Dynamic magnetic information storage or retrieval – Monitoring or testing the progress of recording
Reexamination Certificate
1999-07-19
2002-09-17
Sniezek, Andrew L. (Department: 2651)
Dynamic magnetic information storage or retrieval
Monitoring or testing the progress of recording
C360S025000, C360S075000, C360S053000, C360S060000
Reexamination Certificate
active
06452735
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to digital storage devices and, more particularly, to disk drives which monitor the flying height of dual element transducers that employ magneto-resistive (MR) read elements.
BACKGROUND OF THE INVENTION
A disk drive is a digital data storage device that stores information within concentric tracks on a storage disk. The storage disk is coated on both of its primary surfaces with a magnetic material that is capable of changing its magnetic orientation in response to an applied magnetic field. During operation of a disk drive, the disk is rotated about a central axis at a constant rate. To read data from or write data to the disk, a magnetic transducer (or head) is positioned above (or below) a desired track of the disk while the disk is spinning.
Writing is performed by delivering a polarity-switching write current signal to the transducer while the transducer is positioned above (or below) the desired track. The write signal creates a variable magnetic field at a gap portion of the transducer that induces magnetically polarized transitions into the desired track. The magnetically polarized transitions are representative of the data being stored.
Reading is performed by sensing the magnetically polarized transitions on a track with the transducer. As the disk spins below (or above) the transducer, the magnetically polarized transitions on the track induce a varying magnetic field into the transducer. The transducer converts the varying magnetic field into an analog read signal that is delivered to a preamplifier and then to a read channel for appropriate processing. The read channel converts the analog read signal into a digital signal that is processed and then provided by a controller to a host computer system.
FIG. 1
illustrates a standard disk drive, generally designated
10
. The disk drive
10
includes a disk
12
that is rotated by a spin motor
14
. The spin motor
14
is mounted to a base plate
16
. An actuator arm assembly
18
is also mounted to the base plate
16
.
The actuator arm assembly
18
includes a transducer
20
mounted to a flexure arm
22
, which is attached to an actuator arm
24
that can rotate about a bearing assembly
26
. The actuator arm assembly
18
includes a voice coil motor (VCM)
28
, which radially positions the transducer
20
relative to the disk
12
. The spin motor
14
, transducer
20
and VCM
28
are coupled to electronic circuits
30
mounted to a printed circuit board
32
. The electronic circuits
30
typically include a preamplifier, a read channel, a servo control unit, a microprocessor-based controller and a random access memory (RAM).
The disk drive
10
may include a plurality of disks
12
, each with two recording surfaces. In this case, two actuator arm assemblies
18
are provided for each disk
12
.
The transducer
20
is a dual element transducer that includes separate read and write elements. Single element transducers usually contain a single inductive element that performs both read and write functions, whereas dual element transducers usually contain a magneto-resistive (MR) read element and an inductive write element. The MR read element can be a conventional magneto-resistive element, a giant magneto-resistive (GMR) element, or a similar component.
Since the transducer
20
is a dual element transducer, the read and write elements can be optimized for their respective functions. For example, MR read elements are more sensitive than inductive read elements to small variable magnetic fields, which permits MR read elements to read much fainter signals from the disk surface. Employing an MR read element permits data to be more densely packed on the disk surface.
MR read elements generally include a strip of magneto-resistive material between two magnetic shields. When properly biased, the resistance of the magneto-resistive material varies almost linearly with an applied magnetic field. During a read operation, the MR strip is positioned above (or below) a desired track within the varying magnetic field caused by magnetic transitions on the track and a constant bias current is passed through the strip. By Ohm's law (V=IR), the variable resistance and the constant bias current of the MR strip result in a variable voltage across the MR strip that is proportional to the variable resistance. That is, V+&dgr;V=I(R+&dgr;R). Therefore, the variable voltage is representative of the data stored within the desired track. The variable voltage provides an analog read signal which is then amplified by the preamplifier, processed and converted into digital form by the read channel, and transferred by the controller to a host computer.
FIG. 2
is a diagrammatic representation of an air bearing surface of the transducer
20
which faces the disk
12
. As is seen, the transducer
20
includes an inductive write element
34
, a write gap
36
, a first shield
38
, a second shield
40
, a read gap
42
, and an MR read element
44
.
During a read operation, the magnetically polarized transitions previously written onto the disk
12
are read by the MR read element
44
. The first and second shields
38
and
40
form the read gap
42
which serves to focus the flux from the magnetically polarized transitions onto the MR read element
44
by shielding the MR element
44
from other sources of magnetic flux (e.g., sources of magnetic flux not associated with the particular location from which information is being read). In other words, the first and second shields
38
and
40
shunt extraneous magnetic flux away from the MR read element
44
as reading occurs.
During a write operation, variable current is applied to write coils (not shown) in the transducer
20
which induce magnetic flux across the write gap
36
between the write element
34
and the first shield
38
. The write element
34
and first shield
38
act as poles for an electromagnet which induces the magnetic flux across the write gap
36
that records magnetically polarized transitions on the disk
12
. Furthermore, since the magnetic flux in the write gap
36
has relatively high intensity, and the MR read element
44
is in close proximity to the write gap
36
, a large amount of the magnetic flux across the write gap
36
strikes the MR read element
44
during a write operation. Consequently, the MR read element
44
is typically not used to read data from the disk
12
during a write operation.
FIG. 3
is a simplified diagrammatic representation of a cross-sectional view of an air bearing slider
46
that includes the transducer
20
flying above a disk surface
48
of the disk
12
. The slider
46
is located at the distal end (opposite VCM
28
) of the actuator arm assembly
18
. The slider
46
includes a leading edge
50
and a trailing edge
52
. The transducer
20
is located proximate the trailing edge
52
.
During operation of the disk drive
10
, the disk
12
is rotated in the direction of arrow A from the leading edge
50
to the trailing edge
52
. The slider
46
is aerodynamically designed so that when the disk
12
revolves at its normal operating speed, a small cushion of air between the slider
46
and the disk surface
48
lifts the slider
46
(and hence the transducer
20
) a predetermined distance above the disk surface
48
. The distance between the transducer
20
and the disk surface
48
is known as the flying height (h
f
) of the transducer
20
. The performance of the disk drive
10
will depend, to a large extent, on whether the flying height of the transducer
20
stays within a predetermined flying height range. For instance, if the flying height of transducer
20
is too low then transducer
20
might crash, engage in excessive contact with the disk surface
48
resulting in damage to the transducer
20
and/or disk
12
, or accumulate excessive debris or lubricant from disk surface
48
. On the other hand, if the flying height of transducer
20
is too high then data errors might occur during read and write operations. More particularly, if the transdu
Egan Curtis
Lin Gang Herbert
Maxtor Corporation
Sigmond David M.
Sniezek Andrew L.
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