Abstract:
A seal testing apparatus for testing the integrity of a seal in the packaging of vacuum packed product and a method of testing seal integrity. The apparatus includes a mechanical gripper that grips a portion of the packaging and is urged away from the packaging. A sensor monitors the movement of the gripper relative to the vacuum packed product and an evaluator compares the sensed movement of the gripper with an acceptable profile and accepts or rejects the product based on the comparison.

Description:
FIELD OF THE INVENTION 
       [0001]    The present invention relates to a device for detecting leaks and testing the integrity of vacuum-sealed packages. The present invention also relates to a method for detecting leaks and testing the integrity of vacuum-sealed packages. More particularly, although not exclusively, the present invention relates to an apparatus and method where film packaging is put under tension in a particular area and direction, and in a particular manner, and the result is compared to a standard profile to assess the integrity of the vacuum package. 
       BACKGROUND 
       [0002]    Vacuum packing or vacuum packaging is a method of food packaging in which all or nearly all of the air in a food package is removed prior to the package being sealed. As the amount of oxygen in the sealed package has been significantly reduced, the growth of aerobic bacteria or fungi is inhibited. The reduction of air also helps to prevent or reduce the evaporation of volatile components from the foodstuff. 
         [0003]    Removing air from the container extends the shelf life of foods and reduces the volume of the contents and package. This allows certain foodstuffs that would otherwise spoil quickly to be stored for longer before use. This also enables perishable foodstuffs to be economically and practically transported over longer distances than would otherwise be the case, with space requirements minimised. It is important that the seal is correctly formed before the foodstuffs are transported or stored, and it is important that the seal remains intact until knowingly broken by an end user. Once the seal is broken, bacteria or fungi within the foodstuff are exposed to atmosphere, and their growth is no longer inhibited. If the seal was not initially properly formed (and the foodstuff has remained exposed to atmosphere), or if the seal has been inadvertently broken post-forming, this can lead to inadvertent or unwanted spoilage and wastage. To avoid this, a number of methods and devices have been devised to test the integrity of seals post-packaging. 
         [0004]    One common testing method is to test the packages in evacuated chambers, or to submerge the packages in water. An evacuated chamber is bulky, requires maintenance and can be complex to operate. Immersion requires a water tank, and there is associated expense to build and maintain this tank, an associated complexity of operation and potential contamination of the foodstuffs. 
         [0005]    Another known method is to use suction cups on package film to pull the film away from the product and measure the displacement relative to a control package. One drawback to this method is that it can be difficult to achieve a good seal on the packaging as this requires a relatively flat surface area for the cup to seal onto. It is also preferred that the film or other packaging has sufficient ‘give’ for a useful measurement to be achievable. This can sometimes be difficult to achieve. 
         [0006]    U.S. Pat. No. 3,744,210 describes a method and apparatus where testing for vacuum leaks in cheese blocks is carried out by detecting leakage of tracer gas introduced into packaging. 
         [0007]    U.S. Pat. No. 4,517,827 describes a method and apparatus whereby a compressive force is applied to a vacuum packed package that contains a particulate contents, and the displacement of the packaging is measured and compared to a control package to determine leak integrity. 
         [0008]    U.S. Pat. No. 5,531,101 describes a method and apparatus which applies tension to the surface packaging of a vacuum packed product via a rotatable roller frictionally engaged with the packaging, to determine displacement compared to a control package. The roller imparts a compressive and shear force to the packaging of a vacuum packed product to create tension and displacement across the face of the product. 
         [0009]    U.S. Pat. No. 3,998,091 describes a method and apparatus which tests the packaging of a vacuum-packed product for leaks by applying a rotational force to the package and measuring the deflection relative to that of a standard package with an intact seal. 
         [0010]    US2010/0122570 describes a leak detector system for a sealed food package where a portion of the packaging is deflected, and the deflection compared to the deflection characteristic of a standard, sealed package. 
         [0011]    There are a number of drawbacks associated with the methods which are known in the art. Methods and apparatus which use tracer gases or water immersion are prone to contamination of the foodstuff. Methods and apparatus which apply force to the packaging can subject the packaging material to excessive stress which can result in damage. The known methods and associated apparatus can be expensive, unreliable and slow. 
         [0012]    It is an object of the present invention to provide a device for detecting leaks and testing the integrity of vacuum-sealed packages which goes some way to overcoming the abovementioned disadvantages or which at least provides the public or industry with a useful choice. 
         [0013]    It is a further object of the present invention to provide a method for detecting leaks and testing the integrity of vacuum-sealed packages which goes some way to overcoming the abovementioned disadvantages or which at least provides the public or industry with a useful choice. 
         [0014]    Further objects and advantages of the invention will be brought out in the following portions of the specification, wherein the detailed description is for the purpose of fully disclosing the preferred embodiment of the invention without placing limitations thereon. 
         [0015]    The background discussion (including any potential prior art) is not to be taken as an admission of the common general knowledge. 
       SUMMARY OF THE INVENTION 
       [0016]    In a first aspect, the invention may broadly be said to consist in a seal testing apparatus for testing the integrity of the seal in the packaging of a vacuum packed product, comprising:
       a mechanical gripper for gripping a portion of the packaging;   a first actuator that urges the gripper away from the packaging;   a sensor for monitoring the movement of the gripper relative to the vacuum packed product; and   an evaluator that compares the sensed movement of the gripper with an acceptable profile and accepts or rejects the product based on the comparison.       
 
         [0021]    Preferably the mechanical gripper is a clamp adapted to close and grip each side of a flap extending from the main body of the packaging. 
         [0022]    Preferably the clamp has at least one moving portion which is driven by a second actuator. 
         [0023]    Preferably the second actuator is a pneumatic cylinder with linear travel. 
         [0024]    Preferably the first actuator is a linear actuator. 
         [0025]    Preferably the first actuator is a pneumatic cylinder. 
         [0026]    Preferably the sensing means is an actuator position sensor or mounted position transmitter. 
         [0027]    Preferably the sensing means is a linear variable differential transformer (LVDT) or similar inductive device. 
         [0028]    Preferably the seal testing apparatus further has a frame on which the vacuum-packed product rests in use, and the gripper is mounted on a sub-frame pivotally connected to the frame, the first actuator acting on the sub-frame to urge the gripper away from the frame. 
         [0029]    Preferably the seal testing apparatus further has a gusset manipulator, comprising at least one finger which is inserted into the gusset fold area to manipulate a gusset in the packaging associated with the flap. 
         [0030]    Preferably the gusset manipulator is a pair of fingers that pivot into and out of engagement with the gusset fold, each of the fingers having a hook portion on the inner end which is inserted into the side of the gusset fold as the fingers engage. 
         [0031]    Preferably the fingers are mounted on the sub-frame via vertically-aligned pivot points and are connected via intermeshing gear segments, a third linear actuator connecting between the frame and one of the gear segments to rotate the gear segment and move the fingers into engagement when activated. 
         [0032]    Preferably the gusset manipulator is moveably connected to the sub-frame via a fourth linear actuator which pushes the gusset manipulator away from the frame when activated. 
         [0033]    Preferably an endless linear belt is mounted on the frame, the package resting on and transported by the belt in operation. 
         [0034]    Preferably the belt transports the package from one side of the frame to the other, past the sub-frame and gusset manipulator. 
         [0035]    Preferably the seal testing machine further has a sensor which automatically detects when the package is aligned with the sub-frame and gusset manipulator, the evaluator controlling movement of the belt and stopping the belt when the package is correctly aligned. 
         [0036]    Preferably a linear actuator positions the package towards the gusset manipulator such as to facilitate testing. 
         [0037]    Preferably the evaluator receives input from the sensing means and assesses seal integrity by comparing actual displacement over time to a predefined acceptable profile of displacement and time. 
         [0038]    The acceptable profile may consist of an absolute displacement. 
         [0039]    Alternatively the acceptable profile may consist of displacement over a time interval. 
         [0040]    In a second aspect the invention may broadly be said to consist in a method of testing seal integrity in the packaging of a vacuum packed product comprising the steps of:
       mechanically gripping a portion of the packaging;   applying a force in a direction away from the packaging;   monitoring the movement of the gripped portion relative to the vacuum packed product;   comparing the monitored movement with an acceptable profile; and   accepting or rejecting the product based on the comparison.       
 
         [0046]    Preferably in the step of comparing the monitored movement with an acceptable profile actual displacement over time is compared to a predefined acceptable profile of displacement and time. 
         [0047]    The step of comparing the monitored movement with an acceptable profile the acceptable profile may consist of an absolute displacement. 
         [0048]    Alternatively in the step of comparing the monitored movement with an acceptable profile the acceptable profile may consist of displacement over a time interval. 
         [0049]    Preferably after a predetermined time the mechanical grip is released and the displacement assessed. 
         [0050]    Preferably in the step of mechanically gripping a portion of the packaging a flap or seal is gripped. 
         [0051]    Preferably in the step of mechanically gripping a portion of the packaging mechanical fingers are inserted into the gusset fold area to manipulate a gusset in the packaging associated with the flap. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0052]    Embodiments of the present invention will now be described, by way of example only, with reference to the accompanying drawings, in which: 
           [0053]      FIG. 1 a    shows a perspective view of an embodiment of the seal testing apparatus of the present invention; 
           [0054]      FIG. 1 b    shows a plan view of the embodiment of the seal testing apparatus of the present invention shown in  FIG. 1   a;    
           [0055]      FIG. 1 c    shows a view from the entry end of the embodiment of the seal testing apparatus of the present invention shown in  FIG. 1 a    and  FIG. 1   b;    
           [0056]      FIG. 1 d    shows a side view of the embodiment of the seal testing apparatus of the present invention shown in  FIGS. 1 a , 1 b   , and  1   c;    
           [0057]      FIG. 2  shows a perspective view of the seal testing apparatus of the present invention shown in  FIGS. 1 a - d    mounted to a frame with a protective enclosure around the testing station; 
           [0058]      FIG. 3 a    shows a plan view of a gusset manipulation station that forms part of the seal testing apparatus of the present invention; 
           [0059]      FIG. 3 b    shows a cross-sectional view along line A-A in  FIG. 3 a   ; and 
           [0060]      FIG. 3 c    shows a vacuum packed package of cheese with a flap/seal at one end. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0061]    The preferred embodiments of the invention are described below. The preferred embodiments are described in relation to testing the seal integrity for a generally cuboidal block of cheese weighing 20 kilograms, vacuum-packed in film packaging, the cuboidal block several times wider and longer than it is high. However, the invention may also be applied to any other suitable vacuum-packed items of different sizes with the same or similar configuration—for example a bag of ground coffee or coffee beans which also has a sealed flap—and the description should not be taken as limiting. Also, the preferred embodiment is described in relation to a vacuum-packed item where the item is sealed within a bag formed from film packaging which has a single open end, sealed during the packaging process and with a seal/flap extending from one side or end. The invention could be used with other forms of vacuum-packaging, or other configurations of packaging, for example where the seal or flap is at the top of the packet—e.g. as in a bag of ground coffee or coffee beans. If the seal flap is at the top of the bag, the testing would be carried out either with the bag lying on its side, or a modification of the preferred embodiment as described below would be used in order to test for a package with an upwardly-oriented flap. 
         [0062]    A leak detector  1  is shown in the figures.  FIG. 2  shows the leak detector  1  mounted to a support frame  2  with a protective housing  22  covering the testing station including a human machine interface  24 . The other figures show the detail of the testing mechanisms. The leak detector  1  has a frame  2  which in use rests on a surface (a warehouse floor or similar) to hold the remainder of the apparatus away from the ground. The frame  2  also holds various parts of the remainder of the testing apparatus in position. The leak detector  1  has a central conveyor  3  which in the preferred embodiment is of the linear endless belt type, aligned horizontally to convey items from one (open) end or side of the leak detector  1  to the other, opposite (open) side. As shown in the figures, the conveyor  3  can be formed from a number of smaller sub-belts in parallel or a single wide belt. 
         [0063]    A sub-frame  4  is pivotally connected to the frame  2  to one side of the conveyor  3 . The sub-frame  4  is connected to the frame  2  via a hinge  5  located below the level of the central conveyor  3 , the sub-frame  4  extending upwards above and to the side of the conveyor  3 . A first actuator  6  is mounted on a second sub-frame (not shown) above the conveyor  3 . The actuator  6  is, in the preferred embodiment, a pneumatic cylinder with linear travel. However, the actuator  6  could be a hydraulic cylinder, or any other suitable type of actuator: linear, rotary or otherwise. The active or moving end of the first pneumatic cylinder  6  is connected to the sub-frame  4 . The body of the first cylinder  6  is connected and held rigidly in relation to the conveyor  3 , via the second sub-frame. As the cylinder  6  activates, it pushes the sub-frame  4  so that the sub-frame  4  rotates outwards around the pivot point of the hinge  5  away from the conveyor  3 . 
       Mechanical Gripper and Gusset/Flap Manipulation Station 
       [0064]    A gusset manipulation station  10  is connected to the sub-frame  4 , the station is connected so that it is just above and to the side of the surface of the conveyor  3 . The gusset manipulation station  10  has a number of interlocking and moving elements which are activated by actuating cylinders as described below. 
         [0065]    A fixed anvil  8  is connected to the sub-frame  4 . The fixed anvil  8  has a horizontal upwards-facing anvil striking surface. A second linear actuator—flap clamp cylinder  7 —is connected to the sub-frame  4  between the body of the sub-frame  4  and the conveyor  3 , above the fixed anvil  8 . The preferred embodiment of flap clamp cylinder  7  is a pneumatic cylinder, with a moving piston that has a clamp anvil  9  on the lower end, the clamp anvil  9  having a downwards-facing anvil surface complimentary to and aligned with the upwardly-facing surface of the fixed anvil  8 . When the flap clamp cylinder  7  activates, the downwards-facing anvil surface of the clamp anvil  9  is moved downwards to contact and press against the upwardly-facing surface of the anvil  8 . These items form a mechanical gripper for a package, either by themselves or in combination with other items as described below. In the preferred embodiment, the position of the fixed anvil  8  is vertically adjustable, and most preferably horizontally adjustable also (towards and away from the conveyor  3 ). The position of the flap clamp cylinder  7  and in particular the clamp anvil  9  is adjustable in a complimentary manner, either by adjustment of the position of the flap clamp cylinder  7  in it&#39;s entirety, or by adjusting the stroke length to suit, so that contact is made at all positions between the flap clamp cylinder  7  and the clamp anvil  9 . The linear pneumatic flap clamp cylinder  7  could be replaced by any suitable clamping mechanism—for example by a jaw rotating towards the anvil, or a pair of jaws rotating together towards one another, or clamping elements which screw towards one another. 
         [0066]    A pair of mechanical fingers  11   a ,  11   b  are located one on each side of the gusset manipulation station  10 . Each finger  11  is formed from an elongate member extending towards the conveyor  3 , the two fingers  11   a ,  11   b  angled away from one another (that is, if the lines of the main portion of the bodies of the fingers were extended to convergence, this would occur at a point further away from the conveyor). The outer end (away from the conveyor) of each finger  11   a  and  11   b  is connected to a pivoting element  12   a  and  12   b  that pivots around a substantially vertical axis so that the fingers  11   a  and  11   b  rotate in a substantially horizontal plane. The inner ends of the fingers  11   a  and  11   b  are angled inwards to form hook portions  13   a  and  13   b . In the preferred embodiment, the pivoting elements  12   a  and  12   b  are a pair of meshed, interlocking gear sections or arcs connected to the sub-frame  4 , the interlocking portions located between the vertical rotation axes. A third linear actuator  14  is connected between a fixed point on the sub-frame  4 , and a point on the perimeter of one of the pivoting elements  12   a  and  12   b  (i.e. at a distance from the vertical rotation axis of that pivoting element, and between the rotation axes). The third linear actuator  14  is aligned to activate horizontally away from the conveyor  3  (in the preferred embodiment, substantially perpendicular to the conveyor  3 ). As the third linear actuator  14  activates, it causes the connected one of the pivoting elements  12  to rotate around the vertical rotation axis, which causes the other pivot element to also rotate in the opposite direction due to the meshed gearing. This causes the fingers  11  to rotate inwards, or towards one another. The fingers  11  and the hook portions  13  are shaped and sized so that the inner ends arc towards one another and nearly contact each other just to the side and above the edge of the conveyor  3 . In the preferred embodiment, the third linear actuator is a pneumatic cylinder. As before, this could alternatively be a hydraulic cylinder, a rotary screw, or a similar actuating mechanism. The fingers and their associated elements form another part of the mechanical gripper formed by flap clamp cylinder  7 , clamp anvil  9  and anvil  8 . 
         [0067]    In the preferred embodiment, the gusset manipulation station  10  is mounted to the sub-frame  4  in such a manner that it can move relative to the sub-frame  4 , substantially horizontally towards and away from the sub-frame  4  and conveyor  3 . 
       Operation 
       [0068]    Operation of the apparatus will now be described with reference to the structural elements described above, and further structural description as necessary. 
         [0069]    A single specimen of the product to be tested—i.e. a 20 kg block of vacuum packed cheese  16  in the preferred embodiment (or other similar vacuum packed product) is guided onto the belt of the central conveyor  3  at one end, and moves with the belt along and through the leak detector  1  to a point determined by a photo cell (not shown) mounted either on the frame  2 , or an equally appropriate position. Another similar type of sensor could be used instead of the photo cell (for example a weight sensor placed under the belt at the appropriate position, which activates when the cheese or other product is above the sensor. The bagged cheese  16  is placed on the belt so that the flap/seal  17  extends generally horizontally out to one side of the conveyor, on the same side as the sub-frame  2 . As the preferred embodiment of the apparatus will be used to test multiple specimens of identical size and packaging, the vertical position of the flap/seal is known, as each individual product item is substantially identical to the others. This allows an initial setup/location of items such as the position of the clamp anvil  9  and the fixed anvil  8 . The block of cheese  16  travels along the conveyor  3  until the photo cell detects that the bagged cheese  16  is positioned and/or aligned opposite the gusset manipulation station  10 . Linear actuator  23  may then push the bagged cheese  16  towards the gusset manipulation station  10  until the flap  17  is between the clamp anvil  9  and the fixed anvil  8 . Linear actuator  23  may extend a predetermined distance each time for packages of consistent dimensions or a further sensor may be employed to detect that the flap  17  is correctly located between the anvils. 
         [0070]    The first linear actuator—the flap clamp pneumatic cylinder  7 —is then activated to push the clamp anvil  9  downwards and clamp the flap  17  between the clamp anvil  9  and the fixed anvil  8 . 
         [0071]    The second linear actuator—the bag flap stressing pneumatic cylinder  6 —further has an associated sensing means (not shown). Once the flap  17  is clamped, the bag flap stressing cylinder  6  is then activated to apply a force to the sub-frame  4  and rotate this around the pivot point of the hinge  5  and away from the block of cheese. As the flap  17  is gripped between the clamp anvil  9  and the fixed anvil  8  it will pull away from and to the side of the block of cheese  16 . The sensing means will start to measure the displacement of the sub-frame  4 , which is indicative of a leak in the plastic packaging. In the preferred embodiment, the sensing means is an actuator position sensor or mounted position transmitter, most preferably a linear variable differential transformer (LVDT) or similar inductive device. The product movement is limited towards sub-frame  4  by a fence fitted to the frame of the testing unit and providing a measurement reference for the displacement of the gripped flap. For lighter products a clamp or holding system can be added to the apparatus to secure it in place during the testing sequence. 
         [0072]    At the same time as the bag flap stressing cylinder  6  is activated, the third linear actuator  14  is activated. This causes the two mechanical fingers  11   a ,  11   b  to rotate inwards towards one another. The hook portions  13   a ,  13   b  on the ends of the fingers  11   a ,  11   b  will be inserted into the folded gussets on each side of the flap  17  of the plastic bag. This action is independent of the action of the bag flap stressing cylinder  6  and the flap clamp cylinder  7 . 
         [0073]    Once the fingers  11   a ,  11   b  are in position, the third linear actuator—pneumatic cylinder  14  continues to extend to apply an outwards force to push the fingers  11   a  and  11   b  away from the conveyor  3 . This causes the hook portions to snag into and manipulate the gusset, and in particular the inside of the plastic gusset seal weld, and a pulling force is applied away from the block of cheese  16 . This action will indicate any weakness in the heat sealed area, which will translate to further measurable movement in bag flap stressing cylinder  6  if a leak is present. 
         [0074]    The preferred embodiment of the present invention includes an evaluator or evaluating means which receives signals relating to the sensed movement, and uses these to evaluate whether there is a leak or not. In the preferred embodiment, the leak evaluation is conducted using the sensed amount of movement from bag flap stressing cylinder  6 . The amount of movement is compared with an acceptable or predefined profile, which is held in the memory of the evaluator. The results of this evaluation tags the product acceptable, or to be rejected. 
         [0075]    An additional suction testing method may also be employed. A linear actuator in the form of pneumatic ram  25  may lower suction cup  26  down onto the top surface of the block of cheese  16 . Suction may then be applied to the suction cup  26  and the pneumatic ram may be retracted with a set force. The distance travelled up by the pneumatic ram may be measured to provide an additional assessment as to whether the bag is leaking or not. A suction testing method may be used before, after or during the gusset flap testing method described above. 
         [0076]    After a predetermined time all the actuators—first cylinder  6 , flap clamp cylinder  7 , third cylinder  14  and fourth cylinder(s)  15 —will return to their resting position. This releases the block of cheese  16 . Once the cylinders reach their initial or resting position, movement of the conveyor  3  resumes. 
       Advantages 
       [0077]    The method (and associated apparatus) as outlined above is advantageous as outlined below: 
         [0078]    Pulling the flap/seal  17  is an effective method of detecting large leaks, and pulling in this manner puts lower stress on the packaging. 
         [0079]    Testing the gusset by manipulating and pulling from the inside (using the fingers) allows good detection of slow leaks, and requires the application of minimal force on the packaging. 
         [0080]    Using a mechanical gripper provides a robust and reliable means of engagement with the packaging, and does not require a flat surface for use. The apparatus can therefore provide a useful alternative to an apparatus or method that uses only a suction cup. 
         [0081]    Using a method where the flap/seal is pulled and also the gusset is manipulated or pulled from inside the folds provides both a primary and secondary method of determining leaks (the seal/flap pull and the gusset manipulation, respectively). The gusset manipulation also acts as a useful comparator to the physical manipulation. 
         [0082]    While the present invention has been illustrated by the description of the embodiments thereof, and while the embodiments have been described in detail, it is not the intention of the applicant to restrict or in any way limit the scope of the appended claims to such detail. Additional advantages and modifications will readily appear to those skilled in the art. Therefore, the invention in its broader aspects is not limited to the specific details, representative apparatus and method, and illustrative examples shown and described. Accordingly, departures may be made from such details without departure from the spirit or scope of the applicant&#39;s general inventive concept.