Rotor, method for manufacturing the rotor, and brushless SPM motor

Abstract

By using anisotropic bonded magnets and achieving high output through high-speed rotation of over 200,000 rpm, we aim to reduce size, weight, and cost. [Solution] The rotor of the brushless SPW motor consists of a ring magnet having a maximum energy product of 10 MGOe or more, and a cylindrical iron-based magnetic material. The ring magnet is magnetized in a pseudo-anisotropic manner with four or more magnetic poles and alternating N and S poles via the magnetic material by injection molding of anisotropic bonded magnets. The ring magnet is fixed to the outer circumference of the rotor body by bonding strength due to mechanical, chemical, and magnetic bonding forces, thereby increasing resistance to centrifugal force.

Description

Technical Field

[0001] The present invention relates to a rotor in which a ring-shaped anisotropic bonded magnet is firmly fixed to the outer peripheral portion of a rotor, a method for manufacturing the rotor, and a brushless SPM motor.

Background Art

[0002] In recent years, for small motors for robots of brushless motors, products of Maxon in Switzerland are widely used, but there is a demand for making them smaller, lighter, higher in output, and lower in price by more than 50%. To increase the output, efforts have been made to increase the rotational speed, and in particular, weight reduction of small SPM motors using 200,000-rpm motors is required. In addition, as long as Nd sintered magnets are used, heat generation problems cannot be avoided in high-speed rotation, so compression-molded magnets and injection-molded magnets of bonded magnets are being developed.

[0003] Patent Document 1 discloses a compression-molded magnet, which is obtained by mixing a first magnet powder of NdFeB-based isotropic magnetic powder having a particle size of 20 μm and a second magnet powder having a peak particle size of 80 to 120 μm, followed by compression molding, impregnation with an impregnating resin, and curing. The adhesion is improved by a groove formed by knurling on the central portion of the shaft (rotor surface) having an anti-loosening effect in the axial direction. It is disclosed that it does not crack at 200,000 rpm. However, it is difficult to reduce the price because only a thick ring magnet of a cylindrical shape with a large amount of magnets can be produced, and a compression-molded magnet and a magnetization process over multiple steps are separately required. Also, the magnetic force of an isotropic bonded magnet is weak. Further, in compression molding, uniform molding is difficult due to compression by upper and lower punches, and the coaxiality decreases, making it easy to generate vibration during rotation.

[0004] Patent Document 2 describes an injection-molded magnet in the form of a thin ring, consisting of an anisotropic rare-earth bonded magnet, in which magnetic field orientation and magnetization are performed simultaneously during injection molding in an anisotropic mold. A sinusoidal waveform is achieved through polar anisotropic magnetization. The rotor surface has a roughness of 0.5 μm to 5 μm as a base, and corrugation processing, shot blasting, and application of metal adhesive are performed as needed. In addition to these mechanical holding forces, the magnetic force of stainless steel magnets increases the fixing force (bonding strength), and the document discloses that it has passed a 200,000 rotation test. However, stainless steel magnets consume large amounts of the rare resources Cr and Ni, and because they are manufactured by processing stainless steel at low temperatures, they become extremely hard. Therefore, drilling holes for the shaft after low-temperature processing requires electrical discharge machining, which is very expensive, making it difficult to reduce the price of stainless steel magnet rotors.

[0005] This invention achieves lower costs by employing an injection molding method in a magnetic field and replacing stainless steel magnets with inexpensive iron, while simultaneously achieving high output through high-speed rotation of 200,000 rpm, as well as miniaturization, weight reduction, and low cost. [Prior art documents] [Patent Documents]

[0006] [Patent Document 1] Japanese Patent Publication No. 2020-202369 [Patent Document 1] Patent No. 7426569 [Overview of the project] [Problems that the invention aims to solve]

[0007] Patent documents 1 and 2 disclose that rotors consisting of a shaft-integrated bonded magnet made by compression molding and impregnation resin around a shaft with knurling to improve adhesion, and rotors consisting of a rotor body with a surface treatment by metal adhesive, wave-shaped molding, and shot blasting, and an injection-molded body of anisotropic bonded magnets, have achieved 200,000 revolutions per minute.

[0008] However, the former method is costly due to the large amount of magnets and the need for multiple processes. In addition, the compression molding reduces the degree of coaxiality, causing wobble during rotation, making it difficult to achieve a stable 200,000 rpm. The latter issue presented challenges, including the use of expensive elements such as Cr and Ni in stainless steel magnets, the high cost of laminated steel plate rotor bodies, and the question of whether knurling or shot blasting could be applied to the outer surface of stainless steel magnets or laminated steel plate rotors, which are made of highly hard materials.

[0009] The present invention aims to provide a rotor capable of handling high speeds of 200,000 rpm with the objectives of improving performance, miniaturization, weight reduction, and cost reduction. The first approach involves using an iron-based magnetic material for the rotor and increasing the mechanical and chemical bonding strength between the magnetic powder and the anisotropic bonded magnet made of injection-molded resin via an adhesive (metal adhesive) between them. The second approach involves improving the magnetic bonding force between the iron-based magnetic material (metal) and the anisotropic bonded magnet to maintain motor torque. [Means for solving the problem]

[0010] The inventors conducted a preliminary investigation into the surface condition of the rotor body, which is made of iron, and the adhesion force between it and the bonded magnet. The rotor body was manufactured by machining an iron-based magnetic material made of S45C into an integrated shaft. The rotor body has a diameter of 6 mm and a length of 10 mm. Various surface conditions were prepared on the surface of the rotor body by performing knurling with flat and diagonal patterns, sandblasting with Al2O3 sand, coating with metallic resin, and combinations of these treatments.

[0011] The magnets used are NdFeB-based anisotropic bonded magnets manufactured by injection molding, with a thickness of 2 mm. To investigate the adhesion force, rotational tests were conducted on the unmagnetized magnets. The evaluation was performed by gradually increasing the rotational speed, and the rotational speed at which vibrations increased sharply was defined as the limit rotational speed. A higher limit rotational speed indicates better adhesion force.

[0012] Figure 1 shows the survey results. The rotor base material (a) before surface treatment rotates at 100,000 RPM, but after treatments such as knurling or coating with metallic resin, the rotation speed increases to 120,000 RPM to 150,000 RPM. Knurling creates a diagonal pattern, sandblasting creates larger, harder particles, and when these are combined with coating with metallic resin, a high rotation speed of 250,000 RPM can be achieved.

[0013] This invention was made in consideration of the results of preliminary investigations, and it was conceived that in order to achieve a rotational speed of 200,000 rpm or more, it is necessary to first increase the mechanical bonding force between the iron-based magnetic material (hereinafter referred to as iron) of the rotor body and the bonded magnet (magnetic powder and resin), then to enhance the magnetic coupling between the rotor body and the bonded magnet, and finally to improve the coaxiality and increase the number of magnetic poles.

[0014] To increase the mechanical bonding force, the bonding area between the iron and the bonded magnet, particularly the surface area of ​​the iron, is increased to enlarge the interface between the bonded magnet and the fluid resin, thereby suppressing fracture at the interface. Increasing the surface area of ​​iron is possible by creating irregularities on its surface, but there are limitations to using only large irregularities like those created by knurling or only small, spiky irregularities created by sandblasting. A composite surface with a combination of both, which can be expected to have a synergistic effect, can further increase the surface area (Figure 2).

[0015] Here, the spiky bumps are approximately 0.5 μm to 10 μm in size, while the magnetic powder of bonded magnets has an average particle size of 20 μm to 80 μm, or 100 μm to 200 μm, depending on the type. As a result, direct contact between the spiky iron protrusions and the magnetic particles of the bonded magnet causes interfacial fracture, preventing the full effect of increasing the surface area from being realized.

[0016] We found that the above problem can be solved by applying a metallic adhesive to the composite uneven surface with an enlarged surface area, thereby adding a chemical bonding force between the iron and the bonded magnet. Specifically, by applying a metallic resin to the spiky uneven surface and covering it with a resin layer, interfacial fracture caused by contact between the spiky iron convex surface and the magnetic powder of the bonded magnet can be eliminated (Figure 3). In addition, a chemical bond is formed between the resin of the bonded magnet and the metallic resin. By changing the rotor material from stainless steel magnets to iron, we confirmed that the hardness of the rotor surface decreased, allowing the above surface treatment to be performed effectively. A problem arose where the knurling die wore down rapidly when the surface hardness was Hv300 or higher. Based on the above, knurling, sandblasting, and coating of metallic resin on the surface of the iron rotor strengthens the mechanical and chemical bond, resulting in a greater adhesion between the rotor body and the bonded magnets.

[0017] Next, regarding increasing motor torque, we confirmed that by using injection-molded anisotropic bonded magnets and iron for the rotor, and then applying pseudo-polar anisotropic magnetization, an excellent magnetic circuit can be formed, and a large motor torque similar to that obtained with a stainless steel magnet rotor can be obtained. The above magnets strongly bonded magnetically to the rotor's iron, and in addition to the mechanical and chemical bonding forces, this further enhanced the centrifugal force resistance. Compared to products from Maxon of Switzerland, this technology improves the coaxiality of the rotor, enhances the contact between the magnet and the rotor, enables rotation at 200,000 RPM, and increases the number of magnetic poles of the magnet from 2 to 4 and then 6, while simultaneously increasing the magnetic force and motor torque by applying pseudo-anisotropic magnetization to anisotropic bonded magnets via magnetic materials.

[0018] Furthermore, by using an iron-based magnetic material with a magnetic strength of MS1.8 or higher for the rotor body, we successfully contributed to the formation of pseudo-polar anisotropy, thereby increasing the magnetic coupling force between the anisotropic bonded magnet and the iron-based magnetic material rotor body. Here, pseudo-axial anisotropy refers to the orientation where the magnetic poles of the ring magnet and the magnetic material of the rotor body (rotor core) are integrated and saturated magnetized in axial anisotropy, and the magnetic field emitted from the ring magnet has a sine waveform, enabling smooth rotation. (Fig. 4). In normal axial anisotropy, N and S poles are alternately formed on the surface of a thick ring isotropic magnet, and a magnetic flux path is formed between the poles. However, pseudo-axial anisotropy is defined as a thin ring anisotropic magnet and an iron-based magnetic material inside it, where N and S poles are alternately formed on the magnet surface, and a magnetic flux path is formed between the poles through the iron-based magnetic material. In a ring isotropic magnet, after molding the magnet, axial anisotropy magnetization can easily create a sine function magnetic field distribution between the surface poles. However, in the case of a ring anisotropic magnet, it is a very difficult task to align the anisotropic orientation of the magnet with that of the axial anisotropic magnetic flux path, and to form a magnetic flux path in the anisotropic magnet body and the isotropic iron-based magnetic material to finally create a sine function magnetic field distribution between the surface poles. The present invention was realized by successfully designing and manufacturing an axial anisotropy mold.

[0019] For manufacturing a rotor with excellent coaxiality, attention was paid to injection molding type anisotropic bonded magnets. A precision cylindrical rotor body part manufactured with high accuracy was attached to a precision mold for injection molding, and a bonded magnet was molded by injection molding technology in the gap. As a result, a rotor with extremely excellent coaxiality in terms of shape coaxiality, weight balance, and magnetic distribution balance can be manufactured.

[0020] The manufacturing method of pseudo-axial anisotropy magnetization of magnetic poles is to manufacture an anisotropic magnetization type injection molding mold pole. The injection molding conditions are a mold temperature and an injection temperature of 100 to 150°C, a molding pressure of 50 to 150 MPa, and an injection speed of 50 to 150 cm 3 / min. Here, the orientation magnetic field is 0.7 T or more. Usually, a magnetic field of 3 T is required to saturate magnetize a normal anisotropic bonded magnet. However, since the injection molding temperature is 100°C or higher, the coercive force of the magnet decreases to less than 0.7 T, and the magnet powder can be saturated magnetized with a magnetic field strength of 0.7 T, and the magnet can be oriented along the magnetic flux line. Furthermore, since the magnetic powder is saturated magnetized, the saturated magnetization state is maintained when the temperature drops to room temperature. As the temperature decreases, the magnetization of the magnet increases, reaching the magnetic force strength of a saturated magnetized magnet at room temperature. Anisotropic magnetic powder is oriented and saturated to pseudo-anisotropic by the magnetic force during molding, allowing for the production of pseudo-anisotropic magnets. In other words, the magnetization process after injection molding can be omitted.

[0021] Furthermore, the gap between the outer surface of the rotor's magnets and the inner surface of the stator's electromagnets was reduced from approximately 1.5 mm in conventional Maxon products to less than 0.5 mm. This was only possible thanks to the rotor's superior coaxiality.

[0022] In summary, by employing injection-molded anisotropic bonded magnets, improving centrifugal force resistance through increased mechanical and chemical bonding between the rotor body and bonded magnets, enhancing the sinusoidal magnetic field distribution and magnetic coupling by using iron-based magnetic materials with a high MS for the rotor body and pseudo-polar anisotropy of the bonded magnet's poles, increasing the number of magnetic poles from 2 to 4 or more, and reducing the gap between the rotor and stator to 0.5 mm, we have found that it is possible to achieve a rotor rotation speed of over 200,000 RPM and high output, resulting in a miniaturization and weight reduction of more than 50% compared to the widely used Maxon small motors.

[0023] Furthermore, material costs and processing costs can be reduced for the rotor body by changing from stainless steel magnets to iron, and from laminated steel plates to steel bars. In the case of anisotropic magnets, the same motor torque can be achieved whether the rotor material is stainless steel magnets to increase magnetic energy or iron material to increase MS and reduce magnetic resistance between anisotropic magnetic poles. In other words, the present invention makes it possible to significantly improve costs while maintaining performance compared to Patent Document 2. Compared to the product of Maxon of Switzerland, this invention reduces the amount of Nd magnet used to about one-quarter because only a thin layer of magnet is formed on the surface. Furthermore, Nd sintered magnets generate processing waste during the machining process on a cylindrical shape, resulting in the waste of rare and expensive rare earth elements. Injection-molded magnets utilize magnet powder, resulting in an excellent yield of nearly 100%, thus avoiding the waste of Nd resources. As a result, lower costs can be achieved.

[0024] The SPM motor of the present invention consists of a rotor as described above, a stator having coils evenly arranged around its outer circumference, and a yoke that forms a magnetic circuit on the outer circumference of the coils. The electromagnetic coil can be configured as needed, with or without teeth in the yoke. [Effects of the Invention]

[0025] This invention enables high output by achieving rotational speeds of 200,000 rpm or more compared to general-purpose small SPM motors, while also achieving a 50% reduction in size and weight. At the same time, the manufacturing cost of the rotor can be reduced to about one-tenth. [Brief explanation of the drawing]

[0026] [Figure 1] This figure shows the results of a preliminary investigation with a different surface treatment. [Figure 2] (a) A cross-section of a knurled surface, and (b) A surface of a sandblasted surface. [Figure 3] (c) This figure shows a cross-section of the resin layer of a metallic resin. [Figure 4] This is a plan view showing the magnetic field and N / S poles of the ring-shaped pseudo-anisotropic bonded magnet of the present invention. [Figure 5] This is a cross-sectional view of an SPM motor, which is a first embodiment of the present invention. [Figure 6] This is a cross-sectional view of a four-pole magnet attached to the rotor of the present invention, as seen from the axial direction. [Figure 7]This is a cross-sectional view of the rotor of the present invention, seen from the side. [Figure 8] (a) A comparison of photographs showing the appearance of the present invention and (b) a commercially available product. [Best Mode for Carrying Out the Invention]

[0027] The rotor of the brushless SPM motor, which is the first embodiment of the present invention, It comprises a shaft, a rotor body, and an anisotropic bonded magnet. The rotor body is made of an iron-based magnetic material having an MS (saturation magnetization) of 1.8T or higher and a hardness of Hv180 to Hv280. The surface of the rotor body has a knurled surface shape with spiky irregularities, and a resin layer made of metal adhesive is formed on the surface. The anisotropic bonded magnet is made of a mixture of anisotropic magnet powder and injection molding resin, and is fixed to the outer circumference of the rotor body. It has four or more even-numbered magnetic poles arranged alternately with north and south poles, and each magnetic pole is magnetized in a pseudo-anisotropic manner via the iron-based material. The rotor has an outer diameter of 20 mm or less and a length of 40 mm or less. The rotor is characterized by rotating at a rotational speed of 200,000 RPM or more.

[0028] The second embodiment of the rotor manufacturing method is: (1) Prepare a rotor body made of an iron-based magnetic material with an MS (saturation magnetization) of 1.8T or higher and a hardness of Hv180 to Hv280, into which the shaft is inserted. (2) A knurled pattern with a depth of 50 μm to 200 μm is formed on the surface of the rotor body by knurling. (3) The knurled surface having the diagonal pattern is sandblasted to create a surface with spiky irregularities of 0.5 μm to 10 μm. (4) Apply a metal adhesive to the surface of the unevenness to form a resin layer of 5 μm to 25 μm. (5) Magnetic field injection molding shall be performed using a permanent magnet type mold in a magnetic field, with an orientation magnetic field of 0.7T or higher, mold temperature and injection temperature of 100°C to 150°C, molding pressure of 50 MPa to 150 MPa, and injection speed of 50 cm 3 / min~150cm 3 Performed at a rate of / minutes. (6) Next, remove the rotor from the mold. It is characterized by the following:

[0029] The brushless SPM motor of the third embodiment is In a brushless SPM motor comprising a rotor and a stator manufactured by the rotor described in the first embodiment or the rotor manufacturing method described in the second embodiment, The gap between the rotor and the stator is 0.5 mm or less. The rotor rotates at a rotational speed of 200,000 RPM or more, and the brushless SPM motor has an output of 50W to 400W.

[0030] The following will provide a detailed explanation using Figures 2 to 8. <Brushless SPM Motor> As shown in Figure 5, the brushless SPM motor 1 consists of a rotor 2, a stator 3, and a shaft 4. Rotor 2 is described below.

[0031] <rotor> As shown in Figures 6 and 7, the rotor 2 consists of a shaft 63, a rotor body 61, and bonded magnets 62 (62N, 62S). The rotor body 62 is made of an iron-based magnetic material such as SC (carbon steel) with an MS (saturation magnetization) of 1.8T or higher and a hardness of Hv180 to Hv280. The MS (saturation magnetization) is high, exceeding 1.8T, for iron-based magnetic materials, contributing to the formation of polar anisotropy and increasing the coupling force between the anisotropic bonded magnet and the magnetic material rotor body. This generates a force that counteracts centrifugal force. This facilitates the saturation magnetization of the magnetic powder during the magnetic field molding of anisotropic bonded magnets.

[0032] The hardness is Hv180 to Hv280, preferably Hv200 to Hv250. In primary surface processing that forms irregularities by knurling and secondary surface processing that forms fine irregularities by sandblasting, if the hardness exceeds Hv300, the degree of irregularity formation becomes small, and if it is softer than Hv180, problems arise with the strength of the rotor.

[0033] While the rotor body can be manufactured from laminated steel sheets, surface treatments such as knurling and sandblasting are difficult. By forming a cylindrical ring from an iron-based magnetic material such as carbon steel, which has a saturation magnetization (MS) of 1.8T or higher and a hardness of Hv180 to Hv280, surface treatment processing becomes easier and costs can be reduced.

[0034] <Surface treatment of rotors> The surface of the rotor body has a knurled surface with spiky, uneven textures, and a resin layer made of metal adhesive is formed on this surface. Here, the combination of irregularities caused by diagonal knurling and spiky irregularities is referred to as a composite irregular surface. First, as shown in Figure 2, a knurling pattern is applied to the outer circumference of the rotor body. The knurling pattern has relatively large grooves with spacing of 0.2 mm to 1 mm and a height of 0.05 mm to 0.3 mm. This knurling increases the surface area of ​​the outer circumference by 1.2 to 1.5 times.

[0035] Sandblasting is performed on the knurled surface using hard sand such as Al2O3 with an average particle size of 30 μm to 70 μm. Figure 3 shows the shape of the knurled surface after this treatment. The surface consists of spiky irregularities ranging from 0.5 μm to 10 μm, and the surface area increases by 2 to 5 times. Due to the synergistic effect of the twill knurled surface and the spiky irregularities, it increases by 2.5 to 7 times. This can be attributed to the effect of a composite surface.

[0036] Figure 4 shows a resin layer made of metal adhesive, formed by applying and curing metal adhesive on a composite uneven surface. The types of metal adhesives used are engineering plastics such as polyphenyl sulfide (PPS) and nylon 6 (PA6), which are used as pellet materials for injection molding. Using the same resin ensures good bonding with the adhesive during injection molding, resulting in high bonding strength due to the integration of the metal adhesive and the bonded magnet.

[0037] The metal adhesive is applied along the knurled surface, covering the 0.5 μm to 10 μm spiky protrusions formed on the knurled surface, thus forming a resin layer 5 μm to 25 μm thick that covers the spiky protrusions. This enables strong adhesion between the metal adhesive and the surface of the iron-based magnetic material (metal), which has a large surface area formed by the spiky protrusions. Furthermore, when applying the metal adhesive, any dirt on the metal surface, such as processing oil from knurling or residual sand such as alumina sand, should be removed. Additionally, a surfactant may be applied to the composite surface beforehand if necessary.

[0038] <Anisotropic bonded magnets> For injection-molded anisotropic bonded magnets, it is preferable to have the best possible maximum energy product. Ideally, the present invention achieves the best properties by employing magnets with a maximum energy product of 10 MGOe to 25 MGOe. The magnetic powders used in anisotropic bonded magnets include rare-earth magnetic powders such as NdFeB, SmFe, and SmCo, as well as ferrite anisotropic powders. These can be a single type of magnetic powder or a combination of two or more types. In the case of two types of magnetic powders, a combination of magnetic powders with different particle sizes is also acceptable, for example, a magnetic powder with an average particle size of 100 μm to 200 μm and a magnetic powder with an average particle size of 20 μm to 80 μm. The rotor's surface magnets have at least four magnetic poles, which are alternately magnetized as north and south poles, and are saturated with pseudo-polar anisotropy via the magnetic material (Figure 4).

[0039] <Injection molding in magnetic field> Magnetic field injection molding is performed using a permanent magnet type mold in a magnetic field, with an orientation magnetic field of 0.7T or higher, mold temperature and injection temperature of 100°C to 150°C, molding pressure of 50 MPa to 150 MPa, and injection speed of 50 cm 3 / min~150cm 3 Perform the task per minute. This process results in extremely high dimensional accuracy, a symmetrical arrangement around the rotational axis of the main body, and the ability to control the gap between the stator and rotor to 0.5 mm or less. Depending on the control method, it may be possible to reduce this gap to 0.5 mm or less. Furthermore, the magnets are magnetized in a pseudo-anisotropic manner, resulting in a small demagnetizing field and the ability to draw out a relatively large magnetic flux.

[0040] The specific shape and size of the anisotropic bonded magnet—that is, its outer diameter, thickness, and length—are adjusted appropriately according to the basic specifications of the SPM motor, such as its output and size, and taking into account its rotational speed and centrifugal force. The motor output ranges from 50W to 400W, but the rotor's outer diameter is 20mm or less and its length is 40mm or less. Preferably, the rotor has a diameter of 8mm to 16mm, an inner diameter of 6mm to 12mm, a length of 5mm to 20mm, and uses 0.8g to 4g or less of magnets.

[0041] Regarding the bonding strength between the magnet and the rotor body against centrifugal force, it is necessary to further strengthen both the bonding strength of the adhesive and the magnetic coupling force due to pseudo-polar anisotropic magnetization, taking into account the motor output and rotational speed. This is achieved by making the outer surface of the rotor body a composite uneven surface.

[0042] Regarding the bonding strength of the surface magnets, whether or not they break depends on factors such as the uniformity of the magnets, the coaxiality of the rotor, and the bonding strength. Therefore, we actually attached a rotational speed test machine with a rotational speed of 200,000 RPM and evaluated it, confirming that the ring magnets did not break.

[0043] <Cost> The cost consists of the cost of manufacturing the magnetic material for the rotor body in a cylindrical ring shape, the cost of attaching the shaft to the hole in the center of the rotor body, and the cost of forming anisotropic bonded magnets on the outer circumference using an injection molding process. Because there are no complex and costly parts, precision assembly processes are unnecessary, the magnetization process can be omitted, and the amount of expensive rare earth elements used is small (less than 2g) or not used at all, it is thought that the manufacturing cost can be reduced to less than 1 / 10 of the manufacturing cost of conventional rotors.

[0044] <Motor Specifications> The output power is 50W to 400W, the rotor rotation speed is 200,000 RPM or more, the magnet weight is 4g or less, the number of magnetic poles is 4 or more, and the number of electromagnets on the stator side is 6 or more. The electromagnets on the stator side may be yoke-equipped or coreless without a yoke. [Examples]

[0045] <First Example> This is an example of a 100W output motor. The rotor body of the brushless SPM motor uses a cylindrical ring component made from an iron-based magnetic material, S45C, with a hole drilled in the shaft mounting area. The MS is 1.95 and the hardness is Hv220.

[0046] The motor rotates at 200,000 RPM. To ensure the bonding strength between the magnet and the rotor body against centrifugal force, considering the motor output and rotational speed, the outer surface of the rotor body is made into a composite uneven surface. A metal adhesive (PPS) is applied to this surface to cover the spiky convex surface (the rotor surface) with resin, forming a resin layer. This layer then bonds with the resin of the injection-molded magnet, ensuring high bonding strength. The knurling process involved spacing the grooves 0.8 mm apart, a depth of 0.16 mm, and a bevel angle of 30 degrees. Sandblasting with 50 μm particle size Al2O3 was performed on the knurled surface, creating spiky bumps ranging from 0.7 μm to 8 μm. A 15 μm thick layer of metallic resin PPS was then applied to cover these bumps.

[0047] The injection-molded magnetic anisotropic bonded magnets used were NdFeB-based with a maximum energy product of 18 MGOe. The rotor's surface magnets had four poles, which were alternately magnetized as north and south poles, and saturated in anisotropic manner. Furthermore, these magnets were formed in an injection molding process, resulting in extremely high dimensional accuracy. They were also arranged symmetrically around the rotational axis of the main body, resulting in a gap of 0.3 mm between the stator and rotor. The specific shape and size of the magnets were as follows: rotor diameter 11 mm, rotor body diameter 7 mm, magnet thickness 2 mm, length 7.5 mm, and magnet weight 1 g.

[0048] The conditions for injection molding in a magnetic field are as follows: The mold is a permanent magnet type mold operating in a magnetic field. The orientation magnetic field is 0.9T, and the mold temperature and injection temperature are 130°C. The molding pressure is 90 MPa, and the injection speed is 80 cm. 3 It was done in minutes. This polar anisotropic magnetization means that the magnetic coupling force between the iron-based magnetic material of the rotor body and the anisotropic bonded magnets, along with the aforementioned mechanical and chemical coupling forces, contributes to high-speed rotation.

[0049] Regarding the bonding strength of the anisotropic bonded magnets, we evaluated them by actually attaching a rotation speed test machine with a rotation speed of 200,000 RPM, and all 10 rotors used in the experiment passed the test. The final test rotation speed ranged from 220,000 to 250,000 revolutions per minute.

[0050] Regarding costs, the cost of manufacturing the rotor body's magnetic material as a cylindrical ring of S45C steel bar is 50 yen, the cost of attaching the rotating shaft to the central hole of the rotor body is 40 yen, the cost of forming the rare-earth anisotropic bonded magnet on the outer circumference by injection molding is 100 yen, and the cost of using the expensive rare-earth material is 80 yen for 1.1g, totaling 270 yen. This is considered to be about 1 / 10th the manufacturing cost of the conventional rotor, which is estimated to be 3000 yen.

[0051] The motor specifications of the present invention are as follows: output 100W, motor size 18mm in diameter, 30mm in length, weight 50g, rotor rotation speed 200,000 RPM, magnet weight 1g or less, number of magnetic poles 4, and number of electromagnets on the stator side 6. The electromagnets on the stator side are coreless without a yoke (Figure 8(a)).

[0052] Maxon's 100W motor has a diameter of 19mm, a length of 30mm, a weight of 100g, a rotor rotation speed of 60,000 RPM, a magnet weight of 4.3g, 2 magnetic poles, and 3 electromagnets on the stator side. The invention achieves a 50% reduction in size and weight, as well as a significant reduction in cost (Figure 8(b)).

[0053] <Second Example> In the first embodiment, using a motor output of 200W as an example, the rotor diameter was set to 15mm, the inner diameter to 9mm, the magnet thickness to 3mm, the length to 10mm, and the amount of magnet used to 2g. Although the centrifugal force increased, a rotor rotation speed of 200,000 RPM was achieved. [Industrial applicability]

[0054] The use of small motors for robots is rapidly increasing, but at the same time, there is a demand for smaller size, lighter weight, and lower cost. This invention enables a 50% reduction in size and weight compared to conventional products, and also significantly reduces manufacturing costs, so it is expected to have a wide range of applications in various robots in the future. [Explanation of Symbols]

[0055] 1: Results of preliminary investigation (rotational speed limit) 2a: Knurled product 21: recessed part, 22: convex part 2b: Sandblasted product 31: Spiky protrusions, 32: Spiky recesses 3: Products coated with metallic resin 31: Spiky protrusions, 33: Resin layer of metallic adhesive (solidified product) 4: Rotor 41: Rotor body, 42N: North pole of anisotropic bonded magnet, 42S: South pole of anisotropic bonded magnet, 43: Shaft, 5: Brushless SPM motor 51: Rotor, 52: Stator, 53: Shaft 6: Rotor 61: Rotor body, 6: Anisotropic bonded magnet, 62N: North pole of anisotropic bonded magnet, 62S: South pole of anisotropic bonded magnet, 63: Shaft

Claims

1. The rotor of a brushless SPM motor comprises a shaft, a rotor body, and an anisotropic bonded magnet. The rotor body is made of an iron-based magnetic material having an MS (saturation magnetization) of 1.8T or higher and a hardness of Hv180 to Hv280. The surface of the rotor body has a knurled surface shape with spiky irregularities, and a resin layer made of metal adhesive is formed on the surface. The anisotropic bonded magnet is made of a mixture of anisotropic magnet powder and injection molding resin, and is fixed to the outer circumference of the rotor body. It has four or more even-numbered magnetic poles arranged alternately with north and south poles, and each magnetic pole is magnetized in a pseudo-anisotropic manner via the iron-based magnetic material. The rotor has an outer diameter of 20 mm or less and a length of 40 mm or less. The rotor is characterized by rotating at a rotational speed of 200,000 RPM or more.

2. The method for manufacturing a rotor as described in claim 1 is: (1) Prepare a rotor body made of an iron-based magnetic material with an MS (saturation magnetization) of 1.8T or higher and a hardness of Hv180 to Hv280, into which the shaft is inserted. (2) A twill pattern with a depth of 50 μm to 200 μm is formed on the surface of the rotor body by knurling. (3) The knurled surface having the twill pattern is sandblasted to create a surface with spiky irregularities of 0.5 μm to 10 μm. (4) Apply a metal adhesive to the surface of the unevenness to form a resin layer of 5 μm to 25 μm, (5) Magnetic field injection molding shall be performed using a permanent magnet type mold in a magnetic field, with an orientation magnetic field of 0.7 T or higher, a mold temperature and injection temperature of 100°C to 150°C, a molding pressure of 50 MPa to 150 MPa, and an injection speed of 50 cm ３ / min~150cm ３ Performed at a rate of / minutes. (6) Next, remove the rotor from the mold. A method for manufacturing a rotor, characterized by the following features.

3. A brushless SPM motor comprising a rotor and a stator manufactured by the rotor described in claim 1 or the rotor manufacturing method described in claim 2, The gap between the rotor and the stator is 0.5 mm or less. The brushless SPM motor is characterized in that the rotor rotates at a rotational speed of 200,000 RPM or more, and the brushless SPM motor has an output of 50W to 400W.

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