JP2002266864A - Ceramic dynamic pressure bearing, motor with bearing, hard disc device, and polygon scanner - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a ceramic dynamic pressure bearing in which abrasion or the like is hard to be generated at starting and stopping, and preferable rotation of the dynamic pressure bearing is realized. SOLUTION: This ceramic dynamic pressure bearing comprises: a first member 14 having a cylindrical outer peripheral surface; and a second member 15 having a cylindrical insertion hole 15a. The first member 14 is inserted into the insertion hole 15a. Radial dynamic pressure gap is formed between an inner surface of the insertion hole of the second member 15 and the outer peripheral surface of the first member 14. Both of the first member 14 and the second member 15 have percentage contents of Al component in terms of Al2 O3 of 90 to 99.5 mass %, and are constituted of alminous ceramic including sintering assistant component of oxide system of 0.5 to 10 mass % in terms of oxide. When an inner diameter in an arbitrary cross section perpendicular to axis of the second member 15 is D, and an outer diameter of an outer peripheral surface in the arbitrary cross section perpendicular to axis is d, (D-d)/2 (hereinafter, also referred to as difference of a radial dynamic pressure gap diameter) is adjusted to be within a range from 4.5 to 7 μm.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a ceramic dynamic pressure bearing, a motor with a bearing, a hard disk drive, and a polygon scanner.

[0002]

2. Description of the Related Art Conventionally, ball bearings have often been used as bearings for motor shafts serving as driving sources for electric equipment. However, in precision equipment such as computer peripheral equipment, motors have been rapidly rotating at high speed. In order to obtain excellent bearing performance with low rotation unevenness, abnormal noise and vibration,
Alternatively, in order to extend the life of the bearing, a dynamic pressure bearing mediated by a fluid such as air is used. For example, when a main shaft and a bearing portion disposed to surround the main shaft rotate around an axis, the hydrodynamic bearing is configured to rotate the rotating shaft by a fluid dynamic pressure generated in a gap between an outer peripheral surface of the main shaft and an inner peripheral surface of the bearing portion. To support. In addition, there is a bearing in which a thrust surface of a main shaft or a bearing portion is supported by dynamic pressure.

[0003] In a dynamic pressure bearing, in a high-speed rotation state where the generated dynamic pressure level is sufficiently high, the members facing each other across the dynamic pressure gap do not come into contact with each other. Since sufficient dynamic pressure is not generated, contact between members occurs. As the component material of the dynamic pressure bearing as described above, a metal such as stainless steel or a material obtained by coating these with a resin or the like has been generally used. Wear and seizure may become a problem due to contact of the members at the time of stop. In order to prevent this, an attempt has been made to coat a portion facing the dynamic pressure gap with a lubricating layer such as a resin, but the effect is not always sufficient. Therefore,
In order to sufficiently ensure durability against wear and seizure, members opposed to each other with a dynamic pressure gap therebetween, such as the main shaft or the bearing, are made of ceramic such as alumina.

[0004]

However, conventional dynamic pressure bearings using alumina ceramics for dynamic pressure components have not paid much attention to material design in terms of machining finish accuracy. Therefore, particularly in the gap (radial dynamic pressure gap) between the outer peripheral surface of the main shaft and the inner peripheral surface of the bearing portion, which is responsible for the generation of dynamic pressure in the radial direction, local abrasion tends to occur mainly due to processing accuracy of those surfaces. there were. In addition, when the processing accuracy of the dynamic pressure gap forming surface is low, the state of dynamic pressure generation is naturally affected, and it is difficult to obtain a uniform and stable rotation state.

SUMMARY OF THE INVENTION An object of the present invention is to provide a ceramic dynamic pressure bearing which hardly causes abrasion or the like at the time of starting / stopping and which can realize suitable rotation of the dynamic pressure bearing.

[0006]

In order to solve the above-mentioned problems, a ceramic dynamic pressure bearing according to the present invention comprises a first member having a cylindrical outer peripheral surface and a second member having a cylindrical insertion hole. The first member is inserted through the insertion hole of the second member, and the inner surface of the insertion hole of the second member and the outer peripheral surface of the first member inserted therethrough are respectively formed with a radial dynamic pressure gap. As a surface, a radial dynamic pressure gap is formed between the radial dynamic pressure gap forming surfaces, and is configured to generate fluid dynamic pressure in the radial dynamic pressure gap with the relative rotation of the first member and the second member. Each of the first member and the second member has an Al component content of 90 to 9 in terms of Al ₂ O _3.
9.5 mass%, which is composed of an alumina ceramic containing 0.5 to 10 mass% of an oxide-based sintering aid component in terms of oxide, and further, in the insertion hole of the second member. The outer diameter of the outer peripheral surface of the first member at an arbitrary cross section perpendicular to the axis is d,
(D−d) / 2 (hereinafter also referred to as a radial dynamic pressure gap diameter difference) is adjusted to a range of 2 to 6 μm.

According to the study by the present inventor, in order to prevent a local wear of the radial dynamic pressure gap forming surface and to secure a uniform and stable dynamic pressure generation state and a rotation state, the radial dynamic pressure is required. To ensure the processing finish accuracy of the gap forming surface to a certain level or more, specifically, the inner diameter of the inner peripheral surface of the insertion hole of the second member is D, and the outer diameter of the outer peripheral surface of the first member is d, and It has been found that it is important that (D−d) / 2 satisfies the range of 2 to 6 μm in the section perpendicular to the axis. As a result of further intensive studies, when the first member and the second member are made of alumina ceramic, the alumina content of the ceramic is set to 90 to 90%.
It has been found that the adjustment to 99.5% by mass is effective in securing the processing accuracy as described above, and the present invention has been completed.

If the value of (D−d) / 2 is less than 2 μm, local contact of the radial dynamic pressure gap forming surface at the time of starting / stopping is apt to occur and wear tends to occur. On the other hand,
When the value of (D−d) / 2 exceeds 6 μm, the dynamic pressure generation level becomes insufficient, or a problem such as misalignment due to local pressure fluctuation tends to occur. (D-
More preferably, the value of d) / 2 satisfies the range of 4 to 5 μm in an arbitrary cross section orthogonal to the axis.
Note that the values of the outer diameter D and the inner diameter d at each position in the axial direction are represented by the diameter of a perfect circle having the same area as the cross-sectional outline profile measured using a known shape profile measuring device (however, When a dynamic pressure groove to be described later is formed, a cross-sectional profile profile interpolating the groove opening is used.) According to the revised plan, the range of 3-4 is desirable, but from the data in Table 2, the range of 4-5 seems to be desirable, so I changed it to 4-5.

The alumina content or the sintering aid component content is adjusted to the above range for the following reasons. That is, when the sintering aid component is excessively increased and the alumina content is insufficient, the amount of liquid phase generated during sintering is increased, and the crystal grain growth of the sintered body is excessively advanced. As described above, the content of the sintering aid component is high, and the ceramic structure in which the crystal grain growth has progressed excessively has a low hardness. Resistance decreases. Polishing tends to proceed unnecessarily rapidly,
There is a disadvantage that it is difficult to ensure the accuracy of the polished surface. That is, in order to increase the processing accuracy of the polished surface, it is important that the ceramic material has appropriate hardness.

[0010] Therefore, by securing the alumina content of the ceramic at least 90% by mass or limiting the content of the sintering aid component to 10% by mass or less, excessive crystal grain growth as described above is prevented. Less likely to occur, and eventually
Radial dynamic pressure gap diameter difference (D
−d) / 2 can be easily secured within the above numerical range. As a result, during the use of the dynamic pressure bearing, local wear due to the processing accuracy of the radial dynamic pressure gap forming surface is less likely to occur, and the dynamic pressure generation state in the radial dynamic pressure gap, and eventually the rotation state of the bearing, are reduced. It can be uniform and stable. Further, since the hardness of the alumina ceramic is appropriately secured, the wear resistance itself against contact friction of the member is also improved.

On the other hand, when the content of the sintering aid component decreases and the alumina content becomes excessive, the amount of liquid phase generated during sintering decreases, and the growth of crystal grains is suppressed. It will be a small value. As a result, on the contrary, the resistance to polishing or grinding of the ceramic becomes too large, which leads to a significant decrease in the processing efficiency.

In view of the above, it is desirable that the average particle size of the alumina-based ceramic crystal particles is specifically adjusted in the range of 1 to 7 μm. The alumina content is
Preferably 92 to 98% by mass, more preferably 93 to 9% by mass.
The content is preferably 7% by mass. Further, the oxide-based sintering aid component constituting the grain boundary phase is desirably 2 to 2 in terms of oxide.
8% by mass, more preferably 3 to 7% by mass.

In this specification, the size of a crystal particle (or surface vacancy) is defined as the size of a crystal particle (or a surface pore) as shown in FIG. Or surface vacancies)
When various circumscribed parallel lines which do not intersect the inside are drawn while changing the positional relationship with the outer shape line, the average value of the minimum interval dmin and the maximum interval dmax of the parallel lines (that is, d = (dmin + dmax) ) / 2).

As the oxide-based sintering aid component, for example, the cation component is Li, Na, K, Mg, Ca, Sr, B
a, Sc, Y, La, Ce, Pr, Nd, Sm, Eu,
Oxides that are Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu and Si can be used. in this case,
The alumina ceramic has a total of 0.5 to 10% by mass (preferably 2 to 8% by mass, more desirably 3 to 8% by mass) in terms of an oxide-converted value of one or more selected from the above cationic component group. ７7% by mass).

Of these, the Si component forms the skeleton of the grain boundary phase to increase the strength and has the effect of improving the fluidity of the liquid phase. In addition, alkali metals such as Li and Na
And K lower the melting point of the liquid phase generated during firing,
This has the effect of improving the fluidity of the liquid phase and promoting the densification of the sintered body. Among them, Na is inexpensive, and in general alumina raw material powder manufactured by the Bayer method,
There is an advantage that Na which originally exists as an impurity can be used as a sintering aid. These three components are all converted into oxides by the composition formula M ₂ O (where M is a cationic metal element).

On the other hand, alkaline earth metals such as Mg and C
The four components a, Sr, and Ba also have a large effect of lowering the melting point of the liquid phase generated at the time of firing after the alkali metal. On the other hand,
These elements have the effect of improving their strength when incorporated into the grain boundary phase. As a result, it is possible to improve the strength and wear resistance of the entire sintered body, that is, the dynamic pressure gap forming surface. This effect is particularly large when Ca is used. These four components are all represented by the composition formula MO (where M
Is a cationic metal element).

The rare earth metals Sc, Y, La,
Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, H
o, Er, Tm, Yb and Lu promote crystallization of the grain boundary phase.
Has the effect of improving its strength. as a result,
Strength and wear resistance of the entire sintered body and thus the surface on which the dynamic pressure gap is formed
Can be improved. The effect is obtained when Ce is used.
Especially large. These components are composed only of Ce and have the composition formula MO₂
The other is the composition formula M ₂O₃(However, M is cationic gold
Element) is converted to oxide.

Next, it is desirable that the apparent density of the alumina ceramic is 3.5 to 3.9 g / cm ³ .
2. The density of the alumina ceramic is relatively high.
By adjusting the pressure to ⁵ to 3.9 g / cm ³ , the absolute value of the strength and wear resistance of the alumina ceramic constituting the dynamic pressure gap generating surface can be improved, and furthermore, the rotation that easily causes contact between members can be achieved. When starting and stopping, the abrasion of the dynamic pressure gap forming surface can be effectively prevented.

The density of the ideally densified alumina ceramic reaches a maximum of 4.0 g / cm ³ ,
If it is attempted to sinter the alumina ceramic until it is completely densified as described above, the sintering temperature must be set to a high temperature, and it is difficult to avoid crystal grain growth.
In such a state, it may be difficult to secure the accuracy of the radial dynamic pressure gap forming surface as described above. However, the apparent density of the alumina ceramic was 3.9 g /
If the sintering temperature is not more than about ³ cm, it is not necessary to raise the sintering temperature so much, and the crystal grain growth is suppressed, so that the accuracy of the radial dynamic pressure gap forming surface should be within the above numerical range. It is even more convenient. On the other hand, when the apparent density is less than 3.5 g / cm ³ , the strength and abrasion resistance of the alumina ceramic are impaired, and the wear of the surface on which the dynamic pressure gap is formed at the time of starting / stopping may be more likely to occur. The apparent density of the alumina ceramic is more desirably 3.
It is desirable to adjust within the range of 6 to 3.9 g / cm ³ .

The apparent density of the alumina ceramic is affected not only by the progress of densification but also by the type and content of the sintering aid to be added. When discussing the relationship between the ceramic densification level and the degree of crystal grain growth, the relative density (ie, the value obtained by dividing the apparent density by the true density estimated from the composition ratio of alumina and the sintering aid) is used. It can also be used as a measure. In the present invention, the relative density of the alumina ceramic is preferably 90% or more, more preferably 90 to 98%, and even more preferably 94 to 97%.

The alumina ceramic adjusted to the above density range has a bending strength level of 280.
Relatively high values of ５550 MPa are possible. The Rockwell hardness measured at a load of 15 N was 92 to 98.
Degree. Further, the fracture toughness value is 3-5.
MPa · m ^1/2 . When the strength, hardness or fracture toughness value of the alumina ceramic is in such a range, the effect of preventing or suppressing wear of the dynamic pressure gap forming surface at the time of starting and stopping, and the radial dynamic pressure gap forming surface. And the effect of securing sufficient accuracy can be achieved without extremely lowering the processing efficiency such as polishing or grinding. In the present specification, the bending strength means a three-point bending strength measured at room temperature based on a method specified in JIS: R1601 (1981). The Rockwell hardness measured at a load of 15 N is based on the method defined in JIS: Z2245.
Mean hardness value measured at room temperature. Further, the fracture toughness value is determined by the IF specified in JIS: R1607 (1990).
Means the value measured by the method.

The ceramic dynamic pressure bearing of the present invention has a thrust plate disposed so as to face at least one end face of the second member in the direction of the rotation axis. The opposing surfaces of the thrust plates are formed as thrust dynamic pressure gap forming surfaces, and a thrust dynamic pressure gap is formed between the thrust dynamic pressure gap forming surfaces.

For example, in the case of a dynamic pressure bearing having the structure illustrated in FIG. 1, the radial direction is a direction (and thus a radial direction) perpendicular to the rotational axis direction of the main shaft (vertical direction in the figure). Figure 1
In this case, the outer peripheral surface of the fixed main shaft, which is the first member, and the inner peripheral surface of the bearing portion, which is the second member configured as a cylindrical rotating body, are radial dynamic pressure gap forming surfaces. In the case of a bearing that is long in the direction of the rotation axis, it is important whether or not sufficient radial dynamic pressure is generated in order to stably support the rotation axis.
The thrust direction is the axial direction of the main shaft, that is, the direction of the rotation axis (the vertical direction in the figure). In FIG. 1, the end surface of the bearing portion and the plate surface of the thrust plate facing the end surface of the bearing portion in the axial direction become the thrust dynamic pressure gap forming surface. It should be noted that the thrust dynamic pressure gap forming surface may be slightly inclined from a plane perpendicular to the rotation axis direction. As described later, in the case of a bearing that is short in the rotation axis direction, whether or not thrust dynamic pressure is sufficiently generated is important for stably supporting the rotation axis. In addition, as shown in FIG.
A bearing 251 in which 12 is on the rotation side and the cylindrical bearing portion 221 is on the fixed side is also possible. In the following, the radial dynamic pressure gap (formation surface) and the thrust dynamic pressure gap (formation surface)
Are simply referred to as a dynamic pressure gap (formation surface).

Next, the average particle size of the alumina-based ceramic crystal particles used in the present invention is desirably adjusted to a range of 1 to 7 μm from another viewpoint described below.
That is, when alumina ceramic is used as the material of the dynamic pressure bearing, the surface condition of the ceramic constituting the main shaft and the bearing on the dynamic pressure gap forming surface becomes a problem. That is, generally, fine holes are present on the ceramic surface after polishing, and it is considered that the size of such holes greatly affects the rotating state of the dynamic pressure bearing.

On the other hand, according to the study of the present inventors, it has been found that if the surface on which the dynamic pressure gap is formed is extremely smooth, sufficient fluid dynamic pressure cannot be generated in the dynamic pressure gap. If the generated dynamic pressure level is insufficient, it is naturally impossible to realize a stable supporting state of the rotating shaft, and it is also difficult to secure a suitable rotating state of the dynamic pressure bearing. Therefore,
It is effective to positively form surface pores in a certain size range on the dynamic pressure gap forming surface in order to make the generated fluid dynamic pressure level high and stable.

Specifically, when a large-sized hole exists on the surface of the ceramic where the dynamic pressure gap is formed, for example, when the main shaft rotates, turbulence occurs in the fluid layer between the main shaft and the bearing. However, it is considered that vibration occurs in the main shaft, for example. On the other hand, when the size of the hole existing in the dynamic pressure gap forming surface of the ceramic is small, adhesion tends to occur on the dynamic pressure gap forming surface of the main shaft and the bearing. (Hereinafter referred to as "adhesive wear"). On the other hand, extremely small surface pores hardly contribute to the generation of dynamic pressure.

Since the pores formed on the surface on which the dynamic pressure gap is formed are mainly formed by particles falling off during polishing, the size of the crystal grains of the alumina ceramic on the surface on which the dynamic pressure gap is formed (ie, The crystal grain size) or its distribution plays a very important role in obtaining a suitable state of forming surface vacancies which does not cause the above-mentioned problems. In the present invention, specifically, the generated fluid dynamic pressure level is increased by adjusting the average particle diameter of the ceramic crystal particles constituting the dynamic pressure gap forming surface of the member so as to be in the range of 1 to 7 μm. From the viewpoint of achieving stability and effectively suppressing problems such as adhesion wear and linking at the time of starting or stopping the dynamic pressure bearing, more advantageous surface pore size and formation amount can be realized.

When the average particle size of the ceramic crystal particles is less than 1 μm, the average size of the formed surface pores becomes too small, and adhesion wear and linking are formed on the surface where the dynamic pressure gap is formed when the rotation of the bearing is started or stopped. It is easy to occur. Also, the fluid dynamic pressure level generated in the dynamic pressure gap tends to be insufficient,
Rotational runout and the like are easily caused. On the other hand, if the average particle size of the ceramic crystal particles exceeds 7 μm, the average size of the surface vacancies formed conversely becomes too large, causing excessive turbulence in the dynamic pressure gap and vibration on the rotating shaft. Easier to do. The average size of the ceramic crystal particles is more desirably 2 to 5 μm.

In order to realize the above-mentioned advantageous surface pore size and formation amount on the dynamic pressure gap forming surface,
The area ratio of the ceramic crystal particles having a particle size of 2 to 5 μm is 40%.
More preferably (including 100%). If the amount of ceramic particles in the size range is less than 40%, for example, if the number of particles larger than the upper limit of the size range increases, it is difficult for the particles to drop off, and surface vacancies that effectively contribute to the generation of dynamic pressure May result in a shortage of area ratio. On the other hand, when the number of particles smaller than the lower limit of the size range increases, the average size of the formed surface pores tends to be small. Either case may be disadvantageous in generating a sufficient level of dynamic pressure.

The alumina ceramic is produced by firing a mixture of alumina powder and a sintering aid powder as a raw material. As shown in FIG. 11, such an alumina ceramic has a structure in which crystal grains of an alumina main phase containing alumina as a main component are bound by a grain boundary phase derived from a sintering aid. It is considered that the drop of crystal grains during polishing is mainly caused by the destruction of the grain boundary phase. Then, the space occupied by the crystal grains that have fallen off remains as voids that open to the dynamic pressure gap forming surface. In particular, the grain boundary phase is locally thinned, the grain boundary phase is insufficient due to the presence of internal cavities, etc., or the presence of cracks due to component segregation, thermal stress, etc. Such as the part where the strength of
It is considered that the drop of crystal grains is likely to occur at the portion where the grain boundary phase bonding force is relatively reduced. In the present invention, the term “main component” (also synonymous with “main component” or “mainly”) means that the content of the component in the substance of interest is 50% by mass or more, unless otherwise specified. Means that.

For example, if one crystal particle falls off, the crystal becomes like a hole V1 in FIG. 12A (in FIG. 12A, a particle without white dropout represents a particle with black dropout). Voids corresponding to the shape and size of the particles will be formed. On the other hand, if a plurality of crystal particles drop off in a group, V2
A void such as In addition, as shown in FIG. 12B, since a structure usually includes a mixture of crystal grains of various sizes, a structure portion in which large crystal particles are surrounded by a plurality of small crystal particles is generated. When the surrounding small crystal grains are shed in a chain, the large crystal grains in the middle often fall off. In these cases, the size of the formed pores is naturally larger than the individual crystal grains.

The structure of the alumina-based ceramic is equiaxed with small shape anisotropy of individual crystal grains. When formed with a certain extent, when the polishing force from the grindstone or the abrasive grains is applied over a plurality of crystal grains, the falling form such as V2 is more likely to occur more frequently. In this case, the average size of the formed surface vacancies is larger than the average size of the crystal particles set to 1 to 7 μm. In addition, the surface pores are formed in a form that is substantially isotropically scattered on the dynamic pressure gap forming surface regardless of the polishing direction. By making the average size of the surface vacancies larger than the average size of the crystal grains, the generated dynamic pressure level can be further improved, and more stable rotation of the bearing can be realized.

When producing an alumina ceramic, the average particle size of the alumina powder used as a raw material is 1 to 5 μm.
It is good to do. When the alumina powder having an average particle diameter outside this range is used, the average particle diameter of the crystal particles of the obtained sintered body may not be in the preferable range described above. The average particle diameter of the powder can be measured using a laser diffraction type particle size meter.

The firing temperature is preferably set in the range of 1400 to 1700 ° C. If the firing temperature is lower than 1400 ° C., the densification of the sintered body does not easily progress, which leads to insufficient strength or wear resistance. On the other hand, the firing temperature is 1700 ° C
Exceeding the range may cause excessive grain growth, making it difficult to keep the average grain size of the crystal grains of the obtained sintered body within the range of the present invention. Further, deformation of the sintered body is likely to occur, and the dimensional accuracy may be impaired.

Next, the average size of the surface pores existing on the dynamic pressure gap forming surface made of ceramic is specifically 2 to 20.
It is good to be μm. By actively forming surface pores having an average size of 2 to 20 μm, the level of generated fluid dynamic pressure can be made high and stable. Further, in the case of a dynamic pressure bearing in which a thrust dynamic pressure gap described later is formed,
Linking can be prevented from occurring.

If the average size of the surface pores exceeds 20 μm, excessive turbulence is generated in the dynamic pressure gap, and vibration is likely to occur on the rotating shaft. On the other hand, when the size of the surface pores is less than 2 μm, adhesion wear and linking are likely to occur on the surface on which the dynamic pressure gap is formed when the rotation is started or stopped. In addition, the fluid dynamic pressure level generated in the dynamic pressure gap tends to be insufficient, and it is easy to cause rotational runout and the like. The average size of the surface pores is more desirably 5 to 15 μm.

Next, regarding the size of each surface hole,
Those having a thickness of 2 μm or less cannot contribute much to the generation of dynamic pressure. On the other hand, if there are too many that exceed 20 μm, vibrations and the like are likely to occur. That is, the size of the surface pores that effectively contributes to the generation of dynamic pressure and is suitable for realizing stable rotation is 2 to 20 μm. And
The formation area ratio of the surface pores in such a dimensional range on the dynamic pressure gap forming surface makes it harder for seizure or linking to occur on the dynamic pressure gap forming surface when starting or stopping the rotation, and it is also generated in the dynamic pressure gap. It is preferably 15% or more, more preferably 20% or more, from the viewpoint of increasing the fluid dynamic pressure level. On the other hand, the area ratio is preferably 60% or less, and more preferably 40% or less, from the viewpoint of more effectively suppressing the occurrence of vibration and the like.

Further, in order to effectively contribute to the generation of dynamic pressure and to realize stable rotation, the more preferable size of the surface pores is 2.
It is preferable that the formation area ratio of the surface vacancies in such a dimensional range on the dynamic pressure gap forming surface is 10 to 60%.

In the present specification, the area ratio of surface pores is a value obtained by dividing the total area of pores observed on the dynamic pressure gap forming surface by the area of the dynamic pressure gap forming surface. However, when a well-known dynamic pressure groove is formed on the dynamic pressure gap forming surface, the area ratio of the surface voids is calculated for the dynamic pressure gap forming surface region excluding the dynamic pressure groove portion. . In addition,
The area ratio is measured by observing the dynamic pressure gap forming surface region using a magnifying observation means such as an optical microscope, and 300 mm in the observation visual field.
The calculation is performed by setting a square measurement area of μm × 300 μm and dividing the total area of the surface vacancies identified in the measurement area by the measurement area area. In order to improve the measurement accuracy, it is desirable that the number of measurement regions is arbitrarily set to five or more in one dynamic pressure gap forming surface region, and the area ratio of surface vacancies is calculated as an average value of the measurement regions.

It is desirable that the surface voids on the surface on which the dynamic pressure gap is formed have a size exceeding 20 μm, which is likely to cause vibration or the like. Specifically, the formation area ratio of the surface vacancies exceeding 20 μm on the dynamic pressure gap formation surface is preferably 10% or less, and more preferably 5% or less. In addition, from the viewpoint of preventing the occurrence of vibration, the maximum size of the surface pores existing on the dynamic pressure gap forming surface is 1
It is preferable that the thickness is not more than 00 μm, that is, there is no surface vacancy exceeding 100 μm.

Next, the first member and the second member forming the dynamic pressure gap can be entirely made of alumina ceramic (hereinafter, also simply called ceramic). The ceramic constituting the member has a dense sintered body structure with few pores inside, and the dynamic pressure gap forming surface portion has a structure with relatively many pores formed. And anti-adhesive or linking effects,
It is desirable to achieve both the strength and the abrasion resistance improving effect. Specifically, the dimension 2 existing in the ceramic sintered body
It is preferable that pores having a size of about 20 μm exist mainly in the form of localized pores on the surface on which the dynamic pressure gap is formed. And, to form such a tissue efficiently, as described above,
When processing and finishing the dynamic pressure gap forming surface, it is effective to drop the ceramic crystal particles to form surface pores.

Further, the dynamic pressure bearing according to the present invention is characterized in that the axial length of the dynamic pressure bearing is longer than the outer diameter of the thrust dynamic pressure gap forming surface, or that the thrust dynamic pressure gap is not formed. Can be configured to be restricted by the dynamic pressure generated in the radial dynamic pressure gap. This defines a dynamic pressure bearing having a long rotating shaft, for example, as shown in FIG. 7.
The inclination is defined and corrected by the pressure generated in the radial dynamic pressure gap 37. On the other hand, the axial length of the dynamic pressure bearing is shorter than the outer diameter of the thrust dynamic pressure gap forming surface, and the inclination of the rotating body during rotation is regulated mainly by the dynamic pressure generated in the thrust dynamic pressure gap. Can also be configured. This defines a dynamic pressure bearing having a short rotating shaft as shown in FIG. 3, for example.
The inclination is defined and corrected by the dynamic pressure generated in the thrust dynamic pressure gap.

A dynamic pressure groove can be formed on the dynamic pressure gap forming surface. For example, a smoother rotation can be realized by forming a well-known dynamic pressure groove on the outer peripheral surface of the rotary shaft which is a radial dynamic pressure gap forming surface. As illustrated in FIG. 2A, the dynamic pressure groove is, for example, a shaft outer peripheral surface (a radial dynamic pressure gap forming surface) inserted into a bearing portion.
A plurality of dynamic pressure grooves can be formed at predetermined intervals in the circumferential direction. In this embodiment, the groove is a linear groove array inclined at a certain angle with respect to the generatrix of the shaft outer peripheral surface. However, a mountain-shaped (or boomerang-shaped) groove pattern is formed on the reference line in the shaft circumferential direction. Other known forms, such as a so-called herringbone form, which is formed over the entire circumference at a predetermined interval so that the tip of the head is located, can also be adopted.
As illustrated in (b), for example, a dynamic pressure groove may be formed on the surface of the thrust plate (the thrust dynamic pressure gap forming surface). In this example, in the circumferential direction of the plate surface, a plurality of curved groove portions whose distance from the center of the thrust plate gradually decreases are formed at predetermined intervals in the circumferential direction.

The dynamic pressure bearing according to the present invention is, for example, a hard disk rotating main shaft part of a hard disk drive, or a CD-type.
It can be effectively used as a bearing for a disk rotating spindle of a computer peripheral device such as a ROM drive, an MO drive or a DVD drive, and a polygon mirror rotating spindle of a polygon scanner used for a laser printer or a copier. . For example, 8000 rpm is used for the bearing of the rotary drive unit in these precision instruments.
m or more (if higher speed is required, 1000
Since high-speed rotation (0 rpm or more to 30000 rpm or more) is required, by applying the present invention, the level of generated fluid dynamic pressure can be made high and stable, and the effect of reducing vibration and the like can be particularly effectively brought out. . Further, the present invention provides a motor with a bearing, wherein the ceramic dynamic pressure bearing is used as a bearing of a motor rotation output section. Furthermore, a hard disk drive including the above-described motor with a bearing and a hard disk rotationally driven by the motor with the bearing, or a motor with the above-described bearing and a polygon mirror rotationally driven by the motor with the bearing Polygon scanners are also provided.

In a hard disk drive or a polygon scanner, a hard disk or a polygon mirror is directly pressed into the outer peripheral surface of the second member (including the concept of shrink fit; the same applies hereinafter), or the outer periphery of the second member. When a hard disk or a polygon mirror is attached to the support member pressed into the surface, the second member is inserted when the hard disk or the support member pressed into the second member is removed in consideration of the diameter reduction due to the press-fitting. Assuming that the inner diameter of the inner peripheral surface of the hole at an arbitrary cross-section orthogonal to the axis is D ′, and the outer diameter of the first member at the arbitrary cross-section of the outer peripheral surface at an arbitrary cross-section of the axis is d ′, (D′−d ′) / 2 is 3 It is desirable that the thickness be adjusted to a range of about 7 μm. By doing so, the radial dynamic pressure gap diameter difference (D−d) /
2 can be adjusted to a range of 2 to 6 μm in an arbitrary cross section perpendicular to the axis.

In order to further impart toughness to the alumina ceramic, a composite ceramic material containing zirconia ceramic may be used. Such a composite ceramic material is formed and fired using a ceramic powder in which the ceramic component with the highest content is one of alumina and zirconia, and the ceramic component with the second highest content is the other of alumina and zirconia. Can be obtained. The amount of zirconia ceramic mixed with alumina ceramic is 5-6.
The content is preferably 0% by volume.

Also, an alumina ceramic is used as a substrate, and the metal cation component is Ti, Zr, Nb, Tb.
A composite ceramic material containing a conductive inorganic compound phase that is at least one of a and W can also be used. Such a composite ceramic material can be obtained by blending a powder that is a source of a conductive inorganic compound phase with a base powder for molding a base ceramic, and molding and firing the mixture. By containing the conductive inorganic compound phase, it is possible to impart conductivity to the ceramic material, and it is possible to subject the ceramic material to electric discharge machining such as wire cutting. In addition, by imparting conductivity,
An antistatic effect can be achieved.

The conductive inorganic compounds include Ti, Zr, Nb,
Metal nitride, metal carbide, metal boride, metal carbonitride, and / or tungsten carbide containing at least one of Ta as a metal cation component can be used. Specifically, titanium nitride, titanium carbide, Examples include titanium boride, tungsten carbide, zirconium nitride, titanium carbonitride, and niobium carbide. Note that the content of the conductive inorganic compound phase is 20% in order to sufficiently improve the conductivity while securing the strength and the fracture toughness value of the composite ceramic material.
It is preferable to set to 60% by volume. When using a composite ceramic as described above, the alumina content or sintering aid content already described is not the content of the entire composite ceramic but the content of the alumina ceramic substrate. Shall be replaced.

[0049]

Embodiments of the present invention will be described below with reference to embodiments shown in the drawings. (Embodiment 1) A ceramic dynamic pressure bearing 3 shown in FIG. 3 (hereinafter also simply referred to as a dynamic pressure bearing) is used for a motor with a dynamic pressure bearing for rotating a polygon mirror 8 in a polygon scanner 1, for example. And uses air as a fluid for generating dynamic pressure. In the motor 2 with the dynamic pressure bearing, the permanent magnet 9 is attached to the support 7 integrated on the outer peripheral surface of the bearing 15 in order to rotate the cylindrical bearing 15 (rotary body). Is mounted with a coil 13 facing the permanent magnet 9.
The arrangement relationship between the permanent magnet 9 and the coil 13 may be switched.

The ceramic dynamic pressure bearing 3 has a cylindrical bearing portion 1.
A cylindrical main shaft (for example, an inner diameter of 5 mm, an outer diameter of 15 mm, and an axial length of 8 mm) 14 is rotatably inserted into an insertion hole 15 a of 5 (for example, an inner diameter of 15 mm, an outer diameter of 25 mm, and an axial length of 8 mm). ing. As shown in FIG.
The inner peripheral surface M2 of FIG. 1A and the outer peripheral surface M1 of the main shaft 14 are both cylindrical radial dynamic pressure gap forming surfaces, between which a dynamic pressure in the radial direction with respect to the rotation axis О is generated. A radial dynamic pressure gap 17 filled with air is formed. Here, the main shaft 14 is a first member referred to in the claims, and the bearing portion 15 is also a second member.

On the other hand, a disk-shaped thrust plate (for example, an inner diameter of 5 mm, an outer diameter of 25 mm, a thickness of
mm) 21 and 23 are coaxially integrated, and the inner plate surfaces M4 and M6 of the thrust plates 21 and 23 are opposed to both end surfaces M3 and M5 of the bearing portion 15 as a rotating body. In the present embodiment, as shown in FIG. 3, the thrust plates 21 and 23 are attached to the main shaft 14 at the inner edges of the inner holes 21b and 23b.
Are fixed by pressing a bolt 25 inserted in the center hole 14b of the main shaft 14 into the base 11, but the fixing form is not limited to this.

Then, as shown in FIG.
1 and 23, and both end faces M of the bearing portion 15
3 and M5 form thrust dynamic pressure gap forming surfaces, between which thrust dynamic pressure gaps 18 and 18 filled with air are formed in order to generate a dynamic pressure in the thrust direction about the rotation axis О. Have been. Thrust dynamic pressure gap 1
Each of the sizes 8 and 18 is, for example, about 6 μm. Further, from the viewpoint of forming the thrust dynamic pressure gap 18, the thrust plates 21 and 23 are the first members, and the bearing portion 15 is the second member.

Main shaft 14, bearing part 15 and thrust plate 2
Nos. 1 and 23 are each entirely made of alumina ceramic, and the alumina content is 90 to 99.5.
%, Desirably 92 to 98% by mass, with the balance being oxide-based sintering aid components and inevitable impurities. When the inner diameter of the inner peripheral surface M2 of the through hole 15a of the bearing portion 15 is D and the outer diameter of the outer peripheral surface M1 of the main shaft 14 is d, the radial dynamic pressure gap diameter difference (D−d) / 2 is obtained. The value is 2 to 6 μm, desirably 4 to 6 μm in an axis orthogonal section at an arbitrary position in the axial direction
It is adjusted to a range of 5 μm. Thus, for example, at the start or stop of rotation, the radial dynamic pressure gap forming surface M
It is possible to secure a uniform and stable dynamic pressure generation state and, consequently, a rotation state while preventing local wear of the M1 and M2.

The support 7 (and the polygon mirror 8)
Is made of metal and is press-fitted into the outer peripheral surface of the bearing portion 15 at the center insertion hole 7a. In this case, with the support 7 removed, the radial dynamic pressure gap diameter difference (D′−d ′) /
The value of 2 is 3 to 7 μm, desirably 5 to 6 μm in an axis orthogonal cross section at an arbitrary position in the axial direction. However, the support 7 may be fitted into the outer peripheral surface of the bearing portion 15 in the center insertion hole 7a with a gap, and may be bonded in the gap. In this case, even when the support 7 is removed, the value of the radial dynamic pressure gap diameter difference (D−d) / 2 is the same as the state of attachment of the support 7 in the axial cross section at an arbitrary position in the axial direction. 2
６6 μm, preferably 4-5 μm.

The apparent density of the alumina ceramic constituting each member is 3.5 to 3.9 g / cm ³ , preferably 3.6 to 3.8 g / cm ³ , and the relative density is 90 to 9 g / cm ^3.
8%, desirably 94 to 97%. Further, the average particle size of the ceramic crystal particles on the dynamic pressure gap forming surfaces M1 to M6 is 1 to 7 μm, preferably 2 to 5 μm. As shown in FIG. 5, a large number of surface holes K are formed in the dynamic pressure gap forming surfaces M1 to M6, and the average size thereof is 2 to 20 μm.
m. In addition, the dimension 2 to 20 on the dynamic pressure gap forming surface
By setting the formation area ratio of the surface voids of μm to 10 to 60%, desirably 15 to 40%, the above-mentioned cohesive wear or linking (thrust dynamic pressure gap) is less likely to occur,
In addition, the fluid dynamic pressure level generated in the dynamic pressure gap can be increased. In this case, it is only necessary that at least one of the dynamic pressure gap forming surfaces M1 to M6 has the size and the area ratio of the surface holes K adjusted to the above-described ranges (for example,
Only one of the radial dynamic pressure gap forming surfaces M1, M2, only one of the thrust dynamic pressure gap generating surfaces M3, M4, or only one of the thrust dynamic pressure gap generating surfaces M5, M6). Dynamic pressure gap forming surface, ideally,
In all of the dynamic pressure gap forming surfaces M1 to M6, the surface holes K
It is desirable that the dimensions and the area ratio are adjusted to the above ranges.

At least one of the radial dynamic pressure gap forming surfaces M1 and M2 (for example, M1 on the main shaft 14 side) is provided with a well-known dynamic pressure groove as shown in FIG. Can be formed. A well-known dynamic pressure groove as shown in FIG. 2B may be formed on at least one of the thrust dynamic pressure gap forming surfaces M3 to M6 (for example, M4 and M6 on the thrust plates 21 and 23). it can.

Hereinafter, a method for manufacturing the above-described ceramic dynamic pressure bearing 3 will be described. Each ceramic member, ie,
The main shaft 14, the bearing portion 15, and the thrust plates 21, 23 are
It can be manufactured by a known sintering method. That is, the average particle size 1
Alumina raw material powder ~5μm to, MgO as a sintering aid powder, _CaO, CeO 2, by blending oxide powder _SiO 2, Na ₂ O or the like as a forming material powder, which die molding or cold Press molding into a corresponding shape by a known molding method such as isostatic pressing. The molded body is heated to a temperature of 14
A sintered body is obtained by sintering at 00 to 1700 ° C.

The sintered body is polished to a required surface including a predetermined surface for forming a dynamic pressure gap, and is finished to a predetermined size. Specifically, for example, counts # 100 to # 100 are provided on the inner peripheral surface and both end surfaces of the insertion hole 15a of the bearing portion 15, the outer peripheral surface of the main shaft 14, and the surfaces of both the thrust plates 21, 23 facing the end surfaces of the bearing portion 15. Peripheral speed of 1 with 200 diamond wheels
High-speed polishing is performed at 000 to 1200 m / s, and buffing is performed using diamond abrasives of # 4000 to # 6000 for finishing. As a material of the alumina ceramic constituting each member, the alumina content is 90%.
９９99.5 mass%, desirably 92 to 98 mass%, the radial dynamic pressure gap diameter difference (D−d) /
This is convenient for adjusting the value of 2 to a range of 2 to 6 μm, desirably 4 to 5 μm in an axial cross section at an arbitrary position in the axial direction.

As shown in FIG. 5 (c), on the surface where a dynamic pressure gap is formed by polishing, surface vacancies are formed in the form of grain-dropping holes due to the drop of ceramic crystal particles generated during polishing. The average value, distribution and area ratio of the size of the surface vacancies to be formed are determined by the average value and distribution of the size of the ceramic crystal particles constituting the sintered body, or the size (count) of the polishing grindstone or the abrasive grains, and further, It can be adjusted by adjusting polishing conditions such as time. In addition, the composition and distribution of the grain boundary phase derived from the sintering aid may affect the ease of removal of the ceramic crystal grains during polishing. It is necessary to make appropriate adjustments so as to obtain a state in which holes are formed.

The ceramic member having a finished surface for generating a dynamic pressure gap as described above has a structure in which pores are formed on the surface of a dense sintered body due to falling of ceramic particles, that is, FIG.
As shown in (b), a specific structure in which the inner layer portion is denser than the surface layer portion having surface vacancies is obtained. Therefore,
The presence of surface vacancies can effectively prevent the occurrence of adhesion wear and linking or increase the level of generated dynamic pressure, and the formation of a dense inner layer improves the strength of the ceramic member. In addition, since the surface layer also basically maintains a dense structure in the portion of the structure in which the particles did not fall off, the abrasion resistance is lower than in the case where the porous ceramic sintered body is not densified from the beginning, for example. The performance is greatly improved.

When the working finish of each dynamic pressure gap forming surface M is completed, the above-mentioned dynamic pressure grooves are engraved here by sandblasting, etching, or the like, and the final main shaft 14 and bearing 15 are formed.
Alternatively, thrust plates 21 and 23 are obtained. Then, as shown in FIG. 3, the support 7, the permanent magnet 9 and the coil 13
Is assembled, and the main shaft 14, the bearing portion 15, and the thrust plates 21 and 23 are assembled using the bolts 25, whereby a motor with a dynamic pressure bearing is obtained. Also, the support 7
If the polygon mirror 8 is mounted on the polygon scanner 1, the assembly of the polygon scanner 1 is completed.

The polygon scanner 1 operates as follows. In other words, the motor 2 with the dynamic pressure bearing is configured as an AC induction motor, and when the coil 13 is energized, the polygon mirror 8 is driven to rotate integrally with the bearing 15 and the support 7 with the main shaft 14 as a fixed shaft. The maximum rotation speed is a high-speed rotation of 8000 rpm or more. When a higher scanning speed is required, the maximum rotation speed is 1 rpm.
It may reach 0000 rpm or more, or even 30000 rpm or more (for example, about 50,000 rpm). Therefore, the number of turns of the coil 13, the value of the external magnetic field generated by the exciting permanent magnet 9, and the rated drive voltage are adjusted so that the above-mentioned maximum number of rotations is realized in consideration of the rotational load of the polygon mirror 8. It is set appropriately. The radial dynamic pressure gap 17 between the main shaft 14 and the bearing portion 15 receives radial dynamic pressure on the rotation axis О, and the thrust plates 21, 21.
Similarly, a thrust dynamic pressure is generated in the thrust dynamic pressure gap 18 between the bearing 3 and the bearing portion 15, and the polygon mirror is maintained in a state in which the non-contact state between the relatively rotating members is maintained in both the radial direction and the thrust direction. Eight rotation axes are supported.

FIG. 7 shows another example of a motor used for a polygon scanner (a polygon mirror is not shown). This motor 31 is also configured to include a ceramic dynamic pressure bearing 33 of the present invention having a configuration similar to that of FIG. The ceramic dynamic pressure bearing 33 has a cylindrical bearing portion 3.
5 (for example, an inner diameter of just over 13 mm, an outer diameter of 25 mm, and an axial length of 5 mm), and a main shaft 39 (diameter of less than 13 mm, length of 8 mm) fitted in the through hole 37 in the axial direction of the bearing portion 35.
The main shaft 39 is fixed and does not rotate, and the bearing 35 around the main shaft 39 rotates. Bearing 35
Are defined as the radial dynamic pressure gap forming surfaces M2 and M1, respectively, and a radial dynamic pressure gap 38 is formed therebetween. In the ceramic dynamic pressure bearing 33 of FIG. 7, the axial dimension of the bearing portion 35 and the main shaft 39 is larger than that of the ceramic dynamic pressure bearing 3 of FIG. 3, and the radial dynamic pressure is the main supporting force of the rotation axis О. Therefore, the configuration is such that the thrust plate is omitted.

As in the case of the ceramic dynamic pressure bearing 3 shown in FIG. 3, a permanent magnet 43 is disposed on an annular support 41 integrated with the outer periphery of the bearing 35 in order to rotate the bearing 35. A coil 47 facing the permanent magnet 43 is mounted on a base 45. Further, at least one of the dynamic pressure gap forming surfaces M of the bearing portion 35 and the main shaft 39, for example, a dynamic pressure gap forming surface (outer radial dynamic pressure gap forming surface) M1 outside the main shaft 39 is provided with the configuration shown in FIG. The dynamic pressure groove as shown is formed.

When the inner diameter of the inner peripheral surface M2 of the insertion hole 37 of the bearing portion 35 is D, and the outer diameter of the outer peripheral surface M1 of the main shaft 39 is d, the radial dynamic pressure gap diameter difference (D−d) / 2 is the PCS perpendicular to the axis at an arbitrary position in the center axis direction.
Is adjusted in the range of 2 to 6 μm, preferably 4 to 5 μm. In the state where the support 41 is removed, the value of the radial dynamic pressure gap diameter difference (D′−d ′) / 2 is 3 to 7 μm, preferably 5 to 6 μm in an axial cross section at an arbitrary position in the axial direction. It is.

FIG. 9 shows a more specific configuration example of the polygon scanner. In the polygon scanner 90, the ceramic dynamic pressure bearing 1 of the present invention is provided on the base 100.
One end of a core shaft 102 for supporting and fixing 01 is fixed vertically. A lower thrust plate 103 made of ceramic is fixedly provided on the core shaft 102. A ceramic main shaft 105 is penetrated and fixed to the core shaft 102. Further, the ceramic bearing portion 107 has a radial dynamic pressure gap forming surface 106 which forms the cylindrical outer peripheral surface of the main shaft 105 and a radial dynamic pressure gap forming surface 108 which forms the inner peripheral surface of the bearing portion 107.
, A radial dynamic pressure gap 91 is provided rotatably. Furthermore, a ceramic upper thrust plate 1
09 is penetrated and fixed to the core shaft 102. Also,
Thrust dynamic pressure gap forming surfaces 110 and 111 formed on the upper and lower portions of the bearing portion 107, a thrust dynamic pressure gap forming surface 112 of the lower thrust plate 103, and a thrust dynamic pressure gap forming surface 113 of the upper thrust plate 109, respectively. Between them, thrust dynamic pressure gaps 92 are formed. The material of each ceramic member is again an alumina-based ceramic, and has the same structure or composition as the ceramic dynamic pressure bearings 3 to 33 in FIGS. 3 and 7.

A support portion 114 formed separately is fixed on the outer periphery of the bearing portion 107.
Is fixed to the support portion 114 with the fixing member 117 (the rotating body and the support portion 114 may be integrated). The other end of the core shaft 102 is fixed to the holding seat plate 118 with bolts 119. Further, a dynamic pressure groove 121 similar to that shown in FIG. 2B is formed on the thrust dynamic pressure gap forming surface 112 of the lower thrust plate 103. Although not shown, the outer peripheral surface of the main shaft 105 (hereinafter, also referred to as the outer peripheral surface 106) which forms the radial dynamic pressure gap forming surface 106 has the same dynamic pressure groove as that shown in FIG. To form

A winding 129 is provided on the base 100 via an insulating member 123 as a configuration of the three-phase brushless motor 133, and a winding 129 is provided below the support portion 114 of the bearing 107 in the rotation direction. A magnet 125 facing 129 is provided. When the winding 129 is energized, it functions as a drive motor of the polygon mirror 116 for inductively rotating the bearing 107 at a high speed. The rotation of the three-phase brushless motor 133 generates a dynamic pressure in the radial dynamic pressure gap 91, and enables smooth high-speed rotation.

When the bearing 107 is stopped, the opposing surface 110 of the bearing 107 is in contact with the thrust dynamic pressure gap forming surface 112 of the lower thrust plate 103. And
When the bearing 107 starts rotating around the main shaft 105,
A thrust dynamic pressure is generated in the thrust dynamic pressure gap 92, the contact state is released, and high-speed rotation is enabled.

When the inner diameter of the inner peripheral surface of the insertion hole 108 of the bearing portion 107 is D, and the outer diameter of the outer peripheral surface 106 of the main shaft 105 is d, the radial dynamic pressure gap diameter difference (D−d) / 2
Is an axis orthogonal cross section P at an arbitrary position in the center axis direction.
It is adjusted to a range of 2 to 6 μm by CS, preferably 4 to 5 μm. Further, the fixing member 117 and the support portion 114
Supports the polygon mirror 116, and
Are radially tightened, but in a state where they are removed, the value of the radial dynamic pressure gap diameter difference (D′−d ′) / 2 is 3 to 7 in an axial orthogonal cross section at an arbitrary position in the axial direction.
μm, preferably 5 to 6 μm.

FIG. 10 shows an example in which the present invention is applied to a hard disk drive. The hard disk device 200 includes a magnetic disk 209a on the outer periphery of the hub 211,
209b is fixed, and a motor rotation shaft 212 is fixedly provided at the center. The hub 211 rotates together with the disks 209a and 209b fixed thereto. Motor rotating shaft 2
Reference numeral 12 denotes a fixed bearing portion 22 made of alumina ceramic.
1 and is supported in the thrust direction by a thrust plate 222 made of alumina ceramic.

The motor rotating shaft 212 and the fixed bearing 22
1 and the thrust plate 222 are made of a ceramic material, so that the motor rotating shaft 212 and the fixed bearing portion 221 have mechanical rigidity enough to withstand the load of the disks 209a and 209b rotating at a high speed and the high speed rotation.

Next, between the motor rotating shaft 212 and the fixed bearing 221, the motor rotating shaft 212 and the thrust plate 22
2 is filled with air, and a radial dynamic pressure gap 2 is circumferentially provided between the motor rotating shaft 212 and the fixed bearing portion 221.
40 are formed, and the inner peripheral surface 21 of the fixed bearing portion 221 is formed.
7, a dynamic pressure groove (not shown) is formed. The motor rotation shaft 212 is moved by the radial dynamic pressure gap 240
Radial dynamic pressure is generated, and the fixed bearing portion 221 rotates without contact. The outer peripheral surface of the motor rotating shaft 212 and the inner peripheral surface of the fixed bearing portion 221 forming the radial dynamic pressure gap forming surface are configured in the same manner as the ceramic dynamic pressure bearings 3 to 33 in FIGS. It has the configuration of the ceramic dynamic pressure bearing of the present invention). In addition, the motor rotation shaft 2
Twelve shaft ends 212a have a spherical pivot shape,
A thrust force is supported by a thrust plate 222.

In the hard disk drive 200, the stator core 224 is fixed to the bracket 223. The stator core 224 includes a stator coil 225.
Is wound. Similar to the polygon scanner 90 of FIG.
Core 224 excited by passing current through
Are generated by the rotating magnetic field generated by the motor and the multipolar magnetized drive magnet 214 surrounding the stator core 224. The magnet 214 is fixed to the inner periphery of the hub 211, and forms the rotor 210 together with the hub 211.

Then, the insertion hole 21 of the fixed bearing portion 221 is
7, the value of radial dynamic pressure gap diameter difference (D−d) / 2 is represented by the central axis direction, where D is the inner diameter of the inner peripheral surface of D7, and d is the outer diameter of the outer peripheral surface of the motor rotating shaft (main shaft) 212. 2 to 6 μm, preferably 4 to 5 in the axis orthogonal cross section PCS at an arbitrary position
It is adjusted to the range of μm. Also, the bracket 223
Is press-fitted into the outer peripheral surface of the bearing portion 221 in the insertion hole 223a. When the bearing is removed, the value of the radial dynamic pressure gap diameter difference (D′−d ′) / 2 is changed to an arbitrary position in the axial direction. 3 to 7 μm, preferably 5 to 6 μm in the section perpendicular to the axis. However, bonding may be used instead of press-fitting. In this case, even in the detached state, the value of the radial dynamic pressure gap diameter difference (D−d) / 2 is 2 to 6 μm in an axial cross section at an arbitrary position in the axial direction. , Preferably 4-5μ
m.

In the hard disk drive 200, the outer bearing portion 221 is fixed, and the inner main shaft (rotary shaft) is fixed.
3, the bearing 15 is rotated by replacing the polygon mirror 8 with the magnetic disk 408, and the spindle 1 is rotated.
Of course, a hard disk drive configuration in which the four sides are fixed is also possible.

It should be noted that the present invention is not limited to the above-described embodiment at all, and it goes without saying that the present invention can be implemented in various modes without departing from the gist of the present invention. For example, a gas other than air may be used as the fluid for generating dynamic pressure, or a liquid such as oil or water may be used instead of the gas.

[0078]

EXAMPLES The following experiments were conducted to confirm the effects of the present invention. First, each member of the bearing portion 15, the main shaft 14, and the thrust plates 21 and 23 shown in FIG. 3 was manufactured as an alumina ceramic sintered body as follows. That is, as a raw material, alumina powder (purity: 99.9%) having an average particle diameter of 1.8 μm measured by a laser diffraction type particle sizer, and C
aO powder (average particle size: 4 μm), MgO powder (average particle size: 4 μm) and SiO ₂ powder (average particle size: 4 μm)
And a sintering aid powder mixed at a weight ratio of 3: 1: 1. Then, 0.3 to 15% by mass of the sintering aid powder is mixed so as to be the remaining alumina powder, water and an appropriate amount of PVA as a binder are added, wet-mixed, and then spray-dried. By drying, a granulated raw material base powder was obtained.

The granulated raw material powder was formed into each member shape by a die pressing method, and then fired at a temperature of 1400 to 1700 ° C. The obtained sintered body is formed on the inner peripheral surface and both end surfaces of the insertion hole 15a of the bearing portion 15 which becomes the dynamic pressure gap forming surface, the outer peripheral surface of the main shaft 14, and the bearing portion 1 of the thrust plates 21 and 23.
No. 5 is subjected to high-speed polishing at a peripheral speed of 1000 m / min with a diamond grindstone of # 100 to # 200 on a surface opposed to the end face of # 5, and # 2000 to # 6 for finishing.
Buffing was performed with 000 diamond abrasive grains.
In this state, the inner diameter D of the inner peripheral surface of the insertion hole 15a and the outer diameter d of the outer peripheral surface of the main shaft 14 of the bearing portion 15 are set to 0.5 in the center axis direction by a known shape profile measuring instrument.
Measure each at a cross section perpendicular to the axis at mm intervals, calculate the radial dynamic pressure gap diameter difference (D'-d ') / 2 at each position, and calculate the maximum value, minimum value and average value (processing target value). :
5 μm). Then, after the measurement, regions other than those planned in the groove pattern of each member were masked and shot blasted to form the dynamic pressure grooves shown in FIG.

Then, on each of the dynamic pressure gap forming surfaces, the polished surface area where the dynamic pressure grooves are not formed is observed with an optical microscope, and the observed image is subjected to image analysis using a known method, thereby obtaining alumina crystal particles. Average size (average particle size)
I asked. Further, regarding surface vacancies, dimensions 2 to 20
The area ratio of pores of μm was determined. The apparent density of each member was measured by the Archimedes method, and the value of the relative density was calculated using the true density estimated from the mixing ratio of alumina and the sintering aid.

Next, each of the above members was assembled into a motor with a dynamic pressure bearing shown in FIG. 3 and the following test was conducted. When continuously rotating at a rotation speed of 30,000 rpm,
Rotational runout of the bearing portion 15 that is a rotating part (maximum runout amplitude of the outer peripheral surface measurement position in a direction perpendicular to the rotation axis)
Is measured using a laser interferometer. And
A sample having a runout of less than 0.1 μm is excellent (（).
Good for 1 μm or more and less than 0.2 μm (good), 0.2 μm
Those having a length of not less than m and less than 0.3 μm were evaluated as acceptable (△), and those exceeding 0.3 μm were evaluated as unacceptable (×).

From the stopped state, the rotation speed is accelerated to 30,000 rpm, and after holding for 1 minute, the cycle for stopping is 10 cycles.
Repeat up to 0000 times. Regarding the adhesive wear of the dynamic pressure gap forming surface, the adhesive wear was not observed at all at the dynamic pressure gap forming surface until the end of the cycle (優), and the adhesive wear was observed at the end of the cycle. The test was continued when the test was extremely slight (good), good adhesion was observed at the end of the cycle, but no problem was observed at the end of the cycle (△). Those which became impossible were evaluated as impossible (x). Further, by utilizing the thrust dynamic pressure gap forming surface of the bearing portion 15, JIS: Z2245
The Rockwell hardness was measured at a load of 15 N according to the method specified in (1). At the stage where the support 7 is pressed into the bearing portion 15, the inner diameter D of the inner peripheral surface of the insertion hole of the bearing portion 15 is measured again, while the outer diameter of the outer peripheral surface of the main shaft 14 is assumed to be unchanged, and , And (D-
d) / 2 was determined. The above results are shown in Tables 1 and 2.

[0083]

[Table 1]

[0084]

[Table 2]

As is apparent from these results, by setting the alumina content of the alumina ceramic to 90 to 99.5% by mass, the radial dynamic pressure gap diameter difference (D−d) / 2 was obtained.
Can be set within a range of 2 to 6 μm at an arbitrary position in the axial direction, and as a result, rotation runout and adhesive wear are hardly generated.

[Brief description of the drawings]

FIG. 1 is a schematic cross-sectional view showing one configuration example of a ceramic dynamic pressure bearing of the present invention.

FIG. 2 is an explanatory view showing an example of a dynamic pressure groove formed on a radial dynamic pressure gap forming surface and an example of a dynamic pressure groove formed on a thrust dynamic pressure gap forming surface.

FIG. 3 is a front sectional view showing an example of a polygon scanner motor unit using the ceramic dynamic pressure bearing of the present invention.

FIG. 4 is a front sectional view and an exploded perspective view of a ceramic dynamic pressure bearing which is a main part of FIG. 3;

FIG. 5 is a schematic diagram showing a dynamic pressure gap forming surface in which surface holes are formed, and an explanatory diagram showing a state in which surface holes are formed by grain shedding during polishing.

FIG. 6 is an explanatory view showing the definition of the size of a hole (or crystal particle).

FIG. 7 is a schematic sectional view showing a modified example of a motor unit using the ceramic dynamic pressure bearing of the present invention.

FIG. 8 is a perspective view showing a main part of still another modified example.

FIG. 9 is a front sectional view showing an example of a polygon scanner using the ceramic dynamic pressure bearing of the present invention.

FIG. 10 is a front sectional view showing an example of a hard disk drive using the ceramic dynamic pressure bearing of the present invention.

FIG. 11 is a schematic diagram showing a structure of an alumina ceramic sintered body.

FIG. 12 is a schematic diagram showing various modes of forming pores by dropping of ceramic crystal particles.

[Explanation of symbols]

 1,90 Polygon scanner 3,33,101,251 Ceramic dynamic pressure bearing 14,39,105,212 Main shaft 15,35,107,221 Bearing part 15a Insertion hole 17,38,91,240 Radial dynamic pressure gap 18,92 Thrust dynamic pressure gap 21, 23, 103, 109, 222 Thrust plate M Dynamic pressure gap forming surface M1, M2 Radial dynamic pressure gap forming surface M3 to M6 Thrust dynamic pressure gap forming surface

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat ゛ (Reference) H02K 21/24 C04B 35/10 EF term (Reference) 3J011 AA10 AA20 BA06 CA02 DA01 DA02 JA02 KA02 KA03 LA01 MA02 QA01 SD04 4G030 AA07 AA08 AA36 AA37 BA18 BA20 GA11 GA14 GA19 GA22 GA27 GA32 5H607 BB01 BB07 CC01 DD03 DD16 GG09 GG12 GG14 GG15 KK04 5H621 GA01 JK17 JK19

Claims (22)

[Claims] A first member having a cylindrical outer peripheral surface and a second member having a cylindrical insertion hole, wherein the first member is inserted through the insertion hole of the second member. Along with the inner surface of the insertion hole of the second member and the outer peripheral surface of the first member inserted therethrough as a radial dynamic pressure gap forming surface, a radial dynamic pressure gap is formed between the radial dynamic pressure gap forming surfaces. is formed, with the relative rotation between their first and second members, the is configured to generate a fluid dynamic pressure between the radial dynamic圧隙, both said first member and said second member, Al ₂ O
The content of the Al component in terms of ₃ is 90 to 99.5% by mass, and the oxide-based sintering aid component is 0.5% in terms of oxide.
D is the inner diameter of the second member at an arbitrary axis orthogonal cross section of the inner peripheral surface of the insertion hole, and the other is an arbitrary axis orthogonal to the first member. Assuming that the outer diameter of the outer peripheral surface in the cross section is d,
(Dd) / 2 is adjusted in the range of 2 to 6 μm. 2. The ceramic dynamic pressure bearing according to claim 1, wherein the apparent density of the alumina ceramic is 3.5 to 3.9 g / cm ³ . 3. The ceramic dynamic pressure bearing according to claim 1, wherein the relative density of the alumina ceramic is 90% or more. 4. The ceramic dynamic pressure bearing according to claim 1, wherein the average particle size of the alumina-based ceramic crystal particles is 1 to 7 μm. 5. A thrust plate arranged to face at least one end surface of the second member in a direction of a rotation axis, wherein an end surface of the second member and an opposing surface of the thrust plate facing the end surface are provided. 5. The ceramic dynamic pressure bearing according to claim 1, wherein a thrust dynamic pressure gap is formed between the thrust dynamic pressure gap forming surfaces. 6. The method according to claim 1, wherein an area ratio of ceramic crystal particles having a particle size of 2 to 5 μm is 40% or more on the surface of the dynamic pressure gap forming surface made of the alumina ceramic. The ceramic dynamic pressure bearing according to the paragraph. 7. An average size of surface vacancies existing on a dynamic pressure gap forming surface made of alumina ceramic is larger than an average particle size of ceramic crystal particles.
The ceramic dynamic pressure bearing according to any one of the preceding claims. 8. An average size of surface pores existing on a dynamic pressure gap forming surface made of the alumina ceramic is 2 to 20 μm.
The ceramic dynamic pressure bearing according to any one of claims 1 to 7, wherein m is m. 9. The method according to claim 1, wherein the formation area ratio of surface pores having a size of 2 to 20 μm on the dynamic pressure gap forming surface made of the alumina ceramic is 10 to 60%. Ceramic dynamic pressure bearing. 10. The alumina ceramic is a dense ceramic sintered body having a relative density of 90% or more, and mainly has pores having a size of 2 to 20 μm which are present in the sintered body. The ceramic dynamic pressure bearing according to any one of claims 1 to 9, wherein the ceramic hydrodynamic bearing exists in a form localized on the surface in the form of the surface voids. 11. The ceramic dynamic pressure bearing according to claim 10, wherein the surface pores are formed by dropping ceramic crystal grains when processing and finishing the dynamic pressure gap forming surface. 12. The ceramic dynamic pressure bearing according to claim 1, wherein a dynamic pressure groove is formed on at least one of the radial dynamic pressure gap forming surface and the thrust dynamic pressure forming surface. 13. A hard disk drive as a bearing for a rotating spindle portion of a hard disk drive.
3. The ceramic dynamic pressure bearing according to any one of 2. 14. A polygon scanner used as a bearing for a rotary spindle portion of a polygon mirror of a polygon scanner.
The ceramic dynamic pressure bearing according to any one of the preceding claims. 15. A motor with a bearing, wherein the ceramic dynamic pressure bearing according to any one of claims 1 to 14 is used as a bearing of a motor rotation output section. 16. The motor with a bearing according to claim 15, which is used for a hard disk rotation drive section of a hard disk device. 17. The motor with a bearing according to claim 15, which is used for a polygon mirror driving section of a polygon scanner. 18. The motor with a bearing according to claim 15, which is a high-speed motor having a maximum rotation speed of 8000 rpm or more. 19. A hard disk drive comprising the motor with a bearing according to claim 16 and a hard disk rotationally driven by the motor with a bearing. 20. The hard disk is directly pressed into an outer peripheral surface of the second member, or the hard disk is attached to a support member pressed into an outer peripheral surface of the second member, and the hard disk is attached to the second member. When the press-fitted hard disk or the support member is removed, the inner diameter of the second member at an arbitrary axis orthogonal cross section of the inner peripheral surface of the insertion hole is D ′, and the other is the outer peripheral surface of the first member. (D′−d ′) / 2, where d ′ is the outer diameter in an arbitrary cross section orthogonal to the axis.
The hard disk drive according to claim 19, wherein is adjusted to a range of 3 to 7 µm. 21. A polygon scanner, comprising: the motor with a bearing according to claim 17; and a polygon mirror rotated and driven by the motor with the bearing. 22. The polygon mirror is directly pressed into the outer peripheral surface of the second member, or the polygon mirror is attached to a support member pressed into the outer peripheral surface of the second member, and When the polygon mirror or the support member press-fitted to the member is removed, the inner diameter of the second member at an arbitrary axis orthogonal cross section of the inner peripheral surface of the insertion hole is D ′, and the other of the first member is (D′−d ′) / 2, where d ′ is the outer diameter of the outer peripheral surface at any cross section orthogonal to the axis.
22. The polygon scanner according to claim 21, wherein is adjusted to a range of 3 to 7 μm.