JPH04355639A - Spindle motor - Google Patents

Abstract

PURPOSE:To prevent the scattering of magnetic fluid by magnetizing the sections, where the shaft of a motor is opposed to a pair of pole pieces on both sides, into the polarities opposite to the polarities of the tree ends of a pair of hole pieces. CONSTITUTION:A spindle motor is equipped with a shaft 5, which is fixed to a housing 14, and a hub 11, which can rotate freely through bearing members 8 and 9 to the shaft 5. For the hub 11, a cylindrical hub body 13 and a flange 12 are made integrally and a yoke member 14 and a rotor magnet 32 are installed at the inside periphery. A magnetic fluid seal means 40 and 42 are provided outside the bearing members 8 and 9. The seal members 40 and 42 are equipped with magnetic fluid holding means consisting of circular permanent magnets 50 and a pair of pole pieces 52 and 54 on both sides. The sections where the shaft 5 is opposed to the pole pieces 52 and 54 are magnetized into opposite polarities to the polarities of the free ends of the pole pieces 52 and 54. Hereby, the magnetic force from the pole piece concentrates on the magnetized part of the shaft, and the scattering of the magnetic fluid 3 can be prevented.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a spindle motor for rotationally driving a recording member such as a magnetic disk.

0002

2. Description of the Related Art Generally, a spindle motor includes a shaft fixed to a bracket (or a frame of a recording member driving device), a hub rotatable relative to the shaft, and a shaft interposed between the hub and the shaft. The rotor magnet includes a bearing means mounted on the hub, a rotor magnet mounted on the hub, and a stator disposed opposite to the rotor magnet. Magnetic fluid sealing means is arranged on the outside of the bearing means,
This magnetic fluid sealing means prevents grease and the like from the bearing means from entering the housing chamber (the chamber in which the recording member is housed).

0003

However, this type of spindle motor has the following problems to be solved. The magnetic fluid sealing means in a spindle motor has a magnetic fluid holding means consisting of an annular permanent magnet and a pair of pole pieces arranged on both sides of the annular permanent magnet, and the magnetic fluid holding means is attached to a hub. . A magnetic fluid is filled between the pair of pole pieces and the shaft.

Conventionally, this magnetic fluid is held only by the magnetic force of the permanent magnet of the magnetic fluid holding means, and therefore, the magnetic holding force is not large and conditions such as pressure, temperature, rotation speed, etc. are severe. There was a risk that the magnetic fluid would scatter and enter the containment chamber.

An object of the present invention is to provide a spindle motor that can increase the magnetic holding force for holding the magnetic fluid and prevent the magnetic fluid from scattering even under relatively severe conditions.

[0006]

Means for Solving the Problems In the spindle motor according to claim 1 of the present invention, the magnetic fluid sealing means includes an annular permanent magnet and a pair of pole pieces disposed on both sides of the annular permanent magnet. The portion of the shaft that faces the pair of pole pieces is magnetized to have a polarity opposite to that of the free ends of the pair of pole pieces.

In the spindle motor according to claim 2 of the present invention, an annular sleeve member made of a magnetic material is attached to the shaft, and one end of the annular sleeve member is connected to the free end of one of the pair of pole pieces. The other end of the annular sleeve member is magnetized to a polarity opposite to that of the other free end of the pair of pole pieces.

[0008]

[Operation] In the spindle motor according to claim 1 of the present invention, since the portion of the shaft that faces the pair of pole pieces is magnetized with a polarity opposite to the polarity of the free end portions of the pair of pole pieces, The magnetic force from the pole piece is concentrated on the magnetized portion of the shaft, and the magnetic fluid is held by the relatively strong magnetic force.

Further, in the spindle motor according to claim 2 of the present invention, an annular sleeve member made of a magnetic material is attached to the shaft, and one end of the annular sleeve member is connected to one free end of the pair of pole pieces. The other end of the annular sleeve member is magnetized with a polarity opposite to that of the other free end of the pair of pole pieces. Holding power can be increased.

0010

DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of a spindle motor according to the present invention will be described below with reference to the accompanying drawings.

FIG. 1 shows an embodiment of a spindle motor according to the present invention. In FIG. 1, the illustrated spindle motor includes a housing 14, a shaft 5 fixed to the housing 14, and a hub 11 rotatable relative to the shaft 5. The housing 14 is
It is composed of a substantially disk-shaped member, and is fixed, for example, to a frame (not shown) of a recording member driving device by means such as a mounting screw. Note that the shaft 5 may be directly fixed to the frame.

The shaft 5 is fixed approximately at the center of the housing 14, and the other end extends substantially vertically upward from the housing 14. A hub 11 is connected to the shaft 5 via a pair of bearing members 8 and 9 (constituting bearing means).
is rotatably supported. The hub member 11 has a cylindrical hub body 13, and one end (lower end) of the hub body 13.
is integrally provided with a flange portion 12 that protrudes radially outward. A yoke member 14 is attached to the inner circumference of the hub body 13, and an annular rotor magnet 32 is attached to the inner circumference of the yoke member 14.

In the embodiment, as shown in FIG. 1, one bearing member 8 supports one end of the hub 11 via an annular bush 10 and a yoke member 14, and the other bearing member 9 supports one end of the hub 11 via an annular bush 10 and a yoke member 14. The other end of the hub 11 is supported. Then, a plurality of recording members such as magnetic disks (
(not shown) is attached.

[0014] Rotor magnet 3 attached to hub 11
A stator 34 is disposed opposite to 2. The stator 34 includes a stator core 36 attached to the shaft 5 and coils 38 wound around the stator core 36 as required.
have. By supplying drive current to this coil 38 as required, the stator 34 (housing 14
and shaft 5), the hub 11 (recording member and rotor magnet 32) is rotationally driven in a predetermined direction.

Magnetic fluid sealing means 40 and 42 are arranged on the outside of the bearing members 8 and 9. The magnetic fluid sealing means 40 and 42 have substantially the same configuration, and one of the magnetic fluid sealing means 40 (42) will be described below. The illustrated magnetic fluid sealing means 40 (42) is the bush 10.
(the other sealing means 42 is attached to the yoke member 14 via the non-magnetic bushing 10), the magnetic fluid retaining means includes an annular permanent magnet 50 and an annular permanent magnet 50; A pair of pole pieces 52 and 54 are provided on both sides of the magnet 50. The free ends of the pair of pole pieces 52 and 54 protrude radially inward from the inner circumferential end of the permanent magnet 50, and the magnetic fluid 3 is disposed between the protruding ends and the outer circumferential surface of the shaft 5. Filled. The magnetic fluid sealing means 40 (42) provides a substantially airtight seal between the inside of the motor and the housing chamber 17, and prevents grease and the like from the bearing member 8 (9) from entering the housing chamber 17.

The magnetic fluid sealing means 40 (42) is further configured as follows. That is, shaft 5
An annular sleeve member 56 made of a magnetic material is disposed at a portion of the magnetic fluid sealing means 40 (42) facing the magnetic fluid holding means. This sleeve member 56 can be attached by means such as press fitting, for example. The width of the sleeve member 56 is preferably smaller than the width of the magnetic fluid retaining means, and in the embodiment, one end thereof is located somewhat inside (upper side in FIG. 1) than the outer pole piece 52, and the other end is located somewhat outside (lower side in FIG. 1) than the inner pole piece 54.

Sleeve member 56 is magnetized as shown in FIG. The permanent magnet 50 in the magnetic fluid holding means is
It is magnetized so that the outer end surface becomes the north pole and the inner end surface becomes the south pole. Therefore, as will be readily understood, the free end of the outer pole piece 52 is magnetized to the north pole, and the free end of the inner pole piece 54 is magnetized to the south pole. In connection with this, one end (lower end) of the sleeve member 56 is magnetized to the S pole, which is the opposite polarity to the magnetic pole of the outer pole piece 52, and the other end (upper end) is magnetized to the north pole, which is the opposite polarity to the magnetic pole of the inner pole piece 54.

By magnetizing the sleeve member 56 in this manner, most of the magnetic force from the outer pole piece 52 is
toward the opposite end of the sleeve member 56 (magnetized to the south pole), and further through the sleeve member 56 to the other end (magnetized to the north pole) toward the inner pole piece 54. Therefore, the magnetic fields between the pole piece 52 and one end of the sleeve member 56 and between the pole piece 54 and the other end of the sleeve member 56 become stronger, and the magnetic fluid 3 filled between them becomes magnetic. strongly held,
Its scattering is reliably prevented even under severe environmental conditions.

FIG. 2 shows a modification of the spindle motor. In this modification, improvements have been made on the shaft side. Note that the same members as in FIG. 1 will be described with the same numbers.

In FIG. 2, a small diameter portion 5a is formed at the other end of the shaft 5, and an annular permanent magnet 6 is attached to this small diameter portion 5a.
2 is attached, and magnetic annular members 64 and 66 are further disposed on both sides of the permanent magnet 62. One annular member 66 is disposed opposite to and inside the outer pole piece 52 of the magnetic fluid sealing means 42, and the other annular member 64 is disposed opposite to and inside the inner pole piece 54. ing. As shown in FIG. 2, the permanent magnet 50 in the magnetic fluid retaining means has an outer end face magnetized to the north pole and an inner end face magnetized to the south pole. As a result, the free end of the outer pole piece 52 is magnetized to the north pole, and the free end of the inner pole piece 54 is magnetized to the south pole.

Regarding the magnetic pole arrangement of the permanent magnet 50 of the magnetic fluid holding means, the permanent magnet 62 on the shaft 5 side is magnetized as follows. That is, the permanent magnet 62 is magnetized so that one end (outer end) becomes an S pole and the other end (inner end) becomes an N pole. By being magnetized in this manner, the annular member 66 facing the outer pole piece 52 becomes S.
The annular member 64 facing the inner pole piece 54 is magnetized as a north pole. Thus, similar to the embodiment of FIG. Most of the magnetic force from the inner pole piece 54 is directed toward the inner pole piece 54, and therefore the magnetic fields between the pole piece 52 and the annular member 66 and between the pole piece 54 and the annular member 64 become stronger.
The magnetic fluid 3 filled between these is strongly held magnetically.

In a modified example, as shown in FIG.
It is preferable that the thicknesses (widths) of the pole pieces 4 and 66 are set smaller than the thicknesses (widths) of the pole pieces 52 and 54. With each configuration, the magnetic force is concentrated on the outer circumferential surfaces of the annular members 64 and 66, and scattering of the magnetic fluid can be more effectively prevented.

Although one embodiment of the spindle motor according to the present invention has been described above, the present invention is not limited to this embodiment, and various modifications and modifications can be made without departing from the scope of the present invention. be.

For example, in the illustrated embodiment, the outer diameter of the sleeve member 56 is substantially the same over its entire length, but the outer diameter of the sleeve member 56 is reduced at the axial center, which more effectively prevents scattering of the magnetic fluid. It is preferable that the outer diameter is made larger and the outer diameter gradually decreases from the center toward both ends.

Further, for example, in the illustrated embodiment, the description has been made with application to a spindle motor having a configuration in which magnetic fluid sealing means are provided on both sides of a pair of bearing members, but the present invention is not limited to this. It can be similarly applied to a spindle motor having a structure in which a magnetic fluid sealing means is provided on the outside of one bearing member and a labyrinth sealing means is provided on the outside of the other bearing member, and in such a case, the magnetic fluid sealing means is The present invention can be applied in connection with.

[0026]

As described in detail above, in the spindle motor according to claim 1 of the present invention, the portion of the shaft that faces the pair of pole pieces has a polarity opposite to that of the free ends of the pair of pole pieces. It is magnetized, so that the magnetic force from the pair of pole pieces is directed toward the magnetized portion of the shaft, so that the magnetic fluid can be held by the relatively strong magnetic force and the magnetic fluid is prevented from scattering.

Further, in the spindle motor according to claim 2 of the present invention, an annular sleeve member made of a magnetic material is attached to the shaft, and one end of the annular sleeve member is connected to one free end of the pair of pole pieces. The other end of the annular sleeve member is magnetized with a polarity opposite to the polarity at the other free end of the pair of pole pieces. Magnetic holding power can be increased.

[Brief explanation of the drawing]

FIG. 1 is a partially omitted cross-sectional view showing an embodiment of a spindle motor according to the present invention.

FIG. 2 is a partial sectional view showing a modification of the spindle motor.

[Explanation of symbols]

3 Magnetic fluid 5 Shaft 11 Hub 32 Rotor magnet 34 Stator 40, 42 Magnetic fluid sealing means 50 Permanent magnet 52, 54 Pole piece 56 Annular sleeve member 62 Permanent magnet 64, 66 Annular member

Claims (2)

[Claims] 1. A shaft, a hub rotatable relative to the shaft, a bearing means interposed between the hub and the shaft, a rotor magnet attached to the hub, and a rotor. In a spindle motor comprising a stator disposed facing the magnet, and a magnetic fluid sealing means disposed outside the bearing means, the magnetic fluid sealing means includes an annular permanent magnet and a magnetic fluid sealing means disposed outside the bearing means. Equipped with a pair of pole pieces arranged on both sides of a permanent magnet,
A spindle motor characterized in that a portion of the shaft that faces the pair of pole pieces is magnetized to have a polarity opposite to that of the free end portions of the pair of pole pieces. 2. An annular sleeve member made of a magnetic material is attached to the shaft, and one end of the annular sleeve member has a polarity opposite to that of one free end of the pair of pole pieces. 2. The spindle motor according to claim 1, wherein the annular sleeve member is magnetized, and the other end of the annular sleeve member is magnetized to a polarity opposite to the polarity at the other free end of the pair of pole pieces.