Patent Publication Number: US-2010122570-A1

Title: Method and apparatus for detecting sealing of food packages

Description:
FIELD 
     This disclosure relates generally to leak detection systems, and more specifically to automated systems for detecting leaks in food product packages. 
     BACKGROUND 
     Many types of food products are packaged in sealed packages including vacuum sealed packages. Various approaches are known to determine whether a package is properly sealed. One approach of detecting leaks in sealed packages involves visual inspection. Another approach involves including a tracer gas in a sealed package and sensing for any quantity of the tracer gas that may escape from the package as described in U.S. Pat. No. 3,744,210. Yet another approach, taught in U.S. Pat. No. 5,105,654 includes inserting the package in a vacuum chamber that is subsequently evacuated in order to expand the package and determine whether, over time, the expanded package deflates. Each of these methods can slow package lines, and thereby the speed at which packages can be filled, sealed, and inspected. 
     SUMMARY 
     Leak detection systems for detecting leaks in sealed food packages are disclosed, along with methods for determining whether sealed food packages contain leaks. Food packages are advanced in the leak detection system to a seal testing station. At the seal testing station, a deflection characteristic is measured or determined upon deflection of the food package. The measured or determined deflection characteristic is compared to a predetermined deflection characteristic limit that a sealed food package should undergo when subjected to the predetermined force. If the deflection characteristic is greater than the predetermined deflection characteristic limit, indicating that the food package is not sealed, the food package is rejected. If the deflection characteristic is less than the predetermined deflection characteristic limit, indicating that the food package is sealed, the food package is advanced downstream. 
     The seal testing station may include a deflector for applying a force to the food package to deflect a portion thereof. A first conveyor advances the food package to the seal testing station where the deflector is positioned in a gap formed between the first conveyor and a second conveyor that are arranged end-to-end. An upper restraint is positioned above the deflector and restrains the food package from moving vertically upward so that the force applied by the deflector causes the portion of the food package to deflect rather than causing the entire food package to move upward. 
     In one approach, the package is stopped from continuing advancing along the first and second conveyors when it is positioned in a testing position with the food package located above the deflector. After the food package is stopped, the deflector is urged upward to engage the food package and to move it vertically upward so that the upper surface of the food package engages the upper restraint, generally restricting the food package from additional upward movement. The deflector continues to apply a force, against the portion of the food package. Under the force applied by the deflector, the portion of the food package may deflect upward. A sensor, also located at the seal testing station measures a deflection characteristic, a value that indicates, either directly or indirectly, the amount of deflection of the food package under the applied force. 
     In another approach, the food package is continually advanced as it is deflected by the deflector. In this approach the seal testing station can include an upper conveyor with the same direction of travel as the first and second conveyors. The upper conveyor includes an upper restraint roller for engaging the upper surface of the food package to limit the food package from upward vertical movement, but to allow the food package to continue its longitudinal direction of travel along the first and second conveyor belts. The seal testing station also includes a deflector in the form of a roller deflector located in the gap formed between the first and second conveyors. The roller deflector is urged upward toward the food package as it passes thereover, engaging the lower surface of the food package. The roller deflector applies a force to the bottom of the food package forcing it against the upper restraint. Force is continually applied to the food package, which may cause a portion of the food package to deflect or bend upward. The sensor measures the deflection characteristic. 
     If the measured deflection characteristic exceeds a predetermined deflection characteristic limit, indicating that the food package was deflected beyond the predetermined amount of deflection that a properly sealed container should undergo when subjected to the applied force, the food package can be rejected. If the measured deflection characteristic does not exceed a deflection characteristic limit, indicating that the food package did not deflect beyond the predetermined amount of deflection that a properly sealed container should undergo when subjected to the applied force, the food package should not be rejected and the food package can be advanced on the second conveyor. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is perspective schematic view of a seal testing station configured for testing the deflection of a food package while the food package is stationary, showing a deflector in contact with the package but not deflecting the package past a predetermined deflection characteristic limit; 
         FIG. 2  is a perspective schematic view of the seal testing station of  FIG. 1  showing the deflector retracted and the food package advancing past the predetermined deflection characteristic limit; 
         FIG. 3  is a perspective schematic view of the seal testing station of  FIG. 1  showing the deflector in contact with the food package and deflecting the food package; 
         FIG. 4  is a perspective schematic view of the seal testing station of  FIG. 1  showing the deflector retracted and the ejector rejecting the food package; 
         FIG. 5  is a side cross-sectional elevation view of the seal testing station of  FIG. 1  showing the deflector in contact with the food package and deflecting the food package past the predetermined deflection characteristic limit; 
         FIG. 6  is a side cross-sectional elevation view of the seal testing station of  FIG. 1  showing the deflector in contact with the food package but not deflecting the food package past the predetermined deflection characteristic limit; 
         FIG. 7  is a perspective schematic view of a seal testing station configured for testing the deflection of a food package, while the food package moves downstream; 
         FIG. 8  is a side cross-sectional elevation view of the seal testing station of  FIG. 7  showing a deflector roller in contact with the food package and deflecting the food package past the predetermined deflection characteristic limit; and 
         FIG. 9  is an exploded perspective view of a food package suitable for testing by the seal testing stations of  FIGS. 1 and 7 . 
     
    
    
     DETAILED DESCRIPTION  
     A leak detection system and components thereof are disclosed herein and illustrated in  FIGS. 1-8 . The leak detection system is advantageously configured to mechanically detect leaks in a sealed food package either continuously or intermittently as food packages are advanced on a conveyor. The leak detection system can detect leaks without the costly and inefficient use of visual inspection or inserting tracer gases into the sealed food package. In addition the leak detection system may be configured to quickly determine whether leaks are present in a food package without having to wait while the food package is placed into a vacuum chamber, the vacuum chamber is subsequently evacuated to inflate the food package, and the food package is inspected over time to determine whether it deflates. 
     The leak detection system  1  is generally provided for detecting leaks in a sealed food package. A food package  2  is advanced to a seal testing station  50 , wherein a lower surface of the food package is deflected by applying a predetermined force thereto, while the food package is simultaneously restrained from moving vertically upward. In one approach, the food package does not advance during the deflecting of the lower portion. In another approach, the food package continues advancing during the deflecting of the lower portion. As the lower portion is deflected by applying a force, an actual amount of deflection is determined. If the amount of deflection exceeds a predetermined amount of deflection limit for a sealed package, the food package  2  is rejected. Otherwise the food package  2  is advanced. 
     Referring to  FIG. 1 , the leak detection system  1  includes a first conveyor  40 , a second conveyor  42 , and a seal testing station  50  located therebetween. The first conveyor  40  advances a food package  2  to the seal testing station  50 , where the food package  2  is tested to determine if it contains leaks. The first and second conveyors  40  and  42  are positioned end-to-end with a small gap G formed therebetween. 
       FIG. 9  illustrates an exemplary food package for testing by the present leak detection system, although the leak detection system disclosed and claimed herein can test many different types of sealed food packages for leaks. The package may be of the types disclosed in U.S. Appl. Publ. 2008/0160143, the disclosure of which is hereby incorporated by reference in its entirety. The food package  2 , comprising a rigid synthetic plastic package for storing a food product, which includes a tray  10  and a film  8 . A food product  4 , for example a shingled stack of sliced bacon  6 , is carried in a tray  12 , and typically rests on a tray base  10  located at the bottom of the tray  12 . The tray base  12  is disposed between a pair of opposite longitudinal sidewalls  18  and a pair of opposite endwalls  22 . A ridged flange  16  may extend along the upper portions of the sidewalls  18  and endwalls  22  forming a continuous upper edge of the tray  10 . In this example, a shingled stack of sliced bacon rests on the tray base and the film is vacuum sealed to portions of the base  10  not covered by the food product  4  such that the food product  4  is tightly held between the tray base  12  and the film  8 . In such a package, the base  10  will deflect less when the film  8  is properly sealed to the base  10  for a given applied force. 
     In one approach, the seal testing station  50  includes a deflector  56  for forcibly engaging the food package  2  and an upper restraint  52  to restrict the food package  2  from upward vertical movement. The deflector  56  may be in the form of an elongate rod that is oriented with its length extending vertically between the gap G in this apparatus. The deflector  50  may also be of another shape and configuration that may be positioned in the gap G between the first and second conveyors  40  and  42  such that the deflector  56  is capable of vertical movement between a raised and lowered position. In the lowered position, ( FIGS. 2 and 4 ) the upper surface of the deflector is located below the plane of the upper surfaces of the first and second conveyors  40  and  42 . In this position, the deflector  56  will not interfere with the advancement of the food package  2  as it passes over the gap G in order for a front end of the food package to advance onto the second conveyor  42 , while a rear portion of the conveyor remains on the first conveyor  40 . The deflector  56  remains in the lowered position until actual testing when the food package  2  is deflected by the deflector  56  as described in detail below. 
     The food package  2  is advanced to the seal testing station  50  on the first conveyor  40  into a testing position. In this example, the food package  2  is in the testing position when its front portion rests on the second conveyor  42  and its rear portion rests on the first conveyor  40  and approximately the center of the food package with respect to both the width and length of the food package is located over the deflector  56  upper surface located in the gap G between the first and second conveyor belts  40  and  42 . A sensor senses when the food package  2  is in the testing position and sends a signal to a controller, which in turn stops the food package  2  from advancing from the testing position. The deflector  56  is located between the first and second conveyors  40  and  42  with an upper portion protruding vertically into the gap G located between the first and second conveyors  40  and  42 . In one example, a portion of the deflector is in communication with a pneumatic or hydraulic cylinder  58  to urge the deflector  56  to the raised position during deflection and allow the deflector  56  to return to the lowered position after testing. 
     Once the food package is in the testing position, the cylinder  58  urges the deflector  56  upward such that the deflector upper surface forcibly engages the lower surface of the tray base  12 . The force on the food package tray base  12  causes the food package ridged flange  16  to move vertically upward to engage the upper restraint lower surface  54 . The upper restraint  52  is positioned longitudinally and laterally with respect to the direction of belt travel so that the upper restraint lower surface  54  is located over the food package ridged flange when the food package  2  is in the testing position. The upper restraint is vertically positioned so that a small clearance is formed between the upper restraint lower surface  54  and the ridged flange  16  when testing is not in progress. In this configuration, the upper restraint  52  will not obstruct the longitudinal movement of the food package  2  as it travels along the first conveyor belt  40  toward the seal testing station  50 . Moreover, with only a small clearance between the ridged flange  16  and the upper restraint lower surface  54 , upon engagement of the deflector  56  with the tray base  12  lower surface, the food package  2  will only need to move a small distance in the upward vertical direction before the ridged flange  16  engages the upper restraint lower surface to prevent the food package  2  from further movement in the upward vertical direction. Having only a small clearance between the ridged flange and the upper restraint lower surface provides several advantages including a smaller movement of the deflector before it begins to deflect the food package and also less likelihood that the deflector will destabilize the food package and move it away from its longitudinal course of travel down the first and second conveyor belts  40  and  42 . 
     As stated above, once the food package is in the testing position, the deflector  56  moves upward so that its upper surface engages the lower surface of the tray base  12 . In this approach, the deflector  56  engages the center portion of the lower surface of the tray base  12  with respect to both the length and width of the food package  2 . The upward force causes the food package  2  to move upward such that the ridged flange  16  engages the upper restraint lower surface  54 , limiting the food package  2  from further upward vertical movement. The cylinder  58  in communication with the deflector  56  urges the deflector  56  to continue its upward motion. 
     A sensor measures a deflection characteristic to determine whether the actual amount of deflection of the food package  2  exceeds the predetermined deflection characteristic limit for a properly sealed package. The deflection characteristic is any measureable value that indicates the amount of deflection of the food package  2  under force as it is engaged by the deflector  56 . For example, the deflection characteristic may be a measurement of the vertical distance the deflector travels and may be measured by a displacement sensor as the deflector applies a predetermined force. More specifically, the deflector  56  can extend from a housing when the housing is pressurized using a predetermined amount of pressure. A proximity sensor can sense when a metal piece positioned on the deflector  56  or a plunger is adjacent to the sensor. The metal piece can be positioned so that if it is aligned with the sensor, the predetermined pressure limit has been exceeded. 
     Other ways of measuring or determining displacement can also be used. One alternative is to have an analog linear displacement sensor incorporated into the deflector  56  or plunger. A controller associated with the displacement sensor can be programmed to indicate when the determined level from the displacement sensor exceeds a predetermined limit. The deflection characteristic may alternatively be a measurement of the pressure within the cylinder  58 , which may reduce as the volume of the cylinder  58  increases with vertical movement of the deflector  56  after a known quantity of pressurized gas or fluid is inserted into the cylinder  58 . Yet another alternative would be the use of a strain gauge or load cell for sensing the amount of resistance the deflector  56  encounters. 
     The force that is applied by the deflector  56  against the food package  2  should be sufficiently great so that, at least in the case of a package that is not properly sealed, after the ridged flange  16  engages the upper restraint lower surface, the deflector continues its vertical upward movement so that the tray base  12  is deflected and bends upward at the point of contact between the deflector  56  and the tray base  12 . Thus the tray base  12 , at least at the contact point, is deflected by a distance Δ. The sensor  58  indicates to the controller when a deflection characteristic limit has been exceeded. 
     The deflection characteristic limit is a value that can be determined in advance of testing that indicates the maximum or desired amount of deflection that a properly sealed food package  2  should undergo when placed under the force. The deflection characteristic limit may be determined from empirical data for the same type of food package  2  containing the same food product  4  under substantially the same environmental conditions. Depending on the specific variable that the deflection characteristic comprises, the deflection characteristic limit may the minimum or maximum acceptable value of the deflection characteristic. For example, if the deflection characteristic measures the actual distance the deflector  56  travels, the deflection characteristic limit can be the maximum distance the deflector can travel before the food package  2  being tested is determined to be not properly sealed. Alternatively, if the deflection characteristic measures the amount of pressure remaining in the cylinder  58 , the greater distance the deflector travels will result in a lower pressure measurement, and thus the deflection characteristic limit will be the minimum amount of pressure that may remain in the cylinder before the food package  2  being tested is considered a leaker. For ease of discussion, hereafter, statements referring to the deflection characteristic limit being exceeded, shall mean that the deflection characteristic has either increased or decreased past the deflection characteristic limit into the range where the food package  2  is considered a leaker. 
     It has been found that a food package  2  that contains holes or leaks deflects more under a force than a properly sealed food package  2 , thus indicating that packages that deflect more than the predetermined amount of deflection contain leaks. For example, three food packages  2  were tested by applying a force of 500 g to the tray base  12  of the food packages  2  containing bacon at 31.9° F. The two food packages  2  that were known to be properly sealed underwent no deflection. The one food package  2  that was known to not be properly sealed underwent deflection of ¼ inch. The amount of deflection of a food package  2  may also depend on other variables such as the temperature of the food package  2  or the amount of time that the food package has been sealed. For example, two known sealed food packages  2  were tested by applying a 500 g force to the tray base  12 . A food package  2  at 31.9° F. did not deflect at all. A separate food package  2  at 40.3° F. deflected ¼ inch. Thus, testing is typically conducted on food packages  2  at a constant temperature, so that variations in food product  4  or food package  2  temperatures do not produce inaccurate results of whether a food package  2  is properly sealed. The predetermined amount of deflection should be the maximum amount of deflection that a properly sealed food package should have, or a safe amount of deflection that a properly sealed food package should have after taking into account possible testing errors and slight variations in food package and product properties as well as variations in environmental conditions. Thus the deflection characteristic limit should be the maximum or minimum value of the deflection characteristic that indicates that the food package has deflected beyond the predetermined amount of deflection. 
     The controller determines whether the deflection characteristic exceeds the deflection characteristic limit. If the deflection characteristic exceeds the deflection characteristic limit, indicating that the food package  2  is not properly sealed, the controller will send a signal to reject the food package. In one approach an ejector rejects the food package  2  from the first and second conveyors such that the rejected package  72  falls into a reject collection container  70  ( FIG. 4 ). If the deflection characteristic does not exceed the deflection characteristic limit ( FIGS. 1 and 6 ), indicating that the food package is properly sealed, the ejector will not reject the food package  2 , and the food package  2  will be advanced downstream along the second conveyor  42 . In this example, a rejected package  72  is collected manually from the reject collection container  70  and placed upstream where it is resealed, subsequently returning to the leak detection system  1  to determine if it contains any leaks after being resealed. A food package  2  that does not have a deflection characteristic that exceeds the deflection characteristic limit will continue downstream on the second conveyor where any additional stages of packaging will be completed and the food package will be prepared for distribution. 
       FIGS. 7 and 8  illustrate another approach of the leak detection system  1 . According to this approach, the leak detection system  1  includes first and second conveyors  40  and  42  that are positioned end-to-end, forming a gap G therebetween. The first conveyor  40  advances a food package  2  for testing at the seal testing station  50 . In this approach, the seal testing station  50  also includes an upper conveyor  100 , extending over the gap G at the seal testing station  50 . The upper conveyor  100  is positioned to run generally parallel to the first and second conveyors  40  and  42  and have the same longitudinal direction of belt travel. The upper conveyor  100  is positioned vertically above the first and second conveyors  40  and  42  so that as the food package travels along the first conveyor  42  the flanged ridge of the food package  16  may lightly contact the upper conveyor  100  lower surface or pass under the upper conveyor  100  lower surface so there is a small tolerance between the upper conveyor and the flanged ridge  16 . In this respect, the upper conveyor  100  acts as a guide to gradually move the food package  2  toward and below an upper restraint roller  108  located above the gap G formed between the first and second conveyors  40  and  42 . 
     A deflector roller  102  is positioned in the gap G between the first and second conveyors  40  and  42 . The deflector roller  102  is typically an idler type roller with its axis running transverse to the direction of belt travel such that the deflector roller  102  rotates freely as the food package  2  passes thereover engaging the deflector roller  102 . However, the deflector roller can also be a driven roller to forcibly advance the food package  2  thereover. Several additional idler rollers  106  may be positioned side-by-side alongside the deflector roller  102  to help guide the food package  2  over the gap G and prevent the a side of the food package  2  from going off-balance and moving up or down relative to the opposite side. This will maintain the food package  2  with its tray base  12  in a relatively horizontal orientation with respect to the plane of conveyor travel. 
     The deflector roller  102  is disposed on or integral with a deflector connector member  104  that extends vertically downward from the deflector roller  102 . The deflector connector member  104  is typically attached to the deflector roller  102  at its axis point by a pin or other type of rotatable connection that allows the deflector roller  102  to rotate freely about its axis. A load cell is disposed on or integral with one of the deflector connector member  104  and the deflector roller  102 . The load cell is configured to measure a force applied by the deflector roller  102  against the tray base  12  as the deflector roller  102  engages the lower surface thereof as the food package  2  passes thereover. The deflector connector member  104  is also connected to a hydraulic or pneumatic cylinder  58  configured to urge the deflector connector member  104  and the deflector roller  102  from a lowered position wherein the deflector roller upper roller surface is generally located in the plane of the first and second conveyors  40  and  42  to a raised position wherein the deflector roller engages the lower surface of the base tray  12  as discussed in more detail below. 
     The seal testing station  50  includes a sensor that detects when a food package  2  is in a testing position. In one approach the food package  2  is in the testing position when the center portion of the tray base  12  with regard to both the length and width of the food package  2  is located approximately above the deflector roller  102 . After the food package  2  is advanced on the first conveyor  40  so that its front portion passes onto the second conveyor  42 , into the testing position, the sensor detects the position of the food package and provides a signal to a controller which in turn activates the cylinder  58  to urge the deflector connector member  104  upward forcing the deflector roller  102  to forcibly engage the lower surface of the tray base  12  forcing the food package  2  upward. 
     The seal testing station  50  in this example includes an upper restraint roller  108  disposed in the upper conveyor  100 . The upper restraint roller  108  is positioned longitudinally with respect to belt travel approximately above the deflector roller  102  and vertically a distance above the deflector roller  102  approximately equal to or slightly higher than the height of the food package  2  that will be tested. In this configuration, the food package  2  will pass under the upper restraint roller  108  as it passes over the deflection roller located in the gap G between the first and second conveyors  40  and  42 . The upper restraint roller  108  has its axis of rotation transverse to the direction of belt travel, and may be an idler type roller that freely rotates allowing the food package  2  to continue downstream as it passes thereunder, or a driven roller that urges the food package  2  downstream as it passes thereunder. 
     After the food package  2  is advanced to the testing position, the deflector roller  102  is urged upward by the cylinder  58  to engage the lower surface of the tray base  12 . The food package  2  is simultaneously lifted by the force applied by the deflector roller  102  causing the ridged flange  16  to engage the upper restraint roller  108 , preventing the food package  2  from further movement vertically upward. In this approach, the food package is continuously moved downstream by the first and second conveyors  40  and  42  and the upper conveyor  100  during testing. Thus the food package  2  rolls along the deflector roller  102  as the deflector roller  102  engages the lower surface of the tray base  12 . 
     A sensor determines the deflection characteristic as the food package  2  is deflected under a predetermined force, as described above, and provides the deflection characteristic to a controller. If the deflection characteristic exceeds the deflection characteristic limit, indicating that the food package  2  is not properly sealed, the controller sends a signal to an ejector to reject the food package  2 . However, if the deflection characteristic does not exceed the deflection characteristic limit, indicating that the food package  2  is properly sealed, the food package will continue to advance downstream on the second conveyor  42 . 
     From the foregoing, it will be appreciated that methods and apparatus for use in testing food packages to determine whether they are properly sealed are disclosed. However, the disclosure is not limited to the aspects and embodiments described hereinabove, or to any particular embodiments.