JP2001027226A - Conical hydrodynamic pressure bearing and spindle motor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To mass-produce conical hydrodynamic pressure bearings at a low cost, suppress the generation of precession, prevent a conical shaft member from resting in the state of being fitted into a sleeve member and to make bearing rigidity almost constant in a wide temperature range. SOLUTION: This conical hydrodynamic pressure bearing is formed into double structure with a resin layer 3 applied to a metal core material, and formed into the connected shape of a pair of cones holding the mutual bottom faces in common, that is, composed of a conical shaft member 1 of spindle shape, a lower resin sleeve member 4 and an upper resin sleeve member 5. The conical shaft member 1 is provided with an annular protruding part 3a. An annular stepped part provided at the lower sleeve member 4, and an annular stepped part provided at the upper sleeve member 5, form an annular recessed part, and the lower face of the annular protruding part 3a is seated on the upper face of the annular recessed part when brought to a stop. The conical shaft member 1, lower sleeve member 4 and upper sleeve member 5 are manufactured from liquid crystal polymeric material by molding.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a conical fluid dynamic bearing having two main components, a conical shaft member and a sleeve member into which the conical shaft member is rotatably fitted. The present invention relates to a spindle motor having a fluid dynamic pressure bearing, and more particularly, to a structure of a conical shaft member as a main component and a sleeve member serving as a receiving portion thereof.

[0002]

2. Description of the Related Art A conical fluid dynamic pressure bearing mainly includes a conical conical shaft member and a sleeve member for receiving the conical shaft member, and a tapered outer peripheral surface of the conical shaft member forming a bearing gap. A dynamic pressure generating groove such as a herringbone groove is formed on one of the tapered inner peripheral surfaces of the sleeve member. A conical fluid dynamic bearing that generates a dynamic pressure in which a radial dynamic pressure component and a thrust dynamic pressure component are combined is, so to speak, a combination of a radial dynamic pressure bearing and a thrust dynamic pressure bearing in one bearing. Ideal for small motor bearings. In addition, the conical fluid dynamic pressure bearing has a feature that the radial load and the axial load can be arbitrarily designed by appropriately selecting the apex angle and the dynamic pressure generation groove parameter.

[0003] Conical fluid dynamic pressure bearings having such features are difficult to manufacture in a low cost and in large quantities because it is difficult to manufacture conical shaft members and sleeve members. That is, the conical shaft member and the sleeve member have a cone apex angle of ± 1 ′ or less, or preferably ± 30 ″.
It must be processed with the following processing accuracy. For this reason,
This is because it is difficult to mass-produce the conical shaft member and the sleeve member by grinding or cutting. ,

In a conical fluid dynamic bearing, when stopped, the entire conical surface of the conical shaft member, that is, the tapered outer peripheral surface is in contact with the receiving surface of the sleeve member, that is, the tapered inner peripheral surface. Stand still in the state of being fitted in. For this reason, a large load is generated both at the time of starting and at the time of stopping. Depending on the fitted state, it may become impossible to start. Furthermore, since the conventional conical shaft member is constituted by a conical member, that is, constituted by a single conical member, there is a disadvantage that precession is likely to occur during rotation.

As shown in FIG. 4, a conical fluid dynamic pressure bearing employed in a drive motor of an optical deflecting device disclosed in Japanese Patent Application Laid-Open No. 60-208629 includes a conical shaft member 11 having a truncated conical cross section and a conical shaft member 11 having the same shape. The main body is a sleeve member 13 which is rotatably fitted with the sleeve member 13. A dynamic pressure generating groove G such as a herringbone groove is formed on a tapered outer peripheral surface 11a of a conical shaft member 11 forming a bearing gap. It is a thing. A fixed shaft 12 is integrally formed at the upper end of the conical shaft member 11, and the fixed shaft 12 is fixed to an upper substrate 19. The sleeve member 13 has a tapered inner peripheral surface 13a that forms a bearing gap with the tapered outer peripheral surface 11a of the conical shaft member 11. The sleeve member 13 is
It is supported in a non-contact manner in the thrust direction by a magnetic bearing composed of permanent magnets 14 and 15. Sleeve member 13
Rotor magnet 16 and lower substrate 18 mounted below
Generates a rotational force in cooperation with the stator coil 17 attached to the motor.

As described above, the conical fluid dynamic pressure bearing disclosed in Japanese Patent Application Laid-Open No. 60-208629 uses a magnetic bearing in combination to prevent the conical shaft member from being stopped in a state of being fitted into the sleeve member. It also prevents precession during rotation. However, the combined use of the magnetic bearings increases the size of the device, making the assembling work difficult, and the components of the dynamic pressure bearing are not made of resin, so that it is difficult to manufacture them in large quantities at low cost. Therefore, this conical fluid dynamic bearing cannot be used for a small spindle motor.

[0007]

SUMMARY OF THE INVENTION A first object of the present invention is to provide a conical fluid dynamic pressure bearing having a conical shaft member and a sleeve member as main components, and a spindle motor having the same. Is to be able to produce in large quantities at low cost. A second problem to be solved is to make it difficult for precession to occur in the conical fluid dynamic bearing and the spindle motor having the same. A third problem to be solved is to prevent the conical shaft member from being stopped in the state of being fitted into the sleeve member in the conical fluid dynamic pressure bearing and the spindle motor including the same. The fourth problem to be solved is
In the conical fluid dynamic bearing and the spindle motor including the same, the bearing rigidity is made substantially constant over a wide temperature range.

[0008]

In order to solve the above first and second problems, a conical shaft member and a sleeve member into which the shaft member is rotatably fitted are used as main components to form a bearing gap. A fluid dynamic pressure bearing in which a dynamic pressure generating groove is formed on one of a tapered outer peripheral surface of the conical shaft member and a tapered inner peripheral surface of the sleeve member, and a spindle motor including the same. The shaft member has a double structure in which a resin layer is applied to a metal core material, and has a shape in which a pair of cones are connected to each other while sharing a bottom surface, that is, a spindle shape or a barrel shape.

In order to solve the third problem, an annular convex portion is provided in the vicinity of a maximum diameter portion of the spindle-shaped conical shaft member, and an annular concave portion is provided in a portion of the sleeve member opposed thereto. When stopped, the lower surface of the annular projection is seated on the upper surface of the annular recess so that the tapered outer peripheral surface of the conical shaft member does not contact the tapered inner peripheral surface of the sleeve member.

In order to solve the first problem, the conical shaft member and the sleeve member are formed by molding a resin material. In addition, a liquid crystal polymer material was used as the resin material.

In order to solve the fourth problem, the resin material of the resin layer of the conical shaft member and the resin material of the sleeve member are selected such that their linear expansion coefficients are equal or the former is larger than the latter. did.

[0012]

FIG. 1 is a sectional view of a spindle motor according to a first embodiment of the present invention. In FIG. 1, a conical fluid dynamic pressure bearing is a spindle body in which a resin layer 3 is applied to a cylindrical metal core 2. A conical shaft member 1 is formed, and a lower sleeve member 4 and an upper sleeve member 5 into which the conical shaft member 1 is rotatably fitted. The spindle motor provided with the conical fluid dynamic bearing is a cup-shaped hub 6 attached to the conical shaft member 1, a rotor magnet 7 attached to the inner peripheral surface of the cup-shaped hub 6, and opposed to the rotor magnet 7. And a motor board 9 on which the lower sleeve member 4 is erected.

FIG. 2 is a sectional view of a first embodiment of a conical fluid dynamic pressure bearing according to the present invention, in which a minute gap and a dynamic pressure generating groove are exaggerated. In FIG. This is a resin shaft member formed by applying a resin 3 to the core material 2 and forming the same, and combining a pair of cones into a shape in which the bottom surfaces of the pair are shared with each other, that is, a spindle shape. The lower sleeve member 4 is a bowl-shaped member having a tapered inner peripheral surface inclined at a predetermined angle and a bottom surface, and an annular step portion 4a is formed at an open end thereof. The upper sleeve member 5 is a bowl-shaped member having a tapered inner peripheral surface inclined at a predetermined angle similar to the lower sleeve member 4 and a top surface, and a cylindrical metal core material 2 penetrates through the top surface. A hole is formed, and an annular step 5a is formed at the opening end. The predetermined angle is the same as the inclination angle of the tapered outer peripheral surface of the cone of the conical shaft member 1.

The conical shaft member 1 has an annular convex portion 3a rotatably fitted in an annular concave portion formed by the annular step portion 4a of the lower sleeve member 4 and the annular step portion 5a of the upper sleeve member 5. Is formed. The annular convex portion 3a is formed at the center of the conical shaft member 1, that is, near the maximum diameter portion of the spindle. 1 and 2, the annular convex portion 3
a is an annular band having a rectangular cross section. Therefore, when the dynamic pressure bearing is stopped, the lower surface of the annular convex portion 3a is seated on the upper surface of the annular step portion 4a of the lower sleeve member 4 forming the annular concave portion of the sleeve member. As a result, the entire lower conical surface of the conical shaft member 1 comes into contact with the receiving surface of the lower sleeve member 4 at the time of stoppage, and the stationary state in the fitted state is reliably prevented.

A dynamic pressure generating groove G such as a herringbone groove is
The conical shaft member 1 is formed on the outer peripheral surface of a resin cone. Conical shaft member 1, lower sleeve member 4
Small gaps R1 to R
4 are formed. That is, R1 is a conical shaft member 1.
A small gap between the outer peripheral surface of the upper conical body and the inner peripheral surface of the upper sleeve member 5, R2 is an annular shape formed by the annular step portion 4a of the lower sleeve member 4 and the annular step portion 5a of the upper sleeve member 5. A minute gap between the concave portion and the annular convex portion 3a, R3 is a minute gap between the outer peripheral surface of the lower conical body of the conical shaft member 1 and the inner peripheral surface of the lower sleeve member 4, and R4 is a conical shape. Lower end surface of shaft member 1 and bottom surface 4 of lower sleeve member 4
b is a minute gap.

These minute gaps are on the order of several μm to several hundred μm, depending on the size, rotation speed and viscosity coefficient of the lubricating oil of the fluid dynamic pressure bearing. F is the lubricating oil filled in these minute gaps. In addition, R
1 and R3 function as bearing clearances, and R2 and R4 function as lubricating oil sumps. Further, the tapered minute gap S communicating between the minute gap R1 and the atmosphere prevents the lubricating oil F filled in the fluid dynamic pressure bearing from leaking to the outside by utilizing the capillary phenomenon and the surface tension. It functions as a capillary seal.

In a fluid dynamic pressure bearing filled with lubricating oil, the bearing stiffness decreases as the temperature increases. This is because when the temperature of the lubricating oil increases, its viscosity coefficient decreases. Therefore, in the present invention, the resin material of the resin layer 3 of the conical shaft member 1 and the resin material of the sleeve members 4 and 5 are selected such that their linear expansion coefficients are equal or the former is larger than the latter. did. As a result, in the high-temperature region, the manner of narrowing the interval of the bearing gap R4 became larger as compared with the bearing gap that did not employ such means.

As described above, the distance between the bearing gaps can be changed to be larger than that of the conventional apparatus, and the liquid dynamic pressure bearing according to the present invention has a wider range that can be automatically adjusted depending on the temperature. Therefore, by utilizing the effect of the automatic adjustment of the interval of the bearing gap by this temperature, the bearing stiffness can be more dynamically and automatically adjusted. That is, in a high temperature range, the gap between the bearing gap formed between the shaft member and the sleeve member becomes narrow, and the bearing rigidity increases. This increase in bearing stiffness compensates for a decrease in bearing stiffness due to a decrease in the viscosity coefficient, so that a predetermined bearing stiffness is maintained in a high temperature range. On the other hand, in a low temperature range, the gap between the bearing gap formed between the shaft member and the sleeve member is widened, and the bearing rigidity is reduced. This decrease in bearing stiffness is of a magnitude that compensates for an increase in bearing stiffness due to an increase in viscosity coefficient, and therefore, a predetermined bearing stiffness is maintained even in a low temperature range. That is, a change in bearing stiffness due to a viscosity coefficient of lubricating oil can be compensated for over a wide temperature range by a change in bearing stiffness due to a bearing gap.

The conical fluid dynamic bearing of the second embodiment according to the present invention has basically the same configuration as the conical fluid dynamic bearing of the first embodiment, as shown in the sectional view of FIG. is there. The difference between the two is in the shape of the annular concave portion and the annular convex portion. That is, the annular convex portion 3 serving as the support portion of the conical shaft member 1 when stopped.
In the first embodiment, a is an annular band having a rectangular cross section, but in the second embodiment shown in FIG. 3, it is an annular band having a triangular cross section. The corresponding annular concave portion also has a triangular cross section, and the annular step portion 4a of the lower sleeve member 4 and the annular step portion 5a of the upper sleeve member 5 that form the concave portion also have a triangular cross section. . Thus, when the dynamic pressure bearing is stopped, the lower surface of the annular convex portion 3a is seated on the upper surface of the annular step portion 4a of the lower sleeve member 4 with a smaller contact area than in the first embodiment. . As a result, the entire lower conical surface of the conical shaft member 1 comes into contact with the receiving surface of the lower sleeve member 4 at the time of stoppage, and the stationary state in the fitted state is reliably prevented.

Next, a method of manufacturing the conical shaft member 1 by resin molding will be described. The mold used for the production has a lower mold having a predetermined inner surface shape on which a ridge for forming a thrust dynamic pressure generating groove is formed and a lower mold having a predetermined inner surface on which a ridge for forming a radial dynamic pressure generating groove is formed. Type. First, the metal core material 2 is positioned on the lower mold, and the upper mold is disposed thereon, and is charged into the mold. Then, the weighed liquid crystal polymer material is filled into the mold from the filling port of the upper mold. Next, the mold in this state is set on a press machine, and the resin of the liquid crystal polymer material melted by heating and pressing is poured into a gap between the mold and the metal core material 2 by a plunger. After the molten resin of the liquid crystal polymer material has been poured, the upper mold is opened and the product is taken out of the mold. Since the ridges for forming the dynamic pressure generating grooves are formed in the upper mold, the product taken out of the mold has a resin portion of a predetermined shape formed in the metal core material 2 and the dynamic pressure generating grooves G are formed of resin. A member integrally formed at a predetermined position of the portion, that is, a shaft member with a resin flange. Sleeve members 4 and 5
Is also manufactured by resin molding. In addition, the resin molding process of the resin bearing component according to the present invention is not limited to compression molding, and any method of transfer molding, injection molding, and injection compression molding can be used.

The liquid crystal polymer material is a polymer starting from a polymer of polyhydroxybenzoic acid, bisphenol and terephthalic acid, a polymer starting from polyhydroxybenzoic acid and 6-hydroxynaphthoic acid, or It was selected from polymers using polyethylene terephthalate and polyhydroxybenzoic acid as starting materials. Materials that can be used in addition to these liquid crystal polymer materials include wholly aromatic polyimide resins, polyamideimide resins, polyphthalamide resins, polyetherimide resins, polyimide resins, PEEK resins, polyketone resins, and fluorine-based resins. Also, these resins alone or resin matrix, carbon,
Liquid crystal polymer materials including inorganic fillers such as graphite and silicon dioxide, and reinforcing fibers such as whiskers, carbon fiber, and glass fiber can also be used.

Three samples of the conical fluid dynamic bearing according to the present invention described in detail above were manufactured, and their performances were examined. The results are shown below. The first sample is a conical fluid dynamic bearing with a maximum diameter of 7 mm and a cone apex angle of 35 degrees.
The second sample has a maximum diameter of 7 mm and a cone apex of 4 mm.
The 5 degree conical fluid dynamic bearing, and the third sample is a conical fluid dynamic bearing having a maximum diameter of 7 mm and a cone apex angle of 60 degrees. The dynamic pressure generating groove has a groove angle of 18 degrees and a groove depth of 6μ.
m, a herringbone groove having a groove width ratio of 0.5. The clearance on one side (perpendicular to the side) was 3.5 μm. The conical shaft member 1 was manufactured by injection molding a mixture of a liquid crystal polymer material and quartz beads having a diameter of 5 μm around a stainless steel cylinder. Note that an ester-based synthetic oil was used as the lubricating oil. The above three liquid dynamic pressure bearings are rotated at 50 rpm.
When rotated at 00 rpm, the axial and radial loads were 90 g and 80 g for the first sample, 95 g and 50 g for the second sample, and 105 g for the third sample.
g and 30 g. As described above, according to the present invention, various fluid dynamic bearings can be provided by freely selecting the axial load and the radial load.

[0023]

In the conical fluid dynamic bearing according to the present invention, the conical shaft member and the sleeve member, which are the main components thereof, have a structure that can be easily manufactured by resin processing. It became possible. Also,
The conical fluid dynamic bearing according to the present invention includes a spindle-shaped conical shaft member and a sleeve member for receiving the conical shaft member as main constituent members. Became difficult to occur.

A conical fluid dynamic bearing having the above-mentioned effects and a functional characteristic of being able to support two loads, a radial load and an axial load, is most suitable as a bearing for a small spindle motor. Therefore, the spindle motor provided with the conical fluid dynamic bearing according to the present invention can be further reduced in size and thickness, and the hard disk drive device using the spindle motor as a driving source of the rotating body can be reduced in thickness. Was.

In the present invention, the lower surface of the annular convex portion provided near the maximum diameter portion of the conical shaft member is seated on the upper surface of the annular concave portion provided at the opposing portion of the sleeve member during stop. As a result, the conical shaft member does not stop in a state of being fitted into the sleeve member. Therefore, a large load does not occur at the time of starting and stopping, and the starting cannot be prevented.
Therefore, the spindle motor provided with the conical fluid dynamic pressure bearing according to the present invention starts smooth rotation even when the motor is started, and the friction of the bearing is suppressed, so that a long life can be realized.

[Brief description of the drawings]

FIG. 1 is a sectional view of an embodiment of a spindle motor according to the present invention.

FIG. 2 is a sectional view of a first embodiment of a conical fluid dynamic pressure bearing according to the present invention, in which a gap and a dynamic pressure generating groove are exaggerated.

FIG. 3 is a sectional view of a second embodiment of the conical fluid dynamic pressure bearing according to the present invention, in which a gap and a dynamic pressure generating groove are exaggerated.

FIG. 4 is a sectional view of a conventional conical fluid dynamic pressure bearing.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Conical shaft member 2 Metal core material 3 Resin layer 3a Annular convex part 4 Lower sleeve member 4a Lower annular step part 4b Bottom part 5 Upper sleeve member 5a Upper annular step part 6 Cup-shaped hub 7 Rotor magnet 8 Stator coil 11 Conical type Shaft member 11a Tapered outer peripheral surface 12 Fixed shaft 13 Sleeve 13a Tapered inner peripheral surface 14, 15 Permanent magnet 16 Rotor magnet 17 Stator coil 18 Lower substrate 19 Upper substrate F Lubricating oil G Dynamic pressure generating grooves R1, R2, R3, R4 Small gap S Capillary seal

 ──────────────────────────────────────────────────続 き Continued on the front page (72) Inventor Yukien Hyobu 1-18-2 Nishiikebukuro, Toshima-ku, Tokyo F-term in Kakizaki Manufacturing Co., Ltd. (reference) 3J011 AA04 BA11 CA02 SC01 5H607 AA03 BB01 BB17 BB25 DD03 EE10 GG12 KK07

Claims (6)

[Claims] 1. A conical shaft member having a spindle shape in which a resin layer is applied to a metal core material and a sleeve member in which the conical shaft member is rotatably fitted, and wherein the conical member forms a bearing gap. A conical fluid dynamic bearing in which a dynamic pressure generating groove is formed on one of a tapered outer peripheral surface of a shaft member and a tapered inner peripheral surface of the sleeve member. 2. An annular convex portion is provided in the vicinity of a maximum diameter portion of the spindle-shaped conical shaft member, and an annular concave portion is provided in a portion of the sleeve member opposed to the annular convex portion. 2. A conical fluid dynamic bearing according to claim 1, wherein said bearing is seated on an upper surface of said annular recess. 3. The conical fluid dynamic bearing according to claim 1, wherein said conical shaft member and said sleeve member are manufactured by molding a resin material. 4. The conical fluid according to claim 1, wherein the resin material of the resin layer of the conical shaft member and the resin material of the sleeve member have the same linear expansion coefficient or the former is larger than the latter. Dynamic pressure bearing. 5. The conical fluid dynamic pressure bearing according to claim 1, wherein the resin material of said resin layer is a liquid crystal polymer material. 6. A spindle motor wherein a rotor is rotatably supported on a stator by the conical fluid dynamic bearing of claim 1.