JP2000235766A - Spindle motor and disk device using the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To concentrate magnetic fluid to contact portions and to hold the magnetic fluid in a pivot part by constituting a shaft, the shaft ends of which are formed to a curvilinear form outward, and a thrust bearing for receiving this shaft of a magnetic material, adopting the magnetic fluid for lubricating fluid and constituting a magnetic circuit of the magnet, the thrust bearing 22 and the shaft. SOLUTION: A bearing unit 1 is composed of a housing 21, the thrust bearing 22, a radial bearing 23, the magnet 25 for pressurization, a screw seal 26, a stopper ring 27, a spacer 28 and the magnetic fluid 29. The radial bearing 23 is press fitted to the inner side of the housing 21 and the shaft 3 is supported rotatably and the displacement in a radial direction is restrained by the inside surface of the radial bearing 23. The shaft 3 and the thrust bearing 22 are ferromagnetic materials at ordinary temperature and magnetize the magnet 25 for pressurization in an axial direction, by which magnetical attraction is acted between the shaft 3 and the thrust bearing 22. The magnetic lines of force concentrate near to a revolving shaft near the end of the shaft 3 and the spacing between the end of the shaft 3 and the thrust bearing 22 is filled with the magnetic fluid 29.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a disk drive for recording / reproducing information on / from a disk-shaped information recording medium, and more particularly to reducing a loss of a spindle motor for rotating a disk and improving high-speed rotation performance. And a disk device realizing high-density recording.

[0002]

2. Description of the Related Art A conventional bearing device is disclosed in Japanese Patent Application Laid-Open No. 9-21 / 1997.
Japanese Patent Application Publication No. 0060 discloses a structure having a bearing using a magnetic fluid as a lubricating fluid, and magnetizing a fixed shaft by a ring-shaped permanent magnet constituting a bearing unit to suck the magnetic fluid into a pivot portion. Also, Japanese Patent Application Laid-Open No. 10-19665
Japanese Patent Application Laid-Open No. 7-107703 discloses a magnetic disk drive incorporating a spindle motor using a bearing device using a magnetic fluid lubricant. Further, Japanese Patent Application Laid-Open No. Hei 6-223494 discloses a method of applying pressure to a pivot bearing.

[0003]

SUMMARY OF THE INVENTION Incidentally, Japanese Patent Application Laid-Open No.
In the structure of JP 210060, the magnetic flux from the ring-shaped permanent magnet hardly reaches the pivot portion, and the magnetic flux at the pivot portion is extremely weak. Further, since the thrust receiver rotates and is dragged by the thrust receiver, a centrifugal force acts on the magnetic fluid, so that it is actually difficult to hold the magnetic fluid in the pivot portion, and the pivot portion is worn. Therefore, it is necessary to preload the pivot part by some method,
This publication does not describe a method of applying a preload.

Japanese Patent Application Laid-Open No. 10-196657 describes that the thrust receiver is always immersed in lubricating oil to ensure reliable lubrication. However, since the shaft actually rotates, centrifugal force acts on the lubricating oil, and if even a small amount of air bubbles are mixed in the lubricating oil, the lubricating oil runs short at the contact point between the shaft and the thrust receiver, and the shaft or thrust receiver is Wear out. It is necessary to apply a preload to the pivot part by some method, but this publication does not describe a method of applying the preload.

Japanese Patent Application Laid-Open No. Hei 6-223494 discloses a method of applying pressure to a pivot bearing. However, there is no description about a method of retaining lubricating oil in a pivot portion, and bubbles are mixed in the lubricating oil. In such a case, since the centrifugal force acts on the lubricating oil, the lubricating oil is insufficient at the pivot portion and the pivot portion is worn.

An object of the present invention is to provide a highly reliable spindle motor with low loss and NRRO, and to provide an information recording apparatus with high density, high reliability and low noise.

[0007]

Means for Solving the Problems A shaft whose outer end is curved outwardly and a thrust bearing for receiving the shaft are made of a magnetic material, and the lubricating fluid is a magnetic fluid. Furthermore, a magnet is attached to the thrust bearing, and a magnet, a thrust bearing, and a shaft constitute a magnetic circuit. Since the magnetic flux concentrates on the contact portion between the shaft and the thrust bearing, the magnetic flux is strong at the contact portion and becomes weaker as the distance from the contact portion increases. For this reason, a force for concentrating the magnetic fluid acts on the contact portion. This force can be made stronger than the centrifugal force, and the magnetic fluid can be held at the pivot even when the shaft is rotated.

Even if air bubbles are mixed in the magnetic fluid, no magnetic force acts on the air bubbles, so that only the magnetic fluid can be concentrated on the pivot portion. For this reason, a sufficient lubricating fluid exists in the pivot portion, and the wear of the pivot portion can be significantly reduced.

Since a fluid bearing is used as the bearing, NR
Since a spindle motor with a small RO can be configured and a pivot bearing is used for the thrust bearing, the loss can be reduced. As described above, the wear of the pivot portion can be significantly reduced, so that a highly reliable spindle motor can be configured.

[0010] The NRRO of the spindle motor can be reduced by making the bearing of the HDD spindle motor a fluid bearing. Therefore, the track pitch can be reduced, and an HDD having a high recording density can be configured. HD with low power consumption because the power consumption of the spindle motor can be reduced
D can be configured. Because of the high reliability of the spindle motor, a highly reliable HDD can be configured.

[0011]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A first embodiment of the present invention will be described with reference to FIGS. 1 is a sectional view of a spindle motor using the present invention, and FIG. 2 is an enlarged view of a bearing unit.
3 is an enlarged view of the vicinity of the shaft end, FIG. 4 is a plan view and a cross-sectional side view of a magnetic disk drive using the present invention, FIG. 5 is an explanatory view of a bearing inner surface shape, and FIG. is there.

As shown in FIG. 1, a bearing unit 1 is mounted on a base 2. The bearing unit 1 has a structure to be described later, rotatably supports the shaft 3, and restricts other degrees of freedom. A hub 4 is fixed to the shaft 3, and a plurality of magnetic disks 5, 6 are fixed to the hub 4 with a clamper 8 and a clamp screw 9 sandwiching a spacer 7. Therefore, the hub 4 and the magnetic disks 5 and 6 can rotate around the rotation axis of the shaft 3 determined by the bearing unit 1, and other degrees of freedom are restricted.

The base 2 has a stator yoke 10 (iron core).
, And a coil 11 is wound around the stator yoke 10. Further, a rotor magnet 12 made of a permanent magnet is attached to the hub 4. When a predetermined current flows through the coil 11, a rotational force acts on the rotor magnet 12. As described above, the hub 4 and the magnetic disks 5 and 6 are connected to the shaft 3 determined by the bearing unit 1.
The hub 4 and the magnetic disks 5 and 6 rotate around the rotation axis of the shaft 3 by this rotation force.

Information is recorded on the magnetic disks 5 and 6 by magnetic marks. When the magnetic flux from the rotor magnet 12 leaks to the magnetic disks 5 and 6, the information recorded on the magnetic disks 5 and 6 is recorded. May be destroyed. Therefore, the hub 4 is made of a ferromagnetic material, and shields the magnetic flux from the rotor magnet 12 from leaking to the magnetic disks 5 and 6.

As will be described later, recording and reproduction of information on the magnetic disks 5 and 6 are performed by a magnetic head mounted on a slider.
Must be reduced to 1 μm or less. When rust is generated on the surface of the hub 4, an oxide powder of the material of the hub 4 is generated from the rust, and when the rust enters between the magnetic disks 5 and 6 and the slider, the magnetic disks 5 and 6 are damaged. Therefore, the hub 4 needs to be made of a material that does not easily rust. From these conditions,
The material of the hub 4 needs to be martensitic or ferritic stainless steel, for example, SUS430 or SUS410. The shaft 3 and the hub 4 can be fixed by press-fitting, bonding, shrinkage fitting, welding, etc., or by using residual stress due to plastic deformation.

As shown in FIG. 2, the bearing unit 1 includes a housing 21, a thrust bearing 22, a radial bearing 23, a preload magnet 25, a screw seal 26, a stopper ring 27,
It is composed of a spacer 28 and a magnetic fluid 29. A radial bearing 23 is press-fitted inside the housing 21. The radial bearing 23 has a substantially cylindrical shape,
The inner surface supporting the shaft 3 may be a multi-arc shape such as a 3-arc shape or a groove bearing. The shaft 3 is rotatably supported by the inner surface of the radial bearing 23, and the radial displacement is restricted.

The shaft 3 is a martensitic stainless steel,
For example, it is made of SUS440C and is a ferromagnetic material at room temperature. Thrust bearing 22 is made of martensitic or ferritic stainless steel and is a ferromagnetic material at normal temperature. The radial bearing 23 is made of an alloy obtained by sintering copper and iron at an approximately half ratio, and exhibits weak magnetism. As shown in FIG. 2, the preload magnet 25 is magnetized in the axial direction to form a magnetic circuit like the magnetic field lines in the figure, and the shaft 3, the thrust bearing 22, and the radial bearing 23 are magnetized. Due to this magnetization, a magnetic attractive force acts between the shaft 3 and the thrust bearing 22, and the shaft 3 is pressed against the thrust bearing 22, thereby restraining the displacement of the shaft 3 in the thrust direction.

Hereinafter, the force pressing the shaft 3 against the thrust bearing 22 is referred to as preload. The shaft end of the shaft 3 has an outwardly convex spherical shape, and the shaft end of the shaft 3 and the thrust bearing 22 constitute a so-called pivot bearing. For this reason, it is possible to reduce the loss of the bearing caused by the restriction of the displacement in the thrust direction, as compared with the case where the dynamic pressure bearing is adopted as the thrust bearing. Further, the preload magnet 25, the radial bearing 2
Since the magnetic circuit is constituted by the shaft 3, the shaft 3 and the thrust bearing 22, it is possible to apply a strong magnetic field to a part of the pivot bearing constituted by the shaft end of the shaft 3 and the thrust bearing 22, and to obtain a sufficient magnetic field. It is possible to give pressure.

For example, in the structure shown in FIG. 2, the preload is obtained under the conditions shown in Table 1.

[0020]

[Table 1]

However, the shaft 3 is solid, and the radius of curvature of the shaft end is
20 mm. A preload of approximately 2-6N is obtained.

The housing 21 is made of a non-magnetic material such as austenitic stainless steel, and there is no fear that the magnetic flux of the preload magnet 25 passes through the housing 21 and the magnetic circuit is short-circuited. The spacer 28 is also made of a non-magnetic material, for example, austenitic stainless steel, a copper alloy, or an aluminum alloy, so that the magnetic circuit is not short-circuited even in this portion. However, when the preload is too strong, the housing 21 or the spacer 28 can be made of a ferromagnetic material, and the preload can be adjusted by intentionally short-circuiting the magnetic circuit. When the spacer 28 is made of a ferromagnetic material, the spacer 28 and the thrust bearing 28 may be integrated.

The shaft 3, the thrust bearing 2, which is a ferromagnetic material
2. Both the preload magnets 25 have an axially symmetric structure.
Although the inner surface of the radial bearing showing weak magnetism is slightly asymmetric, the degree of asymmetry is small in view of the overall dimensions, and the magnetic characteristics may be considered to be axially symmetric. Therefore, even if the shaft 3 rotates, the preload does not change. Therefore, the preload does not cause noise during rotation.

Conventionally, for example, in FIG. 1, a method has often been used in which the positions of the stator yoke 10 and the rotor magnet 12 are shifted, and the magnetic force acting on both is used as a preload. However, the magnetic structure of the stator yoke 10 and the rotor magnet 12 periodically changes at different periods in the circumferential direction. Accordingly, the preload periodically changes during rotation, which causes noise. Accordingly, the spindle motor according to the present invention can be configured with less noise than the conventional spindle motor.

In the embodiment of the present invention, both the contacting shaft 3 and the thrust bearing 22 are made of stainless steel, and are made of the same material. When the same kind of material is slid, abrasion may increase. Therefore, the surface of the thrust bearing 22 is coated with TiN.
As this coating, in addition to TiN, CrN coating, Ni-P plating, or the like may be applied.

The screw seal 26 is provided to prevent leakage of the magnetic fluid 29. The housing 21 and the thrust bearing 22 are fixed by press-fitting, bonding, shrink fitting, welding, and the like.
It is also possible to fix using residual stress due to plastic deformation.

The stopper ring 27 has a structure in which a part thereof is hooked in a groove provided in the shaft 3 to prevent the shaft 3 from coming off. The stopper ring 27 is fixed between the radial bearing 23 and the spacer 28. Bearing unit 1
When assembling by inserting the shaft 3 into the
The part caught in the groove of the elastic deformation and spread outward,
Pass the shaft 3. When the groove of the shaft 3 comes to the portion of the stopper ring 27, the hooked portion returns to its original position and is hooked to the groove to prevent the shaft 3 from coming off.

FIG. 3A shows an enlarged view of the vicinity of the shaft end of the shaft 3, and FIG. 3B shows the relationship between the force acting on the magnetic fluid and the distance. The shaft end of the shaft 3 has an outwardly convex spherical shape, and its tip is in contact with the thrust bearing 22. The center of the spherical surface of the shaft end coincides with the rotation axis of the shaft 3 in the range of machining accuracy, and the thrust bearing 22 is mounted so as to be perpendicular to the rotation axis of the shaft 3. Therefore, the shaft end of the shaft 3 and the thrust bearing 22
Contacts the thrust bearing 22 at a point near the rotating shaft at the shaft end. Even if it is a point, since both the shaft 3 and the thrust bearing 22 are not rigid, a Hertz contact actually occurs.

As shown in FIG. 2, the gap between the shaft end of the shaft 3 and the thrust bearing 22 is small in the vicinity of the rotating shaft, and the gap becomes large in the distance from the rotating shaft. Therefore, in the above-described magnetic circuit, the magnetic resistance decreases near the rotation axis, and increases when the distance from the rotation axis increases. Since the lines of magnetic force tend to concentrate on the side with lower magnetic resistance, the axis 3
In the vicinity of the shaft end, the lines of magnetic force concentrate near the rotation axis. Axis 3
Considering the gap between the shaft end and the thrust bearing 22, the above-described concentration of the lines of magnetic force occurs. Therefore, the magnetic flux density is large near the rotation axis of the shaft 3, and the magnetic flux density becomes small away from the rotation axis.

The gap between the shaft end of the shaft 3 and the thrust bearing 22 is
It is filled with a magnetic fluid 29. Generally, the magnetic force acting on the magnetic fluid is a so-called preserving force that satisfies the law of conservation of energy, and the force acts toward a portion having a higher magnetic flux density. As described above, in the gap between the shaft end of the shaft 3 and the thrust bearing 22, the magnetic flux density is large in the vicinity of the rotating shaft, and the magnetic flux density becomes small away from the rotating shaft. Force acts.

When the force per unit volume acting on the magnetic fluid under the above-mentioned conditions is calculated, a graph shown in FIG. 3 (2) is obtained. However, the characteristics of the magnetic fluid 29 were approximated by (Equation 1).

[0032]

(Equation 1)

Here, m (H) is the magnitude m of the magnetization given as a function of the magnetic field H, the saturation magnetization m0 = 68 Gauss,
The constant k = 9.09 × 10 minus the sixth power / (A / m). The magnetic force acting on the magnetic fluid 29 has a rotational speed of 420
It is sufficiently larger than the centrifugal force acting on the magnetic fluid when it is assumed to be 0 rpm.
9 can be held near the contact point between the shaft end of the shaft 3 and the thrust bearing 22.

For example, when a spindle motor is used in a state where gravity acts downward in FIG. 2, the magnetic fluid near the contact point between the shaft end of the shaft 3 and the thrust bearing 22 is generated by the centrifugal force caused by the rotation of the shaft 3. Even when the magnetic fluid 29 is blown outward, since the magnetic fluid 29 is full here, the magnetic fluid 2
9 seems to be replenished soon. However, in actuality, when assembling the bearing unit 1, it is difficult to avoid air bubbles from being mixed into the magnetic fluid 29. When air bubbles are mixed into the magnetic fluid 29, the centrifugal force acting on the air bubbles and the centrifugal force acting on the magnetic fluid 29 are larger than the centrifugal force acting on the magnetic fluid 29. Thrust bearing 2
The magnetic fluid 29 gathers near the contact point 2 and the magnetic fluid 29 runs short near the contact point. This results in poor lubrication,
Wear of the shaft end of the shaft 3 or the thrust bearing 22 occurs.

When abrasion occurs and the amount of abrasion becomes larger than, for example, the gap h1 between the base 2 and the hub 4 shown in FIG. 1, the two come into contact with each other to generate noise and generate abrasion powder, which is generated by the magnetic disks 5 and 6. It may cause damage. Therefore, it is necessary to reduce the wear of the shaft end of the shaft 3 and the thrust bearing 22 as much as possible. As described above, by holding the magnetic fluid 29 near the contact point between the end of the shaft 3 and the thrust bearing 22 by the magnetic force that overcomes the centrifugal force, it is possible to reduce the wear of both.

In this embodiment, the case where the radial bearing 23 has a weak magnetism has been described. However, when the radial bearing 23 is made non-magnetic, the preload becomes small and the magnetic fluid 29
In the vicinity of the contact point between the shaft end of the shaft 3 and the thrust bearing 22 is weakened. However, this problem can be avoided by making the pressurizing magnet 25 a strong magnet. Radial bearing 23
May be made of a ferromagnetic material. In this case, even if the pressurizing magnet 25 is weak, a sufficient pressurizing force and a magnetic fluid holding force can be secured. When the radial bearing 23 is made of a ferromagnetic material, the main component of the radial bearing 23 must be iron in view of the manufacturing cost. The main component of the shaft 3 is also iron, and when poor lubrication occurs, large abrasion is feared. For this reason, when the radial bearing 23 is made of a ferromagnetic material, it is necessary to apply a coating of a copper-based alloy or the aforementioned TiN or CrN to the surface.

FIG. 4 is a plan view (1) and a sectional side view (2) of a magnetic disk drive using the spindle motor shown in FIG. Although not shown in FIG. 4, a bearing unit is mounted on the base 2 as shown in FIG. 1, and the shaft 3 is supported by the bearing unit, and the hub 4 is fixed to the shaft 3. Magnetic disks 5 and 6 are fixed to the hub 4 with a clamper 8 and a clamp screw 9 with a spacer 7 interposed therebetween. The magnetic disks 5 and 6 are rotatable around a rotation axis determined by the bearing unit 1.

The pivot 35 has three arms 36, 3
7 and 38 are attached, and three can be simultaneously rotated around the pivot 35. Three arms 36,
The coils are further attached to 37 and 38.
In FIG. 4, this coil is not shown because it is behind the magnetic circuit 47. A magnetic field is applied to this coil by a magnetic circuit 47.
A moment is generated which causes 6, 37, 38 to rotate about pivot 35. A slider 40 is provided at the tip of the arm 36 via a suspension 39, and sliders 42 and 44 are provided at a tip of the arm 37 via suspensions 41 and 43.
However, a slider 46 is attached to the tip of the arm 38 via a suspension 45. Sliders 40, 4
The magnetic heads 2, 44, 46 are provided with magnetic heads for recording and reproducing information magnetically with respect to the magnetic disks 5, 6.

By rotating the arms 36, 37, 38 around the pivot 35, the sliders 40, 42, 44, 4
6 can be moved in the radial direction of the magnetic disks 5 and 6. Sliders 40, 42,
The magnetic heads provided at 44 and 46 need to be close to the surface of the magnetic disks 5 and 6 to a distance of 1 μm or less. For this reason, the distance between the sliders 40 and 42 and the magnetic disk 6 and the distance between the sliders 44 and 46 and the magnetic disk 5 must be 1 μm or less. If foreign matter is caught between the sliders 40, 42 and the magnetic disk 6, or between the sliders 44, 46 and the magnetic disk 5, the sliders 40, 42, 44, 46 or the magnetic disks 5, 6 may be damaged. There is. Sliders 40, 4
If the magnetic disks 2, 44, 46 are damaged, the magnetic head provided thereon may be damaged, and if the magnetic disks 5, 6 are damaged, the recorded information is lost.
Therefore, the magnetic disks 5, 4, 4, and 4 or the magnetic disks 5, 6 are not damaged.
It is necessary to clean the space where 6 exists so that no foreign matter exists.

The magnetic disk device is provided with a connector 31 through which power is supplied, an information recording / reproducing command is input to the device, information to be recorded is input, and reproduced information is output. Do. When an information recording / reproducing command is input from outside the apparatus while power is supplied from the connector 31, the circuit 32 connected to the connector 31
1 causes a predetermined current to flow through the coil 11 of FIG. 1 to rotate the magnetic disks 5 and 6. Concentric tracks such as tracks 51, 52 and 53 are provided on the magnetic disks 5 and 6, and information is recorded along the tracks.

If the instruction was to record information, the circuit 32
Supplies current to the coils attached to the arms 36, 37, 38 to move the sliders 40, 42, 44, 46 in the radial direction of the magnetic disks 5, 6,
The magnetic head provided on 2, 44, 46 is positioned on a predetermined track on which information is to be recorded. On each track, a mark for detecting a deviation between the track and the magnetic head is provided.
The magnetic heads provided on the reference numerals 4 and 46 read this mark to detect a deviation from a predetermined track. A signal indicating a predetermined track on which information is to be recorded / reproduced and a displacement of the magnetic head are called a track error signal. The circuit 32
The track error signal detected by the magnetic head is output to the arm 3
Feedback is provided to the coils attached to 6, 37 and 38 to position the magnetic head on a predetermined track. After the positioning is performed, the circuit 32 supplies a current to the magnetic head to record information.

When the instruction is to reproduce information, the magnetic head is positioned on a predetermined track from which information is to be reproduced, and marks are detected by using the magnetic head in the same manner as in the case of recording. The circuit 32 reproduces the recorded information from the detected mark and outputs it from the connector 31 to the outside of the device.

A magnetic head and arms 36, 37, 38 provided on the sliders 40, 42, 44, 46;
The electrical connection with the device 2 is made via a connector 33 and an FPC 34.

By increasing the outer diameter of the magnetic disks 5 and 6,
It is possible to increase the amount of information recorded on the magnetic disks 5 and 6. However, this is not an effective method because it increases the size of the apparatus. In order to increase the amount of information without increasing the size of the device, it is effective to reduce the track pitch, which is the distance between tracks.

In FIG. 4, tracks 51, 52 and 53 indicate adjacent tracks, respectively, and tp in FIG. 4 indicates a track pitch. In a normal magnetic disk drive,
It is necessary to position a magnetic head for recording and reproducing information on a track for recording and reproduction with an accuracy of about 5 to 10% of the track pitch. When the magnetic disks 5 and 6 rotate,
In addition to the magnetic disks 5 and 6 vibrating, the bearing unit 1 also generates vibration. The track swings due to these vibrations, and the magnetic head needs to follow this swing.

The positioning mechanism shown in FIG. 4 is similar to the positioning mechanism used in a normal magnetic disk drive, and the crossover frequency of the feedback control is reduced due to the mechanical resonance of the arms 36, 37 and 38. It is difficult to make it 1kHz or more. For this reason, it is impossible to follow the swing of a track having a frequency of 1 kHz or more. Conventionally, a ball bearing has been used as a bearing for a spindle motor of a normal magnetic disk drive, and the ball bearing has a vibration that is not synchronized with rotation of about 0.1 μm, which is called ball passing vibration. This vibration contains a frequency component of 1 kHz or more, and it is difficult for the magnetic head to follow the swing of the track caused by the ball passing vibration.

As described above, in a normal magnetic disk drive,
Since it is necessary to make the magnetic head follow the track with an accuracy of about 5 to 10% of the track pitch, it is difficult to make the track pitch smaller than 1 to 2 μm when using a ball bearing. Therefore, in the present invention, the radial bearing 23 of the bearing unit 1 is a fluid bearing, and unlike the case of a ball bearing, there is no ball passing vibration, and the vibration not synchronized with the rotation can be 0.05 μm or less. Therefore, the track pitch tp
Can be set to 1 μm or less.

Although the present embodiment has been described as a magnetic disk device, it may be a magneto-optical disk device or a phase-change optical disk device capable of optically recording information.

The second embodiment of the present invention will be described with reference to FIG. FIG. 5 is a sectional view of the bearing unit 1.

The bearing unit 1 in the second embodiment,
The difference from the bearing unit 1 in the first embodiment is that the yoke 24 is provided, the lid 61 is provided instead of the screw seal 26, and the radial bearing 23 is non-magnetic.

The housing 21 has a cylindrical shape, and a cylindrical yoke 24 is press-fitted inside the housing 21. A radial bearing 23 is further press-fitted inside the yoke 24. The inner shape of the radial bearing 23 is the same as that of the first embodiment. As the material of the radial bearing 23, an aluminum alloy for bearing, a copper alloy for bearing, and white metal can be used. Further, a sintered oil-impregnated alloy containing copper as a main component may be used.

In the second embodiment, a magnetic circuit is constituted by the preload magnet 25, the yoke 24, the shaft 3, and the thrust bearing 22. For this reason, even if the radial bearing 23 is non-magnetic, a large magnetic flux can be generated near the contact point between the shaft 3 and the thrust bearing 22. The suction force between the shaft 3 and the thrust bearing 22 and the holding force of the magnetic fluid 29 near the contact point between the two are the same as in the first embodiment.

In the second embodiment, the radial bearing 23
Can be made ferromagnetic or have weak magnetism. In the first embodiment, the screw seal 26 is used. However, in the second embodiment, a simple unthreaded lid 61 is used in the inner peripheral portion in order to facilitate processing of components.

A third embodiment of the present invention will be described with reference to FIG. FIG. 6 is a sectional view of the bearing unit 1.

The third embodiment is different from the first embodiment in that the housing 21 has a cylindrical shape, the thrust bearing 22 has a recessed structure, and the stopper ring 27 has a thrust bearing. Edge part of bearing 22 and radial bearing 2
3 and the screw seal 26 serving as the lid 61. Thrust bearing 22 of the third embodiment
The edge portion serves as the spacer 28 of the first embodiment.

The housing 21 has a cylindrical shape, and a radial bearing 23 is press-fitted inside the housing 21.
The inner surface shape and material of the radial bearing 23 are the same as those in the first example. The center of the thrust bearing 22 is hollow,
The rim is higher. The depression is further provided with a depression for positioning the preload magnet 25, and the preload magnet 25 is mounted here. The material of the thrust bearing 22 is a ferromagnetic material such as martensitic or ferritic stainless steel.

In the third embodiment, the preload magnet 25, the radial bearing 23, the shaft 3, and the thrust bearing 22 constitute a magnetic circuit. Regarding the suction force between the shaft 3 and the thrust bearing 22 and the holding force of the magnetic fluid 29 near the contact point between the two,
This is the same as in the first embodiment. In the third embodiment, the magnetic circuit may be short-circuited at the edge of the thrust bearing 22. For this reason, the gap C1 between the shaft 3 and the preload magnet 25 is formed by the edge portion of the thrust bearing 22 and the preload magnet 25.
Of the thrust bearing 2
No short circuit is caused at the edge of the second. Lid 61
Is the same as in the second embodiment.

A fourth embodiment of the present invention will be described with reference to FIG. FIG. 7 is a sectional view of the bearing unit 1.

The difference between the fourth embodiment and the first embodiment is that the housing 21 and the radial bearing 23 of the first embodiment are different.
However, in the fourth embodiment, the point integrated with the housing 21, the point that the preload magnet 25 is located inside the spacer 28, and the stopper ring 27 is sandwiched between the housing 21 and the spacer 28. A point, the shaft end of the shaft 3 is flat, the thrust bearing 22 has a convex shape, and the screw seal 26 is a lid 61.

The inner surface of the housing 21 in the fourth embodiment has the same shape as the inner surface of the radial bearing 23 in the first embodiment, and functions as a radial bearing.
As the material of the housing 21, when the housing 21 is non-magnetic, aluminum alloy for bearing, copper alloy for bearing, white metal, copper-based sintered alloy, etc. is used. When the joined alloy is ferromagnetic, a ferritic or martensitic stainless steel can be used in addition to an iron-based sintered alloy. In the case of using a sintered alloy, it is necessary to fill the pores in advance by a method such as impregnation with a resin in order to prevent seepage of the magnetic fluid 29. Further, since the material of the shaft 3 is martensitic stainless steel, when stainless steel is used as the material of the housing 21, it is necessary to apply a coating as in the case of the first embodiment. Hereinafter, the description will be made assuming that the housing 21 is made of an alloy obtained by sintering stainless steel and copper approximately in half.

The stopper ring 27 is fixed between the housing 21 and the spacer 28. Thrust bearing 2
2 has a convex curved surface at the center. Thrust bearing 2
The material 2 is a ferromagnetic material such as martensitic or ferritic stainless steel.

In the fourth embodiment, the preload magnet 25, the housing 21, the shaft 3, and the thrust bearing 22 constitute a magnetic circuit. Although the end of the shaft 3 is flat and the thrust bearing 22 is convex, the preload magnet 25, the housing 21, the shaft 3, and the thrust bearing 22 constitute a magnetic circuit. The magnetic flux near the point of contact between the thrust bearing 3 and the thrust bearing 22 can be increased, and a sufficient preload can be obtained. Also,
As in the first embodiment, the gap is small near the rotation axis and the gap at a position far from the rotation axis is also small. The force for holding the magnetic fluid 29 in the vicinity of the contact point between the shaft 3 and the thrust bearing 22 can be obtained in the same manner as in the first embodiment. In the fourth embodiment, since the housing 21 has weak magnetism, the magnetic circuit may be short-circuited in a portion outside the housing 21. Therefore, a nonmagnetic spacer 28 is arranged outside the preload magnet 25 so that the magnetic flux goes to the inner peripheral side of the preload magnet 25.

The lid 61 is the same as in the second embodiment.

[0064]

According to the present invention, a highly reliable spindle motor with low loss, NRRO, and low noise can be realized, and an information recording apparatus with high density, high reliability and low noise can be constructed.

[Brief description of the drawings]

FIG. 1 is a sectional view of a spindle motor.

[Fig. 2] Enlarged view of bearing

FIG. 3 is an enlarged view near the shaft end.

FIG. 4 is a plan view and a sectional side view of the disk device.

FIG. 5 is an enlarged view of a bearing.

FIG. 6 is an enlarged view of a bearing.

FIG. 7 is an enlarged view of a bearing.

[Description of Signs] 1 ... Bearing unit, 2 ... Base, 3 ... Shaft, 4 ... Hub, 6
... magnetic disk, 7 ... spacer, 8 ... clamper, 9 ... clamp screw, 10 ... stator yoke, 11 ... coil, 1
2 ... rotor magnet, 21 ... housing, 2 ... thrust bearing, 23 ... radial bearing, 4 ... yoke, 25 ... preload magnet, 26 ... screw seal, 27 ... stopper ring, 2
8 ... spacer, 29 ... magnetic fluid, 31 ... connector, 32
... Circuit, 33 ... Connector, 34 ... FPC, 35 ... Pivot 37, 38 ... Arm, 39 ... Suspension, 40 ...
Slider, 41 suspension, 42 slider, 4
3: Spence, 44: slider, 45: suspension, 46: slider, 47: magnetic circuit, 51, 52,
53: truck, 61: lid.

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Katsutoshi Arai 502, Kandachicho, Tsuchiura-shi, Ibaraki Pref. Machinery Research Laboratories, Hitachi, Ltd. F term in the system division (reference)

Claims (4)

[Claims] 1. A shaft, a rotor comprising a permanent magnet fixed to the shaft, a stator comprising an iron core and a coil provided opposite to the rotor, and a radial for restraining a radial displacement of the shaft. A spindle motor comprising a bearing and a thrust bearing for restraining displacement in a thrust direction, wherein the shaft, the thrust and the radial bearing are lubricated by a lubricant, wherein the shaft, the radial and the thrust bearing are all ferromagnetic. Wherein the lubricant is a magnetic fluid, and a magnetic field generating magnet for applying a magnetic field to the thrust bearing is attached. 2. A spindle motor according to claim 1, wherein said thrust bearing has a flat plate shape, said magnetic field generating magnet has a cylindrical shape, and said magnetic field generating magnet is in contact with a shaft end of said thrust bearing. A spindle motor mounted on a surface on the same side as the surface and in contact with a shaft end of the thrust bearing inside the cylindrical magnetic field generating magnet. 3. A shaft, a rotor comprising a permanent magnet fixed to the shaft, a stator comprising an iron core and a coil provided opposite to the rotor, and a radial for restraining a radial displacement of the shaft. A spindle motor having a housing that fixes a bearing and a thrust bearing that restrains displacement in a thrust direction, wherein the shaft, the thrust and the radial bearing are lubricated by a liquid lubricant, the spindle motor being supported by the radial bearing; A stopper ring for preventing the shaft from coming off, and a leakage preventing means for preventing leakage of the liquid lubricant, wherein the housing is hollow, and the radial bearing is fixed to a hollow portion of the housing; A bearing is fixed to the housing so as to close one end of the hollow housing. The thrust bearing is formed of a ferromagnetic material, a magnetic field generating magnet for applying a magnetic field to the thrust bearing is attached to the thrust bearing, and the liquid lubricant is a magnetic material. A spindle motor characterized by being a fluid. 4. A disk device having a disc-shaped information recording medium, a spindle motor for rotating the same, and a head for recording and reproducing information on and from the information recording medium, wherein the spindle motor is fixed to the shaft and the shaft. , A stator comprising an iron core and a coil provided facing the rotor, a radial bearing for restraining radial displacement of the shaft, and a thrust bearing for restraining displacement in the thrust direction Wherein the shaft, the thrust and the radial bearing are lubricated by a lubricant of a magnetic fluid, the shaft, the radial and the thrust bearing are both formed of ferromagnetic material, and a magnetic field is applied to the radial bearing and the thrust bearing. A disk device, wherein a magnetic field generating magnet is mounted.