Electrical generator or motor structure – Dynamoelectric – Rotary
Reexamination Certificate
1999-10-07
2001-10-23
Enad, Elvin (Department: 2834)
Electrical generator or motor structure
Dynamoelectric
Rotary
C310S06700R, C310S089000, C310S091000, C310S261100, C310S267000
Reexamination Certificate
active
06307291
ABSTRACT:
BACKGROUND OF THE INVENTION
This invention relates to a rotary apparatus such as hard disc drive (HDD), a spindle motor used as a drive source for such a rotary apparatus and to a fluid dynamic pressure bearing adapted for such a spindle motor bearing. More particularly, the invention relates to a shaft-both-end fixed type fluid dynamic pressure bearing to be fixed at respective ends of its shaft onto a chassis, etc. of a utilized apparatus through screws or the like.
Air dynamic pressure bearings are broadly used in rotary apparatuses such as a HDD, a optical disc drive and light polarizing apparatuses because of such as their light weight of light, clean and smooth rotation, durability to heat and cold, long service life and freedom of contamination to storage media such as discs, by virtue of the nonuse of lubrication oil. Recently, however, there has been a significant increase in the information amount required to be processed. Particularly, the large capacity HDD apparatus is required to rotationally drive as many as five or more discs. This requirement an no longer be met by an air dynamic pressure bearing. To cope with this, fluid dynamic pressure bearings have been adopted for HDD apparatuses that can support load weight greater than that of the air dynamic pressure bearings.
There are disclosures of basic structures and operations of fluid dynamic pressure bearings, e.g., in U.S. Pat. No. 5,112,142; U.S. Pat. No. 5,524,985; U.S. Pat. No. 5,524,986; and U.S. Pat. No. 5,533,812.
The conventional fluid dynamic pressure bearings, particularly the fluid dynamic pressure bearings to rotate the sleeve, includes two kinds of devices, if classified by the manner of fixing the shaft onto a utilized apparatus. One is a shaft-one-end fixed type fluid dynamic pressure bearing as shown in
FIG. 18
, and the other is a shaft-both-end fixed type fluid dynamic pressure bearing as shown in FIG.
19
. First, the fluid dynamic pressure bearing of
FIG. 18
is structured by a fixed shaft
1
to be fixed at its lower end onto a chassis
16
or the like through a screw
15
, and a rotary sleeve
2
having an upper end covered completely by a lid member
20
and a lower end having an opening
11
forming a capillary seal. Next, the fluid dynamic pressure bearing of
FIG. 19
is structured by a fixed shaft
1
to be fixed at respective ends onto a chassis
16
or the like of a utilized apparatus through screws
14
and
15
, and a rotary sleeve
2
having openings
11
a
and
11
b
forming respective capillary seals at upper and lower ends.
In FIG.
18
and
FIGS. 19
,
8
,
8
a
, and
8
b
are radial dynamic pressure producing grooves, while
9
a
and
9
b
are thrust dynamic pressure producing grooves.
5
,
5
a
,
5
b
,
17
a
,
17
b
and
17
c
are fine gaps formed between the fixed shaft
1
and the rotary sleeve
2
. These fine gaps are filled therein with lubrication oil
18
. The fine gaps have a width of usually 2 to 15 &mgr;m, although depending on the size of the fluid dynamic pressure bearing.
13
a
is an upper screw hole of the fixed shaft, while
13
,
13
b
denote a lower screw hole.
In the shaft-one-end fixed type fluid dynamic pressure bearing of
FIG. 18
, the lubrication oil
18
filled within the fine gaps
5
,
17
a
,
17
b
and
17
c
is in contact with the air at the tapered opening
11
. However, the filled lubrication oil
18
is prevented from leaking to an outside of the fine gap by the presence of a capillary seal and surface tension in this opening. In particular, the fine gaps
17
a
,
17
b
and
17
c
constitute a closed end.
The filled lubrication oil
18
is made difficult to leak out through the opening
11
due to a fine gap structure having the closed end, i.e. a fine gap structure with one-side closure. In the shaft-both-end fixed type fluid dynamic pressure bearing of
FIG. 19
, on the other hand, the filled lubrication oil
18
filled within the fine gaps
5
a
,
5
b
,
17
a
,
17
b
and
17
c
is in contact with the air at the tapered upper opening
11
a
and lower opening
11
b. However, the filled lubrication oil
18
is prevented from leaking out of the fine gaps by the presence of a capillary seal and surface tension given by the openings.
Of the above related-art apparatus, the shaft-one-end fixed type fluid dynamic pressure bearing of
FIG. 18
has a closed end formed in the fine gaps. Accordingly, even if the apparatus is tilted, the lubrication oil does not easily leak out. Thus, the apparatus is excellent in sealability. However, there is a disadvantage in that the shaft
1
is fixed at only one lower end point and hence may undergo precession motion during rotation at high speed, resulting in unstable rotation. Conversely, the shaft-both-end fixed type dynamic pressure bearing of
FIG. 19
fixes the shaft
1
at its both ends and hence will not undergo precession motion during rotation at high speed, thus offering stable rotation. However, there is a problem in that the fine gaps are opened to the air at upper and lower sides, resulting in insufficient of sealability. Even if the surface tension is increased by providing an air reservoir within a fine gap between the upper and lower radial dynamic pressure producing grooves
8
a
and
8
b
, the surface tension is abruptly decreased upon tilting and horizontally positioning the fluid dynamic pressure bearing. Furthermore, if in this state temperature change or external impact is applied, the lubrication oil filled within the fine gap may readily leak out.
SUMMARY OF THE INVENTION
It is therefore an object of the present invention to maintain, in a shaft-both-end fixed type fluid dynamic bearing, a high sealability not only during rotation at high speed but even upon tilting in a standstill state.
It is a second object of the invention to provide, in a shaft-both-end fixed type fluid dynamic pressure bearing, a capability of supporting greater load weight as compared to the related art apparatus.
It is a third object of the invention to provide a spindle motor which can maintain stability in high speed rotation while supporting large load weight.
It is a fourth object of the invention to provide a rotary apparatus which can rotationally drive as many as five or more hard discs.
In brief, the present invention is a double sleeve type fluid dynamic pressure bearing, comprising: a fixed shaft having respective ends to be fixed to a utilized apparatus; a rotary sleeve arranged to provide a first fine gap between an inner peripheral surface thereof and an outer peripheral surface of the fixed shaft; a fixed sleeve arranged to provide a second fine gap between an inner peripheral surface thereof and an outer peripheral surface of the rotary sleeve; a holder member arranged to cooperate with a lower end surface of the rotary sleeve to provide a third fine gap; and wherein the first fine gap and the second fine gap are formed with radial dynamic pressure producing grooves while the third fine gap is formed with a thrust dynamic pressure producing groove, the first, second and third fine gaps being filled with lubrication oil; the first fine gap and the second fine gap having one end serving as an opening end contacting with the air and the other end serving as an closed end communicated with each other through the third fine gap.
In the double sleeve type fluid dynamic pressure bearing, the radial dynamic pressure producing grooves are provided in the first fine gap and a drawing groove is in the second fine groove so as not to interfere with the dynamic pressure producing grooves so that a drawing force is caused exceeding a centrifugal force to prevent lubrication oil from leaking out. Also, in the double sleeve type dynamic pressure bearing, a capillary seal is provided in one or both of the opening ends of the first fine gap and the second fine gap, and an auxiliary seal of a fluid reservoir type is provided in position of a fine gap close to a minimum groove width portion of the capillary seal portion.
Also, the present invention is, in a spindle motor structured by a rotor including a rotor mag
Goto Hiromitsu
Iwaki Tadao
Kawawada Naoki
Kogure Toshiharu
Nakayama Yukihiro
Adams & Wilks
Enad Elvin
Seiko Instruments Inc.
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