Dynamic information storage or retrieval – With servo positioning of transducer assembly over track... – Optical servo system
Reexamination Certificate
1999-10-12
2002-05-28
Huber, Paul W. (Department: 2653)
Dynamic information storage or retrieval
With servo positioning of transducer assembly over track...
Optical servo system
C369S053140
Reexamination Certificate
active
06396779
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an apparatus for focusing a light beam from a light source such as a semiconductor laser onto a rotating disk-shaped recording medium (hereinafter, referred to as an “optical disk”) so as to record/reproduce signals on/from the optical disk. More particularly, the present invention relates to a tracking control for positioning the light beam along a track on the optical disk.
2. Description of the Related Art
With a conventional optical disk apparatus, a signal is reproduced from an optical disk by irradiating the optical disk with a light beam of a relatively small but constant light amount so as to detect the reflected light from the optical disk whose intensity has been modulated by the optical disk. A signal is recorded on the optical disk by writing information on a recording material film of the optical disk with a light beam while modulating the intensity thereof according to the signal to be recorded (e.g., Japanese Laid-Open Publication No. 52-80802).
A read-only optical disk is produced by recording a plurality of information pits on the disk in a spiral pattern. A recordable/reproducible optical disk is produced by providing an optically recordable/reproducible material film through a process such as vapor deposition on a surface of a substrate which includes spiral concave/convex tracks thereon.
To properly record information on an optical disk or reproduce the recorded information from the optical disk requires a focusing control and a tracking control. The focusing control is for controlling the optical disk in a direction normal to the optical disk surface (hereinafter, referred to as the “focusing direction”) so that the light beam is always in a predetermined focused state at the recording material film. The tracking control is for controlling the optical disk in a radial direction of the optical disk (hereinafter, referred to as the “tracking direction”) so that the light beam is always positioned along a predetermined track.
A conventional tracking control for an optical disk will be described with reference to
FIG. 8. A
disk-shaped optical disk
1
is rotated by a disk motor
50
. An optical head
10
includes a semiconductor laser
11
, a coupling lens
12
, a polarization beam splitter
13
, a ¼ wave plate
14
, a focusing actuator
16
, a tracking actuator
17
, a detection lens
18
, a cylindrical lens
19
and a 4-divided photodetector
20
.
The optical head
10
can be traversed by a traverse motor
43
in the tracking direction. A light beam generated from the semiconductor laser
11
is collimated by the coupling lens
12
, passes through the polarization beam splitter
13
and the ¼ wave plate
14
, and is then focused by a focusing lens
15
on the optical disk
1
.
The light beam is reflected by the optical disk
1
, passes through the focusing lens
15
and the ¼ wave plate
14
, and is then reflected by the polarization beam splitter
13
. Thereafter, the reflected light passes through the detection lens
18
and the cylindrical lens
19
so as to be incident upon the 4-divided photodetector
20
.
The focusing lens
15
is supported by an elastic body (not shown). The focusing lens
15
is moved in the focusing direction by applying a current to the focusing actuator
16
and in the tracking direction by applying a current to the tracking actuator
17
.
The photodetector
20
detects a light amount signal and sends the detected light amount signal to a focusing error detector (hereinafter, referred to as the “FE generator”)
30
and to a tracking error detector (hereinafter, referred to as the “TE generator”)
40
.
Using the light amount signal from the photodetector
20
, the FE generator
30
calculates an error signal (hereinafter, referred to as an “FE signal”) which indicates the focused state of the light beam at the information surface of the optical disk
1
, and sends the FE signal to the focusing actuator
16
via a focusing linear filter (hereinafter, referred to as the “Fc linear filter”)
31
. The focusing actuator
16
controls the focusing lens
15
in the focusing direction so that the light beam is focused on the recording surface of the optical disk
1
in a predetermined state. Thus, the focusing control is performed.
Using the light amount signal from the photodetector
20
, the TE generator
40
also calculates an error signal (hereinafter, referred to as a “TE signal”) which indicates the positional relationship between the light beam and an intended track on the optical disk
1
, and sends the TE signal to the tracking actuator
17
via a tracking linear filter (hereinafter, referred to as the “Tk linear filter”)
41
.
The tracking actuator
17
controls the focusing lens
15
in the tracking direction so that the light beam properly follows a track. The tracks of the optical disk
1
exist over a large area of the optical disk
1
, extending from the inner periphery to the outer periphery of the optical disk
1
. Therefore, the focusing lens
15
needs to be movable over a large extent in order to irradiate the intended track with the light beam.
Since the motion range of the tracking actuator
17
is limited, the optical head
10
needs to be driven in the tracking direction. Therefore, a drive signal output from the Tk linear filter
41
to the tracking actuator
17
is sent to the traverse motor
43
via a traverse linear filter
42
, an average calculator
45
and a pulse generator
44
so as to move the optical head
10
in the tracking direction through the rotation of the traverse motor
43
.
Thus, the optical head
10
moves in the tracking direction so that the drive signal to the tracking actuator
17
approaches zero or, in other words, so that the focusing lens
15
takes a normal position with respect to the optical head
10
. By the two devices, i.e., the tracking actuator
17
and the traverse motor
43
, operating as described above, the light beam follows a track on the optical disk
1
. Thus, the tracking control is performed.
Typically, as compared with the tracking actuator
17
, the traverse motor
43
is only responsive to an input signal having a relatively low frequency. The traverse linear filter
42
extracts a low-band component of the signal from the Tk linear filter
41
, for which the traverse motor
43
can sufficiently follow the track, through a low-pass filter having a low-pass characteristic as illustrated in FIG.
9
. Thus, the traverse motor
43
is driven by the extracted low-band component.
To move the optical head
10
by the traverse motor
43
requires a driving force which overcomes the frictional force of the traverse motor
43
itself or the frictional force of a mechanism for traversing the optical head
10
.
Moreover, when the optical disk
1
has some eccentricity, the drive signal from the Tk linear filter
41
includes eccentricity components so that the light beam can properly follow the track. When the optical disk
1
rotates at a high speed, it is difficult for the traverse motor
43
to follow the eccentricity components of the drive signal. Therefore, it is necessary to drive the traverse motor
43
to eliminate an influence of the eccentricity.
In an optical disk apparatus
800
illustrated in
FIG. 8
, a signal from the traverse linear filter
42
is sent to the traverse motor
43
via the average calculator
45
and the pulse generator
44
.
An operation of the optical disk apparatus
800
will be described with reference to
FIGS. 10A
to
10
D.
FIG. 10A
illustrates a signal from the disk motor
50
,
FIG. 10B
illustrates a signal from the traverse linear filter
42
,
FIG. 10C
illustrates a signal from the average calculator
45
, an
FIG. 10D
illustrates a signal from the pulse generator
44
.
Referring to
FIG. 10A
, the disk motor
50
outputs one cycle of a square wave signal (hereinafter, referred to as the “FG signal”) for each revolution thereof. Referring to
FIG. 10C
, the average calculator
45
calculates the average value of the signal
Fujiune Kenji
Kanda Yoshihiro
Kuze Yuuichi
Moriya Mitsurou
Huber Paul W.
Matsushita Electric Industrial Co. Ltd
Ratner & Prestia
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