Dynamic information storage or retrieval – Condition indicating – monitoring – or testing – Including radiation storage or retrieval
Reexamination Certificate
2001-01-12
2004-03-02
Huber, Paul W. (Department: 2653)
Dynamic information storage or retrieval
Condition indicating, monitoring, or testing
Including radiation storage or retrieval
C369S044360
Reexamination Certificate
active
06700844
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a method and apparatus for measuring the eccentricity of a rotating optical disk.
2. Description of the Related Art
Owing to errors in disk manufacturing process or imperfect clamping operation, most rotating optical disks inherently show eccentric rotation to some extent. The eccentricity impairs focusing and tracking control and may make normal data read-out impossible in the worst case.
FIG. 1
depicts a block diagram of a conventional optical disk drive with eccentricity compensation capability, comprising an optical pickup
20
for reproducing recorded signals from an optical disk
10
, an R/F unit
30
for equalizing and shaping the RF signals reproduced from the optical disk
10
by the pickup
20
, a sled motor
21
for moving the optical pickup
20
along the full length of the disk radius, a spindle motor
11
for rotating the optical disk
10
, a drive unit
50
for driving the sled motor
21
and the spindle motor
11
, a servo unit
40
for controlling the optical pickup
20
and the drive unit
50
using the rotation speed of the optical disk
10
and focus and tracking error signals outputted from the optical pickup
20
, a digital signal processing unit
60
for retrieving original digital data from the binary data stream outputted by the RF unit
30
and for creating track crossing pulse signal (Cout) based on the tracking error signal, a microcomputer
70
for counting the track crossing pulse signal and for adjusting the rotation speed of the optical disk
10
based on the counting result.
When the optical disk
10
is inserted into a disk tray, which is a part of the optical disk drive mechanism, the optical disk
10
is clamped by a clamping device. Then, the microcomputer
50
commands the servo unit
40
to spin the optical disk
10
at a constant angular velocity. Controlled by the servo unit
40
, the drive unit
50
provides electric current to rotate the spindle motor
11
and maintains the rotation velocity of the optical disk
10
constant.
The microcomputer
70
activates focusing control and then measures the eccentricity of the rotating optical disk
10
. To this end, the digital signal processing unit
60
creates track crossing pulse signal (Cout) using the tracking error signal received from the optical pickup
20
. The track crossing pulse signal (Cout) shows state transitions when the optical spot enters and exits the mirror area of the optical disk
10
, as shown in FIG.
2
.
The microcomputer
70
counts the track crossing pulse signal (Cout) during a predefined time interval and calculates the disk eccentricity using the counted number and disk rotation speed. Based on the obtained eccentricity, the microcomputer
70
performs predefined compensation processes such as servo gain setting.
In the conventional method mentioned above, however, the counted number of the track crossing pulse signal (Cout) may change depending upon the displacement of the objective lens with respect to the optical axis. That is, the calculated disk eccentricity might be incorrect around ‘Z’ portion of the tracking error signal of
FIG. 2
, which means that the misalignment between the center of the objective lens and the optical axis is much increased because of the disk vibration.
SUMMARY OF THE INVENTION
It is therefore an object of the present invention to provide a method and apparatus for precisely measuring the eccentricity of a rotating optical disk so that appropriate compensation can be performed according to the measured eccentricity.
The apparatus for measuring the eccentricity of an optical disk in accordance with the present invention comprises drive means for rotating the optical disk, reproducing means for reproducing recorded signals from the optical disk, servo means for performing focusing and tracking servo for the optical disk rotated by the drive means, and control means for detecting the amplitude of tracking error signal and for measuring the eccentricity of the optical disk based on the measured amplitude, the measurement being performed while the servo means is activated.
The method for measuring the eccentricity of an optical disk in accordance with the present invention comprises the steps of activating tracking servo while the optical disk is rotating, detecting the center value of tracking error signal and setting the center value as a reference value, and detecting the eccentricity of the optical disk by comparing the center value and the tracking error signal received right after the reference value is set.
REFERENCES:
patent: 5014256 (1991-05-01), Horie et al.
patent: 6147944 (2000-11-01), Kwon et al.
patent: 6606286 (2003-08-01), Maekawa
Huber Paul W.
LG Electronics Inc.
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