Electrical generator or motor structure – Dynamoelectric – Rotary
Reexamination Certificate
2000-03-24
2001-06-12
Mullins, Burton (Department: 2834)
Electrical generator or motor structure
Dynamoelectric
Rotary
C310S049540, C310S06700R
Reexamination Certificate
active
06246139
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to a spindle motor having a rotor rotatably supported on a stator through a liquid dynamic pressure bearing having a flanged shaft member and a cylindrical receiving member in which the shaft member is rotatably received and having a cup-formed hub press-fitted on the flanged shaft member, and to a method for assembling the spindle motor.
The present assignee applicant has developed and applied for a patent (Japanese Patent Application No. H09-36380/1997) for a liquid dynamic pressure bearing having a flanged shaft member
1
and a cylindrical receiving member
4
, one embodiment of which is shown in
FIG. 7
, and a spindle motor having such a liquid dynamic pressure bearing. That is, the liquid dynamic pressure bearing shown in
FIG. 7
has a flanged shaft member
1
in a cross-formed section integrally formed by a cylindrical member
2
and a thrust dynamic pressure disk member
3
, and a cylindrical receiving member
4
. An annular lid member
5
serves also as a thrust holding plate.
The spindle motor includes, besides the liquid dynamic pressure bearing structured as above, a cup-formed hub
6
coaxially fixed on an end of the flanged shaft member
1
to support a rotary member such as a hard disk, a rotor magnet
7
attached on an inner peripheral surface of a sleeve portion of the cup-formed hub
6
, a stator coil
8
attached on an outer peripheral surface of the cylindrical receiving member
4
to generate a rotation force in cooperation with the rotor magnet
7
, and a base plate
9
in which the cylindrical receiving member
4
is provided.
The liquid dynamic pressure bearing, structured by the flanged shaft member
1
having a cross-formed section formed with a thrust dynamic pressure disk member
3
a
at an axial center and the cylindrical receiving member
4
rotatably accommodating the flanged shaft member, is removed of a problem involved in the conventional dynamic pressure bearing structured by a flanged shaft member having a T-formed section formed with a thrust dynamic pressure disk member
3
a
at one end of the shaft and a receiving member rotatably accommodating the flanged shaft member, i.e., rotation instability resulting from half whale phenomenon caused by disagreement in direction of a shaft displacement and a restoration force against the displacement during high speed rotation.
However, there has been a problem that the flanged shaft member
1
having the cross-formed section integrally formed with two members of the cylindrical member
2
and the thrust dynamic pressure disk member
3
a
is fabricated by machining and hence is high in manufacture cost. To avoid this, a spindle motor one embodiment of which is as shown in
FIG. 6
has been developed. That is, in
FIG. 6
a flanged shaft member
1
is fabricated by machining as respective separate members one cylindrical member
2
and a dynamic pressure producing ring member
3
and then assembling these two members together. This solved the problem with manufacture cost involved in the spindle motor of FIG.
7
.
Nevertheless, another problem has arisen in assembling such a spindle motor. The assembling of the spindle motor of
FIG. 6
includes, after a process of inserting and arranging in a cylindrical receiving member
4
a flanged shaft member
1
fabricated by press-fitting a dynamic pressure ring member
3
onto a cylindrical member
2
, a process of press-fitting an annular holding member
5
in an annular step
4
b
formed in an opening end of the cylindrical receiving member
4
, and thereafter a process of press-fitting a cup-formed hub
6
having a mount hole
6
a
at a center onto the flanged shaft member
1
. The problem lies in that the dynamic pressure ring member
3
deviates off a specified press-fit position when press-fitting the hub
6
onto the flanged shaft member
1
by applying an urging force. This deviation is caused due to receiving an urging force applied to the hub
6
at the annular step
4
a
at a boundary of smaller and larger diameter cylindrical portions of the cylindrical receiving member
4
when press-fitting the hub
6
to the flanged shaft member
1
by applying an urging force. This deviation is slight as small as on the order of a micron, but crucial for a liquid dynamic pressure bearing.
The above problem with assembling would not occur if a cylindrical member
2
and a cup-formed hub
6
were made in one body. However, the integral form with a cylindrical member
2
and a cup-formed hub
6
is extremely difficult to mass-produce at low cost, similarly to a flanged shaft member
1
having a cross-formed section integrally formed with two members of a cylindrical member
2
and a dynamic pressure ring member
3
.
Eventually, for a spindle motor having a liquid dynamic pressure bearing having as basic constituent members a flanged shaft member fabricated by press-fitting a dynamic pressure ring member on a cylindrical member and a cylindrical receiving member rotatably receiving this shaft member, it is left unsolved to press-fit the cup-formed hub onto the flanged shaft member in a manner not to deviate the dynamic pressure ring member off a specified press-fit position. Due to this, it is impossible to meet the requirement of mass-producing the spindle motors at low cost.
SUMMARY OF THE INVENTION
The problem to be solved by the invention is to reduce manufacture cost for a spindle motor having a liquid dynamic pressure bearing having as basic constituent members a flanged shaft member made by press-fitting a dynamic pressure ring member on a cylindrical member and a cylindrical receiving member rotatably fitted with the shaft member. The more concrete problem to be solved is to fit a cup-formed hub onto the flanged shaft member in a manner not to deviate the dynamic pressure ring member press-fitted on the cylindrical member off a specified press-fit position.
In order to solve the above problem, a spindle motor has a liquid dynamic pressure bearing having a flanged shaft member formed by press-fitting a dynamic pressure ring member on a cylindrical member, a cylindrical receiving member rotatably receiving the flanged shaft member and an annular holding member press-fitted in an annular step formed in an opening end of said cylindrical receiving member; a rotor rotatably supported on a stator through the liquid dynamic pressure bearing having a fine gap between a lower end of the cylindrical member and a bottom surface of the cylindrical receiving member, and a hub structuring part of the rotor being press-fitted on the flanged shaft member; wherein the hub is press-fitted on the flanged shaft member by pulling an upper end of the cylindrical member through a mount hole of the hub while holding the hub.
Also, in a method for assembling a spindle motor having a liquid dynamic pressure bearing having a flanged shaft member formed by press-fitting a dynamic pressure ring member on a cylindrical member, a cylindrical receiving member rotatably receiving the flanged shaft member and an annular holding member press-fitted in an annular step formed in an opening end of said cylindrical receiving member; wherein a rotor is rotatably supported on a stator through the liquid dynamic pressure bearing having a fine gap between a lower end of the cylindrical member and a bottom surface of the cylindrical receiving member, and a hub structuring part of the rotor being press-fitted on the flanged shaft member, the method for assembling the spindle includes: a first step of arranging the flanged shaft member on the cylindrical receiving member; a second step of press-fitting the annular holding member in an opening end of the cylindrical receiving member; and a third step of press-fitting the flanged shaft member in the hub by pulling an upper end of the cylindrical member through a mount hole of the hub while holding the hub.
Furthermore, a hub press-fitting apparatus to be used in a method for assembling a spindle motor, i.e., an apparatus for press-fitting a hub on a flanged shaft member by a pulling force ins
Goto Hiromitsu
Iwaki Tadao
Iwamoto Mitsuharu
Kawawada Naoki
Suzuki Takafumi
Adams & Wilks
Mullins Burton
Seiko Instruments Inc.
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