Dynamic information storage or retrieval – With servo positioning of transducer assembly over track... – Optical servo system
Reexamination Certificate
1998-12-22
2001-11-13
Psitos, Aristotelis M. (Department: 2651)
Dynamic information storage or retrieval
With servo positioning of transducer assembly over track...
Optical servo system
C369S044290
Reexamination Certificate
active
06317395
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to an optical disc device for reproducing signals recorded on an optical disc by using a light source such as a laser, and more particularly relates to varying the characteristics of reproduced signal reproduction, focus control and tracking control systems according to the reproduction speed and relates to the detection of an operation out of the focus control in an optical disc device which supports more than one kind of disc and reproduction speed.
BACKGROUND OF THE INVENTION
In recent years, optical reproducing devices for reproducing signals such as video information and data for computers stored on recording media were required to read the data at faster speed. Further, the devices are required to have a plurality of reproduction speeds for music playback and other features.
Hereinbelow, conventional optical recording and reproducing devices will be explained.
FIG. 7
shows a block diagram of a conventional optical reproduction device [such as disclosed in U.S. Pat. No. 6,028,826. ] A light beam emitted from a light source
101
such as a semiconductor laser is formed into a collimated light beam through a collimator lens
102
. Thereafter, the collimated light beam is reflected through a polarizing beam splitter
103
, passes through a quarter-wavelength plate
104
and is focused through a convergent lens
105
on a disc
107
rotated by a motor
111
. The light beam reflected from the disc
107
passes through the convergent lens
105
, quarter-wavelength plate
104
, polarizing beam splitter
103
, condensing lens
108
and then is irradiated on a light detector
109
. The convergent lens
105
is mounted on a movable portion of an actuator
106
. The convergent lens
105
is adapted to shift perpendicularly to the disc surface by the flow of current through the focusing coil of the actuator
106
and to shift in the radial direction of the disc by the flow of current through the tracking coil of the actuator
106
. In a head unit
110
, there are mounted the convergent lens
105
, actuator
106
, quarter-wavelength plate
104
, polarizing beam splitter
103
, collimator lens
102
, light source
101
, condensing lens
108
and light detector
109
.
The output of the light detector
109
passes through amplifiers
114
a
-
114
d
and then is input to a focus error circuit
115
. The focus error circuit
115
processes the output signals from the amplifiers
114
a
-
114
d
and outputs a focus error signal corresponding to the vertical displacement of the focal point of the light beam from the information-recording surface of the disc. The focus error signal is applied to the focusing coil of the actuator
106
via a variable amplifier
116
, a phase compensator
117
for phase compensation, a switch
118
for the on-off control of focus control by the controller
150
and a driving circuit
119
for the amplification of power. Thereby, a control is performed such that the focal point of the light beam may be positioned on the information-recording surface.
Also, the output signal of the light detector
109
inputs to a tracking error circuit
120
through amplifiers
114
a
-
114
d.
The tracking error circuit
120
outputs a tracking error signal corresponding to the positional displacement of the focal point of the light beam from a track. The tracking error signal is applied to the tracking coil of the actuator
106
through a variable amplifier
121
, a phase compensator
122
for phase compensation, a switch
123
for the on-off control of the tracking control by the controller
150
, and a driving circuit
124
for the amplification of power. Thereby, the convergent lens
105
is controlled such that the focal point of the light beam may be positioned on the track.
Further, the output signal of the light detector
109
is input via an adder
126
to an equalizer circuit
130
, which functions as an amplifier and a frequency band limiter in identified frequency bands. The equalizer circuit
130
reproduces a RF (Radio Frequency) signal. The reproduced RF signals are input to a PLL (Phase Locked Loop) circuit
131
, which produces a clock used as a reference in the reproduction process for signals. The PLL circuit
131
provides a reference clock synchronized with the RF signals.
FIG. 2
shows a block diagram of the PLL circuit
131
.
A binarization circuit
301
binarizes the RF signal input to the PLL circuit
131
and outputs an RF binary signal DT. Also, a phase comparator
302
compares the phase of the RF binary signal with that of a lead clock and outputs a signal corresponding to the phase difference obtained. The output signal is amplified by an amplifier
303
and corrected for phase by a phase corrector
304
and input to a variable oscillator
305
. The variable oscillator
305
makes its oscillation frequency vary according to an input signal and outputs an oscillation signal. The oscillation signal is input to a frequency divider
306
. The frequency divider
306
divides the frequency of the oscillation signal according to a specified divide ratio and outputs the divided signal as a lead clock CK.
Further, the output signal of the light detector
109
is applied to a reflected-light-quantity detector
127
, which outputs a signal responsive to the light quantity of the reflected light incident on the light detector
109
.
A driving circuit
112
is intended to drive a disc motor
111
based on the output of the controller
150
. The controller
150
controls the number of rotations of the disc motor
111
to be a predetermined number.
For example, in a device configured for reproducing compact discs (CD) at multiple reproduction speeds such as a standard, two-times, and six-times speeds, the settings of the focus control, tracking control, optimum gain of the PLL circuit, phase compensation characteristic and divide ratio are different at each reproduction speed, respectively.
For the reasons described above, conventional devices have performed the signal processing as follows.
When a reproduction speed is changed, the controller
150
sends to the driving circuit
112
a command for setting the number of rotations of the motor
111
to be a predetermined number. Also, the controller
150
provides signals to the variable amplifiers
116
and
121
, PLL circuit
131
and equalizer circuit
130
for setting them to the characteristics (i.e. frequency or filter) corresponding to the reproduction speed.
Further, when the focus control is lost due to surface flaws on the disc and vibrations of the device, the abnormal driving sometimes damages the actuator
106
. For this problem, conventional systems have used exclusively the reflected-light quantity detector
127
for detecting an improper operation out of focus control and switched off the focus control.
The conventional devices described above have the following problems. At first, in the reproduction method using CAV in which the motor rotates at a constant rate at all times, the (frequency) characteristic of the signal processing system is not varied depending on a position in the radial direction of the disc. Since the reproduction speed is different depending on the radial position during CAV reproduction, the optimum characteristic of the signal processing system also becomes different on the radial position. Therefore, there has been a problem that the quality of reproduced signals is sometimes too wrong to make reproducing operation impossible in some radial position.
Secondly, in the CAV reproduction method in which the number of rotations of the motor
111
is controlled depending on the reproduction position of the disc so as to maintain the reproduction speed constant, the frequency characteristic of the signal processing system is not varied during reproducing. When the heat unit
110
is quickly sent from an inner circumference to an outer circumference or vice versa to restart reproduction, the rotational change of the motor
111
sometimes cannot follow such a quick change. As a result, the reproduction is performed at a di
Kishimoto Takashi
Moriya Mitsurou
Watanabe Katsuya
Yamamoto Takeharu
Matsushita Electric - Industrial Co., Ltd.
Parkhurst & Wendel L.L.P.
Psitos Aristotelis M.
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