Dynamic pressure bearing-unit

Details Dynamic pressure bearing-unit Dynamic pressure bearing-unit

2000-03-31

2002-05-21

Hannon, Thomas R. (Department: 3682)

Bearings

Rotary bearing

Fluid bearing

Reexamination Certificate

active

06390681

ABSTRACT:

BACKGROUND OF THE INVENTION
The present invention relates to a dynamic pressure bearing-unit and a method for manufacturing the same. The bearing unit is suitable particularly for supporting spindles of spindle motors of information equipment, for example, magnetic disk units for such as HDD and FDD, optical disk units for such as CD-ROM and DVD-ROM, and magneto-optical disk units for such as MD and MO. The bearing unit is also suitable for supporting spindles of polygon scanner motors of laser beam printers (LBP).
The spindle motors of the various types of the aforementioned information equipment require highly accurate revolution as well as high speed, low cost, and low noise. One of the components responsible for the performance required is the bearing for supporting the spindle of the motor. These days, as a bearing of this type, dynamic pressure bearings with outstanding properties to meet the aforementioned requirements for performance have been studied or in practical use.
FIG. 10
shows an example of a spindle motor of this type. The motor has a configuration in which a shaft member
22
(comprising a shaft
22
a
and a thrust disk
22
b
which becomes a flange portion when attached to the shaft
22
a
) rotatably supported by means of a bearing unit
21
is rotatably driven by means of the magnetic force produced between a motor stator
4
fixed to a bearing member
27
and a motor rotor
5
mounted to the shaft member
22
. The bearing unit
21
is provided with a radial bearing
30
for supporting the shaft member
22
in the radial direction and a thrust bearing
31
for supporting the thrust disk
22
b
in the direction of thrust. Both the radial bearing
30
and
31
are dynamic pressure bearings which have grooves (dynamic pressure grooves) for producing a dynamic pressure on the bearing surfaces. The dynamic pressure grooves of the radial bearing
30
are formed on the inner periphery of the bearing member
27
. On the other hand, the dynamic pressure grooves of the thrust bearing
31
are formed on the both end surfaces of the thrust disk
22
b
fixed to the lower end of the shaft member
22
. The bearing member
27
is provided, on the bottom portion thereof, with a step portion having the depth of the thickness of the thrust disk
22
b
plus the width of the thrust bearing clearance (t=approximately 5 to 20 &mgr;m). A back metal
33
is incorporated into this step portion, thereby forming thrust bearing clearances Cs
1
, Cs
2
having the aforementioned predetermined depth on the both axial sides of the thrust disk
22
b
(t=Cs
1
+Cs
2
).
The bearing unit
21
is assembled as follows. First, the thrust disk
22
b
and the back metal
33
are incorporated into the bearing member
27
. After that, the shaft
22
a
with a radius smaller than the inner radius of the bearing member
27
by radial bearing clearance Cr is inserted into the inner diameter portion of the bearing member
27
. Then, the distal end of the shaft
22
a
is press-fitted to the inner diameter portion of the thrust disk
22
b.
It may adopt another process that the back metal
33
is incorporated into the bearing body
27
after the shaft member
22
assembled the shaft and thrust disk
22
b
is inserted into the bearing body
27
.
In the aforementioned bearing unit
21
, inaccuracy of the perpendicularity between the shaft
22
a
and the thrust disk
22
b
would cause the thrust disk
22
b
to contact with the surfaces opposite thereto in the thrust bearing clearances Cs
1
, Cs
2
and thus the bearing performance to deteriorate. Therefore, in the assembly process, it is necessary to press-fit the shaft
22
a
to the thrust disk
22
b
with accuracy, however, the press-fitting hardly provides the accuracy required (of the order of 2 &mgr;m in perpendicularity). Moreover, since the shaft
22
a
and the thrust disk
22
b
have been already incorporated into the unit, measurement of the perpendicularity or a check of the accuracy would be usually difficult. Even if possible, the measurement or the check would require time-consuming work, resulting in an increase in assembly cost.
Furthermore, in the aforementioned bearing unit, the dynamic pressure grooves on the both end surfaces of the thrust disk
22
b
can be formed by means of presswork at low cost. However, the dynamic pressure grooves of the inner periphery of the bearing member
27
need to be formed by means of purpose-built high-accuracy equipment to meet individual shapes of the bearing member
27
, thereby raising the manufacturing cost. In addition, this structure requires time-consuming work such as measurement of dimensions to improve the accuracy of the bearing clearances of the thrust bearing, causing a concern to rise about an increase in cost due to an increase in labor.
SUMMARY OF THE INVENTION
In view of the aforementioned problems, a main object of the present invention is to reduce the cost required for manufacturing a dynamic pressure bearing-unit as well as improve the accuracy thereof. More specifically, a first object is to provide a dynamic pressure bearing-unit which can provide improved accuracy between the shaft and the thrust disk (such as perpendicularity) at low cost. A second object is to facilitate setting the bearing clearances (the thrust bearing clearances) of the thrust bearing as well as to implement highly accurate thrust bearing clearances.
In order to achieve the aforementioned first object, in a dynamic pressure bearing-unit comprising a shaft member composed a shaft and a flange portion, a radial bearing portion for supporting the shaft member in a radial direction, and a thrust bearing portion for supporting the flange portion of the shaft member in the direction of thrust, wherein the radial bearing portion and the thrust bearing portion support the shaft member by dynamic pressure action out of contact, respectively, the dynamic pressure bearing-unit according to the present invention is provided with the shaft and the flange portion which are constructed in one piece.
Such integrated structure of the shaft member readily can ensure accuracy such as the perpendicularity between the shaft and the flange portion. Moreover, the perpendicularity can be measured before the shaft and the flange portion are incorporated into the bearing unit, thereby facilitating accuracy measurement and the check thereof.
The radial bearing of the dynamic pressure bearing-unit is configured in such a manner that a bearing member is arranged along the outer periphery of the shaft member, and a radial bearing clearance of the radial bearing portion is formed between the outer periphery of the shaft member and the bearing member facing thereto.
The thrust bearing portion is to have two thrust bearing clearances on both sides of the flange portion. In this case, one end surface of the flange portion and the bearing member facing thereto (for example, the end surface thereof) can form one of the thrust bearing clearances of the thrust bearing portion. Moreover, a thrust support portion can be provided opposite to the other end surface of the flange portion, thereby allowing the thrust support portion and the other end surface of the flange portion to form the other one of the thrust bearing clearances of the thrust bearing portion.
The dynamic pressure grooves of the thrust bearing are preferably formed on either one of the bearing member and the thrust support portion (which is determined depending on the direction of thrust load) or on the both.
One end of the bearing member is preferably sealed with a sealing member. A labyrinth seal is preferable as the sealing member.
According to the present invention described above, the integrated structure of the shaft member readily provides improved accuracy such as the perpendicularity between the shaft and the flange portion, facilitating the accuracy measurement and the check thereof. Therefore, it is made possible to provide an inexpensive high-accuracy bearing unit suitable for use in a spindle motor of information equipment.
Furthermore, the dynamic pressu

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