Measuring and testing – With fluid pressure – Leakage
Reexamination Certificate
1998-02-24
2001-03-20
Williams, Hezron (Department: 2856)
Measuring and testing
With fluid pressure
Leakage
C073S045400, C053S053000
Reexamination Certificate
active
06202476
ABSTRACT:
The present invention relates to a method of and apparatus for testing for leaks in a package. Pre-packaged food products, such as cuts of meat and pre-prepared meals or snacks (such as crisps), are often packaged in one of two ways. The products may be vacuum packed so as to remove air from the interior of the packaging, or the products may be gas filled packed, in which the products, such as meat or crisps, are sealed within a gas tight package together with a quantity of gas. The gas used may vary upon the product that is packed. In either case, it is important that the pack does not leak in order to prevent spoilage and/or to ensure that the product has an acceptable shelf life.
Liquids, for example. fruit juices, are also provided in flexible packages which must be leak-tight in order to keep the product fresh and to avoid making a mess.
U.S. Pat. No. 4,649,740 discloses a testing apparatus in which flexible packages are indexed through at least two test stations. A package is stopped at each test station and a load is applied thereto via probe rods. Two successive stations apply the same load to the package and the effective thickness of the flexible package is measured in each case. The thickness measurements are compared and a difference is deemed to show a defective package.
WO-9317317 discloses a package tester having two test stations in a line. The arrangement does not require the packages to be brought to a halt at each test station. The first test station applies a first load to a package via a pneumatic actuator. The second test station applies a different load, and also uses a pneumatic actuator. Such an arrangement can produce spurious results if the air pressure to each actuator is not well controlled. In fact, because the thickness of the packages must be measured with great precision, such an arrangement can even be affected by changes in ambient air pressure.
According to a first aspect of the present invention, there is provided an apparatus for testing for leaks in a package, comprising a test element which is brought into abutment with a package, and a position sensor for measuring the position of the test element, in which at least a portion of the package is compressed by the weight of the test element.
It is thus possible to provide a package tester in which the load applied to a package is derived solely from the weight of the test element and is not dependent upon the correct functioning of an actuator. The tester can test both gas and liquid filled packages. In this context, gas filled packages includes sealed packages containing a product and a gas. An example of such a package is a bag of crisps.
Preferably, the test element is brought into abutment with the upper surface of the package under test.
The tester may be arranged, in use, to make a first measurement of the position of the test element after it has been lowered onto the package, to wait for a predetermined period, and then to make a second measurement of the position of the test element. The first and second positions are then compared and the package is indicated as being faulty when the second measurement differs from the first measurement by more than a predetermined amount.
However, the applicant has realized that this delay is not always necessary. In a modification, the test can still be set to have a maximum fixed duration, but multiple measurements can be taken during the test period and the test can be terminated if the difference between any two of the measurements exceeds a predetermined value. Thus, if the package has a significant leak, the leak can be detected in a time that is shorter than the maximum time allocated to the test. Consequently, the test time can be shortened for leaky packages and the tester can then commence testing the next package. Thus, the rate at which packages are tested can be increased.
Preferably, the tester is arranged to check that the first measurement falls within an acceptable range of values. It is therefore possible to determine whether a package has become distorted, whether it suffers from a gross leak, or whether it contains an acceptable volume of fluid.
The force applied to the package by the tester head urges fluid to escape from any leaks in the package. The leakage of fluid causes the test head to move as the package deflates. It is thus possible to detect a leak by testing for movement of the test head while it is in contact with the package.
Advantageously, the package tester is removably supported in a frame, such that the package tester can be demounted from the frame and replaced by a different testing arrangement or by a plurality of package testers attached to a common support. Thus, it is possible to convert the tester between single-lane and multi-lane use at a given test station. The products may be moved to and from the test heads on one or more conveyor belts, or on a platen. The test may be performed at each test head of a multihead machine. The data from one test head may also be compared with data derived from another test head.
Advantageously, the test element is lowered in a vertical direction onto the top of the package to be tested. Movement of the test element may be controlled by one or more actuators which engage a downwardly facing surface of the test element such that connection between the test element and the one or more actuator is severed when the test element is supported by the package to be tested. Such an arrangement ensures that the load supplied to the package is derived solely from the weight of the test element and that friction within the actuator. damage to the actuator (such as seal wear) or changes in the actuator force (such as problems in regulating gas pressure in a pneumatic actuator) does not alter the load applied to the package or impede motion of the test element during the test. The actuator is arranged to only apply an upward force which urges the test element away from the package.
Many forms of position sensor may be used to measure the position of the test element. The test element may, for example, carry an upstanding rack which cooperates with a gear to drive a rotary position transducer.
Alternatively, the one or more test heads may comprise a rotary transducer geared to the linear element or coupled to a cam shaped element. The use of a cam shaped element has the advantage that motion of the package to and from the test head causes the cam shaped element to engage and disengage from the package automatically. This avoids the need to provide actuators to control the engagement of the test element with the package.
Preferably, the comparisons of the measurements are made by a programable data processor.
According to a second aspect of the present invention, there is provided a method of testing for leaks in a package, comprising bringing a test element into abutment with at least a portion of the package to be tested, making a first measurement of the position of the test element, making at least one further measurement of the position of the test element, comparing at least one further measurement with a preceding measurement and indicating the package to be faulty if the comparison exceeds a predetermined value.
Preferably, at least one further measurement is compared with the first measurement.
Advantageously, the at least one further measurement is made shortly after the first measurement. The delay between the measurements need not be a predetermined fixed delay but may, for example, be dependent upon the time taken for a data processor to execute other tasks or to cycle through this task.
Advantageously, the test element is placed on at least a portion of the package to be tested, allowing the package or portion thereof to deform under the weight of the test element. The first measurement of the position of the test element is then made. Advantageously, the at least one further measurement includes a second or final measurement of the position of the test element, which is performed a predetermined time after the first measurement. A data processor forms a difference be
Koppel & Jacobs
Politzer Jay L.
Ram Michael J.
Testamatic Limited
Williams Hezron
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