Sensor element

Abstract

The sensor element has several planes (E1 to E7) arranged orthogonally to the sensor axis (A). The coils (21 to 23) surrounded by the first shielding rings (41 to 43) are arranged in at least one first plane (E1 to E3). The sensor element (10) further has at least one second shielding ring (44 to 47). In each case, each second shielding ring (44 to 47) is arranged in a second plane (E4 to E7) without coils (21 to 23).

Description

TECHNICAL FIELD

[0001] The present invention relates to a sensor element. BACKGROUND

[0002] When installing an inductive sensor in a metal surrounding, there is a risk of detecting the surrounding material instead of the object to be detected, depending on the installation situation. The surrounding material can be, in particular, a metal nut or an installation medium, such as aluminum, for example. This problem can be countered, for example, by providing the sensor with a housing that is well shielded electromagnetically, for example, composed of brass. However, such a type of shielded housing is more expensive than a housing made of stainless steel, for example. Similarly, it is only possible to surround all the coils of an inductive sensor with a single shield ring made of copper that is longer than the sensor element by using a large amount of expensive stainless steel. Furthermore, displacement of the copper ring over the service life of the sensor can lead to failure of the sensor.

[0003] It is possible to manipulate the magnetic field of an inductive sensor by using a ferrite core in order to exclude detection of objects behind one coil or multiple coils of the sensor and to recognize only those objects in front of the one coil or multiple coils. However, if a ferrite core is used, the sensor cannot be designed to be field-resistant.

[0004] US 2020 / 0231582 A1 describes an angle sensor with several coils arranged in a superimposed plane. Behind the coil plane are several EMI shielding layers arranged between the coils and the control electronics of the sensor.

[0005] It is an object of the present invention to provide a sensor element that can be installed in a metal surrounding without detecting the installation material. This should be possible without using a large amount of stainless steel to shield the sensor element and without drastically degrading the signal quality of the sensor element. SUMMARY

[0006] This object is solved according to the application by a sensor element, in particular an inductive sensor element, which has several planes arranged orthogonally to a sensor axis. A coil, which is encircled by a first shielding ring, is arranged in at least one first plane. Shielding rings of this type are also referred to as short-circuit rings and serve for the electromagnetic shielding of the coil. In order to enable one embodiment of the sensor element as an inductive sensor element, several first planes are provided, in particular, with one respective coil encircled by a first shielding ring. Furthermore, the sensor element has at least one second shielding ring. In each case, each second shielding ring is arranged in a second plane which does not have a coil. It has been found that, in view of the fact that, on the one hand, all coils of the sensor element are each encircled by a shielding ring and, furthermore, one or more further planes with shielding rings are arranged behind one coil or behind several coils, a reliable shielding of the mounting material can have been achieved. In this case, each plane can in particular be a printed circuit board or a layer inside a multilayer printed circuit board. The coils are thus printed coils and the shielding rings are printed into the first and second planes. These shielding rings consist in particular of copper. The amount of stainless steel required for this object is far lower than in the case of very large shielding rings which extend across and beyond the first planes or even far lower than in the case where the coils would be mounted in a shielding housing consisting of copper or a copper alloy, such as brass.

[0007] In one preferred embodiment of the sensor element, all shielding rings have an equal outer diameter. By this, they define an outer edge of the sensor element which can be encircled by a cylindrical housing consisting of stainless steel.

[0008] The inner diameter of the first shielding rings is determined by the diameter of the coils. Fundamentally, it is possible for all second shielding rings to have the same inner diameter as the first shielding rings. Preferably, however, at least one second shielding ring has an inner diameter which is smaller than the inner diameter of the first shielding rings. Thus, not only a good radial shielding of the coils is achieved, but the shielding rings with a small inner diameter furthermore cause an axial shielding in the direction of an electronic controller connected to the coils. In particular, this controller can be arranged on the side of the second shielding rings which faces away from the coils.

[0009] In another preferred embodiment of the sensor element, all first shielding rings and at least one second shielding ring have a first outer diameter. However, at least one second shielding ring has a second outer diameter which is smaller than the first outer diameter. This second shielding ring having the second outer diameter furthermore has a smaller inner diameter than the second shielding rings having the first outer diameter. This second shielding ring having the second outer diameter is the second shielding ring which is farthest away from the first shielding ring or the plurality of first shielding rings. This embodiment enables a concentrated shielding in the sensor axis. In this case, the sensor element is affected by the small second outer diameter less than in the case where this second shielding ring would also have the first outer diameter. Thus, the sensitivity to the object to be detected on the side of the coil or the plurality of coils facing away from the second shielding ring is increased. This can be used to achieve a shielding of highly interfering, small conductive objects which are components of the sensor element and which are located on the sensor axis.

[0010] In two preferred embodiments of the sensor element, it is further preferred that, when there are several second shielding rings, the inner diameter of the second shielding rings becomes smaller as the distance from the at least one first coil increases. Thus, on the one hand, a good shielding in the axial direction can be achieved, and on the other hand, the sensitivity of the coil system is not reduced by second shielding rings already having a smaller inner diameter close to the at least one first coil.

[0011] At least one distance between the first plane and the second plane is at least 20% of the outer diameter of the first shielding ring. In particular, this distance is the distance between the outermost first plane and the outermost second plane of the sensor element. By arranging the last second shielding ring at such a distance from the coil or the plurality of coils, this ring can be designed to have a smaller inner diameter in order to achieve a good axial shielding without adversely affecting the sensitivity of the sensor element in this case.

[0012] The thickness of the shielding rings is preferably in the range from 10 pm to 105 pm. In this case, the dimension along the sensor axis is understood to be the thickness. In this case, it is particularly preferred that all shielding rings have the same thickness. This thickness is suitable for achieving a reliable radial shielding of the coil in the first plane. In this case, it is advantageous for the sensitivity of the coil system to design the second shielding rings to have the same thickness as the first shielding rings.

[0013] The distance between a first plane and a second plane adjacent to this first plane is preferably in the range of 70 pm to 120 pm. The distance between two adjacent second planes is similarly preferably in the range of 70 pm to 120 pm. The selection of this value range on the one hand enables a good radial shielding, while on the other hand an increase in the number of layers and thus an increase in the cost of the sensor element due to a narrow distance is avoided. It is particularly preferred that all these distances have the same value. Fundamentally, however, the distances can also all be selected to be different. This applies in particular to the distance between the second planes in order to optimize the signal sensitivity and the shielding effect. The greater the distance between the second planes, the lower the shielding effect and the higher the signal sensitivity of the sensor element.

[0014] The width of each second shielding ring is preferably in the range of 70 pm to half of its outer diameter. Here, the width is to be understood to mean the dimension in the second plane, i.e. the difference between the inner diameter and the outer diameter of the second shielding ring. While the width of each first shielding ring is preferably in the range of 70 pm to 120 pm, the second shielding ring can have a significantly greater width in order to thereby achieve a good axial shielding.

[0015] In particular, when the sensor element is to be designed as an inductive sensor, it is preferred that this sensor element has three coils. In this case, it is particularly preferred that the first receiving coil, the transmitting coil and the second receiving coil are arranged one after the other along the sensor axis. The two receiving coils are electrically connected to one another. The provision as a receiving coil is in particular achieved by connecting the coil to a voltage measurement device. The provision as a transmitting coil electrically insulated from the two receiving coils is in particular achieved by electrically connecting this coil to a pulse former. Such an inductive sensor enables all metal objects to be recognized at the same switching distance without a reduction factor. This property is advantageous in applications in which the material of the objects to be detected can vary or when non-ferrous metals are to be detected at high switching distances.

[0016] The shielding according to the application then also enables the sensor element to have a high sensitivity, even when the sensor element is installed in a metal material. The function of the sensor element is not disturbed by strong electromagnetic fields. Thus, for example, the sensor element can be used in a welding system. BRIEF DESCRIPTION OF DRAWINGS

[0017] Exemplary embodiments of the application are represented in the drawings and explained in more detail in the following description.

[0018] Figure 1 The coil arrangement of an inductive sensor according to one exemplary embodiment of the application is shown schematically.

[0019] Figures 2a to 2cThree different mounting situations of an inductive sensor according to the prior art are each shown in cross-sectional view.

[0020] Figures 3a to 3c Mounting situations of an inductive sensor according to one exemplary embodiment of the application are each shown in cross-sectional view.

[0021] Figure 4 A cross-sectional view of an inductive sensor according to one exemplary embodiment of the application is shown.

[0022] Figure 5 A cross-sectional view of an inductive sensor according to another exemplary embodiment of the application is shown.

[0023] Figure 6 A detail selection from Figure 5 is shown.

[0024] Figure 7 A cross-sectional view of an inductive sensor according to yet another exemplary embodiment of the application is shown.

[0025] Figure 8 A detail selection from Figure 7 is shown. DETAILED DESCRIPTION

[0026] Figure 1 A coil arrangement of an inductive sensor element 10 designed as a proximity switch is shown. This coil arrangement has three coils 21 to 23. The first coil 21 and the third coil 23 are electrically connected to one another. In addition, in each case they are connected to a voltage measuring device 11 in order to scan the voltage. The second coil 22 is arranged between the two coils 21, 23. This second coil is connected to a pulse former 12 of an oscillator. The first coil 21 and the third coil 23 serve as receiving coils, and the second coil 22 serves as a transmitting coil. In the case of a metal object 30 being brought close to the sensor element 10 and moving along the cross section s towards the sensor element 10, the object 30 is detected when the distance falls below a switch distance.

[0027] In this type of sensor element 10, each of the coils 21 to 23 can be surrounded by a copper shielding ring 41 to 43. Figures 2a to 2c Several different mounting situations of the sensor element 10 mounted in a metal surrounding 50 are represented in Figure 2a and Figure 2c In the mounting situations shown in Figure 2b , no detection of the surrounding material 50 by the coils 21 to 23 occurs, whereas in the mounting situations according to , this detection does occur.

[0028] In the first exemplary embodiment of the application, therefore, it is proposed that a fourth shielding ring 44 is provided in addition to the three shielding rings 41 to 43 that surround the three coils 21 to 23. This fourth shielding ring additionally shields the coils 21 to 23 in the direction of the sensor element 10 that faces away from the detection direction. Figures 3a to 3c It is shown that in all three mounting situations for sensor elements 10 that have already been represented in Figures 2a to 2c in the middle represent, there is sufficient shielding against the metallic surrounding 50.

[0029] Figure 4 A detailed representation of a sensor element 10 according to the first exemplary embodiment of the application is shown. The coils 21 to 23 are arranged along the sensor axis A. Each of the coils 21 to 23 lies in its own respective plane E1 to E3 orthogonal to the sensor axis A together with the shielding ring 41 to 43 that surrounds it. Behind these three planes E1 to E3 is a fourth plane E4 that has no coil. The fourth shielding ring 44 is arranged in this fourth plane. The fourth plane E4 is likewise orthogonal to the sensor axis A and, therefore, runs parallel to the remaining planes E1 to E3. In this first exemplary embodiment of the sensor element 10, all shielding rings 41 to 44 have the same inner diameter and the same outer diameter. In this exemplary embodiment, as in all the following exemplary embodiments, the outer diameters of the coils 21 to 23 are equal.

[0030] Figure 5 and Figure 6A second exemplary embodiment of a sensor element 10 according to the application is indicated in Fig. 2. This sensor element has an arrangement and dimensioning of the coils 21 to 23 and the first four shield rings 41 to 44 which match the first exemplary embodiment. However, three further shield rings 45 to 47 are provided which are arranged in succession in three further planes E5 to E7. These planes E5 to E7 are likewise arranged orthogonal to the sensor axis A and parallel to the planes E1 to E4. For example, the outer diameter d of all shield rings 41 to 47 is 9 mm, and for example the distance zd between the first plane E1 and the seventh plane E7 is 2.4 mm. This distance zd is thus greater than 20% of the outer diameter d. For example, all shield rings 41 to 47 have a thickness a1 to a7 of 50 pm in each case. For example, the width b1 to b4 of each of the first four shield rings 41 to 44 is 75 pm. For example, the width b5 of the fifth shield ring 45 is 150 pm. For example, the width b6 of the sixth shield ring 46 is 300 pm. For example, the width b7 of the seventh shield ring 47 is 450 pm. For example, the distance between two adjacent planes is 100 pm in each case. Since the widths b4 to b7 of the shield rings 44 to 47 increase with increasing distance from the coils 21 to 23, the inner diameter of these shield rings decreases and a good axial shielding of the coils 21 to 23 is achieved without a negative influence on the sensor sensitivity in the process.

[0031] Figure 7 and Figure 8 A third exemplary embodiment of a sensor element 10 according to the application is indicated in Fig. 3. The third exemplary embodiment matches the second exemplary embodiment in terms of the dimensions, dimensioning and positioning of the coils 21 to 23 and the first five shield rings 41 to 45 in the first five planes E1 to E5. However, instead of the two further shield rings 46, 47 in the second exemplary embodiment, this sensor element has only one further shield ring 46 in the plane E6 which differs from the shield ring 46 of the second exemplary embodiment. The outer diameter of this further shield ring is reduced to 150 pm compared to the remaining shield rings 41 to 45, whereby the outer radius of this further shield ring is reduced to a value zb6 of 75 pm. This value corresponds to the widths b1 to b4 of the first four shield rings 41 to 44.

[0032] Accordingly, the sixth shielding ring 46 does not overlap with the first four shielding rings 41 to 44 along the sensor axis A. While the thickness a6 of the sixth shielding ring matches the value according to the second exemplary embodiment, the width b6 of the sixth shielding ring is 200 pm. Accordingly, although the sixth shielding ring is only 50 pm wider than the fifth shielding ring 45, the sixth shielding ring has an inner diameter similar to the inner diameter of the substantially wider sixth shielding ring of the second exemplary embodiment. The sixth shielding ring 46 is so far from the coils 21 to 23 that its radial shielding is no longer of importance and, thus, a reduction of its outer diameter can be tolerated. However, since the inner diameter of the sixth shielding ring is similar to the inner diameter of the sixth shielding ring 46 of the second exemplary embodiment, a similarly good axial shielding is achieved as well. Accordingly, not only material is saved, but also any negative impact of this shielding ring 46 on the sensitivity of the sensor element is reduced compared to the second exemplary embodiment.

Claims

1. A sensor element (10) having a plurality of planes (E1 to E7) arranged orthogonally to a sensor axis (A), wherein a coil (21 to 23) surrounded by a first shielding ring (41 to 43) is arranged in at least one first plane (E1 to E3), characterized in that the sensor element (10) further has at least one second shielding ring (44 to 47), wherein in each case, each second shielding ring (44 to 47) is arranged in a second plane (E4 to E7) without the coil (21 to 23).

2. The sensor element (10) according to claim 1, characterized in that, All shielding rings (41 to 47) have the same outer diameter (d).

3. The sensor element (10) according to claim 1 or 2, characterized in that, The sensor element has at least one second shielding ring (45 to 47), the inner diameter of which is smaller than the inner diameter of the first shielding ring (41 to 43).

4. The sensor element (10) according to claim 1, characterized in that, All first shielding rings (41 to 43) and at least one second shielding ring (44 to 45) have a first outer diameter (d), and at least one second shielding ring (46) has a second outer diameter (d) smaller than the first outer diameter (d), wherein the second shielding ring (46) having the second outer diameter (d) has a smaller inner diameter than the second shielding ring (44 to 45) having the first outer diameter (d).

5. The sensor element (10) according to claim 3 or 4, characterized in that, The sensor element has a plurality of second shielding rings (44 to 47), wherein the inner diameter of the second shielding rings (44 to 47) becomes smaller as the distance from the at least one first coil (21 to 23) increases.

6. The sensor element (10) according to any one of claims 1 to 5, characterized in that, At least one distance (zd) between the first plane (E1 to E3) and the second plane (E4 to E7) corresponds to at least 20% of the outer diameter (d) of the first shielding ring (21 to 23).

7. The sensor element (10) according to any one of claims 1 to 6, characterized in that, The thickness (a1 to a7) of the shielding rings (41 to 47) along the sensor axis (A) is in the range of 10 µm to 105 µm.

8. The sensor element (10) according to any one of claims 1 to 7, characterized in that, The distance between the first plane (E3) and the adjacent second plane (E4) is in the range of 70 µm to 120 µm.

9. The sensor element (10) according to any one of claims 1 to 8, characterized in that, The distance between two adjacent second planes (E4 to E7) is in the range of 70 µm to 120 µm.

10. The sensor element (10) according to any one of claims 1 to 9, characterized in that, The width (b4 to b7) of each second shielding ring (44 to 47) within its second plane (E4 to E7) ranges from 70 µm to half of its outer diameter (d).

11. The sensor element (10) according to any one of claims 1 to 10, characterized in that, A first receiving coil (21), a transmitting coil (22), and a second receiving coil (23) are arranged in succession along the sensor axis (A), wherein the two receiving coils (21, 23) are electrically connected to each other.

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