Dynamic magnetic information storage or retrieval – Automatic control of a recorder mechanism – Controlling the head
Reexamination Certificate
2001-07-19
2004-01-27
Sniezek, Andrew L. (Department: 2651)
Dynamic magnetic information storage or retrieval
Automatic control of a recorder mechanism
Controlling the head
C360S075000, C360S031000, C360S077040, C360S077030, C324S212000
Reexamination Certificate
active
06683744
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a magnetic-disk evaluation apparatus (i.e., a spin stand) for determining, without writing actual servo signals to a magnetic disk, whether temporary servo signals previously written to a magnetic disk by magnetic transfer are acceptable. The present also further relates to a method for evaluating temporary servo signals previously written to a magnetic disk for use in the self servo writing method for magnetic disk apparatuses.
2. Description of the Related Art
Hard disk drives (HDD) are commonly used as information storage devices, and operate to position their heads on the basis of servo signals written to a magnetic disk.
Referring now to
FIG. 1
, a conventional HDD
30
[hereinafter HDD
30
] includes a magnetic disk
1
rotatable at several thousand rpm by a spindle motor
2
. During rotation, air flow above magnetic disk
1
causes a slider
4
located at the tip of a rotary positioner
3
to float slightly above magnetic disk
1
.
A magnetic head
5
is located at an end of slider
4
. During operation, servo signals are magnetically written on magnetic disk
1
and are detected by magnetic head
5
, amplified by a preamplifier
6
, and demodulated by a servo demodulating circuit
7
, to obtain track information (indicating on which track the magnet head is lying) and a PES (Position Error Signal, which indicates how far the head is separated from the center of a track).
During operation, HDD
30
determines the current head position by using magnetic head
5
to read the servo signals, and positions magnetic head
5
on a track (target track) with desired information written thereto by using a voice coil motor (VCM)
8
to drive rotary positioner
3
.
That is, the difference between the target track position and the head position is detected as the PES, which is input to a compensator
9
. Then, compensator
9
generates a drive command to rotary positioner
3
on the basis of the PES and transmits this drive command to voice coil motor (VCM)
8
through power amplifier
10
. In this manner, voice coil motor (VCM)
8
drives rotary positioner
3
. Thus, feeding back the PES serves to reduce the positional difference between the target track and the head position. Further, in terms of absolute coordinates, the target track position varies in accordance with rotational cycles due to the eccentricity of the disk itself.
During operation, magnetic disk
1
has the above servo signals and data recorded thereon and reproduced therefrom by magnetic head
5
. A defect in magnetic disk
1
prevents proper recording or reproduction. Thus, magnetic disk
1
must be tested before integration (that is, magnetic disk
1
is clamped to spindle motor
2
) to ascertain that magnetic disk
1
can provide minimum required performance.
The test consists of using a magnetic head to sequentially check magnetic disk
1
for its gliding property, its certify property, and its contact start stop (CSS) property. The gliding property check consists of checking the number of projections on magnetic disk
1
. The certify property check consists of checking magnetic disk
1
for its electric properties and defects. The contact start stip (CSS) property check consists of checking the durability of magnetic disk
1
.
It should be understood, that an apparatus used to evaluate the performance of magnetic disk is called a “spin stand.”
Referring additionally now to
FIG. 2
shows a “spin stand” having a base
11
which supports a spindle motor
12
. During operation, spindle motor
12
rotates at an arbitrary rotation speed allowing magnetic disk
1
to be evaluated. An evaluating magnetic head
13
reproduces and records signals on and from magnetic disk
1
in order to evaluate magnetic disk
1
. A carriage
14
supports evaluating magnetic head
13
. A ‘&thgr;’ stage
15
[hereinafter &thgr; stage
15
] adjusts carriage
14
to an arbitrary angle. A stage
16
is movable in at least one direction along a guide
17
in order to freely vary the positional relation ship between spindle motor
12
and evaluating magnetic head
13
. It is to be understood, that stage
16
is movable in a direction in
FIG. 2
along guide
17
.
It is to be understood, that HDD
30
, based on the head positioning method using rotary positioner
3
driven by voice coil motor (VCM)
8
, has the advantage of having a compact structure but also has a drawback in that the head skew angle varies with the track.
The head skew angle relates to the flying head height of magnetic head
13
and causes variations in the reproduction output from magnetic head
13
. Accordingly, the same skew angle as that in conventional HDD
30
must also be used in conducting the above-described gliding, certifying, and CSS property checks in order to evaluate the performance of magnetic disk
1
.
Thus, for these checks, the positional relationship between spindle motor
12
and evaluating magnetic head
13
of the spindle stand must be adjusted to be identical to that in HDD
30
, so that commonly used spin stands must include a positioning mechanism based upon directly moving stage
16
, the rotary &thgr; stage
15
, or similar parts.
The above-described checks are then carried out using the spin stand and, if magnetic disk
1
is determined to be acceptable, magnetic disk
1
is clamped to spindle motor
2
, which is then assembled into HDD
30
.
With magnetic disk
1
integrated into HDD
30
(that is, magnetic disk
1
is clamped to spindle motor
2
), a device called a “servo track writer (STW) ” is used to write servo signals to magnetic disk
1
.
Additionally referring now to
FIG. 3
, during operation, the servo track writer (STW) is used to produce servo tracks. During operation, the servo track writer (STW) conventionally presses a pin
19
, accurately positioned by an external actuator
18
, against rotary positioner
3
inside HDD
30
, via a link
20
for positioning, while setting the head position on the basis of a scale inside actuator
18
using a fine feeding mechanism.
Since the servo signals are each written to a corresponding one of the tracks on magnetic disk
1
, the servo track writer (STW) must write the servo signals to all the tracks on magnetic disk
1
while executing accurate positioning via link
20
. Since an increase in recording density increases the number of tracks while reducing the track width, the servo track writer (STW) must execute more accurate positioning on a larger number of tracks.
Unfortunately, this realization of accurate positioning requires a rigid and expensive mechanical positioning mechanism as well as a large amount of time for writes. Consequently, multiple servo track writers (STW) must be provided for parallel processing, further requiring a larger space in manufacturing clean rooms in which the servo track writers (STWs) are arranged. This requirement also increases costs.
Considerable effort has been put into developing a method for omitting the above described servo track writers (STWs) and causing HDD
30
to execute self servo writing.
Additionally referring now to
FIG. 4
, temporary servo signals
21
have already been written to magnetic disk
1
. It is to be understood, that temporary servo signals
21
can be written to magnetic disk
1
substantially faster than with the servo track writers (STWs). This faster writing may be accomplished, for example, by using a technique such as magnetic printing to copy a magnetic pattern from a master disk (not shown).
After an initial writing, magnetic disk
1
is integrated into HDD
30
, which then writes only actual servo signals
22
to disk
1
on the basis of temporary servo signals
21
.
Subsequently, the magnetic head is positioned on the basis of actual servo signals
22
, and it is confirmed that HDD
30
operates correctly.
Unfortunately, if HDD
30
cannot operate correctly due to any defect in either actual servo signals
22
or temporary servo signals
21
, the positioner section must be disassembled so that magnetic disk
Sato Kiminori
Takano Yukihiro
Darby & Darby
Fuji Electric & Co., Ltd.
Sniezek Andrew L.
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