Optical disc device

Details Optical disc device Optical disc device

2001-11-08

2004-04-13

Dinh, Tan (Department: 2653)

Dynamic information storage or retrieval

Information location or remote operator actuated control

Selective addressing of storage medium

C369S030150, C369S044280

Reexamination Certificate

active

06721239

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an optical disc device that uses an optical beam emitted from a light source such as a laser to reproduce information recorded optically on an information carrier. In particular, the present invention relates to a track jumping control for conducting a shift from an arbitrary track to another track on an information carrier in which a spiral information track formed as an uneven guide groove is divided in a radial direction and has an address part where position information is recorded in advance.
2. Description of the Related Art
In a conventional optical disc device, a tracking control is performed by shifting a converging lens in the radial direction of an information carrier using a tracking actuator. This tracking actuator is constructed of a fixed part and a movable part that is mounted on a converging lens, and the movable part and the fixed part are coupled together with an elastic body such as four pieces of wires (wire rod), rubber or the like. Then, when an electric current is supplied to a coil in the movable part, an electromagnetic force is generated between the coil and a permanent magnet in the fixed part, and this electromagnetic force allows the converging lens to move in the radial direction of the information carrier, that is, in the direction perpendicular to the track.
A search for a desired information track is carried out by deactivating the tracking control, shifting an optical head including the tracking actuator as a whole in the radial direction of the information carrier, and counting tracks which were crossed by a convergent point of an optical beam on the information carrier. Here, when the number of tracks to the desired information track is several tracks, in order to reach the desired information track surely and stably, an accelerating/decelerating pulse is applied to the tracking actuator while retaining the tracking control in the activated state, and a track jumping of moving to the neighboring track is performed repeatedly.
In recent years, along with the improvement of high-density optical disc technology, a recordable optical disc (DVD-RAM) has come into being. This recordable DVD-RAM disc includes an address part and a recordable data part. Furthermore, this DVD-RAM disc is divided into a plurality of zones in the radial direction, and the data part is formed as a convex groove (referred to as a groove track) and a guide groove of a region interposed between adjacent grooves (referred to as a land track).
FIGS. 12A
,
12
B and
12
C are schematic diagrams showing the structure of such an optical disc.
FIG. 12A
is a partial cutaway perspective view showing the whole structure of an optical disc;
FIG. 12B
is a perspective view showing an enlarged cross-section of an optical disc
101
cut in the radial direction; and
FIG. 12C
is a schematic diagram showing the relative position between an address part and a data part. As shown in
FIG. 12C
, the data part is formed as one spiral structure with grooves and a land, and the address part is formed between the grooves/lands. A convergent point of an optical beam on the optical disc
101
is larger than a track width, and when the convergent point of the optical beam scans the grooves or the lands, address information stored in the address part between these tracks also can be read out.
In the following, a conventional track jumping method for this DVD-RAM disc will be explained in detail with reference to the drawings.
FIG. 11
is a block diagram showing a simple configuration of an optical disc device for performing a conventional track jumping method. A conventional optical disc device is provided with a disc motor
102
for rotating the optical disc
101
at a predetermined number of revolutions, an optical head
103
(including a light source such as a semiconductor laser, a coupling lens, a deflected beam splitter, a deflection plate, a converging lens, a condensing lens, a split mirror, a photodetector and so on, which are not shown in the drawing) for reproduction of information from the optical disc
101
, and a traverse motor (not shown in the drawing) for shifting the optical head
103
as a whole in a direction perpendicular to the direction of tracks of the optical disc
101
.
An optical beam spot formed by the optical head
103
is emitted to the optical disc
101
that is rotated by the disc motor
102
. A light reflected from the optical disc
101
passes through a converging lens, a deflection plate, a deflected beam splitter, and a condensing lens and is split into two-way optical beams by a split mirror. One of the split optical beams is input to a focus control device (not shown in the drawing) via a split-structure photodetector to generate a positional displacement signal (a focus error signal, hereinafter abbreviated as a “FE signal”) between the convergent point of the optical beam and the optical disc
101
based on a difference in the output of the photodetector, and performs a focus control based on this FE signal so that the convergent point is positioned on the optical disc
101
. The configuration and the operation of the focus control device is not directly related to the explanation of the track jumping method, so that the explanation thereof is omitted.
On the other hand, the other optical beam that was split by the split mirror is input to a tracking control device via the split-structure photodetector. The tracking control device includes a tracking error signal generator
104
, a digital signal processor (DSP)
1101
, a tracking driving circuit
110
and a tracking actuator (not shown in the drawing). The tracking error signal generator
104
generates a signal indicating a displacement of the convergent point of the optical beam on the optical disc
101
with the track, that is, a tracking displacement signal (tracking error signal, hereinafter abbreviated as a “TE signal”) for controlling the convergent point of the optical beam on the optical disc
101
in order to scan the surface of the track based on a difference in the output of the split-structure photodetector, and this TE signal is input to the DSP
1101
. A method for detecting this TE signal is called “a push-pull method”.
A switch
108
is provided in the DSP
1101
. The switch
108
is set at a position shown by the solid line when a tracking control is switched on, whereas the switch
108
is set at a position shown by the dotted line when a track jumping to a neighboring track is performed. Therefore, the switch
108
is operated to open and close the loop of a tracking control system and also to switch a driving signal to be supplied to the tracking actuator for performing a tracking control and for performing a track jumping.
First, a tracking control will be explained. The TE signal input to the DSP
1101
is converted from an analog signal to a digital signal by an AD converter
105
and input to a compensating filter
106
, which is a digital filter including an adder, a multiplier and a delay element. The compensating filter
106
serves to compensate a phase or the like of the tracking control system. The TE signal whose phase was compensated by the compensating filter
106
is input to the switch
108
via a gain switching circuit
107
that switches a loop gain of the tracking control system. The switch
108
is set at a position shown by the solid line for performing a tracking control, so that the TE signal that passed through the switch
108
is converted from a digital signal to an analog signal by a DA converter
109
and input to the tracking driving circuit
110
.
The tracking driving circuit
110
drives the tracking actuator by appropriately performing a current amplification and a level conversion of an output signal from the DSP
1101
. Thus, the tracking actuator is driven such that the convergent point of the optical beam on the optical disc
101
scans a predetermined surface of the track, thereby achieving a tracking control. Here, in the case of a DVD-RAM disc, a tracking c

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