METHOD AND APPARATUS FOR GUIDING A WEB TO A CENTRATION POINT

Abstract

The present invention relates to a method of guiding a web with a shifting path of the web to a substantially constant centration point. It comprises the steps of providing a web with a shifting path of the web from a source of the web, measuring upstream of said centration point, the position and/or orientation of said web by a sensor arrangement, and guiding said web to said centration point in accordance to the measurement results. The present invention advantageously relates to operations in the manufacturing of absorbent articles such as unwinding web rolls that are wound in a shifted manner, in particular spirally wound web rolls, and removing web from containers of loose web material. The invention also relates to a device for the execution of the method.

Claims

1. A method of guiding a web (2) with a shifting path of the web to a centration point (3) comprising the steps of a. providing the web (2) with a shifting path of the web from a source of the web, b. measuring the position and/or orientation of said web (2) by a sensor arrangement (4), c. guiding said web (2) to said centration point (3) in accordance with the measurement results of step b, characterized in that said centration point (3) has a substantially constant position in respect of the source of the web and in that the measurement of step b is conducted upstream of said centration point (3).

2. A method according to claim 1, wherein said guiding of the web (2) to the centration point (3) is conducted by at least one guiding device (5), said at least one guiding device being pivotably mounted substantially at the centration point (3).

3. A method according to claim 2, wherein said sensor arrangement (4) measures the position and/or orientation of the web (2) upstream and/or downstream of said at least one guiding device (5).

4. A method according to claim 1, wherein said shifting path of the web is adjusted to a substantially linear path of the web and to a substantially in orientation constant path of the web downstream of said centration point (3).

5. A method according to claim 1, wherein the source of the web is a web roll (1) or container and wherein said web (2) comprises a material selected from the group of films, papers, textiles, nonwovens and super absorbent papers.

6. An apparatus for guiding a web (2) with a shifting path of the web from a source of the web to a centration point (3) comprising a guiding device (5) pivotably mounted substantially at a centration point (3), said centration point having a substantially constant position in respect of the source of the web (2), said guiding device being adapted to guide said web (2) to said centration point (3), characterized in that the pivoting of the guiding device (5) is controlled by a control circuit, said control circuit comprising at least one actuator (6) and a sensor arrangement (4) that is located upstream of said centration point (3) and in that said sensor arrangement (4) measures the position and/or orientation of the web (3) upstream of said centration point (3).

7. An apparatus according to claim 6, wherein the apparatus is adapted to guide said web (2) downstream of the centration point (3) in substantially perpendicular direction to an infeed point (10) and the path of the web is adjusted to a substantially linear and in orientation constant movement downstream of said infeed point.

8. An apparatus according to claim 7, wherein at the infeed point (10) a guiding element (7c) is mounted.

9. An apparatus according to claim 6, wherein the sensor arrangement (4) measures the shifting of the path of the web (2) at the entry side of the guiding device (5) and/or between the guiding device (5) and a web roll (1) and/or at the web roll (1).

10. An apparatus according to claim 9, wherein the sensor arrangement (4) is adapted to pivot around an axis at the entry side of the guiding device (5).

11. An apparatus according to claim 10, wherein upstream of the sensor arrangement (4) at least one guiding element (7d) is pivotably mounted.

12. An apparatus according to claim 11, wherein the sensor arrangement (4) and the at least one guiding element (7d) are mounted to the same pivoting frame (15) that can be pivoted around an axis at the entry side of the guiding device (5).

13. An apparatus according to claim 6, wherein the guiding device (5) comprises at least two guiding elements (7a, 7b) of which one guiding element (7a) is mounted to the guiding device (5) at its entry side and one guiding element (7b) is mounted to the guiding device (5) at its exit side.

14. An apparatus according to claim 6, wherein at least one web guiding system for fine tuning of the path of the web is mounted downstream of the centration point (3).

15. An apparatus according to claim 6, wherein said web (2) comprises a material selected from the group of films, papers, textiles, nonwovens and super absorbent papers.

16. An apparatus according to claim 8, wherein the guiding element (7c) comprises an idler roller or a rod.

17. An apparatus according to claim 11, wherein the at least one guiding element (7d) comprises an idler roller or rod.

18. An apparatus according to claim 13, wherein the at least two guiding elements (7a, 7b) comprise at least two idler rollers or rods.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0045] A particularly preferred embodiment of the present invention is illustrated by the following drawings:

[0046] FIG. 1 is a schematic perspective view illustrating an apparatus for guiding a web with a shifting path of the web to a centration point according to the present invention;

[0047] FIG. 2 is a schematic top view of the apparatus from FIG. 1;

[0048] FIG. 3 is a schematic side view of the apparatus from FIG. 1 and FIG. 2;

[0049] FIG. 4a and FIG. 4b and FIG. 4c are schematic side views of the pivoting frame that is mounted at the entry side of the guiding device illustrated in FIG. 1 and FIG. 2 and FIG. 3 in three different positions;

[0050] FIG. 5a and FIG. 5b and FIG. 5c are schematic top views of the apparatus from FIG. 1, FIG. 2 and FIG. 3 during the unwinding of a web roll wound in a shifted manner at three different points of time.

DETAILED DESCRIPTION OF A PARTICULARLY PREFERRED EMBODIMENT

[0051] A particularly preferred embodiment of the present invention will now be described with reference to the figures.

[0052] FIG. 1 illustrates a perspective view of an apparatus for unwinding a web roll wound in a shifted manner, or for removing loose webs from containers, said apparatus in its entirety from now on being called guiding apparatus 100. FIG. 2 illustrates a schematic top view of the guiding apparatus 100. FIG. 3 illustrates a schematic side view of the guiding apparatus 100. Each of the figures shows the web 2 and the guiding device 5 comprising a base plate with two opposing support rails attached to it. One guiding element 7a is mounted between the support rails at the entry side of the guiding device 5 and one guiding element 7b is mounted between the support rails at the exit side of the guiding device 5. Above the guiding element 7b at the exit side of the guiding device 5 another guiding element 7c is mounted at the infeed point 10. Two wheels 11 are mounted to the support rails of the guiding device 5 and rest on a holder 12 at the entry side of the guiding device 5. The guiding device 5 is pivotally mounted on a holder 13 at the centration point 3. The actuator 6 is mounted to the holder 13 and is connected to the guiding device 5 with a lever element 14. At the entry side of the guiding device 5 a pivoting frame 15 is pivotably mounted to the support rails of the guiding device 5. The sensor arrangement 4 and the guiding element 7d are mounted to the pivoting frame 15. All of the guiding elements 7a, 7b, 7c, 7d are illustrated as idler rollers that can rotate around their longitudinal axis.

[0053] FIG. 4a, FIG. 4b and FIG. 4c illustrate side views of the pivoting frame 15 mounted to the entry side of the guiding device 5 in three different positions. Each of the figures shows the entry side of the guiding device 5, the web 2, the guiding element 7a at the entry side of the guiding device 5, the pivoting frame 15 mounted to the guiding device 5, the guiding element 7d and the sensor arrangement 4 mounted on the pivoting frame 15.

[0054] FIG. 5a, FIG. 5b and FIG. 5c illustrate a top view of the guiding apparatus 100 during the unwinding of a spirally wound web roll 1 at three different points of time. Each of the figures shows the unwinding apparatus 100 with its deflection angle (13), the web roll 1 and the web 2 with its winding angle (a) on the web roll 1.

[0055] As illustrated in FIG. 5a, FIG. 5b and FIG. 5c the web 2 leaves the spirally wound web roll 1 during unwinding in a constantly shifting path of the web with an angle to a transverse axis of the web roll 1 equal to its winding angle (a) on the web roll 1. The shifting direction of the path of the web changes from left to right or from right to left (respectively bottom to top or top to bottom in the figures) as soon as a whole layer of the web roll 1 has been unwound.

[0056] The web 2 enters the guiding apparatus 100 from a direction perpendicular to the plane defined by the longitudinal axes of the guiding element 7d and the guiding element 7a. The web 2 runs around the guiding element 7d at the entry side of the pivoting frame 15 and enters the guiding device 5 at the guiding element 7a. The sensor arrangement 4 measures the current position of the web 2 at the pivoting frame 15 between the two guiding elements 7d, 7a and transmits a signal to a controller that compares the actual value with a defined nominal value and sends a correction signal to the actuator 6. The actuator 6 then moves the guiding element 5 in accordance with the correction signal so that the entry side of the guiding device 5 follows the shifting path of the web through pivoting motions around the centration point 3.

[0057] Depending on the current deflection angle (β) of the guiding device 5 the inclination of the guiding element 7d in respect to the path of the web creates a transverse force on the web 2. This transverse force rotates the direction of the path of the web into one line with the longitudinal axis of the guiding device 5. In the process the web 2 becomes slightly twisted upstream to the guiding element 7d due to the rotation of the path of the web. The web 2 then runs over the guiding element 7a at the entry side of the guiding device 5 to the guiding element 7b at its exit side.

[0058] The web 2 runs around the guiding element 7b and leaves the guiding device 5 in perpendicular direction upwards towards the guiding element 7c at the infeed point 10. The guiding element 7c has a constant location and orientation in respect to the web roll 1. The redirection of the path of the web in perpendicular direction and the current inclination of the guiding element 7c in respect to the path of the web through the guiding device 5 translates the current deflection angle (β) of the guiding device 5 into a twisting of the web 2 between the guiding element 7b and the guiding element 7c. The web 2 finally leaves the guiding apparatus 100 at the infeed point 10 whereby the twisted path of the web is translated into a linear and in one direction constant movement downstream of the infeed point 10.

[0059] The twisting of the web 2 at the entry and exit side of the guiding device 5 puts increased stress on the material depending on the distance between the web roll 1 and the guiding element 7d and also depending on the angle in which the direction of the path of the web has to be rotated and the distance between the guiding element 7b and the guiding element 7c. It is therefore beneficial to position the guiding element 7d at an appropriate distance to the web roll 1 and to mount the guiding element 7b in an appropriate distance to the guiding element 7c to avoid tearing of the web 2. In practice a distance of five times the webs 2 width at β=0 at the entry side has proven to be suitable for a web 2 made of rather sensitive nonwoven with a grammage from about 5 g/m.sup.2 to about 60 g/m.sup.2. For the exit side a distance of four times the webs width has proven suitable.

[0060] Furthermore, the rotation of the orientation of the path of the web creates a pulling force on the web 2 that increases with the size of the rotation angle. The effective rotation angle at the exit side of the guiding device 5 is equal to the current deflection angle (β) at any given point of time. The effective rotation angle at the entry side can be calculated by adding up the current deflection angle (β) and the current winding angle (α) of the web 2 on the web roll 1. If the winding angle (α) and the length of the web roll 1 are considered to be constant values the maximum deflection angle (β.sub.max) of the guiding device 5 will increase with an increasing distance of the guiding element 7d in respect to the web roll 1 and will decrease with an increasing length of the guiding device 5 plus its length extension (E) by the pivoting frame 15 as projected into the plane of the guiding device 5. Examples of length extensions E.sub.1 and E.sub.2 are illustrated in FIGS. 4a and 4b. As can be seen in FIG. 4c the projected length extension may become zero at a 90° angle. Since as mentioned above the distance of the guiding element 7d to the web roll 1 should be chosen appropriately, the length of the guiding device 5 plus its length extension (E) by the pivoting frame 15 may become a relevant variable for designing the guiding apparatus 100 in sight of a maximum desired rotation angle (β.sub.max+α.sub.max).

[0061] For example with a web 2 made of nonwoven with a width of 0.1 m and with a grammage of 5 g/m.sup.2 to about 60 g/m.sup.2 and with a maximum winding angle (α.sub.max) of 15° on a spirally wound web roll 1 a length of 1.3 m of the guiding device 5 plus its length extension (E) by the pivoting frame 15 had proven suitable. With a distance of 0.5 m between the guiding element 7d and the web roll 1 the maximum deflection angle (β.sub.max) never exceeded a value of 30° keeping the rotation angle under 45° at all times. The length of the guiding device for other values can easily be calculated by the following formula:

[00001]$a=\tan \left({\alpha }_{\max }\right)*\frac{b}{\sin \left({\beta }_{\max }\right)}+\frac{1}{2}*\frac{L}{\sin \left({\beta }_{\max }\right)}$

[0062] a=length of the guiding device 5 plus its length extension (E) by the pivoting frame 15

[0063] b=distance between the guiding element 7d mounted to the pivoting frame 15 and the web roll 1 for β=0

[0064] L=length of the web roll 1

[0065] α.sub.max=maximum winding angle of the web 2 on the spirally wound web roll 1

[0066] β.sub.max=maximum deflection angle of the guiding device 5

[0067] To ensure that the friction between the guiding element 7d at the entry side of the pivoting frame 15 and the web 2 is sufficient for the rotation of the direction of the path of the web a correct positioning of the guiding device 5 in respect to the web roll 1 may be preferred. For example, if the web 2 would enter the guiding device 5 in the same plane as defined by the longitudinal axes of the guiding element 7d and of the guiding element 7a the web would at a finite friction coefficient slide over the guiding element 7d with no rotation being achieved. A positioning of the guiding device 5 above the web roll 1 or container has therefore proven to be favorable. This way the web 2 enters the unwinding apparatus 100 perpendicular to the plane defined by the longitudinal axes of the guiding element 7d and the guiding element 7a and the contact surface between the web 2 and the guiding element 7d is about one quarter of the guiding elements 7d surface area.

[0068] As illustrated in FIG. 4a and FIG. 4b and FIG. 4c the pivoting frame 15 allows an alternative positioning of the guiding device 5 while keeping a favorable angle of entry of the web 2 into the guiding apparatus 100. Since the sensor arrangement 4 is mounted to the pivoting frame 15 as well there is no need for an additional adjustment of the orientation of the sensor arrangement 4 if the pivoting frame 15 is pivoted.

[0069] Another possibility for a more flexible positioning of the guiding device 5 in respect to the web roll 1 lies with alternative guiding routes of the web 2 around the guiding elements 7a, 7b, 7c, 7d. The guiding route that has been illustrated in each of the figures consists of guiding the path of the web above the first two guiding elements 7d, 7a, then guiding it under the third guiding element 7b and then guiding it above the last guiding element 7c. It is possible to change this guiding route in a multitude of ways such as different paths under and above the guiding elements 7a, 7b, 7c, 7d or by adding additional guiding elements to the guiding apparatus 100. For example if the guiding device 5 is supposed to be positioned beneath the web roll 1 and the infeed point 10 is located at the same level as the web roll 1 or container the web 2 can be guided under the first guiding element 7d then above the second guiding element 7a then under the third guiding element 7b and finally above the last guiding element 7c. It should be noted however that the web 2 in this configuration is angled to the plane defined by the longitudinal axes of the guiding element 7d and the guiding element 7b and the orientation of the sensor arrangement 4 has to be adjusted accordingly.

[0070] With a guiding route as illustrated in FIG. 1, FIG. 2 and FIG. 3 the pulling forces inside the web 2 possess a force component directed perpendicular to the plane defined by longitudinal axes of the guiding element 7a at the entry side of the guiding device 5 and the guiding element 7b at the exit side of the guiding device. The arc-like pivoting motions of the guiding device 5 as illustrated in FIG. 5a and FIG. 5b and FIG. 5c now cause small periodic changes in the distance of the guiding element 7d in respect to the web roll 1.

[0071] Likewise, there are small fluctuations in the pulling forces inside the web 2 and their vertical force component depending on the current deflection angle (β) of the guiding device 5. These fluctuations can cause the guiding device 5 to swing and vibrate especially at higher pivoting speeds. In order to stabilize the guiding device 5 two wheels 11 are mounted to the support rails of the guiding device 5 and rest on top of a holder 12 located in close proximity to the entry side of the guiding device 5. As a side effect the stress on the material in the mounting of the guiding device 5 on the holder 13 at its exit side is reduced as well.

[0072] According to the functional principle of the guiding apparatus 100 a wide variety of types of guiding elements 7a, 7b, 7c, 7d can be used. The question which type to choose only becomes important once the friction between the guiding elements 7a, 7b, 7c, 7d and the web 2 is considered to be an issue. For example using passive idler rollers has proven to be sufficient for a web 2 made of nonwoven. For materials of greater sensitivity however it is possible to use active guiding elements such as motorized rollers. Likewise, for materials of lower sensitivity using passive non-rotating elements like rods can become an option. In case of materials of even lower sensitivity it can be considered an option to design the guiding apparatus 100 without any guiding elements at all and use two spaced plates as guiding device 5 instead.

[0073] It is supposed that the present invention is not restricted to any form of realization described previously and that some modifications can be added to the presented example of fabrication without reappraisal of the appended claims. For example, the present invention has been described referring to web rolls, but it is clear that the invention can be applied to containers of loose web material for instance or to spirally wound web rolls in particular.