Sensor unit and device for monitoring the connection of connectable components and method for monitoring the connection of connectable components

Abstract

Sensor unit (4) for monitoring the connection of connectable components, comprising: a base unit (5), an electrode layer (6) and a sensor layer (7), wherein the electrode layer (6) is formed on the base unit (5), wherein the electrode layer (6) has at least one electrode which is in electrical contact with the sensor layer (7), wherein the sensor layer (7) is formed on a side of the electrode layer (6) facing away from the base unit (5), and wherein the sensor layer (7) is formed from a piezoresistive material such that a change in electrical resistance in the sensor layer (7) can be induced by a mechanical force, wherein the piezoresistive material comprises a carbon nanotube polymer nanocomposite.

Description

[0001] The present invention relates to a sensor unit and a device for monitoring connectable components as well as a method for monitoring connectable components.

[0002] Most mechanical connections in the construction and mechanical engineering sectors are secured using bolted joints. To secure these connections, a tightening torque is specified during assembly. Since the prevailing preload is usually unknown, the tightening torque is set high, with a defined safety factor, to prevent the bolt from loosening and thus avert potential hazards. However, unintended dynamic loads during application can cause the bolted joint to loosen, which can pose a safety risk. For example, rapid environmental changes or cyclical industrial processes can lead to bolt loosening. Different thermal expansion rates of the materials used between the bolt and the joint can also induce unintended bolt loosening.Furthermore, a sudden force applied to the nut, bolt or connection due to dynamic loads can cause a mechanical shock, which also leads to the loosening of the bolted connection.

[0003] Therefore, it is essential to detect and monitor the condition of bolted connections to prevent loosening. Furthermore, monitoring bolt tension is crucial for applications in pipeline networks and can be used as a secondary leak detection system at critical connection points when the primary seal fails.

[0004] Various techniques have been developed to monitor the condition of screws, particularly to prevent overtightening in mechanical and structural engineering applications, as well as in medical and dental implants. Mechanical solutions include, for example, anti-loosening screw units or duplex threaded inserts, which are capable of maintaining a stable anti-loosening effect on screws over extended periods. In civil engineering and construction, screw loosening is often detected through visual inspections by skilled workers or using torque wrenches and torque measuring devices.Alternative solutions based on acoustics and used for assessing the tightness of screws / nuts include a linear acoustic approach based on the dissipation of wave energy, a vibroacoustic modulation based on contact acoustics and nonlinearity, and the Hilbert-Huang transformation method (HHT).

[0005] Improved technologies for detecting bolt loosening, based on sensors and transducers such as piezoelectric transducers and conventional strain gauges, are also employed. These piezoelectric transducers and strain gauges are either attached to a disc between two pre-machined flat metal rings or integrated into the bolts. Some sensors rely on specialized techniques such as electromechanical impedance, magnetic field, and RFID (radio-frequency identification) tags. Furthermore, visual inspection methods have been described, primarily based on image processing techniques. These methods involve capturing images of bolted joints and then using an algorithm to determine changes in rotation angles. This reveals whether and to what extent the bolted joint has loosened.

[0006] On the other hand, several leak detection methods with different approaches and operating principles have been developed over the years. Existing detection systems are based on fiber optic sensors, pressure point analysis, acoustic emission, infrared thermography, negative pressure wave analysis, dynamic modeling, mass-volume balance, and ground-penetrating radar. All these technologies function differently depending on the operating environment, accuracy, and complexity. A market-ready solution for bolt monitoring is the measurement of the circumferential enlargement caused by the bolt preload force. ® The "Boltvalid measuring disc" from Möller Metall-Dichtungen GmbH measures the resistance change of an electrically conductive measuring wire. This wire is wound around the disc and changes its resistance depending on the pressure exerted on the disc, which increases radially outwards and thus affects the length of the measuring wire.

[0007] Another solution for screw monitoring is based on a piezoresistive DiaForce. ® -A coating based on amorphous carbon, deposited from the gas phase using plasma, whose resistance change can be read via RFID. This latter development has not yet reached market maturity, as the manufacturing process is cost-intensive and currently not suitable for mass production.

[0008] Conventional methods, such as determining the maximum torque with torque wrenches, require additional force to detect whether the maximum torque has been reached. This could lead to an already excessive torque being applied to tighten the screw. Furthermore, studies report that inconsistent inspection skills and the limited expertise of skilled workers / inspectors result in numerous errors. These methods are also unsuitable for continuous monitoring of the screw / nut condition. Additionally, both RFID and acoustic methods are expensive and require a complex integration process, a monitoring system, and sophisticated algorithms. Similarly, the full integration of strain gauge-based detection systems into real-world applications can be time-consuming and costly.The construction of a piezoelectric sensor is also expensive due to the additional components required for measurement and data acquisition. The appeal of image processing is generally overshadowed by its limitations in detecting screw changes, as even a slight difference in screw length within the structure can lead to false positives. Furthermore, the performance of the various technologies used in leak detection systems varies depending on complexity, accuracy, and the operating environment.

[0009] Furthermore, the false alarm rate remains a significant problem with existing systems. For example, leak detection systems based on acoustic emissions are sensitive to random noise and prone to false alarms; fiber optic systems are not durable and are expensive to implement; while dynamic modeling systems are costly and require significant computational resources.

[0010] Most existing solutions were designed to determine whether the required torque for tightening the bolt / nut assembly has been achieved, rather than to ascertain the real-time status of the bolt, which is crucial for the early detection of bolt loosening. Furthermore, they are designed for a specific application scenario, making scalability and compatibility with a wide range of torques and bolt dimensions a significant challenge. Moreover, current bolt loosening detection systems can only be implemented through costly installation, maintenance, and bolt readjustment. To date, no solution based on polymer / carbon nanocomposite sensors for bolt loosening detection and monitoring has been presented.

[0011] For example, DE 10 2010 016 211 B4 describes a method for monitoring bolted joints, in which the bolts are marked on their end faces and fitted with measuring pins. The measuring pin consists of a flat, machined surface protruding from the end face. This surface is used to determine the condition of the bolted joint on-site, whereby the specified change in length can be precisely measured or checked using gauges by aligning the opposing flat, machined surfaces. The maximum permissible change in length can also be determined in advance using material certificates, characteristic values, and computer software. This length can then be checked on-site using simple means.

[0012] This invention thus enables simple monitoring of the bolted joint; however, a change in the condition of the affected bolted joint only becomes apparent when it is visually inspected by a person skilled in the art. This means that real-time monitoring is only partially possible. Furthermore, the screws used must be manufactured with very high precision, which complicates the manufacturing process and thus significantly increases the cost of the screw.

[0013] The present invention is therefore based on the objective of proposing a sensor unit, a device and a method for monitoring connectable components, wherein the sensor unit and the device are easily integrated and cost-effective to manufacture and enable precise real-time monitoring.

[0014] This problem is solved according to the invention by a sensor unit according to claim 1, by a device according to claim 6 and by a method according to claim 10. Advantageous embodiments and further developments are described in the dependent claims.

[0015] A sensor unit for monitoring connectable components comprises a base unit, an electrode layer, and a sensor layer, with the electrode layer being formed on the base unit. The electrode layer also includes at least one electrode that is in electrical contact with the sensor layer, the sensor layer being located on the side of the electrode layer facing away from the base unit. Furthermore, the sensor layer is made of a piezoresistive material such that a change in electrical resistance can be induced in the sensor layer by a mechanical force.

[0016] The sensor unit has the advantage of being manufactured simply and cost-effectively due to its layered structure. Furthermore, the direct mechanical contact between the individual layers ensures that the electrical conduction length between the electrode layer and the sensor layer is minimized, thus reducing conduction-induced measurement inaccuracies. Moreover, the sensor unit's design as a "thin-film sensor" allows for the direct and immediate measurement of the relevant mechanical force, even in hard-to-reach locations. Here, mechanical force can be understood as a mechanical pressure force and / or a mechanical torque, particularly the tightening torque of a screw. A mechanical force can then be measured directly and / or...or indirectly act on the piezoelectric sensor layer, inducing a change in resistance that is directly proportional to the applied mechanical force. Thus, the sensor unit enables the measurement of both changes in mechanical force and absolute values ​​of the applied mechanical forces.

[0017] Furthermore, the base unit can be designed as a washer and / or as a polymer-based layer, particularly a polyimide layer. Designing the base unit on a conventional washer ensures that the sensor unit can be integrated into virtually all standard screw connections. Conventional washers also offer a long service life, thus increasing the robustness of the sensor unit. Additionally, washers can be manufactured very cost-effectively, reducing the manufacturing costs of the sensor unit. The polyimide layer, on the other hand, offers the advantage of a high continuous operating temperature, low thermal expansion, and high weather resistance, making this design particularly suitable for harsh environments.It is also possible for the polyimide layer to form on the washer, thus creating a basic unit consisting of the washer and the polyimide layer. Alternatively and / or additionally, the polymer-based layer can, for example, comprise polyethylene terephthalate (PET) and / or other polymers.

[0018] Furthermore, a piezoresistive sensor can be configured, in particular as an annular shape, on the side of the sensor layer facing away from the electrode layer. The term "annular shape" encompasses all circular configurations. By integrating a piezoresistive sensor, in addition to monitoring mechanical forces, continuous monitoring of fluid leakage, such as that contained within connectable components, can be achieved. The annular configuration of the piezoresistive sensor also improves the sealing of the sensor unit against the environment.

[0019] Furthermore, a protective layer can be formed on the side of the sensor layer facing away from the electrode layer to protect the sensor layer. The formation of a protective layer increases the robustness of the sensor unit and thus its reliability and longevity.

[0020] Furthermore, the piezoresistive material can comprise a carbon nanotube polymer nanocomposite, in particular a carbon nanotube epoxy nanocomposite. Carbon nanotube polymer nanocomposites have the advantage of being highly sensitive to changing mechanical forces. This allows, first and foremost, the sensitivity of the sensor unit to be increased. Additionally, the sensitivity of the nanocomposites can be modified by changing the filler concentration of carbon nanotubes or by selecting a different polymer. This means that the sensor unit can be optimally adapted to the specific application by choosing a suitable polymer and / or varying the concentration of carbon nanotubes.

[0021] A device for monitoring connectable components has at least one connecting element by which at least one first component is force-fitted or connectable to at least one second component. The device also includes a sensor unit, which is integrated into the connecting element and / or arranged or can be arranged between the first component and the connecting element. Furthermore, the device comprises a measuring arrangement for processing and converting changes in electrical resistance, a transmission unit for transmitting the signals to a receiving unit, and an electrical supply unit configured to provide the electrical energy for operating the device. The measuring arrangement, the transmission unit, and the electrical supply unit form a system that is pluggable with the connecting element.

[0022] This device allows for real-time and continuous monitoring of the connection between connectable components. Thanks to its power supply unit, the device operates independently of an external electrical supply and can therefore be used continuously for at least 6-8 months. The transmission unit sends the mechanical forces measured in real time to the receiving unit, enabling the rapid and precise detection of changes, such as a loosening or breakage of the connection.

[0023] Furthermore, at least one spacer unit, in particular a washer, can be formed below the base unit and / or above the sensor layer. In this case, "below" means on the side of the base unit facing away from the electrode layer. Similarly, "above" means on the side of the sensor layer facing away from the electrode layer. The additional washers improve the robustness of the device against mechanical shocks and thus better protect the sensor unit integrated into the device.

[0024] Furthermore, the measuring arrangement can include an interface unit for measuring the change in electrical resistance and a converter unit for converting the change in electrical resistance into electrical signals. An analog interface unit provides an alternative transmission option, allowing additional measurement points to be recorded at any time.

[0025] Furthermore, the connecting element can be designed as a screw. This allows the device to be integrated into the most commonly used solution for creating detachable connections between components. This significantly expands the device's range of applications.

[0026] In a method for monitoring connectable components, at least one connecting element force-fits at least one first component to at least one second component, wherein a sensor unit is integrated into the connecting element and / or formed between the first component and the connecting element. The sensor unit comprises a base unit on which an electrode layer is formed, the electrode layer having at least one electrode electrically connected to a sensor layer, the sensor layer being formed on a side of the electrode layer facing away from the base unit. Furthermore, the sensor layer is made of a piezoresistive material such that a mechanical force induces a change in electrical resistance in the sensor layer, and subsequently a measuring arrangement processes the change in electrical resistance and converts it into electrical signals.The signals are then transmitted from a transmission unit to a receiving unit, with an electrical power supply unit providing the electrical energy for operating the transmission unit and the sensor unit. Furthermore, the measuring arrangement, the transmission unit, and the electrical power supply unit form a system that is connected to the connecting element via a plug connector.

[0027] This method enables real-time monitoring of the connection between the joined components. Furthermore, it allows for highly precise measurements, enabling the detection of even the smallest changes and thus allowing for early intervention in case of potential damage or loosening connections.

[0028] The described method is designed to be carried out with the described sensor unit or device, i.e., the sensor unit or device is suitable for carrying out the described method.

[0029] Exemplary embodiments of the invention are shown in the drawings and are described below with reference to the Fig. 1 - 3 described. Recurring features are identified with identical reference symbols.

[0030] They show: Fig. 1 a schematic top view of a base unit, an electrode layer, a sensor layer and a piezoresistive sensor; Fig. 2 a schematic perspective exploded view of a connecting element with a sensor unit and Fig. 3 A schematic frontal view of a device for monitoring connectable components in the connected state.

[0031] In Fig. Figure 1 shows the individual components of a sensor unit 4 side by side. In this embodiment, the sensor unit 4 comprises a base unit 5 on which an electrode layer 6 is applied. The electrode layer 6 comprises four electrodes arranged as four circular segments around a centrally located axis of the base unit 5. Alternatively, only one electrode or more than four electrodes can be provided. In this embodiment, the base unit 5 is circular and designed as a conventional washer. Alternatively, the base unit 5 can also be made of a polymer layer, for example, polyimide, PET, or other plastics. The use of a polyimide layer is particularly advantageous if the sensor unit 4 is to be used under adverse environmental conditions (high temperatures, reactive environments, etc.).

[0032] A sensor layer 7 is applied to the electrode layer 6, which, analogous to the four electrodes, has four sensor elements. The sensor elements are defined as four separate regions of the sensor layer 7 that are electrically isolated from one another. An electrical connection between the sensor elements is only established via at least one electrode on the electrode layer 6. In this embodiment, the number of sensor elements corresponds to the number of electrodes. The sensor elements, or the sensor layer 7, are formed from a carbon nanotube epoxy nanocomposite.

[0033] In addition to carbon nanotube-epoxy nanocomposites, a variety of materials can be used for the sensor layer 7, including graphene, conductive polymers, metal nanoparticles, piezoelectric materials, quantum tunnel composites (QTC), and silicone rubber with conductive fillers. The thickness of the resulting layer stack, i.e., in this embodiment the sum of the thicknesses of the sensor layer 7 and the electrode layer 6, can range from 50 nm to 200 µm. Furthermore, the thickness of the layer stack depends on factors such as the materials chosen, their thicknesses, and the fabrication method used, and preferably lies between a few tens and several hundred micrometers. However, processes such as thin-film deposition can also yield thinner layers in the nanometer to micrometer range, while composite materials or other layer fabrication methods can lead to thicker layer stacks in the millimeter range.

[0034] The nanocomposite can have a filler concentration of carbon nanotubes ranging from 0.05 wt% to 5 wt%. By adjusting the filler concentration, the sensitivity of sensor layer 7 to the applied mechanical pressure can be increased. This enables very precise detection of changes in the mechanical pressure. The filler concentration influences both the mechanical and electrical behavior of the composite.

[0035] In this variant, the nanocomposite comprises catalytic CVD-MWCNTs (Chemical Vapor Deposition - Multi-walled carbon nanotubes) with a purity of > 95%, an outer diameter of 6 nm to 9 nm, and a length of < 1 µm. These MWCNTs are mixed directly with the epoxy resin without further chemical treatment. The mixture is mechanically dispersed for 30 minutes using an ultrasonic sonotrode at 30 W and 25 °C, and then magnetically stirred for 2 hours at 400 rpm. A hardener is then added in a volume ratio of 100:5, and the mixture is blended for 10 minutes at 400 rpm. Finally, the samples are degassed in a vacuum chamber at 120 mbar for 30 minutes to remove water.

[0036] In this embodiment, the sensor layer 7 is printed onto the electrode layer 6. Alternatively, the sensor layer 7 can also be applied by physical vapor deposition.

[0037] In addition to printing and physical vapor deposition, various methods are conceivable for building up the layer system of nanocomposites. These include spray coating, spin coating, dip coating, roll-to-roll coating, inkjet printing, screen printing, stencil printing, mold casting, the Langmuir-Blodgett technique, doctor blade coating, spray pyrolysis, chemical vapor deposition (CVD), and electrophoretic deposition. In spray coating, the nanocomposite solution is sprayed onto the substrate, while in spin coating, uniform deposition is achieved through rapid spinning.In dip coating, the substrate is immersed in the solution, and roll-to-roll coating facilitates large-scale production. Inkjet printing enables precise structuring, while the Langmuir-Blodgett technique allows for controlled monolayer transfer. In doctor blade coating, the solution is spread with a blade, and in spray pyrolysis, atomization and pyrolysis occur. In CVD coating, thin films are deposited using precursor gases, and in electrophoretic deposition, electric fields are used for precise control.

[0038] In addition, another piezoresistive sensor 8 is applied in a circular pattern to the sensor layer 7, so that the sensor elements have an improved seal against environmental influences.

[0039] Fig. Figure 2 shows a connecting element 1, which is formed from a first part 1a and a second part 1b, wherein the units of the sensor unit 4 described above are shown in an exploded view between the first part 1a and the second part 1b. Fig. 3 accordingly represents the in Fig.Figure 2 shows an assembled connecting element 1, which force-fits a first component 2 and a second component 3 together. In this embodiment, the connecting element 1 is designed as a screw. Alternatively, the connecting element 1 can also be designed as a rivet or nail. In addition to screws, rivets, and nails, bolts, pins, clamps, clips, hooks, adhesive bonds, soldered joints, welds, snap fasteners, threaded rods, and locking mechanisms are also conceivable as connecting elements 1. These elements offer various possibilities for attaching and applying pressure to the sensor unit 4, thus providing flexibility for different applications and assembly requirements.

[0040] In this embodiment, the invention comprises a thin piezoresistive layer (sensor layer 7) based on a carbon nanotube polymer nanocomposite layer printed onto a washer (base unit 5). Changing the tightening torque of the screw (fastener 1) alters the resistance of the sensor layer 7, which remains constant at a constant preload. When the screw is loosened, the force exerted on the sensor layer 7 by the screw tension changes, thereby altering the electrical resistance of the sensor layer 7. The sensor layer 7 can be printed onto a commercially available washer or onto a thin film layer, for example, a polyimide layer, which does not impair the function of the washer. This means that the polyimide layer is formed in direct mechanical contact with the washer.Electrode layer 6 is printed on the polyimide layer, and sensor layer 7 is printed on electrode layer 6. Sensor layer 7 comprises the four sensor elements described above to measure the force distribution across the surface of the washer, which is exerted by the screw when tightened.

[0041] This force distribution also provides additional information, namely the orientation of the screw on the sensor unit 4. The sensor layer 7 can also be encased in a protective layer to prevent physical damage from frictional forces and the effects of moisture in harsh environments. Further protection is achieved by placing the sensor unit 4 between two standard washers.

[0042] This means that the sensor unit 4, or device, is a multi-layered system with specific functions, designed as an integrated plug-and-play module for easy installation and monitoring. As previously described, the bottom layer consists of an electrode layer 6, which establishes the electrical contact with the sensitive sensor layer 7. An additional optional layer, particularly advantageous in liquid applications, includes a piezoresistive sensor 8 arranged as a ring. This sensor improves the seal and continuously monitors for liquid leakage in the event of screw loosening, aging, or unwanted impacts. The electrode layer 6, the sensor layer 7, and the piezoresistive sensor 8 are typically arranged coaxially around the axis of rotation.

[0043] The measuring circuit, not shown in the figures, comprises an analog interface unit based on a full bridge circuit for measuring the resistance of the sensors, an extremely low-power microcontroller equipped with a multiplexed analog-to-digital converter, and a module for wired / wireless data / signal transmission. The entire system is designed to fit as a plug-in module over the head of the bolt or screw, i.e., the first part 1a of the connecting element 1. The system is powered by a small coin cell battery, i.e., a power supply unit (not shown), which can provide power for at least 6 months in the case of a wireless module, while the lifespan of the wired module is at least twice as long.

[0044] Advantages of the invention arise from the cost-effective production of the sensor unit 4, which is made possible by mass-production-ready printing processes. The thin piezoresistive sensor layer 7 can be easily integrated without altering the properties of commercially available washers. This means that the proposed invention can be adapted to any existing washer. Furthermore, the composition of the nanocomposite can also be adjusted by changing the concentration of the nanofiller or varying the polymer, thus enabling sensor elements with adjustable performance, particularly regarding key parameters such as sensitivity and detection range. This allows for a wide range of applications for condition monitoring of bolted connections.

[0045] Thus, the invention enables real-time monitoring of the torque applied to tighten the screw / nut during assembly. Deviations in the force exerted during the screw / nut assembly can also be monitored. Even minor force deviations on the order of a few mN, which can be caused by a rotation of less than 1° or a displacement of 5 nm to 10 nm in either direction, can be easily detected / monitored with a response time of less than 500 µs.

[0046] The ability to monitor force in both directions can provide information about the loosening of the screw when the force decreases, as well as about the increase in force when the screw is tightened or when sudden impacts are caused to the screw / nut assembly. Furthermore, leaks in pipelines can be detected. Pipelines are frequently used to transport various liquids and gases over thousands of kilometers worldwide. The proposed invention thus offers an alternative and efficient method for leak detection at pipeline joints when the pipeline components are connected to the proposed device. QUOTES INCLUDED IN THE DESCRIPTION

[0000] This list of documents cited by the applicant was automatically generated and is included solely for the reader's convenience. The list is not part of the German patent or utility model application. The DPMA accepts no liability for any errors or omissions. Cited patent literature

[0000] DE 10 2010 016 211 B4

[0011]

Claims

[1] Sensor unit (4) for monitoring connectable components, comprising: a base unit (5), an electrode layer (6) and a sensor layer (7), wherein the electrode layer (6) is formed on the base unit (5), wherein the electrode layer (6) has at least one electrode which is in electrical contact with the sensor layer (7), wherein the sensor layer (7) is formed on a side of the electrode layer (6) facing away from the base unit (5), and wherein the sensor layer (7) is made of a piezoresistive material, such that a change in electrical resistance in the sensor layer (7) can be induced by a mechanical force. [2] Sensor unit (4) for monitoring connectable components according to claim 2, characterized by, that the base unit (5) is designed as a washer and / or as a polymer-based layer, in particular as a polyimide layer. [3] Sensor unit (4) for monitoring connectable components according to one of the preceding claims, characterized by , that a piezoresistive sensor (8), in particular as a circular ring, is formed on a side of the sensor layer (7) facing away from the electrode layer (6). [4] Sensor unit (4) for monitoring connectable components according to one of the preceding claims, characterized by , that a protective layer is formed on one side of the sensor layer (7) facing away from the electrode layer (6) in order to protect the sensor layer (7). [5] Sensor unit (4) for monitoring connectable components according to one of the preceding claims, characterized by, that the piezoresistive material comprises a carbon nanotube polymer nanocomposite, in particular a carbon nanotube epoxy nanocomposite. [6] Device for monitoring connectable components with a sensor unit (4) according to one of claims 1-5, comprising: at least one connecting element (1) via which at least one first component (2) is force-fit connected or connectable to at least one second component (3), the sensor unit (4) which is integrated into the connecting element (1) and / or is arranged or can be arranged between the first component (2) and the connecting element (1), a measuring arrangement for processing and converting the change in electrical resistance, a transmission unit for transmitting the signals to a receiving unit and an electrical supply unit designed to provide the electrical energy for the operation of the device, wherein The measuring arrangement, the transmission unit and the electrical supply unit form a system that is pluggable with the connecting element (1). [7] Device for monitoring connectable components according to claim 6, characterized by , that at least one spacer unit, in particular one washer, is formed below the base unit (5) and / or above the sensor layer (7). [8] Device for monitoring connectable components according to one of claims 6-7, characterized by , that the measuring arrangement includes an interface unit for measuring the change in electrical resistance and a converter unit for converting the change in electrical resistance into electrical signals. [9] Device for monitoring connectable components according to one of claims 6-8, characterized by , that the connecting element (1) is designed as a screw. [10] Method for monitoring connectable components, in which at least one connecting element (1) connects at least one first component (2) with at least one second component (3) in a force-fit manner, wherein a sensor unit (4) is integrated into the connecting element (1) and / or is formed between the first component (2) and the connecting element (1), wherein the sensor unit (4) has a base unit (5) on which an electrode layer (6) is formed, wherein the electrode layer (6) has at least one electrode which is electrically connected to a sensor layer (7), wherein the sensor layer (7) is formed on a side of the electrode layer (6) facing away from the base unit (5), and wherein the sensor layer (7) is made of a piezoresistive material, such that a mechanical force induces a change in electrical resistance in the sensor layer (7) and subsequently a measuring arrangement processes the change in electrical resistance and converts it into electrical signals and then the signals are transmitted from a transmission unit to a receiving unit, whereby an electrical supply unit that provides the electrical energy for the operation of the transmission unit and the sensor unit (4), wherein The measuring arrangement, the transmission unit and the electrical supply unit form a system that is connected to the connecting element (1) via a plug connection.

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