Thermoform packaging machine with pulling device

A thermoform packaging machine including a forming station, a sealing station, a cutting station and a film conveying unit. The film conveying unit includes a clamp chain arranged on a lateral edge of a bottom film, wherein the clamp chain cyclically conveys the bottom film in a direction of production during operation, the bottom film is advanced one cycle length in each cycle of the thermoform packaging machine. Further, the thermoform packaging machine may include a pulling device that pulls a pull section of the bottom film and/or a top film in a direction parallel to the direction of production relative to the lateral edge of the bottom film held by the clamp chain.

CROSS-REFERENCE TO RELATED APPLICATIONS

This Application claims priority to German Patent Application No. DE 10 2016 122 625.4, filed on Nov. 23, 2016, to Bernhard Grimm and Thomas Müller, currently pending, the entire disclosure of which is incorporated herein by reference.

BACKGROUND OF THE INVENTION

Thermoform packaging machines are known such as that described in EP 2 740 679 A1. For increasing the positioning accuracy of the films during cutting or sealing, the cutting station as well as the sealing station can be displaced in a direction parallel to the direction of production. To this end, a reference element, whose position relative to a packaging trough is known, is detected and the cutting station or the sealing station is adjusted on the basis of the detected position of the reference element and of the packaging trough position known relative thereto. This adaptation is disadvantageous insofar as the position of the respective station can only be adjusted relative to the entire film.

In practice, it may happen that certain sections of the films are distorted relative to one another. This may be due to the product fed into the film trough. The larger the distance between the respective section and the normally used conveyor chains of the thermoform packaging machine is, the higher may be the degree of distortion. In addition, this effect may intensify with each cut carried out in the film compound before the packages are finally individualized. This film distortion may then lead to inaccuracies during sealing or cutting. It is the object of the present invention to provide a thermoform packaging machine that is improved with respect to the above-mentioned drawbacks.

SUMMARY OF THE INVENTION

According to the present invention, a thermoform packaging machine is provided, which comprises a forming station, a sealing station, a cutting station and a film conveying unit. The film conveying unit includes a clamp chain arranged on a lateral edge of a bottom film and used for cyclically conveying the bottom film in a direction of production, the bottom film being advanced in each cycle by one cycle length. The thermoform packaging machine according to the present invention may be characterized in that a pulling device is provided, which may be configured to pull, in a direction parallel to the direction of production, a pull section of the bottom film and/or of a top film relative to the lateral edge of the bottom film held by the clamp chain. One or a plurality of clamp chains may be provided; the film may here be gripped on only one edge by one or a plurality of clamp chains. Thermoform packaging machines in which each of the two lateral edges of a film may be respectively held by one or a plurality of clamp chains may be commonly used as well. In the following, the term lateral edge is to be understood as a margin area of a film/foil, which extends parallel to the direction of production. The term edge also relates to the surfaces of the film which may be inserted in clamps of the clamp chains.

An advantageous effect of the configuration according to the present invention resides in that a distortion in a pull section of the top film and/or bottom film, which may be not directly held by the clamp chain, can be compensated.

It will be advantageous when the pulling device may be arranged upstream of the sealing station or the cutting station at a distance corresponding to two cycle lengths at the most, preferably to not more than one or less than one cycle length. This may be advantageous in view of the fact that downstream of the pull section distortion may again occur, and the closer the pull section may be arranged to the sealing station or the cutting station, the smaller this distortion will be.

It may be conceivable that the pull section of the bottom film and/or of the top film extends outside the lateral edge of the bottom film held by the clamp chain. In the case of a variant in which two clamp chains may be provided for holding at opposed edges of the bottom film; it may be conceivable that the pull section extends between the lateral edges held by the clamp chain.

According to a possible variant, the pulling device comprises a clamping element and a counter-pressure bar, the clamping element being adapted to be pressed against the counter-pressure bar. The counter-pressure bar may be arranged e.g. below the bottom film and the clamping element may be arranged e.g. above the top film. A reversed mode of arrangement may be, however, conceivable as well. The counter-pressure bar and the clamping element may here be connected to one another by a bridge- or portal-shaped structure. Such a force-fit engagement variant has the advantage that no additional engagement features may be required at the film.

According to a particularly advantageous embodiment, the clamping element may be coated with silicone. In this way, the coefficient of friction between the film and the clamping element can be increased and the risk of slipping of the film can be reduced.

It will be advantageous when the clamping element, together with the counter-pressure bar, may be displaceable parallel to the direction of production by a displacement distance. In this way, pulling of the pull section can be enabled.

According to a variant, the clamping element and the counter-pressure bar may be displaceable by a pneumatically or hydraulically operated cylinder.

According to another variant, the clamping element and the counter-pressure bar may be displaceable by a stepping motor or a servomotor, preferably by means of a spindle or a crank.

According to a particularly advantageous embodiment, a distance sensor may be provided for detecting the displacement distance, the distance sensor preferably detecting the displacement distance directly. A direct detection of the displacement distance can be carried out using an optical or ultrasound-based distance sensor. An indirect detection of the displacement distance, e.g. by detecting the position of the stepping motor or the servomotor, is, however, conceivable as well.

It may be conceivable that the displacement distance may be controllable. This control may be of an electronic, mechanical, hydraulic or pneumatic type. This allows a particularly flexible adjustment of the displacement distance and, consequently, a flexible adaptation of the distortion correction. The displacement distance may be controllable, e.g. on the basis of the displacement distance detected by the distance sensor.

According to a further variant, a stop may be provided for limiting the displacement distance. A stop may be of advantage for a controllable displacement distance as well as for a non-controllable displacement distance. A system without a controllable displacement distance having a stop represents a particularly simple and robust variant.

According to a particularly advantageous embodiment, the clamping element may be adjustable in a direction perpendicular to the direction of production and preferably perpendicular to a clamping direction. The term clamping direction means here the direction in which the clamping element moves when it is pressed against the counter-pressure bar. It follows that an adjustment direction of the clamping element extends preferably in a plane parallel to the film plane and perpendicular to the direction of production.

According to a further variant, the pulling device may comprise a plurality of clamping elements, each of them adjustable preferably in a direction perpendicular to, the direction of production and preferably perpendicular to a clamping direction.

According to a particular the advantageous embodiment, a film distortion sensor may be provided, which may be configured for detecting a distortion of the pull section relative to the lateral edge of the bottom film held by the clamp chain. The film distortion sensor may e.g. be a camera capable of detecting e.g. the format of the troughs or the contours of the webs between the troughs. It is also conceivable to provide reference elements, such as print marks or holes, in the film, which may be detected by the film distortion sensor.

According to a possible variant, the pulling device may be configured for pulling between advancing phases of two cycles. Other aspects and advantages of the present invention will be apparent from the following detailed description of the preferred embodiments and the accompanying drawing figures.

DETAILED DESCRIPTION OF THE INVENTION

InFIG. 1atop view of a thermoform packaging machine1is shown. In the present embodiment, the thermoform packaging machine1comprises a film conveying unit2with clamp chains2a,2b. The latter are configured for cyclically advancing a bottom film3. As in the embodiment according toFIG. 1, two clamp chains2a,2bare provided in the following embodiments as well. It is, however, also conceivable to provide only a single clamp chain2a(cf.FIG. 8), i.e. on only one side of the film3.

The thermoform packaging machine1comprises a forming station4. The forming station4is configured for forming troughs5in the bottom film3. A loading track6is provided downstream of the forming station4, when seen in a direction of production P. There, products7are put into the troughs5. A sealing station8is arranged downstream of the loading track6. The former is configured for sealing the troughs5by sealing a top film9onto them (cf.FIG. 2) and producing sealed seams10extending circumferentially around the troughs. In this way, sealed packages11are produced. The sealed packages11are advanced to a cutting station12. In the present embodiment, this cutting station12comprises two cutting devices12a,12b. In principle, the present invention is, however, applicable to all kinds of cutting stations, preferably to those carrying out cuts, which are offset in the direction of production P and which extend transversely to the direction of production P. The sealed packages11can be fully individualized at the cutting station12. Likewise, it is conceivable that the cutting station12only carries out certain cuts and that the packages are individualized further on downstream.

InFIG. 1, a pulling device13according to the present invention (cf.FIG. 5a-5c) is merely indicated by a clamping location14. The latter is arranged in a pull section15, which will be explained in more detail hereinafter making reference toFIG. 2. InFIG. 2, the clamp chains2a,2bare shown in the perspective identified by Z-Z inFIG. 1. The bottom film3is held by the clamp chains2a,2bat lateral edges16a,16b. The pull section15extends between those lateral edges16a,16b. Hence, this pull section15is the area of the bottom film3and of the top film9that is not covered and/or held by the clamp chains2a,2b.

With respect to the embodiment shown inFIG. 1, the clamping location14is arranged centrally in the pull section. Centrally means here in relation to a direction horizontally and transversely to the direction of production P. In the case of packages11or troughs5extending across the whole width of the pull section15, the clamping location14should be arranged on a web17provided between the troughs5. In general, the clamping location14should preferably be disposed on a web17arranged between troughs5.

As regards the fundamental structural design, the thermoform packaging machines1shown inFIGS. 3 and 4mainly differ from the thermoform packaging machine1shown inFIG. 1in that a different number of tracks18of troughs5is formed in the bottom film3. This is merely intended to illustrate that the present invention is also applicable to this kind of thermoform packaging machines1.

InFIGS. 5ato 5cvarious embodiments of pulling devices13are shown. The figures show a front view. The perspective is identified by the arrows A-A inFIGS. 1 and 3and by the arrows B-B inFIG. 4. The pulling devices shown inFIGS. 5ato 5cmainly differ in that different numbers of clamping elements19are provided. For the sake of clarity, only the bottom film3is shown inFIGS. 5ato5c.

In addition to the one or the plurality of clamping elements19, the pulling device13comprises a counter-pressure bar20. The clamping elements19can be pressed against this counter-pressure bar20. In order to connect the counter-pressure bar20with the clamping element19, a bridge- or portal-shaped structure21may be provided. For operating, i.e. pressing, the respective clamping elements19against the counter-pressure bar20, clamping cylinders22may be provided. These clamping cylinders may be conventional hydraulic or pneumatic cylinders. The prefix “clamping” is only used for differentiating more easily between various cylinders.

In order to compensate for a distortion between the lateral edges16a,16band the pull section15, the clamping element19is pressed against the counter-pressure bar20by operating the clamping cylinder22. Thereby, the top film9and the bottom film3are clamped between the clamping element19and the counter-pressure bar20. By displacing the structure21and, consequently, the clamping element22as well as the counter-pressure bar20, a distortion can be compensated. In order to increase the friction between the clamping element19and the top film9, the clamping element may have a coating provided thereon, for example, a silicone coating. The counter-pressure bar20may as well have a coating provided thereon, for example, a silicone coating, for increasing the friction with the bottom film3. Since the displacement for compensating the distortion takes place in the direction of production P and since the perspective shown inFIGS. 5ato 5cis directed in the direction of production P as well, components of the pulling device13which serve the purpose of displacement will be explained with reference toFIGS. 6ato6c.

For the sake of clarity, some components, such as the structure21and the clamp chains2a,2b, are not shown inFIGS. 6ato 6c. The top film9and the troughs5are not shown either. The components shown in each of the three figures are the clamping element19, the clamping cylinder22provided for actuating the latter, and the counter-pressure bar20. For displacing the counter-pressure bar20and thus also the clamping element19, a displacement cylinder23is provided inFIG. 6a. This may be a conventional hydraulic or pneumatic cylinder. Similar to the use in the case of the clamping cylinder22, the prefix “displacement” is only used for making the cylinders more easily distinguishable. A piston rod24of the displacement cylinder23is connected to the counter-pressure bar20or the structure21. This has the effect that the counter-pressure bar20will be displaced in the direction of production P, when pressure is applied to the piston side of the displacement cylinder23. For limiting the displacement, a stop25may be provided. Alternatively or additionally to a stop25, the displacement may be controllable by closed loop control of the extension of the displacement cylinder23. To this end, a distance sensor26may be provided, which detects a displacement distance27. On the basis of the displacement distance detected, the displacement of the counter-pressure bar20can be controlled. The distance sensor26may be based on any principle of distance measurement, for example, on a transit time measurement of ultrasonic or laser signals.

Additionally or alternatively, a distortion sensor28may be provided. As shown inFIGS. 6aand 6b, this sensor may be a camera29. This camera29may detect the position and/or the shape of the webs17between the troughs5and identify on the basis thereof a displacement between the lateral edges16a,16band the pull section15. The desired corrected arrangement of the pull section15can be detected by a camera29as well. As has already been indicated, a combination of the distance sensor26and the distortion sensor28or camera29may also be provided. As can be seen inFIG. 6a, the camera29may be arranged upstream of the clamping element19and, consequently, upstream of the pulling device13. The person skilled in the art will immediately recognize that the camera29may be mounted on the structure21as well as on other structures of the thermoform packaging machine1, which do not move together with the structure21. This last-mentioned configuration should be slightly preferred.

An alternative embodiment of the displacement mechanism is shown inFIG. 6b. An alternative arrangement of the camera29, namely downstream of the pulling device and the clamping element19, is also shown. For displacing the counter-pressure bar20, a motor30is provided. This motor30may be a stepping motor or a servomotor. The rotary movement of the motor30can be converted into a linear movement of the counter-pressure bar20by a spindle31. To this end, it will suffice to provide a nut, for example a recirculating ball nut, which is secured to the counter-pressure bar20.

A further alternative embodiment of a displacement mechanism is shown inFIG. 6c. A motor30is used in this case as well. However, for converting the rotary movement of the latter into a linear movement, a crank32is provided. This crank32is connected to the counter-pressure bar20. The latter is guided on a linear guide33. A linear guide may be provided in all the embodiments described.

In addition to the stop25, a second stop34may be provided, which limits the displacement distance in a direction opposite to the direction of production P. The distortion sensor28shown in this embodiment is not a camera. It may be a sensor, which is based on optical principles, laser or infrared, or on acoustic principles, for example, ultrasound. Similar to the camera, it may be arranged downstream of the clamping element19, as shown inFIG. 6c. However, an arrangement upstream of the clamping element19is conceivable as well.

The use of a motor30for the purpose of displacement has the advantage that conclusions about the displacement distance27can be drawn from the rotary position of the motor30and/or the number of revolutions. Such a determination of the displacement distance27may be provided alternatively or additionally to a distance sensor26.

In combination with all the above described distortion sensors28, reference elements35may be provided on and/or in the bottom film3and/or the top film9. As is exemplarily shown inFIG. 7, these reference elements may be holes36and/or print marks37. These holes and/or print marks may be of advantage when detection is accomplished by simple distortion sensors28, as shown inFIG. 6c, as well as in combination with cameras29, as shown inFIGS. 6aand6b.

As has already been indicated before, the invention is also applicable to thermoform packaging machines1in which only one clamp chain2ais provided. In this case, the pull section15extends, as shown inFIG. 8, outside the lateral edge16a, which is held by the clamp chain2a, up to the ends of the top film9and of the bottom film3located opposite the lateral edge16a.

The constructions and methods described above and illustrated in the drawings are presented by way of example only and are not intended to limit the concepts and principles of the present invention. Thus, there has been shown and described several embodiments of a novel invention.