Dynamic magnetic information storage or retrieval – General recording or reproducing – Recording-or erasing-prevention
Reexamination Certificate
1998-07-14
2001-05-01
Faber, Alan T (Department: 2753)
Dynamic magnetic information storage or retrieval
General recording or reproducing
Recording-or erasing-prevention
C360S075000, C360S031000, C360S053000
Reexamination Certificate
active
06226140
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates generally to direct access storage devices and, more particularly, to control of arm movement in disk drive devices.
2. Description of the Related Art
In a conventional computer data storage system having a rotating storage medium, such as a magnetic or magneto-optical disk, data is stored in a series of concentric or spiral tracks across the surface of the disk. A magnetic disk, for example, can comprise a disk substrate having a surface on which a magnetic material is deposited. The digital data stored on a disk is represented as a series of variations in magnetic orientation of the disk magnetic material. The variations in magnetic orientation, generally comprising reversals of magnetic flux, represent binary digits of ones and zeroes that in turn represent data. The binary digits must be read from and recorded onto the disk surface. A read/write head produces and detects variations in magnetic orientation of the magnetic material as the disk rotates relative to the head.
Conventionally, the read/write head is mounted on a disk arm that is moved across the disk by a servo. A disk drive servo control system controls movement of the disk arm across the surface of the disk to move the read/write head from data track to data track and, once over a selected track, to maintain the head in a path centered over the selected track. Maintaining the head centered over a track facilitates accurate reading and recording of data. Positioning read/write heads is one of the most critical aspects of recording and retrieving data in disk storage systems. With the very high track density of current disk drives, even the smallest head positioning error can potentially cause a loss of data that a disk drive customer wants to record or read. Accordingly, a great deal of effort is devoted to servo control systems.
Servo Control Systems
A servo control system generally maintains a read/write head in a position centered over a track by reading servo information recorded onto the disk surface. The servo information comprises a position-encoded servo pattern of high frequency magnetic flux transitions, generally flux reversals, that are pre-recorded in disk servo tracks. The flux transitions are recorded as periodic servo pattern bursts formed as parallel stripes in the servo tracks. When the read/write head passes over the servo pattern flux transitions, the head generates an analog signal whose repeating cyclic variations can be demodulated and decoded to indicate the position of the head over the disk. The position indicating information can be used to produce a corrective signal that is referred to as a position error sensing (PES) signal. The PES signal indicates which direction the head should be moved to remain centered over a selected track and properly read and write data.
There are a variety of methods for providing servo track information to a disk servo control system. In the dedicated servo method, one surface of a disk is completely recorded with servo track information. Typically, a servo head is positioned over the dedicated servo disk surface in a fixed relationship relative to multiple data read/write heads positioned over one or more other data disk surfaces. The position of the servo head relative to the dedicated disk surface is used to indicate the position of the multiple data read/write heads relative to their respective disk surfaces.
Another method of providing servo track information is known as the sector servo method. In the sector servo method, each disk surface includes servo track information and customer data recorded in concentric or spiral tracks. The tracks on a sector servo disk surface are partitioned by sectors having a short servo track information area followed by a data area. The servo track information area typically includes a sector marker, track identification data, and a servo burst pattern. The sector marker indicates to the data read/write head that servo information immediately follows in the track. The servo read head is typically the same head used for reading data.
FIG. 1
is a schematic representation of a conventional disk drive storage system
100
that includes one or more individual disks
102
on which are deposited a magnetic recording material for storing magnetically encoded information. The disk drive
100
also includes an actuator
104
with a read/write head
106
. An actuator motor
108
pivots the actuator
104
, thereby changing the position of the read/write head
106
with respect to concentric tracks
110
of data contained on the disk
102
. The operation of the disk drive
100
is managed by a disk drive controller
112
, which also serves as an interface between the disk drive
100
and a host computer
113
.
The controller
112
includes a readback signal pre-amplifier
116
(“pre-amp”), which receives electrical representations of the flux changes sensed by the read/write head
106
from the disk
102
. The pre-amp
116
serves a dual purpose by amplifying either data signals or servo signals, depending on whether the read/write head
106
is positioned over stored customer data or over servo pattern data, respectively. Thus, the amplified signal from the pre-amp
116
is directed to two processing channels: a servo channel
118
and a customer data channel
120
. A write circuit
117
is provided to supply the read/write head
106
with customer data signals from the data channel.
The data channel
120
generally reads and writes data to and from the disk
102
in response to requests from the host computer
113
to read or write the data. The write circuit
117
is connected only to the customer data channel. The pre-amp
116
, when operating in conjunction with the customer data channel
120
, amplifies the disk readback signal from the read/write head
106
and directs the readback signal to an automatic gain control and filter circuit
121
. A data pulse detector
122
receives the analog readback signal from the circuit
121
and forms digital data pulses corresponding to the analog signals. Next, a pre-host processor
124
converts the data pulses into formatted data strings that are compatible with the host computer
113
. The components of the data channel
120
also operate in reverse order to write customer data to the disk
102
.
The servo channel
118
generally reads servo data from the disk
102
to aid in properly positioning the read/write head
106
. When operating in conjunction with the servo channel
118
, the pre-amp
116
amplifies servo signals produced when the read/write head
106
senses servo patterns. The servo channel
118
includes an automatic gain control (AGC) and filter circuit
126
, which may comprise any one of various known circuits for automatically adjusting the readback signal gain and filtering it. Next, a demodulator/decoder
128
receives the filtered readback signal and processes the information to derive a position error sensing (PES) signal, which is related to the position of the read/write head
106
with respect to the desired track center and is indicative of the read/write head position error. The PES signal is then used by a servo controller
130
to generate an input signal that, when provided to the actuator
104
, controls the position of the read/write head
106
.
The servo pattern is recorded into, and read from, tracks across the disk
118
. In
FIG. 1
, circular, parallel lines
164
designate servo tracks of the disk, which are divided into sectors that are represented by radial lines
166
. The servo tracks can include several repeated cycles of a servo pattern and can encompass one or more tracks of customer data.
Servo Signals
FIG. 2
shows a representation of various servo pattern bursts
138
,
139
,
140
,
141
recorded on the surface of the disk
102
.
FIG. 2
also illustrates an amplitude-type servo readback signal
144
that is generated when the read/write head
106
is positioned above a first track
136
. Each servo burst
138
-
141
is sensed and processed to provide servo
Serrano Louis Joseph
Yu Mantle Man-Hon
Faber Alan T
International Business Machines - Corporation
Raissinia Abdy
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