JPH01133537A - Spindle motor - Google Patents

Abstract

PURPOSE:To prevent the bursting of a magnetic seal interposed between a hub and a pivotally support shaft by limiting rotational peripheral velocity to 10-20cm/s or less for one sec immediately after the start of the hub pivotally supported around the pivotally support shaft rotatably. CONSTITUTION:A hub 3 is supported rotatably around bearings 2, 2 fixed to the upper and lower sections of a pivotally support shaft 1 disposed in upright to a base 8, and a rotor magnet 7 for a rotor member 5 is installed inside the hub. A stator 6 is fastened to the pivotally support shaft 1 in response to the magnet 7. A magnet seal 4 is formed by a magnetic fluid 9 on the outside in the axial direction of the bearing 2. The seal 4 is composed of the magnetic fluid 9 and a magnetic-fluid holding member 10, and the holding member 10 holds and shapes an intermediate plate ring-shaped magnet 11 by pole pieces 12 and 13 from both surfaces. A power supply is turned ON, currents flowing into the stator coil 6 are delayed by a CR circuit, and the rotational peripheral velocity of the rotor member 5 is limited to 10-20cm/s or less for one sec immediately after start and accelerated successively. Accordingly, the breakdown of the magnetic seal is prevented, thus holding a sealing function for a prolonged time.

Description

[Detailed description of the invention] [Industrial application field] The present invention relates to a spindle motor.

[Conventional technology and its problems]

Generally, in a spindle motor, a magnetic seal consisting of 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 on the pivot shaft. has been done.

However, if the magnetic fluid of the injected magnetic seal is not distributed with a uniform density (usually it is almost non-uniform), that is, if the sealing effect is uneven and there are areas with weak sealing performance, the hub If the magnetic fluid is rotated rapidly, there is a risk that the magnetic fluid seal will rupture due to the sudden change in wind pressure caused by the rotation. If it ruptures, a problem arises in that the magnetic fluid scatters and contaminates the clean magnetic disk chamber.

Therefore, it is an object of the present invention to provide a spindle motor in which the sealing performance of the magnetic fluid seal is maintained over a long period of time without causing the magnetic fluid to scatter.

[Means to solve the problem]

In the spindle motor of the present invention, a magnetic seal consisting of a magnetic fluid and a magnetic holding member that holds the magnetic fluid is interposed between a pivot shaft and a hub rotatably supported on the pivot shaft. In the spindle motor equipped with the spindle motor, the peripheral speed of rotation of the magnetic fluid, which is fluidly rotated by the rotational drive of the hub, is set to 10 to 20 (cm/see) or less one second after the rotation is started.

[Effect]

With the configuration as described above, when the hub is rotationally driven and the magnetic fluid flows and rotates, the rotational circumferential speed of the magnetic fluid 1 second after the start of rotation is 10 to 20 (cm/sec) or less. During this one second, the magnetic fluid flows and rotates as if being stirred, and the sealing pressure is made uniform. Then, even if the hub rotational speed is subsequently accelerated and the flow rotational speed of the magnetic fluid is increased, the fluid will not burst and scatter.

〔Example〕

Hereinafter, the present invention will be explained in detail based on drawings showing embodiments.

FIG. 4 shows a spindle motor according to the present invention, which includes a pivot shaft 1, a bearing 2 on the pivot shaft 1, and a bearing 2 on the pivot shaft 1.
The hub 3 is rotatably supported via the pivot shaft 1 and the hub 3, and magnetic fluid seals 4, 4 are interposed between the pivot shaft 1 and the hub 3. A magnetic storage disk (not shown) is attached to the outer peripheral surface of the hub 3, and a rotor member 5 is attached to the inner peripheral surface. Further, a stator 6 is fitted onto the pivot shaft 1 so as to closely face the rotor magnet 7 of the rotor member 5. Note that the pivot shaft 1 is fixed to the 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. It consists of an intermediate flat plate annular magnet 11, a flat plate annular first pole piece 12 and a second pole piece 13 that sandwich the magnet 11 from both sides in a sandwich shape,
As shown in FIGS. 5 and 6, a magnetic fluid 9 is injected and held in the gap 14 between the first pole piece 12 and the pivot shaft l.

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

The drive circuit 15 is a linear drive, and includes a voltage dividing circuit 17, a time constant circuit (delay circuit) 18, a power switching circuit 19, and an amplifier circuit 20. The time constant circuit 18 includes a resistor R and a capacitor C, and excites the sensor 16 to create a delay time of at least 1 second from when a power switch (not shown) is turned on.

Therefore, the output Rh of this sensor 16 has a waveform as shown in FIG. 3, and the voltage applied to the stator 6 does not rapidly reach the predetermined applied voltage level. Note that Ea is the voltage across the time constant circuit 18.

That is, in a 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 graph (2), the inclination angle becomes small, and then the rated speed N is reached at a slightly larger inclination angle.

Note that the graph ``is a conventional drive circuit 2 as shown in FIG. 10 which is normally used without using the above-mentioned drive circuit 15
1 (that is, a circuit without a time constant circuit 18) is a graph showing the rotational speed of the magnetic fluid 9 at the time of starting.

Here, the peripheral speed of rotation 1 second after the magnetic fluid 9 starts rotating in the drive circuit 15 described above is 10 to 20 (cm/see).
It is set as follows. In other words, the waveform of the sensor output (Eh) shown in FIG. The rotation speed is set. In general, in spindle motors for disks,
Preferably, the magnetic fluid 9 is set to rotate at least about 5 times per second after startup.

Therefore, if configured as described above, the magnetic fluid 9 will slowly flow and rotate for one second after the magnetic fluid 9 starts rotating.
As shown in FIGS. 5 and 6, even when the pivot shaft 1 is slightly eccentric with respect to the magnetic fluid seal 4 and the magnetic fluid 9 is distributed with uneven density, it is as if the fluid 9 were Even if the magnetic fluid 9 is stirred and its density is evenly distributed, and then the rotational speed of the hub 3 is increased and the rotational speed of the fluid 9 is increased, the magnetic fluid 9 will not rupture and will scatter. Things will disappear. However, if it rotates like the waveform shown in graph H in Figure 1, there will be areas where the density is low.
The thin part breaks and the magnetic fluid 9 scatters as shown by the arrow.

Next, FIG. 7 shows another embodiment of the drive circuit 15, and in this case shows the case of digital drive, which includes a power switching circuit 19, a voltage dividing circuit 17, an A/D conversion circuit 22, and a time constant. A circuit 18 is provided.

Therefore, the input from the time constant circuit 18 is controlled to a small value, the exciting current to the stator 6 has a waveform as shown in FIG. 8, and the rotational torque has a waveform as shown in (T) in FIG. In this case as well, the rotational speed of the magnetic fluid 9 has a waveform as shown in graph (3) in FIG. 1, and the magnetic fluid 9 does not scatter. The graph (II) in FIG. 9 is a conventional torque waveform, and tn is the point at which the rated speed is reached.

〔Effect of the invention〕

The spindle motor of the present invention is configured such that even if the magnetic fluid 9 is distributed with non-uniform density, the magnetic fluid 9 becomes uniform immediately after the rotation of the magnetic fluid 9 starts, that is, within 1 second after starting. Since the magnetic fluid 9 is agitated as if it were agitated, even if the rotational speed is increased to the rated speed, the magnetic fluid 9 will not explode (or scatter). This prevents the magnetic fluid 9 from being scattered, etc., and the sealing performance is maintained over a long period of time, resulting in a long service life.

[Brief explanation of the drawing]

Fig. 1 is a graph showing the rotation speed of the 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. 4 is a cross-sectional front view, and Fig. The figure is an enlarged sectional front view of the main part, Fig. 6 is an enlarged sectional top view of the main part, Fig. 7 is a circuit diagram showing another embodiment of the drive circuit, Fig. 8 is an excitation current waveform diagram, and Fig. 9 is a torque FIG. FIG. 10 is a diagram of a drive circuit used in a conventional spindle motor. ■... Pivot shaft, 3... Hub, 4... Magnetic fluid seal, 9... Magnetic fluid, 10... Magnetic fluid holding member. Patent Applicant Nidec Corporation Fig. 2 It: Fig. 1 100 Fig. J Fig. 4, R 14 Fig. 5 Fig. 7 Fig. 7 Fig. 1 O

Claims (1)

[Claims] 1. A magnetic seal 4 consisting of a magnetic fluid 9 and a magnetic holding member 10 that holds the magnetic fluid 9 between a pivot shaft 1 and a hub 3 rotatably supported on the pivot shaft 1. In the spindle motor equipped with a spindle motor, the peripheral speed of rotation of the magnetic fluid 9 fluidly rotated by the rotational drive of the hub 3 one second after the start of rotation is set to 10 to 20 (cm/sec) or less. spindle motor.