Rotating media recording system with adaptive track density

Details Rotating media recording system with adaptive track density Rotating media recording system with adaptive track density

1999-11-03

2003-08-26

Hudspeth, David (Department: 2753)

Dynamic magnetic information storage or retrieval

Automatic control of a recorder mechanism

Controlling the head

Reexamination Certificate

active

06611395

ABSTRACT:

FIELD OF THE INVENTION
The invention disclosed broadly relates to the field of rotating media mass storage devices, and more particularly relates to the field of recording servodata on hard disk drives.
BACKGROUND OF THE INVENTION
In disk drives, the track density is a predetermined function for each product family. The tolerances of the heads, magnetic variations of the media, and variations in mechanical input noise are all taken into account when setting the track pitch (component parameters). Increased storage can be accomplished by increasing the track density. In the current servowriting process used in manufacturing of disk drives the track density is determined for a product family and is not customized for each individual drive manufactured.
Recording System Overview
In a recording system as shown in
FIG. 1
, a rotating media
102
and a data head
106
, which typically consists of a separate read
152
and write
154
elements, are used to store data in roughly concentric tracks on a storage medium. The head is positioned onto the data tracks
112
,
114
by reading sector servo patterns
110
, converting them into a voltage signal using read write interface card
124
and amplitude demodulator
140
. The output of the demodulator is digitized using A/D converter
142
and input to a microprocessor
144
which is executing a servo control program. The processor calculates a control voltage which is output to DAC
146
, converting the value of the control voltage into an analog signal which is input to a VCM driver
148
producing a current which moves the actuator
150
via the voice coil motor (VCM)
108
to position the data head onto the data track. The sector servo patterns are written during the manufacture of the disk drive assembly and are typically spaced at equal angular intervals along the data track. Track densities of modern disk drives are in the range of 10,000 up to 30,000 tracks per inch, so precise placement of the servo tracks is required to define the location of the data tracks.
Sector servo and Data Tracks
In a recording system, the media are servo written with sector servo tracks to allow positioning of the recording head at a radial location, indicated by a track number. An expanded view of a sector is shown in FIG.
2
. The sector field consists of servo patterns which in this example are labeled A, B, C, and D and repeat across the surface of the disk. The servo bursts define the center of the servo tracks, and in the example shown there are two servo tracks for each data track. The read element
202
reads the servo bursts A and C, and produces a signal amplitude which is demodulated to create a voltage proportional to the overlap of the head to the servo burst. The difference of the two amplitudes A−C, is input to the microprocessor
144
which computes a control current to the DAC
146
to move the data head
106
to maintain a difference of zero and center the read element
202
on the data track. For example when the signal amplitude of the A burst
204
on Servo Track
1
is equal to the signal amplitude of the C burst
208
on Servo Track
3
, then the read element (
202
) is centered on Data Track
1
(
216
).
The spacing or track pitch of the servo tracks shown as Servo Track Pitch
212
, determines the track pitch of the data tracks. In this case the Data Track Pitch
214
is twice that of the Servo Track Pitch. One of the determining factors in setting the pitch is the tolerance of the heads. For example in modern heads in which the magnetoresistive read and inductive write transducers are separate elements, the tolerances are given for each element as shown below.
Width
Tolerance (3 sigma)
Write
2.4 um
+/−0.5 microns
Read
2 um
+/−0.4 microns
The pitch would typically be set to insure that when writing Data Track
1
(
216
) the write element does not overlap Data Track
2
(
218
) and overwrite the previously written track which can result in a loss of data. To achieve this, the track pitch is set to exceed the width of the widest write head in the population of write heads used for the disk drive program to insure a gap
220
between adjacent data tracks. In this example the widest write width is 2.9 microns. In addition, magnetic and mechanical inputs which limit the ability of the read head to stay centered on the data track, which are commonly referred to as track misregistration, are part of the statistical calculation performed in setting the track pitch for the product. Today, products have a defined track pitch which is used for all the disk surfaces and drives manufactured, and do not adapt the track pitch for each individual surface or drive manufactured based on drive components such as the read or write heads, spindle bearings, etc. (component parameters) or track misregistration, magnetic performance, etc. (system parameters).
SUMMARY OF THE INVENTION
Briefly, according to the present invention there is provided a method of measuring the gaps between adjacent tracks in a recording system during servowriting and allowing the setting of the servo track pitch based on the component or system parameters of individual drives thereby overcoming a limitation of the statistical method of setting track pitch.


REFERENCES:
patent: 5844742 (1998-12-01), Yarmchuk et al.
patent: 5907447 (1999-05-01), Yarmchuk et al.
patent: 5949603 (1999-09-01), Brown et al.
patent: 6091559 (2000-07-01), Emo et al.
patent: 6437947 (2002-08-01), Uno
patent: 6466387 (2002-10-01), Ogasawara et al.
Computer Professionals, Magnetic Recording Vol. II: “Computer Data Storage,” Chapter Two, “Data Storage on Rigid Disks,” pp. 25-37.

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