JP2002295477A - Ceramic dynamic pressure bearing, motor provided with the same, hard disk device, and polygon scanner - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a ceramic dynamic pressure bearing capable of preventing the occurrence of wear when starting and stopping and realizing favorable rotation of the dynamic pressure bearing. SOLUTION: A dynamic pressure clearance 17 is formed between a first member 14 and a second member 15 rotating relatively around a predetermined rotary axial line, and a fluid dynamic pressure is generated in the dynamic pressure clearance 17 in accordance with the relative rotation of the first member 14 and the second member 15. A part including a surface (dynamic pressure clearance forming face) facing the dynamic pressure clearance 17 is constituted by at least ceramic in at least either of the first member 14 and the second member 15, and an average dimension of a surface hole existing on the dynamic pressure clearance forming face made of ceramic is adjusted to 2 to 20 μm. Furthermore, at least any dynamic pressure clearance forming face of the first member 14 and the second member 15 is covered with a hard carbon film DR having an average film thickness smaller than the average dimension of the surface hole and made of amorphous carbon mainly.

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]

By the way, in a dynamic pressure bearing, in a high-speed rotation state in which 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. At the time of small starting and stopping, sufficient dynamic pressure is not generated, so that 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, members opposed to each other with the dynamic pressure gap interposed therebetween are made of ceramics such as alumina. However, there is a problem that contact wear or the like occurs more or less.

It is an object of the present invention to provide a ceramic dynamic pressure bearing which can generate a sufficient level of dynamic pressure and hardly causes contact wear and the like at the time of starting and stopping.

[0005]

Means for Solving the Problems and Action / Effect To solve the above problems, a ceramic dynamic pressure bearing according to the present invention comprises a dynamic pressure gap between a first member and a second member relatively rotating around a predetermined rotation axis. Is formed, with the relative rotation between the first member and the second member, and is configured to generate a fluid dynamic pressure in the dynamic pressure gap, and the dynamic pressure is generated in at least one of the first member and the second member. The portion including the surface facing the gap (dynamic pressure gap forming surface) is made of at least ceramic, and the average size of the surface pores existing in the dynamic pressure gap forming surface made of ceramic is 2 to 20 μm, and The at least one of the dynamic pressure gap forming surfaces of the first member and the second member was covered with a hard carbon-based coating mainly composed of amorphous carbon having an average film thickness smaller than the average size of the surface pores. Characterized by

When ceramic is used as the material of the dynamic pressure bearing, the surface condition of the dynamic pressure gap forming surface of the ceramic constituting the main shaft and the bearing becomes a problem. In other words, in general, fine holes are present on the ceramic surface after polishing due to particles falling off during polishing, and the size of such holes has a great effect on the rotational state of the dynamic pressure bearing. it is conceivable that.

On the other hand, according to the study of the present inventors, it has been found that if the surface for forming the dynamic pressure gap 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 cavities within 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 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"). Further, when a member such as the main shaft, which forms one side of the dynamic pressure gap forming surface, is formed of metal, seizure may occur. On the other hand, extremely small surface pores hardly contribute to the generation of dynamic pressure.

Therefore, in the present invention, the average size of the surface pores existing on the dynamic pressure gap forming surface made of ceramic is 2 to 2 times.
By setting the thickness to 0 μm, it is possible to effectively prevent the occurrence of vibration, adhesion wear or seizure. Also, 2
By positively forming surface pores having an average size of ２０20 μm, the generated fluid dynamic pressure level can be made high and stable. On the other hand, in the case of a dynamic pressure bearing in which a thrust dynamic pressure generating gap described later is formed, the occurrence of linking can be prevented.

Further, in the ceramic dynamic pressure bearing of the present invention, the surface for forming the dynamic pressure gap is made of a hard carbon-based coating mainly composed of amorphous carbon and having an average film thickness smaller than the average size of the surface pores. Even if the dynamic pressure gap forming surfaces contact each other in the low rotation state where the dynamic pressure is insufficient at the time of starting / stopping, wear and adhesion are unlikely to occur.

In the present specification, the term "hard carbon-based coating mainly composed of amorphous carbon" means that the skeleton structure of carbon, which is the main component of the film, is amorphous and its Vickers hardness is 1500.
It refers kg / mm ² or more coatings. The hardness of the coating is
For example, it can be measured using a dynamic ultra-fine hardness tester (for example, NHT manufactured by Swiss CSEM). The reason why the average film thickness is set smaller than the average size of the surface pores is to prevent excessive clogging of the positively formed surface pores in order to enhance the dynamic pressure generating effect.

In this specification, the size of the surface pores (or crystal grains) is defined as the surface pores (or crystal grains) as shown in FIG. When various kinds of circumscribed parallel lines that do not cross the inside of the outlines are drawn while changing the positional relationship with the outlines, a minimum distance dmin between the parallel lines,
The average value with the maximum interval dmax (that is, d = (dmin + d
max) / 2).

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, seizure, or linking is likely to occur on the dynamic pressure gap forming surface when starting or stopping rotation. 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.

In order to effectively contribute to the generation of dynamic pressure and to realize stable rotation, the more preferable size of the surface holes is 5 μm.
It is preferable that the area ratio of the surface pores in such a size range on the dynamic pressure gap forming surface is 15 to 30%.

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 vacancies 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 surface pores 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 in the dynamic pressure gap forming surface is 100 μm.
m, that is, it is desirable that there are no surface vacancies exceeding 100 μm.

Next, the hard carbon-based coating described above has already been used in various fields such as improving lubrication of sliding members such as magnetic heads and bearings, and improving wear resistance of ceramic tools and the like. Is widely used. As the method for producing the coating, those disclosed in various publications or documents can be adopted.
-91100, Tokiko 6-60404, Tokio Sho 63-
No. 501237, JP-A-63-162870, JP-A-63-162872, JP-A-63-222314,
JP-A-5-296248 can be exemplified. In these methods, a film is formed by a vapor phase film forming method using the principle of a physical vapor deposition method or a chemical vapor deposition method. Specifically, a hydrocarbon as a raw material gas or a mixed gas of hydrocarbon and hydrogen is introduced into a decompressed atmosphere, and is thermally decomposed using high-frequency plasma or a resistance heating filament to be deposited on a substrate surface. To obtain a coating.

Among the above-mentioned coatings, those containing a relatively large number of diamond bonds (covalent bonds by sp3 hybrid orbitals) in the bonds forming the carbon skeleton structure are diamond-like carbon coatings (diamond-like carbon coatings, hereinafter DL).
C film) and is very hard. In addition, the entry of hydrogen atoms into dangling bonds of carbon atoms stabilizes the amorphous structure by closing the carbon chain, and creates a harmful graphite structure that causes a decrease in film strength and adhesion to the base. Is considered to contribute to the realization of a DLC film having high strength and high adhesion (for example, JP-A-63-162872).

The hard carbon-based coating used in the present invention may contain additional elements such as phosphorus, silicon, tungsten and chromium for the purpose of improving the film hardness. A method for producing a coating containing these additional elements is described in, for example,
The methods disclosed in JP-A-162870, JP-A-63-162871 and JP-A-63-162872 can be employed.

Next, the first member and the second member forming the dynamic pressure gap can be entirely made of ceramic. The ceramic has a relative density of 90% from the viewpoint of improving the strength and fracture toughness, and further ensuring the wear resistance (particularly at the time of starting and stopping when the probability of contact with the member is high).
As described above, it is desirable that the content be 95% or more. Therefore,
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. It is desirable to achieve both the effect of preventing cohesive wear, seizure or linking, and the effect of improving strength and abrasion resistance. Specifically, it is preferable that pores having a size of 2 to 20 μm existing in the ceramic sintered body exist mainly in a form localized in the form of surface pores on the surface on which the dynamic pressure gap is formed. And
In order to efficiently form such a structure, it is effective to form the surface pores by dropping the ceramic crystal particles when working and finishing the dynamic pressure gap forming surface.

The formation of the hard carbon-based coating on the surface on which the dynamic pressure gap is formed is performed after the formation of the surface vacancies by the above-mentioned processing finish. And, by forming the average thickness of the hard carbon-based coating smaller than the average size of the formed surface pores, even after forming the hard carbon-based coating, the main part of the surface pores remains as open pores. Therefore, the above-described effects of the formation of holes can be sufficiently ensured. The average thickness of the hard carbon-based coating is more desirably 0.1 to 1.5.
It is good to be about μm. If the average film thickness is less than 0.1 μm, the effect of imparting wear resistance due to the formation of the hard carbon-based film becomes insufficient, and if it exceeds 1.5 μm, the effect of imparting wear resistance is substantially saturated, leading to wasteful cost increase. . In addition,
In the present specification, the average film thickness of the hard carbon-based coating means the average value of the film thickness in a region excluding the inner surface of the pores on the surface on which the dynamic pressure gap is formed.

Next, the dynamic pressure gap forming surface may be a radial dynamic pressure gap forming surface formed in a radial direction with respect to the rotation axis of the bearing. That is, the first member is formed in a shaft shape, and the first member is inserted through the insertion hole formed in the second member, and the inner surface of the insertion hole of the second member and the outer periphery of the first member inserted therein The radial dynamic pressure gap forming surface can be formed between the radial dynamic pressure gap forming surfaces. This radial dynamic pressure gap forming surface can be covered with the hard carbon-based coating.

For example, in the case of a hydrodynamic bearing having the structure illustrated in FIG. 1, the radial direction is a direction (and thus a radial direction) perpendicular to the rotation axis direction (vertical direction in the figure) of the main shaft as the first member.
It is. For example, in FIG. 1, the outer peripheral surface of the main shaft, which is the fixed first member, and the inner peripheral surface of the bearing portion, which is the second member configured as the cylindrical rotating body, are the radial dynamic pressure gap forming surfaces. As will be described later, in the case of a bearing that is long in the direction of the rotation axis, whether or not the radial dynamic pressure is sufficiently generated is important for stably supporting the rotation axis. Therefore, by adjusting the surface pores of the radial dynamic pressure gap forming surface to the above-described form unique to the present invention, and by covering with a hard carbon-based coating, sufficient dynamic pressure can be generated in the radial dynamic pressure gap, and Adhesive wear and seizure during stopping can also be effectively prevented or suppressed. further,

On the other hand, the dynamic pressure gap forming surface may be a thrust dynamic pressure gap forming surface formed in the thrust direction with respect to the rotation axis of the rotating body. That is, the first member is disposed so as to face at least one end surface of the second member in the direction of the rotation axis, and the end surface of the second member and the opposing surface of the first member opposing the second member are thrust-moved. As the pressure gap forming surface, a thrust dynamic pressure gap is formed between the thrust dynamic pressure gap forming surfaces. The thrust dynamic pressure gap forming surface can be covered with the hard carbon-based coating.

For example, in the case of the dynamic pressure bearing having the structure illustrated in FIG. 1, the thrust direction is the axial direction of the main shaft, that is, the direction of the rotation axis (vertical direction in the figure). In FIG. 1, the end surface of a bearing portion, which is a second member configured as a cylindrical rotating body, and the plate surface of a thrust plate as a first member, which faces the end surface of the bearing portion in the axial direction, have a thrust dynamic pressure. It becomes a 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. Therefore, by adjusting the surface pores of the thrust dynamic pressure gap forming surface to a form peculiar to the present invention and covering with a hard carbon-based coating, sufficient dynamic pressure can be generated in the thrust dynamic pressure gap, and start / stop Adhesive wear, seizure and linking at the time can also be effectively prevented or suppressed. In particular, in many cases, the dynamic pressure bearings are often arranged with the rotation axis directed vertically, but in this case, when the thrust plates are arranged so as to face the lower end surface of the bearing portion, they are formed. The bearing portion floats and rotates against the gravity due to the dynamic pressure in the thrust dynamic pressure gap. However, when the dynamic pressure is reduced at the time of starting / stopping, the bearing portion falls into a thrust plate shape due to gravity, and adhesion abrasion, seizure or linking is more likely to occur. Therefore, it can be said that it is more advantageous to form a hard carbon-based coating on the formation surface of the thrust dynamic pressure gap (this is because
The present invention is not limited to the mode in which the hole size of the dynamic pressure gap forming surface unique to the present invention is specially specified, but is applicable to all the dynamic pressure bearing modes in which the thrust dynamic pressure gap is formed.

It is of course possible to form both a radial dynamic pressure gap and a thrust dynamic pressure gap in one bearing as shown in FIG. In this case, depending on the form of formation of each dynamic pressure gap, the first member (or the second member) from the viewpoint of the radial dynamic pressure gap and the first member (or the second member) from the viewpoint of the thrust dynamic pressure gap The substance may be the same member, or may be different members. For example, in the example of FIG. 1, the second member is a bearing portion from any viewpoint, the inner peripheral surface thereof is a radial dynamic pressure gap forming surface, and both end surfaces are thrust dynamic pressure gap forming surfaces. On the other hand, with respect to the first member, the main shaft is the first member when viewed from the viewpoint of the radial dynamic pressure gap, and when viewed from the viewpoint of the thrust dynamic pressure gap, a pair of the main members is opposed to both end surfaces of the bearing portion. The thrust plate is the first member. The main shaft is a non-rotating fixed shaft. As shown in FIG.
A bearing 251 in which the main shaft 212 is on the rotating side and the cylindrical bearing 221 is on the fixed side is also possible.

In the dynamic pressure bearing according to the present invention, the axial length of the dynamic pressure bearing is longer than the outer diameter of the thrust dynamic pressure gap forming surface, or 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-ROM.
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.

Next, as the ceramic material used in the present invention, alumina ceramics can be preferably used. Alumina is relatively inexpensive, has high strength, and has excellent chemical stability. Such an alumina-based ceramic can be manufactured by firing a material obtained by blending an alumina powder with an appropriate sintering aid powder (eg, an oxide such as Mg, Ca, Ce, Si, or Na) as a raw material. . In this case, the amount of the sintering aid component is 0.1% in terms of oxide.
The use of an alumina ceramic containing 5 to 10% by weight and the balance of the Al component in terms of Al ₂ O ₃ makes it possible to improve the strength and toughness, and furthermore, the dynamic pressure gap forming surface formed by the ceramic. It is desirable to improve wear resistance and chipping resistance.

On the other hand, besides alumina ceramics, silicon nitride ceramics are particularly suitable for use in the present invention because of their high strength and excellent wear resistance. Silicon nitride ceramics are mainly composed of silicon nitride.
The remaining components include a sintering aid component, and each group of elements of 3A, 4A, 5A, 3B (for example, Al (alumina)) and 4B (for example, Si (silica)) in the periodic table, and At least one selected from Mg can be contained in an amount of 0.5 to 10% by weight in terms of oxide. These are mainly present in an oxide state in the sintered body (in this case, it means a content ratio in a silicon nitride ceramic as a substrate). If the sintering aid component is less than 0.5% by weight, it becomes difficult to obtain a dense sintered body. On the other hand, when the content exceeds 10% by weight, insufficient strength, toughness or heat resistance is caused, and in the case of a sliding part, the wear resistance is reduced. The content of the sintering aid component is desirably 1 to 8% by weight. In the present invention, “main component” (also synonymous with “subject” or “mainly”) means that the content of the component in the substance of interest is 50% by weight, unless otherwise specified.
It means above.

The 3A group sintering aid component includes S
c, Y, La, Ce, Pr, Nd, Sm, Eu, Gd,
Tb, Dy, Ho, Er, Tm, Yb, and Lu are generally used. The content of these elements R is RO only for Ce.
₂ and others are calculated using R ₂ O ₃ type oxides. Among these, the oxides of the heavy rare earth elements of Y, Ce, Tb, Dy, Ho, Er, Tm, and Yb have the strength of the silicon nitride sintered body,
It is preferably used because it has the effect of improving toughness and wear resistance. In addition, magnesia spinel, zirconia and the like can also be used as a sintering aid.

The structure of the silicon nitride-based sintered member has a form in which main phase crystal grains containing silicon nitride as a main component are bonded by vitreous and / or crystalline binder phases. The main phase has a β conversion of 70% by volume or more (preferably 90% by volume).
(% By volume or more) of Si ₃ N ₄ phase. In this case, the Si ₃ N ₄ phase is a phase in which a part of Si or N is substituted by Al or oxygen, and a phase in which metal atoms such as Li, Ca, Mg, and Y are solid-dissolved. There may be. For example, it can be exemplified Sialon which is expressed by the following general formula; _{beta-sialon: Si 6-z Al z O} z N 8-z (z =
0-4.2) α-sialon: M _x (Si, Al) ₁₂ (O, N)
₁₆ (x = 0 to 2) M: Li, Mg, Ca, Y, R (R is a rare earth element excluding La and Ce).

The above-mentioned sintering aid component mainly constitutes a binder phase, but a part thereof may be taken into the main phase. The binder phase may contain unavoidable impurities, for example, silicon oxide contained in the silicon nitride raw material powder, in addition to components intentionally added as a sintering aid.

It is desirable that the silicon nitride powder used as a raw material has an α-formation ratio (a ratio of α-silicon nitride in total silicon nitride) of 70% or more. At least one element selected from the group consisting of elements of groups 3A, 4A, 5A, 3B and 4B is 0.5 to
10% by weight, preferably 1 to 8% by weight. In addition, at the time of compounding the raw materials, in addition to oxides of these elements, compounds which can be converted to oxides by sintering, for example, carbonates, hydroxides and the like may be mixed.

In ceramics other than the above, zirconium
Near (zirconium oxide) ceramics can be used.
Zirconia ceramic is a so-called partially stabilized zirconia.
By adopting the near composition,
It is possible to strengthen ceramics. Zirconia-based sera
ZrO, the main component of the Mick phase₂And HfO₂Is the temperature
With the change, transformation occurs between three types of phases with different crystal structures
Rubbing is known, specifically at low temperatures including room temperature
Side, monoclinic phase, higher temperature side, tetragonal phase,
At the high temperature side, it becomes a cubic phase. Zirconia ceramic
The whole phase is ZrO₂And HfO₂At least one of
In the vicinity of room temperature,
All are considered to be monoclinic phases. However,
ZrO₂And HfO₂A certain amount as a stabilizing component
Alkaline earth metal oxide or rare earth metal acid
(Eg, calcia (CaO) or yttria
(Y ₂O₃), Etc., to form a monoclinic phase
The transformation temperature between the tetragonal phase decreases and the temperature range near room temperature
Is known to be able to stabilize the tetragonal phase in
You.

Here, it is known that the above-mentioned phase transformation from the tetragonal phase to the monoclinic phase is based on a so-called martensitic transformation mechanism or a similar phase transformation mechanism. When stress is applied, the transformation temperature rises and the tetragonal phase undergoes stress-induced transformation, and the strain energy due to the stress is consumed as a driving force for the transformation, so that the applied stress is relaxed. Therefore, even if stress concentrates on the crack tip generated in the material,
Transformation of the tetragonal phase to the monoclinic phase relaxes the stress, prevents or relaxes the propagation of cracks, and improves the fracture toughness value.

As the stabilizing component of the zirconia-based ceramic phase, one or more of Ca, Y, Ce and Mg are used. Ca is CaO, Y is Y ₂ O ₃ , and Ce is CeO _2.
In addition, Mg is a value converted into an oxide to MgO, and is a total content of 1.4 in the zirconia ceramic phase.
It is desirable to contain it in the range of 4 mol%. When the content of the stabilizing component is less than 1.4 mol, the content ratio of the monoclinic phase is increased, and as a result, the content ratio of the tetragonal phase is relatively reduced, and a sufficient stress relaxation effect is obtained. Gone
Insufficient abrasion resistance or the like may be caused. On the other hand, when the content of the stabilizing component exceeds 4 mol%, the content ratio of the cubic phase increases, and similarly, the wear resistance may be insufficient. The content of the stabilizing component is more desirably 1.5 to 4 mol%, and further desirably 2 to 4 mol%.

As a stabilizing component of the tetragonal phase, specifically, Y ₂ O ₃ has higher strength of the obtained ceramic material as compared with the case where other stabilizing components are used. Since they are relatively inexpensive, they are suitably used in the present invention. On the other hand, CaO and MgO are not as strong as those using Y ₂ O ₃ , but the strength of the obtained ceramic material is relatively high and it is even cheaper than Y ₂ O _3. It is preferably used. Note that Y
₂ O ₃ , CaO and MgO may be used alone or in combination of two or more.

The main component of the zirconia-based ceramic phase
(Not limited to this, the term “principal component” in this specification refers to the most important component.
ZrO which means a component having a high content ratio)₂as well as
HfO₂Are similar in chemical and physical properties,
Use either alone or in combination of both
Anything is possible. However, ZrO ₂
Is HfO₂Zirconia because it is cheaper than
The ceramic phase is ZrO₂Can be composed mainly of
It is more desirable. In addition, usually supplied
Pure ZrO₂The raw material is a trace amount of HfO₂Is contained
However, when using such raw materials,
HfO contained for the reasons described above₂Actively
Very little need to be removed.

The zirconia ceramic phase preferably has a ratio CW / TW of the existing weight CW of the cubic phase to the existing weight TW of the tetragonal phase of less than 1. The cubic phase is easily formed when the content of the above-mentioned stabilizing component increases and the transformation point between the phase and the tetragonal phase decreases, or when the firing temperature exceeds 1600 ° C. Compared with a crystalline phase or a tetragonal phase, it has a property that crystal grains are likely to become coarse during firing. Then, the crystal grains of the cubic phase that are coarsened have a small interfacial bonding force with other crystal grains, so that they are easy to fall off, and when the amount of the cubic phase increases until the above ratio exceeds 1, The formation amount of such coarse crystal grains also increases. In any case, the chipping resistance of the ceramic is impaired. Therefore, the ratio CW
/ TW is preferably less than 1, preferably less than 0.5, and more preferably less than 0.1.

The information on the abundance ratio between the tetragonal phase and the cubic phase can be obtained as follows. For example, a part of a ceramic material is mirror-polished, and X-ray diffraction is performed on the polished surface by a diffractometer method.
In this case, the obtained diffraction pattern is the main diffraction peak of the tetragonal phase and the cubic phase (111).
Since the intensity peak positions appear close to each other, first, the total intensity I of (111) and (11-1) of the monoclinic phase
The abundance of the monoclinic phase is determined from the ratio of m and the sum of the (111) strengths of the tetragonal phase and the cubic phase Im + Ic. Next, the sintered body was mechanically pulverized and subjected to X-ray diffraction again to obtain the (1 1 1) intensity I ′ of the monoclinic phase and the cubic phase.
Find m and I'c. In this case, it is considered that the tetragonal phase of the sintered body is transformed into a monoclinic phase due to the mechanical stress accompanying the above-mentioned pulverization, so that I′c / (I ′m + I′c) is converted to a cubic phase. Abundance can be determined. The value of I'c / (I'm + I'c) thus obtained is preferably 0.5 or less, more preferably 0.1 or less, in order to improve the wear resistance of the member.

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.

Further, each of the above ceramics was used as a substrate, and the metal cation component was 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.

[0047]

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. 2A and the outer peripheral surface M1 of the main shaft 14 form a radial dynamic pressure gap forming surface, and the space between them is filled with air to generate a radial dynamic pressure with respect to the rotation axis О. A radial dynamic pressure gap 17 is formed.
The size of the radial dynamic pressure gap 17 is, for example, about 5 μm. In addition, from the viewpoint of the formation of the radial dynamic pressure gap 17, the main shaft 14 is a first member, and the bearing portion 15 is 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.

In this embodiment, the main shaft 14, the bearing portion 15, and the thrust plates 21 and 23 are entirely made of alumina ceramic, and the dynamic pressure gap forming surfaces M1 to M
6, a large number of surface holes K are formed as shown in FIG. The surface pores K have an average size of 2 to 20.
μm. As already described, by setting the average size of the surface pores existing in the dynamic pressure gap forming surface to 2 to 20 μm, it is possible to effectively prevent the generation of vibration during the rotation operation of the ceramic dynamic pressure bearing 3, In addition, when the rotation is started or stopped, adhesion wear is less likely to occur on the dynamic pressure gap forming surface. In addition, 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. In the thrust dynamic pressure generating gap 18, the thrust plates 21 and
It is also effective in preventing the occurrence of linking between the bearing 3 and the bearing 15. Then, the formation area ratio of the surface pores in such a size range on the dynamic pressure gap formation surface is set to 10 to 60.
%, Desirably 15 to 40%, it is possible to make the above-mentioned cohesive wear or linking less likely to occur and to increase the fluid dynamic pressure level generated in the dynamic pressure gap.

In order to achieve the above-mentioned effects, it is sufficient that at least one of the dynamic pressure gap forming surfaces M1 to M6 has the size and the area ratio of the surface voids K adjusted within the above-mentioned ranges. (For example, the radial dynamic pressure gap forming surfaces M1, M
2, the thrust dynamic pressure gap generating surfaces M3, M4
Or only one of M5 and M6), in order to further enhance the effect, as many dynamic pressure gap forming surfaces as possible, ideally all dynamic pressure gap forming surfaces M1 to M1
In M6, it is desirable that the size and the area ratio of the surface pores K be adjusted to the above ranges.

The radial dynamic pressure gap forming surfaces M1, M2
In order to increase the generated dynamic pressure level, a well-known dynamic pressure groove as shown in FIG. 2A can be formed in at least one of them (for example, M1 on the main shaft 14 side). In addition, 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) is also provided in FIG.
A well-known dynamic pressure groove as shown in (b) can be formed.

On the other hand, as shown in FIG. 11, the radial dynamic pressure gap forming surfaces M1 and M2 and the thrust dynamic pressure gap forming surface M
At least one of 3, M4, M5, and M6 is provided with a hard carbon-based coating DR mainly made of amorphous carbon. In the present embodiment, as shown in FIG. 11, if the floating force due to dynamic pressure is lost, contact with gravity cannot be avoided, and the lower thrust dynamic pressure gap forming surfaces M5, M6 and the shaft shake or fall at low speed rotation The hard carbon-based coating D is formed on the radial dynamic pressure gap forming surfaces M1 and M2 where contact is likely to occur due to
R is formed. As shown in FIG. 12, the average thickness of the hard carbon-based coating DR is set smaller than the average size of the holes K as described above. Specifically, the average film thickness is about 0.1 to 1.5 μm.

It is also possible to form one or more intermediate layers between the hard carbon-based coating DR and the base ceramic layer CR to enhance the adhesion of the hard carbon-based coating DR. Specifically, the lower layer mainly composed of chromium (or titanium) (the contact side with the base ceramic layer CR)
And an upper layer mainly composed of silicon (or germanium) (on the side in contact with the hard carbon-based coating DR). When such an intermediate layer is formed, it is desirable that the total average film thickness of the hard carbon-based coating and the intermediate layer is smaller than the average size of the holes in order to prevent excessive closing of the holes. . On the other hand, the average thickness of the hard carbon-based coating itself is preferably set to 0.1 to 1.5 μm in consideration of, for example, a sufficient abrasion resistance and cost balance.

Hereinafter, a method of 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. In other words, MgO, CaO, C
An oxide powder such as eO ₂ , SiO ₂ , Na ₂ O or the like is blended to obtain a molding base powder, which is press-molded into a corresponding shape by a known molding method such as die molding or cold isostatic pressing. By sintering the molded body at a temperature of 1400 to 1700 ° C., a dense sintered body having a relative density of 90 to 99.5% is obtained. 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.

Here, as shown in FIG. 5C, the surface of the dynamic pressure gap generating surface which is finished by the grinder polishing or the lap polishing with the abrasive grains is caused by the dropping of the ceramic crystal particles generated during the polishing. As shown in (1), surface vacancies are formed in the form of bleeding holes. 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 abrasive grains, and further, the polishing. By adjusting the polishing conditions such as time, it is adjusted so as to be in the above-mentioned range. In addition, the composition and distribution of the grain boundary phase derived from the sintering aid may affect the ease of shedding of the ceramic crystal grains during polishing. It is necessary to make appropriate adjustments so that the state of formation of surface vacancies can be obtained.

The ceramic member whose dynamic pressure gap forming surface has been finished as described above has a structure in which pores are formed on the surface of the dense sintered body by dropping 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 formed here by sandblasting, etching or the like.

Then, a hard carbon-based coating is formed on each dynamic pressure gap forming surface. Specifically, this formation can be performed, for example, by the method described in Japanese Patent Publication No. 6-60404. First, after the surfaces of the ceramic members forming the thrust plates 21 and 23, the main shaft 14 and the bearing portion 15 are degreased and washed, if necessary, the above-described lower or upper intermediate layer is formed by a known vacuum deposition method or ion plating. Law,
They are sequentially formed by a sputtering method or the like (however, they may be omitted). Next, this is set on the cathode side in a vacuum chamber of the plasma polymerization film forming apparatus. Then, the inside of the vacuum chamber is evacuated and a hydrocarbon gas (for example, methane, ethylene, benzene, or the like; hydrogen may be mixed; methane is used in this embodiment) is introduced from a gas inlet. The pressure is, for example, 0.1 to
Adjust to about rr. Then, a high frequency voltage of, for example, about 3.56 MHz is applied between the cathode and the anode in the vacuum chamber to generate plasma. This allows
Hydrocarbons are decomposed and deposited on the dynamic pressure gap forming surface in the form of amorphous carbon while taking in hydrogen, forming a hard carbon-based coating.

Here, as shown in FIG. 13, in order to deposit the hard carbon-based coating DR so as not to block the surface vacancies K contributing to the generation of dynamic pressure, the flow of the material vapor to be deposited is as follows.
It is more effective to grow the film in such a manner as to be obliquely incident on the member surface.

As described above, the main shaft 14, the bearing portion 15, or the thrust plate 2 on which the hard carbon-based coating DR is formed.
As shown in FIG. 3, if the base materials 1 and 23 are obtained, a support (here, formed into a disk shape having a hole 7 a for fitting the bearing 15) 7 by bonding or the like, a permanent magnet 9, By assembling the coil 13 and assembling the main shaft 14, the bearing portion 15, and the thrust plates 21 and 23 using the bolts 25, a motor with a dynamic pressure bearing is obtained. When the polygon mirror 8 is attached to the support 7, 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. In the present embodiment, all the dynamic pressure gap forming surfaces M1 to M6
In, since the average size and area ratio of the surface pores are adjusted in the above range, vibration during rotation is small,
Ceramic members such as the bearing portion 15 and the thrust plates 21 and 23 are hardly damaged. Further, the occurrence of linking and adhesive wear at the time of starting and stopping can be suppressed. Therefore, also from this point, the ceramic members such as the bearing portion 15 and the thrust plates 21 and 23 are hardly damaged.

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. The hard carbon-based coating described above is formed on the radial dynamic pressure gap forming surfaces M2 and M1.

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.

It should be noted that at least one of the main shaft 39 and the bearing portion 35 may be made of a material other than ceramic, for example, a metal. FIG. 8 shows an example in which the main shaft 39 is formed of stainless steel, and the bearing 35 is similarly formed of ceramic. On the other hand, the main shaft 39 may be made of ceramic and the bearing 35 may be made of metal.

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. The core shaft 102 is fixed through a ceramic main shaft 105. Further, the ceramic bearing portion 107 has a radial dynamic pressure gap between a radial dynamic pressure gap forming surface 106 forming the cylindrical outer peripheral surface of the main shaft 105 and a radial dynamic pressure gap forming surface 108 forming the inner peripheral surface of the bearing portion 107. It has a gap 91 (1 to 7 μm) and is provided rotatably. Further, the upper thrust plate 109 made of ceramic is fixedly penetrated by the core shaft 102. Further, thrust dynamic pressure gap forming surfaces 110 and 111 formed on the lower and upper portions of the bearing portion 107, and the lower thrust plate 1
Thrust dynamic pressure gaps 92 are formed between the thrust dynamic pressure gap forming surface 112 and the thrust dynamic pressure gap forming surface 113 of the upper thrust plate 109, respectively. 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. The hard carbon-based coating described above is formed on the thrust dynamic pressure gap forming surfaces 110 and 112 and the radial dynamic pressure gap forming surfaces 106 and 108.

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

As a configuration of the three-phase brushless motor 133, a coil 129 is provided on the base 100 via an insulating member 123, and a coil 129 is provided below the support portion 114 of the bearing portion 107 in the rotational direction. An opposed permanent magnet 125 is provided. By energizing the winding 129,
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 causes the radial dynamic pressure gap 91 to rotate.
The dynamic pressure is generated at this point, enabling 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.

FIG. 10 shows an example in which the ceramic dynamic pressure bearing of the present invention is applied to a hard disk drive. In the hard disk device 200, magnetic disks 209a and 209b are fixed to the outer periphery of a hub 211, and a motor rotation shaft 212 is fixed at the center. The hub 211 rotates together with the disks 209a and 209b fixed thereto. The motor rotating shaft 212 is radially supported by a fixed bearing portion 221 made of alumina ceramic, and a thrust plate 22 made of alumina ceramic is provided.
2 is supported in the thrust direction.

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 213 of the motor rotating shaft 212 and the inner peripheral surface 217 of the fixed bearing portion 221 forming the radial dynamic pressure gap forming surface are configured similarly to the ceramic dynamic pressure bearings 3 to 33 in FIGS. The hard carbon-based coating described above is formed (that is, having the configuration of the ceramic dynamic pressure bearing of the present invention). Note that the motor rotation shaft 212
The shaft end 212a has a spherical pivot shape, and a thrust plate 222 supports a force in a thrust direction.

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 multi-pole magnetized driving permanent magnet 214 surrounding the stator core 224. The permanent magnet 214 is fixed to the inner periphery of the hub 211, and forms the rotor 210 together with the hub 211. In the hard disk drive 200, the outer bearing portion 221 is fixed and the inner main shaft (rotating shaft) 212 is rotated. However, with reference to FIG. By replacement, a hard disk drive configuration in which the bearing portion 15 rotates and the main shaft 14 side is fixed is naturally possible.

It is needless to say that the present invention is not limited to the above-described embodiments, and can be implemented in various modes without departing from the gist of the present invention. For example, the material of each ceramic member is not limited to alumina ceramics, and other types of ceramics described above, such as silicon nitride ceramics and zirconia ceramics, may be used. As the fluid for generating dynamic pressure, a gas other than air may be used, or a liquid such as oil or water may be used instead of the gas.

[0075]

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, an alumina powder (purity: 99.9) having an average particle size measured by a laser diffraction type particle sizer having various values shown in Table 1.
%), SiO ₂ powder, CaO powder and MgO powder,
A sintering aid powder blended at a weight ratio of 3: 1: 1 was prepared. 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 various member shapes by a die pressing method, and then fired at various temperatures shown in Table 1 for various times. In the obtained sintered body, the inner peripheral surface and both end surfaces of the bearing portion 15, which are the surfaces for forming the dynamic pressure gap, the outer peripheral surface of the main shaft 14, and the surfaces of the thrust plates 21 and 23 opposed to the bearing portion 15 are each # After grinding with a diamond grindstone of 100 to # 200, the count is # 6000.
The surface is finished by lap polishing with diamond abrasive grains, and the area other than that planned for the groove pattern is masked and shot blasted,
The dynamic pressure groove shown in FIG. 2 was formed.

Further, in FIG. 4, the dynamic pressure gap forming surface M
The lower layer made of chromium is formed on the inner peripheral surface and lower end surface of the bearing portion 15, M2, M5, and M6, the outer peripheral surface of the main shaft 14, and the surface of the thrust plate 23 facing the bearing portion 15 by a known high-frequency sputtering method. And an upper layer made of silicon were each formed with an average film thickness of 0.2 μm. Further, the hard carbon-based coating was formed with an average film thickness of 0.5 μm by the above-mentioned plasma polymerization method. However, methane was used as the raw material gas, the gas flow rate was 30 cm ³ / min, and the pressure was 0.1 torr.
r, high frequency power 100 W. The Vickers hardness of the hard carbon-based coating was about 3500 kg / mm ² .

Then, on each of the dynamic pressure gap forming surfaces, the polished surface area where the dynamic pressure grooves were not formed was observed with an optical microscope, and the observed image was subjected to image analysis using a known method to obtain alumina crystal particles. And the area ratio of alumina crystal particles having a size of 2 to 5 μm were determined. Further, with respect to surface vacancies, the average size and
The maximum size and the area ratio of pores having a size of 2 to 20 μm were determined. The 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, the above members were assembled into a motor with a dynamic pressure bearing shown in FIG. 3 and the following tests were performed. 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
Excellent when the amount of run-out is less than 0.1 μm (）), also 0.1
good (○), 0.2 μm
Those having a size of less than 0.3 μm were evaluated as acceptable (△), and those exceeding 0.3 μm were evaluated as unacceptable (×).

From the stop 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). Regarding the linking, the rotational torque was estimated from the current value of the motor, and the motor that did not have any abnormal torque at the start, which is considered to be based on the linking until the end of the cycle, was evaluated as excellent (◎). Good (○), in which a torque increase in the range of less than 10%, which is considered to be caused by linking, was observed based on the average starting torque level, and the torque was increased in the range of 10% or more and less than 50%. However, those which did not fail to rotate were evaluated as acceptable (可), and those which frequently failed to start due to a torque increase of 50% or more were evaluated as impossible (x). The above results are shown in Tables 1 and 2.

[0081]

[Table 1]

[0082]

[Table 2]

As is clear from these results, by adjusting the average size of the surface pores on the surface on which the dynamic pressure gap is formed to 2 to 20 μm, a dynamic pressure bearing with less rotational runout and less occurrence of linking and seizure can be obtained. You can see that it has been achieved. Further, it can be seen that the effect is further enhanced by adjusting the void area ratio in the dimension range of 2 to 20 μm to 10 to 60%, preferably 20 to 40%.

[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 cross-sectional view showing an example of a mode of forming a hard carbon-based coating on a surface on which a dynamic pressure gap is formed.

FIG. 12 is an explanatory view showing the concept of the state of formation of a hard carbon-based coating on a surface on which a dynamic pressure gap is formed in which surface pores are formed.

FIG. 13 is an explanatory diagram showing the concept of the state of formation of a hard carbon-based film formed by causing a flow of a material vapor to be deposited to be obliquely incident on a member surface.

[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 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 K Surface void DR Hard carbon-based coating

──────────────────────────────────────────────────の Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI theme coat ゛ (reference) // H02K 21/14 H02K 21/14 MF term (reference) 3J011 AA20 BA06 CA02 CA05 DA01 DA02 JA02 KA02 KA03 LA01 MA02 QA04 SD01 SD03 SD04 SE02 5H605 BB05 BB20 CC03 CC04 CC05 EB06 FF10 GG10 GG21 5H607 BB01 BB07 BB09 BB13 DD03 DD17 GG12 KK10 5H621 AA03 BB07 JK19

Claims (11)

[Claims] 1. A dynamic pressure gap is formed between a first member and a second member that relatively rotate around a predetermined rotation axis, and the dynamic pressure gap is formed with the relative rotation of the first member and the second member. A portion configured to generate a fluid dynamic pressure in the gap, and a portion including a surface facing the dynamic pressure gap (hereinafter, referred to as a dynamic pressure gap forming surface) in at least one of the first member and the second member. Is made of at least ceramic, and the average size of surface pores existing in the dynamic pressure gap forming surface made of the ceramic is 2 to 20 μm, and at least one of the first member and the second member Wherein said dynamic pressure gap forming surface is covered with a hard carbon-based coating mainly composed of amorphous carbon having an average film thickness smaller than the average size of said surface pores. 2. The first member is disposed so as to face at least one end face of the second member in the direction of the rotation axis. A thrust dynamic pressure gap is formed between the opposing surfaces and the thrust dynamic pressure gap forming surface, and the thrust dynamic pressure gap forming surface is covered with the hard carbon-based coating. The ceramic dynamic pressure bearing according to claim 1. 3. The first member is formed in a shaft shape, the first member is inserted into an insertion hole formed in the second member, and the inner surface of the insertion hole of the second member is inserted into the insertion hole. The radial dynamic pressure gap forming surface is formed between the radial dynamic pressure gap forming surface and the outer peripheral surface of the first member to be formed, and the radial dynamic pressure gap forming surface is formed of the hard carbon-based material. The ceramic dynamic pressure bearing according to claim 1, which is covered with a coating. 4. The ceramic dynamic pressure bearing according to claim 1, wherein the ceramic dynamic pressure bearing is used as a bearing for a rotating main shaft portion of a hard disk of a hard disk device. 5. The ceramic dynamic pressure bearing according to claim 1, wherein the ceramic dynamic pressure bearing is used as a bearing for a rotary spindle of a polygon mirror of a polygon scanner. 6. A motor with a bearing, wherein the ceramic dynamic pressure bearing according to any one of claims 1 to 5 is used as a bearing of a motor rotation output section. 7. The motor with a bearing according to claim 6, which is used for a hard disk rotation drive section of a hard disk device. 8. The motor with a bearing according to claim 6, which is used for a polygon mirror driving section of a polygon scanner. 9. The motor with a bearing according to claim 6, which is a motor for high-speed rotation having a maximum rotation speed of 8000 rpm or more. 10. A hard disk drive comprising the motor with a bearing according to claim 7 and a hard disk rotationally driven by the motor with a bearing. 11. A polygon scanner comprising the motor with a bearing according to claim 8 and a polygon mirror rotated by the motor with a bearing.