Abstract:
A method for checking products with labels, wherein: 
     a product is formed and is provided on one side, in particular an outer side, with a label which, at least in fitted condition, forms at least one closed surface; 
     the product is brought between a light source and a light-sensitive device; and 
     with the light-sensitive device, the pattern and/or intensity of light originating from the light source and falling through the product, in particular through and/or alongside the label, is measured; 
     wherein the light-sensitive device produces a rejection signal if the pattern and/or the intensity do not agree with a pre-set pattern and/or intensity.

Description:
BACKGROUND OF THE INVENTION 
     The present invention relates to a method for checking products with labels. 
     It is known to provide products with decorations by providing labels thereon. These labels may be adhered to the inside or outside of a product or, preferably, are provided by in-mold labeling technique. These labels moreover, besides providing the decoration, typically afford protection of goods to be packaged in the products, for instance from the influence of light. In this connection it is highly important for the labels to be fitted in the correct manner. In substantially rectangular holder-shaped products, often labels are used that in flat condition have roughly the shape of a Maltese cross, that is, a central surface having four adjoining cross surfaces. The central surface is then placed against the bottom of the holder, the cross surfaces against the four side surfaces of the holder. The cross surfaces must adjoin each other accurately along the ribs of adjacent side surfaces, such that no light can pass between these surfaces and, moreover, any decorations continue across the ribs. If this has been achieved to an insufficient extent, the products are rejected. 
     Commonly, products are inspected visually. To that end, the products in a production line are looked at by quality inspectors, who remove poorly labeled products from the production line. In more advanced methods, cameras with pattern recognition means are used. The labels are then provided with printings recognizable to the pattern recognition means, which printings can be compared with pre-inputted patterns. In case of insufficient agreement, the product involved is removed. These known methods have the drawback that they are particularly labor-intensive and moreover lead to an undesirably high percentage of errors. In the known method, the use of the pattern recognition means moreover leads to the drawback that only specific patterns are recognizable. Furthermore, for this purpose, a relatively large number of cameras must be used, which is costly and involves susceptibility to trouble. 
     The invention has for its object to provide a method of the type described in the opening paragraph, in which the above drawbacks of the known methods are avoided, while retaining the advantages thereof. To that end, a method according to the invention is characterized by the measures according to claim 1. 
     SUMMARY OF THE INVENTION 
     In a method according to the invention, use is made of a light source and light-sensitive means to trace any errors in a product with a label. It has been found that with a method according to the invention errors can be traced particularly fast and accurately. In the method, moreover, use can be made of simple light-sensitive means. Especially if use is made of both measurement of light falling through and of pattern recognition, a particularly high accuracy can be achieved. Moreover, by means of a rejection signal other parts of the same or a different apparatus may be controlled, for instance discharge means for rejected products or means for positioning the labels. Thus, an optimally automated method can be obtained for manufacturing and checking products with labels. 
     The invention further relates to an apparatus for checking products with labels. According to the invention, such an apparatus is characterized by the features according to claim 7. 
     In an apparatus according to the invention, use is made of a light source and light-sensitive means to trace any errors in a product with a label. It has been found that with an apparatus according to the invention errors can be traced very fast and accurately and use can be made of simple light-sensitive means. Especially if use is made of both measurement of light falling through and pattern recognition, a particularly high accuracy can be achieved. Moreover, by means of a rejection signal, other parts of the same or a different apparatus may be controlled, for instance discharge means for rejected products or means for positioning the labels. 
     An apparatus according to the invention is particularly suitable for checking in-mold labeled injection molded products to be used as packages, with both the bottom and the longitudinal walls labeled, and the labels having edge portions adjoining each other, in particular adjacent the ribs of the holder. An apparatus according to the invention is preferably provided with a table having an opening against which or over which the holder can be placed by an open side thereof, the table being provided with an abutment edge around the opening to provide a substantially light-tight seal between the holder and the table. Thus, the desired light-tightness of the holder can be checked particularly fast. 
     An apparatus according to the invention is preferably provided with a discharge device controlled on the basis of the presence or absence of a rejection signal for a respective product. Thus, products can be automatically conveyed further for later use or be discharged if the labels have not been provided in the correct manner or if other defects are established. The products are preferably supplied by means of belt conveyer means and picked up and displaced within the apparatus with the aid of suction means, at least reduced pressure means, such as suction cups, or the like. By these means, the products can be picked up and displaced simply, rapidly, and accurately, without damage. 
     An apparatus according to the invention is preferably of such design that at least two products can be handled simultaneously, in particular can be checked simultaneously. Also, the apparatus may be of such design that in each case two juxtaposed feeding and discharge means make use of a checking apparatus disposed between them and comprising the at least one light source and light-sensitive device. Furthermore, it is then preferred that the apparatus be of modular construction, such that it can be easily and rapidly adapted to other types of products. 
     Further advantageous embodiments of an apparatus and a method according to the invention are described in the subclaims. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     To clarify the invention, exemplary embodiments of an apparatus and a method according to the invention will be elucidated in more detail with reference to the drawing. In the drawing: 
     FIG. 1 shows a label in flat condition; 
     FIG. 2 diagrammatically shows, in perspective elevation, a holder provided with a label according to FIG. 1; 
     FIG. 3 diagrammatically shows, in perspective elevation, a portion of a label fitted in the right condition; 
     FIG. 4 diagrammatically shows, in perspective elevation, a portion of an incorrectly fitted label; 
     FIG. 5 diagrammatically shows, in top plan view, an apparatus according to the invention; and 
     FIG. 6 diagrammatically shows, in side elevation, an apparatus according to FIG.  5 . 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     In this description, the same or corresponding parts have the same or corresponding reference numerals. In this description, by way of example, a holder, for instance a tub of butter, with a label is shown. It will be clear, however, that all kinds of other products can also be checked in the same manner. 
     FIG. 1 shows, in flat condition, a label  1  for use on a holder  2  as shown in FIG.  2 . The label  1  comprises a substantially rectangular central surface  4  and four cross surfaces  6   a-d  extending therefrom, so that the label  1  is somewhat in the shape of a Maltese cross. The holder  2  comprises a bottom surface  8  and four side walls  10   a-d , to some extent diverging from the bottom  8 . The label  1  may, for instance, be provided on one side with an adhesive layer and be adhered to the holder  2 , with the central surface  4  being adhered to the bottom  8  of the holder and the cross surfaces  6   a-d  being adhered to the respective side walls  10   a - 10   d . Preferably, however, the label  1  is provided in a mold cavity (not shown), after which the holder  2  is injection molded against the label, in a known manner with in-mold labeling technique, so that an integral connection is obtained between the label  1  and the holder  2 . 
     The cross surface  6   a  has a side edge  12 , the cross surface  6   d  has a side edge  14 , which side edges  12 ,  14  meet in an angular point  16  of the central surface  4 . 
     FIG. 3 shows, in perspective elevation, a corner of the holder  2  with a label  1  provided thereon, with the angular point  16  coinciding with a corner  17  of the holder  2 . The cross surfaces  6   a ,  6   d  are folded against the side walls  10   a ,  10   d , such that the longitudinal edges  12 ,  14  of the respective side surfaces  6   a ,  6   b  touch each other along the ribs  18 . In a comparable manner, the other cross surfaces  6   b ,  6   c  are folded against the respective side walls  10   b ,  10   c , so that the longitudinal edges  12 ,  14  thereof lie against each other. The rib  18  is thus no longer visible. Provided on the outer sides of the label  1  is a printing  20 , for instance lines or text (FIG.  6 ). In the embodiment shown in FIG. 3, this printing  20  continues across the ribs  18  from one cross surface  6   a  to the adjacent cross surface  6   d . If the label  1  has been fitted correctly, as shown in FIG. 3, for instance a continuous pattern  20  is thus obtained. 
     FIG. 4 shows the same corner  17  of the holder, on which, however, the label  1  has been provided incorrectly. Visible between the side edge  14  of the cross surface  6   d  and the side wall  12  of the cross surface  6   a  is the rib  18  as well as an uncovered part of the side wall  10   a . The printing  20 , in particular the lines, do not continue across the rib  18 , so that an unwanted pattern is obtained. The position of the label  1  on the holder  2  can be checked with an apparatus according to the invention, as shown in FIGS. 5 and 6. 
     The apparatus  30  according to the invention is shown in part in FIG. 5, comprising two feed-through paths  31   a ,  31   b  for feeding through products, such as the holder  2  as shown in FIGS. 1-4. For clarity&#39;s sake, the holders  2  are omitted in FIG. 5, whilst the apparatus  30  is shown diagrammatically of the apparatus  30 , specifically the left-hand path  31   a  will be described. The right-hand path  31 B is substantially identical thereto. 
     The apparatus  30  comprises first feeding means  32 , a table  34  linking up with the leading end  36  of the first feeding means  32 , as well as discharge means  38 , comprising a valve  40 , arranged on the side of the table  34  remote from the first feeding means  32 , and conveying means  42  placed therebelow, in particular a conveyor belt  44 . The first feeding means  32  have a conveying direction T in the direction of the table  34 , the conveyor belt  44  has a conveying direction K approximately at right angles to the conveying direction T. Connected on the side of the valve  40  remote from the table  34  are second discharge means  46 . In this embodiment, the first feeding mean  32  and the second discharge means  46  are designed as two circular conveyor belts  48  extending side by side, on which holders  2  can be supported. The holders  2 , as shown in FIG. 6, are arranged upside down, that is, with the bottom  8  directed upwards, remote from the belt  48 . The belt elements  48  have been passed around guide wheels  50 . 
     The table  34  is centrally provided with an opening  52 , around which extends a groove  54  in which a longitudinal edge  56  of the holder  2  can be received with a proper fit, such that a substantially light-tight seal is obtained between the groove  54 , at least the table  84 , and the longitudinal edge  56 . The holder  2  shown in FIG. 6 has an outwardly bent longitudinal edge  56 , as known, for instance, in tubs of (low-fat) margarine, on which longitudinal edge  56  a lid (not shown) can be placed. In FIG. 2 this edge is omitted, for clarity&#39;s sake. 
     The table  34  is placed on rails  60  by way of rollers  58 , such that the table  34  can be rolled in a direction S, at right angles to the conveying direction T. Provided between the tables  34  in the paths  31   a ,  31   b , between the rails  60 , is a light box  62 , which is shown in FIG. 6 in sectional view. Included in the light box  62  is a light source  64 , for instance a tubular lamp  66 . In FIG. 6 the distance between the underside of the table  34  and the light box  62  is represented as being relatively large. In reality, the table  34  will preferably move closely above the light box  62 . During use, the table  34  can be moved with the opening  52  above the tubular lamp  66 , for instance by driving one of the rollers  58  with a motor  68 , such that light from the light source  64  can reach through the opening  52  into the inner space of a holder  2  supported on the table  34 . Light from the light source  64  will fall through the side walls  10  and the bottom  8  of the holder  2  and in some measure through the label  1 . There will be a difference between the light falling through parts of the holder  2  covered by the label  1  and parts not covered by the label  1 . Especially relevant here is the difference in light falling through correctly fitted labels  1 , as shown in FIG. 3, in particular between the longitudinal edges  12  and  14 , and incorrectly fitted labels, as shown in FIG. 4, so that space exists between the longitudinal edges  12 ,  14 , and light shines through the uncovered part of the side wall  10   a . Provided between the paths  31   a ,  31   b  is a light-sensitive device  70 , in the embodiment shown in the form of three cameras  72 . It is also possible to use different numbers of cameras, possibly just one camera centrally above the light box  62 . The cameras are connected via suitable cable work  73  to a central control unit  74 , with which, in a manner to be described hereinafter, inter alia the valve  40  can be controlled, as well as the table  34  and transport means  76 , with which a holder  2  can be picked up and placed on the table or can be picked up from the table and placed on the valve  40  or the second discharge means  46 , depending on signals to be described hereinafter. 
     With the light-sensitive device  70 , during use, a holder  2  placed between the light source  64  and the light-sensitive device  70  can be checked, whereby light from the light source  64  shining through the holder can be observed, yielding an image which can be compared by means of the control unit  74  with a previously inputted image or pattern matching a holder  2  of the subject type on which the label  1  has been fitted correctly, as shown, for instance, in FIG.  3 . Moreover, permissible tolerances may be inputted in the control unit  74 , for instance a quantity of light failing between longitudinal edges  12 ,  14  that is considered permissible. In the event of a deviation from the desired image that is greater than is considered permissible, the control unit  74  produces a signal which can be designated as rejection signal. With this signal, the valve  40  can be controlled. This valve can be opened on the basis of a rejection signal, such that a rejected holder  2 , that is, a holder whose image observed by the light-sensitive device  70  deviates unduly from the desired image, can pass the valve and be received in the discharge device  38 , so that it can be carried off by the belt  44 , for instance for recycling. 
     Provided above each path  31   a ,  31   b  is a transfer device  76  supported by guide rails  80  extending in the conveying direction T. The transfer device  76  carries piston-cylinder assemblies  82  provided with suction cups  84  which, by means of the piston-cylinder assemblies  82 , can be placed against the product  2 , in particular the bottom  8 , whereupon a reduced pressure can be generated in the suction cups  84  to pick up the holder  2 . To that end, the piston-cylinder assemblies  82  and the suction cups  84  are connected via a line  86  with a pneumatic device  88 . After the holder  2  in the position shown in FIG. 6 has been seized with the suction cups  84 , it can be lifted from the feeding means  32  and be transferred to the table  34  with the transfer device  76 . There the holder  2  will be released and with the table  34  be moved in the direction S to above the tubular lamp  66 . In that position, the tubular lamp  66  is switched on, and with the light-sensitive device  70  an image of light passing through the holder  2 , in particular through and alongside the label  1 , is recorded and transmitted to the central control unit  74 , in which the image is compared with the desired image. Next, the table  34  with the holder  2  is moved back into the path  31   a , where the holder  2  is picked up again with the transfer device  76  and is moved further in the direction T, at least to above the valve  40 . If on the basis of this holder  2  a rejection signal has been produced by the central control unit  74 , the valve  40  is controlled to open and the holder  2  is released above the thus created opening, so that it falls onto the belt  44  and can be carried off for recycling. If on the basis of this holder  2  no rejection signal is produced, or possibly an acceptance signal, then the holder  2  is moved further by means of the transfer device  76  to above the second discharge means  46  and set down thereon, so that the holder  2  can be passed further for further processing, for instance to be filled, at least stacked for further use. It will be clear, for that matter, that cracks or other imperfections in the label  1  can also be observed with an apparatus according to the invention. 
     It is preferred that with the light-sensitive device  72  not only an image of transmitted light is formed, but also that by means of pattern recognition the labeling is examined and is compared with a desired labeling image. Thus the printing of the label  1  can be checked as well, as a second check. If the correct printing, at least the correct condition of the printing, has not been obtained, likewise a rejection signal can be produced, with the consequences described earlier. 
     It is preferred that at least two transfer devices  76  are provided, one after the other in the conveying direction T, with which at the same time a holder  2  can be picked up from the first feeding means  32  and a holder  2  can be picked up from the table  34  and the two holders can be moved at the same time, one to the table  34  and the other to the valve  40  or the second discharge means  46 , depending on the presence or absence of the rejection signal. Thus, a large number of holders can be checked still faster. 
     The invention is by no means limited to the exemplary embodiments shown in the description and the drawing. Many variations thereof are possible within the scope of the invention outlined by the claims. 
     For instance, the discharge device may be designed in many ways, with the valve  40  possibly omitted. For instance, in the event of a rejection signal, holders may be blown away from the second discharge means or be put away beside the second discharge means in a different manner. In the condition shown in FIG. 5, two paths  31   a, b  are shown, allowing the table  34  of the left-hand path  31   a  and the table of the right-hand path  31   b  to be alternately moved above the light source  64  for alternately testing holders. However, it is, of course, also possible for each path  31  to be provided with a light source. Also, the light source  64  could be arranged directly below the path  31 , in which case, however, a different arrangement of the light-sensitive device  70  is to be chosen to avoid collision of the transfer device  76  and the light-sensitive device  70 . Also, holders  2  may, for instance, be moved over the light box  62  directly with a belt conveyor, such as the first feeding means  32 , so that the holders can be moved directly between the light source and the light-sensitive device. Additionally, for instance the light box, at least the light source, may be arranged for movement in vertical direction, so that it can be moved closely below or even into the holder. Furthermore, the light source may be placed above and the light-sensitive device below the path, or on opposite sides thereof, while the position of the tested products may be simply adjusted. It will be clear that with an apparatus according to the invention, also differently shaped products, for instance flat products, may be tested, in all of which cases a desired image can be stored in the control unit  74  for comparison with a current observed image. 
     These and many comparable variations are understood to fall within the scope of the invention outlined by the claims.