Disk drive with a flat annular spring clamp and components dimensioned to maintain disk flatness

A disk drive with a drive motor having a spindle rotatable around an axis of rotation, one or more disks mounted on the spindle separated by annular spacers which have a radial dimension selected to maintain flatness of the disks, an annular ring dimensioned to distribute force evenly to the disks engaging the last mounted disk, a flat annular spring clamp for applying force uniformly to the annular ring, and a retaining member to hold the annular spring clamp in place.

FIELD OF THE INVENTION 
This invention relates to disk drives, and more particularly, to apparatus 
for mounting a disk or disks thereof to the spindle of a drive motor. 
BACKGROUND OF THE INVENTION 
A typical prior art structure for mounting disks of a disk drive to the 
spindle of a drive motor is shown in FIG. 1. As shown therein, a disk 
drive motor 20 includes a spindle 22 which is rotatable about an axis of 
rotation 24. A first disk 26 includes a central aperture 28 through which 
the spindle 22 is disposed, one side 30 of the disk 26 at its inner 
periphery being in contact with an annular spindle surface 32 which is 
perpendicular to the rotational axis 24 of the spindle 22. An annular 
spacer 34 is fitted about the spindle 22, and has a surface 36 
perpendicular to the axis of rotation 24 and in engagement with the inner 
periphery of the disk 26 on the opposite side 38 of the disk 26. Another 
disk 40 has a central aperture 42 through which the spindle 22 is 
disposed, the disk 40 at its inner periphery having one side 44 in 
engagement with surface 46 of the annular spacer 34, which surface 46 is 
perpendicular to the axis of rotation 24 of the spindle 22. A single-piece 
stamped or formed disk spring clamp 48 is fixed to the spindle 22 by means 
of screw 50 and has an annular portion of U-shaped cross section adjacent 
its outer edge 52 for engagement with the inner periphery of the disk 40 
on the opposite side 54, to force the disk 40 in a direction downward as 
shown in FIG. 1. 
It will be understood that one of the key parameters for optimum 
performance of disk drives is the flatness of the installed disks. In 
general, the best flatness is achieved when the disk is mated against very 
smooth, flat surfaces on both sides of the disk. 
Because of the configuration of the conventional disk spring clamp 48, when 
clamping force is applied to the surface 54 at the inner periphery of the 
disk 40, a small radial force is applied to the disk 40 (away from the 
axis of rotation 24) in addition to the forces parallel to the rotational 
axis 24. 
Several problems exist with the conventional disk spring clamp 48 of FIG. 
1. For example, surface finish and flatness is very difficult to achieve 
and maintain at the region where the disk spring clamp 48 contacts the 
disk 40. The forming or bending process of the disk spring clamp 48 often 
creates microcracks in the clamp 48 at the portion of U-shaped cross 
section that touches the disk 40. Furthermore, the clamping force applied 
to the disk 40 is not uniform. This is due to the anisotropic nature of 
rolled sheet stock used to form the clamp 48, the forming process itself, 
and the screw head torque warping the clamp 48 during installation. All of 
these forces are transmitted through to the disk 40. 
Furthermore, installation and application of the clamp 48 creates 
contamination and residual stresses. As the axial force is applied via the 
screw, the point at which the clamp contacts the disk translates and 
rotates due to the deflection being induced in the clamp 48. This relative 
motion galls the soft aluminum disk surface resulting in particulate 
formation. The resultant and residual radial force contributes to an 
out-of-flat disk. 
SUMMARY OF THE INVENTION 
The present invention overcomes the above-cited problems by providing a 
mounting structure for a disk (or disks) on a spindle of a disk drive 
motor. In a double disk structure, first and second disks are mounted to a 
spindle, with an annular spacer therebetween. An annular member is 
positioned on the second disk for contact with the second disk, and a 
spring member is fastened to the spindle so that the annular member is 
forced against the second disk to in turn force the second disk against 
the spacer, in turn forcing the first disk against the surface portion of 
the spindle. 
The engaging surfaces of the annular member, annular spacer and spindle are 
each perpendicular to the axis of rotation of the spindle, with each 
engaging surface of the annular spacer being flatter and wider than its 
associated engaging surface.

DESCRIPTION OF THE PREFERRED EMBODIMENTS 
With reference to FIG. 2, a disk drive motor 100 includes a spindle 102 
which is rotatable about rotational axis 104. The spindle 102 defines an 
annular surface 106 which is perpendicular to the axis of rotation 104. 
The spindle 102 is disposed through a central aperture 108 defined by a 
first disk 110. The disk 110 at its inner periphery has one side 112 
thereof in engagement with the surface 106. An annular spacer 114 is 
positioned about the spindle 102, and has a surface 116 perpendicular to 
the axis of rotation 104 and in engagement with the inner periphery of the 
disk 110 on the opposite side 118 of the disk 110. 
A second disk 120 is mounted to the spindle 102, with the spindle 102 
positioned in a central aperture 122 of the disk 120. The side 124 of the 
disk 120, adjacent the disk inner periphery, is in contact with the 
surface 126 of the spacer 114, which spacer surface 126 is also generally 
perpendicular to the rotational axis 104 of the spindle 102. 
An annular ring 128 defines a passage 130 through which a portion of the 
spindle 102 is positioned, the annular ring 128 defining a surface 132 for 
engagement with the side 134 of the disk 120 at the inner periphery of the 
disk 120, opposite the side 124. 
A spring clamp 136 includes a central aperture 138 through which a screw 
140 is positioned, which screw 140 is threadably engaged with the spindle 
102, the longitudinal axis of the screw 140 being coincident with the axis 
of rotation 104. The circular outer edge 142 of the spring clamp 136 mates 
with and bears against an annular step 144 defined by the annular ring 
128. 
It will be seen that by tightening the screw 140 into the spindle 102, 
force is applied by the spring clamp 136 uniformly to the annular step 144 
and thus to the annular ring 128 and against the surface 134 of the disk 
120, in a direction generally parallel to the rotational axis 104 of the 
spindle 102, bringing the surface 124 of the disk 120 against the surface 
126 of the spacer 114, in turn forcing the surface 118 of the spacer 116 
against the surface 118 of the disk 110, so that the surface 112 of the 
disk 110 is forced against the spindle surface 106. As will be seen, no 
appreciable radial force (i.e., force perpendicular to the axis of 
rotation 104) is applied by the annular ring 128 to the disk 120. 
Several important features of the invention are shown in more detail in 
FIGS. 3 and 4. 
As shown in FIG. 3, the width Y of the surface 116 of the spacer 114 is 
greater than the width X of the surface 106 of the spindle 102, as 
measured in a direction generally perpendicular to the rotational axis 104 
of the spindle 102. In addition, the surface 116 of the spacer 114 for 
contact with the disk can be made very flat, i.e., typically less than 0.1 
microns, and smooth, less than 0.2 microns, through a double grinding and 
lapping process. On the other hand, it is not readily possible to produce 
a spindle surface 106 with a similar flatness and finish because such 
surface 106 is inaccessible for conventional grinding and lapping 
techniques. 
FIG. 4 shows a series of radial surface finish traces (FIGS. 4a, 4b, 4c) 
taken along different radii for a typical surface 106 of the spindle 102. 
FIG. 5 shows a series of radial traces (FIGS. 5a, 5b) of a lapped spacer 
ring surface 116, taken along different radii. With reference to FIG. 6a, 
and with the dimension X (width) less than the dimension Y (width) as 
measured along a line perpendicular to the rotational axis 104, and 
further with the surface 116 being more flat than the surface 106, we 
assume that the force of clamping is applied by the surface 116 of the 
spacer 114 at points A.sub.1 and B.sub.1, these being the high points of 
the surface 116 of the spacer 114. The resultant force is applied to the 
disk 110 by the surface 106 of the spindle 102 at points C.sub.1 and 
D.sub.1, these being the high points of that surface 106. For purposes of 
analysis, this may be treated as a simple beam as shown in FIG. 6b. The 
forces applied would bend the beam (disk 110) until static equilibrium is 
reached or until the disk 110 would contact the spacer 114 at point 
E.sub.1. The end condition for the beam at that point would be an angle 
somewhere between .theta..sub.1 and zero, with .theta..sub.1 roughly 
described by a line between the points E.sub.1 and B.sub.1, i.e., 
.theta..sub.1 being reached when the point E.sub.1 is contacted. Since the 
flatness of the surface 116 of the spacer 114 is better than the flatness 
of the surface 106, this angle .theta..sub.1 would be near zero. 
FIG. 7a, shows the less desirable case where the dimension X (width) of the 
surface as 106.sup.1 measured along a line perpendicular to the rotational 
axis 104.sup.1 of the spindle 102.sup.1 is greater than the corresponding 
dimension Y (width) of the spacer 114.sup.1. 
A simple beam analyses of this structure is shown in FIG. 7b. The end 
condition of the angle .theta..sub.2 hereagain is constrained by the 
static forces or until the beam contacts the point E.sub.2. Again, because 
the surface 106.sup.1 is less flat than the surface 116.sup.1, the 
location of the point E.sub.2 is more variable on the surface 106.sup.1 
than on the surface 116.sup.1 of the spacer 114.sup.1 so that a much 
greater set of variable conditions exist when this analysis is applied to 
the multitude of radial lines around the surface 106.sup.1 than in the 
above mentioned case of a wider surface 116 (FIGS. 6a, 6b). 
It logically follows that a flatter, more uniform disk 110 surface is 
created from greater uniformity of clamping conditions in the situation 
described in FIGS. 6a, 6b. That is, the disk 110 tends to reference to the 
flatter, wider surface. 
A like analysis applies to the surface 126 of the spacer 114 and the 
surface 132 of the annular ring 128 in engagement with the disk 120. 
FIG. 8 shows two embodiments at FIGS. 8a and 8b for mounting a single disk. 
As shown therein, the apparatus described is quite similar to that shown 
in FIG. 2, but in this case, in FIG. 8a, a spacer 200 has a smooth surface 
202 for engagement with the disk surface 204 mounted about the spindle 
206, and has a surface 208 in engagement with the surface 210 of the 
spindle 206. A disk 212 is mounted to the spindle 206, with the spindle 
206 positioned in a central aperture 214 of the disk 212. An annular 
member 216 is mounted to the spindle 206 and has a surface 218 in 
engagement with the surface 220 of the disk 212, and a spring member 222 
is fixed to the spindle 206 by screw 223 previously described. The outer 
edge 224 of the spring member 222 presses against an annular step 226 of 
the ring 216 so that force is applied by the annular member 216 to the 
surface 220 of the disk 212 uniformly and generally parallel to the 
rotational axis 228 of the spindle 206. In addition, the width of the 
annular ring 216 as measured along a direction perpendicular to the 
rotational axis 228 is less than the width of the surface 202 of the 
spacer 200 as measured in that direction, and the surface 202 of the 
spacer 200 is more flat than the surface 218. Thus, the features and 
analyses described above apply with equal force here. 
With reference to FIG. 8b, this apparatus is similar to that shown in FIG. 
8a, but includes a disk 300 mounted to a hub 302 which is in turn mounted 
on the spindle 304. In this case, the spacer 306 surrounds the hub 302 for 
engagement with the disk 300. 
Because of the structure disclosed it will be seen that no radial force is 
applied to the disks as is the case with the previously described prior 
art. In addition, by fabricating the spring clamp and annular member from 
similar hardness steels, galling and contamination may be greatly reduced. 
Referring now to FIGS. 2 and 3, the spring clamp as at 136 is very easy and 
inexpensive to fabricate because it is essentially a flat stamped 
configuration. The spring clamp acts very much like an ideal spring. 
The force of clamping can easily be varied by adding more spring clamps or 
changing the thickness of the single spring clamp. Furthermore, the spring 
material can be made from a high strength material (not being a formed 
structure) which allows for accurate axial force control. 
Another embodiment of the invention is shown in FIGS. 9-11. 
With reference to FIG. 9, a disk drive assembly 400 includes a spindle 402 
which is mounted by ball bearings 404 to a shaft 406 so as to be rotatable 
about the axis 408 of the shaft 406. The spindle 402 defines an annular 
surface 410 which is perpendicular to the axis of rotation 408, the 
spindle 402 being disposed through a central aperture 412 defined by a 
first disk 414. The disk 414 at its inner periphery has one side 416 
thereof in engagement with the surface 410. An annual spacer 418 is 
positioned about the spindle 402, and has a surface 420 perpendicular to 
the axis of rotation 408 and in engagement with the inner periphery of the 
disk 414 on the opposite side 422 of the disk 414. 
A second disk 424 is mounted to the spindle 402, with the spindle 402 
positioned in a central aperture 426 of the disk 424. The side 427 of the 
disk 426, adjacent the disk inner periphery, is in contact with the 
surface 428 of the spacer 418, which spacer surface 428 is also generally 
perpendicular to the rotational axis 408 of the spindle 402. A second 
annular spacer 430 is positioned about the spindle 402, having a surface 
432 perpendicular to the axis of rotation 408 and in engagement with the 
inner periphery of the disk 424 on the opposite side 434 of the disk 424. 
A third disk 436 is mounted to the spindle 402, with the spindle 402 
positioned in a central aperture 438 of the disk 436. The side 439 of the 
disk 436, adjacent the inner periphery of the disk 436, is in engagement 
with the surface 441 of the spacer 430, which surface 441 is perpendicular 
to the axis of rotation 408. 
An annular ring 440 defines a passage 442 in which a portion of the spindle 
402 is positioned, the annular ring 440 defining a surface 444 for 
engagement with the side 446 of the disk 436 at the inner periphery of the 
disk 436, opposite the side 439. 
An annular spring member 448 (FIGS. 9 and 10) is disposed about the spindle 
402, and a single retaining member 450 in the form of a split ring 
resilient spring member (FIGS. 9 and 11) is disposed about the spindle 402 
and is seated in an annular channel 452 formed about the spindle 402. This 
single retaining member 450 surrounds the spindle 402 and, when so 
positioned, applies force to the spring member 448 so that the spring 
member 448 in turn applies force to the annular ring 440 to force the 
annular ring 440 against the side 446 of a disk 436. It will be seen that 
this force is applied uniformly to the annular ring 440 and thus to the 
side 446 of the disk 436 in a direction parallel to the rotational axis 
408 of the spindle 402, bringing the disks 414, 424, 436 and annular 
spacers 418, 430 together against the surface 410. 
As will be seen, no appreciable radial force (i.e., force perpendicular to 
the axis of rotation 408) is applied by the annular ring 440 to the disk 
436. 
In the ball bearing type design shown in FIG. 9, the clamping structure 
thus described allows the ball bearings 404 to be positioned as closely as 
possible to the top of the overall assembly, allowing increased space for 
motor windings and allowing use of large size bearings, capable of 
withstanding relatively great shock. 
As noted in FIG. 10, the spring member 448 in its free state is a flat 
disk, which can be produced by etching in order to eliminate burring, 
contamination and flatness issues which may arise if such part were to be 
produced by stamping. 
It has been found that a clamping force on the order of 40 to 50 pounds has 
proven efficient, with installed deflection of the spring member 448 in 
the range of 0.35 to 0.45 millimeters. 
The free shape of the retaining member 450 (FIG. 11) is chosen such that 
the inner diameter of the retaining member 450 will conform closely to the 
inner surface 451 of the channel 452 when installed. The retaining member 
450 is fabricated by etching for tighter tolerance control than could be 
achieved with stamping. 
The reaction load of the spring member 448 at 454 is applied to the spindle 
402 at a large radius around the spindle, as compared to the design of 
FIG. 2, so that bending distortion of the spindle 402 is minimized. 
The retaining member 450 is installed with the spring member 448 held in 
its deformed position by an assembly tool (not shown). The spindle 402 is 
supported by pins which are part of the assembly tool to prevent damage to 
the bearings 404 during the installation of member 450. Compared to the 
screw fastening described previously, particle contamination produced 
during retaining member installation is reduced since metal to metal 
sliding action is minimized. 
FIG. 12 shows yet another embodiment of the invention. 
FIG. 12 shows a system similar to that shown in FIG. 9, but with the 
spindle 500 being rotatably mounted to a fixed shaft 502 by means of axial 
fluid bearings as indicated at 504. This embodiment includes the annular 
ring 506, spring member 508 and retaining member 510 all as disclosed in 
FIG. 9. 
In this embodiment, it will be noted that the axial bearings 504 are 
packaged in an area allowing maximization of available motor winding 
space. 
The use of a single retaining member (in the form of a screw 140, 223 
threadably attached to the spindle with its longitudinal axis along the 
rotational axis of the spindle, as described above with reference to FIGS. 
2 and 8, or the single retaining member 450, 510 of FIGS. 9 and 12), 
assures a simple yet effective means for retaining disks on a spindle 
without application of radial force being applied to the disks. Each 
embodiment is of very compact and low-profile design, yet is highly 
effective in its intended function.