Dynamic magnetic information storage or retrieval – Record transport with head stationary during transducing – Disk record
Reexamination Certificate
2003-03-07
2004-12-14
Evans, Jefferson (Department: 2652)
Dynamic magnetic information storage or retrieval
Record transport with head stationary during transducing
Disk record
C384S123000
Reexamination Certificate
active
06831812
ABSTRACT:
BACKGROUND OF INVENTION
1. Field of the Invention
This invention generally relates to a method of manufacturing a thrust plate for a shaft in a dynamic pressure bearing, the shaft having an annular shaft body in which an outer peripheral surface thereof forms a portion of a radial bearing unit. More particularly, the present invention relates to a method of manufacturing a thrust plate that has an annular shape and a central hole formed therein into which the shaft body is fitted, and which has thrust surfaces formed on both end surfaces thereof that form a portion of a thrust bearing unit.
2. Background Information
A recording disk drive device for a hard disk and the like includes a spindle motor for rotatively driving a recording disk, and is concentrically disposed with respect to the recording disk. The spindle motor is primarily comprised of a stationary member to which a stator having an armature coil is fixed, a rotary member that is fixed to a rotor magnet that faces the stator, and a bearing mechanism that supports the rotary member in the stationary member such that the rotary member is freely rotatable with respect thereto.
A hydrodynamic bearing is used as the bearing mechanism in order to achieve higher speeds and lower vibration (noise). The hydrodynamic bearing is comprised of a lubricating fluid such as oil that is disposed in a small gap between the shaft and the sleeve, and a radial/thrust bearing unit that includes dynamic pressure generating grooves that are formed on opposite surfaces.
More specifically, a spindle motor for a hard disk drive in which a dynamic pressure bearing is used has been disclosed in Japanese Published Patent Application 2000-134897 and will be described below. This spindle motor is comprised of a stationary member, a rotary member, and a bearing mechanism that is provided therebetween.
The stationary member is comprised of a motor frame
10
that is fixed to the base of a hard disk drive, a cylindrical boss unit that is integral with the motor frame
10
and disposed such that it is concentric therewith, and a sleeve
14
that is fitted into and fixed to the inner peripheral surface of the cylindrical boss section. A stator
20
is fitted around the outer peripheral surface of the boss section and fixed thereto.
The rotary member is comprised of a rotor hub
16
, and a shaft
22
that is integral therewith. A recording disk is mounted on the rotor hub
16
. Furthermore, an annular rotor magnet
18
is mounted on the inner side of a lower portion of an outer peripheral wall of the rotor hub
16
, and faces the stator
20
in the radial direction. The shaft
22
is disposed such that it is capable of rotating inside the sleeve
14
, and herringbone shaped dynamic pressure generating grooves are formed on one or both of an outer peripheral surface of the shaft
22
and an inner peripheral surface of the sleeve
14
. The gap between both of these opposing surfaces is filled with a lubricating agent such as oil, thus forming a pair of vertically disposed radial dynamic pressure bearing units. A thrust plate (not labeled with a reference numeral) provided on the lower end of the shaft is housed in a lower end large diameter section of the sleeve
14
, and a thrust cover
12
is fitted into fixed to the lower end opening of a boss on the motor frame
10
so as to close the lower end large diameter section of the sleeve
14
. Herringbone shaped or spiral shaped dynamic pressure generating grooves are formed on one or both of the upper surface of the thrust plate and a thrust surface of the sleeve
14
that opposes the upper surface of the thrust plate. The gap between these opposing surfaces is filled with a lubricating agent to thereby form an upper thrust dynamic pressure bearing unit. Herringbone shaped or spiral shaped dynamic pressure generating grooves are formed on one or both of the bottom surface of the thrust plate and the thrust cover
12
that opposes the bottom surface of the thrust plate, and a gap between these opposing surfaces is filled with a lubricating agent to thereby form an lower thrust dynamic pressure bearing unit.
In a dynamic pressure bearing spindle motor constructed in this manner, when the coil of the stator
20
is supplied with electricity, rotational torque is generated by the electromagnetic interaction between a rotating magnetic field of the stator
20
and a multipolar magnetic field of the rotor magnet
18
, thereby rotating a rotary member which includes the rotor hub
16
, the shaft
22
and a rotation load (recording disk). During this rotation, the radial load of the rotary member is supported by the pair of vertically disposed radial dynamic pressure bearing units formed between the shaft
22
and the sleeve
14
, and the thrust load of the rotary member is supported by the pair of thrust dynamic pressure bearing units formed respectively between the thrust plate and the sleeve
14
and the thrust cover
12
.
However, in a dynamic pressure bearing as described above, the dynamic pressure bearing shaft forms both a radial dynamic pressure bearing unit on the shaft body and thrust dynamic pressure bearing units on both surfaces of the thrust plate. This configuration requires a highly precise perpendicular angle between the outer peripheral surface of the shaft body and the planes of the thrust plate. More specifically, the radial gap in the radial bearing unit between the outer peripheral surface of the shaft body and the inner peripheral surface of the sleeve is normally several &mgr;m, and the thrust gap in the thrust bearing units between both surfaces of the thrust plate and the sleeve and the thrust cover is normally about 10 &mgr;m. Thus, there is a need for the degree of precision in the perpendicular angle of the planes of the thrust plate relative to the axial center line of the shaft to be within several &mgr;m or less.
On the other hand, because the end portion of shaft body of the dynamic pressure bearing shaft disclosed in the aforementioned Japanese Published Patent Application 2000-134897 is press fit into and fixed to the central hole of the thrust plate, and the shaft body and the thrust plate are separate components, it will be more difficult to obtain a perpendicular angle between the thrust plate planes relative to the axial center line of the shaft body that it would be when the shaft is manufactured by cutting it from a unitary member and machining it. It is possible, however, to use a tool to secure the proper degree of precision during shaft body press fitting relative to the central hole of the thrust plate. In other words, if a sufficiently high degree of precision in the perpendicular angle of the central hole in relation to the thrust plate planes can be achieved (i.e., a degree of precision of several &mgr;m or less), a dynamic pressure bearing with good rotation run-out precision can be obtained.
Accordingly, we will now look at the problems with the perpendicular angle of the central axis in relation to the surface planes of the thrust plate. In situations in which a spindle motor rotatively drives a recording disk that is, for example, 3.5 inch in diameter, a thrust plate having an outer diameter of 7 to 8 mm, an inner diameter of 4 mm, and a thickness of 2 to 3 mm will be employed, and is normally obtained by press forming.
A machining process that uses press cutting (shearing) to obtain an inner peripheral surface of a blank intermediate will produce sheared surfaces, ruptured surfaces, and/or turned up edges (burrs) on the press-cut surfaces. Thus, at the last step of machining, it will be necessary to both finish the inner and outer peripheral surfaces, and to finish both end surfaces. In this situation, it is difficult to reliably obtain a sufficient degree of precision even when the inner and outer peripheral surfaces are finished, and thus it will be difficult to reliably obtain a sufficient degree of precision in the perpendicular angle of the central axis relative to the surface planes of the thrust plate.
Next, a machining process which uses a coining step
Sode Takayuki
Yoshizawa Kenji
LandOfFree
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