JPH10143875A - Focusing servo controller - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a focusing servo controller capable of performing a stable servo without any possibility of erroneous extraction due to the reflection of the surface of a disk by using a relatively simple method. SOLUTION: This controller is provided with a reproduced high frequency signal detecting means consisting of an RF detector 12 for outputting s detection signal when a high frequency signal to be reproduced from a recording medium is a prescribed lever or above, an RF amplifier 13, an RF detector 14 and a comparator 15 for RF decision. A control circuit 8 starts a focusing servo when a lens position deciding means consisting of a photodetector 1, a differential amplifier 2, a voltage comparator 7 for judging the extracting area outputs a servo enable signal and also the reproduced high frequency signal detecting means is outputting the detection signal.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to an improvement of a focus servo control device in an information reproducing apparatus for reproducing information recorded on an optical recording medium such as a CD, an optical disk, a magneto-optical disk, and an optical memory card.

[0002]

2. Description of the Related Art An optical information reproducing apparatus performs a focus search operation to bring a recording position into a focused state prior to information reproduction. During this focus search operation, the focal point is detected by relying on the focusing error signal. By the way, since the dynamic range of the focusing error signal is as small as several μm,
In order to ensure that the recording surface is within the depth of focus, the focus search must be performed by forcibly moving the objective lens. The objective lens is forcibly moved toward or away from the disk, or is moved away from the disk so as to obtain a focal point. FIG. 7 shows an example of the focus error signal in such a case. By detecting the zero-cross point (0) of this focusing error signal, the in-focus position is detected, and thereafter, focus servo is performed at this point.

[0003] In a focus search operation which is normally performed at present, an aluminum disk (C
D, LD, etc.), a method is adopted in which the objective lens is forcibly moved away from the disk and then brought closer to the disk. However, with other disks, there is a case where the disk is temporarily locked due to reflection on the disk surface before reaching the recording surface. Therefore, in order to avoid this, the focus is detected by bringing the disk closer and then moving away from it. . Therefore, a) The lock-in time (required for pulling in) of the focal point is almost three times as long as that of the aluminum disk. b) Once locked out, there is a possibility of pseudo lock, and this focus search time is required again.

FIG. 8 shows a focus search signal, a focusing sum signal, and a focusing error signal when a focus search operation is performed by a method of forcibly moving the disk away from the disk and approaching the disk. The focus search signal is a signal proportional to the amount of lens displacement. As can be seen from the waveform of this focus search signal, the focus search signal is once approached,
The in-focus position is detected while moving away, further closer, and farther away. Therefore, the lock-in time takes 700 ms or more.

[0005] The focusing error signal is a difference signal between detection signals of a two-segment photodetector by the knife edge method or the critical angle method and a detection signal of a four-segment photodetector by the astigmatism method. In the astigmatism method, a cylindrical lens is placed in the converging optical path of the return path of the reflected beam, intentionally generating large astigmatism, and before and after the minimum circle of confusion at the time of focusing (in this case, the beam shape becomes circular). The beam shape (in this case, the beam shape becomes elliptical) is detected to obtain a focusing error signal. That is, as shown in FIG. 9, when the quadrant photodetector is installed so that the light receiving surface is at the position of the least confusion circle in the focused state, the light amount distribution on the light receiving surface changes to an elliptical shape in the non-focused state. ,
When Ie = (I1 + I3)-(I2 + I4) is formed from the detection signals (I1 to I4) of the four-split photodetectors, this becomes a focusing error signal.

On the other hand, the focusing sum signal is Is = I1 +
I2 + I3 + I4, which is a value indicating the total light receiving level.

The focusing error signal is formed not only by the reflection from the disk recording surface but also by the reflection from the disk surface. FIG. 2 shows this state. Since the reflection from the disk recording surface has a larger amount of reflected light than the reflection from the disk surface, focus focusing should be performed in a place where the level of the focusing sum signal is higher than the threshold value and the level of the focusing error signal is lower than the threshold value. By doing so, a stable focus servo can be realized.

However, in many cases, the reflectance from the disk surface is relatively close to the reflectance from the recording surface. FIG. 10 shows the reflectance from the disk surface and the reflectance from the recording surface for each disk. As can be seen from this figure, with an aluminum disk having a sufficiently large level difference, there is no fear of pseudo-locking, so that the lock-in can be performed while approaching the disk. On the other hand, MO (Magneto-Optical; magneto-optical) disks, PC (Phase Change) disks, WO (Wr
ite Once; write-once) discs such as
There is not much level difference, and there is a risk of pseudo-locking when locking in while approaching the disk. for that reason,
Use a method of locking in once while approaching and separating.

The movable range of the objective lens is approximately ±
Since it is relatively large at 0.5 mm, which is much larger than the range in which the S-shaped output of the focusing error signal is output ± 0.05 mm, if the focus search speed is too fast, the S-shaped negative feedback region may jump out. . In this example, the cycle of the focus search signal was set to 500 ms as shown in FIG.

The focusing error signal is formed by the reflected light, and the threshold value of the focusing sum signal and the threshold value of the focusing error signal are given as absolute values by a control system. Therefore, even if the threshold value is properly selected, SN degradation or error may occur due to fluctuations in the value of the focusing error signal, such as fluctuations in the laser power, variations in the reflectance of the disk surface, variations in the reflectance of the recording surface, and contamination of the lens and disk. Before a rate increase or the like occurs, a level fluctuation occurs, which may cause erroneous detection.

[0011]

As described above, in the conventional focus servo control device, there is a danger of pulling in following the reflection on the disk surface, and the reflectance on the disk surface and the reflectance on the recording surface are different from each other. When the level difference was not so large, it was sometimes difficult to distinguish the absolute level alone. In order to avoid this, if a method is adopted in which the objective lens is once brought close to the disk and locked in while being separated, there is a problem that the focus search time is excessively long.

The present invention solves this problem and uses a relatively simple method that does not make significant changes to the conventional apparatus, and provides a stable method that does not have the possibility of accidentally pulling in the reflection on the disk surface. It is an object to realize a focus servo control device capable of performing servo.

[0013]

In order to achieve the above object, the present invention relates to a first predetermined position in which an objective lens is closer to a recording medium than a focus position and a first predetermined position which is closer to a recording medium than the focus position. A focus error signal generating means for generating a focus error signal whose output indicates a peak at a distant second predetermined position and an output of 0 at a focus position therebetween, and the focus error generated by the focus error signal generating means A lens position determination unit that determines from the signal that the objective lens is between the first predetermined position and the second predetermined position and outputs a servo enable signal; and the lens position determination unit outputs the servo enable signal. A focus servo control device having a focus servo start means for starting focus servo during output, wherein a high-frequency signal reproduced from the recording medium has a predetermined level or higher. A reproducing high-frequency signal detecting means for outputting a detection signal, the focus servo starting means, the lens position determining means outputting the servo enable signal, and the reproducing high-frequency signal detecting means outputting the detection signal. The focus servo is started during the operation.

[0014]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, a focus servo control device according to the present invention will be described in detail with reference to the accompanying drawings. FIG. 1 is a circuit block diagram of a pull-in function block according to an embodiment of the focus servo control device of the present invention. This circuit is obtained by adding a judgment of the presence or absence of a reproduction RF signal to a conventional focus pull-in control system. FIG.
1 is a photodetector (represented here by two divisions), 2 is a differential amplifier, 3 is a phase compensation circuit, 4 is an adder, 5 is a power amplifier, 6 is an actuator for driving a lens system, Reference numeral 7 denotes a voltage comparator for determining a pull-in area, 8 denotes a control circuit, 9 denotes a D / A converter, 10 denotes a threshold voltage for determining a pull-in area, 11 denotes a focusing servo switch, and 12 denotes a focusing servo switch.
Is an RF detector, 13 is an RF amplifier, 14 is an RF detector,
Reference numeral 15 denotes an RF determination voltage comparator, and reference numeral 16 denotes an RF level detection threshold voltage.

The focusing servo system is composed of a photodetector 1, a differential amplifier 2, a phase compensation circuit 3, an adder 4, a power amplifier 5, and an actuator 6, and an RF detector 12, an RF amplifier 1
3, the RF detector 14, the voltage comparator 15, the RF detection block with the RF level detection threshold voltage 16, the photodetector 1, the differential amplifier 2, the power amplifier 5, the actuator 6, the voltage comparator 7, the control circuit 8 , A D / A converter 9, a threshold voltage 10 for determining a pull-in area, and an RF detection block constitute a focusing pull-in control system.

The operation of this circuit will be described. When performing focus pull-in, first, the focusing servo switch 11 is turned off, and then the control circuit 8 changes the digital signal output to the D / A converter 9 to gradually output the D / A converter 9. Make the lens larger and gradually move it closer to the disc and closer to the focal point. At this time, when the threshold voltage 10 for determining the pull-in area is compared with the focusing error signal by the voltage comparator 7, the level of the focusing error signal gradually increases and becomes higher than the threshold voltage 10, and then the lens is further moved to the disk. When approaching, the level of the focusing error signal is now threshold voltage 1
It becomes smaller than 0. At this time, if the focusing servo switch 11 is turned on, stable pull-in can be performed. When the focusing operation is started, the focusing servo system drives the actuator 6 so that the focusing error signal becomes 0, so that the in-focus position is always maintained. FIG. 2 shows the relationship between the so-called S-shaped curve of the focusing error signal voltage and the threshold voltage 10 for determining the pull-in area during this time.

However, the focusing error signal is shown in FIG.
2A, an S-shaped curve is drawn on the disk recording surface, but an S-shaped curve is similarly drawn on the disk surface as shown in FIG. 2B.
This S-shaped curve can be determined from the level difference. Further, as shown in FIG. 2, since the reflection from the disk recording surface has a larger amount of reflected light than the reflection from the disk surface, as described above, the sum of the outputs of the respective light receiving elements of the split photodetector is calculated. The level of the focused sum signal is higher than a predetermined threshold,
By performing the focus pull-in at a place where the level of the focusing error signal is smaller than the threshold value, more stable focus servo can be realized. However, since the threshold value of the focusing error signal is given as an absolute value in the control system, the value of the focusing error signal such as laser power fluctuation, dispersion of the reflectivity of the disk surface, dispersion of the reflectivity of the recording surface, and contamination of the lens and the disk is considered. As described above, there is a possibility that a level change occurs before SN degradation or an increase in an error rate occurs due to a factor that causes the erroneous detection.

In the present invention, an RF detector 12, an RF amplifier 13, an RF detector 14, an RF determination voltage comparator 15,
The output of the RF detection block consisting of the F level detection threshold voltage 16 is further applied to the control circuit 8, and the RF determination voltage comparator 15 detects the RF signal detected by the RF detector 12 and detected by the RF detector 14. The focusing servo switch 11 is turned ON only when is larger than the threshold voltage 16 for detecting the RF level to perform the focusing servo. With this configuration, since the RF signal can be reproduced only from the recording surface, it is possible to distinguish the recording surface from the disk surface.

FIG. 3 shows the waveforms of the focusing sum signal, the RF detection signal, and the focusing error signal near the recording surface during the focus search, and FIG. 4 shows the waveforms near the disk surface. As is clear from FIGS. 3 and 4, an RF signal is detected from the recording surface, but no RF signal is detected on the disk surface. Therefore, it is easy to distinguish between the vicinity of the recording surface and the vicinity of the disk surface.

Since the frequency of the RF signal shown in FIG. 3 is 1800 rpm and the address is 42 sector addresses per track, the number of times the RF signal is fetched is small. In order to detect an RF signal using an address, at least about 80 sectors per track are required. When using data, there is no problem because it is continuous.

The available RF signal varies depending on the disc to be recorded and the recording method, but the following portions are used. 1) Reproduction of a preformat signal (portion in which an address or the like is indicated for each sector). MO disk with DS ERS (direct current erase) or unrecorded WO disk. 2) Reproduction of the recorded data portion. In the case of an overwrite type MO disk, PC disk or other recorded disk. In any case, there is no difference in using the signal on the recording surface.

Although it is possible to perform this pull-in by using only the reproduced RF signal, it is possible to increase the stability against noise by obtaining the pull-in position comprehensively including the focusing sum signal and the focusing error signal. Become.

FIGS. 5 and 6 show the RF detector 14 and specific circuits before and after it. FIG. 5 shows an example in which the S / N is gained by the band-pass filter 141, the reproduced signal is subjected to peak detection by the RF peak detector 142, and the level is compared by the RF determination voltage comparator 15 to determine the presence or absence of the RF signal. , FIG. 6 shows that after clamping by the clamp circuit 143,
The reproduced signal is peak-detected by the RF peak detector 142, and R
The level is compared by the F determination voltage comparator 15 to determine the presence or absence of the RF signal. Since the RF signal is intermittently detected as shown in FIG. 3, in order to stabilize the operation, hysteresis is provided in the RF determination voltage comparator 15 or the detection value is temporarily held during control. A method is conceivable.

With such a configuration, the focus servo control device of the present invention can 1) always realize correct servo without pseudo lock on the disk surface. 2) Since the pull-in can be performed while approaching the disk, the focus search time for lock-in can be shortened. 3) Since there is no false lock on the disk surface, a configuration can be provided which is strong against the influence of fluctuations in the laser output, variations in the reflectance of the disk surface, variations in the reflectance on the recording surface, and contamination of the lens and the disk. 4) Further, it becomes possible to detect dirt on the lens and the disc.

[0025]

As described above, according to the first aspect of the present invention, the objective lens is located at the first predetermined position closer to the recording medium than the in-focus position and at the first position closer to the recording medium than the in-focus position. A focus error signal generating means for generating a focus error signal whose output shows a peak at a distant second predetermined position and an output of 0 at an in-focus position therebetween, and a focus error signal generated by the focus error signal generating means A lens position determining means for determining that the objective lens is between the first predetermined position and the second predetermined position and outputting a servo enable signal; and focusing when the lens position determining means outputs the servo enable signal. A focus servo control device having a focus servo start means for starting a servo, wherein a high-frequency signal reproduced from the recording medium has a reproduction level higher than a predetermined level. Signal focus detection means, wherein the focus servo start means starts focus servo when the lens position determination means outputs a servo enable signal and the reproduction high frequency signal detection means outputs a detection signal. And By doing so, there is no danger of false lock on the disk surface, and stable servo can be performed. Also, since there is no risk of pseudo lock,
Since the pull-in can be performed while bringing the objective lens close to the disk, the focus search time for lock-in can be shortened. Since the modification for this can be achieved by adding a circuit to the conventional apparatus, the present invention can be implemented relatively easily and at low cost.

According to a second aspect of the present invention, a total light receiving level detecting means for detecting the total light receiving level of the reflected light from the recording medium, and the detection level of the total light receiving level detecting means being equal to or higher than a predetermined level. The light receiving level determining means has a light receiving level determining means, and the light receiving level determining means determines that the detection level is equal to or higher than a predetermined level,
And the lens position determination means outputs a servo enable signal,
Further, the present invention is characterized in that the focus servo is started when the reproduction high-frequency signal detection means outputs the detection signal. Thereby, the servoable area can be determined from the total received light level of the reflected light, the focus error signal, and the reproduced high frequency signal,
This eliminates the possibility of false lock on the disk surface, enables stable servo operation, and shortens the focus search time for lock-in.

The invention according to claim 3 of the present invention is characterized in that the reproduced high-frequency signal detecting means has a band furnace wave means and a peak value detecting means. As a result, the peak value of the reproduction frequency signal can be easily detected, and correct servo can always be realized.

According to a fourth aspect of the present invention, the reproduced high-frequency signal detecting means has a level clamp means and a peak value detecting means. As a result, the peak value of the reproduction frequency signal can be easily detected, and correct servo can always be realized.

[Brief description of the drawings]

FIG. 1 is a circuit block diagram of a pull-in function block of an embodiment of a focus servo control device according to the present invention.

FIG. 2 is an explanatory diagram showing a relationship between a focusing error signal voltage and a threshold voltage for determining a pull-in area.

FIG. 3 is a waveform diagram of a focusing sum signal, an RF detection signal, and a focusing error signal near a recording surface during focus search.

FIG. 4 shows the vicinity of the disk surface during focus search.
FIG. 4 is a waveform chart of a focusing sum signal, an RF detection signal, and a focusing error signal.

FIG. 5 is a circuit diagram showing an example of an RF detector and circuits before and after the RF detector.

FIG. 6 is a circuit diagram showing another example of the RF detector and circuits before and after the RF detector.

FIG. 7 is an explanatory diagram showing an S-shaped curve of a focusing error signal.

FIG. 8 is a waveform diagram of a focus search signal, a focusing sum signal, and a focusing error signal when a focus search operation is performed.

FIG. 9 is an explanatory diagram showing the shape of a light spot of reflected light from a four-division photodetector.

FIG. 10 is a table showing the reflectance from the disk surface and the reflectance from the recording surface for each disk.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Photodetector 2 ... Differential amplifier 3 ... Phase compensation circuit 4 ... Adder 5 ... Power amplifier 6 ... Actuator 7 ... Voltage comparator for pull-in area determination 8 ......
Control circuit, 9: D / A converter, 10: threshold voltage for judging the pull-in area, 11: focusing servo switch, 12: RF detector, 13: RF amplifier, 14
... RF detector, 15 ... RF judgment voltage comparator, 16
... RF level detection threshold voltage, 141 band pass filter, 142 RF peak detector, 143 clamp circuit.

Claims (4)

[Claims] 1. The output shows a peak at a first predetermined position where the objective lens is closer to the recording medium than the focal point and at a second predetermined position farther than the focal point with respect to the recording medium. A focus error signal generating means for generating a focus error signal having an output of 0 at the in-focus position, and the objective lens is moved from the focus error signal generated by the focus error signal generating means to the first predetermined position and the A lens position determining means for determining that the position is between two predetermined positions and outputting a servo enable signal; a focus servo starting means for starting focus servo when the lens position determining means outputs the servo enable signal. A focus servo control device comprising: a reproducing high-frequency signal detecting unit that outputs a detection signal when a high-frequency signal reproduced from the recording medium is equal to or higher than a predetermined level. Wherein the focus servo start means starts the focus servo when the lens position determination means outputs the servo enable signal, and the reproduction high frequency signal detection means outputs the detection signal. Focus servo control device. 2. A total light receiving level detecting means for detecting a total light receiving level of reflected light from the recording medium, and a light receiving level determining means for judging that a detection level of the total light receiving level detecting means is equal to or higher than a predetermined level. Wherein the focus servo start means, the light receiving level determination means determines that the detection level is equal to or higher than a predetermined level, and the lens position determination means outputs the servo enable signal, 2. The focus servo control device according to claim 1, wherein the focus servo is started when the reproduction high-frequency signal detection unit outputs the detection signal. 3. The focus servo control device according to claim 1, wherein said reproduced high-frequency signal detecting means includes a band furnace wave means and a peak value detecting means. 4. The focus servo control device according to claim 1, wherein said reproduced high-frequency signal detection means has a level clamp means and a peak value detection means.