JP2002048132A - Fluid bearing - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a fluid bearing in which a fluctuation phenomenon of NRRO during rotation can hardly occur and which has excellent durability in repeated start and stop operation. SOLUTION: In a spindle motor comprising a shaft 3 and a sleeve 2 facing with the shaft 3 by way of a fluid bearing clearance Cr of a radial fluid bearing R, a surface roughness Rpm of at least one of the outer periphery 3f of the shaft 3 and the internal circumference 2f of the sleeve is selected as 15% or smaller of the fluid bearing clearance Cr.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an information device,
The present invention relates to a fluid bearing for video equipment and office equipment, and more particularly to a fluid bearing which is optimal for a magnetic disk drive (HDD), an optical disc drive, and the like.

[0002]

2. Description of the Related Art As a conventional apparatus using such a fluid bearing, there is, for example, a spindle motor for an HDD. The structure will be described with reference to FIG. This spindle motor is configured such that a cylindrical sleeve 2 having a bottom plate 2a is inserted inside a cylindrical portion 1a erected on a base 1, and these are integrally fixed. The shaft 3 is rotatably inserted into such a sleeve 2,
A hydrodynamic bearing is interposed between the shaft 3 and the sleeve 2. An inverted cup-shaped hub 4 is integrally attached to the upper end of the shaft 3.

That is, the lower end surface of the shaft 3 is a thrust receiving surface 3s of the thrust fluid bearing S. The upper surface of the bottom plate 2a of the sleeve 2, which is a mating member, is opposed to the thrust receiving surface 3s via a thrust fluid bearing clearance, and this upper surface is opposed to the thrust bearing surface 2 of the thrust fluid bearing S.
s. Further, at least one of the thrust receiving surface 3s and the thrust bearing surface 2s is provided with a herringbone-shaped or spiral-shaped groove for dynamic pressure generation (not shown) formed by etching or the like, so that the thrust fluid bearing S is formed. It is configured.

[0004] Further, a pair of radial receiving surfaces 3r, 3r are formed on the outer peripheral surface 3f of the shaft 3 at an interval vertically. Further, radial bearing surfaces 2r, 2r are formed on the inner peripheral surface 2f of the sleeve 2 so as to face the radial receiving surfaces 3r, 3r via a radial fluid bearing clearance. Further, at least one of the radial receiving surface 3r and the radial bearing surface 2r is provided with a herringbone-shaped or spiral-shaped groove for generating dynamic pressure 7, 7 to constitute a radial fluid bearing R, R.

A stator 8 is fixed to the outer peripheral surface of the cylindrical portion 1a, and a drive motor M is formed facing the rotor magnet 9 fixed below the inner peripheral surface of the hub 4 via a gap. The shaft 3 and the hub 4 are integrally rotated by the drive motor M. When the shaft 3 rotates, a dynamic pressure is generated in a small amount of lubricant filled in the fluid bearing clearances of the fluid bearings S and R by the pumping action of the dynamic pressure generating grooves of the thrust fluid bearing S and the radial fluid bearing R. Thus, the shaft 3 is not contacted with the inner peripheral surface 2f of the sleeve 2 and the upper surface of the bottom plate 2a and is supported.

In such a spindle motor, the dynamic pressure generating groove 7 has a rectangular cross-sectional shape as shown in the schematic view of FIG. 3 (enlarged vertical cross-sectional view of the shaft 3 and the sleeve 2). An edge 10 of the groove 7 for generating dynamic pressure, that is, a ridge portion where the side surface 7a of the groove 7 for generating dynamic pressure and the outer peripheral surface 3f of the shaft 3 intersect (hereinafter referred to as an edge or a shoulder) It has a sharp angular shape and no roundness.

[0007] This is because when the groove 7 for generating dynamic pressure is formed on the outer peripheral surface 3f of the shaft 3 whose surface hardness is increased by quenching by etching or electrolytic processing, the edge 1 of the groove 7 for generating dynamic pressure is formed.
This is because 0 becomes a sharp edge. The shaft 3 is made of stainless steel, and the sleeve 2 facing the shaft 3 via the fluid bearing clearance Cr of the radial fluid bearing R is made of a copper alloy having a lower surface hardness than stainless steel. And
The outer peripheral surface 3f of the shaft 3 and the inner peripheral surface 2f of the sleeve 2 have the size of the fluid bearing clearance Cr of the radial fluid bearing R.
It was processed to a surface roughness Rpm of about 7% and used for a fluid bearing.

[0008]

In a HDD mounted on a portable device such as a notebook personal computer, the storage capacity is remarkably improved, and in order to increase a recording surface density, a fluctuation (NRRO) of a rotation asynchronous component of a spindle motor is required. ) Is required to be small. Therefore, adoption of a fluid bearing for the spindle motor has been studied in order to reduce NRRO.

However, even if a fluid bearing is used, the NRRO during rotation may increase instantaneously, causing a wobble phenomenon. Therefore, the outer peripheral surface 3f of the shaft 3
When the electrical conduction between the inner peripheral surface 2f of the sleeve 2 (the radial receiving surface 3r and the radial bearing surface 2r) was observed while rotating the spindle motor, the conduction and the NRRO were observed.
It was found that there was a correlation with the wobble phenomenon. From this, the wobble phenomenon of NRRO is caused by the above-mentioned two sides 3f, 2
f fine protrusions (protrusions that make up the surface roughness)
It is presumed to occur due to slight contact during rotation.

On the other hand, recent HDDs for notebook PCs
, Low power consumption is required to prolong the battery life. Therefore, when the HDD does not operate, the spindle motor is frequently stopped, and the spindle motor is rotated only when data is transferred. Therefore, recent HD
The D spindle motor is required to have excellent start / stop durability.

In the case of a fluid bearing, it is inevitable that the two surfaces 3f and 2f come into contact with each other when starting and stopping.
Since the surface roughness of both surfaces 3f and 2f is large (rough),
Initial wear is likely to occur when starting and stopping. Since both edges 10 of the dynamic pressure generating groove 7 provided on the outer peripheral surface 3f of the shaft 3 have sharp edges, when the outer peripheral surface 3f comes into contact with the sleeve 2 made of a soft copper alloy. In addition, the inner peripheral surface 2f of the sleeve 2 is easily damaged, and there is a problem in the start / stop durability.

It is an object of the present invention to provide a fluid bearing which solves the above-mentioned problems of the conventional fluid bearing and which is less likely to cause NRRO wobble during rotation and has excellent start / stop durability. And

[0013]

In order to solve the above-mentioned problems, the present invention has the following arrangement. That is, the hydrodynamic bearing device of the present invention is a hydrodynamic bearing comprising a shaft and a mating member opposed to the shaft via a hydrodynamic bearing clearance,
The surface roughness Rpm of at least one of the outer peripheral surface of the shaft and the inner peripheral surface of the mating member is set to 15% or less of the size of the fluid bearing clearance.

As described above, if the surface roughness Rpm of the outer peripheral surface of the shaft or the inner peripheral surface of the mating member is good, the two surfaces do not easily come into contact during rotation of the fluid bearing, so that the NRRO wobble phenomenon occurs. It is hard to cause initial wear when starting and stopping. If the surface roughness Rpm exceeds 15% of the size of the fluid bearing clearance, the NRRO wobble phenomenon is likely to occur.

Further, in the fluid bearing, a dynamic pressure generating groove is provided on at least one of an outer peripheral surface of the shaft and an inner peripheral surface of the mating member, and an edge of the dynamic pressure generating groove is sharpened. It is preferable to use a curved surface instead of a square shape. Then, even if the outer peripheral surface of the shaft and the inner peripheral surface of the mating member that are opposed to each other via the fluid bearing clearance are in contact with each other when the fluid bearing rotates, the edge is not a sharp corner but a curved surface. , The two sides are hardly damaged. Therefore, the start / stop durability of the fluid bearing is improved.

The edge means a ridge portion at which the outer peripheral surface or the inner peripheral surface provided with the dynamic pressure generating groove and the inner surface of the dynamic pressure generating groove intersect. However, if an excessively wide portion of the edge portion is formed into a curved shape, the function of the dynamic pressure generating groove is lost because the cross-sectional shape of the dynamic pressure generating groove changes greatly, and the dynamic pressure generating groove is not used. The generation of sufficient dynamic pressure may be hindered. Therefore, a portion of the edge portion within a predetermined range from a vertex at which the outer peripheral surface or the inner peripheral surface provided with the dynamic pressure generating groove and the inner surface of the dynamic pressure generating groove intersect with each other is a curved surface. Need to be in a state.

This range is as follows. First, the range in the depth direction of the groove for generating dynamic pressure is a length range from the top to 1/3 or less of the depth of the groove for generating dynamic pressure. The range in the width direction of the dynamic pressure generation groove is a length range of not more than 1/3 of the distance (ridge width) between the apex and the adjacent dynamic pressure generation groove. Also, since the material of the mating member is often a material having a lower hardness than the shaft,
It is preferable to provide the dynamic pressure generating groove on the inner peripheral surface of the mating member because the groove processing is facilitated. Moreover, since the dynamic pressure generating groove is not provided on the outer peripheral surface of the shaft, there is no possibility that the inner peripheral surface of the mating member having low hardness is damaged by the edge of the dynamic pressure generating groove.

The surface roughness Rpm in the present invention means the outer peripheral surface or the inner peripheral surface when a dynamic pressure generating groove is provided on the outer peripheral surface of the shaft or the inner peripheral surface of the mating member. Means the surface roughness Rpm of the portion excluding the dynamic pressure generating groove.

[0019]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of a fluid bearing according to the present invention will be described in detail with reference to the drawings. FIG. 1 is a longitudinal sectional view of a spindle motor which is one embodiment of a fluid bearing according to the present invention. FIG. 2 is an enlarged sectional view showing an enlarged portion of the groove 7 for generating dynamic pressure of the spindle motor of FIG. The configuration of the spindle motor according to the present embodiment is substantially the same as that of the above-described conventional spindle motor. Therefore, the description of the same parts will be omitted, and only different parts will be described.

The surface roughness Rpm of the outer peripheral surface 3f of the shaft 3 and the inner peripheral surface 2f of the sleeve 2 is set to 15.0% or less of the size of the fluid bearing clearance Cr of the radial fluid bearing R. In particular, the surface roughness Rpm of the outer peripheral surface 3f of the shaft 3 having high hardness is
It has been found that if the inner peripheral surface 2f of the sleeve 2 having low hardness is equal to or smaller than the inner peripheral surface 2f, the adaptation due to the contact between the two surfaces 3f and 2f at the time of starting and stopping is quick, and the fluctuation phenomenon of the NRRO during rotation can be reduced.

There are various types of surface roughness, and the center line average roughness Ra is widely used at present. However, in the case of the fluid bearing, since the portion that comes into contact at the time of starting and stopping is the roughest portion of the surface, it has been found that it is inappropriate to evaluate the surface roughness using the center line average roughness Ra. . Therefore, the surface roughness Rpm (average peak height) which is a roughness display indicating the average value of the maximum peak height from the center line of the roughness.
Was used to evaluate the surface roughness. For reference, the surface roughness R
FIG. 4 is an explanatory diagram for explaining the definition of pm.

The dynamic pressure generating groove 7 provided on the inner peripheral surface 2f of the sleeve 2 has a semicircular cross-sectional shape as shown in FIG. Further, the edge portion 10 of the groove 7 for generating dynamic pressure,
That is, the ridge at which the inner surface 7a of the dynamic pressure generating groove 7 and the inner peripheral surface 2f of the sleeve 2 intersect is not a sharp corner, but
It has a curved shape. The shape of the edge 10 will be described in more detail. The curved portion of the edge 10 is within a predetermined range from the vertex V where the inner peripheral surface 2f and the inner surface 7a of the groove 7 for generating dynamic pressure intersect. Part.

This range is as follows. First, the range A in the depth direction of the dynamic pressure generating groove 7 is a length range from the vertex V to 1/3 or less of the depth D of the dynamic pressure generating groove 7. Further, the range B in the width direction of the dynamic pressure generating groove 7 is a length range equal to or less than ３ of the distance L (ridge width) between the apex V and the adjacent dynamic pressure generating groove. In the present embodiment, the range A in the depth direction is a length range from the vertex V to 1/3 of the depth D of the groove 7 for generating dynamic pressure, and the range B in the width direction is adjacent to the vertex V. Of the groove L (ridge width) of the dynamic pressure generating grooves to be formed.

The groove 7 for generating dynamic pressure is formed by subjecting the inner peripheral surface 2f of the sleeve 2 made of a copper alloy, stainless steel or the like to plastic working such as ball rolling or cutting with a cutting tool. Since the cross section of the groove 7 for generating dynamic pressure is semicircular, it is easy to apply plastic working or cutting. That is, the inner periphery of the sleeve 2 is formed by performing ball rolling using a rolling jig holding a plurality of balls on the outer periphery of the shaft, or by turning using a cutting tool having a semicircular tip. Groove processing can be easily performed on the surface 2f.
If a cutting bit having an edge is used, the cutting edge is likely to be damaged. Therefore, it is preferable that the cross section of the groove 7 for generating dynamic pressure be semicircular.

Further, since the dynamic pressure generating groove 7 is provided on the inner peripheral surface 2f of the sleeve 2 having a low hardness, the groove processing is easy, and the outer peripheral surface 3f of the shaft 3 and the inner peripheral surface 2f of the sleeve 2 are easily formed. Of the dynamic pressure generating groove 7 even if the
This is preferable because the inner peripheral surface 2f of the sleeve 2 is not damaged. In addition, as a method of making the edge 10 of the groove 7 for generating dynamic pressure into a curved surface, ball cutting, brushing with a brush or the like is applied to the sharp edge 10 immediately after the groove processing.
Electrolytic polishing, chemical polishing, barrel processing, burnishing, etc. to remove sharp corners, etc.
It can be appropriately selected in consideration of processing accuracy, processing cost, and the like.

Similarly, the outer peripheral surface 3f of the shaft 3 and the sleeve 2
As a method for improving the surface roughness Rpm of the inner peripheral surface 2f of the sleeve 2, in the case of the inner peripheral surface 2f of the sleeve 2, ball passing, honing, lapping and the like can be mentioned, and in the case of the outer peripheral surface 3f of the shaft 3, Super finishing, taping, buffing and the like can be used, and can be appropriately selected in consideration of mass productivity, processing cost, and the like.

The present embodiment is an example of the present invention, and the present invention is not limited to the present embodiment. For example, the dynamic pressure generating groove 7 is provided on the inner peripheral surface 2f of the sleeve 2 in the present embodiment, but may be provided on the outer peripheral surface 3f of the shaft 3 or both. Also,
The cross-sectional shape of the dynamic pressure generating groove 7 is preferably a semicircular shape which is easy to process, hardly contains foreign matter during cleaning, and is easy to clean.
A polygonal shape such as a triangular shape, a square shape, and a rectangular shape may be used.

The material of the members constituting the spindle motor such as the shaft 3 and the sleeve 2 is not particularly limited, and may be stainless steel, copper alloy, sintered metal or the like generally used for the members constituting the spindle motor. Any material, such as sintered oil-impregnated metal, plastic, and ceramic, can be used without any problem. Further, the spindle motor may be a sleeve fixed-shaft rotating type as in the present embodiment, or a shaft fixed-
The sleeve rotation type can be used. Further, the structure of the fluid bearing, the pattern of the grooves 7 for generating dynamic pressure, the detailed structure of the spindle motor, and the like are not limited to the present embodiment, and can be appropriately changed as necessary.

Furthermore, in the present embodiment, the spindle motor has been described as an example of a device using a fluid bearing, but the present invention can be applied to various other fluid bearing devices. Next, with respect to the spindle motor as described above, the wobble phenomenon of NRRO and the start / stop durability were evaluated.

First, the influence of the ratio between the surface roughness Rpm of the outer peripheral surface 3f of the shaft 3 and the inner peripheral surface 2f of the sleeve 2 and the radial fluid bearing clearance Cr on the fluctuation phenomenon of NRRO was examined. The test conditions were as follows: the rotational speed of the spindle motor was 4200 rpm, and the radial fluid bearing clearance Cr was 2 to 2.
4 μm. The lubricant A was filled with a lubricant A (a diester oil containing an additive).

Table 1 shows the surface roughness Rpm of the outer peripheral surface 3f and the inner peripheral surface 2f of the spindle motors of Examples 1 to 3 and Comparative Examples 1 and 2, and the ratio of the surface roughness Rpm to the radial fluid bearing clearance Cr ( It shows the surface roughness Rpm / the radial fluid bearing clearance Cr), the presence or absence of conduction between the outer peripheral surface 3f and the inner peripheral surface 2f, and the presence or absence of the NRRO wobble phenomenon.

[0032]

[Table 1]

From these results, it can be seen that if the surface roughness Rpm of the outer peripheral surface 3f of the shaft 3 and the inner peripheral surface 2f of the sleeve 2 is 15% or less of the radial fluid bearing clearance Cr, the NRRO wobble phenomenon does not occur. I understand. Further, from Comparative Example 2, even if the surface roughness Rpm of the two surfaces 3f and 2f is improved, if the ratio to the radial fluid bearing clearance Cr is large, contact between the two surfaces 3f and 2f cannot be avoided, and the NRRO wobble phenomenon occurs. I know what happens. Further, it is understood that it is preferable that the surface roughness Rpm of the outer peripheral surface 3f of the shaft 3 having high hardness is equal to or smaller than the surface roughness Rpm of the inner peripheral surface 2f of the sleeve 2 having low hardness.

Next, a description will be given of the result of evaluating the start / stop durability of the spindle motor by an on / off test in which the start / stop of rotation is repeated. The test conditions were as follows: the number of rotations of the spindle motor was 4200 rpm, and the number of start / stop times was 10
000 times. The material of the shaft 3 was stainless steel, the material of the sleeve 2 was a copper alloy, and the fluid bearing clearance was filled with a lubricant A (diester oil containing an additive).

Table 2 shows the results.

[0036]

[Table 2]

From these results, it can be seen that the edge 10 of the dynamic pressure generating groove 7
It can be seen that if the (shoulder) is curved, the both surfaces 3f, 2f are less likely to be damaged, and the start / stop durability is improved.

[0038]

As described above, in the fluid bearing of the present invention, the surface roughness Rpm of the outer peripheral surface of the shaft and the inner peripheral surface of the mating member is 15% or less of the size of the fluid bearing clearance. It is difficult for the two surfaces to come into contact during rotation. Therefore, the NRRO wobble phenomenon is unlikely to occur, and the initial wear at the time of starting and stopping is also unlikely to occur.

[Brief description of the drawings]

FIG. 1 is a sectional view showing a spindle motor which is an embodiment of a fluid bearing according to the present invention.

2 is a partially enlarged sectional view of a groove for generating dynamic pressure of the spindle motor of FIG. 1;

FIG. 3 is a schematic diagram illustrating a cross-sectional shape of a groove for generating dynamic pressure of a conventional spindle motor.

FIG. 4 is an explanatory diagram for explaining the definition of surface roughness Rpm.

[Explanation of symbols]

 2 Sleeve 2f Inner peripheral surface 3 Shaft 3f Outer peripheral surface 7 Groove for generating dynamic pressure 10 Edge Cr Radial fluid bearing clearance R Radial fluid bearing S Thrust fluid bearing

 ──────────────────────────────────────────────────続 き Continued on the front page F term (reference) 3J011 AA20 BA04 DA02 JA02 KA02 KA03 5H607 AA04 BB01 BB14 BB17 BB25 CC01 DD03 DD16 GG01 GG09 GG12

Claims (1)

[Claims] 1. A fluid bearing comprising a shaft and a mating member opposed to the shaft via a fluid bearing clearance, wherein at least one of an outer peripheral surface of the shaft and an inner peripheral surface of the mating member has a rough surface. A fluid bearing, wherein Rpm is 15% or less of the size of the fluid bearing clearance.