Sensor element especially for a revolution counter

Abstract

Sensor element (50), in particular for a revolution counter, wherein a change in magnetization can be induced and stored in the sensor element (50) without an energy supply when a magnetic field is moved past the sensor element (50), wherein the sensor element (50) has two spiral strips (13, 14), each with a layer structure which successively contains at least one soft magnetic layer, one non-magnetic layer and one hard magnetic layer, wherein the winding direction of the two spiral strips (13, 14) is opposite, and wherein the two spiral strips (13, 14) are each connected by their outer end to a common wall generator (52).

Description

[0001] The invention relates to a sensor element, in particular for a revolution counter, wherein a change in the magnetization can be induced and stored in the sensor element without a power supply when a magnetic field is moved past the sensor element.

[0002] Such a sensor element is known from EP 1 740 909 B1. The sensor element therein is spiral-shaped and has a layer structure consisting of a soft magnetic layer, a non-magnetic layer, and a hard magnetic layer. If a magnetic field is moved or rotated past this sensor element, a change in the magnetization is caused in the layer structure without the need for a power supply. Due to the spiral design, the sensor element is suitable for storing several such changes in magnetization. This allows, for example, several revolutions of a rotating magnet to be continuously counted by the sensor element without a power supply. With the help of the known sensor element, a so-called true power-on revolution counter can thus be constructed.

[0003] A problem with the known sensor element is that external magnetic interference fields, which are present independently of the rotating magnet mentioned as an example, may influence the sensor element and lead to incorrect counting.

[0004] DE 10 2006 039 490 A1 describes a magnetic sensor and a method for its production. DE 10 2010 010 893 A1 describes an electrical circuit, in particular for a revolution counter. GB 2 452 474 A describes a magnetic rotation sensor. DE 10 2008 063 226 A1 describes a magnetic revolution counter. DIEGEL M. [et. al.], A New Four Bit Magnetic Domain Wall Based Multiturn Counter, In: IEEE Transactions on Magnetics. Vol. 45, No. 10, 2009, pages 3792 - 3795, describes a novel four-bit magnetic domain wall-based multiturn counter.

[0005] The object of the invention is to provide a compact sensor element that increases the reliability of counting, reduces the influence of external interference fields and enables consistent detection of magnetization changes.

[0006] The invention solves this problem by a sensor element according to claim 1.

[0007] In the sensor element according to the invention, a change in magnetization can be induced and stored without a power supply when a magnetic field is moved past the sensor element. Furthermore, the sensor element according to the invention has two spiral strips whose winding senses are opposite.

[0008] In particular, due to the opposite winding sense, incorrect counts, which may be caused by external magnetic interference fields, can be reliably detected by the sensor element according to the invention. The range of application of the sensor element can thus be expanded, in particular, to include safety-relevant applications.

[0009] Advantageously, the two spiral strips are connected to a common wall generator to generate so-called domain walls.

[0010] In another advantageous development of the invention, the two spiral strips each form a diamond-shaped structure. This supports the storage of the domain walls.

[0011] Further features, possible applications, and advantages of the invention will become apparent from the following description of exemplary embodiments of the invention, which are illustrated in the figures of the drawing. All described or illustrated features, individually or in any combination, constitute the subject matter of the invention, regardless of their summary in the patent claims or their reference back to them, as well as regardless of their wording or representation in the description or in the drawing. Fig. 1 shows a schematic plan view of a sensor element according to some examples, Fig. 2 shows a schematic plan view of a sensor element according to some examples, Fig. 3 shows a schematic plan view of a sensor element according to the present invention.

[0012] In the Fig. 1 shows a sensor element 10 comprising two approximately diamond-shaped structures 11, 12 arranged side by side along a longitudinal side. Each of the structures 11, 12 is constructed from an approximately spirally arranged strip 13, 14. For example, each of the two diamond-shaped structures 11, 12 has approximately four windings of its spiral strips 13, 14. The winding direction of the two spiral strips 13, 14 is opposite.

[0013] At the outer end of each of the two spiral strips 13, 14, there is a wall generator 15, 16, which is flat, in particular approximately circular. The two wall generators 15, 16 of the two diamond-shaped structures 11, 12 are arranged adjacent to each other. The strips 13, 14 and wall generators 15, 16 of the two structures 11, 12 are constructed independently of each other and are electrically and magnetically separated from each other.

[0014] The strips 13, 14 and the wall generators 15, 16 of the two diamond-shaped structures 11, 12 each have a layer structure that successively contains at least one soft magnetic layer, one non-magnetic layer, and one hard magnetic layer. The soft magnetic layer forms the actual sensor layer, and the hard magnetic layer forms a reference layer.

[0015] Due to this layer structure, a magnet moving past or rotating past the respective structure 11, 12 in the two wall generators 15, 16 leads to a change in the magnetization of the sensor layer, but not of the reference layer. A so-called domain wall is created in the sensor layer of the wall generators 15, 16, which extends into the two strips 13, 14 and separates two regions from each other, whose magnetization is rotated 180 degrees relative to each other. Repeatedly moving past or rotating the magnet results in several such domain walls, which then migrate into the spiral strips 13, 14, starting from the respective wall generator 15, 16. The domain walls are thus stored in the two structures 11, 12. The generation of the domain walls, as well as their storage, takes place without an energy supply.

[0016] Moving past or rotating the magnet in the opposite direction leads to a migration of a domain wall out of the respective strip 13, 14 and thus to an extinction of this domain wall.

[0017] Due to the four windings of the strips 13, 14 of the two structures 11, 12 provided as an example, the sensor element 10 can thus count up and down four revolutions of a rotating magnet, for example.

[0018] For a more detailed explanation of the layer structure and the resulting functioning of the two structures 11, 12, as well as the spiral configuration, reference is made to the aforementioned EP 1 740 909 B1 and EP 1 532 425 B1. In particular, with regard to explanations of the generation and migration of domain walls in the strips 13, 14 and wall generators 15, 16 of the two structures 11, 12, reference is made to the two aforementioned publications.

[0019] To read, for example, the number of revolutions of a rotating magnet, the so-called GMR or TMR effect (GMR = giant magneto resistance, TMR = tunnel magneto resistance) is exploited. According to this effect, the resistance of strip 13, for example, differs depending on whether the magnetization direction of the sensor layer is aligned approximately parallel or approximately antiparallel to the magnetization direction of the reference layer. Each domain wall present in strip 13 changes the magnetization direction of the sensor layer and thus the resistance present between the ends of strip 13. For further explanations, please refer to the two previously mentioned publications.

[0020] In the Fig. 1, the resistances resulting from the magnetizations within the two strips 13, 14 are shown schematically as individual resistances 23 in each long side of the two diamond-shaped structures 11, 12.

[0021] For reading, a voltage can now be applied to both ends of the spiral strip 13. The measured total resistance between the ends of the strip 13 can then be used to determine, for example, the number of revolutions of a rotating magnet.

[0022] Alternatively, it is possible that the Fig. 1, the corners of the diamond-shaped structure 11, designated by reference numerals 18 and 19, are each connected jointly to the two poles of a voltage source. Individual measurement voltages are then tapped at the corners of the structure 11 designated by reference numerals 20 and 21. From these measurement voltages, the total resistance can then be determined and, for example, the number of revolutions of a rotating magnet can be determined.

[0023] It is also possible to directly determine the number of revolutions of a rotating magnet from the individual measuring voltages, in particular by interpreting the successive measuring voltages as binary values ​​- i.e. without determining the total resistance.

[0024] It is now assumed that in the structure 11 shown on the left, all of the individual resistors 23 shown are high-ohm due to the magnetization of the strip 13; this is indicated by the fact that the individual resistors in the left structure 11 are filled in black. Furthermore, it is assumed that in the structure 12 shown on the right, the individual resistors 23 there are low-ohm; this is indicated by the fact that the individual resistors in the right structure 11 are not filled in black. These states of the individual resistors 23 can be achieved by applying a magnetic field to the sensor element 10 in such a way that corresponding magnetizations of the sensor layer are generated only in the left structure 11, but not in the right structure 12.

[0025] If the sensor element 10 is now Fig. For example, if a magnet moves past or rotates in the exemplary direction indicated by arrow 25, this results in a new domain wall being created in structure 12 and an existing domain wall being eliminated in structure 11. The same applies to further movements past or rotations of the rotating magnet past sensor element 10.

[0026] The number of domain walls in structure 11 thus decreases, and the number of domain walls in structure 12 increases. Thus, the total resistance in each of the two strips 13, 14 changes in a very specific way. This leads to predetermined, mutually associated counting states with respect to the domain walls and thus to predeterminable changes in the total resistances in each of the two structures 11, 12.

[0027] If an external magnetic interference field, which exists independently of the rotating magnet mentioned as an example, potentially influences the sensor element and creates a domain wall in one of the two structures 11, 12 or in both structures 11, 12, or otherwise changes the magnetization direction in one or both strips 13, 14, this can be detected. This results from the fact that the total resistance or the counted number of revolutions in the two structures 11, 12 changes in this error case in a way that deviates from the previously determined total resistances or numbers.

[0028] The same applies vice versa, i.e. for the error case in which the external interference field cancels out one or more existing domain walls or magnetization directions in one of the two structures 11, 12 or in both structures 11, 12.

[0029] It is essential that the winding direction of the two strips 13, 14 is opposite. This ensures that an external interference field, which exists independently of the rotating magnet mentioned above, leads to different changes in the total resistance or the number of counted revolutions in the two structures 11, 12. However, these different changes differ from the changes caused by the rotating magnet mentioned above. Thus, the fault can be detected by the sensor element 10.

[0030] If the winding direction were the same, an external interference field, existing independently of the rotating magnet mentioned as an example, would lead to similar changes in the total resistance or the counted number of revolutions in both structures 11, 12. However, these similar changes would not differ from the changes caused by the rotating magnet, as an example. Thus, the fault would not be detectable.

[0031] In the Fig. 2 shows a sensor element 30 which, in terms of its structure, is largely similar to the sensor element 10 of Fig. 1. Thus, the sensor element 30 of the Fig. 2 comprises two approximately diamond-shaped structures 31, 32 arranged side by side along a longitudinal side. Each of the structures 31, 32 is constructed from an approximately spirally arranged strip 33, 34. For example, each of the two diamond-shaped structures 31, 32 has approximately four windings of its spiral strips 33, 34. The winding direction of the two spiral strips 33, 34 is opposite.

[0032] In contrast to Fig. 1, the two strips 33, 34 of the sensor element 30 of the Fig. 2. Furthermore, the two strips 33, 34 each have a wall generator 35, 36 not at their outer but at their inner end.

[0033] The sensor element 30 of the Fig. 2 can now be used in two ways.

[0034] On the one hand, it is possible to separate the two strips 33, 34 at their connection point and otherwise leave them unconnected. This is shown in the Fig. 2 by a separating line 38. Said separation 38 can be performed with the aid of a laser or the like. After the separation 38, the two structures 31, 32 are electrically and magnetically separated from each other.

[0035] After the separation 38, the sensor element 30 of the Fig. 2 only by the sensor element 10 of the Fig. 1, that the wall generators 35, 36 are not located at the outer end, but at the inner end of the strips 33, 34. However, this does not fundamentally change the functioning of the sensor element 30. The sensor element 10 of the Fig. 1 and the sensor element 30 of the Fig. 2 essentially have the same functionality. In this respect, please refer to the explanations for Fig. 1.

[0036] On the other hand, it is possible, for example, to separate the wall generator 35 of the structure 31 shown on the left and otherwise not to make any separation (including the separation 38). This is shown in the Fig. 2 by a dividing line 39. After the separation 39, the wall generator 35 is no longer functional, but the two strips 33, 34 are still connected to each other.

[0037] In this way, the sensor element 30 of the Fig. 2, with this separation 39, is suitable for detecting a total of eight revolutions of a rotating magnet moving past, for example. This results from the fact that the four windings of each of the two structures 31, 32 are magnetically connected in series due to the connection of the two strips 33, 34. The domain walls are generated using the single wall generator 36. However, it should be noted that with the sensor element 30 with the separation 39, an incorrect count due to an external interference field cannot be detected.

[0038] With the sensor element 30 it is thus possible to realize two different designs by simple separations.

[0039] In the Fig. 3 shows a sensor element 50 which, with regard to its construction - apart from a single difference - is identical to the sensor element 10 of Fig. 1 is identical. The difference is the design of the wall generator. For example, the sensor element 10 of the Fig. 1, two wall generators 15, 16 are present, each of which is assigned to one of the two diamond-shaped structures 11, 12. In contrast, in the sensor element 50, the Fig. 3, a single, common wall generator 52 is present, which is assigned to both diamond-shaped structures 11, 12. The common wall generator 52 of the Fig. 3 is connected to the respective spiral strips 13, 14 of both diamond-shaped structures 11, 12.

[0040] If the sensor element 50 is now Fig. 3 For example, if a magnet moves past or rotates in the exemplary direction indicated by arrow 25, this results in a new domain wall being fed into the diamond-shaped structure 12 via the wall generator 52, and an existing domain wall being eliminated in the structure 11 via the wall generator 52. The same applies to further past movements or rotations of the rotating magnet, or conversely, for rotations in the opposite direction.

[0041] Thus, the sensor element 50 of the Fig. 3 with respect to an external magnetic interference field in the same way as the sensor element 10 of the Fig. 1. In this respect, reference is made to the explanations on Fig. 1.

Claims

[1] Sensor element (50), in particular for a revolution counter, wherein a change in magnetization can be induced and stored in the sensor element (50) without an energy supply when a magnetic field is moved past the sensor element (50), wherein the sensor element (50) has two spiral strips (13, 14), each with a layer structure which successively contains at least one soft magnetic layer, one non-magnetic layer and one hard magnetic layer, wherein the winding direction of the two spiral strips (13, 14) is opposite, and wherein the two spiral strips (13, 14) are each connected by their outer end to a common wall generator (52). [2] Sensor element (50) according to claim 1, wherein the two spiral strips (13, 14) each form a diamond-shaped structure (11, 12). [3] Sensor element (50) according to claim 2, wherein the two diamond-shaped structures (11, 12) are arranged next to one another along a longitudinal side. [4] Sensor element (50) according to at least one of claims 1 to 3, wherein an external magnetic interference field, which is present independently of the passing magnetic field, leads to different changes in a respective total resistance in the two strips (13, 14). [5] A method for operating a sensor element (50), in particular for a revolution counter, wherein a change in magnetization can be induced and stored in the sensor element (50) without a power supply when a magnetic field is moved past the sensor element (50), wherein the sensor element (50) has two spiral strips (13, 14), each with a layer structure that successively contains at least one soft magnetic layer, one non-magnetic layer, and one hard magnetic layer, wherein the winding direction of the two spiral strips (13, 14) is opposite, and wherein the two spiral strips (13, 14) are each connected by their outer end to a common wall generator (52), comprising: storing a plurality of changes in magnetization of the two spiral strips (13, 14) that are induced by the magnetic field moving past,Detection of an external magnetic interference field based on different changes in the total resistance of the two strips (13, 14).

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