Dynamic information storage or retrieval – With servo positioning of transducer assembly over track... – Optical servo system
Reexamination Certificate
1999-04-29
2001-09-25
Tran, Thang V. (Department: 2651)
Dynamic information storage or retrieval
With servo positioning of transducer assembly over track...
Optical servo system
C369S044290, C369S053290
Reexamination Certificate
active
06295254
ABSTRACT:
BACKGROUND
1. Field of the Invention
The present invention relates to seek control technology, and in particular to a seek control method for a disk device used for reading/writing data from and to a disk recording medium, such as a compact disk (CD) or a compact disk-read only memory (CD-ROM).
2. Description of the Related Art
In a disk device, such as a CD-ROM drive, a seek control operation is performed by calculating the number of tracks a pickup has to pass to reach the target track from the present track, and moving the pickup until the number of tracks passed equals the number of tracks calculated.
A generally well known seek method, which includes the step of calculating the number of tracks the pickup passes, is a track zero cross detection seek. The track zero cross detection seek is a seek method which samples a zero cross point or an arbitrary point on the disk for determining when the disk has made one complete revolution. The zero cross point is sampled by detecting a tracking error signal as the pickup moves in a radial direction of the disk and zero crossing the tracking error signal with a desired reference voltage. Every time the zero point is sampled, mirror signals are generated and counted by a CPU, where each mirror signal represents one track in a track pitch direction for every associated period of time. Accordingly, the pickup is moved until the counted number of mirror signals is equal to the calculated number of passing tracks required to reach the target track.
Although the track zero cross detection seek is especially advantageous in seeking the target track, even in a high rate of disk revolution, the operation sometimes misses the mirror signals. For example, if the disk has defects, such as a crack, fingerprints, dust, or stains, the tracking error signal may not be zero crossed with the desired reference voltage, thereby resulting in missing mirror signals. Further, even though there may not be any defects, mirror signals may still be missed due to the occurrence of a servo error, such as the occurrence of a focus drop which may be generated during the seek operation. The servo error may cause a miscount between the counted number of mirror signals and the number of actually passed tracks, thereby causing an inaccurate seek operation.
Accordingly, a need exists for a seek control method which accurately moves a pickup to a target track even when mirror signals are missed or miscounted during a seek operation.
SUMMARY
The present invention provides a seek control method for a disk device used for reading/writing data from and to a disk recording medium. The method includes the steps of counting mirror signals generated for every revolution of the disk recording medium, where each mirror signal corresponds to one of the tracks radially arranged on the disk recording medium; moving a pickup until the counted number of mirror signals is equal to a predetermined number of tracks required for the pickup to pass to reach a target track. The method further includes the steps of checking respective intervals of successive mirror signals; determining if there is a difference in length between intervals of two successive mirror signals; and executing a correction mode by adding or subtracting a correction value to the counted number of mirror signals if there is a difference in length between intervals of two successive mirror signals.
Since a disk has almost equal track widths at different portions thereof, intervals of mirror signals generated in association with successive tracks in a normal seek operation have almost equal lengths. Therefore, if the intervals of successive mirror signals are not equal in length, it is then determined that there are defects on the disk and/or a servo error occurred which resulted in a mirror signal miscount. Accordingly, one of the following methods is then executed in accordance with the present invention in order to counteract the above mentioned defects and/or any focus servo errors.
A first method entails executing a correction mode which is associated with the addition or subtraction of the correction value to the counted number of mirror signals required to reach a target track. According to this method, even when a miscounting of the mirror signals occurs due to an abnormality of the disk or servo system, it is possible to continuously move the pickup in accordance with a seek control which has been corrected by the execution of the correction mode. Accordingly, the pickup can be accurately moved to the target track. Moreover, this method prevents the drive from being damaged due to a seek rush where the pickup may move outside the periphery of a disk reading/writing area.
Another method, which deals with the occasion that there is a difference in length between intervals of successive mirror signals, is to forcibly stop the pickup. In this case, the seek operation is stopped immediately after a seek rush occurs. Accordingly, this method prevents the pickup from moving outside the periphery of the disk reading/writing area which may damage the pickup and the drive.
The determination of whether or not there is a difference in length between intervals of successive mirror signals can be appropriately achieved by defining the disk region between an initiation track and a target track into an acceleration region, a maximum speed region, and a deceleration region. Based on the moving speed of the pickup as driven by a feed motor during the seek operation, the above determination, i.e., if there is a difference in length between intervals of successive mirror signals, is performed in association with the differently defined disk regions. Practically, the length of mirror signal intervals varies according to the moving speed of the pickup. Therefore, the length of mirror signal intervals is different in different regions of the disk.
For example, assuming that “Mi” represents the preceding one of two successive mirror signal intervals, and “Mo” represents the following mirror signal interval, the successive mirror signal intervals satisfy a relationship of “Mi>Mo” in the acceleration region, “M
i
=M
o
” in the maximum speed region, and “M
i
<M
o
” in the deceleration region. Accordingly, there is a difference between successive mirror signal intervals when the mirror signal intervals do not satisfy the above mentioned relationships.
According to this definition of the various areas of the disk, in deciding whether to execute the correction mode or the forced stop mode, the correction mode is executed when the following one of mirror signals associated with two successive tracks has been counted within a predetermined time from the beginning of the preceding mirror signal whereas the forced stop mode is executed when the following mirror signal has been counted in excess of the predetermined time.
If the pickup is forcibly stopped several times during the seek operation, a loss occurs in seek time. In order to solve this problem, the forced stop mode is executed only when there is a high possibility of a seek rush exceeding a predetermined time. Accordingly, it is possible to minimize the loss in seek time by setting the predetermined time differently for the acceleration region, the maximum speed region, and the deceleration region. Therefore, it is possible to make an appropriate determination of whether to forcibly stop the pickup for each region.
REFERENCES:
patent: 5563856 (1996-10-01), Kim
patent: 5844871 (1998-12-01), Maezawa
patent: 6137751 (2000-10-01), Kim
patent: 6154429 (2000-11-01), Grimm
patent: 5054401 (1993-03-01), None
Dilworth & Barrese LLP
Samsung Electronics Co,. Ltd.
Tran Thang V.
LandOfFree
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