Dynamic information storage or retrieval – With servo positioning of transducer assembly over track... – Optical servo system
Reexamination Certificate
1999-03-29
2001-05-15
Edun, Muhammad (Department: 2651)
Dynamic information storage or retrieval
With servo positioning of transducer assembly over track...
Optical servo system
C369S044250, C369S044290, C369S044350
Reexamination Certificate
active
06233207
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a polarity switching signal generator able to stably generate a suitable tracking error signal, a method of the same, and an optical disk drive.
2. Description of the Related Art
Digital versatile disk-random access memory (DVD-RAM) and other rewritable optical disks are now in use.
Such rewritable optical disks include ones which use for example a land groove system as a disk format. In this case, the recording surface of the optical disk is provided with data areas in which only guide grooves for recording and reproducing any information and address areas in which absolute positions on a disk are stored by pits.
The formats of the land-groove system can be roughly divided in a double spiral format and a single spiral format.
In the double spiral format, as shown in
FIG. 1
, a land track
50
and a groove track
51
are located next to each other. Further, in the single spiral format, as shown in
FIG. 2
, a land track
52
and a groove track
53
are located one after the other for every circuit to form one track as a whole.
Below, the tracking servo control of a recording and reproduction apparatus of the related art for recording and reproducing data to and from a DVD-RAM of the single spiral format will be explained.
FIG. 3
is a block diagram of an optical disk drive
1
of the related art for realizing the tracking servo control of a recording and reproduction apparatus of a DVD-RAM disk.
As shown in
FIG. 3
, in the optical disk drive
1
, a DVD-RAM disk
2
is driven to rotate by a spindle motor
15
. A laser beam from a laser
3
is fired through an object lens to a position on the recording surface of the DVD-RAM disk
2
under the control of a tracking coil
4
. The reflected laser beam is received by a photoreceptor
5
.
The photoreceptor
5
converts the reflected laser beam from the DVD-RAM disk
2
to a tracking error signal S
5
a
indicating the deviation of tracking and a sum signal S
5
b
indicating the amount of the light of the reflected laser beam and outputs these to A/D converters
6
and
7
respectively.
The tracking error signal S
5
a
and the sum signal S
5
b
are converted to a digital tracking error signal S
6
and a sum signal S
7
and output to a normalizer
8
.
The normalizer
8
normalizes the tracking error signal S
6
so that its level does not change and outputs the normalized tracking error signal S
8
to a polarity switch
9
.
On the other hand, the address S
5
c
read from the DVD-RAM disk
2
is output from the photoreceptor
5
to the last sector detector
13
. The last sector detector
13
detects a last sector signal S
13
indicating a sector just before the land and the groove are switched on the basis of address S
5
c.
Next, a one-sector delay unit
14
delays the last sector signal S
13
by exactly one sector's worth of time to produce a polarity switching signal S
14
and outputs the polarity switching signal S
14
to the polarity switch
9
.
Based on the polarity switching signal S
14
, the polarity switch
9
inverts the polarity of the tracking error signal S
8
in accordance with need to produce a tracking error signal S
9
of a controlled polarity. It outputs the tracking error signal S
9
to a phase compensation digital filter
10
.
It is necessary to control the polarity of the tracking error signal SB in this way because the polarity of the tracking error signal becomes inverted between when tracing a land and when tracing a groove.
The tracking error signal S
9
is phase-compensated and converted to an analog signal in the D/A converter
11
to produce a drive signal S
11
.
The drive signal S
11
is amplified by a drive amplifier, then output to the tracking coil
4
as a drive signal S
12
to drive the tracking coil
4
.
Summarizing the problems to be solved by the invention, in the optical disk drive
1
of the related art shown in
FIG. 3
, as describe below, the polarity switching signal S
14
is not suitably produced, so if suffers from the disadvantage that the tracking servo control becomes unstable.
Specifically, when the recording surface of the DVD-RAM disk
2
becomes dirty and the last sector cannot be detected, when starting to trace a track after a seek operation, when using a zoned constant linear velocity (CLV) format where the number of the address areas
60
present in one turn of the disk differs for each zone as shown in FIG.
4
and the rotating speed of a spindle motor
15
will not stabilize at the point of change of zones, etc. the polarity switching signal S
14
is not suitably produced.
Note that in a DVD-RAM of the CAV format, as shown in
FIG. 5
, the address areas
70
and the data areas
71
are arranged radially.
When the polarity switching signal S
14
is not suitably produced and the timing of the polarity switching becomes off, a suitable tracking error signal S
9
is not produced while the polarity is wrong and the tracking servo control becomes unstable state.
Further, during a seek operation, since an optical pick-up is moving over the tracks, the last sector cannot be detected and the polarity cannot be suitably controlled in the polarity switch
9
. Therefore, during a seek operation, the tracking error signal S
9
becomes discontinuous at the boundary between a land and a groove, so there is the disadvantage that a count error occurs in the traverse counter which counts the number of tracks being traversed.
SUMMARY OF THE INVENTION
An object of the present invention is to provide a polarity switching signal generator and method able to stably generate a suitable polarity switching signal for inverting the polarity of a tracking error signal and an optical disk drive able to realize stable tracking servo control.
According to a first aspect of the present invention, there is provided a polarity switching signal generator for generating a polarity switching signal for use in switching a polarity of a tracking error signal in accordance with a switching position between a land and groove during tracking servo control of an optical disk in which lands and grooves are alternately arranged in a radial direction, comprising a rotational angle generating means for generating a rotational angle of said optical disk on the basis of a rotation signal based on rotation of said optical disk input from a driving means for driving the rotation of said optical disk; a switching position detecting means for detecting a switching position between a land and groove on the basis of an address signal read from said optical disk; a rotational angle determining means for determining said rotational angle generated by said rotational angle generating means at a timing in accordance with the detection of the switching position between a land and groove; a reference value storing means for storing a reference value to be compared with said rotational angle generated by said rotational angle generating means; a reference value setting means for updating the reference value stored in said reference value storing means with the rotational angle determined by said rotational angle determining means when said address signal is correct; and a comparing means for generating a polarity switching signal instructing the inversion of the polarity of the tracking error signal when the rotational angle generated by said rotational angle generating means matches with the reference value stored in said reference value storing means.
Preferably, said reference value storing means holds the stored reference value when error has occurred in said address signal.
Preferably, said rotation signal comprises an FG signal.
Preferably, further provision is made of a phase synchronization circuit for receiving as input the rotation signal based on the rotation of said optical disk from said driving means and generating a new rotation signal improved in resolution from the input rotation signal and said rotational angle generating means generates a rotational angle of said optical disk on the basis of said new rotation signal input from sai
Edun Muhammad
Frommer William S.
Frommer & Lawrence & Haug LLP
Somy Corporation
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