JP2003166524A - Hydrodynamic bearing unit - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a hydrodynamic bearing unit generating satisfactory hydrodynamic pressure without forming recessed separating grooves. <P>SOLUTION: In the hydrodynamic bearing unit 10 used for a rotary polygon mirror driving device or the like, a protruded portion 37 minimizing dimensions of a fine gap 32, a recessed portion 35 maximizing dimensions of the fine gap 32, and a tapered portion 36 continuously varying the dimensions of the fine gap 32 between the recessed portion 35 and protruded portion 37, are formed on a hydrodynamic pressure generating portion 31 respectively, and the recessed separating grooves are not formed therein. Further, the hydrodynamic pressure generating portion 31 is formed at three places or five places in a peripheral direction at even angular intervals, and a ratio of an arc angle of a region where the protruded portions 37 are formed is set in a range from 0.3 to 0.6. <P>COPYRIGHT: (C)2003,JPO

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a dynamic pressure bearing device for generating a dynamic pressure in a lubricating fluid and supporting the shaft member and the bearing member in a relatively rotatable manner by the dynamic pressure.

[0002]

2. Description of the Related Art In recent years, polygon mirrors, magnetic disks,
Various types of hydrodynamic bearing devices have been proposed for use in devices that rotate various rotating bodies such as optical disks. In this type of dynamic pressure bearing device, generally, the outer peripheral surface of the shaft member and the inner peripheral surface of the bearing member face each other with a minute gap therebetween, and a dynamic pressure generating portion is formed on one of the surfaces. The lubricating fluid such as air or oil present in the minute gap is pressurized by the pumping action in the dynamic pressure generating portion during rotation, and the dynamic pressure of the pressurized lubricating fluid causes the shaft member and the bearing member. Both members are supported so as to be rotatable relative to each other.

In such a dynamic pressure bearing device, there is one in which a groove having a herringbone shape or a spiral shape is provided as a means for generating a dynamic pressure. Especially, in the case of a journal bearing device, a dynamic pressure bearing device is used. A step dynamic bearing device and a taper dynamic bearing device that do not use a generating groove have been proposed.

10 (A) and 10 (B) are a cross-sectional view of a conventional tapered dynamic pressure bearing device and an explanatory view showing a developed dynamic pressure generating portion formed in this dynamic pressure bearing device, respectively.
In the hydrodynamic bearing device 30 'shown in this figure, the minute gap 3 is formed on the inner peripheral surface of the bearing sleeve 15' (bearing member) surrounding the rotary shaft 21 (shaft member) via the minute gap 32 '.
A convex portion 37 'having a minimum size of 2', and a concave separation groove 3 having a depth of 23 μm formed over an arc angle of about 7.5 °.
8, and a dynamic pressure generating portion 31 'having a tapered portion 36' for continuously changing the size of the minute gap 32 'by about 5 μm between the concave separation groove 38 and the convex portion 37' is provided along the circumferential direction. Are formed in three places, and when the rotary shaft 21 rotates in the direction indicated by the arrow r, a narrow gap 32 'formed between the outer peripheral surface of the rotary shaft 21 and the inner peripheral surface of the bearing sleeve 15'.
At, a desired bearing dynamic pressure is obtained by pressurizing a lubricating fluid such as air or oil.

[0005]

However, the dynamic pressure bearing device 30 'having the concave separation groove 38 for eliminating the negative pressure has the following problems because of its low rigidity. First, when a disturbance is applied during low-speed rotation, the rotary shaft 21 easily shakes, and therefore the motor specifications are not satisfied. Also,
Since the rotational speed at which levitation starts due to the dynamic pressure is high, the rotational shaft 21 and the bearing sleeve 1 are rotated at a low rotational speed of 5000 rpm.
Since metal contact occurs with 5'and wear occurs,
The life of the hydrodynamic bearing device 30 'is short. As a measure for solving such a problem, the rotating shaft 21 and the bearing sleeve 2
Although the dimensional tolerance of 1'may be made strict and the clearance of both sides may be made small, such a measure is not preferable because it causes an increase in component cost and an assembly cost.
Further, it is conceivable to increase the peripheral speed by increasing the diameter of the rotary shaft 21, but such measures are not preferable because they also increase the cost of parts. Further, it is conceivable to use a material having high abrasion resistance for the rotary shaft 21 and the bearing sleeve 15 ', but such measures are not preferable because they increase the cost of parts.

Further, when the concave separation groove 38 is formed, the reduction ratio of the lubricating fluid in the minute gap 32 'becomes too large,
There is also a problem that the lubricating fluid that cannot enter the small gap leaks in the axial direction.

Further, the concave separation groove 38 is preferably as deep and narrow as possible in order to obtain good dynamic pressure characteristics, and is usually formed to a depth of 20 μm or more. Therefore, in the manufacturing process of the dynamic pressure bearing device 30 ', cutting is performed to form deep and narrow grooves. This is because it is difficult to form the deep and narrow concave separation groove 38 by a method other than cutting. Therefore, the conventional dynamic bearing device 30 '
Then, a process completely separate from other manufacturing processes is added. In addition to this, the workability of the cutting process itself is not good, and the productivity is greatly reduced due to the workability of the work and the processing efficiency. Therefore, the conventional dynamic pressure bearing device 30 'has a problem that the cost must be increased.

In view of the above problems, it is an object of the present invention to provide a dynamic pressure bearing device which can generate a good dynamic pressure without forming a concave separation groove.

[0009]

In order to solve the above-mentioned problems, according to the present invention, a lubricating fluid is provided in a minute gap between an outer peripheral surface of a shaft member mounted relatively rotatably and an inner peripheral surface of a bearing member. And the outer peripheral surface of the shaft member and the inner peripheral surface of the bearing member, the convex portion that minimizes the size of the minute gap, the concave portion that maximizes the size of the minute gap, and In a dynamic pressure bearing device in which a dynamic pressure generating portion having a tapered portion that continuously changes the size of the minute gap between the concave portion and the convex portion is formed at a plurality of locations along the circumferential direction, The generating portions are formed at three to five locations at equal angular intervals in the circumferential direction, and the arc angle of the area in which the convex portion is formed with respect to the arc angle of the area in which the dynamic pressure generating portion is formed. Is set in the range of 0.3 to 0.6 Characterized in that it is.

According to the present invention, in the dynamic pressure generating portion, the convex portion that minimizes the size of the minute gap, the concave portion that maximizes the dimension of the minute gap, and the size of the minute gap between the concave portion and the convex portion are continuous. The taper portion for changing the shape is formed, and the concave separation groove is not formed. Therefore, since it is not necessary to form the concave separation groove in the bearing sleeve formed by sintering by cutting, the productivity of the dynamic pressure bearing device can be improved. Further, since the concave separation groove is not formed, it is possible to suppress the leakage of the lubricating fluid in the axial direction. Further, the dynamic pressure generating portion is formed at three or five locations at equal angular intervals in the circumferential direction, and the ratio of the arc angles of the area where the convex portion is formed is 0.3 to 0.6. Since the structure is optimized by setting the range, etc., the rigidity toward the center is large. Therefore, shake is less likely to occur even when a disturbance is applied at low speed rotation. Further, since the rotational speed at which the dynamic pressure starts to levitate is low, metal contact is less likely to occur even at low speed rotation, so the life of the dynamic pressure bearing device is long. Therefore,
For the purpose of increasing the rigidity, the dimensional tolerances of the shaft member and the bearing member do not have to be made strict, and it is not necessary to increase the peripheral speed by increasing the diameter of the shaft member. Further, it is not necessary to use an effective material having high abrasion resistance for the shaft member and the bearing member. Therefore, according to the present embodiment, it is possible to provide a dynamic pressure bearing device having good characteristics without increasing the cost.

In the present invention, it is preferable that the arc angle of the region where the recess is formed is set to 10 ° or less. According to this structure, the rigidity in the central direction can be further increased, so that the shake when the disturbance is applied at the low speed rotation can be more reliably prevented.

In the present invention, the arc angle of the region where the recess is formed may be set to about 10 °. In the present invention, since the number of dynamic pressure generating portions and the formation area of the convex portion are optimized, the rigidity is sufficiently large, so that the arc angle of the area where the concave portion is formed is set to about 10 °, Wear of a mold used for sintering the bearing sleeve may be prevented. That is, if the arc angle of the region in which the recess is formed is set to 10 ° or less, the load on the mold becomes large when the bearing sleeve is removed from the mold when the bearing sleeve is sintered and molded, and the mold becomes large. However, if the arc angle of the area where the recess is formed is set to about 10 °, the wear of the mold can be prevented and the decrease in rigidity toward the center can be minimized. Can be suppressed.

In the present invention, the bearing member is preferably made of, for example, a sintered compact of powder containing metal. According to this structure, the bearing member can be manufactured at low cost, so that the cost of the dynamic pressure bearing device can be reduced.

In the present invention, the lubricating fluid is, for example, air.

[0015]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention will be described with reference to the drawings.

(Overall Structure of Polygon Mirror Rotation Driving Device) FIGS. 1 and 2 are a sectional view of a polygon mirror rotation driving device to which the present invention is applied, and a dynamic pressure bearing device used in this polygon mirror rotation driving device. FIG.

In FIG. 1, a polygon mirror rotation driving device 10 is composed of a stator set 1 as a fixed member and a rotor set 2 as a rotating member assembled to the stator set 1 from above.

The stator assembly 1 has a frame 11 on which a circuit board 19 is mounted, and the frame 11
Is a bearing holder 1 made of a substantially hollow cylindrical body having a relatively large diameter.
2 is attached. A stator core 13 radially having a plurality of salient pole portions is fitted on the outer peripheral surface of the bearing holder 12, and a winding 14 is wound around each salient pole portion of the stator core 13.

A bearing sleeve 15 constituting a bearing member of the dynamic pressure bearing device 30 is fitted on the inner peripheral surface of the bearing holder 12. The detailed structure of the bearing sleeve 15 will be described later, but as shown in FIG.
In the hollow hole provided in the central portion of 5, the rotary shaft 21 constituting the shaft body of the rotor set 2 is rotatably supported.
Here, the inner peripheral surface of the center hole of the bearing sleeve 15 and the outer peripheral surface of the rotary shaft 21 are several μm in the radial direction, as described later.
The dynamic pressure bearing device 30 is configured by arranging face-to-face in a circumferential shape with a narrow gap of several tens of μm, and these opposing faces being configured as radial dynamic pressure bearing faces.

Referring again to FIG. 1, a disk-shaped thrust bearing plate 16 is fitted into the opening on the lower end side of the bearing holder 12 so as to close the opening.

On the other hand, the upper end portion of the rotary shaft 21 has the rotor 2
The polygon mirror 26 is pressed and fixed by the cap 24 and the spring 25 on the mirror mounting surface of the rotor 23. Rotor 2
An annular drive magnet 27 is mounted on the inner side of the substantially cylindrical body 3 of FIG. 3, and the drive magnet 27 faces the outer end surface of the salient pole portion of the stator core 13.

(Structure of Dynamic Pressure Bearing Device 30) The structure of the dynamic pressure bearing device 30 used in the polygon mirror rotation drive device 10 will be described in detail with reference to FIGS. 3 (A) and 3 (B). To do.

3 (A) and 3 (B) are respectively a cross-sectional view of the dynamic pressure bearing device shown in FIG. 2 and an explanatory view showing a developed dynamic pressure generating portion formed in this dynamic pressure bearing device. .

As shown in FIGS. 3 (A) and 3 (B), in the hydrodynamic bearing device 30 of this embodiment, the rotary shaft 21 is a perfect circle when cut at any position in the axial direction. The inner surface of the bearing sleeve 15 has a recess 35 that maximizes the size of the minute gap 32 formed between the inner surface of the bearing sleeve 15 and the outer surface of the rotating shaft 21.
The dynamic pressure generating portion 3 includes a convex portion 37 that minimizes the size of the minute gap 32 and a taper portion 36 that continuously changes the size of the minute gap 32 between the convex portion 37 and the concave portion 35.
1 is formed, and FIGS. 3A and 3B exemplify a case where the dynamic pressure generating portions 31 are formed at five positions at equal angular intervals along the circumferential direction.

In the dynamic pressure bearing device 30 having the above-described structure, when the rotary shaft 21 rotates in the direction indicated by the arrow r, the air existing between the rotary shaft 21 and the bearing sleeve 15 in the dynamic pressure generating portion 31 or The oil flows in the wedge-shaped minute gap 32 in which the concave portion 35, the tapered portion 36, and the convex portion 37 are formed in accordance with the rotation direction of the rotating shaft 21. At this time, since the wedge-shaped minute gap 32 is gradually narrowed toward the region where the convex portion 37 is formed, the pressure of air or oil interposed between the rotary shaft 21 and the bearing sleeve 15 is increased. The pressure at this time becomes a dynamic pressure, and the rotating shaft 21 is rotatably supported without contacting the inner peripheral surface of the bearing sleeve 21 with metal.

(Influence of the Number of Dynamic Pressure Generating Portions 31) In constructing such a dynamic pressure bearing device 30, the inventor of the present application uses, as the bearing sleeve 15 shown in FIG. 2, a sintered compact of powder containing metal. , For example, a sintered body made of bronze containing a solid lubricant and having an inner diameter of 10 mm and a length of 15 mm is manufactured, and the rotary shaft 21 made of SUS304 is supported on the rotary shaft 21 at 40,000 rpm. The following examinations were conducted under the test condition of rotating at. Here, the clearance between the bearing sleeve 15 and the rotating shaft 21 is 2.5 μm to 5.0 μm on one side.

In the present embodiment, first, the number of dynamic pressure generating portions 31, the center-direction rigidity corresponding to the actual dynamic pressure, the center-direction rigidity torque ratio obtained by dividing this center-direction rigidity by the friction torque, and the direction of the dynamic pressure are determined. Regardless of the bearing load, which shows its absolute value, and the relationship with the side leakage (air leakage in the axial direction), the eccentricity was used as a parameter, and the results are shown in Fig. 4 (A). , (B), (C),
It shows in (D).

In this figure, the number of dynamic pressure generating portions 31 is three.
The data in the case of a solid line is L13, and the number of dynamic pressure generating parts is 4
The data for the case of a solid line L14, the number of dynamic pressure generating parts is 5
The data in the case of a solid line is L15, and the number of dynamic pressure generating parts is 6
The data in the case of a solid line is L16, and the number of dynamic pressure generating parts is 8
The data for the location is shown by the solid line L18.

Here, the eccentricity is a value obtained by dividing the distance between the center of the bearing sleeve and the center of the rotating shaft by the radial clearance.
Therefore, the eccentricity is 1.0 when the rotating shaft is in contact with the bearing sleeve, and the eccentricity is 0.0 when the rotating shaft is in the center position due to the dynamic pressure. The eccentricity ratio during steady rotation is in the range of 0.2 to 0.4. Further, since the rigidity in the central direction represents the rigidity in the central direction which acts as an actual dynamic pressure, the larger the rigidity, the less the shake due to the disturbance occurs. In addition, the center-direction rigidity torque ratio is a value obtained by dividing the center-direction rigidity by the friction torque, and therefore shows efficiency.
It can be said that it is an efficient dynamic bearing device. The side leakage is preferably small because it represents a leakage of air or oil to the side, and a conventional dynamic bearing device having a concave separation groove has a problem that the leakage is extremely large.

When the number of dynamic pressure generating parts 31 is three, as can be seen from FIGS. 3A and 3B, the arc angle θ1 of the whole dynamic pressure generating part 31 is 120 °, and the convex angle is convex. The arc angle θ2 of the portion 37 was set to 45 °, and the arc angle θ3 of the recess 35 was set to 9 °. When the number of the dynamic pressure generating portions 31 is four, the arc angle θ1 of the entire dynamic pressure generating portion 31 is 90 °, and the arc angle θ2 of the convex portion 37 is 36.
And the arc angle θ3 of the recess 35 was set to 9 °.
When the number of the dynamic pressure generating parts 31 is 5, the dynamic pressure generating parts 3
The arc angle θ1 of the whole 1 is 72 °, the arc angle θ2 of the convex portion 37 is set to 27 °, and the arc angle θ3 of the concave portion 35 is set to 9 °. When the number of the dynamic pressure generating portions 31 is 6, the arc angle θ1 of the entire dynamic pressure generating portion 31 is 60 °, the arc angle θ2 of the convex portion 37 is 21 °, and the concave portion 35.
The arc angle θ3 of was set to 9 °. Dynamic pressure generator 3
When the number of 1s is 8, the arc angle θ1 of the entire dynamic pressure generating portion 31 is 45 °, and the arc angle θ2 of the convex portion is 1
8 °, and the arc angle θ3 of the recess was set to 9 °.

As a result of such a study, as shown in FIG.
As shown in FIG. 4D, the bearing load and the side leakage under the conditions corresponding to the steady state have small differences depending on the number of the dynamic pressure generating portions 31, but FIG.
As can be seen from (B), regarding the center-direction rigidity and the center-direction rigidity torque ratio, good results were obtained when the number of the dynamic pressure generating portions 31 was 3 or 5.

(Influence of Convex Width Ratio) Next, when the number of the dynamic pressure generating portions 31 is three, four, and five, the inventor of the present application, the convex width ratio, the rigidity in the center direction, The relationship between the center-direction rigidity torque ratio, the bearing load, and the side leakage (air leakage in the axial direction) was examined by changing the eccentricity ratio, and the examination results are shown in FIG.
(B), (C), (D), FIG. 6 (A), (B),
(C), (D), and FIGS. 7 (A), (B), (C),
It shows in (D).

In this figure, the solid line L21 shows the data when the eccentricity is 0.1, the solid line L25 shows the data when the eccentricity is 0.5, and the data when the eccentricity is 0.9. The data is shown by the solid line L29. The convex portion width ratio is
It is the ratio of the arc angle θ2 of the convex portion 37 to the arc angle θ1 of the entire dynamic pressure generating portion 31. Therefore, if the number of the dynamic pressure generating portions 31 is three, the arc angle θ1 of the whole dynamic pressure generating portion 31 is 1
Since it is 20 ° (360 ° / 3), the convex portion width ratio is
(Θ2 / 120 °), and the number of dynamic pressure generating parts 31 is 4
If it is a place, the arc angle θ1 of the entire dynamic pressure generating unit 31 is 90.
Since it is (360 ° / 4), the convex portion width ratio is (θ2
/ 90 °), and if the number of dynamic pressure generating parts 31 is 5, the arc angle θ1 of the whole dynamic pressure generating part 31 is 72 ° (36 °).
0 ° / 5), the convex portion width ratio is (θ2 / 72).
°).

As a result of such examination, FIG. 5 (C) and FIG.
As shown in (C) and FIG. 7 (C), as the convex portion width ratio increases, the bearing load tends to increase when the eccentricity ratio is 0.9, but the eccentricity ratio is 0.1, When the ratio is 0.5, no significant change in the bearing load is observed even if the convex portion width ratio changes. Further, as shown in FIG. 5D, FIG. 6D, and FIG. 7D, the side leakage tends to be slightly smaller as the convex portion width ratio becomes larger.

In contrast, FIGS. 5A, 5B and 6
As shown in (A), (B), FIG. 7 (A), and (B), the central rigidity and the central rigidity torque ratio, among others,
Regarding the rigidity torque ratio in the central direction, the width ratio of the convex portion is 0.3.
Good results were obtained in the range of from 0.6 to 0.6.

(Influence of Concavity Width) Next, in the case where the number of the dynamic pressure generating portions 31 is 5, the inventor of the present application, the recess width, the center direction rigidity, the center direction rigidity torque ratio, the bearing load,
And side leaky cage (air leakage in the axial direction)
The relationship between and was examined by changing the eccentricity, and the examination results are shown in FIGS. 8 (A), (B), (C), and (D), respectively.

In this figure, the solid line L31 shows the data when the eccentricity is 0.1, the solid line L35 shows the data when the eccentricity is 0.5, and the data when the eccentricity is 0.9. The data is shown by the solid line L39. As for the recess width, in FIG. 8, the recess width ratio, that is, the dynamic pressure generating portion 31.
This is the ratio of the circular arc angle θ3 of the concave portion to the total circular arc angle θ1. In the example shown here, since the number of the dynamic pressure generating portions 31 is 5, the circular arc angle θ1 of the entire dynamic pressure generating portion 31 is 72 ° (36
0 ° / 5), and the recess width ratio is represented by (θ3 / 72 °).

As a result of such an examination, as shown in FIG. 8D, the smaller the recess width ratio, that is, the recess 35.
When the arc angle θ3 is less than 10 °, the side leakage tends to be slightly small.

As shown in FIGS. 8A, 8B, and 8C, as for the center-direction rigidity, the center-direction rigidity torque ratio, and the bearing load, the smaller the convex part width ratio, that is, the concave part. Good results were obtained when the circular arc angle θ3 of 35 was 10 ° or less.

(Influence of taper amount) Next, the inventor of the present application
When the number of dynamic pressure generating parts is 5, the taper amount, the center-direction rigidity, the center-direction rigidity torque ratio, the bearing load,
And side leaky cage (air leakage in the axial direction)
The relationship between and was examined by changing the eccentricity, and the examination results are shown in FIGS. 9 (A), (B), (C), and (D), respectively. Here, since the number of the dynamic pressure generating portions 31 is 5, the arc angle θ1 of the whole dynamic pressure generating portion 31 is 72 °, the arc angle θ2 of the convex portion 37 is 27 °, and the arc angle of the concave portion 35. θ3 is set to 9 °. The amount of taper referred to here means the size t at which the size of the minute gap 32 in the tapered portion 36 changes, as shown in FIGS. 3 (A) and 3 (B). In FIG. 9, a solid line L41 shows data when the taper amount is 1 μm, a solid line L43 shows data when the taper amount is 3 μm, a solid line L45 shows data when the taper amount is 5 μm, and a taper amount is 7 μm. The data in the case of is shown by the solid line L47.

As a result of such a study, as shown in FIG.
As shown in (B), (C), and (D), the rigidity in the center direction,
The smaller the taper amount in the center-direction rigidity torque ratio, the bearing load, and the side leakage, the better results were obtained.

(Effects of this Embodiment) From the above examination results, in this embodiment, the dynamic pressure generating portion 31 has a convex portion 37 that minimizes the size of the minute gap 32 and a concave portion that maximizes the size of the minute gap 32. 35, and the tapered portion 36 that continuously changes the size of the minute gap 32 between the concave portion 35 and the convex portion 37, and the concave separation groove is not formed. Therefore, since it is not necessary to form the concave separation groove in the bearing sleeve 15 formed by sintering by cutting, the productivity of the dynamic pressure bearing device 30 can be improved.

Further, in this embodiment, the dynamic pressure generating portion 31 is formed at three or five locations at equal angular intervals in the circumferential direction, and the ratio of the arc angles of the area where the convex portion 37 is formed is set. The range is set to 0.3 to 0.6. For this reason, in the hydrodynamic bearing device 30 of the present embodiment, since the rigidity in the central direction is large, the runout is unlikely to occur even when a disturbance is applied at low speed rotation. Further, since the rotational speed at which the dynamic pressure starts to float is low, metal contact is unlikely to occur between the rotary shaft 21 and the bearing sleeve 15 even at a low rotational speed of 5000 revolutions / quantile, so the life of the dynamic pressure bearing device 30 is reduced. long.
Therefore, the dimensional tolerances of the rotary shaft 21 and the bearing sleeve 15 do not have to be tightened for the purpose of increasing the rigidity,
There is no need to increase the diameter of the rotary shaft 21 to increase the peripheral speed. Furthermore, it is not necessary to use an effective material having high abrasion resistance for the rotary shaft 21 and the bearing sleeve 15. Therefore,
According to this embodiment, it is possible to provide the dynamic pressure bearing device 30 having good characteristics without increasing the cost.

Further, in this embodiment, since the arc angle of the region where the concave portion 35 is formed is set to 10 ° or less, the rigidity in the center direction can be further increased, and therefore, when a disturbance is applied at low speed rotation, Runout can be prevented more reliably.

However, if the arc angle of the region in which the concave portion 35 is formed is set to 10 ° or less, the load on the die when the bearing sleeve 15 is removed from the die when the bearing sleeve 15 is sintered and formed. It can become large and wear the mold severely. Even in such a case, in the present embodiment, the number of dynamic pressure generating portions 31 and the formation area of the convex portions 37 are optimized, so that the rigidity is sufficiently large, and therefore the arc angle of the area where the concave portion 35 is formed. May be set to about 10 ° to prevent wear of the mold used for sintering the bearing sleeve 15.

[0046]

As described above, in the dynamic pressure bearing device according to the present invention, the dynamic pressure generating portion has a convex portion that minimizes the size of the minute gap, a concave portion that maximizes the size of the minute gap, and A tapered portion that continuously changes the size of the minute gap is formed between the concave portion and the convex portion, and the concave separation groove is not formed. Therefore, since it is not necessary to form the concave separation groove in the bearing sleeve formed by sintering by cutting, the productivity of the dynamic pressure bearing device can be improved. Further, since the concave separation groove is not formed, it is possible to suppress the leakage of the lubricating fluid in the axial direction. Further, the dynamic pressure generating portion is formed at three or five locations at equal angular intervals in the circumferential direction, and the ratio of the arc angles of the area where the convex portion is formed is 0.3 to 0.6. Since the structure is optimized by setting the range, etc., the rigidity toward the center is large. Therefore, shake is less likely to occur even when a disturbance is applied at low speed rotation. Further, since the rotational speed at which the dynamic pressure starts to levitate is low, metal contact is less likely to occur even at low speed rotation, so the life of the dynamic pressure bearing device is long. Therefore, the dimensional tolerances of the shaft member and the bearing member do not have to be made strict for the purpose of increasing the rigidity, and it is not necessary to increase the circumferential speed by increasing the diameter of the shaft member. Further, it is not necessary to use an effective material having high abrasion resistance for the shaft member and the bearing member. Therefore, according to the present embodiment, it is possible to provide a dynamic pressure bearing device having good characteristics without increasing the cost.

[Brief description of drawings]

FIG. 1 is a sectional view of a polygon mirror rotation driving device to which the present invention is applied.

FIG. 2 is an explanatory diagram of a dynamic pressure bearing device used in a polygon mirror rotation drive device to which the present invention is applied.

FIG. 3 is a cross-sectional view of a dynamic pressure bearing device to which the present invention is applied,
FIG. 3 is an explanatory view showing a developed dynamic pressure generating portion formed in the dynamic pressure bearing device.

4 (A), (B), (C), and (D) are respectively,
In the dynamic pressure bearing device shown in FIG. 3, the number of dynamic pressure generating parts,
It is a graph which shows the result of having examined the relationship with center direction rigidity, center direction rigidity torque ratio, bearing load, and side leakage using the eccentricity as a parameter.

5 (A), (B), (C), and (D) are respectively,
In the dynamic pressure bearing device shown in FIG. 3, the number of dynamic pressure generating parts is three.
9 is a graph showing the results of examining the relationship between the convex portion width ratio, the center-direction rigidity, the center-direction rigidity torque ratio, the bearing load, and the side leakage when changing the eccentricity ratio.

6 (A), (B), (C), and (D) are respectively,
In the dynamic pressure bearing device shown in FIG. 3, the number of dynamic pressure generating parts is 4
9 is a graph showing the results of examining the relationship between the convex portion width ratio, the center-direction rigidity, the center-direction rigidity torque ratio, the bearing load, and the side leakage when changing the eccentricity ratio.

7 (A), (B), (C), and (D) are respectively,
In the dynamic pressure bearing device shown in FIG. 3, the number of dynamic pressure generating parts is 5
9 is a graph showing the results of examining the relationship between the convex portion width ratio, the center-direction rigidity, the center-direction rigidity torque ratio, the bearing load, and the side leakage when changing the eccentricity ratio.

8 (A), (B), (C), and (D) are respectively,
In the dynamic pressure bearing device shown in FIG. 3, the number of dynamic pressure generating parts is 5
FIG. 6 is a graph showing the results of examining the relationship between the recess width, the center-direction rigidity, the center-direction rigidity torque ratio, the bearing load, and the side leakage by changing the eccentricity ratio, in the case of the location.

9 (A), (B), (C), and (D) are respectively
In the dynamic pressure bearing device shown in FIG. 3, the number of dynamic pressure generating parts is 5
Taper amount, center direction rigidity,
It is a graph which shows the result of having examined the relationship between a center direction rigidity torque ratio, a bearing load, and a side leakage by changing eccentricity.

FIG. 10 is a cross-sectional view of a conventional dynamic pressure bearing device and an explanatory view showing a developed dynamic pressure generating portion formed in the dynamic pressure bearing device.

[Explanation of symbols]

1 Stator set 2 rotor sets 30 Dynamic bearing device 10 Polygon mirror rotation drive 15 Bearing sleeve 21 rotation axis 31 Dynamic pressure generator 32 minute gap 35 recess 37 convex 36 Tapered part

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Claims (5)

[Claims] 1. A lubricating fluid intervenes in a minute gap between the outer peripheral surface of a shaft member and the inner peripheral surface of a bearing member mounted so as to be rotatable relative to each other, and the outer peripheral surface of the shaft member and the bearing member. On any of the inner peripheral surfaces of the, the convex portion that minimizes the dimension of the minute gap, the concave portion that maximizes the dimension of the minute gap, and the dimension of the minute gap between the concave portion and the convex portion. In a dynamic pressure bearing device in which a dynamic pressure generating portion having a continuously changing taper portion is formed at a plurality of locations along the circumferential direction, the dynamic pressure generating portion has three or five locations at equal angular intervals in the circumferential direction. The ratio of the arc angle of the area where the convex portion is formed to the arc angle of the area where the dynamic pressure generating portion is formed is set to a range of 0.3 to 0.6 A hydrodynamic bearing device characterized by being provided. 2. The hydrodynamic bearing device according to claim 1, wherein an arc angle of the region where the recess is formed is set to 10 ° or less. 3. The dynamic pressure bearing device according to claim 1, wherein an arc angle of the region where the recess is formed is set to about 10 °. 4. The method according to any one of claims 1 to 3,
The dynamic pressure bearing device, wherein the bearing member is composed of a sintered compact of powder containing metal. 5. The method according to any one of claims 1 to 4,
The dynamic pressure bearing device, wherein the lubricating fluid is air.