Rotational angle measuring device

Abstract

To further increase a permissible amount of deviation because of installation of a permanent magnet and a magnetic field detection section without upsizing.SOLUTION: A rotational angle measuring device includes a permanent magnet 101, a magnetic field detection section 102, and a magnetic field uniformization layer 103, and the magnetic field uniformization layer 103 is composed of a soft magnetic material, and is disposed while facing a first surface 102a facing the permanent magnet 101 of the magnetic field detection section 102 or a second surface 102b opposite to the first surface 102a. The magnetic field uniformization layer 103 is formed while extending in a direction vertical to an axial center 151, and the shape in a plan view of the magnetic field uniformization layer 103 is rectangular.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to a rotation angle measurement device. [Background technology]

[0002] Conventionally, there is a rotation angle measurement device consisting of a permanent magnet and an angle sensor (magnetic field detection unit) for measuring the rotation angle. In this device, a disk-shaped permanent magnet fixed to a shaft is designed to emit a magnetic field perpendicular to the axis of rotation of the shaft, and the direction of the magnetic field of the permanent magnet changes when the shaft rotates. Since the resistance value of the magnetic field detection unit changes depending on the direction in which the magnetic field is applied, the magnetic field detection unit can read the rotation angle of the shaft that rotates together with the permanent magnet.

[0003] In this rotation angle measurement, the magnetic field lines generated by the permanent magnet are not parallel, so the direction of the magnetic field around the magnetic field detection unit is not uniform, resulting in slight variations in the magnetic field direction. Therefore, if the magnetic field detection unit or the magnetic field is installed off-center, the output value of the magnetic field detection unit changes, resulting in a problem of reduced accuracy of the angle read by the magnetic field detection unit.

[0004] To address this issue, a technology has been proposed in which the permanent magnet is made into a rectangular prism, which generates a more uniform magnetic field than would be the case if the magnet were disk-shaped, thereby increasing the tolerance for misalignment due to the placement of the permanent magnet and magnetic field detection unit (see Patent Document 1). [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Patent No. 4947321 Summary of the Invention [Problem to be solved by the invention]

[0006] However, even if the permanent magnet is a rectangular parallelepiped, non-uniformity still exists in the magnetic field direction. In addition, a certain size of permanent magnet is required, and depending on the installation location of the rotation angle measurement device, it may not be possible to assemble the permanent magnet.

[0007] The present invention has been made to solve the above-mentioned problems, and its object is to further increase the tolerance for misalignment due to the installation of permanent magnets and magnetic field detection units without increasing the size. [Means for solving the problem]

[0008] The rotational angle measurement device of the present invention comprises a permanent magnet supported for free rotation around an axis, a magnetic field detection unit arranged facing the permanent magnet with a fixed gap therebetween, and a magnetic field homogenizing layer made of a soft magnetic material, arranged facing a first surface facing the permanent magnet of the magnetic field detection unit or a second surface opposite the first surface, and formed to extend in a direction perpendicular to the axis.

[0009] In one configuration example of the rotation angle measurement device, the shape of the permanent magnet in a plan view, the shape of the magnetic field detection unit in a plan view, and the shape of the magnetic field homogenizing layer in a plan view are rotationally symmetrical about the axis.

[0010] In one configuration example of the rotation angle measurement device, the permanent magnet has a circular shape in a plan view, the magnetic field detection unit has a rectangular shape in a plan view, and the magnetic field homogenizing layer has a rectangular shape in a plan view. Effect of the Invention

[0011] As described above, according to the present invention, the magnetic field homogenizing layer made of a soft magnetic material is used, so that the tolerance for misalignment due to the placement of permanent magnets and magnetic field detectors can be further increased without increasing the size. [Brief description of the drawings]

[0012] [Figure 1] FIG. 1 is a perspective view showing the configuration of a rotation angle measurement device according to an embodiment of the present invention. [Figure 2A] FIG. 2A is a cross-sectional view showing a partial configuration of a rotation angle measurement device according to an embodiment of the present invention. [Figure 2B] FIG. 2B is a cross-sectional view showing a partial configuration of another rotation angle measurement device according to an embodiment of the present invention. [Figure 2C] FIG. 2C is a cross-sectional view showing a partial configuration of another rotation angle measurement device according to an embodiment of the present invention. [Diagram 3] FIG. 3 is a distribution diagram showing a simulation result of the state of the magnetic field direction in a conventional rotation angle measurement device. [Figure 4A] FIG. 4A is a distribution diagram showing a simulation result of the effect of uniforming the magnetic field direction, for illustrating the effect of the rotation angle measurement device according to the embodiment of the present invention. [Figure 4B] FIG. 4B is a distribution diagram showing a simulation result of the effect of uniforming the magnetic field direction, for illustrating the effect of the rotation angle measurement device according to the embodiment of the present invention. [Figure 4C] FIG. 4C is a distribution diagram showing a simulation result of the effect of uniforming the magnetic field direction, for illustrating the effect of the rotation angle measurement device according to the embodiment of the present invention. [Figure 4D] FIG. 4D is a characteristic diagram showing a simulation result of the effect of uniforming the magnetic field direction, for illustrating the effect of the rotation angle measurement device according to the embodiment of the present invention. [Figure 5A] FIG. 5A is a distribution diagram showing a simulation result of the effect of uniforming the magnetic field direction, for illustrating the effect of the rotation angle measurement device according to the embodiment of the present invention. [Figure 5B] FIG. 5B is a distribution diagram showing a simulation result of the effect of uniforming the magnetic field direction, for illustrating the effect of the rotation angle measurement device according to the embodiment of the present invention. [Figure 5C] FIG. 5C is a distribution diagram showing a simulation result of the effect of uniforming the magnetic field direction, for illustrating the effect of the rotation angle measurement device according to the embodiment of the present invention. [Figure 5D]FIG. 5D is a characteristic diagram showing a simulation result of the effect of uniforming the magnetic field direction, for illustrating the effect of the rotation angle measurement device according to the embodiment of the present invention. [Figure 6A] FIG. 6A is a distribution diagram showing a simulation result of the effect of uniforming the magnetic field direction, for illustrating the effect of the rotation angle measurement device according to the embodiment of the present invention. [Figure 6B] FIG. 6B is a distribution diagram showing a simulation result of the effect of uniforming the magnetic field direction, for illustrating the effect of the rotation angle measurement device according to the embodiment of the present invention. [Figure 6C] FIG. 6C is a distribution diagram showing a simulation result of the effect of uniforming the magnetic field direction, for illustrating the effect of the rotation angle measurement device according to the embodiment of the present invention. [Figure 6D] FIG. 6D is a characteristic diagram showing a simulation result of the effect of uniforming the magnetic field direction, for illustrating the effect of the rotation angle measurement device according to the embodiment of the present invention. [Figure 7A] FIG. 7A is a distribution diagram showing a simulation result of the effect of uniforming the magnetic field direction, for illustrating the effect of the rotation angle measurement device according to the embodiment of the present invention. [Figure 7B] FIG. 7B is a distribution diagram showing a simulation result of the effect of uniforming the magnetic field direction, for illustrating the effect of the rotation angle measurement device according to the embodiment of the present invention. [Figure 8A] FIG. 8A is a distribution diagram showing a simulation result of a change in the direction of the magnetic field from the center position of the permanent magnet when there is no magnetic field homogenizing layer, for illustrating the effect of the tolerance for positional misalignment in a rotation angle measurement device according to an embodiment of the present invention. [Figure 8B] FIG. 8B is a distribution diagram showing a simulation result of a change in the direction of the magnetic field from the center position of the permanent magnet when there is no magnetic field homogenizing layer, for illustrating the effect of the tolerance for positional misalignment in a rotation angle measurement device according to an embodiment of the present invention. [Figure 8C] FIG. 8C is a distribution diagram showing a simulation result of the change in the direction of the magnetic field from the center position of the permanent magnet when there is no magnetic field homogenizing layer, for illustrating the effect of the tolerance for positional misalignment in a rotation angle measurement device according to an embodiment of the present invention. [Figure 9A] FIG. 9A is a distribution diagram showing a simulation result of a change in the direction of the magnetic field from the center position of the permanent magnet when a magnetic field homogenizing layer is used, for illustrating the effect of the tolerance for positional misalignment in a rotation angle measurement device according to an embodiment of the present invention. [Figure 9B] FIG. 9B is a distribution diagram showing a simulation result of the change in the direction of the magnetic field from the center position of the permanent magnet when a magnetic field homogenizing layer is used, for explaining the effect of the tolerance for positional misalignment in the rotation angle measurement device according to the embodiment of the present invention. [Figure 9C] FIG. 9C is a distribution diagram showing a simulation result of the change in the direction of the magnetic field from the center position of the permanent magnet when a magnetic field homogenizing layer is used, for explaining the effect of the tolerance for positional misalignment in a rotation angle measurement device according to an embodiment of the present invention. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0013] A rotation angle measurement device according to an embodiment of the present invention will now be described with reference to Fig. 1. This rotation angle measurement device includes a permanent magnet 101, a magnetic field detection unit 102, and a magnetic field homogenizing layer 103.

[0014] Permanent magnet 101 is supported rotatably around axis 151. The shape of permanent magnet 101 in a plan view perpendicular to axis 151 is rotationally symmetric around axis 151. The shape of permanent magnet 101 in a plan view is, for example, circular. Permanent magnet 101 can be fixed to one end of shaft 104 that is supported rotatably around axis 151. Permanent magnet 101, which has a circular shape in a plan view, is magnetized in the in-plane direction so that one end on the circumference is an N pole and the other end is an S pole.

[0015] The magnetic field detection unit 102 is disposed facing the permanent magnet 101 with a certain gap therebetween. The shape of the magnetic field detection unit 102 in a plan view is rotationally symmetric about an axis 151. For example, the shape of the magnetic field detection unit 102 in a plan view may be rectangular. As shown in FIG. 2A, the magnetic field detection unit 102 includes a magnetic sensor layer 123 formed on a substrate 121 with an insulating layer 122 interposed therebetween. The magnetic sensor layer 123 may be formed of a circuit such as a Wheatstone bridge with a tunnel magnetoresistance effect element (TMR) as a resistor.

[0016] The magnetic field homogenizing layer 103 is made of a soft magnetic material and is disposed facing the first surface 102a facing the permanent magnet 101 of the magnetic field detection unit 102, or the second surface 102b opposite to the first surface 102a. The magnetic field homogenizing layer 103 is formed extending in a direction perpendicular to the axis 151. The shape of the magnetic field homogenizing layer 103 in a plan view is rotationally symmetric about the axis 151. The shape of the magnetic field homogenizing layer 103 in a plan view may be, for example, a rectangle. The area of ​​the magnetic field homogenizing layer 103 may be equal to or larger than the area of ​​the first surface of the magnetic field detection unit 102.

[0017] Also, the magnetic field homogenizing layer 103 can be configured integrally with the magnetic field detection unit 102. For example, as shown in FIG. 2A, the magnetic field homogenizing layer 103 can be formed on the magnetic sensor layer 123 of the magnetic field detection unit 102 via an insulating layer 124. Also, as shown in FIG. 2B, the magnetic field homogenizing layer 103 can be formed on the back side of the substrate 121 constituting the magnetic field detection unit 102. Also, as shown in FIG. 2C, the magnetic field homogenizing layer 103 can be formed between the insulating layer 122 on the substrate 121 side of the magnetic sensor layer 123 and the substrate 121.

[0018] By providing the magnetic field homogenizing layer 103 as described above, it is possible to improve the uniformity of the magnetic field, and it is possible to further increase the tolerance for deviation due to the placement of permanent magnets and magnetic field detectors.

[0019] Next, we will show the results of calculations (simulations) on the effect of the magnetic field homogenizing layer in homogenizing the magnetic field direction. First, the permanent magnet was set to a circular shape with a diameter of 15 mm in plan view, a thickness of 5 mm, a relative permeability of 1.05, and a residual magnetization of 1395 mT. An analysis plane was set 10 mm away from the permanent magnet, and the magnetic field rotation direction on the analysis plane was calculated. In the calculations, the shape of the magnetic field homogenizing layer in plan view was set to 2.4 mm x 2.4 mm, and the magnetic field homogenizing layer was placed on the side of the analysis plane farther away from the permanent magnet.

[0020] First, the magnetic field rotation direction on the analysis surface when no magnetic field homogenizing layer is placed is as shown in Figure 3. The magnetic field homogenizing layer has a thickness of 20 nm. The magnetic field direction at the center of the analysis surface is set to 0°, and the angle of the magnetic field direction at each position is shown with contour lines. The wider the light gray area and the wider the overall gray area, the more homogenized the magnetic field direction is.

[0021] Next, the relationship between the relative permeability of the magnetic field homogenizing layer and the distance between the magnetic field homogenizing layer and the analysis surface when the magnetic field homogenizing layer is arranged is shown in Figures 4A, 4B, and 4C. The magnetic field homogenizing layer has a fixed thickness of 20 nm. Figure 4A shows the result when a magnetic field homogenizing layer with a relative permeability of 1000 is used and the distance between the magnetic field homogenizing layer and the analysis surface is set to 0.1 mm. Figure 4B shows the result when a magnetic field homogenizing layer with a relative permeability of 50,000 is used and the distance between the magnetic field homogenizing layer and the analysis surface is set to 1.5 mm. Figure 4C shows the result when a magnetic field homogenizing layer with a relative permeability of 100,000 is used and the distance between the magnetic field homogenizing layer and the analysis surface is set to 2.0 mm.

[0022] From the results shown in Figures 4A, 4B, and 4C, the relationship between the distance between the magnetic field homogenizing layer and the analysis surface and the relative permeability of the magnetic field homogenizing layer is as shown in Figure 4D. If the magnetic field homogenizing layer is more uniform than the magnetic field homogenizing layer shown in Figure 3, it is considered to be in "good conditions." It can be seen that the effect of homogenizing the magnetic field direction by the magnetic field homogenizing layer is greater the higher the relative permeability and the closer the distance from the ferromagnetic layer.

[0023] Next, the relationship between the relative permeability of the magnetic field homogenizing layer and the thickness of the magnetic field homogenizing layer when the magnetic field homogenizing layer is arranged is shown in Figures 5A, 5B, and 5C. The distance between the magnetic field homogenizing layer and the analysis surface was fixed at 1.5 mm. Figure 5A shows the result when a magnetic field homogenizing layer with a relative permeability of 1000 was used and the thickness of the magnetic field homogenizing layer was set to 13 nm. Figure 5B shows the result when a magnetic field homogenizing layer with a relative permeability of 50000 was used and the thickness of the magnetic field homogenizing layer was set to 20 nm. Figure 5C shows the result when a magnetic field homogenizing layer with a relative permeability of 100000 was used and the thickness of the magnetic field homogenizing layer was set to 100 nm.

[0024] From the results shown in Figures 5A, 5B, and 5C, the relationship between the thickness of the magnetic field homogenizing layer and the relative permeability of the magnetic field homogenizing layer is as shown in Figure 5D. If the magnetic field homogenizing layer is more uniform than the magnetic field homogenizing layer shown in Figure 3, it is considered to be in "good conditions." It can be seen that the effect of homogenizing the magnetic field direction by the magnetic field homogenizing layer is greater the higher the relative permeability and the thicker the ferromagnetic layer.

[0025] Next, the relationship between the distance between the magnetic field homogenizing layer and the analysis surface and the thickness of the magnetic field homogenizing layer when the magnetic field homogenizing layer is arranged is shown in Figures 6A, 6B, and 6C. The relative permeability was fixed at 50,000. Figure 6A shows the result when the distance between the magnetic field homogenizing layer and the analysis surface was 1.2 mm and the thickness of the magnetic field homogenizing layer was 13 nm. Figure 6B shows the result when the distance between the magnetic field homogenizing layer and the analysis surface was 1.5 mm and the thickness of the magnetic field homogenizing layer was 20 nm. Figure 6C shows the result when the distance between the magnetic field homogenizing layer and the analysis surface was 2.0 mm and the thickness of the magnetic field homogenizing layer was 100 nm.

[0026] From the results shown in Figures 6A, 6B, and 6C, the relationship between the distance between the magnetic field homogenizing layer and the analysis surface and the thickness of the magnetic field homogenizing layer is as shown in Figure 6D. If the magnetic field homogenizing layer is more homogenized than the magnetic field homogenizing layer shown in Figure 3, it is considered to be in "good conditions." It can be seen that the effect of the magnetic field homogenizing layer in homogenizing the direction of the magnetic field is greater the thicker the ferromagnetic layer is and the closer the distance from the ferromagnetic layer is, the greater the homogenization effect.

[0027] In the above, the magnetic field homogenizing layer was placed on the side farther from the permanent magnet than the analysis surface, but similar results were obtained when simulating by placing the magnetic field homogenizing layer on the side closer to the permanent magnet than the analysis surface (Figs. 7A and 7B). Fig. 7A shows the case where the magnetic field homogenizing layer was placed on the side farther from the permanent magnet than the analysis surface, and Fig. 7B shows the case where the magnetic field homogenizing layer was placed on the side closer to the permanent magnet than the analysis surface. In both cases, a magnetic field homogenizing layer with a relative permeability of 50,000 and a thickness of 20 nm was used.

[0028] Next, we will show the results of a simulation of the effect of the magnetic field homogenizing layer on the tolerance of misalignment. First, the permanent magnet was set to a circular shape with a diameter of 15 mm in plan view, a thickness of 5 mm, and a residual magnetization of 380 mT. The analysis plane was set 10 mm away from the permanent magnet, and the magnetic field rotation direction on the analysis plane was calculated. In the calculation, the shape of the magnetic field homogenizing layer in plan view was set to 2.4 mm x 2.4 mm, and the magnetic field homogenizing layer was placed at a position 0.3 mm away from the analysis plane on the side of the permanent magnet. The magnetic field homogenizing layer was set to a thickness of 100 nm and a relative permeability of 400.

[0029] First, the change in the direction of the magnetic field from the central position of the permanent magnet is shown in Figures 8A, 8B, 8C, 9A, 9B, and 9C. Figures 8A, 8B, 8C, 9A, 9B, and 9C show the rotation angle of the magnetic field with respect to the central position of the permanent magnet. Figures 8A, 8B, and 8C show the case without the magnetic field homogenizing layer, and Figures 9A, 9B, and 9C show the case with the magnetic field homogenizing layer. The square frame in the figure indicates the arrangement of the magnetic field detection unit. The maximum and minimum values ​​of the magnetic field direction within the square frame are also shown numerically in the figure.

[0030] As shown in Figures 8A, 8B, 8C, 9A, 9B, and 9C, it was confirmed that even when the magnetic field detection unit was shifted by 0.5 mm from the center position of the permanent magnet, the use of the magnetic field homogenizing layer reduced the amount of change in the direction of the magnetic field from the center, thereby improving the uniformity of the magnetic field.

[0031] As described above, according to the present invention, a magnetic field homogenizing layer made of a soft magnetic material is used, so that it is possible to further increase the tolerance for misalignment due to the installation of permanent magnets and magnetic field detection units without increasing the size of the rotation angle measurement device.

[0032] It should be noted that the present invention is not limited to the above-described embodiments, and it is apparent that many modifications and combinations can be made by a person having ordinary knowledge in the art within the technical concept of the present invention. [Explanation of symbols]

[0033] 101... permanent magnet, 102... magnetic field detection portion, 102a... first surface, 102b... second surface, 103... magnetic field homogenizing layer, 104... shaft, 151... axis.

Claims

1. A permanent magnet supported so as to be rotatable about a shaft core; A magnetic field detection unit disposed facing the permanent magnet with a certain gap therebetween; a magnetic field homogenizing layer made of a soft magnetic material, disposed facing a first surface of the magnetic field detection unit facing the permanent magnet or a second surface opposite to the first surface, and extending in a direction perpendicular to the axis; A rotation angle measuring device comprising:

2. 2. The rotation angle measurement device according to claim 1, A rotation angle measurement device, wherein the planar shape of the permanent magnet, the planar shape of the magnetic field detection unit, and the planar shape of the magnetic field homogenizing layer are rotationally symmetrical about the axis.

3. 3. The rotation angle measurement device according to claim 2, The permanent magnet has a circular shape in a plan view, The magnetic field detection unit has a rectangular shape in a plan view, The magnetic field homogenizing layer has a rectangular shape in a plan view. Rotation angle measuring device.

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