Stable data writing method by tracking head speed in hard disk drive

A hard disk drive traces a head speed to write data stably on a track of a magnetic disk. The hard disk drive seeks the track to position a head on the track sought, if a few consecutive head position error signals fall within an on-track offset value range, and follows the track sought based on the head position error signal and a head speed. Then, a determination is made as to whether the head position error signal falls within the on-track offset value range, and whether the head speed falls within a predetermined range. If the head position error signal falls within the on-track offset value range and the head speed falls within the predetermined range, then the data will be written on the track. However, if the head position error signal is not within the on-track offset value range or if the head speed is not within the predetermined range, the track following is retried. In this manner, the hard disk drive may accurately follow the track and stably write the data on the magnetic disk.

CLAIM OF PRIORITY 
This application makes reference to, incorporates the same herein, and 
claims all benefits accruing under 35 U.S.C. .sctn.119 from an application 
for STABLE DATA WRITING METHOD BY TRACKING HEAD SPEED IN HARD DISK DRIVE 
earlier filed in the Korean Industrial Property Office on the 31.sup.st of 
December 1996 and there duly assigned Serial No. 82659/1996. 
BACKGROUND OF THE INVENTION 
1. Field of the Invention 
The present invention relates to a hard disk drive, and more particularly 
to a stable data writing method by tracking a head speed. 
2. Description of the Related Art 
With the high capacity and the high access speed, a hard disk drive is 
commonly used for an auxiliary memory of a computer system. Such a hard 
disk drive writes data on tracks arranged along concentric circles on a 
rotating magnetic disk. The hard disk drive includes a plurality of 
magnetic heads for reading and writing data from and onto the tracks. 
Further, the hard disk drive includes a head position servo mechanism for 
radially moving the magnetic head on the disk to position the magnetic 
head on a selected one of the tracks. In order to selectively position the 
magnetic head on a particular track, it is necessary to know current 
positions of the heads with respect to the respective tracks. Such 
positional information of the heads, i.e., servo information is provided 
by using a specific servo pattern read from the magnetic disk. Such a 
servo pattern is permanently recorded on the magnetic disk when assembling 
the hard disk drive. The servo pattern is read by the heads and used as 
positional information of the tracks. 
The servo information is commonly provided by an embedded servo system. In 
accordance with the embedded servo system, the servo information is 
arranged alternately with data areas on the magnetic disk. The servo 
information includes track positional information, a track address, and 
index information. The hard disk drive uses the servo information to 
position the head on a specific track by way of a track seek and a track 
following. The track seek is to move the head to a specific target track 
from the current track, and the track following is to accurately follow a 
center line of the sought track so as to precisely read and write data 
from and onto the track. For example, in a hard disk drive adopting the 
embedded servo system, two bursts are previously recorded, as a part of 
the servo information, on each track. 
An A burst and a B burst are normally alternately recorded on the left and 
right sides of each track, centering on the track center line. If the head 
is not precisely positioned on the track center line and inclines toward 
the A burst, then a detection level of the A burst becomes higher than 
that of the B burst. On the contrary, if the head inclines toward the B 
burst, then the detection level of the A burst will be lower than that of 
the B burst. However, if the head is positioned accurately on the center 
of the track, then the detection levels of the A and B bursts will be the 
same. In that case, a difference between the detection levels becomes zero 
and the hard disk drive determines the deviation of the track with respect 
to the track center and generates a head position error signal PES which 
is equal to the difference between the detection levels of the A and B 
bursts. 
If the head inclines toward the A burst, then the head position error 
signal will have a positive value and if the head inclines toward the B 
burst, then the head position error signal will have a negative value. 
Once the head is on track and the position error signal is equal to zero, 
hard disk drive can stably read and write data from or onto a data area of 
the track. However, the head position error signal is hardly ever zero due 
to vibrations of the magnetic disk and the head. Thus, the head position 
error signal has a signal level varying according to the deviation of the 
head and has an on-track offset value range within a specific range. The 
signal level exceeding the on-track offset value range is called an 
off-track offset range. 
Normally, there is a maximum on-track value and a minimum on-track value of 
the head position error signal. The write gate pulse for writing data on 
the disk is enabled only when the head position error signal is within the 
on-track offset value range. If the head position error signal gets out of 
the on-track offset value range while writing the data, the track seek 
will be retried. 
However, if the head writes data at the maximum on-track value in the 
previous sector and writes data at the minimum on-track value in the 
current sector, then the written data will have an offset value which is 
twice the maximum deviation so that a movement of the head may become 
unstable and accordingly, a data error may occur. 
The following patents each disclose features in common with the present 
invention but do not teach or suggest the stable data writing method of 
the present invention: U.S. Pat. No. 5,285,330 to Masaki, entitled 
Apparatus For Controlling Moving Speed Of Magnetic Head, U.S. Pat. No. 
4,068,269 to Commander et al., entitled Positioning System For Data 
Storage Apparatus And Record Medium For Use Therewith, U.S. Pat. No. 
5,173,647 to Hashimoto, entitled Servo Positioning Circuit, U.S. Pat. No. 
5,164,931 to Yamaguchi et al., entitled Method And Apparatus For Control 
Of Positioning, U.S. Pat. No. 5,126,897 to Ogawa et al., entitled Magnetic 
Recording/Reproducing Apparatus Capable Of Reducing A Setting Time In A 
Head Positioning Control Mode, U.S. Pat. No. 5,036,506 to Bierhoff, 
entitled Record Carrier Scanning Apparatus With Feedback Control System 
For Controlling Scanning Point Position And Velocity, U.S. Pat. No. 
5,428,590 to Ogino, entitled Information Recording And Reproducing 
Apparatus And Method In Which An Information Recording Or Reproducing Head 
Seeks A Desired Track On A Recording Medium, U.S. Pat. No. 5,383,068 to 
Shimizu et al., entitled Head Position Recognition Method, A Speed 
Calculation Method, And A Head Movement Speed Control Device, U.S. Pat. 
No. 5,576,909 to Dierkes et al., entitled Method For Positioning A Data 
Transducer Head In A Rotating Disk Drive Data Storage Device, U.S. Pat. 
No. 5,521,891 to Nakane, entitled Speed Detection Apparatus, Speed Control 
Motor, And Track Jump Control Circuit, U.S. Pat. No. 4,679,103 to Workman, 
entitled Digital Servo Control System For A Data Recording Disk File, U.S. 
Pat. No. 5,381,282 to Arai et al., entitled Inter-Sample Switching Of 
Servo Control In Direct Access Storage Devices, and U.S. Pat. No. 
4,937,803 to Nakane, entitled Track Acquisition Apparatus And Method With 
Specified Velocity Pattern. 
SUMMARY OF THE INVENTION 
It is therefore an object of the present invention to provide a method for 
tracking a head speed in a hard disk drive to write data stably. 
According to an aspect of the present invention, a method for tracking a 
head speed to stably write data on a track in a hard disk drive following 
the track on a magnetic disk, includes seeking a track to position a head 
on the track sought, if a predetermined number of consecutive head 
position error signals fall within an on-track offset value range; 
following the track sought based on the head position error signal and a 
head speed; checking whether or not the head position error signal falls 
within the on-track offset value range; checking whether or not the head 
speed falls within a predetermined range, if the head position error 
signal falls within the on-track offset value range; writing data on the 
track sought, if the head position error signal falls within the on-track 
offset value range and the head speed falls within the predetermined 
range; and retrying the step for following the track, if the head position 
error signal is not within the on-track offset value range or if the head 
speed is not within the predetermined range.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
A preferred embodiment of the present invention will be described in detail 
hereinbelow with reference to the attached drawings, in which like 
reference numerals represent like elements. Further, it should be clearly 
understood that many specifics such as the detailed circuit elements are 
shown only by way of an example to bring about a better understanding of 
the present invention and the present invention may be embodied without 
these specifics. Moreover, it should be noted that detailed descriptions 
of the related prior art may have been intentionally omitted if it was 
believed to be unnecessary in describing the concepts of the present 
invention. 
Referring to FIG. 1, an A burst and a B burst are alternately recorded on 
the left and right sides of each track, centering on the track center 
line. If the head is not precisely positioned on the track center line and 
inclines toward the A burst as shown in FIG. 2A, then a detection level of 
the A burst becomes higher than that of the B burst. On the contrary, if 
the head inclines toward the B burst as shown in FIG. 2B, then the 
detection level of the A burst will be lower than that of the B burst. 
However, if head is positioned accurately on the center of the track as 
shown in FIG. 2C, then the detection levels of the A and B bursts will be 
the same. In that case, a difference between the detection levels of the A 
burst and B burst becomes zero. In the light of the detection level 
difference, the hard disk drive determines the deviation of the track with 
respect to the track center, and generates a head position error signal 
PES which is represented by the following Equation (1). 
EQU PES=Detection Level of A Burst--Detection Level of B Burst Signal(1) 
As can be clearly appreciated from Equation (1), if the head inclines 
toward the A burst, then the head position error signal PES will have a 
positive value. On the contrary, if the head inclines toward the B burst, 
then the head position error signal PES will have a negative value. 
However, if the track is positioned precisely on the center of the track, 
then the head position error signal PES will become zero. The hard disk 
drive controls the head to follow the center of the track by using the is 
head position error signal PES. 
In operation, once the head is on-track when PES=0, the hard disk drive can 
stably read and write data from or onto a data area of the track. However, 
in practice, the head position error signal PES can hardly become zero due 
to vibrations of the magnetic disk and the head or the features of the 
mechanism and the circuit. As illustrated in FIG. 3, the head position 
error signal PES has a signal level varying according to the deviation of 
the head, and has an on-track offset value range within a specific range. 
The signal level exceeding the on-track offset value range is called an 
off-track offset range. 
FIG. 3 illustrates a timing diagram of a write gate pulse WG with respect 
to the head position error signal PES, in which ON.sub.-- 0 represents an 
on-track offset value, ON.sub.-- 0+VL represents a maximum on-track value 
which is higher by a value VL than the on-track offset value ON.sub.-- 0, 
and ON.sub.-- 0-VL represents a minimum on-track value which is lower by 
the value VL than the on-track offset value ON.sub.-- 0. Commonly, the 
on-track offset value ON.sub.-- 0 is set to zero, and the value VL is set 
to a proper value evaluated through a test with respect to the hard disk 
drives. Such an on-track offset value ON.sub.-- 0 is previously set when 
assembling the hard disk drive. The maximum on-track value ON.sub.-- 
0.+-.VL has the positive value and the minimum on-track value ON.sub.-- 
0-VL has the negative value. As illustrated, the on-track offset value 
range is defined as ON.sub.-- 0.+-.VL. The write gate pulse WG for writing 
data on the disk is enabled within the on-track offset voltage range. If 
the head position error signal PES gets out of the on-track offset value 
range while writing the data, the track seek will be retried. 
However, in case that as shown by a dotted circle (A), the head writes data 
at the maximum on-track value ON.sub.-- 0+VL in the previous sector, and 
writes data at the minimum on-track value ON.sub.-- 0-VL in the current 
sector, then the written data will have an offset value which is two times 
the value VL, so that a movement of the head may be unstable. Accordingly, 
the data written in such a condition may be recorded in opposite 
directions. Further, even the same sector may have different information 
recorded, which results in a data error. 
FIG. 4 illustrates a hard disk drive to which an embodiment of the present 
invention is applicable. As illustrated in the drawing, a magnetic disk 10 
is rotated by a spindle motor 40. A head 12 is positioned on a surface of 
the magnetic disk 10. The head 12 is mounted on a front end of an arm 14 
perpendicularly extending from an arm assembly associated with a rotary 
voice coil actuator 34. A pre-amplifier 16 pre-amplifies a signal 
picked-up by the head 12 in a read mode, and drives the head 12 to write, 
onto the disk 10, encoded write data EWD received from an encoder/decoder 
(ENDEC) 22 in a write mode. A pulse and servo detector 18 detects a peak 
value of the signal output from the pre-amplifier 16 to generate a data 
pulse, and detects the A and B bursts shown in FIG. 1 to generate a head 
position error signal PES. The data pulse and the head position error 
signal PES generated by the pulse and servo detector 18 are respectively 
supplied to a data separator 20 and an analog-to-digital converter (ADC) 
26. The analog-to-digital converter 26 converts the head position error 
signal PES into a digital value and provide a microcontroller 28 with the 
digital value. The data separator 20 separates encoded read data ERD from 
the data pulse generated by the pulse and servo detector 18, and provides 
the encoder/decoder 22 with the encoded read data ERD. The encoded read 
data ERD is synchronized with a constant clock pulse. The encoder/decoder 
22 decodes the encoded read data ERD from the data separator 20 and 
supplies the decoded read data RDATA to a disk data controller (DDC) 24, 
and/or encodes the write data WDATA received from the disk data controller 
24 and supplies the encoded write data EWD to the pre-amplifier 16. The 
disk data controller 24 writes data received from a host computer (not 
shown) on the magnetic disk 10 by way of the encoder/decoder 22, and/or 
reads data written on the magnetic disk 10 to transfer the read data to 
the host computer, in response to a read/write command received from the 
host computer. The microcontroller 28 seeks the track by using the head 
position error signal PES received from the analog-to-digital converter 
26. A digital-to-analog converter (DAC) 30 converts a head position 
control signal generated by the microcontroller 28 into an analog signal. 
A servo driver 32 generates a driving current for driving the actuator 34 
according to the signal output from the digital-to-analog converter 30 and 
provides the voice coil of the actuator 34 with the driving current. The 
actuator 34 moves the head 12 on the magnetic disk 10 according to a 
direction and level of the driving current from the VCM driver 32. A motor 
controller 36 generates a disk rotation control value according to a disk 
rotation control signal from the microcontroller 28. A spindle motor 
driver 38 drives the spindle motor 40 according to the disk rotation 
control value from the motor controller 36, to rotate the disk 10. 
In the above described hard disk drive, if the hard disk drive writes the 
data when a few consecutive head position error signals PES fall within 
the on-track offset value range, signifying that the head is on track, 
then a data error may be undesirably caused. Thus, prior to writing the 
data, a difference (i.e., a head speed) between the head position error 
signals PES of the current track and the previous track should be 
evaluated to check whether the difference falls within a permissible 
range, so as to reduce a data write error. 
FIG. 5 illustrates a timing diagram of a write gate pulse WG with respect 
to the head position error signal PES of the respective tracks according 
to the present invention, in which the write gate pulse WG is enabled or 
disabled based on the on-track offset value range and a track shift offset 
value .DELTA.TS for evaluating the head speed. The hard disk drive writes 
the data when the write gate pulse WG is enabled, and retries the track 
seek when the write gate pulse WG is disabled. 
FIG. 6 illustrates a flowchart for tracking an on-track offset value range 
and a head speed based on the consecutive head position error signals PES 
during the track following, so as to write data stably according to an 
embodiment of the present invention. 
Now, how to stably write data by tracking the head speed according to the 
present invention will be described in detail hereinbelow with reference 
to FIGS. 4 thorough 6. 
In order to write data on the magnetic disk 10, the microcontroller 28 
seeks a specific track out of a plurality of tracks on the magnetic disk 
10, and positions the head 12 at the sought track to follow the track as 
described hereinbelow. First, the microcontroller 28 sets the maximum and 
minimum offset values ON.sub.-- 0.+-.VL of the head position error signal 
PES for on-tracking the head 12, at a step 600, and sets the track shift 
displacement .DELTA.TS for evaluating the head speed, at a step 602. The 
track shift displacement is evaluated by a difference between the head 
position error signal value PES (a) of the previous track and the head 
position error signal value PES (b) of the current track. Then, at a step 
604, the microcontroller 28 follows the track on the magnetic disk 10 
based on the on-track offset value ON.sub.-- 0 and the offset value 
.DELTA.TS of the track shift displacement. In the course of the track 
following, the microcontroller 28 compares the head position error signal 
value PES(n) of the current track received from the analog-to-digital 
converter 26 with the on-track offset value range ON.sub.-- 0.+-.VL, at a 
step 606, to check whether the head position error signal value PES(n) 
falls within the on-track offset value range. If the head position error 
signal value PES(n) is not within the on-track offset value range, the 
procedure will return to the step 604 to retry the track seek. However, if 
the head position error signal value PES(n) falls within the on-track 
offset value range, the procedure will proceed to a step 608. The 
microcontroller 28 checks, at the step 608, whether a difference between 
the head position error signal value PES(n) of the current track and the 
head position error signal value PES(n-1) of the previous track is larger 
than the offset value .DELTA.TS of the track shift displacement. If the 
difference between PES(n) and PES(n-1) is larger than the offset value 
.DELTA.TS of the track shift displacement, the procedure will return to 
the step 604 to retry the track seek. However, if the difference between 
PES(n) and PES(n-1) is smaller than the offset value .DELTA.TS of the 
track shift displacement, the microcontroller 28 will execute the 
conventional write mode at a step 610. In the course of executing the 
track mode, the microcontroller 28 compares the head position error signal 
value PES(n) of the current track with the on-track offset value range 
ON.sub.-- 0.+-.VL, at a step 612, and compares the difference between 
PES(n) and PES(n-1) with the offset value .DELTA.TS of the track shift 
displacement, at a step 614. As the result of the comparisons, if the head 
position error signal value PES(n) is not within the on-track offset value 
range or if the difference between PES(n) and PES(n-1) is larger than the 
offset value .DELTA.TS, the procedure will return to the step 604 to retry 
the track following. 
As described in the foregoing, the hard disk drive compares the difference 
between the head position error signal value PES(n) of the current track 
and the head position error signal value PES(n-1) of the previous track 
with the track shift displacement .DELTA.TS for evaluating the head speed, 
to accurately follow the track, so that the hard disk drive may stably 
write data on the magnetic disk. 
Although a preferred embodiment of the present invention has been described 
in detail hereinabove, it should be clearly understood that many 
variations and/or modifications of the basic inventive concepts herein 
taught which may appear to those skilled in the art will still fall within 
the spirit and scope of the present invention as defined in the appended 
claims.