Force sensor and evaluation circuit

Abstract

Force sensor (10, 10', 10'', 10'''', 10'''', 10'''') with the following features: a deformation body (14, 14', 14'', 14'''') which is designed to be subjected to a force and to undergo a deformation under the influence of the force which depends on a stiffness of the deformation body (14, 14', 14'', 14''''); at least one first coil (18), which is arranged at a first lateral position (x1, s1) along the deformation body (14, 14', 14'', 14''') at a first distance (A1) from the deformation body (14, 14', 14''') and is designed to form a first signal characteristic, which is described by a first measured value, as a function of a size of the first distance (A1) at the first lateral position (x1, s1);and a second coil (19) which is arranged at a second lateral position (x2, s2) along the deformation body (14, 14', 14'', 14''') at a second distance (A2) from the deformation body (14, 14', 14''', 14''') and is configured to form a second signal characteristic, which is described by a second measured value, as a function of a magnitude of the second distance (A2) at the second lateral position (x2, s2); wherein the deformation of the deformation body (14, 14', 14'', 14''') changes the first and the second distance (A2) differently;wherein the force can be determined by an evaluation circuit (26) which is configured to determine the force as a function of at least the first measured value and the second measured value, wherein the first measured value is multiplied by a first coefficient and the second measured value is multiplied by a second coefficient, wherein the first and the second coefficient depend on the stiffness of the deformation body (14, 14', 14'', 14''').

Description

[0001] Exemplary embodiments of the present invention relate to a force sensor and a corresponding evaluation circuit for the force sensor. Further exemplary embodiments relate to a force sensor with an evaluation circuit and a corresponding method and computer program. In general, the invention lies in the field of inductive force sensors.

[0002] Force measurement can be found in many applications, such as determining brake pedal force or brake caliper force.

[0003] A conventional force sensor is based on a module with a spring or forming element that deflects under the influence of the applied force to be measured. Strain gauges are bonded to this spring element. Their resistance changes depending on the applied load. The measuring devices are connected in a Wheatstone bridge configuration. A voltage is applied via a circuit, and the output is connected to an amplifier. The small output voltage of the bridge is amplified, corrected for temperature drift and misalignment, and then output. A weakness of these conventional force sensors is the precise and reliable attachment of the strain gauges to the spring element.

[0004] The object of the present invention is to create a concept that enables force sensing and is more robust against temperature drift, lifetime drift and overload.

[0005] The problem is solved by the subject matter of the independent patent claims.

[0006] Exemplary embodiments of the present invention provide a force sensor with a deformation body comprising at least one first and one second coil. The deformation body is configured to be subjected to a force and, under the influence of the force, to undergo a deformation dependent on the (bending) stiffness of the deformation body. The first coil is arranged at a first lateral position along the deformation body at a first distance from the deformation body and is configured to generate a first signal characteristic (such as a resonance frequency, an impedance, inductance, or a quantity derived therefrom), which is described by a first measured value, as a function of the first distance at the first lateral position.The second coil is arranged at a second lateral position along the deformation body, spaced a second distance from the deformation body, and is configured to generate a second signal characteristic (such as a resonant frequency, impedance, inductance, or a derived quantity), described by a second measured value, as a function of the second distance at the second lateral position. The deformation of the deformation body changes the first and second distances differently. The force can be determined by an evaluation circuit configured to calculate the force as a function of at least the first measured value (using a first coefficient) and the second measured value (using a second coefficient), where the first and second coefficients depend on the stiffness of the deformation body.Here, for example, the first measured value is multiplied by a first coefficient and the second measured value is multiplied by a second coefficient.

[0007] Depending on the embodiment, the first signal characteristic can comprise a first resonant frequency, impedance, or inductance (Lm1), or a first derived quantity such as an oscillator frequency, and the second signal characteristic can comprise a second resonant frequency, impedance, or inductance (Lm2), or a first derived quantity such as a second. Such signal characteristics can be determined by the evaluation circuit (also called the excitation circuit), which excites the coil 18 or 19 according to the embodiment, e.g., as in a resonant circuit, using a signal such as an alternating voltage to determine the resonant frequency (which depends non-linearly on the inductance (2πfres = 1 / √(Lm*C))). Depending on the embodiment, the evaluation circuit is configured to excite the first and / or second coil 18 and 19 with an alternating voltage signal and / or to measure a first and second impedance as the first and second measured values.

[0008] Another embodiment provides an evaluation circuit for use with a force sensor comprising a deformation body, at least a first coil and a second coil, wherein the deformation body is configured to be subjected to a force and to undergo a deformation under the influence of the force which depends on a (bending) stiffness of the deformation body; wherein the first coil is arranged at a first lateral position along the deformation body at a first distance from the deformation body and is configured to generate a first signal characteristic, which is described by a first measured value, as a function of the magnitude of the first distance at the first lateral position;and wherein the second coil is arranged at a second lateral position along the deformation body at a second distance from the deformation body and is configured to generate a second signal characteristic, described by a second measured value, as a function of the magnitude of the second distance at the second lateral position; wherein the deformation of the deformation body changes the first and second distances differently. The evaluation circuit is configured to determine the force as a function of at least the first and second measured values, wherein the first and second coefficients depend on the stiffness of the deformation body. Here, for example, the first measured value is multiplied by a first coefficient and the second measured value is multiplied by a second coefficient.

[0009] Another embodiment provides a method for determining a force using a force sensor comprising a deformation body, at least a first coil and a second coil, wherein the deformation body is configured to be subjected to a force and to undergo a deformation under the influence of the force, the deformation depending on a (bending) stiffness of the deformation body; wherein the first coil is arranged at a first lateral position along the deformation body at a first distance from the deformation body and is configured to generate a first signal characteristic, described by a first measured value, as a function of the magnitude of the first distance at the first lateral position;and wherein the second coil is arranged at a second lateral position along the deformation body at a second distance from the deformation body and is configured to form a second signal characteristic, which is described by a second measured value as a function of a magnitude of the second distance at the second lateral position; wherein at least the first distance at the first lateral position varies as a function of the deformation of the deformation body and wherein the deformation of the deformation body changes the first and the second distance differently; with the following step:; Determining the force based on a linear combination of at least the first measurement (using a first coefficient) and the second measurement (using a second coefficient), where the first and second coefficients depend on the stiffness.

[0010] Depending on the embodiment, the invention can also be computer-implemented. Therefore, a method creates a computer program for carrying out this method if the method is executed on a processor.

[0011] Further developments are defined in the claims. Exemplary embodiments of the present invention are explained with reference to the accompanying drawings. These show: Fig. 1 a schematic block representation of a force sensor with two coils and a deformation body according to a basic embodiment; Fig. 2 a schematic block diagram of a force sensor with three coils according to an extended embodiment; Fig. 3 a schematic block diagram of a force sensor with deformation bodies supported on two sides according to a further embodiment; Fig. 4 a schematic block diagram of a force sensor with coils packed in a sensor chip according to further embodiments; Fig. 5 a schematic block diagram of a force sensor with a cranked deformation body according to exemplary embodiments; Fig. 6 a schematic block diagram of a force sensor to explain the measured values ​​for a deformation body with unknown geometry according to exemplary embodiments; Fig. 7 a schematic block diagram of a force sensor to explain the measured values ​​when drift is predominant according to exemplary embodiments; Fig. 8 A schematic block diagram of a force sensor to illustrate the measured values ​​when a drift is superimposed with a force according to exemplary embodiments; and Fig. 9 a schematic block diagram of an evaluation circuit according to exemplary embodiments.

[0012] Before exemplary embodiments of the present invention are explained below with reference to the accompanying drawings, it should be noted that elements and structures with the same effect are provided with the same reference numerals, so that their descriptions are applicable to each other or interchangeable.

[0013] Fig. Figure 1 shows a force sensor 10, which is shown here mounted on a printed circuit board 12 (e.g., a PCB board). The force sensor 10 comprises as its central elements the deformation element 14, which is flexibly mounted, for example, via a bearing area 16. Further central elements include a first and a second coil, designated by reference numerals 18 and 19. The coils 18 and 19 are arranged, for example, laterally on the PCB board 12 in an area where the element 14 is also located. The deformable element 14 is positioned essentially parallel to the PCB board 12 by means of the bearing 16. The deformation element 14, hereinafter also referred to as spring 14, has a cantilever 14k. This cantilever 14k projects from the support area or clamping area 16. For example, coils 18 and 19 can be positioned laterally below the cantilever arm 14k.

[0014] The deformation element 14 is implemented, for example, as a bending beam or cantilever 14k and is therefore spaced apart from the PCB board 12 by a distance A. The distance A is defined here by the height of the bearing element 16. This results in a gap s between the deformation body 14 and the PCB board 12, which forms a distance A1 in the area of ​​the coil 18 and a distance A2 in the area of ​​the coil 19.

[0015] The deformation element 14, hereinafter also referred to as spring 14, has a cantilever arm 14k. This cantilever arm 14k projects from the support area or clamping area 16. For example, coils 18 and 19 can be positioned laterally below the cantilever arm 14k. The deformation body 14, or the cantilever beam 14 formed here, has a free-spanning length x, whereby, for example, the force F is applied at position x0 and the cantilever element 14 is fixedly supported at position xn by the support area 16. The length x represents the length of the cantilever arm 14k. Starting from the lever arms between xn and x0, the deformation element 14 is bent along a deflection curve when the force F is applied. This means that the deformation body14 is designed to experience bending or deflection as a deformation or to be deformed according to a deflection curve which depends on the stiffness.The deflection, and thus the deflection curve, depends on the stiffness of element 14 along the cantilever area, which extends over length x. Further dependencies may exist with respect to the lever arm x, where the lever arm is defined by the first lateral position and a position x1 of the support of the deformation body xn and / or the force application point xo. As a result of the deformation, the distance A1 at position x1 and the distance A2 at position x2 change. Since the positions are freely distributed between the support xn and the force application point 14v, the distances A1 and A2 change differently when a force k is applied. In other words, at least the first distance A1 at the first lateral position x1 varies depending on the deformation of the deformation body 14, and / or the second distance A2 at the second lateral position x2 varies depending on the deformation of the deformation body 14.

[0016] In the following analysis, it is assumed that the deformation element 14 comprises a conductive material, such as a metal, a metal layer, or at least a partially metallized layer. The first coil 18 is configured to generate a first signal characteristic, such as an impedance or inductance, at the first lateral position x1, depending on the first distance A1. Similarly, the second coil 19 is configured at the second lateral position x2, depending on the second distance A2, to generate a second signal characteristic, again such as an inductance or impedance. The first and second signal characteristics depend on the first and second distances A1 and A2, respectively. The first signal characteristic can be described by a first measured value, while the second signal characteristic is described by a second measured value.In other words, the first coil 18 and the second coil 19 form a kind of distance sensor for determining the distances A1 and A2. Since the distances A1 and A2 change differently depending on the applied force k, this signal behavior can also be observed in the first and second signal characteristics. This means, for example, that the first and second measured values ​​behave differently. An evaluation circuit utilizes this property.

[0017] According to exemplary embodiments, force F can be determined by an evaluation circuit (not shown) configured to determine the force F as a function, e.g., a linear function (i.e., in particular a linear function, predominantly linear function, or a region-wise linear or quasi-linear function), of at least the first measured value (using a first coefficient) and the second measured value (using a second coefficient). Here, the first and second coefficients depend on the stiffness of the deforming body. From another perspective, this means that the coefficients depend on the stiffness, where the force is initially unknown but is determined using the predetermined fixed coefficients and the measured inductances.Here, for example, the first measured value is multiplied by a first coefficient and the second measured value is multiplied by a second coefficient.

[0018] Since the stiffness is related to the deflection curve, it can also be said, according to further embodiments, that the first and second coefficients depend on the deflection curve of the deformation body 14 under standard load F (e.g., maximum load). For example, the function can be a linear combination that takes the measured values ​​as input values, taking the coefficients into account. Before going into details, it should be noted here that, depending on the embodiment, the function can be a linear function, a predominantly linear function, a partially linear function, or a quasi-linear function. The reason for this is that the deformation body 14 does not exhibit linear behavior in all areas, but can also exhibit non-linear behavior, in which case the function only describes the linear behavior for this area.Even with perfectly linear deformation behavior of the deformation body 14, deformation components of the clamping area 16 and the base plate 12, as well as adhesive joints between these elements, can cause non-linear deformation behavior. Furthermore, the function need not be precisely defined, but can be approximated, so that it is not necessarily a linear function, but also a different type of function that describes the behavior of the deformation body 14 in relation to the two signal characteristics of the coils 18 and 19.

[0019] Excursus on linear combinations: In mathematics, a linear combination of x,y is defined as a*x+b*y, where a constant c can be added: a*x+b*y+c.. c can be negligibly small; in practice, another small or negligibly small quadratic or cubic term, or a higher-order term, can be added to x,y (e.g., d*x*y+e*x^2+f*y^2). These terms serve, for example, to increase accuracy, and their coefficients can also depend on the stiffness of the deforming body 14. Therefore, the function for determining or estimating the force is described as an essentially linear function of both impedance parameters x,y, where the coefficients of the impedance parameters a, b, c, d, e, f depend on the stiffness of the deforming body. "Essentially" and "estimated" are redundant.

[0020] Now that the structure has been explained above, the operating principle will be discussed below. The force sensor 10 uses, for example, a metallic deformation body 14, e.g., a spring, on which the force F is applied. The coil 18 or 19 is positioned near the spring 14 (distance, for example, 0.5 mm), but not in contact with the spring. The evaluation circuit (not shown) measures the impedance of the coils 18 and 19, e.g., the inductance at 25 MHz. When the force F deflects the spring 14, the distance A between the metal body 14 and the coils 18 and 19 changes, and the inductances of the coils 18 and 19 change accordingly. This change is measured and used to quantitatively determine the force F. The coils 18 and 19, as well as the coil circuit (evaluation circuit), thus resemble an inductance proximity switch / sensor.In exemplary embodiments, it would be conceivable that the coils 18 and 19 are arranged, for example, in a sensor chip (single-chip solution) or on a printed circuit board 12 (PCB) as shown, with a wide variety of sizes and shapes. For example, the spring is typically deflected with a maximum force of 50 µm, so that preferably the evaluation circuit for the coil characteristics of the coils 18 and 19 has a resolution of the distance between the coils and the metal spring of at least 50 nm. This very small distance increment of 50 nm can also be caused, for example, by thermal or hygroscopic expansion of the mounting area 16 or curvature of the circuit board 12, which can lead to an error in the force measurement.This error is reduced according to exemplary embodiments by having the force sensor system measure not merely the distance between the spring and a coil, but the deformation of the spring caused by the force using two or more coils. The objective of the force sensor system is therefore to detect the deformation of the spring, regardless of any change in the spring's position (displacement or rotation).

[0021] The use of at least two coils 18 and 19, which experience different changes in the distances A1 and A2 under load from the force F, has the advantage of enabling a "differential spring" or "differential coil" evaluation. As explained in detail above, the use of two spaced-apart coils 18 and 19 allows for the detection of two different distances A1 and A2 resulting from the deformation of the two sections of the spring 14. Due to the clamping configuration described, the spring 14 is designed such that both distances A1 and A2 are deflected differently, and the sensor system 10 detects the difference in deflections A1 and A2. This allows for the compensation of drifts that arise, for example, due to thermal expansion.The background is that, due to drift, such as that resulting from thermal expansion, the distance between the metal spring or sensing coil can vary by several nanometers even at zero force, leading to measurement errors. Thermal expansion, or drift in general, affects the shape of the spring 14, the spring holder or clamping 16, the PCB board 12, or the chip package (not shown). Since, as a rule, both distances A1 and A2 are affected equally by such drifts, drifts, especially those due to thermal expansion, can advantageously be compensated so that they do not affect the measurement.

[0022] The following refers to Fig. 2 a further development of the arrangement from Fig. 1 explains which uses three coils.

[0023] Fig. Figure 2 shows the sensor arrangement 10', which is comparable to the sensor arrangement 10, wherein a third coil 20 is provided in the area of ​​the spring holder or clamping 14. In addition, a sensor or chip package 25 is arranged on the PCB board 12 next to the deformation body 14, in which the evaluation circuit 26 can be arranged. As in the embodiment from Fig. In Figure 1, coils 18, 19, and 20 are arranged on the surface of the PCB board 12. The sensor chip is also arranged on the same surface. It should be noted that, according to other embodiments, coils 18, 19, and 20 can, of course, be embedded on the surface or formed within the metallization of the PCB board. Preferably, coils 18, 19, and 20 are planar coils, formed by one or more metallization layers of the PCB, which are typically used for the conductive connection of electrical components on the PCB. However, the coils can also be mounted on the PCB as discrete components. The three coils 18, 19, and 20 can be arranged in a line, but need not be; they can also be arranged along a curve when viewed from a lateral perspective.The deflection in the region of coil 18 is greater than the deflection in the region of coil 19 when subjected to force F, while coil 20 is not deflected in the region of clamping 16, provided the clamping is perfectly rigid. However, embodiments are also conceivable where the clamping 16 is not perfectly rigid, as it may be made of a plastic that possesses unavoidable flexibility as well as relatively significant expansion upon temperature increase and volume swelling due to moisture absorption from the environment. Generally, however, the deflection of the spring element in the region of coil 19 is smaller than in the region of coil 18 and larger than in the region of coil 20. To ensure this, the positions of coils 18, 19, and 20 can be defined, according to exemplary embodiments, directly below these critical regions of the spring 14.Technically, coil 18 exhibits a greater change in its impedance and is more sensitive to the force F than coils 19 and 20. Coil 20 has a nearly constant impedance due to its arrangement. Using the evaluation circuit 26, which is located, for example, in the sensor chip / package 25, these impedances can be measured and compared to estimate the force. This estimation is performed using a formula that includes the mechanical stiffness of spring 14 as a parameter. It should also be noted that, according to exemplary embodiments, coils 18, 19, and 20 are connected to the evaluation circuit 16 of the sensor chip. This connection can be made, according to exemplary embodiments, via conductor tracks in the metallization layer of the PCB board.

[0024] As shown, the lateral arrangement of the third coil 20 (position x3) can be in a region where the distance to the spring no longer changes during deflection, or alternatively, of course, in a region, e.g., between x2 and x3, where deflection does occur under force. This means that all (or all three) coils lie below the freely bendable spring 14, as e.g., in Fig. Figure 6 is shown (note: in this case, there is no coil under the spring holder 16). It is irrelevant whether the distance between a coil changes or not – what is relevant is that the distances change differently when the coil is bent.

[0025] This means that, according to exemplary embodiments, the force sensor 10' can have a third coil 20, which is arranged at a third lateral position x3 along the deformation body at a third distance from the deformation body 14 and is configured to output a third measured value as a function of the magnitude of the third distance A3 at the third lateral position, wherein the deformation of the deformation body changes the first, second, and third distances differently. For example, the linear combination can be determined taking the third measured value into additional consideration using a third coefficient that depends on the stiffness. Here, the constant c described above can be omitted.

[0026] The inductive principle is explained below using exemplary embodiments. For example, the evaluation circuit feeds an AC current into coils 18, 19, and 20.

[0027] This generates a magnetic field that induces eddy currents in metal bodies exposed to the magnetic field (according to Faraday's law). These eddies generate their own magnetic field, which opposes the driving field (Lenz's law). This changes the magnetic flux coupled to coil 18, 19, 20, and this changes the impedance of coil 18, 19, 20, which is measured by the voltage (when a current is applied, a voltage is measured. Alternatively, a voltage could be applied and the current response measured).

[0028] Regarding element 14, it should be noted that, according to exemplary embodiments, the force F can be introduced into the spring 14 at a well-defined position, e.g. defined by the projection 14v.

[0029] Regarding the spring, it should be noted that, according to exemplary embodiments, it has a defined stiffness that is partly determined by the bearing 16, the geometry, in particular the length x of the lever arm, and the profile of the cantilever element of the deformation body 14. In the present form, this is a bending stiffness that results in the corresponding deflection curve. The coefficients for use in the function described above, such as the linear function or the linear combination, depend on these stiffnesses (e.g., different positions along the x-axis) or on the deflection curve. According to exemplary embodiments, these coefficients can be determined, for example, by at least one or preferably several measurements with different, more precisely defined forces F.The result is either the coefficients for multiplication with the respective measured values, along with any additional constants, or alternatively, data such as memory in a look-up table (LUT) that contains the coefficients implicitly or in coded form. The look-up table can contain a large number of data points, from which the deflection curve for one or more defined states can be determined, allowing for the estimation of further deflection curves and the forces responsible for them.

[0030] Referring to Fig. Section 3 will now explain another example. Fig. Figure 3 shows a sensor 10'' according to a further embodiment. The sensor 10'' represents a further development of the sensor 10' and essentially has a modified deformation element 14'. This element is clamped on both sides for greater stiffness, i.e., by the support element 16 and the support element 16' on a second side of the deformation element 14'. The coil 20 is arranged in the area of ​​the support 16, while the coils 18 and 19 are provided between the supports 16 and 16'. As a result of the two-sided clamping, the deformation element 14' is designed to deflect when a force k is applied between the two supports 16 and 16'. Both 16 and 16' can be supports, i.e., fixed connections to the deformation body 14'. Alternatively, it would also be conceivable that the deformation body 14' is clamped only on one side and the second side, e.g., B.The side 16' is used as a support to balance the spring 14', allowing the spring 14' to move laterally relative to the element 16' when deflected. As a result, the element 14' does not bend due to thermal contraction of the PCB 12 caused by differing thermal expansion. Both variants have the advantage that the coils 18 and 19 are arranged in a cavity, thus providing good shielding or protection against environmental influences such as iron filings or magnetic dust within the magnetic field's effective range. Iron filings or magnetic dust can cause measurement errors, which are eliminated in this variant. According to another embodiment, the deformation body 14' could also be designed as a plate or disk (generally: a planar structure).

[0031] Depending on the embodiment, the deformation body can comprise one or more of the following elements: - Feather; - Bending beam; - Cantilever; - Element that is arranged essentially parallel to a substrate or printed circuit board or a straight line defined by the first and second coils; - Cranked or curved element, in particular a cranked or curved element with different distances at the first lateral and the second lateral position; - element clamped on one side; - double-sided clamped element; and - Lid or cap.

[0032] The cap is particularly advantageous because it protects the underlying coils and, if applicable, the chip and its fine bond wires on all sides, and is therefore an integral part of the housing.

[0033] It should be noted that, according to exemplary embodiments, the sensor chip 25 or the package can also be arranged on the side of the PCB board 20 facing away from the spring 14'. In this case, in particular, this arrangement of the element 25 on the opposite side offers the advantage of saving lateral space.

[0034] Fig. 4 shows another variant, which is a further development of Fig. 1 represents. The sensor 10''' from Fig. Figure 4 comprises elements 12, 14, and 16, with coils 18' and 19' arranged directly within element 25'. In this embodiment, element 25' with coils 18 and 19 is located in the lateral region of the cantilever arm 14k. Possible implementations of the arrangement of coils 18 and 19 within the sensor package 25 include providing a separate substrate for coils 18 and 19 with an additional evaluation chip 26 within the package 25, or alternatively, arranging coils 18 and 19 directly within the semiconductor chip that also includes the evaluation chip 26.

[0035] Fig. Figure 5 shows another sensor element with a bent spring element 14''. This element has two areas in a first plane directly adjacent to the surface of the PCB board 12 (see reference numerals 14a'' and 14c'') and an intermediate area 14b''. Area 14b'' is spaced from the PCB board 12 by a distance A. The coil 18 is located in area 14c'', the coil 19 in area 14b'', and the coil 20 in area 14a''. In area 14a'', the bent deformation element 14'' is clamped against the PCB board 12 by the element 16'. Viewed from another perspective, this means that area 14c'' of the deformation element 14 is loose. When the force F acts on the projection 14v, the spring in area 14b'' is pushed towards the PCB board 12 and thus approaches the coil 19. In area 14c'' the spring lifts off, resulting in a gap between coil 18 and area 14c''.The background is that a support for the PCB board 12 is formed between the area 14b'' and 14c'', which redirects the force as a gear with a pivot point 14d'. The coil 20 is in turn located in the area of ​​the clamping 16' and therefore serves as a constant reference. Referring to . Fig. 6, Fig. 7 and Fig. Section 8 now refers to the evaluation carried out by the evaluation device and in particular to the consideration of possible imperfections in the setup, e.g. by a gap between PCB board 12 and the surface of the deformation body 14''' (cf. Fig. 6), in which the distance values ​​A1, A2 and A3 already vary in the resting state. Furthermore, the influence of the tilting of element 14''' relative to the PCB board 12, which is already present in the resting state, is also discussed.

[0036] Fig. Figure 6 shows a sensor arrangement 10'''' with a PCB board 12 and three coils 18, 19, and 20 arranged on the PCB board 12 at positions x1, x2, and x3. The sensor arrangement has a deformation body 14''' that extends from a clamping area 16 parallel to the PCB board 12 and has a cantilever 14k. The cantilever extends from the element 16 along the x-axis. In this variant, the three coils 18, 19, and 20 are all arranged in the area of ​​the cantilever. Assuming that the deformation body 14''' has a different surface profile on the side facing the gap, e.g., due to different thicknesses, the distance A varies across positions x1, x2, and x3. The distances A2 and A3 at positions x2 and x3 are approximately comparable in this variant, while the distance A1 at position x1 is significantly larger.Based on the different distances A1, A2 and A3, a gap with varying width is formed, which can be described by the function g(x).

[0037] In the following discussion, it is assumed that three coils 18, 19, 20 are located on the PCB board 12, e.g. along a line (x-axis) at position x1. <x2<x3 oder entlang einer planaren Kurve auf der PCB-Oberseite (s-Achse) s1<s2<s3, angeordnet sind. Die Vertikalrichtung ist z. Die Induktivitäten der Spulen 18, 19 und 20 stellen eine Funktion des vertikalen Abstands A, bzw. hier mit d bezeichnet, zwischen den Spulen 18, 19 und 20 sowie der Metallfeder 14''' dar.

[0038] The inductances of the three coils 18, 19, 20 are L1[d1], L2[d2], L3[d3]. The spring 14''' could be flat and parallel to the PCB 12 (= preferred case), but in general it has an arbitrary shape such that the vertical distance between the flat PCB 12 and the spring 14''' after assembly of the system (= start of service life) and at zero force is g[x], where g = gap => g[x1], g[x2], g[x3] are the vertical distances between coils 18, 19, 20 and the spring 14'''.

[0039] When a force is applied to spring 14''', it is deflected / bent. The deflection curve is the vertical displacement w*Fz as a function of the x-position: w[x]*Fz; the deflection / bend is proportional to the applied force Fz. Thus, the following applies: d[x] = g[x] - w[x]*Fz.

[0040] During its lifetime, the spring 14''' may shift in the vertical direction (dz) and its position may tilt due to heat contraction and moisture swelling of the PCB 12, the spring 14''' and other components (bolts, blocks, clamping devices ...) (tilt angle = gamma).

[0041] Such an inclination and / or displacement originating from the force Fz is in Fig. 7 shown.

[0042] Furthermore, it can happen that the displacement and inclination vary with the applied force (for example, if the PCB 12 and the clamping device are not perfectly rigid). For small displacements and inclinations, the following applies: d[x] = g[x] - w[x]*Fz - dz - tan(gamma)*x. This situation is described in Fig. 8 illustrated.

[0043] We assume that each coil with an inductance L1, L2, L3 is connected to an associated capacitance C1, C2, C3 to give a resonant angular frequency ω1 = 1 / sqrt(L1*C1); ω2 = 1 / sqrt(L2*C2); ω3 = 1 / sqrt(L3*C3).

[0044] This gives us three equations: 1 / ω12 / C1=L1[g[x1]−w[x1]*Fz−dz−gamma*x1] 1 / ω22 / C2=L2[g[x2]−w[x2]*Fz−dz−gamma*x2] 1 / ω32 / C3=L3[g[x3]−w[x3]*Fz−dz−gamma*x3]

[0045] The quantities w, dz, and gamma are small (small deflection / bending of the spring and small displacement and inclination of the spring). We multiply these by s and expand the functions L1, L2, and L3 in Taylor series in s up to the first order:

[0046] For the first equation, for example: 1 / omega12 / C1−L1[g[x1]−s*w[x1]*Fz*Cos[s*gamma[Fz]]−s*dz[Fz]−Tan[s*gamma[Fz]]*x1]FullSimplify [Series[%, {s,0,1}]] Out(2)=1C1 omega12−L1[−s dz[Fz]+g[x1]−x1 Tan[sgamma[Fz]]−Fz s Cos[s gamma[Fz]]w[x1]] Out(3)=(1C1 omega12−L1[g[x1]])+(dz[Fz]+x1 gamma[Fz]+Fz w[x1]) L1'[g[x1]]s+O[s]2

[0047] Dann setzen wir s = 1 und lösen diesen Satz dreier linearer Gleichunge nach den drei Unbekannten Fz, dz, gamma auf. Das Ergebnis ist: In[6]:=FullSimplify[ Solve[{(1C1 omega12−L1[g[x1]])+(dz+x1 gamma+Fz w[x1]) L1'[g[x1]]=0, (1C2 omega22−L2[g[x2]])+(dz+x2 gamma+Fz w[x2]) L2'[g[x2]]=0, (1C3 omega32−L3[g[x3]])+(dz+x3 gamma+Fz w[x3]) L3'[g[x3]]=0},{Fz, dz,gamma}]] Out[6]={{Fz→ (C2 C3 omega22omega32(x2−x3)(−1+C1 omega12L1[g[x1]])L2'[g[x2]]L3'[g[x3]]+ C1 omega12 L1'[g[x1]](C2 omega22(x1−x2)(−1+C3 omega32L3[g[x3]]) L2'[g[x2]]−C3 omega32(x1−x3)(−1+C2 omega22L2[g[x2]])L3'[g[x3]])) / (C1 C2 C3 omega12 omega22 omega32((x2−x3)w[x1]+(−x1+x3)w[x2]+ (x1−x2)w[x3])L1'[g[x1]]L2'[g[x2]]L3'[g[x3]]), dz→(C1 C2 omega12omega22(−1+C3 omega32L3[g[x3]])(x2 w[x1]−x1 w[x2]) L1'[g[x1]]L2'[g[x2]]+C3 omega32 (−C1 omega12(−1+C2 omega22L2[g[x2]])(x3 w[x1]−x1 w[x3]) L1'[g[x1]]+ C2 omega22(−1+C1 omega12 L1[g[x1]])(x3 w[x2]−x2 w[x3]) L2'[g[x2]]) L3'[g[x3]]) / (C1 C2 C3 omega12 omega22 omega32 ((x2−x3)w[x1]+(−x1+x3)w[x2]+(x1−x2)w[x3]) L1'[g[x1]]L2'[g[x2]]L3'[g[x3]]),gamma→(−C1 C2 omega12 omega22(−1+C3 omega32L3[g[x3]]) (w[x1]−w[x2])L1'[g[x1]]L2'[g[x2]]+C3 omega32 (C1 omega12(−1+C2 omega12 L2[g[x2]])(w[x1]−w[x3])L1'[g[x1]]+C2 omega22 (−1+C1 omega12L1[g[x1]])(−w[x2]+w[x3])L2'[g[x2]])L3'[g[x3]]) / (C1 C2 C3 omega12 omega22 omega32((x2−x3)w[x1]+(−x1+x3)w[x2]+ (x1−x2)w[x3])L1'[g[x1]]L2'[g[x2]]L3'[g[x3]])}},

[0048] This result is greatly simplified, if we set all capacities equal to CC, that is C1=CC, C2=CC, C3=CC, and if we set all inductances equal to LL, that is L1=LL, L2=LL, L3=LL, and if we set all discharges equal to Ls: L1'[g[x1]]=Ls, L2'[g[x2]]=Ls, L3'[g[x3]]=Ls Then gilt: Fz = omega12(omega22(−x1+x2)+omega32(x1−x3))+omega22omega32(−x2+x3)CC Ls omega12 omega22 omega32((x2−x3)w[x1]+(−x1+x3)w[x2]+(x1−x2)w[x3])

[0049] The resonant frequencies ω1, ω2, ω3 are measured by the electronic circuitry of the inductive proximity sensor. All other parameters are determined by the circuit design (CC) and mechanical setup (x1, x2, x3, w[x1], w[x2], w[x3]) and by both the circuit design and the mechanical setup (Ls).

[0050] Instead of omega1^2 we can also use 1 / CC / Lm1, a similar principle applies to omega2 and omega3: then the circuit must measure Lm1, Lm2, Lm3 (using state-of-the-art devices) instead of measuring the resonant frequencies (note: Lm1 is the inductance of coil 1 when the spring is deflected, displaced and tilted, while L1[g[x1]] is the inductance of coil 1 at zero force, zero displacement and zero tilt.): FullSimplify[ (omega12(omega22(−x1+x2)+omega32(x1−x3))+omega22omega32(−x2+x3)) / (CC Ls omega12omega22omega32((x2−x3)w[x1]+(−x1+x3)w[x2]+(x1−x2)w[x3])) / ⋅ (omega1→1 / Sqrt[Lm1*CC],omega2→1 / Sqrt[Lm2*CC], omega3→1 / Sqrt[Lm3*CC]), Lm1>0&&Lm2>0&&Lm3>0&&CC>0] (Lm3(−x1+x2)+Lm2(x1−x3)+Lm1(−x2+x3)) / (Ls((x2−x3)w[x1]+(−x1+x3)w[x2]+(x1−x2)w[x3]))

[0051] This is basically a linear combination Fz = k1*Lm1+k2*Lm2+k3*Lm3 with k1 = (x3-x2 / (Ls*((x2-x3)*w[x1]+(-x1+x3)*w[x2]+(x1-x2)*w[x3])), Similar applies to k2 and k3. One also sees that Fz is a linear combination of the three measured inductances Lm1, Lm2, L3, where the coefficients k1, k2, k3 of the through-circuit w[x1], w[x2], w[x3] abhängen, die umso kleiner sind, je stiffer die Feder ist.

[0052] According to one embodiment, a sensor system with three coils is created, which are arranged along the x-axis or along an s-curve, e.g. position x1. <x2<x3 bzw. s1<s2<s3.

[0053] It measures the inductances Lm1, Lm2, Lm3 of the three coils 18, 19, 20 (for example, via the resonant frequency or via their impedance).

[0054] Finally, it calculates the externally applied mechanical force as a linear combination of the three inductances Lm1, Lm2, Lm3 via Fz = k1*Lm1+k2*Lm2+k3*Lm3, where the coefficients k1, k2, k3 are functions of the geometry and the spring deflection curve at a unit force.

[0055] The coefficients k1, k2, k3 can be empirically determined by applying several forces and measuring Lm1, Lm2, Lm3 and using a least squares method to determine the coefficients.

[0056] The system can be easily simplified if w[x1]=0. This means that the spring 14''' above the coil 18, 19, 20 does not bend, but a common displacement dz is still allowed for the entire spring 14''' (and dz can vary with the force Fz).

[0057] The system can be significantly simplified if either displacements or inclinations can be eliminated. Then only one of the parameters dz, gamma, remains; the other is zero. Therefore, we only have two unknowns here: one of dz, gamma, and one of Fz. Thus, we only need two equations to solve for these unknowns and to obtain Fz.

[0058] Therefore, the system only requires two coils 18, 19 (instead of three coils 18, 19, 20). First case: dz = 0. Then we obtain a system of two equations for the inductances of the two coils 18, 19 (* dz = 0: only two coils 18, 19*): FullSimplify[ Solve[{(1C1 omega12−L1[g[x1]])+(dz+x1 gamma+Fz w[x1])L1'[g[x1]]=0, (1C2 omega22−L2[g[x2]])+(dz+x2 gamma+Fz w[x2])L2'[g[x2]]=0} / . dz→ 0,{Fz, gamma}]] {{Fz→−(x1(1C2 omega22−L2[g[x2]])L1'[g[x1]]−x2(1C1 omega12−L1[g[x1]]) L2'[g[x2]]) / ((−x2w[x1]+x1 w[x2])L1'[g[x1]]L2'[g[x2]]), gamma→((−1+C1 omega12 L1[g[x1]])w[x2]) / (C1 omega12(−x2 w[x1]+x1 w[x2]) L1'[g[x1]])+((−1+C2 omega22L2[g[x2]])w[x1]) / (C2 omega22(x2 w[x1]−x1 w[x2])L2'[g[x2]])}} FullSimplify[% / .{L1'[g[x1]]→L1s,L2'[g[x2]]→L2s}] FullSimplify[% / .{L1'[g[x1]]→L1,L2[g[x2]]→L2s}] FullSimplify[% / .{C1→CC,C2→CC}] FullSimplify[% / .{L1→LL,L2→LL,L1s→Ls,L2s→Ls}] FullSimplify[% / .{omega1→1 / Sqrt[Lm1∗CC],omega2→1 / Sqrt[Lm2∗CC]},Lm1>0&&Lm2>0&&CC>0] {{Fz→−(L1s x1C2 omega22−L2s x2C1 omega12+L2s x2 L1[g[x1]]−L1s x1 L2[g[x2]]) / (L1s L2s(−x2 w[x1]+x1 w[x2]〉〉,gamma→(C1 L1s omega12(−1+C2 omega22 L2[g[x2]]〉w[x1]+ C2 L2s omega22(1−C1 omega12 L1[g[x1]]〉w[x2]〉 / (C1 C2 L1s L2s omega12 omega22(x2 w[x1]−x1 w[x2]〉〉}} {{Fz→−(L1s(−L2+1C2 omega22)x1+L2s(L1−1C1 omega12)x2) / (L1s L2s(−x2 w[x1]+x1 w[x2]〉〉,gamma→(C1 L1s omega12(−1+C2 L2 omega22)w[x1]+C2 L2s(1−C1 L1 omega12) omega22 w[x2]〉 / (C1 C2 L1s L2s omega12omega22(x2 w[x1]−x1 w[x2]〉〉}} {{Fz→−(L1s(−L2+1CC omega22)x1+L2s(L1−1CC omega12)x2) / (L1s L2s(−x2 w[x1]+x1 w[x2]〉〉,gamma→ (L1s omega12(−1+CC L2 omega22)w[x1]+L2s(1−CC L1 omega12)omega22 w[x2]〉 / (CC L1s L2s omega12omega22(x2 w[x1]−x1 w[x2]〉〉}} {{Fz→−LL Ls(−x1+x2〉+Ls{x1omega12−x2omega22}CCLs2(−x2 w[x1]+x1 w[x2]〉, gamma→(omega12(−1+CC LL omega22)w[x1]+(1−CC LL omega12) / (CC Ls omega12omega22(x2 w[x1]−x1 w[x2]〉〉}} {{Fz→−LL x1−Lm2 x1−LL x2+Lm1 x2Ls x2 w[x1]−Ls x1 w[x2], gamma→(LL w[x1]−Lm2 w[x1]−LL w[x2]+Lm1 w[x2]) / (Ls x2 w[x1]−Lsx1 w[x2])}}

[0059] Here is Fz im Grunde a linear combination of Lm1 and Lm2 plus an additive number k0

[0060] Second case: Set gamma=0. Then we get a system of two equations for the inductances of both coils 18, 19 (*gamma = 0: only two coils 18, 19*): Fullsimplify[ Solve[{(1C1 omega12−L1[g[x1]])+(dz+x1 gamma+Fz w[x1])L1'[g[x1]]=0, (1C2 omega22−L2[g[x2]])+(dz+x2 gamma+Fz w[x2])L2'[g[x2]]=0} / . gamma→0,{Fz,dz}]]{{Fz→−((1C2 omega22−L2[g[x2]])L1'[g[x1]]−(1C1 omega12−L1[g[x1]])L2'[g[x2]]) / ((−w[x1]+w[x2])L1'[g[x1]]L2'[g[x2]]), dz→((1−C1 omega12L1[g[x1]])w[x2]C1 omega12L1'[g[x1]]+(−1+C2 omega22L2[g[x2]])w[x1]C2 omega22L2'[g[x2]]) / (w[x1]−w[x2])}} FullSimplify[% / .(L1'[g[x1]]→L1s,L2'[g[x2]]→L2s)] FullSimplify[% / .(L1[g[x1]]→L1,L2[g[x2]]→L2)] FullSimplify[% / .{C1→CC,C2→CC}] FullSimplify[% / .{L1→LL,L2→LL,L1s→Ls,L2s→Ls}] FullSimplify[% / .{omega1→1 / Sqrt[Lm1∗CC],omega2→1 / Sqrt[Lm2∗CC]},Lm1>0&&Lm2>0&&CC>0] {{Fz→−(−L2sC1 omega12+L1sC2 omega22+L2s L1[g[x1]]−L1s L2[g[x2]]) / (L1s L2s(−w[x1]+w[x2]〉〉, dz→((−1+C2 omega22L2[g[x2]]〉w[x1]C2 L2s omega22+(1C1 omega12−L1[g[x1]]〉w[x2]L1s) / (w[x1]−w[x2]}} {{Fz→−−L1s L2+L1 L2s−L2sC1 omega12+L1sC2 omega22L1s L2s(−w[x1]+w[x2]〉, dz→((−1+C2 L2 omega22〉w[x1]C2 L2s omega22+(−L1+1C1 omega12)w[x2]L1s) / (w[x1]−w[x2]〉}} {{Fz→−−L1s L2+L1 L2s−L2sC1 omega12+L1sC2 omega22L1s L2s(−w[x1]+w[x2]〉, dz→((−1+CC L2 omega22〉w[x1]CC L2s omega22+(−L1+1CC omega12)w[x2]L1s) / (w[x1]−w[x2]〉}} {{Fz→(omega1−omega2〉(omega1+omega2〉CC Ls omega12omega22(w[x1]−w[x2]), dz→((LL−1CC omega22)w[x1]+(−LL+1CC omega12)w[x2]) / (Ls(w[x1]−w[x2]〉〉}} {{Fz→−Lm1+Lm2Ls(w[x1]−w[x2]),dz→(LL−Lm2)w[x1]+(−LL+Lm1)w[x2]Ls(w[x1]−w[x2])}}

[0061] Here, Fz is a linear combination of Lm1 and Lm2: Fz = k1*Lm1+k2*Lm2. It should be noted again that the mathematical explanations are only exemplary and variations in the calculation method are possible.

[0062] In general, this can be applied according to exemplary embodiments such that the deformation body is separated from the first coil by a gap at least at the first lateral position s1 or x1, or wherein the deformation body is separated from the first and second coils by a gap at least at the first lateral position s1 and x1 and the second lateral position s2 or x2; the gap is described by a function g[x] along the deformation body and / or defined by the inclination angle gamma according to tan[gamma]=dg[x] / dx along the deformation body.

[0063] All embodiments have in common that the evaluation device 26, as described in Fig.Figure 9, with inputs 27a, 27b, and 27c, shows that, starting from at least two measurement signals at coils 18 and 19, or three measurement signals at coils 18, 19, and 20, or even from the measurement signal of more than three coils, the exerted force Fz can be determined or estimated. For this purpose, a linear combination, or more generally, a function of the measured inductances (Lm1, Lm2 or Lm1, Lm2, and Lm3) of at least two or three coils 18, 19, and 20 with positions x1, is used. <x2<x3 bzw. s1<s2<s3 bestimmt.

[0064] Either Fz = k0+k1*Lm1+k2*Lm2, where k0 could also be zero, or Fz = k1*Lm1+k2*Lm2+K3*Lm3, where each coefficient k0, k1, k2, k3 depends on the slope of an inductance with respect to an x-coordinate at an applied zero force (= Ls) and on the mechanical stiffness of the spring 14''' (implied in w[x1]...).

[0065] The coefficients k0, k1, k2, and k3 depend on the stiffness of the spring. This means that if the spring, e.g., 14''', is replaced by a stiffer one, the coefficients must be adjusted. If the stiffness of the spring doubles, the coefficients double. This can be achieved through calibration, according to exemplary embodiments. Therefore, the device 26 can, according to exemplary embodiments, include a calibration device that determines calibration data. In another exemplary embodiment, the device can also simply have a memory for storing the calibration data. The calibration data can, for example, directly contain the coefficients k0, k1, k2, and k3, etc., or it can contain other values ​​from which the coefficients can be derived. From a mathematical perspective, the coefficients generally describe the change in distance or inductance in response to an applied force, depending on the spring's stiffness.the spring stiffnesses. Alternative storage methods, such as the use of look-up tables, are possible according to further embodiments. Preferably, at least one defined force is determined with the system in order to derive the calibration data from it. According to further embodiments, several force states with several defined forces can also be determined.

[0066] Although the above embodiments always assume a PCB board or, more generally, a printed circuit board, it should be noted that, according to alternative embodiments, any type of substrate is of course possible. According to these embodiments, the force sensor has a substrate and / or a printed circuit board on which at least the first and / or second coil is arranged; the first and / or second coil is encapsulated in a single unit. Furthermore, the second or a third coil can be arranged in a clamping area of ​​the deformation body.

[0067] Although some aspects have been described in connection with a device, it is understood that these aspects also constitute a description of the corresponding process, such that a block or component of a device can also be understood as a corresponding process step or as a feature of a process step. Similarly, aspects described in connection with or as a process step also constitute a description of a corresponding block, detail, or feature of a corresponding device. Some or all of the process steps can be performed by (or using) a hardware apparatus, such as a microprocessor, a programmable computer, or an electronic circuit. In some embodiments, some or more of the key process steps can be performed by such an apparatus.

[0068] Depending on specific implementation requirements, embodiments of the invention can be implemented in hardware or in software. The implementation can be carried out using a digital storage medium, for example, a floppy disk, DVD, Blu-ray disc, CD, ROM, PROM, EPROM, EEPROM, FLASH memory, hard disk, or other magnetic or optical storage medium, on which electronically readable control signals are stored. These control signals can interact with, or interact with, a programmable computer system in such a way as to execute the respective method. Therefore, the digital storage medium can be computer-readable.

[0069] Some embodiments according to the invention therefore include a data carrier which has electronically readable control signals which are able to interact with a programmable computer system in such a way that one of the methods described herein is carried out.

[0070] In general, embodiments of the present invention can be implemented as a computer program product with a program code, wherein the program code is effective in carrying out one of the methods when the computer program product runs on a computer.

[0071] The program code can also be stored on a machine-readable medium, for example.

[0072] Other embodiments include a computer program for carrying out one of the methods described herein, wherein the computer program is stored on a machine-readable medium. In other words, an embodiment of the method according to the invention is thus a computer program that includes program code for carrying out one of the methods described herein when the computer program is executed on a computer.

[0073] Another embodiment of the methods according to the invention is therefore a data carrier (or a digital storage medium or a computer-readable medium) on which the computer program for carrying out one of the methods described herein is recorded.

[0074] Another embodiment of the method according to the invention is thus a data stream or a sequence of signals that represents the computer program for carrying out one of the methods described herein. The data stream or sequence of signals can be configured, for example, to be transferred via a data communication connection, such as the Internet.

[0075] Another embodiment comprises a processing device, for example a computer or a programmable logic device, which is configured or adapted to perform one of the methods described herein.

[0076] Another embodiment comprises a computer on which the computer program for performing one of the procedures described herein is installed.

[0077] Another embodiment of the invention comprises a device or system designed to transmit a computer program for carrying out at least one of the methods described herein to a receiver. The transmission can be, for example, electronic or optical. The receiver can be, for example, a computer, a mobile device, a storage device, or a similar device. The device or system can, for example, include a file server for transmitting the computer program to the receiver.

[0078] In some embodiments, a programmable logic device (for example, a field-programmable gate array, an FPGA) can be used to perform some or all of the functionalities of the methods described herein. In some embodiments, a field-programmable gate array can interact with a microprocessor to perform one of the methods described herein. Generally, in some embodiments, the methods are performed by any hardware device. This can be general-purpose hardware such as a computer processor (CPU) or method-specific hardware such as an ASIC.

[0079] The embodiments described above merely illustrate the principles of the present invention. It is understood that modifications and variations of the arrangements and details described herein will be obvious to other people skilled in the art. Therefore, it is intended that the invention be limited only by the scope of protection set forth in the following claims and not by the specific details presented herein by way of description and explanation of the embodiments.

Claims

[1] Force sensor (10, 10', 10'', 10'''', 10'''', 10'''') with the following features: a deformation body (14, 14', 14'', 14''') which is designed to be subjected to a force and to undergo a deformation under the influence of the force which depends on the stiffness of the deformation body (14, 14', 14'', 14'''); at least one first coil (18), which is arranged at a first lateral position (x1, s1) along the deformation body (14, 14', 14'', 14''') at a first distance (A1) from the deformation body (14, 14', 14'', 14''') and is configured to form a first signal characteristic, which is described by a first measured value, as a function of a magnitude of the first distance (A1) at the first lateral position (x1, s1); and a second coil (19) which is arranged at a second lateral position (x2, s2) along the deformation body (14, 14', 14'', 14''') at a second distance (A2) from the deformation body (14, 14', 14''') and is designed to form a second signal characteristic, which is described by a second measured value, depending on a size of the second distance (A2) at the second lateral position (x2, s2); wherein the deformation of the deformation body (14, 14', 14'', 14''') changes the first and second distance (A1, A2) differently; wherein the force can be determined by an evaluation circuit (26) which is configured to determine the force as a function of at least the first measured value and the second measured value, wherein the first measured value is multiplied by a first coefficient and the second measured value is multiplied by a second coefficient, wherein the first and the second coefficient depend on the stiffness of the deformation body (14, 14', 14'', 14'''). [2] Force sensor (10, 10', 10'', 10'''', 10'''', 10'''') according to claim 1, wherein at least the first distance (A1) at the first lateral position (x1, s1) varies depending on the deformation of the deformation body (14, 14', 14'', 14'''') and / or wherein the second distance (A2) at the second lateral position (x2, s2) varies depending on the deformation of the deformation body (14, 14', 14'', 14''''). [3] Force sensor (10, 10', 10'', 10'''', 10'''', 10'''') according to one of the preceding claims, wherein the function is a linear function, predominantly linear function, region-wise linear function or quasi-linear function. [4] Force sensor (10, 10', 10'', 10'''', 10'''', 10'''') according to one of the preceding claims, wherein the force sensor (10, 10', 10'''', 10'''', 10'''', 10'''''') has a third coil (20) which is arranged at a third lateral position (x3, s3) along the deformation body (14, 14', 14'', 14''') spaced at a third distance (A3) from the deformation body (14, 14', 14'', 14''') and is configured to output a third measured value as a function of a magnitude of the third distance (A3) at the third lateral position (x3, s3), wherein the deformation of the deformation body (14, 14', 14'', 14''') determines the first (A1), The second (A2) and third (A3) distances were changed differently. [5] Force sensor (10, 10', 10'', 10'''', 10'''', 10'''') according to claim 4, wherein the linear combination is determined taking additional account of the third measured value using a third coefficient that depends on the stiffness. [6] Force sensor (10, 10', 10'', 10'''', 10'''', 10'''') according to one of the preceding claims, wherein the first signal characteristic comprises a first resonant frequency or impedance or inductance (Lm1) or a first quantity derived therefrom and the second signal characteristic comprises a second resonant frequency or impedance or inductance (Lm2) or a first quantity derived therefrom. [7] Force sensor (10, 10', 10'' 10'''', 10'''', 10'''') according to one of the preceding claims, wherein the deformation body (14, 14', 14'''', 14'''') comprises a conductive material and / or a conductive layer and / or a conductive area. [8] Force sensor (10, 10', 10'', 10'''', 10'''', 10'''') according to one of the preceding claims, wherein the deformation body (14, 14', 14'', 14'''') is configured to undergo bending or deflection as deformation or to be deformed according to a bending curve which depends on the stiffness. [9] Force sensor (10, 10', 10'', 10'''', 10'''', 10'''') according to one of the preceding claims, wherein at least the first distance (A1) at a first lateral position (x1, s1) depends on the stiffness of the deformation body (14, 14', 14'', 14'''') and a lever arm, wherein the lever arm is defined by the first lateral position (x1, s1) and a position of the support of the deformation body (14, 14', 14'', 14''''). [10] Force sensor (10, 10', 10'' 10'''', 10'''', 10'''') according to one of the preceding claims, wherein the evaluation circuit (26) is configured to excite the first and / or second coil (19) with an alternating voltage signal and / or to measure a first and second impedance as the first and second measured value. [11] Force sensor (10, 10', 10'', 10'''', 10'''', 10'''') according to one of the preceding claims, wherein the deformation body (14, 14', 14'', 14'''') comprises one or more of the following elements: - Feather; - Bending beam; - Cantilever; - Element that is arranged substantially parallel to a substrate or printed circuit board or a straight line defined by the first and second coil (19); - cranked or curved element, in particular a cranked or curved element with different distances at the first lateral (x1, s1) and the second lateral position (x2, s2); - element clamped on one side; - double-sided clamped element; and - Lid or cap. [12] Force sensor (10, 10', 10'', 10'''', 10'''', 10'''') according to any one of the preceding claims, wherein the force sensor (10, 10', 10'''', 10'''', 10'''''', 10'''''') comprises a substrate and / or a printed circuit board on which / which at least the first and / or second coil (19) is arranged; and / or wherein the first (18) and / or second coil (19) is encapsulated in a package; and / or wherein the second (19) or a third coil (20) is arranged in a region of a clamping of the deformation body (14, 14', 14'', 14'''). [13] Force sensor (10, 10', 10'', 10'''', 10'''', 10'''') according to one of the preceding claims, wherein the deformation body (14, 14', 14'', 14'''') is separated from the first coil (18) by a gap at least at the first lateral position s1 or x1 or wherein the deformation body (14, 14', 14'', 14'''') is separated from the first (18) and second coil (19) by a gap at least at the first lateral position s1 or x1 and the second lateral position s2 or x2; and wherein the gap is described by a function g[x] along the deformation body (14, 14', 14'', 14''') and / or is defined by the inclination angle gamma according to tan[gamma]=dg[x] / dx along the deformation body (14, 14', 14'', 14'''). [14] Force sensor (10, 10', 10'', 10'''', 10'''', 10'''') according to one of the preceding claims, comprising an evaluation circuit (26). [15] Force sensor (10, 10', 10'', 10'''', 10'''', 10'''') according to one of the preceding claims, comprising a permanent memory containing calibration data from which the at least first and second coefficients can be derived or the function can be adapted; and / or wherein the evaluation circuit (26) comprises a calibration circuit (27) configured to determine calibration data from which the at least first and second coefficients can be derived or the function can be adapted. [16] Evaluation circuit (26) for use with a force sensor (10, 10', 10'', 10'''', 10'''', 10''''''), which has a deformation body (14, 14', 14'''', 14''''), at least a first coil (18) and a second coil (19), wherein the deformation body (14, 14', 14'''', 14'''') is designed to be subjected to a force and to undergo a deformation under the influence of the force which depends on a (bending) stiffness of the deformation body (14, 14', 14'''', 14''''); wherein the first coil (18) is arranged at a first lateral position (x1, s1) along the deformation body (14, 14', 14'', 14''') at a first distance (A1) from the deformation body (14, 14', 14''') and is designed to form a first signal characteristic, which is described by a first measured value, as a function of a magnitude of the first distance (A1) at the first lateral position (x1, s1);and wherein the second coil (19) is arranged at a second lateral position (x2, s2) along the deformation body (14, 14', 14'', 14''') at a second distance (A2) from the deformation body (14, 14', 14''', 14''') and is configured to produce a second signal characteristic, which is described by a second measured value as a function of the magnitude of the second distance (A2) at the second lateral position (x2, s2); wherein the deformation of the deformation body (14, 14', 14'', 14''') changes the first and the second distance (A2) differently;wherein the evaluation circuit (26) is configured to determine the force as a function of at least the first measured value and the second measured value, wherein the first measured value is multiplied by a first coefficient and the second measured value is multiplied by a second coefficient, wherein the first and the second coefficient depend on the stiffness of the deformation body (14, 14', 14'', 14'''). [17] Method for determining a force using a force sensor (10, 10', 10'', 10'''', 10'''', 10'''''') comprising a deformation body (14, 14', 14'''', 14''''), at least a first coil (18) and a second coil (19), wherein the deformation body (14, 14', 14'''', 14'''') is configured to be subjected to a force and to undergo a deformation under the influence of the force which depends on a (bending) stiffness of the deformation body (14, 14', 14'''', 14''''); wherein the first coil (18) is arranged at a first lateral position (x1, s1) along the deformation body (14, 14', 14'', 14''') at a first distance (A1) from the deformation body (14, 14', 14''') and is designed to form a first signal characteristic, which is described by a first measured value, as a function of a magnitude of the first distance (A1) at the first lateral position (x1, s1);and wherein the second coil (19) is arranged at a second lateral position (x2, s2) along the deformation body (14, 14', 14'', 14''') at a second distance (A2) from the deformation body (14, 14', 14''', 14''') and is configured to produce a second signal characteristic, which is described by a second measured value, depending on the magnitude of the second distance (A2) at the second lateral position (x2, s2); wherein at least the first distance (A1) at the first lateral position (x1, s1) varies depending on the deformation of the deformation body (14, 14', 14'', 14''') and wherein the deformation of the deformation body (14, 14', 14''', 14''') changes the first (A1) and the second distance (A2) differently; with the following step:; Determining the force based on a linear combination of at least the first measurement and the second measurement, wherein the first measurement is multiplied by a first coefficient and the second measurement is multiplied by a second coefficient, where the first and second coefficients depend on the stiffness. [18] Computer program for carrying out the method according to claim 17 when the method is executed on a processor.

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