JP7810974B2 - Brushless SPM motor and method for manufacturing its rotor - Google Patents

Description

The present invention relates to a surface permanent magnet synchronous machine (hereinafter referred to as an SPM motor) in which a ring-shaped rare earth anisotropic bonded magnet is fixed to the outer periphery of the rotor, as well as to the rotor and a method for manufacturing the rotor.

There are various types of electric motors (including generators, simply referred to as "motors"). Recently, with the development of inverter control and the widespread use of rare earth magnets with high magnetic properties, brushless motors have been attracting attention because they are energy-efficient, highly efficient, and offer the potential for high torque or high output.

Brushless motors can be broadly divided into surface permanent magnet motors (SPM), in which permanent magnets are arranged on the surface of the rotor, and interior permanent magnet motors (IPM), in which permanent magnets are embedded inside the rotor. SPM motors have excellent controllability and are mainly used in small motors. IPM motors are easy to obtain high output and are mainly used in power motors for power applications.

Miniature robot motors, which require excellent controllability, are widely made by Maxon, a Swiss company, but there is a demand for motors that are at least 50% smaller, lighter, more powerful, and less expensive. To achieve this, efforts have been made to reduce size, weight, and increase power through faster rotation, and motors with rotation speeds of 60,000 to 100,000 RPM have recently been successfully developed. However, attempts to achieve even higher rotation speeds face a major technical hurdle: the use of sintered neodymium magnets.

To solve this problem, Patent Document 1 discloses a polar-anisotropic rare earth bonded magnet and a permanent magnet motor. According to this invention, Sm—Fe—N based magnet powder is used as the rare earth magnet powder, which has a better aligning magnetic field than Nd—Fe—B based magnet powder, and has a maximum energy product of 3 to 14 MGOe.
The manufacturing method involves injection molding a ring-shaped magnet at a mold temperature of 80°C, and the magnet has eight magnetic poles arranged alternately with north and south poles, each of which is polar anisotropically magnetized without the use of a magnetic material, as shown in Figure 6.
However, the invention disclosed in Patent Document 1 has the drawback that the magnetic force is weak and the ring magnet is damaged by the centrifugal force at rotation speeds of 120,000 RPM or more.

Patent Document 2 uses pseudopolar anisotropic orientation to suppress stress concentration that occurs between the magnet and rotor surface during rotation, and increases the adhesive strength between the magnet and rotor surface, thereby resolving the ring breakage problem. Furthermore, Patent Document 3 discloses that, in addition to the measures described in Patent Document 2, the ring breakage problem can also be resolved by dividing the magnet body.

However, in Patent Documents 2 and 3, the rotor is made by stacking thin stainless steel magnet disks, and the laminated stainless steel magnet body has uniaxial anisotropy on the cross section, not isotropy in the radial direction. If the magnetic poles are magnetized with pseudopolar anisotropy, asymmetry will appear in the magnetization state of the four magnetic poles, causing cogging torque problems. Furthermore, stress is generated unevenly at specific points on the surface of the magnet body and rotor body, which can make them more susceptible to damage if the rotational speed is increased to 160,000 RPM or more.

This invention solves the heat generation problem of Maxon's sintered neodymium magnets, the centrifugal force problem of the invention in Patent Document 1, and the cogging torque problem of Patent Documents 2 and 3, achieving a size and weight reduction of more than 50% compared to current products.

Japanese Patent Application Laid-Open No. 2000-195714 Patent No. 7426569 Patent No. 7394428

The standard for small robot motors and widely used is the Maxon motor. To achieve high power, a two-pole magnetized Nd sintered magnet is attached to the rotor, and this is used at 60,000 to 100,000 RPM, resulting in a small, high-output motor (Figures 8 and 9). Attempts to increase speed and performance beyond this are difficult due to the problem of heat generation in the Nd sintered magnet.

Rare earth bonded magnets do not generate heat even when rotated at high speeds of over 120,000 RPM, but because their magnetic force is weak, it is difficult to simply replace them with sintered Nd magnets to reduce their size.
Furthermore, when attaching sintered Nd magnets to the rotor, if mechanical asymmetry or non-uniformity in the coaxiality of the magnetic field distribution created by the magnets occurs due to uneven shape or poor weight balance, cogging torque and vibrations are likely to occur during motor rotation.

Furthermore, high-speed rotation causes large centrifugal forces to act on the magnets attached to the surface, and if there is unevenness in the coaxiality, stress will concentrate in specific areas, causing peeling to begin from those areas, which will then lead to fatigue failure of the ring magnet. Simply replacing the magnet with a rare-earth bonded magnet that does not generate heat will not be enough to design a high-speed rotation motor.

The inventors have succeeded in reducing the size and weight of a small brush motor by 75% by increasing the number of magnetic poles from two to four and doubling the rotation speed from the conventional 3000 RPM to 6000 RPM (Figure 10).
In addition, smooth rotation was achieved by converting the two-pole radially oriented ferrite magnet into a compression-molded rare earth ring magnet, which was then magnetized with pseudopolar anisotropy to create a sinusoidal waveform in the magnetic field distribution.
This design required half the magnet energy and reduced the motor weight to one-quarter, meaning that eight times the performance was achieved per unit of magnet energy.

This experience suggests that even if sintered Nd magnets are replaced with rare earth bonded magnets, i.e., magnets with inferior performance are replaced and the amount of magnetic energy used is reduced, it is entirely possible to make the motor 50% smaller and lighter by eliciting an eight-fold improvement in performance through the motor's structural design.

The present invention was made in light of these circumstances, and was developed based on the idea that by using injection-molded rare earth magnets and magnetizing them with pseudopolar anisotropy, it is possible to improve the coaxiality of the rotor of an SPM motor, and by increasing the number of magnetic poles from two to four to reduce the magnetic force of the magnet and raising the motor rotation speed to 120,000 RPM or more, it is possible to achieve a 50% reduction in size and weight, and that pseudopolar anisotropy magnetization via magnetic material could solve the centrifugal force problem.
Here, pseudopolar anisotropy means that the magnetic poles of the ring magnet and the magnetic material are integrated and anisotropically saturated, and the ring magnet and the magnetic material of the rotor are strongly bonded, which has the effect of generating a force that counteracts centrifugal force, while at the same time the magnetic field emitted from the ring magnet of the rotor has a sinusoidal waveform (Figure 6) .

The inventors first considered it important to enable high-speed rotation of over 160,000 RPM, and therefore considered creating a rotor with excellent coaxiality. To achieve this, they focused on injection-molded rare earth anisotropic bonded magnets. A precisely manufactured cylindrical rotor component is attached to a precision injection mold, and a bonded magnet is molded into the gap using injection molding technology. They realized that this would allow them to create a rotor with extremely high coaxiality in terms of shape and weight balance.

Furthermore, we discovered that the centrifugal force problem can be solved by using a magnetic material with radially isotropic magnetic properties for the rotor body and by magnetizing the ring magnet's poles symmetrically with pseudopolar anisotropy via that material. This makes the strength of the pseudopolar anisotropically magnetized poles symmetrical, and the magnetic flux density distribution on the surface becomes a sinusoidal function. This makes it possible to suppress the motor's cogging torque and vibration generation. To achieve this, we created a pseudopolar anisotropic mold to be used during injection molding and performed magnetic field injection molding.
Magnetic materials with isotropic magnetic properties include heat-treated, drawn, and cold-pressed magnetic materials. Heat-treated products are isotropic in all directions, and naturally are isotropic in the radial direction as well. Drawn and cold-pressed products have axial anisotropy but are isotropic in the radial direction.

Next, we decided to increase the number of magnetic poles from two to four to compensate for the decrease in magnetic force. Furthermore, we decided to reduce the gap between the outer surface of the rotor magnet and the inner surface of the stator electromagnet from approximately 1.5 mm in the conventional Maxon product to less than 0.3 mm. This was only possible thanks to the rotor's excellent coaxiality. Furthermore, increasing the number of poles to six would enable further miniaturization.

As mentioned above, by combining the following factors - the use of injection-molded rare earth anisotropic bonded magnets, making the magnetic poles polar anisotropic, increasing the number of magnetic poles from two to four or more, reducing the gap between the rotor and stator to 0.3 mm or less, and increasing the rotor rotation speed to 160,000 RPM or more - it has been discovered that it is possible to reduce the size of Maxon's widely used small motors by more than 50%.

The biggest problem in design and prototyping is whether the ring magnet can withstand the large centrifugal forces, and whether the adhesion strength between the ring magnet and the rotor main body parts can withstand them. Slight misalignment in coaxiality or rotational vibrations of the motor create stress concentration points at specific locations on the joint surface between the magnet and rotor, which can then initiate cracks and damage the ring magnet. A common solution is to attach a non-magnetic shatterproof cover to the surface of the ring magnet and apply pressure from outside to prevent damage from centrifugal forces. However, this increases the gap between the magnet and stator, making it impossible to achieve sufficient miniaturization.

In addition to the bonding force of the adhesive that acts between the magnet and the magnetic material of the rotor body, the present invention strengthens the magnetic bonding force between the magnet and the magnetic material of the rotor body by using pseudopolar anisotropic magnetization, thereby preventing the ring magnet from flying off due to centrifugal force.

Therefore, we first created grooves on the outer periphery of the rotor body, extending axially symmetrically in the same number as the magnetic poles, and then attached injection-molded magnets to these grooves. The convex portions of the injection-molded magnets fit into the concave portions on the rotor surface, preventing the magnets from rotating during rotation. The stress acting at the interface between the two is the resultant of centrifugal force and rotational force, and by absorbing the rotational force with this rotation stopper, the stress acting at the interface is reduced.

Next, the outer periphery of the rotor body was given a wave-like or knurled texture to increase the adhesive surface area, and then a fine jagged texture of 0.5 to 10 μm was added, and a resin layer was formed on top of this using a metal adhesive to firmly secure the ring magnet to the outer periphery of the rotor body.

Furthermore, the magnetic poles utilize the large magnetic force acting between the magnet body and magnetic material by integrally magnetizing them with pseudopolar anisotropy, strengthening the bonding force between them. These measures have been found to avoid the centrifugal force problem. In other words, high-speed rotation is possible without installing a non-magnetic shatterproof case on the surface of the ring magnet.

By improving the bonding strength between the magnet and rotor, the motor's rotation speed has been increased from over 120,000 RPM to over 160,000 RPM compared to the motors disclosed in Patent Documents 2 and 3, and the motor size has been reduced from an outer diameter of 20 mm or less, a length of 40 mm or less, and a motor output of 20 W to 40 W to an outer diameter of 40 mm or less, a length of 80 mm or less, and a motor output of 100 W to 1,000 W.

When comparing the present invention with previous motors that use sintered Nd magnets, the biggest difference is that while the Nd sintered magnet type has a rotation limit of 100,000 RPM, the present invention is capable of rotating at 160,000 to 240,000 RPM, and has the potential to be 50% smaller and lighter.
This is because sintered magnets have problems such as large iron losses (overcurrent loss and hysteresis loss) and heat generation that deteriorates the magnetic properties, but with bonded magnets, each magnetic particle is insulated by the binder resin, which is an insulator, so the iron loss that occurs is very small.

Furthermore, the problem of rare earth bonded magnets having weaker magnetic force than Nd sintered magnets was resolved by increasing the rotation speed to over 160,000 RPM and the number of magnetic poles to four or more, as well as by reducing the gap from the stator to 0.3 mm or less and devising a magnetic circuit that magnetizes the magnetic poles pseudo-anisotropically. As a result of these comprehensive measures, it was found that the entire motor could be made more compact and lightweight by over 50%.

In terms of rotor processing costs, previous methods using sintered Nd magnets were extremely expensive, requiring processing of the rotor body to house the sintered Nd magnets, as well as an assembly process to attach and glue the sintered magnets, and a process to adjust coaxiality.

The rotor body of the present invention can be manufactured inexpensively by cutting or pressing a round bar, and the rotor is completed simply by integrally molding an injection-molded rare earth magnet into it, an extremely simple process that allows for a significant cost reduction of approximately one-fifth of the manufacturing cost.

At the same time, because only a thin magnet is formed on the surface, the amount of neodymium magnet used is reduced to about one-quarter of that used in Maxson motors. Furthermore, when sintered neodymium magnets are machined into a cylindrical shape, waste is generated, resulting in the wasting of rare and expensive rare earth elements. Injection-molded magnets use magnet powder, resulting in an excellent yield of nearly 100%, and making it possible to avoid wasting neodymium resources.

The SPM motor of the present invention comprises the above-mentioned rotor and a stator having a coil disposed axially symmetrically on the outer periphery of the rotor and a yoke that forms a magnetic circuit on the outer periphery of the coil.
The electromagnetic coil may optionally include teeth within the yoke coil or may have no teeth.

SPM motors basically generate rotational force (magnetic torque) based on the attractive and repulsive forces generated by the magnetic poles formed by the permanent magnets attached to the rotor and the rotating magnetic field formed around the rotor by the stator. The rotational speed of an SPM motor can be controlled by the frequency of the rotating magnetic field, which can be controlled by the excitation frequency. Therefore, SPM motors are not affected by the load and are motors with excellent controllability.

The manufacturing method for pseudo-polar anisotropic magnetization of magnetic poles involves manufacturing an anisotropic magnetization type injection molding die. The injection molding conditions are die temperature and injection temperature 100-150°C, molding pressure 50-150°C,
The injection pressure is 100 MPa, injection speed is 50-150 cm ³ /s, and the aligning magnetic field is 1 T or more. Furthermore, a polar anisotropic magnetic field of 1 T or more is applied to the ring magnet portion, which aligns the magnetic material pseudopolar anisotropically during injection molding and simultaneously magnetizes it to saturation.

Normally, a magnetic field of 3 T is required to saturate magnetize an anisotropic bonded magnet, but because the injection molding temperature is above 100°C, the magnet's coercive force is reduced to below 0.7 T, allowing the magnetic powder to be saturate magnetized with a magnetic field strength of 1 T, and the saturated magnetized magnetic powder can be oriented along the magnetic flux lines. Moreover, because the magnetic powder is saturated magnetized, the saturated state is maintained when the temperature drops, making it possible to produce a saturated magnetized pseudopolar anisotropic magnet. This means that the magnetization process of injection molding can be omitted.

This invention makes it possible to reduce the size and weight of general-purpose small SPM motors by 50%. At the same time, it is possible to reduce the manufacturing cost of the rotor by approximately one-fifth.

1 is a cross-sectional view of an SPM motor according to a first embodiment of the present invention. 1 is a cross-sectional view of a four-pole magnet attached to a rotor of the present invention as viewed from the axial direction. FIG. 2 is a cross-sectional side view of the rotor of the present invention. 1 is a cross-sectional view of a rotor having a recess made of a magnetic material used in the present invention. 5A and 5B show a laminated rotor of uniaxially anisotropic stainless steel magnets, showing (5a) uniaxial anisotropy and (5b) a waveform that is not sinusoidal due to different surface magnetic flux densities at the north and south poles. 6A and 6B show waveforms that are radially isotropic and sinusoidal, respectively, for a rotor made of a magnetic material having radially isotropic magnetic properties according to the present invention. 1 is a comparison of the appearance of an existing SPM motor product and the present invention. This is a plan view showing the magnetic field and north and south poles of a conventional ring-shaped polar anisotropic bonded magnet. FIG. 1A is a cross-sectional view of a magnet of a sintered neodymium type rotor as viewed from the axial direction, and FIG. 1B is a perspective view of the magnet. FIG. 10 is a cross-sectional view of a Nd sintered rotor as viewed from the side. This is a comparison of the appearance of both motors when the brush motor is made 75% smaller and lighter.

The brushless SPM motor is
the rotor comprises a cylindrical rotor body, a ring magnet fixed to an outer surface of the rotor body, and a rotating shaft fixed to a cylindrical central axis,
The rotor body is made of a magnetic material having magnetically isotropic magnetic properties in the radial direction, and has a wavy or knurled irregularity on the outer periphery and a fine jagged irregularity of 0.5 to 10 μm, and has a resin layer of a metal adhesive thereon;
The ring magnet is an injection-molded rare earth anisotropic bonded magnet having a maximum energy product of 10 to 25 MGOe or more and arc-shaped on the outer circumferential surface of the rotor body, and is fixed to the periphery of the magnetic material, and has magnetic poles consisting of an even number of four or more poles with N poles and S poles arranged alternately,
The magnetic poles of the rare earth anisotropic bonded magnet are magnetized axially symmetrically with pseudopolar anisotropy, and the magnetic flux distribution density on the surface has a sinusoidal characteristic,
The rotor has an outer diameter of 40 mm or less and a length of 60 mm or less.
The gap between the rotor and the stator is 0.3 mm or less,
The rotor rotates at a rotational speed of 160,000 RPM or more, and the brushless SPM motor has an output of 40W to 1000W.

In addition, the brushless SPM motor
the rotor comprises a cylindrical rotor body, a ring magnet fixed to an outer surface of the rotor body, and a rotating shaft fixed to a cylindrical central axis,
The rotor body is made of a magnetic material having magnetically isotropic magnetic properties in the radial direction, has grooves on the outer periphery extending axially symmetrically in the same number as the number of magnetic poles, and has wave-shaped or knurled irregularities and jagged fine irregularities of 0.5 to 10 μm on the upper part of the grooves, and has a resin layer of a metal adhesive thereon;
The ring magnet is an injection-molded rare earth anisotropic bonded magnet having a maximum energy product of 10 to 25 MGOe or more and arc-shaped on the outer circumferential surface of the rotor body, and is fixed to the periphery of the magnetic material, and has magnetic poles consisting of an even number of four or more poles with N poles and S poles arranged alternately,
The magnetic poles of the rare earth anisotropic bonded magnet are magnetized axially symmetrically with pseudopolar anisotropy, and the magnetic flux distribution density on the surface has a sinusoidal characteristic,
The rotor has an outer diameter of 40 mm or less and a length of 60 mm or less.
The gap between the rotor and the stator is 0.3 mm or less,
The rotor rotates at a rotational speed of 160,000 RPM or more, and the brushless SPM motor has an output of 40W to 1000W.

The manufacturing method of the rotor of the brushless SPM motor is as follows:
(1) preparing a round bar of a magnetic material having magnetic properties in the radial direction;
(2) The round bar is subjected to heat treatment and then machined or pressed into a cylindrical part;
(3) forming grooves on the outer periphery of the cylindrical part, the number of which is equal to the number of magnetic poles extending axially symmetrically;
(4) subjecting the surface of the cylindrical part on which the groove is formed to a corrugated or knurled processing;
(5) Forming fine jagged irregularities of 0.5 to 10 μm on the surface of the corrugated or knurled surface by shot blasting;
(6) For injection molding of rare earth anisotropic bonded magnets, an anisotropically magnetized injection mold is prepared, the mold temperature and injection temperature are set to 100-150°C, the molding pressure is set to 50-150 MPa, and the injection speed is set to 50-150 ^cm3 /sec. Furthermore, a polar anisotropic magnetic field of 1 T or more is applied to the ring magnet portion to be formed, so that the magnetic material is pseudopolar anisotropically oriented during injection molding and simultaneously pseudopolar anisotropically magnetized to saturation.
(7) Then, remove from the injection mold.
It is characterized by:

In addition, the manufacturing method of the rotor of the SPM motor is as follows:
(5) The next step is
(5-1) Forming a resin layer on the fine irregularities using a metal adhesive;
It is characterized by:

This will be described in detail below with reference to FIGS.
<Brushless SPM motor>
As shown in FIG. 1, the brushless SPM motor 1 comprises a rotor 2, a stator 3, and a rotating shaft 4.
The rotor 2 will now be described.

<Rotor>
As shown in FIGS. 2 and 3, the rotor 2 is made up of a rotor body 21, rare earth anisotropic bonded magnets 22 (22N, 22S), and a rotating shaft 23.

<Rotor body>
The rotor body 21 is made of a magnetic material with radially isotropic magnetic properties and is cylindrical in shape with a hole in the center for attaching the rotating shaft. This allows the magnetic field distribution generated by all four or more magnetic poles to be the same when they are pseudo-polar anisotropically magnetized.

As shown in Figure 4, the outer peripheral surface has four or more grooves (concave portions) extending axially symmetrically. The number of grooves is the same as the number of magnetic poles. The outer peripheral portion of the rotor body has corrugated or knurled irregularities and fine jagged irregularities of 0.5 to 10 μm, on top of which a resin layer is formed using a metal adhesive. This processing of the outer peripheral portion is intended to firmly fix the ring magnet to the outer peripheral portion of the rotor body.

Furthermore, the magnetic poles utilize the large magnetic force acting between the magnet body and magnetic material by integrally magnetizing them with pseudopolar anisotropy, strengthening the bonding force between them. These measures have been found to avoid the centrifugal force problem. In other words, high-speed rotation is possible without installing a non-magnetic shatterproof case on the surface of the ring magnet.

The rotor body is manufactured by machining or pressing a round bar of magnetic material into the required cylindrical shape after heat treatment. The circumferential surface is then polished, and grooves are machined in the same number as the number of poles. The groove depth and width should be no more than one-third the thickness of the magnet. The surface is then corrugated or knurled, and then shot blasted to create fine jagged irregularities of 0.5 to 10 μm. A resin layer is then formed on top of this using a metal adhesive. This is a surface treatment to increase the bonding strength between the magnet and rotor surface.

The rotor radius should preferably be within ±0.010 mm of machining error to keep the gap between the rotor and stator to 0.3 mm or less.

<Rare earth anisotropic bonded magnet>
It is preferable that the injection molded rare earth anisotropic bonded magnet (magnetically anisotropic rare earth bonded magnet) has as high a maximum energy product as possible, but the present invention can be realized by using one having 10 MGOe to 25 MGOe.
Although the magnetic performance is significantly inferior to that of sintered Nd magnets with a maximum energy product of 40 MGOe or more, the number of magnetic poles on the rotor surface magnets is at least four, which are magnetized alternately to north and south poles, and saturation magnetization occurs with pseudopolar anisotropy via the magnetic material.

Furthermore, these magnets are formed using the injection molding process, resulting in extremely high dimensional accuracy. They are also arranged symmetrically around the central axis of rotation of the main body, allowing the gap between the stator and rotor to be controlled to 0.3 mm or less. The magnets are also magnetized with pseudopolar anisotropy, resulting in a small demagnetizing field and enabling the extraction of a relatively large magnetic flux.

As a result, although the performance of the magnet itself is inferior to that of a sintered Nd magnet, it is able to draw out the same or greater amount of magnetic flux as part of the motor's magnetic circuit.

When a magnetic material has uniaxial anisotropy in cross section, such as a laminated plate of stainless steel magnet, and is magnetized with pseudopolar anisotropy, the magnetic field distribution emitted from the four poles will be different, as shown in Figure 5. However, as shown in Figure 6, this invention uses a magnetic material that is isotropic in the radial direction, so the magnetic field distribution emitted by the four poles will be the same. This is important for reducing cogging in the motor.

<Magnetic shape and size>
The specific shape and size of the magnet, that is, the outer diameter, thickness, and length of the magnet, are adjusted appropriately according to the basic specifications of the SPM motor, such as its output and motor size, and also taking into account its rotation speed and centrifugal force.
The motor output is from 100W to 1000W, but the rotor diameter can be 8mm to 32mm, the inner diameter 5mm to 20mm, the length 5mm to 20mm, and the magnet usage amount can be 0.8g to 6g.

<Joint strength between magnet and rotor body>
Regarding the bonding strength between the magnet and rotor body against centrifugal force, it is necessary to further strengthen both the bonding strength of the adhesive and the magnetic bonding force due to pseudopolar anisotropic magnetization, taking into consideration the motor output and rotation speed. If a stronger bonding strength of the adhesive is required, the outer surface of the rotor body is shot blasted to a roughness of 0.5 μm to 5 μm, and then a metal adhesive is applied on top of that to cover the surface of the rotor with resin, which is then bonded to the resin of the injection-molded magnet, ensuring a strong bond.

Furthermore, if it is necessary to strengthen the bond due to centrifugal force, it is possible to increase the bond strength by applying a corrugated or knurled finish to the outer surface of the rotor body, thereby increasing the bond surface area with the magnet.

Regarding the bonding strength of the surface magnet, whether or not it will break depends on factors such as the magnet's shape, weight, uniformity of magnetic properties, the rotor's coaxiality, and bonding strength, so we actually installed a 200,000 rpm rotational speed testing machine to evaluate it and confirmed that the ring magnet would not break.

<Cost>
The cost consists of the cost of manufacturing the rotor body from magnetic material, the cost of fitting the rotating shaft into the hole in the center of the rotor body, and the cost of forming the rare earth bonded magnet on the outer periphery using an injection process.
Because there are no costly parts with complex structures, no precision assembly process is required, the magnetization process can be omitted, and the amount of expensive rare earth used is small at 4g or less, it is thought that the rotor can be manufactured at a manufacturing cost of less than one-fifth of the manufacturing cost of conventional rotor products.

<Motor specifications>
The output is 100W to 1000W, the rotor speed is 160,000 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 yoke of the electromagnet on the stator side may or may not have teeth.

First Example
This is an example of a 100W output motor.
The rotor body of the brushless SPM motor was made by machining a roughly cylindrical ring part from a round bar of magnetic material.

The injection-molded anisotropic rare earth bonded magnet was formed in an arc shape on the outer periphery of the rotor body, and had a maximum energy product of 18 MGOe.
The conditions for injection molding the rare earth anisotropic bonded magnet were a mold temperature and injection temperature of 130°C, a molding pressure of 100 MPa, and an injection speed of 90 ^cm3 /sec. A polar anisotropic magnetic field of 1 T or more was applied to the ring magnet portion to polar anisotropically orient the magnetic material during injection molding and simultaneously magnetize it to saturation.

The rotor's surface magnets have four magnetic poles, alternating north and south poles at the groove boundaries, and are pseudo-polar anisotropically saturated. Furthermore, these magnets are formed using an injection molding process, resulting in extremely high dimensional accuracy. They are also arranged symmetrically around the main body's central axis of rotation, with a gap between the stator and rotor of 0.2 mm.

The specific shape and size of the magnets were: rotor diameter 11 mm, inner diameter 7 mm, magnet thickness 2 mm, length 7.5 mm, and magnet weight 1 g.

The motor's rotation speed is 200,000 RPM, and in order to ensure the strength of the bond between the magnet and rotor body against centrifugal force, the motor output and rotation speed were taken into consideration and the outer surface of the rotor body was knurled and then shot blasted to an average roughness of 3 μm. A metal adhesive was then applied on top of that to cover the surface of the rotor with resin, which was then bonded to the resin of the injection-molded magnet , ensuring a high bond strength.

The bonding strength of the surface magnets was evaluated using a rotational speed tester that could reach 200,000 revolutions per minute. All 10 rotors used in the experiment passed the test without breaking at 200,000 revolutions.

In terms of cost, it costs 30 yen to manufacture the rotor body from magnetic material, 40 yen to fit the rotating shaft into the hole in the center of the rotor body, 80 yen to form the rare earth bonded magnet on the outer periphery using an injection process, and 50 yen for the 1.1g of expensive rare earth used, for a total of 200 yen, which is thought to be about 1/10 of the estimated manufacturing cost of 2,000 yen for a rotor of a conventional product.

The motor specifications of this invention are: output 100W, motor size 18mm diameter, 30mm length, weight 50g, rotor rotation speed 200,000 RPM, magnet weight less than 1g, number of magnetic poles 4, number of electromagnets on the stator side 6. The yoke of the electromagnet on the stator side does not have teeth.

Maxon's 100W motor has a diameter of 19mm, a length of 30mm, and a weight of 100g. The rotor rotates at 60,000 RPM, the magnet weighs 4.3g, there are two magnetic poles, and the electromagnet on the stator side has three poles. It can be seen that the invention has achieved a 50% reduction in size and weight, while also achieving significant cost reductions.

The use of small motors in robots is increasing rapidly, but at the same time, there is a demand for them to be smaller, lighter, and less expensive. This invention makes it possible to reduce the size and weight of conventional motors by 50% and significantly reduce manufacturing costs, and is expected to be widely applied to various types of robots in the future.

1: Brushless SPM motor 2: Rotor 21: Rotor body 22: Rare earth anisotropic bonded magnet (rare earth bonded magnet, magnet)
22N: North pole of rare earth bonded magnet 22S: South pole of rare earth bonded magnet 23: Rotating shaft 24: Groove (recess)
3: Stator 4: Rotating shaft 5: Magnetic field distribution of rotor made of uniaxially anisotropic stainless steel magnet 51: Uniaxial anisotropy 52: Flow of magnetic flux 6: Magnetic field distribution of isotropic magnetic material 61: Isotropy 7: Polar anisotropic magnetization pattern of the magnet in Patent Document 1 8: Rotor made of Nd sintered magnet 81: Case 82: Sintered magnet 82N: North pole of sintered magnet 82S: South pole of sintered magnet 83: Shaft

Claims (4)

In a brushless SPM motor consisting of a stator and a rotor,
the rotor comprises a cylindrical rotor body, a ring magnet fixed to an outer surface of the rotor body, and a rotating shaft fixed to a cylindrical central axis,
The rotor body is made of a magnetic material having magnetically isotropic magnetic properties in the radial direction, and has a wavy or knurled irregularity on the outer periphery and a fine jagged irregularity of 0.5 to 10 μm, and has a resin layer of a metal adhesive thereon;
The ring magnet is an injection-molded rare earth anisotropic bonded magnet having a maximum energy product of 10 to 25 MGOe or more and arc-shaped on the outer circumferential surface of the rotor body, and is fixed to the periphery of the magnetic material, and has magnetic poles consisting of an even number of four or more poles with N poles and S poles arranged alternately,
The magnetic poles of the rare earth anisotropic bonded magnet are magnetized axially symmetrically with pseudopolar anisotropy, and the magnetic flux distribution density on the surface has a sinusoidal characteristic,
The rotor has an outer diameter of 40 mm or less and a length of 60 mm or less.
The gap between the rotor and the stator is 0.3 mm or less,
The rotor rotates at a rotational speed of 160,000 RPM or more, and the brushless SPM motor has an output of 40W to 1000W. In a brushless SPM motor consisting of a stator and a rotor,
the rotor comprises a cylindrical rotor body, a ring magnet fixed to an outer surface of the rotor body, and a rotating shaft fixed to a cylindrical central axis,
The rotor body is made of a magnetic material having magnetically isotropic magnetic properties in the radial direction, has grooves on the outer periphery extending axially symmetrically in the same number as the number of magnetic poles, and has wave-shaped or knurled irregularities and jagged fine irregularities of 0.5 to 10 μm on the upper part of the grooves, and has a resin layer of a metal adhesive thereon;
The ring magnet is an injection-molded rare earth anisotropic bonded magnet having a maximum energy product of 10 to 25 MGOe or more and arc-shaped on the outer circumferential surface of the rotor body, and is fixed to the periphery of the magnetic material, and has magnetic poles consisting of an even number of four or more poles with N poles and S poles arranged alternately,
The magnetic poles of the rare earth anisotropic bonded magnet are magnetized axially symmetrically with pseudopolar anisotropy, and the magnetic flux distribution density on the surface has a sinusoidal characteristic,
The rotor has an outer diameter of 40 mm or less and a length of 60 mm or less.
The gap between the rotor and the stator is 0.3 mm or less,
The rotor rotates at a rotational speed of 160,000 RPM or more, and the brushless SPM motor has an output of 40W to 1000W. A method for manufacturing a rotor of a brushless SPM motor comprising a stator and a rotor,
(1) preparing a round bar of a magnetic material having magnetic properties in the radial direction;
(2) The round bar is subjected to heat treatment and then machined or pressed into a cylindrical part;
(3) forming grooves on the outer periphery of the cylindrical part, the number of which is equal to the number of magnetic poles extending axially symmetrically;
(4) subjecting the surface of the cylindrical part on which the groove is formed to a corrugated or knurled processing;
(5) Forming fine jagged irregularities of 0.5 to 10 μm on the surface of the corrugated or knurled surface by shot blasting;
(6) For injection molding of rare earth anisotropic bonded magnets, an anisotropically magnetized injection mold is prepared, the mold temperature and injection temperature are set to 100-150°C, the molding pressure is set to 50-150 MPa, and the injection speed is set to 50-150 ^cm3 /sec. Furthermore, a polar anisotropic magnetic field of 1 T or more is applied to the ring magnet portion to be formed, so that the magnetic material is pseudopolar anisotropically oriented during injection molding and simultaneously pseudopolar anisotropically magnetized to saturation.
(7) Then, remove from the injection mold.
A method for manufacturing a rotor comprising the steps of:
In claim 3, the step subsequent to (5) is:
(5-1) Forming a resin layer on the fine irregularities using a metal adhesive;
A method for manufacturing a rotor comprising the steps of: