JP2000213543A - Bearing device and spindle motor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a bearing device capable of changing the rotation resistance between a shaft and a bearing member and a spindle motor. SOLUTION: In the bearing device 8 of a spindle motor, an electroviscous fluid 14 using liquid crystal is interposed between the outer peripheral surface of a shaft and the inner peripheral surface 121 of the bearing part 12 of a hub 10. Since the shaft has conductivity, and an electrode part 33 is formed on the bearing part 12, predetermined voltage can be applied between the shaft and the electrode part 33 from a rotation control device 32. Since the fluid 14 changes its viscosity following voltage application, applying voltage between the shaft 3 and the electrode part 33 from the control device 32 can increase the viscosity of the fluid 14, thereby increasing the rotation resistance of the hub 10, while applying no voltage reduces the viscosity of the fluid 14, thereby reducing the rotation resistance of the hub 10.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a bearing device in which a fluid is interposed between a shaft and a bearing member, and a spindle motor using the bearing device.

[0002]

2. Description of the Related Art As a bearing device used for a motor or the like, a groove for generating dynamic pressure is formed on at least one of an outer peripheral surface of a shaft and an inner peripheral surface of a bearing member. 2. Description of the Related Art A hydrodynamic bearing device having a configuration in which lubricating fluid is filled between surfaces is known. The present applicant discloses such a bearing device in Japanese Patent Application Laid-Open Nos. 7-111028 and 7-229514.

[0003]

Here, as a bearing device, if there is a new bearing device capable of changing the rotational resistance between the shaft and the bearing member at an appropriate timing, the shaft side or the bearing member is required. It is convenient to change the rotation speed on the side or stop the rotation.

An object of the present invention is to provide a new type of bearing device capable of changing the rotational resistance between a shaft and a bearing member, and a spindle motor using the bearing device.

[0005]

In order to solve the above-mentioned problems, a bearing device according to the present invention comprises: a shaft; a bearing member having an inner peripheral surface forming a predetermined gap between the outer peripheral surface of the shaft; An electrorheological fluid that is held in the gap and whose viscosity changes according to the applied voltage, and controls the viscosity of the electrorheological fluid by applying a voltage between the bearing member side and the outer peripheral surface side of the shaft. And rotation control means.

In the bearing device of the present invention, the electrorheological fluid is interposed between the shaft and the bearing member. Therefore, by controlling the voltage applied to the electrorheological fluid, the electrorheological fluid is interposed between the shaft and the bearing member. The viscosity of the fluid can be changed. Therefore, if a voltage is applied to the electrorheological fluid to increase the viscosity, the rotational resistance between the shaft and the bearing member can be increased.
The rotation speed of the rotating member can be easily reduced, and when stopping the rotation, it is easy to apply a brake to the rotating member. Conversely, if the application of the voltage to the electrorheological fluid is stopped or the applied voltage is reduced, the rotation resistance between them can be reduced, so that the rotation speed of the rotating member can be easily increased. Also, if the viscosity of the electrorheological fluid is reduced when the rotating member starts rotating, the initial load applied to the rotating member can be reduced.

A liquid crystal compound can be used as such an electrorheological fluid.

In the present invention, it is preferable that a groove for generating dynamic pressure is formed on at least one of the outer peripheral surface of the shaft and the inner peripheral surface of the bearing member.

In the present invention, the outer peripheral surface of the shaft has conductivity, and the bearing member is insulated and separated by an insulator at an intermediate position in the axial direction of the bearing member, and is provided with a counter electrode with respect to the outer peripheral surface of the shaft. It is preferable to include a cylindrical electrode portion.

[0010] Such a bearing device is used in a spindle motor to rotatably support a rotor with respect to a stator. That is, the bearing device of the present invention can be applied to both a fixed shaft motor and a shaft rotation type motor. In these motors, when the shaft is a fixed shaft and the bearing member is a rotating member, the rotation speed of the disk can be easily controlled by configuring the bearing member as a hub on which an optical disk or a magnetic disk is placed. A disk drive can be configured.

[0011]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A spindle motor having a bearing device to which the present invention is applied will be described below with reference to the drawings.

FIG. 1 is a half sectional view of the spindle motor. In FIG. 1, a spindle motor 1 of the present embodiment
Denotes a motor for a hard disk drive, which is rotatably held on a motor frame 2, a shaft (fixed shaft) 3 mounted upright with respect to the motor frame 2, and an outer peripheral side of the shaft 3. It comprises a rotor assembly 4 (rotor) and a stator assembly 5 (stator) fixed to the motor frame 2 side.

A shaft hole 211 is provided at the center of the motor frame 2.
Is formed, and the shaft 3 is fitted and fixed to the shaft hole 211. The rotor assembly 4 includes a hub 10 as a bearing member rotatable around the axis of the shaft 3 and a ring-shaped rotor magnet 11 disposed concentrically around the outer periphery of the stator core 6 of the stator assembly 5. . In the spindle motor 1 of the present embodiment, the bearing 10, which will be described in detail later, is constituted by the hub 10, the shaft 3, and the electrorheological fluid 14 interposed therebetween.

The hub 10 is shaped to cover the stator assembly 5, and has a cylindrical bearing portion 12 having a shaft hole 121,
An overhang 13 protrudes radially outward from an upper portion of the outer peripheral surface of the bearing 12. Bearing part 1
The shaft 3 is inserted into the second shaft hole 121. A groove for generating dynamic pressure is formed on the outer peripheral surface 31 of the shaft 3 facing the inner peripheral surface of the shaft hole 121. In this example, two herringbone-shaped dynamic pressure generating grooves 32a and 32b are formed at predetermined intervals in the axial direction. Further, a minute gap 80 is secured between the outer peripheral surface 31 of the shaft and the inner peripheral surface of the shaft hole 121, and between the portions of the gap 80 where the dynamic pressure generating grooves 32 a and 32 b are formed. The aforementioned electrorheological fluid 14 is held in a corresponding gap 80.

In the hub 10, a yoke 15 extending toward the motor frame 2 is fixed to an outer portion of a lower end surface of the overhang portion 13, and a rotor magnet 11 is fixed to an inner peripheral surface of the yoke 15. An outer portion on the upper surface of the overhang portion 13 is an annular disk mounting surface 13a one step lower than other portions, and the magnetic disk 20a is mounted thereon. Another magnetic disk 20 is placed on this magnetic disk 20a via a spacer 22.
The disk holder 23 is disposed on the magnetic disk 20b. Disc holder 23
Is fixed to the upper end of the overhang portion 13 by a set screw 24, and the two magnetic disks 20a and 20b are pressed against the disk mounting surface 13a with an appropriate force.

In the hub 10, an annular protrusion 13b is formed on the upper surface of the overhang portion 13. In a portion inside the annular protrusion 13b, the outer peripheral surface 3 of the shaft 3
A ring-shaped slip-off preventing member 25 is fitted and fixed to 1. The outer peripheral portion of the detachment preventing member 25 is adapted to cover the hub 10, and the detachment preventing member 25 prevents the hub 10 from being detached upward.

In the position above the stopper 25,
A seal member 26 is attached to the shaft 3 to prevent foreign matter from entering therethrough. The bearing 12
A seal member 29 is attached to the outer peripheral surface of the bearing portion 12 between the bearing portion 12 and the cylindrical portion 21 of the motor frame 2 at the lower end side of the shaft member to prevent foreign matter from entering therethrough.

The stator assembly 5 includes a stator core 6 mounted on the outer peripheral surface of the cylindrical portion 21 of the motor frame 2.
And a drive coil 7 wound around a plurality of salient poles formed on the stator core 6. A terminal wire 7a is drawn out from the drive coil 7, and the terminal wire 7a is a flexible printed circuit board 3 having a conductive pattern formed on the upper surface.
0 is soldered to the electrode part.

A flexible lead 31 is drawn out of the flexible printed circuit board 30, and the lead 31
Is connected to a rotation control device 32 outside the motor. By applying a predetermined drive signal to the drive coil 7 from the rotation control device 32, the magnetic disks 20a, 20
The hub 10 on which b is mounted is driven to rotate with respect to the shaft 3. Further, the rotation control device 32 outputs a signal for driving the rotation of the motor to the drive coil 7 and controls the bearing device 8 described below with reference to FIG. 2 to control the rotation resistance of the motor.

FIG. 2 is a cross-sectional view showing the bearing unit 8 of the hub 10 and a part of the shaft 3 in the bearing device 8.

As shown in FIG. 2, a cylindrical electrode portion 33 is formed at an intermediate portion in the axial direction of the bearing portion 12 so as to surround the shaft 3 concentrically. The electrode portion 33 is connected to the bearing portion 12 via the insulating films 34a and 34b.
It is insulated from other parts. This electrode section 33
A counter electrode that faces the outer peripheral surface 31 of the conductive shaft 3 via the electrorheological fluid 14. The electrode portion 33 is electrically connected to the rotation control device 32 via a contact portion 330,
The shaft 3 is also connected to the rotation control device 3 via the wiring 300.
2 are electrically connected. Note that the shaft 3 is in a grounded state.

Here, the electrode portion 33 and the electrode portion 33
The upper and lower sides sandwiching the inner diameter of the bearing portion 12 are slightly larger over a predetermined range in the axial direction,
Accordingly, the gap 80 in this portion is widened. The electrorheological fluid 14 is held around a portion where the gap 81 is wide.

The electrorheological fluid 14 is a liquid having low fluidity in a normal state, but has a property of increasing the viscosity when a voltage is applied. As the electrorheological fluid 14,
A mixed composition of a thermotropic liquid crystalline polymer compound and a thermotropic liquid crystalline low molecular compound can be used. In this case, as the liquid crystalline polymer compound, for example, a compound represented by the chemical formula (1) can be used.

[0024]

Embedded image

In this formula, R is a hydrogen atom or a methyl group,
p is an integer of 2 to 12, and n indicates the degree of polymerization. That is, poly (4'-cyano-4-biphenyloxyethyl acrylate), poly (4'-cyano-4-biphenyloxypropyl acrylate), poly (4-cyano-4)
-Biphenyloxybutyl acrylate), poly (4 ′
-Cyano-4-biphenyloxypentyl acrylate), poly (4'-cyano-4-biphenyloxyhexyl acrylate), poly (4'-cyano-4-cyano-biphenyloxyheptyl acrylate), and corresponding polymethacrylates And the like.
These liquid crystalline polymer compounds may be used alone or in combination of two or more.

As the liquid crystalline low molecular weight compound, those represented by the chemical formula (2) can be used.

[0027]

Embedded image

In this formula, k is 0 or 1, and m is 4-12.
Is an integer. That is, 4-cyano-4′-butylbiphenyl, 4-cyano-4′-pentylvinylphenyl,
4-cyano-4'-bexylbiphenyl, 4-cyano-
4'-heptylvinylphenyl, 4-cyano-4'-octylbiphenyl, -4,4-cyano-4'-nonylbiphenyl and the like are used. These liquid crystalline low-molecular compounds may be used alone or in combination of two or more.

In the spindle motor 1 configured as described above, when a drive signal is output from the drive coil 7 from the rotation control device 32, the hub 10 rotates around the axis of the shaft 3. At this time, the dynamic pressure generated by the dynamic pressure generating grooves 32a and 32b formed in the shaft 3 causes the hub 10 to rotate in a non-contact state.

Here, the rotation control device 32 sends the shaft 3
When an electric field is generated in a direction indicated by an arrow in FIG. 2 by applying a voltage between the liquid crystal and the electrode portion 33, the orientation direction of the liquid crystal molecules constituting the electrorheological fluid 14 changes according to the direction of the electric field. I do. With this change in the orientation direction, the electrorheological fluid 14
Increase in viscosity. For this reason, when a voltage is applied between the shaft 3 and the electrode portion 33 during rotation of the motor, the rotation resistance between the electrorheological fluid 14 and the bearing portion 12 of the hub 10 increases, and the rotation speed of the hub 10 increases. Can be reduced. Further, when a voltage is applied to the electrorheological fluid 14, the viscosity of the electrorheological fluid 14 increases with a change in the alignment direction of the liquid crystal molecules, and the hub 10 can be braked. Therefore, the deceleration and stop of the hub 10 can be performed smoothly.

On the other hand, when a voltage is applied between the shaft 3 and the electrode portion 33 to increase the viscosity of the electrorheological fluid 14 and the motor is rotating, the application of the voltage is stopped or Is reduced, the orientation direction of the liquid crystal compound molecules is restored, the viscosity of the electrorheological fluid 14 is reduced, and the rotational resistance of the hub 10 is reduced. Therefore, the hub 10 can be smoothly accelerated. Further, when the rotation of the hub 10 is started from the stopped state, if the application of the voltage to the electrorheological fluid 10 is stopped, the initial load of the hub 10 can be reduced.

In the present embodiment, the dynamic pressure generating grooves 32a and 32b are provided on both sides of the region where the electrorheological fluid 14 is filled.
Generates a dynamic pressure toward the portion filled with the electrorheological fluid 14, so that the electrorheological fluid 14 can be prevented from leaking.

The present invention is not limited to a fixed shaft type spindle motor to which the shaft 3 is fixed.
The present invention can also be applied to a shaft rotation type spindle motor in which the shaft 3 is rotatably supported by a bearing member.
The electrorheological fluid 14 may be used not only for the dynamic pressure bearing but also for a general bearing such as a sintered oil-impregnated bearing.

[0034]

As described above, in the bearing device of the present invention, the electrorheological fluid such as liquid crystal is interposed between the shaft and the bearing member, so that the voltage applied to the electrorheological fluid is controlled. The viscosity of the electrorheological fluid can be changed between the shaft and the bearing member. Therefore, if a voltage is applied to the electrorheological fluid to increase the viscosity, the rotational resistance between the shaft and the bearing member can be increased, so that the rotation speed of the rotating member of the shaft and the bearing member is reduced. Can be dropped smoothly.
Conversely, if the application of the voltage to the electrorheological fluid is stopped or the applied voltage is reduced, the rotational resistance between them can be reduced, so that the rotational speed of the rotating member can be smoothly increased.

[Brief description of the drawings]

FIG. 1 is a half sectional view of a spindle motor using a bearing device to which the present invention is applied.

FIG. 2 is an explanatory view showing a part of a shaft and a peripheral part thereof in a bearing device used for the spindle motor shown in FIG. 1 in an enlarged manner.

[Explanation of symbols]

 Reference Signs List 1 spindle motor 3 shaft 4 rotor assembly (rotor) 5 stator core (stator) 8 bearing device 10 hub 12 bearing portion 14 electrorheological fluid 32a, 32b dynamic pressure generating groove 32 rotation control device (rotation control means) 33 cylindrical electrode portion 80 Clearance between shaft and bearing

Claims (5)

[Claims] 1. A bearing member in which an inner peripheral surface forms a predetermined gap between a shaft and an outer peripheral surface of the shaft, an electrorheological fluid held in the gap and having a viscosity that changes according to an applied voltage. And a rotation control means for controlling the viscosity of the electrorheological fluid by applying a voltage between the bearing member side and the outer peripheral surface side of the shaft. 2. The bearing device according to claim 1, wherein the electrorheological fluid is a liquid crystal compound. 3. The bearing device according to claim 1, wherein a groove for generating dynamic pressure is formed on at least one of an outer peripheral surface of the shaft and an inner peripheral surface of the bearing member. . 4. The shaft according to claim 1, wherein an outer peripheral surface of the shaft has conductivity, and the bearing member is insulated and separated by an insulator at an intermediate position in the axial direction of the bearing member. And a cylindrical electrode portion serving as an electrode facing the outer peripheral surface of the shaft. 5. A spindle motor, wherein a rotor is rotatably supported on a stator by a bearing device defined in any one of claims 1 to 4.