Dynamic information storage or retrieval – With servo positioning of transducer assembly over track... – Optical servo system
Reexamination Certificate
2000-04-07
2003-09-30
Tran, Thang V. (Department: 2653)
Dynamic information storage or retrieval
With servo positioning of transducer assembly over track...
Optical servo system
Reexamination Certificate
active
06628580
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an optical recording and reproducing apparatus which optically records information to a recording medium and/or optically reproduces information from a recording medium by using a light beam from a light source such as a laser. In particular, the present invention relates to an optical recording and reproducing apparatus that controls on track jumping, where a light spot is moved from a track to an adjacent track, and focus jumping, where a light spot is moved from an information plane to an adjacent information plane of a medium having a plurality of information planes.
2. Description of Prior Art
In an optical recording and reproducing apparatus, an optical head has a light source such as a laser and an optical sensor. A light beam from the light source is focused on a recording medium such as an optical disk to optically record information in the medium, and a light reflected from the medium is detected with the sensor to reproduce information from the medium. Focus control and tracking control for recording and reproduction are also performed with the optical sensor. An example of such an optical disk apparatus is described in U.S. Pat. No. 6,011,762.
In a search for a specified information track, the tracking is stopped, and the optical head including a tracking actuator is moved in the radial direction of a recording medium while counting the number of tracks on a medium over which the light beam crosses. When the number of tracks to the specified track is a few, in order to surely and stably arrive at the specified track, a pulse for acceleration or deceleration is applied to the tracking actuator while enabling the tracking, and the track jumping to move the light beam to an adjacent track is repeated.
An example off prior art track jumping is explained here. In track jumping to an adjacent track, a drive signal applied to the tracking actuator is changed to control the position of the optical head, as explained below. A tracking error signal obtained with an optical sensor is subjected to gain change and passes a low pass filter. The signal is added next with a pulse signal for acceleration/deceleration, and the sum signal is applied to the tracking actuator for driving it. Track jumping is affected by harmonic components due to partial eccentricity and eccentricity generated by undulation of tracks of an optical disk. The cut-off frequency of the low pass filter is set low to pass the eccentricity components of the optical disk sufficiently. Thus, the low frequency components of the tracking error signal (eccentricity components) are added to the pulse signal for acceleration/deceleration, and the sum signal is used to drive the tracking actuator. Then the unstableness of track jumping due to eccentricity of the optical disk is decreased.
FIGS. 1A-1F
show waveforms on track jumping in a direction to the inner of the disk.
FIG. 1A
shows tracking error (TE) signal while
FIG. 1B
shows tracking drive waveform, in normal situations. On track jumping in a direction to the outer periphery of the disk, only the polarity of the tracking error signal and the tracking drive waveform is changed. Then, the waveform diagrams and the explanation therefor are omitted here. By starting to output a pulse for acceleration (of wave amplitude A
1
), the optical head starts to be moved along the direction, and the sinusoidal tracking error signal appears. The acceleration pulse is outputted in a predetermined time T
1
. Next, when the zero cross point (Z) of the tracking error signal is detected, a pulse for deceleration (of wave amplitude A
2
) is outputted for a time T
2
. Then, track jumping to an adjacent track is completed, and the tracking control is started again. Track jumping in the opposite direction to an outer peripheral, the tracking error signal and the tracking drive waveform are changed only on the polarity.
Focus jumping is controlled for an optical disk having a plurality of information planes from one information plane to another one. Similarly to the track jumping control, pulses for acceleration/deceleration of predetermined amplitude and period are applied to focus actuator successively by considering vibration components of an optical disk. For an optical disk having two information planes, L
0
nearer to the optical head and L
1
farther therefrom, when a focus lens is raised gradually from a sufficiently low position, as shown in
FIG. 2
, a focus error signal is obtained as a sinusoidal (S-like) wave in correspondence to the two information planes. When information in the plane L
0
, focus control is performed at around point X
1
, while when information in the plane L
1
, focus control is performed at around point X
2
. For the focus jumping from information plane L
0
to L
1
, the focus control position is changed from point X
1
to point X
2
. When the jumping is started, the sinusoidal waveform appears as focus error (FE) signal, similarly to track jumping. Then, focus jumping control is performed similarly to the track jumping control.
As explained above, in a prior art optical recording and reproducing apparatus, when the track is jumped to an adjacent track, pulses for acceleration/deceleration of predetermined amplitude and period are applied to a tracking actuator by considering eccentricity components of an optical disk. However, especially when the disk information is recorded or reproduced at high speed, external disturbance frequencies become high due to eccentricity components. Then, the gain of servo is decreased, and the performance to find the track becomes low, so that the degree of off-tracking becomes larger for the external disturbances.
FIG. 1C
shows tracking error signal and
FIG. 1D
shows tracking drive waveform when the moving speed is high, while
FIG. 1E
shows tracking error signal and
FIG. 1F
shows tracking drive waveform when the moving speed is low. In these situations, the moving speed of the light beam is scattered after the acceleration pulse is outputted, and the position of the light beam is fluctuated even when the same deceleration pulse is applied to the tracking actuator. Thus track jumping becomes unstable. A similar problem also occurs when external vibrations or an impact is applied to the apparatus.
Similarly, when focus jumping from one information plane to another is performed in a prior art apparatus for an optical disk having a plurality of information planes, pulses for acceleration/deceleration of a predetermined magnitude and a predetermined period are applied to a focus actuator successively by considering harmonic components of partial plane deflection or plane deflection due to undulation of information planes in an optical disk. However, similarly to the track jumping explained above, especially when the information is recorded or reproduced at high speed, external disturbance frequencies become high due to the harmonic components. Then, the gain of servo is decreased, and the ability to find an information plane becomes low, so that the degree of defocusing becomes larger for the external disturbances. In these situations, the moving speed of the light beam is scattered after the acceleration pulse is outputted, and the position of the light beam is fluctuated when the same deceleration pulse is applied to the focus actuator. Thus focus jumping becomes unstable. A similar problem also arises when external vibrations or an impact is applied to the apparatus.
SUMMARY OF THE INVENTION
An object of the present invention is to provide an optical recording and reproducing apparatus which performs stable track jumping and/or focus jumping.
In one aspect of the present invention, an optical recording and reproducing apparatus comprises a focus device which illuminates and focuses a light beam onto a recording medium on which tracks are formed, and a moving device which moves the focus device in a direction to cross tracks on the recording medium. A tracking error detector generates a tracking error signal in corresponde
Kishimoto Takashi
Takeuchi Tatsuya
Watanabe Katsuya
Yamamoto Takeharu
Matsushita Electric - Industrial Co., Ltd.
Tran Thang V.
Wenderoth , Lind & Ponack, L.L.P.
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