Dynamic magnetic information storage or retrieval – Record transport with head stationary during transducing – Disk record
Reexamination Certificate
1997-09-26
2001-05-22
Korzuch, William R. (Department: 2652)
Dynamic magnetic information storage or retrieval
Record transport with head stationary during transducing
Disk record
C360S097030, C360S098010
Reexamination Certificate
active
06236532
ABSTRACT:
BACKGROUND OF THE INVENTION
(1) Field of the Invention
The present invention relates to magnetic disk drives, and more particularly to high storage density magnetic disk drives which are capable of increasing the reliability of magnetic disks.
(2) Description of the Related Art
In magnetic disk drives, usually at least one magnetic disk is used. To prevent wear of the magnetic disk due to friction with the magnetic head, the magnetic disk has its surface covered by a liquid lubricant, such as PFPE (perfluoropolyether).
However, the liquid lubricant has the problem that its thickness is reduced gradually due to scattering caused by centrifugal forces produced by rotation of the magnetic disk. The extent of the thickness reduction is accelerated by the shearing force of air flow or stream along the surface of the magnetic disk. As the thickness of the liquid lubricant becomes thinner, the lubrication is effect of preventing wear of the magnetic disk caused by friction thereof with the magnetic head is reduced thereby resulting in wear generation. This gives rise to frequent loss of data stored in the magnetic disk, thereby deteriorating the reliability of the system.
SUMMARY OF THE INVENTION
An object of the invention is to provide a magnetic disk drive, in which the influence of shearing force of air flow along the magnetic disk surface is minimized.
The magnetic disk drive according to the invention features a clearance between a magnetic disk and an opposed surface thereto, for instance between adjacent magnetic disks, between a magnetic disk and the inner top or bottom wall surface of a magnetic disk vessel, or between a magnetic disk and a plate disposed between adjacent magnetic disks, that is small enough to eliminate air flow along the magnetic disk surface. The clearance can be determined in terms of a millimeter unit by the following formula:
∑
n
t
n
×
m
n
wherein m
n
is the mole percentage of gas n, and t
n
is the clearance coefficient of the gas n. The clearance coefficient varies with the sealed gas and is found to be 1.0 for air, 1.1 for helium, 1.7 for neon, 1.2 for argon, 1.4 for krypton, and 1.2 for xenon. As for the clearance between the magnetic disk and an opposed surface portion in which the magnetic head is operative on the surface of the magnetic disk, it may be such that the magnetic disk will not be touched by the magnetic head, that is, it may be slightly greater than the thickness of the magnetic head.
Another feature of the invention resides in that the surface of a plate which is disposed between a magnetic disk and the inner top or bottom wall surface of the magnetic disk drive or between adjacent magnetic disks, is formed with a groove having an inclination angle having a value larger than 0 degrees and not larger than 90 degrees in the direction of rotation of the disk with respect to the direction of the inner periphery of the disk.
Further, according to the invention, air flow directed inwardly of magnetic disk is produced between the disk and an opposed surface by means of a fan provided in a shaft, thereby minimizing scattering of liquid lubricant.
There have been several attempts at reducing the clearance between adjacent ones of two or more magnetic disks disposed one above another by making certain modifications in the magnetic head related to size reduction of the magnetic disk drive (as disclosed in, for instance, Japanese Patent Application Kokai Publication No. Sho 61-9818 and Japanese Patent Application Kokai Publication No. Sho 62-185287). However, no specific example of clearance value for clearance value from the standpoint of the scattering of lubricant is shown in the aforesaid prior art publications.
At the position of radius r of a magnetic disk, the shearing force &tgr;o of air flow acting on the liquid lubricant surface in the radial direction of the air flow maybe given as:
&tgr;
o
=(&ohgr;
{fraction (3/2)}
pv
½
r
)/2 (1)
wherein &ohgr; is the angle of rotation speed, v is the viscosity of air, and p is the density of air.
The shearing force &tgr; of air flow is expressed by the equation (2) given below with a slope with respect to distance Z of the direction of the axis of rotation of the velocity V of air stream flowing in the clearance between magnetic disk and an opposed surface (i.e., direction across the clearance). The shearing force &tgr; for Z=0 (i.e., lubricant surface) corresponds to &tgr;o.
&tgr;=∂
V/∂Z
(2)
Thus, when V is positive (i.e., directed outwardly from the magnetic disk), the shearing force &tgr; causes scattering of liquid lubricant. If V becomes zero, the shearing force becomes zero, and thus the scattering of liquid lubricant can be minimized. When air flow is directed inwardly of the magnetic disk, V becomes negative, and the thickness reduction of the liquid lubricant film can be further reduced.
REFERENCES:
patent: 5280403 (1994-01-01), Martin
patent: 5325251 (1994-06-01), Gorove et al.
patent: 5381284 (1995-01-01), Gregory et al.
patent: 5422770 (1995-06-01), Alt
patent: 5453890 (1995-09-01), Takegami et al.
patent: 5675452 (1997-10-01), Nigam
patent: 5850317 (1998-12-01), Gregory et al.
patent: 61-9818 (1986-01-01), None
patent: 62-185287 (1987-08-01), None
patent: 3-32882 (1991-02-01), None
patent: WO 94/11877 (1994-05-01), None
Hayes Soloway Hennessey Grossman & Hage PC
Korzuch William R.
NEC Corporation
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