JP2024139109A - Magnetic Encoder - Google Patents

Abstract

[Problem] To provide a magnetic encoder with high angular accuracy. [Solution] The magnetic encoder is a ring-shaped magnetic encoder containing rare earth magnet powder and a cured resin of a thermosetting resin, and having a magnetic track formed by magnetizing a plurality of magnetic poles at a predetermined pitch in the circumferential direction of the surface, the rare earth magnet powder is an isotropic Nd-Fe-B magnet powder with a particle size of 45 μm or more and less than 75 μm, the cured resin is contained in an amount of 5% by weight or more and 6.5% by weight or less, and the thickness of the ring-shaped magnetic encoder is 0.2 mm or more and 1 mm or less. [Selected Figure] None

Description

The present invention relates to a magnetic encoder, and in particular to a magnetic encoder using rare earth bonded magnets.

Conventionally, magnetic encoders are known as a method for detecting the rotational position of equipment. A rotation detection device has been proposed that includes two magnetic encoders arranged in concentric rings and each having a different number of magnetic poles, and a magnetic sensor that detects the magnetic fields of each of these magnetic encoders, and calculates the absolute angle of the magnetic encoders based on the phase difference between the magnetic field signals detected by the magnetic sensors (see, for example, Patent Document 1).

The magnetic encoder in the rotation detection device of Patent Document 1 is configured as a rubber magnet in which, for example, an elastic member containing magnetic powder is vulcanized and bonded to a core metal made of a magnetic material, and this elastic member is formed with magnetic poles alternately in the circumferential direction to form a magnetic track. In addition, as another configuration example of a magnetic encoder, it is described that a resin molded body made of a resin containing magnetic powder is provided on a core metal made of a magnetic material, and this resin molded body can be used as a resin magnet in which magnetic poles are formed alternately in the circumferential direction to form a magnetic track. In such rubber magnets and resin magnets, ferrite magnet powder is usually used as the magnetic powder.

When considering improving the magnetic properties of a magnetic encoder, it is preferable for the magnetic encoder to contain a larger amount of magnetic material, and it is also preferable for the magnetic powder to have higher magnetic properties. For this reason, the magnetic properties are improved when rare earth magnetic powder is used rather than ferrite magnetic powder. Therefore, it is conceivable to construct the magnetic encoder, which is the object to be magnetized, from a rare earth bonded magnet.

When magnetizing the multiple magnetic poles (N pole, S pole) that become the magnetic track of a magnetic encoder, a magnetization device that uses a coil current method (so-called pulse magnetization method) is generally used. This coil current method magnetization device, for example, passes a pulse current through a field magnet part having a coil wound around a magnetization yoke, and magnetizes the object to be magnetized by the magnetic field generated by this. However, as described in Patent Document 2, for example, if the magnetic pole width of the magnetic sensor that detects the magnetic track of the magnetic encoder is limited to 1.28 mm, it is difficult to form multiple magnetic poles by saturating magnetization with a narrow magnetic pole pitch such as 1.28 mm for the magnetic encoder that is the object to be magnetized and is composed of rare earth bond magnets using the above pulse magnetization method.

For this reason, a method has been proposed that allows for optimal magnetization even in multi-pole magnetization by heating the object to be magnetized to above the Curie point of the magnet, and then continuously applying a magnetizing magnetic field to the object to be magnetized using a permanent magnet that serves as a field source while cooling it to below the Curie point (see, for example, Patent Document 3).

The magnetization device in Patent Document 3 describes an isotropic rare earth iron-based bonded magnet that is made by mixing isotropic magnet powder with epoxy resin, compressing it, and curing it at a specified temperature, and can be effectively magnetized even when multiple poles are magnetized with a narrow magnetic pole pitch such as 1.28 mm.

JP 2008-267867 A JP 2017-32327 A JP 2021-093521 A

In light of the recent rise in the price of rare earth magnet powder, it is preferable to use isotropic rare earth bonded magnets, which contain less rare earth magnet powder, in magnetic encoders, although their magnetic properties are inferior to those of isotropic rare earth iron-based bulk magnets made by sintering magnet powder at a specified temperature. When using rare earth bonded magnets, the magnetizing device of Patent Document 3 can be used to magnetize multiple poles with a narrow magnetic pole pitch, and costs can be reduced.

Rare earth bonded magnets are made by mixing rare earth magnet powder with thermosetting resin and compressing it to create a green body, then heat-curing the resin contained in the green body to create a cured body (thermosetting body), which is then magnetized with a specified magnetic pole pitch to produce a magnetic encoder.

Rare earth bonded magnets are composed of rare earth magnet powder, a thermosetting resin binder, and voids, with the volume ratios of each being approximately 80% magnet powder, 10% resin, and 10% voids (air holes). As magnet powder is a mixture of magnet powders with various particle sizes, it is prone to deformation after thermal curing due to moldability issues when the green body is thinned and variations in density of the green body. Furthermore, since it is only the magnet powder that contributes to the magnetic properties of the magnetic encoder, it is important for the magnet powder to be distributed evenly and for the variation in magnetic properties to be small in order to increase the precision of the magnetic encoder.

Patent document 3 describes that isotropic rare earth iron-based bonded magnets can be magnetized favorably even when multiple poles are magnetized with a narrow magnetic pole pitch. However, there is room for further consideration in terms of the angular accuracy of the magnetic encoder.

Therefore, the object of the present invention is to provide a magnetic encoder using rare earth bonded magnets that reduces the variation in magnetic characteristics and has high angular accuracy.

In order to solve the above-mentioned problems and achieve the object, the magnetic encoder according to one aspect of the present invention is a ring-shaped magnetic encoder that contains rare earth magnet powder and a resin cured product of a thermosetting resin, and has a magnetic track formed by magnetizing multiple magnetic poles at a predetermined pitch in the circumferential direction of the surface, the rare earth magnet powder is an isotropic Nd-Fe-B magnet powder with a particle size of 45 μm or more and less than 75 μm, the resin cured product is contained in an amount of 5% by weight or more and 6.5% by weight or less, and the thickness of the ring-shaped magnetic encoder is 0.2 mm or more and 1 mm or less.

According to one aspect of the present invention, a magnetic encoder with high angular accuracy is obtained.

FIG. 1 is a diagram for explaining a magnetic encoder according to the first embodiment.

Below, an embodiment of the present invention will be described in detail with reference to the drawings. Note that the present invention is not limited to this embodiment. Furthermore, the components in the following embodiment include those that are easily replaceable by a person skilled in the art, or those that are substantially the same.

<Embodiment 1>
The magnetic encoder of embodiment 1 is a ring-shaped magnetic encoder that contains rare earth magnet powder and a cured resin of a thermosetting resin, and has a magnetic track formed by magnetizing a plurality of magnetic poles at a predetermined pitch in the circumferential direction of the surface, the rare earth magnet powder being an isotropic Nd-Fe-B based magnet powder having a particle size of 45 μm or more and less than 75 μm, the cured resin being contained in an amount of 5 wt % or more and 6.5 wt % or less, and the thickness of the ring-shaped magnetic encoder is 0.2 mm or more and 1 mm or less.

When an isotropic rare earth bonded magnet using Nd-Fe-B magnet powder is used in a magnetic encoder, if the rare earth magnet powder used contains magnet powders of various particle sizes, the surface magnetic flux detected by each magnetic pole of the manufactured magnetic encoder will vary. As a result, the output of the magnetic sensor that detects the magnetic flux from the magnetic poles of the magnetic encoder will vary, making it difficult to improve the angular accuracy of the magnetic encoder. For this reason, in order to reduce the variation in surface magnetic flux at each location (each magnetic pole) throughout the magnetic encoder and achieve a homogeneous state, it has been found that it is effective to reduce the particle size of the rare earth magnet powder while narrowing its particle size distribution. In general, the static magnetic properties (residual magnetic flux density) of the magnet powder tend to decrease as the particle size of the magnet powder decreases, but in the magnetic encoder of embodiment 1, priority is given to suppressing the variation in static magnetic properties and achieving a homogeneous state.

Figure 1 is a diagram for explaining a magnetic encoder of embodiment 1. The magnetic encoder 1 is configured as a vernier type in which two magnetic tracks (main track 11 and sub-track 12) are formed concentrically on one axial end face. Specifically, in the axial direction, the main track 11 is magnetized in the circumferential direction at a predetermined magnetic pole pitch on the outer circumferential side, and the sub-track 12 is magnetized in the circumferential direction at a predetermined magnetic pole pitch on the inner circumferential side. When the main track 11 is magnetized with n pole pairs, the sub-track 12 is magnetized with (n-1) pole pairs. When the magnetic pole width of the magnetic sensor that detects the magnetic track of the magnetic encoder is limited, the magnetic pole pitch of the magnetic track formed in the magnetic encoder is formed to the same width as the magnetic pole width of the magnetic sensor. For example, the above-mentioned predetermined pitch is 0.4 mm or more and 2.4 mm or less, more specifically, 1.28 mm. In addition, the magnetic encoder 1 has non-magnetized areas 13 on the end surface between the main track 11 and the sub-track 12 and on the inner side of the sub-track 12.

The rare earth magnet powder contained in the magnetic encoder of the first embodiment is an isotropic Nd (neodymium)-Fe (iron)-B (boron) magnet powder. Examples of isotropic Nd-Fe-B magnet powder include MQP-14-12 (product name), MQP-8-5 (product name), MQP-10-8.5HD (product name), MQP-11-8 (product name), and MQP12-8HD (product name) manufactured by Magnequench.

Alternatively, for example, Nd-Fe-B magnet powder produced by a rapid cooling method may be used. Specifically, an Nd-Fe-B alloy is melted by high-frequency induction heating under reduced pressure or in an argon atmosphere. The molten alloy is then sprayed onto a rotating copper roll and rapidly cooled (cooled at high speed) to produce ribbon-shaped strips. The strips are then broken into pieces of, for example, several mm to several tens of mm, and crushed with a crusher or the like to obtain powder. The crushed powder is classified using a sieve with a specified mesh, and then heat-treated to produce rare earth magnet powder. This rare earth magnet powder is magnetically isotropic because the magnetization easy axis of each crystal grain is not aligned in one direction.

The rare earth magnet powder has a particle size of 45 μm or more and less than 75 μm. This particle size range can be adjusted by classification using a sieve with a specified mesh.

The cured thermosetting resin contained in the magnetic encoder of embodiment 1 is specifically a cured epoxy resin.

In the magnetic encoder of embodiment 1 (100% by weight), the cured resin is contained in an amount of 5% by weight to 6.5% by weight. The rare earth magnet powder is contained in an amount of 93.5% by weight to 95% by weight. In the magnetic encoder of embodiment 1, it is preferable that the rare earth magnet powder and the cured thermosetting resin are uniformly mixed.

In this way, the magnetic encoder of embodiment 1 has the above thickness and contains rare earth magnet powder in the above particle size range and hardened resin in the above ratio, so it has excellent angular accuracy and rolling strength.

Furthermore, from the viewpoint of compression strength, it is preferable that, in the magnetic encoder of embodiment 1 (100% by weight), the cured resin is contained in an amount of 6% by weight or more and 6.5% by weight or less, and the rare earth magnet powder is contained in an amount of 93.5% by weight or more and 94% by weight or less.

The magnetic encoder of the first embodiment can be produced, for example, as follows. First, the rare earth magnet powder and the components constituting the cured resin in the magnetic encoder (the raw material components of the cured resin) are mixed in a predetermined mixing ratio to produce a compound. The mixing ratio of the rare earth magnet powder to the raw material components of the cured resin is considered to be the same as the ratio of the rare earth magnet powder to the cured resin in the magnetic encoder after production. The raw material components of the cured resin include a thermosetting resin (e.g., epoxy resin) as a binder, and a curing agent. Furthermore, when producing the compound, a small amount of a lubricant (e.g., calcium stearate) may be added. Specifically, the lubricant may be mixed in an amount of 0.02% by weight or more and less than 0.5% by weight with respect to the total 100% by weight of the rare earth magnet powder and the raw material components of the cured resin.

Next, the compound is filled into the cavity of the mold and compressed with a specified pressure to produce a doughnut-shaped green body. The green body is then removed from the mold and placed in an oven, where it is thermally cured at a specified temperature for a specified time to produce a cured body (thermosetting body) containing the rare earth magnet powder and the cured resin. It is also preferable to apply a rust-preventing means to the surface of the cured body to prevent oxidation. As a rust-preventing means, known means such as electrocoating and spray coating can be used.

Next, as shown in FIG. 1, a vernier method is constructed in which two magnetic tracks are formed concentrically on one axial end surface of the cured body. This type of configuration is also shown in the figure of Patent Document 1. Specifically, in the axial direction, the main track is magnetized in the circumferential direction at a predetermined magnetic pole pitch on the outer circumferential side, and the sub-track is magnetized in the circumferential direction at a predetermined magnetic pole pitch on the inner circumferential side. When the main track is magnetized with n pole pairs, the sub-track is magnetized with (n-1) pole pairs. When the magnetic pole pitch of the magnetic sensor that detects the magnetic track of the magnetic encoder is limited, the magnetic pole pitch of the magnetic track formed on the magnetic encoder is formed to the same width as the magnetic pole width of the magnetic sensor. Magnetization is so-called magnetization, and the magnetization means can be, for example, as disclosed in Patent Document 3, a means for continuously applying a magnetizing magnetic field to the magnetized object by a permanent magnet, which is a field source, while heating the magnetized object to a temperature above the Curie point of the magnet powder and cooling it to a temperature below the Curie point. In addition, since the sub-track is located on the inner circumference than the main track, the magnetic pole pitch is set to correspond to the inner diameter position of the detection part of the magnetic sensor for the sub-track. In this way, the magnetic encoder of embodiment 1 is obtained.

<Embodiment 2>
The magnetic encoder of the second embodiment is a ring-shaped magnetic encoder including a rare earth magnet powder and a resin cured product of a thermosetting resin, and having a magnetic track formed by magnetizing a plurality of magnetic poles at a predetermined pitch in the circumferential direction of the surface, the rare earth magnet powder being an isotropic Nd-Fe-B magnet powder having a particle size of 45 μm or more and less than 175 μm, the resin cured product being included in an amount of 5% by weight or more and 6.5% by weight or less, and the thickness of the ring-shaped magnetic encoder being 0.2 mm or more and 0.4 mm or less. Except for the thickness of the ring-shaped magnetic encoder, the configuration and function of the components in the magnetic encoder of the second embodiment are the same as the configuration and function of the components in the magnetic encoder of the first embodiment. Therefore, detailed description will be omitted here.

The magnetic encoder of embodiment 2 also has the above thickness and contains rare earth magnet powder in the above particle size range and cured resin in the above ratio, so it has excellent angular accuracy and rolling strength.

<Other embodiments>
The first embodiment is an axial type magnetic encoder having a vernier system in which two magnetic tracks are formed on a donut-shaped (ring-shaped) magnetic encoder as shown in FIG. 1, but it may also be a radial type magnetic encoder having a vernier system in which two magnetic tracks are formed on the cylindrical side surface of a hollow cylindrical magnetic encoder.

The present invention will be described in more detail below with reference to examples, but the present invention is not limited to these examples.

[Example]
<Magnetic Encoder Fabrication>
Isotropic Nd-Fe-B magnet powder was used as the rare earth magnet powder. MQP-14-12 (product name) manufactured by Magnequench was prepared as the isotropic Nd-Fe-B magnet powder. The particle size of MQP-14-12 was classified into three groups: 75 μm or more and less than 150 μm, 45 μm or more and less than 75 μm, and 32 μm or more and less than 45 μm. In this case, the classification was performed using a sieve with a predetermined mesh.
Next, for each of the three groups, a compound was prepared by mixing isotropic Nd-Fe-B magnet powder with raw material components for a cured resin, including an epoxy resin binder and a curing agent (manufactured by Pernock, model number XW2310), in a predetermined mixing ratio. Here, the mixing ratio of the rare earth magnet powder and the raw material components for the cured resin was 2.5% by weight, and 97.5% by weight of the raw material components for the cured resin, with the total weight being 100% by weight. Furthermore, compounds were also prepared in the following cases: when the raw material components of the resin cured product were 5% by weight and the rare earth magnet powder was 95% by weight; when the raw material components of the resin cured product were 5.5% by weight and the rare earth magnet powder was 94.5% by weight; when the raw material components of the resin cured product were 6% by weight and the rare earth magnet powder was 94% by weight; when the raw material components of the resin cured product were 6.5% by weight and the rare earth magnet powder was 93.5% by weight; when the raw material components of the resin cured product were 7.5% by weight and the rare earth magnet powder was 92.5% by weight. The compounds were prepared by mixing the raw material components of the resin cured product dissolved in a solvent with the rare earth magnet powder, evaporating the solvent, and then crushing and classifying the mixture. All the compounds were prepared with the same particle size, and the fluidity conditions for filling the cavity of the mold were the same.
Next, the compound was filled into the cavity of the mold and compressed by applying a predetermined pressure to produce a doughnut-shaped green body. The green body had an outer diameter of Φ56 mm, an inner diameter of Φ41 mm, and a thickness of 1 mm. Furthermore, green bodies with thicknesses of 0.4 mm and 0.2 mm were also produced.
Next, the green body removed from the mold was placed in an oven and thermally cured at a specified temperature (150°C) for a specified time to produce a cured body (thermosetting body). The cured body had an outer diameter of Φ56 mm, an inner diameter of Φ41 mm, and a thickness of 1 mm. Cured bodies with thicknesses of 0.4 mm and 0.2 mm were also produced. Thus, no difference in size was observed between the green body and the cured body.
Next, after applying a rust prevention means (specifically, electrocoating) to prevent oxidation to the surface of the cured body, a vernier system was formed in which two magnetic tracks were formed concentrically on one axial end surface of the thermoset body, as shown in FIG. 1. Specifically, in the axial direction, the main track was magnetized in the circumferential direction at a predetermined magnetic pole pitch on the outer circumferential side, and the sub-track was magnetized in the circumferential direction at a predetermined magnetic pole pitch on the inner circumferential side. The main track was magnetized with 32 pole pairs, and the sub-track was magnetized with 31 pole pairs. In this embodiment, since a magnetic sensor with a magnetic pole width limited to 1.28 mm was used, the main track of the magnetic encoder was magnetized to 1.28 mm. The magnetization is so-called magnetization, and the magnetization means was, for example, as disclosed in Patent Document 3, a means for continuously applying a magnetizing magnetic field to the magnetized object by a permanent magnet as a field source while heating the magnetized object to a temperature above the Curie point of the magnet powder and cooling it to a temperature below the Curie point. Since the sub-track is located on the inner periphery than the main track, the magnetic pole pitch is set to correspond to the inner diameter position of the detection portion of the magnetic sensor for the sub-track.
In this way, a ring-shaped magnetic encoder (samples 1 to 54) was produced, which contained rare earth magnet powder and a cured resin of a thermosetting resin, and had a magnetic track formed by magnetizing multiple magnetic poles at a predetermined pitch around the circumference of the surface.

<Evaluation method>
(Moldability)
The compound was filled into the cavity of a mold and compression molded into a doughnut-shaped green body, and the handleability when removing it from the mold was evaluated. Specifically, when the green body was removed from the mold with an ejector pin attached to the mold, the state of cracks and chips that occurred in the green body was visually observed and evaluated as moldability. The evaluation criteria are as follows.
○: No cracks or chips ×: Cracks or chips

(Thickness precision)
The cured body was taken out of the oven and the thickness was measured at eight diagonal positions with a micrometer to evaluate the variation in thickness (maximum value-minimum value). The evaluation criteria were as follows:
◯: Samples with a variation of less than 0.06 mm are considered to be good.
Δ: Samples having a variation value between 0.06 mm or more and 0.08 mm or less are rated as fair.
×: Samples with a variation value of more than 0.08 mm are unacceptable.

(Ring crushing strength)
The radial crushing strength was measured based on JIS Z 2507. The evaluation criteria were as follows.
⊚: Radial crushing strength is 100 MPa or more.
◯: The radial crushing strength is 60 MPa or more and less than 100 MPa.
Δ: The radial crushing strength is 50 MPa or more and less than 60 MPa.
×: The radial crushing strength is less than 50 MPa.

(Angle accuracy)
The angular accuracy of the magnetic encoder magnetized by the above-mentioned method was measured. The evaluation criteria were as follows. The angular accuracy was evaluated by attaching the magnet and IC board to a reference servo motor shaft equipped with an optical encoder (angle accuracy of ±10 seconds or less, resolution of 20 bits or more), driving the reference motor 1 degree at a time (360 degrees CW and CCW twice), and measuring the difference between the angle output from the IC and the reference angle. The maximum-minimum width was taken as the angular error.
⊚: The variation in magnetic flux is 0.05 deg. or less.
◯: The variation in magnetic flux is greater than 0.05 deg. and equal to or less than 0.07 deg.
Δ: The variation in magnetic flux is greater than 0.07 deg. and less than 0.1 deg.
×: The variation in magnetic flux is 0.1 deg. or more.

(comprehensive evaluation)
A comprehensive evaluation was performed on Samples 1 to 54. The evaluation criteria were as follows.
○: The evaluation results for each evaluation item are only ○ or ◎.
×: The evaluation result for each evaluation item is △ or ×.
The evaluation results of Samples 1 to 54 are shown in Tables 1 to 3 below. In Table 1, the magnetic powder particle size (μm) "75-150" indicates that the particle size of the isotropic Nd-Fe-B system magnet powder is in the range of 75 μm or more and less than 150 μm. In Table 2, the magnetic powder particle size (μm) "45-75" indicates that the particle size of the isotropic Nd-Fe-B system magnet powder is in the range of 45 μm or more and less than 75 μm. In Table 3, the magnetic powder particle size (μm) "32-45" indicates that the particle size of the isotropic Nd-Fe-B system magnet powder is in the range of 32 μm or more and less than 45 μm.

Table 1 shows the evaluation of the magnetic encoder of samples 1 to 18. In samples 1 to 18, the particle size of the isotropic Nd-Fe-B magnet powder is in the range of 75 μm or more and less than 150 μm. In samples 1 to 3, in which the amount of raw material components of the resin cured product is 2.5% by weight, the radial crushing strength was △. This is due to the small amount of raw material components of the resin cured product. When the sample (green body) was ejected from the mold with an ejector pin, chips and cracks occurred on the outer periphery. If the chips and cracks extend to the track formation area when the sample is magnetized to form a track in a later process, the track cannot be formed. In addition, since Nd-Fe-B magnet powder is used as the rare earth magnet powder, it is prone to rust. For this reason, it is necessary to coat the surface of the sample with an anti-rust film in order to prevent oxidation, but the area where the chips and cracks occur does not have a uniform anti-rust film, and there is a risk of rust occurring from this area.
In samples 16 to 18, in which the amount of the raw material component of the cured resin was 7.5% by weight, some of the binder leaked out of the cavity. Therefore, the angle accuracy was not evaluated. This is because the amount of the raw material component of the cured resin was too high.
The angular precision of samples 22 to 33, which will be described later, was all rated as excellent. This is because the particle size of the isotropic Nd-Fe-B magnet powder was in the range of 45 μm or more and less than 75 μm. This is in a smaller range than the particle size range of the Nd-Fe-B magnet powder in samples 1 to 18 shown in Table 1, so there was less variation in the distribution of the magnet powder in a given area (or volume), and generally, there was less variation in the magnetic properties for each magnetic pole.
The angular accuracy was rated as x when the sample thickness was 1 mm, which is a low rating. This is because the particle size of the Nd-Fe-B magnetic powder is in the range of 75 μm or more and less than 150 μm. Since the particle size of the Nd-Fe-B magnetic powder is large, the area occupied by the magnetic powder in the thickness direction in a given area varies greatly, which results in large variation in the magnetic properties for each magnetic pole.

Table 2 shows the evaluation of the magnetic encoders of samples 19 to 36. In samples 19 to 36, the particle size of the isotropic Nd-Fe-B magnet powder was in the range of 45 μm or more and less than 75 μm. Samples 19 to 21, in which the amount of raw material components of the cured resin was 2.5% by weight, had a radial crushing strength of △. This is because the amount of raw material components of the cured resin was too small. Also, in samples 34 to 36, in which the amount of raw material components of the cured resin was 7.5% by weight, some of the binder leaked out from the cavity. For this reason, the angular accuracy was not evaluated. This is because the amount of raw material components of the cured resin was too large.
The evaluations of Samples 22 to 33 other than the sample in which the amount of the raw material component of the cured resin material was 2.5% by weight were all rated as ⊚ or ◯ in all items. Therefore, the overall evaluation of Samples 22 to 33 shown in Table 2 was rated as ◯.
The angular precision of samples 22 to 33 was evaluated as excellent. This is because the particle size of the isotropic Nd—Fe—B magnetic powder was in the range of 45 μm or more and less than 75 μm. This is in a smaller range than the particle size range of the Nd—Fe—B magnetic powder in samples 1 to 18 shown in Table 1, so there is less variation in the area occupied by the magnetic powder in the thickness direction in a given area, and as a result, there is less variation in the magnetic properties for each magnetic pole.

Table 3 shows the evaluation of the magnetic encoders of Samples 37 to 54. In Samples 37 to 54, the particle size of the isotropic Nd—Fe—B magnet powder is in the range of 32 μm or more and less than 45 μm.
Samples 37 to 39, in which the amount of raw material components of the cured resin was 2.5% by weight, had a radial crushing strength of 4.4%. This is because the amount of raw material components of the cured resin was too small. Samples 52 to 54, in which the amount of raw material components of the cured resin was 7.5% by weight, had some of the binder leaking out of the cavity. For this reason, the angle accuracy was not evaluated. This is because the amount of raw material components of the cured resin was too large.
The angular accuracy of all samples other than the above samples was evaluated as △. This is thought to be due to the fact that the particle size of the Nd-Fe-B magnet powder is small, at 32 μm or more and less than 45 μm. The smaller the particle size of the magnet powder, the worse the squareness of the demagnetization curve of the magnet powder itself becomes, and the more likely it is that the magnetic properties will deteriorate due to thermal deterioration, oxidative deterioration, etc., which is thought to be due to the decrease in the surface magnetic flux from the magnetic encoder.
For this reason, the overall evaluation of samples 37 to 54 shown in Table 3 was all rated as x.

1 Magnetic encoder, 11 Main track, 12 Sub-track, 13 Non-magnetized area

Claims (3)

A ring-shaped magnetic encoder including rare earth magnet powder and a cured resin of a thermosetting resin, the magnetic encoder having a magnetic track formed by magnetizing a plurality of magnetic poles at a predetermined pitch in the circumferential direction of a surface thereof,
the rare earth magnet powder is an isotropic Nd—Fe—B magnet powder having a particle size of 45 μm or more and less than 75 μm,
The cured resin is contained in an amount of 5% by weight or more and 6.5% by weight or less,
The thickness of the ring-shaped magnetic encoder is 0.2 mm or more and 1 mm or less.
Magnetic encoder. A ring-shaped magnetic encoder including rare earth magnet powder and a cured resin of a thermosetting resin, the magnetic encoder having a magnetic track formed by magnetizing a plurality of magnetic poles at a predetermined pitch in the circumferential direction of a surface thereof,
the rare earth magnet powder is an isotropic Nd—Fe—B magnet powder having a particle size of 45 μm or more and less than 175 μm,
The cured resin is contained in an amount of 5% by weight or more and 6.5% by weight or less,
The thickness of the ring-shaped magnetic encoder is 0.2 mm or more and 0.4 mm or less.
Magnetic encoder. The magnetic encoder according to claim 1 or 2, characterized in that the magnetization is performed in the axial direction.

Images