JP2002027701A - Spindle motor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a spindle motor with a magnetic seal so that a magnetic fluid does not splash even during high speed rotation and a hard disc is never contaminated with the magnetic fluid. SOLUTION: In the spindle motor provided with a shaft 2, a bearing 4 loaded to the shaft 2, a rotor hub 3 supported for relative rotation against the shaft 2 via the bearing 4 and a magnetic fluid seal 5 between the shaft 2 and the rotor hub 3, the magnetic fluid seal 5 includes an annular permanent magnet 51 fixed to the shaft 2, an annular magnetic material fixed to the rotor hub 3 against the permanent magnet 51 via a fine gap in the radius direction, and a magnetic fluid to be filled between the permanent magnet 51 and annular magnetic material 52.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a spindle motor, and more particularly to a spindle motor having a magnetic fluid seal.

[0002]

2. Description of the Related Art In a hard disk drive, a ball bearing and a stator of a spindle motor used are used.
If contaminants such as oil mist and fine powder generated from a rotor magnet or the like fly out of the motor, defective reading and writing of the magnetic head with respect to the hard disk may occur. For this reason, in a spindle motor used in a hard disk drive that requires such high cleanliness, a magnetic fluid seal has conventionally been used as a seal member.

In a conventional magnetic fluid seal, for example, in the case of a spindle motor of a fixed shaft type, a magnet portion having a permanent magnet sandwiched between pole pieces having magnetism is provided on a rotating rotor hub side, and a shaft facing a radially opposed shaft portion is provided. A magnetic material is provided on the side, a magnetic fluid is injected between the magnet portion and the magnetic material, and the magnetic fluid is held by the magnetic force between the magnet portion and the magnetic material, thereby providing a sealing effect.

[0004]

However, due to the increase in the capacity of the hard disk drive and the high-speed rotation of the spindle motor accompanying the shortening of the seek time, the magnetic fluid constituting the magnetic fluid seal scatters and contaminates the inside of the hard disk drive. Problems have arisen. The scattering of the magnetic fluid is considered to be due to the following mechanism. Even when the motor is not rotating in the first place, the magnetic powder contained in the magnetic fluid is unevenly distributed on the magnet part side (radially outward with respect to the rotation center). When the motor rotates there, the magnetic powder further moves toward the magnet part due to the action of the centrifugal force. As a result, on the rotation center side of the magnetic fluid, the density of the magnetic powder becomes small and it becomes difficult to hold the magnetic fluid by the magnetic force, and when the magnetic force holding the magnetic fluid falls below the centrifugal force, the magnetic fluid scatters. is there.

The present invention has been made in view of such a conventional problem, and provides a spindle motor in which a magnetic fluid constituting a magnetic fluid seal does not scatter into a hard disk drive even during high-speed rotation. It is intended to do so.

[0006]

In order to solve the above-mentioned problems, a spindle motor according to the present invention has a shaft, a bearing member mounted on the shaft, and is supported to rotate relative to the shaft via the bearing member. A spindle motor including a rotor hub and a magnetic fluid seal provided between the shaft and the rotor hub, wherein the magnetic fluid seal includes an annular permanent magnet fixed to the shaft,
An annular magnetic material fixed to the rotor hub and opposed to the permanent magnet via a minute gap in a radial direction, and a magnetic fluid injected between the permanent magnet and the magnetic material are provided.

At this time, from the viewpoint of improving the strength of the permanent magnet,
Preferably, a nickel coating layer is formed on the surface of the permanent magnet.

From the viewpoint of more effectively preventing the magnetic fluid from scattering, it is recommended that the upper portion of the outer peripheral surface of the permanent magnet be tapered.

From the viewpoint of preventing the solvent in the magnetic fluid from leaking into the spindle motor, a shaft comprising a base having a maximum outer diameter and a small-diameter portion formed thereon with a reduced diameter is used.
A permanent magnet is fixed to the outer periphery of the small diameter portion to form an annular groove that opens radially outward between the bottom surface of the permanent magnet and the step formed by the base and the small diameter portion, while the inner periphery of the annular magnetic material is formed. It is preferable that the annular protrusion is extended radially inward on the surface, and the annular protrusion is inserted into the annular groove in a non-contact state.

Further, from the viewpoint of more effectively preventing the scattering of the magnetic fluid, a groove for feeding the magnetic fluid is formed on at least one of the outer peripheral surface of the permanent magnet and the inner peripheral surface of the magnetic material. desirable.

[0011]

BEST MODE FOR CARRYING OUT THE INVENTION The present inventor has conducted intensive studies on a spindle motor provided with a magnetic fluid seal in order to prevent scattering of a magnetic fluid during high-speed rotation. The inventor has found that it is only necessary to reverse the above, that is, to provide an annular permanent magnet on the shaft side and to provide an annular magnetic material on the rotor hub side. That is, by providing a permanent magnet on the shaft side, a magnetic force acts in the direction opposite to the strong centrifugal force generated by high-speed rotation, thereby preventing the magnetic fluid from scattering.

Hereinafter, specific embodiments of a spindle motor having a magnetic fluid seal of the present invention will be described in detail with reference to the drawings. The present invention is not limited to these embodiments.

FIG. 1 is a sectional view showing an embodiment of the spindle motor of the present invention. The bracket 1 includes a base portion 11 provided at a central portion, a peripheral wall 12 provided in an outer peripheral direction of the base portion 11, and a flange portion 13 further extending outward from the peripheral wall 12. And it is formed coaxially.

A hole 14 penetrating in the axial direction is formed in the center of the base 11, and one end of the shaft 2 is fitted and fixed to the hole 14 by, for example, press-fitting. The bracket 1 is fixed to a base member (not shown) of the hard disk drive by screwing a mounting screw into a hole 15 provided in the flange portion 13. Similarly, shaft 2
The mounting screw is screwed into the hole 21 provided at the upper end of the hard disk drive, and is fixed together with the base member of the hard disk drive to a lid member (not shown) which defines a clean space inside. Therefore, the bracket 1 and the shaft 2 serve as fixing members for a hard disk drive (not shown).

A ball bearing (bearing member) 4 is mounted between the shaft 2 and the rotor hub 3. The ball bearing 4 includes an inner race 41 mounted and fixed to the outer periphery of the shaft 2 and an outer race 43 rotatably supported via a ball 42 corresponding to the inner race 41. Then, the rotor hub 3 is mounted and fixed to the outer race 43.

The rotor hub 3 has a substantially cylindrical shape, and a hard disk (not shown) is mounted on a flange 31 formed on the lower side. Specifically, after being positioned by the outer peripheral portion 32 of the rotor hub 3 and a plurality of hard disks are mounted on the flange portion 31, the hard disks are screwed to the holes 33 by a clamp member or the like. It is held and fixed.

A rotor magnet 35, which is multipolarly magnetized in the circumferential direction, is arranged on the entire inner circumference of a hanging portion 34 formed below the flange 31. Further, a stator 15 is provided on an annular protrusion 16 formed on the base 11 of the bracket 1 in a radially inner side of the rotor magnet 35 so as to face the rotor magnet 35. Stator 15
And the annular projection 16 are fixed by press-fitting,
It may be fixed by an adhesive.

A magnetic fluid seal 5 provided between the shaft 2 and the rotor hub 3 is provided with an annular permanent magnet 51 fixed to the shaft 2 and fixed to the rotor hub 3 opposed thereto with a small gap therebetween. And the magnetic fluid 53 injected into the gap between the permanent magnet 51 and the annular magnetic material 52. FIG. 2 is an enlarged sectional view of a main part. An annular permanent magnet 51 is fixed to the outer peripheral portion of the shaft 2, and an annular magnetic material 52 is fixed to the rotor hub 3 so as to oppose the permanent magnet 51 in the radial direction with a small gap therebetween. The ball bearing 4 is disposed below or in contact with or near the magnetic fluid seal 5. Then, on the outside of the motor (outside in the axial direction) of the magnetic fluid seal 5,
A protective cover 54 is attached so that foreign substances cannot enter from the outside or touch the magnetic fluid seal 5 directly. The protection cover 54 is fixed by applying an adhesive 56 to a step 55 formed on the outer peripheral edge of the annular magnetic material 52. At this time, the annular magnetic material 52 is also fixed to the motor.

The annular permanent magnet 51 is magnetized in the radial direction, and the magnetic flux emitted from the outer peripheral surface of the permanent magnet 51 is transferred to the outer peripheral surface of the permanent magnet 51-the annular magnetic material 52-the inner ring portion 41 of the ball bearing 4. -Shaft 2-A magnetic flux path is formed mainly as an inner peripheral surface of the permanent magnet 51, thereby holding the magnetic fluid 53 between the permanent magnet 51 and the annular magnetic material 52.
According to such a configuration, the pole piece that was required in the conventional magnetic fluid seal can be eliminated, and the magnetic fluid seal structure can be more simplified.

Usually, the whole shaft is made of a magnetic material such as SUS material, but it is not always necessary to make the whole magnetic material. The region including the fixed portion of the annular permanent magnet and the fixed portion of the inner ring portion of the ball bearing may be at least a magnetic material. One embodiment of such a configuration is shown in FIG.
A shaft small diameter portion 22 is formed at the upper end of the shaft 2, and an annular magnetic body 23 is fitted on the outer periphery of the shaft small diameter portion 22. An annular permanent magnet 51 and an inner ring portion 41 of a ball bearing are fixed to the outer peripheral surface of the magnetic body 23, respectively. According to such a configuration, a magnetic flux path similar to that described above is formed, and the magnetic fluid 53 is held between the permanent magnet 51 and the annular magnetic material 52.

Here, the permanent magnet which can be used in the present invention is not particularly limited, and a conventionally known permanent magnet such as ferrite or rare earth can be used. However, since a high strength magnet is desirable, a nickel coating layer is formed on the surface. What has been used can be suitably used. When mounted on the shaft, the permanent magnet may crack or chip, and small pieces of the broken or chipped magnet may scatter into the hard disk drive and contaminate the clean space defined inside. However, by coating the magnet surface with nickel, the surface strength is increased, and the above-mentioned problem can be prevented. Further, by nickel coating, the surface roughness of the magnet is reduced, and the gap size between the magnet and the annular magnetic material can be maintained with high accuracy. Such a nickel coating layer can be formed by electrolytic or electroless plating.

It is recommended that the upper part of the outer peripheral surface of the permanent magnet be tapered. This is because, by balancing the surface tension of the magnetic fluid and the air pressure, a surface tension seal in which the interface between the magnetic fluid and air is maintained in a meniscus shape is formed, and scattering of the magnetic fluid is suppressed. Also, the magnetic force acting on the magnetic fluid becomes stronger as the gap between the permanent magnet and the annular magnetic material becomes smaller, so that the gap between the permanent magnet and the annular magnetic material gradually increases toward the outside of the motor. Since the magnetic fluid is pulled and held in the direction toward the inside of the motor, scattering of the magnetic fluid is further suppressed.

Although the rotor hub shown in FIG. 1 is entirely made of a magnetic material, a two-piece structure may be used instead. That is, the outer peripheral side on which the hard disk is mounted is formed of aluminum or an alloy thereof, and the inner peripheral side to which the annular magnetic material or the ball bearing is fixed is formed of a magnetic material such as SUS. Since aluminum is lightweight and excellent in workability, such a configuration can reduce the weight of the rotor hub and facilitate processing of the outer peripheral surface.

Another embodiment of a magnetic fluid seal is shown in FIG. FIG. 4 is a configuration diagram of a main part of the upper part of the shaft. The shaft 2 includes a base portion 24 having a maximum outer diameter and a small diameter portion 25 formed with a reduced diameter on the base portion 24. An annular permanent magnet 51 is fitted to a predetermined position of the small diameter portion 25. In such a situation,
An annular concave groove that opens radially outward is formed on the lower surface of the permanent magnet 51, the outer peripheral surface of the small diameter portion 25, and the step portion 26 of the shaft. On the other hand, an annular projection 57 extends radially inward on the inner peripheral surface of the annular magnetic material 52, and the annular projection 57 is fitted into the annular groove in a non-contact state. Even when oil, which is the solvent of the magnetic fluid 53, diffuses along the surface of the annular magnetic material 52, that is, a so-called oil migration phenomenon occurs, and oil diffusion is promoted by centrifugal force due to rotation of the motor, According to such a configuration, the annular projection 57 extending inward in the radial direction captures oil and prevents oil from leaking into the motor. Furthermore, the permanent magnet 5
1 and the annular spacer 27 shown in FIG.
When the is mounted, an oil repellent may be applied to the side surface to further prevent the oil migration phenomenon.

Also, as shown in FIG.
An annular spacer 27 having a diameter smaller than that of the permanent magnet may be interposed between the annular permanent magnet 51 and the stepped portion 26 from the portion 4 to the small diameter portion 25. Here, the annular spacer 27 is desirably formed of a nonmagnetic material such as aluminum or an aluminum alloy. This is to prevent a decrease in magnetic efficiency. As a result, the magnetic flux path connecting the magnetic poles of the permanent magnets always conducts through the inner ring portion 41 of the ball bearing, so that the magnetic fluid 53 is stably held. Further, the annular spacer 27 is provided with a permanent magnet 51 at a predetermined position of the small diameter portion 25.
And also serves as a positioning member for fixing with high accuracy.

In order to more effectively prevent the magnetic fluid 53 from scattering, a groove for pressure-feeding the magnetic fluid 53 is formed on at least one of the outer peripheral surface of the permanent magnet 51 and the inner peripheral surface of the annular magnetic material 52. It is recommended to form. This is because the uneven distribution of the magnetic fluid is suppressed by agitation by pressure feeding. The principle that the formed groove pumps the magnetic fluid is the same principle as the dynamic pressure generating groove in the hydrodynamic bearing. Unlike the hydrodynamic bearing, the gap between the permanent magnet and the annular magnetic material is as large as several tens of microns in the magnetic fluid seal, so that the groove in the present invention does not generate dynamic pressure enough to act as a bearing, Solely acts to stir so as not to be unevenly distributed.

The shape of the groove to be formed is not particularly limited as long as it has an effect of stirring the magnetic fluid. For example,
A herringbone-shaped groove that bends in the shape of a "ku" at the center in the axial direction and pumps the magnetic fluid from both sides of the groove to the center,
An angularly unbalanced herringbone-shaped groove in which the "U" -shaped bent portion is deflected toward the inside of the motor, and the outer end of the motor in the direction of the rotation axis is inclined in the direction facing the rotation direction, and the inside of the motor is inclined. Spiral grooves for pumping the magnetic fluid in the direction.

[0028]

According to the spindle motor of the present invention, the ring-shaped permanent magnet fixed to the shaft, the ring-shaped magnetic material fixed to the rotor hub facing the permanent magnet via a minute gap in the radial direction, and the permanent magnet Since the magnetic fluid seal having the magnetic fluid injected between the magnetic material and the magnetic material is provided, the magnetic fluid does not scatter even during high-speed rotation, and the inside of the hard disk is not contaminated with the magnetic fluid. Also, if a nickel coating layer is formed on the surface of the permanent magnet,
The strength of the magnet surface is increased so that it does not crack or chip when mounted on the shaft. Furthermore, if the upper portion of the outer peripheral surface of the permanent magnet is tapered, a surface tension seal is formed at the interface between the magnetic fluid and the air, so that the scattering of the magnetic fluid is further suppressed.

The permanent magnet is fixed to the outer periphery of the small-diameter portion using a shaft having a base having a maximum outer diameter and a small-diameter portion formed with a reduced diameter on the base. While forming an annular groove that opens radially outward between the stepped portion and the radially inwardly extending annular protrusion on the inner peripheral surface of the annular magnetic material, the annular protrusion is not contacted. If the configuration is such that the oil is inserted into the annular groove in this state, even if an oil migration phenomenon occurs, oil can be captured by the annular protrusion and oil leakage into the motor can be prevented. If a groove for pumping the magnetic fluid is formed on at least one of the outer peripheral surface of the permanent magnet and the inner peripheral surface of the annular magnetic material, the magnetic fluid can be prevented from being unevenly distributed by the agitating action of the pumping, and the magnetic fluid can be further scattered. Can be prevented.

[Brief description of the drawings]

FIG. 1 is a sectional view showing one embodiment of a spindle motor of the present invention.

FIG. 2 is a sectional view of a main part of a spindle motor of the present invention.

FIG. 3 is a sectional view of a main part showing another embodiment of the spindle motor of the present invention.

FIG. 4 is a partial cross-sectional view of a main part showing another embodiment of the spindle motor of the present invention.

FIG. 5 is a sectional view of a main part showing another embodiment of the spindle motor of the present invention.

[Explanation of symbols]

 2 Shaft 3 Rotor Hub 4 Ball Bearing (Bearing Member) 5 Magnetic Fluid Seal 24 Shaft Base 25 Shaft Small Diameter 26 Shaft Step 51 Annular Permanent Magnet 52 Annular Magnetic Material 53 Magnetic Fluid 57 Annular Protrusion

 ──────────────────────────────────────────────────続 き Continued on the front page F term (reference) 5H605 AA03 AA11 BB05 BB14 BB19 CC04 CC10 DD36 EA07 EA15 EB10 EB16 EB27 EB31 FF14 GG10 5H621 GA01 GA04 HH01 HH08 HH09 JK02 JK05 JK08 JK10 JK17 JK19

Claims (5)

[Claims] 1. A shaft, a bearing member mounted on the shaft, a rotor hub rotatably supported by the shaft via the bearing member, and a magnetic fluid seal provided between the shaft and the rotor hub. Wherein the magnetic fluid seal has an annular permanent magnet fixed to the shaft, and an annular fixed magnet fixed to the rotor hub opposed to the permanent magnet via a minute gap in a radial direction. A spindle motor comprising: a magnetic material; and a magnetic fluid injected between the permanent magnet and the magnetic material. 2. The spindle motor according to claim 1, wherein a nickel coating layer is formed on a surface of said permanent magnet. 3. The spindle motor according to claim 1, wherein an upper portion of an outer peripheral surface of the permanent magnet is tapered. 4. The shaft comprises a base portion having a maximum outer diameter and a small diameter portion formed on the base portion, and the permanent magnet is fixed to an outer periphery of the small diameter portion, so that a bottom surface of the permanent magnet is formed. Forming an annular groove that opens radially outward between the base and the step formed by the small-diameter portion, and extending an annular protrusion radially inward on the inner peripheral surface of the annular magnetic material; The protrusion is inserted into the annular concave groove in a non-contact state.
3. The spindle motor according to any one of 3. 5. The spindle according to claim 1, wherein a groove for feeding a magnetic fluid is formed on at least one of an outer peripheral surface of the permanent magnet and an inner peripheral surface of the annular magnetic material. motor.