Dynamic information storage or retrieval – With servo positioning of transducer assembly over track... – Optical servo system
Reexamination Certificate
1999-12-06
2003-09-30
Tran, Thang V. (Department: 2653)
Dynamic information storage or retrieval
With servo positioning of transducer assembly over track...
Optical servo system
C369S044340, C360S077040, C360S078070
Reexamination Certificate
active
06628579
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The invention relates to a storage apparatus for feedback controlling a moving position of a carriage so as to set a positional deviation amount of a head from a track center to zero and, more particularly, to a storage apparatus for obtaining a control signal to suppress a positional deviation of a repetitive disturbance such as a medium eccentricity by a learning control and performing a feed-forward control.
2. Description of the Related Arts
In a conventional optical disk apparatus, to raise track-following performance of a laser beam to medium tracks, there is used a head mechanism of a double driving type comprising: a carriage actuator for a seek control (also referred to as a coarse control) for moving a carriage supported by a bearing unit for a guide rail fixedly arranged; and a tracking actuator for a track-following control (also referred to as a fine control) for moving the laser beam in the direction which transverses the tracks by the driving of an objective lens mounted on the carriage. In recent years, there has also widely been spread a head mechanism of a single driving type comprising only the carriage actuator by omitting the tracking actuator in order to reduce the costs of the apparatus. In the head mechanism of the single driving type, a slide bearing is employed replacing the ball bearing, thereby reducing the number of parts and the costs. However, in case of constructing the head mechanism as a mechanism of the single driving type comprising only the carriage actuator and, further, removing the ball bearing from the bearing unit of the carriage, a positioning control of the laser beam for the track center based on a tracking error signal is strongly influenced by a Coulomb friction which the carriage bearing unit has.
FIG. 1
shows characteristics of the Coulomb friction in the carriage of the single driving type. Each of a moving velocity V and a frictional force F has a plus or minus value according to the moving direction of the carriage. A case where the moving velocity V of the carriage changes from the minus value to the plus value will now be considered. While the carriage is moving at the moving velocity V having the minus value, an almost constant kinetic frictional force F
1
of a plus value is generated against the moving velocity. When the moving velocity V of the carriage for the guide rail is equal to 0 and, subsequently, the carriage starts to move in the opposite direction, a driving force canceling a static frictional fore -F
2
is needed and, after moving, the driving force should include a force canceling an almost constant kinetic frictional force -F
1
. At the time of the reversal of the moving velocity of the carriage as mentioned above, a steep force change of the frictional force acts as a disturbance on a control system. To sufficiently compensate the disturbance, a feedback control system with a high bandwidth is generally necessary. The reversal of the moving velocity of the carriage occurs, for example, in a track-following control to compensate for a repetitive positional deviation of the track due to an eccentricity of the medium. That is, when the carriage is controlled so as to trace the medium eccentricity, the motion of the carriage for the guide rail becomes a reciprocating motion synchronized with an eccentricity period. Therefore, the moving velocity of the carriage is reversed at least twice for one rotation of the medium and is subjected to the disturbance by the steep force change of the frictional force each time.
FIG. 2
shows a simulation result of a tracking error signal TES for a rotational period (time) when an on-track control is performed by a feedback control system to a head mechanism of a single driving type. In such a simulation, a track pitch is set to 1.1 &mgr;m, a rotational speed of the disk is set to 3600 rpm, and a coefficient &mgr; of friction is set to 0.3. A band of the feedback control system is set to 1.5 kHz in consideration of a high-order resonance having a higher resonance at about 15 kHz of the actual head mechanism. A waveform
200
relates to a case where a peak-to-peak amount of eccentricity is assumed to be 50 &mgr;m. A waveform
202
relates to a case where a peak-to-peak amount of eccentricity is assumed to be 20 &mgr;m. A waveform
204
relates to a case where a peak-to-peak amount of eccentricity is assumed to be 10 &mgr;m. With respect to any of the waveforms
200
,
202
, and
204
as well, the eccentricity disturbance cannot be sufficiently suppressed due to deterioration of low band error compressing performance and reduction of a control band of the feedback control system due to the single driving of the head mechanism. The waveforms are also influenced by the steep change of the frictional disturbance occurring at a point when the moving velocity is equal to 0 when the carriage is allowed to trace the eccentricity, so that large peak-like tracking errors
206
-
1
,
206
-
2
,
206
-
3
, and
206
-
4
occur. If a Coulomb friction F
fric
in association with the movement of the carriage is simply expressed by omitting a static friction, it is modeled by the following equation.
F
fric
=
{
-
μ
mg
,
ϰ
.
≥
0
μ
mg
,
ϰ
<
0
(
1
)
As will be obviously understood from such a model, a cause of difficulty of the compensation by the feedback control is considered because the sign of the Coulomb friction F
fric
suddenly changes, for example, from the minus value to the plus value at the time of reversal of a velocity {dot over (&khgr;)} of the carriage for the guide tail.
Although a method of raising the band of the feedback control system is generally considered as a method of compensating for such a steep frictional disturbance, there is a limitation due to the existence of the high-order mechanical resonance near 15 kHz. Further, since the track-following control is performed by the carriage driving and the driving by the lens actuator is omitted, it is difficult to sufficiently raise the control band for positioning.
SUMMARY OF THE INVENTION
According to the invention, there is provided a storage apparatus in which by combining a feedback control system and a learning control system, a steep frictional disturbance due to a medium eccentricity is certainly compensated for, and a tracking error is reduced.
First, a storage apparatus of the invention, for example, an optical storage apparatus comprises: a head having a carriage for moving an irradiating position of a laser beam onto an arbitrary track position on a medium; a position signal detecting unit (tracking error detecting unit) for detecting and generating a position signal (tracking error signal) TES according to a positional deviation amount in which a predetermined position of a track on the medium is used as a reference on the basis of the light derived from the medium in accordance with an irradiation of the laser beam; a feedback calculating unit for inputting the position signal TES and calculating a control signal (control current) I
FB
to move the carriage of the head so as to set the positional deviation amount to zero; and a driving unit (VCM) for driving the carriage of the head so that the irradiating position of the laser beam traces the track on the basis of the control signal I
FB
of the feedback calculating unit. With respect to such a storage apparatus, the invention is characterized by comprising a learning control unit for getting an unknown function for one medium rotation to set the positional deviation amount for the repetitive disturbance to zero as an approximated function which was approximately presumed by a learning algorithm and storing it. More specifically speaking, according to the learning control unit, the unknown function for one medium rotation period to set the positional deviation amount for the repetitive disturbance such as a medium eccentricity synchronized with the medium rotation to zero is obtained by a learning algorithm as an approximated function
Kawabe Takayuki
Watanabe Ichiro
Fujitsu Limited
Tran Thang V.
LandOfFree
Storage apparatus does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Storage apparatus, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Storage apparatus will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-3050926