Bearings – Rotary bearing – Fluid bearing
Reexamination Certificate
2001-08-07
2004-06-15
Lavinder, Jack (Department: 3683)
Bearings
Rotary bearing
Fluid bearing
Reexamination Certificate
active
06749339
ABSTRACT:
TECHNICAL FIELD
This invention relates to a hydrodynamic bearing assembly, and in particular, relates to the hydrodynamic bearing assembly incorporated with a spindle motor used for driving a memory device such as a hard disk drive (referred to as a “HDD”, hereinafter), or bar code reader. This invention also relates to the spindle motor including the hydrodynamic bearing assembly, as well as the memory device and the bar code reader including the spindle motor.
BACKGROUND ART
The conventional spindle motors used for driving the memory device such as the HDD or a bar code reader, includes a hydrodynamic bearing assembly implementing high rotation in a stable manner for a long effective lifetime. Among various features of the hydrodynamic bearing assembly, since rotational member and stationary member of the hydrodynamic bearing assembly operate without contact to each other, the rotation thereof causes mechanical friction therebetween less than that of another contacting type of the bearing assemblies such as a ball bearing. In comparison with the hydrodynamic bearing assembly using oil for generating dynamic pressure, in particular, the hydrodynamic bearing assembly using gas as fluid has further advantages to reduce the coom caused by shattering lubricant such as oil and grease in addition to the reduced friction.
FIG. 42
shows an exemplary spindle motor with a conventional hydrodynamic bearing assembly. In the drawing, the hydrodynamic bearing assembly comprises, on a base plate
200
, a column shaft
201
, a sleeve
202
rotatably arranged around the shaft
201
leaving a predetermined gap along the axis direction of the shaft
201
for relative rotation therebetween. The hydrodynamic bearing assembly also comprises a thrust plate
202
, which is arranged perpendicular to the shaft
201
and opposes to the bottom surface of the sleeve
202
. A radial bearing is formed between an outer surface of the shaft
201
and the inner surface of the sleeve
202
. Also, a thrust bearing is formed between the bottom surface of the sleeve
202
and the thrust plate
203
. The thrust plate
203
includes grooves
205
for generating thrust dynamic pressure, formed on the surface opposing to the bottom surface of the sleeve
202
, as illustrated by a dashed line.
In this specification, the bottom surface opposing to the thrust plate
203
and defining the thrust bearing in cooperation therewith is referred to as a thrust opposing surface. In
FIG. 42
, one of the end surfaces in the axis direction is the thrust opposing surface
204
. A rotor
207
attached with the sleeve
202
can be rotated about the shaft
201
with the sleeve
202
. The rotor
207
has a rotor magnet
208
arranged on the inner surface of a skirt
207
a
of the rotor
207
. The rotor magnet
208
opposes to the electromagnet
209
arranged on the base plate
200
. In case of the HDD, a plurality of memory media are mounted on the outer surface, also in case of the bar code reader, a polygonal mirror is mounted on the rotor
207
, both of which rotate with the rotor
207
.
According to the spindle motor constructed as described above, an alternating current supplied to the electromagnet
209
causes the attraction and/or repulsion forces between the electromagnet
209
and the rotor magnet
208
. This provides the rotor
207
supporting the rotor magnet
208
with a rotation drive force so that the rotor
207
and the sleeve
202
attached therewith together rotate around the axis of the shaft
201
. The rotation causes the relative movement between the shaft
201
and sleeve
202
, generating the radial dynamic pressure due to the fluid in the radial bearing. In general, although air is often used for the fluid intervening between the shaft
201
and sleeve
202
when the spindle motor is used in the atmosphere, particular gas or oil may be used as the fluid. In this specification, the intervening object for generating the dynamic pressure is referred to as the “fluid”. The aforementioned rotation also causes the relative movement between the thrust opposing surface
204
of the sleeve
202
and the thrust plate
203
, thereby generating another dynamic pressure in a thrust direction due to the grooves
205
. To this end, this thrust dynamic pressure allows the rotational member such as sleeve
202
and rotor
207
to rotate about the shaft
201
keeping the rotational member away from the stationary member such as shaft
201
and the base
200
.
FIG. 43
shows the thrust grooves
205
formed on the surface of the thrust plate
203
for generating the thrust dynamic pressure in the thrust bearing. As shown, the grooves
205
include a plurality of a spiral groove, each of which is angled at a predetermined angle with the circle on the thrust plate
203
, and has a depth in a range of 1 micron through 10 microns. The thrust opposing surface
204
of the sleeve
202
rotates in a direction indicated by the arrow
206
against the grooves
205
so that the fluid such as air is convolved in the grooves
205
. The fluid is pressed along the spiral grooves
205
towards the axis due to the viscosity of the fluid during the above-mentioned rotation, hereby to generate the pressure (dynamic pressure). This dynamic pressure operates the thrust opposing surface
204
to push up the rotational member such as sleeve
202
. Such bearing assembly, which conducts the fluid from the circumference towards the axis of the thrust bearing assembly to generate the dynamic pressure, is referred to as a “pump-in” bearing assembly. The pump-in bearing assembly is commonly used for the hydrodynamic bearing assembly.
A need has been existed in the market to a compact and lightweight hydrodynamic bearing assembly implementing the rotation at high rate and heavy load in a stable manner. There are some problems to be solved for the hydrodynamic bearing assembly to satisfy such market's needs. Firstly, the rotation should be stable in particular at the high rotation rate. Secondary, the bearing assembly should have a certain rigidity sufficient to bear against the oscillation forces provided from external circumstances. Thirdly, the bearing assembly has to be improved in the activation feature to activate rotation of the rotational member in contact with the stationary member. Fourthly, the bearing assembly should be more compact and lightweight. Details for those problems to be solved will be described hereinafter.
(First Problem)
In order to address the first problem, i.e., to realize the high rotation rate in a stable manner, it is necessary to eliminate a phenomenon, so-called half-whirl. The half-whirl is the phenomenon appeared due to the rotation of sleeve
202
relative to the shaft
201
with a predetermined gap for keeping thereof away to each other. The fluid intervening between the outer surface of the shaft
201
and the inner surface of the sleeve
202
for generating the dynamic pressure causes a continuous pressure distribution therebetween due to the relative rotation. When the external disturbance causes either one of the shaft
201
or sleeve
202
to deflect from the rotation axis, the force due to the dynamic pressure is offset to the rotation axis so that the horizontal component of the force revolves the rotational member around the rotation axis without returning the rotational member to its original position. The convergence of the revolution returns the rotational member to the original position so that the rotational member rotates in a stable manner. On the contrary, if the revolution is kept, the rotational member whirls around the central axis of the stationary member resulting in the unstable rotation. This phenomenon is referred to as the half-whirl. The present inventors have discovered that the revolution is likely to be kept with the bearing assembly having the continuous pressure distribution in comparison with one having a discontinuous pressure distribution.
FIG. 44
schematically illustrates the half-whirl phenomenon, showing a cross section along the rotation axis of the stationary shaft
201
and t
Komura Osamu
Murabe Kaoru
Otsuki Makoto
Takeuchi Hisao
Lavinder Jack
McDermott & Will & Emery
Nguyen Xuan Lan
LandOfFree
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