Dynamic information storage or retrieval – Condition indicating – monitoring – or testing – Including radiation storage or retrieval
Reexamination Certificate
2001-04-20
2003-05-20
Edun, Muhammad (Department: 2655)
Dynamic information storage or retrieval
Condition indicating, monitoring, or testing
Including radiation storage or retrieval
C369S053100, C369S044280, C369S044320
Reexamination Certificate
active
06567357
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an optical disk apparatus for optically reproducing information recorded on a recording medium by utilizing a light beam from a light source such as a laser. In particular, the present invention relates to focus jumping control for moving a light beam spot from a recording/reproducing surface to another recording/reproducing surface on a recording medium having a plurality of recording/reproducing surfaces.
2. Description of the Related Art
In general, an optical disk apparatus conducts focus control by moving a converging lens in a direction substantially vertical to a recording/reproducing surface of a recording medium with a focus actuator. The focus actuator is composed of a movable part and a fixed part attached to a converging lens. The movable part and the fixed part are bound to each other via four wires or an elastic substance such as rubber. When an electric current flows through a coil provided in the movable part, an electromagnetic force is generated between the coil and a permanent magnet provided in the fixed part, thereby moving the converging lens in a direction substantially vertical to the recording/reproducing surface of the recording medium. The direction substantially vertical to the recording/reproducing surface refers to a vertical direction and a direction containing a slight deflection from the vertical direction. Furthermore, in the case where a recording/reproducing surface on which focus control currently is conducted is not a desired one, search for a desired information track on a recording medium having a plurality of recording/reproducing surfaces is conducted by repeating focus jumping to an adjacent recording/reproducing surface a plurality of times to conduct focus control on a desired recording/reproducing surface, and searching for a desired track.
Hereinafter, a conventional focus jumping method will be described in detail with reference to the drawings.
FIG. 9
is a block diagram showing a schematic structure of a conventional optical disk apparatus that conducts focus jumping by a conventional focus jumping method.
FIG. 9
shows a state of the optical disk apparatus during focus jumping. The conventional optical disk apparatus includes a disk motor
102
for rotating an optical disk
101
with two recording/reproducing surfaces (L0 surface, L1 surface) at a predetermined rotation speed, an optical head
103
(composed of a light source such as a semiconductor laser, a coupling lens, a polarized beam splitter, a polarizing plate, a converging lens, a condensing lens, a dividing mirror, a photodetector, and the like (not shown)) for reproducing information from the optical disk
101
, and a traverse motor (not shown) for moving the entire optical head
103
in a direction vertical to a track of the optical disk
101
.
A light beam generated by a light source is collimated by the coupling lens, reflected from the polarized beam splitter, passes through the polarizing plate, and is converged by the converging lens. In this manner, a light beam spot with a focus point in a thickness direction of the optical disk
101
is formed. The light beam spot is radiated to the optical disk
101
that is rotated by the disk motor
102
. Light reflected from the optical disk
101
passes through the converging lens, the polarizing plate, the polarized beam splitter, and the condensing lens, and is split into light beams in two directions by the dividing mirror. One of the divided light beams is input to a focus control apparatus through a photodetector with a two-division structure. The focus control apparatus is composed of a focus error signal generating part
104
, a digital signal processor (DSP)
901
as a focus control part, a focus driving circuit
111
, and a focus actuator (not shown). The focus error signal generating part
104
is provided as a converged state detecting part for generating a signal corresponding to a converged state of a light beam. In the focus error signal generating part
104
, an output signal from the two-division photodetector is input to a differential amplifier. An output signal from the differential amplifier becomes a positional shift signal (focus error (FE) signal) representing a shift between a converged point of a light beam and the optical disk
101
, and is input to the DSP
901
. The detection of the FE signal is called an “SSD method”.
Focus control will be described. The FE signal input to the DSP
901
is converted from an analog signal to a digital signal by an AD converter
105
, and is input to a compensating filter
107
, which is a digital filter composed of an adder, a multiplier, and a delay circuit, through a switch
106
. The compensating filter
107
compensates for a phase and the like of a focus control system. The FE signal with its phase compensated by the compensating filter
107
is input to an adder
109
through a gain switching circuit
108
that switches a loop gain of the focus control system. A switch
114
is turned off during focus control. Therefore, the FE signal passing through the gain switching circuit
108
passes through the adder
109
as it is, is converted from a digital signal to an analog signal by a DA converter
110
, and is input to the focus driving circuit
111
. The focus driving circuit
111
amplifies an output signal from the DSP
901
and converts its level in an appropriate manner, thereby driving the focus actuator. In this manner, the focus actuator is driven so that a light beam on the optical disk
101
takes a predetermined converged state, whereby focus control is realized.
On the other hand, the other light beam divided by the dividing mirror is input to a tracking control apparatus (not shown) via a photodetector with a four-division structure, which detects a signal representing a shift between a converged point of a light beam and a track on the optical disk
101
, i.e., a track shift signal (tracking error (TE) signal) for controlling a converged point of a light beam to scan a track on the optical disk
101
, and conducts tracking control based on the TE signal so that a converged point of a light beam scans a predetermined track on the optical disk
101
. A structure and operation of the tracking control apparatus are not related to the description of the focus jumping method directly; therefore, the description thereof will be omitted.
The DSP
901
is provided with the switches
106
and
114
. During focus control, the switch
106
is turned on, and the switch
114
is turned off. During focus jumping, the switch
106
is turned off, and the switch
114
is turned on. The switch
106
opens/closes a loop of the focus control system, and switches between an input signal during focus control and an input signal during focus jumping with respect to the compensating filter
107
Next, the focus jumping method will be described with reference to a waveform diagram in
FIG. 10 and a
flow chart in
FIG. 11
, as well as the block diagram in FIG.
9
.
FIG. 10
is a waveform diagram showing a FE signal and a focus driving waveform during focus jumping from the L0 layer to the L1 layer of the optical disk
101
. During focus jumping from the L1 layer to the L0 layer, the polarity of the FE signal and the focus driving waveform become inverse to that of the waveforms shown in FIG.
10
. Therefore, the waveform diagram and description thereof in this case will be omitted.
As is understood from the block diagram in
FIG. 9
, the switch
106
is turned off during focus jumping, and the compensating filter
107
is operated at an input zero. Therefore, the FE signal passing through the gain switching circuit
108
holds a low-pass component (surface deflection component) at the beginning of focus jumping. The adder
109
adds an acceleration/deceleration pulse signal generated in an acceleration/deceleration pulse generating part
113
to the low-pass component at the beginning of focus jumping, which has passed through the gain switching circuit
108
. The addition sign
Fujiune Kenji
Kishimoto Takashi
Kuze Yuuichi
Watanabe Katsuya
Yamamoto Takeharu
Edun Muhammad
Merchant & Gould P.C.
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