Abstract:
An apparatus for detection of the accuracy of format of a web of corrugated cardboard moved in a conveying direction comprises a light source which emits a light band to the surface of the web of corrugated cardboard in a direction crosswise of the conveying direction and at an angle to the web of corrugated cardboard. A measuring camera detects the different light intensities of the light reflected by the plane portions and the profiled patterns of the web of corrugated cardboard. This electronic image in the camera is evaluated by an evaluation device for determining the distance of the profiled patterns from each other.

Description:
BACKGROUND OF THE INVENTION 
       [0001]    1. Field of the Invention 
         [0002]    The invention relates to an apparatus for detection of the accuracy of format of a web of corrugated cardboard moved in a conveying direction, which corrugated cardboard comprises at least an upper liner with a surface and a total width a and at least two profiled patterns of the upper liner, namely lateral edges and at least one of a longitudinal cut dividing the web of corrugated cardboard into partial webs and at least an upper groove, which profiled patterns run in the conveying direction and which profiled patterns have distances b, c, d from each other, and which corrugated cardboard has plane portions of the surface between the profiled patterns. 
         [0003]    2. Background Art 
         [0004]    In such an apparatus known from U.S. Pat. No. 6,836,311, two sensors are arranged on both sides of the web of corrugated cardboard, of which a first sensor is designed such as to measure the distance of the first liner from the first sensor and of which a second sensor is designed such as to measure the distance of a second liner from the second sensor. In order to detect the position of at least two profiled patterns, the two sensors are arranged relative to each other and are synchronously displaceable crosswise of the conveying direction of the web of corrugated cardboard. Downstream of the sensors is disposed an evaluation device for detecting the distance of the at least two profiled patterns from each other. The accuracy of measurement of this device is satisfactory. A disadvantage is that the constructional effort for crosswise displacement of the sensors is quite extensive and that the time required for the respective measuring process in relation to the high speed of webs of corrugated cardboard in corrugated-cardboard machines is very high. 
         [0005]    Thus it is the object of the invention to provide an apparatus for detection of the accuracy of format of a web of corrugated cardboard moved in a conveying direction, said apparatus combining a high measuring speed and a high accuracy of measurement with a simple design. 
         [0006]    According to the invention, this object is achieved in an apparatus of the generic type, 
         [0007]    wherein a light source emits a light band to the surface of the upper liner across the total width a thereof in a direction crosswise of the conveying direction at an angle α to the surface of the upper liner, 
         [0008]    wherein a measuring camera is arranged above the web of corrugated cardboard which absorbs light reflected by the surface and which detects the profiled patterns by means of a light intensity of the light reflected by the profiled patterns, the light intensity of which deviating from a light intensity of light reflected by plane portions of the surface, and 
         [0009]    wherein an evaluation device is connected to the measuring camera for determination of the distance b, c, d of the at least two profiled patterns from each other on the basis of the differing light intensities of the light reflected towards the measuring camera. 
         [0010]    The gist of the invention is that the light band which is emitted to the surface of the upper liner at an angle thereto and crosswise of the conveying direction is reflected differently by the profiled patterns, in other words by the grooves and/or longitudinal cuts than by the smooth, i.e. plane portions between the profiled patterns. This allows an electronic image of the entire surface of the web of corrugated cardboard, including the profiled patterns, to be generated in a conventional measuring camera, the electronic image being evaluated in a correspondingly programmed computer serving as evaluation device, which allows to determine the respective, exact actual value of the distances of the individual profiled patterns from each other. 
         [0011]    By the measures wherein on both sides of the web of corrugated cardboard is arranged in each case one reference point with a constant distance f from each other whose distance g from each other is continuously detected by the measuring camera, it is attained that temperature-related measuring errors in the camera can be compensated. Thus, the camera constantly receives an exact reference value for the distance between the two reference points which allows for numerical compensation of measuring errors. 
         [0012]    The distance of the camera from the surface of the web of corrugated cardboard should be as large as possible. The distance is limited by constructional conditions in factory buildings and the like. The distance should however be chosen at least such that for the distance e of the measuring camera from a measuring line, formed by the incidence of the light band on the surface of the web of corrugated cardboard, relative to the total width a of the web of corrugated cardboard, applies e≧a. 
         [0013]    Further features, advantages and details of the invention will become apparent from the ensuing description of an embodiment, taken in conjunction with the drawing. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0014]      FIG. 1  shows a schematic perspective view of an apparatus for detection of the accuracy of format of a web of corrugated cardboard; and 
           [0015]      FIG. 2  shows a cross-sectional view of the apparatus according to  FIG. 1 . 
       
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
       [0016]      FIGS. 1 and 2  show a schematic view of a web of corrugated cardboard  1  which may however also be a conventional web of cardboard. The web of corrugated cardboard  1  conventionally comprises at least an upper smooth liner  1   a  and a lower, likewise smooth liner  1   b  between which is disposed a corrugated paper web  1   c  which is glued to the liners  1   a  and  1   b.  In the course of its production, the web of corrugated cardboard  1  is located on an apparatus for producing corrugated cardboard, strictly speaking downstream of a grooving and longitudinal cutting arrangement (not shown) when seen in the conveying direction  2 , as it is for example shown and described in EP 0 692 369 B1 (corresponding to U.S. Pat. No. 5,857,395) which is explicitly referred to. In this arrangement, the web of corrugated cardboard  1  has been provided with upper grooves  3 ,  4  running in the conveying direction  2  and lower counter grooves  5  allocated thereto. In this arrangement, the web of corrugated cardboard  1  has furthermore been provided with a longitudinal cut  6 , running in the conveying direction  2 , by means of which the web of corrugated cardboard  1  has been divided into two partial webs  7 ,  8 . In the mentioned grooving and longitudinal cutting arrangement, the web of corrugated cardboard  1  has furthermore been trimmed laterally in order to have an exactly defined total width a between its outer, trimmed lateral edges  9 ,  10 . 
         [0017]    The web of corrugated cardboard  1  is guided across a perfectly cylindrical roller  11  so as to be completely plane, in other words even, when seen crosswise of the conveying direction  2 . Downstream of the roller  11  in the conveying direction  2  is arranged an apparatus  12  for detection of the accuracy of format by means of which the relevant width dimensions of the web of corrugated cardboard  1  are detected. The width dimensions include for example the distance b of the groove  3  from the lateral edge  9 , the distance c of the longitudinal cut  6  from the lateral edge  9  and the distance d of the groove  4  from the adjacent lateral edge  10 . Naturally, the distances of the grooves  3 ,  4  from each other or from the longitudinal cut  6  or all distances from only one lateral edge  9  or  10  may principally be detected as well. This only depends on the evaluation yet to be described. 
         [0018]    The apparatus  12  for detection of the accuracy of format comprises a light source  13  which emits a light band  14  whose light beams are substantially parallel to each other. Such a light source  13  may for example consist of a plurality of LEDs  15  which are arranged in a straight row in a corresponding longitudinal housing  16  and emit approximately parallel light. Such LEDs are conventionally available. As in particular illustrated by  FIG. 2 , the light source  13  is arranged laterally of the web of corrugated cardboard  1  in a way that the light band  14  hits the web of corrugated cardboard  1  at a small angle α between the light band  14  and the plane surface  17  of the web of corrugated cardboard  1 . The angle α is such that 5°≦α≦30° applies. 
         [0019]    Above the web of corrugated cardboard  1 , strictly speaking centrally above the web of corrugated cardboard  1 , is arranged a digital measuring camera  18  which, as indicated in  FIG. 1 , absorbs the light  19  reflected by the surface  17  of the web of corrugated cardboard  1 . The measuring camera  18  needs to have a very high resolution. The distance e of the camera  18  from the measuring line  20  defined by the incidence of the light band  14  on the surface  17  of the web of corrugated cardboard  1  is at least equal to the total width a of the web of corrugated cardboard  1  but even larger, if possible. If the constructional conditions do not allow the camera to be arranged vertically above the measuring line  20 , the plane defined by the measuring line  20  and the camera  18  may also be inclined in the conveying direction  2  or opposite to the conveying direction  2 . 
         [0020]    The light band  14  hitting the surface  17  at an angle thereto is reflected differently by the grooves  3 ,  4  and the longitudinal cut  6  than by the plane portions of the surface  17 .  FIG. 2  shows the intensity pattern of the light reflected towards the camera in relation to the width of the web of corrugated cardboard  1 . In the region between the lateral edge  9  of the partial web  7  and the groove  3 , the light is reflected uniformly towards the camera. The light intensity pattern of the light  19  reflected towards the measuring camera  18  is thus linear. In the downward portion  3   a  of the groove facing the mentioned portion  21  of constant light intensity of the light  19 , the incidence of light—in relation to a width unit of the web of corrugated cardboard  1 —is lower than before, in other words less light per width unit is reflected towards the camera  18  in this downward portion  3   a  of the groove  3 . The light intensity of the light  19  reflected towards the measuring camera  18  thus shows a portion  22  that decreases in relation to the linear portion  21 . In the portion  3   b  of the groove  3  that is directed upwardly in relation to the direction of the light band  14 , more light per width unit of the web of corrugated cardboard  1  is reflected towards the camera  18 ; the result is an increased light intensity  23 . 
         [0021]    In the region of the longitudinal cut  6 , there is at first a greatly reduced light intensity  24  and then a slightly increased light intensity  25 . Corresponding to the groove  3 , there is a reduced light intensity  26  in the downward portion  4   a  of the groove  4  while in the upward portion  4   b  of the groove  4 , there is an increased light intensity  27  of the light  19  reflected towards the measuring camera  18 .  FIG. 2  shows that there is a uniform light intensity in all regions of the surface  17  between the grooves  3 ,  4  and the longitudinal cut  6  as well as between the lateral edges  9 ,  10  and the adjacent grooves  3 ,  4 . The center of the light intensity portions  22 ,  23  or  24 ,  25  or  26 ,  27 , respectively, thus exactly corresponds to the center of the groove  3  or of the longitudinal cut  6  or of the groove  4 , respectively; a corresponding image is generated in the camera  18 . No light is reflected at the lateral edges  9 ,  10 ; the entire light intensity pattern according to  FIG. 2  thus only extends across the exact width a of the web of corrugated cardboard  1 . 
         [0022]    Generated electronically in the camera  18 , the exact image of the surface  17  with the exact positions of the grooves  3 ,  4  and the longitudinal cut  6  is transmitted to a computer  28  serving as evaluation device in which the actual values of the distances b, c, d are determined and displayed for example on a monitor  29  serving as display device. If there is an aberration from predetermined desired values, the operator may readjust the mentioned grooving and longitudinal cutting arrangement, if necessary. The desired values may naturally also be stored in the computer  28  for comparison with the mentioned actual values, which may be useful for an automatic control of the grooving and longitudinal cutting arrangement. The comparison of the actual values with the desired values takes place by means of a data interface for controlling the grooving and longitudinal cutting arrangement. In this process, the desired values are transmitted automatically. 
         [0023]    On both sides of the web of corrugated cardboard  1  are arranged stationary reference points  30 ,  31  which are in line with the measuring line  20 . These reference points  30 ,  31  have an exact fixed distance f from each other. These reference points  30 ,  31  are detected continuously by the measuring camera  18  as well. Since in particular small temperature variations may lead to minute distortions in the objective of the measuring camera  18  or in other regions relevant for the accuracy of measurement of the measuring camera  18 , such temperature variations result in measurement errors. If in each case the exact distance f of the reference points  30 ,  31  is detected, the described measuring values, i.e. the position of the grooves  3 ,  4  and of the longitudinal cut  6  and therefore the corresponding distances b, c, d, can be corrected numerically. Calculation errors with respect to the distances b, c, d can thus be kept in the range of below 0.5 mm.