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

Abstract

To increase the output by high-speed rotation of 200,000 revolutions or more using an anisotropic bonded magnet, and to achieve miniaturization, weight reduction, and cost reduction. 【Solution means】The rotor of a 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 with a pseudo-polar anisotropy with four or more poles and N and S poles alternatingly through the magnetic material by injection molding of an anisotropic bonded magnet. The ring magnet is fixed to the outer peripheral part of the rotor body with a bonding strength by mechanical, chemical, and magnetic bonding forces to enhance the centrifugal force resistance.

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, among small motors for robots of brushless motors, products of Maxon in Switzerland are widely used, but more than 50% of them are required to be smaller, lighter, have higher output, and be lower in price. For the increase in output, efforts are made by increasing the rotational speed, and in particular, weight reduction of a small SPM motor using a 200,000-rpm motor is required. In addition, as long as it is based on an Nd sintered magnet, since the problem of heat generation cannot be avoided in high-speed rotation, 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 compression-molding using a magnet powder 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, and then impregnating with an impregnating resin and curing. The adhesion is improved by a groove formed by knurling having an anti-loosening effect in the axial direction at the center of the shaft (rotor surface). It is disclosed that it does not crack at 200,000 revolutions. However, it is difficult to reduce the price because only a thick-ring magnet of a cylindrical shape with a large amount of magnet 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 for vibration to occur during rotation.

[0004] Patent Document 2 discloses an injection-molded magnet of a thin ring made of an anisotropic rare-earth bonded magnet, in which magnetic field orientation and magnetization are simultaneously performed during injection molding in an anisotropic mold. A sinusoidal waveform is realized by extreme anisotropic magnetization. The rotor surface is based on an unevenness of 0.5 μm to 5 μm, and waveform processing, shot blasting, and application of a metal adhesive are performed as necessary. In addition to these mechanical holding forces, the adhesive force (bonding strength) is increased by the magnetic force of a stainless-steel magnet, and passing 200,000 revolutions is disclosed. However, stainless-steel magnets consume large amounts of rare resources Cr and Ni, and since they are manufactured by cold working stainless steel, they become very hard. Therefore, drilling for the shaft after cold working requires electrical discharge machining drilling, which is very expensive, and it is difficult to reduce the cost of stainless-steel magnet rotors.

[0005] The present invention is an invention that aims to reduce costs by changing from an injection molding method in a magnetic field and a stainless-steel magnet to inexpensive iron, while achieving high output, miniaturization, weight reduction, and low cost by high-speed rotation of 200,000 revolutions.

Prior Art Documents

Patent Documents

[0006]

Patent Document 1

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0007] Patent Document 1 and Patent Document 2 disclose that rotors composed of a shaft-integrated bonded magnet by compression molding~impregnated resin, a rotor body surface-treated by a metal adhesive, a waveform, and shot blasting around a shaft subjected to knurling processing to improve adhesion, and an injection molded body of an anisotropic bonded magnet have achieved 200,000 revolutions.

[0008] However, the former has a large amount of magnets and requires multiple processes, resulting in high costs. In addition, the coaxiality decreases due to compression molding, and vibration occurs during rotation, making it difficult to achieve a stable rotation of 200,000 revolutions per minute. Next, for the latter, there are problems such as the use of expensive elements such as Cr and Ni in stainless steel magnets, the high cost of the rotor body of the laminated steel plate type, and whether it is possible to perform knurling or shot blasting on the outer peripheral surface of the rotor made of stainless steel magnets or laminated steel plates with high hardness.

[0009] The present invention aims to provide a rotor capable of corresponding to a high speed of 200,000 revolutions per minute for the purpose of high performance, miniaturization, weight reduction, and cost reduction. As a measure, first, an iron-based magnetic material is adopted for the rotor, and the mechanical and chemical bonding strength between the anisotropic bonded magnet made of magnetic powder and injection molding resin is increased through an adhesive (metal adhesive) between the two. Second, the magnetic bonding force between the iron-based magnetic material (metal) and the anisotropic bonded magnet is improved, which is an issue for maintaining motor torque.

Means for Solving the Problems

[0010] The inventors preliminarily investigated the adhesion between the surface state of the rotor body made of iron and the bonded magnet. The rotor body was manufactured by machining in a shaft-integrated type using an iron-based magnetic material made of S45C. The diameter of the rotor body is 6 mm and the length is 10 mm. On the surface of the rotor body, knurling with flat patterns and twill patterns, sandblasting with Al 2 O 3 sand, application treatment of metallic resin, and combined treatment of these were performed to prepare various surface states.

[0011] For the magnet, an NdFeB-based anisotropic bonded magnet by an injection molding method was used, and its thickness is 2 mm. For the investigation of adhesion, the magnet was subjected to a rotation test in an unmagnetized state. The evaluation was carried out by gradually increasing the rotation speed, and the rotation speed at which the vibration increased rapidly was defined as the limit rotation speed. The larger this limit rotation speed is, the better the adhesion.

[0012] The survey results are shown in Fig. 1. The rotor base material (a) before surface treatment rotates at 100,000 RPM. However, when treatments such as knurling or application of metallic resin are performed, the rotational speed increases significantly from 120,000 RPM to 150,000 RPM. In knurling, the pattern is ridged, and in sandblasting, the hard particles are large. In the surface state where these are combined with the application treatment of metallic resin, a large rotational speed of 250,000 RPM is obtained.

[0013] The present invention has been made in view of the results of preliminary investigations. In order to achieve a rotational speed of 200,000 revolutions per minute or more, first, it is necessary to 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). Next, it is to enhance the magnetic coupling between the rotor body and the bonded magnet. And it was conceived that improving the coaxiality and increasing the number of magnetic poles are effective.

[0014] In order to increase the mechanical bonding force, it is to increase the bonding area between iron and the bonded magnet, particularly to increase the surface area of iron to enlarge the interface with the fluid resin of the bonded magnet and suppress the fracture at the interface. The expansion of the surface area of iron can be achieved by forming irregularities on its surface. However, there are limitations with only large irregularities such as knurling or only small, spiky irregularities due to sandblasting. A composite irregular surface that can expect a synergistic effect by combining the two can expand the surface area more (Fig. 2).

[0015] Here, for the spiky irregularities of about 0.5 μm to 10 μm, the magnetic powder of the bonded magnet has an average particle size of 20 μm to 80 μm or an average particle size of 100 μm to 200 μm depending on its type. For this reason, when the convex portions of the spiky iron come into direct contact with the magnetic particles of the bonded magnet, interface fracture occurs, and the effect of expanding the surface area cannot be fully exerted.

[0016] It has been found that the above problems 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 iron and the bonded magnet. That is, by applying a metallic resin to the spiky unevenness and covering it with a resin layer, interfacial failure due to the contact between the convex surface of the spiky iron and the magnetic powder of the bonded magnet can be eliminated (Fig. 3). In addition, a chemical bond is formed between the resin of the bonded magnet and the metallic resin. By changing the material of the rotor from a stainless steel magnet to iron, it was confirmed that the hardness of the rotor surface decreased and the above surface treatment could be effectively performed. There was a problem that when the surface hardness was 300 Hv or more, the wear of the knurling die became severe. From the above, by performing knurling, sandblasting, and application treatment of a metallic resin on the surface of the iron rotor, the mechanical and chemical bonds are strengthened and a large adhesive force between the rotor body and the bonded magnet can be obtained.

[0017] Next, regarding the motor torque increase, by adopting an injection molding type anisotropic bonded magnet for the magnet and iron for the rotor, and subjecting it to pseudo-polar anisotropic magnetization, it was confirmed that an excellent magnetic circuit can be formed and a large motor torque similar to that of a stainless steel magnet rotor can be obtained. The above magnet is strongly magnetically bonded to the iron of the rotor, added to the mechanical and chemical bonding forces, and the centrifugal force resistance characteristics can be further improved. Compared with the products of Maxon in Switzerland, this technology aims to improve the coaxiality of the rotor, enhance the adhesion between the magnet and the rotor, enable rotation at 200,000 RPM, and at the same time increase the number of magnetic poles of the magnet from 2 poles to 4 poles and 6 poles. By subjecting the anisotropic bonded magnet to pseudo-polar anisotropic magnetization through a magnetic material, the magnetic force is increased to achieve motor torque increase.

[0018] In addition, by using an iron-based magnetic material of MS1.8 or more for the rotor body, it contributed to the formation of pseudo-polar anisotropy and succeeded in increasing the magnetic bonding force between the anisotropic bonded magnet and the rotor body of the iron-based magnetic material. Here, pseudo-axial anisotropy refers to an orientation property in which 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 sinusoidal waveform, enabling smooth rotation. (Figure 4). In general, axial anisotropy is formed by alternately forming N and S magnetic poles on the surface of a thick ring isotropic magnet, and forming a magnetic flux path between the magnetic poles. However, pseudo-axial anisotropy is defined as alternately forming N and S magnetic poles on the surface of a thin ring anisotropic magnet and its inner side made of an iron-based magnetic material, and forming a magnetic flux path between the magnetic poles through the iron-based magnetic material. In a ring isotropic magnet, after the magnet is molded, axial anisotropy magnetization can easily create a sinusoidal magnetic field distribution between the surface magnetic 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 sinusoidal magnetic field distribution between the surface magnetic 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 cylindrically shaped rotor component manufactured with high precision was attached to a precision mold for injection molding, and a bonded magnet was molded in the gap by injection molding technology. Thereby, 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 set to 0.7 T or more. Generally, a magnetic field of 3 T is required to saturate magnetize an 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. Moreover, since the magnet powder is saturated magnetized, when the temperature drops to room temperature, the saturated magnetization state is maintained. As the temperature decreases, the magnetization of the magnet improves and reaches the strength of the magnetic force when saturated magnetized at room temperature. The anisotropic magnetic powder can be oriented and saturated in the pseudo-pole anisotropy by the magnetic force during molding, enabling the production of pseudo-pole anisotropic magnets. That is, the magnetization process after injection molding can be omitted.

[0021] Furthermore, the gap between the outer peripheral side surface of the rotor magnet and the inner peripheral side surface of the stator electromagnet is reduced from about 1.5 mm of the conventional product of Maxon to 0.5 mm or less. This is only possible due to the excellent coaxiality of the rotor.

[0022] As described above, by adopting the injection molding type anisotropic bonded magnet, improving the centrifugal force resistance by increasing the mechanical and chemical bonding between the rotor body and the bonded magnet, adopting an iron-based magnetic material with a large MS for the rotor body and pseudo-pole anisotropization of the poles of the bonded magnet to enhance the sine function magnetic field distribution and magnetic coupling, increasing the number of poles from 2 poles to 4 poles or more, and combining the factors such as reducing the gap between the rotor and the stator to 0.5 mm, it is possible to rotate the rotor at a speed of 200,000 RPM or more and achieve higher output, and it has been found that it is possible to reduce the size and weight by more than 50% of the widely used small motor of Maxon.

[0023] Also, for the rotor body, the material cost and processing cost can be reduced by changing from a stainless steel magnet to iron, or from a laminated steel plate to a bar steel. In the pseudo-pole anisotropic magnet, the same motor torque can be achieved when the rotor material is a stainless steel magnet and the magnetic energy is increased, and when the iron material has a large MS to reduce the magnetic resistance between the anisotropic poles. That is, the present invention can maintain the performance and enable a significant cost improvement compared to Patent Document 2. Compared with the products of Maxon in Switzerland, for the magnet, only a thin magnet is formed on the surface, so the usage amount of Nd magnet is reduced by about 1 / 4. Also, in the stage of machining the Nd sintered magnet on a cylinder, machining scraps are generated, resulting in waste of rare earth elements that are rare and expensive. The injection molding type magnet uses magnet powder, so the yield is almost 100% and it is very excellent, and waste of Nd resources can be avoided. Due to these, cost reduction can be achieved.

[0024] The SPM motor of the present invention consists of a stator having the rotor described above, coils evenly arranged around its outer periphery, and a yoke that forms a magnetic circuit on the outer peripheral side of the coils. For the electromagnetic coil, appropriately, when the yoke includes teeth in the coil, the case without teeth can be selected.

Advantages of the Invention

[0025] According to the present invention, for a general-purpose small SPM motor, a rotation speed of 200,000 revolutions or more can be achieved to increase the output, and a 50% reduction in size and weight can be realized. At the same time, the manufacturing cost of the rotor can be reduced to about 1 / 10.

Brief Description of the Drawings

[0026]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Figure 6

Figure 7

Figure 8

Best Mode for Carrying Out the Invention

[0027] The rotor of the brushless SPM motor according to the first embodiment of the present invention comprises a shaft, a rotor body, and an anisotropic bonded magnet, wherein the rotor body An iron-based magnetic material in the shape of a cylinder processed from a bar steel having an MS (saturation magnetization) of 1.8 T or more and a hardness of Hv180 to Hv280, The surface of the rotor body having irregularities of 0.5 μm to 10 μm formed by sandblasting has a shape of a cross-hatched knurled surface with jagged irregularities, and a resin layer is formed on the surface by a metal adhesive, The anisotropic bonded magnet is composed of a mixture of anisotropic magnet powder and resin for injection molding, and is fixed to the outer peripheral portion of the rotor body, has magnetic poles of an even number of 4 or more poles arranged alternately with N poles and S poles, and each magnetic pole is magnetized with pseudo-pole anisotropy through the iron-based material, The size of the rotor is such that the outer diameter is 20 mm or less and the length is 40 mm or less, The rotor rotates at a rotational speed of 200,000 RPM or more.

[0028] The manufacturing method of the rotor according to the second embodiment (1) Prepare a rotor body of an iron-based magnetic material in which a shaft is inserted and the MS (saturation magnetization) is 1.8 T or more and the hardness is Hv180 to Hv280 and having a cylindrical shape processed from a bar steel (2) Form a cross-hatched pattern with a depth of 50 μm to 200 μm on the surface of the rotor body by knurling, (3) By sandblasting the knurled surface having the cross-hatched pattern, the surface is made into a jagged surface with irregularities of 0.5 μm to 10 μm, (4) Apply a metal adhesive to the surface of the irregularities to form a resin layer of 5 μm to 25 μm, (5) Injection molding in a magnetic field uses a permanent magnet type magnetic field mold. The orientation magnetic field is 0.7 T or more, the mold temperature and injection temperature are 100°C to 150°C, the molding pressure is 50 MPa to 150 MPa, and the injection speed is 50 cm 3 / min to 150 cm 3 / min, and (6) Next, the rotor is taken out of the mold. It is characterized by this.

[0029] The brushless SPM motor of the third embodiment is In a brushless SPM motor composed of a rotor manufactured by the method for manufacturing a rotor described in the first embodiment or a rotor manufactured by the method for manufacturing a rotor described in the second embodiment and a stator, 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 is characterized by having an output of 50 W to 400 W.

[0030] This will be described in detail below with reference to FIGS. 2 to 8. <Brushless SPM Motor> As shown in FIG. 5, the brushless SPM motor 1 is composed of a rotor 2, a stator 3, and a shaft 4. The rotor 2 will be described below.

[0031] <Rotor> As shown in FIGS. 6 and 7, the rotor 2 is composed 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 a hardness of Hv180 to Hv280 at an MS (saturation magnetization) of 1.8 T or more. MS (saturation magnetization) is as high as 1.8 T or more in the case of iron-based magnetic materials, contributes to the formation of magnetic anisotropy, increases the bonding force between the anisotropic bonded magnet and the magnetic material rotor body, and generates a force to resist centrifugal force. It facilitates the saturation magnetization of the magnet powder in the magnetic field molding of the anisotropic bonded magnet.

[0032] The hardness is Hv180 to Hv280. Preferably, it is Hv200 to Hv250. In the primary surface treatment for forming unevenness by knurling or the secondary surface treatment for forming fine unevenness by sandblasting, when the hardness exceeds Hv300, the degree of unevenness formation becomes small, and when it is too soft at Hv180 or less, there will be a problem with the strength of the rotor.

[0033] Note that the rotor body can also be manufactured from laminated steel plates, but surface treatment processes such as knurling and sandblasting are difficult. By forming a cylindrical ring shape of an iron-based magnetic material such as carbon steel where MS (saturation magnetization) is 1.8 T or more and the hardness is Hv180 to Hv280, surface treatment processing becomes easy and cost reduction is possible.

[0034] <Surface treatment of the rotor> The surface of the rotor body has a shape of a knurled surface with spiky unevenness, and a resin layer is formed on the surface by a metal adhesive. Here, the combination of the unevenness by knurling and the spiky unevenness is called a composite uneven surface. First, as shown in FIG. 2, knurling is performed on the outer peripheral portion of the rotor body. The interval between the knurling lines is 0.2 mm to 1 mm, and the height is a relatively large uneven surface of 0.05 mm to 0.3 mm. The surface area of the outer peripheral portion increases by 1.2 times to 1.5 times due to this knurling.

[0035] On the uneven surface of this knurling, sandblasting is performed using hard sand such as Al 2 O 3 with an average particle size of 30 μm to 70 μm. The shape of the knurled surface after this treatment is shown in FIG. 3. The surface state consists of spiky unevenness of 0.5 μm to 10 μm, the surface area increases by 2 times to 5 times, and due to the synergistic effect of the uneven surface of the knurling and the spiky unevenness, it increases by 2.5 times to 7 times. This can be said to be the effect of the composite uneven surface.

[0036] Figure 4 shows a resin layer made of a metal adhesive formed by applying and curing a metal adhesive on a composite uneven surface. The types of metal adhesives are engineering plastics such as polyphenylene sulfide (PPS) and nylon 6 (PA6) used for pellet materials for injection molding. By using the same resin, it is well compatible with the bond during injection molding, and a large bonding strength can be obtained by integrating the metal adhesive and the bond magnet.

[0037] The metal adhesive is applied along the uneven surface of the knurling process and is applied to cover the 0.5 μm to 10 μm spike-like unevenness formed on the uneven surface of the knurling process, that is, a resin layer with a thickness of 5 μm to 25 μm that covers the spike-like convex surface is formed. Thereby, a large adhesive force is enabled by the bonding between the surface of the iron-based magnetic material (metal) having a large surface area formed by the spike-like unevenness and the metal adhesive. In the application of the metal adhesive, it is necessary to remove dirt on the metal surface, such as processing oil during the knurling process and residues of sand such as alumina sand. Also, a surfactant may be applied to the composite uneven surface in advance if necessary.

[0038] <Anisotropic Bond Magnet> For the injection molding type anisotropic bond magnet, it is preferable that the maximum energy product is as excellent as possible. Desirably, the present invention can achieve the most excellent characteristics by adopting those having 10 MGOe to 25 MGOe. The magnetic powder of the anisotropic bond magnet is a rare earth-based magnetic powder such as NdFeB-based, SmFe-based, SmCo-based, and ferrite anisotropic powder. These may use one type of magnetic powder or a combination of two or more types of magnetic powder. Also, in the case of two types of magnetic powder, a combination of magnetic powders with different particle sizes, 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 may be used. The number of magnetic poles of the surface magnet of the rotor is at least 4 poles or more, which are magnetized alternately as N poles and S poles, and are pseudo-pole anisotropically saturated magnetized through a magnetic material (Figure 4).

[0039] <Injection Molding in Magnetic Field> Injection molding in magnetic field uses a permanent magnet type mold in a magnetic field. The orientation magnetic field is 0.7 T or more, the mold temperature and injection temperature are 100°C to 150°C, the molding pressure is 50 MPa to 150 MPa, and the injection speed is 50 cm 3 / min to 150 cm 3 / min. Through this process, the dimensional accuracy is extremely excellent, and it is symmetrically arranged around the rotation center axis of the main body. The gap between the stator and the rotor can be controlled to be 0.5 mm or less. It is also possible to make the gap 0.5 mm or less by the control method. In addition, the magnet is magnetized with pseudo-polar anisotropy, has a small demagnetizing field, and can extract a relatively large magnetic flux.

[0040] The specific shape and size of the anisotropic bonded magnet, that is, the outer diameter, thickness, and length of the anisotropic bonded magnet, are appropriately adjusted according to the basic specifications such as the output of the SPM motor and the motor size, and considering its rotation speed and centrifugal force. The motor output ranges from 50 W to 400 W, but the outer diameter of the rotor is 20 mm or less and the length is 40 mm or less. Preferably, the rotor can be realized with a diameter of 8 mm to 16 mm, an inner diameter of 6 mm to 12 mm, a length of 5 mm to 20 mm, and a magnet usage of 0.8 g to 4 g or less.

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

[0042] Regarding the bonding strength of the surface magnet, whether it breaks or not is determined by the uniform finish of the magnet, the coaxiality of the rotor, the bonding strength, etc. Therefore, an actual rotational speed tester with a rotation speed of 200,000 RPM was installed for evaluation, and it was confirmed that the ring magnet did not break.

[0043] <Cost> Regarding the cost, it consists of the cost of manufacturing the magnetic material of the rotor body in the shape of a cylindrical ring, the cost of attaching the shaft to the hole at the center of the rotor body, and further the cost of forming anisotropic bonded magnets on the outer peripheral portion by an injection process. Since there are no costly and complex-structured parts, no precision assembly process is required, the magnetization process can be omitted, and the amount of expensive rare earth used is less than or equal to 2 g or not used at all, it is considered that it can be manufactured at a manufacturing cost of 1 / 10 or less of the manufacturing cost of the rotors of conventional products.

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

Example

[0045] <First embodiment> This is an example of a 100 W output motor. For the body of the rotor of the brushless SPM motor, a cylindrical ring part with a shaft mounting part drilled from a round bar of S45C as an iron-based magnetic material was adopted. The MS is 1.95 and the hardness is Hv220.

[0046] The rotation speed of the motor is 200,000 RPM. Regarding the bonding strength between the magnet and the rotor body against centrifugal force, considering the motor output and rotation speed, the outer peripheral surface of the rotor body was made into a composite uneven surface, and a metal adhesive (PPS) was applied thereon, and the jagged convex surface (the surface of the rotor) was covered with resin to form a resin layer, and the resin of the injection-molded magnet was joined to the resin there to ensure a large bonding strength. The interval between the lines in the knurling process is 0.8 mm, the depth is 0.16 mm, and the inclination angle is 30 degrees. On the unevenness of the knurled surface, sandblasting with Al 2 O 3 with a particle size of 50 μm was performed to form jagged unevenness of 0.7 μm to 8 μm. PPS of metallic resin was applied so as to cover this convex surface to form a resin layer with a thickness of 15 μm.

[0047] For the injection molding type of magnetically anisotropic bonded magnet, an NdFeB-based magnet with a maximum energy product of 18 MGOe was adopted. The number of magnetic poles of the surface magnet of the rotor was set to 4 poles, magnetized alternately to N poles and S poles, and saturated magnetized with pole anisotropy. Moreover, these magnets were molded in the injection molding process, with extremely excellent dimensional accuracy, arranged symmetrically around the central rotation axis of the main body, and the gap between the stator and the rotor was set to 0.3 mm. Regarding the specific shape and size of the magnet, for the rotor, the diameter was 11 mm, the diameter of the rotor main body was 7 mm, the thickness of the magnet was 2 mm, the length was 7.5 mm, and the magnet usage was 1 g.

[0048] The conditions for injection molding in a magnetic field are as follows. The mold is a permanent magnet type mold in a magnetic field. The orientation magnetic field is 0.9 T, the mold temperature and the injection temperature are 130 °C. The molding pressure is 90 MPa, and the injection speed is 80 cm 3 / min. Due to this pole anisotropic magnetization, the magnetic binding force between the iron-based magnetic material of the rotor main body and the anisotropic bonded magnet also contributes to high-speed rotation together with the above-mentioned mechanical and chemical binding forces.

[0049] Regarding the bonding strength of the anisotropic bonded magnet, as a result of actually evaluating by attaching a rotational speed tester with a rotation speed of 200,000 RPM, all 10 rotors used in the experiment passed. The final test rotation speed was from 220,000 rotations to 250,000 rotations.

[0050] Regarding the cost, the cost of manufacturing the magnetic material of the rotor main body in the shape of a cylindrical ring of bar steel S45C is 50 yen, the cost of attaching the rotating shaft to the hole in the center of the rotor main body is 40 yen, and further the cost of forming a rare earth anisotropic bonded magnet on the outer peripheral part in the injection process is 100 yen. Moreover, the usage amount of expensive rare earth is 1.1 g, at 80 yen, and it is considered that it can be manufactured at a manufacturing cost of about 1 / 10 of the estimated manufacturing cost of 3000 yen for the rotor of the conventional product, which is a total of 270 yen.

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

[0052] The 100 W motor of Maxon has a motor size of diameter 19 mm, length 30 mm, weight 100 g, rotor rotation speed 60,000 RPM, magnet weight 4.3 g, number of magnetic poles 2 poles, and number of electromagnets on the stator side 3 poles. It can be seen that the product of the invention has achieved a 50% reduction in size and weight and a significant cost reduction (Fig. 8(b)).

[0053] <Second Embodiment> Taking the motor output of the first embodiment as 200 W as an example, the diameter of the rotor is 15 mm, inner diameter 9 mm, magnet thickness 3 mm, length 10 mm, and magnet usage 2 g. Although the centrifugal force increases, a rotor rotation speed of 200,000 RPM was obtained.

Industrial Applicability

[0054] The usage of small motors for robots is increasing rapidly, and at the same time, miniaturization, weight reduction, and cost reduction are required. The present invention enables a 50% reduction in size and weight compared to conventional products and can significantly reduce the manufacturing cost. It is expected to be widely applied to various robots in the future.

Explanation of Reference Numerals

[0055] 1: Results of preliminary investigation (rotation speed limit) 2a: Knurled product 21: Concave part, 22: Convex part 2b: Sandblasted product 31: Jagged convex part, 32: Jagged concave part 3: Coated product of metallic resin 31: Jagged convex part, 33: Resin layer of metallic adhesive (solidified product) 4: Rotor 41: Rotor body, 42N: N pole of anisotropic bonded magnet, 42S: S 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: N pole of anisotropic bonded magnet, 62S: S pole of anisotropic bonded magnet, 63: Shaft

Claims

1. The rotor of the 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 a cylindrical shape processed from a steel bar with MS (saturation magnetization) of 1.8 T or more and hardness of Hv180 to Hv280. The surface of the rotor body is formed by sandblasting to have a twill knurled surface shape having spiky irregularities of 0.5 μm to 10 μm, and a resin layer made of a metal adhesive is formed on the surface, The anisotropic bonded magnet is made of a mixture of anisotropic magnet powder and a resin for injection molding, and is fixed to the outer periphery of the rotor body, The magnet has an even number of magnetic poles, four or more, which are alternately arranged with N poles and S poles, and each magnetic pole is magnetized with pseudopolar anisotropy 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 in that it rotates at a rotational speed of 200,000 RPM or more.

2. The manufacturing method of a rotor according to claim 1 includes the steps of: (1) Prepare a rotor body made of an iron-based magnetic material having a cylindrical shape and made of a processed steel bar having a MS (saturation magnetization) of 1.8 T or more and a hardness of Hv180 to Hv280, into which a shaft is inserted; (2) A twill pattern having a depth of 50 μm to 200 μm is formed on the surface of the rotor body by knurling, (3) The surface of the knurled surface having the twill pattern is sandblasted to have a thorn-like uneven surface of 0.5 μm to 10 μm; (4) Applying a metal adhesive to the uneven surface to form a resin layer of 5 μm to 25 μm; (5) Injection molding in a magnetic field is performed using a permanent magnet type magnetic mold, with an orientation magnetic field of 0.7 T or more, 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 / min, (6) The rotor is then removed from the mold. A method for manufacturing a rotor comprising the steps of:

3. A brushless SPM motor comprising a rotor and a stator manufactured by the rotor manufacturing method according to claim 1 or the rotor manufacturing method according to claim 2, 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.

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