U.S. patent application number 10/050155 was filed with the patent office on 2002-05-09 for container tightness tester.
Invention is credited to Lehmann, Martin.
Application Number | 20020053235 10/050155 |
Document ID | / |
Family ID | 8226772 |
Filed Date | 2002-05-09 |
United States Patent
Application |
20020053235 |
Kind Code |
A1 |
Lehmann, Martin |
May 9, 2002 |
Container tightness tester
Abstract
For tightness testers with a plurality of in-line test stations
(1) on a conveyor it is proposed to supply the tightness-relevant
measurement signals from the chambers by detecting pressure change
measurements via pressure sensors or electrical impedance
measurements via electrodes that occur at the test stations over a
time interval. The signals are supplied through multiplexers (5) to
a central evaluation (9).
Inventors: |
Lehmann, Martin; (Wohlen,
CH) |
Correspondence
Address: |
ANTONELLI TERRY STOUT AND KRAUS
SUITE 1800
1300 NORTH SEVENTEENTH STREET
ARLINGTON
VA
22209
|
Family ID: |
8226772 |
Appl. No.: |
10/050155 |
Filed: |
January 18, 2002 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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10050155 |
Jan 18, 2002 |
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09691217 |
Oct 19, 2000 |
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09691217 |
Oct 19, 2000 |
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08944471 |
Oct 6, 1997 |
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Current U.S.
Class: |
73/49.3 ;
209/552 |
Current CPC
Class: |
G01M 3/3236 20130101;
G01M 3/3281 20130101; G01M 3/329 20130101 |
Class at
Publication: |
73/49.3 ;
209/552 |
International
Class: |
G01M 003/34; B07C
005/00 |
Foreign Application Data
Date |
Code |
Application Number |
Jul 5, 1997 |
EP |
97 107 520.5 |
Claims
I claim:
1. A method for producing unleaky containers comprising:
manufacturing a plurality of closed containers; providing a number
of leak test stations, each for at least one container, on a
movable conveyor wherein the test stations move with the conveyor;
loading said stations with said closed containers; generating an
electric signal output on the movable conveyor at each of said
stations in dependency of leakage of said container under test in a
station considered and applying the electric output signals of said
stations subsequently, one after the other to an input of a common
evaluation unit on said movable conveyor and generating by said
common evaluation unit leak indicative signals for each of said
containers under test; and rejecting containers indicated by said
leak indicative signals to be leaky.
2. The method according to claim 1, wherein said generating an
electric signal output at each of said stations in dependency of
leakage of said container under test in a station considered
includes performing a pressure measurement on the movable conveyor
at the respective test stations.
3. The method according to claim 2, wherein both pressure
measurement and an electrical impedance measurement are performed
on the movable conveyor at each of said stations.
4. The method according to claim 3, wherein the output signals of
said stations from said pressure measurements and the output
signals of said stations from said impedance measurements are
applied to said input of said common evaluation unit on a
time-staggered basis.
5. The method according to claim 3, wherein the output signals of
said stations from said pressure measurements and the output
signals of said stations from said impedance measurements are
applied to respective ones of different common evaluation units on
said conveyor.
6. The method according to claim 1, wherein a plurality of
containers are loaded at each of the leak test stations.
7. The method according to claim 6, wherein the container loaded at
each of the leak test stations are a set of ampoules.
8. The method according to claim 6, wherein a leak in one of a
plurality of containers at a leak test station results in rejection
of the entire plurality.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] This application is a Divisional application of U.S.
application Ser. No. 09/691,217, filed Oct. 19, 2000, which in turn
is a Divisional Application of U.S. application Ser. No.
08/944,471, filed Oct. 6, 1997, now U.S. Pat. No. 6,167,750, issued
Jan. 2, 2001.
TECHNICAL FIELD
[0002] The present invention relates to a container tightness
tester with a conveyor and with a plurality of test stations, each
for at least one container, with at least one pressure sensor at
each test station, which is operationally connected on the output
side with the input of an evaluation unit.
BACKGROUND
[0003] Testers of the above type are known in which, as viewed on
the carousel, the respective test stations are pressurized in a
first rotation angle position of the carousel, in the case of open
containers, their interiors, or in the case of closed containers,
corresponding test chambers at the test station, and in which the
pressure that depends on the tightness of the container under test
is detected in at least one additional predetermined rotation angle
position of the carousel and then evaluated. This known method
and/or this type of tester are disadvantageous for a number of
reasons. Because pressure detection is performed by the individual
test chamber while passing through a certain rotation angle,
generally for example a certain position for linear conveyors, only
a limited time is available for pressure measurement, as a function
of the rotational speed or of the speed in general, and hence of
the throughput rate. This limits the rate at which containers can
be tested per unit time and is especially problematic in continuous
carousel operation. In addition, it is not possible to follow over
time the pressure that depends on leakage because the pressure
sensors provided perform their measurements only at certain
times.
[0004] Systems for extremely reliable tightness testing therefore
have at least one pressure measurement sensor permanently
associated with each of the test stations that go around with the
carousel, as well as likewise permanently assigned evaluation
electronics that allow testing to be performed at the test stations
freely throughout the entire time interval, during which a
container loaded into a test station on the carousel goes around
with the carousel.
[0005] This latter procedure and/or the corresponding systems
admittedly have an extremely high detection accuracy but they are
also correspondingly expensive in that they are autonomous as
mentioned above, with each test station being equipped with the
necessary evaluation electronics.
SUMMARY OF THE INVENTION
[0006] The goal of the present invention is to provide a container
tightness tester of the species recited at the outset in which, on
the one hand, the detection accuracy with respect to the latter
systems is reduced only insignificantly if at all, but this can be
accomplished at a much lower expense. For this purpose, the system
of the species recited at the outset is characterized by a common
evaluation unit provided for several of the pressure sensors and,
in addition, a multiplexer unit clocked by a timer is connected
between one input of the common evaluation unit and the outputs of
pressure sensors.
[0007] In testing the tightness of filled containers, especially
those filled with a liquid filing, as described in detail in the
additional U.S. application Ser. No. 08/944,183, now U.S. Pat. No.
5,962,776, issued Oct. 5, 1999, filed at the same time as the
present application (a copy of which application was filed herewith
as Attachment A), there is the problem that when there is a vacuum
in the vicinity of the container, it is difficult to detect a leak
in the parts of the wall that are contacted by the liquid filling.
The liquid that escapes to the outside in this case has a
practically self-sealing effect. A reliable tightness test for such
containers is only guaranteed if a leak occurs in a wall area
opposite an air inclusion inside the container. For this reason, in
the abovementioned application (Attachment A) filed at the same
time it is proposed simultaneously with testing of tightness by
observing the pressure in the environment of the container, to
perform an impedance measurement directly at the wall of the
container, in view of the fact that escaping liquid immediately
causes a change in impedance at a measurement point located between
at least one pair of measuring electrodes.
[0008] With this in mind, it is now proposed to provide at least
one pair of electrodes in a receiving chamber for at least one
container when testing containers filled with liquid filling, said
electrodes being spaced and exposed and provided centrally for all
test stations, and connected operationally in turn by a multiplexer
unit with the respective electrode pairs. This makes it possible to
provide both an evaluation unit for pressure-detecting testing as
well as an evaluation unit for central impedance detection testing
for all the test stations provided on the carousel and to multiplex
the respective pressure sensor and impedance measurement section
outputs on a time-staggered basis to the corresponding evaluation
units over time.
[0009] In another preferred embodiment of the evaluation unit that
is connected to the electrodes and the evaluation unit that is
operationally connected with the pressure sensors, one and the same
central evaluation unit is used. This is readily possible in that
pressure sensors usually deliver a voltage signal, especially
during DC resistance measurement as impedance measurement. A
measurement circuit equipped with the variable resistance to be
measured, such as a voltage divider, can likewise be readily
designed so that the resistance-dependent output signal is a
voltage signal. By virtue of this procedure, the cost of
simultaneous pressure and impedance testing is especially low.
[0010] The possibility is also provided for implementing the
multiplexer units connected between the impedance measurement
sections and the evaluation unit on the one hand and the
multiplexer units provided between the pressure sensors and the
evaluation unit on the other hand by a single common
correspondingly time-controlled multiplexer unit, which switches
the number of inputs that corresponds to the pressure sensor and
impedance measurement sections to a single output for the central
evaluation unit provided.
[0011] In W094/05991 of the same applicant, as the present
application, a pressure tightness measurement method is explained
in detail in which the output from a pressure sensor is connected
at a first point in time to both outputs of a differential unit.
The possibly amplified output signal from the differential unit is
interpreted as a zero-offset signal and stored. During pressure
detection at a second point in time, the previously stored
zero-offset signal is connected as a zero-compensation signal
making it possible with high amplification to evaluate the
corresponding pressure differential-signal electrically.
[0012] This procedure can also be used in the system according to
the present invention, with the evaluation unit being so designed
that an input signal-dependent signal that appears at the first
point in time is stored as the zero-reference signal value and
later supplied as the zero compensation signal. At a second,
subsequent point in time, an additional input-dependent signal,
possibly amplified, is evaluated as the evaluation signal relative
to the compensated zero value as a differential. This procedure can
be used for both evaluations when pressure sensor evaluation and
impedance evaluation are present at the same time, since, as far as
impedance measurement is concerned as well, which after all depends
on an impedance difference measurement, the impedance difference
that arises can occur with reference to the exact compensated zero
reference.
[0013] The invention will now be described using the figures as
examples.
BRIEF DESCRIPTION OF THE DRAWINGS
[0014] FIG. 1 is a signal flow/functional block diagram of a
container tightness tester according to the invention in which the
tightness test is performed on the basis of a pressure measurement
at the respective test stations;
[0015] FIG. 2 in a diagram similar to that in FIG. 1 shows the
improvement in the system according to the invention for tightness
testing using both pressure and impedance measurements; and
[0016] FIG. 3 shows an example of the time curve of the test
pressure or test resistance and a preferred procedure for signal
evaluation.
DETAILED DESCRIPTION OF EMBODIMENTS
[0017] According to FIG. 1, on a carousel (not shown), a plurality
of test stations, n for example, 1.sub.1, 1.sub.2, . . . , 1.sub.n
is provided. They are arranged linearly in the figure for the sake
of simplicity and on the carousel they are arranged along the
periphery of the carousel.
[0018] Each test station I has at least one corresponding pressure
sensor 3.sub.1, 3.sub.2, 3.sub.3, . . . , 3.sub.n associated with
it. Pressure sensors 3.sub.x each deliver an electrical signal,
correspondingly p.sub.1 to p.sub.n, that depends on the leakage in
at least one container located in the respective test station
1.
[0019] Stations 1.sub.x and the pressure sensors 3.sub.x associated
with them can be the following stations:
[0020] a) Holding stations for tight sealing of open containers, at
which an internal pressure, overpressure, or vacuum is provided
relative to the ambient pressure. The associated pressure sensor in
this case measures the leak-dependent internal pressure of such a
container.
[0021] b) Closed containers are placed in a tightness-testing
chamber at station 1.sub.x or are closed in a sealing fashion by
the latter, with the containers being full or empty. A pressure
differential is created between the interior of the container and
the surrounding chamber space, by either a vacuum or a positive
pressure being applied to the interior of the container and/or
pressure or a vacuum being applied to the ambient pressure space.
The associated pressure sensor measures the pressure curve inside
the container or in the test chamber. This procedure is usually
employed for closed, filled containers. The test chamber is
subjected to a vacuum, based on the internal pressure of the
container, and the pressure buildup in the chamber space
surrounding the container is recorded using the associated pressure
sensor.
[0022] According to FIG. 1, the electrical outputs of sensors
3.sub.x are connected to a multiplexer unit 5 which, controlled by
a timer 7, sequentially connects one pressure sensor after the
other to an evaluation unit 9, corresponding to signals p.sub.1..n.
At evaluation unit 9, each connected leak-dependent signal p.sub.1
to p.sub.n is evaluated sequentially and output A.sub.9 gives a
reading corresponding to the preset threshold values for these
signals, which shows in which of stations 1.sub.x a container found
to be leaking is located. Of course, a comparator unit is provided
for this purpose on evaluation unit 9, said comparator unit having
the threshold value input into it for the selection leaking/not
leaking and a storage unit can be connected on the output side of
the comparator unit for recording those test stations whose sensor
output signals indicate leakage of the containers inside them.
[0023] In this manner, a situation is created such that a number of
test stations that corresponds to the size of the carousel, each
with a corresponding pressure sensor, can be handled by a single
evaluation unit.
[0024] As mentioned at the outset, especially when containers
filled with a liquid filling are tested for tightness according to
the principle described briefly above under b), and as explained in
detail in the simultaneously submitted application Ser. No.
08/944,183, now U.S. Pat. No. 5,962,776, issued Oct. 5, 1999,
(Attachment A) of this applicant, problems arise that can be
eliminated by simultaneous pressure and impedance evaluation,
directly outside the container.
[0025] In FIG. 2 of the invention according to the present
application, a system suitable for the purpose analogous to the one
in FIG. 1 is shown schematically. Accordingly, each of test
chambers 1.sub.1 to 1.sub.n in addition to at least one pressure
sensor 3.sub.1 to 3.sub.n has an impedance measurement section with
at least two electrodes, shown schematically in FIG. 2 by 11.sub.1
to 11.sub.n. Using the impedance measurement sections containing at
least two tapping electrodes in the test chambers of test stations
1.sub.x, located directly on the outside wall of the individual
containers to be tested, a determination is made whether liquid
filling is escaping to the outside through a provided leak, said
filling being driven outward by a vacuum created in the test
chamber relative to the pressure inside the container.
[0026] According to the principle in FIG. 1, the electrical outputs
with signals p.sub.1 to p.sub.n are connected to multiplexer unit
5.sub.p, while the outputs of impedance measurement sections
11.sub.x are connected to another multiplexer unit 5.sub.R. The
outputs with signals p.sub.1 to p.sub.n and R.sub.1 to R.sub.n
according to FIG. 2 are connected to their respective evaluation
units 9.sub.R and 9.sub.p. Again, in sequence, the signals
connected at the individual evaluation units are measured at a
predetermined threshold value and then an output signal A.sub.R or
A.sub.p is output that indicates the chambers 1 in which a
container found to be leaking is located. If leakage-identifying
signals are picked up with this system configuration at one of the
two evaluation units, i.e. for pressure and/or for impedance, the
corresponding container is determined to be leaking and the
corresponding chamber number is stored.
[0027] Impedance measurement is usually performed as DC resistance
measurement. Because pressure sensors normally deliver a voltage
signal that depends on the detected pressure, and it is readily
possible to perform a resistance measurement such that the
resistance-dependent signal is a voltage signal, as shown by the
dashed lines in FIG. 2, in another preferred embodiment, in
addition to a single multiplexer 5.sub.pR a single evaluation unit
9.sub.pR is provided in particular, with multiplexer 5.sub.pR being
connected by a single output to the input of evaluation unit
9.sub.pR provided. A timer unit (not shown here) switches to the
combined evaluation unit depending on whether a
pressure-measurement signal or a resistance-measurement signal is
connected at the moment, for example a corresponding pressure
threshold value or a corresponding resistance threshold value as a
basis for comparison, and the two test signals which arrive
sequentially and relate to a single chamber are stored on an
intermediate basis for subsequent evaluation, as can be done
without difficulty.
[0028] In W094/05991 of the same applicant as the present
invention, a procedure for pressure testing is described that
allows the resolution obtained to be drastically increased, in
other words very small leaks can be detected. In this regard,
express reference is made to the contents of this document. In FIG.
3, the principle described in the abovementioned WO is shown
briefly and it is explained how this is integrated into the system
that forms the basis of this application.
[0029] Below time axis t in FIG. 3 the curve of a recorded pressure
or of a resistance value R.sub.x recorded in measurement sections
11.sub.x is shown. This curve is to be understood as purely
qualitative. Basically, the presence of a leak means that a vacuum
produced in the test chamber decreases too sharply with time,
because pressure equalization between the interior of the container
and the volume of the test chamber takes place, while a filling
liquid escaping through a leak usually causes a decrease in the
detected resistance directly at the container wall. According to
FIG. 3, following the principle explained above, at each chamber of
stations 1.sub.x at a first point in time t.sub.1x, the pressure
value or the resistance value which then prevails is recorded. This
signal value is stored and supplied on the evaluation unit, to both
inputs of a differential-forming unit provided therein. Under ideal
compensation conditions, on the output side of the
differential-forming unit and following amplification, the signal
"zero" should appear. A signal that differs from zero is
interpreted as a zero point deviation and likewise stored. At a
second subsequent point in time t.sub.2x, another pressure or
resistance value is recorded. The value recorded at the second
point in time is compared with the one recorded and stored at the
first point in time, with the likewise detected zero point
deviation signal being taken into account depending on the sign
before it. The comparison result .DELTA..sub.p or .DELTA..sub.R can
now be evaluated with high amplification without error. If this
procedure is performed using the system according to FIG. 1 or FIG.
2, as is readily apparent, the provided measurement sections,
whether they are the pressure sensor and/or the impedance
measurement sections, are scanned sequentially at first and second
points in time, with this being performed by appropriately
controlling the multiplexers provided. It is not necessary under
these conditions that the scans be performed immediately following
one another according to t.sub.1x and t.sub.2x in FIG. 3. Depending
on the optimization of the time ratios, for example, all the
t.sub.1x values can be recorded first, and stored accordingly, and
then all the t.sub.2x values for evaluation.
[0030] In this case also, the entire evaluation can be performed
using a single evaluation unit whose input is supplied with the
pressure and impedance values that were interrogated on a time
sequence basis. In this manner, even more complex interrogation
rhythms and correspondingly high leakage resolutions can be
accomplished with a single evaluation unit and a multiplexer unit
connected upstream from it.
* * * * *