Disc clamp with head clearance

The present invention includes a data disc support assembly for supporting a data disc relative to a head so data on a surface of the disc is accessible by the head. The support assembly includes a hub which has first and second axial ends and a flange extending from the second axial end. The flange supports the data disc. A clamp is connected to the hub to rigidly connect the data disc to the hub. The clamp has a first generally annular portion contacting the data disc and a second generally annular portion extending axially away from the hub beyond the first annular portion. The second annular portion is spaced from the data disc by a distance greater than the height of the head.

BACKGROUND OF THE INVENTION 
The present invention relates to disc drives. More particularly, the 
present invention relates to a device for clamping discs to a hub in a 
disc drive. 
A typical disc drive includes one or more magnetic discs mounted for 
rotation on a hub or spindle. Where more than one magnetic disc is used, 
the discs are spaced apart from one another axially along the hub by 
spacers mounted between the discs. Conventional hubs typically include a 
flange portion which extends from one of the axial ends of the hub. The 
discs and spacers are placed concentrically about the hub and supported by 
the flange portion of the hub. The plurality of magnetic discs and the 
spacers are clamped down onto the flange portion of the hub using a clamp 
which is placed on the axial end of the hub, opposite the flange. Thus, 
the discs and spacers are all clamped to the hub for rotation with the hub 
about an axis of rotation generally defined by the radial center of the 
hub. 
A typical magnetic disc drive also includes a transducer supported by a 
hydrodynamic air bearing which flies above each magnetic disc. The 
transducer and hydrodynamic air bearing are collectively referred to as a 
data head. A drive controller is conventionally used for controlling the 
disc drive system based on commands received from a host system. The drive 
controller controls the disc drive to retrieve information from the 
magnetic discs and to store information on the magnetic discs. 
An electromechanical actuator operates within a negative feedback, 
closed-loop servo system. The actuator moves the data head radially over 
the disc surface for track seek operations and holds the transducer 
directly over a track on the disc surface for track following operations. 
Information is typically stored on the magnetic discs by providing a write 
signal to the data head to encode flux reversals on the surface of the 
magnetic disc representing the data to be stored. In retrieving data from 
the disc, the drive controller controls the electromechanical actuator so 
that the data head flies above the magnetic disc, sensing the flux 
reversals on the magnetic disc and generating a read signal based on those 
flux reversals. The read signal is then decoded by the drive controller to 
recover the data represented by flux reversals stored on the magnetic 
disc, and consequently represented in the read signal provided by the data 
head. 
As industry pressure requires disc drives to be reduced in size, the axial 
height of the hub, and consequently the axial height of the entire disc 
file, becomes critical. In past systems, the clamp used to hold the discs 
in place about the hub was screwed onto the hub with screws running in the 
axial direction. However, since the axial height of the hub has become 
critical, the screws used to fasten the clamp to the hub take up an 
undesirable amount of axial space. 
Therefore, a heat shrink clamp was developed. Such a clamp is described in 
greater detail in U.S. Pat. No. 4,639,802. Such clamps typically include a 
clamp ring which has an inner diameter that is slightly smaller than the 
outer diameter of one axial end of the hub. The clamp ring is responsive 
to thermal energy and expands when thermal energy is applied to it and 
contracts when thermal energy is removed from it. Therefore, to assemble 
the clamp ring to the hub, the clamp ring is first heated, thereby 
expanding such that the inner diameter of the clamp ring is slightly 
larger than the outer diameter of the hub. The clamp ring is then placed 
about the hub and allowed to cool to establish a frictional fit with the 
outer surface of the hub. 
Just prior to placing the clamp on the hub, the plurality of discs and 
spacers arranged about the hub are subjected to an axial load. The clamp 
ring is put in place and allowed to form its frictional fit before the 
axial load is removed. Thus, the clamp ring clamps the spacers and the 
magnetic discs to the flange located at the second axial end of the hub. 
Such thermally responsive clamps eliminated the need for screws to hold the 
discs in place about the hub. Thus, such clamps have been effective in 
reducing the overall axial height of the disc file. However, the load 
which can be supported by such clamps is directly dependent upon the 
cross-sectional area (i.e., the volume) of the clamp. In disc drives which 
have four discs, the load which the clamp must support is essentially 
twice that of disc drives which have only two discs. Therefore, the 
cross-sectional area of the clamp must double. In order to double the 
cross-sectional area of the clamp without increasing the axial height of 
the clamp, the clamp must be made thicker, in a radial direction, 
extending away from the hub. However, increasing the distance that the 
clamp extends radially away from the hub causes the clamp to cover the 
inner radii of the disc surface over which the clamp is located. This 
reduces useable disc space and hence storage capacity of the disc drive. 
SUMMARY OF THE INVENTION 
The present invention includes a data disc support assembly for supporting 
a data disc relative to a head so data on a surface of the disc is 
accessible by the head. The support assembly includes a hub which has 
first and second axial ends and a flange extending from the second axial 
end. The flange supports the data disc. A clamp is connected to the hub to 
rigidly connect the data disc to the hub. The clamp has a first generally 
annular portion contacting the data disc and a second generally annular 
portion extending axially away from the hub beyond the first annular 
portion. The second annular portion is spaced from the data disc by a 
distance greater than the height of the head.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
FIG. 1 is a cross-sectional view of a rigid magnetic disc support assembly 
10. Support assembly 10 includes hub 12, first rigid magnetic disc 14, 
second rigid magnetic disc 16, spacer 18 and clamp ring 20. Hub 12 
includes first axial end 22 and second axial end 24. An annular flange 26 
is generally disposed at second axial end 24 and is preferably formed 
integrally with hub 12. Discs 14 and 16 are concentrically arranged about 
an exterior surface 28 of hub 12. Discs 14 and 16 are spaced apart axially 
along the exterior surface 28 of hub 12 by spacer ring 18. Clamp ring 20 
is connected, via a frictional fit, to second end 22 of hub 12. Clamp ring 
20 contacts a surface of disc 16 capturing discs 14 and 16 and spacer 18 
between clamp ring 20 and flange 26 about hub 12. 
In the embodiment shown in FIG. 1, clamp 20 is a thermally responsive heat 
shrink clamp which is assembled onto hub 12 by applying thermal energy to 
clamp 20, placing it on exterior surface 28 of hub 12, and allowing it to 
cool and thereby form a frictional fit with hub 12. Thermally responsive 
clamp 20 has worked adequately for systems in which only two discs were 
used. However, in systems in which more than two discs are used, the 
clamping load which must be exerted by clamp 20 in order for assembly 10 
to perform properly increases. In order to increase the clamp load exerted 
by clamp 20, the cross-sectional area (and hence the volume), of clamp 20 
must also be increased. For example, in a system in which four discs are 
to be mounted on hub 12, the clamping load which clamp 20 is required to 
exert roughly doubles. Therefore, the cross-sectional area of clamp 20 
must also double. 
FIG. 1A shows a prior art system in which four discs are carried by hub 12. 
In the system shown in FIG. 1A, clamp ring 20' is shown clamped to the 
first axial end 22 of hub 12. While hub 12 shown in FIG. 1A carries four 
magnetic discs, only one (disc 16') is shown for the sake of clarity. 
Since hub 12 is now carrying twice the number of discs as hub 12 shown in 
FIG. 1, clamp ring 20' must exert roughly twice the clamping force of 
clamp ring 20. Thus, the cross-sectional area of clamp ring 20' is roughly 
twice that of clamp ring 20. While the present figures are not drawn to 
scale, it will be recognized that in order to increase the cross-sectional 
area of clamp ring 20' by a factor of two over that of clamp ring 20, 
without increasing the axial height of clamp ring 20' over that of clamp 
ring 20, the radial dimension of clamp ring 20' must be doubled. However, 
this requires clamp ring 20' to extend well out onto the surface of the 
disc 16' with which it is in contact. This covers the inner radii of disc 
16' thereby consuming disc space and storage capacity of the disc drive in 
which the assembly is used. 
FIG. 2 shows disc support assembly 30 of the present invention. Support 
assembly 30 includes hub 32, magnetic discs 34, 36, 38 and 40, spacers 42, 
44 and 46, and clamp 48. FIG. 2 also illustrates a data head 50 coupled to 
a portion of a flexure arm 52. Hub 32 has a first axial end 54 and a 
second axial end 56. A flange 58 is generally disposed at the second axial 
end 56 of hub 32. In the preferred embodiment, flange 58 is integrally 
formed with the remainder of hub 32. Discs 34, 36, 38 and 40 (which in the 
preferred embodiment are rigid magnetic discs) are concentrically disposed 
about an outer surface 60 of hub 32, and are separated by spacers 42, 44 
and 46. Spacers 42, 44 and 46 are also generally concentrically disposed 
about the outer surface 60 of hub 32. Discs 34, 36, 38 and 40, as well as 
spacers 42, 44 and 46 are supported by flange 58. In assembly, the discs 
and spacers are placed concentrically about surface 60 of hub 32 and an 
axial load is applied holding the discs and spacers against flange 58. 
Then, clamp 48 is clamped to first axial end 54 of hub 32 retaining at 
least a portion of the axial load applied prior to the assembly of clamp 
48 onto hub 32. By retaining this load, clamp 48 captures discs 34, 36, 38 
and 40 as well as spacers 42, 44 and 46 between itself and flange 58 
thereby securing all portions of assembly 30 for rotation with hub 32 
about axis 62. 
In the preferred embodiment, clamp 48 is a thermally responsive clamp which 
has an inner diameter slightly smaller than the outer diameter of hub 32. 
Upon applying thermal energy to clamp 48, it expands so that its inner 
diameter is slightly larger than the outer diameter of hub 32. Clamp 48 is 
then placed over second axial end 54 of hub 32 and allowed to cool. Upon 
cooling, clamp 48 shrinks to its original size thereby establishing a 
frictional fit between its inner diameter and the outer diameter of hub 32 
at second axial end 54. 
Also, in the preferred embodiment, clamp 48 includes a body portion 63 and 
a ring portion 64. Body portion 63 has a lower surface which contacts disc 
40. Ring portion 64 has a lower surface which is spaced from disc 40. 
Thus, body portion 63 and ring portion 64 define a notch 65 which is large 
enough to accommodate data head 50 flying above the surface of disc 40. In 
this manner, while the volume of clamp 48 is twice that of clamp 20 (shown 
in FIG. 1), and while this allows clamp 48 to exert double the clamping 
load of clamp 20, clamp 48 consumes no more disc space (and hence no more 
disc drive memory capacity) than clamp 20. Further, clamp 48 has no 
greater axial height than clamp 20 and therefore does not increase the 
overall axial height of the disc file assembled onto support assembly 30. 
Thus, clamp 48 provides significant advantages over prior disc clamps. 
FIG. 2A shows an enlarged cross-sectional view of clamp 48. In the 
preferred embodiment, ring portion 64 has a lower surface 64' which, when 
clamp 48 is assembled, is approximately 0.031 inches above the surface of 
disc 40. Also, in the preferred embodiment, the overall height H of clamp 
48 is approximately 0.052 inches. Since the head is only typically 15 mils 
in height, it can easily slide below ring portion 64 through notch 65. 
Finally, in the preferred embodiment, clamp 10 is formed of 430 annealed 
stainless steel having 25% minimum elongation and 0.2% minimum yield 
strength. 
FIG. 2A also illustrates that clamp 48 preferably has a cylindrical axial 
opening 70 which has a lower end 72 defined by a chamfered periphery. The 
chamfered periphery of lower end 72 provides for easier assembly of clamp 
48 over second end 54 of hub 32. 
FIG. 2B illustrates another embodiment of the present invention. FIG. 2B 
shows a portion of support assembly 30 with a modified clamp 48'. Clamp 
48' includes annular ring portion 64 and notch 65. However, body portion 
63 of clamp 48' is modified to include a second notch 68. Notch 68 is 
defined by two fingers 70 and 72 in body portion 63. Finger portion 70 
contacts the exterior surface 60 of hub 32 while finger portion 72 
contacts the surface of disc 40. Finger portion 72 is spaced from the 
exterior surface 60 of hub 32 in a radial direction. By radially spacing 
finger portion 72 from surface 60, the load applied to disc 40 is more 
evenly distributed to avoid coning or warping of disc 40 under the load 
applied by clamp 48'. The radial distance by which finger portion 72 is 
spaced from surface 60 will vary depending upon the axial load applied by 
clamp 48', but is preferably optimized to minimize coning of disc 40. 
FIG. 3 is a cross-sectional view of a portion of disc support assembly 30 
showing another embodiment of the present invention. Similar items are 
similarly numbered to those shown in FIG. 2B. In the preferred embodiment 
shown in FIG. 3, clamp 74 is provided for applying the clamping load to 
the remainder of assembly 30. As with clamps 48 and 48', clamp 74 is a 
thermally responsive clamp which is heated and expanded to fit over hub 
32. Clamp 74 is then allowed to cool forming a frictional fit with hub 32. 
Clamp 74 has an annular ring portion 76 which extends about the exterior 
surface 60 of hub 32. Clamp 74 also has a connecting portion 78 which 
extends across substantially the entire first axial end 54 of hub 32. 
Connecting portion 78 also preferably has a central aperture for 
communicating with the center of hub 32. Annular ring portion 76 extends 
axially away from hub 32 no further than body portion 63 of clamp 48. 
Thus, as with clamp 48, clamp 74 does not consume any additional space on 
the surface of disc 40. Rather, connecting portion 78 is provided to 
increase the cross-sectional area of clamp 74 to facilitate application of 
the increased axial load required for clamp 74 to connect more than two 
discs to hub 32. 
Clamp 74 is preferably used in systems in which disc space is more critical 
than the axial height of the disc file. In the alternative, the first 
axial end 54 of hub 32 can be reduced to accommodate the added height of 
connecting portion 78 so that the overall axial height of the disc file in 
support assembly 30 is within acceptable limits. 
FIG. 3A illustrates another embodiment of the present invention having 
modified clamp 74'. As with clamp 48' (shown in FIG. 2B), clamp 74' is 
provided with a pair of notches 65' and 68'. Notch 65' is provided to 
further increase the disc space available on disc 40. Notch 65' is 
dimensioned to allow data head 50 to pass within notch 65', below the 
radial outer diameter of connecting portion 78. Notch 68' is provided to 
space the portion of clamp 74' which contacts disc 50 from the outer 
surface 60 of hub 32. This causes favorable distribution of the axial load 
applied by clamp 74' to reduce coning or other deformation of disc 40 
caused by the applied axial load. 
FIG. 4 shows another preferred embodiment of the present invention 
including modified hub 32' and clamp 80. Modified hub 32' is provided with 
an annular notch in first axial end 54. Clamp 80 has a body portion 82 and 
an axially inwardly extending finger portion 84. As with clamps 48 and 74, 
clamp 80 is a thermally responsive clamp which expands to fit over the 
exterior surface 60 of hub 32' and the notch in the first axially end 54 
of hub 32'. When clamp 80 is allowed to cool, it forms a frictional fit 
with hub 32'. 
Finger portion 84 extends into, and mates with, the notch in the first 
axial end 54 of hub 32'. Finger portion 84 thus increases the 
cross-sectional area of clamp 80 without either increasing the axial 
height of clamp 80, or increasing the distance by which clamp 80 extends 
radially out onto the surface of disc 40. Clamp 80 is capable of exerting 
the axial load required to clamp an increased number of discs in assembly 
30 without increasing the axial height of assembly 30 and without 
consuming disc space on disc 40. 
FIG. 4A illustrates another preferred embodiment of the present invention 
which includes modified clamp 80'. As with clamp 80, clamp 80' includes 
body portion 82 and finger portion 84. Finger portion 84 mates with the 
annular notch in the first axial end 54 of hub 32'. However, body portion 
82 is provided with a first notch 86 and a second notch 88. Notch 86 is 
preferably dimensioned such that head 50 can pass through notch 86 when 
flying over the surface of disc 40. Notch 88 is provided to space body 
portion 82 from the exterior surface 60 of hub 32' to better distribute 
the load applied by clamp 80' to reduce coning or other warping of disc 
40. 
The present invention provides a support assembly 30 that includes a hub 
about which a plurality of discs are concentrically arranged. The hub has 
a first axial end 54 and a second axial end 56. A support member is 
disposed about second axial end 56 to support the discs. A clamp is 
disposed about the first axial end 54 of the hub to hold the discs in 
place and rigidly attach them for rotation with the hub about axis 62. The 
clamp has increased cross-sectional area to facilitate provision of an 
increased axial load without consuming additional disc space. In addition, 
the clamp preferably has increased cross-sectional area without increasing 
the axial height of assembly 30. 
Although the present invention has been described with reference to 
preferred embodiments, workers skilled in the art will recognize that 
changes may be made in form and detail without departing from the spirit 
and scope of the invention.