Magnetic encoder

Abstract

The ring-shaped magnetic encoder is obtained by mixing and compressing a rare earth magnet powder and a resin to form an unheated body, and then thermally curing the resin contained in the unheated body to form a thermally cured body, and has magnetic tracks in which magnetic poles different from each other in the circumferential direction are magnetized at a predetermined magnetic pole pitch. When T (mm) is the thickness of the unheated body and G ([mu] m) is the maximum particle diameter of the rare earth magnet powder, the ratio R is 6.67 or more, and the particle diameter of the rare earth magnet powder is 45-150 [mu] m.

Description

Technical Field

[0001] The invention relates to a magnetic encoder. Background Art

[0002] In the past, a magnetic encoder for detecting the rotation position of a device was known. A rotation detection device has been proposed, which includes: a magnetic encoder, as the above-mentioned magnetic encoder, having two magnetic tracks arranged in a concentric ring shape and having different numbers of magnetic poles; and a magnetic sensor, which detects the magnetic fields of the two magnetic tracks respectively, and the rotation detection device is configured to calculate the absolute angle of the magnetic encoder based on the phase difference of the magnetic field signal detected by the magnetic sensor (for example, refer to Patent Document 1).

[0003] The magnetic encoder in the rotation detection device of Patent Document 1, for example, vulcanizes and bonds an elastic member mixed with magnetic powder to a core bar made of a magnetic system, so that the elastic member is formed into a rubber magnet that alternately forms magnetic poles in the circumferential direction to form a magnetic track. In addition, as another structural example of the magnetic encoder, it is recorded that a resin molded body formed by molding a resin mixed with magnetic powder can also be set on a core bar made of a magnetic system, and the resin molded body is set as a resin magnet that alternately forms magnetic poles in the circumferential direction to form a magnetic track. Such rubber magnets and resin magnets usually use ferrite magnet powder as magnetic powder.

[0004] If the improvement of the magnetic properties of the magnetic encoder is considered, it is preferred that the amount of magnetic body contained in the magnetic encoder is large, and it is also preferred that the magnetic properties of the magnetic powder be high. Therefore, the magnetic properties are improved when rare earth magnetic powder is used compared to ferrite magnetic powder. Therefore, it is considered to use rare earth bonded magnets to form a magnetic encoder as a magnetized object.

[0005] In the case of magnetizing a plurality of magnetic poles (N poles, S poles) as a magnetic track formed in a magnetic encoder, a coil-energizing type magnetizing device (so-called pulse magnetizing method) is generally used. This coil-energizing type magnetizing device, for example, causes a pulse current to flow through an excitation portion having a coil wound around a magnetizing yoke, and magnetizes the magnetized object by the magnetic field generated thereby. However, as described in the column "Problems to be Solved by the Invention" in Patent Document 2, for example, when the magnetic pole width of a magnetic sensor for detecting the magnetic track of the magnetic encoder is limited to 1.28 mm, it is difficult to form a plurality of magnetic poles by saturation magnetization at a magnetic pole pitch as narrow as 1.28 mm in the above-mentioned pulse magnetizing method for the structure of the magnetic encoder as a magnetized object based on a rare earth bonded magnet.

[0006] Therefore, the following scheme has been proposed: during the period of heating to above the Curie point of the magnet in the magnetized object and cooling to below the Curie point, a magnetizing magnetic field is continuously applied to the magnetized object by a permanent magnet as an excitation source, thereby enabling proper magnetization even when multi-pole magnetization is performed (for example, refer to Patent Document 3).

[0007] The magnetizing device of Patent Document 3 records: anisotropic rare earth iron-based block magnets, which are imparted with anisotropy by thermoplastic processing of magnet powder at a specified temperature; isotropic rare earth iron-based block magnets, which are formed by sintering magnet powder at a specified temperature using a spark plasma sintering (SPS) device; isotropic rare earth iron-based bonded magnets, which are formed by mixing and compressing isotropic magnet powder and epoxy resin and then solidifying them at a specified temperature; and isotropic rare earth iron-based bonded magnets, which are formed by mixing and compressing isotropic magnet powder and epoxy resin and then solidifying the epoxy resin at a specified temperature. It is also recorded that even multi-pole magnetization with a narrow pole pitch of 1.28 mm can be properly magnetized.

[0008] Prior art literature

[0009] Patent Literature

[0010] Patent Document 1: Japanese Patent Application Publication No. 2008-267867

[0011] Patent Document 2: Japanese Patent Application Publication No. 2017-32327

[0012] Patent Document 3: Japanese Patent Application Publication No. 2021-093521 Summary of the invention

[0013] Problems to be solved by the invention

[0014] After rare earth magnet powder and resin are mixed and compressed to form an unheated body as a green body, the resin contained in the green body is thermally cured to form a thermally cured body as a solid body, and the solid body is magnetized with a specified magnetic pole spacing, thereby obtaining a rare earth bonded magnet.

[0015] However, since magnet powders with various particle sizes are mixed in the magnet powder, deformation after thermal curing is likely to occur due to the formability when the green body is thinned and the deviation of the density of the green body. In addition, only the magnet powder contributes to the magnetic properties, and the unbiased distribution of the magnet powder is very important for the high precision of the magnetic encoder. However, although Patent Document 3 records that even if multi-pole magnetization is performed with a narrow magnetic pole spacing, isotropic rare earth iron bonded magnets can be properly magnetized, there is no record of the formability when the green body is thinned and the deformation after thermal curing, and there is room for further research.

[0016] The present invention has been completed in view of the above situation, and its purpose is to provide a magnetic encoder, which is a magnetic encoder based on rare earth bonded magnets, which can improve the formability when the green body is thinned, is not easy to produce deformation of the green body after thermal curing, and can be properly magnetized even when multi-pole magnetization is performed with a narrow magnetic pole pitch.

[0017] Solutions for solving problems

[0018] In order to solve the above-mentioned problems and achieve the purpose, a magnetic encoder of one scheme of the present invention is an annular magnetic encoder, which is obtained by mixing and compressing rare earth magnet powder and resin to form an unheated body, and then thermally curing the resin contained in the unheated body to form a thermally cured body, and the annular magnetic encoder has a magnetic track obtained by magnetizing magnetic poles that are different from each other in the circumferential direction at a predetermined magnetic pole pitch, wherein:

[0019] When the ratio R is T / G, where the thickness of the unheated body is T (mm) and the maximum particle size of the rare earth magnet powder is G (μm), the ratio R is greater than or equal to 6.67, and the particle size of the rare earth magnet powder is 45 μm to 150 μm.

[0020] Effects of the Invention

[0021] According to the scheme of the present invention, the following effects can be provided: the moldability is ensured, deformation after heat curing is not easy to occur, the thickness accuracy is high, and the thickness can be reduced. Therefore, the magnetic encoder of the scheme of the present invention is suitable for various robot joints, motor angle detection, vehicle bearing rotation detection, etc. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Figure 1 It is a schematic perspective view of the magnetic encoder according to the embodiment.

[0023] Figure 2 It is a schematic partial plan view of the magnetic encoder according to the embodiment. DETAILED DESCRIPTION

[0024] Hereinafter, a magnetic encoder according to an embodiment of the present invention will be described in detail based on the drawings. It should be noted that the present invention is not limited to this embodiment.

[0025] [Magnetic Encoder of Embodiment]

[0026] From the viewpoint of improving the magnetic properties of the magnetic encoder, it is preferred to use an isotropic rare earth bonded magnet for the magnetic encoder, and when a rare earth bonded magnet is used, magnetization can be performed appropriately even when multi-pole magnetization is performed with a narrow magnetic pole pitch, and cost reduction can be expected.

[0027] After rare earth magnet powder and resin are mixed and compressed to form a green body as an unheated body, the resin contained in the green body is thermally cured to form a cured body as a thermally cured body, and the cured body is magnetized at a predetermined magnetic pole pitch, thereby obtaining a rare earth bonded magnet. Rare earth bonded magnets are composed of rare earth magnet powder, resin as a binder, and voids, and the volume ratio of each is approximately 80% of rare earth magnet powder, 10% of resin, and 10% of voids (holes).

[0028] Rare earth magnet powders have various particle sizes and are mixed together. Therefore, due to the formability of the green body when it is thinned and the deviation of the density of the green body, deformation after thermal curing is likely to occur. In addition, only the rare earth magnet powder contributes to the magnetic properties, and the uniform distribution of the rare earth magnet powder is important for the high precision of the magnetic encoder. It should be noted that the particle size of the rare earth magnet powder is almost unchanged in the unheated body, the thermally cured body, and the magnetic encoder after magnetization.

[0029] Figure 1 is a schematic perspective view schematically showing a magnetic encoder according to an embodiment. Figure 2 FIG. 1 is a schematic partial top view schematically showing a magnetic encoder according to an embodiment. Figure 1 and Figure 2 As shown, a magnetic encoder 1 using a rare earth bonded magnet has two magnetic tracks, a main magnetic track 2 and an auxiliary magnetic track 3 , and the main magnetic track 2 and the auxiliary magnetic track 3 are respectively arranged on the outer and inner circumferences of a concentric shape with an unmagnetized region 4 interposed therebetween.

[0030] like Figure 2 As shown in FIG. 1 , the main track 2 and the auxiliary track 3 are magnetized in a manner that the N poles and the S poles are alternately arranged adjacent to each other. The main track 2 and the auxiliary track 3 are magnetized with multiple poles (N poles and S poles) at equal intervals in the circumferential direction, and the number of poles of the main track 2 and the auxiliary track 3 are different. Figure 2 As shown, the sensor module 5 including the magnetic sensors 6A and 6B for detecting the magnetic fields of the main track 2 and the sub-track 3 , respectively, is arranged on a part of the magnetic poles of the main track 2 and a part of the magnetic poles of the sub-track 3 .

[0031] When the magnetic encoder 1 is rotated around the concentric center, a phase deviation occurs between the magnetic sensor 6A and the magnetic sensor 6B because the number of magnetic poles of the main track 2 is different from the number of magnetic poles of the secondary track 3. By detecting this phase deviation and calculating the absolute angle of the magnetic encoder 1, the rotation position of the device provided with the magnetic encoder 1 can be detected.

[0032] [Manufacturing of Magnetic Encoder According to Embodiment]

[0033] The manufacture of the magnetic encoder 1 uses rare earth bonded magnets because it is possible to properly magnetize even with a narrow magnetic pole pitch and to expect cost reduction. Rare earth bonded magnets are used to manufacture rare earth magnet powder, for example, by a super-quenching method. Specifically, a rare earth alloy is melted by high-frequency induction heating under negative pressure or in an argon atmosphere. Next, the molten alloy melt is sprayed onto a copper rotating roller for super-quenching (high-speed cooling) to produce a ribbon-shaped thin strip sheet. Next, after the thin strip sheet is broken into, for example, several mm to tens of mm, it is crushed by a pulverizer or the like to obtain a powder.

[0034] Next, the crushed powder is classified with a sieve with a specified mesh and then heat-treated. Furthermore, the rare earth magnet powder and the thermosetting resin (epoxy resin) as a binder are mixed in a specified mixing ratio to produce a mixture. The specified mixing ratio is, for example, 2% to 3% by weight of thermosetting resin relative to 97% by weight to 98% by weight of the rare earth magnet powder. In addition, a small amount of lubricant (for example, calcium stearate) can also be added to the mixture. Next, the mixture is filled into a mold and compressed under a specified pressure to produce a ring-shaped green body. The green body taken out of the mold is placed in an oven and cured (thermosetting) at a specified temperature, for example, around 150°C, for a specified time to produce a cured body.

[0035] After the solidified body is formed, the surface of the solidified body is subjected to rust-proof treatment for preventing oxidation. The rust-proof treatment is carried out by a known method such as electrodeposition coating or spray coating. After the surface of the solidified body is subjected to rust-proof treatment, a coating such as Figure 2 As described above, a vernier-type magnetic encoder is provided with two tracks concentrically formed on one axial end face of a solid body. Specifically, the main track 2 is magnetized at a predetermined magnetic pole pitch on the outer circumference, and the auxiliary track 3 is magnetized at a predetermined magnetic pole pitch on the inner circumference. Here, the magnetic pole pitch is the interval between adjacent N poles and S poles in each track in the circumferential direction.

[0036] When the main track 2 is magnetized with n pole pairs, the secondary track 3 is magnetized with (n-1) pole pairs. With respect to the magnetic pole pitch, when the magnetic pole width of the magnetic sensors 6A and 6B for detecting the magnetic track of the magnetic encoder 1 is limited, the magnetic pole pitch formed in the magnetic track of the magnetic encoder 1 is formed to be the same width as the magnetic pole width of the magnetic sensors 6A and 6B. For example, when the magnetic pole width of the magnetic sensor 6A is limited to 1.28 mm (or 1.5 mm), Figure 1 The main track 2 of the magnetic encoder 1 shown is magnetized to 1.28 mm (or 1.5 mm).

[0037] Magnetization is so-called magnetization. For the magnetization method, for example, as disclosed in Patent Document 3, a method is used in which a permanent magnet as an excitation source continuously applies a magnetizing magnetic field to the magnetized object during the period when the magnetized object is heated to a temperature above the Curie point of its magnetic powder and cooled to a temperature below the Curie point. This allows for proper magnetization even when multi-pole magnetization is performed with a narrow magnetic pole pitch. A magnetic encoder based on a rare earth bonded magnet is manufactured in the above manner.

[0038] Example

[0039] Hereinafter, the above-mentioned embodiment will be described in more detail based on examples. It should be noted that the above-mentioned embodiment is not limited in any way by the following examples and comparative examples.

[0040] [Example 1-Example 2 and Comparative Example 1-Comparative Example 3]

[0041] As rare earth magnet powder, samples 1 to 5 corresponding to Examples 1 to 2 and Comparative Examples 1 to 3 were prepared. All samples 1 to 5 used Nd-Fe-B magnet powder (manufactured by Magnequench, model MQP-10-11), which is a magnetically isotropic rare earth iron magnet powder produced by ultra-rapid cooling, as rare earth magnet powder.

[0042] The rare earth iron-based magnetic powder preferably includes a magnetically isotropic rare earth iron-based quenched magnetic powder having the following structure: an R-Fe-B-based magnet (wherein R is a rare earth element such as cerium, praseodymium, neodymium, gadolinium, terbium, dysprosium, holmium, etc. containing yttrium) or an R-Fe(Co)-B-based magnet (wherein R represents the above meaning) obtained by replacing a portion of Fe in the magnet with Co, and further using an R-Fe-B-M-based magnet or an R-Fe(Co)-B-M-based magnet (wherein R represents the above meaning, and M represents one or more of silicon, aluminum, niobium, zirconium, hafnium, molybdenum, gallium, phosphorus, and carbon) and an R2Fe having an alloy component composed of inevitable impurities. 14 B. R2Fe(Co) 14 B nanocrystalline structure (nanocrystalline); or αFe and R2Fe 14 B. R2Fe(Co) 14 B is a nanocomposite (the R has the above-mentioned meaning).

[0043] Alternatively, the rare earth-iron magnetic powder of the embodiment may also use a magnetically isotropic rare earth iron-based quenched magnetic powder having the following structure: a Sm-Fe-N magnet, a Sm-Fe-M'-N magnet using one or a combination of two or more of hafnium, zirconium, silicon, niobium, titanium, gallium, aluminum, tantalum and carbon (wherein M' represents one or more of hafnium, zirconium, silicon, niobium, titanium, gallium, aluminum, tantalum and carbon), and an Sm2Fe having an alloy component composed of inevitable impurities. 17 N x (x≈3) nanocrystalline structure; or αFe and Sm2Fe 17 N x (x≈3) nanocomposite structure. In addition, the above-mentioned R—Fe—B system magnetic powder and Sm—Fe—N system magnetic powder may be mixed, and either or both of them may be magnetically anisotropic magnetic powder.

[0044] Next, the rare earth magnet powder of each sample and a thermosetting resin (epoxy resin: manufactured by Ponnuo Co., Ltd., model XW2310) as a binder are mixed in a specified mixing ratio (97.5% by weight of rare earth magnet powder and 2.5% by weight of thermosetting resin) to prepare a mixture. The mixing ratio of rare earth magnet powder and binder is prepared under the same conditions for samples 1 to 5. In addition, a lubricant (for example, calcium stearate) may be added to the mixture. Then, the mixture is filled into a mold and compressed under a specified pressure to form a green body (samples 1 to 5). The shape of the green body is as follows. Figure 1 As shown, it is in the shape of a ring with an outer diameter B of Φ56 mm, an inner diameter A of Φ41 mm, and a thickness T of 1.0 mm.

[0045] In order to achieve saturation magnetization of the sample, the thickness T of the sample is preferably at least 1 / 2 of the magnetic pole pitch. When the thickness T is at least 1 / 2 of the magnetic pole pitch, the semicircle of the magnetic force lines falls into the sample, thereby suppressing the reduction of the magnetic force. For example, in the case of Figure 2 In the case where the magnetic pole width of the magnetic sensor 6A for detecting the magnetic track of the magnetic encoder is limited to 1.28 mm, the magnetic pole pitch formed on the magnetic track (main track 2) of the magnetic encoder is formed to be 1.28 mm.

[0046] Therefore, the thickness T of the sample is not particularly limited as long as it is 1 / 2 of the magnetic pole spacing of 1.28mm of the track, that is, 0.64mm or more. However, when the thickness T of the sample is increased to a greater extent than necessary, the depth of magnetization during track formation cannot be achieved, which does not contribute to magnetic force, and thus becomes a useless thickness, resulting in increased costs. On the other hand, when the thickness T of the sample is set to about 0.7mm, although it is more than 1 / 2 of the magnetic pole spacing, for example, the handling property is poor, and the possibility of damage to the green body when the green body is discharged by compression molding of the mold becomes high. In addition, it is easy to be damaged during manual processing, so from the perspective of preventing damage, the thickness T of the sample is set to 1.0mm.

[0047] Here, the handleability of the green body of each sample was evaluated (○: good, no notch, △: medium, a few notches, ×: unqualified, many notches). The handleability is obtained by evaluating the operability when the mixture made by mixing rare earth magnet powder and binder is filled into a mold and the ring-shaped green body after compression molding is taken out from the mold. When the green body is taken out from the mold using the push rod provided by the mold, the state of cracks and notches generated in the green body is visually observed and evaluated as the handleability. The evaluation results including the handleability are summarized in Table 1 together with other evaluation results.

[0048]

[0049] Next, the green body taken out from the mold is placed in an oven and cured (thermosetting) at a temperature of about 150°C for a predetermined time to form a cured body as a thermosetting body. For the cured body taken out from the oven, the thickness of eight locations is measured at the diagonal position with a micrometer, and the thickness deviation (maximum value - minimum value) and thickness accuracy are evaluated, and the evaluation results are shown in Table 1. In Table 1, samples with a thickness deviation value greater than 0.08 mm are considered unqualified, and thickness accuracy is indicated by ×, samples with a deviation value between 0.08 mm and 0.06 mm are considered medium, and thickness accuracy is indicated by △, and samples with a deviation value less than 0.06 are considered good, and thickness accuracy is indicated by 0.

[0050] According to Table 1, regarding the evaluation of the handling properties, when the samples (green billets) were ejected from the mold by the push rod, cracks and notches were generated on the outer periphery of samples 1 to 3. In particular, samples 1 and 2 generated large notches and were unqualified. The generation of such notches will cause the following problems: when the samples are magnetized to form magnetic tracks in the subsequent process, magnetic tracks cannot be formed if the notches extend to the magnetic track forming area. In addition, Nd-Fe-B magnet powder is used as rare earth magnet powder, so it is easy to rust. Therefore, although it is necessary to cover the surface of the sample with an anti-rust film to prevent oxidation, a uniform anti-rust film cannot be formed at the location where the notches are generated, and there is a fear that rust will occur from this location. In contrast, regarding samples 4 and 5, no notches were generated when the samples (green billets) were ejected from the mold, and the handling properties were good.

[0051] In addition, from the thickness accuracy obtained by evaluating the deviation (maximum value - minimum value) of the thickness of the solidified body made by solidifying the green body, the deviation of samples 1 and 2 was greater than 0.06 mm, which was unqualified, and the deviation of samples 3 to 5 was less than 0.06 mm, which was good. In particular, the deviation of samples 4 and 5 was 0.03 mm, and the thickness accuracy showed good results. If the thickness deviation becomes larger, when the sample is used as a magnetic encoder, the size of the magnetic flux from the magnetic track detected by the magnetic sensor that detects the magnetic track will deviate, resulting in a decrease in the angle accuracy of the magnetic encoder.

[0052] According to the evaluation results of handling properties and thickness accuracy in Table 1, both Sample 4 and Sample 5 showed good results. Here, referring to the maximum particle size in the particle size distribution of the rare earth magnet powder, it can be seen that the maximum particle size in Sample 4 and Sample 5 is smaller than the maximum particle size in Samples 1 to 3.

[0053] Here, when the ratio R of the thickness T (mm) of the green body (samples 1 to 5) to the maximum particle size G (μm) of the rare earth magnet powder in each sample 1 to 5 is T / G, as shown in Table 1, the ratio is about 2.82 for sample 1, about 3.92 for sample 2, about 4.44 for sample 3, and about 6.67 for samples 4 to 5. Based on this, considering the evaluation results of the handling property and thickness accuracy in Table 1, the thickness T of the sample is preferably about 4.5 times or more of the maximum particle size of the rare earth magnet powder, and more preferably about 6.7 times or more of the maximum particle size of the rare earth magnet powder.

[0054] In addition, according to the evaluation results of handling properties and thickness accuracy in Table 1, the optimal particle size of rare earth magnet powder is 45μm to 225μm, preferably 45μm to 150μm. It should be noted that when the particle size of rare earth magnet powder is less than 45μm, there is a hidden danger that it is easy to get stuck in the gap (clearance) between molds and difficult to form. In addition, if the particle size of rare earth magnet powder exceeds 150μm, cracks and gaps will occur in the green body, so it is not expected.

[0055] It should be noted that, in the above-mentioned embodiment, a vernier-type axial magnetic encoder having two magnetic tracks concentrically formed in an annular rare earth bonded magnet is described, but a magnetic encoder having one magnetic track can also be applied. In addition, a radial magnetic encoder having a magnetic track formed on the outer peripheral surface of a cylindrical rare earth bonded magnet can also be applied.

[0056] Description of Reference Numerals

[0057] 1: magnetic encoder; 2: main track; 3: secondary track; 4: unmagnetized area; 5: sensor module; 6A, 6B: magnetic sensors; A: inner diameter; B: outer diameter.

Claims

1. A magnetic encoder, which is an annular magnetic encoder, wherein rare earth magnet powder and resin are mixed and compressed to form an unheated body, and the resin contained in the unheated body is thermally cured to form a thermally cured body, and the annular magnetic encoder has a magnetic track obtained by magnetizing magnetic poles that are different from each other in the circumferential direction at a predetermined magnetic pole pitch, wherein: When the ratio R is set to T / G and the thickness of the unheated body is set to T and the maximum particle size of the rare earth magnet powder is set to G, the ratio R is greater than 6.67 and the particle size of the rare earth magnet powder is 45μm to 150μm, wherein the unit of T is mm and the unit of G is μm.

2. The magnetic encoder according to claim 1, wherein: The particle size of the rare earth magnet powder is 75 μm to 150 μm.

3. The magnetic encoder according to claim 1 or 2, wherein: The magnetic track includes a main magnetic track and a sub-magnetic track which are arranged concentrically, and the main magnetic track is located on the outer peripheral side of the sub-magnetic track with an unmagnetized area interposed therebetween.

4. The magnetic encoder according to claim 1 or 2, wherein: The rare earth magnet powder is rare earth iron system, ie, Nd—Fe—B system magnet powder.

5. The magnetic encoder according to claim 3, wherein: The rare earth magnet powder is rare earth iron system, ie, Nd—Fe—B system magnet powder.

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