Sensorelement

Abstract

A sensor element has several planes (E1 - E7) arranged orthogonally to a sensor axis (A). In at least one first plane (E1 - E3) a coil (21 - 23) is arranged, which is surrounded by a first shield ring (41 - 43). The sensor element (10) further has at least one second shield ring (44 - 47). Each second shield ring (44 - 47) is arranged in a second plane (E4 - E7) which does not contain a coil (21 - 23).

Description

[0001] The present invention relates to a sensor element. State of the art

[0002] When installing inductive sensors in a metallic environment, there is a risk, depending on the installation situation, that the surrounding material will be detected instead of the intended object. This surrounding material could be a metal nut or an installation medium such as aluminum. This problem can be addressed, for example, by equipping the sensor with a housing that provides good electromagnetic shielding, such as one made of brass. However, such a shielding housing is more expensive than, for example, one made of stainless steel. Similarly, only by using a large quantity of an expensive precious metal can all the coils of the inductive sensor be surrounded by a single copper shielding ring that is longer than the sensor element. Furthermore, any displacement of the copper ring over the sensor's lifetime can lead to its failure.

[0003] Steering the magnetic field of an inductive sensor to prevent the detection of objects behind the sensor's coil(s) and only detect objects in front of the coil(s) can be achieved by using a ferrite core. However, if a ferrite core is used, the sensor cannot be made magnetically field-resistant.

[0004] US patent 2020 / 0231582 A1 describes an angle sensor with multiple coils arranged in stacked planes. Several EMI shielding layers follow the coil planes and are positioned between the coils and the sensor's control electronics.

[0005] It is an object of the present invention to provide a sensor element that can be installed in a metallic environment without the installation material being detectable. This should be possible without using large quantities of precious metals to shield the sensor element and without significantly degrading the signal quality of the sensor element. Disclosure of the invention

[0006] This problem is solved according to the invention by a sensor element, in particular an inductive sensor element, which has several planes arranged orthogonally to a sensor axis. A coil is arranged in at least one first plane and is surrounded by a first shielding ring. Such a shielding ring is also referred to as a short-circuit ring and serves to electromagnetically shield the coil. To enable the sensor element to be implemented as an inductive sensor element, several first planes, each with a coil surrounded by a first shielding ring, are provided. Furthermore, the sensor element has at least one second shielding ring. Each second shielding ring is arranged in a second plane that does not contain a coil.It was found that reliable shielding against an installation material can be achieved by surrounding each coil of the sensor element with a shielding ring and by arranging one or more additional layers with shielding rings behind the coil(s). Each layer can be a printed circuit board or a layer within a multilayer printed circuit board. The coils are typically printed circuit board coils, and the shielding rings are printed onto the first and second layers. The shielding rings are made of copper. The precious metal consumption required in this way is considerably lower than if a solid shielding ring extending over and beyond the first layers were used, or if the coils were even mounted in a shielding housing made of copper or a copper alloy, such as brass.

[0007] In a preferred embodiment of the sensor element, all shield rings have an identical outer diameter. They thus define the outer edge of the sensor element, which can, for example, be surrounded by a circular cylindrical housing made of stainless steel.

[0008] The inner diameter of the first shielding rings is determined by the diameter of the coils. In principle, it is possible for all second shielding rings to have the same inner diameter as the first. Preferably, however, at least one second shielding ring has an inner diameter that is smaller than the inner diameter of a first shielding ring. This not only achieves good radial shielding of the coils, but the shielding ring with the smaller inner diameter also provides axial shielding in the direction of an electronic control unit connected to the coils. This control unit can be located, in particular, on the side of the second shielding rings facing 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 that is smaller than the first outer diameter. This second shielding ring with the second outer diameter also has a smaller inner diameter than the second shielding ring with the first outer diameter. The second shielding ring with the second outer diameter is the one located furthest from the first shielding ring(s). This embodiment enables focused shielding along the sensor axis. The sensor element is less affected by the smaller second outer diameter than if this second shielding ring also had the same outer diameter as the first.The sensitivity to a detectable object on the side of the coil(s) exposed by the second shielding rings therefore increases. This can be used to achieve shielding against a highly interfering, small conductive object that is part of the sensor element and located on the sensor axis.

[0010] In both preferred embodiments of the sensor element, it is further preferred that, in the presence of several second shielding rings, the inner diameter of the second shielding rings decreases with increasing distance from the at least one first coil. This achieves good shielding in the axial direction without reducing the sensitivity of the coil system by using second shielding rings that already have a small inner diameter close to the at least one first coil.

[0011] The minimum distance between a first and a second level is at least 20% of the outer diameter of a first shielding ring. Specifically, this is the distance between the outermost first level and the outermost second level of the sensor element. By positioning the last second shielding ring at such a large distance from the coil(s), it can be designed with a small inner diameter to achieve good axial shielding without compromising the sensitivity of the sensor element.

[0012] The thickness of the shielding rings is preferably in the range of 10 µm to 105 µm. Thickness is defined here as the dimension along the sensor axis. It is particularly preferred that all shielding rings have the same thickness. This thickness is suitable for ensuring reliable radial shielding of the coils in the first layers. For the sensitivity of the coil system, it is advantageous to make the second shielding rings with the same thickness as the first shielding rings.

[0013] The distance between a first layer and an adjacent second layer is preferably in the range of 70 µm to 120 µm. The distance between two adjacent second layers is also preferably in the range of 70 µm to 120 µm. This range is chosen to achieve good radial shielding while avoiding an increase in the number of layers and thus the cost of the sensor element due to close spacing. Preferably, all these distances have the same value. However, the distances can also be chosen differently. This applies particularly to the distances between the second layers, in order to optimize signal sensitivity and shielding effectiveness. The greater the distance between the second layers, the lower the shielding effect, but the higher the signal sensitivity of the sensor element.

[0014] The width of each second shielding ring is preferably in the range of 70 µm to half its outer diameter. The width is defined here as the dimension in the second plane, i.e., the difference between the inner and outer diameters of the second shielding ring. While the width of each first shielding ring is preferably in the range of 70 µm to 120 µm, the second shielding rings can have a considerably larger width to achieve good axial shielding.

[0015] Particularly when the sensor element is to be designed as an inductive sensor, it is preferred that it has three coils. A first receiving coil, a transmitting coil, and a second receiving coil are preferably arranged one behind the other along the sensor axis. The two receiving coils are electrically connected to each other. The configuration as receiving coils is achieved particularly by connecting the coil to a voltmeter. The configuration as transmitting coils, which is electrically isolated from the two receiving coils, is achieved particularly by electrically connecting this coil to a pulse shaper. Such an inductive sensor makes it possible to detect all metallic objects without a reduction factor at the same switching distance. This feature is advantageous in applications where the material of the objects to be detected can vary or when non-ferrous metals are to be detected at a large switching distance.

[0016] The shielding according to the invention gives the sensor element high sensitivity even when it is installed in metallic material. Its function is not disrupted by strong electromagnetic fields. It can therefore be used, for example, in welding systems. Brief description of the drawings

[0017] Exemplary embodiments of the invention are shown in the drawings and are explained in more detail in the following description. Fig. Figure 1 schematically shows a coil arrangement of an inductive sensor according to an embodiment of the invention. Fig. Figures 2a to 2c each show three different installation situations of an inductive sensor according to the state of the art in a sectional view. Fig. Figures 3a to 3c each show a sectional view of an installation situation of an inductive sensor according to an embodiment of the invention. Fig. Figure 4 shows a sectional view of an inductive sensor according to an embodiment of the invention. Fig. Figure 5 shows a sectional view of an inductive sensor according to another embodiment of the invention. Fig. 6 shows a detail section from Fig. 5. Fig. Figure 7 shows a sectional view of an inductive sensor according to yet another embodiment of the invention. Fig. 8 shows a detail section from Fig. 7. Exemplary embodiments of the invention

[0018] Fig. Figure 1 shows a coil arrangement of an inductive sensor element 10, which is designed as a proximity switch. This element has three coils 21-23. The first coil 21 and the third coil 23 are electrically connected to each other. Furthermore, they are each connected to a voltmeter 11 for measuring the electrical voltage. The second coil 22 is arranged between these two coils 21 and 23. It is connected to a pulse shaper 12 of an oscillator. The first coil 21 and the third coil 23 serve as receiving coils, and the second coil 22 serves as the transmitting coil. When a metallic object 30 is brought near the sensor element 10 and moves along a distance s towards it, the object 30 is detected when it falls below a switching distance.

[0019] In such a sensor element 10, each of the coils 21–23 can be surrounded by a copper shielding ring 41 to 43. Several different installation situations in which the sensor element 10 is installed in a metallic environment 50 are described in the Fig. 2a to 2c are shown. While in an installation situation in the Fig. 2a and Fig. 2c where no detection of the surrounding material 50 occurs by the coils 21 - 23, such detection occurs in the installation situation according to Fig. 2b.

[0020] In a first embodiment of the invention, therefore, in addition to the three shielding rings 41-43 which surround the three coils 21-23, a fourth shielding ring 44 is provided. This additionally shields the coils 21-23 in the direction of the sensor element 10 away from the detection direction. Fig. Figures 3a to 3c show that in all three installation situations, which are for the non-inventive sensor element 10 in the Fig. As shown in Figures 2a to 2c, sufficient shielding against the metallic environment 50 is present.

[0021] Fig. Figure 4 shows a detailed representation of the sensor element 10 according to the first embodiment of the invention. The coils 21-23 are arranged along a sensor axis A. Each of the coils 21-23, together with the surrounding shielding ring 41 to 43, lies in its own plane E1-E3, which is orthogonal to the sensor axis A. These three planes E1-E3 are followed by a fourth plane E4, which does not contain a coil. The fourth shielding ring 44 is arranged in this plane. The fourth plane E4 is also orthogonal to the sensor axis A and thus runs parallel to the other planes E1-E3. In this first embodiment of the sensor element 10, all shielding rings 41-44 have the same inner diameter and the same outer diameter. The outer diameters of the coils 21-23 are also identical in this and in all subsequent embodiments.

[0022] A second embodiment of the sensor element 10 according to the invention is described in the Fig. 5 and Fig. Figure 6 shows the arrangement and dimensions of the coils 21-23 and the first four shielding rings 41-44, which are identical to those of the first embodiment. However, three further shielding rings 45-47 are provided, arranged one behind the other in three further planes E5-E7. These planes E5 to E7 are also arranged orthogonally to the sensor axis A and parallel to the plane E1-E4. While the outer diameter d of all shielding rings 41-47 is, for example, 9 mm, the distance zd between the first plane E1 and the seventh plane E7 is, for example, 2.4 mm. This distance zd is therefore greater than 20% of the outer diameter d. All shielding rings 41-47 have a thickness a1-a7, which is, for example, 50 µm each. The width b1-b4 of the first four shielding rings 41 to 44 is, for example, 75 µm each. The width b5 of the fifth shielding ring 45 is, for example, 150 µm.The width b6 of the sixth shielding ring 46 is, for example, 300 µm. The width b7 of the seventh shielding ring 47 is, for example, 450 µm. The distances between two adjacent planes are, for example, 100 µm each. Due to the increasing width b4 - b7 of the shielding rings 44 - 47 with increasing distance from the coils 21 - 23, their inner diameter decreases, and good axial shielding of the coils 21 - 23 is achieved without negatively affecting the sensor sensitivity.

[0023] A third embodiment of the sensor element 10 according to the invention is described in the Fig. 7 and Fig.Figure 8 illustrates this. This corresponds to the second embodiment with respect to the dimensions, dimensioning, and positioning of the coils 21-23 and the first five shielding rings 41-45 in the first five planes E1-E5. However, instead of the two additional shielding rings 46, 47 of the second embodiment, this sensor element has only one additional shielding ring 46 in plane E6, which differs from the shielding ring 46 of the second embodiment. Its outer diameter is reduced by 150 µm compared to the other shielding rings 41 to 45, thereby reducing its outer radius by a value of zb6 of 75 µm. This corresponds to the width b1 - b4 of the first four shielding rings 41 - 44. As a result, the sixth shielding ring 46 does not overlap with these first four shielding rings 41 - 44 along the sensor axis A. While its thickness a6 corresponds to the value according to the second embodiment, its width b6 is 200 µm.Although it is only 50 µm wider than the fifth shielding ring 45, it has an inner diameter similar to that of the significantly wider sixth shielding ring of the second embodiment. The sixth shielding ring 46 is located so far from the coils 21-23 that it no longer has a significant impact on radial shielding, and the reduction in its outer diameter is therefore acceptable. However, because its inner diameter is similar to that of the sixth shielding ring 46 of the second embodiment, a similarly effective axial shield is also achieved. This not only saves material but also reduces the negative impact of this shielding ring 46 on the sensitivity of the sensor element compared to the second embodiment. QUOTES INCLUDED IN THE DESCRIPTION

[0000] This list of documents cited by the applicant was automatically generated and is included solely for the reader's convenience. The list is not part of the German patent or utility model application. The DPMA accepts no liability for any errors or omissions. Cited patent literature

[0000] US 2020 / 0231582 A1

[0004]

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