Dynamic information storage or retrieval – Information location or remote operator actuated control – Selective addressing of storage medium
Reexamination Certificate
2001-03-01
2001-12-04
Neyzari, Ali (Department: 2651)
Dynamic information storage or retrieval
Information location or remote operator actuated control
Selective addressing of storage medium
C369S044280
Reexamination Certificate
active
06327229
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates generally to a storage device and its seek control method providing a seek control for moving a head in a disk radial direction by drive of an actuator to position the head at a target track, and more particularly to a storage device and its seek control method improving the seek performance through a reduction of the seek time while keeping the stability of lead-in to a target track in the short distance seek not exceeding several tens of tracks.
2. Description of the Related Arts
In conventional information storage devices, in particular removable disk units represented by optical disk units, disks are removed or mounted for use with a need to provide a stable seek control against various disturbances proper thereto. For example, fixed disk units such as hard disk units are rarely affected by disturbances in the track radial direction arising from the disk eccentricity, whereas the optical disk units, e.g., a 3.5 inch 1.3 GB magneto-optical disk may suffer from a radial disturbance as much as 50 &mgr;m relative to 0.9 &mgr;m track pitch. In such disturbance conditions, a stable migration from the target track seek control to the track following control may remarkably be impaired, which may lead to frequent retries in the track following control and thus to a heavy degradation of the drive performances. To cope with this, the seek control upon the migration to the track following control provides a velocity control so as to allow the radial relative velocity with respect to the target track to be a desired value. In a typical velocity control, the target velocity corresponding to the number of remaining tracks to the target track is acquired by derivation from a previously provided table or from calculating expressions.
FIG. 1
is a block diagram of the conventional velocity control. A tracking error signal from a tracking error signal detection circuit
320
is converted into a TES zero-cross signal TZCS by a zero-cross signal detection circuit (TZC circuit)
300
. A position/velocity detector
302
acquires a position signal and a relative velocity signal in the disk radial direction of an objective lens mounted on the head moving mechanism of the actuator. From this position signal, a target velocity generator
304
issues a target velocity signal. An addition unit
306
finds a difference between the relative velocity signal and the target velocity signal to issue a velocity error signal, which in turn is fed to a phase compensator
308
for proportional gain or phase compensation to obtain a velocity feedback signal. The position signal is fed to a target acceleration generator
312
to obtain a target acceleration signal at the same time. The target acceleration signal results in an acceleration feedforward signal serving as an acceleration signal for moving the actuator to the target track. The velocity feedback signal and the acceleration feedforward signal are added together in an addition unit
314
at the output stage, the added signal resulting via a driver
316
in a seek control signal for driving a head moving mechanism
318
. Upon the acceleration, a switch
310
may be opened so as to permit the output of only the acceleration feedforward signal without any output of the velocity feedback signal.
In such a conventional seek control, however, the signal quality of the TES zero-cross signal TZCS may possibly induce any degradation of both the position signal and the relative velocity signal, with the result that the velocity feedback signal may become noisy. This deficiency remarkably appears in the low-velocity region immediately before the migration to the track lead-in. In the event of occurrence of hunting where the actuator velocity may vary to a great extent by noises, the target track may be reached previous to the recovery of the hunting. Accordingly, in the case of seek control in the low-velocity region immediately before lead-in to the track or of low-velocity seek control as in the short distance seek crossing a relatively short track interval, the influences of the noises need to be minimized. In order to solve such a problem, the present inventors conceived a way of generating a target velocity function or a target velocity relative to the elapsed time from the start of seek control, instead of the conventional generation of the target velocity or the target acceleration relative to the position. This seek velocity control system generating a target velocity through the input of the elapsed time is free from any influences by the position detection errors or detection noises, with the result that the effects of the noises on the velocity feedback signals can be reduced to a minimum.
FIGS. 2A
to
2
C are time charts of the short distance seek control system using the method conceived by the present inventors. Herein, with respect to the time t on the axis of abscissas,
FIG. 2A
depicts the velocity,
FIG. 2B
depicts the acceleration and
FIG. 3C
depicts the position. The seek control section is divided into three segments, i.e., an acceleration control segment, a deceleration control segment and a constant-velocity control segment such that the respective control segments are changed over depending on the elapsed time from the start of seek. In the acceleration control segment immediately after the start of seek, the actuator is subjected to an acceleration control at a certain acceleration A
0
for a predetermined time T
0
or for a predetermined distance X
0
so that the relative velocity V
D
upon the termination of acceleration is measured. In the next deceleration control segment, the decelerated acceleration control and the velocity control are carried out at one time. From the detected velocity V
D
upon the changeover to the deceleration, the decelerated acceleration control figures out a target decelerated acceleration trajectory A(t) of
FIG. 2B
for deceleration to a predetermined velocity V
C
allowing a changeover to the track following control for the target track in a predetermined time T
1
using
A
(
t
)
=
A
1
(
1
-
t
T
1
)
(
1
)
This decelerated acceleration trajectory A(t) is a function achieving an acceleration A
1
at the start of deceleration and acceleration zero after the elapse of time T
1
. In this case, the acceleration A
1
at the start of deceleration is derived from
A
1
=
2
(
V
C
-
V
D
)
T
1
(
2
)
A target velocity trajectory V(t) is derived on the basis of the decelerated acceleration A
1
of the expression (1) from the following expression, to represent the trajectory at the time T
1
of FIG.
2
B. The target velocity V(t) at that time is represented by the time function
V
(
t
)
=
V
D
+
A
1
t
(
1
-
t
2
T
1
)
(
3
)
achieving the velocity V
C
after the elapse of time T
1
. Afterward, a constant-velocity control is provided at the target velocity V
C
and, when reaching the vicinity of the target track, a migration is carried out to the track following control. The migration to the track following control is effected for example by providing a seek control till the track precedent one track to the target track, whereat a deceleration pulse is issued to allow a movement to a region capable of follow-up on the target track previous to the migration to the track following control. Generation of such a target trajectory reducing the target velocity and the target decelerated acceleration depending on the elapsed time is advantageous in lessening the influences of variances of viscosity resistance on the actuator moving mechanism relying on the velocity variations or in suppressing the excited vibrations of the mechanism arising from the rapid change of acceleration.
In the event of the control generating the target trajectory based on the elapsed time, however, a longer seek distance to the target track may cause an extension of only the time of movement to the target track by the constant-velocity control at the constant velocity V
C
after the termination of deceleration, that is, only the time T
Fujitsu Limited
Greer, Burns & Crain,Ltd.
Neyzari Ali
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