web points cause paper web polishing and possible breaks.

In the prior art, the problems described above have been eliminated by influencing the structure of the web in order to achieve the desired tension. However, changing the structure of the web * 1 I iU t lilll Evening · 3 94779 is often relatively expensive and it is not always even possible to change the structure of the web (eg slitters).

The object of the invention is to provide a method and a device in which a transverse variation of the web tension 5 can be made desired without having to try to change the structure of the web.

The object of the invention is achieved by a method characterized in that in the method, based on the measurement result of the transverse variation of the web tension, the device influencing the transverse variation of the distance traveled by the web is adjusted so as to make the transverse variation of the web tension desired.

The device according to the invention is characterized in that the device has a controller which, on the basis of the measurement result of the transverse variation of the web tension, adjusts the device influencing the transverse variation of the distance traveled by the web 15 so that the transverse variation of the web tension can be changed as desired.

Numerous significant advantages are achieved with the method and device according to the invention. The method and device according to the invention are suitable for cases in which, in principle, it is no longer possible to influence the structure of the web. Naturally, the method and device according to the invention can also be applied to situations in which it would still be possible to change the structure in principle (e.g. a local runnability problem with a coating machine), but even then it is not primarily necessary to try to change the web structure. Thanks to the method 25 and the device according to the invention, it is possible to avoid, for example, the runnability problems described above with slitters, coating machines as well as paper machines and other disadvantages caused by local variation in web tension.

The invention will be explained in detail with reference to some preferred embodiments of the invention shown in Figures 30 of the accompanying drawings, to which, however, the invention is not intended to be exclusively limited.

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Figure 1 shows a schematic side view of a method for measuring the transverse variation of web tension used in the method and apparatus according to the invention.

Fig. 2 shows a schematic side view of a preferred support solution for the floating strip used in the embodiment according to Fig. 1.

Fig. 3 shows a schematic block diagram representation of a web tension adjustment method used in the embodiment of Figs. 1 and 2.

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Figure 4 shows a schematic side view of another preferred embodiment of the method and device according to the invention.

The measuring method shown in Fig. 1 for measuring the transverse variation 15 of the tension of the web 10 is in principle exactly the same as the measuring method presented in Finnish patent 80,522. The floating strip 11 is provided with a plurality of spaced measuring openings 12 which are substantially perpendicular to the direction of travel of the web 10. The measurement result is led through a hose 13 to a pressure measuring device 14. According to Fig. 2, the floating strip 11 is supported on the frame 15 by spaced apart support points 16.

As shown in Figure 3, pressure values or web tension-proportional values 17 are derived from the pressure measuring unit 14 to a controller 18 which provides position signals 19 to actuators (not shown) which move the support points 16 as indicated by arrow 25. Thus, in the method and device according to the invention, the support point 16 can be adjusted locally vertically so that the distance traveled by the web 10 in the direction of travel, i.e. in the machine direction, changes and thus the transverse distribution of the machine direction tension of the web 10 changes.

In the embodiment of Fig. 4, the pressure measurement is performed in the same way as in the embodiment of Figs. 1 and 2, but in the embodiment of Fig. 4 the controller 18 provides a position signal 19 to a device for transverse variation of web travel, in this embodiment on a spreading strip 20 spaced from the production line. 11, i.e. apart from the measuring device. An embodiment according to Figure 4 illustrates an embodiment in which the web 10 passes from the roll 22 5 under the guidance of a guide roller 23 to a floating strip 11 or other similar measuring device and then guided by a guide roller 24 onto a spreading strip 20. After the spreading strip 20 the web 10 passes into a winding structure 25,26.

In the method and apparatus according to the invention, pressure measurement values describing the variation of the transverse tension 10 of the web 10 or values proportional to tension derived therefrom are input to a controller 18, where position signals 19 are calculated . The method and device according to the invention are not critical to the selected tension measuring method and measuring device, but the transverse variation of the tension of the web 10 can be measured by any measuring method known per se. Instead of the floating strip 11 or the spreading device 20, it is also possible to use, for example, a spreading roller or a spreading tube or another similar solution. The method according to the invention generally does not affect the tension level of the web 10, but locally affects the transverse variation of the longitudinal tension of the web 10 20. However, there are cases, such as a coating machine, in which the tension level can be affected by the application, but in this case other adjustments known per se restore the tension level.

Only some preferred embodiments of the invention have been described above, and it will be apparent to those skilled in the art that numerous modifications may be made thereto within the scope of the inventive idea set forth in the appended claims.

Claims (13)

1. A method for controlling the transverse variation in the voltage of a path (10), in which method one measures the transverse variation of the voltage on the path (10), characterized in that in the method on the basis of the measurement result of the transverse variation on the tension of the web (10) regulates the device (11, 20) which affects the transverse variation of the distance which the web (10) ran in such a way that the transverse variation in the tension of the web (10) is changed in the desired manner. 10 Method according to Claim 1, characterized in that the device (11) which affects the transverse variation of the distance traveled by the web (10) consists of a floating strip (11) located adjacent the web (10) and which in the running direction of the web (10). ) has at least a partially curved surface, which strip is supported by spaced apart support points (16). Method according to claim 2, characterized in that the floating strip (11) is used as a measuring device (11,12,13,14) for the transverse variation of the tension on the web (10). 20 Method according to claim 1, characterized in that the device (20) which affects the transverse variation of the distance traveled by the web (10) is a propagation strip separate from the measuring device (11,12,13,14), a propagation roller, a propagation tubes or other equivalent solution (20). 25 5. A method according to any of claims 1-4, characterized in that the: transverse variation in the tension of the web (10) is measured indirectly by measuring the pressure on the air mattress formed between the moving web (10) and the floating strip (11). curved surface in the running direction of the web (10), and the measured values of the pressure 30 or values derived from these proportional to the voltage are passed in the form of signals (17) to a controller (18) which gives position signals (19) a functional device. means which move the supporting points (16) of the device (11, 20) which affect the transverse variation of the distance traveled by the web in such a way that the transverse variation of the tension on the web (10) is altered in the desired manner. 5 Method according to claim 5, characterized in that the transverse variation of the tension on the web (10) is measured indirectly by measuring the pressure on the air mattress formed between the moving web (10) and the floating strip (11) with at least partially curved surface in the running direction. of the path (10), and that the measured values of the pressure or values derived from these proportional to the voltage are passed in the form of signals (17) to a regulator (18), which provides position signals (19) with operating devices which move at the support points (16) of the floating strip (11) in such a way that the transverse variation in the tension of the web (10) is changed in the desired manner. Method according to any of claims 1-4, characterized in that the transverse variation of the tension on the web (10) is measured indirectly by measuring the pressure on the air mattress formed between the movable web (10) and the floating strip (11) with a minimum of partially curved surface in the running direction of the web (10), and that the measured values of the pressure or values derived from these that are proportional to the voltage are passed in the form of signals (17) to a regulator (18) which gives a position signal (19). the device (20) affecting the transverse variation of the distance traveled by the web, which device is arranged separately from the measuring device (11,12,13,14). Method according to claim 7, characterized in that the transverse variation of the tension on the web (10) is measured indirectly by measuring the pressure on the air mattress formed between the movable web (10) and the floating strip (11) with at least partially curved surface in the the running direction of the path (10), and that the measured values of the pressure or values derived from these which are proportional to the voltage are passed in the form of signals (17) to a regulator (18), which provides a position signal (19) for the propagation device ( 20) located separately from the measuring device (11,12,13,14). > * ID! liiti I IIH 1 30 π 94779 Method according to Claim 8, characterized in that, as a spreading device (20), a spreading strip, a propagating roll, a propagating pipe or other similar solution is used. Apparatus for controlling the transverse variation in the tension of a web (10), comprising a measuring device (11,12,13,14) for measuring the transverse variation in the tension of the web (10), characterized in that: the device has a regulator (18) which on the basis of the measurement result of the transverse variation of the voltage on the path (10) regulates the device (11, 20) which affects the transverse variation of the distance which the path (10) runs in such a way that it the transverse variation of the tension on the web (10) is fixed as desired. Device according to claim 10, characterized in that the device (11) which affects the transverse variation of the distance traveled by the web (10) is a floating strip (11) having at least partially curved surface in the direction of the web (10), which strip is supported against the body (15) with support points (16) spaced from each other and that the controller (18) provides position signals (19) with operating devices which move the support points (16) of the floating strip (11) in such a way that the transverse direction the variation in the tension of the web (10) is changed as desired. 20 Device according to claim 10, characterized in that the device (20) which affects the transverse variation of the distance traveled by the web (10) is a propagation device (20) which is separate from the measuring device (11,12,13,14) and that the controller (18) provides position signals (19) with operating devices which move the support points (16) of the propagating device (20) in such a way that the transverse variation of the voltage on the path (10) is changed in the desired manner. « Device according to claim 10, characterized in that the propagating device (20) is a propagating strip, a propagating roll, a propagating tube or other similar solution.