JP4977307B2 - Small motor - Google Patents

Description

The present invention relates to a small type motor using a sintered magnet such as Nd-Fe-B system or Pr-Fe-B system.

Specifically, in a sintered magnet such as the Nd-Fe-B system, Y and Nd, Dy, Pr, and more inside the magnet than the depth corresponding to the radius of the crystal particles exposed on the outermost surface of the magnet. Ho, relates to a small motor using one or magnet which two or more diffuse infiltration from the magnet surface of a rare earth element selected from Tb.

Nd-Fe-B based sintered magnets are known as the highest performance magnets among permanent magnets and are widely used in motors and the like. In addition, this magnet is known to have a high magnetic energy product by generating a coercive force by having a microstructure in which the internal structure is surrounded by a thin Nd-rich subphase around the Nd ₂ Fe ₁₄ B main phase. .
On the other hand, when the magnet is used in a motor, the final shape is obtained by machining such as grinding. At this time, the Nd-rich phase of the magnet surface layer is damaged by minute cracks or oxidation, and as a result, As a result, the magnetic properties of the magnet surface portion are reduced to a fraction of the inside of the magnet. The work-deteriorated layer has a thickness of about several tens of μm. When the entire magnet is considered, the smaller the volume and the larger the specific surface area (surface area / volume), the lower the characteristics. In other words, this is due to an increase in the proportion of the processing damaged portion with respect to the total volume.
In order to remedy the above drawbacks, the present inventors previously filed a patent application as “a microscopic, high performance rare earth magnet for a micro product and a manufacturing method thereof” in Japanese Patent Application No. 2003-096866.
In the previous patent application, the surface area / volume ratio is 2 mm ^-1 or more (preferably 3 mm ^-1 or more) and the volume is 100 mm ³ or less (preferably 20 mm) for micro, high performance rare earth magnets for micro products. ³ or less), and one kind of rare earth elements selected from Y and Nd, Dy, Pr, Ho, Tb inside the magnet more than the depth corresponding to the radius of the crystal grains exposed on the outermost surface of the magnet Alternatively, two or more kinds are diffused and permeated from the surface of the magnet to modify the damaged part due to the processing, and (BH) max has a magnetic property of 280 kJ / m ³ or more, and a method for producing the magnet Has proposed.
The inventors of the present invention have studied the sintered magnet proposed here for a small motor, mounted it on a small motor, and focused on the torque constant, which is an index that generally represents the motor characteristic. As a result of repeated research and countermeasures, we focused on the characteristics of a motor magnet, developed a magnet, and obtained an ultra-small motor.

Nd-Fe-B based sintered magnets are considered to be the most powerful magnets among permanent magnets, and are widely used in magnetic circuits for hard disk drive voice coil motors (VCM) and magnetic tomography (MRI). in use. In addition, this magnet is known to have a high magnetic energy product by generating a coercive force by having a microstructure in which the internal structure is surrounded by a thin Nd-rich subphase around the Nd ₂ Fe ₁₄ B main phase. .

  Also, when using sintered magnets in actual motors, etc., the final dimensions and concentricity are actually obtained by grinding, but at this time, due to minute grinding cracks, oxidation, etc. The Nd-rich phase of the magnet surface layer is damaged, and as a result, the magnetic properties of the magnet surface portion are reduced to a fraction of the inside of the magnet.

This phenomenon is particularly noticeable in micro magnets with a large surface area ratio relative to volume. For example, when a square block magnet (BH) max of 360 kJ / m ³ and a side of 10 mm is cut and ground to 1 mm × 1 mm × 2 mm, (BH) max decreases to about 240 kJ / m ³ , and the original characteristics of the Nd—Fe—B rare earth magnet cannot be obtained.

  In order to improve such a defect of the Nd—Fe—B based sintered magnet, there has been proposed a method of removing the altered layer generated by machining by mechanical polishing or chemical polishing (for example, Patent Document 1). ). In addition, a method has been proposed in which a rare earth metal is deposited on a ground magnet surface and subjected to diffusion heat treatment (for example, Patent Document 2). In addition, a method of forming an SmCo film on the surface of an Nd—Fe—B magnet can be seen (for example, Patent Document 3).

JP 9-270310 A Japanese Patent Laid-Open No. Sho 62-74048 (Japanese Patent Publication No. 6-63086) JP 2001-93715 A

  In the method described in Patent Document 1, it is estimated that the deteriorated layer is about 10 μm or more, so that it takes time for polishing, a new deteriorated layer is generated when high-speed polishing is performed, and an acid solution is generated in chemical polishing. There existed problems, such as remaining in the hole of a sintered magnet and being easy to generate | occur | produce a corrosion mark.

Patent Document 2 discloses that a rare earth metal thin film layer is formed on a work-affected layer of a surface to be ground of a sintered magnet body, and a trade layer is formed by a diffusion reaction. Specifically, By merely describing the experimental results of forming a sputtered film on a thin test piece of length 20 mm × width 5 mm × thickness 0.15 mm, the (BH) max obtained is at most 200 kJ / m ³ .

Further, in the method described in Patent Document 3, it is difficult to recover the magnetic characteristics because there is no metallic reaction to the Nd ₂ Fe ₁₄ B phase or the Nd rich phase if the film is formed as it is. When it diffuses in the magnet, the crystal magnetic anisotropy of the Nd ₂ Fe ₁₄ B phase is lowered, so that it is difficult to recover the characteristics. Furthermore, since a method is used in which the sample is turned over and sputtered twice during film formation, there are difficulties in film formation productivity and film thickness uniformity.

In recent years, for example, Nd-Fe-B-based cylindrical sintered magnets having an outer diameter of about 4 mm are often used for vibration motors for mobile phones, but when measuring their magnetic properties, they are around 230 kJ / m ³ , It is difficult to further reduce the size without reducing the vibration intensity. Furthermore, it will be more difficult to apply to high-power, ultra-compact actuators that will be required for micro-robots and micro motors for in-vivo diagnosis.
An object of the present invention is to solve the above-described problems of the prior art and provide an ultra-small motor using a high-performance magnet.

As a result of intensive investigation and countermeasure experiment on the deterioration of magnetic properties due to processing damage when manufacturing a micro magnet machined by cutting, drilling, grinding, polishing, etc., the sintered magnet block has been obtained as a result of rare earth magnets. minute for the ultra-small products that were allowed to recover the original magnetic properties, has succeeded in the development of high-performance magnet.

The present invention uses a cylindrical or disk-shaped Nd-Fe-B-based or Pr-Fe-B-based sintered magnet having a holed inner surface having a surface that has been altered and damaged by machining. The value of the specific surface area (surface area / volume) is 4 mm ^-1 or more and the volume is 10 mm ³ or less, and the inside of the magnet exceeds the depth corresponding to the radius of the crystal grains exposed on the outermost surface of the magnet. The alteration damage portion is modified by diffusing and infiltrating R metal (where R is Y or one or more of rare earth elements selected from Nd, Dy, Pr, Ho, and Tb) from the magnet surface. Te (BH) max is it characterized by having a magnetic characteristic of more than 280 kJ / m ^3.
A method of producing a sintered magnet for small motors used in the present invention, the cylindrical or disk shape having an inner surface with holes having a surface alteration damaged by machining Nd-Fe-B system or Pr-Fe -B-based sintered magnet is supported in a vacuum chamber and vaporized or finely divided by a physical method in the vacuum chamber, or an alloy containing R metal or R metal (provided that R is Y and Nd, Dy, One or more rare earth elements selected from Pr, Ho, and Tb) are three-dimensionally deposited on all or part of the surface of the magnet, and are exposed to the outermost surface of the magnet. It is characterized in that the damaged part due to machining is modified by diffusing and penetrating R metal from the surface of the magnet beyond the depth corresponding to the radius of the crystal grains.
Further, a method for producing a sintered magnet for small motors used in the present invention, the cylindrical or disk shape having an inner surface with holes having a surface alteration damaged by machining Nd-Fe-B system or Pr-Fe -B-based sintered magnet is supported in a vacuum chamber and vaporized or finely divided by a physical method in the vacuum chamber, or an alloy containing R metal or R metal (provided that R is Y and Nd, Dy, One or more rare earth elements selected from Pr, Ho, and Tb are three-dimensionally deposited on all or part of the surface of the magnet to form a film, and exposed to the outermost surface of the magnet. The modified damaged portion due to the machining is modified by diffusing and infiltrating R metal into the magnet at a temperature of 900 to 1000 ° C. beyond the depth corresponding to the radius of the crystal grains. To do.
Method of manufacturing a miniature motor sintered magnet used in the present invention, wherein the magnet interior R metal magnet surface at 900 ° C., to modify the altered damaged part by the machining by cementation And
Method for producing a sintered magnet for small motors used in the present invention, the physical approach, R metals or alloys containing R metal and disposed around the magnet (wherein, R is, Y and Nd, Dy, Pr, This is a spackling method in which a plurality of targets composed of one or more rare earth elements selected from Ho and Tb are atomized by ion bombardment to form a film on the magnet surface.
Method for producing a sintered magnet for small motors used in the present invention, the physical means is an alloy containing R metals or R metal and disposed around the sintered magnet (wherein, R is, Y and Nd, Dy, An ion plating method in which particles generated by melting and evaporating a plurality of targets composed of one or more rare earth elements selected from Pr, Ho, and Tb are ionized to form a film on the surface of the magnet. It is characterized by being.

The present invention includes a housing, a field winding provided inside the housing, a shaft rotatably supported by a bearing portion, and provided on the shaft and magnetized in a direction perpendicular to the shaft axis. A small motor comprising a cylindrical rotor magnet, the cylindrical rotor magnet comprising a cylindrical Nd-Fe-B system or Pr-Fe having a perforated inner surface having a surface that is altered and damaged by machining -B-based sintered magnet, which has an R metal (provided that R is Y and Nd, Dy, R) within the magnet at a depth equal to or greater than the radius corresponding to the radius of the crystal grains exposed on the outermost surface of the magnet. A rare earth element selected from Pr, Ho and Tb is diffused and infiltrated from the surface of the magnet to modify the damaged part (BH) with a max of 280 kJ / m ³ or more. consists sintered magnet, in yet the small motor, the permeance coefficient (Operating point) is 1 or more, the specific surface area of the rotor magnet (surface area / volume) 4 mm ^-1 or more, the volume of the rotor magnet, characterized in that it is selected to 10 mm ³ or less.
The present invention relates to a cup-type rotor in which one end of an axial opening of a cylindrical winding coil is fixed to a rotating shaft, and is disposed inside the cup-shaped rotor and provided in a cylindrical yoke, and is orthogonal to the rotating shaft. A small-sized motor comprising a cylindrical stator magnet magnetized in a direction in which the cylindrical stator magnet has a cylindrical Nd with a perforated inner surface having a surface that has been altered and damaged by machining. -Fe-B-based or Pr-Fe-B-based sintered magnet, and an R metal (provided that the depth of the magnet corresponds to the radius of the crystal grains exposed on the outermost surface of the magnet) R is Y or a rare earth element selected from Nd, Dy, Pr, Ho, and Tb, and diffuses and penetrates from the magnet surface to modify the damaged portion (BH) max. the a sintered magnet was 280 kJ / m ³ or more, and in yet the small motor, Pami Nsu factor (operating point) is 1 or more, the specific surface area (surface area / volume) of the stator magnet 4 mm ^-1 or more, the volume of the stator magnet is characterized in that it is selected to 10 mm ³ or less.
The present invention is characterized in that a small motor has a permeance coefficient (operating point) of 1.4 or more.
The present invention is characterized in that, in the small motor, the thickness of the film formed by diffusion and penetration on the surface of the magnet is set to 0.02 to 2 μm.
The present invention is characterized in that in the small motor, the R metal is Dy, and the thickness of the coating formed by diffusion and penetration on the magnet surface is 1.4 μm.
The present invention is characterized in that, in a small motor, the outer diameter of the motor is selected to be 3 mm or less.

If the magnet block is machined by cutting, drilling, grinding, polishing, or the like, the magnet surface portion is altered and damaged, and the magnetic properties deteriorate. An alloy containing a considerable amount of one or more rare earth metals selected from Dy, Pr, Ho, and Tb, as well as Y and Nd, or a substantial amount of each metal is formed on the surface of the magnet having the damaged surface. When diffused, for example, in the case of Nd-Fe-B rare earth magnets, these rare earth metals are compatible with Nd because they are the same kind of rare earth metals as Nd ₂ Fe ₁₄ B main phase and Nd rich grain boundary phase. It has a good function, and reacts mainly with the Nd-rich phase to easily repair parts damaged by machining and restore the magnetic properties.

In addition, when some of these rare earth metals enter the Nd ₂ Fe ₁₄ B main phase by diffusion and are substituted for the Nd element, any rare earth metal increases the magnetocrystalline anisotropy of the main phase and increases the coercive force. Has a function of increasing the magnetic properties and restoring the magnetic properties. In particular, Tb ₂ Fe ₁₄ B in which Tb is substituted for all Nd elements in the main phase has a crystal magnetic anisotropy at room temperature that is about three times that of Nd ₂ Fe ₁₄ B, and thus a large coercive force can be easily obtained. A similar recovery function can be obtained for Pr-Fe-B magnets.

The depth at which the rare earth metal penetrates by the diffusion treatment is set to be equal to or greater than the depth corresponding to the radius of the crystal grains exposed on the outermost surface of the magnet. For example, since the crystal grain size of the Nd—Fe—B based sintered magnet is about 6 to 10 μm, the minimum is required to be 3 μm or more corresponding to the radius of the crystal grain exposed on the outermost surface of the magnet. If it is less than this, the reaction with the Nd-rich phase enclosing the crystal grains becomes insufficient, and the recovery of the magnetic properties becomes slight. When it becomes deeper than 3 μm, the coercive force increases slowly, and it has the effect of further increasing the coercive force by substituting Nd of the Nd ₂ Fe ₁₄ B main phase. It is desirable that the processing conditions be adjusted to achieve a desired magnetic characteristic.

In the present invention, the recovery of the magnetic properties by surface modification, as the magnet volume is small, also shows a significant effect larger magnet surface area to volume ratio. According to our research on the size and magnetic properties of Nd-Fe-B sintered magnets, the squareness of the demagnetization curve deteriorates when the magnet size is about 2 mm square block or less. It has become clear that the coercive force is reduced.

At this size, it is simply calculated that the magnet volume is 8 mm ³ and the surface area / volume ratio is 3 mm ⁻¹ . In the case of a cylindrical magnet, the surface area / volume ratio further increases, and the squareness and coercive force are significantly reduced. As an example, the outer diameter, inner diameter, and length of a magnet mounted on a commercially available mobile phone vibration motor are about 2.5 mm, 1 mm, and 4 mm, respectively, and the volume corresponds to about 16.5 mm ³

Thus, a specific surface area (surface area / volume) 4Mm- ¹ or more, and the volume of approximately 10 mm ³ or less of the small magnet, Nd-Fe- being particularly effective significantly by surface modification, mounted to a commercially available vibration motor against (BH) max of approximately 240kJ / m ³ of B magnets, in those of the onset bright, 280 kJ / m ³ or more, such as high characteristics of 300~360kJ / m ³ is obtained.

  According to the present invention, the rare earth metal rich phase such as Nd in the altered magnet surface layer is repaired by depositing and diffusing the rare earth metal on the surface of the magnet damaged by the machining, and the magnetic properties are sufficiently improved. Can be recovered. As a result, it is possible to realize a micro, high-power motor using a small, high-performance magnet.

Hereinafter, first, it is described in more detail in accordance with manufacturing process a method for manufacturing a miniature motor magnet Ru used in the present invention.
The magnet block material that is the object of the method of the present invention is manufactured by a raw powder sintering method or a hot plastic working method after hot pressing the raw material powder.
These magnet block materials are machined by cutting, drilling, grinding, polishing, etc. to produce a cylindrical or disk-shaped small magnet having an inner surface with a hole.
Thus, a micro magnet having a surface area / volume ratio of 4 mm ⁻¹ or more and a volume of 10 mm ³ or less is manufactured. Nd—Fe—B and Pr—Fe—B systems are typical examples of alloy systems suitable as small magnets. Among these, Nd—Fe—B based sintered magnets have the greatest deterioration in properties due to machining, despite the highest magnetic properties.

  The metal deposited on the surface of the magnet having a damaged surface is from Dy, Pr, Ho, Tb, including Y and Nd, for the purpose of strengthening the repair of rare earth metal-rich phases such as Nd constituting the magnet. One or more of the selected rare earth metals or an alloy containing a considerable amount of rare earth metals such as Y, Nd, Dy, Pr, Ho, Tb, for example, an Nd—Fe alloy or a Dy—Co alloy is used.

The film formation method on the magnet surface is not particularly limited, and physical film formation methods such as vapor deposition, sputtering, ion plating, and laser deposition, and chemical vapor deposition methods such as CVD and MO-CVD. , And plating methods can be applied. However, it is preferable that the film forming process and the heat diffusion process are performed in a clean atmosphere other than 10 ⁻⁷ Torr and air-derived gases such as oxygen and water vapor of several tens of ppm or less.

  When the atmosphere when the R metal is diffused and infiltrated from the magnet surface by heating is about the purity of the high-purity argon gas that is usually obtained, the atmosphere-derived gas contained in the argon gas, that is, oxygen, water vapor, carbon dioxide, The R metal deposited on the surface when the magnet is heated by nitrogen or the like becomes oxides, carbides or nitrides, and may not efficiently diffuse and reach the internal tissue phase. Therefore, it is preferable that the concentration of the air-derived impurity gas contained in the atmosphere during the heat diffusion of the R metal is about 50 ppm or less, preferably about 10 ppm or less.

  In order to form a uniform film as much as possible on all or part of the surface of a micro magnet shaped like a cylinder or a disk, a sputtering method in which metal components are three-dimensionally deposited on the magnet surface from multiple targets, Alternatively, an ion plating method in which a metal component is ionized and a film is formed using electrostatic attraction and strong deposition characteristics is particularly effective.

  As for holding the rare earth magnet in the plasma space in the sputtering operation, one or a plurality of magnets can be rotatably held by a wire or a plate, or a plurality of magnets can be loaded into a metal mesh cage. It is possible to adopt a method of holding the roll freely. By such a holding method, a uniform film can be formed three-dimensionally on the entire surface of the micro magnet.

  In the above-mentioned rare earth metal for film formation, recovery of magnetic properties is not observed only by simply covering the magnet surface, so that at least a part of the deposited rare earth metal component diffuses inside the magnet and rare earth such as Nd. It is essential to react with the metal rich phase. For this reason, normally, after the film formation, a short-time heat treatment is performed at 500 to 1000 ° C. to diffuse the metal film. In the case of sputtering, since the magnet during film formation can be raised to the above temperature range, for example, about 800 ° C. by increasing the RF and DC output during sputtering, the film is substantially formed. However, diffusion can be performed simultaneously.

FIG. 1 is an explanatory view of a three-dimensional sputtering apparatus suitable for use in the present invention. In FIG. 1, a target 1 and a target 2 made of a ring-shaped metal film are placed facing each other, and a water-cooled copper high-frequency coil 3 is placed between them. An electrode wire 5 is inserted inside the cylinder of the cylindrical magnet 4, and the electrode wire 5 is fixed to the rotating shaft of the motor 6 and holds the cylindrical magnet 4 so that it can rotate.

  Here, in order to prevent slippage during rotation between the inside of the cylindrical magnet 4 and the electrode wire 5, the electrode wire 5 is twisted into a fine waveform and is in contact with the inside of the tube. Since the weight of the micro magnet is about several tens of mg, there is almost no slip when the electrode wire 5 and the cylindrical magnet 4 are rotated.

Furthermore, it has a mechanism capable of performing reverse sputtering of the cylindrical magnet 4 by the cathode changeover switch (A). During reverse sputtering, the surface of the magnet 4 is etched by setting the magnet 4 to a negative potential through the electrode wire 5. Switch to switch (B) during normal sputtering.
Normally, sputtering is generally performed without applying a potential to the electrode wire 5 during sputtering, but in order to control the type of metal to be deposited and the film quality, in some cases, a positive electrode is applied to the magnet 4 through the electrode wire 5. A sputtering potential may be formed by applying a bias potential. During normal sputtering, a plasma space 7 in which Ar ions, metal particles generated from the targets 1 and 2 and metal ions are mixed is formed, and the metal particles are three-dimensionally viewed from the top, bottom, left, and right of the surface of the cylindrical magnetic core 4. The film comes in flight.

  When the magnet formed by such a method is not diffused while forming a film, the magnet is transferred to a glove box connected to the sputtering apparatus after returning to the atmospheric pressure without touching the atmosphere. Heat treatment is performed to load the film in a small electric furnace installed in the glove box and diffuse the film into the magnet.

  In general, since rare earth metals are easily oxidized, it is desirable to form a corrosion-resistant metal such as Ni or Al or a water-repellent silane-based film on a magnet surface after film formation for practical use. In addition, when the modified surface metal is Dy or Tb, the progress of oxidation in air is significantly slower than that of Nd. Therefore, depending on the application of the magnet, it is possible to omit providing a corrosion-resistant coating.

First, a method for manufacturing a magnet Ru used in the present invention.
(Reference Example 1)
An alloy flake having a thickness of 0.2 to 0.3 mm was manufactured from an alloy ingot having a composition of Nd _12.5 Fe _78.5 Co ₁ B ₈ by strip casting. Next, this thin piece is filled in a container, and hydrogen gas of 500 kPa is occluded at room temperature and then released, so that the size is about 0 . An amorphous powder of 15 to 0.2 mm was obtained, and was subsequently pulverized by jet mill to produce a fine powder of about 3 μm.

  After adding 0.05 wt% of calcium stearate to this fine powder, it was press-molded in a magnetic field, charged in a vacuum furnace and sintered at 1080 ° C. for 1 hour to obtain an 18 mm square cubic magnet block material.

Next, this cubic magnet block material was subjected to grinding wheel cutting, outer diameter grinding, and ultrasonic drilling to produce a cylindrical magnet having an outer diameter of 1 mm, an inner diameter of 0.3 mm, and a length of 3 mm. The sample in this state was used as a comparative sample (1). The volume is 2.14 mm ³ , the surface area is 13.67 mm ² , and the specific surface area (surface area / volume) is 6.4 mm ⁻¹ .

  Next, a metal film was formed on the surface of the cylindrical magnet using the three-dimensional spuck apparatus shown in FIG. As the target, dysprosium (Dy) metal was used. Inside the cylinder of the cylindrical magnet, a tungsten wire having a diameter of 0.2 mm was inserted as an electrode wire. The size of the used ring-shaped target was 80 mm in outer diameter, 30 mm in inner diameter, and 20 mm in thickness.

The film forming operation was performed according to the following procedure. A tungsten wire was inserted and set inside the cylinder of the cylindrical magnet, and the inside of the sputtering apparatus was evacuated to 5 × 10 ⁻⁵ Pa, and then high purity Ar gas was introduced to maintain the inside of the apparatus at 3 Pa. Next, the cathode changeover switch was set to the (A) side, RF output 20 W and DC output 2 W were added, and reverse sputtering was performed for 10 minutes to remove the oxide film on the magnet surface. Subsequently, with the changeover switch set to the (B) side, RF output 80 W and DC output 120 W were added, and normal sputtering was performed for 6 minutes.

  The obtained film-forming magnet was transferred to the glove box connected to the sputtering apparatus without returning to the atmospheric pressure after returning the inside of the apparatus to the small electric furnace, which was also installed in the glove box, The first stage was heat-treated at 700 to 850 ° C. for 10 minutes and the second stage at 600 ° C. for 30 minutes.

These were used as reference example samples (1) to (4). In order to prevent the magnet from being oxidized during the heat treatment, purified Ar gas was circulated in the glove box to maintain the oxygen concentration at 2 ppm or less and the dew point at −75 ° C. or less.

The magnetic properties of each sample were measured using a vibrating sample magnetometer after applying a pulse magnetization of 4.8 MA / m. Table 1 shows the magnetic characteristic values of each sample, and FIG. 2 shows the demagnetization curves of the comparative example sample (1) and the reference example samples (1) and (3).

As is apparent from Table 1, the reference sample showed a higher energy product (BH) max than the comparative sample by the Dy metal film formation and the subsequent heat treatment, and in particular, the sample (3) had the comparative sample (1 ), A recovery of 38% was observed. The reason for this is presumed to be that the Nd-rich layer damaged by machining was repaired and strengthened. As a result, as is apparent from the shape of the demagnetization curve in FIG. In comparison, the squareness (Hk / Hcj) of the reference example surface-modified is remarkably improved. Here, Hk means a magnetic field when the magnetization value corresponds to 90% of the residual magnetization on the demagnetization curve.

The Dy film was observed for the sample after the measurement. First, the reference example sample (1) was embedded and polished in a resin, and then lightly etched with nitric alcohol and observed with a 500-fold optical microscope. As a result, it was found that a film of about 2 μm was uniformly formed on the entire outer periphery of the sample.

Moreover, about the reference example sample (2), the internal structure of the magnet was observed using the analytical scanning electron microscope. As a result, as shown in the backscattered electron image of FIG. 3A, the sample surface portion exhibited a structure different from the inside by Dy film formation and subsequent heat treatment. Further, according to the Dy element image of FIG. 3B, it can be seen that a high concentration of Dy exists in the surface layer, and at the same time, the Dy element diffuses and penetrates into the sample, and the diffusion depth is about 10 μm. I found out. In addition, it is presumed that the surface layer peeled off at the time of polishing was partially transferred at the Dy high density portion seen in the center of the image.

( Reference Example 2)
Nd, Dy, Pr, Tb, and Al metals were formed on the cylindrical magnets having an outer diameter of 1 mm, an inner diameter of 0.3 mm, and a length of 3 mm manufactured in Reference Example 1, respectively. Here, the target dimensions of Nd and Al are 80 mm in outer diameter, 30 mm in inner diameter, and 20 mm in thickness, similar to Dy in Reference Example 1. The Pr and Tb targets are 2 mm in thickness only on the surface of the Al target facing the sample. Each metal was attached and fixed.

  After attaching each of these metal targets to a three-dimensional sputtering apparatus, two cylindrical magnets were set on the tungsten electrode wire, and the respective targets were exchanged to form each metal film. In the film forming operation, Ar gas was introduced into the apparatus to maintain the pressure in the apparatus at 3 Pa, RF output 20 W and DC output 2 W were added, and reverse sputtering was performed for 10 minutes, followed by RF output 100 W and DC output 200 W. And was sputtered for 5 minutes.

As for the thickness of each metal film, one of the two magnets was embedded in a resin and observed with a microscope. As a result, Al was 3.5 μm, and the rare earth metal was in the range of 0.02 to 2 μm. On the other hand, the other magnets were loaded into a small electric furnace in the glove box and subjected to diffusion heat treatment at 800 ° C. for 10 minutes and 600 ° C. for 30 minutes, and the reference sample samples (5) to (8) and the comparative sample sample ( 2).

The comparative sample (1) is listed again from Table 1, and the comparative sample (3) is a sample that is not subjected to heat treatment while Nd is deposited. Table 2 shows the magnetic properties of the obtained magnet sample. As is apparent from Table 2, when the deposited metal is Al, the characteristics are almost the same as those of the comparative sample (1) having no metal film, and the effect of surface modification is not observed. Further, since the comparative sample (3) is not subjected to the diffusion heat treatment, the diffusion layer is not formed, and the recovery of the magnetic characteristics is not observed. On the other hand, in all of the reference example samples, the coercive force Hcj and the energy product (BH) max recovered significantly.

( Reference Example 3 )
A sintered magnet having an outer diameter of 5.2 mm, an inner diameter of 1.9 mm, and a thickness of 3 mm was manufactured from an alloy of Nd _12.5 Fe _78.5 Co ₁ B ₈ composition in the same process as in Reference Example 1. . This magnet is subjected to outer diameter grinding and inner diameter grinding, and then using a surface grinder, the outer diameter is 5 mm, the inner diameter is 2 mm, and the thickness is 0.1 mm, 0.2 mm, 0.5 mm, 0.8 mm. Disk-shaped magnets with various dimensions of 2 mm and 1.8 mm were obtained. Volume approximately ^{2mm 3 ~30mm} 3, specific surface area (surface area / volume) is in the range of about ^21mm -l ^{~4mm -1.}

These magnets were held through stainless steel electrode wires and attached to an arc discharge ion plating apparatus. Then, after evacuating the inside of the apparatus to 1 × 10 ⁻⁴ Pa, high-purity Ar gas was introduced to maintain the inside of the apparatus at 2 Pa. While applying a voltage of −600 V to the stainless steel wire and rotating at 20 rpm, Dy particles dissolved and evaporated by an electron gun and ionized by a thermionic emission electrode and an ionization electrode are deposited on the magnet surface for 15 minutes to form a film. A magnet sample having a thickness of 2 μm was manufactured.

Next, this sample was loaded into a small electric furnace in the glove box, and the first stage was subjected to diffusion heat treatment at 850 ° C. for 10 minutes and the second stage at 550 ° C. for 60 minutes to obtain a sample thickness of 0.1 mm. A reference example sample (19) having a thickness of 1.8 mm was obtained from the reference example sample (14). In addition, the magnet after grinding was used as comparative example samples (7) to (12) in order of thickness.

FIG. 4 shows the results of magnetic properties (BH) max when the thickness dimension, specific surface area (surface area / volume), and volume of these samples are used as parameters. As shown in FIG. 4, the reference sample samples (14) to (19) obtained by forming a Dy metal film and subjecting it to diffusion heat treatment are (BH) in any dimension compared to the untreated comparative sample samples (7) to (12). ) A recovery of max was seen. In particular, when the volume is smaller than 10 mm ³ and the volume ratio to the surface area is larger than 4 mm ^−1, it has been found that the effect of recovering the magnetic properties by the surface modification is remarkable.

Here, the modification characteristics of the magnet, particularly the Dy film thickness and the magnetic characteristics will be described.
FIG. 8 shows the relationship between the Dy film thickness and the magnetic characteristics, and shows that the optimum film thickness is 1.4 μm.
Further, regarding the heat treatment temperature of the motor magnet, FIG. 9 shows the relationship between the heat treatment temperature and the magnetic properties. Particularly, 900 ° C. to 1000 ° C. is suitable as the motor magnet, and 900 ° C. is particularly optimum. I found out. It was confirmed that the characteristics deteriorated at 1100 ° C.

It will now be described small motor according to the present invention provided with a magnet obtained as described above.
FIG. 6 shows an example of a small motor in which a magnet according to the present invention is provided on a rotor.
11 is a housing, 12 is a flange, and a field winding 15 is mounted in the housing 11.
The rotor magnet 14 is formed in a cylindrical shape, is fixed to the shaft 13, and is magnetized in a direction orthogonal to the shaft axis.
The shaft 13 is held by a bearing 16 fixed to the flange 12. Reference numeral 17 denotes a wiring board for supplying power.

Here, the permeance coefficient is defined as follows.
In FIG. 5, the point (Hd, Bd) represented by the magnetic flux density value Bd on the BH curve corresponding to the demagnetizing field Hd is called an operating point. A straight line passing through the operating point and the origin in the BH demagnetization curve is referred to as an operating line, and −B / H = Pc is referred to as a permeance coefficient.
For example, in the case of a motor, the permeance coefficient Pc has the following relationship.
(Lm · Ag) / (Am · Lg) · (Kf / Kr) (1)
In equation (1),
Lm is the magnet thickness Ag is the magnetic gap cross-sectional area Am is the effective magnet cross-sectional area Lg is the magnetic gap length Kf is the leakage coefficient Kr is the magnetomotive force loss coefficient. The permeance coefficient is set so that the magnetic flux density at the operating point does not fall below the inflection point so that the magnet does not cause significant irreversible demagnetization due to the influence of the magnetic field or heat. Then, the permeance coefficient is set to 1 or more, preferably 1.4 or more. In this way, a small motor having an outer diameter of 4 mm as a whole can be obtained.

FIG. 7 shows an embodiment of a small motor using the above-described magnet as a stator.
A cup-type rotor in which one end of the axial opening of the cylindrical winding 25 is fixed to the rotary shaft 23;
The cylindrical stator magnet 24 is disposed inside the cup-shaped rotor, provided in the cylindrical housing 21 and magnetized in a direction perpendicular to the rotation axis. 22 is a flange.

表４は、本発明と比較例の磁石仕様による（ＢＨ）max向上率と、それぞれの磁石を実装したモータのトルク定数（Ｋｔ）の向上率を示す。

Table 4 shows the (BH) max improvement rate according to the magnet specifications of the present invention and the comparative example, and the improvement rate of the torque constant (Kt) of the motor on which each magnet is mounted.

From Table 4, when the inflection point is obtained from the relationship between the specific surface area of the magnet and the Kt improvement rate, the specific surface area is 4 mm ⁻¹ , while the inflection point is obtained from the relationship between the volume and the Kt improvement rate. If it calculates | requires, it will obtain | require that a volume exists in 10 mm < ³ > and the limited range of this invention is specified from the inflection point. In addition, the smaller the volume and the larger the specific surface area, that is, the smaller the magnet, the greater the ratio of the processing deteriorated portion, and the (BH) max improvement rate due to the repair by Dy increases. As shown in Table 4, it can be seen that Examples A, B and C are superior to Comparative Examples D and E.
In the present invention , when the permeance coefficient (operating point) is 1 or more, the specific surface area (surface area / volume) of the magnet is 4 mm ^-1 or more, and the magnet volume is 10 mm ³ or less, the outer diameter of the motor is 3 mm or less. Can be manufactured.

The coercive force (H _cj = ~ 1.18 MA / m) of the surface-modified cylindrical Nd-Fe-B sintered magnet (outer diameter φ0.9mm and φ1.2mm) The accelerated heat treatment rose to H _cj = ~ 1.39 MA / m, and the obtained (BH) _max value was almost equivalent to that of the magnet bulk material before processing ((BH) _max = ~ 379 kJ / m ³ ). Table 5 shows various characteristics of the prototype motor of the present invention, together with that of a commercially available motor (outside diameter φ2.0 mm) manufactured by our company. Here, the prototype motor of Table 5 is the one in which the magnet of Table 4 is mounted. The magnet of Example B is a prototype motor with an outer diameter of φ1.7 mm, and the magnet of Example C is an prototype motor with an outer diameter of φ2.0 mm. Is applied. Compared with our commercially available motor (using Sm-Co magnet for the rotor: (BH) _max = ~ 225kJ / m ³ , other specifications are the same) The torque constant was improved by about 23% and the maximum efficiency was improved by about 11%. In addition, by using the modified magnet and special field coil, it was possible to obtain a starting torque equal to or greater than that of the above-mentioned commercially available motor (outer diameter φ2.0 mm) at an outer diameter φ1.7 mm.

本発明の外径φ２．０ｍｍ試作モータと当社製市販モータの比較(同サイズでの比較）にて
トルク定数、最大効率及び起動トルク、特にトルク定数が顕著に向上している。
また、外径寸法がφ1.7ｍｍのものについても、大きな起動トルクを得ることができた。

The torque constant, the maximum efficiency and the starting torque, especially the torque constant are remarkably improved by comparing the prototype motor of the present invention with an outer diameter of φ2.0 mm and a commercially available motor manufactured by our company (comparison with the same size).
In addition, a large starting torque could be obtained even with an outer diameter of φ1.7 mm.

〔The invention's effect〕
First, the torque constant of the micro motor is improved.
That is, low rotation / high torque and low current consumption are sufficient. Since the mechanical time constant is small, the responsiveness is improved, and the fluctuation in the rotational speed with respect to the load can be further reduced.
Furthermore, since the coercive force of the rotor magnet or stator magnet can be improved as a modification effect, it is difficult to demagnetize against heat or an external magnetic field, and high reliability can be expected. Thus, a micro motor and a driving motor having an outer diameter of 1.7 mm could be obtained.

  According to the present invention, a rare-earth metal film is diffused on the surface of a magnet that has been altered and damaged by machining, thereby repairing the magnet surface layer that has been altered and damaged by machining such as cutting, drilling, grinding, and polishing. It can be recovered significantly. Moreover, as a result, it is useful for manufacturing a micro motor using a small, high-performance magnet.

This small motor can be used as medical devices, industrial devices, etc., as well as devices for driving various types of endoscopes, micromachine power devices such as self-propelled inspection robots in narrow tubes, etc. An ultra-compact device with current and high response can be obtained.
It can also be applied to board mounting by reflow of ultra-small motors that will become the mainstream in the future.

To the onset bright is a schematic view of a target near suitably three-dimensional sputtering apparatus can be used. It is a graph which shows the demagnetization curve of reference example samples (1) and (3), and a comparative example sample (1). It is a drawing substitute photograph which shows the SEM image (a: reflected electron image, b: Dy element image) of the reference example sample (2) heat-processed after Dy film-forming. It is a related figure of a magnet sample size and (BH) max of a reference example and a comparative example sample. It is explanatory drawing of a permeance coefficient. The magnet is a cross-sectional view of a miniature motor according to the present invention used in the rotor. The magnet is a cross-sectional view of a miniature motor according to the present invention used in the stator. It is a figure which shows the relationship between Dy film thickness and a magnetic characteristic. It is a figure which shows the relationship between heat processing temperature and a magnetic characteristic.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Target 2 Target 3 High frequency coil 4 Magnet 5 Electrode wire 6 Motor 7 Plasma space 11 Housing 12 Flange 13 Shaft 14 Cylindrical rotor magnet 15 Field winding 16 Bearing 17 Wiring board 21 Housing 22 Flange 23 Shaft 24 Cylindrical stator Magnet 25 Cylindrical winding

Claims (6)

A housing, a field winding provided inside the housing, a shaft rotatably supported by a bearing portion, and a cylindrical rotor magnet provided on the shaft and magnetized in a direction perpendicular to the shaft axis A small motor with
The cylindrical rotor magnet is a cylindrical Nd-Fe-B-based or Pr-Fe-B-based sintered magnet having a perforated inner surface having a surface that has been damaged by machining. An R metal (where R is one of rare earth elements selected from Y and Nd, Dy, Pr, Ho, Tb) or more than a depth corresponding to the radius of the crystal grain exposed on the outermost surface. by cementation of two or more) from the magnet surface, the altered lesion Ri Do sintered magnet was by reforming (BH) max 280kJ / m ³ or more, and in yet the small motor,
Permeance coefficient (operating point) is 1 or more,
The specific surface area (surface area / volume) of the rotor magnet is 4 mm ⁻¹ or more,
A small motor, wherein the volume of the rotor magnet is selected to be 10 mm ³ or less. A cup-type rotor in which one end of an axial opening of a cylindrical winding coil is fixed to a rotating shaft;
A small motor comprising a cylindrical stator magnet disposed inside the cup-shaped rotor, provided on a cylindrical yoke, and magnetized in a direction perpendicular to the rotation axis;
The cylindrical stator magnet is a cylindrical Nd-Fe-B-based or Pr-Fe-B-based sintered magnet having a perforated inner surface having a surface that has been altered and damaged by machining. An R metal (where R is one of rare earth elements selected from Y and Nd, Dy, Pr, Ho, Tb) or more than a depth corresponding to the radius of the crystal grain exposed on the outermost surface. by cementation of two or more) from the magnet surface, the altered lesion Ri Do sintered magnet was by reforming (BH) max 280kJ / m ³ or more, and in yet the small motor,
Permeance coefficient (operating point) is 1 or more,
The specific surface area (surface area / volume) of the stator magnet is 4 mm ^-1 or more,
A small motor, wherein a volume of the stator magnet is selected to be 10 mm ³ or less. Small motor according to any one of claims 1 or 2, characterized in that the permeance coefficient (operating point) is 1.4 or more. The small motor according to any one of claims 1 to 3 , wherein a thickness of a film formed by diffusion penetration on the magnet surface is set to 0.02 to 2 µm. Wherein R metals, Dy der connexion, miniature motor according to any one of claims 1 to 4, characterized in that a 1.4μm thickness of the coating formed by diffusion coating on the surface of the magnet . Small motor according to any one of claims 1 to 5 the outer diameter of the motor, characterized in that it is chosen to 3mm or less.

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