JP2000120664A - Ceramic dynamic pressure bearings - Google Patents

Abstract

(57) [Problem] To provide a ceramic dynamic pressure bearing capable of preventing breakage of ceramics by preventing occurrence of linking and seizure and realizing stable rotation. SOLUTION: A dynamic pressure generating part 7 at both ends of an outer cylinder 7 in a vertical direction.
The flatness of a and 7b is set in a range of 3 μm or less. The flatness of the end face dynamic pressure generating portion 21a below the upper thrust plate 21 and the flatness of the end face dynamic pressure generating portion 23b above the lower thrust plate 23 are also set within a range of 3 μm or less. Further, the outer cylinder 7 includes upper and lower end face dynamic pressure generating portions 7a and 7a.
b, the inner peripheral portion 7d has a lower value than the outermost peripheral portion 7c.
The height is set to be higher than μm and not more than 2.5 μm. On the other hand, both thrust plates 21 and 23 are flat plates, and there is no difference in height between the inner peripheral portion and the outermost peripheral portion.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a ceramic dynamic pressure bearing in which the outer cylinder rotates when the outer cylinder and the thrust plate do not contact when the outer cylinder and the inner cylinder are not in contact with each other during rotation. Things.

[0002]

2. Description of the Related Art Conventionally, a high-precision motor that rotates at high speed uses a gas such as air as a medium in order to obtain excellent bearing performance at high speed rotation and to prevent occurrence of unevenness in low rotation. A hydrodynamic bearing is used.

[0003] The dynamic pressure bearing is such that when the outer cylinder rotates, the outer cylinder rotates while being supported in a non-contact manner with the bearing surface of the inner cylinder during rotation. In general, a metal such as stainless steel or a material obtained by applying a coating such as a nitride or a resin thereto is used.

[0004] Apart from this, in recent years, seizure hardly occurs and the abrasion resistance is excellent.
2. Description of the Related Art A ceramic dynamic pressure bearing using a ceramic dynamic pressure component such as alumina in part or in whole has been developed.

[0005]

However, even in the case of such a dynamic pressure bearing made of ceramics, the bearing portion composed of the inner cylinder as the fixed portion and the outer cylinder as the rotating portion is provided with two disk-shaped thrust bearings. In a dynamic pressure bearing having a structure in which a plate is sandwiched,
There were cases where problems occurred during startup and shutdown.

More specifically, when the outer cylinder and the thrust plate come into contact with each other when the dynamic pressure bearing is started or stopped, linking (ie, a phenomenon in which the gap becomes a vacuum and the members come into close contact with each other).
In the worst case, there was a case where ceramic members such as an outer cylinder and a thrust plate were damaged.

[0007] Apart from this, when the hydrodynamic bearing rotates, there is a problem that the outer cylinder vibrates and the rotation becomes unstable. The present invention has been made to solve the above-described problems, and an object of the present invention is to provide a dynamic pressure bearing made of ceramics that can prevent the occurrence of linking and seizure to prevent damage to ceramics and realize stable rotation. And

[0008]

(1) In order to achieve the above object, the invention of claim 1 is to provide a bearing unit having an inner cylinder as a fixed part and an outer cylinder as a rotating part with two bearings. Having a structure in which a thrust plate is sandwiched, the inner cylinder, the outer cylinder and the thrust plate are:
A gas dynamic pressure bearing formed of ceramics, wherein the flatness of an end face dynamic pressure generating portion of the outer cylinder facing the thrust plate is 3 μm or less. I do.

In the present invention, since the flatness of the end face dynamic pressure generating portion facing the thrust plate of the outer cylinder is 3 μm or less, when the outer cylinder rotates, the distance between the end face of the outer cylinder and the thrust plate becomes circumferential. Direction, and the generated dynamic pressure also has less unevenness due to rotation. Therefore, the occurrence of vibration in the outer cylinder can be prevented, and the rotational operation of the dynamic pressure bearing can be stabilized. In addition, since the vibration of the outer cylinder can be prevented, it is possible to prevent the ceramic member such as the outer cylinder from contacting the surroundings and being damaged.

As described above, according to the present invention, it can be seen that if the flatness is processed to be 3 μm or less, the generation of vibration can be suppressed. The waste of processing can be eliminated, and the effect is great in actual production of industrial products.

In the present invention, the end face dynamic pressure generating portions for generating dynamic pressure are formed on both sides (upper and lower sides) in the thickness direction of the outer cylinder (axial direction of the rotating shaft). It is desirable that the definition of the degree be satisfied not only on the end face dynamic pressure generating portion on one side but also on both sides. In the present invention, as defined in JIS B 0621, the flatness is defined as the distance between two planes when the distance between the parallel two planes is minimized when a plane shape is sandwiched between two parallel geometric planes. Is represented by
The degree of flatness is expressed as what mm or what μm.

(2) The invention according to claim 2 has a structure in which a bearing portion provided with an inner cylinder as a fixed portion and an outer cylinder as a rotating portion is sandwiched between two thrust plates. An outer cylinder and a thrust plate are gas dynamic pressure bearings formed of ceramics, wherein the flatness of an end face dynamic pressure generating portion of the thrust plate facing the outer cylinder is 3 μm or less. The gist is a dynamic pressure bearing.

In the present invention, the flatness of the end face dynamic pressure generating portion facing the outer cylinder of the thrust plate is 3 μm or less, so that when the outer cylinder rotates, the distance between the end surface of the outer cylinder and the thrust plate becomes circumferential. Direction, and the generated dynamic pressure also has less unevenness due to rotation. Therefore, the occurrence of vibration in the outer cylinder can be prevented, and the rotational operation of the dynamic pressure bearing can be stabilized. In addition, since the vibration of the outer cylinder can be prevented, it is possible to prevent the ceramic member such as the outer cylinder from contacting the surroundings and being damaged.

As described above, according to the present invention, it can be seen that if the flatness is processed to be 3 μm or less, the generation of vibrations can be suppressed. The waste of processing can be eliminated, and the effect is great in actual production of industrial products.

Further, in the present invention, an end face dynamic pressure generating portion for generating dynamic pressure is formed inside (on the side facing the outer cylinder) in the thickness direction (axial direction of the rotating shaft) of both thrust plates. However, it is desirable that the above-mentioned definition of the flatness be satisfied not only at the end face dynamic pressure generating portion of one thrust plate but also at both thrust plates.

(3) The invention according to claim 3 has a structure in which a bearing portion provided with an inner cylinder as a fixed portion and an outer cylinder as a rotating portion is sandwiched between two thrust plates. The outer cylinder and the thrust plate are gas dynamic pressure bearings formed of ceramics, and the flatness of the end face dynamic pressure generating portion of the outer cylinder facing the thrust plate, and the end face dynamic pressure generating portion of the outer cylinder. The sum of the flatness of the end face dynamic pressure generating portion of the thrust plate facing
The gist of the present invention is a dynamic pressure bearing made of ceramics, which is not more than m.

The present invention shows the relationship between the flatness of each of the end face dynamic pressure generating portions facing each other in the outer cylinder and the thrust plate, and the total flatness of the both end face dynamic pressure generating portions is 3 μm or less. In this case, as in the first and second aspects of the invention, vibration of the outer cylinder can be prevented and ceramics can be prevented from being damaged.

As described above, according to the present invention, it can be understood that if the processing is performed so that the total of the flatness is 3 μm or less, the generation of vibration can be suppressed. , Can eliminate waste due to excessive processing, in the production of actual industrial products,
The effect is great.

(4) The invention according to claim 4 has a structure in which a bearing portion provided with an inner cylinder as a fixed portion and an outer cylinder as a rotating portion is sandwiched between two thrust plates. The outer cylinder and the thrust plate are gas dynamic pressure bearings formed of ceramics, and the inner peripheral portion of the outer cylinder is 0 μm with respect to the outermost peripheral portion at an end face dynamic pressure generating portion facing the thrust plate of the outer cylinder. And a convex in a range of 2.5 μm or less.

In the present invention, in the end face dynamic pressure generating portion facing the thrust plate of the outer cylinder, the inner peripheral portion is 0 μm with respect to the outermost peripheral portion.
m and is convex in the range of 2.5 μm or less,
When starting or stopping, it is possible to prevent the occurrence of linking and seizure, thereby preventing the ceramic from being damaged.

That is, according to the present invention, at the outermost peripheral portion of the outer cylinder, the distance between the outer cylinder and the thrust plate is apart from the inner peripheral portion within the above-described predetermined range. Even when the outer cylinder is seated on the lower thrust plate, the outermost peripheral portion is unlikely to contact the thrust plate. Therefore, at startup,
Rotation starts smoothly without causing linking and seizure, and at the time of stopping, the outermost peripheral portion is in close contact with the thrust plate, and there is no sudden stop due to linking and seizure.

If the range of the protrusion exceeds 2.5 μm, the generation of dynamic pressure is not stable and the vibration increases, which is not preferable (the same applies hereinafter). In the present invention, the end face dynamic pressure generating portions for generating dynamic pressure are formed on both sides (upper and lower sides) in the thickness direction of the outer cylinder (axial direction of the rotating shaft). Is desirably satisfied not only at the end face dynamic pressure generating portion on one side (particularly below) but also on both sides.

(5) The invention according to claim 5 has a structure in which a bearing portion having an inner cylinder as a fixed portion and an outer cylinder as a rotating portion is sandwiched between two thrust plates. The outer cylinder and the thrust plate are gas dynamic pressure bearings formed of ceramics, and at the end face dynamic pressure generating portion of the thrust plate facing the outer cylinder, the inner peripheral portion is 0 μm with respect to the outermost peripheral portion. And a convex in a range of 2.5 μm or less.

In the present invention, at the end face dynamic pressure generating portion facing the outer cylinder of the thrust plate, the inner peripheral portion is 0 μm with respect to the outermost peripheral portion.
m and is convex in the range of 2.5 μm or less,
As in the case of the fourth aspect, it is possible to prevent the occurrence of linking and seizure at the time of starting or stopping, thereby preventing the ceramic from being damaged.

In the present invention, an end face dynamic pressure generating portion for generating a dynamic pressure is formed inside (on the side facing the outer cylinder) in the thickness direction (axial direction of the rotating shaft) of both thrust plates. However, it is preferable that the above-mentioned definition of the convex dimension is satisfied not only at the end face dynamic pressure generating portion of one (particularly lower) thrust plate but also at both thrust plates.

(6) The invention according to claim 6 has a structure in which a bearing portion having an inner cylinder as a fixed portion and an outer cylinder as a rotating portion is sandwiched by two thrust plates. The outer cylinder and the thrust plate are gas dynamic pressure bearings formed of ceramics, and in the outer cylinder and the thrust plate, a distance between outermost peripheral portions of end face dynamic pressure generating portions facing each other exceeds 0 μm. In addition, the gist of the present invention is a dynamic pressure bearing made of ceramics, characterized in that the diameter is not more than 2.5 μm.

According to the present invention, the distance between the outermost peripheral portions of the end face dynamic pressure generating portions facing each other in the outer cylinder and the thrust plate is specified.
When the thickness is not more than μm, the effects of suppressing linking and seizure at the time of starting and stopping and suppressing breakage of ceramics can be obtained in the same manner as the inventions of the fourth and fifth aspects.

(7) The invention according to claim 7 is the ceramic dynamic pressure bearing according to claim 1, wherein an end face dynamic pressure generating portion of the outer cylinder facing the thrust plate has an inner periphery. The gist of the present invention is a dynamic pressure bearing made of ceramics, characterized in that the portion is more than 0 μm and convex in the range of 2.5 μm or less with respect to the outermost peripheral portion.

The present invention is obtained by adding the configuration of the fourth aspect to the configuration of the first aspect. Therefore, the effect of the invention of claim 1 and the effect of the invention of claim 4 are obtained, and the synergistic action of the dynamic pressure bearing on the rotation further enhances the effect of preventing ceramic breakage.

(8) The invention of claim 8 is the ceramic dynamic pressure bearing according to claim 1, wherein an end face dynamic pressure generating portion of the thrust plate facing the outer cylinder has an inner periphery thereof. The gist of the present invention is a dynamic pressure bearing made of ceramics, characterized in that the portion is more than 0 μm and convex in the range of 2.5 μm or less with respect to the outermost peripheral portion.

The present invention is obtained by adding the configuration of claim 5 to the configuration of claim 1. Therefore, not only the effects of the invention of claim 1 and the effect of the invention of claim 5 are exhibited, but also the synergistic action on the rotation of the dynamic pressure bearing further enhances the effect of preventing the ceramic from being damaged.

(9) The ninth aspect of the present invention is the ceramic dynamic pressure bearing according to the first aspect, wherein the outer cylinder and the thrust plate have outermost peripheral surfaces of end face dynamic pressure generating portions facing each other. The gist of the present invention is a ceramic dynamic pressure bearing, wherein the interval between the parts is more than 0 μm and not more than 2.5 μm.

The present invention is obtained by adding the configuration of claim 6 to the configuration of claim 1. Therefore, the effect of the invention of claim 1 and the effect of the invention of claim 6 described above are exhibited, and the synergistic action on the rotation of the dynamic pressure bearing further enhances the effect of preventing the ceramic from being damaged.

(10) The tenth aspect of the present invention is the ceramic dynamic pressure bearing according to the second aspect, wherein an inner peripheral surface of the end face dynamic pressure generating portion of the outer cylinder facing the thrust plate is provided. Part exceeds 0 μm and 2.5 μm with respect to the outermost peripheral part
A gist is a ceramic dynamic pressure bearing characterized by being convex in the following range.

The present invention is obtained by adding the configuration of the fourth aspect to the configuration of the second aspect. Therefore, the effect of the invention of claim 2 and the effect of the invention of claim 4 described above are exhibited, and the effect of preventing breakage of the ceramics is further enhanced by the synergistic action on the rotation of the dynamic pressure bearing.

(11) The invention of claim 11 is the ceramic dynamic pressure bearing according to claim 2, wherein the end surface dynamic pressure generating portion of the thrust plate facing the outer cylinder has an inner periphery thereof. Part exceeds 0 μm and 2.5 μm with respect to the outermost peripheral part
A gist is a ceramic dynamic pressure bearing characterized by being convex in the following range.

The present invention is obtained by adding the configuration of the fifth aspect to the configuration of the second aspect. Therefore, the effect of the invention of claim 2 and the effect of the invention of claim 5 are exhibited, and the synergistic action on the rotation of the dynamic pressure bearing further enhances the effect of preventing breakage of ceramics.

(12) The twelfth aspect of the present invention is the ceramic dynamic pressure bearing according to the second aspect, wherein the outer cylinder and the thrust plate have outermost peripheries of end face dynamic pressure generating portions facing each other. The interval between the parts is more than 0 μm and 2.5 μm
The gist of the present invention is a ceramic dynamic pressure bearing characterized by a range of not more than m.

The present invention is obtained by adding the configuration of claim 6 to the configuration of claim 2. Therefore, the effect of the invention of claim 2 and the effect of the invention of claim 6 described above are exhibited, and the synergistic action on the rotation of the dynamic pressure bearing further enhances the effect of preventing breakage of ceramics.

According to a thirteenth aspect of the present invention, there is provided the ceramic dynamic pressure bearing according to the third aspect, wherein an inner peripheral surface of the outer cylinder has a dynamic pressure generating portion facing the thrust plate. Part exceeds 0 μm and 2.5 μm with respect to the outermost peripheral part
A gist is a ceramic dynamic pressure bearing characterized by being convex in the following range.

The present invention is obtained by adding the configuration of the fourth aspect to the configuration of the third aspect. Therefore, the effect of the invention of claim 3 and the effect of the invention of claim 4 described above are exhibited, and the synergistic action on the rotation of the dynamic pressure bearing further enhances the effect of preventing breakage of the ceramics.

(14) The invention according to claim 14 is the ceramic dynamic pressure bearing according to claim 3, wherein the thrust plate has an end face dynamic pressure generating portion which faces the outer cylinder and has an inner periphery. Part exceeds 0 μm and 2.5 μm with respect to the outermost peripheral part
A gist is a ceramic dynamic pressure bearing characterized by being convex in the following range.

The present invention is obtained by adding the configuration of the fifth aspect to the configuration of the third aspect. Therefore, the effect of the invention of claim 3 and the effect of the invention of claim 5 are exhibited, and the synergistic action on the rotation of the dynamic pressure bearing further enhances the effect of preventing breakage of the ceramics.

(15) The invention of claim 15 is the ceramic dynamic pressure bearing according to claim 3, wherein the outermost periphery of the end face dynamic pressure generating portion facing each other in the outer cylinder and the thrust plate. The interval between the parts is more than 0 μm and 2.5 μm
The gist of the present invention is a ceramic dynamic pressure bearing characterized by a range of not more than m.

The present invention is obtained by adding the configuration of claim 6 to the configuration of claim 3. Therefore, the effect of the invention of claim 3 and the effect of the invention of claim 6 are exhibited, and the synergistic action of the dynamic pressure bearing on the rotation further enhances the effect of preventing ceramic breakage.

[0046]

Next, an embodiment of the ceramic dynamic pressure bearing of the present invention will be described. (Example 1) a) As shown in FIG. 1, a ceramic dynamic pressure bearing of this example is used for a motor unit 1 for rotating a polygon mirror, for example, and uses air as a medium. A dynamic pressure bearing (gas dynamic pressure bearing) 3.

In this motor unit 1, a permanent magnet 9 is arranged on the lower surface of an annular portion 7 attached to the outer periphery of the outer cylinder 5 in order to rotate the outer cylinder 5.
An electromagnet 13 is arranged on a base 11 facing the above. b) Next, the dynamic pressure bearing 3 which is a main part of this embodiment will be described.

As shown in FIG. 2, the dynamic pressure bearing 3 of this embodiment
Is a cylindrical inner cylinder (inner diameter 15 mm, outer diameter 2
An outer cylinder (inner diameter 5 mm, inner diameter 5 mm, axial length 8 mm) 15
Outer diameter 15 mm, axial length 8 mm) 7 and this inner cylinder 15
A pair of thrust plates (inner diameter 5 mm, outer diameter 2 mm) sandwiching the radial bearing portion 19 composed of
5 mm, thickness 2 mm) 21 and 23. The inner cylinder 15, the outer cylinder 7, and the thrust plates 21 and
3 is made of alumina ceramic.

The dynamic pressure bearing 3 has an inner cylinder 15 sandwiched between thrust plates 21 and 23 and pressed and fixed by screws 25 (see FIG. 1), and an outer cylinder sandwiched between the thrust plates 21 and 23. Only 7 rotates. The outer cylinder 7 is arranged eccentrically with respect to the inner cylinder 15, and the center axis of the outer cylinder 7 is slightly shifted from the center axis of the inner cylinder 15 by, for example, 5 μm. Therefore, according to the principle of the dynamic pressure bearing 3, the outer cylinder 7 is not in contact with the inner cylinder 15, and the outer cylinder 7 is not in contact with the thrust plates 21, 23.
It rotates at high speed without contact. During rotation of the dynamic pressure bearing 3, the distance between the inner cylinder 15 and the outer cylinder 7 is 0.0
A gap of 05 mm is formed, and the outer cylinder 7 and the strass plate 1
1 and a gap of 0.006 mm is formed between the upper and lower sides.

In particular, in this embodiment, the flatness of both end faces (end face dynamic pressure generating parts) 7a and 7b in the vertical direction of the outer cylinder 7 is 3 μm.
It is set in the following range (for example, 15 μm). The flatness of the lower end face (end face dynamic pressure generating section) 21a of the upper thrust plate 21 and the upper end face (end face dynamic pressure generating section) 23b of the lower thrust plate 23 are also within a range of 3 μm or less (for example, 1 μm). .0 μm).

Further, in this embodiment, as shown in FIG. 3, the outer cylinder 7 has upper and lower end face dynamic pressure generating portions 7a, 7a.
b, the inner peripheral portion 7d on the side facing the through-hole is more than 0 μm and 2.5 μm more than the outermost peripheral portion 7c.
It is higher in the following range (for example, 1.0 μm). That is, at each end surface, the inner peripheral portion 7d is smoothly convex (crowned) so that the inner peripheral portion 7d is thicker than the outermost peripheral portion 7c by the height difference ΔH (therefore, 2 ° on both sides).
H is thicker). On the other hand, both thrust plates 21 and
Reference numeral 3 denotes a flat plate, and there is no difference in height between the inner peripheral portion and the outermost peripheral portion.

In order to smoothly rotate the outer cylinder 7 in a non-contact manner with the inner cylinder 15 on at least one rotation surface (for example, only the inner cylinder 15 side) of the outer cylinder 7 and the inner cylinder 15, Are formed (not shown). The rotation of the outer cylinder 7 is smoothly applied to at least one end face (for example, only the thrust plates 21 and 23 side) of the facing end faces of the outer cylinder 7 and the thrust plates 21 and 23 so as not to contact the thrust plates 21 and 23. For this purpose, a well-known dynamic pressure groove (not shown) is formed.

C) The dynamic pressure bearing 3 described above can be manufactured by the following method. A ceramic powder made of alumina is press-molded corresponding to each ceramic member, that is, the inner cylinder 15, the outer cylinder 7, and the thrust plates 21 and 23, and a green compact as each ceramic member is sintered. The sintered product is polished and finished to predetermined dimensions. In particular,
The outer cylinder 7 is polished so as to form a height difference ΔH between the end face dynamic pressure generating portions 7a and 7b.

Thereafter, a dynamic pressure groove is formed on the rotating surface. This dynamic pressure groove is formed by, for example, sandblasting or etching. Then, the obtained dynamic pressure bearing 3 is incorporated into the motor unit 1. As described above, in the present embodiment, the dynamic pressure generating portions 7a and 7b on both end surfaces of the outer cylinder 7 and the thrust plates 21 and 23 are provided.
Since the flatness of the end face dynamic pressure generating portions 21a and 23b is 3 μm or less, an appropriate clearance can be secured on the rotating surface where the dynamic pressure is generated when rotating. Therefore, vibration during rotation is small, and the outer cylinder 7 and the thrust plate 2
The ceramic members such as 1, 23 are hardly damaged.

Further, the dynamic pressure generating portions 7a, 7
b, the difference in height between the outermost peripheral portion 7c and the inner peripheral portion 7d △
Since H is in the range of more than 0 μm and more than 2.5 μm, it is possible to suppress the occurrence of linking and image sticking at the time of starting and stopping. Therefore, the ceramic members such as the outer cylinder 7 and the thrust plates 21 and 23 are hardly damaged.

In terms of the relationship between the flatness and the height difference ΔH between the inner peripheral portion and the outermost peripheral portion, the undulation (for example, 0.5 μm) is generated at the outermost peripheral portion of the end face dynamic pressure generating portion. In this case, the sum of the undulation at the outermost periphery and the height difference ΔH corresponds to the actual flatness.

Next, another embodiment other than the first embodiment will be described. In the ceramic dynamic pressure bearing of another embodiment, in addition to the dimensions and configuration of the ceramic members of the outer cylinder and the thrust plate shown in the first embodiment, the following ceramic members having the following dimensions and configuration can be adopted.

A) As shown in FIG. 4 (a), the dynamic pressure generating portions at both end surfaces of the outer cylinder and the dynamic pressure generating portions at the end surfaces of the respective thrust plates are parallel to each other, and at least one of the dynamic pressure generating surfaces of the outer cylinder is generated. Only those having a flatness of 3 μm or less. In the figure, 3 μm
Place the following flatness (here the dynamic pressure generating parts on both ends)
This is schematically shown by oblique lines (the same applies hereinafter).

B) As shown in FIG. 4 (b), the dynamic pressure generating portions at both end surfaces of the outer cylinder and the dynamic pressure generating portions at the end surfaces of the respective thrust plates are parallel to each other, and the dynamic pressure generating portion of at least one of the thrust plates is formed. Only the flatness of the generating part is in the range of 3 μm or less. c) As shown in FIG. 4 (c), the dynamic pressure generating portions on both end surfaces of the outer cylinder and the end surface dynamic pressure generating portions of each thrust plate are parallel, and the plane of at least one end surface dynamic pressure generating portion of the outer cylinder is Degree, and the flatness of at least one end face dynamic pressure generating portion of each thrust plate,
Those having a size of 3 μm or less.

D) As shown in FIG. 4 (d), the flatness of the end face dynamic pressure generating portion is not specified, but the inner peripheral portion of the outer cylinder is at least one of the end face dynamic pressure generating portions. Those that are more than 0 μm and 2.5 μm or less from the outer periphery. It should be noted that the figures show that there is a difference in height between the dynamic pressure portions on both end faces (the same applies hereinafter).

E) As shown in FIG. 4 (e), the flatness at the end face dynamic pressure generating portion is not specified, but at least one end face dynamic pressure generating portion of both thrust plates has an inner peripheral portion. Those that are more than 0 μm and 2.5 μm or less from the outermost periphery. f) As shown in FIG. 4 (f), the flatness of the end face dynamic pressure generating portion is not specified, and it is not specified how much of the outer cylinder or the thrust plate is convex. The distance ΔS between the outermost peripheral portion of at least one end face dynamic pressure generating portion of the cylinder and the outermost peripheral portion of the end face dynamic pressure generating portion of the thrust plate opposed thereto exceeds 0 μm when rotation of the dynamic pressure bearing is stopped. In addition, those having a range of 2.5 μm or less. Note that ΔS is the clearance between the two members on the outer peripheral side when the outer cylinder and the thrust plate are in contact with each other.

Further, in addition to the above-mentioned embodiments a) to f), a combination of each of them can be considered. For example, as shown in FIG. 4, (ad), (ae), (af), (b-
d), (be), (bf), (cd), (c-
e) and (cf).
Incidentally, of these, (cd) corresponds to the first embodiment described above, but is redundantly described for organization.

(Experimental Example) Next, an experimental example performed to confirm the effect of the above-described embodiment will be described. In the motor unit having the structure of the above-described embodiment, various dynamic pressure bearing samples were manufactured by changing the conditions of the flatness and the height difference ΔH as described below.

The dynamic pressure bearing was rotated at a rotation speed of 20000 rpm with respect to the sample of the dynamic pressure bearing. Then, the following measurement items (1) and (2) were examined. (1) Flatness experiment ・ Confirmation of vibration (measurement during rotation) However, non-contact type laser displacement meter (500
(00 times / second sampling possible).

In the following tables, the results are shown as ◎: minimum vibration, ；: small vibration, ×: unusable. (2) Difference in height (end surface height) △ H (interval of outermost periphery △ S)
Experiments on * Confirmation of the presence or absence of burn-in (confirmation of whether or not burn-in has occurred at the time of start-up and stop) In the following tables, the results are shown as ○; no burn-in, ×;
Image sticking occurred.

[0066]

[Table 1]

However, the flatness of the outer cylinder is the flatness of the dynamic pressure generating portions on both ends of the outer cylinder. The flatness of the dynamic pressure generating portions on both end surfaces of both thrust plates is 0.1 μm.
m or less As is evident from Table 1, when the flatness of the end face dynamic pressure generating portion of the outer cylinder is 3 μm or less, it is preferable that the vibration is small.

[0068]

[Table 2]

However, the flatness of the thrust plate is the flatness of the dynamic pressure generating portions at the end faces of both thrust plates. The flatness of the dynamic pressure generating portions at both end faces of the outer cylinder is 0.1 μm or less. It is preferable that the flatness of the end face dynamic pressure generating portion of the thrust plate is 3 μm or less, since the vibration is small.

[0070]

[Table 3]

As is clear from Table 3, the sum of the flatnesses of the facing outer cylinder and the end face dynamic pressure generating portion of the thrust plate is 3 μm.
The following cases are preferable because they have less vibration.

[0072]

[Table 4]

Here, the outer cylinder end face height is the difference ΔH between the height of the inner peripheral part and the outermost peripheral part in the end face dynamic pressure generating portion of the outer cylinder. + Indicates that the inner peripheral portion is higher and convex. In addition, the undulation of the outermost peripheral portion of the end surface dynamic pressure generating portion of the outer cylinder is 0.5 μm or less,
The flatness of the end face dynamic pressure generating portion of the thrust plate is set to 0.1 μm or less.

As is clear from Table 4, when the height of the outer cylinder end face exceeds 0 μm and is 2.5 μm or less, it is preferable that there is no image sticking and there is little vibration.

[0075]

[Table 5]

However, the end face height of the thrust plate is the difference ΔH between the height of the inner peripheral portion and the outermost peripheral portion at the end face dynamic pressure generating portion of the thrust plate, and-indicates that the inner peripheral portion is lower and concave. + Indicates that the inner peripheral portion is higher and convex.
The undulation at the outermost peripheral portion of the end face dynamic pressure generating portion of the outer cylinder is 0.
5 μm or less, the flatness of the end face dynamic pressure generating portion of the thrust plate is:
0.1 μm or less.

As is apparent from Table 5, when the height of the end face of the thrust plate is more than 0 μm and not more than 2.5 μm, it is preferable because there is no image sticking and the vibration is small.

[0078]

[Table 6]

However, ± of the outer cylinder end face height and the thrust plate end face height are the same as the definitions shown in Tables 4 and 5. In addition, the undulation of the outermost peripheral portion of the end surface dynamic pressure generating portion of the outer cylinder and the thrust plate is set to 0.5 μm or less.

As is clear from Table 6, when the distance between the outermost peripheral portions of the outer cylinder and the end face dynamic pressure generating portion of the thrust plate exceeds 0 μm and is 2.5 μm or less, it is preferable because there is no image sticking. . It should be noted that the present invention is not limited to the above-described embodiment at all, and it goes without saying that the present invention can be implemented in various modes without departing from the gist of the present invention.

For example, in the first embodiment, the inner cylinder, the outer cylinder, and the thrust plate were manufactured by using alumina as a material. In addition, zirconia, a mixed material of alumina and zirconia, silicon nitride, and the like were used. Is also good.

[0082]

As described in detail above, claims 1 to 5 of the present invention.
In the ceramic dynamic pressure bearing of No. 3, since the flatness of the end face dynamic pressure generating portions of the outer cylinder and the thrust plate is 3 μm or less, respectively, the vibration is less likely to occur in the outer cylinder. This can prevent the ceramic members such as the outer cylinder and the thrust plate from being damaged.

Further, in the ceramic dynamic pressure bearing according to claims 4 to 6, in the dynamic pressure generating portion of the end surface of the outer cylinder or the thrust plate, the inner peripheral portion exceeds the outermost peripheral portion by more than 0 μm and 2.5 μm.
m, or the distance between the outermost peripheral portions exceeds 0 μm and is 2.5 μm or less, so that linking and seizure hardly occur at the time of starting or stopping. This can prevent the ceramic members such as the outer cylinder and the thrust plate from being damaged.

[Brief description of the drawings]

FIG. 1 is a partially cutaway front view of a motor unit using a dynamic pressure bearing of an embodiment.

2A and 2B show a dynamic pressure bearing according to an embodiment, in which FIG. 2A is a plan view showing the dynamic pressure bearing, and FIG. 2B is an exploded perspective view showing the dynamic pressure bearing.

FIG. 3 is an explanatory diagram showing the features of the outer cylinder of the embodiment in an emphasized manner.

FIG. 4 is an explanatory view showing another embodiment.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... Motor unit 7 ... Outer cylinder 15 ... Inner cylinder 21, 23 ... Thrust plate 7a, 7b, 21a, 23b ... End face dynamic pressure generation part

Claims (15)

[Claims] 1. A bearing having an inner cylinder as a fixed part and an outer cylinder as a rotating part has a structure in which two thrust plates are sandwiched, and the inner cylinder, the outer cylinder and the thrust plate are made of ceramics. A dynamic pressure bearing made of ceramics, characterized in that a flatness of an end face dynamic pressure generating portion of the outer cylinder facing the thrust plate is 3 μm or less. 2. A structure in which a bearing portion including an inner cylinder as a fixed portion and an outer cylinder as a rotating portion is sandwiched between two thrust plates, wherein the inner cylinder, the outer cylinder and the thrust plate are made of ceramics. Wherein the flatness of an end face dynamic pressure generating portion of the thrust plate facing the outer cylinder is 3 μm or less. 3. A bearing having an inner cylinder as a fixed part and an outer cylinder as a rotating part has a structure in which two thrust plates are sandwiched, and the inner cylinder, the outer cylinder and the thrust plate are made of ceramics. Wherein the flatness of the end face dynamic pressure generating portion of the outer cylinder facing the thrust plate and the end face dynamics of the thrust plate facing the end face dynamic pressure generating portion of the outer cylinder. A dynamic pressure bearing made of ceramics, wherein the sum of the flatness of the pressure generating portion and the flatness is 3 μm or less. 4. A structure in which a bearing portion including an inner cylinder as a fixed portion and an outer cylinder as a rotating portion is sandwiched between two thrust plates, wherein the inner cylinder, the outer cylinder and the thrust plate are made of ceramics. In the gas dynamic pressure bearing formed from the above, at the end face dynamic pressure generating portion facing the thrust plate of the outer cylinder, the inner peripheral portion exceeds 0 μm with respect to the outermost peripheral portion and is 2.5 μm or less. A ceramic dynamic pressure bearing characterized by being convex in a range. 5. A structure in which a bearing portion including an inner cylinder as a fixed portion and an outer cylinder as a rotating portion is sandwiched between two thrust plates, wherein the inner cylinder, the outer cylinder and the thrust plate are made of ceramics. A gas dynamic pressure bearing formed from: wherein at an end face dynamic pressure generating portion of the thrust plate facing the outer cylinder, an inner peripheral portion thereof is larger than 0 μm with respect to an outermost peripheral portion and is 2.5 μm or less. A ceramic dynamic pressure bearing characterized by being convex in a range. 6. A structure in which a bearing portion including an inner cylinder as a fixed portion and an outer cylinder as a rotating portion is sandwiched between two thrust plates, wherein the inner cylinder, the outer cylinder and the thrust plate are made of ceramics. A distance between outermost peripheral portions of end face dynamic pressure generating portions facing each other in the outer cylinder and the thrust plate is more than 0 μm and not more than 2.5 μm. A dynamic pressure bearing made of ceramics. 7. The dynamic pressure bearing made of ceramics according to claim 1, wherein an inner peripheral portion of the outer peripheral portion of the outer cylindrical portion with respect to an outermost peripheral portion is formed at an end face dynamic pressure generating portion facing the thrust plate. A ceramic dynamic pressure bearing characterized by being convex in a range of more than 0 μm and not more than 2.5 μm. 8. The dynamic pressure bearing made of ceramic according to claim 1, wherein an inner peripheral portion of the thrust plate has an inner peripheral portion with respect to an outermost peripheral portion at an end face dynamic pressure generating portion facing the outer cylinder. A ceramic dynamic pressure bearing characterized by being convex in a range of more than 0 μm and not more than 2.5 μm. 9. The ceramic dynamic pressure bearing according to claim 1, wherein, in the outer cylinder and the thrust plate, a distance between outermost peripheral portions of end face dynamic pressure generating portions facing each other is 0 μm. A dynamic pressure bearing made of ceramics, which is larger than 2.5 μm. 10. The dynamic pressure bearing made of ceramic according to claim 2, wherein an inner peripheral portion of the outer cylinder is located at an outer peripheral portion with respect to an outermost peripheral portion at an end face dynamic pressure generating portion facing the thrust plate of the outer cylinder. A ceramic dynamic pressure bearing characterized by being convex in a range of more than 0 μm and not more than 2.5 μm. 11. The ceramic dynamic pressure bearing according to claim 2, wherein an inner peripheral portion of the thrust plate at an end face dynamic pressure generating portion facing the outer cylinder has an inner peripheral portion with respect to an outermost peripheral portion. A ceramic dynamic pressure bearing characterized by being convex in a range of more than 0 μm and not more than 2.5 μm. 12. The ceramic dynamic pressure bearing according to claim 2, wherein, in the outer cylinder and the thrust plate, an interval between outermost peripheral portions of end face dynamic pressure generating portions facing each other is 0 μm. A dynamic pressure bearing made of ceramics, which is larger than 2.5 μm. 13. The dynamic pressure bearing made of ceramics according to claim 3, wherein an inner peripheral portion of the outer peripheral portion of the outer cylinder is located at an outer peripheral portion with respect to an outermost peripheral portion at an end face dynamic pressure generating portion facing the thrust plate. 0
A ceramic dynamic pressure bearing characterized by being convex in the range of more than μm and not more than 2.5 μm. 14. The dynamic pressure bearing made of ceramic according to claim 3, wherein an inner peripheral portion of the thrust plate has an inner peripheral portion with respect to an outermost peripheral portion at an end face dynamic pressure generating portion facing the outer cylinder. A ceramic dynamic pressure bearing characterized by being convex in a range of more than 0 μm and not more than 2.5 μm. 15. The ceramic dynamic pressure bearing according to claim 3, wherein, in the outer cylinder and the thrust plate, a distance between outermost peripheral portions of end face dynamic pressure generating portions facing each other is 0 μm. A dynamic pressure bearing made of ceramics, which is larger than 2.5 μm.