Dynamic magnetic information storage or retrieval – Record transport with head stationary during transducing – Disk record
Reexamination Certificate
2001-10-16
2004-04-06
Heinz, A. J. (Department: 2653)
Dynamic magnetic information storage or retrieval
Record transport with head stationary during transducing
Disk record
C369S261000, C369S258100
Reexamination Certificate
active
06717768
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an information storage device and method for reducing airborne noise and vibration. Particularly, the present invention relates to an airflow damper that reduces airborne noise and vibration in hard disk drive devices.
2. Description of the Related Art
Airflow within a hard disk drive assembly generally tends to vibrate the disks during rotation, generating undesired noise in the hard disk drive assembly. In order to understand why airflow has such an important role in regulating airborne noise, it is necessary to examine airflow characteristics in a hard disk assembly (HDA).
FIG. 1
illustrates the main airflow streams in a conventional hard disk assembly.
As shown in
FIG. 1
, the hard disk assembly (HDA)
100
includes a hub
110
, first and second disks
120
and
130
mounted on hub
110
, and a housing cover
140
. The first and second disks
120
and
130
are rotated by hub
110
. In
FIG. 1
, h is understood to be the distance between upper disk
120
and the top inner surface of housing cover
140
, and d
&thgr;
d
&thgr;
is understood to be the distance between the edges of disks
120
,
130
and the sidewall of housing cover
140
.
When first and second disks
120
and
130
are rotatably driven by hub
110
, the disks pull fluid (air) axially downward and pump the air radially outward. For example, air is pulled downward along hub
110
from the space above rotating disk
120
. This axial downward air then flows radially outward along the upper surface of rotating disk
120
.
The main airflow in HDA
100
is thus tangential to the circumferential edge of rotating disks
120
and
130
, as represented by the upward and downward arrows along the periphery of rotating disks
120
and
130
. The radially outward flow along the surface of the disks operates as a secondary flow caused by a rotating boundary layer. The rotating boundary layer that is formed is designated by &dgr;
m
and &dgr;
f
in
FIG. 1
, and is commonly referred to as the Ekman layer, which will be described in greater detail as follows.
A qualitative description of airflow and the boundary layers is as follows. Because of the no-slip condition of disks
120
and
130
with respect to airflow, fluid in contact with the surface of the rotating disks
120
and
130
rotates with the same angular velocity as the disk surface, and experiences the same centripetal acceleration. At the start of motion of the disks, a boundary layer of fluid begins to form in the circumferential direction. The fluid in the boundary layer begins to spin, but cannot maintain the same centripetal acceleration as the surface of the disk, because of fluid viscosity. Because of this, the boundary layer acquires an outward radial component. As the radial component of fluid flow increases in magnitude, a secondary fluid layer develops in a radial direction, having stresses that are centrally directed. These stresses provide the secondary fluid layer with a central force, and have a centripetal acceleration that is greater than zero but less than that of the surface of the disk. This secondary fluid layer, which may be understood as having components &dgr;
m
and &dgr;
f
as designated in
FIG. 1
, comprises the Ekman layer.
The Ekman layer component &dgr;
m
is formed near the surface of the disk
120
by disk rotation, and is defined as having a thickness (depth in the vertical direction) of 4&dgr;, whereby:
δ
~
v
Ω
,
Eq
.
(
1
)
and wherein v is the dynamic viscosity of the fluid forming the boundary layer and &OHgr; is the angular velocity of the disk. The Ekman layer component &dgr;
f
is formed near the top inner surface of housing cover
140
by fluid (air) rotation, and is defined as having a thickness (or depth in the vertical direction) of 8&dgr;.
By way of example, if &OHgr;=5,400 rpm, &dgr;=0.17 mm (the dynamic viscosity of air is 1.59×10
−5
/m
2
/s). The Ekman layer component &dgr;
m
thus has a thickness of 0.68 mm and the Ekman layer component &dgr;
f
has a thickness of 1.36 mm. Likewise, if &OHgr;=7,200 rpm, &dgr;=0.15 mm, the Ekman layer component &dgr;
m
has a thickness of 0.60 mm and the Ekman layer component &dgr;
f
has a thickness of 1.2 mm.
As further illustrated in
FIG. 1
, a large vortex
102
is created between secondary fluid layers &dgr;
m
and &dgr;
f
which comprise the Ekman layer. The creation of large vortex
102
excites disk fluttering during operation of the HDA, thus increasing noise level.
SUMMARY OF THE INVENTION
The present invention is therefore directed to an information storage device and method for reducing airborne noise and vibration, which substantially overcomes one or more of the problems due to the limitations and disadvantages of the related art.
Accordingly, to solve the above and other problems, it is an object of the present invention to provide a hard disk drive and method for reducing airborne noise and vibration, that prevents formation of a large air vortex above the disks in the hard disk assembly during rotation of the disks.
The above and other objects may be achieved by a hard disk assembly including in combination a housing; a hub within the housing; at least one disk mounted on the hub and rotated by the hub; and an airflow damper, mounted on an upper surface of an interior of the housing, that prevents formation of a vortex above the at least one disk during rotation of the at least one disk, the airflow damper having a thickness related to rotational speed of the at least one disk.
The above and other objects may also be achieved by a method of preventing vortex formation in a hard disk assembly, the hard disk assembly having a housing with a hub therein on which at least one disk is mounted and driven to be rotated, the method including providing an airflow damper on an upper surface of an interior of the housing, the airflow damper having a thickness related to rotational speed of the disk.
Further scope of applicability of the present invention will become apparent from the detailed description given hereinafter. However, it should be understood that the detailed description and specific examples, while indicating preferred embodiments of the invention, are given by way of illustration only, since various changes and modifications within the spirit and scope of the invention will become apparent to those skilled in the art from this detailed description.
REFERENCES:
patent: 4280155 (1981-07-01), Scott et al.
patent: 4583213 (1986-04-01), Bracken et al.
patent: 5631787 (1997-05-01), Huang et al.
patent: 5898545 (1999-04-01), Schirle
patent: 6128159 (2000-10-01), Ino
patent: 6236532 (2001-05-01), Yanagisawa
patent: 6487038 (2002-11-01), Izumi et al.
Blouin Mark
Heinz A. J.
Volentine & Francos, PLLC
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