JP2568865B2 - Spindle motor - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a spindle motor.

[Conventional technology and its problems]

Generally, in a spindle motor, a magnetic seal including a magnetic fluid and a magnetic holding member that holds the magnetic fluid is interposed between a pivot shaft and a hub that is rotatably supported by the pivot shaft. Have been.

However, when the magnetic fluid of the magnetic seal to be injected is not distributed at a uniform density (usually almost non-uniform), that is, when the sealing effect is non-uniform and a part having poor sealing properties is generated, the hub is not used. Is rapidly rotated, there is a risk that the seal made of the magnetic fluid may burst due to a sudden change in wind pressure caused by the rotation. If ruptured, a problem arises that the magnetic fluid scatters and contaminates a clean magnetic disk chamber.

Therefore, in the present invention, without scattering the magnetic fluid,
An object of the present invention is to provide a spindle motor in which the sealing performance of a magnetic fluid seal is maintained for a long time.

[Means for solving the problem]

According to the present invention, the pivot shaft 1, the hub 3 rotatably supported by the pivot shaft 1, the magnetic seal 4 disposed between the pivot shaft 1 and the hub 3, And a position sensor 16 for detecting a rotational position.
And a magnetic holding member 10 for holding the magnetic fluid 9, a delay means 18 is provided in association with the position sensor 16, and the delay means 18 moves the position sensor within a predetermined time after the power switch is operated. When the hub 3 is started to reach the rated rotation speed, the hub 3 is driven to rotate at a high rotation speed after a relatively low rotation speed period for a predetermined time, so that the magnetic fluid is scattered due to rapid acceleration. Is prevented.

[Action]

According to the spindle motor of the present invention, the delay means delays the operation of the position sensor within a predetermined time after the power switch is operated. Therefore, the applied voltage supplied to the stator does not increase rapidly, and the hub is driven to rotate at a relatively low rotation speed. Therefore, the rotation of the hub does not rapidly increase within a predetermined time after the start, and during this time, the magnetic fluid flows and rotates as if being stirred, and the sealing pressure is made uniform. Even if the rotation speed of the hub is rapidly accelerated after the elapse of the predetermined time, the magnetic fluid does not burst and scatter.

〔Example〕

Hereinafter, the present invention will be described in detail with reference to the drawings showing examples.

FIG. 4 shows a spindle motor according to the present invention. The spindle motor has a pivot shaft 1 and bearings 2,
And a hub 3 rotatably supported via 2. Magnetic fluid seals 4 are interposed between the pivot shaft 1 and the hub 3. The hub 3 has a magnetic storage disk (not shown) mounted on the outer peripheral surface and a rotor member 5 mounted on the inner peripheral surface. A stator 6 is provided on the pivot shaft 1 so as to approach and face the rotor magnet 7 of the rotor member 5.
Is externally fitted. The pivot 1 is fixed to a bracket 8.

Thus, the magnetic fluid seal 4 includes a magnetic fluid 9 and a magnetic fluid holding member 10 that holds the magnetic fluid 9 and is fixed to the inner peripheral surface of the hub 3. As shown in FIG. 5 and FIG. 6, an intermediate plate-shaped annular magnet 11, a plate-shaped first pole piece 12 and a second pole piece 13 sandwiching the magnet 11 from both sides in a sandwich shape. The magnetic fluid 9 is injected and held in a gap 14 between the first pole piece 12 and the pivot 1.

The spindle motor is provided with a drive circuit 15 as shown in FIG. 2, and sequentially energizes the coils of the stator 6 in accordance with the rotational position of the rotor magnet 7 detected by the rotor position sensor 16. This causes the hub 3 to rotate.

The drive circuit 15 shows a case of linear drive, and includes a voltage divider circuit 17, a time constant circuit (delay circuit) 18 (constituting delay means), a power switching circuit 19, and an amplifier circuit 20. , Is provided. The time constant circuit 18 includes a resistor R and a capacitor C. The time constant circuit 18 excites the sensor 16 by making a delay time within a predetermined time, for example, at least one second or less, when a power switch (not shown) is turned on. Accordingly, the output Eh of the sensor 16 has a waveform as shown in FIG. 3, and the applied voltage to the stator 6 is rapidly increased to the predetermined applied voltage Eh.
Will not be reached. Ea is a voltage between the time constant circuits 18.

That is, in the spindle motor using such a circuit 15, when the hub 3 rotates, the magnetic fluid 9 of the magnetic fluid seal 4 flows and rotates. As shown in the graph I, the inclination angle becomes small, and thereafter reaches the rated speed N at an angle where the inclination angle is slightly large. Graph II shows a case where the above-described drive circuit 15 is not used, and a conventional drive circuit 21 (ie, a circuit having no time constant circuit 18) which is generally used as shown in FIG. 10 is used. 6 is a graph showing the rotation speed of the magnetic fluid 9 at the time of starting.

Here, in the present embodiment, the rotational peripheral speed of the magnetic fluid 9 after one second of rotation is set to 10 to 20 (cm / sec) or less in the drive circuit 15 described above. That is, the waveform until the sensor output (Eh) reaches the predetermined applied voltage E shown in FIG.
The rotation speed is determined in consideration of the amount of the magnetic fluid 9, the magnetic flux density, and the like, and the rotation speed of the magnetic fluid 9 one second after the start of rotation is set. In addition,
Usually, in a spindle motor for a disk, it is desirable that the magnetic fluid 9 is set to rotate at least about 5 times in one second after starting.

Therefore, if the magnetic fluid 9 is configured as described above, the magnetic fluid 9 slowly flows and rotates for one second after the rotation of the magnetic fluid 9 is started, and as shown in FIGS. Even when the magnetic fluid 9 is distributed at an uneven density with a slight eccentricity with respect to the fluid seal 4, it is as if this fluid 9
Is agitated, and its density is evenly distributed,
Thereafter, the rotation speed of the hub 3 increases and the fluid 9
When the rotation speed of the magnetic fluid 9 is increased, the magnetic fluid 9 does not burst and does not scatter. However, the graph in FIG.
If it rotates like the waveform shown in II, there is a place where the density is thin, and the thin place is broken and the magnetic fluid 9 as shown by the arrow.
Will scatter.

Next, FIG. 7 shows another embodiment of the drive circuit 15, in which the case of digital drive is shown, in which a power switching circuit 19, a voltage dividing circuit 17, an A / D conversion circuit 22, a time constant And a circuit 18. Therefore, the input from the time constant circuit 18 is controlled to a small value, and the exciting current to the stator 6 is reduced to the eighth.
The waveform is as shown in the figure, and the rotational torque is (I) in FIG.
In this case as well, the rotation speed of the magnetic fluid 9 also becomes a waveform as shown by the grab I in FIG. 1, and the magnetic fluid 9 does not scatter. Note that (II) in FIG.
Is a conventional torque waveform, and tn is a rated speed reaching point.

〔The invention's effect〕

In the spindle motor according to the present invention, the delay means 18 is controlled by the position sensor 16 within a predetermined time after the power switch is operated.
To delay operation. Therefore, the applied voltage supplied to the stator 6 does not increase rapidly, and the hub 3 is driven to rotate at a relatively low rotation speed. Therefore, the rotation of the hub 3 does not rapidly increase within a predetermined time after the start, and during this time, the magnetic fluid 9 flows and rotates as if being stirred, and the sealing pressure is made uniform. Even if the rotation speed of the hub 3 is rapidly accelerated after the elapse of the predetermined time, the magnetic fluid does not burst and scatter due to the uniform sealing pressure. Thus, the sealing performance is maintained for a long time, and the life of the magnetic seal 4 is prolonged.

In addition, since it is not necessary to change the shape of each part, change the material, add components, and the like in the configuration of the conventional motor, especially the magnetic seal, it is possible to prevent the magnetic fluid from scattering at low cost.

[Brief description of the drawings]

FIG. 1 is a graph showing the rotation speed of a magnetic fluid according to an embodiment of the present invention, FIG. 2 is a drive circuit diagram, FIG. 3 is a graph showing applied voltage, FIG. Fig. 6 is an enlarged sectional front view of a main part, Fig. 6 is an enlarged cross-sectional plan view of a main part, Fig. 7 is a circuit diagram showing another embodiment of the drive circuit, Fig. 8 is an exciting current waveform diagram, and Fig. 9 is a torque. It is a waveform diagram. FIG. 10 is a drive circuit diagram used for a conventional spindle motor. 1 ... Pivot shaft, 3 ... Hub, 4 ... Magnetic fluid seal, 9
...... Magnetic fluid, 10 ... Magnetic fluid holding member.

Claims (1)

(57) [Claims] A pivot shaft, a hub rotatably supported by the pivot shaft, a magnetic seal disposed between the pivot shaft and the hub; A spindle motor comprising a position sensor 16 for detecting the rotational position of the hub 3, wherein the magnetic seal 4 comprises a magnetic fluid 9 and a magnetic holding member 10 for holding the magnetic fluid 9. The delay means 18 is provided for delaying the position sensor 16 within a predetermined time after the power switch is actuated, whereby the hub 3 is started until the rated speed is reached. A spindle motor which is driven to rotate at a high rotation speed after a relatively low rotation speed period for a predetermined time, thereby preventing the magnetic fluid from being scattered due to rapid acceleration.