Bearings – Rotary bearing – Fluid bearing
Reexamination Certificate
2000-12-12
2002-07-02
Footland, Lenard A. (Department: 3682)
Bearings
Rotary bearing
Fluid bearing
Reexamination Certificate
active
06412984
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a dynamic pressure bearing apparatus for a spindle motor used with information equipments, acoustic equipments or imaging equipments, particularly for a spindle motor suitable for optical disc devices and magnetic disc devices, and, a dynamic pressure bearing apparatus for a fan motor, particularly using a radial/thrust integral resin bearings, and more particularly, it relates to a dynamic pressure bearing apparatus for a fan motor, which has excellent performance and endurance and which can easily be worked and assembled.
2. Related Background Art
Conventionally, although a bearing apparatus utilizing a sliding bearing or a ball bearing has been used in such a system, recently, due to request for high speed transferring of data, higher speed rotation of a rotary member (shaft) has been requested. As a result, there arose a problem that whirling of the rotary member is increased by the influence of a centrifugal force. To minimize an amount of the whirling, a dynamic pressure bearing apparatus (dynamic pressure spindle motor) utilizing a dynamic pressure bearing has been used.
An example of a conventional dynamic pressure bearing apparatus is shown in
FIG. 15
which is a sectional view.
FIG. 16
is an enlarged view showing a bearing member of FIG.
15
. In this conventional example, a bearing member
1004
defines a cylindrical bore
1013
including a metallic sleeve
1002
and a thrust bearing member
1003
, and the sleeve
1002
has an inner diameter surface
1009
which is provided with dynamic pressure generating grooves
1014
to define a radial bearing surface
1010
. In the thrust bearing member
1003
connected to the sleeve
1002
, a thrust bearing surface
1012
defining a part of the cylindrical bore
1013
has a convex spherical shape to provide a sliding bearing. The thrust bearing member
1003
has a vent hole
1005
. A turn table
1015
is attached to a shaft
1007
which is driven by a rotor
1018
and a stator
1019
.
In the dynamic pressure generating grooves
1014
, when it is assumed that axial lengths from bent portions to upper (open) sides are A, C and axial lengths from the bent portions to lower (bottom) sides are B, D, relationships A>B, C>D and (A+C)>(B+D) are established, and, thus, the grooves are asymmetrical in the axial direction. The reason is that, by generating axial load capacity, a thrust force for floating the shaft
1007
(rotor) is generated to prevent the bearing portions (particularly, lower portion of the radial bearing and the thrust bearing) from being subjected to negative pressure. If the bearing portions are subjected to the negative pressure, the whirling (of the shaft) will be generated to worsen bearing performance.
On the other hand, since the thrust bearing surface
1012
has the vent hole
1005
at its one end, when the shaft
1007
is inserted into the bearing, lubricating oil leaks through the vent hole
1005
, thereby not ensuring reservation of the lubricating oil. Further, in an inoperative condition of the bearing after insertion of the shaft
1007
, if an environmental temperature is increased, viscosity of the lubricating oil is decreased, and the lubricating oil may leak through the vent hole
1005
.
To prevent the leakage of the lubricating oil, there has been proposed a dynamic pressure bearing apparatus (not shown) of type which has similar construction as that shown in
FIG. 16
but has no vent hole
1005
in the thrust bearing member
1003
.
However, in the type having no vent hole
1005
, when the bearing is operated, oil in an oil reservoir
1008
is sucked toward the bottom, which causes a new problem that the rotary members (shaft, rotor, turn table, disc) are floating above the thrust bearing surface
1012
. It is very difficult to suppress such floating particularly when a circumferentially opposed motor (in which a rotor
1018
and a stator
1019
are opposed to each other in a radial direction) is used.
A floating amount of the rotary members depends upon an amount of oil in the oil reservoir
1008
.
In a disc driving system, in which a disc
1016
rotated, when the disc is floating due to rotation of the drive, a gap between the disc and a recording/reproducing head is decreased to make recording/reproducing impossible. The space (gap) between the recording/reproducing head and the surface of the disc in the disc driving system must be maintained with high accuracy. Thus, some control for the floating amount of the shaft is required in the bearing apparatus.
However, for this requirement, the floating of the rotor cannot be prevented by using the above-mentioned groove pattern.
On the other hand, an example of a conventional fan motor used in office equipments is described in Japanese Utility Model Registration No. 2553251.
FIG. 17
is a sectional view showing a conventional dynamic pressure bearing apparatus for a fan motor. A rotor
2031
is secured to an inner peripheral surface of a support member
2033
, and vanes
2030
are secured to an outer peripheral surface of the support member
2033
. The rotor
2031
is constituted by a magnet
2032
. The support member
2033
is secured to one end of a rotary shaft
2037
having a dynamic pressure generating portion (dynamic pressure generating grooves
2036
). A cylindrical sleeve
2035
is mounted on a central portion of a case
2039
, and a stator
2034
is secured to an outer peripheral surface of the sleeve
2035
in a confronting relation to the rotor
2031
. Below the sleeve
2035
, a resin receiver member
2040
for supporting the rotary shaft
2037
is attached to the case
2039
. A dynamic pressure bearing
2038
is constituted by rotatably fitting the rotary shaft
2037
into the sleeve
2035
, and a cylindrical space formed between the sleeve
2035
and the rotary shaft
2037
is filled with grease
2041
. The vanes
2030
and the rotor
2031
are supported in the radial direction via the dynamic pressure bearing
2038
so that the vanes
2030
and the rotor
2031
can be rotated around the stator
2034
. That is to say, the rotor
2031
is rotated by a rotational magnetic field generated by the stator
2034
to rotate the vanes
2030
(in a direction shown by the arrow Z in FIG.
17
), thereby generating air streams directing toward a direction shown by the arrow X to effect air blast. A thrust load (shown by the arrow Y) acting on the rotary shaft
2037
as a thrust force generated by rotation of the vanes
2030
(reaction force of the blasting operation) is supported by an axial component of an attracting force acting between an iron core (not shown) of the stator
2034
and the magnet
2032
of the rotor
2031
. The stator
2034
and the rotor
2031
are offset in the axial direction so that the attracting force becomes greater than the thrust force generated by the rotation of the vanes
2030
by a predetermined rate. By the remaining axial component thrust load obtained by subtracting the thrust force of the vanes
2030
from the attracting force acting between the stator
2034
and the rotor
2031
, an end surface of the rotary shaft
2037
is urged against the resin receiver member
2040
of the case
2039
to support the rotary shaft.
However, in the conventional bearing for the fan motor, since the number of parts of the bearing is increased (i.e., becomes two; radial bearing and thrust receiver member (resin receiver member
2040
)), the assembling steps are increased and the construction of the bearing becomes complicated. Further, since perpendicularity of the end surface of the rotary shaft
2037
supporting the thrust load must be maintained with high accuracy, the apparatus cannot be made cheaper. In addition, since the end surface of the shaft and the surface of the receiver member which support the thrust load are flat, the peripheral edge of the end surface of the shaft contacts with the surface of the receiver member to easily damage the latter. Further, since the rotor
2031
is attracted in the axial direction
Asai Hiromitsu
Sugimori Yoichiro
Footland Lenard A.
Miles & Stockbridge P.C.
NSK Ltd.
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