Web twister removal process

An apparatus for detecting and eliminating a twister in a running web of flexible material. The apparatus includes a catch section for twisters, a rotor, a scanner arrangement for detection of a twister that has entered a catch section and a control unit , which, upon detection of a twister by the scanner, triggers the drive of the rotor for untwisting the twister.

FIELD OF THE INVENTION

The invention relates to an apparatus for detecting and eliminating a twister in a running web of flexible material.

BACKGROUND

As for the background of the invention, in the manufacture of sanitary articles such as diapers, napkins and pantyliners, various webs of nonwoven fabric and film are wound off supply rolls or bales and combined and united by way of corresponding web guides, with various working operations taking place on the way. Then detachment of individual pieces of the web takes place for configuration of the virtual product.

Problems posed in these manufacturing processes include the comparatively high velocities of the web of several meters per second and the great number of deflectors, conveying rollers and the like for the webs of strip material that frequently have only few centimeters of width. Conditioned by these circumstances, so-called twisters occur as the web winds off and flaps to and fro, in particular in the case of “festooned” supplies—which is a long web of material placed in loops one on top of the other. These twisters can proceed in the running direction via web guides such as deflection rollers, guide gaps etc. so that the twister will ultimately be found in the final product.

Problems arise from the fact that, mostly, at least some of the webs of a multilayer product have definitely allocated top and bottom sides. For example, the impermeable outer layers of diapers often have imprints suitable for children which a twister would turn upside down in the diaper. Another example is the punched cover film in pantyliners which also must be placed correctly during manufacture—i.e. with the projections from punching turned inwards.

A twister that has ultimately passed into the assembly operation of the individual webs will lead to a faulty waste product.

Another problem posed by twisters resides in that the web, where twisted, is exposed to increased strain by the twisting. Furthermore, web guide elements, such as guide gaps, offer some resistance when the twisters pass along, which means additional strain on the web. In this regard, twisters also cause an increase in web rupturing in the manufacturing plant, meaning standstill, downtime and renewed charging, which considerably affects manufacturing efficiency.

It is an object of the invention to embody an apparatus for detecting and eliminating a twister in a running web of flexible material.

SUMMARY

An apparatus with the following features is provided:Provision is made for a twister catch section which extends between a guide gap on the inlet side and a guide gap on the outlet side;a rotor houses the guide gap on the inlet side and is set in controlled rotary motion about an axis that is parallel to the web running direction;a scanner and detection arrangement detects a twister that has entered the catch section; andupon detection of a twister by the scanner and detection arrangement, a control unit triggers the drive of the rotor so that the guide gap on the inlet side is rotated and the twister is eliminated.

“Catching” the twister along the catch section prevents it from migrating through the manufacturing plant and passing as far as to the operation of assembly. Furthermore, the fact that the twister remains within the catch section offers the possibility that it is recognized by corresponding detectors and that untwisting is initiated.

The scanner and detection arrangement preferably works on an optical basis, detecting web twisting by means of a light barrier, light curtain, camera, photoelectric detectors or the like.

If two scanner arrangements are disposed at a defined distance along the catch section, the number of twisters that have entered the catch section can be determined—as explained in detail in the exemplary embodiment. In doing so, it can be sufficient only to detect a deflection of the web without recording the extent to which it is deflected and to emit a correspondingly encoded, digital detection signal for further processing in the control unit. It is easily possible to differentiate between numbers ranging from no twister to as many as three twisters.

In keeping with another preferred embodiment, a detection arrangement for the existence of a twister is provided as an arrangement determining the way in which a twister is directed, so that untwisting takes place in the correct sense right from the beginning. By advantage, proximity sensors will detect the position of the side edges of the web in relation to the normal plane of running, which is also explained in detail below.

DETAILED DESCRIPTION

FIGS. 1 and 2illustrate the main components of an apparatus for the detection and elimination of twisters in a running web, hereinafter called anti-twister system. Any bearing and mounting elements for the components seen in these figures are omitted for reasons of clarity.

The two above-mentioned drawings show a web1of flexible material such as non-woven fabric. This web1has two different surfaces2,3, which is symbolized by light and dark coloring of the surfaces inFIGS. 1 and 3. The web1passes in the running direction4through a catch section5, which is defined by a gap6on the inlet side—hereinafter called inlet gap—and a gap7on the outlet side—hereinafter called outlet gap. While the outlet gap7is incorporated stationarily in the anti-twister system, which is roughly outlined by the rectangular plate8that houses the gap7, the inlet gap6is lodged in a rotor9that is mounted rotatably in the anti-twister system. Related to the width and thickness of the web1, the inlet gap6is slightly longer and wider than the outlet gap7that seizes the web1comparatively closely. This makes it easy for twisters to enter the catch section5, but slows down any migration of twisters from the catch section5in the running direction4at least until the anti-twister system has been set in action and eliminated the twister. In this regard, the anti-twister system efficiently and very reliably prevents twisters of the web1to pass as far as to the place of assembly with other webs, which would lead to waste products.

A stepper motor10is drivably coupled with the rotor by way of a timing belt11and triggered by a control unit12. The control unit12, by its signal inlets, is coupled with two scanners13.1,13.2, which are positioned along the catch section5and optically detect any twisting of the web1in a manner still to be explained, and with a detection arrangement15for determining how a twister is oriented.

The two scanners13.1,13.2each comprise a so-called light curtain16.1,16.2which is generated by a corresponding light source17.1,17.2and directed vertically to the normal plane of running18(FIGS. 3 and 4). Opposing the light sources17.1,17.2are corresponding light detectors19.1,19.2, quantitatively detecting the extent to which the light barrier16.1,16.2is shaded over its width across the web1.

The detection arrangement15comprises two proximity sensors20,21which are disposed horizontally side by side crosswise of the running direction4, and for which any form of distance sensing may fundamentally be used—for instance optical sensing by photoelectric cells, mechanical sensing by feelers, electrical sensing by capacitive or inductive sensors, but also ultrasonic and infrared proximity sensors.

The mode of operation of the scanners13.1,13.2and the detection arrangement15is specified as follows, taken in conjunction withFIGS. 3 and 4:

The two scanners13.1,13.2serve—as mentioned—for optically detecting the twisting of the web1and in particular also for determining the number of twisters. To this end, the scanner13.1is positioned—as seen in FIG.3—centrally of the length of the catch section5, and the scanner13.2is positioned upstream of the other scanner13.1at a distance of one sixth of the length of the catch section5. If a twister22enters the catch section5through the inlet gap6—as outlined in FIG.1—it will set symmetrically to the length of the catch section5within a short period. In a lateral view—as outlined in FIG.3—the contour of the web1twisted by 180° is an upright halfwave (seeFIG. 3B).

If two twisters22have entered the catch section4, the contour, in a side view, of the web1twisted by 360° is an upright wave (seeFIG. 3C) with two wave loops and a central wave node. If there is another twister22—i.e. the web1twisted by 540°—the appearance is that of one and a half upright wave (seeFIG. 3D) with three wave loops and two nodes along the catch section5.

The above characteristic of the web1in its various twisted contours is used for determining the existence and number of twisters22. An untroubled web1(seeFIG. 3A) will run properly horizontally, virtually not interfering with the light curtains16.1,16.2. Both light detectors19.1,19.2of the scanners13.1,13.2have a high signal level S1=1 and S2=2.

If a twister22arrives, both light detectors19.1,19.2are covered by the contour of the twisted web1because of their substantially central position relative to the catch section5; both signals of the light detectors19.1,19.2are set to zero: S1=0 and S2=0.

In the case of two twisters22, the central scanner13.1is in the vicinity of the node so that the corresponding light detector19.1is virtually not shaded, whereas the light detector19.2of the off-center scanner13.2is shaded by the wave loop arriving there. This gives the signal combination S1=1 and S2=0 for two twisters.

In the case of three twisters22, the central light detector19.1of the scanner13.1is shaded by the central wave loop, whereas the off-center light detector19.2of the scanner13.2is in the vicinity of a wave node. This gives a signal combination S1=0 and S2=1 for three twisters.

As becomes apparent from the above explanations, the conditions of no twister/a single twister/two twisters/three twisters are distinctly digitally encoded by the signal combination S1-S2. This detection signal can conventionally be used by the control unit12for triggering the rotor9.

Independently of the detection arrangement15, the control unit12, after determination of a twister within the catch section5, can rotate the rotor9by 180° for example in the direction of rotation23seen inFIG. 1, which is noticeably the “wrong” direction in the case shown. Then the scanners13will recognize two twisters along the catch section5instead of one. This means that this was the wrong direction of rotation23and that the web1must be rotated twice by 180° in the opposite direction. After this operation, the twister22is eliminated from the catch section5.

In order to enable twisters to be eliminated as rapidly as possible and without any faulty rotation, provision is made for the detection arrangement15, which can be used for recognition of twisters fundamentally without the scanners13.1,13.2. By its proximity sensors20,21, this detection arrangement15detects the position of the two opposite lateral edges24,25of the web for corresponding distance sensing. The signals of the proximity sensors20,21that represent the distance are compared by a differentiator26in the control unit12. In the case of a horizontal web1that runs properly, the two distances a1, a2between the lateral edges24,25and the proximity sensors20,21are equal so that no action of the rotor9is needed—which is confirmed by the scanners13if available. As soon as a single twister22or several twisters2arrive within the catch section5, the web1tilts due to its being twisted so that the proximity sensors20,21measure different distances. Depending on whether the distance is smaller on one side or the other, the direction of the twisting can be clearly determined and the correct direction of rotation and correct number of rotations of the rotor9by 180° can be determined, possibly by logical linkage to the signal of the scanners13. Without the scanners13, when a twister is detected by different distances a1, a2of the lateral edges24,25being measured, rotation of the rotor9will simply be initiated via the control unit12until the two distances a1, a2are measured to be equal.