JP2000283165A - Dynamic pressure bearing device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To easily and certainly form a favourable lubricating painting surface against a shaft body or a shaft fitting and inserting body. SOLUTION: Reliability of electrodeposition coating is improved by easily providing a lubricating coat furnished with favourable lubricity in accordance with uniform painting work of electrodeposition coating by applying electrodeposition on at least on a surface of one of both dynamic pressure bearing surfaces of a shaft body 21 and a shaft fitting and inserting body and by uniformizing film thickness on an end edge part of a painting surface by forming a liquid trap part 21c on an end edge part of the electrodeposition coating so as to be furnished with a proper dimensional relation with film thickness of the lubricating coating film.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a hydrodynamic bearing device having a structure in which a dynamic pressure is generated in a lubricating fluid, and the shaft pressure and a shaft-fitting insert are relatively rotatably supported by the dynamic pressure.

[0002]

2. Description of the Related Art In recent years, polygon mirrors, magnetic disks,
Various proposals have been made regarding dynamic pressure bearing devices for supporting various types of rotating bodies such as optical disks at high speed. In this hydrodynamic bearing device, the hydrodynamic bearing surface on the shaft body side and the hydrodynamic bearing surface on the shaft insertion body side are provided so as to face each other in a radial direction with a predetermined gap therebetween. A pressure bearing is formed. Further, a dynamic pressure generating groove is formed on at least one of the two opposed dynamic pressure bearing surfaces,
A lubricating fluid such as air or oil injected into the dynamic pressure bearing portion is pressurized by the pumping action of the dynamic pressure generating groove during rotation, and the dynamic pressure of the lubricating fluid causes the shaft body and the shaft insert to rotate. The rotation support is performed in a state where both members are relatively floated.

[0003] A lubricating paint for preventing seizure is generally applied to one surface of both dynamic pressure bearing surfaces of a shaft body or a shaft fitting insert in such a dynamic pressure bearing device, and is applied to the other surface. Are plated and used in combination. However, when applying such a lubricating paint, a large amount of time is required for the coating process for thick coating, and finishing such as lace processing for forming a uniform thickness. Process must be applied. Further, since a very large number of steps (about 50 steps) must be performed in the plating process, the conventional hydrodynamic bearing device has a problem that the productivity is low and the product cost is high. Furthermore, the plating treatment is not sufficiently durable against corrosion, and the surface grows granularly, so that the surface roughness (smoothness) is not good and abrasion powder is easily generated during use. This can be a major problem in the case of devices that require reliability.

[0004] Based on such a viewpoint, the inventors of the present application have proposed forming a lubricating film by electrodeposition coating on one of the two hydrodynamic bearing surfaces of the shaft body and the shaft fitting insert. It has already been proposed in Japanese Patent Application No. 10-235785. According to this prior invention, a lubricating coating can be easily obtained with a uniform layer thickness all around by the uniform coating action of electrodeposition coating,
The electrodeposited lubricating film is formed to have extremely good lubricity because the lubricating particles (PTFE) float on the surface of the coating at the time of electrodeposition coating. Improvement is achieved.

[0005]

However, even with the electrodeposition coating having such uniform coating properties, in the dynamic pressure bearing device, the shaft and the shaft insertion member have an extremely small clearance (several μm). (Approximately 10 μm), the swelling phenomenon due to paint dripping at the edge of the painted surface, which can be ignored in a normal apparatus, may be a problem. For example, as shown in FIG. 5, electrodeposition is performed on a surface from a dynamic pressure bearing surface 1 of a shaft body or a shaft fitting to a bearing end surface 2 extending in a direction intersecting the dynamic pressure bearing surface 1. If the lubricating coating 3 is continuously formed by painting, a raised portion 3a of the lubricating coating 3 will be formed near the intersection edge 4 between the two surfaces 1, 2. It is considered that such a swelling phenomenon of the lubricating coating film 3 is caused by the fact that the coating film deposited by the electrodeposition coating is reduced in viscosity during the heating and curing process to be in a fluid state, and has a fluidity. The lubricating coating 3 is pulled in both side directions of the vertex by the surface tension acting on the crossing edge portion 4, and as a result, the film thickness at the vertex portion becomes thinner, and the excess paint is removed by the crossing edge portion 4. It is presumed that it rises on both sides of the vertex.

The raised portion 3a of the lubricating coating 3 is
For example, since the height may be about 5 μm, the height of the raised portion 3a may be larger than the minute clearance between the shaft body and the shaft insertion body. As a result, although the shaft body and the shaft-fitting insert cannot be fitted or the two members can be fitted together, the shaft body and the shaft-fitting insert rub through the raised portion 3a during rotation. In some cases, a good floating state cannot be obtained during rotation.

Therefore, the present invention provides a dynamic pressure bearing device which can form an electrodeposition coating film with a uniform structure on a shaft or a shaft-inserted body with a simple structure. Aim.

[0008]

In order to achieve the above object, according to the first aspect of the present invention, an outer peripheral surface of a shaft body and a shaft fitting body rotatably mounted on the shaft body are provided. The inner peripheral surface forms a hydrodynamic bearing surface that faces in the radial direction,
A lubricating fluid is interposed in a gap between the two dynamic pressure bearing surfaces of the shaft body and the shaft fitting insert, and a dynamic pressure generating groove having a predetermined shape is formed in at least one of the two dynamic pressure bearing surfaces. In the hydrodynamic bearing device, the surface from the hydrodynamic bearing surface of the shaft body or the shaft-fitting insert to a bearing end surface extending in a direction intersecting at the end portion of the hydrodynamic bearing surface is formed by electrodeposition coating. While the lubricating film is continuously formed, the dynamic pressure bearing surface and the bearing end surface of the shaft body or the shaft insert have a predetermined notch shape for equalizing the thickness of the lubricating film. The liquid reservoir is continuously provided with a liquid reservoir provided therein, and the liquid reservoir has an axial length that is an extending direction of the dynamic pressure bearing surface,
The length of the lubricating coating is set to be at least 10 times the thickness of the lubricating coating, and the length in the direction intersecting with the axial direction, which is the extending direction of the bearing end face, is １ ／ times the thickness of the lubricating coating. The size is set to at least two times the size.

According to the second aspect of the present invention, the dynamic pressure bearing surface according to the first aspect is either a radial dynamic pressure bearing surface or a thrust dynamic pressure bearing surface.

Further, according to the third aspect of the present invention, the predetermined notch shape in the liquid reservoir according to the first aspect connects between the dynamic pressure bearing surface and the bearing end surface of the shaft or the shaft insert. , A step, an inclined surface, or a curved surface.

According to the present invention having such a configuration,
A uniform lubricating film can be easily obtained with a uniform layer thickness all over the circumference by the uniform coating action of electrodeposition coating.
Since the lubricating particles (PTFE) float on the surface of the coating at the time of electrodeposition coating, the lubricating particles (PTFE) are formed to have extremely good lubricity, and the bearing characteristics are improved.

On the other hand, even in such an electrodeposition coating having uniform coating properties, in a dynamic pressure bearing device, the shaft body and the bearing body are arranged to face each other with a minute clearance therebetween, so that the coated surface is not coated. The swelling phenomenon due to paint dripping at the edge portion of cannot be ignored. In other words, the swelling of the coating may tend to be equal to or greater than the fitting clearance between the shaft body and the shaft fitting insert. Therefore, in the present invention, a liquid reservoir having an appropriate dimensional relationship with the thickness of the lubricating film is provided at the edge portion of the hydrodynamic bearing surface serving as a dimension reference, and the electrodeposition is performed by the function of uniforming the film thickness of the liquid reservoir. The thickness of the coating is made uniform even at the edges, so that a good lubricating coating can be easily obtained without performing post-processing such as lace processing.

In this case, if the liquid reservoir is formed by any one of a step, an inclined surface, and a curved surface, the liquid reservoir having a good function can be easily formed. Formed.

[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.

FIG. 2 shows an example of an outer rotor type motor provided with a fixed shaft air dynamic pressure bearing device for rotatingly driving a polygon mirror. This air dynamic pressure bearing motor includes a stator set 20 as a fixing member assembled on the frame 10 side,
And a rotor set 30 as a rotating member fitted so as to be fitted from the upper side in the figure. Among these, the stator set 20 is a fixed shaft (shaft) mounted to stand substantially at the center position of the frame 10. And a bearing holder 22 that surrounds the fixed shaft 21 in a cylindrical shape at a constant distance in the radial direction from the outer peripheral surface of the fixed shaft 21. A stator core 23 is fitted around the outer periphery of the bearing holder 22, and a drive coil 24 is wound around salient pole portions of the stator core 23.

On the outer peripheral surface of the fixed shaft 21, a herringbone type dynamic pressure generating groove 25 is axially divided into two blocks and is annularly recessed. , 25, a cylindrical body (shaft fitting) 31 of the rotor set 30 is rotatably mounted with a gap of several μm to tens of μm. A radial bearing for generating air dynamic pressure is formed between the outer peripheral surface of the fixed shaft 21 and the inner peripheral surface of the cylindrical body 31 of the rotor set 30. The fixed shaft 21
An air supply hole 26 extends in the axial direction from a shaft tip (upper end in the figure) of the fixed shaft 21, and the air supply hole 26 is provided with the dynamic pressure generating grooves 25, 25 of the two blocks. The opening is open toward the outside of the fixed shaft 21 at the portion between the two.

Further, an outer peripheral portion of the shaft end (upper end in the figure) of the fixed shaft 21 projects axially by a predetermined amount, and a fixed side magnet 27 for thrust floating is annularly formed on an inner peripheral wall of the projected portion. It is attached to. On the other hand, a porous air orifice 32 having a predetermined air flow resistance penetrates axially as a damper means at a center portion of the cylindrical body 31 of the rotor set 30 at a base side (upper end side in the figure). The damping action of the air orifice 32 due to the airflow resistance reduces the impact on the rotor set 30 in the axial direction. The air inside the rotor set 30 is supplied to the portion between the dynamic pressure generating grooves 25 by the air supply holes 26, and the pumping action of the dynamic pressure generating grooves 25, 25 causes the air to flow outward in the vertical direction in the drawing. And discharged to the outside.

Further, around the air orifice 32, a rotating magnet 33 for thrust floating is annularly mounted. The rotating magnet 33 is magnetized in the axial direction (vertical direction in the drawing) so as to mutually generate a magnetic attraction with the fixed magnet 27 on the fixed shaft 21. The set 30 is configured to be held in a state of floating by a predetermined amount in the thrust direction.

On the other hand, a flat hexagonal polygon mirror 34 as a rotating plate is fitted around the outer periphery of the cylindrical body 31 of the rotor set 30 on the base side (upper side in the figure) so as to constitute the rotating plate. I have. The polygon mirror 34 has a holding unit 38 extending radially outward from the cylindrical body 31.
It is mounted on the upper side in the axial direction, and is fixed from the outside in the axial direction by a pressing spring 39 serving as a clamping means.

A rotor flange portion 35 extends radially outward from the holding portion 38. The rotor flange portion 35 includes the cylindrical body portion 31 and the holding portion 3.
8, and is arranged so as to separate a space inside the rotor where the drive coil 24 is arranged and a space outside the rotor where the polygon mirror 34 is arranged.

Further, a driving magnet 37 is provided on the inner peripheral wall surface of an annular mounting plate 36 projecting from the outer peripheral portion of the rotor flange portion 35 in the axial direction (downward in the drawing) via a back yoke made of a magnetic material. It is mounted in a ring.
The drive magnet 37 is connected to the stator core 23 described above.
Is arranged so as to face the outer peripheral surface in the radial direction,
It constitutes a motor drive unit.

In the embodiment shown in FIG. 2, the holding portion 38,
Although the cylindrical body portion 31, the rotor flange portion 35, and the mounting portion 36 are integrally formed, each of them may be formed separately.

When a predetermined drive voltage is applied to the drive coil 24, the polygon mirror 34 and the cylindrical body 31 are applied.
Is rotated, and the laser light converged on the polygon mirror 34 by the rotation of the polygon mirror 34 scans an image recording medium (not shown). At this time, the cylindrical body 31 is supported in the radial direction by the dynamic pressure of air generated between the cylindrical body 31 and the fixed shaft 21, and the magnetic force between the rotating magnet 33 and the fixed magnet 27 is increased. Due to the suction action, the rotor set 30 is held in a state of floating by a predetermined amount in the thrust direction.

The fixed shaft 21 is made of an aluminum material such as aluminum or an aluminum alloy. The outer peripheral surface of the fixed shaft 21 including the hydrodynamic bearing surface is coated with a lubricating film by electrodeposition coating as described later. Are formed. The detailed structure of the fixed shaft 21 as such a shaft body will be described together with a manufacturing method thereof.

In manufacturing the fixed shaft 21, first, a blank material for the fixed shaft 21 is formed by casting using aluminum, an aluminum alloy material or a magnesium alloy, die casting, or other processing methods. The dynamic pressure generating groove 25 is first processed and formed by applying masking printing to portions other than the formed portion of the dynamic pressure generating groove 25 and performing an etching process or the like.

Next, the outer surface of the blank material of the fixed shaft 21 is subjected to electrodeposition coating. Prior to that, the radial dynamic pressure bearing surface (reference surface) for which high precision dimensional accuracy is required. A liquid reservoir for uniforming the film thickness in the electrodeposition coating is formed at a portion corresponding to the terminal portion. For example, as shown in FIG. 1, a surface (reference surface) 21a corresponding to the upper radial dynamic pressure bearing surface and an axial end portion (upper end portion) of the surface 21a corresponding to the radial dynamic pressure bearing surface are illustrated. 3), a surface 21b corresponding to a bearing end face extending in the orthogonal direction is formed so as to be continuous with a notched liquid reservoir 21c formed of a step.

In FIG. 1 described above, a liquid reservoir 21c provided at the upper end edge portion of the fixed shaft 21 is shown. The outer peripheral edge portion of the bearing end surface 21c on the upper end side of the fixed shaft 21 has
First, a chamfered tapered surface 21d is formed so as to cut off a corner obliquely, and a chamfered tapered surface 21d continuous from its upper end bearing end surface 21b and a radial dynamic pressure bearing surface 2d are formed.
The liquid reservoir 21c formed of the above-mentioned step is provided between the liquid reservoir 1a and the liquid reservoir 1a.

The stepped portion forming the liquid reservoir 21c in the present embodiment has a shape in which the outer surface of the radial dynamic pressure bearing surface 21a is depressed inward in the radial direction. It is formed so as to have a predetermined dimensional relationship with respect to the film thickness of the lubricating film 21 e formed on the outer surface of the lubrication film 21. That is, the length (step width dimension) Z in the extension direction (axial direction) of the radial dynamic pressure bearing surface 21a in the liquid reservoir 21c is 10 times the thickness T of the lubricating film 21e.
It is formed to be twice as long. In addition, the liquid reservoir 21
The length (step depth dimension) R in the extension direction of the bearing end face 21b, which is the step amount at c, is set to be not less than 1/3 times and not more than 2 times the film thickness T of the lubricating film 21e. More specifically, the film thickness T of the lubricating film 21e in the present embodiment
Is set to 18 μm.
The dimensions Z and R of c are 300 μm and 15 μm, respectively.
m.

In performing the electrodeposition coating, the outer surface of the blank material having the above-mentioned liquid reservoir 21c is subjected to a base treatment such as a chromate treatment (alodine treatment) for improving corrosion resistance and coating adhesion. After being applied, the blank material is immersed in an electrodeposition tank (not shown), and the entire surface of the blank material is coated by electrodeposition (electric swimming). In this electrodeposition coating, a blank material is put into a paint dispersed in water, and the paint is applied by passing an electric current so that the blank material and the other metal body become both poles.

As described above, the film thickness T of the lubricating film 21e in this embodiment is set to 18 μm. Can be adjusted arbitrarily. After the electrodeposition coating, a heat treatment is performed to cure the resin, and a portion corresponding to the dynamic pressure bearing surface 21a is subjected to a predetermined lubrication process.

According to such an embodiment, the lubricating coating 21e can be easily obtained with a uniform thickness on the surface of the fixed shaft 21 by the uniform coating action of the electrodeposition coating. The lubricating film 21e composed of the electrodeposition coating formed portion is formed to have extremely good lubricity because the lubricating particles float on the surface of the coating at the time of electrodeposition coating. Improvement is achieved. Furthermore, in this electrodeposition coating, even if there is a defect such as a nest in the material of the coating partner,
Since the paint enters the inside, the formed lubricating film 21e has strong adhesion. And
By using the fixed shaft 21 having the lubricating film 21e formed by electrodeposition coating having good lubrication, the wear resistance on the dynamic pressure bearing surface is improved, and the generation of wear powder is greatly reduced. In addition, the maintenance of the bearing gap and the prevention of seizure can be achieved.

On the other hand, in the dynamic pressure bearing device, the fixed shaft 21 as the shaft and the cylindrical body 31 as the shaft fitting are opposed to each other with a small clearance (several μm to several tens μm). Even with electrodeposition coating having uniform coating properties, the swelling phenomenon due to paint dripping at the edge of the coating surface cannot be ignored. That is, since the swelling of the paint tends to occur equal to or larger than the fitting clearance between the fixed shaft 21 and the cylindrical body 31, in the present invention, the edge of the radial dynamic pressure bearing surface 21 a serving as the dimension reference is used. A liquid reservoir 21c is provided for the portion, and the film thickness of the electrodeposition coating is made uniform even at the edge portion by the film thickness uniforming function of the liquid reservoir 21c. Thus, a good lubricating film 21e can be easily obtained without performing post-processing such as lace processing. The thickness of the lubricating film 21e for obtaining such action and effect and the liquid reservoir 2
Next, the dimensional relationship with respect to 1c will be described.

First, the relationship between the above-mentioned respective dimensions Z and R in the liquid reservoir 21c and the swelling amount of the lubricating film 21e (see reference numeral 3a in FIG. 5) with respect to the ratio and the thickness of the lubricating film 21e. This is shown in FIGS. FIG. 3 shows a step depth R (step width Z is 250 μm) of the liquid reservoir 21c.
) And the thickness (vertical axis) of the lubricating film 21e with respect to the ratio (horizontal axis; film thickness / step depth) between the film thickness and the lubricating film 21e. As is clear from this figure, in the region where the ratio between the thickness of the lubricating film 21e on the horizontal axis and the step depth of the liquid reservoir 21c is between "1/3" and "2",
The amount of protrusion of the lubricating film 21e is very small,
It is below the standard value (1 μm).

FIG. 4 shows the step width Z of the liquid reservoir 21c.
(The depth R is fixed at 15 μm) and the film thickness of the lubricating film 21e (horizontal axis; film thickness / step width), and the lubricating film 2
The excitement amount (vertical axis) of 1e is shown. As is clear from the figure, in the region where the ratio of the film thickness of the lubricating film 21e on the horizontal axis to the step width of the liquid reservoir 21c is "10" or more, the lubricating film 21e has a very high rise. It is smaller than the standard value (1 μm). In both of the figures described above, when the swelling amount of the lubricating film 21e becomes negative, the swelling amount of the lubricating film 21e is represented as "0".

As is apparent from these results, the length (step width dimension) Z in the extending direction (axial direction) of the hydrodynamic bearing surface of the liquid reservoir 21c is set to 10 times or more the thickness of the lubricating film 21e. And the length (step depth dimension) R in the extending direction of the bearing end face 21b, which is the step amount of the liquid reservoir 21c, is at least 1/3 times the thickness of the lubricating film. If the thickness is set as follows, the thickness of the lubricating film 21e formed by electrodeposition coating is excellently uniform.

The electrodeposition coating in which the liquid reservoir 21c for making the film thickness uniform is not limited to the fixed shaft 21a as in the above-described embodiment, but may be a cylinder as a shaft insertion member. The same can be applied to the trunk 31.

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, the liquid reservoir 21c can be formed in a shape other than the step connecting the dynamic pressure bearing surface 21a and the bearing end surface 21b as in the above-described embodiment. In any case, the liquid reservoir 21c having a good function can be easily formed as in the case of the stepped portion.

The present invention can be applied not only to the case where the dynamic pressure generating groove 25 is provided on the shaft body side but also to the case where the dynamic pressure generating groove 25 is formed on the shaft insertion body side as in the above-described embodiments. it can. In addition, the present invention can be similarly applied to a case where electrodeposition coating is performed on the shaft fitting insert side.

Further, each of the above-described embodiments is a case of a hydrodynamic bearing device using air as a lubricating fluid, but the present invention is similarly applied to a device using other hydrodynamic fluid such as oil. Can be applied.

Further, the present invention can be similarly applied to a hydrodynamic bearing device used for other than the above-described motor, for example, a hydrodynamic bearing device provided in a hard disk drive (HDD) motor. .

[0042]

As described above, the present invention provides a uniform coating effect of electrodeposition coating by applying electrodeposition coating on either one of the hydrodynamic bearing surfaces of the shaft body and the shaft insertion member. Thus, a lubricating film having extremely good lubricity can be easily obtained, and the bearing characteristics can be improved. In addition, when the electrodeposition coating is performed, the swelling portion of the minute coating that is likely to be generated at the edge portion also has a notch shape in a liquid reservoir portion having an appropriate dimensional relationship with the thickness of the lubricating film at the edge portion. By providing the electrodeposited surface, a highly reliable electrodeposited surface can be easily and reliably obtained without performing post-processing such as lace processing.

At this time, the liquid reservoir is formed by any one of a step, an inclined surface, and a curved surface to easily form the liquid reservoir having a good function. If this is possible, productivity can be improved while maintaining the above-described effects.

[Brief description of the drawings]

FIG. 1 is an enlarged partial cross-sectional view illustrating an upper end portion of a fixed shaft according to an embodiment of the present invention.

FIG. 2 is an explanatory cross-sectional view showing an example of a fixed shaft type polygon mirror driving motor provided with a dynamic pressure bearing to which the present invention is applied.

FIG. 3 is a diagram illustrating a relationship between a length of a liquid reservoir in a surface direction of a dynamic pressure bearing and a swelling amount of a coating film.

FIG. 4 is a diagram showing a relationship between a length of a liquid reservoir in a bearing end surface direction and a swelling amount of a coating film.

FIG. 5 is a schematic explanatory view showing a state in which a conventional lubricating film is formed.

[Explanation of symbols]

 21 Fixed shaft (shaft) 25 Groove for generating dynamic pressure 31 Cylindrical body (shaft fitting) 21a Radial dynamic pressure bearing surface 21b Bearing end surface 21c Liquid reservoir

Claims (3)

[Claims] An outer peripheral surface of a shaft body and an inner peripheral surface of a shaft fitting inserted rotatably with respect to the shaft body form radially opposed dynamic pressure bearing surfaces. A lubricating fluid is interposed in a gap between both the dynamic pressure bearing surfaces of the shaft body and the shaft fitting insert, and a dynamic pressure generating groove having a predetermined shape is formed in at least one of the dynamic pressure bearing surfaces. In the hydrodynamic bearing device, lubrication by electrodeposition coating on a surface from the hydrodynamic bearing surface of the shaft body or the shaft-fitting insert to a bearing end surface extending in a direction intersecting at a terminal portion of the hydrodynamic bearing surface. While the coating is continuously formed, the dynamic pressure bearing surface of the shaft or the shaft insert and the bearing end surface have a predetermined notch shape for uniformizing the thickness of the lubricating coating. The liquid reservoir is provided in the direction of extension of the hydrodynamic bearing surface. The axial length of the lubricating coating is set to be at least 10 times the film thickness of the lubricating coating, and the length of the lubricating coating in a direction intersecting the axial direction, which is the extending direction of the bearing end face, is set. A dynamic pressure bearing device characterized in that the thickness is set to be at least 1/3 and at most 2 times the thickness of the film. 2. The dynamic pressure bearing device according to claim 1, wherein the dynamic pressure bearing surface is one of a radial dynamic pressure bearing surface and a thrust dynamic pressure bearing surface. 3. A predetermined notch shape in the liquid reservoir,
2. A stepped portion, an inclined surface, or a curved surface formed so as to connect between a dynamic pressure bearing surface and a bearing end surface of the shaft body or the shaft insertion member. Dynamic bearing device.