Abstract:
A method of detecting adhesive material applied to a blank from which to form a container for tobacco articles, wherein the adhesive material forms at least one continuous mass of adhesive material on one face of the blank; the method providing for reproducing an image of at least one part of the face including a first portion corresponding to the face portion covered by the mass, and a second portion corresponding to the face portion free of the mass; electronically defining an application region in the image; and emitting a cover signal depending on the portion of the application region occupied by the first image portion.

Description:
BACKGROUND OF THE INVENTION 
     The present invention relates to a method of detecting adhesive material on a blank from which to form a container for tobacco articles. 
     In particular, the invention relates to a method of detecting adhesive material on a blank from which to form a hinged-lid packet of cigarettes, to which the following description refers purely by way of example. 
     Adhesive material is applied to cigarette packet blanks to join parts of the blank to one another, as well as to parts of a collar and to parts of a foil wrapping containing the cigarettes. 
     The adhesive material is applied by a gumming unit comprising a conveyor for feeding the blanks along a given path, and one or more gumming devices arranged along the path to apply the adhesive material to the blanks. 
     One commonly used type of gumming device comprises at least one gumming roller, which is positioned contacting adhesive material in a tank, and rolls along the blanks to deposit the adhesive material as the blanks are fed along the path. 
     Alternatively, adhesive material is applied by spray guns, which spray a quantity of adhesive material through nozzles as the blanks are fed past the guns. 
     Adhesive material is also applied to the blanks by means of spreading guns, which, like spray guns, dispense a controlled quantity of adhesive material through nozzles, but which, unlike spray gumming devices, is spread as opposed to being sprayed, onto the blanks. 
     The gumming unit provides for applying adhesive material to given portions of the blanks, and in sufficient quantities to ensure the packets formed from the blanks are stable. 
     The gumming devices described above do not always provide for applying the adhesive material correctly and in the right quantities to the given portions of the blanks. Which means the gumming must be checked to enable any improperly gummed blanks to be rejected immediately and prevented from being formed into packets, which will inevitably have to be rejected and opened to salvage the cigarettes inside. This is especially so when applying adhesive material using spray or spreading gun gumming units, the nozzles of which are subject to clogging, due to impurities in the adhesive material, or due to the adhesive material drying and hardening at the nozzle outlets. 
     One known method of eliminating the above drawbacks is to check the flow of adhesive material along a supply conduit common to a number of nozzles remains constant, or varies within predetermined limit values and in time with the passage of the blanks past the guns. Such a method, however, fails to meet current requirements, by failing to determine small variations in flow, and is especially inaccurate in the case of gumming units with a large number of nozzles. 
     Another known method is to check the flow of adhesive material through each nozzle by means of a sensor located along the conduit supplying the adhesive material to the nozzle or at the outlet of each nozzle. Though more effective, this solution complicates the design of the guns by requiring a flow sensor for each nozzle. 
     A further drawback of the above methods is that they fail to provide for determining whether the adhesive material is applied to the correct portion of the blank. That is, even if the flow of adhesive material indicates correct operation of the guns, there is no guarantee that the adhesive material has been applied at the right points. Moreover, methods based on measuring the flow of adhesive material cannot be applied when depositing adhesive material using the gumming rollers described previously. 
     From GB-A-2297616 it is known to check the masses of adhesive material applied to the blank in order to find whether the masses of adhesive material are applied in the correct position and cover a given length. According to the method referred above, a check is made in a comparison device between a predetermined linear pattern and a detected linear pattern, in case the two patterns do not coincide, the comparison device transmits an error signal. 
     This method, even though it has proved to be more reliable than the methods previously described, has the drawback that the comparison device, which acts on a strict coincidence between the predetermined pattern and the detected pattern, produces an error signal even when the masses adhesive material contain a sufficient quantity of adhesive material and are arranged in an acceptable position. 
     Moreover, the detection of glue masses is based on the difference between peaks of darkness and peaks of brightness, which are generated by inclined light beams impinging upon the blank and the glue masses. The glue masses are offset in respect of the flat blank and, for this reason generates shadows, which correspond to the peaks of darkness, and reflect part of the beams generating in this way the peaks of brightness. A blank from which to form a container for tobacco articles is provided with prescored lines along which the blank is folded. The prescored lines are offset in respect of the level of a flat blank in the same way as the masses of adhesive material applied on the blank itself, then the check method described in GB-A-2297616 is not suitable for checking the presence of glue on blanks from which to form a container for tobacco articles, because of the prescored lines. 
     SUMMARY OF THE INVENTION 
     It is an object of the present invention to provide a method of detecting adhesive material on blanks from which to form packets of cigarettes, and which provides for overcoming the aforementioned drawbacks. 
     According to the present invention, there is provided a method of detecting adhesive material applied to a blank from which to form a container for tobacco articles, the adhesive material forming at least one continuous mass of adhesive material on one face of the blank; and the method being characterized by comprising the steps of reproducing an image of at least one part of said face comprising a first image portion corresponding to a face portion covered by said mass, and a second image portion corresponding to a face portion free of said mass; electronically defining a given application region in said image; and emitting a cover signal depending on the portion of said application region occupied by said first image portion. 
     The method of the present invention is particularly advantageous in respect of the prior art because with only one signal, namely the cover signal, it is possible to acquired an information concerning the quantity of adhesive material contained in a mass and information relating to the position, in fact the control is made solely inside said given region and the cover signal is acquired solely inside said region. Moreover, the cover signal is compared with a range of acceptability, which alone represent a level of acceptability of the position and the quantity of adhesive material. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     A non-limiting embodiment of the present invention will be described by way of example with reference to the accompanying drawings, in which: 
     FIG. 1 shows a schematic side view, with parts removed for clarity, of a gumming unit implementing the method according to the invention; 
     FIG. 2 shows a plan view of a blank gummed in the course of a gumming step; 
     FIG. 3 shows a schematic electronic reproduction of a portion of the FIG. 2 blank. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Number  1  in FIG. 1 indicates a gumming unit for applying adhesive material  2  to blanks  3  from which to form known hinged-lid packets of cigarettes (not shown). 
     Gumming unit  1  is located between a supply unit  4  for supplying blanks  3 , and a feed unit  5  for the gummed blanks  3 , i.e. the blanks  3  to which adhesive material  2  has been applied, and comprises a conveyor  6 , a spray gumming device  7 , and a control unit  8 . 
     Conveyor  6  comprises a drum  9 , which is rotated anticlockwise in FIG. 1 about a respective axis  10  by a motor  11  to feed blanks  3  along a path P and in a given traveling direction D. Drum  9  has a number of plates  12  equally spaced about axis  10  and having known suction holes (not shown) for retaining a respective blank  3  on each plate  12 . 
     Spray gumming device  7  is located along path P, and comprises a number of guns  13  arranged in two rows  14  and  15  extending crosswise to traveling direction D. Each gun  13  receives adhesive material  2  via a valve body  16  for metering adhesive material  2 , and comprises a nozzle  17  for injecting measured quantities of adhesive material  2 , which assume the form of drops  18  on blank  3 . 
     With reference to FIG. 2, blank  3  has a longitudinal axis  19 , and is divided into a central portion  20  comprising flat panels  21  separated from one another by transverse bend lines  22 , and into two lateral portions  23  and  24 , each comprising flat tabs  25  connected to central portion  20  along longitudinal bend lines  26 . 
     Blank  3  has a relatively rough face  27 , which eventually forms the inner surface of the cigarette packet (not shown), and on which are indicated by the dash lines in FIG. 2 a number of application regions  28  determined according to the acceptability of the location of drops  18  with respect to blank  3 . That is, the location of each drop  18  is considered acceptable when drop  18  falls within a respective region  28 . 
     The size of application regions  28  is determined according to the application precision required, which in turn varies according to the location of regions  28  with respect to blank  3 . For example, drops  18  deposited close to the outer perimeter of blank  3  must be applied more accurately than those deposited on the central portion of blank  3 , to prevent adhesive material  2  from oozing out when tabs  25  are brought into contact with one another and compress drops  18 , thus increasing the surface of blank  3  coated with adhesive material  2  and possibly resulting in leakage of adhesive material  2 . 
     Blanks  3  are fed along path P with respective longitudinal axes  19  perpendicular to traveling direction D, and the adhesive material  2  injected by guns  13  is deposited on blanks  3  in the form of drops  18  arranged along straight application lines  29  substantially perpendicular to longitudinal axis  19  and parallel to traveling direction D. FIG. 2 shows nozzles  17  of rows  14  and  15  of guns  13 , and each nozzle  17  is aligned with a respective straight application line  29 . 
     Control unit  8  comprises a microprocessor  30  to which are connected an encoder  31  for determining the angular position of plates  12  of conveyor  6  with respect to axis  10 , and a sensor  32  located upstream from gumming device  7  and for determining the position of blank  3  on plate  12  of conveyor  6 . Microprocessor  30  is connected to each gun  13  to control operation of respective valve body  16 , and to motor  11  to arrest, if necessary, both injection of adhesive material  2  and rotation of drum  9 . 
     Control unit  8  also comprises a detecting device  33  located along path P, immediately downstream from gumming device  7  in traveling direction D. Detecting device  33  in turn comprises a light source  34  for illuminating face  27  of blanks  3 ; and a television camera  35  located alongside light source  34  and for forming an analog image “IMA” of face  27 . 
     Analog image “IMA” corresponds with a signal depending on the brightness of blank  3  and defined by a matrix of dots or so-called “pixels”  36 , each of which is assigned an analog value “VA” depending on the brightness of the blank at pixel  36 , and two coordinates “X” and “Y” depending on the location of pixel  36  in the image formed by camera  35 . 
     The brightness of blank  3  varies according to the light reflected by face  27  and by drops  18  on face  27 . That is, though normally light-coloured, relatively rough face  27  reflects less light than drops  18 , which normally have a smooth surface and, regardless of the colour of adhesive material  2 , reflect more light. 
     Camera  35  is connected to an analog-digital converter  37  for converting the analog values “VA” of pixels  36  into digital values “VD”, and which is in turn connected to microprocessor  30  to transmit the digital values “VD” and the coordinates of pixels  36  to microprocessor  30  and so convert analog image “IMA” into a digital image “IMD”. 
     Control unit  8  also comprises an indicator panel  38 , which is connected to microprocessor  30  and in turn comprises a number of indicator lights  39 , each indicating the operating state of a respective gun  13 . 
     The FIG. 3 portion of digital image “IMD”. substantially corresponds to a given application region  28  of blank  3 , and is represented by a set of pixels  36  in the form of small squares with respective “1” or “0” values and arranged in orderly manner along the “X” and “Y” coordinates. The values of pixels  36  represent digital values “VD”, which, when equal to 1, indicate the presence, and, when equal to 0, indicate the absence of adhesive material  2  at the respective “X” and “Y” coordinates. 
     Each set of pixels  36  assigned digital values “VD” equal to 1 defines a respective image portion IMD 1  corresponding to the part of blank  3  covered with adhesive material  2 ; and each set of pixels  36  assigned digital values “VD” equal to 0 defines an image portion IMD 2  corresponding to the part of blank  3  free of adhesive material  2 . 
     That is, as opposed to being shown on inner face  27  of blank  3 , application regions  28  are simply created electronically on digital image “IMD” formed by camera  35 , and are predefined in a memory of microprocessor  30  by memorizing given “X1” and “Y1” values of coordinates “X” and “Y”. 
     In actual use, blanks  3  are transferred by supply unit  4  to drum  9 , which feeds blanks  3  along path P and transfers the gummed blanks  3  to feed unit  5 . 
     As drum  9  rotates, encoder  31  determines the angular position of drum  9  and plates  12 , while sensor  32  determines the position of blank  3  on respective plate  12 . The signals emitted by encoder  31  and sensor  32  are transmitted to microprocessor  30 , which activates guns  13  independently of one another to apply drops  18  of adhesive material  2  to application regions  28 . Adhesive material  2  is released according to the position of blank  3  with respect to nozzles  17 . 
     When the gummed blank  3  is illuminated by light source  34 , face  27  and respective drops  18  partly reflect the light towards camera  35 , which detects the brightness of the various parts of blank  3 . The analog image “IMA” signal, i.e. the respective analog values “VA” and “X” and “Y” coordinates of the relevant pixels  36 , is transmitted to converter  37 , which provides for converting analog values “VA” into digital values “VD”. 
     In converter  37 , each analog value “VA” is compared with a discriminating or threshold value “VS”, and, whenever an analog value “VA” is greater than or equal to value “VS”, the corresponding digital value “VD” is assigned a “1” value. Conversely, the digital value “VD” is assigned a “0” value. The digital values “VD” and the values of the “X” and “Y” coordinates of pixels  36  are transmitted to microprocessor  30 , in which the “X1” and “Y1” values of the “X” and “Y” coordinates of each application region  28  of blank  3  have been set beforehand, and which contains a signal corresponding to a digitized image “IMD” of blank  3 , and the “X1” and “Y1” values of the application regions  28  of blank  3 . 
     Each pixel  36  assigned a “0” digital value “VD” forms part of image portion IMD 2 , and each pixel  36  assigned a “1” digital value “VD” forms part of one of portions IMD 1 . 
     The analog-digital conversion is preferably only performed for the analog values “VA” of pixels  36  in regions  28 . 
     For each region  28 , microprocessor  30  counts and adds the pixels  36  with “1” digital values “VD” , the resulting sum representing the value of a cover signal “SR” relative to that particular region  28 . That is, cover signal “SR” depends on the portion of application region  28  occupied by said first image portion “IMD  1 ”. 
     Microprocessor  30  compares cover signal “SR” with a preset range of values “I”, and, if the cover signal “SR” is outside the given range “I”, emits an error signal “SE” to arrest gumming unit  1  (that is, to arrest motor  11  of drum  9  and guns  13 ). 
     Microprocessor  30  assigns each error signal “SE” an address signal “SI” defined by the mean values “X1M” and “Y1M” of the “X1” and “Y1” values of the “X” and “Y” coordinates of the region  28  causing the emission of error signal “SE”, and activates light  39  indicating the operating state of the respective gun  13  responsible for applying adhesive material  2  to the region  28  corresponding to mean values “X1M” and “Y1M”, the indicator light  39  to be activated being determined by means of address signal “SI”. 
     As application regions  28  are arranged along straight application lines  29 , each of which is aligned with a given gun  13 , according to a variation, address signal “SI” is defined solely by mean value “X1M” of value “X1”, which determines the location of straight application line  29  and therefore of the respective gun  13 . 
     Besides preventing the supply of improperly gummed blanks  3 , this therefore provides for rapidly determining the malfunctioning gun  13 . 
     The method described is especially advantageous by only determining the presence of adhesive material  2  in application regions  28 . 
     One way of using the method described, which is especially suitable for controlling the operating state of guns  13  when drum  9  is rotated at particularly high speed, is to check a small portion of each blank  3  as blanks  3  travel past detecting device  33 , and vary the small check portion cyclically for successive blanks traveling past detecting device  33 . That is, each blank  3  is divided theoretically into three portions “A”, “B”, “C” extending parallel to longitudinal axis  19  of blank  3  and corresponding, say, to portions  23 ,  20 ,  24  as shown in FIG. 2, and each of the three portions is examined singly every three successive blanks. This does of course mean not all of regions  28  are checked, and improperly gummed blanks  3  may be supplied to unit  5 . Nevertheless, in the event of a nozzle  17  or a gun malfunctioning and going undetected, the malfunction is definitely detected when checking the next two blanks.