Method for setting a strip tension of a label strip

Abstract

The invention relates to a method for adjusting a strip tension of a label strip (120; 220; 320; 420), wherein the label strip is transported along a transport direction by means of a transport device (100), wherein a drive element (200, 201, 202; 300, 301, 302) of the transport device moves the label strip along the transport direction and generates a strip tension in the label strip, wherein a sensor (110; 203; 303; 403) measures a value indicative of the strip tension and a control unit (180; 280; 380; 480) controls the drive element on the basis of the indicative value and a target value of the strip tension, and wherein the sensor measures the indicative value substantially without influencing the strip tension.

Description

[0001] Method for adjusting the tape tension of a label tape

[0002] The present invention relates to a method for adjusting the tension of a label tape according to claim 1 and to a transport device for transporting a label tape along a transport direction according to claim 9.

[0003] State of the art

[0004] Transport devices and methods for adjusting tape tension are generally known from the prior art. For example, transport devices are known that transport a label tape, which either consists of labels or comprises labels or the like on a transfer belt, along a transport direction via one or more drive rollers and one or more deflection rollers. A tape tension prevailing in the label tape can be set by adjusting the torques acting on the drive rollers.

[0005] However, existing techniques only allow for an insufficient determination of the actual tape tension in the label tape or have an influence on the actual tape tension that is not readily identifiable, so that adjustment problems and / or damage to the label tape can occur when regulating the tape tension.

[0006] Furthermore, various parameters also influence the actual belt tension that occurs, such as the belt material properties, the geometric design of the labels and / or the label tape, the feed rate, the friction properties of the conveyor components, and the climatic environmental conditions.

[0007] Task

[0008] Based on the known state of the art, the technical problem to be solved is therefore to specify a method for adjusting and / or controlling the tape tension and a device for transporting a label tape, with which a reliable transport of the label tape and a precise adjustment and / or control of the tape tension of the label tape are possible.

[0009] Solution

[0010] This problem is solved according to the invention by the method for adjusting the tension of a label tape according to claim 1 and the transport device for transporting a label tape along a transport direction according to claim 9. Advantageous embodiments of the invention are described in the dependent claims.

[0011] The inventive method for adjusting the tape tension of a label tape comprises transporting the label tape along a transport direction by means of a transport device, wherein at least one drive element of the transport device moves the label tape along the transport direction and generates a tape tension in the label tape, wherein a sensor measures a value indicative of the tape tension, and a control unit controls the at least one drive element based on the indicative value and a setpoint value of the tape tension, and wherein the sensor measures the indicative value essentially without influencing the tape tension.

[0012] The drive element can be understood as exactly one drive, such as exactly one servo motor. However, it can also be provided that the drive element comprises several separate drive units, such as a plurality of servo motors. Furthermore, the invention is not limited to exactly one drive element; regardless of the precise configuration, several drive elements can also be provided for moving the label tape along the transport direction.

[0013] The indicative value can be, but does not necessarily have to be, the tape tension of the label tape itself. It could, for example, also be another physical quantity that, in principle, allows a conclusion to be drawn about the tape tension (possibly taking other values ​​into account).

[0014] The target value of the belt tension can be a value of the belt tension or a value indicative of the belt tension, wherein preferably the target value and the indicative value can describe the same physical quantity (for example, a torque, a tensile force, a polarization or a belt tension).

[0015] The fact that the sensor measures the indicative value essentially without influencing the tape tension is to be understood in particular as meaning that the sensor or the selected measuring method is designed in such a way that it has no influence on the tape tension of the label tape, so that the actual tape tension can be determined and adjusted. Depending on the selected measuring method or sensor, however, minor influences on the actual tape tension of at most 5%, preferably at most 2%, and particularly preferably at most 0.5% may be included in embodiments of this disclosure. The term "sensor" is to be understood as any device that is suitable for determining the indicative value using any measuring method that has the required properties, i.e., in particular, that it does not substantially influence the tape tension.For example, the sensor can also be understood as a complete sensor system or sensor assembly, which, in addition to a device for measuring the band tension, may include further components such as internal logic or evaluation units (such as electronics) for evaluating the measured indicative value, and / or a transmitter for transmitting or evaluating the indicative value. In particular, the sensor may include a measuring roller with a displacement measuring strip for determining the indicative value, logic for converting the measured indicative value into a digital or analog signal, and a transmitter for transmitting the indicative value to a control unit.

[0016] This process can be used, in particular, in the beverage, cosmetics, or pharmaceutical processing industries. The labels provided by the label tape can therefore be labels for labeling containers such as bottles, cans, tubes, or the like.

[0017] This method allows for reliable determination of the tape tension, and the tape tension can be adjusted without any feedback effect from the tape tension measurement itself. This increases the reliability of tape tension adjustment, enabling highly accurate setting of the actual tape tension. Since any potential influence of the measurement method used to determine and adjust the tape tension does not need to be considered, the control system complexity for tape tension adjustment is also reduced.

[0018] It may be provided that the sensor measures a torque acting on a drive roller of the drive element as an indicative value and that the control unit determines the belt tension based on the torque and a torque transmitted from a drive to the drive roller.

[0019] The drive can be, for example, a servo motor connected to the drive roller. Since the label tape exerts a torque on the drive roller due to its tension, counteracting the drive torque, the tape tension can be determined by calculating the difference between the applied and measured torque. Because this measurement can be performed without affecting the tape tension itself, for example, using a suitable force or torque sensor on the drive roller, precise measurement and adjustment of the tape tension can be achieved.

[0020] It can be designed so that the control unit controls the drive element based on the specified belt tension and the target value of the belt tension. This reduces the control engineering effort.

[0021] In one embodiment, the drive element comprises at least one active element and / or at least one second active or passive element, and the sensor determines a first tensile force acting on the at least one active element and a second tensile force acting on the at least second active or passive element as an indicative value, and the control unit controls the drive element based on the first and second tensile forces and the setpoint value of the belt tension.

[0022] It may be provided that the drive element comprises at least one active and / or at least one second active or passive element, and that the sensor determines a first tensile force acting on the at least one active element and a second tensile force acting on the at least second active or passive element as an indicative value, and that the control unit controls the drive element based on the first and second tensile forces and the setpoint value of the belt tension.

[0023] An active element is defined here as an element that exerts a torque or, more generally, a force on the label tape in the transport direction. A passive element is defined as an element that is set in motion by the label tape passing by it. A passive element could be, for example, a deflection roller or guide roller without an associated drive; an active element could be, for example, a drive roller with a motor, such as a servo motor, mounted on the drive side.

[0024] For measuring tensile forces, load cells or strain gauges can be used, for example, at the bearings of the respective elements. This measuring method also does not affect the actual tension of the label tape, enabling highly accurate measurement and, at the same time, very precise adjustment of the tape tension.

[0025] It may be provided that the active element includes a drive roller for driving the label tape and the passive element includes a deflection roller for deflecting the label tape.

[0026] Another embodiment involves a drive element applying a braking or clamping effect. In one embodiment, the sensor measures the polarization of a portion of the label tape as an indicative value.

[0027] This embodiment is particularly advantageous for transparent or at least partially transparent label tapes, as no mechanical components are required, thus avoiding any influence on the tape tension. For measuring the polarization, a polarization camera can be provided as part of the sensor, capable of detecting the light emitted by the label tape. The control unit already described, or a control component of the sensor, can compare the detected polarization, for example, with the polarization of the emitted light and determine the tape tension by utilizing a relationship between tape tension and the change in the polarization of incident light during transmission through the material.

[0028] In one embodiment, the sensor can measure at least two indicative values ​​at different points along the transport direction, and the control unit can control the drive element based on the at least two indicative values ​​and the target value of the belt tension.

[0029] By determining two indicative values, changes in the tape tension and / or a more precise determination of the tape tension can be made.

[0030] The label tape can be designed to comprise a backing strip and labels arranged on the backing strip, the labels comprising a printing layer and an adhesive layer bonded to the printing layer. However, other embodiments of the label tape are also conceivable, for example, a continuous label tape in which the labels are present as a label strip without an additional backing strip.

[0031] It can be provided, in particular, that the printing layer is arranged directly on and bonded to the adhesive layer, without a substrate (such as paper or plastic) being present between the printing layer and the adhesive layer. This type of label tape is particularly sensitive to changes in tape tension, as this can lead to damage to the printing layer (for example, tearing of the printing layer). The method according to the invention can achieve improved labeling quality, especially in conjunction with such labels.

[0032] According to the invention, a transport device for transporting a label tape along a transport direction is further provided, the transport device comprising a drive element for moving the label tape along the transport direction and for generating tape tension in the label tape, a sensor for determining a value indicative of the tape tension and a control unit which is configured to control the drive element based on the indicative value and a setpoint value of the tape tension, and wherein the sensor is configured to measure the indicative value essentially without influencing the tape tension.

[0033] With this embodiment, reliable transport can be achieved with regard to maintaining the belt tension.

[0034] It can be provided that the sensor is configured to measure a torque acting on a drive roller of the drive element as an indicative value, and wherein the control unit is configured to determine the belt tension based on the torque and a torque transmitted from a drive to the drive roller.

[0035] The use of such a sensor allows for a very precise determination of the tape tension without causing any change to the tape tension.

[0036] In one embodiment, the drive element comprises an active and a passive element, and the sensor is configured to determine a first tensile force acting on the active element and a second tensile force acting on the passive element as indicative values. The control unit is configured to control the drive element based on the first and second tensile forces and the target value of the belt tension. This embodiment also allows for a more precise determination and adjustment of the belt tension.

[0037] It may be provided that the active element includes a drive roller for driving the label tape and the passive element includes a deflection roller for deflecting the label tape.

[0038] In one embodiment, the sensor is configured to measure the polarization of a portion of the label tape as an indicative value.

[0039] This allows for an accurate determination of the tape tension without any influence on the tape tension itself.

[0040] The sensor can be configured to measure at least two indicative values ​​at different points along the transport direction, and the control unit can be configured to control the drive element based on these at least two indicative values ​​and the target value of the belt tension. This allows for selective adjustment of the belt tension at different points in the transport direction, or for more precise adjustment of the belt tension by using multiple indicative values, thus minimizing errors.

[0041] Brief description of the characters

[0042] Fig. 1 shows an exemplary embodiment of a transport device for transporting a label tape along a transport direction.

[0043] Fig. 2 shows an embodiment of a sensor for measuring a torque acting on a drive roller.

[0044] Fig. 3 shows an embodiment of a sensor for measuring a tensile force.

[0045] Fig. 4 shows an embodiment of a sensor for measuring polarization

[0046] Fig. 5 shows an embodiment of a label tape.

[0047] Detailed description

[0048] Fig. 1 shows a transport device 100 for transporting a label tape 120. In the embodiment shown here, the transport device 100 also includes a dispensing edge 107, via which a label 131, which is held on the label tape 120, for example as a self-adhesive label, can be transferred to a container 130 to be labeled, which is transported, for example, along the periphery of a transport carousel 160. However, this embodiment is not mandatory, and the invention is applicable to any transport device for transporting label tapes 120.

[0049] In the embodiment shown here, the transport device 100 comprises a stationary frame 150, which can, for example, be the frame of a labeling unit. Furthermore, in the transport direction of the label tape 120, the transport device 100 initially comprises a label tape dispenser 101. The label tape can be, for example, in the form of a roll on this dispenser. The label tape 120 is unwound from this label dispenser 101 and can be transported via a plurality of rolls 102, 103, 104, and 105 along the direction of the arrow shown. In the illustrated embodiment, the label tape passes the dispensing edge 107, so that labels 131 are released from the label tape. Downstream of the dispensing edge 107, a label tape receptacle 106 is arranged, onto which the label tape can be wound without the labels 131 that have been transferred to the containers 130. This embodiment is to be understood as exemplary and not as limiting.According to the invention, the transport device 100 comprises at least one drive element with which the label tape can be moved in the transport direction. For this purpose, the drive element is configured to exert a force on the label tape in the transport direction, so that the label tape is moved in this direction. The drive element also thereby creates tension in the label tape, since the force transmitted by the drive element to the label tape counteracts the inertia of the label tape. The drive element can, for example, comprise one or more of the rollers 102 to 105 shown and / or also the label tape holder 106. In particular, the drive element can comprise a drive that can actively drive one of the described rollers or the label tape holder 106, for example by transmitting a torque to it.

[0050] In some embodiments, it may be provided that only the label tape holder 106 is actively driven, i.e., that a torque is transmitted to it by a drive (such as a servo motor). Alternatively or additionally, it may also be provided that one or more of the rollers 102 to 105 are connected to a drive (for example, a servo motor) on the drive side and that a torque is transmitted to these rollers by this drive. The invention is not limited with regard to the number of components of the drive element, wherein the drive element, however, comprises at least one active element that can exert a force on the label tape in the transport direction. Furthermore, one or more passive elements that are not connected to a drive but are driven (for example, set in rotation) by forces transmitted to them from the label tape may be included.The passive elements can include, for example, guide rollers and / or deflection rollers that guide and / or deflect the label tape along the transport direction.

[0051] Furthermore, the transport device according to the invention comprises a sensor 110, which is designed to determine the tape tension of the label tape and / or an indicative value for the tape tension of the label tape. The determination of the tape tension of the label tape or the indicative value of the tape tension can take place at any point along the transport of the label tape 120, but preferably outside the label tape dispenser 101 and / or the label tape holder 106, for example between the rollers 102 and 103.

[0052] According to the invention, the sensor 110 is designed such that it can determine at least one indicative value for the tape tension of the label tape. This indicative value can, in principle, be any physical parameter that, optionally with the aid of further measured quantities or fixed quantities (for example, physical constants or material properties of the label tape 120), allows a conclusion to be drawn about the numerical value of the tape tension.

[0053] Furthermore, according to the invention, a control unit 180 is provided as part of the transport device or a general machine (such as a labeling machine) of which the transport device 100 is a component. The control unit can, for example, be designed as the central control unit of the machine (for example, a labeling machine) and can generally comprise a processor and associated memory in which instructions are stored, the execution of which by the control unit controls at least one function of the transport device.

[0054] According to the invention, the control unit controls the drive element based on the indicative value measured by the sensor 110 and a target value for the belt tension of the conveyor belt, so that the target value for the belt tension of the label belt is achieved (optionally with a tolerance of, for example, ± 1% or up to ± 2%).

[0055] The target value of the tape tension need not specify the tape tension itself, but can, analogously to the indicative value, also specify a target value for the indicative value, so that a conversion of the indicative value to a tape tension is not necessary. Therefore, whenever the target value of the tape tension is mentioned in this disclosure, this also includes any target value of a parameter that, with regard to its physical meaning, corresponds to the indicative value measured by the sensor.

[0056] Instead of controlling the tape tension, a regulation of the tape tension can also be implemented. In this case, based on a defined indicative value and a setpoint, the control unit initially controls the drive element so that the indicative value is expected to be reached when an operating parameter of the drive element is changed. For example, the torque transmitted from a servo motor to a drive roller can be increased or decreased if the comparison between the setpoint and the indicative value of the tape tension indicates that the tape tension of label tape 120 is too high or too low. After this adjustment, the indicative value can be measured again, and the control unit 180 can determine, by comparing it with the setpoint of the tape tension, whether the setpoint has now been reached. If not, the drive element can be controlled again.This process can be repeated until the target value of the belt tension is reached and / or the belt tension corresponds to the target value within a given tolerance (see above).

[0057] The system can be designed to use a deterministic algorithm that determines a change in at least one operating parameter of the drive element (for example, the torque of a servo motor) from a deviation of the belt tension from the setpoint (or a deviation of the respective indicative parameters). Alternatively, the system can be designed to use a neural network and / or a non-deterministic program.

[0058] According to the invention, the sensor 110 measures the indicative value using a measuring method that leaves the tape tension of the label tape 120 essentially unaffected or has essentially no influence on the tape tension. This avoids or reduces any nonlinearities that may occur when controlling the drive element and the subsequent adjustment of the tape tension of the label tape 120, so that the tape tension 120 can be determined with its actual value and adjusted to the desired tape tension (the target value). Particularly with label tapes that are sensitive to changes in tape tension (see, for example, the label tape according to the embodiments of Figure 5), this ensures that damage to the label tape is reliably prevented.However, the invention is not limited to such sensitive label tapes and can, in principle, be used to adjust the tape tension 120 of any type of label tape. The advantage here is always that a more precise adjustment of the tape tension of the label tape and thus a more reliable transfer of the labels to the containers 131 can be achieved.

[0059] Figures 2 to 4 show exemplary embodiments of a sensor which determines the indicative value using a measuring method without influencing the band tension or keeping it essentially constant.

[0060] Figure 2 shows an exemplary drive element 200 comprising a drive roller 201 and a drive 202 connected to the drive roller on the drive side. The drive 202 can, for example, be designed as a servo motor and, in this embodiment, is configured to apply a torque to the drive roller 201 in the direction of rotation shown, so that the drive roller 201 is set in rotation and can transmit a tensile force to the label tape 220 in the transport direction. In the embodiment shown here, the sensor 203 is designed as a sensor that can determine the actual torque acting on the drive roller 201. This torque is determined, on the one hand, by the torque transmitted from the drive 202 to the drive roller 201.Secondly, the torque acting on the drive roller also depends on the tape tension of the label tape 220, since this either counteracts the torque acting on the drive roller 201 on the drive side due to the inertia of the label tape or causes an additional torque on the drive roller if the tangential velocity of the label tape at the point of contact with the drive roller is greater than the tangential velocity of the surface of the drive roller at this point.

[0061] The sensor determines an indicative value for the tape tension by measuring the torque acting on the drive roller. The sensor can be either a mechanical or an electronic torque sensor. Sensor 203 then transmits the measured torque acting on drive roller 201 to control unit 280 as an indicative value. Control unit 280 can then, for example, determine the tape tension of the label tape 220 based on a comparison between the torque transmitted from drive 202 to drive roller 201 and the torque measured by sensor 203. This tension can then be compared with a target value for the tape tension, and the torque transmitted from drive 202 to drive roller 201 can be controlled accordingly.

[0062] As an alternative to determining the belt tension via the measured torque and the torque generated by the drive 202, and subsequently using the belt tension to control the drive element, it can also be provided that the control of the drive 202's torque is determined based on a comparison between the measured torque of the drive roller 201 and a target value for the drive roller's torque (corresponding to a target value for the belt tension). This simplifies the control engineering implementation of this method.

[0063] Fig. 3 shows an alternative embodiment to Fig. 2, in which the drive element 300 comprises an active element 301 and a passive element 302. The active element can be configured as a drive roller 301 (see, for example, Fig. 2) and an associated drive 311 (for example, a servo motor). The passive element 302 can, for example, be a deflection roller not driven by a drive, which can deflect the conveyor belt and thus change the transport direction of the label tape 320. Alternatively, the passive element 302 can also be configured as a guide roller that merely guides the label tape 320 along its transport direction without changing the transport direction.

[0064] In this embodiment, the sensor 303 is configured to determine an indicative value of a first tensile force acting on the active element 301 and a second tensile force acting on the passive element 302. The acting tensile forces, and in particular their difference, depend on the acting belt tension in the label tape, as this influences the degree to which the passive element (here, for example, the deflection roller) is set into rotation when the active element exerts a given tensile force on the label tape. The tensile forces can also be understood as, or derived from, the torques acting on the respective rollers.

[0065] The sensor can either transmit the first and second measured tensile forces to the control unit 380 as indicative values, or transmit the difference between the two as an indicative value. As previously described, the control unit can then determine the tape tension of the label tape by utilizing the relationship between the difference in tensile forces and the effective tape tension. The determined tape tension can then be used to control the drive of the active element by comparing it to the target tape tension. Alternatively, the drive can also be controlled solely based on the difference in tensile forces compared to a target value for this difference, thus eliminating the need for a separate determination of the tape tension.

[0066] The acting tensile forces can be determined, for example, using strain gauges or load cells, which are integrated into the sensor and can be connected to the active and passive elements. A strain gauge or load cell can be provided for each active and passive element, or assigned to the respective elements. However, it is also conceivable to use, for example, a single load cell to directly determine a difference in tensile force, with this single load cell then being connected to both the active and passive elements.

[0067] Fig. 4 shows another alternative embodiment of a sensor for determining the band tension.

[0068] In this embodiment, the sensor 403 comprises an element 432 that can determine the polarization of light emitted by the label tape 420. The element 432 can, for example, be configured as a polarization camera or include one. Furthermore, the sensor 403 comprises a light source 431 arranged on the side of the label tape 420 opposite the element 432. The light source 431 preferably emits light with a predetermined / known polarization in the direction of the element 432. If the label tape is transparent or at least partially transparent (for example, made of plastic), the element 432 detects at least a portion of the light emitted by the light source 431 and transmitted through the label tape.Since the tape tension within the label tape affects the electromagnetic radiation passing through the label tape and can change the polarization of this radiation, the tape tension can be determined by comparing the polarization of the emitted light from the light source 431 with the polarization detected by the control unit 480.

[0069] The sensor 403 can either transmit data to the control unit 480 as an indicative value based on the polarization of the detected light measured by the element 432, or it can transmit the difference between the polarization of the light emitted by the light source 431 and the polarization of the light transmitted through the label tape as an indicative value to the control unit 480. Based on this, the tape tension of the label tape 420 can then be determined and compared with a target tape tension value to control the drive element.

[0070] The drive element is shown here by way of example as a pair of rollers 401 and 402, wherein, for example, the roller 402 arranged downstream in the transport direction can be designed as a drive roller with an associated drive (for example, servo motor), or both rollers 401 and 402 can be designed as drive rollers, or only the roller 401 can be designed as a drive roller and the roller 402 as a deflection roller.

[0071] With this embodiment, any influence on the tape tension of the label tape 420 by the measurement of the tape tension is avoided, since a detection of the light passing through the label tape cannot influence the tape tension.

[0072] Fig. 5 shows an embodiment of a label tape 500, which, in conjunction with the described embodiments, can be used particularly advantageously for determining and controlling the tape tension. In the embodiment shown here, the label tape 500 comprises a carrier tape or substrate 501. A label is arranged on this substrate, comprising printing ink 502, which essentially defines the image information of the label, and an adhesive layer 503 bonded to the printing ink 502. Here, the adhesive layer is arranged on the side of the printing layer 502 facing away from the carrier tape 501. However, a reversed layer structure is also conceivable, such that the adhesive layer 503 rests on the carrier tape 501 and the printing ink 502 is arranged on the adhesive layer.In this embodiment, the label formed from layers 502 and 503 does not include an intermediate substrate, so that the label consists solely of the printing layer 502 and the adhesive layer 503. This label can be detached from the carrier tape 501, for example at the dispensing edge (see Figure 1), and transferred to a downstream transport device or directly to a container. The carrier tape can be removed (as described in Figure 1).

[0073] This label is susceptible to changes in tape tension, as the printing layer and / or the adhesive layer 503 can tear if the tape tension changes or becomes too high. This damages the label. If this label tape 500 is transported using the transport device according to the invention and the tape tension is adjusted according to the above embodiments, for example, to a target value that reliably prevents damage to the labels, negative influences from the measuring method or an incorrect tape tension setting are avoided, thus reducing label damage. This allows for reliable and high-quality transfer of the labels to containers.

Claims

Claims 1. Method for adjusting the tension of a label tape, wherein the label tape is transported along a transport direction by means of a transport device, wherein a drive element of the transport device moves the label tape along the transport direction and generates tension in the label tape, wherein a sensor measures a value indicative of the tape tension and a control unit controls the drive element based on the indicative value and a setpoint value of the tape tension, and wherein the sensor measures the indicative value essentially without influencing the tape tension.

2. Method according to claim 1, wherein the sensor measures a torque acting on a drive roller of the drive element as an indicative value and wherein the control unit determines the belt tension based on the torque and a torque transmitted from a drive to the drive roller.

3. Method according to claim 2, wherein the control unit controls the drive element based on the determined band tension and the target value of the band tension.

4. Method according to claim 1, wherein the drive element comprises at least one active and / or at least one second active or passive element, and the sensor determines a first tensile force acting on the at least one active element and a second tensile force acting on the at least second active or passive element as an indicative value, and wherein the control unit controls the drive element based on the first and second tensile forces and the setpoint value of the belt tension.

5. Method according to claim 4, wherein the at least one active element comprises a drive roller for driving the label tape and the at least one passive element comprises a deflection roller for deflecting the label tape.

6. Method according to claim 1, wherein the sensor measures a polarization of a part of the label tape as an indicative value and / or wherein the sensor measures a tensile force acting on the label tape as an indicative value.

7. Method according to any one of claims 1 to 7, wherein the sensor measures at least two indicative values ​​at different locations along the transport direction and wherein the control unit controls the drive element based on the at least two indicative values ​​and the target value of the belt tension.

8. Method according to any one of claims 1 to 7, wherein the label tape comprises a carrier tape and labels arranged on the carrier tape, the labels comprising a printing layer and an adhesive layer connected to the printing layer.

9. Transport device for transporting a label tape along a transport direction, the transport device comprising a drive element for moving the label tape along the transport direction and for generating tape tension in the label tape, a sensor for determining a value indicative of the tape tension, and a control unit configured to control the drive element based on the indicative value and a setpoint value of the tape tension, wherein the sensor is configured to measure the indicative value substantially without influencing the tape tension.

10. Transport device according to claim 9, wherein the sensor is configured to measure a torque acting on a drive roller of the drive element as an indicative value, and wherein the control unit is configured to determine the belt tension based on the torque and a torque transmitted from a drive to the drive roller.

11. Transport device according to claim 9, wherein the drive element comprises at least one active and at least one active or passive element, and the sensor is configured to determine a first tensile force acting on the at least one active element and a second tensile force acting on the at least second active or passive element as an indicative value, and wherein the control unit is configured to control the drive element based on the first and second tensile forces and the setpoint value of the belt tension.

12. Transport device according to claim 11, wherein the at least one active element comprises a drive roller for driving the label tape and the at least one passive element comprises a deflection roller for deflecting the label tape.

13. Transport device according to claim 9, wherein the sensor is configured to measure a polarization of a part of the label tape as an indicative value, and / or wherein the sensor is configured to measure a tensile force acting on the label tape as an indicative value.

14. Transport device according to one of claims 9 to 13, wherein the sensor is configured to detect at least two indicative values ​​at different intervals along the transport direction 17 to measure positions, and wherein the control unit is designed to control the drive element based on the at least two indicative values ​​and the target value of the belt tension.

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