DE102024207535A1 - Pressure sensor and method for its manufacture - Google Patents

Abstract

A pressure sensor, in particular a resistive pressure sensor, is described, comprising a first and a third layer (12a, 12c) of a rubber material, each provided with an electrically conductive structure (16a, 16c), and a second layer (12b) of a rubber material, which has an electrical resistance dependent on an applied pressure.

Description

The present invention relates to a pressure sensor and to a method for its manufacture according to the preamble of the independent claims.

State of the art

Sensors are already known that, for example, serve to detect touch on a surface. These include both capacitive and resistive sensors. The latter offer particular technical advantages when the weight or pressure exerted on a surface needs to be precisely measured, as this type of sensor exhibits greater robustness. Typical resistive pressure sensors have a multilayer structure, with a first layer containing parallel conductive traces or electrodes, followed by a second layer with piezoelectric capabilities, and a final layer that also features parallel conductive traces or electrodes, but these are arranged perpendicular to the traces of the first layer. This type of sensor is also already used in textile applications.

In this context, it is also relevant from the DE 10 2006 060 188 A1 A pressure sensor is known that uses the change in electrostatic capacitance of a rubber-elastic body. Furthermore, it is known from the DE 100 39 774 C1 A tactile sensor is known which has a pressure-sensitive rubber layer, wherein electrodes integrated into the sensor show different currents depending on the pressure applied to the sensor.

Disclosure of the invention

The present invention relates to a pressure sensor and to a method for its manufacture and its use with the characterizing features of the independent claims.

Advantages of the invention

According to the invention, a pressure sensor is provided, in particular a resistive pressure sensor. The pressure sensor comprises at least three layers of a rubber material, wherein a first and a third layer of a rubber material are each provided with an electrically conductive surface structure, and a second layer of a rubber material has an electrical resistance that depends on the applied pressure.

The particular advantage of using layers of rubber material in a pressure sensor lies in the fact that rubber materials exhibit a high degree of elasticity and elongation, and are largely resistant to moisture, corrosive environments, and temperature fluctuations. This allows for the creation of a pressure sensor that is robust against mechanical and corrosive influences.

Further advantageous embodiments of the present invention are the subject of the dependent claims.

It is therefore advantageous if the first and third layers of a rubber material are each in physical contact with a large area of the second layer of a rubber material that exhibits an electrically conductive resistance dependent on the applied pressure, with the surface on which an electrically conductive structure is applied. This can also be characterized as piezoelectric behavior.

The resulting three-layer structure has the advantage that the respective large areas of the three-layer structure are formed by rubber material, thus protecting the electrically conductive structures located between the first and second, and between the second and third, layers from environmental influences. Furthermore, this increases the accuracy of pressure measurement, as conductivity paths between the electrically conductive structure applied to the surface of the first rubber layer and the electrically conductive structure applied to the surface of the third rubber layer can be determined by observing a drop in electrical resistance when pressure is applied.

Furthermore, it is advantageous if the second layer, made of a rubber material that exhibits an electrical resistance dependent on applied pressure, contains electrically conductive particles. These can be, for example, carbon black, graphite, graphene, carbon nanotubes, or metallic particles such as silver, copper, or aluminum. The advantage of this measure is that, depending on the amount of electrically conductive particles added, the electrical resistance of the second rubber layer can be adjusted to achieve the desired sensor sensitivity.

For example, a rubber material with an increasing content of electrically conductive particles shows Initially, at a low concentration of electrically conductive particles, the material exhibits an electrical resistance that is essentially determined by that of the rubber material itself. As soon as the concentration of electrically conductive particles increases to a level where, for example, mechanical pressure is applied to a surface of the second layer, the electrical resistance of the second layer of rubber material drops sharply when pressure is applied, thus allowing the generation of a measurement signal. This region of the rubber material, whose pressure-dependent electrical resistance exhibits electrically conductive paths depending on the amount of electrically conductive particles added, is called the percolation zone.

In practice, this means that a sensor layer intended to react to even the smallest pressures is, for example, implemented in the form of thin layers and/or has a high content of electrically conductive particles. Conversely, pressure sensors can also be designed that only register a signal at relatively high applied pressures and, for this purpose, incorporate, for example, thicker layers of a rubber material and/or a lower content of electrically conductive particles. For instance, a pressure sensor can be implemented with a total layer thickness of 1–6 mm, where each of the three rubber layers has a thickness of 0.3–2 mm, and the second layer, made of a pressure-dependent rubber material, exhibits a volume resistance of 100 ohms per centimeter. The resulting pressure detection range is then 1–200 g/ ^cm² .

According to a particularly preferred embodiment of the present invention, the electrically conductive structures provided on the first and third layers of a rubber material are designed in the form of parallel electrically conductive conductor tracks. Within the pressure sensor, these parallel electrically conductive conductor tracks are positioned such that the electrically conductive conductor tracks of the first layer of a rubber material are not parallel or are rotated, for example, by 80–100°, in particular 90°, relative to the electrically conductive conductor tracks of the electrically conductive structure of the third layer of a rubber material.

Furthermore, it is advantageous if the pressure sensor layers are made of a rubber material, such as natural or synthetic rubber. Synthetic rubbers used include, for example, ethylene propylene diene monomer (EPDM), ethylene propylene copolymer (EPM), polychloroprene (CR), or styrene-butadiene rubber (SBR). These rubber materials exhibit high long-term durability and sufficient resistance to environmental influences. The individual layers of the pressure sensor can be made from the same or different rubber materials.

According to the invention, a method for manufacturing the pressure sensor according to the invention is also provided. For this purpose, a first and a third layer of a rubber material are each provided with an electrically conductive structure on their surface and then each is applied with its electrically conductive surface to a large area of a second layer of a rubber material, wherein the second layer is made of a rubber material that has an electrical resistance that depends on an applied pressure.

Applying an electrically conductive structure to the surface of the first or third layer of a rubber material can be achieved, for example, by printing with a dispersion of electrically conductive particles in a suitable dispersion medium. Inkjet printing is preferred. Alternatively, electrically conductive particles can be superficially implanted into the rubber material of the first or third layer, directly into the matrix of the rubber material itself. Surface plasma treatment methods are preferred in this case. Other printing, transfer, laminating, and coating technologies suitable for permanently applying the conductive structures to the rubber materials with the required accuracy and resolution can also be used.

The pressure sensor according to the invention can be advantageously used in the field of robotics, for example for touch-sensitive surfaces or force-sensitive grippers, as well as in safety-relevant rooms, for example for correspondingly intelligent or pressure-sensitive floor coverings, as well as in shoe insoles and also in the transport sector, for example for detecting load distribution within transport vehicles.

Brief description of the drawing

• 1 die schematische Darstellung eines Drucksensors gemäß einem Ausführungsbeispiel der vorliegenden Erfindung.

An embodiment of the present invention is shown in the drawing and explained in more detail in the following description of the figures. It shows

• 1 The schematic representation of a pressure sensor according to an embodiment of the present invention.

Character description

In 1 An embodiment of a pressure sensor according to the invention is shown both in a schematic 3D representation and in a schematic cross-section.

The pressure sensor 10 comprises, for example, three layers 12a, 12b, 12c, each made of a rubber material. The second layer 12b of the pressure sensor is made of a rubber material that exhibits an electrical resistance dependent on an externally applied pressure or force and, for example, displays piezoelectric properties. For this purpose, the rubber material of the second layer 12b of the pressure sensor 10 can contain electrically conductive particles in such a quantity that electrically conductive percolation paths appear within the rubber material of the second layer 12b of the pressure sensor 10 when a force or pressure is applied. The application of such a force or pressure is 1 for example, illustrated by an arrow 14.

To detect a locally decreasing electrical resistance of the second layer 12b of the pressure sensor 10 when a force or pressure is applied, the first layer 12a and the third layer 12c of the pressure sensor 10 each comprise, for example, an electrically conductive structure on their side facing the second layer 12b of the pressure sensor 10 in the form of electrically conductive conductor tracks 16a, 16c arranged parallel to each other. The electrically conductive conductor tracks 16a are arranged, for example, parallel to each other and not parallel to each other, or rotated by, for example, 80–100°, in particular 90°, relative to the electrically conductive conductor tracks 16c of the third layer 12c, which are arranged parallel to each other.

This arrangement enables the highly accurate local detection of a force or pressure applied locally to the pressure sensor. When a force is applied locally to the surface of the pressure sensor 10, as indicated by arrow 14, this leads to percolation paths 18 within the second layer 12b of the pressure sensor 10. These paths exhibit a significantly reduced electrical resistance compared to the other areas of the second layer 12b of the pressure sensor 10. In this way, very precise sensor signals can be generated.

The pressure sensor 10 is manufactured, for example, by first providing the surface of the first layer 12a of the pressure sensor 10, which is made, for example, of a first rubber material, with an electrically conductive structure in the form of parallel electrically conductive conductor tracks 16a. This can be done, for example, by printing a dispersion containing electrically conductive particles. Inkjet techniques are suitable for this purpose.

Similarly, the third layer 12c of the pressure sensor 10, which is also made of a first rubber material 12c, can likewise be surface-coated with an electrically conductive structure in the form of parallel electrical conductors 16c, in a manner comparable to the first layer 12a of the pressure sensor 10. The electrically conductive structures formed by the conductors 16a and 16c in the first and third layers 12a and 12c can differ in their structure. For example, the density of the electrically conductive conductors can vary. This allows for different sensitivities of the pressure sensor 10 in the X and Y directions.

The surfaces of the first and third layers 12a and 12c of the pressure sensor 10, which are provided with an electrically conductive structure, are then positioned on large areas of the second layer 12b of the pressure sensor 10 and connected to it. The positioning of the first and third layers 12a and 12c is such that the electrically conductive structures of the respective layers 12a and 12c, in the form of parallel electrical conductors 16a and 16c, are not parallel to each other or are rotated, for example, by 80–100°, in particular 90°, on the surfaces of the second layer 12b of the pressure sensor 10. The layers 12a–12c of the pressure sensor 10 can be fixed, for example, by clamping or taping the layers, preferably in the area of the outer corners of the pressure sensor 10.

Alternatively, the application of an electrically conductive structure to a surface of the first or third layer 12a, 12c of the pressure sensor 10 can also be achieved by implanting electrically conductive particles into the matrix of the respective rubber material of the first or third layer 12a, 12c of the pressure sensor 10. Plasma-based techniques are suitable for this purpose.

Another alternative for manufacturing the pressure sensor 10 is to equip the second layer 12b with electrical conductors arranged parallel to each other on both of its large surfaces. to provide the second layer 12b with, for example, layers 12a and 12c that do not have electrical conductors, in the form of a cover. In this case, layers 12a and 12c can also be made of a different material than the previously described layers 12a and 12c.

QUOTES INCLUDED IN THE DESCRIPTION

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

• DE 10 2006 060 188 A1 [0003]
• DE 100 39 774 C1 [0003]

Claims (11)

Pressure sensor, in particular resistive pressure sensor, comprising a first and a third layer (12a, 12c) of a rubber material, each provided with an electrically conductive structure (16a, 16c), and a second layer (12b) of a rubber material having an electrical resistance that depends on an applied pressure. Pressure sensor after Claim 1 , characterized in that the first and third layers (12a, 12c) made of a rubber material are each positioned with their surface having an electrically conductive structure (16a, 16c) on each large area of the second layer (12b) made of a rubber material which has an electrical resistance which depends on an applied pressure, wherein the two large areas of the second layer (12b) made of a rubber material are opposite each other. Pressure sensor after Claim 1 or 2 , characterized in that the rubber material of the second layer (12b) contains electrically conductive particles made of a rubber material. Pressure sensor after Claim 3 , characterized in that the electrically conductive particles contain soot, graphite, carbon nanotubes, graphene or a metallic material. Pressure sensor according to one of the preceding claims, characterized in that the electrically conductive structure (16a, 16c) applied to the first and/or third layer (12a, 12c) made of a rubber material is designed from electrically conductive conductor tracks arranged parallel to each other. Pressure sensor after Claim 5 , characterized in that the electrically conductive structure (16a) applied to the first layer (12a) made of a rubber material in the form of parallel electrically conductive conductor tracks is positioned rotated by 80-100°, in particular 90°, relative to the electrically conductive structure (16c) in the form of parallel electrically conductive conductor tracks of the third layer (12c) made of a rubber material. Pressure sensor according to one of the preceding claims, characterized in that the rubber material is natural rubber or a synthetic rubber, in particular ethylene propylene diene terpolymer (EPDM), ethylene propylene copolymer (EPM), polychloroprene (CR) and/or styrene butadiene rubber (SBR), wherein the layers (12a - 12c) of the pressure sensor (10) are made of the same or different rubber materials. Method for manufacturing a pressure sensor according to one of the preceding claims, characterized in that a first and a third layer of a rubber material is superficially provided with an electrically conductive structure and then the first and the third layer of a rubber material are each applied to a large area of a second layer of a rubber material, wherein the second layer of a rubber material has an electrical resistance that depends on an applied pressure. Procedure according to Claim 8 , characterized in that the electrically conductive structure is applied to a surface of the first and/or third layer of a rubber material by printing a dispersion of electrically conductive particles in a dispersion medium, in particular by inkjet printing. Procedure according to Claim 8 , characterized in that the first and/or third layer of a rubber material of the pressure sensor is provided in a near-surface area of the layer with electrically conductive particles within the rubber material, in particular by plasma treatment of the layer of a rubber material. Use of a pressure sensor according to one of the Claims 1 until 7 in the field of robotics, especially for touch-sensitive surfaces or force-sensitive grippers, in safety areas, especially for pressure-sensitive floor coverings, in the medical field, especially for shoe insoles and intelligent floor coverings, and in the transport sector, especially for the detection of load distributions in transport vehicles.