WO2005005949A1

WO2005005949A1 - Seal integrity testing apparatus and method

Info

Publication number: WO2005005949A1
Application number: PCT/GB2004/002933
Authority: WO
Inventors: Robert Bennett
Original assignee: Ishida Europe Limited
Priority date: 2003-07-08
Filing date: 2004-07-07
Publication date: 2005-01-20
Also published as: GB0315973D0

Abstract

Seal testing apparatus for determining the integrity of a seal of a sealed bag is described. The apparatus comprises a transport path defined between a datum surface and an array of at least three rollers located opposite the datum surface and spaced apart therealong. Each roller is substantially immovable in a direction along the transport path and is urged towards the datum surface but is displaceable away from the datum surface in response to the passage of the bag along the datum surface. At least two of the rollers in the array are measuring rollers. A is monitoring system monitors the displacement of each measuring roller with respect to the datum surface and compares the displacements to detect the presence of a bag with a faulty seal.

Description

SEAL INTEGRITY TESTING APPARATUS AND METHOD

The invention relates to seal testing apparatus for determining the integrity of a seal of a sealed bag. The invention is particularly concerned with bags which are gas-filled (generally air-filled) bags of loose articles, typically snack foods. Many types of apparatus for testing bag seal integrity have been proposed in the past. In most, a test head is lowered onto a bag which is either stationary or moving to apply a load which will cause a leaky bag at least partially to deflate. To achieve a measurable effect in a short time, quite large loads are applied (for example 2.5kg) and the process is relatively slow since only one bag can be tested at any one time so that the spacing between successive bags must be equal to at least two bag lengths plus the test head length. Such an apparatus is described in GB 2234076. In this apparatus, packages are conveyed along a first conveyor above which are suspended two pressurizing conveyors. Each of these pressurizing conveyors applies a force to the package as it passes beneath them and a force/displacement profile is produced for each conveyor. By comparing these, the apparatus can determine if the package seal is faulty. In addition to the problem described above, this apparatus suffers from the significant disadvantage that the throughput is low as only one package may be beneath a conveyor at any one time. Another disadvantage that is inherent with this apparatus is that the conveyors tend to flatten the bag profile, and are therefore likely to touch the product contained therein thereby causing an incorrect reading . Another apparatus for testing the seals of pillow bags is disclosed in EP 1186876. This describes a complicated conveyor arrangement having a plurality of displaceable probes that engage the bags as they are conveyed underneath. The displacement of each probe is measured by a sensing device which thereby allows the bag profile to be measured. This measurement is performed at two locations along the conveying path, and if the bag seal is faulty the profile will change at these two measurement positions. However, this is a complicated and costly mechanism which is difficult to set up initially and to maintain. It also suffers from the disadvantage that the force applied by each probe is the same and cannot be varied and therefore the force may either shock the bag or be too weak to produce a measurable affect. Yet another bag seal tester is described in EP 1344727. This application which was published after the priority date of the current application describes a system in which bags are trapped between two belts and in which a pair of measuring probes ride over the bag in succession. The displacement of these probes is compared to detect the presence of a faulty seal. In accordance with a first aspect of the present invention there is provided seal testing apparatus for determining the integrity of a seal of a sealed bag, the apparatus comprising a transport path defined between a datum surface and an array of at least three rollers located opposite the datum surface and spaced apart therealong, each roller being substantially immovable in a direction along the transport path and being urged towards the datum surface but being displaceable away from the datum surface in response to the passage of the bag along the datum surface, wherein at least two of the rollers in the array are measuring rollers; and a monitoring system for monitoring the displacement of each measuring roller with respect to the datum surface and comparing the displacements to detect the presence of a bag with a faulty seal . In accordance with a second aspect of the invention, there is a method for determining the integrity of a seal of a sealed bag using the apparatus of any of the preceding claims, the method comprising conveying a bag along the datum surface thereby causing each roller to be displaced away from the datum surface in response to the passage of the bag and in accordance with the bag's profile, monitoring the displacement of each measuring roller, and comparing the displacements to detect a faulty seal. With this invention, we avoid the need for the conventional test head completely. Instead, we provide an array of rollers with at least two measuring rollers whose displacement can be individually monitored as a bag passes and which have a much smaller dimension in the direction of travel as compared with a test head. Consequently, bags can be fed with a much shorter spacing between them leading to a significant increase in throughput. Thus, as long as there is some gap between successive bags, the system of the present invention will enable seal integrity to be determined. In practice, the length of the test is relatively longer than conventionally, due to the fact that the bags will be conveyed at a lower speed but this will produce a better test as the articles are under pressure for longer enabling more gas to be pushed out of a faulty bag and making a comparison of displacements more pronounced. Overall, however, throughput is increased because of the fact that bags can be much closer together. Further advantages are that inertia problems associated with moving a large test head up and down are avoided and overall a more robust machine can be used since there are no driven reciprocating parts. There is also no need for mechanical set up and thus intervention by shop floor personnel . Futhermore, by providing individually displaceable rollers, a more natural curved profile is assumed and this prevents the rollers riding on the product contained in the bag. These advantages are provided without resorting to an expensive and complicated apparatus such as described in EP

1186876. The reduced complexity results in a more robust and easily maintained system. The invention is typically used to test the seal integrity of pillow bags used, for example, in the packaging of potato chips and other snack foods. Typically, the array comprises a multiplicity (for example 18 or more) of rollers each having a dimension in the direction of travel much less than the size of the bag to be tested, and the rollers are spaced at a pitch much less than the size of the bag being tested. As such, when a bag is entirely between the array of rollers and the datum surface, a plurality of rollers is displaced in accordance with the bag's profile. In some examples, bags will be driven along the transport path solely by means of a drive system associated with the datum surface such as an endless belt or set of rollers. In other examples, drive may be achieved by a set of rollers or a belt located above the datum surface and in the most preferred arrangement, both upper and lower rollers or belts are driven. The measuring rollers may be driven in the case where drive is communicated to bags from above the datum surface although typically they will comprise idler rollers either in line or laterally displaced from any other rollers forming the upper drive system, if provided. The comparison of displacements can be achieved in a variety of ways. In a simple case, the monitoring system is adapted to compare the maximum displacements detected by each measuring roller and to indicate the presence of a faulty bag if the difference between the maximum displacements exceeds a predetermined threshold. However, the system can be used in a more sophisticated manner by arranging for the monitoring system to monitor the displacement of each measuring roller at a plurality of positions during the passage of a single bag and to generate a displacement profile for each measuring roller, the system being adapted to compare the profiles to detect the presence of a faulty bag. These profiles can be compared using a pattern matching technique or the like or instead can be used to determine the cross-sectional area of a bag as it passes each measuring roller following which these areas can be compared. This provides a much more accurate indication of whether there has been any leakage. In all these cases, a difference will arise between the two measurements if air or gas has leaked out of the seal as the bag passes from one measuring roller to the other. This will have been caused due to the urging of the rollers towards the datum surface and hence the application of pressure on the bags. The rollers opposite the datum surface including the measuring rollers may be individually mounted on respective supports but conveniently they are mounted on a common frame which is movable towards and away from the datum surface. This enables the apparatus to handle bags of a wide variety of thicknesses and also enables the urging (or spring) pressure to be varied to a desired level. Preferably, the apparatus further comprises a bag sensor upstream of the measuring rollers for determining the arrival of a bag at a predetermined location along the transport path. This bag sensor can simply provide the monitoring system with a time of arrival of a bag at the predetermined location which can then be used to control the sampling of displacement data from the measuring rollers and any subsequent diversion process. In addition, if the bag sensor is able to determine the thickness of a bag, for example if it is in the form of a light curtain, this information can be used by the monitoring system to control the position of the common frame on which the rollers are mounted if such a frame is provided. Typically, the first bag in a batch will be used by the monitoring system to adjust the frame location which is then fixed for the remaining bags in the batch. In one embodiment, the endless belt is entrained about the displaceable rollers. Typically, this belt extends across the entire widths of the rollers and is fabricated from a flexible material . In a preferred embodiment, each roller is urged towards the datum surface by a respective tension spring. Typically, each tension spring is provided with a respective adjuster for adjusting the tension in the spring. In this way, the force applied by each roller to the bag can be individually adjusted. This not only provides a controlled and constant force but also allows the force supplied by the first rollers in the array to be relatively low with respect to the subsequent rollers. As a result of this, the bag is not shocked by a high force as it arrives at the array of rollers and this has been found to improve settling of the product within the bag thereby lowering the likelihood of a false reading due to riding on the product. Downstream of the measuring rollers, bags can be handled in any conventional manner. Thus, the detection of a faulty bag could be used to halt the transport process so that the bag can be removed. Much more preferably, however, the apparatus further comprises a diverter downstream of the measuring rollers and responsive to the detection of a faulty bag by the monitoring system to divert the faulty bag to a cull location. This enables bags to continue to be transported along the path with faulty bags being diverted away from the path, for example by a solenoid controlled pusher member or the like. An example of seal testing apparatus according to the present invention will now be described with reference to the accompanying drawings, in which: - Figure 1 is a schematic side view of the apparatus; Figure 2 is a block diagram of the monitoring system; Figure 3 is an end view of part of the upper section of the transport system; and, Figure 4 is an enlarged side view of part of the upper transport system. The apparatus shown in Figure 1 comprises an in-feed conveyor 1 which feeds bags of snack products 2 to an inlet 3 of a transport system defining a transport path . The transport path 4 is defined by one or more laterally spaced lower conveyor belts 5, the upper runs of which pass over a fixed surface so that the belts define a datum surface 6. The belt(s) 5 are driven by a motor 7 via a drive belt 8. The belts could be replaced by rollers. Suspended above the conveyor belts 5 is a frame 10 on which are mounted a multiplicity of rollers 11 defining an upper part of the transport path 4 and including two similarly mounted measuring rollers 12A,12B. Each of the rollers 11,12A,12B is mounted for vertical movement and is urged under spring action towards the datum surface 6. Figures 3 and 4 illustrate the mounting arrangement of the rollers 11,12 in more detail. Each roller 11 is suspended from a pair of brackets 40. The bracket 40 shown in Figure 3 is coupled with a pivot shaft 41 which is journalled in a support block 42. The pivot shaft 41 is fixed to a hook-shaped bracket 43 which is urged to pivot in a clockwise direction about the pivot shaft 41 (Figure 4) by a tension spring 44 thus urging the roller 11 in a downward direction. The other end of the tension spring is mounted to a flange 45 and the position of the flange 45 can be adjusted using a bolt 46 thereby allowing the tension in the spring 44 to be adjusted. Vertical movement or displacement of the measuring rollers 12A, 12B is monitored by respective measuring devices 13,14. The measuring devices 13,14 can take a variety of forms. For example, they could sense rotation of the rollers 12 about the pivot shafts 41 by attaching an encoder to the pivot shafts or by including other mechanical linkages whose movement is detected or for example a linear actuator. Optical methods could also be used. In all these methods, simple mathematical processing can be used to convert the detected movement to vertical movement of the rollers 12A,12B. One or more endless belts 15 are entrained about the rollers 11,12A,12B and end rollers 16 and in the preferred embodiment, this belt (s) 15 is also driven from the motor 7. An in- feed photocell detector array 20 is provided at an upstream end of the transport path 4 to detect the arrival of a bag 2. In the preferred arrangement, the photocell array 20 comprises a linear array of photocells onto which a light curtain from a source (not shown) shines across the transport path 4. By determining how many of the photocells are obscured from the light curtain upon the passage of a bag 2, it is possible to determine the thickness (height in this case) of the bag. The apparatus is controlled by a microprocessor 30 (Figure 2) which receives as inputs signals from the sensors 13,14 and photocell array 20. The microprocessor 30 controls a solenoid operated plunger system 31 located downstream of the transport path 4 and also a stepper motor

32 coupled with the frame 10 for controlling the vertical position of the frame 10 relative to the datum surface 6. As can be seen in Figure 1, as a bag 2 passes along the transport path 4, it will cause adjacent rollers 11,12A,12B to displace upwardly in a wave-like manner. The upward (and downward) movement of the measuring rollers 12A, 12B is sensed by the sensors 13,14 which output corresponding signals to the microprocessor 30. The microprocessor 30 regularly samples these signals and in some cases, the sampling times can be linked to the time of arrival of a bag at the photocell array 20. In a simple example, the microprocessor 30 determines the maximum displacement of each of the measuring rollers 12A,12B during passage of the same bag 2 and then compares these. If these maximum displacements differ by more than a predetermined amount, this indicates that gas or air has leaked out of the bag between the times in which it passed the first measuring roller 12A and the second measuring roller 12B. In that event, using the timing information from the photocell array 20, the microprocessor 30 will activate the plunger 31 as the bag passes so that the bag is pushed away from the transport path to a cull location. In another approach, the microprocessor 30 stores values of the displacements of the rollers 12A, 12B throughout the passage of the same bag so as to build up a profile of the curvature of the upper surface of the bag. These two profiles can then be compared using a conventional pattern matching technique or alternatively converted to cross-sectional area values, typically on the assumption that the cross-sectional area is substantially symmetrical about a horizontal centre line. These areas can then be compared and if the area of the bag as it passes the roller 12B is less than that when it passed the roller 12A by a predetermined amount this will again indicate a faulty seal . As mentioned above, the position of the frame 10 can be adjusted by suitably operating the stepper motor 32. This adjustment is determined by the microprocessor 30 following passage of the first bag 2 of a batch past the photocell array 20. Thereafter, the frame 10 will remain fixed.

Claims

1. Seal testing apparatus for determining the integrity of a seal of a sealed bag, the apparatus comprising a transport path defined between a datum surface and an array of at least three rollers located opposite the datum surface and spaced apart therealong, each roller being substantially immovable in a direction along the transport path and being urged towards the datum surface but being displaceable away from the datum surface in response to the passage of the bag along the datum surface, wherein at least two of the rollers in the array are measuring rollers; and a monitoring system for monitoring the displacement of each measuring roller with respect to the datum surface and comparing the displacements to detect the presence of a bag with a faulty seal .

2. Apparatus according to claim 1, wherein the array comprises a multiplicity of rollers.

3. Apparatus according to claim 2, wherein the array comprises 18 or more rollers.

4. Apparatus according to any of the preceding claims, further comprising an endless belt entrained about the displaceable rollers.

5. Apparatus according to claim 4, wherein the endless belt extends across the entire width of the rollers.

6. Apparatus according to claim 4 or claim 5, wherein the endless belt is flexible.

7. Apparatus according to any of the preceding claims, wherein the datum surface is defined by an endless belt. 8. Apparatus according to any of the preceding claims, wherein the monitoring system is adapted to compare the maximum displacements detected by each measuring roller and to indicate the presence of a faulty bag if the difference between the maximum displacements exceeds a predetermined threshold.

9. Apparatus according to any of claims 1 to 7, wherein the monitoring system is adapted to monitor the displacement of each measuring roller at a plurality of positions during the passage of a single bag and to generate a displacement profile for each measuring roller, the system being adapted to compare the profiles to detect the presence of a faulty bag.

10. Apparatus according to claim 9, wherein the monitoring system is adapted to determine the cross-sectional area of a bag as it passes each measuring roller and to compare the areas to detect the presence of a faulty bag. 11. Apparatus according to claim 10, wherein a faulty bag is detected if the difference between the areas exceeds a predetermined value.

12. Apparatus according to any of the preceding claims, wherein the rollers opposite the datum surface are mounted on a common frame which is movable towards and away from the datum surface.

13. Apparatus according to any of the preceding claims, further comprising a bag sensor upstream of the measuring rollers for determining the arrival of a bag at a predetermined location along the transport path.

14. Apparatus according to claim 12 and claim 13, wherein the bag sensor provides an indication of bag height or thickness to the monitoring system, the monitoring system causing an adjustment in the frame position in response thereto.

15. Apparatus according to any of the preceding claims, wherein each roller is urged towards the datum surface by a respective tension spring.

16. Apparatus according to claim 15, wherein each tension spring is provided with a respective adjuster for adjusting the tension in the spring.

17. Apparatus according to any of the preceding claims, further comprising a diverter downstream of the measuring rollers and responsive to the detection of a faulty bag by the monitoring system to divert the faulty bag to a cull locatio .

18. A method for determining the integrity of a seal of a sealed bag using the apparatus of any of the preceding claims, the method comprising conveying a bag along the datum surface thereby causing each roller to be displaced away from the datum surface in response to the passage of the bag and in accordance with the bag's profile, monitoring the displacement of each measuring roller, and comparing the displacements to detect a faulty seal.

19. A method according to claim 18, wherein the bag is a pillow bag.

20. A method according to claim 18 or claim 19, wherein at any instant when the bag is entirely between the array of rollers and the datum surface, a plurality of the rollers is displaced in accordance with the bag's profile. 21. A method according to any of claims 18 to 20, wherein the maximum displacements of each measuring roller are compared, and the presence of a faulty seal is indicated if the difference between the maximum displacements exceeds a predetermined threshold. 22. A method according to any of claims 18 to 20, wherein the displacement of each measuring roller at a plurality of positions during the passage of the bag is monitored, a displacement profile is generated for each measuring roller, and the profiles are compared in order to detect the presence of a faulty seal.

23. A method according to claim 22, wherein the cross- sectional area of the bag is determined as it passes each measuring roller and the areas are compared to detect the presence of a faulty seal . 2 . A method according to claim 23, wherein a faulty seal is detected if the difference between the areas exceeds a predetermined threshold.

25. A method according to any of claims 18 to 23, wherein a bag with a faulty seal is diverted to a cull location. 26. Seal testing apparatus substantially as hereinbefore described with reference to the accompanying drawings.

27. A method substantially as hereinbefore described with reference to the accompanying drawings.