WO1993019464A1

WO1993019464A1 - Apparatus for clamping a rigid disk

Info

Publication number: WO1993019464A1
Application number: PCT/US1993/002730
Authority: WO
Inventors: John D. Read; Charles E. Vaillant
Original assignee: Digital Equipment Corporation
Priority date: 1992-03-20
Filing date: 1993-03-19
Publication date: 1993-09-30

Abstract

A clamping apparatus for a disk (24) mounted about a spindle (20) of a disk storage device (10) including a heat shrink ring (30) having an annular groove (31) formed partially on one side surface (32) of the ring and partially on an inner cylindrical surface (33) of the ring.

Description

APPARATUS FOR CLAMPING A RIGID DISK

FIELD OF THE INVENTION

This invention relates to rigid disk storage devices, and more

particularly to an apparatus for compressively clamping a rigid disk to

a disk stack of a storage device.

BACKCROTINP OF THE INVENTION

Rigid disk storage devices attain high storage densities by utilizing

the maximum number of data surfaces for recording information within

a given volume. The number of data surfaces that can be accommodated

within a given form factor, or industry standard dimensions is limited by the height of the disk stack, the thickness of the disks, and the

spacing between the disks.

When these parameters have been optimized to the current state

of the art, the manner in which the disks are clamped to a rotatably

mounted spindle of the device becomes a critical concern. Typically, the

bottom disk in a disk stack is fixed to the spindle at a hub located at the

bottom portion of the spindle. The other disks in the stack are generally

positioned one above the other, axially spaced apart by means of spacer

rings, with a clamping ring at the top of the stack used to fix the disks

to one and another and the spindle. The disks must be clamped to the

spindle with sufficient force to prevent radial or axial shifting of the

disks on the spindle caused by impact shocks during shipping, or

imbalanced rotational forces during operation.

It is also important that the disks, when clamped, are maintained

in a flat and parallel configuration, free of deformation. Also, as the

radial and axial dimensions of disk storage devices continue to decrease,

the size of the clamping means needs to be kept to a minimum to maximize the surface area available for data recording, and to minimize

the spacing between adjacent disks.

Clamping techniques include interference shrink fits. A traditional

shrink type clamp ring is heated prior to assem bly to increase its radial

dimensions. The heated shrink ring is then positioned, in its expanded

state, about the spindle and allowed to cool down to reduce the radial

dimensions and produce an interference fit. The prior art shrink rings

generally grip the spindle with high forces in the radial direction.

However external forces need to be applied axially between the ring and

an axial support surface, such as a hub, while it is cooling to effectively

fix the disks in position about the spindle. Unfortunately, sufficient axial

force on the ring during cooling to clamp the disks in place on the

spindle is likely to cause brinelling damage to the spindle bearings.

Therefore, during assembly, the disk stack needs to be placed in an

assembly fixture which includes a means for applying axial force and a

means for supporting the hub to prevent damage or destruction of the

spindle bearings. SUMMARY OF THE INVENTION

In accordance with one aspect of the invention, there is provided

an apparatus for clamping disks of a storage device to a spindle having

an axial support surface which overcomes the foregoing disadvantages

of the prior art. The apparatus comprises a shrink ring having an inner

diameter less than the outer diameter of the spindle. The geometry of

the shrink ring is optimized to permit a portion of the ring to twist or

rotate radially inward about an annular axis of the ring as it is cooling

and shrinking in a manner effective to exert concurrently, radial and

axial forces on the spindle, the disk, and the axial support surface to fix

the disk in place while it is cooling and shrinking without the use of

potentially damaging, external clamping forces.

To enable the twisting of the ring to effect the desired result, the

ring has material removed to form an annular groove partially in one

side surface of the ring, and partially in the cylindrical inner surface of

the ring. The amount of material removed from the ring is sufficient to

allow the ring to rotate inward along an annular axis during cooling. The amount of material left in the remainder of the ring has sufficient

mass to absorb enough heat to cause the ring to expand during heating

to overcome interference with the spindle. Furthermore, the annular

center of gravity of the grooved ring is positioned between the annular

point of interference between the ring and spindle and the disk surface

to be clamped.

To clamp the disk to the spindle, the shrink ring is heated to

increase its inner diameter to a size that is larger than the outer

diameter of the spindle. The heated ring is placed in its assembly

position about the spindle with the annular groove of the ring adjacent

to one surface of the disk and the spindle.

As the ring cools, radial shrinking is stayed at the point of

interference between the ring and spindle. Because of the annular groove

in the ring, an annular clearance exists between the disk, the spindle,

and the shrink ring. This clearance permits the ring to rotate about an

annular axis of the ring. Since the annular center of mass of the ring is

well below the point of interference between the ring and spindle an inwardly and downwardly directed tangential forces is generated as the

ring continues to shrink and rotate to cause the disk also be clamped in

an axial direction. These and other features and advantages of the

present invention will become apparent from a reading of the detailed

description in conjunction with the attached drawings in which like

reference numerals refer to like elements in the several views.

STATEMENT OF THE INVENTION

An apparatus for clamping a disk of a disk storage device to a

spindle having a support surface for supporting the disk in one axial

direction, comprising a ring having a side surface and an inner

cylindrical surface, the diameter of said inner cylindrical surface being

smaller than the outer diameter of the spindle; an annular groove

formed partially on said side surface and partially on said inner

cylindrical surface, the depth of said groove sufficient to provide

clearance between said ring and the disk and the spindle, the ring having

sufficient mass to absorb heat to overcome the interference between said

ring and the spindle, the annular center of gravity of said ring being between a portion of said ring having the smallest inner diameter and

said side surface.

BRIEF DESCRIPTION ΩHTHE DRA ING

Figure 1 is a vertical axial section of a disk stack for a storage

device incorporating the shrink ring structure according to one em bodi¬

ment of the invention;

Figure 2 is a vertical section of the shrink ring of Figure 1.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

Now with reference to Figure 1 there is shown a disk stack 10 for

a disk storage device that can be used with the present invention. The

disk stack 10 includes a spindle 20, a spindle hub 21, bearings 22, an

electric motor 23, and plurality of disks of which only the lower disk 24

is shown. As shown, the spindle 20 has a generally cylindrical outer surface

25 with the spindle hub 21 secured to a bottom portion thereof. The

spindle 20 and the hub 21 are rotatable coupled to the spindle motor 23,

and are supported axially by means of the bearings 22. It should also be

noted in passing that a clearance 26 is generally maintained between the

inner diameter of the disk 24 and the outer surface 25 of the spindle 20

to avoid thermally induced distortion and dislocation of the disk 24

during temperature changes.

In practice, the disk stack 10 is rotated by motor 23 at a high

speed, for example 3600 rpm, to permit the recording and retrieval of

information on the surfaces of the disk 24 by means of a read/write

head, not shown. During the starting and stopping of the motor 23, the

disk 24 and spindle 20 experience varying and harsh rotational forces.

Therefore the disk 24 needs to be clamped to the spindle 20 with

sufficient radial force to prevent radial creepage and axial shifting of the

disk 24 on the spindle 20. Also, during shipping, and particularly, when used in portable

computer equipment, the disk stack 10 is subjected to high G-forces.

Thus, it is a further requirement that the disk 24 be firmly held in place

to prevent axial shifting on the spindle 20. According to the invention,

clamping of the disk 24 to the spindle 20 and the hub 21 is effected by

a heat shrink ring 30 specifically configured to generate axial and radial

forces during assembly of the disk stack 10.

Now also with reference to Figure 2, the structure of the shrink

ring 30 is explained in further detail. The ring 30 is in the form of an

annulus with an inner diameter less than the outer diameter of the

surface 25 of the spindle 20.

An annular groove 31 is formed, partially in one side surface 32

of the ring 30, and partially in the inner cylindrical surface 33. The

profile of the groove 31 is, by way of example, angular as shown in

Figures 1 and 2,for creating a generally annular L-shaped clearance 34

between the spindle 20, the disk 24, and the shrink ring 30. To enable

the twisting of the ring 30 to effect the desired result, the material removed from the ring 30 is just sufficient to allow the ring 30 to rotate

inward along an annular axis during cooling. The amount of material

left in the remainder of the ring 30 has sufficient mass to absorb enough

heat to cause the ring 30 to expand during heating to overcome interfer-

ence with the spindle 25. Furthermore, the annular center of gravity of

the grooved ring 30, generally indicated by letter G, is positioned

between the annular point of interference 35 and disk 24.

Now during assembly of the disk 24 on the disk stack 10, the

interference between the inner cylindrical surface 33 of the shrink ring

30 and the outer surface 25 of the spindle 20 is overcome by heating the

shrink ring 30 to a temperature of approximately 400 degrees fahrenheit

with, for example, an induction heater coil, not shown. Heating expands

the ring 30 so that it may be positioned about the outer surface 25 of the

spindle 20. The ring 30 is positioned on the spindle 20, with the grooved

side surface 32 facing the disk 24 to be clamped, to form the L-shaped

annular clearance 34. While the ring 30 is cooling, the ring 30 is held in place, about the

spindle 30 and against the surface of the disk 24, without the use of any

axial force that would cause brinelling damage to the bearings 22. As the

ring 30 cools, the ring 30 attempts to resume its original preheated

dimensions, realizing a radial interference fit between the inner

cylindrical surface 33 and the outer surface 25, thus clamping the ring

30 to the spindle 20.

However, as the temperature of the ring 30 continues to decline

the ring 30 continues to move towards its unheated dimension, which is

smaller in diameter than the outer diameter of the spindle 20. The

annular L-shaped clearance 34 between the spindle 20, the disk 24, and

the ring 30 allows the lower portion of the ring 30 to rotate. Because the

annular center of gravity G of the mass of the ring is below the point of

interference the ring rotates radially inwardly, as generally indicated by

arrows A, about an annular axis located approximately at the points of

contact between the spindle 20 and the ring 30, generally indicated by

numeral 35. This rotation, or twisting of the ring 30 generates tangential

forces, generally indicated by arrows B, clamping the disk 24 between the hub 21 and the ring 30. The amount of tangential force can be

increased by shifting the annular center of gravity of the ring 30 closer

to the grooved side of the ring 30 in contact with disk 24.

Additional disks are similarly clamped to one and another, and the

spindle 20 by a corresponding number of similarly configured shrink

rings 30. Should it become necessary to disassemble the disk stack 10 for

rework, the ring 30 can be removed by re-heating it to an expanded

state with, for example, an induction heater.

As shown in the specific embodiment that has been described, the

ring 30 is constructed of aluminum and is dimensioned, with appropriate

tolerances, as follows. The ring 30 has an outer diameter of

approximately 22.8 mm. The diameter of the un-grooved portion of the

inner cylindrical surface 33 is 19.93 mm when used with a spindle 20 for

industry standard 2 1/2 inch, or 65 mm disks. The thickness of the ring

30 is 2.54 mm. The groove 31 is dimensioned such that the annular

clearance 34 between the spindle, the disk 24 and the ring 24 is

approximately 0.5 mm. These dimensions are exemplary only and would not necessarily

be applicable to other combinations of disks, spindles, and hubs. Also

grooves with profiles other than angular, by way of example, quarter

round, giving the requisite clearance to permit the annular rotation of

the ring as it cools, can similarly be adapted.

Therefore the invention is not necessarily limited to the particular

embodiment shown herein. It is to be understood that various other

adaptations and modifications may be made within the spirit and scope

of the invention.

EFFECT OF THE TNVENTTON

To providing the desired effect of a twisting shrink ring, the ring

has material removed to form an annular groove partially in one side

surface of the ring, and partially in the cylindrical inner surface of the

ring. The amount of material removed from the ring is sufficient to

allow the ring to rotate inward along an annular axis during cooling.

The amount of material left in the remainder of the ring has sufficient mass to absorb enough heat to cause the ring to expand during heating

to overcome interference with the spindle. Furthermore, the annular

center of gravity of the grooved ring is positioned between the annular

point of interference between the ring and spindle and the disk surface

to be clamped. The ring is heated to position it about the spindle. As the

ring cools, radial shrinking is stayed at the point of interference between

the ring and spindle. Because of the annular groove in the ring, an

annular clearance exists between the disk, the spindle, and the shrink

ring. This clearance permits the ring to rotate about an annular axis of

the ring. Since the annular center of mass of the ring is well below the

point of interference between the ring and spindle an inwardly and

downwardly directed tangential forces is generated as the ring continues

to shrink and rotate to cause the disk also be clamped in an axial

direction.

Claims

1. An apparatus for clamping a disk (24) of a disk storage device (10)

to a spindle (20) having a support surface (21) for supporting the disk

in one axial direction, comprising:

a ring (30) having a side surface (32) and an inner cylindrical

surface (33), the diameter of said inner cylindrical surface being smaller

than the outer diameter (25) of the spindle;

an annular groove (31) formed partially on said side surface and

partially on said inner cylindrical surface, the depth of said groove

sufficient to provide clearance between said ring and the disk and the

spindle, the ring having sufficient mass to absorb heat to overcome the

interference between said ring and the spindle, the annular center of

gravity (G) of said ring being between a portion of said ring having the

smallest inner diameter and said side surface.

2. The apparatus as in claim 1 wherein the annular center of gravity

is substantially nearer to said side surface than said portion of the ring

having the smallest inner diameter.

3. The apparatus as in claim 1 wherein said groove is generally L-

shaped.

4. In a disk storage device (10) an apparatus for clamping a disk

(24), comprising:

a disk (24) mounted on a spindle (20) having means (21) for

supporting said disk in one axial direction;

a ring (30) having an inner diameter (33) less than an outer

diameter (25) of said spindle, said ring having an annular groove (31)

formed partially on one side surface (32) and partially on an inner

cylindrical surface (33) of said ring, said ring mounted on said spindle

with said side surface facing said disk, the annular center of gravity (G)

of said ring being between a portion of said ring having the smallest

inner diameter and said side surface, the ring having sufficient mass to

absorb heat to overcome the interference between said ring and the

spindle, the depth of said groove sufficient to provide clearance between

said ring, disk and spindle.

5. The apparatus as in claim 4 wherein said supporting means is an

annular hub.

6. The apparatus as in claim 4 wherein said annular groove has an

angular profile forming an L-shaped clearance between said spindle, said

disk, and said ring.