Dynamic magnetic information storage or retrieval – Automatic control of a recorder mechanism – Controlling the head
Reexamination Certificate
1997-12-02
2001-05-29
Hudspeth, David (Department: 2651)
Dynamic magnetic information storage or retrieval
Automatic control of a recorder mechanism
Controlling the head
Reexamination Certificate
active
06239940
ABSTRACT:
BACKGROUND OF THE PRESENT INVENTION
1. Field of the Invention
The present invention relates to a disk device and a disk device calibrating method for performing stable high-speed movement by a feedforward servo control for movement of a head to a target track.
Recently, advances have been made in making the capacity a disk device larger and increasing the speed of the disk device, and making of a servo technique for moving a head at a higher speed is required. However, in a servo technique which moves a head, only by feedback control, delay of a driving signal is large so that the delay of the driving signal cannot be ignored with respect to a seeking time, and thereby, high-speed movement cannot be achieved. (In the feedback control, the head is driven using a feedback error between target information for moving the head to a target position and demodulated information which is obtained as a result of demodulating feedback information from the head.) Therefore, a feedforward control has been used in general, in which a current waveform which moves the head is previously stored as feedforward information, which is added to the feedback error, and the head is controlled thereby.
2. Description of the Related Art
With reference the following figures, a disk device in the related art will now be described.
FIG. 1
shows an example of an arrangement of the disk device in the related art, in which feedforward servo control is performed.
As shown in
FIG. 1
, the disk device includes servo control circuit
21
, VCM (Voice Control Motor)
22
, a power amplifier
23
and a position demodulating circuit
24
. The servo control circuit
21
performs servo control for moving a head
33
to a target track on a disk
25
. The VCM
22
moves the head
33
to a target position. The power amplifier
23
drives the VCM
22
using a driving current which is output from the servo control circuit
21
. The position demodulating circuit
24
converts position information which is provided from the head
33
in a feedback manner into a digital signal.
Further, the servo control circuit
21
includes a servo control device
26
, a target information table
27
, a demodulated information table
28
, a feedforward table
29
, a detection control device
30
, a comparator
31
and an adder
32
. The servo control circuit
21
has a function of performing the servo control for desired movement of the head
33
. The servo control device
26
controls a series of sequences of the servo control for moving the head
33
to a target track on the disk
25
. The target information table
27
stores target information. The demodulated information table
28
stores demodulated information. The feedforward table
29
stores feedforward information which is common for all the disk devices. The detection control device
30
acts as a detection control unit. The comparator
31
compares the target information and the demodulated information with one another and sends a feedback error to the detection control device
30
. The adder
32
adds the feedforward information and the feedback error to one another and drives the power amplifier
23
.
In the above-described arrangement, when a user of the disk device performs an operation for reading data stored in the disk
25
, the servo control device
26
, which receives a reading instruction from the outside or externally, performs the servo control for movement of the head
33
. This operation will be described with reference to an operation flowchart shown in FIG.
2
.
The VCM
22
moves the head
33
to a measurement starting track which corresponds to an initial value of position measurement in accordance with the instruction of the servo control device
26
(in a step S
101
).
The servo control device
26
reads a parameter for moving the head
33
, for example, such as that shown in
FIG. 3A
, from the feedforward table
29
, and supplies a current to the power amplifier
23
, which current corresponds to the parameter. The power amplifier
23
, having the current supplied thereto, drives the VCM
22
. As a result of being driven by the VCM
22
, the head
33
starts seeking for the specified number of tracks (in a step S
102
). The above-mentioned parameter of the feedforward table
29
is previously set.
The head
33
sends position information from seek start (in a step S
102
) to seek end (in a step S
104
) in analog values, such as that shown in
FIG. 3B
, to the position demodulating circuit
24
. The position demodulating circuit
24
, receiving the position information, converts the analog signal to a digital signal at each sampling position, and sends demodulated position information, for example, such as that shown in
FIG. 8C
, to the demodulated information table
28
. The information demodulated table
28
stores the information (in a step S
103
). The head
33
finishes the seeking (in the step S
104
), and enters an on-track condition at the target position (in a step S
105
).
The comparator
31
obtains the difference between the demodulated position information stored in the demodulated information table
28
and the target position information previously stored in the target information table
27
, for example, such as that shown in FIG.
3
D. Then, the comparator
31
sends the feedback error, for example, such as that shown in
FIG. 8E
, to the detection control device
30
. The detection control device
30
, receiving the feedback error, determines, based on a predetermined determination reference range, whether the feedback error is within the range (in the step S
106
).
When the feedback error is within the predetermined range (Yes in the step S
106
), the detection control device
30
informs the servo control device
26
that the head
33
has moved to the target position. Thus, the user of the disk device can cause the disk device to read the data recorded on the disk
25
.
When the feedback error is out of the predetermined range (No in the step S
106
), the detection control device
30
informs the servo control device
26
that the head
33
has not moved to the target position. The servo control device
26
, receiving the information, instructs the VCM
22
to move the head
33
to the measurement starting track which corresponds to the initial value of the position measurement (in a step S
107
). Then, the servo control device
26
again reads, from the feedforward table
29
, the parameter for moving the head
33
, and supplies, to the adder
32
, the current value corresponding to the parameter. The adder
32
adds the feedback error to the current value, and supplies the addition result to the power amplifier
23
. The power amplifier
23
, having the current supplied thereto, drives the VCM
22
, and the head
33
again starts seeking as a result of being driven by the VCM
22
.
The servo control circuit
21
repeats the operation from the step S
101
to the step S
107
until the feedback error becomes within the predetermined range.
If the disk device is ideal, the head
33
can move to the target track only with the feedforward information.
However, in an actual operation, because the performance of each component varies among disk devices, it is not possible to provide an accurate movement of the head
33
in a condition where the feedforward information is fixed among all the disk devices. In the servo control, the feedback error between the target position information and the demodulated position information is added to the feedforward information, and head movement is performed also using the feedback control. Thereby, delay occurs due to the feedback loop, and high-speed seeking cannot be achieved.
Further, as the track density increases, the determination reference range for determining whether the head has reached a target accurately becomes narrower. However, in the related art, the feedforward information in a stage of simulation or debug of the disk device is commonly stored in a ROM or the like for all the disk devices. Therefore, a position error, occurring when the head has moved only in accordance with the feedfor
Kosugi Tatsuhiko
Mori Kazunori
Sasamoto Tatsuro
Yoshida Susumu
Fujitsu Limited
Greer Burns & Crain Ltd.
Habermehl James L
Hudspeth David
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