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(11) | EP 2 003 060 A1 |
| (12) | EUROPEAN PATENT APPLICATION |
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| (54) | Packaging machine with a torque-controlled motor |
| (57) The present invention relates to a packaging machine whereas a packaging material
is unwound from a coil and converted into a package.
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[0001] The present invention relates to a packaging machine whereas a packaging material is unwound from a coil and converted into a package. The present invention also relates to a process for the production of a package from the packaging material.
[0002] Such packaging machines are well known from the state of the art and are for example so-called form-fill-seal packaging machines, traysealers as well as vertical or horizontal flowwrappers. A form-fill-seal packaging machine is a machine that forms a planar plastic film into a tray, for example by deep drawing, which is subsequently filled with a packaging item and then covered with a cover plastic film which is sealed to the tray. A traysealer is a packaging machine in which a preformed plastic tray is filled with the packaging item and then covered with a cover plastic film, which is normally sealed to the tray. Vertical and horizontal flowwrappers are machines that form planar plastic films into bags, which are subsequently filled with a packaging item and then closed by a seal. The machines can be operated continuously or index-wise.
[0003] All these packaging machines have in common, that a plastic packaging material is converted into a package. However, the packaging machines according to the state of the art are either not fast enough or the closure of the trays with a cover film is too complicated.
[0004] It was therefore the objective of the present invention to provide a packaging machine which overcomes the problems of the state of the art.
[0005] This problem is solved with a packaging machine, whereas a packaging material is unwound from a coil and converted into a package, and the coil is driven by a torque motor.
[0006] The packaging machine according to the present invention can be any packaging machine known by the person skilled in the art. However, preferably, the packaging machine is a so-called form-fill-seal packaging machine, a traysealer, a vertical- or a horizontal flowwrapper as described above. These packaging machines comprise a coil of packaging material, which is converted into a package. In a form-fill-seal packaging machine, this coil can either comprise the film from which the tray is made or the cover film which covers the tray after it has been filled with the packaging item. In a traysealer, the coil comprises the cover film to cover the trays, after they have been filled with the packaging item. In the application with the vertical and horizontal flowwrapper, the coil comprises the packaging material from which the individual bags are formed.
[0008] According to the present invention, the coil is driven by a torque motor. With this torque motor, it is possible to keep the packaging material under an essentially constant tension without the need of a brake or the like. The torque controlled motor can be either used to unwind the coil and/or to tension the packaging material. Furthermore, the torque motor can be used to adjust the cover film exactly on the trays or relative to parts, for example sealing means, of the inventive packaging machine.
[0009] A torque motor are motors with a small electric time constant and therefore high dynamic responses. This results in very short response times so that even a large coil can accelerated and stopped instantaneously, so that an essential constant tension can be maintained in the packaging material. The torque motor uses a permanent magnet for high efficiency. Torque motors have preferably a relatively large diameter to length ratio and short axial dimensions. More preferably, the torque motor has a large diameter, resulting in a motor that is a little thicker than a thin ring. Thus, mass can be quite low as a function of diameter. The large diameter helps the motor develop high torque levels, which are advantageous due to the at least initially high inertia of the coil. The large diameter to length ratio gives additional freedom in designing the inventive packaging machine. Preferably, the torque motor is frameless, which means that they do not have a housing or the like, but can be part of the structure of the inventive packaging machine. The torque motor is preferably used as a direct drive. They eliminate the need a gearbox or the like but directly couple the payload to the axis on which the coil is located. This makes it possible to drive with dynamic response and without hysteresis. The angular stiffness of the torque motor is preferably also very high. A preferably large inner diameter allows to locate the axis for the coil into the inner diameter of the torque motor. It is also possible to locate the motor into the axis of the coil. This has especially hygienic advantages, because the packaging machine can be cleaned easily. Preferably, the torque motor does not add excessive moving mass or inertia, which is advantageous for the response time of the motor. Preferably, the torque motor produces a high torque at stall. More preferably, the torque motor has high precision, high resolution feedback control system in order to achieve optimal performance of the motor. Since the load is directly coupled to the torque motor, higher accuracy is possible in comparison to conventional drives. Preferably, the torque motor a a cooling, more preferably a water cooling.
[0010] According to another aspect of the present invention or in a preferred embodiment of the above-mentioned invention, the tension in the packaging material is essentially constant.
[0011] This embodiment of the present invention has the advantage, that length oscillations of the film due to variations in the tension in the packaging material can be essentially avoided. Consequently, the packaging machine can be operated with much higher production rates and/or the production process of the resulting packaging items can be carried out much more precisely.
[0012] Preferably, the variation of the tension in the packaging material is less than 10 %, more preferably less than 5%.
[0013] Preferably, the inventive packaging machine comprises a buffer for the packaging material. This preferred embodiment has the advantage, that the torque motor that drives the coil, can be operated more smoothly and need not be constantly turned on and off. One option for a buffer is a so called dancer. Due to a movement of the dancer, the packaging material stored in the buffer can be increased or decreased.
[0014] In a preferred embodiment, the inventive packaging machine comprises tensioning means for the packaging material. These tensioning means can be realized with a spring-like component, whereas the spring constant and the spring deflection should be low in order to achieve an essentially constant tension in the packaging material. More preferably, the tension means and the buffer means are combined.
[0015] Preferably, the motor is controlled by the buffer means. As soon as the amount of packaging material stored in the buffer increases, the torque of the torque motor is decreased and vice versa. If for example the buffer comprises a dancer with is normally in a vertical position, the motor is controlled as soon as the dancer deflects slightly from its vertical position. Preferably, the dancer is spring-loaded. Due to the immediate reaction of the motor based on a slight deflection of the dancer, the tension in the packaging material is essentially constant, even though the dancer is spring loaded.
[0016] Preferably, the torque of the motor is adjusted according to the radius of the coil. In an even more preferred embodiment, the torque provided by the motor decreases with the radius of the coil (Is this correct?).
[0017] In another preferred embodiment, the torque motor is used to adjust the packaging material relative to another part of the package and/or relative to the packaging machine. This preferred embodiment of the present invention is especially used to correctly adjust a printed cover film on a tray and or to align the film relative to parts of the machine.
[0018] Preferably, the motor operates in one direction to unwind the packaging material and in the opposite direction to adjust the packaging material to the tray; i. e. the motor unwinds the packaging material and then rotates in the opposite direction to tension the film over the tray.
[0019] In an even more preferred embodiment, the inventive machine comprises a sensor, for example a photocell, to detect a print mark on the packaging material. In this preferred embodiment of the present invention, the motor unwinds the packaging material until a print mark passes the sensor. Subsequently, the motor is stopped and turns in the opposite direction until the print mark is detected again by the sensor. The such adjusted packaging material can then be sealed to the tray.
[0020] Preferably, the inventive packaging machine comprises means to calculate the actual radius of the coil. Preferably this information is used to provide a warning signal in case the coil falls below a certain value. Thus, scrap can be avoided and the down time of the machine due to coil-change can be reduced.
[0021] Another embodiment of the present invention is a process for producing a package from a packaging material, whereas the packaging material is unwound from a coil and converted into a package, and the unwound packaging material is held under an essentially constant tension.
[0022] The entire disclosure regarding the inventive machine also applies to the inventive process and vice versa.
[0024] The inventive process can be carried out on every packaging machine known from the state of the art. However, preferably, the machine is a packaging machine as described above.
[0025] Preferably, the packaging material is buffered between the coil and the next process step, e.g. forming and/or sealing.
[0027] In an other preferred embodiment, the motor is used to adjust the film relative to an other part of the package, especially relative to the tray and/or relative to a part of the packaging machine, for example the cross-sealing-means of a flowwrapper.
[0028] In a preferred embodiment, the motor adjusts the print mark on the packaging material relative to a sensor. This is done as described above.
[0029] The invention is now explained according to figures 1 and 2. These explanations do not limit the scope of protection and are applicable likewise to the inventive process as well as the inventive packaging machine.
[0032] Figure 1 shows the infeed of the packaging material of a so-called flowwrapper. In a flowwrapper, a planar packaging material, especially a planar plastic film is formed around a form shoulder into a film tube. This film tube is provided with a longitudinal seal and a cross seal. Subsequently, the package is filled with the packaging item and then another cross seal is applied and the package is separated from the film tube by cutting means. In the present example, the packaging material 1 is provided on a coil 2, which sits on an axis which is driven by the torque motor 5. Downstream of the coil, a buffer 3 is located which comprises several roles 3', 3", whereas the role 3" is located on a dancer, which can as shown by the dashed lines, oscillate around its vertical position. The dancer is tensioned by a spring 4. Since the spring has a very low spring constant and since the deviation of the dancer around the vertical axis are kept in very small boundaries, the tension of the film 1 is essentially constant. This is advantageous, because oscillations in the film are capped to a minimum so that the machine can be operated with higher speed and higher accuracy. The deviation of the dancer around the vertical axis controls the motor. As soon as the dancer is drawn by the spring to the left, i. e. if too much film is available, the torque motor is stopped or reduced in its rotational speed until the dancer is in the vertical position again, if the dancer deviates to the right, the rotation of the motor is either started again or increased. In order to achieve an essentially constant tension in the packaging material, it is essential, that the deviations of the dancer are kept to a minimum. The inventive machine also comprises means to calculate the radius of the coil 2. Therefore, the torque motor 5 provides a signal of the angle of rotation while a certain length of packaging material 1 is drawn from the coil. Knowing the length that has been drawn from the coil and knowing the angle by which the coil has rotated during the unwinding of this length of packaging material, the radius of the coil can be calculated. This signal can be used to control the torque provided by the torque motor and/or to provide a warning signal if the remaining packaging on the coil is below a certain value. The inventive machine can be operated continuously or discontinuously. The inventive machine can comprise one or more form shoulders.
[0033] Figure 2 shows the inventive packaging machine which is in the present example a so-called form-fill-seal packaging machine. In a form-fill-seal packaging machine, trays 6 are formed from a planar material, which are subsequently filled with a packaging item and then closed with a cover material, which is in the present example the packaging material 1. The cover film 1 is sealed to the trays. Normally, the trays are not moved continuously, in the present example from the left to the right, but index wise. As soon as the cover film 1 is sealed to the trays, it is advanced with every index of the trays 6. This packaging material 1 is unwound from a coil 2, then passes a buffer as described in figure 1 and is subsequently sealed to the trays 6. In the present example, the coil 2 is also driven by a torque motor 5. Additionally, the packaging machine according to the present example comprises a sensor 7, which detects print marks on the packaging material 1. The print marks are used to correctly seal the cover film one to the trays. This is especially important when printed films 1 are used, because the print on the film has to be correctly sealed to the tray. When the form-fill-seal packaging machine makes an index; i.e. moves one format further and then stops, the film tensioning will be controlled as described according to figure 1. At the end of the index, a sensor 7 detects the print mark on the film. When the motion of the film 1 stops, the tension in the film will be increased, so that the film is stretched, for example until the sensor sees the print mark again. This is for example achieved by turning the torque motor in a reverse direction or increasing the torque of the motor
[0034] In order to avoid, that the dancer moves too much to the right, another spring 8 is provided, that has a higher spring constant than spring 4. When the torque is increased the dancer compresses spring 8, which reduces the movement of the dancer.
[0035] The tension in the film will be held on this level until the sealing of the film to the trays has taken place. Then the tension is released again to its level during transportation of the film. The dancer moves to its vertical positon.
Reference list
1. Packaging machine, whereas a packaging material (1) is unwound from a coil (2) and
converted into a package, characterized in, that the coil (2) is driven by a torque motor (5).
2. Packaging according to claim 1 or the preamble of claim 1, characterized in, that the tension in packaging material is essentially constant.
3. Packaging machine according to claim 2, characterized in, that the variation of the tension in the packaging material is less than 10 %, preferably
< 5%.
4. Packaging machine according to one of the preceding claims, characterized in, that it comprises a buffer (3) for the packaging material.
5. Packaging machine according to one of the preceding means, that it comprises tensioning
means (4) for the packaging material.
6. Packaging machine according to claim 5, characterized in, that the motor (5) is controlled by the buffer means (4).
7. Packaging machine according to one of the preceding claims, characterized in, that the torque of the motor is adjusted according to the radius of the coil.
8. Packaging machine according to claim 7, characterized in, that the torque provided by the motor decreases with the radius of the coil.
9. Packaging machine according to one of the preceding claims, characterized in, that it comprises means to calculate the radius of the coil.
10. Packaging machine according to one of the preceding claims or the preamble of claim
1, characterized in, that a torque motor is used to adjust the packaging material (1) relative to another part
(6) of a package and/or the packaging machine.
11. Packaging machine according to claim 10, characterized in, that the motor operates in one direction to unwind the packaging material and in the opposite
direction to adjust the packaging material (1) to part (6).
12. Packaging machine according to claim 10 or 11, characterized in, that it comprises a sensor (7) to detect a print mark on the packaging material (1).
13. Process for producing a package from a packaging material (1), whereas the packaging
material (1) is unwound from a coil (2) and converted into a package, characterized in, that the unwound packaging material (1) is held under an essentially constant tension.
14. Process according to claim 1, characterized in, that the constant tension is facilitated by a torque motor.
15. Process according to one of the preceding claims, characterized in, that the packaging material is buffered after the coil.
16. Process according to one of the preceding claims, characterized in, that the torque provided by the motor is adjusted relative to the radius of the coil.
17. Process according to one of the preceding claims, characterized in, that the motor is used to adjust the film relative to another part (6) of a package and/or
the packaging machine.
18. Process according to claim 17, characterized in, that the motor adjusts a print mark on the packaging material relative to a sensor (7).