Optical disk reproducing device

Details Optical disk reproducing device Optical disk reproducing device

2000-03-14

2002-12-03

Hindi, Nabil (Department: 2753)

Dynamic information storage or retrieval

With servo positioning of transducer assembly over track...

Optical servo system

C369S044290, C369S053280

Reexamination Certificate

active

06490234

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an optical disk reproducing device, and, more specifically, relates to an improvement in a focusing servo mechanism for an optical disk reproducing device which eliminates a disturbance injection, permits a focusing (an automatic focus control) with a further simple circuit, and increases an S/N ratio as well as unnecessitates a readjustment even when such as an external pick up unit is exchanged.
2. Conventional Art
Recently, with regard to CD-ROM devices, the data read out speed thereof is rapidly increasing, for example, from a double speed to 32 times speed or more than that speed, for this reason, it is required to read data in a speed range from double speed to 32 times speed or more that speed. Further, also with regard to optical disk memory devices, the memory density thereof is rapidly increasing, for example, to double, four times, six times, eight times and so on.
For these sorts of the optical disk reproducing devices, a focusing servo mechanism with a very high accuracy is required.
FIG. 5
is a diagram for explaining such a focusing servo mechanism.
In
FIG. 5
, numeral
1
is a focusing servo mechanism, numeral
2
is an optical disk therefor, numeral
3
is a rotation mechanism therefor, and numeral
4
is an optical system therefor which is constituted by a laser unit
41
for irradiating laser beams onto the optical disk
2
and a half mirror
42
. Numeral
5
is a focusing servo circuit which is constituted by a photo detector (pick-up)
51
, a focus position error generation circuit
52
, a level detection circuit
53
, a response wave form generation circuit
54
, an amplitude detection circuit
55
, a focus automatic adjustment controller
56
, a focus servo controller
57
, an offset amount adjustment circuit
58
, a signal level synthesis circuit
59
performing a subtraction synthesis of the signal levels, a disturbance oscillator
60
, another signal level synthesis circuit
61
performing an addition synthesis of the signal levels, a phase compensation loop filter (a so called low pass filter of CR)
62
, a search wave form generation circuit
63
, a change over circuit
64
, a drive amplifier
65
and a focus position adjustment mechanism
66
.
Herein, the tetra-section photo detector
51
uniformly divides the sensor area into four sections and generates respective detection signals of the corresponding sectioned areas. The tetra-section photo detector
51
receives reflection beams from the half mirror
42
of the optical beams from the optical disk
2
, converts the received optical beam amount irradiated on the respective areas into electrical signals, generates sum signals of opposing sensor areas in different directions as detection signals A and B and sends out the detection signals A and B to the focus position error generation circuit
52
.
The focus position error generation circuit
52
generates a sum signal of the detection signals A and B as a detection signal RF with regard to the total received optical beam amount (which is a detection signal representing an optical beam amount of the reflection optical beams from the optical disk received by the photo detector, and is a signal corresponding to a reflection level of the reflection optical beams from the optical disk, and which is hereinbelow called as a RF detection signal RF), as well as generates a difference signal of the detection signals A and B as a position error signal FE (FE is an abbreviation of Focus Error). Among these signals, the position error detection signal FE is applied to the phase compensation loop filter
62
via the signal level synthesis circuits
59
and
61
. Then, low pass components in the signal are extracted in the phase compensation loop filter
62
and are applied to the drive amplifier
65
under a condition of an automatic focus control (hereinbelow, called as a just focus control), and the drive amplifier
65
applies an output in a direction correcting the focus error depending on the level of the low pass components to the focus position adjustment mechanism
66
to drive the laser unit
41
so that the level of the position error detection signal FE is reduced and the focusing position is automatically adjusted to a focused position.
Further, the just focus control is effected in a direction so as to eliminate the position error depending on the level of the position error detection signal FE.
On the other hand, the RF detection signal RF is applied to the level detection circuit
53
to detect whether the RF detection signal RF falls within a range of the just focus control depending on the level thereof. When the RF detection signal RF reaches the level of the just focus control, the level detection circuit
53
detects the same and the detection signal thereof is inputted to the focus servo controller
57
. When the focus servo controller
57
receives the detection signal from the level detection circuit
53
, the focus servo controller
57
changes over the change over circuit
64
to the side of the phase compensation loop filter
62
and sends out the same to the drive amplifier
65
. Thereby, the just focus control is effected.
Further, the change over circuit
64
, for the first time, is set to the side of the search wave form generation circuit
63
which is designed to generate a ramp voltage for searching a just focus point by the focus servo controller
57
(the search wave form generation circuit is a so called ramp voltage generation circuit which generates signals which cause to advance or back the focusing position continuously with respect to the disk in order to search the focusing position), and in response to the rotation drive of the optical disk
2
the search wave form generation circuit
63
is activated by the focus servo controller
57
and outputs the ramp voltage to drive the drive amplifier
65
. Thereby, the drive amplifier
65
drives the focus position adjustment mechanism
66
, and the focus position adjustment mechanism
66
moves a focusing lens incorporated in the laser unit
41
depending on the ramp voltage so that the focusing position of the laser beams irradiated from the laser unit
41
onto the optical disk is raised from the lowest point. Thus, the level of the RF detection signal RF increases and in response to the detection signal of the level detection circuit
53
which detects the level thereof the control moves into a condition which permits the just focus control, and at this moment the above referred to change over of the change over circuit
64
is performed by the focus servo controller
57
.
Further, the pick-up unit includes the tetrasection photo detector
51
, the laser unit
45
having a laser beam source and a lens disposed in an optical passage of the laser beam source and the focus position adjustment mechanism
66
which moves the lens back and forth directions, and through movement by the focus position adjustment mechanism
66
of the focusing lens which is provided in the laser unit
41
and is disposed movably along the optical axis of the laser beams from the laser beam source, the focusing position of the laser beams which are outputted from the laser beam source onto the irradiation face of the optical disk
2
can be moved in back and forth directions. Further, herein either with the drive amplifier
65
or with the focus position adjustment mechanism
66
a so called negative feed back control is formed which receives the synthesized signal from the signal level synthesis circuit
61
via the phase compensation loop filter
62
and generates an output which drives the focusing lens in the direction for reducing the position error detecting signal FE.
Accordingly, at the moment when the change over circuit
64
is changed over to the side of the phase compensation loop filter
62
, the focusing servo mechanism
1
moves into the just focus control. At this instance, the focus automatic adjustment controller
56
which has received a signal from the focus servo controller
57
activates t

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