U.S. patent application number 11/120187 was filed with the patent office on 2006-01-26 for method for controlling a vacuum packaging machine and vacuum packaging machine.
Invention is credited to Andreas Oesterlein.
Application Number | 20060016155 11/120187 |
Document ID | / |
Family ID | 34936033 |
Filed Date | 2006-01-26 |
United States Patent
Application |
20060016155 |
Kind Code |
A1 |
Oesterlein; Andreas |
January 26, 2006 |
Method for controlling a vacuum packaging machine and vacuum
packaging machine
Abstract
In a method for controlling the evacuation process in a chamber
to be evacuated in a vacuum packaging machine, the switching time
starting with initiation of the evacuation process until reaching a
specified threshold value or switching pressure (p.sub.s) is
determined, then the evacuation time required for reaching a
desired ultimate pressure is extrapolated from this switching time
and the evacuation process is terminated upon reaching this
evacuation time.
Inventors: |
Oesterlein; Andreas;
(Duggendorf, DE) |
Correspondence
Address: |
Stewart L. Gitler;HOFFMAN, WASSON & GITLER, P.C.
Suite 522
2461 South Clark Street
Arlington
VA
22202
US
|
Family ID: |
34936033 |
Appl. No.: |
11/120187 |
Filed: |
May 3, 2005 |
Current U.S.
Class: |
53/432 ;
53/510 |
Current CPC
Class: |
B65B 31/02 20130101 |
Class at
Publication: |
053/432 ;
053/510 |
International
Class: |
B65B 31/02 20060101
B65B031/02 |
Foreign Application Data
Date |
Code |
Application Number |
May 6, 2004 |
DE |
10 2004 023 025.0 |
Sep 11, 2004 |
DE |
10 2004 044 077.8 |
Claims
1. A method for controlling the evacuation process in a processing
chamber of a vacuum packaging machine, wherein the switching time
starting with initiation of the evacuation process until reaching a
specified threshold value or switching pressure (p.sub.s) in the
processing chamber is determined, and then the evacuation time
required for reaching a desired ultimate pressure is extrapolated
from this switching time and that the evacuation process is
terminated when reaching this evacuation time.
2. A method for controlling gas injection in a processing chamber
of a vacuum packaging machine, wherein switching time starting with
initiation of the evacuation process until reaching a specified
threshold value or switching pressure (p.sub.s) in the processing
chamber is determined, then an evacuation time required for
reaching a desired ultimate pressure is extrapolated from this
switching time and the evacuation process is terminated upon
reaching this evacuation time.
3. The method according to claim 1, wherein after initiation of the
evacuation process, the switching times are determined until one
first and at least one second switching pressure (p.sub.s) are
reached, and the evacuation time or gas injection time is then
extrapolated from these switching times.
4. The method according to claim 1, wherein the evacuation time is
determined using a formula that takes into account a typical,
exponential curve of the evacuation process.
5. The method according to claim 1, wherein the evacuation time is
determined using data or data sets stored in a memory of an
electronic measuring and/or control unit.
6. The method according to claim 1, wherein a total time T.sub.ges,
after which the evacuation process is terminated, is determined by
the following function: T.sub.ges=K.times.F.times.t.sub.s, where K
is a constant, t.sub.s is the time until the pressure threshold
value is reached and F is a factor which is stored as a function of
t.sub.s in tabular form in the memory of an electronic measuring
and control unit that controls a vacuum source or a vacuum
pump.
7. The method according to claim 1, wherein the pressure in one
processing chamber of the packaging machine is measured with the at
least one sensor.
8. The method according to claim 1, wherein during the evacuation,
a switching pressure (p.sub.s) is a multiple, at least
approximately 10 times greater than an ultimate pressure.
9. The method according to claim 2, wherein during the gas
injection, a switching pressure (p.sub.s) is a multiple, at least
approximately 10 times less than an ultimate pressure.
10. A vacuum packaging machine with at least one processing chamber
to which a vacuum or negative pressure can be applied during an
evacuation process, with at least one sensor designed as a pressure
switch that responds to the pressure in the processing chamber, and
with one control unit that controls the evacuation process based on
the signal from the sensor, wherein the sensor has a first and a
second electric state and switches from the first state to the
second state upon reaching a threshold or switching pressure
(p.sub.s) in the processing chamber, the electronic control and
analysis unit comprises means for measuring the switching time
between the initiation of the evacuation process and the response
of the at least one sensor upon reaching the switching pressure
(p.sub.s) in addition to further means to create a time signal for
terminating the evacuation process based on the at least one
switching time and taking into account a specified or configured
ultimate pressure.
11. The vacuum packaging machine according to claim 10, wherein for
controlled gas injection, the electronic control unit comprises
means for measuring the switching time between the initiation of
the gas injection and the response of the at least one sensor upon
reaching the switching pressure (p.sub.s) in addition to further
means to create a time signal for terminating the gas injection
based on the at least one switching time and taking into account a
specified or configured ultimate pressure.
12. The vacuum packaging machine according to claim 10, wherein at
least two sensors, which respond at different switching pressures
(p.sub.s) and therefore at different switching times (t.sub.s), and
that the electronic control and analysis unit creates the time
signal for terminating the evacuation process taking into account
the at least two switching times (t.sub.s).
13. The vacuum packaging machine according to claim 10, wherein the
electronic control and analysis unit comprises at least one memory,
in which typical data is stored for the time of the evacuation
process or of the gas injection depending on the at least one
switching time (t.sub.s).
14. The vacuum packaging machine according to claim 10, wherein the
electronic control and analysis unit determines the total time
T.sub.ges after which the evacuation process is terminated, by the
following function: T.sub.ges-K.times.F.times.t.sub.s, where K is a
constant, t.sub.s is the time until the pressure threshold value is
reached and F is a factor which is stored as a function of t.sub.s
in tabular form in the memory of an electronic measuring and
control unit that controls a vacuum source, or a vacuum pump.
Description
BACKGROUND OF THE INVENTION
[0001] The invention relates to a method for controlling a vacuum
packaging machine and to a vacuum packaging machine.
[0002] The following methods have been in use thus far for
controlling the evacuation process in vacuum packaging
machines:
[0003] The simplest method used is time control, i.e. the
evacuation process is positively ended after a specified time,
which can be pre-selected at the machine, for example. The end
result obtained by this method is very imprecise. The inaccuracy of
this purely time-controlled process results from a number of
parameters that affect the progression of the evacuation process,
in particular also from the fact that the chamber volume changes
depending on the quantity of goods inserted for packaging, and due
to insertion or removal of compensating plates, etc. In order to
attain a specific vacuum with this method, it is necessary to set
the evacuation time somewhat higher, however with the disadvantage
of a significant reduction in the efficiency of a vacuum packaging
machine (number of packaged units per time unit).
[0004] A further known method consists in terminating the
evacuation process upon reaching a pressure indicated on a
measuring instrument (vacuum gauge). The essential disadvantage of
this method consists in the fact that the very low pressure at the
end of the evacuation process (ultimate pressure) can be measured
only very inaccurately with such instruments.
[0005] A further known method is the use of sensor controls, in
which the prevailing pressure in one of the chambers of the
packaging machine is constantly monitored by a sensor in order to
control the evacuation process. Suitable sensors and the
corresponding analysis electronics are expensive and especially
also susceptible to breakdowns.
[0006] It is an object of the invention to provide a method which
enables the optimized control of the evacuation process and gas
injection process in a vacuum packaging machine.
SUMMARY OF THE INVENTION
[0007] In the invention, the evacuation process and/or the gas
injection are controlled based on the signal of one single sensor,
which depending on the type of sensor, switches from one state to a
second state, as soon as the pressure in the evacuated or
gas-injected chamber has reached a specified threshold value or
switching pressure. The switching pressure during the evacuation is
considerably higher than the desired ultimate pressure. For
example, the switching pressure is on the order of 200 mbar, while
the desired ultimate pressure is 20 mbar or 2 mbar.
[0008] Based on the elapsed time or time period between the
initiation of the evacuation process or of the gas injection and
the point at which the switching pressure is reached (switching or
response time), the evacuation time required until the desired
ultimate pressure is reached or the entire evacuation time or gas
injection time is determined by an electronic control and analysis
unit. This time is then used, for example, to set a timer in the
electronic control and analysis unit so that the evacuation or gas
injection process is terminated after the evacuation time or gas
injection time has elapsed.
BRIEF DESCRIPTION OF THE DRAWINGS
[0009] The invention is described in more detail below based on an
exemplary embodiment with reference to the drawings, wherein:
[0010] FIG. 1 shows a very simplified schematic representation of a
vacuum packaging machine; and
[0011] FIG. 2, illustrates the control of the evacuation process,
shows the time-pressure curve during evacuation of the chamber of
the packaging machine, with different parameters, such as chamber
volume and/or air humidity and/or air temperature and/or state of
the packaging machine, etc.
DETAILED DESCRIPTION OF THE INVENTION
[0012] The vacuum packaging machine 1 depicted very schematically
in FIG. 1 and used for packaging foods in vacuum-tight packages or
containers 2, has a vacuum chamber 3 located in a packaging line,
in which the containers 2 to be packaged are inserted and then
sealed after evacuation. The vacuum chamber 3 is connected by means
of a vacuum line 4 with a source for the vacuum, e.g. with a vacuum
pump 5.
[0013] The evacuation time is controlled by means of an electronic
analysis and control unit 6 and the signal of a pressure sensor 7,
which in the depicted embodiment is provided at the vacuum chamber
3 and responds to the prevailing negative pressure in the vacuum
chamber 3. Of course, the sensor 7 can also be located elsewhere,
for example in the vacuum line 4 or in a separate measuring line
connected with the interior of the chamber 3.
[0014] The sensor 7 is designed as a simple switch that responds to
a negative pressure or a threshold pressure or a switching pressure
p.sub.s and that upon reaching the pressure p.sub.s switches from
one electrical state to a second electrical state, e.g. switches on
or off. The sensor 7 consists, for example, of a mechanical
pressure measuring element that works together with a switch, said
measuring element being, for example, a pressure cell or a cylinder
pressurized by spring force or a curved tube (tube spring), which
changes its radius of curvature depending on the inner pressure.
Other designs are also conceivable.
[0015] FIG. 2 shows three different curves, which are designated
there as "Evakuiervorgang x, Evakuiervorgang y, Evakuiervorgang z"
means "evacuation process x, evacuation process y and evacuation
process z" and which depict the curve of the pressure in chamber 3
in dependence on the time during the evacuation process. The
progression of these curves varies depending on various parameters,
e.g. volume of the chamber 3, air humidity, air temperature, state
of the packaging machine and in particular of the pump 5.
[0016] Independent of this, all the curves have in common that the
reduction of the pressure P in chamber 3 always takes place
exponentially in dependence on the evacuation time. This enables a
very simple control of the evacuation process, namely in that after
initiation of the evacuation process, at the time t.sub.o the
switching time t.sub.s is measured at which the pressure p.sub.s is
reached and the sensor 7 responds or sends a sensor signal to the
electronic analysis and control unit 6.
[0017] The switching times are designated for the various
progression of the evacuation in FIG. 2 with the additional index
x, y and z, i.e. t.sub.sx, t.sub.sy and t.sub.sz. Taking into
account the switching time within which the sensor 7 responds after
initiation of the evacuation process, i.e. the difference between
the time t.sub.s and the time t.sub.o, and taking into account the
basic progression of the pressure-time curve of the evacuation
process, the time can then be determined at which a desired
ultimate pressure, for example a pressure of 20 mbar or 2 mbar, is
reached and at which the evacuation process can be terminated. The
switching pressure p.sub.s at which the sensor 7 responds, is for
example 200 mbar and therefore considerably above the desired
ultimate pressure, which is for example only 10% or less than the
switching pressure.
[0018] This means that the control of the evacuation process is
purely a time control, however not a positive control but rather a
control in which the termination of the evacuation process is
determined taking into account the switching time until the
pressure p.sub.s is reached and taking into account the basic
exponential pressure-time curve. This type of control takes into
account not only the parameters defined by the design of the
packaging machine 1, e.g. volume of the chamber 3 and flow volume
of the vacuum pump 5, but also changing parameters, such as air
humidity, air temperature, changes in the state of the machine,
e.g. of the vacuum pump 5.
[0019] Based on these parameters, the following time values can be
derived for reaching the switching pressure p.sub.s:
[0020] Evacuation process x: duration of the evacuation of
atmospheric pressure to p.sub.s e.g. 6 seconds
[0021] Evacuation process y: duration of the evacuation of
atmospheric pressure to p.sub.s e.g. 8 seconds
[0022] Evacuation process z: duration of the evacuation of
atmospheric pressure to p.sub.s e.g. 10 seconds
[0023] If a vacuum or negative pressure of 20 mbar is desired, for
example, then the total evacuation time is as follows:
[0024] Evacuation process x: total evacuation time e.g. 15
seconds
[0025] Evacuation process y: total evacuation time e.g. 20
seconds
[0026] Evacuation process z: total evacuation time e.g. 25
seconds
[0027] If a vacuum or negative pressure of 2 mbar is desired, for
example, then the total evacuation time is as follows:
[0028] Evacuation process x: total evacuation time e.g. 30
seconds
[0029] Evacuation process y: total evacuation time e.g. 40
seconds
[0030] Evacuation process z: total evacuation time e.g. 50
seconds
[0031] The time for which the evacuation process is maintained
after reaching the switching pressure p.sub.s until the termination
of the evacuation process is then determined for example in the
control unit 6 taking into account the switching time t.sub.s that
elapses until the switching pressure p.sub.s is reached and taking
into account the desired pressure (e.g. 20 mbar or 2 mbar) at the
end of the evacuation process, namely taking into account an
algorithm stored in the control unit or using data stored in
tabular form in memory 6.1 of the control unit 6, e.g. data or data
sets in tabular form that contain the total evacuation time as a
function of the switching time.
[0032] In detail, the control takes place so that the total time
T.sub.ges of the evacuation process, i.e. the total time from
switching on of the vacuum pump until switching off of the pump is
based on a definite function, namely:
T.sub.ges-K.times.F.times.t.sub.s,
[0033] where K is a constant, for example with the value of 0.5 or
1.0 and F is a factor, which in turn is a function of the time
t.sub.s, so that a specified ultimate pressure is reached at
switching off of the vacuum pump at a specified value for the
factor F independent of the fill volume of the vacuum chamber and
therefore independent of the volume of air to be evacuated from the
chamber. For this purpose, the values determined, e.g. by
measuring, for the factor F for different times t.sub.s and for the
particular model of the packaging machine are stored in tabular
form in the memory 6.1 of the electronic measuring and control unit
6.
[0034] In a preferred embodiment the vacuum that is reached at the
time when the vacuum pump is switched off can be set for different
applications of the packaging machine, for example by means of an
adjusting device, e.g. a rotary knob etc., by changing the factor F
progressively or incrementally so that the vacuum corresponding to
the respective setting is reached independent of the fill level of
the vacuum chamber 3, i.e. independent of the volume of air to be
evacuated. In this embodiment also the values for different factors
F allocated to a particular vacuum are stored in tabular form for
different times t.sub.s in the electronic measuring and control
unit 6 or in memory 6.1 there.
[0035] The logic of the electronic measuring and control unit 6 is
designed so that in case a measured time t.sub.s does not exactly
correspond to a time value stored in the table, the next higher
time value t.sub.s and its corresponding factor F stored in the
table are used for calculating the total time T.sub.ges.
[0036] Furthermore, the logic of the electronic measuring and
control unit can also be designed for calculation of intermediate
values from values stored in the table.
[0037] The invention was described above based on an exemplary
embodiment. It goes without saying that numerous modifications are
possible without abandoning the underlying inventive idea upon
which the invention is based.
[0038] Instead of only one sensor 7, for example, it is possible to
provide two or more such sensors, which then switch or respond at
different switch pressures p.sub.s, so that by determining two or
more switching times t the expected curve of the evacuation process
can be calculated or extrapolated even more precisely, resulting in
further optimization of the control of the evacuation process.
[0039] The measurement of the time t starts for example at
atmospheric pressure, e.g. by means of a contact or sensor upon
closing of the chamber 3, or after closing of the chamber and
switching on of the vacuum pump, upon reaching a specified initial
pressure threshold value.
[0040] Furthermore, a measurement of the changing sound level
dependent on the pressure is possible.
[0041] For facilities or machines with gas injection, the method
according to the invention can also be executed in reverse manner.
The invention was described above in connection with a vacuum
packaging machine, in which the evacuation process takes place in a
chamber 3. Other designs are also conceivable.
[0042] Furthermore, it was assumed above that the control of the
evacuation process, i.e. the beginning and the end of the
evacuation process, takes place by controlling the vacuum pump 5.
Generally it is also possible to control the evacuation process by
providing a valve arrangement, which is used to connect the
interior of the chamber 3 with the vacuum source, i.e. with the
pump 5, for initiating the evacuation process and then to
disconnect the interior of the chamber 3 from the vacuum source and
connect it with the atmosphere upon termination of the evacuation
process.
REFERENCE NUMBERS
[0043] 1 vacuum packaging machine
[0044] 2 package
[0045] 3 chamber
[0046] 4 vacuum line
[0047] 5 vacuum pump
[0048] 6 electronic measuring and control unit
[0049] 6.1 memory
[0050] 7 sensor responding to a switching pressure ps
* * * * *