Dynamic information storage or retrieval – Condition indicating – monitoring – or testing – Including radiation storage or retrieval
Reexamination Certificate
1998-10-29
2001-05-01
Huber, Paul W. (Department: 2651)
Dynamic information storage or retrieval
Condition indicating, monitoring, or testing
Including radiation storage or retrieval
C369S044320
Reexamination Certificate
active
06226246
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to an apparatus and a method for measuring characteristics of an optical pickup and/or an optical disc.
DESCRIPTION OF THE RELATED ART
There has so far been known a device for inspecting characteristics of an optical pickup used in an optical disc drive. The device for inspecting characteristics of an optical pickup is used for example in inspection for shipment or reception of an optical pickup in connection with whether or not the optical pickup satisfies the prescribed specifications.
FIG. 1
shows a block diagram of a conventional device
100
for inspecting characteristics of an optical pickup.
The conventional device
100
for inspecting characteristics of an optical pickup shown in
FIG. 1
is designed to inspect an optical pickup.
The conventional device
100
for inspecting characteristics of an optical pickup includes a test bench
102
on which the optical disc is set, a matrix circuit
103
supplied with an output of a photodetector of the optical pickup
101
for outputting a playback signal (RF signal) and a servo control circuit
104
for performing servo control for reproducing an optical disc based on an output of the matrix circuit
103
.
The conventional device
100
for inspecting characteristics of an optical pickup also includes n measurement circuits
105
a
to
105
n
for measuring various characteristic values of the optical pickup based on an output of the matrix circuit
103
, a multiplexer
106
for switching between outputs of the measurement circuits
105
a
to
105
n
and a multiplexer
106
for switching between outputs of the measurement circuits
105
a
to
105
n
. The conventional device
100
for inspecting characteristics of an optical pickup further includes an analog-to-digital converter
107
for converting an output of one of the circuits
105
a
to
105
n
selected by the multiplexer
106
into digital data and a computer
108
for statistically processing output data of the analog-to-digital converter
107
for displaying the results.
The optical pickup
101
is a subject of inspection by this device
100
for inspecting characteristics of an optical pickup. The optical pickup
101
is detachably mounted on this device
100
for inspecting characteristics of an optical pickup. The optical pickup
101
includes a laser diode, a beam splitter, an objective lens and a photodetector. This optical pickup
101
condenses a laser light beam outgoing from a laser diode via beam splitter and an objective lens on the optical disc. The optical pickup also forms an image of the reflected light from the optical disc on the photodetector. The photodetector provided on the optical pickup
101
is a photoelectric converting device and converts the imaged reflected light into electrical signals.
The optical pickup
101
usually includes plural photodetectors. For example, the optical pickup
101
includes a four-segment photodetectors and a pair of photodetectors arranged on both sides of the four-segment photodetectors for side spot detection. Outputs of these photodetectors are routed to the matrix circuit
103
.
The test bench
102
, on which is set the optical disc, runs this optical disc in rotation for reproducing the disc. The optical disc set on the test bench
102
is used as reference for this device
100
for inspecting characteristics of the optical pickup.
The matrix circuit
103
is fed with outputs of the photodetectors of the optical pickup
101
to generate playback (RF) signals, focusing error (FE) signals and tracking error (TE) signals from the photodetector outputs.
If the photodetector provided on the optical pickup
101
is made up of four-segment photodetectors and both side photodetectors for detecting side spots, the matrix circuit
103
outputs the following signals: That is, the matrix circuit
103
finds the sum of the respective outputs of the four-segment detectors to output the result as RF signal. The matrix circuit
103
also outputs FE signal by the astigmatic method. Specifically, the matrix circuit
103
computes the sums of the two photodetectors lying across the four-segment detectors to find the difference between the sums to output the resulting difference as the FE signal. The matrix circuit
103
also computes the difference between the side spot detecting photodetectors to output the resulting difference as TE signal.
The matrix circuit
103
routes the RF, FE and TE signals, thus computed, to the servo control circuit
104
and the measurement circuits
105
a
to
105
n.
The servo control circuit
104
performs servo control during reproduction of the optical disc based on the RF, FE and TE signals. Specifically, the servo control circuit
104
performs focusing servo control, tracking servo control, thread servo control and tilt servo control.
The measurement circuits
105
a
to
105
n
calculate characteristic values of the optical pickup
101
. The measurement circuits
105
a
to
105
n
measure respective different characteristic values. Therefore, the number of the measurement circuits
105
a
to
105
n
corresponds to that of the characteristic values to be measured.
The measurement circuits
105
a
to
105
n
perform filtering, peak detection or frequency/voltage conversion by analog processing in order to compute the characteristic values. The first measurement circuit
105
a
measures the signal level of an S-shaped curve at the time of capturing a focusing servo loop based on, for example, the FE signals. The second measurement circuit
105
b
measures the level of the TE signals based on the TE signals. The third measurement circuit
105
c
measures the level of the RF signal based on the RF signal. The fourth measurement circuit
105
d
measures jitter components of the RF signal based on the RF signal.
The multiplexer
106
switches between outputs of the measurement circuits
105
a
to
105
n
to route an output of the selected measurement circuit to the analog-to-digital converter
107
.
The analog-to-digital converter
107
converts outputs of the measurement circuits
105
a
to
105
n
supplied via multiplexer
106
into digital data which is routed to the computer
108
. The rate of conversion of the analog-to-digital converter
107
is low because the outputs of the measurement circuits
105
a
to
105
n
are substantially at the dc level. For example, the rate of conversion of the analog-to-digital converter
107
is on the order of 1 KHz.
The computer
108
performs statistic processing of digital data supplied from the analog-to-digital converter
107
to display the results.
In the conventional device
100
for inspecting characteristics of an optical pickup, as described above, the characteristic values of the optical pickup
101
are measured by, for example, n measurement circuits
105
a
to
105
n
, with the number n corresponding to the number of the characteristic values to be measured. The measured results are displayed for the user on the computer
108
.
The method for measuring the level of the TE signal by this conventional device
100
for inspecting characteristics of the optical pickup is explained in detail.
This device
100
for inspecting characteristics of the optical pickup measures the level of the TE signal using eccentricity of rotation of the optical disc.
Such eccentricity of rotation of the optical disc occurs when the center of the optical disc set on the test bench
102
for rotational driving is offset from the axis of rotation.
For example, if eccentricity of rotation is caused in optical disc rotation, the optical disc is set on the test bench
102
so that the center O of the optical disc D differs from the axis of rotation of the optical disc D, as shown in FIG.
2
.
Therefore, the separation x between a position of irradiation Lx on the optical disc D of the laser light beam L radiated from the optical pickup and the center O of the optical disc D is varied with the rotational position of the optical disc D.
Specifically, if the center O of the optical disc D is furthest from the point of illumination Lx o
Hashimoto Yukari
Kato Hideo
Kohama Shunsuke
Nakayama Akihito
Shintani Kenji
Frommer William S.
Frommer Lawrence & Haug LLP.
Huber Paul W.
Sony Precision Engineering Center (Singapore) Pte Ltd.
LandOfFree
Apparatus and method for measuring characteristics of... does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Apparatus and method for measuring characteristics of..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Apparatus and method for measuring characteristics of... will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2545821