JP2007263209A - Hydrodynamic bearing and motor using the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a hydrodynamic bearing having high wear resistance and hardly producing particles while suppressing the attraction of sliding opposed faces to each other. <P>SOLUTION: The hydraulic bearing 10 comprises a rotor having mutually opposed faces 1a, 2a, 2b, 3a and a stator one of which is a shaft member, the opposed faces 1a, 2a, 2b, 3a having hydrodynamic pressure generating grooves 1b, 3b on one side and at least one of them being a ceramics polished face. Herein, a groove recessed portion is formed along the grain boundary of ceramics crystal grains exposed to the polished face. With the groove recessed portion, fluid exists among the opposed faces 1a, 2a, 2b, 3a at all times to secures flowability, therefore suppressing the suction of the opposed faces due to direct contact and avoiding higher friction resistance. This suppresses the problem that the opposed faces 1a, 2a, 2b, 3a to the stator are attracted each other and worn to easily produce particles when starting/stopping rotation. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a sliding member, in particular a polygon mirror used in a laser beam printer (hereinafter referred to as LBP), a dynamic pressure bearing used in a hard disk drive (hereinafter referred to as HDD), and the dynamic pressure bearing. It is related with the motor using.

  Conventionally, ceramics have been used as a sliding member having high hardness and excellent wear resistance. In recent years, in addition to the above characteristics, it has excellent heat resistance, high-precision processing and high-speed sliding, etc. are used to take advantage of such features as polygon mirrors used in LBP, etc., hydrodynamic bearings and motors used in HDDs It is used for.

  FIG. 5A is a perspective view showing an example of a conventional hydrodynamic bearing, and FIG. 5B is a cross-sectional view taken along line E-E ′ shown in FIG.

  The hydrodynamic bearing 50 is configured by a combination of a shaft 51, a sleeve 52, and a thrust 53. The columnar shaft 51 is disposed in a hollow portion of the cylindrical sleeve 52, and the shaft 51 is respectively provided at both ends of the column. Connected with Thrust 53. At this time, the shaft 51 and the sleeve 52 and the thrust 53 and the sleeve 52 are arranged with gaps 54 and 55, respectively. In addition, the thrust 53 may be formed integrally with the shaft 51, or may be formed integrally with an adhesive or a screw after being formed separately, taking into consideration the product shape, processing accuracy, manufacturing cost, etc. Designed.

  A dynamic pressure generating groove 51b that generates dynamic pressure in the radial direction is formed on the facing surface 51a of the shaft 51 that faces the sleeve 52, and the dynamic pressure is applied to the facing surface 53a of the thrust 53 that faces the sleeve 52. A generation groove 53b is formed.

  In such a dynamic pressure bearing 50, a shaft 51 and a thrust 53 are used as a rotating body and a sleeve 52 is used as a fixed body as in a dynamic pressure bearing for an LBP polygon mirror, and a dynamic pressure bearing for an HDD. Some use the sleeve 52 as a rotating body and the shaft 51 and the thrust 53 as a stationary body. In any case, when rotation is started, fluid flows into the dynamic pressure generating grooves 51b and 53b to generate dynamic pressure, and a certain distance between the sleeve 52 and the shaft 51 and between the sleeve 52 and the thrust 53. Rotates in a non-contact state while maintaining F and G. Thus, the hydrodynamic bearing 50 can be used in both cases. The rotational driving force can be obtained by assembling a motor component such as a coil or a magnet to either the shaft 51 or the sleeve 52 via a rotor hub or the like.

  However, since the dynamic pressure bearing 50 has a low rotation speed and a low dynamic pressure at the start of rotation, the dynamic pressure bearing 50 rotates in a state where the rotating body and the fixed body are partially in contact with each other. Further, when the rotation is stopped, the dynamic pressure decreases as the rotation speed decreases, and the rotation body and the stationary body rotate in a state of partial contact as in the rotation start, and stop by the abrasion force.

  The hydrodynamic bearing 50 is required to have wear resistance that does not generate particles during high-speed sliding in response to the sliding environment at the start and stop of this rotation.

  Further, the distances F and G of the gaps 54 and 55 are set to about 1 to 5 μm in the case of a small dynamic pressure bearing used in an electronic device. This is because when the distances F and G of the gaps 54 and 55 are set to 1 μm or less, a large dynamic pressure is obtained, but the roundness, cylindricity, There is a problem that it is necessary to process the surface roughness with extremely high accuracy and the manufacturing cost becomes high. Conversely, when the distances F and G of the gaps 54 and 55 are set to 5 μm or more, the rotation is performed. This is because the problem is that the shaft is likely to shake and vibrate easily.

  Such gaps 54 and 55 are filled with oil, air, or the like as a fluid. However, when oil is used, oil does not scatter from the gaps 54 and 55 of the hydrodynamic bearing 50 when the rotor is lifted. It has been designed in consideration of the usage environment, such as heat generation and rotation speed, to ensure sealing and to prevent the oil from oxidizing and deteriorating. In addition, when air is used as the fluid, the members of the rotating body and the fixed body are in direct contact with each other at the start / stop of rotation, so that the members may be composed of ceramics having excellent wear resistance and heat resistance, For example, a DLC (diamond-like carbon) coating is applied to the moving surface as a lubricating layer.

  And as such a dynamic pressure bearing, there exist some which are indicated by patent documents 1-3, for example.

  In Patent Document 1, in a hydrodynamic bearing that self-lubricates by the viscous pump action of a bearing surface, a small protrusion having a height lower than the minimum thickness of an oil film generated during operation at a normal rotational speed and having a small width is provided. It is disclosed that the adsorption action between the bearing surfaces can be suppressed by forming a large number.

  Further, in Patent Document 2, in the dynamic pressure generating groove of the hydrodynamic bearing, the bottom surface of the groove is formed smoothly, and a large number of dimple-shaped concave portions are formed on the surface of the hill portion between the grooves. It is disclosed that the hydrodynamic bearing can be formed by preventing the suction with the mating member and easily cleaning the groove bottom surface by forming the part surface flat.

Further, Patent Document 3 discloses that the use of a sliding member having a maximum height difference of unevenness of the surface of the sliding surface of 0.3 μm or less makes it difficult for wear powder to be generated and reduces the wear rate. Yes.
JP 2001-295834 A JP-A-11-82482 JP-A-5-248442

  However, the hydrodynamic bearing disclosed in Patent Document 1 covers the bearing material with a shadow mask, and after removing the shadow mask after fixing a thin layer on the bearing contact surface by means of vapor deposition, sputtering, plating, etc. There was a problem that the small protrusions were peeled off, and the tip of the small protrusions were chipped into particles, which damaged the sliding surface and easily induced new particles.

  Further, the hydrodynamic bearing shown in Patent Document 2 has a problem that the corners of the dimples are missing and particles are formed, and the shape of the hydrodynamic bearing is reduced when firing is shrunk even if a fine dimple is formed on the ceramic generation form with a mold. There is a problem of collapse, and dimples are formed without distinguishing crystal grains and crystal grain boundaries, so that there are problems that the crystal grains are destroyed and particles are generated during sliding. Furthermore, since the dimples are individually recessed, the fluidity of the fluid in the dimples is low, and depending on the conditions, there is a problem that a suction cup action occurs in which the pressure of the fluid in the dimples is lower than the surrounding pressure. there were.

  In addition, the sliding member shown in Patent Document 3 has been shown to suppress wear of the sliding portion by reducing the unevenness of the sliding surface as much as possible to cope with high speed sliding. In such a sliding surface, the sliding surfaces are adsorbed to each other, so that an excessive starting torque is required at the time of starting, and the excessive starting torque has a problem that the surface of the sliding surface is lost to generate particles.

  The present invention has been made in view of the above-described problems in the prior art, and an object thereof is to provide a hydrodynamic bearing with high wear resistance that suppresses the adsorption of sliding opposed surfaces and is less likely to generate particles. And Another object of the present invention is to provide a long-life motor using the hydrodynamic bearing.

  The dynamic pressure bearing of the present invention comprises a rotating body and a fixed body, one of which is a shaft member and having opposed surfaces facing each other, and the opposed surfaces facing each other have a dynamic pressure generating groove formed on one side. In addition, in the hydrodynamic bearing at least one of which is made of a ceramic polishing surface, a groove-like recess is formed along the grain boundary of the ceramic crystal grains exposed on the polishing surface.

  Further, the hydrodynamic bearing of the present invention has the above-described configuration, wherein the depth of the groove-shaped recess is 1/30 to 1/1 of the average crystal grain size of the ceramic crystal grains exposed on the polishing surface. It is characterized by being 5.

  The hydrodynamic bearing of the present invention is characterized in that, in the cross section of the polished surface having the above-described configuration, the shape of the crystal grains on both sides of the groove-shaped recess is an R shape toward the groove-shaped recess. To do.

  The motor of the present invention is characterized in that any one of the above-described dynamic pressure bearings of the present invention is used as a bearing portion.

  According to the dynamic pressure bearing of the present invention, one of the shaft members is a rotating body having a facing surface facing each other and a fixed body, and the facing surfaces facing each other have a dynamic pressure generating groove formed on one side. In addition, in a hydrodynamic bearing in which at least one of the surfaces is a ceramic polishing surface, a groove-shaped recess is formed along the grain boundary of the ceramic crystal grains exposed on the polishing surface. Since the fluid is always present and fluidity is ensured by the groove-like recesses arranged on the surface, adsorption due to direct contact of the opposing surface is suppressed and the frictional resistance does not increase, so the rotating body of the hydrodynamic bearing starts rotating -It can suppress the problem that the opposing surfaces are abraded due to adsorption of the opposing surfaces to the fixed body when stopped and particles are likely to be generated.

  Further, according to the hydrodynamic bearing of the present invention, when the depth of the groove-like recess is 1/30 to 1/5 of the average crystal grain size in the polished surface of the ceramic crystal grains exposed on the polished surface, While holding the fluid in the groove-shaped recess, the groove-shaped recess does not hinder the force of bonding the crystal grains of the ceramics to each other. Crystal grain shedding can also be suppressed.

  Furthermore, according to the hydrodynamic bearing of the present invention, when the shape of the crystal grains on both sides of the groove-shaped recess is R-shaped toward the groove-shaped recess in the cross section of the polished surface, the groove exists. Since the fluid is more likely to flow, the starting torque can be reduced, and the time during which the opposing surfaces are in direct contact with each other can be shortened, so that the generation of particles can be further suppressed.

  In addition, according to the motor of the present invention using the dynamic pressure bearing of the present invention for the bearing portion, particles generated from the facing surface of the bearing portion are reduced, so that there is an effect of extending the life.

  Hereinafter, a dynamic pressure bearing of the present invention and a motor of the present invention using the same will be described with reference to the drawings.

  FIG. 1A is a perspective view showing an example of an embodiment of a hydrodynamic bearing of the present invention, and FIG. 1B is a cross-sectional view taken along the line AA ′ shown in FIG. .

  The hydrodynamic bearing 10 is composed of a combination of a shaft 1, a sleeve 2 and a thrust 3. A cylindrical shaft 1 is disposed in a hollow portion of the cylindrical sleeve 2, and the shaft 1 is respectively provided at both ends of the column. It is connected to the thrust 3. At this time, the shaft 1 and the sleeve 2 and the thrust 3 and the sleeve 2 are arranged with gaps 4 and 5, respectively. Further, the thrust 3 may be formed integrally with the shaft 1 or may be fixed integrally with an adhesive, a screw or the like after being formed individually, but the product shape, processing accuracy, manufacturing cost, etc. Designed with consideration.

  A dynamic pressure generating groove 1b for generating a radial dynamic pressure is formed on the facing surface 1a of the shaft 1 facing the sleeve 2, and a dynamic pressure is formed on the facing surface 3a of the thrust 3 facing the sleeve 2. A generation groove 3b is formed.

  In such a dynamic pressure bearing 10, the shaft 1 and the thrust 3 are used as a rotating body and the sleeve 2 is used as a fixed body as in a dynamic pressure bearing for an LBP polygon mirror, and the dynamic pressure bearing for an HDD. Some use the sleeve 2 as a rotating body and the shaft 1 and the thrust 3 as a stationary body. In any case, when rotation is started, fluid flows into the dynamic pressure generating grooves 1b and 3b to generate dynamic pressure, and a certain distance is provided between the sleeve 2 and the shaft 1 and between the sleeve 2 and the thrust 3. Rotate in a non-contact state while maintaining B and C. Thus, the hydrodynamic bearing 10 can be used in both cases. The rotational driving force can be obtained by assembling a motor component such as a coil or a magnet to either the shaft 1 or the sleeve 2 via a rotor hub or the like.

  Since the dynamic pressure bearing 10 has a low rotation speed and a low dynamic pressure at the start of rotation, the dynamic pressure bearing 10 rotates in a state where the rotating body and the fixed body are in partial contact. As the rotational speed increases, dynamic pressure is generated by the dynamic pressure generating grooves 1b and 3b and rotates in a non-contact state while maintaining the constant gaps B and C with the opposing surfaces 2a and 2b. When the pressure decreases, the dynamic pressure decreases, and the rotating body and the fixed body rotate in a state where they are partly in contact with each other as at the start of rotation, and are stopped by the abrasion force.

  The hydrodynamic bearing 10 is required to have wear resistance that does not generate particles during high-speed sliding in response to the sliding environment at the start and stop of this rotation.

  The dynamic pressure bearing according to the present invention is composed of a rotating body and a fixed body, one of which is a shaft member and having opposed surfaces facing each other, and the opposed surfaces facing each other are formed with a dynamic pressure generating groove on one side. In addition, in the dynamic pressure bearing 10 having at least one of a ceramic polished surface, groove-shaped recesses are formed along the grain boundaries of the ceramic crystal grains exposed on the polished surface. , The shaft 1 integrally formed with the thrust 3 is a shaft member, opposed surfaces 1a and 2a, 2b and 3a facing each other, and dynamic pressure generating grooves 1b and 3b formed on one side. And at least one of the facing surfaces 1a and 2a, 2b and 3a is constituted by a ceramic polishing surface, and a groove-like recess is formed along the grain boundary of the ceramic crystal grains exposed on the polishing surface. That is.

  Next, this polished surface will be described with reference to FIG.

  FIG. 2A is a partial cross-sectional view showing an example of the polished surface in the hydrodynamic bearing of the present invention, and FIG. 2B is a partially enlarged view showing the surface of the polished surface.

  As shown in FIG. 2A, the polished surface 20 is composed of a crystal grain surface 16 of the ceramic crystal grain 12 and a groove-like recess 11 along the grain boundary of the crystal grain 12.

  There are minute irregularities due to crystal grains on the fired surface of ordinary ceramics, but the height of the irregularities is irregular and there are also large irregularities. Severe wear is caused between the member and the opposing surface of the mating member or the member itself is worn away to generate a large amount of particles. In addition, minute flaws on the surface of the formed body that are generated when the formed ceramic body is formed or handled also become unevenness that causes intense wear with the mating member after firing, which causes generation of particles. Therefore, the reason why at least one of the facing surfaces 1a, 2a, 2b, and 3a is the ceramic polishing surface 20 is to eliminate wear on the facing surfaces 1a, 2a, 2b, and 3a and to suppress generation of particles. Therefore, as shown in FIG. 2A, for example, when the crystal grain size of the crystal grains 12 is relatively uniform, such as one-component high-purity alumina or zirconia, it is 10 times the average crystal grain diameter. By polishing to the above depth, the surface is used as a smooth polished surface 20.

  Next, as shown in a partially enlarged view of the surface of the polishing surface 20 in FIG. 2B, a groove-shaped recess 11 is formed along the grain boundary of the crystal grains 12. Here, the respective groove-like recesses 11 are connected to each other and spread in a mesh shape on the polishing surface 20. For this reason, the fluid (gas / liquid) present in the groove-like recess 11 is always in a highly fluid state, and a sufficient amount of gas or liquid is supplied to the entire surface of the polishing surface 20. Adsorption of the surfaces 1a and 2a, 2b and 3a can be effectively prevented. That is, even when a part of the opposed surfaces 1a and 2a, 2b and 3a facing each other when the hydrodynamic bearing 10 is stopped, fluid (gas / liquid) is caused by slight vibration at the time of start-up and movement of low-speed rotation. Is transferred to the entire surface of the polishing surface 20 through the groove-shaped recess 11, so that the adsorption of the opposing surfaces 1a and 2a, 2b and 3a is quickly eliminated, and the generation of particles due to contact and sliding is suppressed. can do.

  The average crystal grain size of the ceramic crystal grains 12 is preferably 0.2 to 10 μm. When the thickness is less than 0.2 μm, the depth of the groove-shaped recess 11 that can be formed around the crystal grains 12 becomes too small, so that a sufficient amount of fluid (gas / liquid) is formed in the groove-shaped recess. This is because it becomes difficult to flow through 11 and the effect of preventing the adsorption of the polished surface 20 cannot be obtained. The reason why the particle size is 10 μm or less is that when the particle size exceeds 10 μm, the crystal grains 12 are in contact when sliding. This is because it becomes easy to drop off from the polished surface 20.

  Further, in the dynamic pressure bearing 10 of the present invention, the groove-like recesses 11 are formed along the grain boundaries of the crystal grains 12 because the crystal grains 12 are damaged when the surfaces facing each other contact and slide, This is to prevent this. When a recess is simply formed on the polished surface 20 by grinding or the like, such a recess is formed without distinguishing the crystal grains 12 and the crystal grain boundaries, so the crystal grains 12 are broken to form recesses. It is not preferable.

  That is, by forming the groove-like recesses 11 along the grain boundaries of the ceramic crystal grains 12, the crystal grains 12 can maintain their original strength, and between the opposed surfaces 1a and 2a, 2b and 3a. Since fluid is always present and fluidity is ensured, adsorption due to direct contact with the opposing surface is suppressed, and the abrasion resistance does not increase. Therefore, when the rotating body of the hydrodynamic bearing 10 starts and stops rotating, the fixed body The opposing surfaces 1a, 2a, 2b, and 3a are not adsorbed between them, and generation of particles due to wear of the opposing surfaces 1a, 2a, 2b, and 3a can be suppressed.

  Further, in the hydrodynamic bearing 10 of the present invention, the depth of the groove-like recess 11 is 1/30 to 1/5 of the average crystal grain size in the polished surface 20 of the ceramic crystal grains 12 exposed on the polished surface 20. It is preferable.

  Here, the depth of the groove-like recess 11 is defined as a partial cross-sectional view of an example of a cross section of the polished surface in the hydrodynamic bearing of the present invention shown in FIG. The distance (h) to the bottom of the groove-shaped recess 11 is indicated.

  The depth h of the groove-like recess 11 is set to 1/30 or more of the average crystal grain size of the ceramic crystal grains 12 on the polished surface 20 because an amount of fluid necessary for preventing the adsorption between the opposing faces is reduced. The reason is that it is included in the groove-shaped recess 11 and is 1/5 or less in order to secure a holding force for preventing the crystal grains 12 from falling off the polished surface 20.

  On the other hand, when the depth h is less than 1/30 of the average crystal grain size, it becomes difficult to sufficiently contain the amount of fluid necessary to prevent the polishing surface 20 from adsorbing in the groove-like recess 11. There is a problem that the surfaces adhere to each other, and if it exceeds 1/5, the crystal grains 12 drop off from the polishing surface 20 and become particles, or the dropped particles damage the polishing surface 20 and generate new particles. Problem arises.

  Further, in the hydrodynamic bearing 10 of the present invention, it is preferable that the shape of the crystal grains 12 on both sides of the groove-shaped recess 11 is R-shaped toward the groove-shaped recess 11 in the cross section of the polished surface 20.

  This will be specifically described with reference to a partial cross-sectional view of the polishing surface 20 shown in FIG. In the cross section of the polished surface 20, if the shape of the crystal grains 12 on both sides of the groove-like recess 11 is an R shape toward the groove-like recess 11, the fluid movement is not disturbed and the fluid is more likely to flow. Since the starting torque is reduced and the time during which the opposing surfaces are in direct contact with each other can be shortened, the generation of particles can be suppressed.

  3B is a partial cross-sectional view similar to FIG. 3A, the polished surface 20 has a groove-like recess 11 compared to the case where the crystal grain surface 16 shown in FIG. Even if the depth h is the same, it is the R-shaped end that makes direct contact with the opposing polishing surface 20, and the contact area of the entire polishing surface 20 is small, so that the fluid flows in the groove-shaped recess 11. It tends to exist not only in the inside but also on the crystal grain surface 16, and therefore, the factor of increasing the abrasion resistance between the opposing surfaces is reduced, and adsorption between the opposing surfaces can be more effectively prevented. The R shape may be formed on at least one polishing surface 20 of the opposed surfaces.

  The size of R in the R shape as described above is not particularly limited, but as described above, the depth h of the groove-like recess 11 is 1/30 to 1/5 of the crystal grain size of the crystal grain 12. Adjust to the range.

  Further, as shown in FIG. 3C in the same partial cross-sectional view as FIGS. 3A and 3B, crystals that are greatly different like a binary ceramic having large crystal grains 14 and small crystal grains 15 are used. When the grain sizes are adjacent to each other, it is preferable to determine the depth h of the groove-like recess 11 based on the crystal grain size of the small crystal grains 15. This is because if the depth h of the groove-like recess 11 is determined in accordance with the crystal grain size of the large crystal grains 14, the small crystal grains 15 are likely to fall off.

  When this dynamic pressure bearing 10 is used in the structure as shown in FIG. 1, it can be suitably used as a dynamic pressure bearing for the bearing portion of the motor 40 as shown in a sectional view in FIG.

  The motor 40 in FIG. 4 is a cross-sectional view showing an example of an embodiment of the motor of the present invention using the dynamic pressure bearing 10 of the present invention. The motor 40 includes a shaft 41, a rotor hub 45, and a thrust 43, which are rotating bodies, and a base 48, a sleeve 42, and a thrust plate 44, which are stationary bodies. A fixed stator 47 and a magnet 46 in which N poles and S poles are alternately arranged in an annular shape on the inner wall of the rotor hub 45 are provided. A plurality of the same number of stators 47 and magnets 46 are installed on the base 48 and the rotor hub 45, respectively, and are arranged concentrically with respect to the rotation axis D.

  In the motor 40, the shaft 41, the thrust 43, the sleeve 42 of the fixed member, and the thrust plate 44 are constituted by the dynamic pressure bearing of the present invention. The shaft 41 is rotatably inserted into the sleeve 42 with the central portion of the rotor hub 45 fixed to the upper end, and the thrust 43 is fixed to the lower end. The sleeve 42 and the thrust plate 44 are fixed to the base 48 and receive dynamic pressures in the radial direction and the thrust direction, respectively. In this example, the hydrodynamic bearing 10 of the present invention is used for the shaft 41, the sleeve 42, the thrust 43, and the thrust plate 44, and the dynamic pressure generating grooves 41b and 43b are formed on the opposing surfaces 41a and 43a, respectively. In some cases, dynamic pressure is generated in the gap between the opposing members, and it floats and rotates without contact.

  The shape of the dynamic pressure generating grooves 41b and 43b is a general herringbone or a flat surface parallel to the axial direction at equal intervals on the outer periphery of the shaft 41 as disclosed in JP-A-9-14257. It doesn't matter what type. In the case of a small motor used in an electronic device, the depth of the dynamic pressure generating grooves 41b and 43b is preferably about several μm, and the depth of the dynamic pressure generating grooves 41b and 43b when a flat surface is regarded as a groove is 20 μm. The following is desirable.

  And if the grinding | polishing surface 20 in which the groove-shaped recessed part 11 was formed in the circumference | surroundings of the crystal grains 12-15 was formed in at least one of the opposing surfaces of the opposing surfaces 41a and 42a, 43a and 42a, and 43a and 44a, respectively. In particular, it is preferable that the opposing surfaces 43a and 44a are formed so that the opposing surfaces are easily attracted when the motor is stopped.

  In the motor 40 configured as described above, when an alternating current flows through the stator 47, a magnetic field is generated, attracting or repelling the magnetic force of the magnet 46, and the rotor hub 45 rotates. When the rotor hub 45 rotates, the shaft 41 and the thrust 43 also rotate. At the start of rotation, the opposing surfaces come into contact with each other and slide, but when the rotation speed increases, the dynamic pressure generating grooves 41b and 43b formed in the respective members. As a result, dynamic pressure is generated, the rotating body floats, and non-contact rotation is continued with a certain gap maintained.

  Then, a hard disk, a polygon mirror or the like is mounted on the outer peripheral portion 49 of the rotor hub 45 and used for an HDD, LBP, or the like.

  In addition, the motor 40 of the present invention includes, for example, a server HDD having a rotation speed of 10,000 rpm or more, a personal computer HDD having a rotation speed of 15000 rpm or more, an LBP having a rotation speed of 50,000 rpm or more, and a DLP (digital Light processor). These motor rotational speeds are values that cannot be used with conventional ball bearings due to wear and seizure, and by using the motor 40 of the present invention to form a hydrodynamic bearing that uses air as a fluid, it is said that wear and seizure will occur. The problem can be solved.

  Next, a method for manufacturing the hydrodynamic bearing of the present invention will be described.

  Ceramics used for the hydrodynamic bearing 10 of the present invention include alumina, zirconia, titanium carbide, titanium nitride, silicon carbide, silicon nitride, and composite materials thereof. A general method is used for manufacturing these ceramics. be able to. Each ceramic raw material is pulverized and mixed with a solvent with a ball mill, vibration mill, etc. to a predetermined particle size to form a slurry. A binder is added to the slurry as necessary, and the slurry is dried and formed using a spray dryer or the like. Granulate the raw material for molding. Next, the forming raw material is formed into a formed body using a mechanical press or the like, and fired at a firing temperature and firing atmosphere corresponding to each ceramic to obtain a ceramic.

  Then, the ceramic is processed into the shape of each member of the dynamic pressure bearing 10 such as the shaft 1, the sleeve 2 and the thrust 3 described above. The polished surface 20 of the hydrodynamic bearing 10 of the present invention is processed from the fired surface of the ceramic to a depth of 10 times or more of the average crystal grain size to remove unevenness remaining on the fired surface, and then subjected to mirror finishing. A smooth surface is formed, and then groove-shaped recesses 11 are formed around the crystal grains 12 to 15. The method of forming the groove-shaped recess 11 around the crystal grains 12 to 15 is a method using the difference in the etching rate of the crystal grain boundaries surrounding the crystal grains 12 to 15, and the surface energy of the crystal grains 12 to 15 is There are ways to use it.

  The etching rate is obtained by performing ion etching, chemical etching, and fire etching on the mirror-polished polished surface 20, and forming a crystal grain boundary surrounding the crystal grains 12 to 15 exposed on the polished surface 20 in a groove shape. There is a method of forming the recess 11. At this time, it is necessary to prepare the ceramic composition so that the etching rate of the crystal grain boundaries is larger than that of the crystal grains 12-15. For example, if it is alumina, a glass component such as magnesia, calcia, and silica may be added in a small amount. If alumina-titanium carbide (hereinafter referred to as Altic), a small amount of yttria, magnesia, zirconia, and the like are added, A crystal grain boundary having an etching rate larger than that of the crystal grains 12 to 15 can be formed. As shown in FIG. 3A, the polished surface 20 of the hydrodynamic bearing 10 formed by this method often has a smooth crystal grain surface 16 and a groove-like recess 11 around the surface. Argon ions or the like may be used for ion etching, various acids and alkalis may be used for chemical etching, and an oxidation furnace or vacuum furnace may be used for fire etching depending on the ceramic material.

  In addition, as a method of using surface energy, a heat treatment is applied to the mirror-polished polished surface 20, and the phenomenon that the smooth crystal grain surface 16 exposed on the polished surface 20 forms an R shape by its surface tension is used. There is a way. As shown in FIG. 3B, the polished surface 20 of the hydrodynamic bearing 10 formed by this method often has a gentle R-shaped surface of the crystal grains 13 and a groove-shaped recess 11 around the surface. . However, in the case of ceramics having two components such as Altic, there are cases where the crystal grain surface 16 has a smooth surface and a smooth R shape, but this is also within the scope of the present invention. Needless to say. Further, the heat treatment temperature varies depending on the ceramic composition, particle size, atmosphere, etc., but it is preferable to use 1500 to 1800 ° C. for alumina and 1600 to 1800 ° C. for Altic.

  By performing the heat treatment in this manner, the shape of the crystal grains 13 can be made a gentle R shape from the crystal grain surface 16 toward the groove-shaped recess 11 as shown in FIG.

  As described above, when the hydrodynamic bearing of the present invention is used, the adsorption between the opposing surfaces is effectively prevented, so that the time required for the polishing surface to come into contact with and slide when the motor is started and stopped is reduced. Since the amount of particles to be reduced is reduced, the life of the hydrodynamic bearing is extended.

  Hereinafter, detailed examples of the hydrodynamic bearing of the present invention and the motor of the present invention using the same will be described.

First, the shaft 41, the sleeve 42, the thrust 43, and the thrust plate 44 constituting the motor 40 using the dynamic pressure bearing were manufactured by the following procedure. Alumina was mixed at 98% by mass, and magnesia and silica were mixed at a ratio of 2% by mass as a sintering aid. Then, the prepared raw material was wet pulverized with water using a ball mill to form a slurry, a binder was added to the slurry, and spray dried by spray drying to obtain a powder raw material.
Thereafter, an appropriate amount of this powder raw material was weighed and pressure-molded at a pressure of about 100 kPa using a powder press machine, and a molded body of the shaft 41, sleeve 42, thrust 43 and thrust plate 44 shown in FIG. 4 was produced. .

  Next, this molded body was fired at 1600 to 1700 ° C. for 2 to 3 hours in an electric furnace in an air atmosphere to obtain a sintered body of the shaft 41, the sleeve 42, the thrust 43, and the thrust plate 44.

  Then, the sintered body of the shaft 41 was subjected to centerless processing, and then the facing surface 41a of the shaft 41 was mirror-finished with a surface roughness Ra of 0.1 to 0.3 μm by super finishing. The superfinishing conditions were such that the workpiece feed speed was 0.5 to 1.0 m / min, the workpiece peripheral speed was 30 to 40 m / min, and the grinding wheel count was adjusted in the range of # 2000 to # 6000.

  The sintered bodies of the thrust 43 and the thrust plate 44 were processed with a lapping machine in the thickness direction and then processed with a cylindrical grinder. In the lapping machine, a casting surface plate was used for roughing, and a copper surface plate was used for finishing. In the finishing process, the surface roughness Ra of the thrust facing surface 43a and the thrust plate facing surface 44a is 0.1 to 0.3 μm while dripping a slurry obtained by stirring diamond powder having a particle diameter of 2 to 4 μm into water onto a copper surface plate. Mirror finished.

  The sintered body of the sleeve 42 was subjected to centerless processing to the outer diameter, and then roughed the inner diameter using a cylindrical grinder, and then the sleeve facing surface 42a was polished using an inner diameter finisher. Polishing of the sleeve facing surface 42a was performed by supplying a polishing liquid to the inner diameter surface of the sleeve 42 and adjusting the count of the grindstone in the range of # 800 to # 3000.

  Then, a resin mask on which a predetermined pattern was formed was attached to the shaft facing surface 41a and the thrust facing surface 43a, and the dynamic pressure generating grooves 41b and 43b were formed by blasting.

  Next, heat treatment is performed at 1300 to 1800 ° C. for 1 to 10 hours in order to form groove-like recesses 11 around the individual crystal grains exposed on the polishing surface 20 of the shaft 41, sleeve 42, thrust 43, and thrust plate 44. As shown in FIG. 3 (a), a material having a smooth crystal grain surface 16 and a material having a smooth R-shaped crystal grain surface 16 as shown in FIG. 3 (b) are prepared, and these members are used. The motor 40 was manufactured. As a comparative example, a motor using a polished surface member that was not heat-treated was also produced.

  Further, the state of the thrust facing surface 43a was observed with a scanning electron microscope (hereinafter referred to as SEM). As a result, it was confirmed that a groove-like recess 11 was formed around the crystal grains on the thrust facing surface 43a of the hydrodynamic bearing of the present invention. The average crystal grain size of the crystal grains exposed on the polished surface 20 is obtained by taking a photograph of the polished surface 20 in which the groove-like recess 11 is formed around the crystal grains using an SEM or a metal microscope, A straight line was drawn, the number of crystal grains existing on the straight line was measured, and the length of the three straight lines was divided by the number of crystal grains. Further, the depth of the groove-shaped recess 11 was determined by measuring the polished surface 20 using an atomic force microscope.

  Then, the rotation speed of the motor was 10000 rpm, 50,000 start-stop tests were performed, and the amount of particles adhering to the thrust plate 44 at the end of the test was evaluated.

  To measure the amount of particles, disassemble the motor 40 after the test, remove the thrust plate 44, soak the thrust plate 44 in pure water, perform ultrasonic cleaning at 1200W for 1 minute, and liquid the particles diffused in the pure water It was measured by using a particle counter. The particles having a particle amount of 8000 or less were marked with ◯, and those with a particle amount exceeding 8000 were marked with ×.

Table 1 shows the test evaluation results.

  From the results shown in Table 1, No. 1 is an example of the present invention. Nos. 1 to 9 show that the amount of particles is 8000 or less and the wear resistance is excellent.

  It should be noted that sample No. From the results of SEM observation, it was found that the reason why the amount of one particle is slightly larger than that of the other examples is that the average crystal grain size is large and the crystal grains are often dropped. Sample No. as an example. The depth of the groove-like recess is the same as 2 but the difference in the average crystal grain size is thought to affect the difference in the amount of particles. That is, it is considered that the crystal grain size of the ceramic used for the hydrodynamic bearing of the present invention is preferably 10 μm or less.

  In addition, sample No. 2 and No. 3 is the same as the average crystal grain size. No. 2 is No. It can be seen that the amount of particles is larger than 3. Sample No. as an example. 2 and No. No. 3 was observed with an SEM. In the case of No. 2, more traces of crystal grains were observed. This is because when the two samples are compared, the average crystal grain size is the same, but the depth of the groove-like recesses is no. No. 2 is larger. Since the polishing surface of No. 2 has a relatively weak force for retaining crystal grains, it is considered that the crystal grains dropped and the amount of particles increased. That is, it is considered that the depth of the groove-like recess is preferably 1/5 or less of the average crystal grain size.

  In addition, sample No. 8 and no. As compared with No. 9, the average crystal grain size is the same. No. 9 is No. It can be seen that the amount of particles is greater than 8. Sample No. as an example. 8 and no. When the polished surface of No. 9 was observed by SEM, No. 9 was observed. No. 9 had more scratches on the polished surface and fewer traces of groove-like recesses. This is because when the two samples are compared, the average crystal grain size is the same, but the depth of the groove-like recess is no. No. 9 is No. This is probably because a sufficient amount of air required to prevent adsorption between the polished surfaces could not be supplied. That is, it is considered that the depth of the groove-like recess is preferably 1/30 or more of the average crystal grain size.

  In addition, sample No. 9 and the comparative example No. 9. As compared with No. 10, the average crystal grain size is the same. No. 10 is No. It can be seen that the amount of particles is greater than 9. Sample No. as an example. 9 and the comparative example No. 9. When the polished surface of No. 10 was observed by SEM, No. 10 was observed. No. 10 had more scratches on the polished surface. This is the same as that of the comparative example. No. 10 has no groove-like recesses around the crystal grains, and it is considered that the time for the opposing surfaces to adsorb, contact, and slide is increased.

  Next, an Altic composed of 70% by mass of alumina as a main component, 20% by mass of titanium carbide, 1% by mass of ytterbium oxide as a sintering aid, 7% by mass of zirconia, 2% by mass of magnesia, and inevitable impurities In the same manner as in Example 1, ceramics used for a dynamic pressure bearing member were produced. The firing temperature of Altic was 1600 to 1800 ° C., fired for 1 to 5 hours, and after firing, a treatment at 1500 to 1600 ° C. and 202 MPa was performed with a hot isostatic press. The polished surface is processed into a mirror surface of Ra 0.05 to 0.2 μm, and then heat treatment is performed to form groove-like recesses around the crystal grains. The heat treatment temperature is 1200 to 1800 ° C. in a vacuum atmosphere, and 1 to 10 Heat treatment for hours was performed.

  And the motor 40 was comprised similarly to Example 1, the abrasion resistance test was done, and the amount of particles adhering to the thrust board 44 was measured. Moreover, in the dynamic pressure bearing made from Altic, the thing with a particle amount of 4000 or less was made into (circle), and the thing over 4000 was made into x.

The results are shown in Table 2.

  From the results shown in Table 2, sample No. which is an example of the present invention is shown. 1 to 6 show that the amount of particles is 4000 or less and the wear resistance is excellent.

  In addition, No. which is an example. 5 and no. As compared with No. 6, the depth of the groove-like recess is the same, but No. 6 is No. It can be seen that the amount of particles is greater than 5. Sample No. as an example. 5 and no. No. 6 was observed with an SEM. No. 6 had more scratches on the polished surface and fewer traces of groove-like recesses. This is because the average crystal grain size is No. 1. No. 6 is No. This is presumably because the depth of the groove-like recesses was reduced because it was smaller than 5, and a sufficient amount of air required to prevent adsorption between the polished surfaces could not be supplied. That is, it is considered that the average crystal grain size is preferably 0.2 μm or more.

  Furthermore, sample No. which is an example. 2 and Comparative Example No. As compared with No. 7, the average crystal grain size is the same. No. 7 is No. It can be seen that the amount of particles is larger than 2. Sample No. as an example. 2 and Comparative Example No. No. 7 was observed with an SEM. No. 3 had more scratches on the polished surface. This is the same as that of the comparative example. In No. 7, since there is no groove-like recess around the crystal grains, it is considered that the time for the opposing surfaces to adsorb, contact, and slide is increased.

(A) is a perspective view which shows an example of embodiment of the hydrodynamic bearing of this invention, (b) is sectional drawing in the A-A 'line | wire shown to (a). (A) is a fragmentary sectional view which shows an example of the grinding | polishing surface in the dynamic pressure bearing of this invention, (b) is the elements on larger scale which show the surface of a grinding | polishing surface. (A)-(c) is a fragmentary sectional view which shows an example of the cross section of the grinding | polishing surface in the dynamic pressure bearing of this invention, respectively. It is sectional drawing which shows an example of embodiment of the motor of this invention using the dynamic pressure bearing of this invention. (A) is a perspective view which shows an example of the conventional dynamic pressure bearing, (b) is sectional drawing in the E-E 'line | wire shown to (a).

Explanation of symbols

DESCRIPTION OF SYMBOLS 1,41: Shaft 1a, 41a: Opposite surface 1b (with sleeve), 41b: Dynamic pressure generating groove 2, 42: Sleeve 2a, 42a: Opposing surface 2b (with shaft), 42b: Opposed (with thrust) Surfaces 3, 43: Thrusts 3a, 43a: Opposing surfaces 3b, 43b (dynamic sleeves) 4, 5: Clearances
10: Dynamic pressure bearing
11: Groove-shaped recess
12, 13, 14, 15: crystal grains
16: Crystal grain surface
20: Polished surface
40: Motor
44: Thrust board
44a: Opposite surface (with thrust)
45: Rotor hub
46: Magnet
47: Stator
48: Base
49: Perimeter

Claims (4)

One of the shaft members is a rotating body and a fixed body having opposing surfaces facing each other, and the opposing surfaces facing each other have a dynamic pressure generating groove formed on one side and at least one is a ceramic polishing surface A hydrodynamic bearing comprising: a groove-like recess formed along a grain boundary of the ceramic crystal grains exposed on the polished surface. 2. The motion according to claim 1, wherein the depth of the groove-shaped recess is 1/30 to 1/5 of the average crystal grain size of the ceramic crystal grains exposed on the polishing surface. Pressure bearing. 2. The hydrodynamic bearing according to claim 1, wherein in the cross section of the polished surface, the shape of the crystal grains on both sides of the groove-shaped recess is an R shape toward the groove-shaped recess. A motor using the hydrodynamic bearing according to any one of claims 1 to 3 as a bearing portion.

Images