JP2001140863A - Fluid bearing motor for disk - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a fluid bearing motor for a disk having a shaft and a hub separately to facilitate manufacture, capable of improving the fastening strength of the shaft and the hub, and having large moment yield strength. SOLUTION: The shaft 3 fastened at one end to the hub 4 mounted with the disk is supported and rotatively driven by a sleeve 2 via a radial fluid bearing R and a thrust bearing S in this fluid bearing motor. The shaft diameter of a portion 3a fastened to the hub 4 is made larger than the shaft diameter of a portion supported by the radial fluid bearing R. The fastening strength can be increased, the release load of the shaft 3 against the hub 4 is increased, the bearing span Lp between two radial fluid bearings R, R can be secured, and large moment yield strength is obtained. The perpendicularity between the shaft 3 and the hub 4 can be easily secured, and the deflection precision of the disk mount face of the hub 4 is improved.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an information device,
BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a fluid bearing motor for rotating a magnetic disk or an optical disk of a video device or the like, and more particularly, to a fluid bearing motor for a disk in which the deflection accuracy of a disk mounting surface is improved to improve reliability.

[0002]

2. Description of the Related Art FIG. 2 is a sectional view of a conventional HDD spindle motor, which is a fluid bearing motor for a disk in an early stage of development. The hub 1 is attached to the fastening portion 100a at one end of the rotating shaft 100.
10 are integrally fastened, and a disc (not shown) is mounted on the outer periphery of the hub 110. A sleeve 120 having a cylindrical hole in the center is attached to the shaft 10.
0 and fixed to the base 130.

[0003] The sleeve 120 has radial bearing surfaces 120r at two locations above and below the inner peripheral surface of the cylindrical hole, and has a thrust bearing surface 123s on the upper surface of a counter plate 123 which is attached so as to close the bottom of the cylindrical hole. Have. The shaft 100 has the radial bearing surface 120 on its outer peripheral surface.
and two radial receiving surfaces 100r opposed to each other with a small gap therebetween, and a thrust receiving surface opposed to the thrust bearing surface 123r via a small gap on the lower surface of the flange-shaped thrust plate 103 attached to the lower end. 103s.

[0004] At least one of the opposed radial bearing surface 120r and the radial receiving surface 100r (in the figure, the radial receiving surface 100r) is provided with a groove m for generating dynamic pressure to constitute two upper and lower radial fluid bearings R. At least one of the opposed thrust bearing surface 123s and the thrust receiving surface 103s is provided with a groove for generating dynamic pressure (not shown) to form a thrust fluid bearing S, and both fluid bearings are filled with a lubricant such as oil. ing.

[0005] Rotor magnet 1 fixed to the inner periphery of hub 110
40 and a motor M composed of a stator 141 fixed to the base 130 and disposed on the base 130 so as to face the peripheral surface thereof.
The shaft 100 and the hub 110 are driven to rotate integrally. By the rotation, the lubricating fluid is automatically supplied to the thrust fluid bearing S and the radial fluid bearing R by the pumping action of the groove for generating the dynamic pressure, and the dynamic pressure is generated respectively, and the shaft 100 and the hub 110 float integrally. Then, it is supported by the sleeve 120 in a non-contact manner.

[0006]

In recent years, magnetic disk drives for mobile devices have been required to be increasingly thinner and more resistant to rocking and external impact. In order to meet such demands, it is necessary to increase the moment resistance during swing while suppressing the motor height. In order to increase the moment resistance, the bearing span Lp between the two upper and lower radial fluid bearings R, R is preferably as wide as possible. However, if the bearing span Lp is to be widened within a limited motor height range, it is difficult to increase the axial length of the fastening portion between the shaft and the hub, and the fastening strength between the shaft and the hub is weak. Become. Conversely, if the fastening strength between the shaft and the hub is lengthened in the axial direction to increase the fastening strength, the bearing span Lp becomes narrower, and the swing resistance and the impact resistance are reduced. There was a problem.

Here, it is conceivable to integrally manufacture the shaft and the hub. However, since the hub material is usually made of difficult-to-cut stainless steel, the integrated processing is performed at a limited cost. Therefore, it is difficult to secure a predetermined dimensional accuracy. Although an aluminum alloy can be used for the hub material, the aluminum alloy is liable to be scratched on the surface, and thus the start / stop durability of the radial fluid bearing may be impaired. In any case, it was practically difficult to integrate the shaft and the hub.

Accordingly, the present invention has been made in view of such an unsolved problem of the conventional fluid dynamic bearing motor for a disk, and has a structure in which the shaft and the hub are separated from each other while the fastening strength between the shaft and the hub is reduced. It is an object of the present invention to provide a disk hydrodynamic bearing motor that can be improved and has a large moment proof strength.

[0009]

In order to achieve the above object, the invention according to claim 1 is characterized in that a shaft having a hub on which a disc is mounted is fastened to one end of a hub via a radial fluid bearing and a thrust bearing. In a fluid bearing motor supported and driven to rotate, a shaft diameter of a portion to be fastened to the hub is larger than a shaft diameter of a portion supported by the radial fluid bearing.

According to the hydrodynamic bearing motor of the present invention, since the shaft diameter of the portion to be fastened to the hub is larger than the shaft diameter of the portion supported by the radial fluid bearing, the axial length of the fastening portion between the shaft and the hub is increased. Therefore, it is possible to increase the fastening strength between the shaft and the hub while securing the bearing span while keeping the motor height low without increasing the motor height. That is, since the shaft diameter is large, the fixing area between the shaft and the hub can be increased, and as a result, the load of the shaft coming off from the hub can be increased and the fastening strength can be improved. Further, since the bearing span can be widened, the moment resistance is large, and the oscillation resistance and the impact resistance are guaranteed.

Further, since the shaft diameter of the hub fastening portion is increased, a perpendicularity between the shaft and the hub is easily secured, and the runout accuracy of the disk mounting surface of the hub is improved.

[0012]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a sectional view of a fluid dynamic bearing motor for a disk according to the present invention. First, the structure will be described. The sleeve 2 is fixed to the base 1. The sleeve 2 has a cup-shaped outer sleeve 2a and a flanged cylindrical inner sleeve 2 integrally fixed to the upper end thereof.
b is formed in a double structure.

On the other hand, the shaft 3 is provided with a thick fastening portion 3a whose diameter is increased stepwise at the upper end thereof, and the shaft 3 is fastened and integrated with the shallow inverted cup-shaped hub 4 at the fastening portion 3a. The fastening means is not limited to press-fitting, but means such as press-fitting and bonding, press-fitting and caulking or welding may be employed. The shaft diameter of the shaft extension 3b below the fastening portion 3a is smaller than that of the fastening portion 3a. For example, when the outer diameter of the hub 4 is about 20 mm, the shaft diameter of the fastening portion 3a is preferably 4 mm or more to secure the fastening strength, while the shaft diameter of the shaft extension 3b is the friction of the radial fluid bearing portion R described later. It is preferably less than 4 mm to reduce the loss.

The shaft extension 3b is inserted into the inner sleeve 2b and penetrated therethrough. A disk-shaped thrust plate 6 is press-fitted and fixed to the protruding lower end of the shaft. Both upper and lower planes of the thrust plate 6 are formed as a thrust receiving surface 6s, and a lower end surface of the inner sleeve 2b opposed to the upper thrust receiving surface 6s and a bottom surface of the outer sleeve 2a opposed to the lower surface thrust receiving surface 6s are formed. , The thrust bearing surfaces 2bs and 2 respectively
The thrust fluid bearing S is provided with at least one of the opposed thrust receiving surface and the thrust bearing surface, for example, a herringbone-shaped dynamic pressure generating groove (not shown).

A pair of upper and lower radial receiving surfaces 3r are formed on the outer peripheral surface of the extension 3b of the shaft 3 at an interval in the axial direction, and a radial bearing surface 2r facing the radial receiving surface 3r is formed inside. It is formed on the inner peripheral surface of the sleeve 2b, and includes at least one of a radial receiving surface and a radial bearing surface (in the radial receiving surface 3r in the figure), for example, a herringbone-shaped dynamic pressure generating groove m, and includes two grooves. The radial fluid bearings R, R are configured. In order to increase the bearing span Lp while securing the radial load capacity of the radial fluid bearing R, the value of the ratio (B / D) between the groove width B of the dynamic pressure generating groove m and the shaft diameter D in each radial fluid bearing R is required. Is preferably 0.7 or less, preferably 0.5 or less. On the other hand, in order to prevent whirl, which is an unstable phenomenon of the fluid bearing, from easily occurring, the value is preferably 0.2 or more.

In the sleeve 2 having the inner / outer double structure,
An annular clearance is provided between the inner sleeve 2b and the outer sleeve 2a, and forms a lubricant reservoir 9. The lubricant reservoir 9 has a gap 9a at the lower end serving as a lubricant supply passage 10 and is opened between the thrust fluid bearing S and the radial fluid bearing R. The gap 9a forming the lubricant supply passage 10 has a size of an opening portion,
The lubricant is held by a capillary action based on surface tension so as to be equal to or slightly larger than the bearing clearance of each fluid bearing. On the other hand, the upper end side of the lubricant reservoir 9 is closed by a flange of the inner sleeve 2b, and is provided with an air vent hole 11 penetrating the flange to communicate with the outside.

The outer sleeve 2 surrounding the lubricant reservoir 9
By forming the inner peripheral surface 2an of a into a tapered shape,
The lubricant reservoir 9 is gradually narrowed toward the lubricant supply passage, thereby facilitating the lubricant supply. However, the tapered surface is not necessarily the inner peripheral surface 2 of the outer sleeve 2a.
an, and may be formed on the outer peripheral surface 2bg of the inner sleeve 2b, or may be formed on the outer sleeve 2b.
a and the outer peripheral surface of the inner sleeve 2b.

A stator 12 fixed to the outer periphery of the base 1 and a rotor magnet fixed to the inner surface of the hub 4 for rotating the inverted cup-shaped hub 4 on which a magnetic disk (not shown) as a rotating body is mounted. 13 is mounted. Here, the material of the components in the fluid dynamic bearing motor for a disk of the present invention will be described. For example, in order to prevent the disk mounted on the hub 4 from moving in the radial direction due to a change in the ambient temperature, the line between the hub 4 and the disk is It is desirable that the expansion coefficients be approximately the same. On the other hand, in order to reduce the load capacity of the hydrodynamic bearing at high temperatures,
It is desirable that the linear expansion coefficient of the shaft 3 and the sleeve 2 be substantially equal or the linear expansion coefficient of the shaft 3 be larger than that of the sleeve 2. Further, it is necessary to improve the dimensional accuracy of the outer peripheral surface of the shaft 2 constituting the radial fluid bearing portion R, and a shaft material having good cutting workability is desired. Shaft 3 material and inner sleeve 2b
The material of the outer sleeve 2a is stainless steel S
US303, SUS304, SUS420, SUS4
30F, a copper-based material, an aluminum alloy, a ceramic, a resin, and the like can be considered, and these are used in appropriate combination. Also,
If necessary, the bearing surface may be plated or coated. The material of the hub 4 is stainless steel SUS430
F or an aluminum alloy is selected according to the coefficient of linear expansion of the disk material. It is preferable that the shaft 3 is hardened by heat treatment in order to increase the surface hardness. However, if necessary, the heat treatment can be omitted for cost reduction.

Next, the operation will be described. In the disk fluid bearing motor of the present invention, since the shaft diameter of the fastening portion 3a between the shaft 3 and the hub 4 is larger than the shaft diameter of the radial fluid bearing portion R, the axial length of the fastening portion 3a Can be increased without making the length particularly long. That is, since the fastening area between the shaft 3 and the hub 4 can be increased, the load of the shaft 3 coming off the hub 4 increases. In addition, by increasing the diameter of the shaft of the fastening portion 3a, it is easy to secure a perpendicularity between the shaft 3 and the hub 4, and the deflection accuracy of the disk mounting surface of the hub 4 is improved. Further, the bearing span Lp of the two radial fluid bearings R, R can be ensured, the moment resistance is increased, and excellent oscillation resistance and impact resistance are obtained.

An example of a procedure for assembling the spindle motor having the above-described configuration will be described. A predetermined amount of lubricant is poured into the bottom of the cup-shaped outer sleeve 2a in advance. Next, the thrust plate 6 is placed flat on the bottom of the outer sleeve 2a, and then the inner sleeve 2b is assembled. Then, the tip of the shaft 3 integrated with the hub 4 is pressed into the thrust plate 6 and fixed.

When the shaft 3 is inserted, the lubricant at the bottom is filled in the bearing clearances of the thrust fluid bearing S and the radial fluid bearing R, and at the same time, is also accumulated in the lubricant reservoir 9 via the lubricant supply passage 10. . At the time of this assembling, there is a possibility that the air entrapped in the lubricant becomes air bubbles and enters the lubricant. However, in the case of the present embodiment, since the bearing gap communicates with the lubricant reservoir 9, the air in the bearing clearance space is pushed out toward the lubricant reservoir 9 having a larger volume, and is discharged from the air vent hole 11 to the outside. As a result, the air bubbles are entrapped and the amount of air bubbles in the lubricant is small. Further, the entrained lubricant bubbles are also discharged to the outside from above the radial fluid bearing R, while most are separated in the lubricant reservoir 9 and discharged to the outside from the upper air vent hole 11. Therefore,
During transportation or use of the fluid bearing motor, it is possible to prevent the bubbles in the lubricant from expanding and pushing out the lubricant in the bearing clearance to the outside, thereby causing a shortage of the lubricant.

As described above, since the lubricant reservoir 9 holding the replenishing lubricant has the function of separating and discharging air bubbles,
The assembly work of the hydrodynamic bearing motor of the present invention can be performed in the atmosphere. In addition, since the thrust plate 6 press-fitted and fixed to one end of the shaft 3 has a function of preventing the shaft 3 from coming off, there is no possibility that the shaft 3 will come off the sleeve 2 due to an external impact during transportation or use. Of course, the assembling method need not be limited to the above.

When the shaft 3 and the hub 4 are integrally driven to rotate by the motor M, dynamic pressure is generated by the pumping action in the lubricant filled in the bearing clearances of the thrust fluid bearing S and the radial fluid bearing R. Thus, the shaft 3 and the hub 4 are supported without contact with the sleeve 2 and the thrust plate 6. If the lubricant retained in the bearing clearance gradually decreases due to evaporation and scattering during rotation for a long period of operation and becomes insufficient, the lubricant in the lubricant reservoir 9 is tapered in accordance with the shortage. It is guided to the lubricant supply passage 10 while being guided by the surface 2an, and is sucked by capillary action between the bearing gaps having a narrow clearance communicating therewith. Then, the lubricant is stabilized at a position where the surface tension of the lubricant surface in the lubricant reservoir 9 is balanced.

In the present embodiment, since the clearance of the lubricant reservoir 9 is tapered, the lubricant is sucked by the surface tension to the narrower one, while the residual air bubbles entrained at the time of assembly are removed by the larger one. Separated and discharged. Therefore, a lubricant free of air bubbles is automatically and reliably replenished by the reduced amount of the lubricant, and the inside of the bearing clearance is always filled with the lubricant. As a result, a highly durable and highly reliable fluid bearing motor is obtained. The effect is that it can be done. Further, since the lubricant reservoir is tapered, even if the fluid bearing motor is inverted during transportation or use, the retained excess lubricant can be prevented from flowing out. Further, the provision of the lubricant reservoir 9 has a great practical advantage that the overall height of the hydrodynamic bearing motor can be reduced.

In the above-described embodiment, the non-contact rotary support type thrust fluid bearing S which is in non-contact at the rated rotation is used.
However, instead of the thrust fluid bearing, a contact type pivot bearing which is always in contact may be employed.

[0026]

As described above, according to the first aspect of the present invention, it is possible to improve the fastening strength between the shaft and the hub while keeping the shaft and the hub separate from each other for easy manufacture. In addition to this, there is an effect that the moment resistance is large and the squareness between the shaft and the hub is easily secured.

[Brief description of the drawings]

FIG. 1 is a cross-sectional view of a first embodiment of the present invention.

FIG. 2 is a sectional view of a conventional disk hydrodynamic bearing motor.

[Explanation of symbols]

 Reference Signs List 2 sleeve 2a outer sleeve 2b inner sleeve 3 shaft 3a fastening portion (with hub) 4 hub S thrust fluid bearing R radial fluid bearing

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Ikuki Sakatani 1-5-50 Kugenuma Shinmei, Fujisawa City, Kanagawa Prefecture Nippon Seiko Co., Ltd. (72) Inventor Katsuhiko Tanaka 1-50-50 Kugenuma Shinmei, Fujisawa City, Kanagawa Prefecture No. N-Seiko Co., Ltd. F-term (reference) 3J011 AA04 BA02 BA08 CA02 CA05 5H605 BB05 BB19 CC01 CC03 CC04 CC05 CC09 CC10 EB01 EB02 EB06 EB28 5H607 AA12 BB01 BB17 CC01 DD14 FF12 GG01 GG02 GG12 GG06 JJ06

Claims (1)

[Claims] In a fluid bearing motor in which a shaft having a disk mounting hub fastened to one end thereof is supported by a sleeve via a radial fluid bearing and a thrust bearing and is driven to rotate, a shaft diameter of a portion fastened to the hub is adjusted. A fluid bearing motor for a disk, wherein the shaft diameter of the portion supported by the radial fluid bearing is larger than the shaft diameter.