Note: Descriptions are shown in the official language in which they were submitted.
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METHOD FOR TESTING CONTAINERS, USE OF THE METHOD,
AND A TESTING DEVICE
This invention pertains to a method for manufacturing
tight containers and a testing device and arrangement for
testing containers.
This invention pertains to a testing device such as is
known from US-PS 5,029,464 and EP-A-O 313 678 and
EP-A-O 432 143.
From these items a way is known that a pressure
differential is to be created between a pressure in the
interior of the container and a pressure in said container's
environment in order to test the gas tightness of containers
and, from the behavior of one of the pressures, it is to be
established whether the container under test satisfies the
gas-tightness conditions or volume conditions or not.
In this process the container to be tested is placed in
a sealing chamber that is connected to a pressure medium
source or a suction source; said arrangement is_to be used to
create the above-mentioned pressure differential. After the
pressure differential is created, a pressure value for the
environment of the container is stored as a starting
condition in a reference pressure chamber, which is placed in
front of a pressure differential sensor, and is compared with
subsequent pressure values for the environment of the
container.
The above-mentioned documents are thus declared to be an
integral part of the present description.
A drawback to the known method is the fact that a
pressure differential sensor with extremely accurate control
valves must be provided to ensure that even very small leaks
or slight deviations of the container volume from a nominal
volume are detected.
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The goal set for the present invention is to simplify
this known method significantly. The present invention
accordingly provides a method for manufacturing containers
which are tested on predetermined test conditions, in which
containers are construed and a pressure difference is created
between a pressure inside the container and a pressure in its
environment, and from the behavior of one of the pressures it
is established whether the container satisfies predetermined
test conditions, wherein, after said one of the pressures
reaches a predetermined test value as said pressure
difference is being created and after creation of said
pressure differences, in an equalization phase said one of
said pressures rereaches said predetermined test value, the
change in pressure of said one of the pressures is measured
with a pressure sensor and with respect to said predetermined
test value immediately after the time at which said one of
said pressures rereaches said predetermined test value and
utilizing results of said measuring for establishing whether
the container satisfies said predetermined test conditions.
The present invention also provides a test arrangement
for testing containers, said arrangement comprising a
pressure or suction source, which can be effectively
connected to a container to be tested with respect to its
interior and exterior pressure for creating a pressure
difference between said interior and exterior pressures, at
least one pressure sensor, an electronic pressure-value
storage arrangement and a comparator unit, wherein the
pressure sensor is a converter that converts an input-side
pressure value into an output-side electrical signal, and
means for feeding the output of the sensor, on the one hand,
and the output of said electronic pressure-value storage
arrangement, on the other to said comparator unit to commence
a measuring test interval at a point in time immediately
after the input-side pressure value of said sensor reaches a
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predetermined test value as said pressure difference is being
created and after creation of said pressure difference, in an
equalization phase said one of said pressures rereaches said
predetermined test value.
The present invention further provides a method for
manufacturing a tight container comprising: construing a
container; establishing a differential pressure between a
first pressure in the interior of said container and a second
pressure in the vicinity of said container; monitoring at
least one of said first and second pressures and generating
an electrical monitoring output signal; storing said
electrical output signal at a first moment to generate a
stored signal; comparing said electrical output signal at a
second deferred moment with said stored signal and concluding
from a result signal of said comparing, whether said
container is tight or not; further comparing said stored
signal with said electric output signal at said first moment,
the result signal of said further comparing being exploited
as a zero offset signal.
Accordingly, a pressure differential sensor is no longer
used, nor are pneumatic storage chambers; instead, the
pressure that is of interest is determined by means of a
relative-pressure sensor and converted into an electrical
signal; when checking for leaks, this signal is stored at a
predetermined time and compared with at least one subsequent
value that is determined by this same sensor. When checking
volume, a pressure value is pre-specified and stored as a
basis for comparison. This obviates the need for awkward
devices of the previously known type, namely the pressure
differential sensor and, in particular, the stop valves that
are quite difficult as regards control characteristics.
The method of the invention is implemented in a
configuration wherein an electrical output signal of the
sensor is compared to one or more predetermined values, e.g.,
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on a computer into which the sensor output is entered. A
value of the sensor output signal is stored as a pressure
value. Either the pressure in the interior of the container
or that in the environment of the container is increased or
decreased, and a value of the pressure in the container or in
the environment of the container is measured.
In a preferred embodiment, both the source connection to
admit the pressure medium or to ensure suction and the sensor
input are hooked up to either the interior of the container
or the container's environment.
The creation of the pressure differential can be done in
different ways, with which the specialist is well acquainted
from the above-mentioned documents. Thus, for example, the
pressure differential can be created by carrying out
pressurization or suction at a predetermined level for a
predetermined time, and then analyzing both a pressure value
that is reached and its plot. In addition, pressurization
can be done to a predetermined pressure differential, and
then the plot of the pressure value that is of interest can
be observed.
As is known from the above-mentioned documents,
pressurization can also be accomplished by precharging a pre-
chamber to a predetermined pressure and then discharging said
chamber into the container or into an enclosure that is
formed by a sealable chamber.
When checking volume, a volume that is dependent on the
volume of the container, either the interior volume of said
container itself or its volume differential compared to a
testing chamber, can be pressurized by a predetermined
quantity of pressure medium, or a predetermined amount of gas
can be removed from this volume. The volume of the container
is then determined from the resulting pressure.
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Of course, the values that are measured are compared
with nominal values or nominal plots, as is also known from
the above-mentioned documents.
Storage, wherein the pressure in the environment of the
container is increased or decreased and a value of the
pressure of the environment of the container is measured, is
preferably undertaken in such a way that, with control at a
predetermined time, an analog/digital converter is enabled to
convert the sensor output signal, and the then stationary
output signal of this analog/digital converter is used as a
reference value for the subsequent analysis of the sensor
output signal. In this process, either another
analog/digital converter can be installed behind the sensor
output and the output signal of the latter converter can then
be digitally compared to that of the storage unit A/D
converter or, preferably, a D/A converter is placed
immediately behind the storage A/D converter and thus the
stored, re-converted signal is fed as an analog reference
signal to an analog comparator unit, to which the output
signal of the sensor is also fed directly.
In addition, and wherein the pressure in the environment
of the container is increased or decreased and a value of the
pressure of the environment is measured, a null balance is
preferably undertaken by determining, essentially during the
value storage process at the comparator, whether an output
signal of the device encompasses the null value, at least
approximately; if a signal appears that deviates from the
null value or from a predetermined minimum value, then said
signal is used as a null-balance signal.
Preferred embodiments of the test arrangement of the
invention for testing containers comprise a pressure or
suction source which can be effectively connected to a
container to be tested with respect to its interior and
exterior pressure, at least one pressure sensor, an
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electronic pressure-value storage arrangement and a
comparator unit. The pressure sensor is a converter that
converts an input-side pressure value into an output-side
electrical signal. Means are provided for feeding the output
of the sensor, on one hand, and the output of the electronic
pressure-value storage arrangement, on the other to the
comparator unit to commence a measuring test interval at a
point in time immediately after the input-side pressure value
of the sensor reaches risingly a predetermined test value and
rereaches the predetermined test value diminishingly.
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The invention is hereinafter explained by way of
examples, using figures.
Here:
Fig. 1 shows a schematic of an arrangement of the
invention, in which the pressurization source and
suction source are connected to the environment of
the container;
Fig. 2 shows a schematic, as per Fig. 1, of a section of
the system as shown in Fig. 1, in another
embodiment;
Fig. 3 similar to Fig. 2, shows the section of a third
embodiment;
Fig. 4 similar to Fig. 2, shows the section of another
preferred embodiment;
Fig. 5 shows a functional block diagram of a preferred
arrangement as described by the invention for
implementing a test method of the invention;
Fig. 6 provides a purely schematic illustration of the plot
of a measurement curve.
As mentioned, Fig. 1 schematically depicts a closed
container 1 that is to be checked for leaks or to determine
its volume; said container may, for example, be already filled
and be in a testing chamber 3. Chamber 3 can be sealed by
means of, for example, insert cover 5. Via a controlled
valve 7, the test volume, here the volume differential between
chamber 3 and container l, is pressurized by means of a
suction or pressure source 9 in such a way that a pressure
gradient is created across the walls of container 1. In this
embodiment, source 9 empties into chamber 3.
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At or in chamber 3 is another relative-pressure sensor
11, which converts the input-side pressure value into an
electrical output signal. Via a storage control circuit, as
indicated in the schematic by S, electrical output signal el
from sensor 11 is stored in a storage unit 13 in response to
a control signal s that is emitted by a time control unit
(not shown). Output signal elofrom storage unit 13 is fed to
a comparator unit 15 as a pressure reference value. Output
signal el of sensor 11 is present directly at said comparator
unit's second input. After reference value elo is stored,
the plot of the pressure in chamber 3 is monitored at
compa~ator unit 15.
Let us now first consider leakage testing. If container
1 is sealed and storage has been done in storage unit 13,
then sensor output signal el will remain at stored value e1o
once all differential-induced shape changes in container 1
have subsided. On the output side of comparator 15, a
comparison result that at least approximately equals zero
indicates that container 1 is sealed.
If leaks are present in container 1, after reference
value elo is stored as mentioned signal value el will vary
depending on the direction of the pressure gradient across
the container wall; the higher the rate of variation, the
larger the leak. On the output side of comparator 15 there
will be an output signal. The value of this output signal is
a function of the change in pressure in chamber 3 from the
reference pressure associated with the stored pressure
reference value elo.
Comparing the output signal of comparator unit 15 with
predetermined nominal values (not shown) provides an
indication, on the one hand, as to whether a leak is present
as well as, on the other, as to how large said leak is.
Depending on the containers to be tested, minor leaks may be
tolerated.
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If the leak in container 1 is large, then absolutely no
pressure differential will develop across the walls of
container 1: the pressures between the interior of the
container and its environment will quickly equalize via the
leak. Then, however, on the output side of comparator 15 a
null signal will appear, i.e., just as in the case of a sealed
container, and lead to testing errors.
Therefore, as indicated by the dotted lines; preferably
after value elo is stored in storage unit 13, this stored value
is compared to a reference value ref at another comparator
unit 17. The output signal of other comparator unit 17
indicates whether a large leak is present or not. Either when
a predetermined amount of pressure medium is allowed to enter
chamber 3 or when a predetermined amount of gas is removed
from said chamber, in the case of a large leak the pressure
value indicated by reference value ref will not be reached;
this will cause the test result at container 1 to be indicated
by the output signal of other comparator 17.
To test volume, a predetermined amount of pressure medium
is fed to chamber 3 or a predetermined amount of gas is
removed therefrom. As indicated by dotted lines at refs,
storage unit 13 is used here as a reference-value storage unit
in which reference values corresponding to the nominal volumes
of containers that are to be tested are prestored. By
comparing above-mentioned volume reference values refs and the
pressure value that actually arises corresponding to el in the
volume differential in chamber 3 that is dependent on the
interior volume of container 1, i.e., from the output signal
of comparator unit 15, a determination is made as to whether
container 1 has nominal volume or not, or how large the
nominal/actual volume differential is.
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In the case of the embodiment shown in Fig. 2, where the
references used in Fig. 1 are used for the same parts, only
source 9 empties into chamber 3. Via a sealed closure 19,
the input of sensor 11 is connected to the interior of
container 1 that is fitted with an opening. The electronic
analyzer, which is placed behind sensor 11, is depicted just
as in Fig. 1.
As in Fig. 2, Fig. 3 shows another variant in which,
compared to Fig. 2, the arrangements of source 9 and sensor
11 are switched.
In the case of the arrangement shown in Fig. 4, on the
one hand source 9 empties into the interior of a container 1
via sealing connection 19 [and on the other] the input of
sensor 11 is connected to the interior of container 1. The
electronic analyzer shown in Fig. 1, to which sensor 11 is
connected, is provided here as well. The embodiment shown in
Fig. 1 or Fig. 4 is preferably used.
Fig. 5 shows, in the form of a block diagram, a
preferred embodiment of analysis unit I that is partially
outlined with dotted lines in Fig. 1. In the preferred
embodiment, the output signal of sensor 11 is fed to a
converter stage 21, which on the input side comprises an
analog/digital converter 21a, which is immediately followed
by an digital/analog converter 21b. Like the output signal
of sensor 11, the output of digital/analog converter 21b is
fed to a differential amplifier unit 23 that is
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of a known design. The output of differential amplifier unit
23, corresponding to comparator unit 15 of Fig. 1, is
connected to another amplifier stage 25, whose output is
overlaid 28 on the input signal to amplifier 25 via a storage
element 27.
Converter unit 21 and storage unit 27 are controlled via
a timing signal generator 29. This arrangement works as
follows
To store value elo as shown in Fig. 1, from timing
signal generator 29 at measurement point tl in Fig. 6 after
the pressure reaches risingly a predetermined test value 1
and rereaches the predetermined test value diminishingly as
shown in Fig. 6, a conversion cycle at converter unit 21 is
enabled, at which point signal value eloappears at the input
of differential amplifier unit 23. At essentially the same
time, timing signal generator 29 preferably actuates storage
unit 27, causing the output signal value of amplifier 25 to
be fed back as a null-value-balance signal to the amplifier
input. If when value elo was stored the output signal of
amplifier 25 was not equal to zero, then this signal value is
used as a null compensation signal via storage unit 27. By
nulling the signal from amplifier stage 25 at time tl in
Fig. 6, the output signal from amplifier stage 25 from time
tl over the measuring time interval from tl to t2 will be a
function of the change in pressure in chamber 3 from the
reference pressure associated with the stored value e1o at
time ti. Thus, the arrangement permits the direct
measurement of the change in pressure in the chamber during
the measuring time interval tl-tZ using pressure sensor 11,
without the need for use of a reference pressure chamber or a
differential pressure sensor as in the prior art.
As indicated in reference to Fig. 1, the detection of
major leaks can be done in different ways by, e.g., feeding
the output signal value of converter unit 21 to another
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comparator (not shown), where said output signal value is
compared to reference signal value ref as indicated in Fig. 1
or, as indicated by dotted lines at S1, by switching the
differential amplifier output, which is otherwise connected
to sensor 11, to a reference potential, such as to ground,
immediately before or after, and preferably after,
storage unit 27 is set, and then on the output side of
amplifier unit 25 directly testing the value of e1o to
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determine whether said value has reached the reference value
as per ref of Fig. 1 or not.
Unlike what is indicated in the case of the preferred
embodiments mentioned above, it is readily possible to omit
the second converter stage, namely digital/analog
converter 21b, and instead, as indicated at 22b by dotted
lines, to provide an analog/digital converter and then
subsequently to process both signals, i.e., elo and el,
digitally.
To check volume, either volume reference values are pre-
entered at converter unit 21, provided, as indicated by
dotted lines at refs, or another digital storage unit is
connected to digital/analog converter 21b directly in order
to convert input digital volume reference values into the
corresponding analog signals and thus to use the arrangement
shown to perform volume measurement as well.
The unit that is shown is exceptionally well suited for
in-line testing of containers such as in a carrousel conveyor
for, e.g., bottles, plastic bottles, etc.
In principle, it is also possible, after a predetermined
test pressure is reached, to compare the electrical output
signal of the sensor to this value or to several pre-entered
values; this can be done on, e.g., a computer, where the
sensor output is read in. The differential with respect to
the set test pressure, i.e., the pressure drop, is determined
by computer (compared to a boundary value entered into the
computer or to a value that is determined from a reference
leak) .
