Packaging machine and method of forming a vacuum package

The disclosure relates to a packaging machine and to a method of forming a vacuum package. A first evacuable chamber is used for accommodating therein a product-accommodating section of a package, whereas a second evacuable chamber is used for accommodating therein an opening section of the package. Pressure gauges measure the pressure in both chambers, and a supply air valve serves to supply air into the first chamber. The disclosure is characterized in that the supply air valve is a control valve and is adapted to be controlled in dependence upon the difference between the pressures which prevail in the first and second chambers and which are measured by means of the two pressure gauges. The disclosure also relates to the fact that a gap is provided in a partition between the two chambers and that an adjuster is provided for varying and adjusting the cross-sectional area of said gap.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims foreign priority benefits under 35 U.S.C. §119(a)-(d) to German patent application number DE 10 2010 055 438.3, filed Dec. 21, 2010 and EP patent application No. 11 007 717.9, filed Sep. 22, 2011 which are incorporated by reference in their entirety.

TECHNICAL FIELD

The disclosure relates to a packaging machine and to a corresponding method of forming a vacuum package.

BACKGROUND

A packaging machine of the type in question and a method of forming a vacuum package are disclosed by EP 1564147 A1. There, a first and a second evacuable chamber (i.e. a chamber in which a vacuum can be created) are provided. A sealable vacuum bag is introduced in the packaging machine such that a package main section accommodating the packed product is disposed in the first chamber, whereas the opening of the bag is located in a smaller, second chamber. The advantage of this packaging machine is that different vacuums can be created in the two chambers so that the pressure applied to the package from outside is higher than the pressure prevailing in the interior of the package. This higher external pressure stabilizes sensitive products within the package, such as cheese or other porous products, which, if the pressure applied is too low, tend to release bubbles from the porous structures or in which the porous structures tend to burst, whereby the product in question will be damaged. A disadvantage of this conventional packaging machine is that it is comparatively complicated to operate.

Another packaging machine for packaging objects under vacuum is disclosed by DE 3411917 A1. Here, a sealing chamber is divided by the package into a lower chamber and an upper chamber. After creating first a predetermined vacuum, rapid, abrupt venting of the chamber establishes a pressure difference between the inside and the outside space of the package.

SUMMARY

It is the object of the present disclosure to improve a packaging machine and a packaging method for forming a vacuum package with respect to an increased stability of operation and an improvement in the quality of the packaging results.

A first variant of the disclosure is so conceived that the supply air valve is a control valve, which is adapted to be controlled in dependence upon the difference between the pressures in the first and second chambers, which are measured by means of the two pressure gauges, and/or in dependence upon the difference between the pressure prevailing in a chamber and a target final pressure predetermined for this chamber. In the context of the present disclosure, the term “control valve” means that the valve can not only assume a fully open and a fully closed position but also a plurality of intermediate positions at which the control valve is partially open. These intermediate steps can be distributed in the form of discrete opening stages or in a continuous mode between the fully open and the fully closed position. It would also be imaginable that the control valve is continuously adjustable only in a specific range. It differs therefore substantially from the above-cited prior art, where shift valves were used, which could only be adjusted between a fully open and a fully closed position.

Another advantage of the disclosure originates from the fact that the difference of the pressures measured by means of the two pressure gauges in the two chambers is determined and used as an input variable for controlling the supply air valve. The amount of air supplied to the first chamber per unit time therefore depends on this pressure difference. If the pressure difference is small, more air per unit time will be supplied to the first chamber. If the pressure difference is, however, comparatively large, no or at least less air per unit time will be supplied to the first chamber so as to prevent the pressure difference between the two chambers from becoming excessively large. This guarantees that an ideal pressure will always prevail on the outer side of the packages in the first chamber, so that the products will reliably be prevented from being damaged through bursting of porous structures or through bubbles released therefrom. The continuous maintenance of an optimum pressure difference can additionally reduce the processing time during the formation of a vacuum package.

It would be imaginable that the supply air valve is a proportional valve whose opening degree is inversely proportional to the pressure difference in the two chambers. Such a proportional valve allows a continuous adjustment of its opening degree between the fully closed and the fully open position.

The supply air valve may have a linear or a non-linear control curve. In particular a non-linear control curve having a non-linear profile relative to the pressure difference between the two chambers is of advantage. This control curve may e.g., be S-shaped so as to allow the pressure to be controlled as gently as possible.

According to an expedient embodiment, a target final pressure for one or both chambers and/or a target pressure difference between the pressures prevailing in the two chambers is/are adjusted on the packaging machine. The supply air valve can then be controlled through a suitable control unit such that this target pressure difference will be maintained with the least possible variation. According to a still more advantageous solution, the target pressure difference is adjustable, e.g., through suitable operating elements on the packaging machine. The target pressure difference can thus be adapted to different products or to different materials of the package so as to accomplish always the best possible packaging results.

The target pressure difference need not be a single concrete value, but it may preferably be a pressure range. If, for example, the desired pressure difference between the two chambers is 100 mbar, the target pressure difference can be a pressure range between 90 mbar and 110 mbar.

Preferably, the opening degree of the supply air valve is inversely proportional to the extent to which the actual pressure difference between the pressures prevailing in the two chambers deviates from the target pressure difference. When the pressure difference lies within the range defined by the target pressure difference, the supply air valve has a first opening degree. When the pressure difference between the two chambers exceeds the range of the target pressure difference, the supply air valve will open still further, in proportion to the extent to which the actual pressure difference exceeds the target pressure difference. The actual pressure difference can thus return as soon as possible to the range of the target pressure difference.

According to an expedient embodiment, a partition is provided between the two evacuable chambers. This partition offers the advantage that different pressures can prevail in the two chambers.

Preferably, an opening of the supply air valve leading into the first chamber is arranged in a wall of said first chamber located exactly opposite the partition. This mode of arrangement ensures that the air supplied will first act on the package end that is remote from the partition, before it sweeps along the package and flows to the partition. This has the advantage that the residual air still contained in the package will be forced to the opening of the package so that the package can be evacuated more easily and more rapidly.

The partition may have provided therein a gap through which the first chamber and the second chamber are in fluid communication with one another. This gap can have inserted therein part of the package so as to support and stabilize the package relative to the packaging machine. In addition, a minor exchange of air can take place between these two chambers. This has the advantage that an air current flowing along the package can be created, said air current being directed along the package and towards the opening thereof. The package can thus be evacuated more easily. Moreover, the fluid communication between the two chambers allows a variant according to which each chamber is not evacuated separately, but an evacuation opening is provided in only one chamber—preferably in the second chamber, which accommodates the opening of the package. When the second chamber is being evacuated, the first chamber is, by means of the gap, automatically evacuated as well.

When a gap is provided, the opening of the supply air valve leading into the first chamber is preferably arranged on the level of this gap. This additionally supports the formation of an air current along the package, said air current being directed from the package end to the package opening and forcing the residual air still contained in said package to the opening thereof.

According to an advantageous embodiment, an adjuster is provided for varying and adjusting the cross-sectional area of the gap. It is thus possible to adjust the volume flow between the two chambers, i.e., the amount of air exchanged between the two chambers per unit time.

According to the present disclosure, such an adjuster for varying and adjusting the cross-sectional area of the gap in the partition between the two chambers may also be provided independently of the pressure measurement in the two chambers and independently of the implementation of a supply air valve as a control valve. As has already been explained, the adjuster allows an adjustment of the volume flow exchanged between the two chambers. Depending on the nature of the products to be packed and the materials used for the package, this volume flow can be varied so as to achieve an evacuation of the package within the shortest possible time or to the highest possible extent.

Although the adjuster may be operable or adjustable by hand, the packaging machine will be easier to operate when the adjuster is driven by a motor and when the operator inputs, to this end, suitable adjusting commands, e.g., by means of an operator control panel or an operating element. The values adjusted can be stored in a control unit of the machine.

The adjuster may e.g., comprise an adjusting screw, which projects into the gap or which moves a blocking element projecting into the gap.

According to a preferred embodiment, the partition between the two chambers, or at least a part of said partition, is supported such that the cross-sectional area of the gap will not change, not even if one or both chambers are evacuated. This can be achieved in that the partition, or at least a part thereof, is elastically mounted (spring mounted) relative to the base, the lid or a wall of the chambers. Through this, it is avoided that e.g., bending of a lid of the packaging machine under conditions of a substantially reduced internal pressure will lead to a displacement of the partition and, consequently, to a change in the cross-sectional area of the gap, which may either prevent a pressure adaptation between the chambers or lead to an immediate pressure compensation; this would be two equally disadvantageous effects. In particular, the gap may also have provided thereon protrusions or projections, which enter into contact with the opposite side of the gap and prevent the gap from closing to such an extent that a specific minimum opening area would no longer exist.

Another substantial improvement of the packaging machine can additionally be achieved in that a bypass is provided between the two evacuable chambers, said bypass having arranged therein a controllable bypass valve. By means of the opening degree of the bypass valve it can be controlled how much air flows from one of the chambers into the other chamber so as to determine the differential pressure between the two chambers also independently, or at least largely independently of the gap. The controllable bypass valve additionally allows pressure compensation between the two chambers to be adapted to different numbers of bags or to bags having different wall thicknesses, without a change in the gap being absolutely necessary for this purpose. Alternatively, it would, however, also be imaginable to dispense with the provision of a bypass between the two chambers, but to evacuate the smaller chamber at full capacity and the larger chamber at reduced capacity.

The present disclosure additionally relates to a method of forming a vacuum package, comprising the steps of measuring the pressures in a first and in a second evacuable chamber, ascertaining therefrom the actual pressure difference and controlling a controllable supply air valve in dependence upon this actual pressure difference between the pressures prevailing in the two chambers, or in dependence upon the difference between the pressure prevailing in one chamber and a target final pressure predetermined for this chamber.

As has already been described hereinbefore, it will be advantageous when the supply air valve is opened proportionally to a pressure difference and/or when the target pressure difference is predetermined by an operator. The supply air valve can then be opened proportionally (or inversely proportionally) to the extent to which the pressure difference between the pressures prevailing in the two chambers deviates from the target pressure difference. As has already been explained, the target pressure difference need not be a single, concrete value, but the target pressure difference is preferably a finite pressure range.

According to a preferred embodiment, a bypass comprising a bypass valve is provided between the two chambers for executing the method according to the present disclosure. In this case, the final pressure achieved in the two chambers or the final vacuum achieved there is determined through the position of the supply air valve and thus adapted to a predetermined final vacuum, whereas the position of the controllable bypass valve is used for determining the differential pressure between the two chambers and for adapting this differential pressure e.g., to a predetermined differential pressure.

In the following, an advantageous embodiment of the disclosure will be described in more detail with reference to the below drawings.

DETAILED DESCRIPTION

Identical components are designated by identical reference numerals throughout the figures.

FIG. 1shows a schematic representation of an embodiment of a packaging machine1according to the present disclosure. It serves to render a package2around a product3into a vacuum package through adequate evacuation and sealing. The package2is preferably a bag made of a sealable plastic material. The product3may e.g., be cheese or some other product comprising bubbles or having porous structures, which may damage the product3under an excessively high external vacuum.

The packaging machine1is provided with a first evacuable chamber4and a second evacuable chamber5. The first chamber4is larger than the second chamber5. The first chamber4is adapted to accommodate therein a product-accommodating section2aof the package2, whereas the second chamber5is adapted to accommodate therein an opening section2bof the package2, so that an opening2cof the package2is freely disposed within the second chamber5.

A partition6, which the first chamber4and the second chamber5have in common, extends between said first and second chambers. The two chambers4,5are in fluid communication with one another via a gap7in the partition6, so that fluid can flow from one chamber4into the other chamber5. The package2extends through the gap7from the first chamber4into the second chamber5. The edges of the gap7may have provided thereon a sealing material8so as to seal the gap7, at least in certain section thereof, against the package2.

The first chamber4has provided thereon a first evacuating valve9through which said first chamber4can be evacuated. The second chamber5has provided thereon a second evacuating valve10by means of which the second chamber5can be evacuated. Both evacuating valves9,10are connected to a common vacuum pump (not shown) and can be opened or closed independently of one another.

A first pressure gauge11for measuring the pressure in the first chamber4is provided on or in said first chamber4. A second pressure gauge12is provided on or in the second chamber5and is used for measuring the pressure in said second chamber5.

The packaging machine1is additionally provided with a supply air valve13. This valve allows a supply of air to the first chamber4via a supply air opening14. The supply air valve13is a control valve that can preferably be adjusted between a fully closed and a fully open position.

A control unit15of the packaging machine1is connected to the valves9,10,13and the pressure gauges11,12via control and data lines16. The measurement values of the pressure prevailing in the two chambers4,5, which are ascertained by means of the pressure gauges11,12, are transmitted to the control unit15via the data lines16. The control unit is configured for ascertaining, from the values received from the two pressure gauges11,12, the pressure difference between the pressures prevailing in the two chambers4,5. In addition, it is also configured for controlling the evacuating valves9,10depending on the pressure prevailing in the respective chamber4,5and for controlling the supply air valve13depending on the difference between the pressures prevailing in the two chambers4,5.

An adjuster or positioning member17is provided so as to allow the cross-sectional area of the gap7to be varied and adjusted. In the present embodiment, the adjuster17is configured as an adjusting screw which is guided in the partition6. An electric motor18located outside of the two chambers4,5is provided with a drive nut19encompassing the adjusting screw17. When the nut19is driven by the motor18, it will raise or lower the adjusting screw17so as to vary the free cross-sectional area of the gap7. Also the motor18is connected to the control unit15via a suitable control line.

The supply air opening14, through which supply air can be conducted from the supply air valve13into the first chamber4, is arranged in the wall20of the first chamber4, said wall20being located opposite the partition6. In particular, the supply air opening14is there disposed on approximately the same level H, relative to the bottom21of the chamber4, as the gap7of the partition6.

The packaging machine1additionally comprises a sealing tool comprising an upper sealing tool part22and a lower sealing tool part23. The sealing tool is arranged in the second chamber5and is also controlled by the control unit15. Alternatively, the sealing tool22,23may also be arranged in the first chamber4. The sealing tool parts22,23are adapted to be moved towards one another so as to apply pressure and a sealing temperature and thus seal the opening area2bof the package2in an airtight manner.

Finally, the packaging machine1is also provided with operator facilities24, which can be a group of operating elements, such as buttons or the like, and/or a touch screen. By means of the operator facilities24, an operator can input commands in the packaging machine or set specific values, in particular a target pressure difference for the pressure difference in the two chambers4,5as well as the desired final pressure in one or both chambers. This target pressure difference may either be a single, concrete value or a pressure range between two values. In the latter case, the range may either be determined in that the operator determines the lower and the upper limit of this target pressure difference range. Alternatively, the operator may determine a specific value within the target pressure difference range, e.g., a medium range. The packaging machine1itself or the operator determines a tolerance range about this central value, e.g., a percentage deviation of 5 or 10%, plus and minus. When the actual pressure difference lies within this tolerance range about the predetermined pressure difference value, it is regarded as lying within the target pressure difference range.

The operation of the packaging machine1according to the present disclosure and the method according to the present disclosure take place as follows hereinbelow. Making use of the operator facilities24, the operator inputs in the control unit15in the packaging machine1a target pressure difference value or a target pressure difference range as well as the desired final pressure in one or both chambers, e.g., 100 mbar, 150 mbar, 200 mbar or 250 mbar. Depending on the specified target pressure difference or in response to a respective input of the operator, the adjuster17can be moved by means of the motor18so as to vary the free cross-sectional area of the gap7, if said cross-sectional area should not yet have the desired value.

The operator opens both chambers4,5of the packaging machine1and inserts a package2, filled with a product3, into the packaging machine1. This insertion can be carried out manually or automatically. After insertion of the package2, the product-accommodating section2aof the package2is located in the first chamber4, whereas the opening area2bof the package2is located in the second chamber5. The chambers4,5are closed.

As soon as the chambers4,5have been closed, the control unit15causes the two evacuating valves9,10to open. The pressure in the two chambers4,5decreases. Since the volume of the second chamber5is smaller than that of the first chamber4, the pressure in the second chamber5decreases faster than that in the first chamber4. Since the opening2cof the package2communicates with the second chamber5, the lower pressure prevailing in the second chamber5is also applied to the interior of the package2. This has the effect that the product-accommodating section2aof the package2is drawn into contact with the product3.

The pressure gauges11,12monitor the pressure in each of the chambers4,5continuously or at discrete intervals. The respective pressure measurement values are transmitted to the central control unit15, which calculates the pressure difference between the two chambers4,5. This pressure difference increases until it reaches the tolerance range of the target pressure difference. In order to make the pressure difference arrive more quickly at this predetermined value, either the first evacuating valve9is opened after the second evacuating valve10or the supply air valve13is opened while the two chambers4,5are being evacuated. The higher external pressure in the first chamber4presses the product-accommodating section2aof the package2onto the product3. Favored by the position of the supply air opening14in the wall20of the first chamber4, an air current is established, preferably a laminar air current, flowing from this supply air opening14to the gap7. It sweeps along the product-accommodating section2aof the package2, thus forcing the residual air contained in the package2to the opening2cof the package2.

When the evaluation of the measurement results of the two pressure gauges11,12shows that the pressure difference approaches the tolerance range of the predetermined target pressure difference, the supply air valve13implemented as a control valve is slowly closed. This closing of the supply air valve13can take place proportionally to the velocity with which the pressure difference approaches the target pressure difference. While the pressure difference is in the tolerance range of the target pressure difference, the supply air valve13assumes a partially open condition. This condition is chosen such that, while the evacuating valves9,10remain open, the pressure will decrease in both chambers4,5at a rate which is as identical as possible, so that the pressure difference between the two chambers4,5will remain in the predetermined tolerance range of the target pressure difference. If, however, the pressure difference should increase still further, the supply air valve13will be closed still further in accordance with the degree of deviation from the target pressure difference. Due to the continuously strong evacuation of the first chamber4via the evacuating valve9, the pressure in said first chamber4will decrease and, consequently, also the pressure difference between the two chambers4,5will decrease until it is back in the tolerance range about the target pressure difference. In other words, the control unit15controls the valves9,10,13such that the pressure difference between the two chambers4,5will be observed as quickly as possible and as long as possible during the evacuation.

As soon as the package2has been evacuated to a sufficient extent, the sealing tool parts22,23are closed around the opening area2bof the package2so as to seal said opening area2b. The vacuum package2is now finished. When the two chambers4,5have been opened, it can be removed from the packaging machine1.

FIG. 2shows in a schematic representation a second embodiment of the packaging machine1according to the present disclosure. This second embodiment is largely identical with the first embodiment shown inFIG. 1. Other than the first embodiment, the packaging machine1according toFIG. 2comprises, however, a bypass25between the two chambers4,5, i.e. an air duct interconnecting said two chambers4,5. This bypass25has provided therein a controllable bypass valve26. By means of the adjustable opening area of the bypass valve26, the rate at which air flows through the bypass25, when there is a pressure difference in the two chambers4,5, can be controlled. In this way, the rate of pressure compensation between the two chambers4,5can be controlled simultaneously. For controlling the bypass valve26in a suitable manner, also said bypass valve26is connected to the central control unit15via a control and data line16. The provision of the bypass25and of the bypass valve26provides the advantage that pressure adaptation between the two chambers4,5can take place independently of the gap7in the partition6. It is thus possible to control the desired differential pressure between the two chambers4,5.

FIG. 3shows, in a time-pressure diagram, the pressure profile in the two chambers4,5within one cycle of the method according to the present disclosure. In the situation shown inFIG. 3, two proportional valves are provided, viz. the supply air valve13and the bypass valve26in the bypass interconnecting the two chambers4,5. InFIG. 3, p4indicates the pressure profile in the large chamber4, p5the pressure profile in the small chamber5, and p22the pressure applied by the sealing tools22,23. The curve S13does not represent any pressure, but the position of the supply air valve13; the higher the rise in curve S13in the diagram according toFIG. 3, the smaller the opening degree of the supply air valve13.

At the beginning of the cycle shown inFIG. 3, the pressures p4, p5in the two chambers4,5are at normal pressure until said chambers4,5are closed at a moment in time t1and evacuation of the chambers4,5begins. At a moment in time t2, approximately five seconds after the beginning of the cycle, the pressures p4, p5reach a plateau phase. In this plateau phase the pressure p4in the larger chamber4exceeds the pressure p5in the smaller chamber5by a differential pressure Δp1. At the moment in time t3, slow closing of the supply air valve13begins, which finds expression in the beginning rise in curve S13. At the moment in time t4, at approximately 12.5 seconds, the pressures p4and p5leave the plateau phase and decrease gradually, since from this position of the supply air valve13onwards the amount of air supplied is smaller than the amount of air discharged. This also has the effect that the differential pressure Δp between the pressures p4, p5prevailing in the two chambers4,5decreases.

At the moment in time t5, at approximately 45.5 seconds, the pressure p5in the smaller chamber5reaches the predetermined final pressure, which is here 100 mbar. From this moment in time onwards, the supply air valve13is held at a constant opening width, i.e. at a constant supply air rate, and a differential pressure Δp2between the two chambers4,5is maintained. Between the moments in time t6(at approximately 54 seconds) and t7(and at approximately 56 seconds) the package2is sealed by applying a pressure p22by means of the sealing tools22,23to which a sealing pressure is applied by means of a sealing membrane (not shown). Subsequently, the chambers4,5are vented and opened until normal pressure prevails once more in said chambers4,5at the moment in time t8, whereupon the sealed package2can be removed from the packaging machine1. A complete operating cycle has now been finished.

FIG. 4shows in a further time-pressure diagram how the pressures p4, p5in the two chambers4,5behave when the bypass valve26is gradually opened during the evacuation of the two chambers4,5. This opening of the bypass valve26causes a gradual decrease in the differential pressure Δp between the two pressures p4, p5. The comparison betweenFIGS. 3 and 4shows that the position of the supply air valve13determines the final pressure or final vacuum obtained in the two chambers4,5, whereas the position of the bypass valve26determines the differential pressure Δp between the two chambers4,5.

FIG. 5shows in a time-pressure diagram a problematic situation which, unless suitable precautionary measures are taken, may arise under specific exceptional circumstances when the packaging machine1according to the present disclosure is in operation. Also this figure shows the profiles of the pressures p4, p5in the two chambers4,5, said profiles being initially similar to those shown inFIG. 3. At a moment in time t9, however, the lid of the chambers4,5begins to deform under the pressure built up due to the sealing membrane. This deformation has the effect that the parts of the partition6suspended from the lid shift so that the opening area of the gap7suddenly enlarges. The consequence is that a fast pressure compensation between the two chambers4,5takes place, and that the differential pressure Δp between the two chambers4,5collapses from the moment in time t9onwards, i.e. that the pressures p4and p5approximate one another.

In order to prevent this, the part of the partition6defining the gap can be elastically suspended (e.g., spring mounted). In this way, bending of the lid of the packaging machine1during sealing pressure build-up through the membrane can be compensated for, so that the cross-sectional area of the gap7will not change, not even if the lid should undergo deformation. The result can be seen inFIG. 6: under the same conditions as inFIG. 5, the differential pressure Δp between the two pressures p4, p5in the two chambers4,5does not collapse inFIG. 6. The gap7can, for example, be maintained constantly at a gap height of 0.5 mm.