Magnetic disk storage device with shroud enclosing disk assembly

A magnetic disk storage device capable of avoiding the occurrence of vibration of magnetic disks and off-track of magnetic heads with respect to the magnetic disks, including an inner shroud enclosing a disk assembly composed of a multiplicity of magnetic disks stacked in superposed relation with spacers being interposed therebetween and formed at its outer peripheral wall with first ports for inserting access arms therethrough and at its top above a spindle supporting the disk assembly with a second port, a cylindrical filter for removing dust from air flowing through the second port of the inner shroud into the interior thereof, and a dust cover enclosing the inner shroud, actuators and filter. The provision of the inner shroud is conductive to prevention of development of turbulent air flow in the vicinity of the magnetic disks. The inner shroud is further formed at its outer peripheral wall with a multiplicity of small apertures for releasing heat generated in the inner shroud to outside, to thereby avoid thermal off-track of the magnetic heads.

BACKGROUND OF THE INVENTION 
This invention relates to magnetic disk storage devices, and more 
particularly it is concerned with a magnetic disk storage device capable 
of avoiding generation of vibration and production of dust in magnetic 
disks and magnetic heads and off-track of the magnetic heads with respect 
to the magnetic disks. 
In order to increase capacity and improve system throughput, a magnetic 
disk storage device has in recent years been developed which comprises a 
multiplicity of magnetic disks stacked in superposed relation, and two 
actuators arranged symmetrically with respect to a spindle supporting the 
magnetic disks and having access to the magnetic disks. This type of 
magnetic disk storage device is described in U.S. Pat. No. 4,190,870, for 
example. 
In this type of magnetic disk storage device, the magnetic disks rotate at 
high speed or at a speed of rotation in the range between 3000 and 3600 
rpm. Thus, currents of air which are large in volume would flow at high 
speed in a head disk assembly and cause the magnetic disks and magnetic 
heads to vibrate, thereby adversely affecting operations of recording and 
reproducing data on and from the magnetic disks by means of the magnetic 
heads. 
Owing to the high speed at which the magnetic disks rotate, windage loss 
might generate heat in the magnetic disk storage device. The heat thus 
generated would cause expansions of the magnetic disks each including a 
base formed of aluminum and tilting of the spindle supporting the magnetic 
disks, with a result that an error would be made in positioning the 
magnetic head on a desired track of one of the magnetic disks of the 
device. 
SUMMARY OF THE INVENTION 
A first object of this invention is to provide a magnetic disk storage 
device capable of avoiding the vibration of the magnetic disks and 
magnetic heads which would be caused by air currents. 
A second object is to provide a magnetic disk storage device capable of 
avoiding the occurrence of thermal off-track of a magnetic head with 
respect to a magnetic disk which would be caused by changes undergone by 
the magnetic head and magnetic disk due to heat generated by windage loss 
in the magnetic disk device. 
One of the outstanding characteristics of the invention enabling the 
aforesaid objects to be accomplished is that the magnetic disk storage 
device provided by the invention comprises an inner shroud including a 
cylindrical outer peripheral wall enclosing a disk assembly composed of a 
multiplicity of magnetic disks superposed one above another with spacers 
interposed therebetween while being spaced apart a predetermined distance 
from an outer edge of the disk assembly, an upper cover providing a cover 
to a top surface of the cylindrical outer peripheral wall and a lower 
cover providing a cover to a bottom surface of the cylindrical outer 
peripheral wall, the outer peripheral wall being formed with first 
openings each located in a position corresponding to one of actuators and 
the upper cover being formed with a second opening located above a 
spindle, a filter located in the vicinity of the second opening formed in 
the upper cover of the inner shroud for removing dust from a current of 
gaseous fluid flowing through the second opening, and a dust cover 
enclosing the inner shroud, filter and actuators as a unit to prevent dust 
from entering the disk assembly from outside. 
Another outstanding characteristic is that the filter is cylindrical in 
shape and located between the second opening formed in the upper cover of 
the inner shroud and the dust cover and that the outer peripheral wall of 
the inner shroud is formed with a multiplicity of small apertures in 
positions corresponding to outer edges of the magnetic disks.

DESCRIPTION OF THE PREFERRED EMBODIMENTS 
Before describing the embodiments of the invention in detail, a magnetic 
disk storage device of the prior art will be outlined. FIGS. 1 and 2 show 
in a sectional plan view and a sectional side view, respectively, the 
magnetic disk storage device invented previously by us. As shown, the 
magnetic disk storage device comprises a multiplicity of magnetic disks 1 
stacked in superposed relation through spacers 16 on a spindle 50 
supported on a base 5, linear actuators 4a and 4b located in diametrically 
opposed relation to each other with respect to the magnetic disks 1, a 
motor 8 for driving the magnetic disks 1 for rotation by rotating a pulley 
6 connected to a lower end of the spindle 50 through a belt 7, and a dust 
cover 9 located on the base 5 for enclosing the magnetic disks 1 and 
linear actuators 4a and 4b as a unit. The linear actuators 4a and 4b 
include carriages 3a and 3b supporting magnetic heads, not shown, through 
access arms 2a and 2b, respectively, at end portions so as to move the 
magnetic heads on surfaces of the magnetic disks 1. An air filter 12 of an 
annular shape is located in a position of the dust cover 9 above the 
spindle 50. Each spacer 16 is formed at an outer peripheral portion with a 
plurality of air exhaust apertures 11 enabling air introduced into the 
spacer through an upper portion to be discharged therethrough from the 
spacer when the spacers 16 are assembled with the spindle 50. The 
multiplicity of magnetic disks 1 stacked one above another with the 
interposed spacers shall be called a disk assembly. 
In the magnetic disk storage device of the aforesaid construction, rotation 
of the motor 8 causes the magnetic disks 1 to rotate, and the magnetic 
heads supported by the access arms 2a and 2b of the carriages 3a and 3b 
respectively have acess to the data storing surfaces of the rotating 
magnetic disks 1 to perform recording and reproducing of data. 
Currents of air produced in the dust cover 9 as the magnetic disks 1 rotate 
will be described. When the magnetic disks 1 rotate at high speed or at a 
speed in the range between 3000 and 3600 rpm., for example, air flows from 
the spacers 16 through the air exhaust apertures toward outer marginal 
portions of the magnetic disks 1 and causes the pressure in the vicinity 
of central portions of the magnetic disks 1 to drop, so that the air 
flowing out of the spacers 16 through the air exhaust apertures 11 are 
drawn by suction through the filter 12 and air suction apertures 10 formed 
in positions above the spindle 50 into the spacers 16, from which the air 
is discharged again through the air exhaust openings 11. 
As the currents of air flow as described hereinabove, air in the outer 
marginal portions of the magnetic disks 1 in the dust cover 9 flows, as 
indicated by arrows A, in the direction of rotation of the magnetic disks 
1. When the actuators 4a and 4b are located in diametrically opposed 
positions with respect to the magnetic disks 1, however, the speed at 
which the air flows tends to vary on account of the actuators 4a and 4b 
and the magnetic disks 1 being enclosed as a unit by the dust cover 9, and 
the air currents tend to flow in turbulent flow due to the existence of 
the actuators 4a and 4b. 
Research conducted by us into the turbulent flow of the air currents in the 
outer marginal portions of the magnetic disks 1 has revealed that the 
outer marginal portions of the magnetic disks 1 vibrate vertically. It has 
been ascertained that when magnetic disks each including a base formed of 
aluminum of 2 mm thickness are rotated at 3600 rpm., the vertical 
vibration of the outer marginal portions of the magnetic disks has an 
amplitude of about 0.1-0.2 mm and aggravates the floating stability of the 
magnetic heads which float on a film of air formed on a surface of each 
magnetic disk. The turbulent flow of air directly causes springs of the 
magnetic heads floating under light load to vibrate, thereby aggravating 
the floating stability of the magnetic heads. Aggravation of the floating 
stability of the magnetic heads raises the problem that stable performance 
of recording and reproducing operations on the magnetic disks by the 
magnetic heads is far from being achieved. 
We have invented a magnetic disk storage device which is free from the 
vibration of the magnetic disks experienced in the magnetic disk storage 
device of the prior art shown in FIGS. 1 and 2. 
FIGS. 3-5 show one embodiment of the invention in sectional side and 
sectional plan views. As shown, the magnetic disk storage device comprises 
a base 5, a multiplicity of magnetic disks 1 stacked in superposed 
relation on the base 5 and supported by a spindle 50 with spacers 16 of 
cylindrical shape formed with apertures being interposed between the 
magnetic disks 1, a plurality of actuators 4a and 4b located in 
diametrically opposed positions at different levels with respect to the 
magnetic disks 1, a motor 8 driving the magnetic disks 1 for rotation by 
rotating a pulley 6 attached to a lower end of the spindle 50 through a 
belt 7, an inner shroud 13 enclosing within its cylindrical outer 
peripheral wall the magnetic disks and spacers which is a characterizing 
feature of the invention, and a dust cover 9 enclosing the inner shroud 13 
and actuators 4a and 4b as a unit. The inner shroud 13, which is supported 
on an inner shroud support bed 14 on the base 5, is formed with ports 15a 
and 15b for inserting access arms 2a and 2b supported on carriages 3a and 
3b of the actuators 4a and 4b, respectively, therethrough into the 
interior of the inner shroud 13, and an air inlet port 17 for introducing 
air into the interior of the inner shroud 13 through an air cleaning 
filter 12 of a larger diameter than the air inlet port 17. As shown in 
FIG. 4, the inner shroud 13 is circular in cross section and its inner 
wall surface is spaced apart a predetermined distance D from an outer 
circumferential surface of each magnetic disk 1 except at portions thereof 
at which the arm inserting ports 15a and 15b are formed. Thus, the inner 
shroud 13 encloses the multiplicity of magnetic disks 1 and the spacers 
interposed therebetween, which are supported by the spindle 50 and 
constitute a disk assembly, substantially in the entirely. 
When the magnetic disks 1 of the magnetic disk storage device of the 
aforesaid construction rotates at high speed in the range between 2400 and 
3600 rpm., currents of air generated in the interior of the inner shroud 
13 are discharged through the arm inserting ports 15a and 15b on the side 
of the inner shroud 13 and flow through the air inlet opening 17 formed at 
a top surface of the inner shroud 13 and via the air cleaning filter 12 
into a space in each of the spacers between the magnetic disks 1 in the 
inner shroud 13. 
Currents of air flowing through discharge ports formed at the spacers in 
the inner shroud 13 flow along an inner wall surface of the inner shroud 
13 as shown in FIG. 5 before being discharged to the outside through the 
arm inserting ports 15a and 15b, so that no turbulent flow of air occurs 
in the interior of the inner shroud 13. The air discharged through the arm 
inserting ports 15a and 15b impinges on the actuators 14a and 14b and the 
flow thereof becomes slightly turbulent. However, no influences are 
exerted by this turbulent flow on the magnetic disks 1 and magnetic heads 
because it occurs outside the inner shroud 13. 
FIG. 6 shows the results of experiments conducted on influences which might 
be exerted by the distance D between the inner wall surface of the inner 
shroud 13 and the outer circumferential surface of each magnetic disk 1 to 
study whether changes in the distance D might affect the development of 
vibration in the magnetic disks 1. It will be clearly seen in the figure 
that when the distance D is about 12 mm, the amplitude of vertical 
vibration in one direction has a value H of about 20.mu. which is 
relatively great in value, when the distance D is 10 mm, it has a value G 
of about 10.mu., when the distance D is 6 mm, it has a value F of about 
15.mu., and when the distance D is less than 3 mm, it has a value E of 
about 8.mu.. Thus, by reducing the distance D between the inner wall 
surface of the inner shroud 13 and the outer circumferential surface of 
each magnetic disk 1 to a level below 3 mm, it is possible to minimize the 
vibration of the magnetic disks 1 in the embodiment of the invention shown 
and described hereinabove. 
As can be seen in the embodiment described hereinabove, the air currents 
inside the dust cover 9 and the air currents inside the inner shroud 13 
flow in convection flow through the air cleaning filter 12. This enables 
the air inside the inner shroud 13 to be kept clean at all times and 
minimizes the dust which might otherwise invade the most important 
floating gaps between the magnetic disks 1 and the magnetic heads in which 
the magnetic heads move in floating movement. 
The embodiment of the magnetic disk storage device shown in FIGS. 3 and 4 
has achieved the effect of avoiding the development of vibration in the 
magnetic disks 1. However, further experiments have shown that when 
rotation of the magnetic disks 1 is initiated, accurate positioning of the 
magnetic heads with respect to the magnetic disks 1 is unobtainable, that 
is to say, off-track of the magnetic heads occurs due to thermal expansion 
of the disks. More specifically, as the magnetic disks 1 are started and 
begin to rotate, heat is generated by the rotation of the disks 1 and 
remains in the interior of the inner shroud 13 and causes the magnetic 
disks 1 to expand, but on the other hand the temperature of the base 5 
remains unchanged, so that off-track occurs. After lapse of a certain 
period of time, the heat is released from the inner shroud 13 through the 
arm inserting ports 15a and 15b into the dust cover 9. The off-track is 
reduced in value when the temperature in the dust cover 9 or the 
temperature of the magnetic heads and magnetic disks 1 in the inner shroud 
13 becomes substantially equal to the temperature in the vicinity of the 
base 5. 
The fact that it takes time for the off-track to be reduced in value and to 
disappear has raised the problem that startup of equipment of a system 
with which the magnetic disk storage device is associated would lag 
behind. 
In order to obviate the aforesaid problem, we have developed another 
embodiment of the magnetic disk storage device in conformity with the 
invention which has the effect of avoiding thermal off-track. This 
embodiment will be described by referring to FIG. 7. 
The shroud 130 of this embodiment is formed with a multiplicity of small 
apertures 100 in positions along the outer circumferential surfaces of the 
magnetic disks 1 and encloses the multiplicity of magnetic disks 1 in 
their entirety with a clearance of about 3 mm between the inner wall 
surface of the inner shroud 130 and the outer circumferential surface of 
each magnetic disk 1. Like the inner shroud 13 shown in FIGS. 3 and 4, the 
inner shroud 130 is formed with the ports 15a and 15b for inserting the 
access arms 2a and 2b, respectively, therethrough, and the air inlet port 
17 for introducing into the inner shroud 130 clean air admitted through 
the air cleaning filter 12. The provision of the inner shroud 130 inside 
the dust cover 9 enables air currents flowing about the magnetic disks 1 
as described by referring to FIG. 5 to be regulated by the inner shroud 
130 to flow as indicated by solid line arrows in FIG. 7 and causes the air 
in the inside of the inner shroud 130 to flow in the direction of rotation 
of the magnetic disks 1. Exchange of air between the inside and outside of 
the inner shroud 130 is achieved by allowing the air in the inside of the 
inner shroud 130 to be released therefrom through the ports 15a and 15b 
for inserting the arms 2a and 2b and the multiplicity of small apertures 
100 formed at the wall of the inner shroud 130 and letting clean air 
introduced into the interior of the inner shroud 130 through the air inlet 
port 17 via the air cleaning filter 12. 
As shown in FIG. 8, the small apertures 100 formed at the wall of the inner 
shroud 130 are located in positions corresponding to the outer 
circumferential surfaces or outer edges of the magnetic disks 1 located 
inside the inner shroud 130. This allows air currents generated by the 
rotation of the magnetic disks 1 to flow along top surfaces of the 
magnetic disks 1 and be released through the small apertures 100, so that 
air currents impinging on the inner wall surface of the inner shroud 130 
and rebounding therefrom are very small in volume. 
Inside the inner shroud 130, the temperature at the intermediate portion is 
higher than those at higher and lower portions. To release greater amounts 
of heat from the intermediate portion than from the higher and lower 
portions in the inner shroud 130, those small apertures 100 which are 
located at the intermediate portion may have their diameters or numbers 
increased, as shown in FIG. 9, as compared with those small apertures 100 
which are located at the higher and lower portions. The reason why the 
temperature at the intermediate portion is relatively high is that the 
heat of the higher and lower portions is also released from the upper and 
lower covers of the inner shroud 130 as compared with the intermediate 
portion, so that a greater amount of heat remains in the intermediate 
portions of the inner shroud 130. 
The provision of the multiplicity of small apertures 100 at the wall of the 
inner shroud 130 enables the thermal off-track to be minimized while 
greatly reducing the turbulent flow of air. The effects achieved by the 
provision of the small apertures 100 will be described by referring to 
FIG. 10. 
FIG. 10 is a diagram showing chronological changes in the off-track 
phenomenon occurring in the magnetic heads with respect to the magnetic 
disks when the inner shroud is formed with apertures and when the inner 
shroud is formed with no apertures. In the diagram shown in FIG. 10, a 
line X represents a chronological change occurring when the inner shroud 
is formed with no apertures, and a line Y indicates a chronological change 
occurring when the inner shroud is formed with apertures. It will be 
clearly seen in the figure that when no apertures are formed, the 
off-track does not become stable in value until the magnetic disks are 
driven for rotation for over one hour, and that when the apertures are 
formed, the value of the off-track falls within an allowable range in 
several minutes following initiation of rotation of the magnetic disks. 
This is accounted for by the fact that the heat generated by friction 
between the air and the surfaces of the magnetic disks during the rotation 
of the magnetic disks remains inside the inner shroud when no apertures 
are formed at its wall, and a temperature difference is produced between 
the inside and the outside the inner shroud, so that it takes time to 
eliminate the temperature difference by allowing the magnetic disks to 
rotate. On the other hand, when the inner shroud is formed with the 
apertures, the heat generated inside the inner shroud is released to the 
outside through the apertures and the temperature difference is eliminated 
earlier than when no apertures are formed, thereby enabling the off-track 
value to become stable in a few minutes. 
From the foregoing description, it will be appreciated that the magnetic 
disk storage device according to the invention comprises an inner shroud 
for enclosing the disk assembly in its entirety along the outer 
circumferential surfaces of the magnetic disks and being formed with a 
multiplicity of small apertures. The provision of such inner shroud makes 
it possible to achieve the effects of eliminating turbulent flow of air 
currents and avoiding vibration of the magnetic heads and the magnetic 
disks and minimizing the off-track phenomenon caused by heat generated by 
the rotation of the magnetic disks. 
In the embodiments shown and described hereinabove, the actuators of the 
magnetic disk storage device have been shown and described as being of the 
linear movement type. The invention is not, however, limited to this 
specific form of actuators and actuators of the rotary type may also be 
used without departing from the scope of the invention.