Dynamic information storage or retrieval – With servo positioning of transducer assembly over track... – Optical servo system
Reexamination Certificate
2000-05-31
2004-03-02
Korzuch, William (Department: 2753)
Dynamic information storage or retrieval
With servo positioning of transducer assembly over track...
Optical servo system
Reexamination Certificate
active
06700841
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to an optical-disc recording and reproducing apparatus acting as an optical information reproducing and recording apparatus which is applicable to a mini disc (MD) player, a recorder, a CD player, or the like which reproduces information from an optical disc or records information thereon for reproduction.
BACKGROUND OF THE INVENTION
Tracking control in a conventional optical-disc recording and reproducing apparatus will be described with reference to FIG.
8
. As shown in this figure, this optical-disc recording and reproducing apparatus is comprised of an optical disc
1
capable of at least either recording or reproduction; a spindle motor
2
for rotating the optical disc
1
; an optical pickup
6
for recording/reproducing signals on or from the optical disc, the optical pickup having an objective lens
3
for irradiating the optical disc
1
with light, a tracking actuator
4
for supplying a current to a tracking actuator coil to move the objective lens
3
, and a light receiving section
5
for receiving an optical spot from the optical disc
1
; an optical head
7
for holding the optical pickup
6
; a traverse mechanism
8
for moving the optical head
7
in a radial direction A of the optical disc
1
; a traverse mechanism-controlling section
9
for controlling the traverse mechanism
8
; an arithmetic section
10
for calculating a signal received by the light receiving section
5
of the optical pickup
6
; a tracking error signal-generating section
11
for generating a tracking error signal based on an output signal from the arithmetic section
10
; a tracking controlling section
12
for determining a gain, a frequency characteristic, and a phase characteristic required for continuous tracking on the optical disc
1
based on the signal generated by the tracking error signal-generating section
11
; a tracking driving section
13
for driving the tracking actuator
4
; and a controller
14
for controlling the traverse mechanism-controlling section
9
and the tracking controlling section
12
.
The tracking driving section
13
drives the tracking actuator
4
to move the objective lens
3
in a radial direction B of the optical disc
1
within an internal movement range of the optical head
7
in a fashion following tracks of the optical disc
1
.
The traverse mechanism-controlling section
9
controls the traverse mechanism
8
to move the entire optical head
7
in the radial direction A of the optical disc
1
.
As shown in
FIG. 9
, the light receiving section
5
is comprised of abeam splitter (not shown) for splitting (a split line
34
) the optical spot from the optical disc
1
in a direction generally in parallel with the tracks of the optical disc
1
and outputting the obtained beams, and a photodetector
15
having a plurality of light receiving elements
30
to
36
for receiving the split light. The arithmetic section
10
is comprised of an amplifier
38
for generating an optical-spot offset signal and an amplifier
39
for generating the tracking error signal.
FIG. 9
represents the photodetector
15
of the optical pickup
6
and an optical spot
37
on the photodetector
15
in a pseudo manner.
A tracking control operation performed by this optical-disc recording and reproducing apparatus will be described below. While being rotated by the spindle motor
2
, the optical disc
1
is irradiated with laser light for reproduction/recording which is controlled to focus on the optical disc
1
. The tracking error signal generating section
11
generates the tracking error signal based on a signal received by the photodetector
15
of the light receiving section
5
of the optical pickup
6
. Based on the tracking error signal, a signal having a gain, a frequency characteristic, and a phase characteristic required for continuous tracking on the optical disc
1
is supplied to the tracking actuator
4
of the optical pickup
6
through the tracking controlling section
12
and the tracking driving section
13
to perform the tracking operation.
In a tracking controlling method used by such an optical-disc recording and reproducing apparatus, if this apparatus assumes a position in which the optical disc
1
lies horizontally, the tracking driving section
13
provides no output before starting tracking control and is thus located in such a manner as to balance itself with the gravity G (generally at the center of the movement range of the tracking actuator
4
). Since an electric offset or the like is provided in this position, in the above tracking conditions, the tracking operation is performed around the position in which the tracking driving section
13
balances itself with the gravity G.
In addition, if this apparatus assumes a position in which the optical disc
1
stands vertically, the tracking drive section
13
provides no output before starting tracking control and is thus located in such a manner as to balance itself with the gravity G (at a position outward or inward offset from the movement range of the tracking actuator
4
). Accordingly, the movement range of the tracking actuator
4
may shift outward or inward significantly depending on the weight of the objective lens
3
or the characteristics of a member supporting the objective lens
3
. Then, the tracking operation is performed for reproduction or recording around a position in which the objective lens
3
is substantially displaced. Consequently, in the worst case, signals cannot be read or information cannot be recorded accurately.
Such tracking control carried out by conventional optical-disc recording and reproducing apparatuses is disadvantageous in that the displacement of the objective lens caused by the gravity depending on the position of this apparatus cannot be corrected, thereby degrading reproduced signals.
It is an object of the present invention to provide an optical-disc recording and reproducing apparatus that realizes stable tracking control capable of correcting the displacement of the objective lens caused by the gravity depending on the position of the apparatus.
SUMMARY OF THE INVENTION
An optical-disc recording and reproducing apparatus according to the present invention comprises optical-spot offset-controlling means operating before a tracking operation to calculate an output signal from the light receiving section to detect relative displacement of an optical spot on a light receiving section in order to drive and position a tracking actuator in a manner such that the relative displacement is maintained at a fixed value.
According to the present invention, in every position of the present apparatus, displacement of the objective lens caused by the gravity depending on the position of the present apparatus can be controlled to place the object lens at a position substantially corresponding to a horizontal position of the present apparatus, thereby minimizing variations in the tracking actuator originating from the displacement of the objective lens caused by the gravity depending on the position of the present apparatus. Consequently, a movement range of the tracking actuator can be set within a range in which the tracking actuator can be stably controlled.
A first aspect of the present invention is an optical-disc recording and reproducing apparatus comprising an optical pickup having an objective lens for irradiating an optical disc with light beams, a light receiving section for receiving an optical spot from the optical disc, and a tracking actuator for moving the objective lens in a radial direction of the optical disc, the apparatus performing a tracking operation by driving the tracking actuator based on a tracking error signal obtained from an output signal from the light receiving section, wherein the optical disc recording and reproducing apparatus further comprises optical-spot offset-controlling means adapted, before the tracking operation, for calculating the output signal from the light receiving section to detect relative displacement of the optical spot on the light receiving secti
Shimizu Masanobu
Sumida Katsutoshi
Teshirogi Kazuhiro
Korzuch William
Le Kimlien
Matsushita Electric - Industrial Co., Ltd.
Parkhurst & Wendel L.L.P.
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