Capacitive force measuring device comprising an elastic dielectric

Abstract

The present disclosure relates to a capacitive force measuring device (100), having a multilayered film layer stack (110) comprising a first film layer (111), a second film layer (112) and a dielectric (113) arranged between the film layers (111, 112), said dielectric being elastically deformable under the action of force. The first film layer (111) and the second film layer (112) have respective sensor electrode structures (121, 122) which face the dielectric (113) and which are respectively situated opposite one another in pairs, each sensor electrode structure pair (120) having in each case a capacitance that varies with the electrode distance d thereof. A control unit (140) is designed to detect a deformation of the dielectric (113) from a change in capacitance of the sensor electrode structure pairs (120) and, on the basis of this, to determine a force that is the cause of the deformation.

Description

[0001] CAPACITIVE FORCE MEASURING DEVICE WITH ELASTIC DIELECTRIC

[0002] Description

[0003] The innovative concept described herein relates to a miniaturized force-measuring device that can detect an externally acting force based on a change in capacitance between two electrode surfaces. The electrodes are arranged on two opposing foils. This allows the force-measuring device to be designed very flat. According to the invention, an elastically deformable dielectric is arranged between the two foils.

[0004] In many applications, it is desirable to determine a pressure distribution over a surface and to specify the corresponding values ​​for the determined force or pressure. However, the space available for force or pressure measurement is often very limited.

[0005] An example of a pressure measurement with very limited space would be measuring the pressure inside a battery pack consisting of several individual battery cells. The individual cells can change their thickness or shape (e.g., crowning) over the course of their use. This results in an alternating increase and decrease in pressure within the respective battery cell. Monitoring this behavior is often desirable for battery condition monitoring, especially for vehicle batteries in the field of electromobility.

[0006] An important goal here is to prevent overloading or even explosion in a battery system. Critical pressure conditions should be detected as early as possible so that appropriate measures can be initiated to maintain safe operating conditions if necessary. For the purpose of such condition monitoring, pressure or force sensors can be installed between the individual cells. However, there is very limited space available for this, as only very narrow gaps remain between the individual battery cells. Within such a gap, the pressure distribution should also be recorded over the entire surface of the respective cell, if possible.

[0007] For area force measurement in applications with limited installation space, pressure-measuring foils can be used, for example, which change their color or color saturation under pressure. While this allows for qualitative recording of the pressure distribution in the contact area, quantitative force values ​​cannot be derived in this way.

[0008] Pressure sensing foils containing piezoresistive layers can also be used. Under pressure, the electrical resistance changes, which can then be interpreted as the pressure value. These layers are also known as "FSR: force sensing resistors". However, such piezoresistive layers often suffer from mechanical and / or electrical changes over their service life. Particularly in cases where pressure is applied to the piezoresistive layer of the sensor for an extended period of time, the piezoresistive layer no longer fully returns to its original position, causing the zero value to shift or no longer be reached, with the sensor's sensitivity increasingly deteriorating. In addition, hysteresis effects are known with piezoresistive layers, i.e. when the pressure increases or decreases, different characteristics are passed through during the resistance measurement.This makes it difficult to implement precise, reproducible force or pressure sensors in practice.

[0009] Piezoelectric layers are somewhat less susceptible to this adverse effect. Here, an external force generates a small electrical voltage spike. However, this only occurs during a change in the force. If the external force remains constant, no signal is measured. This therefore does not allow for continuous monitoring of the applied force.

[0010] Capacitive measurement methods are also known as an alternative to piezo technology. These are used primarily for so-called "touch sensors," for example, in smartphones and tablets. Such touch sensors are designed to trigger a signal upon approach or even upon the slightest touch. However, in many applications, such as the aforementioned battery condition monitoring, the exact opposite is desired: that is, a change in capacitance due to external touch or proximity should be prevented. Touch sensors also do not allow pressure measurement.

[0011] Another example of miniaturized pressure sensors is MEMS (Micro Electro Mechanical System). These sensors consist of membranes made of silicon or insulating materials, arranged closely spaced from counter electrodes. Pressure-induced deformation of the membrane leads to a change in capacitance. However, such sensor systems are not suitable for force measurement in very confined spaces, such as gaps between battery cells, because the rigid body of the MEMS component absorbs the pressure, and the membrane can no longer be deformed beyond a certain external pressure.

[0012] Another challenge in the production of miniaturized force measuring devices for use in flat, confined spaces is the flatness and plane-parallelism of the respective sensor layer. Topographical irregularities would result in the pressure no longer being applied across the entire surface of the sensor layer, but only via the highest surface areas. For example, if the sensor layer has a raised area, the entire pressure would be applied to the sensor layer only at this raised area. However, this changes both the pressure distribution and the absolute pressure values.

[0013] Therefore, it would be desirable to improve miniaturized force measuring devices so that they can be used in flat and very space-limited areas, while at the same time force values ​​can be determined largely hysteresis-free without the long-term behavior of the force measuring device changing noticeably.

[0014] This aim is achieved with a force measuring device according to claim 1. The force measuring device according to the invention has a multi-layer film stack with a first film layer, a second film layer, and a dielectric arranged between the film layers, wherein the dielectric is elastically deformable under the action of force. The film layer stack can optionally have further film layers. A film is very thin, wherein the thickness of a film is significantly smaller than its lateral extent, i.e. length and width. A film spans a surface or a plane, so to speak, which can also be referred to as the film plane. The film layers present in the film layer stack are stacked on top of one another in the vertical direction, i.e. perpendicular to the respective film planes. This is also referred to herein as the layer stack direction.The first film layer and the second film layer each have one or more sensor electrode structures. The sensor electrode structures each face the dielectric and are arranged in pairs opposite each other, i.e. one sensor electrode structure on the first film layer and one sensor electrode structure on the second film layer lie opposite each other vertically, i.e. in the layer stack direction. Two opposing sensor electrode structures each form a sensor electrode structure pair. Each sensor electrode structure pair has a capacitance that varies with their electrode spacing. If, for example, a compressive force acts perpendicularly on the film layer stack, the film layer stack, including the elastic dielectric, is compressed, causing the two sensor electrode structures of a sensor electrode structure pair to approach each other.This increases the capacitance measurable at a sensor-electrode structure pair, which in turn can be interpreted as a force value. To determine the force value, the force-measuring device according to the invention has a control unit. This control unit is designed to detect a deformation of the dielectric based on a change in the capacitance of the existing sensor-electrode structure pairs and, based on this, to determine a force causing the deformation.

[0015] Further embodiments and advantageous aspects of the force measuring device according to the invention are recited in the respective dependent patent claims. Some exemplary embodiments are illustrated by way of example in the drawings and are explained below. They show:

[0016] Fig. 1 is a schematic side sectional view of a capacitive force measuring device according to an embodiment,

[0017] Fig. 2 is a schematic side sectional view of a capacitive force measuring device according to a further embodiment,

[0018] Fig. 3A is a schematic plan view of a film layer equipped with a sensor electrode structure according to an embodiment,

[0019] Fig. 3B is a schematic plan view of the back side of the foil layer of Figure 3A, wherein an active shielding electrode structure and a passive metallic ground plane are arranged on this back side,

[0020] Fig. 4A is a schematic plan view of a further film layer equipped with a sensor electrode structure according to an embodiment,

[0021] Fig. 4B is a schematic plan view of the back side of the foil layer from Fig. 4A, wherein an active shielding electrode structure and a passive metallic ground plane are arranged on this back side, Fig. 5 is a schematic perspective view of a foil layer stack for use in a capacitive force measuring device according to an embodiment, and

[0022] Fig. 6 is a schematic plan view of a battery according to an embodiment, wherein several force measuring devices according to the invention are arranged between individual battery cells.

[0023] In the following, embodiments are described in more detail with reference to the figures, wherein elements with the same or similar function are provided with the same reference numerals.

[0024] Method steps depicted or described within the scope of the present disclosure may also be performed in a different order than that depicted or described. Furthermore, method steps relating to a specific feature of a device are interchangeable with that same feature of the device, and the same applies vice versa.

[0025] Figure 1 initially shows a schematic side sectional view of a capacitive force measuring device 100 according to the invention according to one exemplary embodiment. The capacitive force measuring device 100 comprises a multilayer foil stack 110. The multilayer foil stack 110 comprises, among other things, a first foil layer 111, a second foil layer 112, and a dielectric 113 arranged between the two foil layers 111, 112. The dielectric 113 is characterized, among other things, by the fact that it is elastically deformable under the action of force.

[0026] Each foil layer 111, 112 forms a foil plane within the foil layer stack 110. The foil layers 111, 112 arranged in the foil layer stack 110, as well as the dielectric 113 arranged therebetween, are stacked one above the other in a vertical direction, i.e., perpendicular to the respective foil planes. This is also referred to as the layer stacking direction.

[0027] Both the first film layer 111 and the second film layer 112 each have one or more sensor electrode structures 121, 122 facing the dielectric 113 and arranged opposite each other in pairs, with each sensor electrode structure pair 120 having a capacitance that varies with their electrode spacing d. Optionally, the first film layer 111 and / or the second film layer 112 can each have one or more additional active or passive components (not explicitly shown here).

[0028] The capacitive force measuring device 100 according to the invention also has a control unit 140, which can be coupled to the sensor-electrode structure pairs 120, or to the individual sensor-electrode structures 121, 122 of the respective sensor-electrode structure pairs 120. The control unit 140 is configured to detect a deformation of the dielectric 113 based on a change in the capacitance of the sensor-electrode structure pairs 120 and, based thereon, to determine a force causing the deformation.

[0029] For this purpose, the control unit 140 can, for example, determine the electrical charge at the sensor electrode structures 121, 122. The electrical charge absorbed or released by the sensor electrode structures 121, 122 is a measure of the variable electrical capacitance of the respective sensor-electrode structure pair 120.

[0030] Within the foil layer stack 110, the two foil layers 111, 112 can directly and immediately, i.e., without further intermediate layers, adjoin the dielectric 113. The sensor electrode structures 121 can be arranged, for example, on a side or surface 151 of the first foil layer 111 facing the dielectric 113. One or more sensor electrode structures 122 can also be arranged on a side or surface 152 of the second foil layer 112 facing the dielectric 113.

[0031] The sensor electrode structures 121 arranged on the first film layer 111 are positioned vertically, i.e., in the layer stacking direction, opposite the sensor electrode structures 122 arranged on the second film layer 112. In particular, exactly one sensor electrode structure 121 arranged on the first film layer 111 can be positioned opposite each other from exactly one sensor electrode structure 122 arranged on the second film layer 112. Each pair of opposing sensor electrode structures 121, 122 forms a sensor electrode structure pair 120.

[0032] The individual sensor electrode structures 121, 122 of a sensor electrode structure pair 120 are arranged at a specific distance d from one another. This distance d is also referred to as the electrode spacing within the present disclosure. As mentioned above, the control unit 140 can, for example, determine the electrical capacitance of the individual sensor electrode structure pairs 120. The capacitance of each sensor electrode structure pair 120 changes with the electrode spacing d between the individual sensor electrode structures 121, 122 of a sensor electrode structure pair 120.

[0033] The force measuring device 100 shown in Figure 1 is in an initial state in which no external force acts on the foil layer stack 110. However, if an external force acts on the foil layer stack 110, the foil layer stack 110 deforms together with the elastic dielectric 113 arranged centrally therein. Due to this deformation, the electrode spacing d between the individual sensor electrode structures 121, 122 of a sensor electrode structure pair 120 changes, and thus the respective electrical capacitance of the corresponding sensor electrode structure pair 120 also changes. The control unit 140 is designed to determine the magnitude and / or direction of the force acting on the foil layer stack 110 based on the determined capacitance or the determined change in capacitance.

[0034] For example, if a compressive force F1 directed in the vertical direction, ie, in the layer stack direction, acts on one or both sides of the film layer stack 110, the film layer stack 110 is compressed. Accordingly, the electrode spacing d between the individual sensor electrode structures 121, 122 of the respective sensor electrode structure pairs 120 decreases, and their respective capacitance increases.

[0035] If, however, a tensile force F2 directed in the vertical direction, ie, in the layer stack direction, acts on one or both sides of the film layer stack 110, the film layer stack 110 is pulled apart. Accordingly, the electrode spacing d between the individual sensor electrode structures 121, 122 of the respective sensor electrode structure pairs 120 increases, and their respective capacitance decreases.

[0036] If a tensile force F3 directed in a horizontal direction, i.e., perpendicular to the layer stack direction, acts on one or both sides of the foil layer stack 110, the foil layer stack 110 is compressed. Accordingly, the electrode spacing d between the individual sensor electrode structures 121, 122 of the respective sensor electrode structure pairs 120 decreases, and their respective capacitance increases.

[0037] If a compressive force F4 directed in a horizontal direction, i.e., perpendicular to the layer stack direction, acts on one or both sides of the foil layer stack 110, the foil layer stack 110 is pressed apart. Accordingly, the electrode spacing d between the individual sensor electrode structures 121, 122 of the respective sensor electrode structure pairs 120 increases, and their respective capacitance decreases.

[0038] The corresponding forces F ±to F4 can each act individually, or in combination, on the foil layer stack 110. In principle, forces can also act obliquely on the foil layer stack 110. The control unit 140 is in any case designed to detect the respective capacitance changes occurring or the current capacitance of the sensor-electrode structure pairs 120 and, based thereon, to determine a force causative of the deformation of the foil layer stack 110. The force can be determined here, in particular, in terms of magnitude.

[0039] A force acting externally on the foil layer stack 110 thus causes the deformation of the foil layer stack 110 and the elastically deformable dielectric 113 arranged therein, which leads to the capacitance change of the respective sensor-electrode structure pairs 120 just discussed. The force can have various causes. For example, the force can result from an overpressure or underpressure caused by a pressure change. Thus, the force measuring device 100 according to the invention can be used, for example, as a pressure sensor.

[0040] However, it is also conceivable that the force could be temperature-dependent forces, general deformation forces, or strain or tension forces. Accordingly, the force-measuring device 100 according to the invention can be used in the form of a sensor to determine the respective mechanical property (force, strain, pressure, deformation, etc.).

[0041] For the purpose of permanently consistent force measurement, the dielectric 113 arranged within the foil layer stack 110 is, according to the invention, permanently elastically deformable, meaning that it always returns to its original state after deformation caused by a force. The elastically deformable dielectric 113 therefore exhibits no permanent change in shape or thickness after deformation. The use of a purely elastic dielectric 113 prevents, among other things, hysteresis behavior of the sensor electrode structures 121, 122.

[0042] Advantageously, the dielectric 113 should therefore comprise a material that returns to its original thickness upon mechanical pressure relief or is compressed as uniformly as possible upon mechanical stress, whereby this particularly applies to a defined temperature range. Such materials are also referred to as elastomers, i.e., the elastically deformable dielectric 113 can comprise an elastomer or consist of an elastomer. Elastomers exhibit what is known as permanent elasticity.

[0043] Permanent elasticity is also described by the term "compression set." This refers to the remaining permanent deformation (in %) after a defined thermal and / or mechanical compressive load compared to the original starting shape. According to embodiments, the elastically deformable dielectric 113 has a compression set of less than 5%, or preferably less than 2%.

[0044] It is clear that exceeding a certain force results in elastic deformation transforming into plastic deformation. Therefore, the dielectric 113 used in the force-measuring device 100 according to the invention must be dimensioned such that it is subjected to forces below this limit within its intended range of use, and is therefore always subject to elastic deformation. This means that the elasticity of the dielectric 113 must be selected such that the dielectric 113 is permanently elastic within its intended range of use.

[0045] Silicone is a suitable material for many applications. For example, silicone-containing elastomers, such as silicone rubber, can be used for the dielectric 113. Accordingly, embodiments provide for the dielectric 113 to contain silicone or be made of silicone. An additional advantage of using elastic silicone as the dielectric 113 is its vapor permeability and hydrophobicity. This greatly reduces the dependence of the capacitance measurement on ambient humidity.

[0046] The elastically deformable dielectric 113 can be configured in the form of a film layer that is arranged within the film layer stack 110 between the two other film layers 111, 112. Alternatively, the elastically deformable dielectric 113 can be configured in the form of elastic structural bodies that are each arranged between the individual sensor electrode structures 121, 122 of the sensor electrode structure pairs 120. This means that, for example, several separate small elastomers could be positioned between the individual sensor electrode structures 121, 122, which serve as the dielectric 113. The elastic dielectric 113 can therefore be arranged, for example, in the form of a plurality of separate surfaces between each two sensor electrode structures 121, 122 of a sensor electrode structure pair 120. This can be achieved, for example, by punching a dielectric film.

[0047] While the dielectric 113 is preferably permanently elastically deformable, it may be advantageous if the foil layers 111, 112 are each bendable but not stretchable. This means that they can, for example, elastically bend vertically, ie, in the layer stacking direction, in order to follow a deformation of the dielectric 113. The foil layers

[0048] 111 , 112 should, however, not be able to be elastically deformed or stretched, or only minimally, in the horizontal direction, ie perpendicular to the layer stacking direction.

[0049] This can be achieved by ensuring that the elastically deformable dielectric 113 in the center of the foil layer stack 110 has a much lower stiffness (Young's modulus) than the foil layers 111, 112 on which the sensor electrode structures 121, 122 are arranged. The Young's modulus of the material used for the elastically deformable dielectric 113 can therefore be much lower than the Young's modulus of the material used for the foil layers 111, 112 above and below it; preferably, by a factor of 10 to 1000 lower (softer).

[0050] Accordingly, embodiments may provide that the elastically deformable dielectric 113 has a modulus of elasticity (E-modulus) that is at least a factor of 10 lower than the modulus of elasticity of the two film layers 111, 112, so that the elastically deformable dielectric 113 is significantly softer than the first and second film layers 111, 112.

[0051] A combination of film layers 111, 112 made of non-stretchable material (such as polyimide, PET) together with a dielectric 113 made of permanently elastic material (e.g. silicone) can advantageously result in the electrode geometry or the electrode surfaces of the sensor electrode structures 121, 122 arranged on the non-stretchable film layers 111, 112 being maintained even when the layer stack 110 is deformed. This means that the non-elastic or non-stretchable film layers 111,

[0052] 112, which are equipped with the sensor electrode structures 121, 122, do not change their geometry, whereby the electrode surfaces of the sensor electrode structures 121, 122 also remain unchanged. Thus, a measured change in capacitance value can be clearly assigned to a change in pressure. In order to achieve the most uniform application of force over the largest possible area for the purpose of force measurement, it is also advantageous if the outer surfaces of the foil layer stack 110 are designed to be as flat as possible and have as few elevations as possible. This results in a largely homogeneous distribution of the forces acting on the foil layer stack 110, so that the entire foil layer stack 110, including the dielectric 113 arranged therein, is deformed as uniformly as possible.Embodiments of the invention therefore provide that the first and second film layers 111, 112, in an initial state in which no force acts on the film layer stack 110, run essentially plane-parallel.

[0053] The dielectric 113 should also have surfaces that are as plane-parallel as possible, i.e., it should have a thickness D that is as consistent as possible over its entire length L. With regard to the dielectric 113, it is therefore advantageous if, in the initial state within the foil layer stack 110, it has a thickness tolerance AD ​​of less than 5%, or preferably less than 1%, over its entire length L. It should be noted that the thickness D is measured vertically, i.e., in the layer stack direction, and that the length L is measured horizontally, i.e., perpendicular to the layer stack direction.

[0054] Since the dielectric 113 is connected to the film layers 111, 112, a deformation of the dielectric 113 can correspondingly lead to a bending of the film layers 111, 112, which can cause slight lateral distortion. This can lead to the two individual sensor electrode structures 121, 122 of a sensor electrode structure pair 120 no longer being precisely aligned with one another. As a result, the field lines running between the two sensor electrode structures 121, 122 can have an inhomogeneous course, which can lead to slight inaccuracies in the capacitance measurement. To prevent or compensate for this, exemplary embodiments of the invention provide that the two sensor electrode structures 121, 122 each belonging to a sensor electrode structure pair 120 have electrode areas of different sizes.

[0055] As shown schematically in Figure 1 using the example of the leftmost sensor electrode structure pair 120, for example, the sensor electrode structure 121 arranged on the first film layer 111 can have a larger electrode area than the sensor electrode structure 122 arranged on the second film layer 112. The opposite would also be conceivable, as shown by way of example using the rightmost sensor electrode structure pair 120 in Figure 1. Figure 2 shows a further embodiment of a capacitive force measuring device 100 according to the invention. Elements with the same or similar function as in Figure 1 are provided with the same reference numerals, which is why reference is made to the above text sections for their structural and functional description.

[0056] One difference is, among other things, that the film layer stack 110 shown in Figure 2 has one or more optional protective layers 114. These can be configured as protective films 114. For example, a protective film 114 can be arranged on the side 153 of the first film layer 111 facing away from the dielectric 113. Alternatively or additionally, a protective film 114 can be arranged on the side 154 of the second film layer 112 facing away from the dielectric 113.

[0057] The optional protective films 114 can promote plane-parallelism of the film layer stack 110. Furthermore, the protective films 114 can protect additional electrode structures 123, 124, which can optionally be provided on the first and / or second film layer 112, 113, from external contact.

[0058] These additional electrode structures 123, 124 can be actively controllable shielding electrode structures 123 and passively shielding ground planes 124. For example, one or more active shielding electrode structures 123 can be arranged on the side 153 of the first film layer 111 facing away from the dielectric 113, with each shielding electrode structure 123 being arranged opposite a respective sensor electrode structure 121.

[0059] The same applies to the second film layer 112. Here too, for example, one or more active shielding electrode structures 123 can be arranged on the side 154 of the second film layer 112 facing away from the dielectric 113, wherein a shielding electrode structure 123 is arranged opposite a sensor electrode structure 122.

[0060] The first film layer 111 and the second film layer 112 can each comprise an electrically insulating material or consist of an electrically insulating material. Thus, the sensor electrode structures 121, 122 arranged on one side of the respective film layer 111, 112 are electrically insulated from the shielding electrode structures 123 and ground planes 124 arranged on the opposite side of the respective film layer 111, 112. The shielding electrode structures 123 shield the sensor electrode structures 121, 122 directly opposite them from external fields. To achieve the best possible shielding effect, the electrode area of ​​a shielding electrode structure 123 can be larger than the electrode area of ​​the sensor electrode structure 121, 122 directly opposite it.

[0061] The shielding electrode structures 123 can be actively controlled and can thus form an active shield, which is also referred to as a "driven shield." In this case, the shielding electrode structures 123 are controlled with an electrical signal, which results in the electrical potential difference between the respective shielding electrode structure 123 and the directly opposite sensor electrode structure 121 or 122 being as close to zero as possible. In other words, the electrical potential difference between the shielding electrode structures 123 and the sensor electrode structures 121, 122 can be kept at zero by means of an external control. The active shielding electrode structures 123 can be controlled with low resistance.

[0062] Embodiments of the invention therefore provide that the control unit 140 is designed to control the shielding electrode structures 123 with a signal that is designed to minimize or eliminate an electrical potential difference between a shielding electrode structure 123 and the sensor electrode structure 121, 122 directly opposite it.

[0063] Optionally, a passive shield may be provided alternatively or in addition to the actively operated shielding electrode structures 123. This can be provided by ground planes or grounded metal surfaces 124. The passive metal surfaces 124 can be arranged around the active shielding electrode structures 123 and electrically insulated from them. In other words, the active shielding electrode structures 123 can be surrounded by the passive ground planes 124 and insulated from them.

[0064] Figures 3A-4B each show a plan view of the electrode structures 121, 122, 123, 124 just discussed. Figure 3A first shows a plan view of the side 151 of the first film layer 111 facing the dielectric 113, including a sensor electrode structure 121 of a sensor electrode structure pair 120 arranged there. Figure 3B shows a plan view of the rear side, ie of the side 153 of the first film layer 111 facing away from the dielectric 113. Here, the previously described shielding electrode structure 123 can be seen, which is surrounded by a ground plane 124 and electrically insulated from it.

[0065] Figure 4A shows a plan view of the side 152 of the second film layer 112 facing the dielectric 113, including a sensor electrode structure 122 arranged there, which belongs to the same sensor electrode structure pair 120 as the sensor electrode structure 121 shown in Figure 3A. Figure 4B shows a plan view of the rear side, ie of the side 154 of the second film layer 112 facing away from the dielectric 113. Here, too, a previously described shielding electrode structure 123 can be seen, which is surrounded by a ground plane 124 and is electrically insulated from it.

[0066] Embodiments of the invention accordingly provide that the side 153, 154 of the first and / or second foil layer 111, 112 facing away from the elastically deformable dielectric 113 is covered with a grounded metal surface 124, wherein the grounded metal surface 124 laterally surrounds the one or more shielding electrode structures 123, and wherein the grounded metal surface 124 and the one or more shielding electrode structures 123 on the respective foil layer 111, 112 are electrically insulated from one another.

[0067] The sides 153, 154 of the first and / or second foil layers 111, 112 facing away from the elastically deformable dielectric 113 can be completely covered with the grounded metal surface 124, with the exception of the shielding electrode structures 123 (and a free section running around them for the purpose of electrical insulation). However, it would also be conceivable for the sides 153, 154 of the first and / or second foil layers 111, 112 facing away from the elastically deformable dielectric 113 to be only partially covered with the grounded metal surface 124. Embodiments of the invention therefore provide that the foil surfaces between the active shielding electrode structures 123 are largely covered with conductive metal surfaces that are at ground potential and that are electrically insulated from the shielding electrode structures 123.

[0068] As mentioned at the beginning, Figures 3A and 4A each show sensor electrode structures 121, 122 that belong to the same sensor electrode structure pair 120 and are therefore located opposite one another within the film layer stack 110 (not explicitly shown here). As can be seen here, the sensor electrode structures 121, 122 on the first film layer 111 (Figure 3A) and on the second film layer (Figure 4A) can each have their own electrical supply line 131, 132. The electrical supply lines 131, 132 can each be connected to the control unit 140 (see Figure 2). For example, the sensor electrode structure 121 arranged on the first film layer 111 can have its own electrical supply line 131, which can be connected to the control unit 140.Alternatively or additionally, the sensor electrode structure 122 arranged on the second film layer 112 can have its own electrical supply line 132, which can be connected to the control unit 140. This allows individual sensor electrode structure pairs 120 to be controlled and / or read individually or in groups. Thus, the capacitance of the electrode surfaces of the sensor electrode structures 121, 122 can also be read individually, since a single conductor path 131, 132 leads to the individual sensor electrode structures 121, 122 of a sensor electrode structure pair 120, or to groups of sensor electrode structure pairs 120. The capacitive sensor electrode structure pairs 120 can thus be controlled and read individually.

[0069] Based on the top views depicted in Figures 3A and 4A, it can be seen that the electrical leads 131, 132 of the two sensor electrode structures 121, 122, as seen in the top view, do not overlap or cross. For example, the electrical leads 131, 132 can be routed away from the respective sensor electrode structure 121, 122 in different or opposite directions (e.g., upwards and downwards), as schematically depicted here. This prevents crossover.

[0070] Avoiding overlap or crossing of the electrical leads 131, 132 is desirable in order to prevent the formation of unwanted parasitic capacitances between the electrical leads 131, 132. Thus, the formation of capacitances for the purpose of force measurement is limited purely to the areas of the individual sensor electrode structures 121, 122. In principle, therefore, the individual leads 131, 132 of the sensor electrode structures 121, 122 should, if possible, have no or only a few crossings with conductor tracks on other film levels 122 within the film layer stack 110.

[0071] Embodiments of the invention therefore provide that the two sensor electrode structures 121, 122 each belonging to a sensor electrode structure pair 120 each have their own electrical supply line 131, 132, wherein, viewed in a plan view of the film layer stack 110, these two electrical supply lines 131, 132 run largely without overlap. As can be seen in Figures 3B and 4B, the actively controllable shielding electrode structures 123 arranged on the rear side can also each have their own electrical supply line 133. Here, however, an overlap of the electrical supply lines 133 of the shielding electrode structures 123 with the electrical supply lines 131, 132 of the sensor electrode structures 121, 122 is desirable for shielding reasons.This means that the electrical leads 133 of the shielding electrode structures 123 can be routed such that they cover the electrical leads 131, 132 of the two sensor electrode structures 121, 122, if possible over their entire length. The electrical leads 133 of the shielding electrode structures 123 can have essentially the same shape and the same routing layout as the electrical leads 131, 132 of the sensor electrode structures 121, 122.

[0072] For visualization purposes, Figure 5 shows a schematic perspective view of a foil layer stack 110 with a first foil layer 111, a second foil layer 112 and an elastically deformable dielectric 113 arranged therebetween.

[0073] The first sensor electrode structure 121, including its electrical supply line 131, is arranged on the side 151 of the first film layer 111 facing the dielectric 113. An active shielding electrode structure 123, including its electrical supply line 133, is arranged on the side 153 of the first film layer 111 facing away from the dielectric 113. As can be seen, the active shielding electrode structure 123, including its electrical supply line 133, preferably completely covers the first sensor electrode structure 121, including its electrical supply line 131.

[0074] The second sensor electrode structure 122, including its electrical supply line 132, is arranged on the side 152 of the second film layer 112 facing the dielectric 113. An active shielding electrode structure 123, including its electrical supply line 133, is arranged on the side 154 of the second film layer 112 facing away from the dielectric 113. As can be seen, the active shielding electrode structure 123, including its electrical supply line 133, preferably completely covers the second sensor electrode structure 122, including its electrical supply line 132.

[0075] Embodiments of the invention accordingly provide that the individual shielding electrode structures 123 each have an electrical supply line 133, wherein, viewed in a plan view of the film layer stack 110, an electrical supply line 133 of a shielding electrode structure 123 covers the electrical supply line 131, 132 of the sensor electrode structure 121, 122 directly opposite it. The conductive electrode surfaces of the sensor electrode structures 121, 122, and optionally also their respective supply lines 131, 132, can thus be backed or covered on the outside with approximately uniform shielding electrode structures 123 and their respective supply lines 133. The sensor electrode structures 121, 122 and the shielding electrode structures 123 are electrically insulated from one another.The shielding electrode structures 123 can, in turn, optionally be surrounded by grounded metal surfaces (“ground”) 124 and electrically insulated from these.

[0076] It would be conceivable for the active (driven) shielding to be implemented by means of the active shielding electrode structures 123 over the entire surface of a film layer 111, 112. However, this can lead to problems during EMC testing, since very large areas with low resistance would be exposed to the pulse of the active (driven) shielding. Advantageous embodiments therefore provide for only the relevant areas, i.e., above the sensor electrode structures 121, 122 themselves, to be protected against stray capacitances. The rest can be filled with ground surfaces 124. However, the individual supply lines 131, 132 to the sensor electrode structures 121, 122 should, if possible, not spatially cross each other.

[0077] The conductive structures, e.g., the respective sensor electrode structures 121, 122 as well as the shielding electrode structures 123 and their respective electrical leads 131, 132, 133, can be configured in the form of a thin metal layer (e.g., copper), wherein this metal layer can have a thickness of 200 nm to 36 pm, and preferably 2 pm to 10 pm. Thus, the total thickness of the foil layer stack 110 can be kept as thin as possible, despite a large number of conductive structures.

[0078] The electrode surfaces of the sensor electrode structures 121, 122 can be dimensioned such that the capacitance values ​​for individual sensor electrode structures 121, 122 are preferably in a range from 0.5 pF to 100 pF. This enables signal evaluation of individual sensor electrode structure pairs 120 using commercially available evaluation ICs or microcontrollers.

[0079] Some elastic materials exhibit temperature-dependent electrical behavior, whereby their dielectric constant can change depending on the temperature. Such behavior of a dielectric 113 would be counterproductive in the film layer stack 110 described herein. Therefore, embodiments of the invention provide that only elastic materials are arranged between the sensor electrode structures 121, 122 that have virtually constant mechanical and electrical properties over a wide temperature range. This means that the dielectric constant of the material used for the elastically deformable dielectric 113 should remain constant even at varying temperatures.

[0080] To minimize temperature fluctuations, in some embodiments, additional temperature sensors, e.g., in the form of meandering conductor tracks, can optionally be applied to the film layers 111, 112. The temperature measurement thus made possible can be used for temperature compensation for the force measuring device 100. Alternatively or additionally, regions of the sensor electrode structures 121, 122 can be maintained within a defined temperature range using meander-shaped heating elements.

[0081] The capacitive force measuring device 100 described herein can be used in a variety of applications. A non-limiting example would be its use in a battery for monitoring the condition of the battery cells.

[0082] Figure 6 schematically shows a top view of a battery 200. This can be, for example, a vehicle battery. The battery 200 has several battery cells 210 arranged side by side and connected in series. Between each individual battery cell 210, at least one capacitive force measuring device 100 according to the invention can be arranged. Furthermore, at least one capacitive force measuring device 100 according to the invention can be arranged between the last battery cell 210 and the battery wall 220.

[0083] The battery cells 210 can change their geometric shape over their service life. For example, the battery cells 210 can change their thickness or shape (e.g., crowning). This results in an alternating increase and decrease in the pressure between the battery cells 210, which can be monitored using the force measuring device 100 according to the invention.

[0084] Due to its miniaturized design, which results in particular from the foil-based technology described herein, the force measuring device 100 according to the invention can advantageously be arranged in such narrow gaps between individual battery cells 210. For example, the entire foil layer stack 110 can have a total thickness Ds (see Figure 1) measured in the layer stack direction of between 100 μm and 2 mm. Alternatively or additionally, the elastically deformable dielectric 113 can have a thickness D (Figure 1) measured in the layer stack direction of between 20 μm and 1 mm. The plane-parallel surface quality of the foil layer stack 110 enables the most homogeneous force introduction possible over a large area.

[0085] Rolling or lamination is a suitable method for producing the film layer stack 110. Individual film layers 111, 112 can be rolled on or laminated to one another under vacuum, thereby preventing air inclusions.

[0086] The elastomeric dielectric 113 can be inserted as a film between the two film layers 111, 112. However, the dielectric 113 can also be applied as a liquid layer or printed with a defined geometric shape. If liquid layers are applied, they should be subsequently cycled or thermally cured.

[0087] Alternatively or additionally, the elastic dielectric 113 could be arranged in the form of a plurality of separate surfaces between the two sensor electrode structures 121, 122 of a sensor electrode structure pair 120. This can be achieved, for example, by punching a dielectric foil.

[0088] Instead of using an elastic film, the film layers 111, 112 with the sensor electrode structures 121, 122 can also be coated with a liquid or pasty polymer (i.e., not yet crosslinked or cured). After coating the electrode film layers 111, 112 with the elastic polymer (or a precursor), the film layers 111, 112 can be joined together and, if necessary, subjected to a heat treatment in order to achieve a full-surface, air bubble-free layer composite. The coating can be applied to only one of the two electrode film layers 111, 112, or to both electrode film layers 111, 112. It is advantageous to bond the coated film layers 111, 112 before complete crosslinking of the polymer layer. Then, during later temperature-induced crosslinking, a chemical bond can also be achieved between the polymer coatings.

[0089] In summary, the present invention describes a capacitive force measuring device 100 with a foil layer stack 110, which can be in the form of a thin, largely planar multilayer foil structure, for example, in which sensor electrode structures 121, 122 are arranged vertically one above the other in pairs and separated from one another by an elastic, electrically insulating dielectric 113. A plurality of opposing sensor electrode structures 121, 122 can be realized on the multilayer foil structure 110.

[0090] For the individual layers 111, 112, 113 within the foil layer stack 110, foils of different hardness can be used, i.e., with a different modulus of elasticity (E-modulus) for different layers in the multilayer structure. This applies both to the individual foil layers 111, 112 described herein, as well as to the elastically deformable dielectric 113, which can also be in the form of a foil layer.

[0091] As mentioned at the beginning, an external force can lead to a change in the thickness D (e.g., a reduction in thickness) of the dielectric 113. In the event of a reduction in thickness, the distance between the electrode surfaces of the sensor electrode structures 121, 122 of a sensor electrode structure pair 120 is reduced, and thus its electrical capacitance increases. To eliminate the influence of stray electrical fields to the outside, active "driven shield" shielding electrode structures 123 can be applied to both film layers 111, 112, and thus on both sides of the sensor electrode structures 121, 122 arranged there. This type of shielding thus describes exactly the opposite of an otherwise known capacitive touch sensor technology.

[0092] The capacitance at the opposing sensor electrode structures 111, 112 (top and bottom) of a sensor electrode structure pair 120 can thus be measured, with a change in the thickness of the elastic dielectric 113 causing a change in the capacitance. The change in thickness depends on the magnitude of the external force. By measuring a force-capacitance characteristic curve, the force measuring device 100, designed in the form of a multilayer film structure, can be used as a force or pressure sensor. To convert the change in capacitance into values ​​for the externally acting force (e.g., pressure), the elastically deformable dielectric 113 should preferably have a suitable thickness homogeneity.

[0093] According to exemplary embodiments, the film structure or film layer stack 110 can also be designed to be largely plane-parallel. This allows forces to be measured as homogeneously as possible over large surface areas.

[0094] In further embodiments, the sensor electrode structures 121, 122 can be individually readable and also convertible into absolute force or pressure values. This allows for highly precise force measurements with high spatial resolution, i.e., a plurality of sensor electrode structure pairs 120 can be provided on a surface of defined size, each of which can be read individually or in groups.

[0095] Advantageously, no temperature- or humidity-sensitive materials are required for the force-measuring device 100 according to the invention. Furthermore, it would be conceivable to use a non-purely elastic material as the dielectric 113 between the electrode surfaces of the sensor electrode structures 121, 122. While this could achieve pressure sensitivity, the absolute values ​​of the pressure measurement would not be realistically assessable.

[0096] The miniaturized force measuring device 100 according to the invention can be used in a wide variety of applications. An exemplary application would be a spatially resolved pressure sensor for batteries, e.g., for electric vehicles, to measure the pressure between individual cells 210 of a battery block 200 as well as between the outermost cell 210 and the surrounding casing / encapsulation 220 of the battery block 200.

[0097] Another conceivable application scenario would be the measurement of pressure distribution between a vessel for gases or liquids and the surrounding walls. A foil-based force measuring device 100 according to the invention can also be applied there, whereby the flexibility or bendability of the multilayer structure according to the invention is also advantageous in this case.

[0098] The force-measuring device 100 according to the invention can also be used in variable, mechanically flexible gripping systems, e.g., grippers on robot arms. The gripping fingers or tongs can be equipped with the force-measuring device 100 according to the invention (sensitive films) on their surface. This allows, for example, the gripping pressure to be determined and controlled. The flexibility of the film layer stack 110 allows the sensor surfaces to be applied in a form-adaptive manner. It is also helpful here that individual small areas can be read. This allows individual elements of a gripping mechanism to provide individual values.

[0099] The force measuring device 100 according to the invention can also be used in the production of composite materials, e.g. for process control during the compression molding of semi-finished products into finished components.

[0100] It would also be conceivable to use the force measuring device 100 according to the invention in mobile devices, for example, to monitor their batteries. This is because even in mobile devices, the rechargeable battery can swell and cause serious damage. Due to the miniaturized design of the force measuring device 100 according to the invention (sensor foil), it can be easily installed or retrofitted in laptops and mobile phones.

[0101] The force measuring device 100 according to the invention can also be used as a base film with multiple sensor surfaces in a drawer, such as a toolbox. This allows the presence of objects, such as tools, to be automatically detected or monitored. The same applies to storage areas or shelves in a supermarket, which could, for example, enable automated detection of the inventory of available goods.

[0102] The above-described embodiments merely illustrate the principles of the innovative concept described herein. It is understood that modifications and variations of the arrangements and details described herein will be apparent to others skilled in the art. Therefore, it is intended that the concept described herein be limited only by the scope of the following claims and not by the specific details presented in the description and explanation of the embodiments herein.

[0103] Although some aspects have been described in connection with a device, it is understood that these aspects also represent a description of the corresponding method, so that a block or component of a device can also be understood as a corresponding method step or as a feature of a method step. Similarly, aspects described in connection with or as a method step also represent a description of a corresponding block, detail, or feature of a corresponding device.

Claims

Patent claims 1. A capacitive force measuring device (100), comprising: a multi-layer film stack (110) with a first film layer (111), a second film layer (112), and a dielectric (113) arranged between the film layers (111, 112), which is elastically deformable under the action of force, wherein the first film layer (111) and the second film layer (112) each have sensor electrode structures (121, 122) which face the dielectric (113) and are each arranged opposite one another in pairs, wherein each sensor electrode structure pair (120) each has a capacitance which varies with their electrode spacing d, and a control unit (140) which is designed to detect a deformation of the dielectric (113) based on a change in capacitance of the sensor electrode structure pairs (120) and, based thereon, to determine a force which causes the deformation.

2. Capacitive force measuring device (100) according to claim 1, wherein the elastically deformable dielectric (113) is designed in the form of a film layer, or wherein the elastically deformable dielectric (113) is designed in the form of elastic structural bodies which are each arranged between the individual sensor electrode structures (121, 122) of sensor electrode structure pairs (120).

3. Capacitive force measuring device (100) according to claim 1 or 2, wherein the elastically deformable dielectric (113) has a compression set of less than 5%, or less than 2%.

4. Capacitive force measuring device (100) according to one of the preceding claims, wherein the elastically deformable dielectric (113) has a modulus of elasticity which is at least a factor of 10 lower than the modulus of elasticity of the first and second film layers (111, 112), so that the elastically deformable dielectric (113) is significantly softer than the first and second film layers (111, 112).

5. Capacitive force measuring device (100) according to one of the preceding claims, wherein the first and second film layers (111, 112) are each bendable but not stretchable.

6. Capacitive force measuring device (100) according to one of the preceding claims, wherein one or more shielding electrode structures (123) are arranged on the side (153) of the first film layer (111) facing away from the dielectric (113), wherein a respective shielding electrode structure (123) is arranged opposite a respective sensor electrode structure (121), wherein the control unit (140) is designed to control the shielding electrode structures (123) with a signal which is designed to minimize or eliminate an electrical potential difference between a shielding electrode structure (123) and the respective sensor electrode structure (121) directly opposite it.

7. Capacitive force measuring device (100) according to one of the preceding claims, wherein one or more shielding electrode structures (123) are arranged on the side (154) of the second film layer (112) facing away from the dielectric (113), wherein a respective shielding electrode structure (123) is arranged opposite a respective sensor electrode structure (122), wherein the control unit (140) is designed to control the shielding electrode structures (123) with a signal which is designed to minimize or eliminate an electrical potential difference between a shielding electrode structure (123) and the respective sensor electrode structure (122) directly opposite it.

8. Capacitive force measuring device (100) according to one of claims 6 or 7, wherein the side (153, 154) of the first and / or second foil layer (111, 112) facing away from the elastically deformable dielectric (113) is covered with a grounded metal surface (124), wherein the grounded metal surface (124) laterally surrounds the one or more shielding electrode structures (123), and wherein the grounded metal surface (124) and the one or more shielding electrode structures (123) on the respective foil layer (111, 112) are electrically insulated from one another.

9. Capacitive force measuring device (100) according to one of the preceding claims, wherein the electrode area of ​​a shielding electrode structure (123) is larger than the electrode area of ​​the sensor electrode structure (121, 122) directly opposite it.

10. Capacitive force measuring device (100) according to one of the preceding claims, wherein the individual shielding electrode structures (123) each have an electrical supply line (133), and wherein the individual sensor electrode structures (121, 122) each have an electrical supply line (131, 132), and wherein, viewed in a plan view of the film layer stack (110), an electrical supply line (133) of a shielding electrode structure (123) covers the electrical supply line (131, 132) of the sensor electrode structure (121, 122) directly opposite it.

11. Capacitive force measuring device according to one of the preceding claims, wherein the two sensor electrode structures (121, 122) belonging to each sensor electrode structure pair (120) each have their own electrical supply line (131, 132), and wherein, viewed in a plan view of the film layer stack (110), these two electrical supply lines (131, 132) run without overlap.

12. Capacitive force measuring device (100) according to one of the preceding claims, wherein the sensor electrode structures (121) on the first film layer (111) and the sensor electrode structures (122) on the second film layer (112) each have separate electrical leads (131, 132) which are each connected to the Control unit (140) are connected so that individual sensor-electrode structure pairs (120) can be controlled and / or read individually or in groups.

13. Capacitive force measuring device (100) according to one of the preceding claims, wherein the two sensor electrode structures (121, 122) each associated with a sensor electrode structure pair (120) have electrode areas of different sizes.

14. Capacitive force measuring device (100) according to one of the preceding claims, wherein the first and the second film layer (111, 112) run plane-parallel in an initial state in which no force acts on the film layer stack (110).

15. Capacitive force measuring device (100) according to one of the preceding claims, wherein the elastically deformable dielectric (113) has a thickness D to be measured in the layer stack direction and a length L to be measured perpendicular to the layer stack direction, and wherein the elastically deformable dielectric (113) within the foil layer stack (110), over its entire length L, has a thickness tolerance AD ​​of less than 5%, or preferably of less than 1%.

16. Capacitive force measuring device (100) according to one of the preceding claims, wherein the elastically deformable dielectric (113) has a thickness to be measured in the layer stack direction between 20 pm and 1 mm, and / or wherein the film layer stack (110) has a total thickness between 100 pm and 2 mm.

17. Capacitive force measuring device (100) according to one of the preceding claims, wherein the dielectric constant of the elastically deformable dielectric (113) is constant at varying temperatures.

18. Battery (200), in particular a vehicle battery, with several battery cells (210), wherein at least one capacitive force measuring device (100) according to the preceding claims is arranged between one or more battery cells (210), and wherein the one or more capacitive force measuring devices (100) are each designed to detect a pressure change between two battery cells (210).

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