Disc clamp assembly for a disc drive

A disc clamp assembly is provided for securing a plurality of information storage discs to a spindle hub on a disc drive spindle motor assembly. The disc clamp assembly includes a clamping ring and a resilient grip ring. The clamping ring has a raised Inner portion and rests on the information storage disc. The resilient grip ring has an inner diameter smaller than the diameter of the spindle hub, a middle portion to receive an axial force and a means for receiving radial force. The middle portion of the grip ring rests on the raised inner portion of the clamping ring. While the means for receiving radial force of the grip ring receives a radial force to radially expand the grip ring, the middle portion of the grip ring receives an axial force and applies the axial force to the clamping ring and the information storage discs. Upon removal of the radial force to the grip ring, the grip ring maintains the axial force applied to the information storage discs by gripping the spindle hub.

The present invention relates generally to an improved disc clamp for 
securing rotational information storage discs within disc drives. 
BACKGROUND OF THE INVENTION 
Disc drive machines record and reproduce information stored on a recording 
media. Conventional Winchester-type disc drives include a plurality of 
vertically-aligned, rotating information storage discs, each having at 
least one associated magnetic head that is adapted to transfer information 
between the disc and an external computer system. The information storage 
discs are journaled about a spindle motor assembly capable of rotating the 
discs at high speeds. The heads are carried by a plurality of 
vertically-aligned, elongated flexure arms that in turn are carried by a 
head positioner assembly. The head positioner assembly is adapted to move 
the heads back and forth in unison across the face of the 
vertically-aligned, elongated flexure arms that in turn are carried by a 
head positioner assembly. The head positioner assembly is adapted to move 
the heads back and forth in unison across the face of the 
vertically-aligned discs. The head positioner assembly are traditionally 
either rotationally mounted, or take the form of a carriage that is free 
to move back and forth along a single axis. In either case, the head 
positioner assembly is adapted to precisely position the heads relative to 
the magnetic information storage discs. 
The spindle motor assembly includes a rotatable spindle hub that is carried 
by a fixed spindle shaft securely mounted to the housing. A plurality of 
information storage discs are journaled about the spindle hub. Spacer 
discs are provided between adjacent information storage discs. The 
vertically aligned information storage discs are clamped to the spindle 
hub by a disc clamp secured by a plurality of screws. 
In practice, the disc clamp design is quite critical to high performance 
disc drives and there are several design criteria that must be met in 
order to provide an effective disc clamp. Specifically, the disc clamp 
must provide a uniform clamping force along its clamping surface to avoid 
such problems as top disc distortion. The clamp must also be designed to 
uniformly distribute its internal stress in order to minimize clamping 
force variations due to thermal expansions. Similarly, to facilitate 
installation and repair of the discs, it is important that resultant 
stress distribution within the clamp be relatively independent of the 
sequence in which the clamp screws are attached and the magnitude of the 
intermediate torques applied during installation. 
Another drawback of many prior art disc clamps is that the screws that 
secure the disc clamp to the spindle hub tend to loosen as a result of 
thermal cycling of the drive due to stress imbalances with the clamp. 
Although several suitable disc clamps have been designed in the past, 
effective disc clamp designs have traditionally required expensive alloys 
with high yield strength to accommodate the high stress concentration. 
However, the use of specialized alloys significantly increases production 
costs and fabrication complexity. 
Further, one of the drawbacks of prior art disc clamps that have used 
screws as an attachment means is that the disc clamp is designed through 
an iterative process that begins with the creation of a force deflection 
curve and torque-deflection measurements that establish the relationship 
between the screw-tightening torque and the actual clamping force applied 
by particular disc clamps. Non-operating shock tests are performed using 
an actual drive to determine the minimum screw tightening torque needed to 
maintain the discs in place without any disc slippage. 
Further, in the prior art, the use of screws creates localized point 
loading, thus not inherently providing equal clamping over the 360.degree. 
contact surface. 
More recently, heat shrink clamps have been employed, wherein a sleeve is 
heated to a high temperature and cooled after the application of 
appropriate clamp load. Such a method of attachment requires custom 
heaters which are capable of selectively heating the clamp and the 
assembly process requires time to heat the clamp to the desired 
temperature and then cooling them back to room temperature. 
SUMMARY OF THE INVENTION 
Accordingly, it is an objective of the present invention to provide a novel 
disc clamp design that does not use screws to attach the disc clamp, thus 
eliminating any localized point loading. 
It is a further object of this invention to reduce the amount of time 
required to assemble a disc pack. 
It is a further objective of this invention to provide equal clamping load 
over the 360.degree. contact surface. 
To achieve the foregoing and other objects in accordance with the purpose 
of the present invention, a disc clamp assembly is provided for use within 
a disc drive to secure a plurality of information storage discs arranged 
as a disc pack to a spindle hub on a spindle motor assembly disposed 
within the drive. The disc clamp assembly includes a clamping ring and a 
grip ring. The clamping ring is slipped over the spindle hub and rests on 
the information storage disc. The grip ring has an inner diameter smaller 
than the diameter of the spindle hub. The grip ring is expanded by 
applying a radial force and then installed over the hub. While maintaining 
the radial force, an axial force is applied to the grip ring, around the 
middle portion, which is transferred to the clamping ring and then to the 
disc pack, until there is no further motion of the disc pack. Then, the 
radial force upon the grip ring is removed. The grip ring firmly holds on 
to the outer diameter of the spindle hub, still maintaining the axial 
clamp load to the disc pack. The clamping ring, around its outer periphery 
has a rounded convex surface which transfers the clamping load to the disc 
pack. In the preferred embodiment, the grip ring has an outer raised 
portion, which can receive the radial force. 
In an alternate embodiment, the grip ring has plurality of slots to receive 
tips of a tool capable of providing radial force.

DETAILED DESCRIPTIONS 
As is generally known in the art, the illustrative disc drive unit 10 
includes a head positioner assembly (not shown) mounted within the housing 
16 at a position along the disc stack. The head positioner assembly 
supports a plurality of individual arms having electro-magnetic transducer 
heads at the distal ends there of in close proximity with respective upper 
and lower surfaces on the information storage disks. A suitable actuator 
motor (not shown) such as a movable coil DC motor, and a corresponding 
motor controller function to displace the magnetic transducer head through 
generally radial traverses relative to the information storage disks 14 
for the purposes of reading and writing data, all in a well known manner. 
With reference to FIG. 1, a central shaft 20 is securely fixed to a portion 
of the housing lower base 16, and the information storage disks 14 are 
mounted for rotational movement within the housing 16 about the shaft 20. 
Central shaft 20 is also attached to the inner races of upper bearing and 
lower bearing. 
The outer races of the upper bearing 22 and the lower bearing 24 support 
the rotor of the spindle motor. The rotor 25 includes sleeve 27 and 
spindle hub 26. Sleeve 27 is preferably stainless steel and spindle hub 26 
is preferably aluminum. Spindle hub 26 is preferably heated and shrink fit 
over the outer surface of the sleeve 27 to securely attach spindle hub 26 
and sleeve 27. The sleeve has a radially and inwardly extending middle 
flange on which the outer races of the upper bearing 22 and lower bearing 
24 rest. The sleeve supports, at its lower end, a plurality of permanent 
magnets which interact with an electromagnetic stator core to rotate the 
spindle hub about the center shaft in a known manner. 
The spindle hub near the lower end, has a radially and outwardly extending 
hub flange 32. A disc centering sleeve 29 with plurality of symmetrically 
located axial ribs both on the inner diameter and outer diameter is slid 
over the spindle hub 26 such that inner axial ribs rest against the outer 
surface of the spindle hub 26. A first information storage disc 14 is 
stacked on top of the hub flange 32. A disc spacer 48 is stacked on top of 
the first information disc and a second disc 14 is stacked on top of the 
disc spacer 48. A circular support ring 49 is placed on top of the second 
information storage disc. The outer ribs of the disc centering sleeve 29 
radially push and center the information storage discs, the disc spacer 
and the support ring so that they are all positioned concentric with the 
central hub, thus aiding in maintaining a balanced load along the axis of 
the central hub. A novel disc clamp assembly 58 of the present invention 
including a clamp ring 60 and a grip ring 62 applying clamp load to the 
disc pack as shown, features of which will be fully explained below. 
The clamping ring 60 is a stamped sheet metal part. The clamping ring 60 
has an inner diameter larger than the outer diameter of the spindle hub 
26, so that the clamping ring 60 can be slipped over the spindle hub 26 
and rest on the top surface of the support ring 49. The clamping ring 60 
further having a rounded convex surface 64 near the outer periphery, so 
that the clamp force is applied away from the inner diameter of the 
information storage discs 14. The clamping ring further having a raised 
inner portion 66 on which the lower surface of the grip ring 62 rests. 
The grip ring 62 is an extruded and machined part. The grip ring 62 inside 
diameter is smaller than the diameter of the spindle hub 26, however the 
grip ring 62 is resilient so that it can be mechanically expanded radially 
to a point below its yield strength, and larger than the outer diameter of 
the spindle hub 26. The grip ring 62 further having a means for receiving 
such a radial force. The grip ring 62 further having a means for receiving 
an axial force. During assembly process, the grip ring 62 is radially 
expanded and slid over the spindle hub 26 and while still maintaining the 
radial force, an axial force is applied to the clamping ring 60 and the 
disc pack until there is no further movement of the disc pack. While still 
maintaining the axial force, the radial force is removed so that the grip 
ring 62 can grip the spindle hub 26 and continue to maintain the axial 
force. 
FIG. 2 is a plan view of the grip ring 62 of the present invention. The 
figure shows plurality of slots 67 to receive tips of a tool capable of 
applying radial and axial force. The arrows 68 represent the direction of 
application of radial force. The grip ring further includes a middle 
portions 70 to receive the axial force applied to the disc pack. The lower 
surface of the middle portion 70 rests on the inner portion 66 of the 
clamping ring 60. 
FIG. 3 is a plan view of an alternate embodiment of the grip ring 62 of the 
present invention. The figure shows plurality of slots 67 to receive tips 
72 of a tool capable of applying radial and axial force. The arrows 68 
represent the direction of application of radial force. The grip ring 
further includes a middle portions 70 to receive the axial force applied 
to the disc pack. The lower surface of the middle portion 70 rests on the 
inner portion 66 of the clamping ring 60. 
FIG. 4 shows the grip ring 62 of the present invention along with a tool 74 
capable of applying both radial and axial force. The tool 74 includes an 
arm 76, ends of which have tips 72. The arm 76 is pivotally mounted at 78 
so that the tips can move in a radial direction. The tool 74 further 
includes a middle portion 80, ends of which rests on the middle portion 70 
of the grip ring 62 so that an axial force can be applied to the grip ring 
62. The radial movement of the arm 76 is limited so that the radial force 
applied to the grip ring 62 is sufficient to expand the grip ring 62 so 
that it can slide over the spindle hub 26, but yet below the yield 
strength of the grip ring 62. 
From the above description, it is apparent that many modifications and 
variations of the present invention are possible in light of the above 
teachings. It is therefore to be understood that, within the scope of the 
appended claims, the invention may be practiced otherwise than as 
specifically described hereinabove.