JPH0963183A - Spindle motor for magnetic disk and magnetic disk device - Google Patents

Abstract

(57) [Abstract] [Purpose] In a dynamic pressure bearing, the viscosity change due to the temperature of the lubricating fluid changes the bearing rigidity and deteriorates the positioning accuracy of the magnetic disk. [Composition] Maximum vibration amplitude fluctuation in operating temperature range
The bearing rigidity is determined so that it is 1/5 or more and 2/3 or less of the track interval of the magnetic disk. [Effect] Sufficient bearing rigidity can be obtained without unnecessarily increasing bearing loss, and a large-capacity magnetic disk device can be realized.

Description

Detailed Description of the Invention

[0001]

INDUSTRIAL APPLICABILITY The present invention can be applied to magnetic disk devices, optical disk devices, polygon mirror motors for laser beam printers, cylinder motors for video tape recorders, small cooling fans, and other devices that require high-speed and high-precision rotation.

[0002]

2. Description of the Related Art Conventionally, ball bearings have been used in spindle motors used in information equipment. Ball bearings are widely used because they are cheap and easy to handle, but vibration and noise are inevitably caused by scratches or deformation of the balls and the rolling surface of the balls, and there is also a limit to high-speed rotation. there were. On the other hand, in recent years, the precision of ball bearings has been improved by improving the processing and assembling precision, but at present, it is almost the limit. On the other hand, the demand for high-speed, low-vibration and low-noise of bearings in the field of information equipment has become extremely strict with the rapid spread of computer equipment and higher performance. The gap is one of the causes of hindering the performance improvement of equipment.

On the other hand, a fluid lubrication type dynamic pressure sliding bearing (Fl
The uid film bearing (FFB) supports the rotating body in a non-contact manner due to the dynamic pressure effect that accompanies rotation, so it can rotate with much lower vibration and higher precision than ball bearings, and even for advanced needs. There is a good possibility to answer.

As an example of these conventional techniques, Japanese Patent Laid-Open No. 4-27
7317, flat 5-137206, flat 5-240241, etc.

[0005]

Synthetic oil such as turbine oil is usually used as the lubricating fluid in FFB. Although these oils have some differences depending on their components,
It has the property that its viscosity changes greatly with temperature. This change in viscosity greatly affects the properties of FFB. That is, when the temperature becomes high and the viscosity of the lubricating fluid decreases, the oil film rigidity, that is, the bearing rigidity decreases, and conversely, when the temperature becomes low and the lubricating fluid viscosity increases, the bearing rigidity increases. From the viewpoint of vibration, this means that the magnitude of vibration fluctuates depending on temperature even if the force for generating vibration, that is, the external force is constant. This is very problematic for a device such as a magnetic disk or an optical disk, which requires relatively high-precision positioning of a recording element such as a magnetic head or an optical pickup with respect to a recording surface driven by a spindle motor. Becomes Because
When the information written at one temperature is read at another temperature, if the amplitude of vibration is different, the relative position between the written information and the element to be read differs from that at the time of writing, and a position error occurs, which causes an information error. This will cause it to occur.

Since there is almost no such temperature fluctuation in the ball bearing, if the temperature fluctuation amount of the FFB is larger than the vibration amount generated by the ball bearing, the vibration merit of the FFB with respect to the ball bearing is offset. Will be done.

Therefore, an object of the present invention is to record in a recording / reproducing apparatus provided with a rotating recording medium for recording information and a recording element for performing recording / reproducing operation on this recording medium, even if the temperature changes. (EN) Provided is a recording / reproducing device capable of positioning an element with respect to a recording medium with an accuracy that does not impair the recording / reproducing performance, or a fluid lubrication type dynamic pressure sliding bearing which enables this.

[0008]

In order to achieve the above object, a spindle motor for a magnetic disk according to the present invention has a hub on which one or more magnetic disks can be stacked, a motor for rotating the hub, and a hub. It has a fluid lubrication type dynamic pressure bearing that is supported at the center of rotation and is freely rotatable, and its bearing rigidity is changed by a change in vibration amplitude within the operating temperature range of the device to a radial recording interval of 5 written on the magnetic disk. It is set so that it is less than 1/3 and less than 2/3.

In order to achieve the above object, a spindle motor for a magnetic disk according to the present invention comprises a hub on which one or more 2.5-inch magnetic disks can be stacked, a motor for rotationally driving the hub, and a rotation of the hub. It has a fluid-lubricated hydrodynamic bearing that is supported in the center and can rotate freely, and its bearing rigidity should be 3kN / mm or more and 15kN / mm or less at 20 ° C.

In order to achieve the above object, the magnetic disk device of the present invention is free to support a hub on which one or more magnetic disks can be stacked, a motor for rotating the hub and a hub at a certain rotation center. A spindle motor for a magnetic disk having a fluid lubrication type dynamic pressure bearing that can be rotated is used, and the amplitude fluctuation of the bearing vibration due to temperature is set within the range of 1/5 to 2/3 of the track interval. To do.

[0011]

Operation: It is obvious that the vibration amplitude becomes smaller as the bearing rigidity increases, but the bearing loss, which is one of the important characteristics of the spindle motor, is almost proportional to the rigidity. And increase. The smaller this bearing loss is, the more desirable it is as a device. Therefore, an important point in FFB design is to determine the necessary and sufficient bearing rigidity to satisfy the performance of the device.

The positioning accuracy in the magnetic disk device is determined by its radial recording density (Track Per Inch or less TPI) and is approximately one track interval (the reciprocal of TPI).
It takes a value less than 1/0.

FIG. 6 shows the result of analysis of factors that hinder the positioning accuracy of the conventional device. The factors that hinder the positioning accuracy are electrical noise, disk head vibration,
It has been found that there are three types of bearing asynchronous vibration, and the magnitudes are almost equal. The bearing non-synchronous vibration in this case is a vibration that is not synchronized with the rotation peculiar to the ball bearing, and in the case of the dynamic pressure bearing, the vibration amplitude fluctuation due to the temperature described above corresponds to this.

Electrical noise and disk head vibration are TP
It is considered that the size of the magnetic head is reduced with the increase of I, and the flying height between the disk and the head is reduced, so that the magnetic head is reduced almost in proportion to the track interval. On the other hand, the bearing vibration is not related to the head, so if nothing is done, the bearing component will not be reduced and TPI cannot be increased. From this, it can be seen that in order to increase TPI, it is necessary to design the bearing so that the position error due to the bearing is always less than one third of the positioning accuracy.

Further, since increasing bearing rigidity inevitably increases bearing loss, it is necessary to avoid unnecessarily increasing. Considering variations in factors other than the bearing, it is considered sufficient that the bearing vibration component satisfies 1/10 of the positioning accuracy. If this condition is converted into the relationship between the amount of vibration of the bearing and the track spacing, the following relationship holds.

Positioning accuracy / 10 <Vibration amplitude fluctuation / Servo system compression ratio <Positioning accuracy / 3 ... (1) ◆ Track interval / 100 <Position error <Track interval / 30 ... (1) '◆ Servo system The following relationship is established, assuming that the compression ratio is 20. ◆ 1/5 track interval <vibration amplitude fluctuation <2/3 track interval (2) The largest external force that can cause a position error is unbalanced vibration. FIG. 7 shows an example of the relationship between the position error and the bearing rigidity in the 2.5-inch magnetic disk device. The vertical axis represents the position error due to unbalanced vibration (positional error = unbalanced vibration amplitude ÷ servo system compression rate) divided by the positioning accuracy to make it dimensionless, and the horizontal axis represents the bearing rigidity. The change in the vertical axis at high temperature and low temperature is 0.
If the bearing rigidity is selected to be 3 or less, the position error will always be 1/3 or less of the positioning accuracy.

In the figure, as an example, a spindle (SP1; bearing rigidity about 1 kN / mm) having a small bearing rigidity and a spindle (SP2; bearing rigidity about 5 kN / mm) having a large bearing rigidity are shown. In both cases, the right side of the range is the low temperature side (5 ° C),
The left side is the high temperature side (55 ℃).

A spindle having a large bearing rigidity has a smaller amplitude change than a spindle having a small bearing rigidity with respect to the same temperature change. This is because the rate of change in vibration amplitude with respect to the change in bearing rigidity is not uniform, and the rate of change is greater in areas where the bearing rigidity is lower than in areas where the bearing rigidity is high.

In the case of the SP1 spindle, the magnitude of change between high temperature and low temperature is 0.4 or more, and the required positioning accuracy cannot be satisfied. In the case of the SP2 spindle, the magnitude of change at high and low temperatures is about 0.2, which satisfies the condition. 2 for 2.5 inch device from this figure
It can be seen that the condition can be satisfied if the bearing rigidity at 0 ° C is 3 kN / mm or more and 15 kN / mm or less. Thus, the bearing stiffness
The bearing rigidity necessary and sufficient for the device can be determined by obtaining it from the TPI condition of (1) or (2).

[0020]

FIG. 1 shows a first embodiment of the present invention. The magnetic disk 17 is laminated on the hub 1 with a spacer interposed therebetween. A motor rotor magnet 3 is provided on the inner peripheral side of the hub 1.
And a stator coil 8 provided on the fixed side to form a motor, and the rotational system of the magnetic disk 17 and the hub 1 is rotationally driven at a high speed. The stator coil 8 is fixed to the outer periphery of the bracket 7, and the bracket 7 is fixed to the base 10. A bearing 6 is fixed inside the bracket 7.

A shaft 2 is press-fitted into the hub 1,
This shaft 2 is inserted in a bearing 6. Shaft 2
The upper and lower thrust receivers 5 are attached to the bearing so as to sandwich the bearing 6. The dynamic pressure bearing is the shaft 2
Is formed between the bearing 6 and the bearing 6 and between the upper and lower thrust receivers 5 and the bearing 6, and the gap is filled with lubricating oil or magnetic fluid to support the rotary system by the dynamic pressure effect of the fluid accompanying the rotation. The sealed lubricating liquid is completely sealed by the seal 10 provided on the bearing end surface and the lid 4 at the lower end of the motor, so that the leakage to the outside is completely contained.

The radial bearing portion is formed on the inner circumference of the bearing 6 or the outer circumference of the shaft 2. The type of the dynamic pressure bearing is shown in FIG.
The arc type as shown or the groove groove type as shown in FIG. 4 can be considered, and the present invention can be applied to any type.

The bearing type of the thrust portion may be the taper land type shown in FIG. 3 or the spiral type shown in FIG. 5, and in either case, it can be applied to the present invention in combination with the radial bearing described above. The thrust bearing may be formed between both surfaces of the lower thrust bearing 5 and the end surface of the bearing 6 and the lid.

The radial bearing rigidity is determined by the viscosity and the rotational speed of the lubricating fluid, the bearing clearance and the bearing length in both the circular groove bearing of FIG. 2 and the groove groove bearing of FIG. By properly designing these, the temperature change of bearing unbalance vibration amplitude is 2/3 when the track interval is 1/5 or more.
Determine the bearing stiffness so that

FIG. 8 shows an example of a 2.5-inch magnetic disk 17 device using the present invention. The spindle motor shown in the first embodiment is formed on the base 10, and two magnetic disks 17 having a diameter of 2.5 inches are laminated on this spindle motor. A rotary actuator 23 is provided on the base 10 so as to be swingable via a pivot shaft 24 and a bearing. The rotary actuator 23 is provided with four magnetic heads 20 via the load arm 21 so as to contact both sides of each of the two magnetic disks 17.
The structure is such that the magnetic information can be read and written by moving to an arbitrary track position on the magnetic disk 17. Base 1
0 is configured to be completely covered by the cover 22, and the magnetic disk 17 and the magnetic head 20 are isolated in a clean environment and protected from dust in the outside world.

In the example of this device, an asymmetrical three-circle bearing as shown in FIG. 2 is used, the minimum bearing clearance is 3 μm at a rotation speed of 4600 rpm, and the bearing rigidity is 5 kN / mm at a bearing width of 2 mm. It is designed to have almost the same rigidity as the SP2 of 7.

[0027]

EFFECTS OF THE INVENTION By setting the bearing rigidity to ⅕ or more and ⅔ or less of the track interval, the temperature change of the unbalanced vibration amplitude can be suppressed to a size that always satisfies the positioning accuracy. A highly accurate spindle can be realized without unnecessarily increasing loss. This enables high-density recording on the magnetic disk 17 device, and makes it possible to increase the capacity of the device.

[Brief description of drawings]

FIG. 1 is a diagram showing a first embodiment of the present invention.

FIG. 2 is a component diagram of the first embodiment of the present invention.

FIG. 3 is a component diagram of the first embodiment of the present invention.

FIG. 4 is a component diagram of the first embodiment of the present invention.

FIG. 5 is a component diagram of the first embodiment of the present invention.

FIG. 6 is a diagram illustrating a means for solving the problem.

FIG. 7 is a diagram illustrating a means for solving the problem.

FIG. 8 is a diagram showing a second embodiment of the present invention.

[Explanation of symbols]

1 ... Hub, 2 ... Shaft, 3 ... Motor magnet, 4 ...
Lid, 5 ... Thrust receiver, 6 ... Bearing, 7 ... Bracket,
8 ... Motor stator, 9 ... Seal, 10 ... Base, 11
... Oil groove, 12 ... Land portion, 13 ... Tapered portion, 14 ... Groove groove, 15 ... Spiral groove, 16 ... Land portion, 17
... magnetic disk, 18 ... spacer, 19 ... clamp, 2
0 ... magnetic head, 21 ... load arm, 22 ... cover,
23 ... Rotary actuator, 24 ... Pivot axis.

Continuation of the front page (72) Inventor Tomoaki Inoue 502 Kintatecho, Tsuchiura City, Ibaraki Pref., Institute of Mechanical Research, Hiritsu Manufacturing Co., Ltd.

Claims (3)

[Claims] 1. A hub provided with one or more magnetic disks, a motor for rotating the hub, and a fluid-lubricated dynamic bearing for supporting the hub around a certain rotation center and allowing the hub to rotate freely. A magnetic disk characterized in that the bearing rigidity is determined so that the change of the vibration amplitude in the device operating temperature range is not less than 1/5 and not more than 2/3 of the radial recording interval written on the magnetic disk. Spindle motor. 2. A hub capable of laminating one or more 2.5-inch magnetic disks, a motor for rotationally driving the hub, and a fluid-lubricated dynamic pressure bearing which supports the hub at a certain rotation center and is freely rotatable. It has a bearing rigidity of 20
Spindle motor for magnetic disk, characterized by 3kN / mm or more and 15kN / mm or less at ℃. 3. A magnetic disk having a hub on which one or more magnetic disks can be stacked, a motor for rotating the hub, and a fluid lubrication type dynamic pressure bearing for supporting the hub at a certain rotation center and allowing the hub to rotate freely. A magnetic disk drive characterized in that the amplitude fluctuation of the bearing vibration due to temperature is in the range of ⅕ or more and ⅔ or less of the track interval, using a spindle motor for use in the vehicle.