Leak detection in containers

Abstract

A leak detection system is provided for detecting breaks in sealed food containers (T). The leak detection system comprises an air sampling device configured to analyze the composition of an air sample supplied to the device. The food container is conveyed through an air sampling zone by a conveyor belt (702), and a second conveyor belt (701) presses it from the opposite side. Both conveyor belts have perforations (703). At least one air sampling port (711, 712) is located within one of the conveyor belts in the sampling zone. An air sample conduit is provided, extending between the sampling port and the air sampling device.In operation, at least one air sampling port takes an air sample from the air sampling region at least during or after at least one pressure element applies pressure to the sealed food container in the air sampling region and communicates such air sample through the air sampling duct to the air sampling test equipment.

Description

Leak detection in containers Field of invention The present invention relates to systems, methods and devices for detecting breaches in sealed containers and, in particular, in sealed and modified atmosphere food containers, such as trays and packages. Background of the invention Modified atmosphere packaging (MAP) is widely used in the food packaging industry to reduce product spoilage and extend shelf life. MAP typically involves modifying the gas composition surrounding the food product within a food container to differ from standard atmospheric composition, thereby maximizing the product's longevity. This usually entails adjusting the ratio of oxygen, nitrogen, and / or carbon dioxide in the atmosphere inside the food package. When food is packaged using modified atmosphere packaging, any incomplete sealing of the packaging reduces or completely negates the increased shelf life provided by the MAP process, as it allows the atmosphere inside the package to return to its standard atmospheric composition. To identify containers with a gap—an opening in the package that incompletely seals them—the packages are mechanically tested, typically in-line. Mechanical testing usually involves compressing the container and identifying the expected response as pressure increases within the sealed package and the package resists the compression. These mechanical testing methods are often very slow, which can limit maximum production speed or require many separate lanes to keep up with faster packaging systems. Such methods can also have limited sensitivity, leading to false negatives. There are alternative offline systems available that use vacuum to expel gases from the package through any gaps. However, these are also typically very slow, and therefore, to maintain production speeds, multiple packages must be tested simultaneously. This has numerous limitations: there is no way to identify the defective package when a leak is detected, and all tested packages must be rejected. Consequently, many "good" packages are lost, increasing operating costs. These systems are usually placed later in the packaging process, typically after the packages have been grouped into large boxes containing multiple packages. This results in a longer delay in error feedback, and a packaging error can continue to produce "incorrect" packages for some time. The system size is also much larger and requires more factory space to operate. A laser technology has recently been developed that, when supplied with an air sample, can accurately and precisely identify, for example, its carbon dioxide content. It has been identified as desirable to incorporate this technology into food packaging production lines as a means of identifying gaps in sealed food containers by taking a sample of the air surrounding the container after packaging and identifying elevated levels of one of the relevant gases relative to the standard atmospheric composition. This laser technology is based on a principle called tunable diode laser absorption spectroscopy (TDLAS), which measures the concentration of species in gas mixtures using tunable diode lasers and laser absorption spectrometry.Compared to other measurement techniques, such as paramagnetic detectors (PMDs) and chemiluminescence, TDLAS offers multi-element detection capabilities, high accuracy with a wide dynamic range, low maintenance requirements, and a long lifespan. The use of lasers as spectroscopic light sources enables high-resolution spectroscopy (HRS), while quantum cascade lasers (QCLs) provide access to the valuable mid-infrared (MIR) portion of the electromagnetic spectrum. An example of a QCL system can be found in WO 03087787 A1. Other leak detection systems known in the prior art are described in JP2007108101 A, JP2005257577A, and JP2014215070A. Compendium of the invention The present inventors have discovered, while attempting to implement laser gas detection technology in systems and methods for detecting gaps in sealed food containers, that the sensitivity required to detect gaps in food containers is such that normal fluctuations occurring in real-world packaging facilities prevent the consistent and reliable identification of a change in gas levels that would be associated with a gap in a modified atmosphere package. Therefore, the present invention has been developed to make the implementation of this technology feasible. According to a first aspect of the invention, a leak detection system is provided according to claim 1. The present inventors have discovered that a pressure member applying pressure to the food container causes gas inside a ruptured container to escape and enter the region surrounding the container. This increases the amount of gas from inside the container in the air sampling region—that is, the region surrounding the container and near the air sampling port—thereby increasing the likelihood that the air sampling test equipment will detect the change in gas proportions resulting from a gap with respect to normal background fluctuations. In order to integrate most conveniently into existing production lines and maximize throughput, in preferred embodiments, the pressure member is configured to apply pressure to the sealed food container while the sealed food container moves relative to the pressure member. Multiple air sampling ports are located on the pressure member. Providing an air sampling port on the pressure member can improve system performance by allowing the air sample to be taken very close to the point of contact between the pressure member and the sealed food container. The pressure member comprises a porous material configured to come into contact with the sealed food container during use. This prevents the pressure member itself from temporarily obstructing a gap in the food container when applying pressure. Furthermore, the porous material may cover at least one air sampling port. Embodiments in which a porous material covers at least one air sampling port advantageously allow air sampling through the porous material via an air sampling port located on or within the pressure member. The system further comprises at least a first conveyor, preferably a first conveyor belt, for transporting the sealed food container to, through and / or away from the air sampling region. At least one pressure member comprises a conveyor belt configured to apply pressure to the sealed food container as it is transported through the air sampling region. Similar to a roller or wheel, a conveyor belt can maintain contact with the surface of a sealed food container as it moves through the air sampling region. The pressure member's conveyor belt is positioned opposite the first conveyor, such that the sealed food container is transported through the air sampling region between the pressure member's conveyor belt and the first conveyor. That is, the sealed food container will be sandwiched between the conveyor belt and the first conveyor as it passes through the air sampling region.The material forming one or both of the conveyor belts described above is porous by means of perforations in the surface of the conveyor belts. More preferably, a surface of one or both of the first conveyor and the pressure member conveyor belt comprises a series of protrusions for contact with the sealed food container during use. The series of protrusions may take the form of bumps or ridges. Such protrusions will prevent the conveyor surface from blocking any gap in the sealed food container. Air sampling ports are arranged within one or both of the first conveyor and the pressure member conveyor belt. An air sampling port may be arranged within a conveyor belt by providing the air sampling port between opposite halves of a conveyor belt assembly. A plurality of air sampling ports are arranged in an air sampling port header located within the pressure member conveyor belt, and / or a plurality of air sampling ports are arranged in an air sampling port header located within the first conveyor. Preferably, the system also includes a vacuum pump connected to the air sampling line to deliver vacuum suction to at least one air sampling port. It will be noted that when the sealed food container is a tray with a film lid, leaks are most likely to be found at the top of the container. However, leaks can also occur on other surfaces, such as the sides and bottom of a container, which is particularly true when the sealed food container is, for example, a sealed bag.Therefore, some embodiments comprise a plurality of air sampling ports, wherein a first subset of air sampling ports takes an air sample from a first side of a sealed food container and a second subset of air sampling ports takes an air sample from a second side of the sealed food container. According to a second aspect of the invention, a method is provided according to claim 5. This method for detecting breaches in sealed containers is suitable for implementation using a system according to the first aspect of the invention, and is particularly suitable for detecting breaches in sealed food containers. The method provides the same advantages as the system according to the first aspect of the invention. The method according to the second aspect of the invention is particularly suitable for detecting breaches in sealed modified atmosphere containers. However, it will be appreciated that the method could also be used to detect breaches in containers without a modified atmosphere by performing the method in a controlled atmosphere, different from the atmosphere inside the container. In preferred embodiments, the pressure member applies pressure to the sealed vessel while the sealed vessel moves relative to the pressure member. In preferred embodiments, taking an air sample from the air sampling region comprises taking an air sample through a porous material that forms part of the pressure member used to come into contact with the sealed vessel when pressure is applied to the sealed vessel. In some embodiments, taking an air sample from the air sampling region during and / or after applying pressure to the sealed vessel comprises taking an air sample from a first side of a sealed vessel and taking an air sample from a second side of the sealed vessel. Preferably, the first and second sides are opposite each other. The preferred features of the method according to the second aspect of the invention provide the same advantages as the equivalent features of the system according to the first aspect of the present invention. Furthermore, in the methods according to the invention, it is preferable that the air sample composition test using the air sample testing equipment comprises testing the carbon dioxide, oxygen, and / or nitrogen content of the air sample, and that a gap in the sealed container is determined to exist when the carbon dioxide, oxygen, and / or nitrogen content of the air sample meets pre-established criteria. Preferably, the pre-established criteria include that the rate of change in the carbon dioxide, oxygen, and / or nitrogen content of the air sample be greater than a threshold value. This threshold value may be, for example, at least two to three times greater than the average rate of change caused by background noise. Brief description of the drawings Examples of systems, methods, and devices according to the present invention will now be described with reference to the accompanying drawings, in which: Figure 1 shows a first comparative example of a leak detection system and a leak detection head according to the invention; Figures 2A to 2C show a leak detection head according to the first comparative example in cross-sectional, perspective and bottom views, respectively; Figures 3A to 3C show a leak detection head according to a second comparative example in perspective, cross-sectional and longitudinal section views, respectively; Figures 4A and 4B show the leak detection head according to the second comparative example in top and bottom perspective views, respectively, and in the first and second disassembly states, respectively; Figures 5A to 5C show a leak detection head according to a third comparative example in a perspective view, in a perspective view with an outer casing removed, and in an enlarged view with an outer casing removed; Figure 6 shows a cross-sectional view of the air sampling head of the third comparative example; Figures 7A to 7F show a leak detection head according to a fourth comparative example in perspective, side, rear, bottom, front and cross-section views, respectively; Figures 8A to 8D show a leak detection head according to a fifth comparative example in a first and second perspective view, front view and bottom view, respectively; Figure 9 schematically shows a leak detection system according to a sixth comparative example; Figure 10 is a flowchart showing a method for detecting gaps in sealed containers; and Figures 11A to 11D show a leak detection system according to a first embodiment of the invention in perspective views, from above, side and front, respectively. Detailed description Figure 1 shows a first comparative example of a system 1 for detecting gaps in sealed food containers. The system comprises a conveyor 10 for transporting the sealed food containers through an air sampling region 5. A leak detection head 100 is adjustableally positioned above the conveyor 10 in the air sampling region. The leak detection head 100 is supported on the conveyor by a mounting arm 60 attached to the outside of an equipment housing 50 located adjacent to the conveyor 10. An air sampling tube 51 (air sampling duct) and compressed air tubes 52 extend from the equipment housing 50 to the leak detection head 100, as will be described in more detail below.The leak detection head 100 comprises a pressure member, in this case a roller 101, having an axis of rotation parallel to the conveyor surface and perpendicular to the conveyor's direction of travel. The roller 101 has a radius such that it projects downward from the leak detection head 100 into the conveyor 10, leaving a gap between the roller 101 and the conveyor that is configured, adjusting the height of the leak detection head 100, to be slightly smaller than the height of the type of sealed food container to be tested. As a sealed food container is conveyed along conveyor 10, through air sampling region 5, it passes under leak detection head 100. Roller 101, which projects downward from leak detection head 100 onto conveyor 10, makes contact with the top surface of the container and rotates as the container passes through air sampling region 5. Since the gap between roller 101 and conveyor 10 is slightly less than the height of the food container, a force is applied to the container's surface through the contact area between the container and the roller. This pressure exerts pressure on the container to expel a quantity of gas through any gaps in the container. If there are no gaps in the container, no gas will be expelled from the package. Next, air sampling ports 102 located on the leak detection head 100 sample any gas expelled through gaps in the vessel and transfer it through air sampling tube 51 to the equipment housing 50. The sample is introduced into the air sampling ports 102 and along the air sampling tube 51 by a vacuum pump (not shown) located inside the housing 50 in fluid communication with the air sampling ports 102 via the air sampling tube 51. Also located within the housing is a test unit (not shown) comprising a quantum cascade laser. The sample is supplied to the test unit for testing via the air sampling tube 51. In this comparative example, the test unit measures the rate of change in carbon dioxide levels and displays them in a graphical format. The construction of the 100 leak detection head will now be described in more detail with reference to Figure 2. The leak detection head 100 comprises a generally cuboid housing 110 whose longitudinal axis extends across the width of the conveyor 10 in use. The housing 110 extends across the entire width of the conveyor and is open on its lower surface (i.e., the surface facing the conveyor in use). The cylindrical roller 101 is rotatably mounted within the housing 110. The axis of rotation of the roller lies along the longitudinal axis of the housing, and the radius of the roller is such that it protrudes through the opening in the lower surface of the housing. The roller is mounted on bearings 101a, 101b located on the respective end plates of the housing 110. In this comparative example, the roller is driven by means well known in the art.In other comparative examples, the roller can be made to rotate around its axis through contact with a tray, which the conveyor 10 moves under the leak detection head. The leak detection head 100 comprises a plurality of air sampling ports 102. The air sampling ports are small circular openings in the leak detection head arranged in two rows extending along the longitudinal axis of the housing 110, on the lower surface of the housing, with one row on each side of the opening in which the roller 101 is located. Each row of air sampling ports 102 has a respective manifold 102a, 102b. The air sampling ports 102 in each row are in fluid communication with their respective manifold via a respective conduit. The manifolds 102a, 102b are fed into additional air sampling conduits, located on the upper surface of the housing 110, and communicate with a test equipment port 104 through the upper surface of the housing 110.When incorporated into system 1 of Figure 1, the test equipment port 104 is connected to the air sampling tube 51. During use, vacuum suction is communicated through the air sampling tube 51, and through the test equipment port, to the individual air sampling manifolds and ports 102, so that each of the air sampling ports 102 draws air into it, thereby collecting a sample from the air sampling region. The air sample is then conveyed along the air sampling tube 51 to the test equipment. The leak detection head 100 further comprises a plurality of gas outlet ports 108. The gas outlet ports 108 are small circular openings in the leak detection head provided around the periphery of the lower surface of the housing. The gas outlet ports 108 define a rectangle on the lower surface of the housing, within which are located the air sampling ports 102 and the roller 101. The gas outlet ports 108 are connected via respective conduits to one of the two manifolds 108a and 108b of the leak detection head 100. Those gas outlet ports 108 on one side of the roller shaft are connected to the first manifold 108a, and those on the other side of the roller shaft are connected to the second manifold 108b.Each manifold 108a, 108b is connected via a respective conduit 107a, 107b to a respective compressed gas port 106a, 106b through a respective side wall in the housing 110. During operation, each compressed gas port 106a, 106b supplies compressed gas from a compressed gas source (not shown) through the conduits and manifolds to the plurality of gas outlet ports 108. The compressed gas source will normally comprise gas of standard atmospheric composition so as not to affect the tests performed by the test equipment.During use, compressed gas is directed diagonally downward and away from the leak detection head 100 through each gas outlet port 108. The combination of these ports 108 creates an air curtain that extends downward and outward from the periphery of the lower surface of the leak detection head 100 (as shown by arrows A in Figure 2A). This air curtain isolates the atmosphere below the leak detection head 100 from turbulence and other environmental factors that could cause fluctuations in atmospheric composition. When a vessel moves beneath the leak detection head 100, it enters the air curtain.Any carbon dioxide from the packaging process that is carried into the sampling area by the movement of food packages along the conveyor is displaced by the air curtain. An air sample can then be taken from the area around the container within the controlled environment inside the air curtain. When a leaking container leaves the air sampling area, the air curtain helps purge the elevated levels of carbon dioxide, stabilizing the environment in the sampling area and preparing it for the inspection of the next package. The system described with reference to Figure 1 can be implemented with several different types of leak detection heads. A second leak detection head will now be described with reference to Figures 3 and 4. The leak detection head 200 according to the second comparative example comprises a single roller 201. The roller comprises a cylindrical sleeve 202 formed from a porous material, for example, an open-cell foam or a laser-printed open-structure roller. The cylindrical sleeve 202 is closed at each end by end plates 203, which are rotatably mounted on a fixed shaft 210 extending coaxially through the sleeve and beyond each end plate 203. The rotatable end plates 203 allow the sleeve 202 to rotate about the shaft 210 while the shaft remains fixed. During use, the rotation of the sleeve 202 is driven using a belt 251 and a motor 250, mounted next to the roller, which cooperate with one of the end plates 203. Inside the rotating sleeve 202 there is a roller core coupled or integrally formed with the fixed shaft, so that it does not rotate with the sleeve 202.The roller core comprises an air purge system 216 and an air sampling system 211, which will be described in more detail below. The air sampling system 211 comprises a sampling head 213 extending downward from the fixed shaft 210. The lower surface of the sampling head is close to the inner surface of the sleeve 202 and extends along the entire length of the roller, within the sleeve 202. The lower surface of the sampling head has a line of air sampling ports 212 passing through it, facing the inner surface of the porous sleeve 202 along the length of the roller, and in fluid communication within a manifold 213a inside the sampling head 213. The manifold 213a opens into a hollow interior of the fixed shaft 210. The hollow interior of the fixed shaft extends with the shaft outward from both ends of the roller 201 and continues with the shaft, which rotates to generally face upward, where it terminates.Both ends of the shaft are connected during use to a respective tube 210a and 210b. Tubes 210a and 210b are connected to an inverted Y-connector and provide seamless communication with a single port 204 on the test equipment. During use, port 204 on the test equipment is connected to an air sampling tube (51 in Figure 1) through which the vacuum suction is transmitted. The vacuum suction is conveyed through the port on the test equipment, tubes 210a and 210b, the interior 210 of the hollow shaft, and the manifold to the individual air sampling ports 212, so that each of the air sampling ports 212 draws air into it for return communication to the test equipment. In this comparative example, the air drawn into the sampling ports has been drawn through the porous material of the sleeve 202. The air purge system 216 comprises a gas outlet sleeve 217 mounted on the fixed shaft 210. The outer surface of the gas outlet sleeve 217 is close to the inner surface of the porous sleeve 202. The gas outlet sleeve 217 extends the entire length of the roller, inside the sleeve 202, and extends below approximately three-quarters of the circumference of the inner surface of the porous sleeve 202. The space in the gas outlet sleeve 217, i.e., approximately one-quarter of the circumference where the gas outlet sleeve 217 is not provided, allows the sampling head 213 to extend to the inner surface of the porous sleeve. The gas outlet sleeve 217 has a surface covered by small, slotted gas outlet ports 217a.The gas outlet ports are connected to one of the two compressed gas sources, during use, by means of one of the two tubes 217a, 217b, each of which extends from the inner surface of the gas outlet sleeve 217 to the fixed shaft. Each tube 217a, 217b is connected to a respective duct within the fixed shaft, separated from the hollow interior to communicate an air sample, which extends along the fixed shaft, in opposite directions, and beyond the respective end plate 203 that forms the ends of the roller 201. Each duct is then connected to a respective compressed gas inlet port 218a, 218b on the fixed shaft, which can be connected to a respective compressed gas source, in use, by means that will be obvious to those skilled in the art. The operation of the leak detection head 200 will now be described. During use, the leak detection head 200 is positioned above a conveyor, such that the gap between the roller 201 and the conveyor is slightly less than the height of the type of sealed food container to be tested. The end plates 203 and the sleeve 202 of the roller 201 are driven by the belt 251 and the motor 250 to rotate so that the surface of the sleeve 202 moves at the same speed as the conveyor. A container is conveyed along the conveyor and passes under the roller 201. Since the gap between the roller 201 and the conveyor is slightly less than the height of the food container, a force is applied to the surface of the container through the contact area between the container and the roller 201.This pressure applied to the vessel causes a quantity of gas to be expelled from the vessel through any gaps in the vessel. While the roller 201 applies pressure to the vessel, the air sampling ports 212 continuously draw air into the air sampling system 211 through the porous material where it comes into contact with the vessel. The porous material, located between the air sampling ports 212 and the vessel, provides some protection against turbulence and other environmental changes that could affect the composition of the sampled air. An air sample is continuously supplied through the air sampling ports 212, the manifold 213a, the shaft 210, the tubes 210a and 210b, the test equipment port 204, and the air sample tube 51 to the test equipment for composition testing.As roller 201 rotates, the area of ​​the sleeve through which a sample was extracted rotates about the axis, so that it lies over the gas outlet sleeve 217. Compressed gas is expelled through the gas outlet ports 217a and forced through the porous material, purging it of any trapped gas. Sleeve 202 continues to rotate until the now purged area of ​​porous material passes through the end of the gas outlet sleeve 217 and returns to the air sampling location, i.e., between the air sampling ports 212 and a container (if present). A third leak detection head 300 will now be described with reference to Figures 5 and 6. The leak detection head 300, as shown in Figure 5A, is partially enclosed within an outer housing 360. Two side walls 361 and 362, in combination with the top surface of the leak detection head and the conveyor 10, define a generally cuboidal, partially enclosed region with openings at the front and rear ends of the conveyor through which containers can enter. The partially enclosed region helps to protect the internal air sampling region from the wider system environment and to reduce fluctuations in the atmospheric composition within it. As mentioned previously, the front and rear inlets could also optionally be closed by an air curtain to further isolate the air sampling region. Figure 5B shows the leak detection head 300 with the outer housing side walls 361 and 362 removed. The leak detection head comprises the leak detection head housing 310, which is defined by an upper surface from which two side walls project downwards. A series of rollers or wheels 301 form a pressure surface of the leak detection head on a lower surface of the leak detection head, facing the upper surface of the conveyor 10. The wheels 301 are mounted in tightly repeating rows, each row having a spindle (not shown) around which the wheels in that row rotate. Each spindle is positioned parallel to the conveyor surface below 10 and perpendicular to the conveyor's direction of travel.All spindles, and the 301 wheels on them, are mounted between the side walls of a 310 leak detection head housing, at the lower edge of the side walls. The first three rows of 301 wheels on the 300 leak detection head are positioned progressively lower, so that when the 300 leak detection head is positioned above conveyor 10, the second row is closer to the conveyor than the first, and the third row is closer to the conveyor than the second. The remaining rows of 301 wheels are positioned at the same height above the conveyor during operation as the third row of wheels. This configuration of the 301 wheels allows the pressure applied to the vessel to gradually increase as the vessel enters below the leak detection head, before reaching and maintaining a relatively constant pressure. Approximately at the center of the leak detection head 300, in a space between two rows of wheels 301, is an air sampling head 311. The air sampling head is also shown in cross-section in Figure 6. The air sampling head extends in the same direction as the rows of wheels, across the conveyor 10. The air sampling head 311 comprises, on a lower surface facing the conveyor during use, a plurality of air sampling ports 312, aligned in a row extending across the conveyor. Each air sampling port 312 is connected via a respective conduit to a manifold 313 in the air sampling head 311.At each side end of the air sampling head 311, there is a test equipment port 314, which, during use, is connected to be in fluid communication with an air sampling tube (51 in Figure 1), which connects to the test equipment and provides vacuum suction to the air sampling head 311. During use, a container is fed onto conveyor 10 and conveyed into the outer housing 360 and under leak detection head 300. The height of the wheel array 301 above the conveyor is set lower than the height of the container to be tested so that, as the container enters under leak detection head 300, it is pressed against the leak detection head. The container is then conveyed along and past air sampling head 311. As it passes through air sampling head 311, air, which is continuously drawn into air sampling head 311 through air sampling ports 312, is sampled from a region above the container and communicated through the test equipment. The container then continues on and exits under leak detection head 300 at the rear of conveyor 10. A fourth leak detection head 400 will now be described with reference to Figure 7. The leak detection head 400 comprises a housing 410, which accommodates a first and a second rotatably mounted roller 401a, 401b. The first and second rollers are mounted horizontally between opposite side walls 411, 412 of the housing 410. The shafts of the first and second rollers are parallel and, during operation, the shafts extend across the width of the conveyor 10 in a plane above and parallel to the conveyor 10. Each roller 401a, 401b has an internal drum motor for rotating the rollers during operation. The internal drum motors are powered via respective cables 411a, 411b that extend through the side wall 411 of the housing 410. The housing is open on its underside to allow the rollers to protrude through the opening and make contact with the containers being conveyed along the conveyor. The housing is also open at its front (upstream end relative to the conveyor), as shown in Figure 7E, to expose the front surface of the front roller 401a. Exposing the front surface of the front roller helps guide the sealed bags under the leak detection head 400. The first and second rollers 401a and 401b are separated from each other in the housing 410 along the conveyor 10's transport direction. A wall 405 is located between the rollers 401a and 401b within the housing. The wall 405 extends from one side of the housing 410 to the other and from the top of the housing 410 to the opening at the bottom. At its lowest point, the wall 405 is slightly higher than the lowest point of the rollers 401a and 401b, which protrude through the lower opening to contact the food containers. On the lower surface of the wall 405, there are a plurality of air sampling ports 402, as shown in Figure 7D.The air sampling ports are arranged in a single row located in a slot 465 that extends along the lower surface of the wall 405, such that the air sampling ports 402 extend substantially across the entire width of the leak detection head 400. Each of the air sampling ports 402 is in fluid communication with a central manifold (not shown) within the wall via a respective conduit. The manifold communicates with a port 404 of the test equipment through the upper surface of the housing 410. When incorporated into system 1 of Figure 1, the port 404 of the test equipment is connected to the air sampling tube 51.During use, vacuum suction is communicated through the air sampling tube 51 and, via the test equipment port, to the collector and individual air sampling ports 402, so that each of the air sampling ports 402 draws air into it, thereby collecting a sample from the air sampling region, between the two rollers 401a, 401b. Along each side of the row of air sampling ports 402, there are a first and a second set of gas outlet ports 408a, 408b. Each gas outlet port is connected via a respective conduit to one of the two gas outlet manifolds (not shown) in the center wall 405 of the housing 410. The two gas outlet manifolds are in fluid communication with a respective compressed gas port 406a, 406b on the upper surface of the housing 410. The gas outlet port sets 408a, 408b are configured to generate respective first and second air curtains on each side of the row of air sampling ports 402. The gas outlet ports 408a, 408b point diagonally downwards and away from the row of air sampling ports, so that the air curtains are directed downwards and away from the center wall 405 of the housing 410. The leak detection head 400 also features first and second arms 421, 422 located on either side of the leak detection head and extending forward beyond the front roller 401a to be upstream of the leak detection head 400 in use. Each arm is adjustable to the upper side of the housing 410 by means of a respective thumbscrew. At the end of each arm 421, 422 are the first and second sensors 423, 424. The sensors are photo-optical and are configured to detect an approaching food container. The first sensor 423 transmits a light source, which is detected by the second sensor 424 in the absence of any food container. The sensors, together, act as a light gate, which is broken when a food container passes between the sensors, thus allowing the passage of the food container through the system to be detected and timed.A control system knows the conveyor speed and can therefore calculate the position of each individual food container for both sampling and rejection actions. The first and second sensors 423 and 424 detect an approaching food container in use, so that the test equipment readings can be associated with the correct food container. A fifth leak detection head will now be described with respect to Figure 8. The fifth comparative example is substantially identical to the fourth and, in addition, comprises the first and second side sampling accessories 460, 470. Each 460, 470 side sampling fitting has an inverted T-shaped construction. The upper end of the 460, 470 side sampling fittings features a projection (not shown) that cooperates with the groove 465 on the lower surface of the wall 405, and allows the 460, 470 side sampling fittings to be mounted, each, on the lower surface of the sampling head in a laterally adjustable manner. Once mounted on the underside of the sampling head 400 wall 405, the arms of each side sampling fitting 460, 470, which give it an inverted T-shaped appearance, extend upstream and downstream, parallel to the conveyor 10's direction of travel. During operation, a container to be tested passes between these side sampling fittings, beneath the air sampling head 400. Each side sampling fitting 460, 470 has, on its inner surface (i.e., the surface facing the opposite side sampling fitting), a row of air sampling ports 462, 472. The row of air sampling ports extends along the arms of their respective side sampling fittings 460, 470, parallel to the direction of transport in use. The air sampling ports 462, 472 of each side sampling fitting 460, 470 are in fluid communication with a respective manifold internal to the side sampling fitting. Each manifold connects to a conduit, which extends upward through the side sampling fitting 460, 470, via an opening in the upper surface of the projection located in the slot 465 of the air sampling head 400.The opening on the upper surface of each side sampling fitting 460, 470 cooperates with at least one of the air sampling ports 402 to communicate vacuum suction to the air sampling ports 462, 472, and to allow the air sample collected by the air sampling ports 462, 472 to be communicated to the air sampling test equipment in use. Although this comparative example uses side sampling accessories, it will be seen that, as an alternative, separate and different side sampling heads could be used. A sixth comparative example will now be described with respect to Figure 9. This comparative example shows a lower sampling device 600, which can be incorporated into an air sampling system and used with any of the air sampling heads described above. Figure 9 schematically shows the first and second conveyors 10a and 10b, which, for example, can replace conveyor 10 in the system of the first comparative example. The conveyors are arranged adjacent to each other, with the downstream end of the first conveyor 10a separated from the upstream end of the second conveyor 10b by a narrow gap. An air sampling head, which in this case is the air sampling head from the fourth comparative example, is located above this gap. A sampling device 600 is located below the conveyors in the space between them. The sampling device 600 below is a long, narrow, and generally trapezoidal prism-shaped head. The sampling device 600 below comprises, on its upper surface facing the leak detection head in use, a plurality of air sampling ports 602 arranged in a row extending the length of the space between the conveyors. Each air sampling port 602 is connected via a respective conduit to a manifold 603 in the sampling device 600 below. At each lateral end of the sampling device 600 below, there is a port 604 for the test equipment, which, during use, is connected so as to be in fluid communication with an air sampling tube for connection to the test equipment and to provide vacuum suction to the sampling device 600 below. During use, when a container is conveyed by the first conveyor 10a under the air sampling head 400 and through the space to the second conveyor, the air sampling head presses against the top surface of the container and obtains an air sample from the top side of the container, substantially as described above. The lower sampling device 600 simultaneously obtains an air sample from the bottom of the container as it is pressed against by the air sampling head 400. Although the sampling device located below this comparative example is separate from the leak detection head, it will be appreciated that, alternatively, it could be incorporated into a leak detection head, which would define a portal through which a container is transported during use. A method for detecting gaps in vessels, suitable for implementation using the systems and devices described above, will now be described, with reference to the flow diagram in Figure 10. One embodiment of the method comprises step S100, which involves applying pressure to a sealed vessel located in an air sampling region using a pressure member. This step expels air from any gaps in the vessel, thereby improving the detectability of gases within the vessel. Optionally, this step can be performed while the sealed vessel is moving relative to the pressure member. Next, in step S200, an air sample is taken from the air sampling region during and / or after pressure is applied to the sealed vessel. The air sample taken in step S200 will include at least some of the gas expelled through any gaps in the vessel. Optionally, this sample can be taken through a porous material that forms part of the pressure member used to contact the sealed vessel. Furthermore, the quality of the air sample obtained can be improved by performing this step with a gas expulsion step (not shown), either in the form of an air curtain, preferably surrounding the sampling location, or in the form of gas expelled through an area of ​​the porous material before the air sample is taken, or both. Next, in stage S300, the air sample is communicated to the air sample testing equipment. In this stage, the air sample, which may include gas expelled through a gap in a vessel, is supplied to the air sample testing equipment. Finally, in stage S400, the composition of the air sample is tested using air sample testing equipment to determine if there is a breach in the sealed vessel. If the air sample composition is found to meet user-defined criteria, then the vessel from which the sample was taken is identified as having a breach. Specifically, the carbon dioxide, oxygen, and / or nitrogen content of the air sample can be tested, and a breach can be identified when the carbon dioxide, oxygen, and / or nitrogen content of the air sample meets pre-established criteria. These criteria may include the rate of change in carbon dioxide, oxygen, and / or nitrogen exceeding a threshold value. If, during the S400 stage, a container is found to have a breach, it can be identified for disposal or repackaging. When implemented as part of a production line, a breached container can be diverted from the production line at a point downstream of the air sampling region for reprocessing. A first embodiment will now be described with reference to Figures 11A to 11D. This embodiment comprises a first conveyor belt 701, acting as a pressure member, opposite a second conveyor belt 702. The conveyor belts are driven around a plurality of rollers (not shown) to hold the conveyor belts in the desired arrangement and to feed the conveyor belts, as is generally known in the art. A sealed food container T is provided in the space between the first and second conveyor belts. The sealed food container rests on the lower conveyor belt 702, and the upper conveyor belt 701 contacts the upper surface of the sealed food container T to apply pressure to the sealed food container.During use, both conveyor belts 701, 702 rotate at the same speed, so that the sealed food container moves through the system. Within the upper and lower conveyor belts 701, 702 are the respective upper and lower air sampling heads 711, 712. These can be constructed similarly to the lower sampling device 600 described above. Both air sampling heads 711, 712 extend the full width of the conveyor belts and have a plurality of air sampling ports facing a sealed food container that passes between the conveyor belts. As shown, in particular, in Figure 11B, each of the conveyor belts 701, 702 comprises a series of perforations 703, such that the conveyor belts are permeable to air.During operation, vacuum suction is connected via air sampling tubes (not shown) to the air sampling heads and individual air sampling ports, so that each air sampling port draws air into it. In this way, air sampling heads 711 and 712 can sample the air near the sealed food container T as it passes between the conveyor belts, i.e., in the air sampling region. During operation, air sampling heads 711 and 712 will sample any gas that passes through gaps in the sealed food container through the interleaving action of the upper and lower conveyors 701 and 702 and will communicate this gas to the test means, described above, for gap detection.

Claims

1. A leak detection system for detecting gaps in sealed food containers, the leak detection system comprising: air sampling equipment (50) configured to test the composition of an air sample provided to the air sampling equipment; a first conveyor (702) for transporting the sealed food container to, through, and / or away from the air sampling region; at least one pressure member configured to, during use, apply pressure to the sealed food container (T) located in an air sampling region, wherein the at least one pressure member comprises a conveyor belt (701) configured to apply pressure to the sealed food container (T) as it is transported through the air sampling region, wherein the conveyor belt of the pressure member (701) opposes the first conveyor (702),wherein the sealed food container is conveyed through the air sampling region between the pressure member conveyor belt (701) and the first conveyor (702), and wherein a surface of one or both of the first conveyor and the pressure member conveyor belt is perforated (703); characterized by a plurality of air sampling ports located in the air sampling region, wherein the plurality of air sampling ports are located in an air sampling head (711, 712) disposed within one of the first conveyor and the pressure member conveyor belt (701, 702); an air sampling conduit extending between the plurality of air sampling ports and the air sampling test apparatus (50); wherein, during use,The plurality of air sampling ports takes an air sample from the air sampling region at least during or after at least one pressure member (701) applies pressure to the sealed food container (T) in the air sampling region and communicates said air sample through the air sampling duct to the air sampling testing equipment (50).

2. A leak detection system according to claim 1, wherein a surface of one or both of the first conveyor (702) and the conveyor belt of the pressure member (701) comprises a series of protrusions for contacting the sealed food container during use.

3. A leak detection system according to any of the preceding claims, further comprisingA vacuum pump connected to the air sampling duct to impart vacuum suction to the plurality of air sampling ports.

4. A leak detection system according to any of the preceding claims, comprising a plurality of air sampling ports located in a second air sampling head (711, 712) disposed within the other of the first conveyor (702) and the pressure member conveyor belt (701),such that a first subset of air sampling ports takes an air sample from a first side of a sealed food container (T), and a second subset of air sampling ports takes an air sample from a second side of the sealed food container (T) opposite the first side.

5. A method for detecting gaps in sealed containers comprising: transporting a sealed food container (T) through an air sampling region using a first conveyor (702); applying pressure to the sealed container located in the air sampling region using a pressure member, wherein the at least one pressure member comprises a conveyor belt (701) configured to apply pressure to the sealed food container as it is transported through the air sampling region.wherein the pressure member conveyor belt (701) opposes the first conveyor (702), such that the sealed food container (T) is conveyed through the air sampling region between the pressure member conveyor belt (701) and the first conveyor (702), and wherein a surface of one or both of the first conveyor and the pressure member conveyor belt is perforated (703); taking an air sample from the air sampling region during and / or after applying pressure to the sealed container (T); communicating the air sample to the air sampling test equipment (50); testing the composition of the air sample using the air sampling test equipment to determine if there is a gap in the sealed container (T); characterized in that the air sample is taken using a plurality of air sampling ports,wherein the plurality of air sampling ports are located in an air sampling head (711, 712) disposed within one of the first conveyor (702) and the conveyor belt of the pressure member (701).

6. A method according to claim 5, wherein testing the composition of the air sample using the air sampling testing equipment comprises testing the carbon dioxide, oxygen, and / or nitrogen content of the air sample, and a gap in the sealed container is determined to exist when the carbon dioxide, oxygen, and / or nitrogen content of the air sample meets pre-established criteria.

7. A method according to claim 6, wherein the pre-established criteria include a rate of change in the carbon dioxide, oxygen, and / or nitrogen content of the air sample that is greater than a threshold value.

8. A method according to any one of claims 5 to 7,wherein taking an air sample from the air sampling region during and / or after the application of pressure to the sealed vessel comprises taking an air sample from a first side of a sealed vessel using the plurality of air sampling ports in the air sampling head (711, 712) and taking an air sample from a second side of the sealed vessel opposite the first side using a plurality of air sampling ports located in a second air sampling head (711, 712) disposed within the other of the first conveyor (702) and the conveyor belt of the pressure member (701).