Dynamic magnetic information storage or retrieval – Fluid bearing head support – Disk record
Reexamination Certificate
1999-07-21
2002-07-09
Miller, Brian E. (Department: 2652)
Dynamic magnetic information storage or retrieval
Fluid bearing head support
Disk record
C360S236300, C360S236100, C360S236900, C360S245100
Reexamination Certificate
active
06417992
ABSTRACT:
The present invention relates generally to a magnetic head assembly including a magnetic head slider having a plurality of pads, and more particularly to a magnetic head assembly capable of preventing stiction of a magnetic head slider to a magnetic disk during the start of rotation of the magnetic disk drive.
BACKGROUND OF THE INVENTION
In recent years, there is a desire for reducing the size and increasing the capacity of magnetic disk drives for use as external storage devices in computers. One method of increasing the capacity of the magnetic disk drive is to increase the number of magnetic disks mounted on a spindle, and in association therewith the spacing between the magnetic disks in recent magnetic disk drives has increasingly been reduced in order to reduce the overall height of the disk drive unit.
In recent magnetic disk drives, flying type magnetic head sliders employing the contact start and stop (CSS) system are frequently used. In such flying type magnetic head sliders with the CSS system, the magnetic head slider comes into contact with the magnetic disk when the disk drive stops rotating, but whereas during rotation, the magnetic head slider is kept flying at a microscopic height from the disk surface by an air flow generated over the surface of the magnetic disk, which rotates at a high speed during the recording or reproduction of information.
In flying type magnetic head sliders with the CSS system, an electromagnetic transducer (i.e., a magnetic head element) is built into the slider, which receives the air flow generated over the disk surface. To maintain the slider in position, it is supported by a suspension. Accordingly, when the magnetic disk is not being rotated, the slider (including the electromagnetic transducer) is in contact with the disk surface, whereas when the magnetic disk is rotated, an air bearing surface of the slider that is opposed to the magnetic disk receives an air flow generated by the rotation of the magnetic disk, and the slider flies a small distance either above or below the disk surface. As a result, the electromagnetic transducer built into the slider is moved over the disk surface while being supported by the suspension, and performs recording or reproduction of information on a given track.
In a magnetic disk drive employing a conventional flying type magnetic head slider, a pair of rails are generally provided along opposite side portions of the surface of the magnetic head slider that opposes the disk surface. Each of these two rails includes a flat air bearing surface. Further, a tapering surface is formed on each rail at its air inlet end portion. The air bearing surface of each rail receives an air flow generated by the high-speed rotation of the magnetic disk, which makes the slider fly above (or below) the disk, maintaining a microscopic distance between the disk surface and the electromagnetic transducer.
With the CSS system, a relatively steady microscopic flying height (in the submicron range) can be obtained when the disk is rotated at a constant speed. However, when the disk is not being rotated, the rail surfaces (air bearing surfaces) of the slider are in contact with the disk. Accordingly, when the magnetic disk drive starts or stops rotating, the air bearing surfaces slide on the surface of the magnetic disk. If the surface roughness of the magnetic disk is low (i.e., if the disk surface is relatively smooth), the contact area between the air bearing surfaces and the magnetic disk surface during periods of non-rotation is large, and there arises a stiction problem between the magnetic head slider and the magnetic disk during the start of rotation of the magnetic disk.
To avoid stiction, the surface roughness of the magnetic disk has conventionally been increased to a suitable level. However, such increases in surface roughness have the drawback of causing an increase in the flying height. Thus, in order to reduce the flying height of the magnetic head slider in response to the requirement for high-density recording, the surface roughness of the magnetic disk needs to be decreased, even though such a decrease in roughness increases stiction in conventional devices.
In general, to improve the durability of the magnetic disk, a protective film made of a hard material such as carbon, and a lubricating layer for reducing friction and wear of the protective film are formed on a recording layer of the disk. Due to the presence of the lubricating layer, friction and wear of the protective film can be reduced. However, when the disk stops rotating, there is a possibility that stiction between the disk and the slider may occur, preventing the disk drive from being restarted.
In association with increases in the amount of information being processed, the developments in high density, large capacity, and compact size magnetic disk drives been remarkable, and the occurrence of stiction has been greatly highlighted as a cause of faulty operation of the disk drive. One of the reasons for such faulty operation is the use of spindle motors with reduced torque (because of their small size). Another reason for such faulty operation is the smoothing out of the disk surface in order to achieve high density recording.
To prevent this stiction problem, it has been proposed to provide a plurality of pads, or projections, on the flying surfaces (i.e., air bearing surfaces) of the slider, thereby reducing the contact area between the slider and the disk surface. In assembling a magnetic head assembly by mounting such a magnetic head slider having a plurality of pads upon a front end portion of a suspension formed of stainless steel, the magnetic head slider is mounted on the front end portion of the suspension so that its load point (the point where the spring load of the suspension is applied to the magnetic head slider) coincides with the center of gravity of the magnetic head slider.
At present, a three-phase Hall-less motor employing no Hall element is generally used as the motor for rotating the spindle. In a CSS type magnetic disk drive, the magnetic head slider comes into contact with the magnetic disk when the disk drive is powered off, as mentioned above. Upon restarting the disk drive, a current is passed through any one of the three-phase coils to position the coil near a permanent magnet. At this time, the motor is rotated in either the forward direction or the reverse direction, depending upon the positional relationship between the coil and the permanent magnet upon stopping of the disk drive, so that the motor is rotated forwardly or reversely by about 60° to position the coil near the permanent magnet. After this positioning, the current passing through each phase is controlled to be switched, thereby continuously rotating the motor in the forward direction. In this manner, the rotating direction of the motor is determined according to the positional relationship between the coil and the permanent magnet upon stopping of the disk drive. Accordingly, the initial reverse rotation of the motor occurs with a probability of about 50%.
In the case of a magnetic head slider having pads formed on an air bearing surface, it has been found that such reverse rotation of the motor causes the following problem, which will now be described with reference to
FIG. 1
, which is a schematic side view of a magnetic head slider
2
parked on a magnetic disk
4
.
FIG. 4
, an arrow R
1
denotes the forward rotating direction of the magnetic disk
4
, and an arrow R
2
denotes the reverse rotating direction of the magnetic disk
4
. Two pads
6
are formed on the air bearing surfaces of the head slider
2
near the air inlet end of the head slider
2
, although only one pad
6
is shown in the
FIG. 1
view. Similarly, two pads
8
are formed on the air bearing surfaces of the head slider
2
at an intermediate position between the air inlet end and the air outlet end of the head slider
2
, although only one is shown in FIG.
1
. In particular, the pad
8
that is formed on the air bearing surface where a head element (transducer) is f
Kameyama Masaki
Ohwe Takeshi
Sugimoto Masaharu
Fujitsu Limited
Greer, Burns & Crain LTD
Miller Brian E.
LandOfFree
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