JP5866797B2 - Ring magnet magnetization method - Google Patents

Description

  The present invention relates to a magnetizing method of an encoder used as a detection object in a magnetic sensor mechanism (for example, an electric power steering (EPS) angle sensor mechanism) for measuring a rotation angle of a rotating shaft of various mechanical devices. Regarding technology.

  Conventionally, in order to measure the rotation state (for example, the rotation angle) in order to rotate the rotation shaft of various mechanical devices in an appropriate state, a configuration in which a predetermined sensor mechanism is provided for the device is known. Yes. As such a sensor mechanism, for example, an encoder formed by magnetizing a predetermined magnetic material is attached to a rotating wheel of a bearing that rotatably supports a rotating shaft, and a change in magnetic flux density that occurs when the encoder rotates. There is a magnetic sensor mechanism that measures the rotation state (rotation angle) of the rotation shaft by detecting the rotation with a magnetic sensor fixed to a member (such as a housing or a stationary wheel) that is stationary with respect to the rotating wheel.

In the magnetic sensor mechanism, since the magnetized state of the encoder affects the measurement accuracy of the rotational state (rotation angle) of the rotating shaft, various improvements have been made to the magnetizing technique of the encoder. For example, Patent Document 1 discloses one configuration of a magnetic sensor mechanism (absolute position detecting device for a rotation side member) using a ring magnet (annular magnetic body) as an encoder (bipolar magnetic encoder). Such a ring magnet has an outer peripheral surface portion of a semicircular portion (first semicircular portion) on one side that is bisected in the radial direction as a magnetization region of an S pole, and an outer peripheral surface portion of a semicircular portion (second semicircular portion) on the other side. Is a two-pole magnet with an N-pole magnetized region, and an annular mold is filled with a magnetic material obtained by kneading anisotropic magnetic powder in an unvulcanized rubber material, thereby making a metal reinforcing ring In addition, it is integrally vulcanized.
At that time, the direction of easy magnetization (magnetization facilitating axis) of each anisotropic magnetic powder is parallel to the radial direction of the ring magnet (the center line connecting the central portions of the first and second semicircular portions). The anisotropic magnetic powder is magnetized by being oriented and applying a magnetic field parallel to the easy magnetization direction (that is, a magnetic field parallel to the radial direction of the ring magnet). That is, a ring magnet (anisotropic magnet) is configured by simultaneously forming the magnetic material and the metal reinforcing ring, and simultaneously orienting and magnetizing the anisotropic magnetic powder. And the ring magnet which makes such a structure is assembled | attached to a bearing as an encoder, and the detection (measurement) of the absolute position (absolute angle) of the rotation side member (for example, the rotating shaft fitted in the inner ring) is performed.

Anisotropic magnets are magnetized only in a specific direction. If the direction of the magnetic field is aligned with the orientation direction of the anisotropic magnet, it is strongly magnetized in the aligned direction (that is, in the specific direction). Because it has a characteristic that a large magnetic force can be obtained), when magnetized in parallel as in the encoder magnetizing method disclosed in Patent Document 1 (specifically, magnetically parallel to the radial direction of the ring magnet) In many cases, it is used as a magnetic material when the powder is magnetized in a state of magnetic field orientation. That is, when detecting a change in magnetic flux density with a magnetic sensor, an anisotropic magnet is considered to be a very suitable magnetic body as an encoder because a larger magnetic flux obtained from the encoder can be detected stably. .
On the other hand, in order to have anisotropic characteristics, it is necessary to orient the magnetic field during magnet molding (align the easy magnetization direction in the same direction) and to apply a magnetic field in accordance with the orientation direction during magnetization. There are also problems peculiar to anisotropic magnets, which require more management, labor, and costs compared to the case of simply magnetizing, and these problems are a concern when using anisotropic magnets as encoders. The

JP 2008-145284 A

  One way to avoid such problems is to use isotropic magnets. Since an isotropic magnet can be magnetized in any direction, it can be magnetized in parallel by applying a parallel magnetic field (for example, a magnetic field parallel to the radial direction of an annular isotropic magnet). However, compared with an anisotropic magnet, the magnetization strength (magnetic force) decreases. Therefore, when the encoder made of an isotropic magnet is rotated, the amplitude of the fluctuation waveform of the magnetic flux density detected by the magnetic sensor is reduced (that is, the sensor output is reduced), and the rotation state of the rotating shaft (for example, There is a risk that the measurement accuracy of (absolute angle) may be reduced. Further, depending on the degree of magnetization intensity (magnetic force), there is a possibility that a change in magnetic flux density cannot be detected by the magnetic sensor.

  The present invention has been made in order to solve such problems, and its purpose is to manage the magnetic field orientation (alignment of the easy magnetization direction in the same direction) and alignment work between the orientation direction and the magnetic field direction. Energizing technology for encoders (angle detecting encoder and magnetizing method thereof) that can reduce the cost and expand the peak without reducing the amplitude of the fluctuation waveform of the magnetic flux density during rotation It is to provide.

In order to achieve such an object, the ring magnet magnetization method according to the present invention is an isotropic encoder for a magnetic sensor that detects a rotational state of a rotating body that rotates around an axis. A method for magnetizing a ring magnet, wherein the ring magnet has a length in an extending direction that is orthogonal to a central axis thereof and linearly extends along a radial direction of the ring magnet. With a magnetizing yoke member set to be larger than the outer diameter dimension and having a width perpendicular to the extending direction smaller than the inner diameter dimension of the ring magnet, a predetermined current is applied. Magnetization is performed by arranging an air-core coil that generates a magnetic field by flowing and applying a magnetic field parallel to the radial direction.

The yoke member according to the present invention is a structure having a plane portion that is orthogonal to the central axis of the ring magnet and extends linearly along the radial direction.

The ring magnet of the present invention is equipped with a magnetizing yoke member so that a plane portion orthogonal to the central axis and extending linearly along the radial direction faces the side surface of the ring magnet. In this state, magnetization is performed by applying a magnetic field parallel to the radial direction.

In the present invention, a magnetic field is applied to the magnetized region of the outer peripheral surface portion of the ring magnet to magnetize it, and the two magnetic sensors are arranged to face each other at a predetermined interval from the magnetized region. The ring magnet is positioned 90 ° shifted in the circumferential direction.

  According to the encoder for angle detection and the magnetizing method of the present invention, an isotropic magnet (for example, an isotropic ring magnet) is used and a magnetic flux is intentionally magnetized when the isotropic magnet is magnetized. By applying a parallel magnetic field with a back yoke that concentrates the magnetic field, it is possible to manage the magnetic field orientation (alignment of the easy magnetization direction in the same direction), alignment work between the orientation direction and the magnetic field direction, labor, cost, etc. Can be reduced, and the peak can be enlarged without reducing the amplitude of the fluctuation waveform of the magnetic flux density during rotation. Therefore, by using the encoder magnetizing technique (angle detecting encoder and magnetizing method thereof) according to the present invention, the rotation angle of the rotating shaft or the like by the magnetic sensor mechanism (specifically, the absolute angle of one round of the encoder) ) Measurement accuracy can be improved compared to the conventional case.

1A and 1B are diagrams illustrating an encoder according to the present invention, in which FIG. 1A is a diagram for explaining a magnetizing method of a ring magnet serving as an encoder, and FIG. 2B is a ring after magnetized according to FIG. It is a figure which shows the state of a magnet (encoder). It is the schematic which shows the structure of the magnetic sensor mechanism which uses the encoder of this invention as a to-be-detected body. It is a figure which shows the state which generated the parallel magnetic field by the air-core coil when magnetizing a ring magnet. It is a figure for demonstrating the calculation principle of the absolute angle of a rotating shaft (an example is a steering shaft), Comprising: (a) is the positional relationship of an encoder and two magnetic sensors, and the detection component of the magnetic flux density by a magnetic sensor. The figure shown, (b) is a figure which shows the output waveform by each magnetic sensor.

Hereinafter, an encoder (a detection object of a magnetic sensor) of the present invention and a magnetization method thereof will be described with reference to the accompanying drawings.
The encoder of the present invention includes a magnetic sensor (for example, a Hall IC (Integrated Circuit), a Hall element, an MR element, and the like) that measures a rotation state (rotation speed, rotation direction, rotation angle, etc.) of a rotating body that rotates around an axis. As a detected body of a GMR element or the like, it becomes a constituent member of a magnetic sensor mechanism together with the magnetic sensor (magnetic detection body). Although the application of the magnetic sensor mechanism is not particularly limited, in the present embodiment, a magnetic sensor mechanism for measuring the rotation angle of the rotation shaft of various mechanical devices, for example, an electric power steering (EPS) such as an automobile. And an encoder is used as a detected body of the angle sensor mechanism.

  1 and 2 show an encoder 2 according to the present embodiment, and the encoder 2 includes a ring magnet 4 formed by magnetizing an annularly shaped magnetic body. . That is, the encoder 2 only needs to include at least the ring magnet 4, and may be a single configuration of only the ring magnet 4. For example, the ring magnet 4 and a ring-shaped member for reinforcing the ring magnet 4 ( It may be a structure formed by integrally molding a metal core or the like and a seal member (lip seal or the like) for sealing the inside of the detection target from the outside. In addition, the ring magnet 4 is configured by magnetizing an annularly shaped magnetic body. In the present embodiment, the magnetic material includes an isotropic magnetic material in the material. Used. For example, as the ring magnet 4, an isotropic ferrite magnet, a bonded magnet, or the like can be assumed. In the case of bonded magnets, isotropic magnetic powder (ferrite powder, etc.) is mixed with various resins and formed into a ring shape by various resin molding methods such as injection molding and compression molding (pressurization / vulcanization molding). The ring magnet 4 may be configured by magnetizing the magnetic material. At that time, the ratio of the isotropic magnetic powder (mixing ratio with the resin) can be arbitrarily set according to the magnitude of the magnetic force required for the ring magnet 4 (in other words, the encoder 2). Therefore, there is no particular limitation here. Moreover, as resin mixed with magnetic powder, it is possible to use thermoplastic resins, such as polyethylene, a polypropylene, polyamide, and thermosetting resins, such as an epoxy, phenol, and polyester, for example.

  Thus, in this embodiment, since the ring magnet 4 is configured as an isotropic magnet, the magnetic field orientation of the magnetic material (the direction of easy magnetization of the magnetic powder or the like is the same when the magnetic material to be the ring magnet 4 is formed. No special process is required for alignment in the direction. Therefore, the magnetic field orientation (alignment process in the easy magnetization direction) required when the ring magnet is configured as an anisotropic magnet can be omitted. Note that the outer diameter and thickness of the ring magnet 4 (magnetic material) are not particularly limited here because they may be arbitrarily set according to the size of the encoder, the form of the sensor mechanism, and the like.

  The ring magnet 4 configured as an isotropic magnet is perpendicular to the central axis C (axis passing through the radial center perpendicular to the radial direction) C, and is a magnetized yoke member along the radial direction. In the state where 6 is mounted, it is magnetized by applying a magnetic field Mf parallel to the radial direction. As an example, in FIG. 1A, a yoke member (a magnetic material such as metal (hereinafter referred to as a back yoke) is perpendicular to the central axis C and extends along the vertical direction (one of the radial directions) in the drawing. 6) is attached to the ring magnet 4, and a magnetic field Mf parallel to the vertical direction is applied to magnetize the ring magnet 4. In this case, the back yoke 6 has a structure having a flat surface portion 6a extending linearly along the radial direction of the ring magnet 4 (vertical direction in FIG. 1A). The length of the flat portion 6a in the extending direction (the vertical dimension in the figure) is set larger than the outer diameter dimension of the ring magnet 4, and the width with respect to the extending direction (the horizontal direction in the figure). ) Is set smaller than the inner diameter of the ring magnet 4. The back yoke 6 is attached to the ring magnet 4 so that the flat surface portion 6a faces the side surface (a peripheral surface region sandwiched between the outer and inner circumferences) 4a.

  By attaching the back yoke 6 to the ring magnet 4 in this way, when the magnetic field Mf parallel to the radial direction is applied to the ring magnet 4 to which the back yoke 6 is attached, the magnetic field lines due to the magnetic field Mf are centered. While being orthogonal to C, the magnetic flux can be concentrated in the vicinity of the mounting portion of the back yoke 6 (the portion facing the flat portion 6a). As a result, even when the ring magnet 4 is configured as an isotropic magnet, the magnetizing strength (magnetic force) of the ring magnet 4 is increased as compared with the case where the magnet is magnetized without the back yoke 6 attached. Can be made. Therefore, when the encoder 2 composed of the ring magnet 4 is rotated, the amplitude of the fluctuation waveform of the magnetic flux density detected by the magnetic sensor can be increased (that is, the sensor output can be increased).

  The magnetic field Mf that is parallel to the radial direction of the ring magnet 4 may be generated by applying a predetermined current to the air core coil 8 as shown in FIG. 3, and in FIG. By arranging the magnet 4, a magnetic field Mf (magnetic field in a direction from the bottom to the top) that is parallel to the radial direction is given to the ring magnet 4. Specifically, the ring magnet 4 is arranged in the air-core coil 8 so that the direction of the magnetic field Mf (in the same figure, the direction from the bottom to the top) is parallel to the radial direction. In the present embodiment, by applying such a magnetic field Mf to the ring magnet 4 to which the back yoke 6 is attached (FIG. 1 (a)), a semicircular portion on one side divided in the radial direction (FIG. In b), the outer peripheral surface portion 4s of the lower semicircular portion) is magnetized to the S pole, and the outer peripheral surface portion 4n of the other semicircular portion (upper semicircular portion in FIG. 5B) is magnetized to the N pole. doing. That is, the ring magnet 4 (in other words, the encoder 2) is a two-pole isotropic magnet (two-pole encoder) having the outer peripheral surface portion 4s as the S-pole magnetized region and the outer peripheral surface portion 4n as the N-pole magnetized region. (FIG. 2). The magnetizing of the ring magnet 4 may be performed simultaneously with the molding of the ring magnet 4 or may be performed as a completely separate process from the molding.

Using the encoder 2 formed by the magnetized ring magnet 4 as a detection target of the magnetic sensor, the rotational angle of the rotating shaft of various mechanical devices, for example, the absolute angle (steering angle) of the steering shaft of the EPS is calculated. At this time, the following principle may be used.
In this case, as shown in FIG. 2 and FIG. 4 (a), two magnetic sensors S1 and S2 are arranged, and these are detected at the encoder 2 (ring magnet 4 magnetized in parallel along the radial direction). The encoder 2 is positioned by being shifted by 90 ° in the circumferential direction (with a phase difference of 90 °) so as to be opposed to the magnetized region (outer peripheral surface portions 4s, 4n) with a predetermined gap (sensor gap). . The encoder 2 is attached to a rotating body that rotates with the rotation of the steering shaft of the EPS, such as a rotating wheel (not shown) of a bearing that rotatably supports the steering shaft, and is the same as the steering shaft. It can be rotated in the rotation state (rotation angle). On the other hand, the two magnetic sensors S1 and S2 are fixed to a member (such as a housing or a stationary wheel of the bearing) that is stationary with respect to a steering shaft (in the end, a rotating wheel or the like) in the above-described positional relationship. Then, a change in magnetic flux density that occurs when the encoder 2 rotates is detected. The magnetic sensors S1 and S2 include, for example, a substrate (not shown) on which a predetermined circuit is wired, and power is supplied from a predetermined power supply device (not shown) by the substrate, and these magnetic sensors It can be assumed that the signal output from S1 and S2 (electric signal indicating the rotation angle of the encoder 2) is transmitted to a predetermined signal processing unit (not shown). In this case, the sensors S1 and S2 and the signal processing unit may be directly connected to the substrate, or may be connected via a signal cable (not shown).

According to such a configuration (sensor mechanism), when the steering shaft rotates, the encoder 2 rotates with it, and the positions of the magnetic poles (S pole or N pole) with respect to the two magnetic sensors S1 and S2 are alternately and continuously. Change. At this time, the magnetic flux density (in other words, the number of lines of magnetic force) M2 passing through each of the magnetic sensors S1 and S2 continuously changes, and the change is detected by the magnetic sensors S1 and S2. The magnetic flux density M2 to be detected is output as a waveform such as a sine wave because it has the magnitude of the thick line direction component (thick arrow 10 shown in the figure) shown in FIGS. 2 and 4A show, as an example, the component state of the magnetic flux density M2 detected when the magnetic sensor S1 faces the outer peripheral surface portion 4n (N-pole magnetized region) of the encoder 2. In the case of the magnetic sensor S2, the magnetic flux density M2 is detected as the same component state.
At that time, since the two magnetic sensors S1 and S2 are arranged with a phase difference of 90 °, as shown in FIG. 4B, a sine wave (magnetic sensor S1 as an example) and a cosine wave (same as above). Each of the magnetic sensors S2) will be output. Therefore, the output (BA) of the magnetic sensor S1 is BA = B0 · sin θ (B0 is the peak value of the waveform), and the output (BB) of the magnetic sensor S2 is BB = B0 · cos θ (B0 is the peak value of the waveform). Based on this, θ (the absolute angle of one revolution of the encoder 2) can be calculated by θ = atan (BA / BB). As a result, the absolute angle (steering angle) of the steering shaft can be measured as the absolute angle θ of one revolution of the encoder 2 that rotates in the same rotational state as the steering shaft. At that time, the change in the magnetic flux density M2 detected by the magnetic sensors S1 and S2 is converted into an electric signal by the substrate, and the electric signal is transmitted to the signal processing unit. The absolute angle of the steering shaft may be measured by calculating the amount of change in the angle of the hit encoder 2.

  As described above, in the present embodiment, the fluctuation waveform of the magnetic flux density M2 of the encoder 2 composed of the ring magnet 4 is obtained by magnetizing the ring magnet 4 with the back yoke 6 attached to the ring magnet 4. Is increased (ie, sensor output). As shown in FIG. 2 and FIG. 4 (a), when detecting the fluctuation waveform of the magnetic flux density M2 of the encoder 2 with the two magnetic sensors S1 and S2, generally an A / D converter (analog-digital conversion) is used. This is because, when the bit resolution is the same, angle measurement (calculation) with higher accuracy can be performed with a larger waveform amplitude.

  As described above, according to the encoder 2 and the magnetizing method thereof according to the present embodiment, the isotropic magnet (isotropic ring magnet 4 as an example) is used and the ring magnet 4 is intended to be magnetized. By applying the parallel magnetic field Mf with the back yoke 6 for concentrating the magnetic flux, the magnetic field orientation (alignment of the easy magnetization direction in the same direction) and the alignment work between the orientation direction and the magnetic field direction are managed. In addition, it is possible to reduce the labor, cost, and the like, and it is possible to expand the peak without reducing the amplitude of the fluctuation waveform of the magnetic flux density M2 during rotation. Therefore, by using the magnetizing technique (encoder 2 and its magnetizing method) of the encoder 2 according to the present embodiment, the rotation angle of the steering shaft by the magnetic sensors S1 and S2 (specifically, one round of the encoder 2) The measurement accuracy of (absolute angle) can be reliably improved as compared with the conventional case.

2 Encoder 4 Ring magnet 6 Yoke member (back yoke)
C ring magnet central axis Mf magnetic field (radial parallel magnetic field)
S1, S2 Magnetic sensor

Claims (4)

A method for magnetizing an isotropic ring magnet for an encoder to be detected by a magnetic sensor that measures the rotational state of a rotating body that rotates about an axis,
The ring magnet is set to have a length in the extending direction that is orthogonal to the central axis and linearly extends along the radial direction, and is set to be larger than the outer diameter of the ring magnet. An air-core coil that generates a magnetic field by passing a predetermined current with a yoke member for magnetization whose width orthogonal to the outgoing direction is set smaller than the inner diameter of the ring magnet is arranged. A ring magnet magnetization method in which magnetization is performed by applying a magnetic field parallel to the radial direction . The ring magnet magnetization method according to claim 1, wherein the yoke member is a structure having a flat portion that is orthogonal to a central axis of the ring magnet and extends linearly along a radial direction thereof. The ring magnet is mounted with a magnetizing yoke member so that a plane portion orthogonal to the central axis and extending linearly along the radial direction faces the side surface of the ring magnet. The ring magnet magnetization method according to claim 1 or 2, wherein magnetization is performed by applying a magnetic field parallel to the radial direction. Magnetizing by applying a magnetic field to the magnetized area of the outer peripheral surface of the ring magnet,
4. The magnetic sensor according to claim 1, wherein two magnetic sensors are arranged, and each of the magnetic sensors is opposed to the magnetized region at a predetermined interval and is shifted by 90 ° in the circumferential direction of the ring magnet. Ring magnet magnetization method.

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