Dynamic information storage or retrieval – Condition indicating – monitoring – or testing – Including radiation storage or retrieval
Reexamination Certificate
2000-07-26
2002-09-17
Hindl, Nabil (Department: 2653)
Dynamic information storage or retrieval
Condition indicating, monitoring, or testing
Including radiation storage or retrieval
C369S047440
Reexamination Certificate
active
06452882
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The invention relates to an apparatus and a method of determining a rotational frequency of an optical disc for enhancement in a transfer rate.
2. Description of the Related Art
In recent CD-ROM drivers and video disc drivers, there is a need for increasing a rotational frequency of an optical disc up to a rotational frequency in the range of 4,000 rpm to 5,000 rpm. The present standard rotational frequency for CD-ROM driver is about 500 rpm. Hence, if a rotational frequency of an optical disc is gradually increased, an oscillation of a track becomes greater, and accordingly, it is quite difficult or almost impossible to stably draw a track in. In particular, an optical disc having a greater eccentricity tends to oscillate more remarkably.
It is prescribed that an allowable eccentricity of an optical disc is equal to or smaller than 140 &mgr;m. Since a track pitch in an optical disc is about 1.6 &mgr;m, it would be necessary to prepare a device for moving an optical beam spot, which is able to cover an area at least 87.5 times greater than a track pitch (140/1.6=87.5). In addition, when an optical disc is secured to a drive shaft under a certain fitting tolerance, since the drive shaft also has an eccentricity, a total eccentricity would be increased. Accordingly, a servo system for drawing a track therein would be heavily burdened.
The assignee has already suggested a tracking controller in Japanese Unexamined Patent Publication No. 8-96379. This tracking controller satisfies a transfer rate of 140 Mbps which is required for digitally recording incompressive PAL video signals.
FIG. 1
illustrates the suggested tracking controller.
An optical head
202
emits a laser beam to an optical disc
201
through a focusing lens
221
, and receives a laser beam reflected from the optical disc
201
through the focusing lens
221
. The thus received laser beam is introduced to and detected by an optical sensor
222
. The optical sensor
222
has a light-receiving plane which is divided into two portions in a track-wise direction of the optical disc
201
. The focusing lens
221
is movably supported with an actuator
223
.
A subtracting section
203
receives two output signals from the optical sensor
202
, and emits a subtraction signal S
201
indicative of a difference between the two output signals. An adding section
204
also receives two output signals from the optical sensor
202
, and emits an addition signal S
205
indicative of a sum of the two output signals.
AGC
205
level-controls the subtraction signal S
201
in dependence on the addition signal S
205
to thereby absorb a fluctuation in reflectivity of the optical disc
201
for keeping a loop gain constant. An error amplifier
206
compares an output from AGC
205
with a standard input to thereby generate a tracking error signal. A phase compensator
207
gives a suitable frequency-phase characteristic to the tracking error signal. A loop switch
208
operates in response to a tracking start signal S
210
emitted from a D-type flip-flop
213
. A drive amplifier
209
drives the actuator
223
in accordance with the tracking error signal to thereby cause the laser beam to follow a track.
A relative speed detector
210
is comprised of a binary circuit
101
, an edge detecting circuit
102
and a retriggerable monostable multivibrator
103
. The relative speed detector
210
monitors a relative speed of the laser beam between a speed in a track-wise direction and a speed in a radius-wise direction of the optical disc. When the relative speed is below a predetermined speed, the relative speed detector
210
emits a speed detecting pulse S
204
. In other words, the relative speed detector
210
detects a time when the laser beam reaches an intermediate center between a track and a groove of the optical disc
201
, and emits the speed detecting pulse S
204
when an interval between the detection is longer than a predetermined value. The speed detecting pulse S
204
has a predetermined pulse width.
A track detector
211
is comprised of an AC component extracting circuit
111
, a binary circuit
112
and a retriggerable monostable multivibrator
113
. The track detector
211
monitors a time when the laser beam reaches an edge of a track, based on the addition signal S
205
, and emits a track detecting pulse S
208
having a predetermined pulse width.
The thus generated speed detecting pulse S
204
and track detecting pulse S
208
are input to an AND circuit
212
, which emits a signal S
209
indicative of a logical product of the pulses S
204
and S
208
.
The D-type flip-flop
213
receives the signal S
209
at a clock input terminal, and also receives a tracking indicating signal S
211
at D input terminal, to thereby emit the above-mentioned track start signal S
210
. Specifically, the D-type flip-flop
213
emits the track start signal S
210
just on receipt of the signal S
209
when the tracking indicating signal S
211
is in H-level, to thereby turn the loop switch
208
on for starting drawing a track in.
The above-mentioned tracking controller illustrated in
FIG. 1
can stably draw a track therein under conditions that a rotational frequency of an optical disc is 4500 rpm, an eccentricity of an optical disc is 90 &mgr;m, and a track pitch is 1.2 &mgr;m.
As mentioned earlier, the tracking controller illustrated in
FIG. 1
can deal only with an optical disc having an eccentricity of 90 &mgr;m or smaller. However, some optical discs have an eccentricity of 100 &mgr;m or greater. The tracking controller illustrated in
FIG. 1
would fail to draw a track therein in such optical discs.
Apart from the apparatus illustrated in
FIG. 1
, many attempts have been made in order to compensate for an eccentricity of an optical disc, as follows.
Japanese Unexamined Patent Publication No. 62-109273 has suggested an apparatus for compensating for an eccentricity of an optical disc, comprising an eccentricity detector for detecting an eccentricity of an optical disc in view of three signals: an output signal emitted from a pick-up position controller for controlling a pick-up to move in a radius-wise direction of a compact disc; an output signal emitted from a pick-up angle controller for controlling an inclination angle of the pick-up to thereby control a position at which the pick-up reads data out of the compact disc; and a signal indicative of a rotation angle of the compact angle, and a memory for storing an eccentricity of the compact disc detected by the eccentricity detector and reading out an eccentricity about a rotation angle.
Japanese Unexamined Patent Publication No. 62-121938 has suggested a servo system comprising an actuator to which feedback servo is applied in order to keep a position relative to a recording track of a rotary recording medium. The actuator is designed to have a transfer characteristic by which a peak value varies in accordance with an eccentric fundamental wave component of the rotary recording medium.
Japanese Unexamined Patent Publication No. 1-184643 has suggested an apparatus for detecting an eccentricity of an optical disc, comprising an optical head including a lens equipped with an actuator for following a track of an optical disc, a first circuit for emitting a first signal indicative of a gap between the track and the lens, a second circuit for emitting a second signal indicative of a rotational period of the optical disc divided by N wherein N is a positive integer, a third circuit for driving the actuator by a lens drive signal having the same period as that of the second signal, and a fourth circuit for calculating an eccentricity of the track in each half of a period of the lens drive signal by means of the first and second signals.
Japanese Unexamined Patent Publication No. 1-256045 has suggested an apparatus for checking an optical disc, comprising first means for detecting an eccentricity of an optical disc, and second means for switching a tracking servo loop of an actuator. The second means releases the tracking servo l
Hindl Nabil
McGinn & Gibb PLLC
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