Spindle assembly for a disk drive using less than a full compliment of disks

A spindle assembly for a disk drive uses fewer than the maximum number of disks, reducing power consumption of a spindle motor without reducing the dust collecting ability of an air filter. The spindle assembly includes a shaft adapted to be fixed to a housing of the disk drive, and a spindle hub rotatably mounted on the shaft. A first set of disks spaced from each other a given distance is mounted on a lower portion of the spindle hub, and a second set of disks spaced from each other the above given distance is mounted on an upper portion of the spindle hub. A dummy ring is mounted on an intermediate portion of the spindle hub to define a large space between the first set and the second set. The intermediate portion does not have disks. A clamp is secured to the spindle hub by screws, thereby fixing the first and second sets of disks to the spindle hub.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
The present invention relates to a spindle assembly for a magnetic disk 
drive. 
2. Description of the Related Art 
In general, a usual magnetic disk drive is of a maximum-capacity type such 
that a maximum number of disks are accommodated in a housing having a 
standard external size to ensure a maximum storage capacity. In contrast 
with such a maximum-capacity type disk drive, development is frequently 
made on a small-capacity type disk drive having a reduced number of disks 
and heads to reduce the storage capacity. Usually, such a small-capacity 
type disk drive employs the same spindle motor and the same housing in 
external size as those of the maximum-capacity type disk drive. However, 
since the total height of the stacked disks is smaller than the total 
length of a spindle hub by an amount corresponding to a reduction in 
number of the disks, the difference is filled by a cylindrical dummy 
spacer or by stacked dummy disks, thus constructing a spindle assembly. 
In general, a plurality of disks and annular spacers are alternately 
stacked from the flange side of the spindle hub, and the cylindrical dummy 
spacer or the dummy disks is/are stacked at the remaining portion of the 
spindle hub as mentioned above. However, in the case that the cylindrical 
dummy spacer is used, an air flow by rotation of the disks is not 
generated at the remaining portion of the spindle hub. Accordingly, the 
ability of an air filter for circulating and removing dust in the magnetic 
disk drive by using the air flow generated by rotation of the disks is 
largely reduced, causing a reduction in reliability of the magnetic disk 
drive. On the other hand, in the case that the dummy disks are used, the 
effect of reduction in power consumption of the spindle motor by the 
reduction in number of the disks as the principal merit of the 
small-capacity type disk drive cannot be obtained, and an extra cost for 
the dummy disks is required. 
For the purposes of improvement in recording density and improvement in 
impact resistance of the magnetic disk drive, a plurality of disks in a 
stacked condition are mounted on the spindle hub, and a clamp ring is 
secured to an end surface of the spindle hub by screws to fix the disks to 
the spindle hub. At this time, the disk nearest to the clamp ring is 
influenced by tightening of the screws in such a manner that a portion of 
the disk in the vicinity of the screws is pressed by a large force, but a 
portion of the disk between the screws is pressed by a small force. 
As a result, the disk is so deformed as to be undulated, causing a 
degradation in flying stability of the magnetic head, which adversely 
affects the improvement in recording density and the reliability of the 
disk drive. This defect is known in the art. The deformation of the disk 
due to screw tightening can be suppressed by reducing the tightening 
torque of the screws. In this case, however, a depression force to the 
disks is reduced to cause a problem such that when an external shock is 
received by any disk in its in-plane direction, the disk is slipped and 
therefore data cannot be properly recorded and reproduced. In particular, 
a recent small-sized magnetic disk drive is required to have a high impact 
resistance against about 100 G in an inoperative condition, so that the 
reduction in tightening torque of the screws to the clamp ring is not 
effective. 
SUMMARY OF THE INVENTION 
It is therefore an object of the present invention to provide a spindle 
assembly for a small-capacity type disk drive which can reduce the power 
consumption of a spindle motor without reducing the dust collecting 
ability of an air filter. 
It is another object of the present invention to provide a spindle assembly 
for a small-capacity type disk drive which can prevent application of 
offset load to a pair of bearings. 
It is still another object of the present invention to provide a spindle 
assembly for a small-capacity type disk drive which can prevent 
deformation of disks due to screw tightening to a clamp ring and ensure 
sufficient impact resistance. 
In accordance with an aspect of the present invention, there is provided a 
spindle assembly for a disk drive having a housing consisting of a base 
and a cover fixed to the base, comprising a shaft adapted to be fixed to 
the housing; a stator coil fixed to the shaft; a spindle hub rotatably 
mounted on the shaft, the spindle hub having an upper portion, an 
intermediate portion, and a lower portion; a rotor magnet fixed to the 
intermediate portion of the spindle hub so as to be opposed to the stator 
coil; a pair of bearings for rotatably supporting the spindle hub at the 
upper portion and the lower portion of the spindle hub; a first set of 
disks spaced from each other a given distance and mounted on the lower 
portion of the spindle hub; a second set of disks spaced from each other 
the given distance and mounted on the upper portion of the spindle hub; a 
dummy ring mounted on the intermediate portion of the spindle hub and 
interposed between the uppermost disk of the first set of plural disks and 
the lowermost disk of the second set of plural disks, the dummy ring 
having an axial length two or more times the given distance; a clamp for 
pressing down the uppermost disk of the second set of plural disks; and a 
fixing means for fixing the clamp and the first and second sets of disks 
to the spindle hub. 
The first set of disks and the second set of disks are separately mounted 
on the lower portion and the upper portion of the spindle hub, 
respectively, and the dummy ring is mounted on the intermediate portion of 
the spindle hub. Accordingly, an air flow coming into the air filter 
becomes a substantially laminar flow although a slight reduction in flow 
velocity occurs at the intermediate portion of the spindle hub. Further, 
since no dummy disks are used, an increase in power consumption of the 
spindle motor due to the use of dummy disks does not occur, which allows 
an improvement in reliability and a reduction in power consumption of the 
disk drive. 
Preferably, the fixing means comprises a plurality of screws. The 
tightening torque of each screw to the clamp is set smaller than a normal 
value to temporarily fix the disks to the spindle hub. Thereafter, an 
adhesive is injected into an axial groove formed on the outer 
circumferential surface of the spindle hub to thereby finally fix the 
disks to the spindle hub by the adhesive. 
In accordance with another aspect of the present invention, there is 
provided a spindle assembly for a disk drive having a housing consisting 
of a base and a cover fixed to the base, comprising a shaft adapted to be 
fixed to the housing; a stator coil fixed to the shaft; a spindle hub 
rotatably mounted on the shaft, the spindle hub having an upper half 
portion and a lower half portion; a pair of bearings for rotatably 
supporting the spindle hub at one of the upper half portion and the lower 
half portion of the spindle hub; a plurality of disks spaced from each 
other a given distance and mounted on either the upper half portion or the 
lower half portion of the spindle hub supported by the bearings; a rotor 
magnet fixed to either the upper half portion or the lower half portion of 
the spindle hub so as to be opposed to the stator coil; a dummy ring 
mounted on either the upper half portion or the lower half portion of the 
spindle hub, the dummy ring having an axial length two or more times the 
given distance; and a fixing means for fixing the plurality of disks to 
the spindle hub.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
Referring to FIG. 1, there is shown an external perspective view of a 
magnetic disk drive. Reference numeral 2 denotes a housing (disk 
enclosure) composed of a base 4 and a cover 6 fixed to the base 4, and 
defining a sealed chamber therein. A spindle assembly 8 having a plurality 
of disks 10 is accommodated in the housing 2. Reference numeral 12 denotes 
a head actuator having a front end on which a head 14 for reading/writing 
data on each disk 10 is mounted. 
Referring to FIG. 2, there is shown a partially sectional view of the 
spindle assembly 8 according to a first preferred embodiment of the 
present invention. The spindle assembly 8 includes a flange 20 secured by 
screws to the base 4 of the disk drive. A shaft 22 is fixed at its lower 
end to the flange 20, and fixed at its upper end to the cover 6 by means 
of a screw 23 (see FIG. 1). A spindle hub 24 is rotatably mounted on the 
shaft 22 by a pair of bearings 28. An annular bushing 26 is fixed to the 
inside of a lower end portion of the spindle hub 24, and is rotatably 
supported by one of the bearings 28. 
A stator coil 30 is mounted on an intermediate portion of the shaft 22. An 
annular rotor magnet 34 is fixed through an annular yoke 32 to an 
intermediate portion of the spindle hub 24. A gap having a given width is 
defined between the stator coil 30 and the rotor magnet 34. An annular 
flange 24a is formed integrally with the spindle hub 24 at its lower end 
portion. A first magnetic disk set 10A consisting of a plurality of 
magnetic disks 10 (three magnetic disks 10 in this preferred embodiment) 
is mounted on a lower portion of the spindle hub 24. The lowermost 
magnetic disk 10 is set on the annular flange 24a of the spindle hub 24, 
and all the disks 10 of the first set 10A are equally spaced by annular 
spacers 36 mounted on the lower portion of the spindle hub 24 so as to be 
alternately stacked. 
A cylindrical dummy ring 38 instead of magnetic disks is mounted on an 
intermediate portion of the spindle hub 24. That is, the lower end surface 
of the cylindrical dummy ring 38 is set on the uppermost magnetic disk 10 
of the first set 10A. Further, a second magnetic disk set 10B consisting 
of plural magnetic disks 10 (three magnetic disks 10 in this preferred 
embodiment) is mounted on an upper portion of the spindle hub 24. The 
lowermost magnetic disk 10 of the second set 10B is set on the upper end 
surface of the cylindrical dummy ring 38, and all the disks 10 of the 
second set 10B are equally spaced by annular spacers 36 mounted on the 
upper portion of the spindle hub 24 so as to be alternately stacked. In 
this manner, all the magnetic disks 10 of the first set 10A are spaced 
from each other a given distance defined by each annular spacer 36 mounted 
on the lower portion of the spindle hub 24, and all the magnetic disks 10 
of the second set 10B are spaced from each other the above given distance 
defined by each annular spacer 36 mounted on the upper portion of the 
spindle hub 24. 
The axial length of the cylindrical dummy ring 38 is set two or more times 
the axial length of each annular spacer 36 (i.e., the above given 
distance). A clamp ring 40 is set on the uppermost magnetic disk 10 of the 
second set 10B, and is secured to the spindle hub 24 by a plurality of 
screws 42, thereby fixing the first set 10A and the second set 10B to the 
lower portion and the upper portion of the spindle hub 24, respectively. 
In this preferred embodiment, the tightening torque of each screw 42 to the 
clamp ring 40 is set smaller than a normal value, and each disk 10 is 
temporarily fixed by tightening the screws 42 to such an extent that each 
disk 10 comes to close contact with the adjacent annular spacers 36 to 
ensure a proper disk spacing. As shown in FIG. 3, the clamp ring 40 is 
formed with two adhesive injecting holes 44. As shown in FIG. 2, two axial 
grooves 46 (one of which is shown) are formed on the outer circumferential 
surface of the spindle hub 24 so as to be respectively aligned to the two 
adhesive injecting holes 44 of the clamp ring 40. 
After temporarily fixing the magnetic disks 10 by tightening the screws 42 
as mentioned above, an adhesive is injected through the holes 4 into the 
grooves 46 to thereby finally fix the magnetic disks 10 to the spindle hub 
24 by the adhesive. Accordingly, each magnetic disk 10 is firmly fixed to 
the spindle hub 24, so that even if an external shock is received by any 
disk 10 in its in-plane direction, there is no possibility of slip of the 
disk 10. As described above, the tightening torque of each screw 42 to the 
clamp ring 40 is set smaller than the normal value, and all the magnetic 
disks 10 are bonded to the spindle hub 24 by the adhesive injected into 
the grooves 46. Accordingly, deformation of each disk 10, especially, the 
uppermost disk 10, can be prevented, and sufficient impact resistance can 
also be ensured. 
In the magnetic disk drive manufactured by fixing the magnetic disks 10 to 
the spindle hub 24 by the adhesive as mentioned above, there is a 
possibility that when a defect on any disk 10 is found in delivery 
inspection of the disk drive, it may be difficult to replace and repair 
the defective disk. To cope with this, the magnetic disks 10 are 
temporarily fixed by the screws 42 until the delivery inspection is 
finished. Further, as shown in FIG. 1, the cover 6 is formed with a hole 
48 for exposing the adhesive injecting hole 44 (actually, two holes 48 are 
formed so as to respectively correspond to the two adhesive injecting 
holes 44). 
After finishing the delivery inspection, the adhesive is injected through 
the hole 48 of the cover 6 to the corresponding adhesive injecting hole 
44, thereby firmly fixing the magnetic disks 10 to the spindle hub 24. 
After injecting the adhesive, the hole 48 of the cover 6 is closed by a 
seal 49 as shown in FIG. 1. The adhesive must have a relatively good 
fluidity, so as to securely bond all the disks 10 to the spindle hub 24. 
However, there is a possibility that when such a well-fluidic adhesive is 
injected, it may flow from between each disk 10 and the adjacent annular 
spacer 36 to the disk surface. 
To cope with this, a pair of annular grooves are formed on the outer 
circumferential surface of each annular spacer 36 so as to be exposed to 
the upper and lower surfaces of the annular spacer 36, and each annular 
groove is lined with a seal member 50. Similarly, a pair of annular 
grooves are formed on the outer circumferential surface of the dummy ring 
38 so as to be exposed to the upper and lower surfaces of the dummy ring 
38, and each annular groove is lined with a seal member 52. The seal 
members 50 and 52 come to close contact with the disk surfaces, thereby 
preventing the flow of the adhesive to the disk surfaces. Although not 
shown, by similarly providing a seal member at a given position on the 
clamp ring 40, the flow of the adhesive to the disk surface of the 
uppermost disk 10 can be prevented. 
According to this preferred embodiment, the first set of plural magnetic 
disks 10 and the second set of plural magnetic disks 10 are separately 
mounted on the lower portion and the upper portion of the spindle hub 24, 
respectively, and the dummy ring 38 is mounted on the intermediate portion 
of the spindle hub 24. Accordingly, an air flow coming into an air filter 
provided in the magnetic disk drive becomes a substantially laminar flow 
although a slight reduction in flow velocity occurs at the intermediate 
portion of the spindle hub 24. Therefore, a large reduction in dust 
collecting effect by the air filter can be prevented. Furthermore, since 
no dummy disks are used, an increase in power consumption of the spindle 
motor due to the use of dummy disks does not occur. Thus, the reliability 
of the small-capacity type magnetic disk drive can be improved. 
Referring to FIG. 4, there is shown a partially sectional view of a spindle 
assembly 8A according to a second preferred embodiment of the present 
invention. In the description of this preferred embodiment, substantially 
the same parts as those of the first preferred embodiment are denoted by 
the same reference numerals, and the description thereof will be omitted 
herein to avoid repetition. In the spindle assembly 8A according to the 
second preferred embodiment, a plurality of magnetic disks 10 equally 
spaced from each other are mounted on only an upper half portion of a 
spindle hub 24. The spindle hub 24 is rotatably supported at its upper 
half portion by a pair of bearings 28. A dummy ring 38' instead of disks 
is mounted on a lower half portion of the spindle hub 24. A stator coil 30 
is fixed to a lower portion of a shaft 22, and an annular magnet 34 
opposed to the stator coil 30 is mounted through a yoke 32 on a lower 
portion of the spindle hub 24. 
According to this preferred embodiment, the plurality of magnetic disks 10 
are mounted on the upper half portion of the spindle hub 24 supported by 
the pair of bearings 28. Accordingly, a load is substantially uniformly 
applied to the pair of bearings 28. Therefore, even in the small-capacity 
type magnetic disk drive configured by mounting the magnetic disks 10 on 
only a part of the spindle hub 24, there is no possibility that when an 
external force is received by any disk 10, the disk 10 may be inclined 
because of offset load to the bearings. Thus, the reliability of the 
small-capacity type magnetic disk drive can be improved. 
Although not shown, like the first preferred embodiment, adhesive injecting 
holes may be formed through a clamp ring 40, and axial grooves 
communicating with the adhesive injecting holes may be formed on the outer 
circumferential surface of the spindle hub 24 in the spindle assembly 8A 
according to the second preferred embodiment. In this case, after 
temporarily fixing the disks 10 by screws 42, an adhesive is injected into 
the axial grooves to finally fix the disks 10 to the spindle hub 24 by the 
adhesive. Accordingly, deformation of the uppermost disk 10 due to 
tightening of the screws 42 to the clamp ring 40 can be effectively 
prevented. 
Referring to FIG. 5, there is shown a partially sectional view of a spindle 
assembly 8B according to a third preferred embodiment of the present 
invention. In the description of this preferred embodiment, substantially 
the same parts as those of the first and second preferred embodiments are 
denoted by the same reference numerals, and the description thereof will 
be omitted to avoid repetition. In the spindle assembly 8B according to 
the third preferred embodiment, an annular clamp 54 is fixed to an upper 
end portion of a spindle hub 24' by using shrink fit rather than screw 
tightening. Like the second preferred embodiment, the spindle hub 24' is 
supported at its upper half portion by a pair of bearings 28, and a 
plurality of magnetic disks 10 are mounted on only the upper half portion 
of the spindle hub 24'. 
More specifically, the inner diameter of the annular clamp 54 is set 
slightly smaller than the diameter of the spindle hub 24' at room 
temperature. After alternately stacking the disks 10 and annular spacers 
36 and mounting them together on the upper half portion of the spindle hub 
24', the annular clamp 54, heated to a given temperature in a furnace or 
the like, is mounted on the upper end portion of the spindle hub 24' to 
press down each disk 10. Since the inner diameter of the annular clamp 54 
is made larger than the diameter of the spindle hub 24' by heating, the 
annular clamp 54 can be easily mounted on the spindle hub 24'. Further, 
since the inner diameter of the annular clamp 54 is reduced when cooled to 
room temperature, the annular clamp 54 can be firmly fixed to the upper 
end portion of the spindle hub 24'. 
Although not shown, like the first preferred embodiment, bonding of the 
magnetic disks 10 by the injection of an adhesive may be applied in 
addition to the shrink fit of the annular clamp 54. Further, instead of 
the shrink fit of the annular clamp 54, press fit of the annular clamp 54 
may be used to fix the annular clamp 54 to the upper end portion of the 
spindle hub 24'. In this case, the inner diameter of the annular clamp 54 
is set equal to or slightly larger than the diameter of the spindle hub 
24', and the annular clamp 54 is press-fitted to the spindle hub 24' by 
using a jig. 
In the case of press fit, the process can be simplified as compared with 
shrink fit, and a furnace or the like for shrink fit is not necessary. 
However, in the case of press fit, the fixation of each magnetic disk 10 
to the spindle hub 24' is insufficient, so that it is necessary to 
additionally apply bonding of each magnetic disk 10 to the spindle hub 24' 
by the injection of an adhesive as described in the first preferred 
embodiment. While the plurality of magnetic disks are mounted on only the 
upper half portion of the spindle hub in the second and third preferred 
embodiments, they may be mounted on only the lower half portion of the 
spindle hub. In this case, the dummy ring is mounted on the upper half 
portion of the spindle hub. 
According to the present invention, it is possible to provide a spindle 
assembly for a small-capacity type disk drive which can reduce the power 
consumption of the spindle motor without reducing the dust collecting 
ability of the air filter. Further, it is possible to provide a spindle 
assembly for a small-capacity type disk drive which can prevent 
deformation of the disks due to screw tightening to the clamp ring and 
ensure sufficient impact resistance.