Coated magnetic material and magnetic encoder

Abstract

This coated magnetic material comprises: an annular magnetic material body including magnetic particles and a resin cured product of a thermosetting resin; and a coating film covering the magnetic material body. The coated magnetic material has two end surfaces extending in the radial direction, and an inner peripheral surface and an outer peripheral surface disposed between the two end surfaces in the axial direction. The two end surfaces form reference surfaces parallel to each other, or the outer peripheral surface and the inner peripheral surface are coaxial.

Description

Coated magnetic material and magnetic encoder

[0001] The present invention relates to a coated magnetic body and a magnetic encoder.

[0002] Patent Document 1 describes a magnet body in which the entire surface of a bonded magnet made of rare earth iron-based alloy magnetic powder and a synthetic resin binder is covered with a rust-preventive coating. In Patent Document 1, the rare earth iron-based alloy magnetic powder is Nd—Fe—B or Sm—Fe—N magnetic powder with an average particle size of 10 to 100 μm, either alone or in combination. The rust-preventive coating is formed using a thermoplastic resin that does not contain tin.

[0003] JP 2009-074124 A

[0004] However, the magnet body of Patent Document 1 is difficult to position during magnetization.

[0005] Therefore, an object of the present invention is to provide a coated magnetic body that can be positioned easily and accurately during magnetization.

[0006] In order to solve the above-mentioned problems and achieve the object, a coated magnetic body according to one embodiment of the present invention comprises an annular magnetic body containing magnetic particles and a cured resin of a thermosetting resin, and a coating film covering the magnetic body, and comprises two end faces extending radially, and an inner peripheral surface and an outer peripheral surface located between the two end faces in the axial direction, wherein the two end faces form reference planes parallel to each other, or the outer peripheral surface and the inner peripheral surface are coaxial.

[0007] The coated magnetic body according to one aspect of the present invention can be positioned easily and accurately during magnetization.

[0008] FIG. 1-1 is a diagram illustrating the coated magnetic body of the first embodiment. FIG. 1-2 is a diagram illustrating the coated magnetic body of the first embodiment. FIG. 1-3 is a diagram illustrating the coated magnetic body of the first embodiment. FIG. 2 is a diagram illustrating the sizing process. FIG. 3 is a diagram illustrating the magnetic encoder of the first embodiment. FIG. 4-1 is a diagram illustrating the coated magnetic body of the second embodiment. FIG. 4-2 is a diagram illustrating the coated magnetic body of the second embodiment. FIG. 4-3 is a diagram illustrating the coated magnetic body of the second embodiment. FIG. 5 is a diagram illustrating the sizing process. FIG. 6 is a diagram illustrating the magnetic encoder of the second embodiment.

[0009] Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. However, the present invention is not limited to these embodiments. Furthermore, the components in the following embodiments include those that are easily replaceable by those skilled in the art, or those that are substantially the same.

[0010] In this specification, unless otherwise specified, the coated magnetic body includes the coated magnetic body before magnetization and the coated magnetic body after magnetization. In addition, the magnetic body contained in the coated magnetic body before magnetization is also referred to as the object to be magnetized, and the magnetic body contained in the coated magnetic body after magnetization is also referred to as the magnetized body.

[0011] <Coated Magnetic Body of Embodiment 1> Figures 1-1, 1-2, and 1-3 are diagrams illustrating the coated magnetic body of Embodiment 1. Figure 1-2 is a cross-sectional view taken along the line X-X in Figure 1-1. Before magnetization, the coated magnetic body 1 includes an annular magnetic body 2 (object to be magnetized) and a coating film (hereinafter referred to as the "coating film 4") covering the magnetic body 2. Therefore, the coated magnetic body 1 before magnetization is also annular. That is, before magnetization, the coated magnetic body 1 includes two end faces 101 and 102 extending in the radial direction, and an outer peripheral surface 103 and an inner peripheral surface 104 located between the two end faces 101 and 102 in the axial direction A. Furthermore, in the coated magnetic body 1 before magnetization, the two end faces 101 and 102, the outer peripheral surface 103, and the inner peripheral surface 104 are formed by continuous flat surfaces of the coating film 4. Here, the two end faces 101, 102 form a surface (i.e., a reference surface) that is parallel to each other. As will be described later, the reference surface is the surface that faces the sensor and the surface that is fixed to the base when the magnetic encoder is manufactured. Specifically, in this specification, the end faces 101, 102 forming surfaces that are parallel to each other means that the parallelism is ±0.2 mm or less.

[0012] Because the coated magnetic body 1 before magnetization has a high degree of parallelism, it can be positioned accurately and easily on a magnetizing device during magnetization, for example, during UHM magnetization as disclosed in JP 2021-093521 A. Therefore, the coated magnetic body 1 before magnetization can be magnetized with high precision.

[0013] As described above, the magnetic body 2 is annular, having two radially extending end faces and an outer peripheral surface and an inner peripheral surface between the two end faces in the axial direction. The coating film 4 is formed on the two end faces, the outer peripheral surface, and the inner peripheral surface of the magnetic body 2, thereby forming the two end faces 101, 102, the outer peripheral surface 103, and the inner peripheral surface 104 of the coated magnetic body 1. The magnetic body 2 includes magnetic particles and a cured thermosetting resin. Typically, the magnetic body 2 includes a plurality of magnetic particles. The magnetic body 2 also includes Ce as a rare earth. That is, the magnetic particles include Ce as a rare earth. The magnetic body 2 also preferably includes a rare earth other than Ce as a rare earth, with Ce being contained in an amount of 20% by weight or more relative to 100% by weight of the rare earths. That is, the magnetic particles preferably further contain a rare earth other than Ce as a rare earth, with Ce being contained in an amount of 20% by weight or more relative to 100% by weight of the rare earth. Examples of rare earths other than cerium (Ce) include lanthanum (La), praseodymium (Pr), and neodymium (Nd). Praseodymium (Pr) and neodymium (Nd) may be contained as didymium (PrNd alloy, an alloy of praseodymium and neodymium). Specifically, the magnetic particles are preferably Nd—Fe (iron)—B (boron) based magnetic powder, and contain Ce as a rare earth. Furthermore, an epoxy resin is preferably used as the thermosetting resin.

[0014] The coating film 4 is preferably an epoxy resin coating film (cured coating film). The decomposition temperature of the coating film 4 is usually 300°C or less, specifically 250°C or more and 300°C or less.

[0015] The Curie temperature of the magnetic body 2 is preferably below the decomposition temperature of the coating film 4. In this specification, the Curie temperature of the magnetic body 2 refers to the Curie temperature of the magnetic particles contained in the magnetic body 2. Because the magnetic particles contain Ce as a rare earth, specifically the above-mentioned amount of Ce, the Curie temperature of the magnetic body 2 can be lowered to below the decomposition temperature of the coating film 4. Incidentally, UHM magnetization, as disclosed in JP 2021-093521 A, involves heating an object to be magnetized above the Curie point of the magnetic powder and continuously applying a magnetizing magnetic field to the object to be magnetized using a permanent magnet as a field source while cooling it below the Curie point. If the Curie temperature of the magnetic body 2 is below the decomposition temperature of the coating film 4, the coating film 4 will not decompose even when heated during UHM magnetization, and deformation or peeling of the coating film 4 will not occur. In this way, the shape of the coated magnetic body 1 after magnetization remains the same as that of the coated magnetic body 1 before magnetization, and the two end faces 101, 102 remain parallel to each other. Therefore, the coated magnetic body 1 is magnetized with high precision. Furthermore, when a magnetic encoder is manufactured using the magnetized coated magnetic body 1, it can be assembled with high precision. Furthermore, the obtained magnetic encoder has excellent rotation angle detection precision.

[0016] Specifically, in the coated magnetic body 1 after magnetization, the magnetic body 2 (magnetized body) has multiple magnetic regions arranged in the radial direction, and each of the multiple magnetic regions has multiple magnetic poles arranged in the circumferential direction. Figure 1-3 shows the magnetic body 2 (magnetized body) in the coated magnetic body 1 after magnetization. That is, it is a diagram of the coated magnetic body 1 after magnetization with the coating film 14 removed. For example, as shown in Figure 1-3, the magnetic body 2 (magnetized body) has a vernier structure in which two concentric magnetic tracks (main track 11 and sub-track 12) are formed on one end face 101. Specifically, in the axial direction, the main track 11 is magnetized circumferentially at a predetermined magnetic pole pitch on the outer periphery, and the sub-track 12 is magnetized circumferentially at a predetermined magnetic pole pitch on the inner periphery. 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 detecting the magnetic track of the magnetic encoder is limited, the magnetic pole pitch of the magnetic track formed on the magnetic body 2 (magnetized body) is set to the same width as the magnetic pole width of the magnetic sensor. For example, the predetermined pitch is 0.4 mm or more and 2.4 mm or less, more specifically, 1.28 mm. Furthermore, the magnetic body 2 (magnetized body) has, on the end surface, non-magnetized regions or regions generating a weaker magnetic flux than the magnetized regions (hereinafter referred to as "non-magnetized regions 13") between the main track 11 and the sub-track 12 and on the inner side of the sub-track 12. For example, the magnetic body 2 (magnetized body) has a thickness of 0.2 mm or more and 1 mm or less.

[0017] Here, the manufacturing method of the coated magnetic body of embodiment 1 will be described. First, magnetic particles and the components constituting the cured resin in the magnetic body 2 (raw material components of the cured resin) are mixed in a predetermined ratio to prepare a compound. It is assumed that the ratio of the magnetic particles to the raw material components of the cured resin is the same as the ratio of the magnetic particles to the cured resin in the magnetic body 2 after preparation. Raw material components for the cured resin include a thermosetting resin binder (e.g., epoxy resin) and a curing agent. Furthermore, a small amount of lubricant (e.g., calcium stearate) may be added when preparing the compound. Specifically, the lubricant may be mixed in an amount of 0.02 wt % or more but less than 0.5 wt % relative to the total weight of the raw material components of the magnetic particles and the cured resin (100 wt %). Next, the compound is filled into the cavity of a mold and compressed under a predetermined pressure to prepare a ring-shaped green body.

[0018] Next, the uncured green body removed from the mold is subjected to a sizing process. FIG. 2 is a diagram illustrating the sizing process. The sizing device 40 includes a base plate 42 and a pressing plate 44. A green body 48 is set in the sizing device 40 together with a spacer 46. The surface of the pressing plate 44 that contacts the green body 48 and the surface of the base plate 42 that contacts the green body 48 have a high degree of parallelism. For example, the parallelism of the two surfaces that contact the green body is ±0.2 mm or less. The pressing plate 44 applies pressure to the green body 48, deforming it into a predetermined shape and dimensions. By using the base plate 42 and pressing plate 44 described above, the parallelism of the two end faces of the final magnetic body 2 and the two end faces 101, 102 of the coated magnetic body 1 can be maintained at ±0.2 mm or less. Furthermore, since the green body is deformed during the sizing process, it is preferable that the height dimension of the green body is slightly larger than the desired dimension of the finally obtained magnetic body 2. Furthermore, portions where high precision in parallelism is not required (for example, the outer diameter and inner diameter) are provided as reliefs.

[0019] The sized green body is then placed in an oven and thermally cured at a predetermined temperature for a predetermined time to produce a cured body (thermoset) containing magnetic particles and a cured resin.

[0020] Next, a coating film 4 is formed on the surface of the cured body as a rust prevention means for preventing oxidation, thereby obtaining a coated magnetic body 1 including a magnetic body 2 (object to be magnetized). For example, the coating film 4 is formed by a known means using an epoxy resin.

[0021] Next, as shown in FIG. 1-3, a vernier system is constructed in which two concentric magnetic tracks are formed on one end face of the magnetic body 2 (object to be magnetized) in the axial direction of the coated magnetic body 1. Specifically, for the magnetic body 2 (object to be magnetized), a main track 11 is magnetized circumferentially on the outer periphery with a predetermined magnetic pole pitch, and a sub-track 12 is magnetized circumferentially on the inner periphery with a predetermined magnetic pole pitch. If 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 on the magnetic body 2 (object to be magnetized) is set to the same width as the magnetic pole width of the magnetic sensor. Magnetization is so-called magnetization, and can be performed, for example, by UHM magnetization as disclosed in JP 2021-093521 A. That is, the magnetization can be performed by heating the object to be magnetized to a temperature above the Curie point of the magnetic powder, and then continuously applying a magnetizing magnetic field to the object to be magnetized using a permanent magnet as a field source while the object is cooled to a temperature below the Curie point. Since the sub-tracks are located more inward than the main tracks, the magnetic pole pitch is set to correspond to the inner diameter position of the detection section of the sub-track of the magnetic sensor. In this way, a magnetized coated magnetic body 1 having a magnetic body 2 (magnetized object) is obtained.

[0022] In the above example, the green body is sized and then thermally cured. Alternatively, sizing and thermal curing may be performed simultaneously. Specifically, the green body (uncured state) may be heated to a temperature at which the binder resin softens and melts using a sizing device, while being pressurized and deformed using the sizing device. Also, in the above example, the green body is deformed by applying pressure using a pressing plate during sizing. Alternatively, the green body may be deformed by the weight of the pressing plate during sizing. Specifically, the green body (uncured state) may be heated to a temperature at which the binder resin softens and melts using the sizing device, while being pressurized and deformed using the weight of a pressing plate provided in the sizing device.

[0023] <Magnetic Encoder of Embodiment 1> Figure 3 is a diagram for explaining the magnetic encoder of Embodiment 1. The magnetic encoder 10 includes a magnetized coated magnetic body 1. The magnetized coated magnetic body 1 has, in an axial direction A, two end faces 101, 102, an outer circumferential surface 103 connected to the two end faces 101, 102, and an inner circumferential surface 104 connected to the two end faces 101, 102. Here, the axial direction A coincides with the axial direction of a rotating shaft of, for example, a motor to which the magnetic encoder is fixed.

[0024] The magnetic encoder 10 further includes a sensor 6 and a base 8. In the axial direction A, one end face 101 of the two end faces faces the sensor 6, and the other end face 102 of the two end faces is fixed to the base 8. As described above, the shape of the coated magnetic body 1 after magnetization remains the same as that of the coated magnetic body 1 before magnetization, and the two end faces 101, 102 remain parallel to each other. Therefore, when a magnetic encoder is manufactured using the magnetized coated magnetic body 1, it can be assembled with high precision. Furthermore, the obtained magnetic encoder 10 has excellent rotation angle detection precision.

[0025] <Coated Magnetic Body of Embodiment 2> Figures 4-1, 4-2, and 4-3 are diagrams illustrating the coated magnetic body of Embodiment 2. Figure 4-2 is a cross-sectional view taken along the line X-X in Figure 4-1. The coated magnetic body 1' before magnetization includes an annular magnetic body 2 (object to be magnetized) and a coating film 4 covering the magnetic body 2. Therefore, the coated magnetic body 1' before magnetization is also annular. That is, the coated magnetic body 1' before magnetization includes two end faces 101', 102' extending in the radial direction, and an outer peripheral surface 103' and an inner peripheral surface 104' located between the two end faces 101', 102' in the axial direction A. Furthermore, in the coated magnetic body 1 before magnetization, the two end faces 101', 102', the outer peripheral surface 103', and the inner peripheral surface 104' are formed by the continuous flat surface of the coating film 4. Here, the outer peripheral surface 103' and the inner peripheral surface 104' are coaxial. Specifically, in this specification, the outer peripheral surface 103' and the inner peripheral surface 104' being coaxial means that the coaxiality is within ±0.2 mm.

[0026] Because the coated magnetic body 1' before magnetization has high coaxiality, it can be accurately and easily positioned on a magnetizing device during magnetization, for example, during UHM magnetization as disclosed in JP 2021-093521 A. Therefore, the coated magnetic body 1' before magnetization can be magnetized with high precision.

[0027] As described above, the magnetic body 2 is annular, having two radially extending end faces and an outer peripheral surface and an inner peripheral surface between the two end faces in the axial direction. The coating film 4 is formed on the two end faces, the outer peripheral surface, and the inner peripheral surface of the magnetic body 2, thereby forming two end faces 101', 102', an outer peripheral surface 103', and an inner peripheral surface 104' of the coated magnetic body 1'. The magnetic body 2 includes magnetic particles and a cured thermosetting resin. Typically, the magnetic body 2 includes multiple magnetic particles. The magnetic body 2 also includes Ce as a rare earth. That is, the magnetic particles include Ce as a rare earth. The magnetic body 2 also preferably includes a rare earth other than Ce as a rare earth, with Ce being contained in an amount of 20% by weight or more relative to 100% by weight of the rare earths. That is, the magnetic particles preferably further contain a rare earth other than Ce as a rare earth, with Ce being contained in an amount of 20% by weight or more relative to 100% by weight of the rare earth. Details of the rare earth and specific examples of the magnetic particles are the same as those in the case of the coated magnetic body of embodiment 1. Furthermore, an epoxy resin is preferably used as the thermosetting resin.

[0028] The coating film 4 is preferably an epoxy resin coating film (cured coating film). The decomposition temperature of the coating film 4 is usually 300°C or less, specifically 250°C or more and 300°C or less.

[0029] The Curie temperature of the magnetic body 2 is preferably below the decomposition temperature of the coating film 4. As with the coated magnetic body of embodiment 1, the magnetic particles of the coated magnetic body of embodiment 2 also contain Ce as a rare earth, specifically in the amount described above. Therefore, the Curie temperature of the magnetic body 2 can be lowered to below the decomposition temperature of the coating film 4. As with the coated magnetic body of embodiment 1, in the coated magnetic body of embodiment 2, if the Curie temperature of the magnetic body 2 is below the decomposition temperature of the coating film 4, the coating film 4 will not decompose when heated during UHM magnetization, and deformation or peeling of the coating film 4 will not occur. Thus, the shape of the coated magnetic body 1' after magnetization remains unchanged from the coated magnetic body 1' before magnetization, and the outer peripheral surface 103' and the inner peripheral surface 104' remain coaxial. Therefore, the coated magnetic body 1' can be magnetized with high precision. Furthermore, when a magnetic encoder is manufactured using the magnetized coated magnetic body 1', it can be assembled with high precision. Furthermore, the obtained magnetic encoder has excellent rotation angle detection accuracy.

[0030] Specifically, in the coated magnetic body 1' after magnetization, the magnetic body 2 (magnetized body) has multiple magnetic regions aligned in the axial direction, and each of the multiple magnetic regions has multiple magnetic poles aligned in the circumferential direction. Figure 4-3 shows the magnetic body 2 (magnetized body) in the coated magnetic body 1' after magnetization. That is, it is a diagram of the coated magnetic body 1' after magnetization with the coating film 14 removed. For example, as shown in Figure 4-3, the magnetic body 2 (magnetized body) has a vernier structure in which two magnetic tracks (main track 11' and sub-track 12') are formed axially aligned on the outer peripheral surface 103'. Specifically, in the radial direction, the main track 11' is magnetized circumferentially with a predetermined magnetic pole pitch on the upper axial side, and the sub-track 12' is magnetized circumferentially with a predetermined magnetic pole pitch on the lower axial 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 on the magnetic body 2 (magnetized material) is set to the same width as the magnetic pole width of the magnetic sensor. For example, the predetermined pitch is 0.4 mm or more and 2.4 mm or less, more specifically, 1.28 mm. Furthermore, the magnetic encoder 10' has a non-magnetized region 13' between the main track 11' and the sub-track 12' on the outer circumferential surface.

[0031] Here, the manufacturing method of the coated magnetic body of the second embodiment will be described. The green body is prepared in the same manner as the coated magnetic body of the first embodiment. Next, the uncured green body is removed from the mold and subjected to a sizing process. Unlike the first embodiment, the second embodiment uses a sizing device 40 shown in FIG. 5 in which the inner surface of the spacer 46, which contacts the outer surface of the green body, and the outer surface of the spacer 50, which contacts the inner surface of the green body, have high coaxiality. For example, the coaxiality between the inner surface of the spacer 46 and the outer surface of the spacer 50 is ±0.2 mm or less. A green body 48 is placed in the sizing device 40 together with the spacers 46 and 50. The green body 48 is pressurized by a pressing plate 44 to deform it into a predetermined shape and dimensions. Here, the green body 48 is pressed by the pressing plate 44 so that the outer peripheral surface of the green body 48 is pressed against the inner peripheral surface of the spacer 46, and the inner peripheral surface of the green body 48 is pressed against the outer peripheral surface of the spacer 50. By using the spacers 46 and 50 described above, the outer peripheral surface and inner peripheral surface of the finally obtained magnetic body 2 and the outer peripheral surface 103' and inner peripheral surface 104' of the coated magnetic body 1' can be made to have a coaxiality of ±0.2 mm or less. Furthermore, because the green body is deformed during the sizing process, it is preferable that the height dimension of the green body be slightly larger than the desired dimension of the finally obtained magnetic body 2.

[0032] The sized green body is then placed in an oven and thermally cured at a predetermined temperature for a predetermined time to produce a cured body (thermoset) containing magnetic particles and a cured resin.

[0033] Next, a coating film 4 is formed on the surface of the cured body as a rust prevention measure to prevent oxidation, thereby obtaining a coated magnetic body 1' including the magnetic body 2 (object to be magnetized). For example, the coating film 4 is formed by a known means using an epoxy resin.

[0034] Next, as shown in FIG. 4-3, a vernier method is constructed in which two magnetic tracks are formed on the outer peripheral surface of the magnetic body 2 (object to be magnetized) in the coated magnetic body 1'. Specifically, in the radial direction, a main track is magnetized circumferentially at a predetermined magnetic pole pitch on the upper axial side, and a sub-track is magnetized circumferentially at a predetermined magnetic pole pitch on the lower axial side. If the main track is magnetized with n pole pairs, the sub-track 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 on the magnetic body 2 (object to be magnetized) is set to the same width as the magnetic pole width of the magnetic sensor. Magnetization is so-called magnetization, and the magnetization is similar to that in embodiment 1. In this way, a magnetized coated magnetic body 1' having a magnetic body 2 (object to be magnetized) is obtained.

[0035] In the second embodiment, as in the first embodiment, the sizing process and the thermal curing may be carried out simultaneously, and the green body may be deformed by the weight of the pressing plate during the sizing process.

[0036] <Magnetic Encoder of Embodiment 2> Figure 6 is a diagram illustrating a magnetic encoder of Embodiment 2. A magnetic encoder 10' includes a coated magnetic body 1' after magnetization. The coated magnetic body 1' after magnetization has, in an axial direction A, two end faces 101', 102', an outer circumferential surface 103' connected to the two end faces 101', 102', and an inner circumferential surface 104' connected to the two end faces 101', 102'. Here, the axial direction A coincides with the axial direction of a rotating shaft of, for example, a motor to which the magnetic encoder is fixed.

[0037] The magnetic encoder 10' further includes a sensor 6' and a base 8'. In the axial direction A, the outer peripheral surface 103' faces the sensor 6', and the inner peripheral surface 104' is fixed to the base 8'. As described above, the shape of the coated magnetic body 1' after magnetization remains the same as that of the coated magnetic body 1' before magnetization, and therefore the outer peripheral surface 103' and the inner peripheral surface 104' remain coaxial. Therefore, when a magnetic encoder is manufactured using the coated magnetic body 1' after magnetization, it can be assembled with high precision. Furthermore, the obtained magnetic encoder 10' has excellent rotation angle detection precision.

[0038] <Coated Magnetic Bodies and Magnetic Encoders of Other Embodiments> In the coated magnetic bodies of Embodiments 1 and 2, the magnetic body 2 contains Ce as a rare earth. In contrast, the magnetic body does not need to contain Ce as a rare earth (coated magnetic body of Embodiment 3). In this case, too, the coated magnetic body before magnetization has high parallelism, so that during magnetization, it can be accurately and easily positioned on a magnetizing device. Note that, in this case, too, a coated magnetic body magnetized with high precision can be obtained by using a magnetization method that does not involve heating. Furthermore, when a magnetic encoder is manufactured using the magnetized coated magnetic body, it can be assembled with high precision. Furthermore, the resulting magnetic encoder has excellent rotation angle detection precision.

[0039] In the coated magnetic bodies of Embodiments 1 and 2, the two end faces 101, 102, 101', and 102', the outer peripheral faces 103, 103', and the inner peripheral faces 104, 104' of the coated magnetic body 1 are formed by continuous flat surfaces of the coating film 4. In contrast, the coated magnetic body before magnetization only needs to have a coating film formed on at least one of the two end faces, the outer peripheral face, and the inner peripheral face (coated magnetic body of Embodiment 4). In this case, too, the coating film does not decompose, deform, or peel when heated during UHM magnetization. Therefore, a coated magnetic body magnetized with high precision can be obtained. Furthermore, when a magnetic encoder is fabricated using the magnetized coated magnetic body, it can be assembled with high precision. Furthermore, the resulting magnetic encoder has excellent rotation angle detection accuracy.

[0040] The magnetic encoders of the third and fourth embodiments are obtained by using the coated magnetic materials of the third and fourth embodiments instead of the coated magnetic materials of the first and second embodiments. Such magnetic encoders also have excellent rotation angle detection accuracy.

[0041] The present invention will be explained in more detail below based on examples, but the present invention is not limited to these examples.

[0042] [Examples] [Example 1] Isotropic Nd—Fe—B magnet powder (product name: MQP10-11HD, manufactured by Magnequench, containing 10.6 wt % Nd, 3.5 wt % Pr, and 14.1 wt % Ce; i.e., a total of 28.2 wt % rare earth) was used as the magnetic particles. It is believed that the type and amount of rare earth in the magnet powder are maintained in the magnetic body of the resulting coated magnetic body (1). Next, the isotropic Nd—Fe—B magnet powder was mixed with raw materials for a cured resin (manufactured by Pelnox, model number XW2310), including an epoxy resin binder resin and a curing agent, to prepare a compound. The rare earth magnet powder and raw materials for the cured resin were mixed so that the resulting annular magnetic body would contain 75 vol % magnetic particles and 25 vol % cured resin. The compound was prepared by mixing the raw material components of the cured resin dissolved in a solvent with rare earth magnet powder, evaporating the solvent, and then crushing and classifying the mixture. The compound was then filled into a mold cavity and compressed under a predetermined pressure to produce a ring-shaped green body. The uncured green body was then removed from the mold and subjected to a sizing process. A sizing device 40, as shown in FIG. 2, was used. The parallelism between the surface of the pressing plate 44 contacting the green body and the surface of the base plate 42 contacting the green body was within ±0.2 mm. A green body 48 was placed in the sizing device 40 together with a spacer 46. The pressing plate 44 applied pressure to the green body 48, deforming it into the desired shape and dimensions. The sized green body was then placed in an oven and thermally cured at a predetermined temperature (150°C) for a predetermined time to produce a cured body (thermoset). The inner diameter, outer diameter, and thickness of the cured body were unchanged from those of the green body that had been subjected to sizing. Next, a coating film was formed using an epoxy resin on the entire surface of the cured body, resulting in a coated magnetic body including a magnetic body (object to be magnetized). The coated magnetic body had an outer diameter of φ29 mm, an inner diameter of φ16.5 mm, and a thickness of 0.3 mm. Next, as shown in Figure 1-3, a vernier system was constructed in which two concentric magnetic tracks were formed on one axial end face of the magnetic body (object to be magnetized) in the coated magnetic body.Specifically, in the axial direction, the main track was magnetized circumferentially on the outer periphery with a predetermined magnetic pole pitch, and the sub-track was magnetized circumferentially on the inner periphery with a predetermined magnetic pole pitch. The main track was magnetized with 32 pole pairs, and the sub-track was magnetized with 31 pole pairs. In this example, since a magnetic sensor with a magnetic pole width limited to 1.28 mm was used, the main track of the magnetic body (magnetized object) was magnetized to 1.28 mm. Magnetization is so-called magnetization, and the magnetization method is, for example, as disclosed in JP 2021-093521 A, in which the object to be magnetized is heated to above the Curie point of the magnet powder and then cooled to below the Curie point, continuously applying a magnetizing magnetic field to the object to be magnetized using a permanent magnet as a field source. Note that since the sub-track is located more inward than the main track, the magnetic pole pitch is set to correspond to the inner diameter position of the magnetic sensor's sub-track detection section. In this way, a coated magnetic body (1) containing rare earth magnet powder and a cured thermosetting resin was produced, and having magnetic tracks formed by magnetizing multiple magnetic poles at a predetermined pitch around the circumferential direction of the magnetic body surface. The coated magnetic body (1) had an outer diameter of 29 mm, an inner diameter of 16.5 mm, and a thickness of 0.3 mm, and was unchanged from before magnetization. The coating film also remained unchanged compared to before magnetization.

[0043] [Example 2] The same procedure as in Example 1 was carried out up to the point where a cured body (thermoset body) was obtained, except that isotropic Nd-Fe-B magnet powder (product name: MQP14-12, manufactured by Magnequench, containing 26.0 wt% Nd, i.e., containing a total of 26.0 wt% rare earths) was used as the magnetic particles. Next, a coating film was formed using an epoxy resin on the entire surface of the cured body, and a coated magnetic body (2) including a magnetic body (object to be magnetized) was obtained. The coated magnetic body (2) had an outer diameter of φ29 mm, an inner diameter of φ16.5 mm, and a thickness of 0.3 mm.

[0044] [Example 3] A coating film was formed using an epoxy resin on the entire surface of the cured body, and the process was repeated as in Example 1 until a coated magnetic body including a magnetic body (object to be magnetized) was obtained. The coated magnetic body had an outer diameter of 29 mm, an inner diameter of 16.5 mm, and a thickness of 0.3 mm. Next, as shown in Figure 4-3, a vernier system was constructed in which two magnetic tracks were formed on the outer surface of the thermoset body. Specifically, in the radial direction, a main track was magnetized circumferentially at a predetermined magnetic pole pitch on the upper axial side, and a sub-track was magnetized circumferentially at a predetermined magnetic pole pitch on the lower axial side. The main track was magnetized with 32 pole pairs, and the sub-track was magnetized with 31 pole pairs. In this example, a magnetic sensor with a magnetic pole width limited to 1.28 mm was used, so the main track of the magnetic body (object to be magnetized) was magnetized to 1.28 mm. The magnetization is so-called magnetization. The magnetization method, as disclosed in JP 2021-093521 A, involves heating the object to above the Curie point of the magnet powder and continuously applying a magnetizing magnetic field to the object using a permanent magnet as a field source while cooling it below the Curie point. Since the sub-track is located below the main track, the magnetic pole pitch was set to correspond to the position of the sub-track detection unit of the magnetic sensor. In this way, a coated magnetic body (3) was produced, containing rare earth magnetic powder and a cured thermosetting resin, and having magnetic tracks formed by magnetizing multiple magnetic poles at a predetermined pitch around the circumferential direction of the magnetic body surface. The coated magnetic body (3) had an outer diameter of 29 mm, an inner diameter of 16.5 mm, and a thickness of 0.3 mm, and showed no change compared to before magnetization. The coating film also showed no change compared to before magnetization.

[0045] <Evaluation Method and Results> [Curie Temperature of Magnetic Body] The Curie temperature of the magnetic particles contained in the magnetic body was measured as follows. The Curie temperature was measured using a VSM (vibrating sample magnetometer). Specifically, the change in magnetization of magnetized rare earth magnet powder was measured using the VSM while increasing the temperature from room temperature. The temperature at which the magnetization became approximately 0 was taken as the Curie temperature.

[0046] [Decomposition temperature of coating film] The decomposition temperature of the coating film was measured as follows. Only the coating film after heat curing was subjected to thermal analysis, specifically thermogravimetry (TG), to evaluate the resin decomposition temperature. Specifically, the weight change of the resin coating was measured in an air atmosphere at a temperature rise rate of 10 (°C / min). The lower temperature at the maximum value of the weight change rate was taken as the resin decomposition temperature. For coated magnetic bodies (1) and (3), the Curie temperature of the magnetic body was below the decomposition temperature of the coating film, and the decomposition temperature of the coating film was below 300°C.

[0047] [Parallelism] The parallelism of the coated magnetic materials (1) and (2) obtained in Examples 1 and 2 was evaluated by the following method. A dial gauge or height gauge placed on a surface plate was brought into contact with the measurement surface, and the gauge was moved parallel to the surface plate to measure the parallelism from the amount of gauge deflection. The parallelism of the coated magnetic materials (1) and (2) obtained in Examples 1 and 2 was ±0.2 mm or less. The parallelism of the surface of the pressing plate 44 in contact with the green body 48 and the surface of the base plate 42 in contact with the green body 48 was also measured in the same manner as above. As a result, the parallelism was ±0.2 mm or less.

[0048] [Coaxiality] The coaxiality of the coated magnetic body (3) obtained in Example 3 was evaluated by the following method. Coaxiality requires measuring at least two or more circles and determining their center positions. In order to measure with high accuracy, the center positions of each circle were determined using a circularity measuring device, and the difference between them was taken as the coaxiality. The coaxiality of the coated magnetic body (3) obtained in Example 3 was ±0.2 mm or less. The coaxiality of the inner peripheral surface of the spacer 46 and the outer peripheral surface of the spacer 50 used in Example 3 was also measured in the same manner as above. As a result, the coaxiality was ±0.2 mm or less.

[0049] The coated magnetic bodies (1) and (3) obtained in Examples 1 and 3 were magnetized with high precision because positioning during magnetization could be performed easily and accurately. Furthermore, it is believed that a magnetic encoder obtained using these bodies will have excellent rotation angle detection precision. Incidentally, the coated magnetic body (2) obtained in Example 2 was also easy to position on a magnetizing device with high precision during magnetization. Furthermore, in this case too, it is believed that magnetization can be performed with high precision by using a magnetization method that does not involve heating. Furthermore, it is believed that a magnetic encoder obtained using this body will have excellent rotation angle detection precision.

[0050] 1, 1' Coated magnetic body, 2 Magnetic body, 4 Coating film, 6, 6' Sensor, 8, 8' Base, 10, 10' Magnetic encoder, 101, 102, 101', 102' End face, 103, 103' Outer circumferential surface, 104, 104' Inner circumferential surface, 11, 11' Main track, 12, 12' Sub-track, 13, 13' Non-magnetized area, 40 Sizing device, 42 Base plate, 44 Pressing plate, 46, 50 Spacer, 48 Green body

Claims

1. A coated magnetic body comprising: an annular magnetic body containing magnetic particles and a cured resin of a thermosetting resin; and a coating film covering the magnetic body; and comprising two end faces extending in a radial direction, and an inner peripheral surface and an outer peripheral surface located between the two end faces in the axial direction, wherein the two end faces form reference planes parallel to each other, or the outer peripheral surface and the inner peripheral surface are coaxial.

2. The coated magnetic body according to claim 1, wherein at least one of the two end faces, the inner peripheral surface and the outer peripheral surface is formed by a continuous flat surface of the coating film.

3. The coated magnetic body according to claim 1 or 2, wherein the magnetic body contains Ce as a rare earth, and the Curie temperature of the magnetic body is equal to or lower than the decomposition temperature of the coating film.

4. The coated magnetic body according to claim 3, wherein the decomposition temperature of the coating film is 300° C. or lower.

5. The coated magnetic body according to claim 3, wherein the magnetic body further contains a rare earth other than Ce as the rare earth, and the Ce content is 20% by weight or more relative to 100% by weight of the rare earth.

6. The coated magnetic body according to claim 1 or 2, wherein one of the two end faces and the outer circumferential face is a surface to be magnetized.

7. The coated magnetic body according to claim 1 or 2, wherein the coating film is an epoxy resin coating film.

8. The coated magnetic body according to claim 1 or 2, wherein the concentricity of the outer peripheral surface and the inner peripheral surface is ±0.2 mm or less.

9. The coated magnetic body according to claim 1 or 2, wherein the parallelism between one end face and the other end face of the two end faces is ±0.2 mm or less.

10. A magnetic encoder comprising: the coated magnetic body according to claim 1 or 2; a sensor; and a base, wherein one of the two end faces in the axial direction faces the sensor, and the other of the two end faces is fixed to the base.

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