JPH0828035B2 - Spindle motor - Google Patents

Description

The present invention relates to a spindle motor provided with a magnetic fluid sealing means.

[Conventional technology]

Generally, a spindle motor for rotationally driving a recording member such as a magnetic disk includes a housing body and a hub member rotatable relative to the housing body.

In the shaft fixed type motor, the shaft member is fixed to the housing body, and the hub member is rotatably supported by the shaft member via the bearing means. In addition, in the shaft rotation type motor,
The shaft member is rotatably supported by the housing body via bearing means, and the hub member is fixed to the shaft member thus supported.

This kind of spindle motor is further provided with a magnetic fluid sealing means in order to prevent grease from scattering from a ball bearing which constitutes the bearing means. The magnetic fluid sealing means has a pair of pole pieces and a magnetic fluid forming a sealing layer, and forms a substantially magnetic sealing layer outside the bearing means.

[Problems to be Solved by the Invention]

However, the conventional spindle motor has the following problems to be solved. That is, although the pair of pole pieces have substantially the same structure, they are arranged at intervals in a predetermined direction, one of them is adjacent to the bearing means, and the other of them is separated from the bearing means. . Therefore, the magnetic flux from the pole piece partially leaks outside through the bearing means (so-called shunt through the bearing means).

For example, FIG. 5 shows a part of a shaft rotation type spindle motor. A shaft member d is rotatably supported inside a cylindrical portion b of the housing main body a via a bearing member c, and a magnetic field is formed on the outer side in the axial direction of the bearing member c between the cylindrical portion b and the shaft member d. A fluid sealing means e is provided. The magnetic fluid sealing means e includes an annular permanent magnet f mounted on a cylindrical portion c, a pair of pole pieces g and h arranged on both sides thereof, and both of the pole pieces g and h and a shaft member d. It is composed of a magnetic fluid filled between them, and this magnetic fluid forms magnetic fluid layers i and j.

In such a configuration, the pole piece h located on the inner side in the axial direction of the pair of pole pieces g, h is close to the bearing member c which is a magnetic body, and therefore, as shown by the arrow in FIG. A part of the magnetic flux from the magnetic flux easily flows into the bearing member c, and a shunt of the magnetic flux occurs.

Therefore, the magnetic flux density in the inner pole piece h becomes smaller than the magnetic flux density in the outer pole piece g, and the magnetic flux densities in the magnetic fluid between the pole pieces g, h and the shaft member d differ. Due to the imbalance of the magnetic flux density, the magnetic fluid is scattered in a relatively short period of time.
The magnetic fluid layer may be damaged.

The present invention has been made in view of the above facts, and a main object of the present invention is to provide a spindle motor that can obtain a sufficiently stable magnetic sealing effect for a long period with a relatively simple structure. is there.

[Means for solving the problem]

To achieve the above object, in a spindle motor of the present invention, a stationary member, a rotating member that is rotatable relative to the stationary member, and a bearing interposed between the stationary member and the rotating member. Member, and a magnetic fluid sealing means arranged axially outside the bearing member between the stationary member and the rotating member, wherein the magnetic fluid sealing means is mounted on the stationary member or the rotating member. And a pair of pole pieces arranged on both sides of the permanent magnet, and a magnetic fluid filled between each of the pole pieces and the rotating member or the stationary member, and the bearing member is a ball. As the bearing, the magnetic fluid sealing means is disposed in the vicinity of the bearing member, and between the inner pole piece positioned on the inner side in the axial direction and adjacent to the bearing member and the rotating member or the stationary member, of the pair of pole pieces. Voids and out those that have been formed to be smaller than the gap between the outer pole piece spaced from the bearing member located axially outwardly with the rotating member or the stationary member.

Further, in order to achieve the above-mentioned object, the spindle motor of the present invention, among the pair of pole pieces in the magnetic fluid sealing means, has an area of a magnetic pole end surface of an inner pole piece located axially inside and adjacent to the bearing member, It is formed to be smaller than the area of the magnetic pole end surface of the outer pole piece located axially outside and separated from the bearing member.

Further, in the spindle motor of the present invention, in order to achieve the above-mentioned object, among the pair of pole pieces in the magnetic fluid sealing means, the magnetic permeability of the inner pole piece located on the inner side in the axial direction and adjacent to the bearing member is set to the axial direction. The outer pole piece is formed to have a larger magnetic permeability than the outer pole piece located outside and separated from the bearing member.

[Action]

In such a spindle motor, in the case of the first invention, of the pair of pole pieces of the magnetic fluid sealing means,
Since the gap of the inner pole piece located axially inward, that is, adjacent to the bearing member, with respect to the rotating member or the stationary member is formed smaller than that of the outer pole piece axially located outside, that is, separated from the bearing member. The magnetic flux density in the air gap on the inner pole piece side becomes larger than that in the conventional case. As a result, a part of the magnetic flux from the inner pole piece adjacent to the bearing member is prevented from being shunted to the bearing member, which prevents a decrease in the magnetic flux density in the inner pole piece, and prevents the magnetic flux density in the outer magnetic fluid layer generated by the outer pole piece. And the magnetic flux density in the inner magnetic fluid layer generated by the inner pole piece become substantially equal,
A stable two-layer magnetic fluid layer is formed over a long period of time,
The magnetic fluid is prevented from scattering and the magnetic fluid layer is prevented from being damaged.

Further, in the case of the second invention, since the area of the magnetic pole end surface of the inner pole piece adjacent to the bearing member is formed smaller than that of the outer pole piece separated from the bearing member, the magnetic pole end surface of the inner pole piece is The magnetic flux density is higher than in the conventional case, and the decrease in the magnetic flux density in the inner pole piece due to the shunt of a part of the magnetic flux from the inner pole piece to the bearing member is prevented, and the same effect as described above is obtained. .

Further, in the case of the third invention, since the magnetic permeability of the inner pole piece adjacent to the bearing member is formed to be larger than that of the outer pole piece separated from the bearing member, the magnetic resistance in the inner pole piece is larger than that in the outer pole piece. The magnetic flux density in the air gap between the inner pole piece and the rotating member or stationary member becomes larger than in the conventional case, and a part of the magnetic flux from the inner pole piece is shunted to the bearing member. The decrease in the magnetic flux density in (1) is prevented, and the same effect as described above is obtained.

[Examples] Hereinafter, further details will be described with reference to the accompanying drawings.

First Embodiment showing a first embodiment of a spindle motor of the present invention
In FIG. 2 and FIG. 2, the illustrated spindle motor includes a housing main body 2 serving as a stationary member and a shaft member 4 serving as a rotating member rotatable with respect to the housing main body 2. The housing body 2 is a frame (not shown)
And a cylindrical portion 8 extending substantially vertically from the bracket portion 6 in the vertical direction.
The shaft member 4 is rotatably supported in the cylindrical portion 8 via a pair of bearing members 10 (comprising ball bearings, only one of which is shown in FIGS. 1 and 2), for example, an arrow (FIG. 1). It is driven to rotate in the direction indicated by. The hub member 12 is fixed to one end (upper end) of the shaft member 4. The illustrated hub member 12 is the shaft member 4
The end portion 14 fixed to the end wall portion 14, a cylindrical main body portion 16 extending downward from the outer peripheral end of the end wall portion 14, and a flange portion 18 extending radially outward from the lower end of the cylindrical main body portion 16, the cylindrical main body portion 18 A plurality of recording members 20, such as magnetic disks, are mounted on the outer circumference of the disk via spacer members 22.

A magnetic fluid sealing means 24 is further arranged outside the one (upper) bearing member 10 shown. The magnetic fluid sealing means 24 includes an annular permanent magnet 26 and a pair of pole pieces 28 and 30 arranged on both surfaces of the permanent magnet 26, which are mounted on the inner peripheral surface of the cylindrical portion 8 of the housing body 2. Has been done.

A magnetic fluid is filled between the pair of pole pieces 28 and 30 and the shaft member 4, and the magnetic fluid substantially 2
Layered magnetic fluid layers 32 and 34 are formed. Magnetic fluid layer
32 and 34 are formed in an annular shape on the outer peripheral surface of the shaft member 4 and prevent grease and the like from the bearing member 10 from entering the disk chamber.

With respect to the magnetic fluid sealing means 24, the first embodiment is further configured as follows.

Mainly referring to FIG. 2, an inner pole piece 30 adjacent to the bearing member 10 (lower side in FIGS. 1 and 2)
Has an inner diameter smaller than that of the other (upper side in FIGS. 1 and 2) outer pole piece 28, so that the pole tip of the inner pole piece 30 projects radially inwardly from the pole tip of the outer pole piece 28. The gap W1 between the magnetic pole end surface (inner end surface) of the outer pole piece 28 and the outer peripheral surface of the shaft member 4 is larger than the gap W2 between the magnetic pole end surface (inner end surface) of the inner pole piece 30 and the outer peripheral surface of the shaft member 4. Has become. In the first embodiment, the outer pole piece 28 and the inner pole piece 30 are made of a magnetic material such as iron, and their thicknesses are set to be substantially the same.

Since it is configured in this way, it has the following advantages. As shown in the figure, when the bearing member 10 is arranged near the pair of pole pieces 28 and 30, a magnetic circuit is generated through the bearing member 10, and a part of the magnetic flux passing through the inner pole piece 30 is generated by the bearing member. Flow as 10 shunts. Therefore, in the case where the pole pieces 28 and 30 are arranged on both sides of the permanent magnet 26 as in the embodiment, the magnetic flux densities from the pole pieces 28 and 30 are substantially equal, but a part of the magnetic flux flowing in the inner pole piece 30. Is split and flows through the bearing member 10, so that the magnetic flux density acting on the magnetic fluid (magnetic fluid layer 34) from the inner pole piece 30 is smaller than the magnetic flux density acting on the magnetic fluid (magnetic fluid layer 32) from the outer pole piece 28. There is a risk that it will become smaller and a stable sealing effect will not be obtained. On the other hand, in the first embodiment, in order to eliminate the above-mentioned inconvenience, the gap W1 between the magnetic pole end surface (inner end surface) of the outer pole piece 28 and the outer peripheral surface of the shaft member 4 has a magnetic pole of the inner pole piece 30. It is set to be larger than the gap W2 between the end surface (inner end surface) and the outer peripheral surface of the shaft member 4. Therefore, the magnetic pole end surface (inner end surface) of the outer pole piece 28
The magnetic flux density acting on the air gap between the shaft member 4 and the outer peripheral surface of the shaft member 4 is increased, and the imbalance of the magnetic resistance due to the presence of the bearing member 10 is compensated as required by the difference in the magnetic resistance of the two air gap portions, thus the inner pole. The magnetic flux density acting on the magnetic fluid from the piece 30 and the magnetic flux density acting on the magnetic fluid from the outer pole piece 28 become substantially equal, and a stable sealing effect is obtained for a long period of time.

FIG. 3 shows a second embodiment of the spindle motor of the present invention. In the second embodiment, the magnetic end faces of the pair of pole pieces are improved in order to compensate for the asymmetry of the magnetic resistance. The same members as those shown in FIGS. 1 and 2 will be described with the same reference numerals.

In FIG. 3, also in the second embodiment, the magnetic fluid sealing means 24 'includes an annular permanent magnet 26 and this annular permanent magnet.
A pair of pole pieces 28 'and 30' arranged on both sides of 26
It has. The outer pole piece 28 'and the inner pole piece 30' have substantially the same inner diameter and outer shape,
Therefore, the distance between the magnetic end surface (inner end surface) of the outer pole piece 28 'and the outer peripheral surface of the shaft member 4 and the distance between the magnetic end surface (inner end surface) of the inner pole piece 30' and the outer peripheral surface of the shaft member 4 are Although substantially the same, the thickness T1 of the magnetic end of the outer pole piece 28 'is greater than the thickness T2 of the magnetic end of the inner pole piece 30', so that the magnetic end surface of the inner pole piece 30 '(the shaft member 4 is smaller than the magnetic end surface of the outer pole piece 28 '. The other structure of the second embodiment is substantially the same as that of the first embodiment.

Thus configured, in the second embodiment,
The area of the magnetic end surface of the inner pole piece 30 'is smaller than that of the outer pole piece 28', and the inner pole piece 30 '
The ratio of the flux flow to the side area is increased, which compensates for the reduction in the flux density due to the shunt of the flux to the bearing member 10 as required. As a result, the magnetic flux density acting on the magnetic fluid from the inner pole piece 30 'and the outer pole piece 28'.
Therefore, the magnetic flux density acting on the magnetic fluid becomes substantially equal, and a stable sealing effect can be obtained as in the case of the first embodiment.

Incidentally, in FIG. 3, the thickness of the inner pole piece 30 'is made thin throughout, but instead of this, for example, the thickness of only a part of the magnetic end of the inner pole piece 30' may be changed. The area of the magnetic end face can be reduced by adopting a configuration such as making it thinner to concentrate the magnetic flux density locally, or partially thickening the thickness of the magnetic end (inner peripheral end) of the outer pole piece 28 '. You may make a difference.

FIG. 4 shows a third embodiment of the spindle motor of the present invention. In this embodiment, in order to compensate for the imbalance of the magnetic resistance, the magnetic permeability of the pair of pole pieces is made different.

Referring to FIG. 4, also in the third embodiment, the magnetic fluid sealing means 24 ″ includes an annular permanent magnet 26 and a pair of pole pieces 28 ″ and 30 ″ arranged on both surfaces of the permanent magnet 26. 28 ″ outer pole piece and 30 ″ inner pole piece
Have substantially the same inner diameter and outer diameter. Therefore, the distance between the magnetic end surface (inner end surface) of the outer pole piece 28 ″ and the outer peripheral surface of the shaft member 4 and the magnetic end surface of the inner pole piece 30 ″ ( The distance between the inner end surface) and the outer peripheral surface of the shaft member 4 is substantially the same, and the thickness thereof is substantially the same throughout, but they are made of different materials. That is, the outer pole piece 28 ″ is made of a material having a relatively low magnetic permeability, and the inner pole piece 30 ″ is made of a material having a relatively high magnetic permeability. The other structure of the third embodiment is substantially the same as that of the first embodiment.

Thus configured, in the third embodiment,
The magnetic flux density in the air gap between the magnetic end surface of the inner pole piece 30 ″ and the outer peripheral surface of the shaft member 4 is increased by the reduction of the magnetic resistance due to the material, and the magnetic resistance of both pole pieces 28 ″, 30 ″ by the bearing member 10 is increased. The imbalance of the magnetic field is compensated as required by the non-uniformity of the magnetic resistance due to the difference in magnetic permeability, so that the magnetic flux density acting on the magnetic fluid from the inner pole piece 30 ″ and the magnetic fluid acting on the outer pole piece 28 ″ The magnetic flux density is substantially the same, and a stable sealing effect can be obtained over a long period of time, as in the case of the first embodiment.

In the third embodiment, the materials of the pole pieces 28 ″ and 30 ″ are changed to give different magnetic permeability, but instead of this, only a part of them may be changed, or Through-holes or surface treatment (for example, unevenness may be made on the surface) may be applied to the same member to give different magnetic permeability.

Although the embodiments of the spindle motor according to the present invention have been described above, the present invention is not limited to these embodiments, and various modifications and changes can be made without departing from the scope of the present invention.

For example, the air gap between the pole piece and the shaft member in the first embodiment, the area of the magnetic pole end surface of the pole piece in the second embodiment, and the magnetic permeability of the pole piece in the third embodiment cause imbalance in magnetic resistance. It can be set appropriately to compensate.

Further, for example, in the first embodiment, the gap between the pole piece and the shaft member, in the second embodiment, the area of the magnetic end surface of the pole piece, and in the third embodiment, the magnetic permeability of the pole piece is different. Although it is provided to compensate for the imbalance of the magnetic resistance, these may be combined to compensate for the female doctor's machine imbalance.

Further, in each of the first to third embodiments, description has been made by applying to a shaft member rotating type spindle motor (a form in which the shaft member and the hub member rotate relative to the housing body). The present invention is not limited to this, and the shaft member fixed type spindle motor (for example, the form disclosed in Japanese Utility Model Laid-Open No. 1-146776, in which the hub member is rotated relative to the shaft member fixed to the housing body). The same can be applied to the form). In such a case, the bearing member is interposed between the hub member and the shaft member, the magnetic fluid sealing means is mounted on the shaft member (or the hub member), and the magnetic fluid is a pair of magnetic fluid sealing means thus mounted. It is filled between the pole piece and the hub member (or shaft member).

〔The invention's effect〕

Since the present invention is configured as described above,
The following effects are achieved.

In the spindle motor according to the first aspect of the invention, of the pair of pole pieces of the magnetic fluid sealing means, the outer pole piece in which a gap between the rotating member or the stationary member of the inner pole piece adjacent to the bearing member is separated from the bearing member. Since it is formed smaller than that of the above, the magnetic flux density in the air gap on the inner pole piece side can be made larger than in the conventional case, and part of the magnetic flux from the inner pole piece adjacent to the bearing member is shunted to the bearing member. It is possible to prevent a decrease in magnetic flux density in the inner pole piece, and to make the magnetic flux density in the outer magnetic fluid layer generated by the outer pole piece and the magnetic flux density in the inner magnetic fluid layer generated by the inner pole piece substantially equal. It is possible to form a stable two-layer magnetic fluid layer over a long period of time, and the magnetic fluid can be scattered.
It is possible to prevent damage to the magnetic fluid layer.

Further, in the spindle motor of the second invention, the area of the magnetic pole end surface of the inner pole piece adjacent to the bearing member is formed smaller than that of the outer pole piece separated from the bearing member. The magnetic flux density at the magnetic pole end surface can be increased compared to the conventional case, and it is possible to prevent a decrease in the magnetic flux density at the inner pole piece due to shunting of a part of the magnetic flux from the inner pole piece to the bearing member. Is obtained.

Furthermore, in the spindle motor of the third invention,
Since the magnetic permeability of the inner pole piece adjacent to the bearing member is formed to be larger than that of the outer pole piece separated from the bearing member, the magnetic resistance of the inner pole piece becomes smaller than that of the outer pole piece, and the inner pole piece and the rotating member or The magnetic flux density in the air gap between the stationary member and the stationary member becomes larger than in the conventional case, and it is possible to prevent the decrease of the magnetic flux density in the inner pole piece due to a part of the magnetic flux from the inner pole piece being shunted to the bearing member. The same effect as described above can be obtained.

[Brief description of drawings]

FIG. 1 is a sectional view showing an essential part of a first embodiment of a spindle motor according to the present invention, and FIG. 2 is an enlarged sectional view showing a part of the spindle motor of FIG. 1 in an enlarged manner. FIG. 4 is an enlarged cross-sectional view showing an enlarged main portion of a second embodiment of a spindle motor according to the present invention, and FIG. 4 is an enlarged enlarged view showing an essential portion of a third embodiment of the spindle motor according to the present invention. FIG. 5 is a partial sectional view showing the magnetic field distribution of the magnetic fluid sealing means in the conventional spindle motor. 2 ... Housing body, 4 ... Shaft member, 8 ... Cylindrical part,
10 …… Bearing member, 12 …… Hub member, 20 …… Recording member, 2
4,24 ′, 24 ″ …… Magnetic fluid sealing means, 28,28 ′, 28 ″…
… Outer pole pieces, 30,30 ′, 30 ″ …… Inner pole pieces, 32,34 …… Magnetic fluid layer.

Claims (3)

[Claims] 1. A stationary member, a rotating member which is rotatable relative to the stationary member, a bearing member interposed between the stationary member and the rotating member, the stationary member and the rotating member. A magnetic fluid sealing means disposed axially outside the bearing member between the member and the member, wherein the magnetic fluid sealing means is an annular permanent magnet mounted on the stationary member or the rotating member, In a spindle motor comprising a pair of pole pieces arranged on both sides of a permanent magnet and a magnetic fluid filled between each of the pole pieces and the rotating member or the stationary member, the bearing member is a ball. A bearing, wherein the magnetic fluid sealing means is arranged in proximity to the bearing member, and the inner pole piece located axially inward of the pair of pole pieces and adjacent to the bearing member and the front pole piece. The gap between the rotating member or the stationary member is formed to be smaller than the gap between the rotating member or the stationary member and the outer pole piece that is located outside in the axial direction and is separated from the bearing member. A spindle motor characterized in that a magnetic flux density acting on the magnetic fluid from a pole piece and a magnetic flux density acting on the magnetic fluid from the outer pole piece are substantially equal to each other. 2. A stationary member, a rotating member which is rotatable relative to the stationary member, a bearing member interposed between the stationary member and the rotating member, the stationary member and the rotating member. A magnetic fluid sealing means disposed axially outside the bearing member between the member and the member, wherein the magnetic fluid sealing means is an annular permanent magnet mounted on the stationary member or the rotating member, In a spindle motor comprising a pair of pole pieces arranged on both sides of a permanent magnet, and a magnetic fluid filled between each of the pole pieces and the rotating member or the stationary member, the bearing member is a ball. A bearing, wherein the magnetic fluid sealing means is arranged close to the bearing member, and the magnetic pole of the inner pole piece located axially inward of the pair of pole pieces and adjacent to the bearing member. The area of the extreme surface is formed to be smaller than the area of the magnetic pole end surface of the outer pole piece located axially outside and separated from the bearing member, and the magnetic flux density acting on the magnetic fluid from the inner pole piece and the outer pole piece. And a magnetic flux density acting on the magnetic fluid are substantially equal to each other. 3. A stationary member, a rotating member which is rotatable relative to the stationary member, a bearing member interposed between the stationary member and the rotating member, the stationary member and the rotating member. A magnetic fluid sealing means disposed axially outside the bearing member between the member and the member, wherein the magnetic fluid sealing means is an annular permanent magnet mounted on the stationary member or the rotating member, In a spindle motor comprising a pair of pole pieces arranged on both sides of a permanent magnet, and a magnetic fluid filled between each of the pole pieces and the rotating member or the stationary member, the bearing member is a ball. A bearing, the magnetic fluid sealing means is arranged in proximity to the bearing member, the inner pole piece located axially inside and adjacent to the bearing member, of the pair of pole pieces, The magnetic permeability is formed to be larger than that of the outer pole piece located axially outside and separated from the bearing member, and the magnetic flux density acting on the magnetic fluid from the inner pole piece and the magnetic flux acting on the magnetic fluid from the outer pole piece. A spindle motor characterized in that the density and the density are substantially equal.