Abstract:
Flaw detection apparatus includes an electrode disposed in a region surrounded by a packaging material including a layer of an electrically-conductive material; a cutting member made of an electrically-conductive material and adapted to cut a predetermined portion of the packaging material; a variable detector, disposed between the electrode and the cutting member, for detecting an electrical variable; and flaw detection processor for reading the detected variable and for determining, on the basis of the detected variable, a flaw in the packaging material. In this case, the variable detector is disposed between the electrode and the cutting member.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
   The present application is a 371 of PCT/JP01/11432 filed Dec. 27, 2000 and claims priority under 35 USC 365 of Japanese Application No. 2000-399148 filed Dec. 26, 2001. 
   TECHNICAL FIELD 
   The present invention relates to a flaw detection apparatus. 
   BACKGROUND ART 
   Conventionally, liquid foods such as milk and other beverages have been sold while accommodated within, for example, packaging containers formed from a packing material having a paper substrate. Examples of such packaging containers include polyhedral packaging containers and brick-shaped packaging containers each having a flat top wall. Of these packaging containers, packaging containers having a capacity which enables a purchaser to drink liquid food in a single serving are formed through a process of longitudinally sealing a web-shaped packaging material into a tubular shape, transversely sealing and cutting the tube-shaped packaging material at predetermined intervals to thereby form initial-shape containers, and processing the initial-shape containers to complete the packaging containers. Further, a discharge opening is formed in the top wall of each packaging container and is covered with a pull tab from the outer side and with an inner seal from the inner side, and the pull tab and the inner seal are welded together. 
   During fabrication of the above described packaging container, heat is applied to the packaging material, the pull tab, and the inner seal in order to seal the packaging material in the longitudinal and transverse directions and to weld the pull tab and the inner seal together. At that time, stress acts on resin layers which constitute the pull tab and the inner seal, respectively, possibly resulting in formation of flaws such as pinholes and cracks in the packaging material. If such a flaw is generated in, for example, the innermost resin layer of the packaging material, an aluminum foil layer, and the inner seal, the liquid food contained in the packaging container soaks into the paper substrate, and oozes from an end surface of the packaging material or from the interface between the container body of the packaging container and the pull tab. 
   In view of the forgoing, there has been provided a flaw detection apparatus which samples packaging containers at proper intervals; forms an opening in the top wall of each sampled packaging container; charges water into the packaging container; and immerses a portion of the water-charged packaging container into water stored in a vessel. Since an end surface of the aluminum foil layer is exposed to the outside of the packaging container, when electrodes are dipped in the water within the packaging container and the water within the vessel, respectively, electrical continuity is established between the two electrodes if a pinhole has formed in the packaging container to a depth reaching the aluminum foil layer. 
   However, since the conventional flaw detection apparatus requires the labor of charging water into each packaging container and partially immersing the packaging container in water stored in the vessel, the labor for flaw detection is cumbersome. Further, the flaw detection apparatus cannot inspect all packaging containers. In addition, since the flaw detection apparatus forms an opening in the top wall of packaging containers to be inspected, the inspected packaging containers are destroyed. 
   An object of the present invention is to solve the problems involved in the above described conventional flaw detection apparatus and to provide a flaw detection apparatus which can simplify the labor necessary for flaw detection, which can inspect all packaging containers, and which does not destroy the packaging container during inspection. 
   DISCLOSURE OF THE INVENTION 
   In order to achieve the above object, a flaw detection apparatus according to the present invention comprises an electrode disposed in a region surrounded by a packaging material including a layer of an electrically-conductive material; a cutting member made of an electrically-conductive material and adapted to cut a predetermined portion of the packaging material; variable detection means, disposed between the electrode and the cutting member, for detecting an electrical variable; and flaw detection processing means for reading the detected variable and for determining, on the basis of the detected variable, a flaw generated in the packaging material. 
   In this case, since inspection for detecting a flaw in the packaging container does not require charging water into each packaging container and partially immersing the packaging container in water contained in a vessel, the labor for flaw detection is simplified. Further, all packaging containers can be inspected. Moreover, since no opening is formed in the top wall of each of packaging containers to be inspected, the packaging containers are not destroyed during inspection. 
   The flaw detection apparatus of the present invention may further include a sealing apparatus for sealing the packaging material; and the predetermined portion of the packaging material is a seal formed by the sealing apparatus. 
   In the flaw detection apparatus of the present invention, the flaw detection processing means preferably reads the electrical variable at the time when the cutting member cuts the seal. 
   In using the flaw detection apparatus of the present invention liquid food may be charged into the region, and the electrode dipped in the liquid food. 

   
     BRIEF DESCRIPTION OF DRAWINGS 
       FIG. 1  is a schematic view of a flaw detection apparatus according to an embodiment of the present invention; 
       FIG. 2  is a schematic view of a main portion of a charging machine according to the embodiment of  FIG. 1 ; and 
       FIG. 3  is a block diagram of the flaw detection apparatus according to the embodiment of  FIG. 1 . 
   

   DESCRIPTION OF THE PREFERRED EMBODIMENT 
   The embodiment of the present invention will next be described in detail with reference to the drawings. 
   In the drawings, reference numeral  11  denotes a packaging material formed from a flexible material; e.g., a laminate that includes a first resin layer  12  made of polyethylene or like resin, an electrically conductive aluminum foil layer  13 , a paper substrate  14 , and a second resin layer  15  made of polyethylene or like resin, which are arranged in this order from the inner side. When the packaging material  11  is unwound from a reel (unillustrated), the packaging material  11  assumes a web-like shape. Subsequently, the packaging material  11  is sealed longitudinally, while being transported, so as to form a longitudinal seal portion (unillustrated), whereby the packaging material  11  becomes a tubular packaging material; i.e., a tube T. 
   The tube T is continuously transported downward by means of a transfer apparatus (unillustrated) and is nipped by two seal-cut units  16  (only one seal-cut unit  16  is shown in  FIG. 2 ) at predetermined intervals, whereby the tube T is sealed transversely and a belt-shaped lateral seal portion S is formed. Each of the seal-cut units  16  includes a cutting jaw  26  and a pressure jaw  27 . A cutting bar  31  is disposed at the front end (the right-hand end in  FIG. 2 ) of the cutting jaw  26 . An inductor  32  serving as seal means is disposed at the front end (the left-hand end in  FIG. 2 ) of the pressure jaw  27 . By advancing both the cutting jaw  26  and the pressure jaw  27  (moving the cutting jaw  26  rightward in  FIG. 2  and the pressure jaw  27  leftward in  FIG. 2 ), the tube T is nipped from both sides, so that opposing portions of the packaging material  11  are pressed against each other, and opposing portions of the first resin layer  12  are welded. Thus, the tube T is sealed transversely. 
   A liquid food  17  is charged into the region surrounded by the packaging material  11 ; i.e., within the tube T, from above. For this charging, a charge pipe  18 , which is formed of an electrically conductive material such as a metal and which serves an electrode, is inserted into the tube T. The charge pipe  18  extends downward and has an open lower end. The liquid food  17  is supplied from a liquid food supply source (unillustrated) to the charge pipe  18 , so that the liquid food  17  is discharged from the lower end of the charge pipe  18  into the tube T in the direction of arrows B shown in  FIG. 2 . Thus, the lower end of the charge pipe  18  is dipped in the liquid food  17  and is in electrical contact with the liquid food  17 . Although the charge pipe  18  is formed of a metal in the present embodiment, alternatively the charge pipe  18  may be formed of an electrically conductive resin. 
   In order to maintain the liquid food  17  at a constant level within the tube T, there are provided: a float  21 ; an open/close valve  22  disposed within the charge pipe  18  for movement between an open position and a closed position; and a link  23  which connects the float  21  and the open/close valve  22 . As the level of the liquid food  17  rises, the float  21  moves upward, and the open/close valve  22  is closed by means of the link  23  so as to stop charging of the liquid food  17 . When the level of the liquid food  17  falls, the float  21  moves downward, and the open/close valve  22  is opened by means of the link  23  so as to charge the liquid food  17 . 
   After completion of charging of the liquid food  17  and formation of the lateral seal portion S, the lateral seal portion S is cut in order to obtain an initial-shape container  25  containing a predetermined amount of the liquid food  17 . 
   For such cutting operation, a horizontally extending flat cutter  33  is disposed at the center of the cutting bar  31  in such a manner that the cutter  33 ′ can advance and retract (in the direction of arrow A). When the cutter  33  is advanced (moved rightward in  FIG. 2 ), the cutter  33  cuts the tube T at a predetermined location (in the present embodiment, at the center of the lateral seal portion S) of the packaging material  11 . Specifically, an air cylinder  39 , serving as an actuator, is disposed at the rear end (the left-hand end in  FIG. 3 ) of the cutter  33 , and an operation medium such as compressed air is supplied from a compressed air source  38  via a changeover valve  40 . Through supply and release of compressed air via the changeover valve  40 , the cutter  33  can be advanced and retracted. The changeover valve  40  assumes position A or B in accordance with a changeover signal from a control section  45 . At position A, the changeover valve  40  supplies compressed air from the compressed air source  38  to a chamber  39   a  of the air cylinder  39 , and discharges compressed air from a chamber  39   b  of the air cylinder  39 . At position B, the changeover valve  40  supplies compressed air from the compressed air source  38  to the chamber  39   b  of the air cylinder  39 , and discharges compressed air from the chamber  39   a  of the air cylinder  39 . A groove  34  is formed in the inductor  32  so as to accommodate a tip end of the cutter  33  when the cutter  33  is advanced. 
   In  FIG. 2 , the seal-cut unit  16  is shown located in a seal-cut start position, at which the cutting jaw  26  and the pressure jaw  27  are advanced. Subsequently, the seal-cut unit  16  is moved downward (in the direction of arrow B) while nipping the tube T, while the cutting bar  31  and the inductor  32  are strongly pressed against the tube T, and the inductor  32  heats the aluminum foil layer  13  by means of inductive heating. As a result, the opposed portions of the first resin layer  12  are welded to thereby seal the tube T transversely. Although in the present embodiment the tube T is sealed by use of the inductor  32  through inductive heating, the tube T may be sealed by use of a resistor which generates Joule heat. 
   Subsequently, the seal-cut unit  16  is moved further downward (in the direction of arrow B), while cutting processing means (unillustrated) of the control section  45  causes the changeover valve  40  to assume position A in order to advance the cutter  33  to thereby cut the lateral seal portion S at the-center thereof. Thus, a rectangular initial-shape container  25  is separated from the tube T. The seal-cut unit  16  then reaches a seal-cut end position. 
   Subsequently, the cutting processing means causes the changeover valve  40  to assume position B in order to retract the cutter  33  and simultaneously retract the cutting jaw  26  and the pressure jaw  27  (move the cutting jaw  26  leftward in  FIG. 2  and the pressure jaw  27  rightward in  FIG. 2 ). Subsequently, the seal-cut unit  16  is moved upward and then moved along the direction or arrow C to the seal-cut start position. 
   The initial-shape container  25 , which has been formed in the above-described manner, is transported to a forming machine (unillustrated), and is formed into a predetermined shape by the forming machine, whereby a packaging container is obtained. 
   During fabrication of the above-described packaging container, because heat is applied to the packaging material  11  in order to seal the packaging material  11  in the longitudinal and transverse directions, stress acts on the first resin layer  12 , the second resin layer  15 , and the aluminum foil layer  13 , which constitute the packaging material  11 , possibly resulting in formation of flaws such as pinholes and cracks in the packaging material  11 . If such a flaw is formed in the first resin layer  12  or the aluminum foil layer  13 , the liquid food  17  contained in the packaging container soaks into the paper substrate  14 , and oozes from an end surface of the packaging material  11 . 
   In view of the foregoing, the cutter  33  is formed of an electrically conductive material such as a metal; and the charge pipe  18  and the cutter  33  are in electrical contact via a power source  41  and a current sensor  43 , which serves as variable detection means, in order to detect any flaw formed in the packaging material  11 . Again, the electrically conductive material may be an electrically conductive resin. 
   Current is detected by the current sensor  43  as an electrical variable, and a sensor output representing the detected current is fed to the control section  45 . At the time the cutting processing means causes the changeover valve  40  to assume position A in order to cut the lateral seal portion S by means of the cutter  33 , the flaw detection processing means of the control section  45  reads the sensor output fed from the current sensor  43 , and detects any flaw in the packaging material  11  on the basis of the sensor output. 
   Thus, electrical continuity is established between the cutter  33  and the aluminum foil layer  13  when the advancing cutter  33  is cutting the lateral seal portion S at the center thereof. Therefore, when a flaw such as pinhole or crack is formed in at least the first resin layer  12 , electrical continuity is established between the liquid food  17  and the aluminum foil layer  13  at the location where the flaw has formed, so that a closed loop is formed by the cutter  33 , the current sensor  43 , the power source  41 , the charge pipe  18 , the liquid food  17 , and the aluminum foil layer  13 , and current flows through the closed loop in the direction of arrow D in  FIG. 1 , which current is detected by the current sensor  43 . 
   As described above, since the detection of a flaw in the packaging material does not require charging water into each packaging container and partially immersing the packaging container in water contained in a vessel, the labor for flaw detection is simplified. Further, all packaging containers can be inspected. Moreover, since an opening is not formed in the top wall of each of the packaging containers to be inspected, the packaging containers are not destroyed during inspection. 
   In the present embodiment, the current sensor  43  is used as the variable detection means in order to detect current serving as the electrical variable. However, as an alternative, a voltage sensor may be used as the variable detection means in order to detect voltage as the electrical variable. 
   In the present embodiment, the aluminum foil layer  13  is formed within the packaging material  11  and electrical continuity between the liquid food  17  and the aluminum foil layer  13  at the location of a flaw is detected. However, instead of the aluminum foil layer  13 , a layer of an electrically conductive material such as a metal (e.g., steel) or an electrically conductive resin may be formed within the packaging material  11 , in which case electrical continuity between the liquid food  17  and the electrically conductive material layer at the location of a flaw is detected. 
   In the present embodiment, the charge pipe  18  serves as an electrode. However, an electrode provided in the tube T separately from the charge pipe  18  may be dipped in the liquid food  17 , in which case electrical continuity between the electrode and the cutter  33  via the power source  41  and the current sensor  43  is established in order to detect a flaw formed in the packaging material  11 . 
   In the present embodiment, sealing and cutting are performed simultaneously by the inductor  32  and the cutter  33 , respectively. However, cutting may be performed after completion of sealing. 
   The present invention is not limited to the embodiments described above. Numerous modifications and variations of the present invention are possible in light of the spirit of the present invention, and they are not excluded from the scope of the present invention.