JP2001173643A - Pneumatically dynamic pressure bearing device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To attain high abrasion resistance and low dusting characteristics as well as high workability at low cost. SOLUTION: This bearing device is constructed by forming one-side member consisting of a shaft member 21 and a bearing member 31 therein from a ceramic material and forming the other side member from a metallic material.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an air dynamic pressure bearing device for generating a dynamic pressure in air between opposed dynamic pressure surfaces provided on a shaft member and a bearing member.

[0002]

2. Description of the Related Art In recent years, polygon mirrors, magnetic disks,
2. Description of the Related Art Dynamic pressure bearing devices are being widely used in devices for rotating various types of rotating bodies such as optical disks at high speed. For example, in the dynamic pressure bearing device used for the driving motor of the polygon mirror 1 shown in FIG. 3, the outer peripheral surface of a fixed shaft (shaft member) 2a constituting the motor stator set 2, and A dynamic pressure surface is formed on an inner peripheral surface of a bearing rotating sleeve (bearing member) 3a constituting the rotor set 3 so as to face each other via a narrow gap in a radial direction.
Air existing as a lubricating fluid in the opposing gap between the two opposing dynamic pressure surfaces is applied by a pumping action of a dynamic pressure generating groove (not shown) formed on at least one of the two opposing dynamic pressure surfaces. The entire rotor set 3 is radially supported in the radial direction with respect to the stator set 2 on the basis of the air dynamic pressure generated thereby.

On the other hand, annular thrust magnets 2b, 3c are provided at the upper end of the fixed shaft 2a, which constitutes the stator set 2, and the polygon mirror fixing member 3b mounted on the top of the rotor set 3. The rotor set 3 is rotatable in the thrust direction while the rotor set 3 is floated in the axial direction with respect to the stator set 2 by the magnetic interaction between the two thrust magnets 2b and 3c. It is configured to be supported.

[0004] In such an air dynamic pressure bearing device, as the material of the shaft member and the bearing member, a material in which both members are made of a metal material and a material in which the surface of the metal material is subjected to a surface treatment are generally adopted. ing. On the other hand, the shaft member and the bearing member come into contact with each other particularly at the time of starting or stopping, and in the worst case, there is a risk of seizure. Attempts and developments have been made to form from various ceramic materials such as alumina, silicon nitride, and silicon carbide. In a hydrodynamic bearing device employing such a ceramic material for the shaft member and the bearing member, high wear resistance and low dust generation can be suitably obtained.

[0005]

However, in the pneumatic dynamic bearing device, the shaft member and the bearing member must be opposed to each other with a small gap therebetween. If various ceramic materials are used, high-precision machining of, for example, about ± 2 μm must be performed on ceramic materials that are not easily machined by using expensive grinding tools such as diamond grindstones. No. In particular, the process of forming the inner peripheral surface of the bearing member into a dynamic pressure surface or forming a groove for generating dynamic pressure requires a great deal of labor, and the entire dynamic pressure bearing device is not expensive. There is a problem that does not get.

Accordingly, an object of the present invention is to provide an air dynamic pressure bearing device capable of obtaining good high wear resistance and low dust generation with an inexpensive structure.

[0007]

In order to achieve the above-mentioned object, it is preferable that the metal member or the ceramic member is used as both the shaft member and the bearing member. The dynamic pressure bearing device includes a shaft member having a dynamic pressure surface and a bearing member that are opposed to each other, and a dynamic pressure generation device that generates a dynamic pressure in air between the dynamic pressure surfaces on at least one of the opposed dynamic pressure surfaces. In the pneumatic bearing device provided with the means, one of the shaft member and the bearing member is formed of a ceramic material, and the other member is formed of a metal material.

In the air dynamic pressure bearing device according to a second aspect, the surface of the metal material according to the first aspect is coated with a slidable resin material.

Further, in the air dynamic pressure bearing device according to the third aspect, the resin material according to the second aspect is made of a resin containing a polyamideimide resin (PAI) containing polytetrafluoroethylene (PTFE).

Furthermore, in the air dynamic pressure bearing device according to the fourth aspect, a dynamic pressure generating means is provided on the other member made of the metal material according to the first aspect.

According to a fifth aspect of the present invention, the shaft member according to the fourth aspect is formed of a ceramic material, and the bearing member is formed of a metal material. A concave groove constituting the dynamic pressure generating means is formed on the surface.

According to the air dynamic pressure bearing device according to the present invention having the above-described structure, of the shaft member or the bearing member,
Since one member made of a ceramic material and the other member made of a metal material, both members are inexpensive and have good workability compared to those made of a ceramic material. Thus, high wear resistance and low dust generation, which are almost the same as those obtained by combining ceramic materials, can be obtained.

According to the present invention, a metal material which is easy to machine is used for a bearing member having an inner peripheral surface which is difficult to machine, and a ceramic material is used for a shaft member which has an outer peripheral surface which is easy to machine. Therefore, in addition to the effects described above,
The efficiency of the processing step has been greatly improved.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiments of the present invention will be described below. Prior to that, the structure of a fixed-shaft type 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. Will be described in detail based on the above.

The polygon mirror rotation driving motor shown in FIG. 1 is an outer rotor type having a fixed shaft air dynamic pressure bearing device, and is a stator assembly as a fixed member assembled to the frame 10 side. The stator assembly 20 includes a rotor assembly 30 as a rotating member that is fitted into the stator assembly 20 from above in the figure. Of these, the stator set 20 is
And a fixed shaft (shaft member) 21 attached to stand substantially at the center position of the fixed shaft 21.
A cylindrical bearing holder 22 is provided concentrically around the fixed shaft 21 at a certain distance in the radial direction from the fixed shaft 21. A stator core 23 is fitted on the outer periphery of the bearing holder 22, and a driving coil 24 is wound around each salient pole portion of the stator core 23.

The fixed shaft 21 is made of various ceramic materials such as alumina (99% alumina) and silicon nitride, and a dynamic pressure surface is formed on the outer peripheral surface of the fixed shaft 21. The bearing rotating sleeve (bearing member) 31 of the rotor set 30 is rotatably mounted with a gap of several μm to several tens μm from the dynamic pressure surface.

Bearing rotating sleeve 3 as the above bearing member
1 is formed in a hollow cylindrical shape formed of a metal base material such as aluminum such as aluminum or aluminum alloy,
The surface including the dynamic pressure surface formed on the inner peripheral surface of the bearing rotation sleeve 31 is coated with a lubricating resin film having good slidability by electrodeposition coating or the like. As the lubricating resin film, for example, a polyamideimide resin (PAI) containing polytetrafluoroethylene (PTFE) is employed.

On the inner peripheral side dynamic pressure surface of the bearing rotary sleeve 31, for example, a herringbone type dynamic pressure generating groove (not shown) is divided into two blocks in the axial direction so as to be annularly arranged in parallel. A dynamic pressure is applied to air as a lubricating fluid between the inner peripheral side dynamic pressure surface of the bearing rotating sleeve 31 provided with the dynamic pressure generating groove and the outer peripheral side dynamic pressure surface of the fixed shaft 21. A radial dynamic pressure bearing portion to be generated is formed.

On the other hand, a polygon mirror 32 having a flat hexagonal shape
Is fitted. The polygon mirror 32 is mounted on a holding plate 33 a corresponding to the bottom of a rotor body 33 extending radially outward from the bearing rotation sleeve 31. The center portion is pressed from the outside in the axial direction by a clamp member 32a attached to the bearing rotating sleeve 31 from the pressing spring 32b.
It is fixed by being tightened through.

Further, an outer peripheral wall portion 21b is formed in an annular shape so as to protrude by a predetermined amount in the axial direction (upward direction in the drawing) at a distal end portion (upper end portion in the drawing) of the fixed shaft 21. A fixed-side thrust magnet 25 for thrust floating is annularly mounted on the inner peripheral side of the portion 21b. The fixed-side thrust magnet 25 is magnetized in the axial direction (vertical direction in the drawing).

A fine air orifice 32c is formed in the center of the inside of the clamp member 32a in the axial direction.
A rotating thrust magnet 34 for floating the thrust is mounted in a ring shape so as to surround the periphery. The rotation-side thrust magnet 34 is connected to the fixed shaft 21 described above.
It is disposed so as to face the fixed-side thrust magnet 25 in the radial direction, and is attached in the axial direction (vertical direction in the drawing) so as to generate magnetic attraction or repulsion between the fixed-side thrust magnet 25 and the fixed-side thrust magnet 25. It is magnetized. Then, due to the mutual magnetic action between the two magnets 34 and 25, the entire rotor set 30 is brought into the stator set 2
It is configured to be held in a state of floating a predetermined amount in the thrust direction with respect to 0.

Further, the air orifice 32c provided at the center of the clamp member 32a is formed so as to penetrate in the axial direction as damper means having a predetermined air flow resistance. The shock in the axial direction on the rotor set 30 floating in the thrust direction is reduced by the damper action by the resistance.

The above-mentioned rotor body 33 is formed of a substantially cylindrical member integrally formed with the bearing rotating sleeve 31, and has a rotor internal space in which the drive coil 24 is disposed.
The polygon mirror 32 is arranged so as to partition the space outside the rotor in which the polygon mirror 32 is arranged. A drive magnet 35 is annularly mounted on the inner peripheral wall surface of a cylindrical mounting plate 33b provided on the outer peripheral edge of the rotor body 33 via a back yoke 33c made of a magnetic material. Drive magnet 3
Numeral 5 is arranged so as to be closely opposed to each salient pole portion of the stator core 23 from the outside in the radial direction so as to constitute a motor drive unit.

When a predetermined drive voltage is applied to the drive coil 24, the polygon mirror 32 rotates together with the bearing rotating sleeve 31, and the laser light converged on the polygon mirror 32 by the rotation of the polygon mirror 32 is rotated. It scans on an image recording medium (not shown). At this time, the bearing rotating sleeve 31 is supported in the radial direction by the dynamic pressure of air generated between the bearing rotating sleeve 31 and the fixed shaft 21, and the rotating side thrust magnet 34 and the fixed side thrust magnet 25 Of the rotor set 30 by the mutual magnetic action of
Are held in a state of being floated by a predetermined amount in the thrust direction with respect to the stator set 20.

In the hydrodynamic bearing motor having the above-structured hydrodynamic bearing device according to the present embodiment, the fixed shaft 21 is formed of a ceramic material as described above, and the bearing rotation as a bearing member is performed. The sleeve 31 is formed of a metal material such as an aluminum material. Therefore, as compared with a conventional device in which both the fixed shaft 21 and the bearing rotating sleeve 31 are made of a ceramic material, the structure is inexpensive and good workability is obtained. In addition, high abrasion resistance and low dust generation are obtained, which are almost the same as the combination of ceramic materials.

That is, the inventor of the present invention used a ring-shaped test piece made of a first material and a plate-shaped test piece made of a second material as various test pieces in order to examine the amount of wear between the materials. It is formed of a combination of materials, the tip of the plate-shaped test piece is brought into contact with the outer peripheral surface of the ring-shaped test piece at an appropriate pressure, and the ring-shaped test piece is rotated for a predetermined time, whereby the The wear amount (specific wear amount) generated on the plate-shaped test piece was measured. More specifically, as the ring-shaped test piece (first material), as shown on the horizontal axis of FIG. 2, 99% alumina and nitrided material forming the fixed shaft 21 of the embodiment are used. As a ceramic material of silicon and a comparative material with those ceramic materials, metal materials of brass (C3604) and stainless steel (SUS420J2) were used.
Further, as a plate-shaped test piece (second material) to be brought into contact with each of the ring-shaped test pieces, a surface of an aluminum base material corresponding to the rotary bearing sleeve 31 in the above embodiment is
Using a coating of a polyamide-imide resin (PAI) containing polytetrafluoroethylene (PTFE), a comparison was made between these two ceramic materials, each of which was 99% alumina.

As a result, as shown in FIG. 2, the combination of metal materials (combination of aluminum and brass or stainless steel) resulted in a large amount of wear as expected, and in particular, stainless steel was used. It was confirmed that the amount of abrasion in the case where it was present was remarkable. On the other hand, when a ceramic material (99% alumina and silicon nitride) and a metal material (aluminum base material + resin coating) are combined,
Contrary to most predictions, it has been confirmed that the amount of micro wear is almost the same as the combination of ceramic materials.

As described above, in the present invention, the material of the shaft member and the bearing member, which is usually considered only by the combination of the metal part materials or the combination of the ceramic materials, is used in the present invention. It has been found that by selecting a combination, inexpensive and extremely good wear resistance can be obtained.

In particular, in the above-described embodiment, the metallic member is used for the bearing rotating sleeve 31 as the bearing member having the inner peripheral surface, which is difficult to machine, and the shaft member having the outer peripheral surface, which is easy to machine. However, since a ceramic material is used, the processing efficiency is greatly improved as compared with a combination of ceramic materials.

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 ceramic material and the metal material in the present invention are not limited to those in the above-described embodiment, and various kinds of materials can be used. In that case, the shaft member and the bearing member in the above-described embodiment are
Naturally, it is also possible to set the material relationship in the opposite manner, and the grooves for generating dynamic pressure can be formed in both the shaft member and the bearing member.

The present invention can be similarly applied to an air dynamic pressure bearing device other than the above-described polygon mirror rotating device, for example, an air dynamic pressure bearing device for a hard disk drive (HDD). Further, the present invention can be similarly applied to a rotating shaft type dynamic pressure bearing device different from the fixed shaft type dynamic pressure bearing device as in the above-described embodiment.

[0032]

As described above, in the pneumatic dynamic bearing device according to the present invention, one of the shaft member and the bearing member is formed of a ceramic material, and the other member is formed of a metal material. Therefore, it is possible to obtain an air dynamic pressure bearing device that is inexpensive and has good high wear resistance and low dust generation, and has extremely excellent practicality.

In particular, in the present invention, a metal material which is easy to machine is used as a bearing member having an inner peripheral surface which is difficult to machine, and a ceramic material is used for a shaft member which has an outer peripheral surface which is easy to machine. Since it is used, processing efficiency can be improved in addition to the effects described above.

[Brief description of the drawings]

FIG. 1 is an explanatory sectional view showing an example of a dynamic pressure bearing motor for driving a polygon mirror according to an embodiment of the present invention.

FIG. 2 is an experimental diagram showing the amount of wear for each material in comparison.

FIG. 3 is an explanatory cross-sectional view showing an example of a conventional dynamic bearing motor for driving a Rigon mirror.

[Explanation of symbols]

 Reference Signs List 20 Stator set 21 Fixed shaft (shaft member) 23 Stator core 30 Rotor set 31 Bearing rotating sleeve (bearing member) 32 Polygon mirror

Claims (5)

[Claims] 1. A dynamic pressure generating means, comprising: a shaft member having a dynamic pressure surface arranged opposite to a bearing member; and a dynamic pressure generating means for generating a dynamic pressure in air between the dynamic pressure surfaces on at least one of the opposed dynamic pressure surfaces. In the pneumatic pressure bearing device provided with, a member on one side of the shaft member and the bearing member is formed of a ceramic material, and a member on the other side is formed of a metal material. Pneumatic bearing device. 2. The pneumatic bearing device according to claim 1, wherein a surface of the metal material is coated with a resin material having slidability. 3. The method according to claim 1, wherein the resin material is a polyamide-imide resin (P) containing polytetrafluoroethylene (PTFE).
The air dynamic pressure bearing device according to claim 2, wherein the air dynamic pressure bearing device is made of a resin containing AI). 4. The air dynamic pressure bearing device according to claim 1, wherein a dynamic pressure generating means is provided on the other member made of said metal material. 5. The shaft member is formed of a ceramic material, the bearing member is formed of a metal material, and a concave groove forming dynamic pressure generating means is formed on an inner peripheral surface of the bearing member. The air dynamic pressure bearing device according to claim 4, wherein: