Testing of packages

Measuring and testing – With fluid pressure – Leakage

Patent

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Details

G01M 334

Patent

active

057865302

DESCRIPTION:

BRIEF SUMMARY
The present invention relates to an apparatus and method for testing packages, e.g. packages of snack foods such as bags of crisps.
It is known to test a package by applying a load which tends to compress the package, and monitoring the effect. After an interval, the package may be tested again. For a good package, if the two tests use identical loads, then the package should behave identically, e.g. in terms of the amount of compression. But if the package contains air or other fluid and has a leak, the first test will cause some deflation. Thus the amount of compression will be greater than for a good package. Furthermore the package will already be in a deflated state at the start of the second test, and will undergo further deflation (unless it is already fully deflated). Testing equipment working on this principle has been brought to quite a high level of sophistication, e.g. as described in WO93/17317. But we have now found ways to improve the operation of such test systems.
In a first aspect, the invention provides test apparatus having conveyor means for conveying test substrates, and one or more test stations arranged along the conveying path; there being at least one such test station having a test head adapted to be moved towards and away from the conveying path; wherein the head is normally urged towards the conveying path so that a package being conveyed along the path contacts the head and urges it away from the conveying path; and wherein the resulting displacement of the head is monitored.
Desirably, the test head is urged solely by gravity towards the conveying path. Its contact surface is desirably such as to allow continuing movement of packages along the conveying surface. It preferably uses an array of low back line pressure rollers.
Since it is the arrival of a substrate that causes the movement of the test head directly, there is no need for sophisticated devices for synchronising the action of a test station with the arrival of a package, or for synchronising the actions of a plurality of test stations. Since the arrival of a substrate acts to raise a test head, if a second substrate arrives while a first substrate is still at the head, this merely causes further raising of the head, if necessary. In contrast, with prior art systems using powered pistons, the result tended to be the bursting of one or more packages. Furthermore, since a test head can be urged by gravity, the mechanism can be very simple. It is also very consistent and reliable, whereas pneumatic systems in particular are prone to variability. They also inevitably introduce vibration.
Preferably the apparatus has two test stations, each having a test head adapted to be raised by a substrate moving along the conveying path. Preferably each test station includes means for deriving a signal related to the displacement of the test head. The apparatus may also include computing means which receives data from the displacement detectors.
When a substrate reaches a test station, the test head is raised thereby. If the substrate is "leaky", the test head will then fall somewhat. Preferably the first test station is adapted to produce an additive output signal, or the data are treated additively by the computer. That is, if a substrate causes the head to rise by x and then to descend by y, the resulting datum corresponds to (x+y). Preferably the second test station leads to a differential datum corresponding to (x-y).
In conventional apparatus having two or more test stations, it is necessary to make careful mechanical adjustments to the relative heights of the test heads. In the present invention, particularly with gravity-urged heads, this is much less of a problem. Furthermore, adjustment can be made electronically, rather than mechanically. Thus if a "good" (non-leaky) substrate is passed through the system, it should give identical values at all test stations. If it does not, a correction can be applied by the computer to the data from one or more test stations.
Should it be desired to vary the load applied by a test head

REFERENCES:
patent: 4148213 (1979-04-01), Prakken
patent: 4649740 (1987-03-01), Franklin
patent: 4671101 (1987-06-01), Franklin
patent: 5284003 (1994-02-01), Goodman et al.
patent: 5531101 (1996-07-01), Fenlon
patent: 5533385 (1996-07-01), Frievalt
patent: 5542288 (1996-08-01), Fenlon

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