EP0524196B1 - Slewing mechanism for screw closures and process for mounting screw closures on containers - Google Patents

Abstract

PCT No. PCT/EP91/00394 Sec. 371 Date Oct. 8, 1992 Sec. 102(e) Date Oct. 8, 1992 PCT Filed Mar. 2, 1991 PCT Pub. No. WO91/15422 PCT Pub. Date Oct. 17, 1991.A slewing device for screw closures for containers includes a screw closure receiving member, a drive for rotating the receiving member, and a control arrangement for controlling power supply to the drive and including a torque sensor for sensing an instantaneous drive torque, a comparator for comparing the instantaneous drive torque with a closing torque having a predetermined value, and a sensor for sensing an angle of rotation of the receiving member and actuatable only upon the instantaneous drive torque reaching the predetermine value. The method of placing a screw closure on a container includes applying a drive torque to the screw closure to screw it down onto the container, sensing an instantaneous drive torque applied to the screw closure, comparing the instantaneous drive torque with a closing torque having a predetermined value, and sensing an angle of rotation of the screw closure only upon the instantaneous drive torque reaching the predetermined value of the closing torque.

Description

The invention relates to a turning device for screw caps according to the preamble of claim 1 and a method for applying screw caps to containers according to the preamble of claim 8.

A rotating device for screw closures and a method for applying such closures to containers are known (DE-OS 37 15 935). The known rotating device is used to screw closures onto containers and to maintain a predetermined closing torque. A torque limiting device prevents the desired torque from being exceeded. One measures Control circuit the drive current received by the drive motor of the rotating device and triggers control signals by which the drive current of the drive motor is interrupted when the current rises to a specific value which corresponds to a specific torque of the unscrewed closure. This directly affects the energy supply of the drive.

From FR-A-2 629 440 a rotary device for screw closures is known, which shows a drive, a control device influencing the energy supply of the drive, a torque sensor and a comparison of the currently achieved angle of rotation with a predeterminable angle of rotation enabling the angle of rotation sensor.

It has been found, however, that in some cases, in particular when using all-plastic closures, a secure sealing of the containers cannot be achieved with the known turning devices, even when a certain closing torque is specified. This is especially true when containers or bottles that are under excess pressure are to be closed. By specifying a certain closing torque, it is moreover possible that the mouth area of the containers to be closed is damaged, in particular in the case of glass bottles, which endangers the consumer. Finally, it has been shown that the opening moment, that is, that required for the first opening of the container Torque, often much larger than desired.

It is therefore an object of the invention to provide a rotating device and a method with which containers with screw closures, in particular also with those made of plastic, can be closed, containers under an overpressure being closed in a pressure-tight manner but not being damaged in the mouth region and a certain opening moment is set.

This object is achieved in a rotating device of the type mentioned with the help of the features listed in claim 1. Characterized in that the control device has at least one comparator circuit which compares the closing torque currently achieved with a predeterminable value for the moment, that the control device only detects the angle of rotation after reaching a predetermined closing torque and that the control device is designed so that the angle of rotation by the the screw cap is rotated further after reaching the certain closing torque, can be limited to a predeterminable value, a defined starting point for the further measurements during the closing process is established. After reaching this application torque, the angle of rotation is detected by which the screw cap is rotated by the rotating device. The detection of the angle of rotation after reaching the application torque ensures a particularly sensitive closure of the container. This can cause damage exclude the mouth area with high security and ensure a very exact adherence to a desired opening torque. In particular, this leads to a particularly sensitive setting of the desired closing torque, the predetermined opening torque being able to be adhered to very precisely.

In a preferred embodiment of the rotating device, the torque acting on the screw closure is detected with the aid of the control device serving as a torque limiting device. The current supplied to the drive of the rotary device or the voltage applied to the drive is detected. Since the power consumed by the drive is proportional to the voltage or current, the instantaneous torque can be determined from the instantaneous values of the current or the voltage. This moment detection is particularly easy to carry out.

In a further preferred closing device, the change in the tightening torque over time is recorded. If, therefore, the closure suddenly catches or cant when screwing it on, which is recognized by a rapid increase in the torque per unit of time, the closing process can be interrupted so that the mouth region of the container is not damaged.

Further refinements and advantages of the turning device result from the subclaims.

The stated object is also achieved by a method of the type mentioned at the outset with the aid of the features mentioned in claim 8. In order to achieve a particularly sensitive control of the desired closing torque, the closure is screwed onto the container until a predeterminable closing torque (contact torque) is reached, the instantaneous closing torque being compared with a predeterminable torque value and then the angle of rotation being recorded and the instantaneous angle of rotation being recorded with a predeterminable angle of rotation is compared. This defines a defined initial state of the closing process. The closure is then rotated further by a predeterminable angle of rotation relative to the container. This leads to a secure setting of the desired closing torque, with damage to the muzzle being practically excluded.

According to a preferred embodiment of the method, the change in the tightening torque over time is also detected after the application torque has been reached. Faults in the process during this phase, for example tilting of the closure on the container, can thus be reliably detected.

Finally, an embodiment of the method is preferred in which the screw cap is screwed on until a high limit torque which is above the closing moment is reached. The closure is then rotated through a predeterminable angle of rotation in the opposite direction in order to set the desired closing torque - and thus also a specific opening torque. Especially It is advantageous in this method that containers can also be closed, the threads of which have minor damage and in which an increased closing torque must therefore be applied in order to screw the closure onto the container.

Even if the closure is equipped, for example, with a guarantee ring, an increased torque must be applied when closing, because the closure torque is often already reached before the screw closure is in its final position. The initially selected high limit torque also ensures that the seal is pressed particularly well against the mouth region of the container, so that it can compensate for minor damage. A particularly good seal of the container is achieved in this way.

Further embodiments of the method result from the remaining subclaims.

The invention is explained in more detail below with reference to the figure. This shows a schematic diagram of the rotating device according to the invention.

The illustration shows a container 1, here a bottle, onto which a screw cap 3 made of plastic is to be screwed. The closure is grasped by a sketched sealing cone 5 of a rotating device 7 and placed on the container 1. It is irrelevant to the invention whether the sealing cone 5 is rotated relative to the container 1 or whether the sealing cone is fixed and the container 1 is rotating.

The closing cone 5 is set in rotation here by a motor 9 serving as a drive, which is supplied with current or voltage via a switching device 11. A sensor 13 is provided between the power supply and the switching device, which detects the current or the voltage. In principle, it is also possible to provide the sensor 13 between the switching device 11 and the motor 9.

A torque sensor 15, which detects the torque and which detects the closing torque acting on the screw closure 3, is assigned to the motor 9 or the closing cone 5. In addition, the closing cone 5 is assigned a rotation angle sensor 17 which detects the angular position of the cone.

A strain gauge system (DMS) integrated in the spindle of the motor 5, which is not explicitly shown in the figure, is preferably used as the torque sensor 15. An in. Is preferably used for the angle measurement the spindle integrated opto-electronic incremental encoder.

The signals of the current or voltage sensor 13, the torque sensor 15 and those of the angle of rotation sensor 17 are fed to a control device 19 which evaluates and processes the measured values. In addition, these signals are fed to a comparator circuit 21. This also receives, via suitable actuators, predeterminable values M1, M2, M3, M7 and Mö for given tightening torques as well as certain values W and Wl for given rotation angles. The output signals of the comparator circuit 21 are fed to the control device 19.

The control device 19 is connected to the switching device 11 of the motor 9 via a control line 23. It is also provided with a differentiator 25 to which the output signals of the torque and angle sensors are fed.

The sensor 13, which detects the supply voltage and / or the supply current of the motor 9, serves to determine the torque currently applied by the motor, it being assumed that the torque is proportional to the voltage or the current. By detecting the changes in the supply voltage or the supply current of the motor over time, changes in the torque over time can also be determined. In this case, the torque sensor 15 described above could be omitted.

The function of the rotating device 7 and the method for closing containers are explained in more detail below.

Basically, the device and the method are suitable for closing any container. It is preferred to use the device or the method for closing bottles with the aid of plastic closures. The bottles can be made of glass or plastic, for example PET.

The screw cap 3 is introduced into the sealing cone 5 in any manner, for example in a so-called pick process. The sealing cone 5 with the screw cap 3 clamped therein is then arranged over a container 1 to be sealed. Here, the sealing cone 5 rotates with respect to the fixed container 1.

The rotating screw cap 3 is now placed on the container 1. For this purpose, a corresponding switching signal is sent from the control device 19 via the control line 23 to the switching device 11, which, for example, has an electronic switch or a relay, so that the motor 9 is supplied with energy. During the screwing of the closure 3 onto the container 1, the closing torque or tightening torque exerted by the motor 9 on the closing cone 5 or the screw closure 3 is recorded. The instantaneous moment can be determined on the one hand with the help of the sensor 13, which measures the energy supply to the motor 9 delivered current or the applied voltage. It is also possible to directly record the torque transmitted from the motor 9 to the closing cone 5 with the aid of the torque sensor 15. The output signal of the sensor 13 or the torque sensor 15 is fed to the control device 19 but also to the comparator 21. This compares the current torque value with a specifiable tightening torque M1, the so-called application torque. As soon as this moment M1 is reached, the rotation angle sensor 17 is activated via the control device 19. The control device 19 now evaluates the signals of the rotation angle sensor. The current angle of rotation of the closing cone 5 or the closure 3 is compared by means of the comparator 21 with a predetermined angle value W. As soon as the closure has been screwed on by the desired rotation angle W after the application torque M1 has been reached, the control device 19 outputs a signal to the switching device 11 via the line 23, so that the latter interrupts the energy supply to the motor 9. This prevents further twisting of the closure.

If the application torque M1 or the closing torque is not reached, the following conclusion can be drawn: The closure fell out of the closing cone before reaching the container; due to a control error, no container was moved under the closing cone or the thread on the container or that The thread provided on the inner wall of the closure has been destroyed.

The control device 19 can, for example, be provided with a timing element which specifies a specific time within which the application or closing torque must be reached. If this is not the case, a control signal is emitted via a signal line S and the container 1 currently located below the sealing cone 5 is separated from the sealing system.

Instead of specifying a specific time, which may pass a maximum until the application torque M1 is reached, a specific angle of rotation can also be specified. This means that the closure is screwed onto the container by one full revolution, for example. After that, the application torque must be reached. If this is not the case, it is concluded that there is damage to the container or the closure. The corresponding container is discarded.

On the other hand, when the application torque M1 is reached and the rotation angle sensor 17 has been activated by the control device 19, the closing cone 5 is rotated further until the instantaneous rotation angle reaches the value W entered into the comparator 21. The predetermined angle of rotation W is determined on the basis of experiments. This ensures that the desired closing torque M2 is reached. With such a predetermined closing moment, it is ensured on the one hand that the container is closed in a pressure-tight manner by the screw closure 3. On the other hand, it is ensured that the opening torque Mö, the torque required to open the container for the first time, is also maintained.

While the screw cap 3 is rotated further by the predetermined angle of rotation W, the torque sensor 15 can be used to further monitor the instantaneous tightening torque and to compare it in the comparator circuit 21 with a second torque value, a predetermined maximum value M3. If this maximum value M3 is reached during the further rotation of the closure, it can be concluded that there is a muzzle error. If, for example, the thread on the outside of the container is jagged, it cuts into the inner wall or into the thread of the plastic screw cap 3. The torque required to turn the shutter further increases so much that the predetermined maximum value M3 is exceeded.

Will 5 during the further rotation of the closing cone until the predetermined angle of rotation W is reached Maximum value of the desired tightening torque M3 exceeded, this may also be due to the fact that the internal thread is damaged in its further course within the screw cap 3. As a result, the closure cannot be screwed in far enough so that the seal provided there does not come into sufficient engagement with the mouth region of the container 1. An internal pressure in the container can escape unhindered. Therefore, in such a case, a signal is emitted via the control line S of the control device 19, so that this container is separated from the closing device.

In addition, each time the maximum torque M3 is exceeded before the predetermined rotation angle W is reached, the switching device 11 is actuated via the control line 23 so that the motor 9 does not drive the closing cone 5 any further. This prevents excessive torque from acting on the mouth area of the container 1 and causing damage.

Finally, the maximum tightening torque M3 could also be exceeded before the desired angle of rotation W is reached if the closure 3 jams on the thread of the container after the application torque M1 has been reached. Even then, on the one hand, it would not be ensured that the seal provided in the closure tightly seals the container pressure, on the other hand, if the closure process is continued, an excessive moment could act on the mouth region of the container due to the tilting and lead to damage.

A differentiator 25 is provided within the control device 19, which determines the time derivative of the output signal of the torque sensor 15 but also of the output signal of the angle of rotation sensor 17.

From a detected with the help of this differentiator 25 too large temporal change in the angle of rotation z. B. can also be found when the sealing cone 5 suddenly turns, that is, the screw cap 3 has no hold on the container 1. This can be due, for example, to the fact that the side wall of the closure has burst or the thread on the container has broken. In such a case, a signal is emitted via the control line S and the corresponding container is separated out.

It turns out that the increase in torque after reaching the application torque M1 and before reaching the desired angle of rotation W is too small, it can be concluded that either the seal in the closure is defective, that the closure before the application on the Container was torn or that the bottle thread is not properly formed. In any case, it can be concluded that the closure on the container is spinning. In this case, too, the corresponding container is separated out by a signal on the control line S.

If, on the other hand, after the application torque M1 has been reached, the torque increases too quickly before the desired angle of rotation W is reached, it can be concluded that damage to the thread, the closure or the container has occurred or that the closure has tilted on the container. In this case too, a signal is emitted via the control line S and the associated container is separated out.

By specifying a maximum torque M3 for the closing process, the opening torque, the torque Mö required for the first opening of the container, can be set to a desired value. On the other hand, additional security is also achieved in this way by recognizing a tilting of the closure or damage to the thread of the closure or of the container and the containers concerned being able to be separated out.

Because the torque and, on the other hand, the angle of rotation are predetermined after a predetermined application torque has been reached, the moments which occur when a container is closed with the aid of a screw cap can be limited. On the one hand, this prevents damage to the muzzle, but on the other hand it also ensures that the closing device is overloaded so that its wear can be minimized. The service life of this facility is then extended very much.

The method can be modified in that the screw cap 3 is screwed on by the motor 9 until the torque sensor 15 and the comparator 21 determine that a torque limit value Mg has been reached which is above the closing torque M2.

Due to the increased tightening torque, container 1 with small thread damage can also be securely closed. Basically, it should be noted that in the event of thread damage, the ultimately desired closing torque M2 is reached before the closure has assumed its final position on the container thread, because the friction creates additional frictional forces.

Even when using closures with a guarantee ring, which is intended to indicate the first opening of the closure, the ultimately desired closure moment M2 is often reached before the closure has reached its final position on the container, because the guarantee ring creates an additional friction torque. Therefore, when using such closures, a torque that is above the ultimately desired closing torque M2 must first be applied.

Due to the increased tightening torque, an optimal pressure of the seal on the mouth area of the container is finally achieved. As a result, it forms itself onto the mouth, even in the case of minor damage, in such a way that an optimal sealing of the container is ensured even with contents under pressure.

In order to prevent excessive opening torques from occurring due to the closure with an increased tightening torque, a reversal is carried out after the closure has been screwed on up to the limit moment Mg by a control signal from the control device 19 which is fed via line 23 to the switching device 11 the energy supply to the motor 9 is reached. This then turns in the opposite direction. The rotation angle sensor 17 is activated simultaneously with this control signal. Its output signals are compared in the comparator 21 with an angle value W1 assigned to the left rotation or the opening movement. As soon as the predetermined angle of rotation, which can be, for example, in the range from 10 ° to 15 °, is reached, i.e. as soon as the current angle of rotation reaches the limit value W1 present in the comparator 21, the switching device 11 is activated by a control signal from the control device 19 via the control line 23 controlled that the motor 9 is disconnected from the power supply. As a result, the opening movement of the closure 3 is ended.

Experiments determine how far the closure has to be turned in the opposite direction up to the limit torque Mg until the desired opening torque Mö is reached. The required angle of rotation can depend on the combination of the materials chosen for the container, closure and seal.

Characterized in that the switching device 11 can be controlled so that an energy reversal or polarity reversal of the energy supply to the motor 9 is achieved, it is possible that the rotating device of the type described above is controlled so that when an error occurs during the closing of a container initially reversed the direction of rotation and the closure is unscrewed from the container. Then the closing process is started again. Should now be a proper one Set the closing state, the container is left in the normal manufacturing process. Only when an error occurs again, for example because the closure or the mouth area of the container has been destroyed, is the container discharged from the process. In this way, rejects can be reduced to a minimum, which means that further processing steps have to be carried out outside the normal workflow. A further improvement in the closing process can thus be achieved by reversing the energy supply.

Due to the possibility of energy reversal, it is also possible to turn the closure 3 against the closure direction after the first placement on the container 1. In this way, an optimal alignment of the thread provided in the closure with respect to the container thread can take place. After a certain left turn, the closure engages on the container, which can be determined, for example, by the axial movement of the closure relative to the container. This movement can be sensed by a suitable displacement sensor.

The rotation of the closure in the opposite direction to that of screw closures with a guarantee ring ensures that the latter is optimally aligned. This prevents the guarantee ring from jamming during the subsequent screwing on of the closure.

Claims (13)

1. A turning device for screw closures, in particular of plastics, for containers, having a drive and a control unit controlling the power supply of the drive, the said control unit comprising a turning moment sensor and a turning angle sensor permitting a comparison of the instantaneous turning angle with a predeterminable turning angle, characterised in that the control unit (19) has at least one comparator circuit (21) which compares the instantaneous closing moment with a predeterminable value for the moment (M1, M2, M3), in that the control unit (19) only determines the turning angle after a predetermined closing' moment (M1) has been reached, and in that the control unit (19) is designed in such a way that the turning angle, about which the screw closure (3) is turned further after the determined closing moment (M1) has been reached, can be limited to a predeterminable value.
2. A turning device according to claim 1, characterised in that, in order to determine the instantaneous turning moment, the control unit (19) has at least one current and/or voltage detection device associated with the power supply of the drive.
3. A turning device according to either one of claims 1 and 2, characterised in that the control unit (19) determines the temporal change in the closing moment.
4. A turning device according to any one of claims 1 to 3, characterised in that, in order to determine the closing moment and/or the temporal change in the closing moment, the control unit (19) has at least one sensor (13) for detecting the supply current and/or the supply voltage of the drive of the closing device (7).
5. A turning device according to any one of claims 1 to 4, characterised in that a power supply reversing circuit is associated with the control unit (19).
6. A turning device according to claim 5, characterised in that a turning moment sensor (15) detecting the opening moment (Mö) is associated with the power supply reversing circuit.
7. A turning device according to any one of claims 1 to 6, characterised in that the control unit (19) is designed as a regulating circuit.
8. A method of mounting screw closures, in particular of plastics, on containers, in particular by means of a turning device according to any one of claims 1 to 9, in which method the instantaneous turning angle is compared with a predeterminable turning angle, characterised in that the screw closure (3) is screwed up until a p redeterminable closing moment (contact moment M1) has been reached, the instantaneous closing moment being compared with a predeterminable moment value (M2) and the turning angle then being determined, and in that the instantaneous turning angle is compared with a predeterminable turning angle (W).
9. A method according to claim 8, characterised in that the turning moment acting on the screw closure (3) is determined with the aid of a turning moment sensor (15) or by means of a current and/or voltage detection device associated with the power supply of the drive of the turning device.
10. A method according to either one of claims 8 and 9, characterized in that, after reversal of the power supply, the instantaneous opening moment is determined as soon as the turning angle is > 0°.
11. A method according to claim 8, characterised in that a limit moment (Mg) lying above the desired closing moment (M2) is selected as the predetermined closing moment, and in that, after this limit moment has been reached the closure is turned at a predeterminable turning angle in opposition to the closing device.
12. A method according to any one of claims 8 to 11, characterised in that, in the case of containers (1) in which incorrect angle and/or moment values are established, at least one renewed closing process is initiated.
13. A method according to any one of claims 8 to 12, characterised in that containers (1) in which incorrect angle and/or moment values have been established are rejected.

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