JP2000213533A - Dynamic pressure bearing device and motor using it - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve wear resistance with simple, low-cost constitution by forming a lubricating film containing amorphous carbon, in specified thickness on the dynamic pressure bearing surface of a shaft member and a bearing member. SOLUTION: Base material of a rotor 3 is formed of metallic material such as aluminum or its alloy, and a lubricating film formed of amorphous carbon is formed in thickness of 2 μm or more on the dynamic pressure bearing surface of the outer peripheral surface of the base material. Substrate treatment of silicon oxide is applied to the surface of the base material to heighten adhesion of the lubricating film. Amorphous carbon contains amorphous diamond-like carbon. The lubricating film is provided with an extremely smooth surface of close amorphous structure without a grain boundary, but surface-finishing is further applied thereto. A bearing member 2 is provided with the same metallic base material, and the same lubricating film as the rotor 3 is formed on the inner peripheral surface through a substrate treated film. With this constitution, excellent wear resistance can be obtained at a low cost to permit long-term use for a device harsh in environment of dust or the like.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a dynamic pressure bearing device for supporting a shaft member and a bearing member rotatably relative to each other by dynamic pressure of air, and a motor using the same.

[0002]

2. Description of the Related Art Various proposals have conventionally been made for an air dynamic pressure bearing device using air as a lubricating fluid for bearings to generate dust due to wear and improve wear resistance. For example, in Japanese Patent Application Laid-Open Nos. Hei 3-356622 and Japanese Patent Application No. Hei 8-110072, a shaft base made of aluminum is coated with SiC composite plating or Ni-P.
A shaft member subjected to electroless plating and a bearing member obtained by applying a lubricating alumite treatment or a highly lubricating fluororesin coating to a bearing base material also made of aluminum. Further, as disclosed in Japanese Patent Application Laid-Open No. 5-288214, there is a type in which a ceramic material such as silicon carbide is used for both a shaft member and a bearing member.

[0003]

However, even in the pneumatic pressure bearing device thus proposed, a small amount of abrasion powder may be generated at the time of starting and stopping, and the hard disk drive in a severe use environment may be generated. When used in a device or a polygon mirror driving device, it may not be possible to adopt it because a sufficient degree of cleanliness cannot be obtained. In addition, especially in a case where a ceramic material is used, there is a problem in that the cost of the material is high and the entire apparatus is also expensive.

Accordingly, an object of the present invention is to provide a dynamic pressure bearing device and a motor using the same that can improve the wear resistance of the shaft member and the bearing member with a simple and inexpensive configuration. And

[0005]

According to the first aspect of the present invention, a dynamic pressure bearing surface formed on a shaft member and a dynamic pressure bearing surface formed on a bearing member are circumferentially opposed to each other. In addition, air is interposed between the two dynamic pressure bearing surfaces as air as a bearing fluid, and the dynamic pressure obtained by pressurizing the air by the dynamic pressure generating means provided on at least one side of the two dynamic pressure bearing surfaces is used. In a hydrodynamic bearing device that rotatably supports a shaft member and a bearing member, each of the dynamic pressure bearing surfaces of the shaft member and the bearing member has an amorphous structure with respect to the base material of the shaft member and the bearing member. 2 lubricating films containing carbon
The film is formed to a thickness of at least μm.

According to the second aspect of the present invention, the dynamic pressure bearing surface formed on the shaft member and the dynamic pressure bearing surface formed on the bearing member are circumferentially opposed to each other, and between the two dynamic pressure bearing surfaces. Air is interposed as a bearing fluid, and the shaft member and the bearing member are relatively rotated by a dynamic pressure obtained by pressurizing the air by dynamic pressure generating means provided on at least one of the two dynamic pressure bearing surfaces. A motor for rotatably driving a stator portion provided on one of the shaft member and the bearing member and a rotor portion provided on the other side, wherein On each dynamic pressure bearing surface of the bearing member, a lubricating film containing amorphous carbon is formed to a thickness of 2 μm or more with respect to the shaft member and the base material of the bearing member.

Further, in the invention according to claim 3, the amorphous carbon according to claim 1 or 2 is DLC
(Diamond-like carbon) and its DLC
The surface roughness of the lubricating film made of Ra: 0.7 μm or less;
Rmax: 1.1 μm or less, Rz: 0.8 μm or less.

Further, in the invention according to claim 4, each of the base members of the shaft member and the bearing member according to claim 1 or 2 is made of aluminum or an alloy thereof, and the base material and the amorphous carbon are used. A base treatment film made of silicon oxide is provided between the substrate and the lubricating film.

According to a fifth aspect of the present invention, the motor according to the second aspect is used in a hard disk drive or a polygon mirror drive.

According to the first or second aspect of the present invention having the above-described structure, the shaft member of the hydrodynamic bearing device and the opposing surface portions of the hydrodynamic bearing surfaces of the bearing member are formed by a lubricating film made of amorphous carbon. By forming a lubricating film made of amorphous carbon over a thickness of 2 μm or more with good wear resistance, the initial dynamic pressure characteristics can be maintained for a long time.

In particular, by setting the surface roughness of the amorphous carbon lubricating film as in the third aspect of the present invention, the above-described wear resistance is further improved.

At this time, according to the invention described in claim 4,
The durability of the amorphous carbon lubricating film is improved by the base treatment.

Such an effect is particularly remarkably obtained in a hard disk drive or a polygon mirror drive having a severe use environment as described in claim 5.

[0014]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiments of the present invention will be described below. Prior to that, the structure of a shaft-rotating polygon mirror driving motor having an air dynamic pressure bearing to which the present invention is applied will be described with reference to the drawings. It is explained based on.

The motor for driving the polygon mirror shown in FIG. 1 constitutes a laser scanner in a digital copy, a laser printer or the like.
In order to rotate at a high speed of about 0000 RPM, an air dynamic pressure bearing or the like which can support rotation in a non-contact manner is used as a bearing.

That is, in FIG. 1, a rotor (rotating member) as a shaft member is provided in a hollow cylindrical bearing member (fixing member) 2 fixedly screwed to a base 1 with a gap of several μm to several tens μm. 3) is inserted, and an air dynamic pressure generating portion 4 composed of a dynamic pressure bearing surface on the outer peripheral surface side of the rotor 3 and a dynamic pressure bearing surface on the inner peripheral surface side of the bearing member 2
The rotor 3 is supported so that it can rotate at high speed. A large number of radial herringbone grooves 6 as a dynamic pressure generating means are annularly arranged on the dynamic pressure bearing surface 5 on the rotor 3 side. These radial herringbone grooves 6 are composed of inclined grooves formed symmetrically in the axial direction, and are configured so as to form a maximum pressurizing portion substantially at the center of the air dynamic pressure generating portion 4 in the axial direction. I have.

A drive coil 7 constituting a stator portion is provided on the outer periphery of the central columnar portion 1a erected on the base 1.
The annular magnet 8 for forming a driving magnetic circuit in the rotor unit is disposed so as to face the driving coil 7 in a circumferential direction. The annular magnet 8 is disposed inside the rotor 3 via an iron yoke 9 and constitutes a motor driving unit together with the driving coil 7 constituting the stator unit.

Further, an annular convex portion 11 is protruded from a tip portion (an upper end portion in the figure) of the rotor 3, and a polygon mirror 12 is fitted to the annular convex portion 11. A balance plate 14 is coaxially mounted on the polygon mirror 12 via a wave spring 13, and a fixing screw 15 inserted from the balance plate 14 is screwed to the annular convex portion 11 of the rotor 3. As a result, the polygon mirror 12 is fixed.

Further, a pair of annular magnets 16 and 17 are attached to the upper outer periphery of the central columnar portion 1a of the base 1 and the inner periphery of the balance plate 14 so as to oppose each other. These annular magnets 16 and 17 are magnetized with their polarities reversed in the axial direction, thereby forming a magnetic thrust bearing.

At this time, the base material of the rotor (shaft member) 3 is formed of a metal material such as aluminum or an aluminum alloy, and the outer circumferential surface of the base material, that is, the outer circumferential surface corresponding to the above-described hydrodynamic bearing surface. The surface has a lubricating film made of amorphous carbon over a thickness of 2 μm or more. At this time, the surface of the base material of the rotor 3 is subjected to a base treatment with silicon oxide (SiO ₂ ), and the adhesion of the lubricating film made of the amorphous carbon is reduced by interposing the base treatment layer. Has been enhanced.

The amorphous carbon in the present embodiment includes non-crystalline DLC (diamond-like carbon). The lubricating film made of the DLC-containing amorphous carbon has a dense amorphous structure, has no crystal grain boundaries, and has a very smooth and smooth surface. In particular, in this embodiment, the lubricating film is further surface-finished. The surface roughness of the lubricating film made of the DLC-containing amorphous carbon was determined by measuring the center line average roughness Ra to 0.7 μm.
m, the maximum roughness Rmax is 1.1 μm or less, and the average roughness Rz is 0.8 μm or less.

However, in the above-mentioned radial herringbone groove 6 as the dynamic pressure generating means, the surface roughness is not subjected to the above-mentioned surface roughness, and the rough state as it is formed by vapor deposition as will be described later. Has been made. The rough surface of the radial herringbone groove 6 has an effect that air as a bearing fluid is favorably pressurized.

On the other hand, the bearing member 2 also has a base material also made of a metal such as aluminum or aluminum alloy, and has the above-described rotor on its inner peripheral surface corresponding to the dynamic pressure bearing surface of the base material. A lubricating film made of DLC-containing amorphous carbon similar to that of No. 3 is formed over a thickness of 2 μm or more via a similar undercoating film.

Such a lubricating film made of DLC-containing amorphous carbon is formed, for example, by using a plasma deposition apparatus (CVD) as shown in FIG.
That is, in this plasma deposition apparatus (CVD) apparatus, as shown in FIG. 2, a cup-shaped reflector 21 having one end opened in a high vacuum is arranged, and the inside of the reflector 21 is disposed. A filament 23 connected to a filament power supply 22 is disposed on the closed side, and an anode 25 connected to an anode power supply 24 is disposed on the open side of the reflector 21 close to the filament 23. . Further, a work 26 is arranged so as to face the open end of the reflector 21 at a predetermined distance, and a reflector power supply 27 and a bias power supply 28 are provided between the work 26 and the reflector 21. , A predetermined voltage is applied.

A hydrocarbon gas such as ethylene gas is supplied into the reflector 21, and the hydrocarbon gas is decomposed by arc discharge plasma under heating at 200 ° C. to 500 ° C. in the reflector 21. The generated ions and excited molecules in the plasma collide with the surface of the work 26 with a predetermined electric acceleration energy, and as a result, an amorphous carbon film is formed.

The lubricating film formed of DLC-containing amorphous carbon, which is formed as described above, is formed over a thickness of 2 μm or more as described above. A description will be given of a wear resistance test which is the basis of the lubricating film.

First, a wear resistance test apparatus 31 as shown in FIG. 3 is used for the wear resistance test. In this wear resistance test apparatus 31, a cylindrical sample 32 having a diameter of about 15 mm in which the above-mentioned amorphous carbon lubricating film containing DLC is deposited over a predetermined thickness, and a similar amorphous carbon lubricating film containing DLC having a predetermined thickness are formed. The plate-shaped sample 33 deposited over the entire surface is placed in a pressure-contact state with each other. That is, the plate-shaped sample 33 is fixed to the distal end portion of a leaf spring 35 extending substantially horizontally from the fulcrum 34, and the lever 3 is moved substantially horizontally from the opposite side of the fulcrum 34.
6 is extended, and the weight of the weight 38 is applied to the tip of the lever 36 via a fixed pulley 37.

In the wear resistance test, the load on the plate-shaped sample 33 by the weight 38 was set to 40 g, and the cylindrical sample 32 was driven to rotate at a speed of 7000 rpm for 10 minutes. Was actually measured with a surface roughness meter. As a result, as shown in (j) of FIG.
The wear depth (vertical axis) was 1 μm on average.

Next, using a similar abrasion resistance test apparatus 31, a plate-like sample 33 was subjected to a compound of aluminum and titanium (Al _x T).
i _y O _z ), and (a) alumite, (b) Ni plating, (c) acrylic melamine coating, (d) fluorine-based polyamideimide (PAI) coating (conventional product) ), (e) a fluorine resin coated (L6201CL), (f) a compound of aluminum and titanium _{(Al x Ti y O z)} , (g) potassium titanate (ceramic), (h) alumina, (i) tool steel, Were applied in the form of a film or a layer, respectively, and a similar test was performed.

Further, using a similar abrasion resistance tester 31, a plate-like sample 33 is coated with a fluorine-based polyamideimide (PAI) coating similar to that of a conventional product, and a cylindrical sample 32 as a mating member is formed as ( A similar test was performed by depositing k) anodized aluminum and (m) Ni plating, respectively.

The test results are shown in correspondence with the same reference numerals in FIG. 4. In each of the above-mentioned cases (a) to (f) and (k) and (m), According to the invention (j)
, The wear depth (vertical axis) became very large. In addition, the results based on the ceramic materials are shown in (g) to (g).
In the case of (i), the wear depth was almost the same as that of (j) according to the present invention. That is, as in the present embodiment, with respect to each of the dynamic pressure bearing surfaces of the rotor (shaft member) 3 and the bearing member 2,
By forming a lubricating film composed of DLC-containing amorphous carbon, it has been found that the wear depth is significantly reduced as compared with the conventional product, and that the wear resistance is substantially the same as that of ceramic materials such as alumina. Turned out to be.

Next, in the above-described abrasion resistance test apparatus 31, the surfaces of the cylindrical sample 32 and the plate-like sample 33 on which the amorphous carbon lubricating film containing DLC was deposited were polished with paper abrasive paper (# 1000) as follows. The test was performed by polishing as follows.

First, the surface roughness of each sample before polishing was Ra (μm) Rmax (μm) Rz (μm) 0.08 1.86 0.81 Sample 2. 0.11 1.57 1.38 Sample 3. Although it was 0.22 2.89 1.84, Ra (μm) Rmax (μm) Rz (μm) Sample 1. 0.06 0.75 0.52 Sample 2. 0.07 1.04 0.77 Sample 3. 0.06 0.67 0.47 Sample 4. 0.22 2.89 1.84.

When performing the test using the abrasion resistance test apparatus 31 described above, the load on the plate-like sample 32 by the weight 37 is started from 40 g, and is increased in increments of 10 g to 100 g.
It was driven to rotate at a speed of rpm for 5 minutes, and the depth of the wear mark at that time was actually measured by a surface roughness meter. In the wear resistance test under such conditions, the overload condition is set to be much severer than the actual use condition, and the result obtained under this condition is that in the normal use condition in the actual machine. It is empirically known to show almost the same state as the result.

FIG. 5 shows the average values of the test results for the samples 1, 2, and 3 finished to each of the surface roughnesses described above. As is clear from the figure, the wear depth (vertical axis) is the lowest 0.2 when the load is 80 g to 100 g.
Judging from the fact that the thickness is 3 μm, the amorphous carbon lubricating film containing DLC has abrasion resistance equal to or higher than that of the ceramic material, and a thickness of about 2 μm is sufficient. It has been found.

Further, when the dynamic pressure bearing device according to the present embodiment was mounted on an actual motor and subjected to a test of repeating start / stop of rotation, the initial dynamic pressure characteristics were maintained for a long time, and the wear was reduced. The amount was very small and good use was confirmed.

Further, in the present embodiment, since the surface roughness of the dynamic pressure generating groove 6 is set to be large, the pressurizing function is enhanced, so that better dynamic pressure characteristics can be obtained. .

Furthermore, in the present embodiment, the durability of the device is improved because the adhesion of the amorphous carbon lubricating film is enhanced by the underlying treatment layer.

Although the embodiments of the present invention made by the inventor have been specifically described above, the present invention is not limited to the above-described embodiments, and can be variously modified without departing from the gist thereof. Needless to say.

For example, in the above embodiment, DLC is used as the amorphous carbon. However, other materials may be contained in DLC, or other amorphous carbon may be used.

Further, the present invention is not limited to the polygon mirror driving motor according to the above-described embodiment. Similarly, the present invention is not limited to a motor for a hard disk drive (HDD) which requires a high degree of cleanliness. The present invention can be similarly applied to the rotary drive device.

[0042]

As described above, according to the first or second aspect of the present invention, the lubricating film made of amorphous carbon is formed on the shaft member of the hydrodynamic bearing device and the bearing surface of each bearing member to a thickness of 2 μm or more. It is possible to obtain extremely excellent wear resistance at low cost, and it can be favorably used for a long period of time even in various devices where the use environment related to generation of dust and the like is severe. .

In particular, by setting the surface roughness of the amorphous carbon lubricating film as in the third aspect of the present invention, the above-described effects can be more reliably obtained.

In this case, since the invention according to claim 4 has been subjected to a base treatment for improving the adhesion of the amorphous carbon lubricating film, in addition to the above-mentioned effects, it also enhances the reliability particularly during long-term use. be able to.

According to the present invention, a particularly good effect can be obtained particularly in a hard disk drive or a polygon mirror drive having a severe use environment.

[Brief description of the drawings]

FIG. 1 is an outer cross-sectional explanatory view showing a structural example of a polygon mirror driving motor as an example of an apparatus to which the present invention is applied.

FIG. 2 is an explanatory view showing in principle the structure of a plasma deposition apparatus (CVD) as an example of an apparatus for forming an amorphous carbon film according to the present invention.

FIG. 3 is a structural explanatory view showing an example of a wear resistance tester.

FIG. 4 is a diagram showing an example of a test result obtained by the wear resistance test apparatus shown in FIG.

FIG. 5 is a diagram showing another example of test results obtained by the wear resistance test apparatus shown in FIG.

[Explanation of symbols]

 Reference Signs List 2 bearing member 3 shaft member (rotor) 4 air dynamic pressure generating section 6 dynamic pressure generating means (radial herringbone groove) 7 drive coil (stator section) 8 annular magnet (rotor section) 12 polygon mirror

 ────────────────────────────────────────────────── ─── Continued on the front page F term (reference) 3J011 AA04 AA20 BA02 BA04 CA05 QA04 SB04 SD03 SE02 4H104 AA04A EA01A LA03 PA01 PA04 QA12 5H607 AA04 AA06 BB01 BB17 CC01 DD03 EE10 GG12 KK00

Claims (5)

[Claims] 1. A dynamic pressure bearing surface formed on a shaft member and a dynamic pressure bearing surface formed on a bearing member are circumferentially opposed to each other, and air is interposed between the two dynamic pressure bearing surfaces as a bearing fluid, A dynamic pressure bearing device that supports the shaft member and the bearing member relatively rotatably by dynamic pressure obtained by pressurizing the air by dynamic pressure generating means provided on at least one of the two dynamic pressure bearing surfaces. In the above, the lubricating film containing amorphous carbon is formed on the hydrodynamic bearing surfaces of the shaft member and the bearing member to a thickness of 2 μm or more with respect to the base material of the shaft member and the bearing member. Characteristic hydrodynamic bearing device. 2. A dynamic pressure bearing surface formed on a shaft member and a dynamic pressure bearing surface formed on a bearing member are circumferentially opposed to each other, and air is interposed between the two dynamic pressure bearing surfaces as a bearing fluid, A dynamic pressure bearing device that supports the shaft member and the bearing member relatively rotatably by dynamic pressure obtained by pressurizing the air by dynamic pressure generating means provided on at least one of the two dynamic pressure bearing surfaces. A motor that rotationally drives a stator portion provided on one of the shaft member and the bearing member and a rotor portion provided on the other side, wherein each of the dynamic pressure bearing surfaces of the shaft member and the bearing member is provided. Wherein a lubricating film containing amorphous carbon is formed in a thickness of 2 μm or more on the base material of the shaft member and the bearing member. 3. The method according to claim 1, wherein the amorphous carbon is DLC.
(Diamond-like carbon), and the surface roughness of the lubricating film composed of DLC is Ra; 0.7
μm or less, Rmax; 1.1 μm or less, Rz; 0.8 μm
The dynamic bearing device according to claim 1 or 2, or a motor using the same. 4. The base member of each of the shaft member and the bearing member is made of aluminum or an alloy thereof, and an undercoating film made of silicon oxide is provided between the base member and the lubricating film containing amorphous carbon. The hydrodynamic bearing device according to claim 1 or 2 or a motor using the hydrodynamic bearing device. 5. A motor using a hydrodynamic bearing device, wherein the motor according to claim 2 is used in a hard disk drive or a polygon mirror drive.