Strapping device with tension force measurement

Abstract

The present invention relates to a strapping device having at least one drive and tensioning unit (2) and a closure unit (3) for connecting the strap ends of a strapping band (7) wrapped around a product. Furthermore, the at least one drive and tensioning unit (2) is connected to the closure unit (3). According to the invention, the drive and tensioning unit (2) is rotatably connected to the closure unit (3) and is supported on the closure unit (3) with the interposition of a connecting element (4) equipped with a measuring element for tensioning force.

Description

[0001] The invention relates to a strapping device with at least one drive and tensioning unit and a closure unit for connecting the strap ends of a strapping band wrapped around a product, wherein the at least one drive and tensioning unit is connected to the closure unit. The drive and tensioning unit typically has a drive roller and a tensioning roller.

[0002] Strapping devices are generally used to bundle together items to be strapped, such as stacks of newspapers, paper rolls, packages, etc. For this purpose, the strapping band is first wound around the item to be strapped. This is done using the drive roller. The strapping band is then tensioned using the tensioning roller. In this tensioned state, the strapping band is separated from the band supply. The two ends of the strapping band are then pressed against each other and joined together in the sealing unit. With plastic strapping, the ends are generally joined by welding, for example, friction welding.

[0003] Depending on the characteristics of the goods being strapped, compression may occur during the strapping process, and especially during the tensioning process. Especially with goods with relatively high elasticity or low stiffness, such compression during the tensioning process can result in the goods not being adequately secured.

[0004] Strapping devices for strapping such goods are known, for example, from EP 0 847 922 A1. In this case, the strapping device controls the tensile force by limiting the current consumption of the drive motor for the tensioning drum. If a defined motor current is exceeded, for example, the motor is stopped or a strapping clamp is inserted to secure the strap.

[0005] The known teaching of EP 2 489 597 B1 defines the tensioning force as a function of the article to be strapped. For this purpose, the prior art provides a device for detecting the article's properties, such as a sensor or measuring device. After detecting the article's properties, the tensioning force is to be adjusted accordingly. However, the document leaves open how this tensioning force should be measured and adjusted in practice.

[0006] Overall, the state of the art lacks precise measurement of tension force. Rather, EP 0 847 922 A1 uses indirect equivalent values ​​as a rough guide to tension force, allowing for a somewhat controlled tensioning process. A precise measurement of the actual tension force during a tensioning process in known strapping devices is desirable, but not yet known.

[0007] The invention is based on the technical problem of further developing such a strapping device in such a way that the tensioning force can be precisely measured during the strapping process and especially during the tensioning process in order to ensure a constant tensioning force regardless of the goods to be strapped.

[0008] To solve this technical problem, a strapping device of the generic type within the scope of the invention is characterized in that the drive and tensioning unit is rotatably connected to the closing unit and is supported on the closing unit with the interposition of a connecting element equipped with a measuring element for measuring the tensioning force.

[0009] According to the invention, the strapping device is designed in several parts, comprising at least the drive and tensioning unit and the closing unit. The drive and tensioning unit is rotatably connected to the closing unit and preferably connected to it by means of the pivot bearing. The only other "connection" between the drive and tensioning unit and the closing unit is the connecting element, with the aid of which the drive and tensioning unit, which is rotatably connected to the closing unit, is supported on the closing unit. The connecting element is equipped with the measuring element for measuring the tension force, or the connecting element itself can also be designed as such for measuring the tension force.

[0010] Due to the preferred pivot bearing of the drive and tensioning unit on the closure unit, force is only transmitted at or via the connecting element. During the tensioning process, the entire drive and tensioning unit exerts a clamping force around the pivot bearing, which is countered exclusively by the connecting element. The clamping force to be countered results from the force transmitted to the at least one tensioning roller provided as a component of the drive and tensioning unit during the tensioning process. A tangential force of the tensioning roller acts on the material to be wrapped, whereby the material naturally and depending on the specific material has a resistance force opposite to the clamping force, which acts on the tensioning roller. This force ratio results in the entire drive and tensioning unit striving to rotate around the pivot point of the pivot bearing of the two units and is prevented or prevented from doing so exclusively by the connecting element.is countered.

[0011] This makes it possible, according to the invention, to perform precise clamping force measurements using the measuring element. The measuring element is preferably designed as a load cell. Other measuring element designs, such as piezoelectric force sensors, Hall sensors, or capacitive sensors, are also possible.

[0012] For particularly simple clamping force measurement, it is preferred that the measuring element measures the clamping force linearly in the direction of force action. According to the invention, the direction of force action refers to a tangential force emanating from the pivot point of the pivot bearing between the drive and clamping unit and the locking unit. A radius extends from the pivot point of the pivot bearing as the center point, for example, to the connecting element. The tangential force then acts tangentially from this assumed circle toward the locking unit. This defines a tangential force vector and thus the direction of force action.

[0013] This preferably linear force measurement advantageously allows for the use of particularly simple and inexpensive measuring elements, such as a load cell. To eliminate other vertical force components acting on the measuring element and thus enable linear force measurement, the orientation of the measuring element follows the tangential force vector around the pivot point. The resulting exclusively linear clamping force ensures that particularly precise measurements are possible using the measuring element.

[0014] The drive and tensioning unit of the strapping device preferably has at least one tensioning roller and / or at least one transport roller. In addition, the drive and tensioning unit has at least one tensioning counter-roller associated with the tensioning roller and / or at least one transport counter-roller associated with the transport roller. When the drive counter-roller engages the drive roller, it ensures that the strapping band clamped between the drive roller and the drive counter-roller is transported. In contrast, the tensioning counter-roller, in conjunction with the tensioning roller, ensures that the strapping band clamped between them is or can be tensioned.

[0015] The at least one tensioning counter roller thus works together with the tensioning roller, and the transport counter roller works together with the transport roller for the belt drive. Typically, the drive and tensioning unit specifies two opposing rotation directions to provide two different belt conveying modes. One rotation direction provides for the belt to be conveyed through a belt channel by the transport roller and the transport counter roller, preparing the belt for strapping the goods. In the opposite rotation direction, however, the belt is tensioned by the tensioning roller and the tensioning counter roller.

[0016] To ensure this, at least the tension roller and / or the transport roller are preferably designed to be free-running. The freewheel can be provided, for example, by a pawl freewheel in the desired direction of rotation.

[0017] Furthermore, the tensioning counter roller and the transport counter roller are preferably coupled to each other by a coupling element, so that only one of the counter rollers assigned to the respective tensioning roller or the transport roller is pivoted in at a time. This reciprocal pivoting allows the belt to be guided in opposite directions without causing the belt to buckle. Thus, the tensioning counter roller is not engaged with the tensioning roller during the belt conveying process, as otherwise conveying would not be possible, whereas the transport counter roller is not engaged with the transport roller during the tensioning process.

[0018] The mutual engagement or connection is preferably achieved by pivoting the eccentrically mounted transport counter roller or the eccentrically mounted tensioning counter roller against the transport roller or the tensioning roller by a spring-loaded coupling element. The eccentric mounting of the transport counter roller or the tensioning counter roller, together with the coupling by the spring-loaded coupling element, ensures that only one of the counter rollers of the respective corresponding roller is pivoted in at a time during an actuation of the coupling element.

[0019] According to the invention, the spring-loaded coupling element is preferably designed as a plunger. The coupling element can be a single-piece or multi-piece design. It is also conceivable that the coupling element be spring-loaded and / or be equipped with a spring effect itself.

[0020] The spring-loaded coupling element is preferably acted upon by an eccentric. The eccentric can, for example, be designed as a cup wheel with at least one cam. The eccentric is preferably connected to a camshaft mounted in the closure unit and thus follows the orientation or position of the camshaft. The plunger can have a roller that rolls on the front outer surface of the eccentric or cup wheel and thus initiates the linear adjustment of the plunger with the aid of an elevation, for example a cam, depending on the position of the cup wheel or camshaft. This method is particularly advantageous for the strapping device according to the invention, since it avoids a further rigid connection that could influence the measurement result of the measuring element.

[0021] The configuration is preferably such that the contact point between the ram and the eccentric and the pivot point of the pivot bearing are aligned in cross-sectional and frontal views. The pivot point of the pivot bearing and the contact point between the ram and the eccentric are therefore both located on a predominantly horizontal rotation axis R. This advantageous design ensures that no additional torque is transmitted to the strapping device or the two connected units by the ram and / or the eccentric. This, in turn, ensures an accurate and precise measurement of the tension force.

[0022] A strapping device according to the invention can preferably also have a tension control loop (feedback loop). The tension can thus preferably be measured in real time, the result processed and analyzed, and the tension subsequently adjusted. This ensures safe and controlled strapping with precisely known tension parameters.

[0023] Within the scope of the invention, the drive and tensioning unit comprises at least one drive motor. Such drive motors in strapping devices are typically electric motors, but other known motor types such as combustion engines or hydraulic motors are also possible. Preferably, the drive motor drives both the transport roller and the tensioning roller. It is also conceivable for the transport roller and the tensioning roller to be driven by separate motors.

[0024] As already explained, it is advantageous to use a single drive motor that drives both the drive roller and the tension roller. For this purpose, the drive motor generally applies force to the tension roller via a gear. The gear is preferably a reduction gear, since high torques are generally required to tension the strapping band after it has been wrapped around the material to be strapped, and the drive motor is generally designed as a high-speed electric motor. In contrast, no gear ratio is usually required to apply force to the drive roller.

[0025] The drive motor is generally coupled to the transmission upstream of the tension pulley, on the one hand, and to the drive pulley, on the other, via a motion transmission device. This motion transmission device can be a belt, particularly a toothed belt.

[0026] In the following, the invention is explained in more detail with reference to drawings which merely represent an exemplary embodiment;

[0027] They show: Fig. 1 the strapping device according to the invention schematically in a front view and Fig. 2 a section through the object according to the Fig. 1 schematically in the front view and Fig. 3 the drive and tensioning unit according to the invention in a rear view and Fig. 4 the locking unit according to the invention schematically in the front view.

[0028] The figures show a strapping device 1. The strapping device 1 consists of two main components, the drive and tensioning unit 2 and the sealing unit 3. These are only connected or in contact with each other by the connecting element 4 and the pivot bearings 5, 6. The Fig. 1 The pivot bearing 5, 6 shown is composed of a pin 5 assigned to the closure unit 3 and a bore 6 on the drive and tensioning unit 2 associated with the pin 5. Overall, the strapping device 1 serves to guide the strapping band 7 around objects or goods to be strapped, as is generally known and explained in detail in the prior art already referred to in the introduction.

[0029] For this purpose, the strapping band 7 is pulled by a Fig. 1 fed from a strap supply (not shown) and then guided around the goods and then tensioned. The strapping band 7 is conveyed by the drive and tensioning unit 2. After the strapping band 7 has been strapped and tensioned, the strap is closed in the closing unit 3, which in the exemplary embodiment and not restrictively is designed as a friction welding unit. The closing unit 3 ensures that the ends of the strapping band 7 to be connected to one another are coupled after tensioning around the goods to be strapped, in this case by friction welding. Of course, the closing unit 3 can also ensure the desired connection of the ends of the strapping band 7 in another way.

[0030] Decisive for the present invention are the Fig. 2 The pivot bearings 5, 6 with the pivot point D and the connecting element 4 can be seen. The sectional view in the Fig. 2 It can be seen that the strapping band 7 is guided here, for example, by a total of four rollers 8, 9, 10, and 11. A transport roller 8 and a transport counter roller 9 ensure, by way of example and not limitation, that the strapping band 7 is guided to the goods to be strapped, in order to subsequently strap the goods. A tensioning roller 10 and a tensioning counter roller 11 subsequently ensure that the strapping band 7 of the already strapped goods is sufficiently tensioned.

[0031] The tensioning force applied is of great importance, as it can compensate for any material differences in the goods to be strapped. With precise tensioning force measurement, the strapping device 1 can also react to compressions of the goods to be strapped and adjust the overall tensioning force or keep it constant. Such continuous tensioning force measurements also make it possible to compensate for delayed compressions or other changes in the goods in such a way that the tensioning force remains constant in a controlled manner.

[0032] This tensioning force measurement is performed in the strapping device 1 shown as an example by the connecting element 4. In the illustrated embodiment, the connecting element 4 itself is designed as a measuring element; however, it is equally possible according to the invention for the connecting element 4 to have a measuring element. For this purpose, the drive and tensioning unit 2 is rotatably connected to the closing unit 3 via the pivot bearings 5, 6 and the pivot point D and is supported on the closing unit 3 via the connecting element 4.

[0033] During the tensioning process, the tensioning roller 10 rotates clockwise and, with the aid of the tensioning counter-roller 11, generates a tensioning force on the strapping band 7 and on the material to be strapped. As a result, the entire drive and tensioning unit 2 strives to rotate counterclockwise around the pivot point D of the two units. Since, apart from the pivot bearings 5, 6, the connecting element 4 is the only rigid contact point between the drive and tensioning unit 2 and the closing unit 3, all of the force resulting from the tensioning process acts on the connecting element 4. The connecting element 4 is, by way of example and particularly advantageously, selected such that it is oriented tangentially to a circle with the pivot point D and the radius up to the connecting element 4 and consequently to the torque around the pivot point D, so that ultimately only a linear force vector F acts on the connecting element 4.The connecting element 4, designed as a measuring element, measures the clamping force linearly in the direction of the force vector F, thus enabling particularly simple and loss-free, or unadulterated, measurement of the clamping force. The exact clamping force is calculated based on the leverage ratios in relation to the pivot point D, depending on the positioning of the connecting element 4.

[0034] In order to be able to provide the opposing band guiding directions, namely a transport direction and a tensioning direction, the strapping device 1 operates with two mutually coupled counter rollers 9, 11 for the respective transport 8 or tensioning roller 10. The Fig. 3 shows the rear view of the drive and tensioning unit 2 and in particular the coupling of the transport counter roller 9 with the drive counter roller 11. In the exemplary embodiment, this mutual relationship to the simultaneous pivoting in and out of the counter rollers 9, 11 involved is not restrictively expressed as follows.

[0035] The two counter rollers (transport counter roller 9 and tension counter roller 11) are connected to each other by a tappet 12 and a lever 13 acted upon by the tappet 12. The tappet 12 has a roller 14 at its end pointing towards the connecting unit 3. In the exemplary embodiment, the roller 14 is located opposite an eccentric 16 located on a camshaft 15 of the connecting unit 3. As shown in the Fig. 4 As shown, the eccentric 16 is designed here, by way of example and not by way of limitation, as a cup wheel 16 with at least one cam 17. The force introduction or the movement of the tappet 12 is thus realized by the cup wheel 16 or by the cam 17 located on the cup wheel 16, which is located at the end of the camshaft 15. The roller 14 rolls on the outer surface of the cup wheel 16 and thus initiates the linear movement of the tappet 12.

[0036] The tappet 12 moves in accordance with the camshaft position and the associated position of the cup wheel 16 including the cam 17, thereby moving the two counter rollers 9, 11 in the drive and clamping unit 2.

[0037] If we now return to the core of the invention, the clamping force measurement in a linear direction, it can be stated that no external forces may act on the drive and clamping unit 2, as these would falsify the measurement of the clamping force.

[0038] This is achieved, on the one hand, by the movement of the plunger 12 being provided by an at least low-resistance contact between the cup wheel 16 and the roller 14. In the exemplary embodiment and particularly advantageous for the clamping force measurement, the position of the roller 14 and the cup wheel 16 is selected such that the linear force introduced by the cup wheel 16 runs on a rotation axis R, which runs horizontally through the pivot point D and the contact point between the cup wheel 16 and the roller 14, specifically in the top view of the contact point between the coupling element 12 and the eccentric 16 and the pivot point D according to the Figur 4 . In a cross-sectional view, the pivot point D and the contact point between the cup wheel 16 and the roller 14 are therefore located one above the other. This advantageously prevents any additional torque from being introduced into the drive and clamping unit, so that no additional linear force component acts on the connecting element 4, resulting in an overall unadulterated measurement of the clamping force.

[0039] The plunger 12 is moved linearly within the drive and clamping unit 2 by the eccentric 16. The Fig. 3 shows the drive and tensioning unit 2 in a rear view, in a state in which the transport counter roller 9 is "ventilated," i.e., pivoted out. If the ram 12 moves linearly to the right in this exemplary illustration, the eccentrically mounted tensioning counter roller 11 is pressed against the tensioning roller 10. The lever and the eccentricity increase the applied ram force accordingly, resulting in increased pressure of the tensioning counter roller 11 against the tensioning roller 10.

[0040] The resetting of the tensioning counter roller 11 is in turn carried out by a spring which is attached to a lever arm 18 which is attached to the eccentric associated with the tensioning counter roller.

[0041] The transport counter roller 9 of the transport roller 10 also has an eccentric bearing. The contact pressure for conveying the strap 7 is ensured by a spring attached to a lever 13 mounted on the eccentric. This lever 13 is also used for manual lifting or pivoting to feed the strapping device 1 with strap if necessary. A bolt is attached to the back of the ram 12, for example, which acts on the lever 13 and thus on the transport counter roller 9. However, other methods of applying pressure to the lever 13 by the ram 12 are also conceivable.

[0042] A linear movement to the left, viewed from the rear, therefore leads to the swiveling in of the transport counter roller 9 and thus to a belt transport using the transport roller 8.

[0043] This reciprocal relationship ensures simultaneous inward and outward pivoting of the associated counter rollers 9, 11 through the linear movement of the plunger 12. For example, the plunger 12 is actuated by an eccentric 16 as previously mentioned, but other actuation options are also conceivable.

[0044] The configuration of the strapping device 1, and specifically of the drive and tensioning unit 2, shown in the exemplary embodiment is such that the plunger 12 acts linearly in the direction of the sealing unit 3 under spring pressure. This ensures that the roller 14 maintains continuous contact with the eccentric 16 or the cup wheel 16.

[0045] Overall, the transport roller 8 and the tension roller 10 in the illustrated embodiment are driven by a drive motor 19. The respective rollers are connected to the drive motor, e.g., an electric motor 19, by a toothed belt 20. This embodiment of the drive motor application to the rollers 8, 10 is merely exemplary and not restrictive (cf. Fig. 3 ).

[0046] In the embodiment shown, the tension roller 10 is actuated by the drive motor 19 via a gear 21. The gear 21 is designed, for example, such that a reduction gear is provided between the drive motor 19 and the gear 21. This design particularly advantageously results in high torques being available for tensioning the strapping band 7 after it has been guided around the material to be strapped. List of reference symbols

[0047] 1Strapping device 2Drive and tensioning unit 3Closing unit 4Connecting element 5Pivot bearing 6Pivot bearing 7Strapping band 8Transport roller 9Conveyor counter roller 10Tensioning roller 11Tensioning counter roller 12Coupling element, tappet 13Lever 14Roller 15Crankshaft 16Eccentric, cup wheel 17Cam 18Lever arm 19Drive motor 20Timing belt 21Gearbox DPivot point FLinear force vector RRotation axis

Claims

1. Strapping device, with at least one drive and tensioning unit (2), and with a closing unit (3) for connecting the strap ends of a strapping band (7) guided around a product, wherein the at least one drive and tensioning unit (2) is connected to the closing unit (3), characterized by that the drive and tensioning unit (2) is rotatably connected to the locking unit (3) and is supported on the locking unit (3) with the interposition of a connecting element (4) equipped with a measuring element for measuring the tensioning force.

2. Device according to claim 1, characterized in that the complete drive and clamping unit (2) exerts a clamping force around a pivot bearing (5, 6) during the clamping process, which is countered exclusively by the connecting element (4).

3. Device according to claim 1 or 2, characterized in that the measuring element is designed as a load cell.

4. Device according to claim 1 to 3, characterized in that the measuring element measures the clamping force linearly in the direction of force action.

5. Device according to one of claims 1 to 4, characterized in that the drive and tensioning unit (2) has at least one tensioning roller (10) and / or at least one transport roller (8).

6. Device according to one of claims 1 to 5, characterized in that the drive and tensioning unit (2) has at least one tensioning counter-roller (11) assigned to the tensioning roller (10) and / or at least one transport counter-roller (9) assigned to the transport roller (8).

7. Device according to one of claims 1 to 6, characterized in that at least the tensioning roller (10) and / or the transport roller (8) are designed to be free-running.

8. Device according to claim 6, characterized in thatthe tensioning counter roller (11) and the transport counter roller (9) are coupled to one another by a coupling element (12), so that only one counter roller (11, 9) assigned to the respective tensioning roller (10) or the transport roller (8) is pivoted in at a time.

9. Device according to claims 6 or 7, characterized in that the eccentrically mounted transport counter roller (9) or the eccentrically mounted tensioning counter roller (11) is pivoted against the transport roller (8) or the tensioning roller (10) by a spring-loaded coupling element (12).

10. Device according to claim 8, characterized in that the spring-loaded coupling element (12) is designed as a plunger (12).

11. Device according to one of claims 6 to 9, characterized in that the spring-loaded coupling element (12) is acted upon by an eccentric (16).

12. Device according to one of claims 1 to 11, characterized in thatthe contact point between the coupling element (12) and the eccentric (16) and the pivot point (D) of the pivot bearing (5, 6) lie one above the other in cross-sectional view.

13. Device according to claim 1 and 5, characterized in that at least one drive motor (19) provides for the drive of both the transport roller (8) and the tension roller (10).

14. Device according to claim 13, characterized in that the drive motor (19) acts on the tensioning roller (10) via a gear (21).

15. A method for producing a strapping using a strapping device according to one of claims 1 to 14, wherein the drive and tensioning unit (2) is rotatably connected to the closing unit (3) and is supported on the closing unit (3) with the interposition of a connecting element (4) equipped with a measuring element for measuring the tensioning force.

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