Dynamic information storage or retrieval – Information location or remote operator actuated control – Selective addressing of storage medium
Reexamination Certificate
2000-04-03
2003-09-30
Psitos, Aristotelis M. (Department: 2653)
Dynamic information storage or retrieval
Information location or remote operator actuated control
Selective addressing of storage medium
C369S030150, C369S053370
Reexamination Certificate
active
06628576
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The invention relates to a storage apparatus such as an optical disk drive or the like for recording and reproducing information to/from a medium such as an optical disk or the like and, more particularly, to a storage apparatus which can stably move a light spot to an adjacent track by a track jump even under a circumstance of an eccentricity of a disk, a frictional disturbance occurring by a positioner mechanism, or a disturbance from the outside of the apparatus.
2. Description of the Related Arts
In a conventional optical disk drive, to raise track-following performance of a light spot to a medium track, there is used a double stage (fine/coarse separation driving type) positioner comprising: a carriage actuator (VCM) for a seek control (also referred to as a coarse control) for moving a carriage supported by a ball bearing for a guide rail which is fixedly arranged; and a tracking actuator for a track-following control (also referred to as a precision control or tracking control) for moving a laser beam in the direction which transverses the tracks by the driving of an objective lens mounted on the carriage. In recent years, however, an apparatus using a single stage (fine/coarse integrated driving type) positioner in which a tracking actuator is omitted and only a carriage actuator is used is also widespread for the purpose of the reduction of costs of the apparatus. In the single stage positioner, a simple slide bearing is formed by removing a ball bearing from a bearing portion, thereby reducing the number of parts and costs.
Since the optical disk has a spiral track, a track jump for moving a light spot to an adjacent track is performed at a predetermined position for every rotation of the optical disk during a track-following control. As a conventional track jumping method, generally, a low band component of a control output of a feedback control system is held during the track jump, thereby stabilizing the track jump (JP-A-2-152020, JP-A-7-110950). In an apparatus such as a single stage apparatus in which the frictional disturbance of the positioner cannot be ignored, however, there is a case where a sufficient compensation is not performed.
FIG. 1A
shows a positioner displacement
300
in the seeking direction of a carriage for a guide rail during a track-following control with respect to an apparatus of a conventional single stage positioner.
FIG. 1B
shows a positioner speed
302
in the seeking direction.
FIG. 1C
shows a positioner acceleration
304
in the seeking direction. Further,
FIG. 1D
shows a relation of a driving current
306
which is supplied to a VCM. For simplicity of explanation, it is assumed that an eccentricity of the disk comprises only a primary eccentricity, a rotational speed is set to 4500 rpm (75 Hz), and an eccentricity displacement amplitude is set to ±35 &mgr;m. In the eccentricity tracking state, as shown in
FIG. 1A
, the positioner reciprocates on the rail synchronously with the eccentricity of the disk and causes the positioner speed
302
in FIG.
1
B and the positioner acceleration
304
in FIG.
1
C. If there is no friction or the like between the rail and the slide bearing portion of the carriage, the ideal track-following performance is realized by applying the VCM driving current
306
shown by a broken line in FIG.
1
D. However, in the single stage positioner, a disturbance due to a Coulomb friction in the bearing portion between the rail and the carriage cannot be ignored. The disturbance due to the Coulomb friction usually becomes a disturbance which acts in the direction opposite to the moving direction, namely, in the direction so as to obstruct the movement. Due to the eccentricity tracking, the moving direction of the carriage which reciprocates on the rail is reversed twice a disk rotation. Actually, if the secondary eccentricity or the like cannot be ignored, there is also a case where the moving direction is reversed two or more times. A situation that the moving direction of the carriage is reversed twice a disk rotation and the Coulomb frictional disturbance occurs corresponds to a timing when the positioner speed
302
in
FIG. 1B
crosses the zero point and the sign is inverted as shown by circles
308
-
1
to
308
-
4
. When such a Coulomb frictional disturbance is simply modeled, it can be regarded as a step-like disturbance in which the direction of the disturbance force is abruptly inverted in dependence on the sign of the positioner speed and becomes a frictional disturbance
310
as shown by a broken line in
FIG. 1C. A
case where a coefficient of friction (&mgr;) is equal to &mgr;=0.4 is presumed here. In such a storage apparatus, to realize an ideal track-following control, the drive current is not limited to the VCM driving current to generate the positioner acceleration but it is necessary to use a VCM driving current
312
as shown by a solid line in
FIG. 1D
by further multiplexing the driving current to cancel the frictional disturbance to the VCM driving current. When considering a case of the 1-track jump for moving the light spot to the adjacent track, it is considered that time that is required to move the light spot to the adjacent track is generally equal to about 500 &mgr;sec or less. On the other hand, a disk rotating frequency is a relatively low frequency of, for example, 75 Hz (13.3 msec per period). In such an apparatus that the Coulomb frictional disturbance can be ignored, it is considered that a change in disturbance force that is presumed for a short time during the track jump is very small. A valid effect can be expected even if a low frequency component of an output of a feedback control system is multiplexed during the track jump as in the conventional method. In the apparatus of the single stage positioner in which the Coulomb frictional disturbance cannot be ignored, however, there exists a rotational phase area of the disk in which the VCM driving current needs to be steeply changed like a VCM driving current
312
shown by a solid line in
FIG. 1D
to compensate the abrupt change of the frictional disturbance
310
in FIG.
1
C. Such an area exists at a position near a point shown by each of the circles
308
-
1
to
308
-
4
where the positioner speed
302
in
FIG. 1B
becomes zero. When considering a case where a 1-track jump command is received just before the positioner speed becomes zero, there is a large change between a disturbance amount at a start point of the track jump and that at an end point of the track jump. When the track jump command is received just before the positioner speed becomes zero, it is considered that the value of the low frequency component of the feedback control system is almost converged to the disturbance amount just before the track jump. In the conventional track jump, however, with respect to the low band component of the feedback control system, the value just before the track jump is held and a feed-forward outputted during the track jump. Therefore, at the end point of the track jump, a large error occurs between the actual disturbance amount and the value of the low band component which is feed-forward outputted, so that there is a case where the track jump becomes unstable or the track jump fails. Since the track jump command is instructed from an upper controller irrespective of the rotational phase of the disk, if the track jump command is instructed in such an area where the frictional disturbance changes, according to the conventional method of feed-forward outputting the low band component of the feedback control system during the track jump, there is a case where the output is incomplete. To solve such a problem, there is a method whereby the eccentricity speed is detected and the track jump command is outputted excluding an area where it is influenced by a static friction and the eccentricity speed becomes a value near zero (JP-A-9-35282). However, when the track jump command is issued in an area where the track jump is inhibited, a time lag occurs bef
Kawabe Takayuki
Watanabe Ichiro
Fujitsu Limited
Greer Burns & Crain Ltd.
Psitos Aristotelis M.
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