Dynamic information storage or retrieval – With servo positioning of transducer assembly over track... – Optical servo system
Reexamination Certificate
1999-11-24
2002-12-31
Edun, Muhammad (Department: 2653)
Dynamic information storage or retrieval
With servo positioning of transducer assembly over track...
Optical servo system
C369S044290, C369S044350
Reexamination Certificate
active
06501714
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to a method and apparatus for controlling track jump, and more particularly, to a method and apparatus for controlling track jump in a data reproduction apparatus that reads digital data from a disc type recording medium and transfers the data to a computer.
A compact disc (CD) is mainly used as a digital audio recording medium, but it can also be used as a read only memory (CD-ROM) for storing various types of digital data read by computers.
FIG. 1
is a schematic block diagram showing a conventional disk reproduction apparatus. A disc
1
has a spiral recording track formed on at least one of its surfaces. Digital data, which is in a predetermined format, is recorded along the recording track. The disc reproduction apparatus includes a pickup
3
to read the data recorded on the recording track. The disc reproduction apparatus further includes a servo mechanism for controlling the position of the pickup
3
relative to the disc
1
so that the pickup
3
tracks the recording track properly.
The pickup
3
is arranged opposite the recording track of the disc
1
. An actuator
4
, which is operated in accordance with a drive signal TD, moves the pickup
3
in the radial direction of the disc
1
. The pickup
3
includes laser beam sources and sensors. Referring to
FIG. 2
, the pickup
3
generates a main reading beam P and a pair of auxiliary reading beams T
1
, T
2
which are radiated toward the recording track. The pickup
3
has a main beam receiving portion and an auxiliary beam receiving portion. The main reading beam P is received by the main beam receiving portion to detect pits on the recording track surface. The auxiliary reading beams T
1
, T
2
are received by the auxiliary beam receiving portion to detect when the pickup
3
moves away from the recording track. The reading beams P, T
1
, T
2
radiated against the pits of the disc
1
are reflected toward the beam receiving portions as weak lights. The reading beams D, T
1
, T
2
radiated against portions other than the pits of the disc
1
are reflected toward the beam receiving portions as strong lights. When the beam receiving portion associated with each of the reading beams P, T
1
, and T
2
receives the corresponding reflection beam, the receiving portion generates a voltage having a value which corresponds to the intensity of the reflected light. The actuator
4
supports the pickup
3
and performs track jump to move the pickup
3
radially along the disc
1
in response to the drive signal TD.
The pickup
3
sends a voltage signal, the value of which corresponds to the main reading beam P, to a signal processor
5
. The signal processor
5
performs a waveform shaping process and a digitizing process on the voltage signal to generate an EFM signal. The EFM signal repetitively goes back and forth between a low level and a high level in accordance with the existence of pits.
The signal processor
5
generates a tracking error signal TE from the difference between the voltage values of the auxiliary reading beams T
1
, T
2
and an off track signal OT from a low frequency component of the EFM signal. The waveform of the tracking error signal TE is a sine wave, the polarity of which is inverted each time the pickup
3
moves across the recording track. The tracking error signal TE is digitized to generate a track jump signal TJ.
The voltage value corresponding to the auxiliary reading beam T
1
is substantially the same as the voltage value corresponding to the auxiliary reading beam T
2
when the pickup
3
is accurately tracking the recording track (i.e., when the pickup
3
is at the proper position). Under these conditions, the tracking error signal TE is at a null level. When the pickup
3
is not accurately tracking the recording track (i.e., when the pickup
3
is not at the proper position), for example, when the position of the pickup
3
is offset inward from the recording track, the voltage value corresponding to the auxiliary reading beam T
1
becomes smaller than the voltage value corresponding to the auxiliary reading beam T
2
and causes the tracking error signal TE to take a negative value. On the other hand, if the position of the pickup
3
is offset outward from the recording track, the voltage value corresponding to the auxiliary reading beam T
2
becomes smaller than the voltage value corresponding to the auxiliary reading beam T
1
and causes the tracking error signal TE to take a positive value. When the pickup
3
is completely separated from the recording track, the voltage values of the auxiliary reading beams T
1
, T
2
become equal to each other and cause the tracking error signal TE to become null. The track jump signal TJ is generated from the tracking error signal TE using the null level as a threshold value. Further, the track jump signal TJ goes high or low when the center of the pickup
3
is located at the center of the recording track.
when the pickup
3
is properly tracking the recording track of the disc
1
, the signal processor
5
continuously outputs the EFM signal. Thus, the EFM signal has a predetermined amplitude and does not include a low frequency component. Accordingly, the off track signal OT is maintained at a low level when the pickup
3
is properly tracking the recording track. The off track signal OT rises or falls when the center of the pickup
3
is located near an edge of a pit.
As shown in
FIG. 1
, the signal processor
5
sends the EFM signal, the tracking error signal TE, and the off track signal OT to the servo controller
6
. The servo controller
6
generates a spindle motor drive signal SD and the actuator drive signal TD based on the tracking error signal TE and the off track signal OT. The spindle motor drive signal SD controls the spindle motor
2
so that the frequency of the EFM signal is maintained at a predetermined value. The actuator drive signal TD controls the actuator
4
so that the tracking error signal TE has a null level and the off track signal OT is maintained at a low level. The spindle motor drive signal SD and the actuator drive signal TD servo control the spindle motor and tracking.
FIGS.
3
(
a
) and
3
(
b
) are charts showing the waveforms of the signals detected when the pickup
3
moves across the lines of the recording track on the disc
1
(when a so-called track jump is performed). The horizontal axis represents time. FIGS.
3
(
a
) and
3
(
b
) show a state in which the pickup
3
gradually decelerates.
As described above, the track jump signal TJ rises or falls when the center of the pickup
3
is located at the center of the recording track. The off track signal OT rises or falls when the center of the pickup
3
is located near the edges of the pits. Accordingly, the phase difference between the off track signal OT and the tracking error signal TE is normally +90°. The tracking error signal TE or the off track signal OT are counted to detect the number of recording tracks the pickup
3
traverses. The moving direction of the pickup
3
is detected by the difference between the phase of the tracking error signal TE and the phase of the off track signal OT. The movement of the pickup
3
is controlled based on the two detection results.
The moving speed of the pickup
3
must be detected to perform the track jump. In other words, the pickup
3
is moved to the desired position by monitoring the moving speed of the pickup
3
and accelerating and decelerating the pickup
3
at optimal timings to decrease the moving time of the pickup
3
. During a single cycle of the track jump signal TJ or the off track signal OT, a clock signal CLK is counted to measure the time of the cycle and detect the moving speed. The clock signal CLK, which is sent to the servo controller
6
, has a cycle sufficiently advanced from the track jump signal TJ and the off track signal OT.
However, only the average speed during one cycle is obtained in the above speed measuring method. The resolution of the measured speed may then be insufficient and the measured speed may be inaccu
Kajitani Yuji
Takano Koji
Edun Muhammad
Fish & Richardson P.C.
Sanyo Electric Co,. Ltd.
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