JP2001027224A - Dynamic pressure gas bearing - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a dynamic pressure type gas bearing excellent in whirl suppressing effect and manufactured with high accuracy at a low cost. SOLUTION: A bearing member 4 is disposed at the outer periphery of a shaft member 2 through a bearing clearance 3 to constitute a dynamic pressure type gas bearing 1 generating dynamic pressure of gas in the bearing clearance 3 during the relative rotation of the shaft member 2 and to support either one of the members in a contactless state to the other member. In this bearing, a wavy surface 5 formed of harmonic waveform is provided at the opposed face of the bearing member 4 to the bearing clearance, and the bearing member 4 is formed of sintered metal. Sealing treatment is applied to the wavy surface 5 to prevent the escape of pressure to pores.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a hydrodynamic gas bearing for supporting a shaft member or a bearing member in a non-contact manner by a dynamic pressure of gas generated in a bearing gap between the shaft member and the bearing member. Polygon mirror motors for beam printers, spindle motors for magnetic disk drives, etc.
It is suitable for supporting spindles of information equipment requiring high rotational accuracy.

[0002]

2. Description of the Related Art The most basic circular bearing as a dynamic pressure gas bearing has an advantage that machining is easy.
When the number of rotations exceeds a certain value, a self-excited whirling vibration called "whirl" occurs, which causes a problem that the rotation accuracy is significantly deteriorated. In particular, under the condition that the eccentric force due to the weight of the rotating body (shaft or bearing sleeve) does not act, such as a polygon mirror motor that often uses a bearing system arranged vertically, an unstable whirl from a low rotation range. The phenomenon occurs. Therefore, it is difficult to apply a perfect circular bearing to a polygon mirror motor or the like.

On the other hand, in order to prevent the above whirling,
A herringbone-type dynamic pressure groove is formed on the inner peripheral surface of the bearing sleeve and the outer peripheral surface of the shaft (hereinafter, referred to as a "bearing with a herringbone groove"). 2. Description of the Related Art A hydrodynamic gas bearing that generates a dynamic pressure by being retracted is conventionally known. With this herringbone grooved bearing, whirling does not occur even when there is no eccentricity of the rotating body, and it can be operated stably up to the high rotation region, but about 10 to 20 herringbone grooves are etched. ,
It is necessary to form the sheet with a depth of the order of several μm by rolling or the like, which causes a problem that the manufacturing cost is high.

[0004]

In view of the above problems,
For example, as disclosed in Japanese Patent Application Laid-Open No. 7-145812, there has been proposed a dynamic pressure gas bearing in which irregularities formed of a plurality of cycles of harmonic waveforms are formed in the circumferential direction on the outer periphery of a shaft member or the inner periphery of a cylindrical member. . This type of bearing can prevent whirl by utilizing the compressibility of the hydrodynamic gas lubricating film.Since its structure is simpler than that of a bearing with a herringbone groove, it can reduce manufacturing costs. Have been. In addition, as the manufacturing method, the above publication discloses a method of pressing a pressing member having a convex curved surface against a shaft member or a cylindrical member, a method by extrusion molding, and a method by injection molding of a resin material.

[0005] However, this type of bearing has the characteristic that the Whirl stability is very sensitive to the magnitude of the amplitude of the harmonic waveform. Therefore, in order to achieve design performance, high workability is required, which is not necessarily directly linked to reduction in manufacturing cost.

Accordingly, an object of the present invention is to provide a dynamic pressure type gas bearing which is excellent in the effect of suppressing whirl and can be manufactured at low cost and with high accuracy.

[0007]

In order to achieve the above object, according to the present invention, a bearing member is arranged on the outer periphery of a shaft member via a bearing gap, and the above-mentioned structure is realized by relative rotation between the shaft member and the bearing member. In a bearing that generates a gas dynamic pressure in a bearing gap to support one of the members in a non-contact manner with respect to the other member, the shaft gap or the bearing member may be provided with any one of the members and the bearing gap. A wave-like surface having a harmonic waveform was provided on the facing surface, and the member having the wave-like surface was made of sintered metal. When a wave-like surface having a harmonic waveform is formed on the surface of one member facing the bearing gap, a hydrodynamic gas film of gas is formed in the bearing gap, and one member is supported non-contact with the other member. Is done. The generation of whirl is also prevented by the compressive effect of the hydrodynamic gas film. In particular, by forming a member having a wavy surface with a sintered metal, a high-precision wavy surface can be easily formed by putting the sintered metal into a mold having a shape corresponding to a harmonic waveform and pressing it. Costs can be reduced.

[0008] When the corrugated surface is provided on the bearing member, a relative motion can be imparted between the metal powder and the core rod when the metal powder is compressed, whereby coarse atmospheric holes on the corrugated surface can be eliminated. Therefore, escape of pressure to the coarse pores is prevented, and the stability of whirl is enhanced.

By performing the sealing treatment on the corrugated surface, the escape of the pressure to the pores can be prevented, and the whirl stability can be further improved.

[0010]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to FIGS.

As shown in FIG. 1, a dynamic pressure type gas bearing 1 according to the present invention has a small journal bearing gap 3 (the width of which is A substantially cylindrical bearing sleeve (bearing member) 4 is arranged via an exaggerated). As shown in FIG. 2, a wavy surface 5 having a harmonic waveform is formed on a surface of one of the shaft member 2 and the bearing member 4 facing the bearing gap 3, for example, on the inner peripheral surface of the bearing member 4. On the other hand, the surface of the other member facing the bearing gap 3, for example, the outer peripheral surface of the shaft member 2 is formed in a perfect circular cross section. The corrugated surface 5 may be formed on the entire inner peripheral surface of the bearing member 4 or may be provided at a plurality of locations separated in the axial direction.

Here, the width h of the bearing gap 3 is approximately expressed by the following equation when there is no eccentricity.

H = c + aw · COS (Nwθ) where c, aw and Nw are constants, c is the average bearing radius gap, aw is the wave amplitude, θ is the phase in the circumferential direction,
Nw represents a wave number (however, Nw ≧ 2; Nw = 3 in the present embodiment).

As described above, by providing the wavy surface 5 having a harmonic waveform on one of the two opposing surfaces (in the present embodiment, the inner peripheral surface of the bearing member 4) sandwiching the bearing gap 3 therebetween. When the two members 2 and 4 rotate relative to each other, a dynamic pressure gas film that supports a radial load is formed in the bearing gap 3, whereby one member is supported non-contact with the other member. Which of the shaft member 2 and the bearing member 4 is the rotation side can be arbitrarily selected. In addition to the shaft member 2 being the rotation side, the bearing member 4 being the fixed side, the shaft member 2 is being the fixed side, the bearing member 4 may be the rotation side.

Among the shaft member 2 and the bearing member 4, the member having the above-mentioned corrugated surface 5, for example, in the present embodiment, the bearing member 4 is formed of a porous sintered metal. The sintered metal is obtained by, for example, compression-molding a metal powder mainly containing copper or iron, or both, and preferably using 20 to 95% of copper, followed by firing. The bearing member 4 can be manufactured by subjecting the sintered metal material 6 (see FIG. 3) after firing to, for example, a sizing → rotational sizing → wave-shaped surface forming step.

The sizing step is a step of sizing the outer peripheral surface and the inner peripheral surface of the sintered metal material 6, and press-fitting the outer peripheral surface of the cylindrical sintered metal material 6 into a die having a cylindrical inner peripheral surface. At the same time, a sizing pin is pressed into the inner peripheral surface of the sintered metal material 6. The rotation sizing step is a step of pressing a polygonal sizing pin into the inner peripheral surface of the cylindrical sintered metal material 6 and rotating the same to rotate the inner peripheral surface to size the inner peripheral surface. By rotating sizing, the porosity of the inner peripheral surface of the sintered metal material 6 can be adjusted to 10% or less (preferably 5% or less).

The corrugated surface forming step is performed by pressing a mold having a shape corresponding to the corrugated surface 5 of the finished product on the inner peripheral surface of the sintered metal material 6 subjected to the two types of sizing. Is a step of compression molding. This step is performed by, for example, a molding apparatus having a core rod 11, a die 12, and a pair of punches 13a and 13b, as shown in FIG. That is, as shown in FIG. 4, as shown in FIG. 4, a mold portion 11 a having an uneven shape corresponding to the shape of the harmonic waveform is formed on the outer peripheral surface of the core rod 11 (sizing pin), and the sintered metal material 6 is formed on the outer peripheral surface of the core rod 11. And press the sintered metal material 6 with the die 12 and the punches 13a and 13b. With the pressurization, the sintered metal material 6 is deformed by the compressive force, and the surface portion of the inner peripheral surface undergoes plastic flow and bites into the mold portion 11a on the outer peripheral surface of the core rod 11. Thereby, the sintered metal material 6
Is formed into a harmonic waveform shape corresponding to the contour of the mold portion 11a of the core rod 11 (see FIG. 5).

Thus, the bearing member 4 having the wavy surface 5
Is formed of a sintered metal, the wavy surface 5 can be formed at low cost and with high accuracy by utilizing the compression molding. As will be described later, the magnitude of the amplitude of the harmonic waveform on the wavy surface 5 has a large effect on the whirl stability, but high processing accuracy is ensured by compression molding, so that stable quality with respect to whirl characteristics is ensured. be able to.

By the way, the surface porosity of a general sintered metal is about 20%, and the area of one hole is often 0.01 to 0.02 mm in diameter in terms of the area of a perfect circle. Some of the pores exceed 0.1 mm. Since the pressure generated in the bearing gap 3 may escape into such coarse pores and the stabilizing effect of the whirl may be reduced, such coarse pores (those having a diameter exceeding 0.05 mm in terms of a perfect circle) are previously sealed. It is desirable to keep.

As a specific method of the sealing treatment, for example, at the time of compression molding of the metal powder, after filling the metal powder 30 into the forming mold 25 shown in FIG.
A method of giving a relative motion between the metal powder 9 and the metal powder 30 is conceivable. The generation of the coarse air holes is caused by friction between the metal powder 30 and the surface of the core rod 29 when the metal powder 30 is filled into the forming mold 25, whereby the flow of the metal powder 30 is hindered and a so-called bridge phenomenon in which a space is generated in the metal powder is one of the causes. It is considered as a factor. Therefore, the metal powder 30 and the core rod 2
9 with respect to the core rod 29.
It is considered that the metal powder 30 staying due to friction with the surface of the metal powder can be dropped, thereby avoiding the bridging phenomenon.

Specifically, first, a core rod 29 is inserted into the lower punch 28 as shown in FIG. The powder 30 is filled.

After the metal powder 30 is filled, the core rod 29 is raised and its upper end is inserted into the upper punch 27 as shown in FIG. The die 26 is raised by the rise of the core rod 29.
The metal powder 30 staying in the inner space of the core rod 29 due to friction with the surface of the core rod 29 falls, so that the bridging phenomenon can be prevented.

Next, as shown in FIG.
The upper punch 27 guided by
6, and the metal powder 30 is compressed to form a green compact 31. Thereafter, as shown in FIG.
And the die 26 is lowered to the lower punch 28, and the core rod 29 is further lowered to the lower punch 28 and the die 26 as shown in FIG. The green compact 6 is obtained by firing the compact 31 taken out.

In addition to the above-mentioned method, for example, before filling the metal powder 30, the core rod 29 is arranged at a position where the upper end surface thereof is flush with the upper end surface of the lower punch 28, and the die 26 Even if the inner space is filled with the metal powder 30 and then the core rod 29 is raised in the metal powder 30 of the die 26, the relative movement between the core rod 29 and the metal powder 30 can be similarly provided. . As another method, after filling the metal powder 30 into the internal space of the die 26,
By applying vibration to the core rod 29 in a state where the core rod 29 is inserted into the metal powder 30, relative movement between the core rod 29 and the metal powder 30 can also be provided.

In addition, since the coarse air holes can be eliminated even in the above-described rotational sizing step, the sealing treatment can be performed through this step.

FIG. 7 shows a dynamic pressure in which the inner peripheral surface of the bearing member 4 is a perfect circle and the outer peripheral surface of the shaft member 2 opposed thereto is a wavy surface 5 'formed with a harmonic waveform. This is an embodiment of the gas bearing 1 ', and the same effect as that of the embodiment of FIG. In this case, the corrugated surface forming step does not use the core rod 11 shown in FIGS. 3 and 4, but forms a mold portion corresponding to the waveform on the inner peripheral surface of the mold (die 12), and forms a solid portion on the mold portion. This can be performed by pressing the outer peripheral surface of the cylindrical sintered metal material 6, whereby the shaft member 2 ′ having the corrugated surface 5 ′ on the outer peripheral surface can be manufactured as shown in FIG. Other manufacturing methods are basically the same as those in FIG. 2. For example, the corrugated surface forming step is performed through the steps of compression molding, firing, sizing, and rotation sizing of metal powder. h, c, a
The same relationship as the above equation is established between the values of w and Nw. In FIG. 7, members corresponding to the members shown in FIG. 2 are denoted by the same reference numerals, and further denoted by (′).

As described above, according to the present invention, it is possible to manufacture either the inner peripheral surface of the bearing member 4 or the outer peripheral surface of the shaft member 2 with the corrugated surfaces 5, 5 '. In the case where the inner peripheral surface of 4 is a wavy surface 5 (FIG. 2),
Since the sealing process (the process of FIG. 6) by the relative motion between the core rod 29 and the metal powder 30 becomes possible, it is possible to provide a dynamic pressure type gas bearing with less pressure relief and excellent whirl stability. .

FIG. 10 shows the results of analysis performed to verify the effect of the present invention. The analysis target was a system in which the shaft member 2 to be rotationally driven was fitted to the bearing member 4 on the fixed side, and the system was arranged vertically. A bearing with a herringbone groove shown in FIG. 9 was prepared as a comparison target. In FIG. 9, ag represents the circumferential width of the groove 33, ar represents the circumferential width of the back portion (hill) 34 between the grooves 33, βg represents the groove angle, and δg represents the depth of the groove. As the bearing with a herringbone groove, a bearing member in which a herringbone groove is provided on the inner peripheral surface of the bearing member 40 (S
Two types were prepared, an MR type) and a type in which a herringbone groove was provided on the outer peripheral surface of the shaft member 20 (GMR type). Similarly,
A hydrodynamic gas bearing (hereinafter referred to as a wave bearing) according to the present invention has a wavy surface 5 on the inner peripheral surface of a bearing member 4 (WI type: see FIG. 2), and a hydrodynamic gas bearing on the outer peripheral surface of the shaft member 2. Two types having a wavy surface 5 (WII type: see FIG. 7) were prepared.

In this analysis, the bearing width b and the bearing diameter r of the wave bearing and the bearing with the herring horn groove (FIGS. 1 and 9)
The ratio [b / (2r)] was set to 1. In the case of a wave bearing, the wave number is set to Nw = 3, and the amplitude (aw / c) of the dimensionless wave at the average bearing gap c is set to 0.4.
In the herringbone grooved bearing, the dimensionless groove depth (δg / c) is set to 1.3, ag: ar = 1, and βg = 25 °. The bearing number の in FIG. 10 is a dimensionless physical quantity, which is directly proportional to the rotation speed, and
Is inversely proportional to the square of The number of bearings shown in FIG.
= 1 to 15) are those that can be obtained with a normal bearing clearance and rotation speed. The stability limit mass parameter Mc of FIG.
Is the stability limit mass of the dimensionless rotating shaft. When the rotational speed, that is, the number of bearings is fixed and this mass parameter is gradually increased, there is a limit mass parameter at which unstable whirl begins to occur. According to FIG. 10, in the case of the WI type and the WII type in the wave bearing, Λ = 1.
Although the stability limit mass parameter of the herringbone grooved bearing is lower than that of the GMR type in the range of １５15, the stability is superior to that of the SMR type.

FIG. 11 shows the result of analyzing the effect of machining accuracy on the whirl stability of the bearing. The number of bearings is set to Λ = 5. Mc in the table is the stability limit mass parameter, and the rate of change is the rate of change of Mc based on aw / c = 0.4 (corrugated bearing) or δg / c = 1.3 (bearing with herringbone groove). is there. According to FIG. 11, the waveform bearing has a stability limit of about 40 to 50 with an aw / c change of -0.1.
% And a +0.1 change increases about 55-75%. On the other hand, in the herringbone grooved bearing, a change of less than ± 10% is recognized with respect to a change of δg / c of ± 0.1. The variation of aw / c and δg / c of ± 0.1 is a variation of only ± 0.5 μm when the average bearing gap c is, for example, 5 μm. As described above, it is understood that the whirl stability of the waveform bearing is extremely sensitive to the amplitude of the harmonic waveform, and high machining accuracy is required to realize the design performance of the waveform bearing.

[0031]

According to the present invention, it is possible to provide a dynamic pressure type gas bearing which can effectively suppress unstable whirl vibration and can be manufactured at low cost and with high accuracy.

[Brief description of the drawings]

FIG. 1 is an axial sectional view of a dynamic pressure type gas bearing according to the present invention.

FIG. 2 is a cross-sectional view taken along line AA (FIG. 1) showing an embodiment in which a wavy surface is provided on the inner peripheral surface of the bearing member.

FIG. 3 is a sectional view showing a corrugated surface forming step.

FIG. 4 is a sectional view of the core rod shown in FIG. 3;

FIG. 5A is a side view of a bearing member provided with a wavy surface on an inner peripheral surface, and FIG. 5B is a cross-sectional view thereof.

FIG. 6 is a cross-sectional view illustrating a compression molding step of the metal powder.

FIG. 7 is a cross-sectional view taken along line AA (FIG. 1) showing an embodiment in which a corrugated surface is provided on the outer peripheral surface of the shaft member.

8A is a side view of a shaft member provided with a corrugated surface on an outer peripheral surface, and FIG. 8B is a cross-sectional view thereof.

FIG. 9 is an axial sectional view of a bearing with a herringbone groove used as a comparative example.

FIG. 10: Number of bearings Λ and stability limit mass parameter M
It is a figure showing the analysis result of c.

FIG. 11 is a diagram showing a result of measuring a relationship between processing accuracy and whirl stability of a bearing.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Dynamic pressure type gas bearing 1 'Dynamic pressure type gas bearing 2 Shaft member 2' Shaft member 3 Bearing gap 3 'Bearing gap 4 Bearing member 4' Bearing member 5 Wavy surface 5 'Wavy surface

Claims (3)

[Claims] 1. A bearing member is disposed on the outer periphery of a shaft member via a bearing gap, and a relative rotation between the shaft member and the bearing member generates a gas dynamic pressure in the bearing gap, so that any one of the bearing members is provided. In a member that supports the member in a non-contact manner with respect to the other member, a wave-like surface having a harmonic waveform is provided on a surface of one of the shaft member and the bearing member facing the bearing gap,
A hydrodynamic gas bearing characterized in that a member having a wavy surface is made of sintered metal. 2. The hydrodynamic gas bearing according to claim 1, wherein the wavy surface is provided on the bearing member. 3. The hydrodynamic gas bearing according to claim 1, wherein the corrugated surface is subjected to a sealing treatment.