Shortened rail glide head

Details Shortened rail glide head Shortened rail glide head

1999-08-25

2001-05-15

Miller, Brian E. (Department: 2754)

Dynamic magnetic information storage or retrieval

Fluid bearing head support

Disk record

C360S236800, C360S236100, C360S236200, C073S105000

Reexamination Certificate

active

06233119

ABSTRACT:

FIELD OF THE INVENTION
This invention relates to glide heads used to detect defects on the surface of magnetic or magnetic-optical memory disks such as those used in hard disk drives.
BACKGROUND OF THE INVENTION
A computer hard disk drive comprises a magnetic memory disk mounted on a spindle which is driven by a motor to rotate the magnetic disk at high speed. A read/write head, kept in close proximity to the surface of the rotating magnetic disk, reads or writes data on the magnetic disk. The read/write head is separated from the surface of the magnetic disk by an air bearing created by the high speed rotation of the magnetic disk. The read/write head flies on this air bearing, e.g., at a height of approximately one microinch. The closer the read/write head is to the surface of the magnetic disk, the more information may be written on the disk. Thus, it is desirable for the read/write head to fly as close as possible to the surface of the magnetic disk.
Typical memory disks comprise a substrate that is plated with a hard material such as a nickel phosphorus alloy. The nickel phosphorus is then textured or roughened. An underlayer, a magnetic alloy or magnetic-optical material, and a protective overcoat are then deposited on the nickel phosphorus, e.g., by sputtering. As mentioned above, the disk manufacturing process leaves the surface of the disk in a slightly roughened condition.
The precision with which the read/write head flies over the magnetic disk requires that care is taken during manufacturing to assure that there are no protrusions or asperities on the disk surface that may interfere with the read/write head. A protrusion on the surface of the disk that contacts the read/write head during use may damage the head or the disk.
Accordingly, during manufacturing of magnetic or magnetic-optical disks, tests are performed with “glide heads” to determine if there are any asperities, voids or contamination that might interfere with the read/write head. Accurate testing of disks for such defects assures that the disk manufacturer does not unnecessarily reject good quality disks or pass on poor quality disks that may later fail.
During testing, the glide head must fly over the surface of the disk at a height no greater than the minimum fly height of the read/write head.
FIG. 1
illustrates a glide head
1
flying over the surface of a magnetic disk
2
. Disk
2
spins in the direction of arrow
3
about a spindle
4
. Glide head
1
is connected to a suspension arm
5
, which maintains the position of glide head
1
relative to disk
2
. Suspension arm
5
is controlled by an actuator
7
, such as a stepper-motor actuator or a voice-coil actuator, which moves glide head
1
laterally over the surface of magnetic disk
2
in the direction of arrow
6
. The lateral movement of glide head
1
is slow relative to the high speed rotation of magnetic disk
2
. Similar to a read/write head, glide head
1
flies over an air bearing that is created by the high speed rotation of magnetic disk
2
.
FIG. 2
is a side view of magnetic disk
2
with a down facing glide head
1
A and an up facing glide head
1
B flying over and testing surfaces
2
A and
2
B of magnetic disk
2
, respectively. Air bearings
8
A,
8
B, created by the high speed rotation of magnetic disk
2
, lie between glide heads
1
A and
1
B and surfaces
2
A and
2
B, respectively. As in
FIG. 1
, glide heads
1
A and
1
B are connected to suspension arms
5
A,
5
B. Arms
5
A,
5
B are controlled by actuator
7
to laterally move glide heads
1
A,
1
B over surfaces
2
A,
2
B of magnetic disk
2
in the direction of arrow
6
.
FIG. 3
shows glide head
1
flying over a section of magnetic disk
2
rotating in the direction of arrow
3
. The roughened texture of top surface
2
A of magnetic disk
2
is schematically shown in FIG.
3
.
FIG. 4A
shows a bottom surface of down facing glide head
1
A.
FIG. 4B
shows a trailing side
15
of down facing glide head
1
A. As shown in
FIGS. 4A and 4B
, glide head
1
A comprises a slider
9
, a suspension arm
5
connected to a top surface of slider
9
, and a transducer
10
, such as a piezoelectric crystal. (Transducer
10
and suspension arm
5
are schematically represented in
FIG. 4B.
) Slider
9
comprises an inside rail
11
, an outside rail
12
, and a wing
13
. Inside rail
11
and outside rail
12
both have forward tapered ends
14
, which are tapered at an angle less than one degree from horizontal (typically an angle between thirty minutes and fifty minutes). Tapered ends
14
provide lift to glide head
1
A. Wing
13
provides additional surface area to the top surface of slider
9
upon which transducer
10
is mounted. When rail
11
or
12
impact an asperity or contamination on disk
2
or sink in response to encountering a void, transducer
10
converts the mechanical energy from the event into an electrical signal which can be measured. Generally, however, inside rail
11
generates a stronger signal output voltage when detecting a defect than outside rail
12
when at the same fly height. Accordingly, it is difficult to determine when outside rail
12
is detecting a defect. Also, when a signal is generated by transducer
10
, it is difficult to know the size of the defect that caused the signal, because one cannot know whether the signal was created by an encounter with the more sensitive inside rail
11
or the less sensitive outside rail
12
.
Because tapered ends
14
of inside rail
11
and outside rail
12
create lift, it is important that as slider
9
moves laterally across the rotating surface of magnetic disk
2
, both inside rail
11
and outside rail
12
remain over the surface of magnetic disk
2
. In other words, one cannot move slider
9
such that outside rail
12
extends past the outer circumference of disk
2
. If outside rail
12
is moved beyond the outer circumference of disk
2
, slider
9
will lose its lift under outside rail
12
and will roll, causing slider
9
to contact magnetic disk
2
. Accordingly, only outside rail
12
can detect asperities over the outermost portion of the surface of magnetic disk
2
. Obviously, the surface of disk
2
adjacent the outer circumference must be tested for asperities. Thus, a glide head that can accurately test the outermost portion of the surface of a magnetic disk without losing its lift is needed.
The distance that slider
9
may move laterally outward along the surface of magnetic disk
2
is determined by the width of rails
11
and
12
. In order to cover the entire surface area on magnetic disk
2
, slider
9
is moved laterally, step by step, across the surface of magnetic disk
2
. Each step must be at least slightly less than the width of one rail in order to test the entire surface of the disk for defects. Accordingly, in order to minimize the time necessary to test each magnetic disk, a glide head with wide rails is desirable.
SUMMARY
A glide head in accordance with our invention uses the outside rail of the slider as the active testing rail. In addition, the rails of the slider are wide so that during testing the length of the steps that the slider is moved laterally over the surface of the magnetic disk can be greater, thereby minimizing testing time.
In one embodiment, the outside rail is longer than the inside rail so that the trailing end of the outside rail extends beyond the trailing end of the inside rail and, thus, the outside rail is more sensitive than the inside rail. The inside rail is wider than the outside rail to compensate for the additional lift on the outside rail created by the greater length of the air bearing surface of the outside rail. By keeping the area of the two rails approximately equal, the slider maintains an equal amount of lift under both rails, thereby preventing the slider from rolling during flight. In another embodiment, the area of the rails is unequal and the location of contact with the suspension arm may be moved to compensate for the increased lift created by the greater area of the outside rail.
In another embodiment, each rail

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