Electrical generator or motor structure – Dynamoelectric – Rotary
Reexamination Certificate
1996-10-24
2001-11-13
Tamai, Karl (Department: 2834)
Electrical generator or motor structure
Dynamoelectric
Rotary
C310S156210, C310S156050, C360S098070, C360S099080
Reexamination Certificate
active
06316853
ABSTRACT:
The present invention relates generally to disc drives. More particularly, an improved spindle motor assembly is described.
BACKGROUND OF THE INVENTION
Disc drives for modern desktop computer systems record and reproduce information on a recording medium. The medium generally takes the form of a stack of circular information storage discs having a multiplicity of concentric tracks. Conventional Winchester type disc drives include a disc stack having one or more vertically aligned information storage discs which are journaled about the hub portion of a single spindle assembly. Each disc has at least one associated magnetic head that is adapted to transfer information between the disc and an external system. The heads are typically arranged to move back and forth radially across the disc and a spindle motor assembly is provided to rotate the discs. The movements of the spindle and the magnetic heads cooperate to allow random access to any portion of the disc.
Although disc drives are a relatively old and established technology, consumer demands continuously push for more compact, higher capacity, faster accessing designs. One of the size limiting components in traditional designs has been the spindle motor assembly used to rotate the information storage discs.
A conventional spindle motor assembly used in disc drive applications is shown in FIG.
1
. As seen therein, traditional spindle motor assemblies typically include a non-rotating spindle flange
100
that is securely fastenable to the drive housing. A rotatable spindle hub
106
is journaled about spindle flange
100
, and is carried by an elongated rotatable shaft
112
that extends co-axially with the hub and flange. A pair of spaced apart ball bearings
115
are coupled between the shaft and flange to allow the spindle shaft
112
to rotate freely within the confines of spindle flange
100
. A motor
118
is disposed directly underneath the spindle arrangement such that the motor components are located outside of the disc housing when the drive is assembled. The motor
118
includes a stator assembly
121
and a rotor assembly
124
. The stator assembly includes a plurality of lamination stacks each having a winding wrapped thereabout. The rotor assembly
124
is attached to the spindle shaft by a lower hub
127
. It includes a cup shaped rotor cap
130
, a raised annular flange portion
132
with a plurality of magnets
133
disposed about the interior surface of the flange. Such an arrangement does not readily lend itself to miniaturization when used in conventional disc drives, since it has numerous components having large airspaces therein. Further, mere reduction in component size tends to weaken the component's structure, which tends to lead to faster wear and to lower the mechanical resonance frequencies of the motors. Such mechanical resonances generate acoustic noises which are irritating to users and therefore are preferably minimized.
One spindle motor design approach that has better space utilization than the traditional design incorporates an in-hub motor, as shown in FIG.
2
. In this approach, a fixed shaft
150
is provided about which a spindle hub
152
is journaled. A pair of spaced-apart ball bearings
154
,
155
are mounted directly between the fixed shaft and the rotatable hub
152
. The rotor magnets
156
are carried directly by the spindle hub
152
, and the stator windings
157
are disposed between the spaced apart ball bearings
154
,
155
. Although such a design is more compact than the traditional design described above, it suffers a drawback in that the bearings
154
,
155
and the windings
157
compete for space within the hub region. This is not a particular problem in high profile disc drives, since there is ample room to provide sufficiently sized bearings and stator windings. However, in low profile disc drives, either the size (and strength) of the bearings or the size (and power) of the stator windings must suffer. Such a sacrifice is unacceptable for high quality, high performance disc drives.
Yet another recent approach is shown in FIG.
3
. In this approach, a fixed shaft
170
is again used and the spindle hub
172
has a cup-shaped radial cross section. The bearings
174
,
175
are placed between the shaft
170
and an inner wall
171
of the spindle hub
172
. The hub has a large U-shaped trough
176
outside of the inner wall, and motor components are positioned within the enlarged trough
176
. Specifically, the rotor magnets
178
are carried by an outer wall
179
of the spindle hub while the stator windings
181
are carried by a support ring
183
extending upward from the motor housing's base within the U-shaped trough. While such an arrangement allows adequately-sized bearings and stator windings, it requires a disc with a large inner diameter, since the hub must be quite large.
In view of the drawbacks of the prior art designs, there is a need for a compact spindle motor design that is capable of providing the performance required by state-of-the-art disc drives.
SUMMARY OF THE INVENTION
Accordingly, it is a primary objective of the present invention to provide a compact spindle motor assembly that is relatively significantly smaller and adaptable for use in a low-profile disc drive.
Another objective is to provide a high torque spindle motor assembly that is rugged, easy to manufacture, and has a small parts count.
To achieve the foregoing and other objectives, and in accordance with the purpose of the present invention, a novel spindle motor assembly is disclosed that utilizes a fixed shaft and places the motor components on the outside wall of the spindle hub directly below its flange. More specifically, the disclosed spindle motor assembly for disc drives includes a fixed shaft having a spindle hub journaled coaxially thereabout. The spindle hub has several distinct portions including an enlarged thickness flange portion which support the drive's disc stack, and a reduced thickness rotor carrying portion located adjacent the side of the flange opposite the disc stack. A pair of spaced apart bearings rotatably couple the spindle hub to the fixed shaft, with each of the bearings having its inner race secured to the fixed shaft and its outer race secured to the inner surface of the spindle hub. The rotor assembly includes a magnetic arrangement having a number of poles, and is carried by the outer surface of the rotor carrying portion of the spindle hub. The stator has a plurality of fixed windings that cooperate with the rotor to rotate the spindle hub (and thus the disc stack) with the shaft. The stator assembly is preferably substantially positioned within the space defined by the hub's flange and rotor carrying portions.
In a preferred embodiment, Hall effect sensors are set in a fixed place adjacent the rotor magnet to detect the passage of the poles to control commutation. To improve the Hall effect sensors' sensitivity, the magnet is magnetized to establish two nonparallel flux regions for each pole.
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Seagate Technology LLC
Tamai Karl
Thomason Moser & Patterson LLP
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