WO2000065591A1

WO2000065591A1 - Fluid bearing device and magnetic disk device using fluid bearing device

Info

Publication number: WO2000065591A1
Application number: PCT/JP2000/002561
Authority: WO
Inventors: Takumi Kawano
Original assignee: Matsushita Electric Industrial Co., Ltd.
Priority date: 1999-04-26
Filing date: 2000-04-20
Publication date: 2000-11-02
Also published as: TW515872B; JP2000310225A

Abstract

A fluid bearing device which fills a conductive lubricant (6) containing an electrostatic charge preventive agent in a bearing clearance between a bearing sleeve (2) (sleeve 2) and bearing shaft (3) (shaft 3), and a magnetic disk device using this fluid bearing device. This configuration enables to continuously discharge static electricity charged in the shaft (3), a rotary part, to the sleeve (2), a fixed part, through the conductive lubricant (6). Accordingly, electrostatic charge is not built up in the shaft (3), which is the rotary part, even at high speed rotation.

Description

DESCRIPTION

FLUID BEARING DEVICE AND MAGNETIC DISK DEVICE USING FLUID

BEARING DEVICE

FIELD OF THE INVENTION

The present invention relates to the field of dynamic pressure fluid bearing devices used typically in spindle motors for driving magnetic disks in magnetic disk devices, and magnetic disk devices employing this type of fluid bearing device. More particularly, the present invention relates to fluid bearing devices which prevent buildup of static electricity, which may occur at high rotation speeds, in rotary parts.

BACKGROUND OF THE INVENTION Fig. 5 shows a rotor shaft radial bearing and Fig. 6 shows a fixed shaft radial bearing as examples of conventional dynamic pressure fluid bearing devices.

First, the configuration and operation of the rotor shaft radial bearing is described with reference to Fig. 5. The rotor shaft radial bearing includes a bearing sleeve 2 (sleeve 2), bearing shaft 3 (shaft 3) having a dynamic pressure generating groove 4, and lubricant 7. The lubricant 7 is retained by capillary action in the bearing clearance between bearing faces of the sleeve 2 and shaft 3.

During operation of the rotor shaft radial bearing, the shaft 3 is rotated by a driver (not illustrated), and the shaft 3 separates from the sleeve 2 by dynamic pressure of the lubricant 7 generated by the dynamic pressure generating groove 4 when rotation starts. As rotation becomes faster, the dynamic pressure of the lubricant 7 also increases, and the shaft 3 becomes accurately centered against the sleeve 2. Subsequently, the shaft 3 rotates while completely separated from the sleeve 2 through the lubricant 7.

Next, the configuration and operation of the fixed shaft radial bearing is described with reference to Fig. 6. As in Fig. 5, the fixed shaft radial bearing includes the sleeve 2, shaft 3 having a dynamic pressure generating groove 4, and lubricant 7. The lubricant 7 is retained by capillary action in the bearing clearance between bearing faces of the sleeve 2 and shaft 3.

During operation of the fixed shaft radial bearing, the sleeve 2 is rotated by a driver (not illustrated), and the sleeve 2 separates from the shaft 3 by dynamic pressure of the lubricant 7 generated by the dynamic pressure generating groove 4 when rotation starts. As rotation becomes faster, the dynamic pressure of the lubricant 7 also increases, and the sleeve 2 becomes accurately centered against the shaft 3. Subsequently, the sleeve 2 rotates while completely separated from the shaft 3 through the lubricant 7.

During rotation, the shaft 3 and sleeve 2 do not contact through the lubricant 7 in either the rotor shaft or the fixed shaft fluid bearing devices. These conventional dynamic pressure fluid bearing devices use a mineral oil, synthetic hydrocarbon oil, or a non-conductive synthetic oil such as ester oil, silicone oil, or fluorocarbon oil as a lubricant.

In line with the rapid advancement of information recording apparatuses including magnetic disk devices that achieve higher speed and capacity, the development of fluid bearing devices used in spindle motors for driving magnetic disks also continues to advance to achieve further faster rotation and thus reduce access time. Consequently, a new technical problem which was not an issue previously has arisen, i.e., generation of static electricity on the fluid bearing device and magnetic disk.

The shaft or sleeve in a fluid bearing device rotates through a lubricant. Static electricity is generated in this rotary part due to the movement of the lubricant. Static electricity is also generated in mechanical parts, including the magnetic disk mounted on the rotary part due to friction with air. Buildup of electrostatic charge increases in proportion to speed of rotation. Since the conventional fluid bearing device has a shaft and sleeve which do not come into contact, and uses a lubricant made of a non-conductive material between the shaft and sleeve, electrostatic charge accumulated on the rotary part of the bearing and on the magnetic disk fixed onto the bearing has no path to allow grounding.

Accordingly, the electrostatic charge that accumulates on the rotary part of the bearing and magnetic disk is continuously at a risk of being unexpectedly discharged by some kind of trigger, making unstable electrical state. Discharge, when it occurs, may lead to erroneous operation such as erroneous data writing and reading, as well as physical damage to the magnetic disk or magnetic head.

SUMMARY OF THE INVENTION

A fluid bearing device of the present invention and a magnetic disk device using the fluid bearing of the present invention prevents generation of static electricity in rotary parts by the use of a conductive lubricant for filling a bearing clearance in a configuration of the fluid bearing device. This conductive lubricant enables to electrically connect the rotary and fixed parts to prevent buildup of electrostatic charge on rotary parts. In the fluid bearing device of the present invention, a bearing face provided on a bearing sleeve (sleeve) faces a bearing face provided on a bearing shaft (shaft) through a lubricant filled in a bearing clearance. At least one of the sleeve and shaft has a groove for generating dynamic pressure, and the sleeve and shaft are electrically connected through the lubricant. With this configuration, buildup of electrostatic charge on the shaft or sleeve is preventable by discharging static electricity generated in the shaft or sleeve to the sleeve or shaft through the lubricant. Accordingly, discharge of static electricity to a mechanical component mounted on the bearing device is preventable, enabling to realize a high speed rotation with stable electrical structure. The magnetic disk device of the present invention includes a fluid bearing device in which a bearing face provided on the sleeve faces a bearing face provided on the shaft through the lubricant filled in the bearing clearance, and at least one of the sleeve and shaft has a groove for generating dynamic pressure. The magnetic disk is fixed onto one of the shaft and sleeve of the fluid bearing device, and the magnetic disk is electrically connected to the sleeve and shaft through the lubricant. This configuration prevents electrostatic charge by releasing static electricity generated in the magnetic disk to the sleeve or shaft through the lubricant. Accordingly, stable performance of the magnetic disk device without causing static breakdown in the magnetic disk or magnetic head is realizable. The fluid bearing device and magnetic disk device of the present invention use the lubricant containing an electrostatic charge preventive agent. The use of the electrostatic charge preventive agent in the present invention enables to continuously give a certain conductivity to the lubricant, and thus secures a stable electrical path between the shaft and sleeve. Furthermore, the electrostatic charge preventive agent in the fluid bearing device and magnetic disk device of the present invention contains at least one of: organic compounds having a hydroxyl group; polyethers and their derivatives; esters and their derivatives; azoles and their derivatives; the quaternary ammonium salts and their derivatives; betaines; and carbon materials. The electrostatic charge preventive agent is selected and added to the lubricant based on the type of base oil of the lubricant for efficiently exhibiting conductivity.

BRIEF DESCRIPTION OF THE DRAWINGS

Fig. 1 is a schematic sectional side view of a key part of a rotary shaft fluid bearing device in accordance with a first exemplary embodiment of the present invention.

Fig. 2 is a schematic sectional side view of a key part of a fixed shaft fluid bearing device in accordance with the first exemplary embodiment of the present invention. Fig. 3 is a sectional side view of a magnetic disk device using a rotary shaft fluid bearing device in accordance with a second exemplary embodiment of the present invention.

Fig. 4 is a sectional side view of a magnetic disk device using a fixed shaft fluid bearing device in accordance with the second exemplary embodiment of the present invention.

Fig. 5 is a schematic sectional side view of a key part of a conventional rotary shaft fluid bearing device.

Fig. 6 is a schematic sectional side view of a key part of a conventional fixed shaft fluid bearing device. DESCRIPTION OF THE PREFERRED EMBODIMENTS

First exemplary embodiment A dynamic pressure fluid bearing device in a first exemplary embodiment of the present invention is described with reference to Figs. 1 and 2. Fig. 1 is a sectional side view of the part concerned of a rotor shaft radial bearing, and Fig. 2 is a sectional side view of the part concerned of a fixed shaft radial bearing.

As shown in Fig. 1 , the rotor shaft radial bearing includes an electrically conductive bearing sleeve 2 (sleeve 2), electrically conductive bearing shaft 3 (shaft 3) with a dynamic pressure generating groove 4, and conductive lubricant 6. The lubricant 6 is retained by capillary action in the clearance between the sleeve 2 and shaft 3. In other words, the first exemplary embodiment has the same configuration as that of the prior art except that the conductive lubricant 6 is used. The sleeve 2 is grounded through the frame (not illustrated) of the bearing device.

During operation of the rotor shaft radial bearing, a driver (not illustrated) starts rotating the shaft 3, and the shaft 3 separates from the sleeve 2 as a result of the dynamic pressure of the lubricant 6 generated by the dynamic pressure generating groove 4. Subsequently, the shaft 3 and sleeve 2 are in non- contact state through the lubricant 6. However, since the lubricant 6 is conductive, the shaft 3 is always electrically connected to the sleeve 2.

Next, a fixed shaft radial bearing device is described with reference to Fig. 2. The fixed shaft radial bearing includes the electrically conductive sleeve 2, electrically conductive shaft 3 with the dynamic pressure generating groove 4, and conductive lubricant 6. The shaft 3 is grounded through the frame (not illustrated) of the bearing device.

During operation of the fixed shaft radial bearing, the sleeve 2 separates from the shaft 3 as a result of the dynamic pressure of the lubricant 6 generated by the dynamic pressure generating groove 4 when the sleeve 2 starts to rotate. Subsequently the sleeve 2 and bearing 3 are in non-contact state through the lubricant 6. However, since the lubricant 6 is conductive, the sleeve 2 is always electrically connected to the shaft 3.

The dynamic pressure generating groove 4 is provided on the bearing shaft in the first exemplary embodiment. However, the dynamic pressure generating groove 4 may be provided either on the bearing shaft or bearing sleeve.

In the fluid bearing device in the first exemplary embodiment, as described above, bearing faces provided on the electrically conductive sleeve 2 and the electrically conductive shaft 3 face each other through the lubricant occupying the bearing clearance, and either one of the sleeve 2 and shaft 3 has a groove for generating dynamic pressure. In addition, the sleeve 2 and shaft 3 are electrically connected through the conductive lubricant.

The above configuration makes the shaft 3 permanently electrically connected to the sleeve 2 through the lubricant 6 in both the rotor shaft and the fixed shaft fluid bearing devices. This enables the easy discharge of electrostatic charge which may build up on a rotary part, which is the shaft 3 or sleeve 2, during rotation to a fixed part, which is the sleeve 2 or shaft 3. In the first exemplary embodiment, the sleeve 2 in the rotary bearing device and the shaft 3 in the fixed bearing device are grounded through the frame of the bearing device. Metals such as brass or stainless steel are generally used for the shaft 3. Moreover, insulating materials such as plastics, ceramics, or glass may also be used if conductivity is conferred by surface treatment such as vacuum deposition, metal plating, or thermal spraying. The lubricant 6 contains an elelctrostatic charge preventive agent for conferring conductivity to the base oil in the lubricant 6. The base oil is not limited to a specific unless it satisfies a required viscosity for generating dynamic pressure in the bearing, i.e., those conventionally used including mineral oil, synthetic hydrocarbon oil, ester oil, silicone oil, and fluorocarbon oil.

Static charge preventive agents contain at least one of the following constituents, and are selected based on the type of base oil to ensure easy dissolution or dispersion in the base oil and no reaction such as decomposition or polymerization of the base oil: organic compounds having a hydroxyl group; polyethers such as polyethylene glycol, polyoxyethylenediamine and their derivatives; esters such as sorbitan mono fatty acid esters, hydroxylethylimidedrine acid esters, and their derivatives; azoles such as benzotriazole and oxazole and their derivatives; the quaternary ammonium salts such as polyvinyl benzyltrimethyl ammonium chloride, polydimethyl aminoethyl methacrylate, and their derivatives; betaines such as trimethyl glycine; and carbon materials such as carbon black and graphite.

Second exemplary embodiment

A magnetic disk drive in a second exemplary embodiment of the present invention is described next with reference to Figs. 3 and 4. Fig. 3 is a sectional side view of the magnetic disk drive into which a rotor shaft fluid bearing device is built, and Fig. 4 is a sectional side view of a magnetic disk device into which a fixed shaft fluid bearing device is built. The same reference numerals are given to the same configurations as the first exemplary embodiment, and thus their explanation is omitted here.

First, the magnetic disk device into which the rotor shaft fluid bearing device is built is described below. In Fig. 3, three magnetic disks 13 are stacked in a hub 10 with a spacer 12 in between, and fixed with a clamp 11. A rotor magnet 9 is disposed on the inner radius of the hub 10, and includes a motor with a stator coil 8 disposed on a fixed part. This motor rotates the rotating parts, including the magnetic disk 13 and hub 10, at high speed. The stator coil 8 is disposed on the outer radius of the electrically conductive sleeve 2, and the sleeve 2 is fixed onto a base 1 which is grounded. The electrically conductive shaft 3 is press-fitted into the hub 10, and is inserted into the sleeve 2. A conductive lubricant occupies a thrust clearance 15 between the thrust bearing 5 attached to the shaft 3 and the sleeve 2, and a radial clearance 14 between the shaft 3 and sleeve 2 so that the shaft 3 floats as a result of the dynamic pressure generated by rotation. In the above configuration, a conductive material such as metal or conductive resin is used for the spacer 12 and clamp 11 contacting the magnetic disk 13 to create an electrical connection between the magnetic disk 13 and hub 10. The hub 10 is generally made of aluminum or iron system metal, and has the same electric potential as the shaft 3 to which it is press-fitted. Accordingly, the magnetic disk 13 is electrically connected to the sleeve 2 through the lubricant.

Next, the magnetic disk device into which the fixed shaft fluid bearing device is built is described below. In Fig. 4, one end of the electrically conductive shaft 3 is fixed onto the base 1 connected to the ground. A thrust bearing 5 is attached to the other end of the shaft 3. The magnetic disks 13 are stacked in the hub 10 with the spacer 12 in between, and fixed with the clamp 11. The electrically conductive bearing sleeve 2 is press-fitted to the inner radius of the hub 10. The rotor magnet 9 is disposed at inside of the outer radius of the hub 10, and includes a motor with the stator coil 8 vertical to the base 1. This motor rotates the rotating parts, including the magnetic disk 13 and hub 10, at high speed. The conductive lubricant occupies the thrust clearance 15 between the thrust bearing 5 attached to the shaft 3 and the sleeve 2, and the radial clearance 14 between the shaft 3 and sleeve 2 so that the sleeve 2 floats as a result of the dynamic pressure generated by rotation. In the above configuration, a conductive material such as metal or conductive resin is used for the spacer 12 and clamp 1 1 contacting the magnetic disk 13 to create an electrical connection between the magnetic disk 13 and hub 10. The hub 10 is generally made of aluminum or iron system metal, and has the same electric potential as the sleeve 2 press-fitted. Accordingly, the magnetic disk 13 is electrically connected to the shaft 3 through the lubricant.

With the above configuration, the magnetic disk 13 and sleeve 2 or shaft 3 are electrically connected through the lubricant in the magnetic disk drive into which are built either rotary shaft or fixed shaft fluid bearing devices. Accordingly, any electrostatic charge which may be generated on the magnetic disk 13 during rotation can be safely discharged to the base 1.

Industrial applicability

The fluid bearing device of the present invention electrically connects the sleeve and shaft through a conductive lubricant containing a static charge preventive agent. This prevents buildup of electrostatic charge on the rotating parts, including the sleeve and shaft. Accordingly, appliances using fluid bearing devices of the present invention may demonstrate stable performance without erroneous operation or failure due to discharge of static electricity.

Claims

1. A bearing device comprising: an electrically conductive bearing sleeve; an electrically conductive bearing shaft disposed at a position facing said bearing sleeve through a clearance; and lubricant filled in said clearance between said bearing sleeve and said bearing shaft, said lubricant exhibiting electrical conductivity.

2. A fluid bearing device in which a bearing face provided on a bearing sleeve faces a bearing face provided on a bearing shaft through lubricant filled in a bearing clearance, and at least one of said bearing face of said bearing sleeve and said bearing face of the bearing shaft has a groove for generating dynamic pressure; wherein said bearing sleeve and said bearing shaft are electrically connected through said lubricant exhibiting electrical conductivity.

3. The fluid bearing device as defined in Claim 2, wherein said lubricant contains an electrostatic charge preventive agent.

4. The fluid bearing device as defined in Claim 3, wherein said electrostatic charge preventive agent contains at least one of: organic compounds having a hydroxyl group; polyethers and their derivatives; esters and their derivatives; azoles and their derivatives; the quaternary ammonium salt and their derivatives; betaines; and carbon materials.

5. A magnetic disk device comprising: an electrically conductive bearing sleeve; an electrically conductive bearing shaft disposed at a position facing said bearing sleeve through a clearance; lubricant filled in said clearance between said bearing sleeve and said bearing shaft; and a magnetic disk; wherein said lubricant exhibits conductivity, and said magnetic disk is fixed in a way to electrically contact with one of said bearing shaft and said bearing sleeve.

6. A magnetic disk device comprising: a fluid bearing device in which a bearing face provided on a bearing sleeve faces a bearing face provided on a bearing shaft through a conductive lubricant filled in a bearing clearance, and at least one of said bearing face of said bearing sleeve and said bearing face of said bearing shaft has a groove for generating dynamic pressure; and a magnetic disk fixed onto one of said bearing shaft and said bearing sleeve of said fluid bearing device; wherein said magnetic disk is electrically connected to said bearing shaft and said bearing sleeve through said lubricant.

7. The magnetic disk device as defined in Claim 6, wherein said lubricant contains an electrostatic charge preventive agent.

8. The magnetic disk device as defined in Claim 7, wherein said electrostatic charge preventive agent contains at least one of: organic compounds having a hydroxyl group; polyethers and their derivatives; esters and their derivatives; azoles and their derivatives; the quaternary ammonium salt and their derivatives; betaines; and carbon materials.