WO2009143989A1

WO2009143989A1 - Capacitive sensor and a method for producing a capacitive sensor

Info

Publication number: WO2009143989A1
Application number: PCT/EP2009/003637
Authority: WO
Inventors: Heinz Kueck; Volker Mayer; Adrian Schwenck; Karl-Peter Fritz
Original assignee: Hahn-Schickard-Gesellschaft für angewandte Forschung e.V.
Priority date: 2008-05-27
Filing date: 2009-05-22
Publication date: 2009-12-03
Also published as: DE102008025236B4; DE102008025236A1

Abstract

A capacitive sensor for detecting a measurement variable comprises a hollow space (10), which has an outwardly curved external wall (20), wherein a dielectric liquid (30) can be introduced in the hollow space (10), which dielectric liquid (30) leaves part (40) of the hollow space (10) free, with the part (40) having a dielectric constant which is different to that of the dielectric liquid (30). The capacitive sensor furthermore has a first surface electrode (50) and a second surface electrode (60), which are configured in the hollow space (10) such that a movement (?s) of the part (40) in the dielectric liquid (30) along the outwardly curved external wall (10) in response to the measurement variable results in a change in capacitance between the first and second surface electrodes (50, 60).

Description

Capacitive sensor and a method for producing a capacitive sensor

description

The present invention relates to a capacitive sensor and to a method for producing a capacitive sensor, and more particularly to a capacitive tilt sensor for highly accurate measurement of small tilt.

Capacitive sensors can be used for a variety of household, industrial and research applications. Examples include inclination sensors, which can be used as rollover sensors in motor vehicles, as monitoring sensors of alarm systems in vehicles and buildings and as position sensors in automated machines, irons, washing machines, etc. A concrete example is the detection of a tilt of a parked vehicle in order to alert the driver to the risk of rolling away of the vehicle.

A number of conventional sensors are used to determine a measured variable, such as the inclination with respect to a horizontal surface, by detecting a capacitance-dependent capacitance difference of a capacitor arrangement.

For this purpose, for example, conventional inclination sensors are used, which determine the inclination via a measurement of a differential capacitance in the case of inclination-dependent changes in the covered area of a differential capacitor arrangement formed with an electrically conductive pendulum. Other conventional capacitive sensors perform a differential capacitance measurement, wherein a change in inclination caused by an arrangement of an electrically conductive liquid is determined with respect to the capacitor electrodes partially covered by it.

In addition, conventional capacitance sensors can be used to detect the rotation angle of a shaft by means of a measurement of an angle-dependent differential capacitance of a differential capacitor arrangement.

In this case, the differential capacitor arrangement can be realized via an electrically conductive disk connected to the shaft.

Although conventional capacitance sensors are capable of measuring inclinations and rotations over a wide range of angles, they have low sensitivity to small tilting or inclinations. Such a tilt sensor is disclosed, for example, in DE 4141324 A1, in which the cavity is cylindrically shaped. US 5079847 discloses another capacitive tilt sensor in which the electrode shapes are formed such that inclinations with respect to two mutually perpendicular axes of rotation can be measured. In addition to the capacitive tilt sensors, there are still resistive sensors, as described for example in DE 19821923 Al. These examples are also sensitive over a large angle range. For many applications, however, it is not necessary to determine inclinations or rotations in an angle range between 0 and 360 ° or between 0 and 180 °, but instead it is sufficient to determine inclinations in an angle range between, for example, 0 and 30 ° as precisely as possible and in particular pinpoint small inclination changes in an angular range of a few degrees or fractions of a degree.

Based on this prior art, the present invention has the object to provide a capacitive sensor that can measure very particular inclinations in a small angular range very accurately. This object is achieved by a capacitive sensor according to claim 1 and 18 or by a method according to claim 19.

The present invention is based on the finding that a capacitive sensor for detecting a measured variable can be created by a cavity has an outwardly curved outer wall and is partially filled with a dielectric fluid, so that a part of the cavity remains free, and the free The remaining part has a different dielectric constant than the dielectric liquid. Furthermore, a first and second surface electrode is arranged in the cavity such that movement of the part in the dielectric liquid along the outwardly curved outer wall in response to the measurand results in a capacitance change between the first and second surface electrodes.

Thus, embodiments describe a capacitive liquid-based tilt sensor with a special electrode design that is capable of measuring minute angle changes with high accuracy. For this purpose, the electrode structure is designed so that when the sensor is tilted, a large capacitance change occurs, which can be measured so finely with a high-resolution evaluation electronics that even the slightest tilting of the sensor is detected.

In detail, embodiments may be realized as follows. A first electrode carrier is provided with a first electrode structure that is electrically isolated from the first electrode carrier. Opposite the first electrode structure is a second electrode structure, which is arranged on a second electrode carrier, and is also electrically insulated from the second electrode carrier. By means of a spacer element a fixed distance can be set between the two electrode carriers so that the first electrode structure and the second electrode structure form a plate capacitor. The two electrode carriers, together with the spacer, form a sealed cavity (the cavity) which is partially filled with a dielectric fluid (dielectric fluid), thereby increasing the capacitance of the plate capacitor. The greater the degree of coverage of the electrode structures achieved (or mediated) by the dielectric fluid, the greater the capacitance of the capacitor array.

When the dielectric fluid almost completely fills the cavity, for example, an air bubble forms in the dielectric fluid at the top of the cavity. However, a bubble of another medium or a vacuum bubble may also be formed. When tilting the sensor, the exemplary air bubble always moves to the highest point of the cavity. Now, if the top of the cavity and the electrode structures designed geometrically suitable, it can be realized in tilting opposing differential capacitor arrangement. For example, a measured capacitance increases while the other capacitance decreases with increasing tilt. This can be achieved by dividing the first electrode structure into two regions which are electrically insulated from one another and which each form a separately readable capacitor with the second electrode structure.

From the illustrated principle it is clear that the measured variable corresponds to a movement of the exemplary air bubble along the curved cavity. The movement of the exemplary air bubble can, as stated, be achieved by an inclination of the capacitive sensor, which leads to a change of direction of the acting gravity and the exemplary air bubble therefore moves to the new highest point within the cavity. Age- Alternatively, movement of the exemplary air bladder may also be caused by subjecting the capacitive sensor to a centrifugal force or other force that acts differently on the dielectric fluid and the exemplary air bladder, thereby causing movement of the exemplary air bladder , Although the following statements are usually limited to an application as a tilt sensor, it is clear that embodiments can also be used to determine acceleration changes, which may also include, for example, centrifugal forces.

In embodiments, it is not necessary to form the electrodes over the entire area within the cavity, but for the highest possible sensitivity, it is sufficient that the electrodes are formed in those areas along which the exemplary air bubble during operation or use of the inclination sensor for a moved certain angle range. In addition, it is possible to form the electrode surfaces or the electrode structures by a plurality of components, which may be electrically connected to one another, so that the result is a sensor signal which is as linear as possible as a function of the exemplary change in inclination. The linearity refers to the dependence of the sensor signal on the measured variable. If z. For example, if the slope doubles from a first angle to a second angle, the measured sensor signal also doubles. However, it is also possible to choose the electrodes in such a way that, with very small changes in angle, a non-linear change in the measurement occurs, during which a linear behavior sets in with larger angle changes. This makes it possible to specifically form or form the electrodes in such a way that there is a reinforcement effect with regard to the detected change in inclination. In this case, for example, when the inclination angle is doubled, the sensor signal may be more than doubled. In further embodiments, it is also possible to shape the cavity such that no exemplary air bubble forms, but that the part not filled by the dielectric liquid moves along a channel (eg, as a free passage section) and that movement z. B. by a change in inclination or, as described above, by an acting centrifugal force or additional acceleration occurs.

Furthermore, it is possible to select the electrode structures such that the exemplary air bubble moves along the first electrode structure and the second electrode structure is arranged vertically below it (eg, in the direction of gravity during operation). With such an arrangement of the electrode structures, moreover, it is easily possible to provide a capacitive sensor which can detect not only an inclination with respect to a rotation axis highly sensitive, but at the same time can detect rotations with respect to two axes. This is z. For example, then the case when the outwardly curved outer wall of the cavity has a convex lens shape, so that the exemplary air bubble can move with respect to a surface, wherein the movement along the two directions of the surface inclinations with respect to different axes of rotation correspond. In this case, an electrode structure is formed along the curved outer wall.

Embodiments of the present invention will be explained below with reference to the accompanying drawings. Show it:

1 shows a cross-sectional view through the cavity according to an embodiment of the present invention düng; Fig. 2 is a perspective view of a capacitive tilt sensor for detecting rotation about an axis of rotation;

Fig. 3 is a cross-sectional view through the capacitive tilt sensor of Fig. 2;

Fig. 4 is an equivalent circuit diagram for switching the electrode structures shown in Figs. 2 and 3;

5 shows a cross-sectional view through the cavity with an electrode structure according to a further exemplary embodiment;

Fig. 6 is a cross-sectional view through the cavity with a formed channel;

7 is a perspective view of the capacitive sensor with an alternative configuration of the electrodes;

Fig. 8 is a plan view of the capacitive sensor shown in Fig. 7; and

Fig. 9 is a plan view of a capacitive sensor for detecting rotations with respect to two independent axes of rotation.

With regard to the following description, it should be noted that in the different embodiments, identical or equivalent functional elements have the same reference numerals and thus ^' the description of these functional elements in the various embodiments are interchangeable.

1 shows a cross-sectional view through a cavity 10 of a capacitive sensor, wherein the cavity 10 has an outwardly curved outer wall 20 and in the cavity 10, a dielectric liquid 30 is introduced. The dielectric liquid 30 exposes a portion 40 of the cavity 10 with the portion 40 disposed along the outwardly bulging outer wall 20 and having a dielectric constant other than the dielectric constant of the dielectric fluid. Further, a first area electrode 50 is formed in the cavity and a sidewall of the cavity, respectively, and a second area electrode 60 (not shown in Fig. 1) is formed on a side wall opposite to the sidewall.

In this exemplary embodiment, the first area electrode 50 has a first area 50a and a second area 50b, wherein both areas are electrically insulated from each other along a parting line 51. The first and second area electrodes 50 and 60 are thus formed such that a movement Δs of the portion 40 in the dielectric liquid 30 along the outwardly curved outer wall 20 in response to a measured quantity (eg, a slope) to a capacitance change between the first Area of the first area electrode 50 a and second area electrode 60 leads. Correspondingly, the capacitance change between the second area of the first area electrode 50b and the second area electrode 60 behaves in the opposite direction.

The outwardly curved outer wall 20 has a slightly curved surface, so that a surface normal Nl along a lateral or lateral extent B of the convex outer wall 20 in a range of less than 45 ° or in a range of less than 20 ° or in a range of less than 10 ° changes. Alternatively, the slightly outwardly curved outer wall 20 may be configured such that twice the radius of curvature of the curved surface of the outer wall 20 is greater than or more than twice or at least five times greater than the lateral extent B. The lateral extent B may be, for example, a maximum diameter of the Be cavity 10. It can thus be achieved that if the curvature Diameter is already slightly larger than the lateral extent B, not the full 180 ° angle range is covered in turns / inclinations, which is a feature of embodiments of the present invention. The degree of curvature of the outer wall 20 can be optimized, for example, with regard to a desired sensitivity of the inclination sensor: the lower or lower the curvature the higher the sensitivity. The width or extent B then determines (with the curvature selected) the angular range that can be measured.

The concrete shape of the part 40 depends in large part on the wetting properties of the outwardly curved outer wall 20 or the side walls of the cavity 10 with respect to the dielectric liquid 30. According to the invention, for example, so much dielectric fluid is introduced into the cavity 10 that the part 40 is bounded laterally by the dielectric fluid 30 and not by a wall of the cavity 10 (laterally, for example, refers to the direction of movement Δs). The part 40 may thus be, for example, an air bubble which has formed in the dielectric liquid 30. Alternatively, however, the member 40 may also include a vacuum or other medium that does not mix with the dielectric liquid 30 and has a dielectric constant other than that of the dielectric liquid 30. It is advantageous if the difference in the dielectric constant is as large as possible.

2 shows a spatial view of the capacitive sensor for detecting a measured variable, wherein the cavity 10 is delimited by a first electrode carrier 11 and a second electrode carrier 12 as well as by a spacer element 13. In this case, the spacing element 13 defines the outwardly bulging outer wall 20 along which the filler 40 forms with the dielectric liquid 30 of the part 40 after the cavity 10 has been filled. The spacer element 13 has a Layer thickness d, which defines a fixed distance between the first and second electrode carrier 11, 12.

The first surface electrode 50 or a first electrode structure is formed on the first electrode carrier 11, and the second surface electrode 60 or a second electrode structure is formed on the second electrode carrier 12. The first and second surface electrodes 50, 60 may be produced, for example, by vapor deposition on the first and second electrode carriers 11, 12 or may also be integrated in these. Optionally, an insulation between the first electrode carrier 11 (second electrode carrier 12) and the first surface electrode 50 (second surface electrode 60) may be formed. The first area electrode 50 has the first area 50a and the second area 50b, which are electrically insulated from each other along the parting line 51. The dividing line 51 is not given by a straight line in this embodiment, but has a curvature that can be chosen such that the capacitive measurement as linear as possible relationship between the measured variable (inclination or rotation) about a rotation axis 80 and recorded capacity change.

From Fig. 2 it can be seen that with slight rotations about the axis of rotation 80, a displacement of the part 40 along the convex outer wall 20 is generated, but that with larger rotations about the rotation axis 80, the part 40 hardly moves and consequently no further capacity change leads. For example, with a rotation between 45 and 90 ° about the axis of rotation 80 in the situation illustrated in FIG. 2, the part 40 will be located in one of the vertices of the cavity 10 defined by the spacer 13. However, with smaller rotations (eg, less than 10 °), there is a strong shift Δs of the part 40 along the outwardly bulging outer wall 20, and consequently, a significant change in capacitance between the first region first area electrode 50a and the second area electrode 60.

FIG. 3 shows a cross-sectional view through the spacer element 13 in FIG. 2. It can thus be seen how the spacer element 13 defines the cavity 10 and in particular the outwardly curved outer wall 20. Furthermore, it can be seen that the first surface electrode 50 is not formed over the entire surface on the first electrode carrier 11, but extends only in a region which is swept by the part 40 in the lateral movement Δs parallel to the outwardly curved outer wall 20. The first area electrode 50 in turn has the first area 50a and the second area 50b, which are electrically insulated from one another along the dividing line 51. Both parts are electrically contacted and are connected to an evaluation unit or measuring electronics 90. In FIG. 3, the second surface electrode 60, which is likewise connected to the evaluation unit 90, is not shown.

Thus, Fig. 3 shows an arrangement in section through the spacer 13 and also illustrates the electrical readout of the sensor. The two mutually insulated partial surfaces 50 a, b of the first electrode structure 50 are connected to the measuring electronics 90. The second electrode structure 60, which may be formed over the entire surface of the second electrode holder 12, for example, is also connected to the measuring electronics 90, so that between the first portion 50a of the first Elektrodenstruk- and the second electrode structure 60 (= first partial capacitor arrangement) a first partial capacitance Cl and between the second region 50b of the first electrode structure and the second electrode structure 60 ^■ (= second partial capacitor arrangement) a second partial capacitance C2 can be measured.

The first partial capacitor arrangement thus forms along a first overlap area Al as well as along a sectional area of the first area 50a with the part 40 (exemplary air bubble). In an analogous manner, the second partial capacitor arrangement forms along a second overlapping area A2 and a further sectional area of the second area 50b with the part 40. Both contributions to the first (and also both contributions to the second) partial capacitor arrangement supply parallel capacitive contributions to the first (and second) partial capacitance Cl (and C2), as will be described in more detail in FIG. The capacitances of the two contributions differ because the dielectric constant of the part 40 is different from the dielectric constant of the dielectric liquid.

The first overlap area Al is given by the degree of overlap of the first area 50a of the first electrode structure 50 with the second electrode structure 60, the overlap being defined by the dielectric liquid 30. Similarly, the second overlapping area A2 is given by the degree of overlap of the second part 50b of the first area electrode 50 with the second area electrode 60. The first overlapping area Al is thus within the first area 50a complementary to the sectional area forming the exemplary air bladder 40 with the first area 50a. Similarly, the second overlapping area A2 is complementary to the sectional area that the second area 50b forms with the exemplary air bubble 40.

A tilting of the sensor and thus a movement .DELTA.s of the exemplary air bubble 40 changes in opposite directions the two partial capacitances Cl and C2, since in this case the coverage Al increases in the first partial capacitor arrangement, while the overlap A2 of the second partial capacitor arrangement decreases or vice versa (depending on the direction of rotation). This results in a clear relationship between the tilt (inclination) of the sensor and the measurable capacitance difference of the two sub-capacitor arrays. Due to the shape of the exemplary air bubble 40 does not necessarily result in the zero position of the sensor, the capacitance difference zero, since in the upper (first) sub-capacitor assembly, a larger area is not covered by the dielectric fluid 30 than in the lower (second) sub-capacitor assembly. This circumstance also causes a non-linear capacitance change as a function of the tilting, but the unambiguous assignment between tilt angle (rotation about the rotation axis 80) and the capacitance difference is always given. By a suitable choice of the electrode shape, however, a quasi-linear characteristic can also be achieved in this case. This selection of the electrodes can be effected, for example, by a selection of the separation line 51 which separates the two regions of the first surface electrode 50. As already shown in FIGS. 2 and 3, it is generally not advantageous to choose a linear configuration of this parting line 51, but instead to curve the parting line 51 in such a way that the result is a linear characteristic (capacity change as a function of the inclination angle) , In general, a relationship will exist between the curvature and the curvature of the outer wall 20, the relationship depending, for example, on the shape of the part 40. The shape of the part 40 in turn depends on the one hand on the surface tension of the dielectric liquid 30 and on the other hand on the degree of wetting of the outer wall 20 of the dielectric liquid 30th

4 shows an equivalent circuit diagram for the first partial capacitance Cl and the second partial capacitance C2. The first partial capacitance Cl is given by the above-mentioned two contributions, wherein the first contribution CIa the dielectric liquid 30 and the second contribution CIb the part 40 as a dielectric medium between the first region of the first surface electrode 50a and the second surface electrode 60th is arranged. In an analogous manner, the second partial capacitance C2 is likewise given by two contributions, the first contribution C2a likewise the dielectric fluid 30 and the second contribution C2b the dielectric medium portion 40 which is between the second region of the first surface electrode 50b and the second surface electrode 60 is arranged. The second area electrode 60 can be connected to ground, for example, so that the two signals at the first and second area of the first area electrode 50a, 50b can be used as a measurement signal. It may be advantageous if the partial capacitances C1 and C2 are not measured directly, but instead the difference between the two partial capacitances C1-C2 is used instead as the measured variable to be detected. The measurement of this difference capacity of the oppositely changing partial capacitances Cl and C2 is advantageous because it can compensate for disturbing influences such as temperature and / or humidity. It should be noted in this equivalent circuit diagram that the capacitances CIa, CIb, C2a and C2b depend on the inclination of the capacitive sensor. However, although the areas of the first and second area electrodes 50, 60 do not change as such, the dielectric medium, and hence the effective dielectric constant, changes between the first and second area electrodes 50, 60. Specifically, the dielectric liquid 30 overlaps depending on the Inclination (or the position of the part 40) a more or less large part of the first and second surface electrode 50, 60th

With this equivalent circuit diagram, it is thus taken into account that the area of the electrodes which is not covered by the fluid (dielectric fluid 30) contributes to the capacitance. The partial capacitor arrangement (C1, C2) is thus, as shown, a parallel connection of a capacitor with dielectric (CIa, C2a) and a second capacitor with air (CIb, C2b). In a slope ^', the area of the capacitor CIa increases example with Dielekt- while the area of the condenser decreases with air CIb. In sum, ¹ results in an increase in the partial capacitor C1 in the parallel connection since the change of the capacitor with dielectric CIa "overcompensates" the reduction of the air capacitor CIb, as it were because of the higher dielectric constants. Analogous considerations apply to the partial capacitor arrangement C2, with both partial capacitor arrangements opposing each other to each other (to achieve, for example, the said temperature and humidity compensation), so that when the partial capacitor arrangement C2 decreases, the partial capacitor arrangement Cl increases.

FIG. 5 shows another embodiment in which the shape of the first surface electrode 50 has been changed as compared with the embodiment shown in FIG. Overall, the exemplary embodiment in FIG. 5 has four parts for the first area electrode 50, wherein a first area 50a and a third area 50c are electrically connected to one another. Further, the second region 50b is electrically connected to a fourth region 50d.

The first and second regions 50a and 50b of the first electrode structure 50 essentially form a rectangle which is (slightly) curved parallel to the convex outer wall 20 and the dividing line 51 follows a slightly curved diagonal of the rectangle. In FIG. 5, the electrode structure of FIG. 3 has been duplicated in that in addition to the first region 50a and the second region 50b, a third region 50c and a fourth region 50d have been added, the third and fourth regions 50c, 50d being analogous Shape as the first and the second region 50a, 50b. The third and fourth regions 50c, d thus also substantially form a rectangle which is curved parallel to the outwardly curved outer wall 20 and the parting line 51 of a slightly curved diagonal the rectangle follows. The two rectangles thus formed are arranged electrically isolated from each other along their long side. This ensures that, for example, all four areas 50a, b, c, d are electrically isolated from one another on the first Elektrσdenträger 11, wherein the electrical connection can be done circuitry outside the capacitive sensor.

The height of the first surface electrode 50 may again be given, for example, by a radial extent R of the exemplary air bubble 40 and extend substantially over the lateral width B of the cavity 10.

Thus, FIG. 5 shows an alternative design of the first electrode structure 50. The comb-like subdivision of the first electrode structure 50 into a plurality of superimposed strips thus minimizes the negative influence of the round shape of the exemplary air bubble 40 on the linearity of the output signal the changes covered by the dielectric fluid 40

Areas in the two sub-capacitor assemblies Cl and C2 approach each other.

Fig. 6 shows a further embodiment in which within the cavity 10, a further spacer element 14 is arranged such that the part 40 of the cavity 10 is formed between the spacer element 13 and the further spacer element 14 and the part 40 only laterally (along the direction of movement Δs) is limited by the dielectric fluid 30. Thus, the part 40 is limited on the curved outer wall 20 opposite side 21 of the further spacer element 14. In the intermediate space between the spacer element 13 and the further spacer element 14 in which the part 40 is formed, the first surface electrode 50 is formed on a side wall (electrode carrier 11), wherein the first surface electrode 50 again has a first region 50a and a second region Area 50b, which, as shown in FIG. 3rd shown interrupted along the parting line 51. The further spacer element 14 may be arranged in the cavity 10 such that its surface bulges into the cavity 10, so that the outwardly curved outer wall 20 and a side wall 21 of the further spacer element 14 extend substantially parallel to one another. The channel between the convex outer wall

20 and the side wall 21 can be chosen such that the distance between the two walls is smaller than a lateral extent (in the direction of movement Δs) of the part 40th

Thus, Fig. 6 shows another alternative to improve the linearity of the sensor signal. By introducing the capillary forming member 14, a tubular region 16 is formed by allowing the exemplary air bladder 40 to be located. As it adheres to the upper and lower walls 20 and 21 of the tubular region 16, the surface of the exemplary air bubble 40 forms approximately perpendicular to the two walls 20,

21 and thus in the radial direction within the entire cavity. In this way, an approximately equal degree of coverage (Al = A2, see FIG. 3) is achieved for both partial capacitor arrangements in the zero position and a linear sensor output signal, since the surface of the air bubble 40 forms in the radial direction and moves in the circumferential direction , The radial direction in this case refers to a direction parallel to the surface normal along the convex outer wall, and the circumferential direction corresponds to the direction of movement Δs of the exemplary air bubble 40.

Fig. 7 shows another embodiment in which the first and second surface electrodes 50 and 60 are not formed along sidewalls, but in which the first surface electrode 50 is disposed along the convex outer wall 20 and the second surface electrode 60 is disposed on the opposite electrode carrier 12 (floor) is trained. Fig. 7 thus shows a spatial view of the capacitive sensor, wherein the introduced in the cavity dielectric liquid 30 is bounded by the second electrode carrier 12 down and laterally bounded by a first side wall 15a and a second side wall 15b. The outwardly bulging outer wall 20 is formed along the first electrode carrier 11 so that the first area electrode 50 and the second area electrode 60 are at a distance d from each other defined by the first and second side walls 15a and 15b. It may be advantageous if the second electrode carrier 12 also has a curvature, which may be formed in particular parallel to the curvature of the outer wall 20. This ensures that the (effective) distance d, which determines the capacitance of the capacitor arrangements, remains constant within the cavity. Furthermore, the exemplary air bubble may also extend over the entire height of the cavity.

As in the previous embodiments, the first area electrode has a first area 50a and a second area 50b, which are electrically insulated from one another along a dividing line 51, such that when the dielectric liquid 30 is inserted, the first partial capacitor again lies between the first area 50a and of the second area electrode 60 and the second subcondenser between the second area 50b and the second area electrode 60 are formed. The dividing line 51 between the first and second regions 50a and 50b may in this embodiment in turn be formed as a diagonal along the rectangularly formed first surface electrode 50. With an upright position of the capacitive sensor, the exemplary air bubble 40 thus forms along the convex outer wall 20, which, when rotated about the rotation axis 80, moves along the outwardly curved outer wall 20 onto which the first surface electrode 50 is formed , describes. Consequently, in this embodiment, the first area electrode 50 is curved along a tangential direction that is parallel to the movement Δs. The dividing line 51 between the first and second regions 50a, 50b therefore appears in a plan view as a straight line. The second surface electrode 60 can in turn be formed over the entire area of the second electrode carrier 12 (eg by vapor deposition) and is therefore not shown explicitly in the figure.

8 shows the same embodiment in a plan view of the side of the first electrode carrier 11, wherein the rectangle-shaped first surface electrode 50 with the first and second regions 50a and 50b is visible from above and the exemplary air bubble 40 appears in the middle. Laterally, the capacitive sensor is separated by the first and second side walls 15a and 15b, and the first and second regions of the first surface electrode 50a, 50b are electrically contacted and connected to an evaluation unit 90. The second surface electrode 60 is not visible in the plan view shown, whereby this second surface electrode 60 is also connected to the evaluation unit 90. Since the first surface electrode 50 is curved perpendicular to the top view, it appears as a rectangle, along the diagonal from bottom left to top right, the dividing line 51 is shown, which electrically isolates the first and second regions 50a and 50b from each other. The first partial congestion arrangement Cl thus comprises two regions: a first region of the first surface electrode 50a, which is not contacted by the exemplary air bubble 40, and a second region, which is contacted by the exemplary air bubble 40. Similarly, the second Teilkondensatora- arrangement C2 also comprises two contributions: a first contribution, which determines by that area ratio of the second part of the first area electrode 50b, which is not in contact with the exemplary air bubble 40, and a second Contribution, which in turn is complementary to that and corresponds to that surface part of the second part of the first surface electrode 50b, which is in contact with the exemplary air bubble 40. As described above, due to the different dielectric properties of the exemplary air bubble 40 and the dielectric fluids 30, both contributions have different capacitances, the sensitivity of the capacitive sensor increasing as the difference in dielectric constant (of the part 40 compared to the dielectric fluid 30) increases. is.

Thus, a second basic variant of the sensor principle is shown in FIGS. 7 and 8, which differs from the exemplary embodiments shown in FIGS. 2 to 6 (FIG. 7 shows an exploded view and FIG. 8 shows the same variant in plan view). The transparent representation of the first surface electrode 50 and the first electrode carrier 11 is for illustrative purposes and is generally not given. In this embodiment, as said, the first electrode carrier 11 is curved with the first surface electrode 50 and forms with the second electrode carrier 12, which carries the second surface electrode 60 (which is not shown in the drawing), without the use of a spacer element 13, the cavity 10th At the front and back side walls 15a and 15b are formed as the completion of the cavity 10 only. The cavity 10 is in turn partially filled with a dielectric liquid 30, wherein an exemplary air bubble 40 is similar to the other embodiments at the highest point of the cavity. An advantage of this arrangement is that the degree of coverage Al, A2 of the two partial capacitor arrangements in the zero position is identical. Further, _'at a tilt of the sensor about the rotation axis 80, the change in area of the uncovered electrode surface of both partial capacitor arrays Cl and C2 is equal in magnitude. An effective change in the distance between the two electrode tracks can, as described above, be compensated in that the second surface electrode 60 is curved parallel to the first surface electrode 50. Thus, this embodiment is characterized by a high linearity of the sensor output signal (sensor characteristics).

Fig. 9 shows a direct continuation of the embodiment shown in Figs. 7 and 8, in which a determination of a rotation or inclination with respect to two different axes of rotation 80a, b is possible. To this end, the outwardly curved outer wall 20 shown in Fig. 7 is curved in two directions (eg, in the form of a convex lens), and the thus curved surface serves as an electrode carrier 11 for the first surface electrode 50. To independently detect various rotations with respect to different axes of rotation, the first area electrode 50 in this embodiment has four areas: a first area 50a, a second area 50b, a third area 50c, and a fourth area 50d. All four areas are electrically insulated from each other by a separating line 51 (in the form of a cross) and form an outwardly curved convex surface (perpendicular to the plane of the drawing of FIG. 9). The exemplary air bubble 40 is again shown centrally in FIG. 9, whereby a zero position can be defined. Upon rotation about the axis of rotation 80a, the exemplary air bladder 40 moves along the direction 8a, and upon rotation about the axis of rotation 80b, the exemplary air bladder 40 moves along the direction 8b. By a differential detection of the capacitances, for example with respect to the areas 50b, 50d, an inclination with respect to the rotation axis 80b can thus be established. In an analogous manner, for example by a differential detection with respect to the capacitor surfaces 50a, 50c, an inclination or rotation relative to the axis of rotation 80a can be detected. In FIG. 9, the first and second electrode carriers 11, 12, which lie one above the other in the plan view shown here, as well as the first and second side wall 15a, b, are shown only schematically (see room view FIG. 7). By a correspondingly small curvature of the lens-shaped configured outwardly curved first surface electrode 50 can thus - as in the other embodiments - the sensitivity to the inclinations or rotations are set.

Thus, Fig. 9 shows an extension of the embodiment of Figs. 7 and 8. In this embodiment, the first electrode carrier 11 (as stated) is not only curved in one dimension, but has, for example, a spherically shaped inner surface. As a result, the measuring principle can be extended to two tilting axes (with respect to the axis 80a, 80b). For this purpose, the first electrode structure 50 is subdivided into four subareas (50a, 50b, 50c, 50d) which are electrically insulated from one another, wherein their respective capacitance is measured against the second electrode structure 60, configured for example over the entire area, on the second electrode carrier 12. By means of a suitable connection and evaluation, it is then possible to deduce the tilting of the sensor in two spatial axes.

In the embodiments described so far, it has been assumed that the dielectric fluid 40 has a greater density than the exemplary air bladder 40 such that the exemplary air bladder is vertically up and the dielectric fluid is down (in gravity) in the vertical direction. However, it is equally possible that the dielectric fluid is lighter than, for example, a medium located within the exemplary part 40 (no bubble in this case). This can be achieved, for example, by first placing the dielectric liquid 30 in the cavity 10 and then another dielectric liquid that does not interfere with the dielectric dielectric liquid 30 is mixed, is filled. Both dielectric liquids advantageously have as many different dielectric constants as possible. Depending on which of the two dielectric fluids is heavier or has a higher density, in this embodiment the part 40 is either up or down. In any case, the capacitive sensor is to be arranged so that the part 40 is arranged along the convex outer wall 20 (which may be up or down). However, the inclination or rotation about the axis of rotation described so far in embodiments is equivalent to the fact that in addition to gravity, a (lateral) acceleration or force occurs, which causes a displacement of the part 40 along the outwardly curved outer wall 20. This lateral force may be, for example, a centrifugal force or another acceleration, which acts laterally on the capacitive sensor.

Another embodiment of the present invention is that both surface electrodes - both the first

Surface electrode 50 and the second surface electrode 60 are divided (two differential capacitor structures) and arranged such that the measurable capacitance difference on the second divided electrode structure changes in the opposite direction to the capacitance difference at the first divided electrode structure. This can be achieved, for example, by the dividing line 51 extending between the electrodes in the one divided electrode structure from bottom left to top right, as shown for example in FIG. 3, and from bottom right to left in the case of the other electrode structure goes up. In this case, the redundant design of the measuring electrodes can be used to calculate out the effects of humidity and temperature which change the measuring signal. As a result, an even higher accuracy of the system is achieved and extends the application of the capacitive tilt sensor. 10 shows a concrete exemplary embodiment in which both the first area electrode 50 and the second area electrode 60 are divided, wherein the first area electrode has a first area 50a and a second area 50b and also the second area electrode 60 likewise has a first area 60a and a second region 60 b, which are isolated by a (curved) dividing line 61 from each other. The dividing line along the first surface electrode 51, which electrically separates the first and second regions 50a, b, runs along the one diagonal of the rectangle-shaped first surface electrode 50, whereas the dividing line 61 runs along the other diagonal of the second surface electrode, also shaped as a rectangle 60 runs. The first and second surface electrode 50, 60 are in the distance d, which can be realized for example by the spacer element 13.

The sensitivity of the capacitive sensor can be achieved on the one hand by a variation of the design of the surface electrodes 50, 60 and on the other hand by a variation of the outwardly curved outer wall 20 can be achieved. Regarding the design of the surface electrodes 50, 60, some concrete implementations have already been shown in the different embodiments. As already described with reference to FIG. 1, the outwardly curved outer wall 20 can be selected such that the movement Δs of the part 40 changes particularly strongly for certain inclinations. In general, a high degree of sensitivity is achieved with a slightly convexly curved outer wall 20, whereas a strong, outwardly curved outer wall will show a low sensitivity. Often it will be less advantageous that the outwardly curved outer wall has a semi-circular shape, but instead represents only a circle segment, the circle should have a very large radius in order to achieve the highest possible sensitivity. When setting the high sensitivity However, it must be borne in mind that a high level of sensitivity is usually associated with the fact that only a limited angular range can be detected and that, starting at a certain critical angle, further inclinations can hardly or only to a limited extent be detected.

In further embodiments, the dielectric fluid and the cavity 10 may be such that the inner walls of the sensor cavity 10 are wetted better or worse. These characteristics may influence the shape of the exemplary air bubble 40 that forms as the cavity 10 is filled with the dielectric liquid 30. Also, the number of regions of the first and second surface electrodes 50, 60 and their shape may be further varied (eg, three regions per area electrode).

Claims

claims

1. Capacitive sensor for detecting a measured variable, with:

a cavity (10) having a lateral extent (B), wherein the cavity (10) has a slightly outwardly curved outer wall (20) compared to the lateral extent (B), wherein in the cavity (10) a dielectric liquid (10) 30) exposing a portion (40) of the cavity (10), and wherein the portion (40) has a dielectric constant other than that of the dielectric fluid (30); and

a first area electrode (50) formed on a side wall of the cavity (10) and a second area electrode (60) formed on a side wall opposite to the side wall, the first and second area electrodes (50, 60) being disposed in the one side wall Cavity (10) are formed such that a movement (Δs) of the part (40) in the dielectric liquid (30) along the outwardly curved outer wall (10) in response to the measured variable to a capacitance change between the first and second surface electrode ( 50, 60),

and wherein the slightly outwardly curved outer wall (20) has a radius of curvature, the double radius of curvature being greater than the lateral extent (B).

2. Capacitive sensor according to claim 1, wherein the measured variable is an inclination of the capacitive sensor in the direction of a curvature of the outwardly curved outer wall (20).

3. A capacitive sensor according to claim 1 or claim 2, wherein the convex outer wall (20) has a Curvature, so that surface normals of the outwardly curved outer wall (20) in an angular range of less than 40 ° or less than 20 ° over the lateral extent (B) of the outwardly curved outer wall (20) vary.

A capacitive sensor according to any one of the preceding claims, wherein the first area electrode (50) has a first area (50a) and a second area (50b) electrically isolated from each other along a separation line (51) so that a first area and a second overlay area (Al, A2) of the dielectric liquid (30) with the first and second areas (50a, 50b), the first and second overlap areas (Al, A2) being formed during the movement (Δs) of the part (40 ) change in opposite directions.

5. Capacitive sensor according to claim 4, further comprising an evaluation unit (90), and the evaluation unit (90) is adapted to detect a difference between a first capacitance (Cl) and a second capacitance (C2),

wherein the first capacitance (Cl) between the first area (50a) and the second area electrode (60) and the second capacitance (C2) between the second area (50b) and the second area electrode (60) is formed.

The capacitive sensor according to claim 4 or claim 5, wherein said first area electrode (50) has a rectangular shape, and said line (51) is formed along a diagonal of said rectangular-shaped first area electrode (50).

7. Capacitive sensor according to one of claims 4 to 6, wherein the second surface electrode (60) has a first and second region (60a, 60b), which along a Separate line (61) are separated from each other, wherein the dividing line (51) and the further dividing line (61) are skewed to each other.

8. Capacitive sensor according to one of the preceding claims, wherein the cavity (10) by a spacer element (13) is defined, wherein the spacer element (13) has the outwardly curved outer wall (20) and between a first electrode carrier (11) the first surface electrode (50) and a second electrode carrier (12) with the second surface electrode (60) is arranged.

9. Capacitive sensor according to one of the preceding claims, wherein the first surface electrode (50) has four regions (50a, 50b, 50c, 50d), wherein in each case two of the four regions are arranged comb-like with each other and electrically connected.

10. A capacitive sensor according to any one of claims 6 to 9, wherein a long side of the rectangular-shaped first area electrode (50) is curved such that the long side is formed in parallel with the convex outer wall (20).

11. A capacitive sensor according to any one of the preceding claims, further comprising a capillary-forming member (14) and the capillary-forming member (14) is arranged such that between the capillary-forming member (14) and the outwardly arched Outer wall (20) forms a capillary (16), wherein the part (40) of both the capillary forming member (14) and of the outwardly curved outer wall (20) is limited.

12. Capacitive sensor according to one of claims 4 to 7, wherein the first surface electrode (50) is formed along the convex outer wall (20) and the second surface electrode is disposed on an opposite side of the outwardly curved outer wall (20) so that movement of the part (40) to changing cut surfaces of the part (40) leads to the first and second regions (50a, 50b) ,

13. The capacitive sensor of claim 12, wherein the outwardly curved outer wall (20) has a convexly outwardly shaped surface in two directions, such that the part (40) rotates about a first axis of rotation (80a) along a first axis of rotation Direction (8a) moves and in a rotation about a second rotation axis (80b) along a direction (8b) moves, wherein the first and second rotation axis (80a, 80b) are perpendicular to each other.

The capacitive sensor of claim 12 or claim 13, wherein said first area electrode (50) has four areas (50a, 50b, 50c, 50d), said four areas (50a, 50b, 50c, 50d) being defined by a cross-shaped dividing line (51) are electrically isolated from each other.

15. Capacitive sensor according to one of the preceding claims, wherein the inner walls of the cavity (10) for the dielectric liquid (30) are not wetting.

A capacitive sensor according to any one of the preceding claims, wherein the part (40) is an air bubble or vacuum.

17. A capacitive sensor according to any one of the preceding claims, wherein the portion (40) comprises a further dielectric fluid, the further dielectric fluid differing in density and dielectric constant from the dielectric fluid (30) and both dielectric fluids are immiscible.

18. Capacitive sensor for detecting a measured variable, comprising:

a cavity (10) having an outer wall (20), wherein in the cavity (10) a dielectric liquid (30) leaving a part (40) of the cavity (10) is inserted, said part (40 ) has a dielectric constant other than that of the dielectric fluid (30) and only so much dielectric fluid (30) is introduced that the part (40) is bounded laterally by the fluid and not by a wall of the cavity (10); and

a first and second area electrode (50, 60) formed in the cavity (10) such that movement (Δs) of the portion (40) in the dielectric liquid (30) along the outer wall (20) in response to the measurand to a capacitance change between the first and second surface electrode (50, 60) leads.

19. A method of manufacturing a capacitive sensor for detecting a measured variable, comprising the following steps:

Providing a cavity (10) having an outer wall (20);

Forming first and second area electrodes (50, 60) in the cavity (10); and

Introducing a dielectric fluid (30) into the cavity (10) such that a portion (40) of the cavity (10) is left open, the portion (40) having a different dielectric constant than that of the dielectric fluid (30) ;

wherein the first and second area electrodes (50, 60) are formed such that a movement (Δs) of the Part (40) in the dielectric liquid (30) along the outer wall (20) in response to the measured variable to a capacitance change between the first and second surface electrode (50, 60) leads.