EP1779082A2

EP1779082A2 - Method and device for detecting a leak in packaging

Info

Publication number: EP1779082A2
Application number: EP05767937A
Authority: EP
Inventors: Karel Auguste Loth
Original assignee: Lothgenoten BV
Current assignee: Lothgenoten BV
Priority date: 2004-07-20
Filing date: 2005-07-20
Publication date: 2007-05-02
Also published as: WO2006009442A2; WO2006009442A3

Abstract

The invention relates to a method for detecting a leak in a package at least partly filled with a gas, comprising the steps of exposing a package to a reduced pressure, measuring the concentration of the gas in the vicinity of the package, comparing the measured concentration to a limit value, and emitting a signal when the measured value exceeds the limit value. The concentration measurement does not herein have to take place simultaneously with the exposure to the reduced pressure, but a sample can for instance be taken from the vicinity of the package, the gas concentration of which sample is measured over a longer period of time. The invention further relates to a leak detecting device (101) for performing this method, provided with means (102) for exposing the package (P) to a reduced pressure, means (110) for measuring the concentration of the gas in the vicinity of the package, means connected to the measuring means for comparing the measured gas concentration to a limit value, and means connected to the comparing means for emitting a signal when the measured value exceeds the limit value. The measuring means can herein comprise an NDIR (non-dispersive infra red) gas detector.

Description

METHOD AND DEVICE FOR DETECTING A LEAK IN A PACKAGING

The invention relates to a method^' for detecting a leak in a packaging.

Products are often packaged in a package sealed in gas-tight manner, wherein a part of the content of this package consists of a gas mixture which has a composition other than the ambient air. A gas or gas mixture is added to the air in the package so as to influence the conditions of the product, particularly to improve the storage life hereof. If the package is not gas-tight, or not wholly so, the package then has a leak, and there is therefore a risk of the protective gas or gas mixture escaping or being displaced by ambient air. The storage life of the packaged products is hereby adversely affected.

It is thus important to be able to test the gas- tightness of sealed packages filled with product before the thus packaged products are made commercially available, thus at the end of the packaging operation. This testing must herein take place such that the total time involved in packaging the products does not increase, or hardly so. For this purpose the present invention provides a method for detecting a leak in a package at least partly filled with a gas, comprising the steps of exposing a package to a reduced pressure, measuring the concentration of the gas in the vicinity of the package, comparing the measured concentration to a limit value and emitting a signal when the measured value exceeds the limit value.

By reducing the pressure around the package a part of the gas mixture present herein will flow out of the package when the package has a leak. The concentration of the gas in the vicinity of the package will hereby change. By measuring this concentration and comparing it to a predetermined limit value it is possible to determine whether the package has a leak and, if so, whether the degree of leakage is such that the package must be rejected and removed from the packaging process. Instead of measuring the concentration of the gas per se and comparing this to a limit value, the change in this concentration can otherwise also be measured in time and compared to a limit value. This change in concentration is after all also a measure for the leakage. Where the measuring of concentration is mentioned in the text hereinbelow, this is therefore also understood to mean measuring of the change of concentration in time.

The concentration measurement preferably does not take place simultaneously with the exposure to the reduced pressure. By as it were uncoupling the concentration measurement from the pressure decrease, the packaging process and the concentration measurement can be individually optimized.

When the concentration measurement takes place over a longer period of time than the exposure to the reduced pressure, the time for which the package is exposed to the pressure decrease can be kept very short so that the packaging process is not hereby delayed, or hardly so, while sufficient time can still be taken for an accurate measurement of the gas concentration.

This can be achieved in efficient manner when at least one sample is taken from the vicinity of the package, the gas concentration of which sample is measured over a longer period of time. In order to guarantee the quality of the sample, it is preferably stored separated from the vicinity of the package prior to the concentration measurement.

In order to achieve an optimal accuracy of measurement, a plurality of samples can be taken successively, the gas concentration of each sample can be measured and the measured values can be compared to each other. It is also possible to envisage the concentration measurement taking place in different steps, wherein the manner in which a subsequent measurement is performed depends on the result of a previous measurement. The order of magnitude of a leak can thus be determined in a first measurement, whereafter a second, more precise measurement can be adjusted hereto.

The present invention also provides a device for carrying out the above described method. According to the invention such a leak detecting device comprises means for exposing the package to a reduced pressure, means for measuring the concentration of the gas in the vicinity of the package, means connected to the measuring means for comparing the measured gas concentration to a limit value, and means connected to the comparing means for emitting a signal when the measured value exceeds the limit value.

As elucidated above, it is possible to opt for the measuring means not being active simultaneously with the pressure reducing means, wherein the measuring means can have a longer cycle time than the pressure reducing means. It is hereby possible to still perform an accurate measurement of concentration in a packaging line where packages are passing at high speed, while making use of relatively simple measuring means.

The measuring means can here for instance comprise an NDIR gas detector, an effective detector type which is commercially available at relatively low cost. In order to enable the concentration measurement to be performed very quickly, the NDIR gas detector preferably comprises a measuring cell having means for optimizing the flow therein.

When the measuring means comprise a buffer connected to the pressure reducing means via a sample line, as well as valves placed in the sample line between the buffer and the pressure reducing means on the one hand and between the buffer and the measuring means on the other, samples of the gas from the vicinity of the package can be stored interim before being analysed. It is recommended here that the buffer is connected to the environment or to a space in which a determined pressure prevails, so that the sample stored in the buffer can be supplied to the measuring means at ambient pressure or under the determined pressure. This is particularly important when the measuring means are of a type adapted to process a constant gas flow. The measuring means are preferably connected releasably to the pressure reducing means, whereby they can be exchanged when for instance packages with a different gas or a different concentration of the gas therein must be tested for leaks. If the measuring means are then connected by plug connections and rapid-action couplings to the pressure reducing means, the exchange can take place rapidly and in simple manner.

When the leak detecting device according to the invention is provided with a number of sets of measuring means connected in parallel and each connected to the pressure reducing means, packages which pass very quickly, and are thus exposed to an underpressure only very briefly, can still also be tested in reliable manner by performing different measurements simultaneously. A preferred embodiment of the leak detecting device is provided with a number of sets of measuring means connected in series and having a diversity of measurement sensitivities . A first set of measuring means can thus determine the order of magnitude of the leak, whereafter on the basis hereof a smaller sample than normal can for instance be added to the subsequent, more sensitive set of measuring means. It is thus possible to prevent these second measuring means being as it were "flooded" by the high gas concentration, whereby the measurement sensitivity could be temporarily reduced.

A structurally simple leak detecting device is obtained when the pressure reducing means comprise a housing at least partly enclosing the package and a vacuum pump connected thereto. This housing is preferably placed above a conveyor supplying and discharging the package, has an open bottom and is movable substantially transversely of the conveyor. The housing can thus be placed over a package for testing and removed therefrom quickly and easily. In order to enable rapid movements of the housing, this latter can advantageously be manufactured from a lightweight plastic material such as a plastic composite reinforced with glass fibre or carbon fibre. The leak detecting device can further be provided with drive means connected to the housing for causing this latter to move transversely of the conveyor, which drive means are placed under the conveyor, whereby a relatively compact device is obtained. In order to enable an underpressure to be created relatively quickly in the housing using a relatively light vacuum pump, the leak detecting device is preferably provided with a buffer placed between the housing and the vacuum pump, and with a valve placed between the buffer and the housing. The invention will now be elucidated on the basis of a number of exemplary embodiments, wherein reference is made to the accompanying drawing, in which corresponding components are designated with reference numerals which are increased by "100" at a time, and in which:

Fig. 1 shows a schematic side view of a first embodiment of the leak detecting device according to the invention, which is suitable for a so-called "direct" detection,

Fig. 2 is a view corresponding with fig. 1 of a second embodiment of the leak detecting device according to the invention, which is suitable for a so-called "indirect" detection, Fig. 3 shows a variant of the embodiment of fig. 2 with a plurality of sets of measuring means connected in parallel,

Fig. 4 in turn shows another variant of the indirect leak detecting device according to the invention with a pressureless buffer, and

Fig. 5 shows a variant of the indirect leak detecting device with two sets of measuring means in series. A device 1 for detecting a leak in a package P at least partly filled with gas - in this example a gas mixture with an increased concentration of carbon dioxide relative to the ambient air - comprises means 2 for exposing package P to a reduced pressure (fig. 1) . Leak detecting device 1 further comprises means 3 for measuring the concentration of the gas in the vicinity of package P, means connected to measuring means 3 for comparing the measured gas concentration to a limit value, and means connected to the comparing means for emitting a signal when the measured value exceeds the limit value. The comparing means and the signal-emitting means are not shown individually here. In the shown embodiment the pressure reducing means

2 comprise a housing 4 at least partly enclosing package P, and a vacuum pump 6 connected to the housing via a line 5 with a valve 9 herein. Housing 4 is here placed above a conveyor 7 supplying and discharging the package (with conveying direction T) , and has an open bottom. By means of drive means (not shown here) housing 4 is movable transversely of conveyor 7 (as according to arrow M) between the shown measuring position, in which housing 4 defines a closed space together with conveyor 7, and a position allowing passage, in which housing 4 hangs above conveyor 7 at a height such that a tested package P can be discharged and a subsequent package P' can be supplied. A further seal 8 is arranged around the open bottom of housing 4.

Measuring means 3 here comprise a gas detector 10, for instance of the NDIR type, which is based on the Non- Dispersive Infra Red absorption principle. This gas detector 10 comprises a measuring cell 11 with a source 12 of IR light on one side and a sensor 13 on the opposite side. The IR source 12 is further provided with a filter which allows through as much radiation as possible with a wavelength for which the gas for detecting has a relatively great absorption value. Sensor 13 must of course also be sensitive to radiation of precisely this wavelength. The higher the concentration of the gas in measuring cell 11 becomes, the more IR radiation will thus be absorbed and less will reach sensor 13. The ratio between the intensity of the absorbed radiation and the emitted radiation is thus a measure for the concentration. Gas detector 10 is otherwise connected to the above mentioned comparing means and signal generating means via lines 16 (shown schematically here) .

Measuring means 3 further comprise a second vacuum pump 14 with which a gas sample can be pumped from housing 4 via a line 15 to gas detector 10. This sample pump 14 can create a lower pump pressure than vacuum pump 6 of pressure reducing means 2, and is in operation as long as housing 4 lies on conveyor 7. The operation of this embodiment of leak detecting device 1 is as follows. When a package P for testing is supplied by conveyor 7, housing 4 is moved downward by the drive means and placed over this package P, whereby a closed and airtight space is created around package P. Just as the ambient air, the air in this closed space has a determined concentration of the gas with the same composition as the gas mixture present in the package. When valve 9 is opened, vacuum pump 6 reduces the pressure in the space until it is lower than the pressure in package P. If package P is not fully sealed and therefore has a leak, gas mixture will flow out of package P into the space and the concentration of this gas mixture in the space will thereby change. The sample pump 14 draws air out of the space enclosed by housing 4 and pumps it through measuring cell 11 of the NDIR gas detector 10.

Here the concentration of the gas or gas mixture to which the detector 10 is sensitive is determined on the basis of the detected absorption of IR radiation, thus the difference between the radiation emitted by source 12 and the radiation absorbed by sensor 13. This detection is transmitted to the comparing and signal-emitting means via lines 16.

By processing the measurement data of gas detector 10 such that it is possible to determine that there is a significant change in the time that the gas is supplied from the closed space, a leak in package P is hereby demonstrated. A detected leak can be indicated and/or, transmitted in the form of a signal or action whereby a process or system can be controlled. On the basis of this detection package P can for instance be taken out of the packaging line at a subsequent station.

This manner of detecting the presence of a leak is known as "direct" measurement, since the detection takes place while package P is exposed to the underpressure. An alternative embodiment of the leak detecting device 101 according to the invention is provided with a buffer 117 in line 115 between sample pump 114 and gas detector 110 (fig. 2) . Controllable valves 118, 119 are accommodated in line 115 on either side of this buffer 117. A branch line 120 with valve 121 is further connected to line 115 between sample pump 114 and the first valve 118. Provisions 122, for instance in the form of a spring-loaded piston or bellows, are otherwise arranged in buffer 117 to enable variation of the volume thereof.

Owing to the presence of buffer 117 the concentration measurement can be separated in time from the exposure of package P to an underpressure. The package therefore only has to remain stored in housing 4 for a short time, whereafter gas samples stored in buffer 117 can be supplied to gas detector 110 at a suitable speed. Housing 104 can be taken off package P and conveyor 107 can supply the subsequent package P' while the concentration measurement of the gas is still taking place or has yet to start, so-called "indirect" measurement. As long as the space defined by- housing 104 remains closed, a plurality of samples can be taken successively and supplied to gas detector 110. Change in the measured gas concentration over a plurality of measurements is an indication of a leaking package or packages (serial application) .

The operation of this embodiment is thus as follows. When all valves are closed and valve 118 is opened, sample pump 114 draws a gas sample out of the space bound by housing 104 and pumps this gas sample into buffer 117, wherein the pressure in buffer 117 increases. After closing of valve 118 the gas sample is buffered. This latter can now be guided through measuring cell 111 of gas detector 110 by opening valve 119, whereafter the buffer is emptied by piston 122. The gas sample displaces the gas present in gas detector 110 and remains there until the following gas sample is presented. While gas detector 110 analyses the gas, buffer 117 can be filled again at a random time with a subsequent gas sample. When valve 118 is closed, flushing valve 121 can be opened in order to flush or aerate sample pump 114 and pump line 115.

In this embodiment the pressure reducing means 102 are otherwise also provided with a buffer 123 between vacuum pump 106 and valve 109. By continuously suctioning out this buffer 123, so also at moments when housing 104 is not placed over a package P, a considerable underpressure can be created using a relatively small vacuum pump, whereby the desired pressure reduction in housing 4 in the measuring position can be brought about relatively rapidly.

In addition, measuring cell 111 of gas detector 110 is adapted in this embodiment to optimize the flow of the gas sample. By adapting the form of measuring cell 111 such that it has the smallest possible volume and the smallest possible flow resistance to the gas mixture, measuring cell 111 can be filled in the shortest possible time with new gas mixture for measuring, whereby measurement can take place more rapidly. It is also important to select the form of measuring cell 111 such that the least possible mixing occurs in cell 111 and in all other components of device 101. This is realized here by embodying measuring cell 111 with rounded corners and the smallest possible "dead volume", which means volume which is not functional but does disrupt the flow pattern.

In a third embodiment of device 201 the sample line 215 is divided into two parallel branches 215A and 215B, each having a buffer 117A, ^' 117B and associated valves 118A, 118B and 119A, 119B (fig. 3) . By opening and closing the relevant valves and operating sample pump 214 in suitable manner, both buffers 117A, 117B can be alternately filled or emptied in gas detector 210. The capacity and therewith the flexibility of the leak detecting device 201 is hereby increased. Each branch 215A, 215B of the sample line could otherwise also be connected to its own gas detector (not shown here) .

By assembling a device from combinations of the above described apparatus a measuring device can be assembled which, depending on the given conditions, is most satisfactory in a determined situation. By embodying a device with controlled parallel measuring systems which can be operated and activated independently of each other and which alternately measure one or more supplied package (s), it is possible to operate with a total measuring time which is longer than the cycle time of the leak tester (parallel measuring systems) .

Instead of a buffer of variable volume in which the pressure increases when it is filled, it is also possible to envisage working with a buffer 317 in which a determined, constant pressure prevails (fig. 4) . This is particularly important when use is made of a gas detector which operates with a constant volume flow. Here the varying pressure resulting from emptying of the buffer would result in varying volume flows and thus erratic measuring results. A pressureless buffer 317 consists of a space with open outlet opening to the ambient air, in which the flow profile is such that during the sampling time there occurs no or little mixing with the ambient air, such as a hose or pipe with a small internal diameter, a labyrinth or space of other form in which no or hardly any mixing occurs under the stated conditions. Sample valve 318 is opened for a length of time such that at least as much gas is stored in the buffer 317 with constant pressure as the gas detector 310 with its own suction pump 324 needs for a measurement. After closing of valve 318 the pressure in buffer 317 becomes the same as the ambient air and the gas sample in buffer 317 is supplied at ambient pressure to gas detector 310.

Finally, in a fifth embodiment (fig. 5) the device 401 is provided with a relatively insensitive gas detector 425, once again for instance an NDIR detector, which is connected between housing 404 and the actual gas detector 410. This advance detector 425 detects very high concentrations resulting from large leaks, and controls sample valve 418 on the basis thereof such that only a small sample is supplied to detector 410. This prevents this detector 410 being "flooded", whereby the measurement accuracy would be temporarily reduced.

Although the invention is elucidated above with reference to a number of exemplary embodiments, it is not limited thereto. Types of gas detector other than as stated above, such as potentiometric gas concentration measuring instruments, hot-wire gas concentration measuring instruments and other types of gas concentration measuring instrument could thus also be used. Other aspects of the device and method can also be varied. The scope of the invention is therefore defined solely by the following claims.

Claims

1. Method for detecting a leak in a package at least partly filled with a gas, comprising the steps of:

- exposing a package to a reduced pressure,

- measuring the concentration of the gas in the vicinity of the package,

- comparing the measured concentration to a limit value, and

- emitting a signal when the measured value exceeds the limit value.

2. Method as claimed in claim 1, characterized in that the concentration measurement does not take place simultaneously with the exposure to the reduced pressure.

3. Method as claimed in claim 2, characterized in that the concentration measurement takes place over a longer period of time than the exposure to the reduced pressure.

4. Method as claimed in claim 3, characterized in that at least one sample is taken from the vicinity of the package, the gas concentration of which sample is measured over a longer period of time.

5. Method as claimed in claim 4, characterized in that the sample is stored separated from the vicinity of the package prior to the concentration measurement.

6. Method as claimed in claim 4 or 5, characterized in that a plurality of samples are taken successively, the gas concentration of each sample is measured and the measured values are compared to each other.

7. Method as claimed in any of the foregoing claims, characterized in that the concentration measurement takes place in different steps, wherein the manner in which a subsequent measurement is performed depends on the result of a previous measurement.

8. Device for detecting a leak in a package at least partly filled with a gas, comprising means for exposing the package to a reduced pressure, means for measuring the concentration of the gas in the vicinity of the package, means connected to the measuring means for comparing the measured gas concentration to a limit value, and means connected to the comparing means for emitting a signal when the measured value exceeds the limit value.

9. Leak detecting device as claimed in claim 8, characterized in that the measuring means do not operate simultaneously with the pressure reducing means.

10. Leak detecting device as claimed in claim 9, characterized in that the measuring means have a longer cycle time than the pressure reducing means.

11. Leak detecting device as claimed in claim 10, characterized in that the measuring means comprise an NDIR gas detector.

12. Leak detecting device as claimed in claim 11, characterized in that the NDIR gas detector comprises a measuring cell having means for optimizing the flow therein.

13. Leak detecting device as claimed in any of the claims 9-12, characterized in that the measuring means comprise a buffer connected to the pressure reducing means via a sample line, as well as valves placed in the sample line between the buffer and the pressure reducing means on the one hand and between the buffer and the measuring means on the other.

14. Leak detecting device as claimed in claim 13, characterized in that the buffer is connected to the environment or to a space in which a determined pressure prevails.

15. Leak detecting device as claimed in claims 8- 14, characterized in that the measuring means are connected releasably to the pressure reducing means.

16. Leak detecting device as claimed in claim 15, characterized in that the measuring means are connected by plug connections and rapid-action couplings to the pressure reducing means.

17. Leak detecting device as claimed in any of the claims 8-16, characterized by a number of sets of measuring means connected in parallel and each connected to the pressure reducing means.

18. Leak detecting device as claimed in any of the claims 8-17, characterized by a number of sets of measuring means connected in series and having a diversity of measurement sensitivities .

19. Leak detecting device as claimed in any of the claims 8-18, characterized in that the pressure reducing means comprise a housing at least partly enclosing the package and a vacuum pump connected thereto.

20. Leak detecting device as claimed in claim 19, characterized in that the housing is placed above a conveyor supplying and discharging the package, has an open bottom and is movable substantially transversely of the conveyor.

21. Leak detecting device as claimed in claim 19 or 20, characterized in that the housing is manufactured from a lightweight plastic material such as a plastic composite reinforced with glass fibre or carbon fibre.

22. Leak detecting device as claimed in claim 21, characterized by drive means connected to the housing for causing this latter to move transversely of the conveyor, which drive means are placed under the conveyor.

23. Leak detecting device as claimed in any of the claims 19-22, characterized by a buffer placed between the housing and the vacuum pump, and a valve placed between the buffer and the housing.