Method for manufacturing a foil-based pressure sensor

Abstract

The present invention relates to a method for manufacturing a foil-based pressure sensor (1). In order to facilitate the precise setting of the conduction points of the sensor units in the foil-based pressure sensor, the present invention provides the method, which comprises: - providing a bottom element (2) having a bottom foil (3) and at least one bottom electrode (4, 6, 8) provided on the bottom foil (3), - providing a plurality of top elements (20), each top element (20) comprising a top foil (21) having at least one top electrode (22) provided below the top foil (21), the combined area of the top elements (20) being smaller than the area of the bottom element (2), - placing the top elements (20) individually and connecting the top elements (20) to the bottom element (2) at least indirectly, such that at least one top electrode (22) of each top element (20) is provided above at least one bottom electrode (4, 6, 8) of the bottom element (2) to form a sensor unit (30), which sensor unit (30) is adapted to be activated when the pressure (p ext ) acting on the sensor unit (30) exceeds the conduction point, wherein, for at least one sensor unit (30), the conduction point is adjusted by selecting the position (A1, A2, B1, B2) of the top element (20) from a plurality of positions (A1, A2, B1, B2), the sensor unit (30) operating at the plurality of positions, but the conduction points of the plurality of positions being different.

Description

Technical Field

[0001] The present invention generally relates to methods for manufacturing foil-based pressure sensors and foil-based pressure sensors. Background Art

[0002] Modern transportation vehicles are typically equipped with occupancy detection systems that automatically detect the presence of a driver or passenger on a vehicle seat, for example as an input for a seat belt reminder. In addition to capacitive detection systems, there are also pressure sensor-based systems that detect the pressure generated by the weight of a person on a vehicle seat. Some of these systems use foil-based pressure sensors. Such sensors typically include an array of individual but electrically connected sensor units. Each unit includes a bottom electrode and a top electrode, and an external pressure acting on the unit can cause the bottom electrode and the top electrode to make electrical contact, thereby activating the unit. The amount of pressure required to activate a unit is also referred to as the turn-on point.

[0003] Sensors are typically composed of three complete, i.e., full-area foil layers, namely a printed bottom substrate with conductor lines and a bottom electrode, a structured spacer foil with a double-sided adhesive, and a printed top substrate foil with conductor lines and a top electrode. The spacer foil includes holes or cuts, and the top electrode and the bottom electrode are disposed in the holes and cuts. All three foils are laminated on top of each other in a two-step process to form a pressure-sensitive unit. An occupant detection sensor used in an automotive seat consists of an array of sensing units (usually 4 - 10), and 4 - 50 sensors are placed on a laminate. For lamination, alignment marks can be used for the accurate overlay of the three sheets. However, due to process and material tolerances (printing, heating, cutting, lamination, foil shrinkage), not all sensor units will be perfectly aligned, i.e., not all top electrodes will be placed exactly on top of the bottom electrodes. The overall prior art tolerance is in the range of 0.75 mm. This results in a wide distribution of turn-on points, which is a shift of approximately 5 - 10 mbar for every 0.1 mm displacement of the top electrode relative to the bottom electrode. However, for some applications, the turn-on points within a sensor unit should be as reproducible as possible to ensure correct activation of the sensor in, for example, an automotive seat environment, so as to reliably detect the presence of a person compared to not detecting an object on the automotive seat.

[0004] In some situations, it is necessary to modify the turn-on point of a specific sensor unit in a pressure sensor without changing the overall configuration of the sensor. For example, when there are different variants of automotive seats with different seat cushions. According to the prior art, the modification of the turn-on point is typically accomplished by changing the size of the spacer holes or the foil thickness for a given set of materials, i.e., changing the unit design or changing the materials used. Therefore, even when adjusting the turn-on point of a single unit, a redesign of the spacer foil and / or the top foil is required.

[0005] Object of the Invention

[0006] Therefore, the object of the present invention is to facilitate the accurate setting of the conduction points of the sensor units in the foil-based pressure sensor. Summary of the Invention

[0007] The present invention provides a method for manufacturing a foil-based pressure sensor. The sensor can be used in various applications. For example, it can be used in an occupancy detection system in a vehicle (e.g., an automobile). The sensor is pressure-sensitive, which means that the pressure acting on the sensor can be detected electrically. This generally does not mean that the exact amount of pressure can be detected.

[0008] In one step of the method, a bottom element is provided, which includes a bottom foil and at least one bottom electrode disposed on the bottom foil. The bottom element can also be referred to as a substrate element or a base element, etc. Terms such as "bottom", "top", "horizontal", and "vertical" refer to a reference system, in which the pressure to be detected acts vertically downward on the pressure sensor that at least partially extends along a horizontal plane. However, the vertical direction mentioned here does not necessarily correspond to the direction of gravity, and the overall sensor is not necessarily planar, but can be curved or bent at least in some parts. Therefore, more generally, the horizontal plane can be referred to as a (possibly non-planar) "sensor surface" or "tangent surface", and the vertical direction can be referred to as the "normal direction" that is locally perpendicular to the sensor surface. The bottom foil is usually made of an electrically insulating material (e.g., plastic, rubber, or silicone, etc.). Specifically, it can be an elastic material. The present invention generally does not limit the thickness of the bottom foil, which often ranges from 0.01 to 0.5 mm. Due to the low thickness of the bottom foil and possibly due to the material properties of the bottom foil, the bottom element is usually flexible. At least one bottom electrode is disposed on the bottom foil, that is, the corresponding bottom electrode is at least partially disposed on the upper side of the bottom foil. The bottom electrode can be printed on the bottom electrode, for example, as a conductive ink material, or the bottom electrode can be a metal foil attached to the upper surface of the bottom electrode. There are also other options for providing the (one or more) bottom electrodes. Usually, the thickness of the corresponding bottom electrode is less than the thickness of the bottom foil. Although reference is made to at least one bottom electrode, the bottom element usually includes at least two bottom electrodes.

[0009] In another step of the method, a plurality of top elements are provided, each top element including a top foil having at least one top electrode disposed beneath the top foil, the combined area of the top elements being less than the area of the bottom element. The top foil may be made of the same material as that used for the bottom foil, and its thickness may be similar or equivalent to the thickness of the bottom foil. Similarly, the top electrodes may be made of the same material as that used for the bottom electrode(s). The corresponding top electrodes are disposed beneath the top foil, i.e., at least partially on the underside of the top foil, with reference to the orientation of the top element in the assembled sensor. The combined area or total area of the top elements is less than the area of the bottom element. In this context, the area is measured along the surface of the corresponding top foil or bottom foil. Since their combined area is smaller, all the top elements combined cannot completely cover the bottom element.

[0010] In another step, the top elements are placed individually and are connected to the bottom element at least indirectly such that at least one top electrode of each top element is disposed above at least one bottom electrode of the bottom element to form a sensor unit that is adapted to be activated when the pressure applied to the sensor unit exceeds a conduction point. Placing the top elements individually on the bottom element includes the possibility of placing all the top elements simultaneously, but their positions may be selected or determined independently of each other. When placing each bottom element, it is connected directly or indirectly (e.g., via an interpolation element) to the bottom element. Generally, the top elements are arranged in an offset manner such that they do not overlap in pairs. The connection method is generally not limited, but typically includes lamination or gluing, with the possibility of using elevated temperatures. The placement and connection are performed such that at least one top electrode is disposed above at least one bottom electrode.

[0011] A sensor unit is formed by connecting a top element to a bottom element. It is also possible to form multiple sensor units using a single top element, but this solution is often not preferred. Since there is at least one sensor unit for each of the multiple top elements, there are also multiple sensor units. Each sensor unit is activated when the pressure acting on it (or more specifically, on the top element) exceeds the conduction point. When the sensor unit is activated, an electrical detection can be made. In some embodiments, only the simultaneous activation of multiple sensor units can be detected. Generally, at least one top electrode and at least one bottom electrode are separated when the pressure is below the conduction point, but at least one top electrode is in electrical contact with the bottom electrode when the pressure exceeds the conduction point. However, the present invention is not limited to this operating principle. For example, the sensor unit can include two bottom electrodes and a single top electrode, and the single top electrode is separated from the bottom electrodes when the sensor is unloaded, i.e., when no (significant) pressure acts on the sensor unit. When pressure acts on the top element, the top element deforms and is pushed downward towards the bottom element. When the conduction point is exceeded, the top electrode is in electrical contact with the two bottom electrodes, thereby closing the electrical connection between the bottom electrodes. This electrical connection can be detected. It should be recognized that the "modular concept" according to the present invention can also be extended to other types of foil-based sensors, for example, sensors based on the capacitance difference between the top electrode and the bottom electrode.

[0012] The conduction point can depend on various parameters. Specifically, it often depends on the position of the corresponding top electrode relative to the bottom electrode with respect to the horizontal plane (or more generally, with respect to the sensor surface). This position will hereinafter be referred to as the "horizontal position", and this position can be determined with high precision because each top element (including at least one top electrode) is placed individually. This is very different from the prior art, in which all "upper" electrodes are connected by a single foil that usually has the same area as the bottom element. As explained above, it is almost impossible to place all the electrodes for all sensor units adequately in the previously known concept, mostly due to material tolerances, shrinkage, etc. However, with the concept of the present invention, this is possible because all top elements are placed individually. In addition, the concept of the present invention helps to reduce the amount of material required because the combined area of the top elements is smaller than the area of the bottom element. For example, the top foil is only required at the corresponding sensor unit, and the top foil can be omitted between the sensor units.

[0013] For at least one sensor unit, the conduction point is adjusted by selecting the position of the top element from a plurality of positions at which the sensor unit operates, but at which there are differences in their conduction points. It should be understood that the position of the top element is relative to the position of the bottom element. Generally, this position can be characterized by the above-mentioned (two-dimensional) horizontal position and by the orientation about the vertical axis. The conduction point for at least one sensor unit is adjusted by selecting the position of the top element from a plurality of possible positions. All of these possible positions will result in a working sensor unit, but with different conduction points for different positions.

[0014] In addition to the top and bottom electrodes, the sensor often needs to be electrically connected to a circuit of an external device (e.g., a control unit) that determines whether the sensor is activated. Highly preferably, the bottom element includes this circuit, which can include, for example, conductor lines, electrical terminals, and / or at least one resistor.

[0015] According to one embodiment, the conduction point of at least one sensor unit is adjusted by selecting one of a plurality of horizontal positions of the top element relative to the bottom element, at which the sensor unit operates, but at which there are differences in their conduction points. In other words, for this specific sensor unit, there are a plurality of possible horizontal positions at which the sensor unit operates, but at which there are differences in their conduction points. As mentioned above, the horizontal position is a position along a two-dimensional horizontal plane. The conduction point is adjusted by selecting one of the plurality of possible horizontal positions. For example, if the top electrode is symmetrically arranged relative to two bottom electrodes, the conduction point can be lower than in the case where the same top electrode is arranged asymmetrically. Thus, the conduction point can be tuned for specific requirements, for example, for different automotive seats at locations where the sensor is covered by different foam layers. If the covering foam is softer, the conduction point should be adjusted to a higher value compared to the case where the covering foam is harder. The relationship between the horizontal position and the conduction point can be determined, for example, by a series of experiments.

[0016] Preferably, the method includes connecting at least one top element to a bottom element via at least one spacer element, thereby interposing the spacer element between a top foil and a bottom foil. The spacer element is typically made of a non-conductive material. For example, the spacer element can be at least partially made of the same material as the top foil and the bottom foil. The spacer element is interposed between the top foil and the bottom foil, and there is a possibility that at least a part of the spacer element does not directly contact the top foil and / or the bottom foil but is inserted into another element. For example, a part of the top electrode can be interposed between the top foil and the spacer element. However, at least one spacer element does not cover (or at least does not completely cover) the area of the electrode. Therefore, in the vicinity of the electrode, there is a vertical space between the top foil and the bottom foil, and this vertical space more or less corresponds to the thickness of at least one spacer element. In the unloaded state, the vertical space between at least one top electrode and at least one bottom electrode can be maintained by at least one spacer element.

[0017] It will be envisaged to place and connect the spacer element to the bottom element before placing and connecting the corresponding top element. However, this generally makes the assembly process more complex. Therefore, at least one top element is preferably provided with a spacer element which is connected to the top foil before the top element is connected to the bottom element. It can also be said that the spacer element in this case is part of the top element. The corresponding top element including the spacer element can be prepared in advance, and it only needs to be placed and connected to the bottom element in a relatively simple process. This eliminates any risk of misalignment between the top element and the spacer element, and misalignment will also affect the conduction point.

[0018] At least one spacer element can include an adhesive material which bonds to the bottom element, thereby connecting the top element to the bottom element. There are various options for using the adhesive material. One option is that the spacer element is generally composed of the adhesive material, for example, it is applied to the top foil by spraying, printing or any suitable method, and bonds to the bottom element when the top element is placed. Another option can be that the spacer element includes a foil with a double-sided adhesive liner. One side of the liner is used to bond the spacer element to the top foil before placing the top element, and the other side of the liner is used to bond the top element to the bottom element.

[0019] Preferably, the spacer element includes an opening, and at least a part of the top electrode is disposed in the opening. This opening can also be referred to as a cutout, which is circumferentially surrounded by the material of the spacer element. The opening largely defines the sensor unit. At least a part of the top electrode - and at least a part of the bottom electrode after the top element and the bottom element are assembled - is disposed in the opening. "Disposed in the opening" can be more generally described as "vertically aligned with the opening". The shape of the opening is not limited in any way and can be, for example, rectangular or circular, etc. The conduction point also depends in part on the size and shape of the opening.

[0020] To facilitate the placement process, the bottom element preferably includes a first alignment mark, and the first alignment mark is used to determine the position of the top element relative to the bottom element. In other words, the position of the corresponding top element relative to the first alignment mark can be considered as a reference for the top element relative to the bottom element. Relative to the horizontal plane, the first alignment mark is disposed in the area of the bottom element. The alignment mark can be, for example, a tactile mark, but is usually an optical mark that can be printed on the bottom foil. One possibility can be that the first alignment mark indicates the optimal position of the diagonal of the (rectangular) top element.

[0021] In addition, at least one top element can include a second alignment mark, and the first and second alignment marks can be used to determine the position of the top element relative to the bottom element. Relative to the horizontal plane, the second alignment mark is disposed in the area of the top element. Moreover, the second alignment mark is usually also an optical mark that can be printed on the top foil. By aligning the first and second alignment marks, the horizontal position of the top element can be easily determined. This purpose can be facilitated by the fact that the top foil is usually transparent or at least translucent, so that the first alignment mark is visible even when the top foil is disposed on top of the bottom foil. However, if one of several conduction points is to be selected by choosing a specific horizontal position, this purpose can also be facilitated by the alignment marks. For example, the top element or the bottom element can include different alignment marks indicating different positions corresponding to different conduction points.

[0022] As mentioned above, as long as the sensor is in an unloaded state, each top electrode can be electrically isolated from the bottom electrode. However, a permanent electrical connection can also exist between at least one top electrode and one bottom electrode. According to such an embodiment, at least one top element includes a vertically extending connector element in electrical contact with at least one top electrode, and the connector element is brought into contact with at least one bottom electrode by connecting the top element to the bottom element, thereby establishing a permanent electrical connection between the top electrode and the bottom electrode. It should be understood that the connector element is conductive and establishes a permanent electrical connection between the top electrode and the bottom electrode after assembly. In some cases, the connector element can also be regarded as part of the top electrode.

[0023] Since each top element is placed separately and independently of other top elements, there are various possibilities to adapt or customize the sensor according to different requirements. According to one embodiment, the method of the present invention includes: selecting one of a plurality of possible orientations of the top element relative to the bottom element about a vertical axis before placing and connecting the top element to the bottom element. The vertical axis (more generally, it can be a normal axis) is perpendicular to the horizontal plane (or more generally, perpendicular to the sensor surface). Since one of a plurality of orientations about the vertical axis is selected, this means that there are different positions of the top element, which differ by a certain rotation in the horizontal plane. For example, two of these orientations differ by a 180° rotation. However, the corresponding angle can also be 90°, or even an odd angle. In one aspect, this can be used to adjust the on-point in addition to or as an alternative to adjusting the horizontal position. On the other hand, it can even be used to establish completely different switching states. For example, in one orientation, a specific top electrode can be set to connect to the first and second bottom electrodes, while in another orientation, this top electrode is set to connect to the third and fourth bottom electrodes. Similarly, alignment marks as described above can be used to indicate the appropriate orientation.

[0024] The on-point can also be adjusted by selecting one of a first position and a second position of the top element. In the first position, at least one top support structure extending downward from the top foil is set to be vertically opposite to at least one bottom support structure extending upward from the bottom foil, and in the second position, at least one top support structure is horizontally offset from at least one bottom support structure relative to each other. Generally, the top support structure and the bottom support structure are set to be offset relative to at least one spacer element, or if the spacer element includes an opening, they are generally disposed within the opening. The combined vertical dimension (i.e., the combined height or combined thickness) of the top support structure and the bottom support structure is generally less than the distance between the top foil and the bottom foil. When the first position of the top element is selected, the two support structures are set to be opposite to each other in the vertical direction. When the top foil deforms due to pressure, even after a relatively small deformation of the top foil, the support structures will come into contact. When the support structures come into contact, it is only possible for the top foil to further deform under a considerably increased pressure, which means an increase in the on-point. However, in the second position, the first and second support structures are horizontally offset, so that they do not come into contact with each other under the deformation of the top foil, which promotes the deformation of the top foil. Thus, the on-point is lower than that in the first position. Generally, the top support structure is disposed near the top electrode, and / or the bottom support structure is disposed near the bottom electrode.

[0025] One possibility is that the difference between the first and second positions mentioned above lies in the horizontal offset of the top element relative to the bottom element, i.e., these positions are different horizontal positions. According to another possibility, the first and second positions correspond to different orientations around the vertical axis. For example, the first and second positions can differ by a 180° rotation.

[0026] In addition to changing the horizontal position of a given top element or its orientation around the vertical axis, the switching point can be adjusted by selecting one of a plurality of top elements with different characteristics for a given sensor unit. In other words, the present invention allows for the manufacture of sensors according to a modular design, where for at least one sensor unit and possibly for all sensor units, a given bottom element is combined with various top elements. A great advantage is that if it is only necessary to adjust the switching point for one sensor unit or for some sensor units, this can be easily achieved by selecting an appropriate top module for these (one or more) sensor units while keeping the top modules for the remaining (one or more) sensor units the same. Different top elements often have different mechanical characteristics that affect the switching point.

[0027] There are many possibilities for influencing the switching point through the characteristics of the top element. For example, the openings in the spacer element of the top element can have different sizes and / or shapes. Another example can be that the top support structure of the top element has different numbers, sizes, and / or materials. Another possibility is that the top foils of at least two top elements have different flexibilities. This flexibility can be attributed in particular to different thicknesses of the top foils. Alternatively or in addition, different materials can be used for the top foils.

[0028] The present invention also provides a foil-based pressure sensor. The sensor includes a bottom element having a bottom foil and at least one bottom electrode disposed on the bottom foil, and a plurality of top elements, each top element including a top foil having at least one top electrode disposed beneath the top foil. The combined area of the top elements is less than the area of the bottom element. The top elements are disposed above the bottom element and are at least indirectly connected to the bottom element such that at least one top electrode of each top element is disposed above at least one bottom electrode of the bottom element to form a sensor unit that is adapted to be activated when the pressure acting on the sensor unit exceeds the switching point. For at least one sensor unit, the position of the top element is one of a plurality of positions at which the sensor unit operates, but there is a difference in the switching point at these plurality of positions. All of these terms have been explained above with reference to the method of the present invention and will not be repeated here.

[0029] Preferred embodiments of the sensors of the present invention correspond to those of the method of the present invention. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] The following detailed description of non - limiting embodiments with reference to the accompanying drawings will make other details and advantages of the present invention apparent, wherein:

[0031] Figure 1 is a perspective view of a first embodiment of the pressure sensor of the present invention before assembly;

[0032] Figure 2 is from Figure 1 a top view of a part of the pressure sensor;

[0033] Figure 3 is a sectional view taken along line III - III in Figure 2 ;

[0034] Figure 4 is a perspective view of a second embodiment of the pressure sensor of the present invention;

[0035] Figure 5 is a sectional view taken along line V - V of Figure 4 ;

[0036] Figure 6 is a top view of a third embodiment of the pressure sensor of the present invention; and

[0037] Figure 7 is a sectional view taken along line VII - VII according to Figure 6 ; DETAILED DESCRIPTION OF THE INVENTION

[0038] Figures 1-3A first embodiment of the foil-based pressure sensor 1 of the present invention, which can be used for occupancy detection in a vehicle seat, is schematically shown. The sensor 1 includes a bottom element 2 having a bottom foil 3 that extends in a horizontal plane defined by a first horizontal axis X and a second horizontal axis Y. The vertical axis Z may correspond to the direction of gravity when the sensor 1 is mounted in a vehicle seat, but the sensor 1 may also be aligned in a different manner. The bottom foil 3 may be made of, for example, a flexible plastic material, silicone, or rubber. The bottom element 2 includes two terminals 10 that are respectively connected to a first conductor path 5 and a second conductor path 7. The first conductor path 5 connects two first bottom electrodes 4, while the second conductor path 7 connects two second bottom electrodes 6. A third conductor path 9 connects four third bottom electrodes 8. All the bottom electrodes 4, 6, 8 are provided on the upper side of the bottom foil 3 and may be made of, for example, conductive ink printed on the bottom foil 3 or metal foil laminated to the bottom foil 3. Each third bottom electrode 8 is respectively provided near a first bottom electrode 4 and a second bottom electrode 6. In this embodiment, the overall shape of the bottom element 2 corresponds to a fork or the letter "Y", but this is only for example.

[0039] The sensor 1 further includes four top elements 20, each of the four top elements 20 including a top foil 21 that may be made of the same material as the bottom foil 3. Top electrodes 22 are provided on the lower side of the top foil 21. Similar to the bottom electrodes 4, 6, 8, the top electrodes 22 may be made of, for example, conductive ink or metal foil. The top foil 21 of each top element 20 has a rectangular shape. On the lower side of the top foil 21, each top element 20 includes a spacer element 23. The spacer element 23 may also be made of a flexible plastic, silicone, or rubber foil, but generally has a greater thickness in the vertical direction Z compared to the bottom foil 3 and the top foil 21. The outer dimensions of the spacer element 23 correspond to those of the top foil 21. Each spacer element 23 has a rectangular cutout or opening 24 in which the corresponding top electrode 22 is provided. The top elements 20 are prefabricated before being assembled with the bottom element 2. Each spacer element 23 may include a double-sided adhesive liner to laminate or bond the spacer element 23 to the top foil 21 during the manufacturing process of the top element 20.

[0040] To manufacture the pressure sensor 1 according to the method of the present invention, each prefabricated top element 20 is placed on the bottom element 2 and connected to the bottom element 2 by a bonding process using an adhesive layer of a respective spacer element 23. Since the top elements 20 are spaced apart from each other, each of them can be placed individually, which achieves high precision. To facilitate this precise placement, the bottom element 2 includes a plurality of first alignment marks 11, and each top element 20 has a corresponding second alignment mark 26. The respective first alignment marks 11 and second alignment marks 26 are optical marks printed on the respective foils 3 and 21. The top foil 21 and the spacer element 23 can be transparent or translucent, so that the first alignment marks 11 are visible through the top element 20. By aligning the first alignment marks 11 and the second alignment marks 26, the horizontal position of the respective top element 20 relative to the bottom element 2 can be accurately adjusted.

[0041] During assembly, each top element 20 together with the bottom element 2 forms a sensor unit 30, one of which is shown in Figure 2 and Figure 3 The top electrode 22 is disposed above both the first bottom electrode 4 and the third bottom electrode 8. Due to the presence of the spacer element 23, when no pressure acts on the sensor unit 30, i.e., when the sensor 1 is in an unloaded state, the top electrode 22 is vertically spaced apart from either of the bottom electrodes 4, 8. However, when the external pressure p ext exceeds the conduction point, this situation changes, as shown in Figure 3 . Figure 3 The upper part of shows the top element 20 relative to the bottom element 2 in the first horizontal position A1, in which the top electrode 22 is symmetrically disposed relative to the bottom electrodes 4, 8. Through the elastic deformation of the top foil 21, the top electrode 22 comes into contact with the bottom electrodes 4, 8, thereby establishing an electrical contact that enables current to flow between the first bottom electrode 4 and the third bottom electrode 8. By exceeding the conduction point, the sensor unit 30 is activated. Figure 3 The lower part of shows the top element 20 relative to the bottom element 2 in the second horizontal position A2, in which the top electrode 22 is asymmetrically disposed relative to the bottom electrodes 4, 8. The first position A1 and the second position A2 differ by a horizontal offset s along the first horizontal axis X. Although the pressure p ext and the elastic deformation of the top foil 21 are the same as in the upper part of Figure 3 , the top electrode 22 only comes into contact with the third bottom electrode 8. Since there is no electrical contact between the top electrode 22 and the first bottom electrode 4, the sensor unit 30 is not activated. Activation is only possible by exceeding a significantly higher conduction point.

[0042] Since the conduction point can depend on the horizontal position of the top element 20 relative to the bottom element 2, the separate placement of the top element 20 allows for the accurate determination of the conduction point of the corresponding sensor unit 30 of the top element. For example, if the first alignment mark 11 and the second alignment mark 26 are made to coincide, which will correspond to the symmetric position of the top electrode 22, the conduction point can be determined in advance through experiments. However, if the first alignment mark and the second alignment mark are horizontally offset relative to each other, as shown in Figure 2 it will correspond to the asymmetric position of the top electrode 22 with different conduction points, and the conduction point can also be determined in advance through experiments.

[0043] In addition to allowing for the separate placement of the top element 20 and the accurate determination of the conduction point, it should be understood that the concept of having a small and separate top element 20 in the present invention will significantly reduce the material usage, because only the area of the top element 20 requires the top foil 21 and the spacer element 23, and this area is significantly smaller than the area of the bottom element 2.

[0044] Figure 4 and Figure 5 shows a second embodiment of the sensor 1 (more precisely, a part of the sensor 1) of the present invention. In this embodiment, the top electrode 22 horizontally extends beyond the opening 24 in the spacer element 23 and is electrically connected to the connector element 27 which is also part of the top element 20. The connector element 27 vertically extends downward from the top electrode 22, and its vertical thickness is selected such that a permanent electrical connection is established between the top electrode 22 and the first bottom electrode 4 in the assembled state, as can be seen from Figure 5 In Figure 4 and Figure 5 in the unloaded state shown, the top electrode 22 is arranged to be vertically spaced from the second bottom electrode 6. When the pressure p ext acts on the sensor unit 30, the top foil 21 undergoes elastic deformation, and when the pressure p ext exceeds the conduction point, an electrical contact is established between the top electrode 22 and the second bottom electrode 6.

[0045] Figure 6 and Figure 7 show a third embodiment of the sensor 1 of the present invention, which has a sensor unit 30 similar to the sensor unit shown in Figure 2 and Figure 3 However, the top element 20 includes six top support structures 28 extending downward from the top foil 21, and the bottom element 2 includes six corresponding bottom support structures 12. On the one hand, the presence of the top support structures 28 affects the deformation of the top foil 21, but if the total area of the top support structures 28 is much smaller than the area of the opening 24, this effect is generally small. Figure 6 andFigure 7 On the right side of Figure 7 , a first orientation B1 is shown, and each top support structure 28 is arranged to be vertically opposite to the corresponding bottom support structure 12. Therefore, when the top foil 21 undergoes elastic deformation, the top support structure 28 is adjacent to the bottom support structure 12, which significantly increases the stiffness of the sensor unit 30. At this point, the top electrode 22 still does not contact the bottom electrodes 4, 6, that is, the sensor unit 30 is not activated. Only by the pressure p ext can the significant increase be possible.

[0046] Figure 6 On the left side of Figure 6 , a second orientation B2 of the top element 20 around the vertical direction Z is shown, which is rotated 180° around the vertical axis Z from the first orientation B1. In this orientation, all the top support structures 28 are horizontally offset relative to the bottom support structures 12. However, when at least one top support structure 28 is adjacent to the bottom element 2, and / or at least one bottom support structure 12 is adjacent to the top element 20, only the significantly increased pressure p ext can cause further deformation of the top foil 21. However, this occurs at a significantly greater deformation than in the first orientation B1. By appropriately adjusting the thicknesses of the top electrode 22, the bottom electrodes 4, 8, and the top support structure 28, it is possible to activate the sensor unit 30 before the top support structure 28 contacts the bottom element 2. In other words, the first orientation B1 corresponds to a significantly higher conduction point than the second orientation B2.

[0047] It should be noted that in all the shown embodiments, the conduction point can also be affected by other parameters. For example, different top elements 20 with different characteristics can be used for each sensor unit 30. During the manufacturing process, one of these top elements 20 is selected, thereby affecting the conduction point of the sensor unit 30. For example, the openings 24 of the top element 20 can have different shapes and / or sizes. Moreover, they can have top foils 21 made of different materials or having different thicknesses.

[0048] List of reference numerals

[0049] 1 Sensor

[0050] 2 Bottom element

[0051] 3 Bottom foil

[0052] 4, 6, 8 Bottom electrodes

[0053] 5, 7, 9 Conductor paths

[0054] 10 Terminals

[0055] 11, 26 Alignment marks

[0056] 12, 28 Support Structure

[0057] 20 Top Element

[0058] 21 Top Foil

[0059] 22 Top Electrode

[0060] 23 Spacer Element

[0061] 24 Opening

[0062] 27 Connector Element

[0063] 30 Sensor Unit

[0064] A1, A2 Horizontal Positions

[0065] B1, B2 Orientations

[0066] I Current

[0067] p ext Pressure

[0068] s Offset

[0069] X First Horizontal Axis

[0070] Y Second Horizontal Axis

[0071] Z Vertical Axis

Claims

1. A method for manufacturing a foil-based pressure sensor (1), comprising: - providing a bottom element (2) having a bottom foil (3) and at least one bottom electrode (4, 6, 8) disposed on the bottom foil (3), - providing a plurality of top elements (20), each top element (20) including a top foil (21) having at least one top electrode (22) disposed thereunder, the combined area of the top elements (20) being less than the area of the bottom element (2), wherein the at least one top electrode is vertically spaced from the at least one bottom electrode, - placing the top elements (20) individually and connecting the top elements (20) to the bottom element (2) at least indirectly such that at least one top electrode (22) of each top element (20) is disposed above at least one bottom electrode (4, 6, 8) of the bottom element (2) to form a sensor unit (30), the sensor unit (30) being adapted to be activated when the pressure acting on the sensor unit (30) exceeds a conduction point, wherein for at least one sensor unit (30), the conduction point is adjusted by selecting the position of the top element (20) from a plurality of positions at which the sensor unit (30) operates, but the conduction points of the plurality of positions are different, wherein the conduction point depends on the position of the top element relative to the bottom element, and wherein the position of the top element (20) includes a first position and a second position, and wherein the conduction point is adjusted by selecting one of the first position and the second position of the top element (20).

2. The method according to claim 1, characterized in that: the conduction point of at least one sensor unit (30) is adjusted by selecting one horizontal position from a plurality of horizontal positions of the top element (20) relative to the bottom element (2), the sensor unit (30) operating at the horizontal positions, but the conduction points of the horizontal positions being different.

3. The method according to claim 1 or 2, characterized in that: the method includes connecting at least one top element (20) to the bottom element (2) via at least one spacer element (23) such that the spacer element (23) is interposed between the top foil (21) and the bottom foil (3).

4. The method according to claim 3, characterized in that: at least one top element (20) is provided with the spacer element (23), the spacer element (23) being connected to the top foil (21) before the top element (20) is connected to the bottom element (2).

5. The method according to claim 1, characterized in that: at least one spacer element (23) includes an adhesive material that engages the bottom element (2) to connect the top element (20) to the bottom element (2).

6. The method according to claim 3, characterized in that: the spacer element (23) comprises an opening (24), and at least a part of the at least one top electrode (22) is arranged in the opening.

7. The method according to claim 1, characterized in that: the bottom element (2) comprises a first alignment mark (11), and the first alignment mark (11) is used to determine the position of the top element (20) relative to the bottom element (2).

8. The method according to claim 7, characterized in that: at least one top element (20) comprises a second alignment mark (26), and the first alignment mark (11) and the second alignment mark (26) are used to determine the position of the top element (20) relative to the bottom element (2).

9. The method according to claim 1, characterized in that: at least one top element (20) comprises a vertically extending connector element (27) in electrical contact with at least one top electrode (22), and the connector element (27) comes into contact with at least one bottom electrode (4, 6, 8) by connecting the top element (20) to the bottom element (2), thereby establishing a permanent electrical connection between the top electrode (22) and the bottom electrode (4, 6, 8).

10. The method according to claim 1, characterized in that: the method comprises, before placing the top element (20) and connecting the top element (20) to the bottom element (2), selecting one orientation from a plurality of possible orientations of the top element (20) relative to the bottom element (2) around a vertical axis.

11. The method according to claim 1, characterized in that: in the first position, at least one top support structure (28) extending downward from the top foil (21) near the top electrode (22) is arranged to be vertically opposite to at least one bottom support structure (12) extending upward from the bottom foil (3) near the bottom electrode (4, 6, 8), and in the second position, the at least one top support structure (28) and the at least one bottom support structure (12) are horizontally offset relative to each other.

12. The method according to claim 11, characterized in that: the first position and the second position correspond to different orientations around a vertical axis.

13. The method according to claim 1, characterized in that: the conduction point is adjusted by selecting one top element from a plurality of top elements (20) having different characteristics for a given sensor unit (30).

14. The method according to claim 13, characterized in that: at least two top elements (20) have top foils (21) with different flexibilities.

15. A foil-based pressure sensor comprising: - a bottom element (2), the bottom element (2) having a bottom foil (3) and at least one bottom electrode (4, 6, 8) arranged on the bottom foil (3), and - A plurality of top elements (20), each top element (20) including a top foil (21) having at least one top electrode (22) disposed below the top foil (21), the combined area of the top elements (20) being less than the area of the bottom element (2), wherein the at least one top electrode is vertically spaced apart from the at least one bottom electrode, wherein the top elements (20) are disposed above the bottom element (2) and are at least indirectly connected to the bottom element (2) such that at least one top electrode (22) of each top element (20) is disposed above at least one bottom electrode (4, 6, 8) of the bottom element (2) to form a sensor unit (30), the sensor unit (30) being adapted to be activated when the pressure acting on the sensor unit (30) exceeds a conduction point, and for at least one sensor unit (30), the position of the top element (20) is selected from a plurality of positions at which the sensor unit (30) operates, but the conduction points of the plurality of positions are different, and wherein the conduction point depends on the position of the top element relative to the bottom element, and wherein the position of the top element (20) includes a first position and a second position, and wherein the conduction point is adjusted by selecting one of the first position and the second position of the top element (20).

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