JP2000149395A - Magnetic disk device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To reduce the dimensional change in an axial direction by constituting a thrust bearing while using one end of a rotary shaft as a pivot bearing having a spherical shape and also reducing the surface pressure of the sliding surface while allowing the radius of curvature of this sphericality to have a specific dimension and applying a ceramic coating on the sliding surface to enhance wear resistance of the pivot bearing. SOLUTION: A sealing ring 7, dynamic pressure radial bearings 2, a permanent magnet 3 which is to be provided between dynamic pressure bearings, a stopper ring 16 and a thrust bearing 5 are arranged from the side of opening part of a bearing housing 6 and along a rotary shaft 1. Magnetic fluid for lubrication 4 is sealed among the rotary shaft 1, the radial bearings 2 and the thrust bearing 5. A ceramic film 27 is applied on the surface of the thrust bearing 5 (the range of diameters of the shaft is 2 mm to 5 mm). The top end of the rotary shaft 1 which supports the thrust loading in the axial direction is made in a spherical shape (the radius of curvature of the curved surface is 10 mm to 50 mm) and constitutes a pivot bearing. Moreover, the stopper ring 16 is arranged at the part of a groove to be provided in the shaft 1 between the thrust bearing 5 and the radial bearing 2.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a magnetic disk drive, and more particularly to a magnetic disk drive using a dynamic pressure sliding bearing device suitable for precision and high-speed rotation.

[0002]

2. Description of the Related Art With the remarkable spread of personal computers, magnetic disks have been increasing in recording density and capacity, and have been reduced in size and speed. Magnetic disk drives used for this purpose are increasingly required to have high speed, high precision rotation and low cost. Conventionally, ball bearings have been used in motors for magnetic disk drives, and rotational accuracy has been improved by improving processing accuracy, lubrication, and the like.

[0003] The ball bearing has a limitation in improving the machining accuracy, the rotational accuracy is inevitably degraded due to the abrasion of the rolling surface, and the ball bearing has a small diameter in order to cope with the miniaturization of the device. When the motor is used, there is a limit in increasing the recording density because the inner and outer races are likely to be deformed during the assembly of the motor. For this reason, in recent years, in response to the increase in density of magnetic disk drives, Japanese Patent Laid-Open No. 6-189489 discloses a motor equipped with a dynamic pressure sliding bearing as a bearing in place of a ball bearing.
No. 6,086,045.

[0004]

The above-mentioned magnetic disk drive incorporates a disk drive motor as a storage device for a desktop or notebook personal computer. Therefore, as described above, in addition to high speed and rotational accuracy, handling is required, that is, impact resistance is required so that the device does not fall down on a desk or while being carried, thereby impairing the function as a magnetic disk device. Regarding the impact resistance, a large impact such as 1000 G sometimes acts on the magnetic disk device.

[0005] When such a large impact acts, the magnetic disk drive may have a reduced strength of components and a change in dimensional accuracy, resulting in a loss of function. In addition, a notebook-type personal computer requires a disk drive with low power consumption in terms of battery drive.

In the bearing device disclosed above, a groove bearing having a shallow groove for generating a dynamic pressure is used as a thrust bearing for supporting an axial load on a surface receiving the thrust load in the same manner as a radial bearing. Since the groove type thrust bearing receives a thrust load on the shaft end face and the bearing end face, the bearing loss is large as compared with the ball bearing method, and there is a limit in reducing power consumption.

Further, in the groove type dynamic pressure radial bearing unit, if the supply of the lubricating fluid to the bearing surface is not complete, an insufficient oil vibration occurs, and precise rotation cannot be obtained. Further, the impact resistance required for the motor, that is, the bearing may be deformed when an impact load (1000 G in acceleration) acts. In particular, a ball bearing has no impact resistance because of a rolling mechanism by point contact, but a sliding bearing has excellent impact resistance because of a supporting mechanism by surface contact.

[0008] However, among the plain bearings, the dynamic pressure type groove bearing has a groove for generating dynamic pressure of about several microns, and when the groove is deformed by an impact load, sufficient dynamic pressure cannot be generated, and the groove is unstable. This may cause excessive vibration or decrease the load supporting capacity of the thrust bearing portion, causing wear. Pivot bearings with a spherical surface at the tip of the shaft are plain bearings with point contact like ball bearings, so when such a large impact load is applied, the bearing surface is concavely deformed and the axial dimension is, for example, 10 μm or more. If it changes, the magnetic head arm may come into contact with the outer peripheral portion of the magnetic disk.

An object of the present invention has been made in view of such disadvantages of the prior art, and an object of the present invention is to provide a low-cost, low-cost spherical pivot bearing which is excellent in impact resistance, wear resistance and mass productivity. An object of the present invention is to provide a highly reliable magnetic disk device capable of minimizing an axial dimensional change by providing the magnetic disk device.

[0010]

According to the present invention, as a means for the above-mentioned object, a thrust bearing as a pivot bearing is formed by making one end of a rotating shaft into a spherical shape with respect to an impact load applied to a disk drive from the outside. With this configuration, the radius of curvature of the spherical surface is set to an appropriate size to reduce the surface pressure on the sliding surface and reduce the load deformation. In addition, since a pivot bearing cannot be expected to form an oil film on a sliding surface as compared with a groove bearing and cannot avoid abrasion, at least one of the sliding parts is made of titanium carbide (TiN) or titanium nitride (Ti).
The wear resistance is improved by applying the ceramic coating of C).

Further, a plastic load is applied to the thrust receiving surface on the stationary side by applying a load 10 times or more the impact load in advance so that the thrust receiving surface is hardly deformed even when the impact load is applied. Further, the wear resistance of the shaft is improved by improving the surface roughness by plastic working of the thrust receiving surface.

[0012]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a longitudinal sectional view of a magnetic disk drive showing one embodiment of the present invention. In FIG.
The housing 24 of the magnetic disk drive includes a casing 15 and a casing cover 20. In this figure, the above-mentioned parts are partially omitted. A motor (spindle motor) 25 for driving the magnetic disk 13 is disposed in the housing 24. The drive motor 25 includes a multi-pole magnetized permanent magnet 10 provided on the inner periphery of the cup-shaped hub 11, an armature winding 9 and an armature core 8 for generating a magnetic field provided on the casing 15 side. It is composed of That is, the armature core 8 is fitted to the projecting portion of the casing 15.

The bearing device comprises a seal ring 7, a dynamic pressure radial bearing 2, a permanent magnet 3 provided between the dynamic pressure bearings, a stopper ring 16, and a thrust bearing 5 from the opening side (upper side in the drawing) of the bearing housing 6. It is arranged along the rotation axis 1. Further, a lubricating magnetic fluid 4 is sealed between the rotary shaft 1 and the radial bearing 2 and the thrust bearing 5.

The rotating shaft 1 press-fitted to the hub 11 is rotatably supported by dynamic pressure radial bearings 2 provided at both ends of a permanent magnet 3 for holding a magnetic fluid 4 in a bearing housing 6. In addition, stainless steel (for example, SUS420) having a ceramic coating film 27 on the thrust bearing surface
J2 and SUS440C) thrust bearings 5 are arranged, and the tip of the rotating shaft 1 receiving an axial thrust load is formed into a spherical shape as a pivot bearing so that these bearings can be rotatably supported. I have. Further, the magnetic disk clamper 18 is rotated by the bolt 19 with the rotating shaft 1.
And the hub 11. Further, the stopper ring 16 sandwiched between the thrust bearing 5 and the radial bearing 2 is disposed in the groove 26 provided in the rotating shaft 1, so that the rotating shaft 1 does not come off in the axial direction.

A plurality of magnetic disks 13 are mounted on the outer periphery of the hub 11 at predetermined intervals by spacers 14, and the uppermost portion is fixed by a magnetic disk clamper 18.

FIG. 2 is a partial cross-sectional view of the pivot thrust bearing. The shaft diameter D of a spindle motor for a magnetic disk drive often has a dimension of φ5 mm or less from the viewpoint of low power consumption of the motor, and when a plain bearing is used, D = φ3.
A shaft with dimensions of mm is used. Further, the radius of curvature R of the spherical surface of the pivot axis is R = 3 mm or R = D = φ3 mm.
A shaft having a size of 4 mm is used, and a shaft having a larger radius of curvature is not commercially available. Usually, D = φ3mm,
A shaft of R = 4 mm is used.

With this dimension, for example, an impact force of 10
When 00G acts, a load of 30 kgf acts on the thrust receiving portion even if the weight of the rotating body is at most 30 gr. Therefore, when a load of 30 kgf acts on the thrust bearing, the surface pressure at the pivot contact portion becomes 380 kg / mm ² , and deformation of at least several μm occurs. Also, as a material of the thrust bearing, a copper alloy is usually used in many cases, but in consideration of such an impact load, in the present invention, the deformation is reduced by using a stainless alloy having a larger longitudinal elastic coefficient than the copper alloy. I have.

Further, in order to suppress the axial displacement of the rotating body in the thrust bearing 5, the magnetic center of the permanent magnet 10 and the magnetic center of the armature 8 are shifted in addition to the weight of the rotating body so as to attract magnetically. The force acts between 100 grf and 200 grf.

[0019] Therefore, the sliding surface pressure becomes 54kg / mm ² ~68kg / mm ² in dimensions of the shaft 1 as described above, the thrust bearing surface occurs abrasion of several tens μm in about 100 hours Experimental results I understood. Abrasion-resistant surface treatment is effective in reducing this abrasion. However, as a result of an abrasion test using a combination of a magnetic fluid and various surface treatments, as shown in FIG. 3, the ceramic-coated TiN film or TiC film has excellent abrasion resistance. I knew it was. Further, the ceramic coating may be peeled off when an impact load as described above is applied.

To prevent this, it is necessary to reduce the surface pressure of the thrust receiving surface. Therefore, in the present invention, the radius of curvature R of the pivot is set to R = 10 mm to R = 50 mm and the surface pressure is set to 1
94kg / mm ² ~67kg / mm ² to reduce the handles several μm of TiN or TiC layer as the ceramic coating 27 on the thrust bearing surface improves the impact resistance, and improved wear resistance by a surface pressure reducing Let me.

In this case, if the radius of curvature R is made larger than R = 50 mm, not only the loss of the thrust bearing increases, but also when the magnetic fluid is used, the heat resistance of the magnetic fluid (allowable value of about 100 ° C.) , The magnetic fluid may be thermally degraded. For this reason, in the present invention, the radius of curvature R of the pivot is set from R = 10 mm to R = 5.
0 mm.

By the way, the shaft 1 is usually made of SUS420J2 or SUS440C and hardened by HV750 to HV80.
However, the hardness of the ceramic coating film TiN is around HV2300 and the hardness of TiC is around HV2900. 1 wears prematurely. Usually, grinding is performed to form a submicron or sub-micron surface, or lapping is performed after grinding to produce the required surface roughness. However, a thrust bearing having such a shape is difficult to grind.

Therefore, in the present invention, as shown in FIG. 4, for example, the end surface 28a of a jig 28 made of WC is made to have a surface roughness of about 0.05 μm, and the jig 28 is thrusted with a load of several hundred kg or more. The thrust receiving surface of the bearing 5 is pressed to form a submicron or submicron surface by plastic working. That is, when the thrust receiving surface is pressed by such a method, the thrust receiving surface becomes a smooth surface similar to the surface of the jig as shown in FIG. The thrust bearing of the present invention is coated with a ceramic coating after the thrust bearing surface is smoothed by such a method.

The wear of the shaft 1 can also be reduced by applying a ceramic-coated TiN or TiC film 27 to a part of the spherical surface as shown in FIG. In this case, the combination of sliding between the ceramic coatings effective for abrasion resistance is T
A combination of an iN film and a TiC film is preferable.

The above-described processing method and surface treatment method are techniques for mass production. When the present invention is applied to a magnetic disk drive requiring mass production, it is effective for improving reliability, reducing power consumption, and reducing cost. is there.

[0026]

In the magnetic disk drive according to the present invention, as described above, a low-loss pivot bearing is used as the slide bearing device, and the radius of curvature of the pivot shaft is set to be larger than that of the conventional R = 3 mm or R = 4 mm. = 10mm-R = 50
mm, the impact resistance can be greatly improved, and ceramic coating TiN or Ti is applied to the stationary thrust bearing that slides with the pivot shaft.
Since C is treated to improve the wear resistance, the dimensional change in the axial direction can be suppressed minutely, and the reliability of the magnetic disk drive can be improved. Further, according to the present invention, a mass-produced, low-cost magnetic disk drive can be provided because a slide bearing device using a pivot bearing that can cope with mass productivity and cost reduction is used.

[Brief description of the drawings]

FIG. 1 is a partial longitudinal sectional view of a magnetic disk drive of the present invention.

FIG. 2 is a partial longitudinal sectional view showing the structure of the pivot bearing of the present invention.

FIG. 3 is a characteristic diagram showing wear characteristics of the present invention.

FIG. 4 is an explanatory view of a plastic working method for a thrust bearing according to the present invention.

FIG. 5 is a characteristic diagram showing surface roughness before and after plastic working according to the present invention.

FIG. 6 is a partial longitudinal sectional view showing a ceramic coating of the pivot bearing of the present invention.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... shaft, 2 ... radial bearing, 3 ... permanent magnet, 4 ... magnetic fluid, 5 ... thrust bearing, 6 ... bearing housing, 7 ... seal ring, 8 ... armature core, 9 ... armature winding, 10 ... drive Magnet, 11 hub, 13 magnetic disk, 14 spacer, 15 casing, 16 stopper ring, 1
8 clamper, 19 bolt, 20 casing cover, 24 housing, 25 driving motor, 26 groove, 27
... ceramic coating, 28 ... jig, 28a ... jig end face.

──────────────────────────────────────────────────の Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat ゛ (Reference) H02K 5/167 H02K 5/167 B 7/08 7/08 A (72) Inventor Masaru Muranishi Tsuchiura, Ibaraki 502 Kandatecho, Machinery Research Laboratory, Hitachi, Ltd. No. 2520, Hitachi, Ltd. Automotive Equipment Division (72) Inventor Kenji Tomita 2880, Kofu, Odawara-shi, Kanagawa Prefecture F-term (Reference) 3J011 AA02 BA02 BA10 CA02 CA05 PA02 QA04 SC20 SD01 5D109 BB01 BB12 BB17 BB21 BB23 BB27 BB40 5H605 BB05 BB19 CC01 CC02 CC04 CC05 DD03 EB02 EB07 GG06 GG10 5H607 AA00 BB01 BB14 CC01 DD02 DD03 DD09 DD16 FF01 GG01 GG02 GG12 GG19 JJ05

Claims (1)

[Claims] 1. A magnetic disk drive comprising: a magnetic disk on which information is recorded / reproduced; a housing comprising a casing and a casing cover; and a spindle motor for driving the magnetic disk in the housing. A radial bearing and a thrust bearing are arranged in a housing, and a bearing device for rotatably supporting the rotating shaft with a lubricating fluid interposed between the rotating shaft and the bearing is provided. The diameter of the rotating shaft is D = 2 mm. A magnetic disk device having a dimension range of D = 5 mm, a spindle motor having a spherical surface at one end receiving a thrust load and having a radius of curvature of R = 10 mm to R = 50 mm.