Dynamic information storage or retrieval – With servo positioning of transducer assembly over track... – Optical servo system
Reexamination Certificate
2000-04-28
2003-08-05
Young, W. R. (Department: 2655)
Dynamic information storage or retrieval
With servo positioning of transducer assembly over track...
Optical servo system
C369S053280
Reexamination Certificate
active
06603717
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 optical disk reproducing device which permits to restore in a short time from an out of focus servo to a focus servo condition.
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.
A focus servo device in a CD reproducing device receives reflection beams from a CD by a tetra-section photo detector (pick-up) in a pick-up unit and generates, through a focus position error generation circuit, RF detection signals representing detection signals of total optical beam amount received at the respective optical beam receiving areas (which are detection signals representing an optical beam amount received by the photo detector of the reflection beams from the optical disk, in other words, signals representing reflection level of the reflection beams from the optical disk, and hereinbelow are called as RF detection signals) and a position error detection signal FE (FE is an abbreviation of Focus Error) representing a detection signal determined by a mutual difference of the respective sums of detection signals of the opposing optical beam receiving areas.
Then, through level detection of the position error detection signal FE or the RF detection signals it is detected whether the operation enters into a just focus control range. When the position error detection signal FE or the RF detection signal reaches a just focus control level, in case of an analogue control, a focus servo loop is formed which includes a pick-up unit, an amplifier (or a gain adjusting use amplifier) in the focus position error generation circuit, a servo filter and a focus position adjusting mechanism (lens moving mechanism) in the pick-up unit, and the loop is automatically controlled so that the position error detection signal FE is rendered to be zero, thereby, a focusing of the laser beams outputted from the pick-up unit is performed so that the irradiation surface of the optical disk assumes a focusing position of the laser beams. Such focusing is performed, for example, by moving a lens disposed in an optical path for laser beams in the focus position adjusting mechanism into a focusing position.
Like operation is performed in case of a digital control, in that in the digital control processings corresponding to the functions of the respective circuits as has been explained above in connection with the analogue control are realized by executing predetermined corresponding programs through a MPU. Therein, a signal value which renders the position error detection signal FE to zero is calculated, the calculated error correction value is converted into an analogue value via a D/A converter and sends out the analogue signal, which is converted so as to focus the laser beams onto the irradiation surface of the optical disk, to the focus position adjusting mechanism as a driving signal.
FIG. 3
is a block diagram for explaining such sort of a conventional focus servo device.
In
FIG. 3
, numeral
1
is a focus servo device, numeral
2
is an optical disk therefor (illustration of which rotation mechanism is omitted), numeral
3
is a pick-up unit which includes a tetra-section photo detector (pick-up), a laser beam source, a lens disposed in an optical path of the laser beams and a focus position adjusting mechanism for moving the lens in back and forth direction, and through the movement of the lens a focusing position of the laser beams outputted from the laser beam source is moved in back and forth direction with respect to the optical disk
2
.
Numeral
4
is a driver, when a drive signal is received, the driver
4
moves the lens in the focus position adjusting mechanism in back and forth direction.
Numeral
5
is an RF amplifier which includes inside thereof a focus position error generation circuit, receives a detection signal from the tetra-section photo detector (pick-up) in the pick-up unit
3
and outputs the RF detection signal and the position error detection signal FE.
Numeral
6
is a just focus detection circuit which receives clocks CLK from a clock circuit
11
and the position error detection signal FE with respect to a focus point, detects in synchronism with the clocks CLK the zero crossing point of the position error detection signal FE as well as detects whether the level of the position error detection signal FE is in a predetermined range (which corresponds to a focus position covered by the automatic focus control loop) with reference to the zero crossing point to detect a just focus position and sends out a detection signal Dj to a focus controller
7
. The just focus detection circuit
6
continuously generates the detection signal Dj so long as the level of the position error detection signal FE at this moment is kept at the above predetermined range.
The focus controller
7
receives the clocks CLK from the clock generation circuit
11
and the just focus position detection signal Dj, generates in synchronism with the clocks CLK a control signal LOOPON representing a servo loop on signal and outputs the same to a change-over circuit
9
to change over to the side A of servo control (the condition as illustrated). Thereby, the focus servo device
1
enters into an automatic focus control loop (just focus control). Further, the focus controller
7
continuously generates the control signal LOOPON during when the just focus position detection signal Dj is received and when no just focus position detection signal Dj is received, the generation of the control signal LOOPON is stopped. When no control signal LOOPON is generated, the change-over circuit
9
is changed over to the side B of focus search. Further, at this instance, the focus controller
7
sends out a control signal SS to a search signal generation circuit
8
to operate the same.
A servo filter circuit
10
receives the position error detection signal FE from the RF amplifier
5
, performs a servo filter processing (which is a processing performed through a phase compensation filter, usually a loop filter is used therefor) for correcting a position error with respect to focusing, sends out the output to the change-over circuit
9
and outputs the same via the side A of servo control to the driver
4
. As a result, a servo loop for the automatic focus control is formed with the pick-up unit
3
, and the laser beams are focused onto the irradiation face of the optical disk
2
.
Numeral
8
is the search signal generation circuit which is constituted by an up and down counter
81
and a D/A converter
82
and is operated by the control signal SS from the focus controller
7
, wherein the up and down counter
81
counts the clocks CLK from the clock generation circuit
11
and the D/A converter
82
converts the count value into an analogue value to generate a ramp voltage. The generated ramp voltage is applied to the change-over circuit
9
and then applied to the driver
4
via the side B of focus search. Thereby, the focus position of the laser beams irradiated from the pick-up unit
3
onto the face of the optical disk
2
is continuously moved in backward or forward.
As an overall operation of the device, at first the change over circuit
9
is set to the side B of focus search by the focus controller
7
, and the focus controller
7
activates with the control signal SS the search signal generation circuit
8
which generates the ramp voltage and drives the driver
4
. Thereby, the driver
4
drives the focus position
Kawada Yuichi
Oyabu Hiroshi
Mattingly Stanger & Malur, P.C.
Rohm & Co., Ltd.
Young W. R.
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