Abstract:
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.

Description:
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; and   upon 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. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a perspective diagrammatic illustration of an apparatus for detecting and eliminating a twister; 
         FIG. 2  is a perspective diagrammatic illustration of an apparatus for detecting and eliminating a twister; 
         FIG. 3  is a diagrammatic graph illustrating the double scanner alimgement for determining the number of twisters along the catch section; and 
         FIG. 4  is a diagrammatic illustration of the detection arrangement for determining how a twister is oriented. 
     
    
    
     DETAILED DESCRIPTION 
       FIGS. 1 and 2  illustrate 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 web  1  of flexible material such as non-woven fabric. This web  1  has two different surfaces  2 ,  3 , which is symbolized by light and dark coloring of the surfaces in  FIGS. 1 and 3 . The web  1  passes in the running direction  4  through a catch section  5 , which is defined by a gap  6  on the inlet side—hereinafter called inlet gap—and a gap  7  on the outlet side—hereinafter called outlet gap. While the outlet gap  7  is incorporated stationarily in the anti-twister system, which is roughly outlined by the rectangular plate  8  that houses the gap  7 , the inlet gap  6  is lodged in a rotor  9  that is mounted rotatably in the anti-twister system. Related to the width and thickness of the web  1 , the inlet gap  6  is slightly longer and wider than the outlet gap  7  that seizes the web  1  comparatively closely. This makes it easy for twisters to enter the catch section  5 , but slows down any migration of twisters from the catch section  5  in the running direction  4  at 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 web  1  to pass as far as to the place of assembly with other webs, which would lead to waste products. 
     A stepper motor  10  is drivably coupled with the rotor by way of a timing belt  11  and triggered by a control unit  12 . The control unit  12 , by its signal inlets, is coupled with two scanners  13 . 1 ,  13 . 2 , which are positioned along the catch section  5  and optically detect any twisting of the web  1  in a manner still to be explained, and with a detection arrangement  15  for determining how a twister is oriented. 
     The two scanners  13 . 1 ,  13 . 2  each comprise a so-called light curtain  16 . 1 ,  16 . 2  which is generated by a corresponding light source  17 . 1 ,  17 . 2  and directed vertically to the normal plane of running  18  ( FIGS. 3 and 4 ). Opposing the light sources  17 . 1 ,  17 . 2  are corresponding light detectors  19 . 1 ,  19 . 2 , quantitatively detecting the extent to which the light barrier  16 . 1 ,  16 . 2  is shaded over its width across the web  1 . 
     The detection arrangement  15  comprises two proximity sensors  20 ,  21  which are disposed horizontally side by side crosswise of the running direction  4 , 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 scanners  13 . 1 ,  13 . 2  and the detection arrangement  15  is specified as follows, taken in conjunction with  FIGS. 3 and 4 : 
     The two scanners  13 . 1 ,  13 . 2  serve—as mentioned—for optically detecting the twisting of the web  1  and in particular also for determining the number of twisters. To this end, the scanner  13 . 1  is positioned—as seen in FIG.  3 —centrally of the length of the catch section  5 , and the scanner  13 . 2  is positioned upstream of the other scanner  13 . 1  at a distance of one sixth of the length of the catch section  5 . If a twister  22  enters the catch section  5  through the inlet gap  6 —as outlined in FIG.  1 —it will set symmetrically to the length of the catch section  5  within a short period. In a lateral view—as outlined in FIG.  3 —the contour of the web  1  twisted by 180° is an upright halfwave (see  FIG. 3B ). 
     If two twisters  22  have entered the catch section  4 , the contour, in a side view, of the web  1  twisted by 360° is an upright wave (see  FIG. 3C ) with two wave loops and a central wave node. If there is another twister  22 —i.e. the web  1  twisted by 540°—the appearance is that of one and a half upright wave (see  FIG. 3D ) with three wave loops and two nodes along the catch section  5 . 
     The above characteristic of the web  1  in its various twisted contours is used for determining the existence and number of twisters  22 . An untroubled web  1  (see  FIG. 3A ) will run properly horizontally, virtually not interfering with the light curtains  16 . 1 ,  16 . 2 . Both light detectors  19 . 1 ,  19 . 2  of the scanners  13 . 1 ,  13 . 2  have a high signal level S 1 =1 and S 2 =2. 
     If a twister  22  arrives, both light detectors  19 . 1 ,  19 . 2  are covered by the contour of the twisted web  1  because of their substantially central position relative to the catch section  5 ; both signals of the light detectors  19 . 1 ,  19 . 2  are set to zero: S 1 =0 and S 2 =0. 
     In the case of two twisters  22 , the central scanner  13 . 1  is in the vicinity of the node so that the corresponding light detector  19 . 1  is virtually not shaded, whereas the light detector  19 . 2  of the off-center scanner  13 . 2  is shaded by the wave loop arriving there. This gives the signal combination S 1 =1 and S 2 =0 for two twisters. 
     In the case of three twisters  22 , the central light detector  19 . 1  of the scanner  13 . 1  is shaded by the central wave loop, whereas the off-center light detector  19 . 2  of the scanner  13 . 2  is in the vicinity of a wave node. This gives a signal combination S 1 =0 and S 2 =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 S 1 -S 2 . This detection signal can conventionally be used by the control unit  12  for triggering the rotor  9 . 
     Independently of the detection arrangement  15 , the control unit  12 , after determination of a twister within the catch section  5 , can rotate the rotor  9  by 180° for example in the direction of rotation  23  seen in  FIG. 1 , which is noticeably the “wrong” direction in the case shown. Then the scanners  13  will recognize two twisters along the catch section  5  instead of one. This means that this was the wrong direction of rotation  23  and that the web  1  must be rotated twice by 180° in the opposite direction. After this operation, the twister  22  is eliminated from the catch section  5 . 
     In order to enable twisters to be eliminated as rapidly as possible and without any faulty rotation, provision is made for the detection arrangement  15 , which can be used for recognition of twisters fundamentally without the scanners  13 . 1 ,  13 . 2 . By its proximity sensors  20 ,  21 , this detection arrangement  15  detects the position of the two opposite lateral edges  24 ,  25  of the web for corresponding distance sensing. The signals of the proximity sensors  20 ,  21  that represent the distance are compared by a differentiator  26  in the control unit  12 . In the case of a horizontal web  1  that runs properly, the two distances a 1 , a 2  between the lateral edges  24 ,  25  and the proximity sensors  20 ,  21  are equal so that no action of the rotor  9  is needed—which is confirmed by the scanners  13  if available. As soon as a single twister  22  or several twisters  2  arrive within the catch section  5 , the web  1  tilts due to its being twisted so that the proximity sensors  20 ,  21  measure 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 rotor  9  by 180° can be determined, possibly by logical linkage to the signal of the scanners  13 . Without the scanners  13 , when a twister is detected by different distances a 1 , a 2  of the lateral edges  24 ,  25  being measured, rotation of the rotor  9  will simply be initiated via the control unit  12  until the two distances a 1 , a 2  are measured to be equal.