Dynamic information storage or retrieval – With servo positioning of transducer assembly over track... – Optical servo system
Reexamination Certificate
1998-11-19
2001-06-19
Edun, Muhammad (Department: 2651)
Dynamic information storage or retrieval
With servo positioning of transducer assembly over track...
Optical servo system
C369S044340, C369S044290, C369S044350
Reexamination Certificate
active
06249496
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an optical storage apparatus for optically recording and reproducing information to/from an exchangeable medium such as an MO cartridge or the like. More particularly, the invention relates to an optical storage apparatus for suppressing a waveform fluctuation occurring in a tracking error signal each time a laser beam passes an ID portion of a medium track during an on-track control.
2. Description of the Related Arts
Attention is paid to an optical disk as a storing medium as a core of multimedia which has rapidly been developing in recent years. For example, as for an MO cartridge of 3.5 inches, in addition to a conventional MO cartridge of 128 MB, media of a high density recording of 230 MB, 540 MB, and 640 MB have also been provided in recent years. In an optical storage apparatus known as an optical disk drive using such an MO cartridge medium, when a write command or a read command is received from an upper apparatus, a seek control for positioning a laser beam to a target track designated on the medium is executed and the laser beam is pulled in. Subsequently, an on-track control for allowing the laser beam to trace a track center on the basis of a tracking error signal is performed and a writing or reading operation based on a command from the upper apparatus is executed. The on-track control is performed in a manner such that the tracking error signal indicative of a deviation amount from the track center is sampled and read as a digital signal value by an A/D converter every predetermined time, an actuator mounted on a carriage is driven to set an error between a target position showing the track center and the present position to zero, and the position of the laser beam is feedback controlled. When the laser beam passes an ID area constructed by emboss pits arranged at regular intervals on the medium tracks during the on-track control, there is a phenomenon such that a level fluctuation occurs in the tracking error signal. For the fluctuation of the tracking error signal caused by the return light of the ID area, when the signal value sampled by the A/D converter is transmitted through a PID filter, gains of P and D terms or a gain of a D term is reduced from a normal gain by a DSP which executes the on-track control, and a tracing response speed to a sudden level change in the tracking error signal due to the ID area is made dull, thereby preventing the fluctuation of the tracking error signal caused by the return light of the ID area from being added as a disturbance. The suppression of the level fluctuation of the tracking error signal caused by the ID area is basically performed by dropping the gain of the PID filter and making a servo response speed dull. When the gain of the PID filter is dropped, however, since the traceability of the servo becomes dull also with respect to a detection component of an inherent deviation amount included in the fluctuated tracking error signal from the track center, there is naturally a limit for the reduction in the filter gain. Consequently, the suppression of the level fluctuation of the tracking error signal caused by the ID area becomes insufficient and there is a problem that the on-track control becomes unstable. Since the suppression of the level fluctuation of the tracking error signal caused by the ID area is insufficient, there is also another problem such that the signal level exceeds an off-track slice level set for offtrack detection and the off-track is erroneously detected.
SUMMARY OF THE INVENTION
According to the invention, there is provided an optical storage apparatus for reducing an adverse influence by sufficiently suppressing a level fluctuation of a tracking error signal caused by an ID area on a medium track without deteriorating a servo response speed of an on-track control.
According to the invention, there is provided an optical storage apparatus comprising: an actuator for moving an objective lens for irradiating a laser beam onto a medium in the direction traversing tracks of the medium; a tracking error signal forming circuit for forming a tracking error signal according to a position of the laser beam in the direction traversing the tracks on the basis of a photosensitive output of medium return light; a seek control unit for moving the laser beam to a target track by a control of the actuator; and an on-track control unit for allowing the laser beam to trace the target track by the control of the actuator based on the tracking error signal. In the optical storage apparatus, according to the invention, there is provided a correction processing unit for discriminating an interval in which a signal fluctuation appears on the tracking error signal when the laser beam passes an ID area on the medium track during the on-track control and for correcting the tracking error signal so as to reduce the signal fluctuation in the discrimination interval, thereby suppressing the fluctuation of the tracking error signal caused by the ID area and preventing a feedback control for the on-track control from becoming unstable. The correction processing unit comprises a correction timing discriminating unit, a correction value determining unit, and a correcting unit (adder). The correction timing discriminating unit determines the interval in which the level fluctuation of the tracking error signal (TES) due to the ID area on the medium tracks appears as a correction timing. The correction value determining unit determines a correction value which is used to correct the tracking error signal. Further, the correcting unit corrects a read signal value obtained by sampling and digitally converting the tracking error signal by an A/D converter in a predetermined period by using the correction value determined by the correction value determining unit at the correction timing decided by the correction timing discriminating unit. As specific modes of the correction processing unit, there are the following five modes.
(Correction by the difference before and after fluctuation)
The correction value determining unit obtains a difference between the signal value sampled by the A/D converter for the first time after a correction start timing and the signal value sampled by the A/D converter before the correction start timing and determines the difference as a correction value. The correcting unit executes a correction by subtracting the correction value from each of the signal values as many as predetermined sampling periods including the signal value sampled by the A/D converter for the first time after the correction start timing. A change amount between the values before and after the signal fluctuation caused by the ID area is used as a correction value and the fluctuation is reduced by subtracting the correction value from the signal value in the fluctuation interval, thereby enabling the correction according to the degree of the actual signal fluctuation to be properly performed.
(Correction by the difference between the target value and the value just after the fluctuation) The correction value determining unit obtains a difference between the signal value sampled by the A/D converter for the first time after the correction start timing and a predetermined target value and determines the difference as a correction value. The correcting unit executes a correction by subtracting the correction value from each of the signal values as many as predetermined sampling periods including the signal value sampled by the A/D converter for the first time after the correction start timing. As mentioned above, by using the difference between the value just after occurrence of the signal fluctuation and the predetermined target value as a correction value and reducing the fluctuation by subtracting the correction value from the signal value in the fluctuation period, even if there is a variation in the value just before the signal fluctuation, the correction using the correction value according to the signal drop from the target value can be alway
Ikeda Toru
Tsukahara Wataru
Yanagi Shigenori
Edun Muhammad
Fujitsu Limited
Greer Burns & Crain Ltd.
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