Dynamic information storage or retrieval – With servo positioning of transducer assembly over track... – Optical servo system
Reexamination Certificate
2000-02-03
2003-10-14
To, Doris H. (Department: 2652)
Dynamic information storage or retrieval
With servo positioning of transducer assembly over track...
Optical servo system
C360S077040, C714S002000, C711S004000, C711S112000
Reexamination Certificate
active
06633521
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a storage apparatus having a head for reading data from a track on a storage medium, and to a servo recovery method, and more particularly to the storage apparatus and servo recovery method for detecting when the head goes off track, and restoring the head to the track.
2. Description of the Related Art
Data storage devices which use storage medium and a head have been widely used. Magnetic storage devices uses a magnetic medium as the storage medium, and optical storage devices uses optical medium as the medium. In these kinds of data storage devices, after the head is positioned on the track of the storage medium, it reads and writes data from or to the track. In order to perform this reading or writing, the head must follow the track.
A servo control unit is used in order to follow the head to the track. This servo control unit detects the head position from the signal read from the head, and performs following control to follow the head to the track. The track following control is explained using an example of a magneto-optical storage device which is used as an external storage device for a computer.
In a magneto-optical storage device, a magneto-optical medium is used as the data storage unit. This medium has a storage layer made from a magnetic material that is formed on top of a substrate. This medium takes advantage of the heat from a light and the change in magnetic field to store information. This medium is formed with a data track for recording and reproducing data. Generally, there is a groove (tracking grooves) formed in a spiral shape on the substrate of the medium. The track for recording or reproducing data is provided on the land that is located between grooves.
The light beam from an optical head tracks this track. In addition, when recording, the heat applied from the light and the change in magnetic field is used in recording information. Moreover, when reproducing the information, the magneto-optical effect is used to reproduce the information from the reflected light of the light beam. In order to record or reproduce information, the laser beam from a laser diode passes through the objective lens of the optical head, and concentrates on the surface of the medium (recording surface). It is necessary to maintain this concentrated state and to constantly maintain a just focused state. The control needed to do this is called focus servo control.
Moreover, in order to record or reproduce data on the data track described above, the laser beam in the just-focused state must follow the data track. The following control is called track servo control. The optical head generates a track error signal (TES) which indicates the amount of track position deviation from the reflected light. The track servo control generates a track drive signal from this track error signal for doing away with the track position deviation. This track drive signal drives the track actuator, which moves the objective lens of the optical head, in order that the light beam follows the track.
With this kind of light-beam following control, the light beam always follows the track accurately, however there are cases when there are causes for error in the detected track error signal. These causes for error may include, external disturbance (vibration), medium defects, or changes in parameters of the servo circuit. Therefore, an off-track state may occur where the light beam strays off the track.
When the light beam strays off the track and this off-track state occurs, recording or reproducing data becomes difficult. Therefore, when the off-track state is detected, it is necessary to quickly perform a servo recovery process in order to restore the light beam to the track. Normally, the amount of track position deviation appears in the amplitude of the track error signal, so the servo error (off track) is detected by detecting when the track error signal exceeds the off-track slice level. When a servo error is detected (off track is detected), the track servo loop is opened to prevent overrun, as well as the servo recovery process is activated.
Multiple recovery processes have been prepared as the servo recovery process. For example, a first recovery process has been prepared, which is a simple restoration process for restoration to the on-track state in the shortest time, and a second recovery process has been prepared which performs complex restoration processes such as calibration.
Also, as the selection method for selecting the recovery process, selection is made according to the number of retries of the recovery processes. That is, first the first recovery process is executed. If the restoration is not possible with this first recovery process, the second recovery process is executed. This method makes it possible to perform restoration in the shortest amount of time by the first recovery process when off track if the cause of error is not serious (for example; vibration or medium defects). On the other hand, in the case of off track due to serious causes of error (for example; fluctuations in the circuit offset), restoration is possible by the second recovery process.
In other words, in this method, as the cause of off-track error is unknown, first the simple first recovery process is performed, and if restoration in unsuccessful, then recovery is retried with the complex second recovery process.
However, the technology of the prior art had the following problem.
Regardless of the state, when an error occurs in the normal state (on-track state) and the servo recovery process is called, the simple first recovery process is always performed according to the number of recovery tries. Also, if restoration is successful by the first recovery process, the number of recovery tries (recovery counter) is cleared (“0”). The second recovery process is only performed if restoration by the first recovery process failed.
Therefore, after an error occurs and recovery is successful by the first recovery process, there is a possibility that a process which an error occurs again thereby the first recovery process is called may be endlessly repeated.
The reason for this is that there may be an error in the calibration parameters. Normally, the calibration parameters are adjusted to the proper value by performing calibration when the medium is loaded or when a change in temperature occurs. After the calibration process has been performed, it is easy for this phenomenon to occur in the period before the next calibration.
For example, as shown in
FIG. 17
, control is performed such that the light beam B
1
follows the center of the track TRK, however if there is a shift in the offset of the track error signal (TES), control will be performed so that the light beam B
2
follows the edge of the track TRK. In this case, following operation becomes unstable, and it is easy for the off-track state to occur by just a little external disturbance.
Moreover, if restoration is successful by the first recovery process, then the on-track state in this unstable state is repeated. Therefore, it is not possible to follow in cases such as external disturbance, eccentricity, or surface deflection, the off-track state is repeated, and the process above of where the first recovery process is repeated many times may occur. The second recovery process should be performed in such a case, however, there was a problem of not being able to effectively use this second recovery process.
SUMMARY OF THE INVENTION
In view of the above problem in the prior art, the objective of the present invention is to provide a storage apparatus and a servo recovery method for the storage device which prevents retrying recovery using the same recovery process.
Another objective of the present invention is to provide a storage apparatus and a servo recovery method for the storage device which executes the proper recovery process by detecting the unstable state of the servo system.
A further objective of the present invention is to provide a storage apparatus and servo re
Ikeda Toru
Mochizuki Hideshi
Fujitsu Limited
Gree, Burns & Crain, Ltd.
Patel Gautam R.
To Doris H.
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