JPH0589492A - Focus servo circuit - Google Patents

Abstract

(57) [Abstract] [Purpose] To improve the detection accuracy of focus servo deviation. [Structure] 4-division photodetector 9 for receiving reflected light from optical disk 6, amplifiers 10 and 11 for amplifying this output, and gain switching circuits GC1 and GC2 for switching the gain of amplifiers 10 and 11
A differential amplifier 12 that differentially amplifies the outputs of the gain switching circuits GC1 and GC2, a summing amplifier 13 that performs additive amplification, and a differential amplifier
The differential signals X output from 12 are normalized by the sum signal Y output from the addition amplifier 13, and the dividers 14 and 20 and the header section in which information about the information recording section of the optical disc 6 is recorded from the sum signal Y. Header detection circuit 25 for detection, CPU 24 for control operation based on the header and sum signal Y, and divider
A switch SW ₁ for turning on / off the focus error signal X ′ output by 14 and a switch SW ₂ for turning on / off the focus error signal X ″ output by the divider 20 are provided.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a focus servo circuit for obtaining a focus of a light beam on the surface of an optical disk.

[0002]

2. Description of the Related Art FIG. 8 is a block diagram of a focus servo circuit of this type. The laser light of the laser diode 1 passes through the convex lens 2, the half mirror 3 and the focusing lens 4,
It is designed to be projected onto an optical disk 6 which is rotated by a motor 5, and the focusing lens 4 has an actuator 7
This makes it possible to move in the optical axis direction. Optical disc 6
The reflected light of the laser light projected on the condenser lens 4 passes through the focusing lens 4 and is reflected by the half mirror 3, and then the cylindrical lens 8
The light is incident on the four-division photodetector 9 through.

The outputs of the four-division photodetector 9 are input to amplifiers 10 and 11, respectively. The output of the amplifier 10 is input to the positive input terminal 12a of the differential amplifier 12 and the one side input terminal 13a of the summing amplifier 13. The output of the amplifier 11 is input to the negative input terminal 12b of the differential amplifier 12 and the other input terminal 13b of the summing amplifier 13. The difference signal X and the sum signal Y, which are the outputs of the differential amplifier 12 and the addition amplifier 13, are both input to the divider 14, and the sum signal Y is input to the level comparator 15. The level comparator 15 outputs the focus servo deviation signal S _D when the level of the input sum signal Y is within the reference level range. The output of the divider 14 is a phase compensation circuit 16 for stabilizing the focus servo.
Is input to the actuator driving amplifier 17, and its output is given to the actuator 7.

Next, the operation of this focus servo circuit will be described. The laser light emitted from the laser diode 1 is converted into parallel light by the convex lens 2, passes through the half mirror 3, and then is focused on the surface of the optical disc 6 by the focusing lens 4. The reflected light of the laser light reflected by the optical disk 6 passes through the cylindrical lens 8 and is condensed on the four-division photodetector 9. The output of the 4-division photodetector 9 is amplified by the amplifiers 10 and 11 and input to the differential amplifier 12 and the addition amplifier 13. As a result, the differential amplifier 12 outputs the difference signal X, which is the difference between the outputs of the amplifiers 10 and 11, and the summing amplifier 13 is the amplifier.
The sum signal Y, which is the sum of the outputs of 10 and 11, is output.

The difference signal X and the sum signal Y are divided by the divider 14
The divider 14 divides the difference signal X by the sum signal Y so as to remove the level change of the difference signal X due to the change of the reflectance of the optical disk 6 or the change of the light amount of the laser beam. The signal X'is output. The focus error signal X'is input to the amplifier 17 through the phase compensation circuit 16 for stabilizing the servo system, and the amplifier 17 corresponds to the output capable of driving the actuator 7 by amplification, that is, the focus error signal X '. The focus servo is performed so that the output of the amplifier 17 is given to the actuator 7 and the focusing lens 4 is moved to constantly obtain the focused point of the laser light on the surface of the optical disk 6.

When the level of the sum signal Y becomes equal to or lower than the reference level set in the level comparator 15, the level comparator 15 outputs a focus servo out signal S _D to notify the focus servo out, for example, a display unit. To display. The levels of the difference signal X and the sum signal Y change as shown in FIGS. 9 (a) and 9 (b) with respect to the change in the distance between the optical disc 6 and the focusing lens 4, and the levels deviate from the in-focus distance. As a result, the voltage level of the difference signal X linearly increases toward the positive or negative voltage side, and the voltage level of the sum signal Y gradually decreases in a curve.

[0007]

As described above, the conventional focus servo circuit outputs the focus servo out-of-focus signal when the level of the sum signal obtained by adding the outputs of the four-division photodetector is below a predetermined reference level. , If the light reflectance of the optical disc or the light intensity of the emitted light of the laser diode that projects the light to the optical disc fluctuates because the reference level is constant, or the header of the optical disc or the flaw of the optical disc is detected. When the light intensity of the reflected light from the optical disc is lowered, there is a possibility that the focus servo deviation may be erroneously detected.

Further, when there is no reflected light from the optical disk, an output appears in the four-division photodetector, so-called stray light occurs, and when the signal level due to the stray light is high, there is a problem that the focus servo deviation cannot be detected. is there. In view of such a problem, the present invention reduces the light intensity of the reflected light from the optical disc when the light reflectance of the optical disc or the light intensity of the emitted light of the laser diode fluctuates or the flaw of the header portion or the optical disc is detected. In this case, it is another object of the present invention to provide a focus servo circuit capable of detecting a focus servo deviation even when the signal level due to stray light is high.

[0009]

A focus servo circuit according to a first aspect of the present invention comprises means for measuring the level of a sum signal a plurality of times, means for setting a threshold value by an average value of the levels of the sum signals measured, and a plurality of times. A means for comparing the level of the sum signal measured after the measurement with the threshold value a plurality of times and a means for prohibiting the control operation for obtaining the focal point of the light projected on the optical disk are provided, and the level of the sum signal measured is the threshold value. In the following cases, the control operation for obtaining the focus of light on the optical disk is prohibited.

The focus servo circuit according to the second invention is
Means for measuring the level of the signal due to stray light received by the light receiving section in the absence of reflected light from the optical disk, means for measuring the level of the sum signal multiple times, and the average value of the measured sum signal levels and the measured stray light Means for setting a threshold value based on the signal level, means for comparing the level of the measured sum signal with the threshold value, and means for prohibiting a control operation for obtaining the focal point of the light projected on the optical disk. When the measured level of the sum signal is below the threshold value, the control operation for obtaining the focused point of light on the optical disk is prohibited.

The focus servo circuit according to the third invention is
Means for periodically measuring the level of the sum signal, means for setting a threshold value to be compared with the level of the measured sum signal, means for comparing the level of the measured sum signal with the threshold value, and output of the light receiving section Means for controlling the gain of the amplifier for amplifying the signal, means for measuring the level of the signal due to stray light received by the light receiving section in the absence of the reflected light from the optical disk from the output of the amplifier, and the level of the measured sum signal and / Or means for setting at least one predetermined value to be compared with the level of the stray light signal, and the level of the measured sum signal and / or
Alternatively, means for comparing the level of the signal due to stray light with the predetermined value, means for calculating the level of the signal due to stray light from the gain of the amplifier, and means for inhibiting the control operation for obtaining the focal point of the light projected on the optical disk And controlling the gain so that the level of the sum signal is equal to or higher than a predetermined value and / or the signal level due to stray light is equal to or lower than the predetermined value. The control operation for obtaining the in-focus point is prohibited.

The focus servo circuit according to the fourth invention is
Means for determining whether or not the header portion in which the address of the information recording portion of the optical disc is recorded is detected, means for measuring the level of the sum signal a plurality of times, and timing for measuring the level of the sum signal is changed. When the header portion is detected, the level of the sum signal is not measured.

[0013]

According to the first aspect of the invention, the sum signal of these outputs of the plurality of light receiving sections for receiving the reflected light from the optical disk is obtained. The level of the sum signal is measured a plurality of times, and the threshold value is set based on the average value of the levels of the sum signal measured. Then, the measured level of the sum signal is compared with the threshold value a plurality of times, and when the level of the sum signal becomes equal to or lower than the threshold value, the control operation for obtaining the in-focus point of the light projected on the optical disc is prohibited. As a result, when the level of the sum signal temporarily changes, the focus servo deviation is not detected.

According to the second aspect of the invention, the sum signal of the outputs of the plurality of light receiving sections that receive the reflected light from the optical disk is obtained.
The level of the signal due to the stray light received by the light receiving section is measured in the absence of the reflected light from the optical disk. In addition, the level of the sum signal is measured multiple times. The threshold value is set based on the average value of the levels of the measured sum signal and the level of the signal due to the measured stray light. When the level of the measured sum signal is less than or equal to the threshold value, the control operation for obtaining the in-focus point of the light projected on the optical disc is prohibited. As a result, the focus servo deviation can be detected without being affected by stray light.

In the third invention, the sum signal of these outputs of the plurality of light receiving portions for receiving the reflected light from the optical disk is obtained.
The threshold value to be compared with the level of the measured sum signal is set.
The level of the signal due to the stray light received by the light receiving section in the absence of the reflected light from the optical disk is measured from the output of the amplifier that amplifies the output of the light receiving section. Also, the level of the signal due to stray light is calculated from the gain set in the amplifier. The measured gain signal level and / or the stray light signal level is compared with a predetermined value, and the gain of the amplifier is controlled so that the sum signal level is equal to or higher than a predetermined value and the stray light signal level is equal to or lower than the predetermined value. To do. When the level of the measured sum signal is less than or equal to the threshold value, the control operation for obtaining the in-focus point of the light projected on the optical disc is prohibited. As a result, the threshold value is always located between the level of the sum signal and the level of the signal due to stray light, and the focus servo deviation can be detected without being affected by the stray light.

According to the fourth aspect of the invention, the sum signal of the outputs of the plurality of light receiving sections for receiving the reflected light from the optical disk is obtained.
The level of this sum signal is measured multiple times. Whether or not the header section is detected is determined by the output of the light receiving section. When the header section is detected, the timing of measuring the level of the sum signal is changed and the level of the sum signal is not measured. As a result, the focus servo deviation can be accurately detected by the level of the sum signal when the header portion is not detected.

[0017]

The present invention will be described in detail below with reference to the drawings showing the embodiments thereof. FIG. 1 is a block diagram of a focus servo circuit according to the present invention. Laser light from a laser diode 1, which is a light source, passes through a convex lens 2, a half mirror 3 and a focusing lens 4, and is projected onto the surface of an optical disk 6 rotated by a motor 5. The focusing lens 4 is an actuator. It is movable in the optical axis direction by 7 and in the direction traversing the track of the optical disk 6 by a carriage 28 described later.

The reflected light of the laser light projected on the optical disk 6 and reflected by the optical disk 6 passes through the focusing lens 4, is reflected by the half mirror 3, and then passes through the cylindrical lens 8 to enter the 4-split photodetector 9. It has become. Four
The outputs of the split photodetector 9 are input to amplifiers 10 and 11, respectively.

The output of the amplifier 10 is one gain switching circuit GC
It is inputted to the positive input terminal 12a of the differential amplifier 12 and the one side input terminal 13a of the adding amplifier 13 via 1. The output of the amplifier 11 is output to the differential amplifier 12 via the other gain switching circuit GC2.
Negative input terminal 12b and the other input terminal 13b of the summing amplifier 13
Have been entered respectively.

The difference signal X and the sum signal Y, which are the outputs of the differential amplifier 12 and the addition amplifier 13, are both input to the dividers 14 and 20, respectively. The difference signal X is normalized by the sum signal Y, and the divider 14 The focus error signal X'output from the switch
Via SW ₁ , it is input to a phase compensation circuit 16 that performs phase lead compensation to stabilize the focus servo, its output is input to an actuator driving amplifier 17, and its output is given to the actuator 7.

The sum signal Y is input to an analog / digital converter 22 and the digital signal converted from analog to digital is a CP having a memory and an arithmetic unit (not shown).
It is provided to the control unit 24 composed of U. Also the sum signal Y
Is inputted to a header section detecting circuit 25 for detecting a header section in which an address and the like of the information recording section of the optical disc 6 are recorded, and the detection output thereof is an analog / digital converter.
It is input to 26. Analog / Digital Converter 26
The digital signal that has been analog-to-digital converted by is input to the control unit 24.

The focus error signal X ″ output from the divider 20 is input to the drive circuit 27 via the switch SW ₂ , and the drive circuit 27 amplifies the input focus error signal X ″ and outputs the amplified signal. The focusing lens 4 is applied to a carriage 28 which moves the optical disc 6 in the radial direction (a direction traversing a track).

Next, the operation of the focus servo circuit according to the first aspect of the invention will be described with reference to the flow chart of FIG. The laser light emitted from the laser diode 1 is collimated by the convex lens 2, passes through the half mirror 3, is condensed by the focusing lens 4, and is projected onto the surface of the rotating optical disc 6. Then, the reflected light of the laser light reflected by the rotating optical disc 6 passes through the cylindrical lens 8 and is condensed on the four-division photodetector 9. The output of the four-division photodetector 9 is amplified by the amplifiers 10 and 11, and then input to the differential amplifier 12 and the summing amplifier 13 via the gain switching circuits GC1 and GC2, respectively.

The differential amplifier 12 outputs the difference signal X which is the difference between the outputs of the amplifiers 10 and 11, and the summing amplifier 13 outputs the sum signal Y which is the sum of the outputs of the amplifiers 10 and 11. These difference signals X
And the sum signal Y are input to the dividers 14 and 20, respectively, and the dividers 14 and 20 are used to remove the level change of the difference signal X due to the light reflectance change of the optical disk 6 or the light intensity change of the laser beam. focus error signal is normalized by dividing the signal X with the sum signal Y X ', and outputs the X ". the focus error signal X' is a stable servo operation is inputted through the switch SW ₁ to the phase compensation circuit 16 After the phase lead compensation is performed, the signal is input to the amplifier 17 and amplified so that the actuator 7 can be driven.

Then, the output of the amplifier 17 is given to the actuator 7 to move the focusing lens 4 in the optical axis direction in accordance with the focus error signal X ', so that the focus servo is always performed on the optical disk 6 to obtain the focal point of the laser light. I do. On the other hand, the focus error signal X ″ output from the divider 20
Is input to the drive circuit 27 via the switch SW ₂ and amplified so that the carriage 28 can be driven. The output of the drive circuit 27 is given to the carriage 28 so that the focusing lens 4 moves in the radial direction of the optical disk 6 (direction crossing the track).
Go to and access the track.

The header section detection circuit 25 periodically detects the header section of the rotating optical disc 6 based on the level change of the sum signal Y input thereto, and outputs the detection output to the analog / digital converter 26. The signal given and digitally converted is input to the control unit 24. The control unit 24 determines the level of the sum signal Y from the signal related to the header portion of the optical disk 6 having, for example, 31 header portions per track.
When rotated at 00 revolutions / minute, control is performed to set the timing of periodic measurement in 4.2 milliseconds (S1), and the level of sum signal Y is measured at each timing (S2) in a memory not shown. Remember.

Subsequently, the control unit 24 calculates an average value of the measured values of the sum signal level which has already been measured, for example, eight times,
Multiply it by a factor of 1/4 to set the first threshold (S
3). Then measure the level of the 9th new sum signal (S
4), the level of the measured sum signal and the first threshold value are compared (S5). Here, if the focus servo is not disengaged and the level of the sum signal just measured is 1/4 or more of the calculated average value, that is, if it is determined that it is the first threshold value or more, the focus from the divider 14 Focus servo is performed according to the error signal X '(S6). Then, it is judged whether or not the servo operation is necessary (S7), and if it is judged that the servo operation is necessary, the process returns to step (S1), and then the sum signal Y measured
The same flow is repeated as long as the level of does not fall below the first threshold value and the focus servo is continued.

By the way, if dust is attached to the optical disc 6 or if it is flawed, the light intensity of the reflected light from the optical disc is lowered and the level of the sum signal Y is lowered.
If it is determined that the level of the sum signal measured at the 9th time is less than or equal to the first threshold value, the level of the sum signal is measured at the 10th time (S8), and the level of the sum signal measured at the 10th time and the level of the sum signal are measured. The second threshold equal to the first threshold is compared in magnitude (S9). When it is determined that the level of the sum signal measured at the 10th time is equal to or higher than the second threshold value, focus servo is performed as described above (S6).

However, if it is judged that the sum is less than the second threshold value (S9), then the level of the sum signal is measured eleventh time.
(S10), the level of the sum signal measured at the 11th time is compared with the third threshold value equal to the first threshold value (S11), and if it is determined that the threshold value is equal to or higher than the third threshold value, focus servo is performed (S6). However, if it is determined that it is below the third threshold value again, the level of the sum signal is measured for the twelfth time (S12).
Then, the level of the sum signal measured at the 12th time is compared with the fourth threshold value equal to the first threshold value (S13), and if it is determined that the threshold value is equal to or higher than the fourth threshold value, focus servo is performed (S6).

However, if it is determined that the voltage is still below the fourth threshold value, the switch SW is activated by the signal from the control unit 24.
₁ is opened to shut off the focus error signal X ',
The drive of the actuator 7 is prohibited and the focus servo operation is prohibited (S14). That is, if the levels of the sum signal measured multiple times with different measurement timings are all lower than the threshold value, it is determined that the focus servo deviation is not due to a temporary decrease in the sum signal level due to dust or scratches on the optical disc. Will be detected.

After the focus servo operation is prohibited, the emission of light by the laser diode 1 is stopped to prohibit the recording, reproducing and erasing of data (S15). Then, it is determined whether or not the track is being accessed (S16), and if the track is being accessed, the switch SW ₂ is opened by a signal from the control unit 24 and the focus error signal X from the divider 20 is output. ″ Is cut off to prohibit driving of the carriage 28 to prohibit track access (S17). When the track access is prohibited in this way, terminals of a linear motor (not shown) of the carriage are opened or short-circuited.

When the track access is prohibited in this way, the number of tracks crossed is detected, and when the tracks are accessed based on the detected number of tracks, the number of tracks crossed due to the focus servo deviation. Even if the detection becomes impossible, the focusing lens 4 can be surely prevented from running away in the radial direction of the optical disk 6. Next, it is determined whether or not the focus servo operation is necessary, and if it is determined that the focus servo operation is necessary, the focusing lens 4 is brought closest to the optical disk 6 and the focusing lens 4 is retracted. On the other hand, if it is determined that it is unnecessary (S7), the focus servo and the servo operation for accessing the track are ended.

When the light intensity of the light emitted from the laser diode 1 fluctuates, the level of the sum signal Y fluctuates accordingly. In this case as well, the focus servo similar to that when the reflected light from the optical disk 6 fluctuates. Take action.

In this way, the sum signal is measured a plurality of times at different timings, and the level of the sum signal measured is compared with the threshold value each time. You can judge whether or not. Therefore, the focus servo deviation is not erroneously detected due to a temporary change of the optical reflectance of the optical disc or the light intensity of the emitted light of the laser diode, and the light intensity of the reflected light from the optical disc is not detected due to dust or scratches on the optical disc. Even if it falls, the focus servo deviation is not detected.

In this embodiment, the level of the measured sum signal can be compared with the threshold value four times, but the number of times is an example and the number of times is not limited. Also,
In the present embodiment, the first, second, third and fourth threshold values are selected to be equal, but, for example, 1/2 of the average value of the sum signal levels measured m times in the past is set as the first threshold value, and / 3 as the second threshold, 1 /
4 may be selected as a third threshold value and 1/5 may be selected as a fourth threshold value, which are sequentially lower. When it is determined that the level of the measured sum signal is equal to or higher than the threshold value, of the past m times (e.g., 8 times) of the measured values used for the calculation of the average value, the more recent ones are sequentially arranged in order from the past one. You may replace with the measured value of a sum signal, calculate a moving average value, and may set a threshold value based on that moving average value. Then, for example, when the light intensity of the emitted light of the laser diode 1 changes at the time of recording, reproducing, and erasing information,
Alternatively, even if the light intensity of the reflected light from the optical disc changes between the recorded portion and the unrecorded portion of the information on the perforated optical disc, the threshold value can be set according to the level of the sum signal at that time, and the focus servo deviates. There is no false detection.

Next, the operation of the focus servo circuit according to the second aspect of the invention will be described with reference to the flow chart of FIG. The operation from projecting light from the laser diode 1 to the optical disk 6 and receiving the reflected light by the photodetector 9 to obtain the sum signal Y is similar to the operation described in FIG. Now, the control unit 24 first takes in the level of the sum signal Y when the reflected light from the optical disk 6 is not present, and measures the level of the signal due to stray light (S21).

Subsequently, the control section 24 sets timings for periodically measuring the level of the sum signal Y by the signal related to the header section (S22), and measures the level of the sum signal Y at each timing (S23). ) Is stored in a memory (not shown). Subsequently, the control unit 24 calculates the average value of the plurality of measured values of the level of the sum signal that has already been measured, subtracts the value of the signal level due to stray light from the average value of the levels of the sum signal, and subtracts Multiply the value at the specified level by a coefficient. Then, the threshold value is set by adding the value of the level of the signal related to stray light measured previously to the numerical value of the level multiplied by the coefficient (S24).

That is, as shown in FIG. 4, the threshold value Q is set to the level P of the signal due to stray light and the level value calculated by multiplying the average value of the level R of the sum signal by the coefficient. Then measure the level of the new sum signal (S
25) Then, the measured sum signal level is compared with the set threshold value (S26). If it is determined that the focus servo is not out of order and the level of the sum signal just measured is equal to or higher than the threshold value, the focus servo is performed according to the focus error signal X'from the divider 14 (S27).

Subsequently, it is judged whether or not the focus servo operation is necessary (S28), and if it is judged that the servo operation is necessary, the process returns to step (S22), and the same is done unless the level of the measured sum signal is equal to or lower than the threshold value. Repeat this flow to continue the focus servo.

Subsequently, the measured sum signal level and the threshold value are compared in magnitude (S26), and if it is determined that the sum signal level is less than or equal to the threshold value, the switch SW ₁ is opened by a signal from the control unit 24 and the focus error signal is output. X'is cut off to prohibit the driving of the actuator 7 and the focus servo (S29).
.. Then, the emission of light by the laser diode 1 is stopped to prohibit the recording, reproduction and erasing of data (S30).

Subsequently, it is judged whether or not the track is being accessed (S31). When it is judged that the track is being accessed, the switch SW ₂ is opened by the signal from the control section 24 and the divider 20 The focus error signal X ″ is cut off to inhibit the drive of the carriage 28 and inhibit the track access (S32). After that, it is determined whether the focus servo operation is necessary, and if it is determined that the focus servo operation is necessary (S28), The focusing lens 4 is brought closest to the optical disk 6 to pull in the focusing lens 4. On the other hand, when it is judged that the focusing lens 4 is not necessary, the focus servo and the servo operation for accessing the track are ended.

When the track access is prohibited in this way, the number of crossed tracks is detected, and when the tracks are accessed based on the detected number of tracks, the number of tracks crossed due to the focus servo deviation. Even if the detection becomes impossible, the focusing lens 4 can be surely prevented from running away in the radial direction of the optical disc. Then, it is determined whether or not the servo operation is necessary (S28). When it is determined that the servo operation is unnecessary, if the focus servo and the track are being accessed, each servo operation is ended.

According to this focus servo circuit, as shown in FIG.
Since the level P of the signal due to stray light does not exceed the threshold value Q as shown in (4), when the level R of the sum signal reaches the threshold value Q, the focus servo deviation can be detected. Therefore, even if there is a lot of stray light and the level of the signal is high, it is possible to reliably detect the focus servo deviation without being affected by the stray light.

Next, the operation of the focus servo circuit according to the third invention will be invented together with the flowchart of FIG. 5 showing the control contents of the control section 24. The operation of projecting light from the laser diode 1 to the optical disk 6 and receiving the reflected light by the photodetector 9 to obtain the sum signal Y is similar to the above-described operation. Here, the first prescribed value L _{1 and} the second prescribed value L ₂ and the threshold value Q
Are set in advance in a memory (not shown) so as to establish the relationship shown in FIG. To fix the threshold value, set the first specified value L ₁ as a reference for controlling the sum signal level on the higher level side than the threshold value, and control the signal level due to stray light on the lower level side than the threshold value. The second prescribed value L ₂ which is the reference of is set.

Now, the control section 24 controls the gain switching circuit GC1,
A predetermined gain K is set in GC2 (S40), and the level of a signal due to stray light corresponding to the gain K is measured in the absence of reflected light from the optical disk 6 (S41). Subsequently, the control unit 24 sets the timing for periodically measuring the level of the sum signal Y by the signal related to the header section (S42), measures the level of the sum signal Y at each timing, and sets the sum signal level. Monitor (S43).

Subsequently, the level of the sum signal is the first specified value L ₁
It is determined whether or not (see FIG. 6) (S44), the first specified value L
_When it is determined that the sum signal is ₁ or less, the gain K of the gain switching circuits GC1 and GC2 is incremented (S45), and the sum signal level is increased so that the sum signal level becomes equal to or more than the first specified value L ₁ .

When it is determined that the level of the sum signal is equal to or higher than the first specified value L ₁ (S44), the level of the signal due to stray light corresponding to the incremented gain K is calculated (S46). The signal level associated with stray light is second
It is determined whether the value is equal to or less than the specified value L ₂ (S47). Here, when it is determined that the second specified value L ₂ or more, the gain switching circuit GC
1 decrements the gain K of GC2 (S48), so that the signal level associated with stray light becomes the second predetermined value L ₂ or less.

As a result, the threshold value Q is located between the sum signal level R and the signal level P due to stray light, as shown in FIG. 6, and the signal level P due to stray light becomes equal to or higher than the threshold value Q. There is no. Subsequently, it is determined whether or not the monitored sum signal level is equal to or higher than the threshold value Q (S49), and if it is determined to be equal to or higher than the threshold value, focus servo is performed according to the focus error signal X '(S50) as described above. .. Next, it is judged whether focus servo operation is necessary (S51).
When it is determined that the servo operation is necessary, the process returns to step (S42), and the same flow is repeated until the measured sum signal level is equal to or lower than the threshold value, and the focus servo is continued.

Then, when the focus servo goes out,
If it is determined that the level of the measured sum signal is less than or equal to the threshold value (S49), the focus error signal X'is cut off in the same manner as described above, the driving of the actuator 7 is prohibited, and the focus servo is prohibited (S52). ). Further, the emission of light by the laser diode 1 is stopped to prohibit data recording, reproduction and erasing (S53). Subsequently, it is determined whether or not the track is being accessed (S54). When it is determined that the track is being accessed, the focus error signal X ″ is cut off to prohibit the carriage 28 from being driven, and the track is accessed. Prohibit (S55).

When the access to the tracks is prohibited in this way, the focusing lens 4 does not run away in the radial direction of the optical disk 6 even if the number of tracks traversed cannot be detected due to the out-of-focus servo. Make sure to prevent. Next, it is judged whether servo operation is necessary (S51),
When it is determined that the focusing lens 4 is necessary, the focusing lens 4 is brought closest to the optical disk 6 and the focusing lens 4 is retracted. When it is determined that it is unnecessary, the focus servo and the servo operation for accessing the track are ended. With this focus servo circuit, even if the threshold value is fixed, the level of the signal related to stray light can be below the threshold value, and the level of the sum signal can be above the threshold value. There is no stopping it.

In this embodiment, the first specified value L ₁ and the second specified value L ₂ are set, but either one may be set. Further, the first specified value and the second specified value may be equal, or may be equal to the threshold value.

Next, the operation of the focus servo circuit according to the fourth aspect of the invention will be described with reference to the flow chart of FIG. The operation of projecting light from the laser diode 1 to the optical disk 6 and receiving the reflected light by the photodetector 9 to obtain the sum signal Y is similar to the above-described operation. Now, the control section 24 sets the timing for periodically measuring the level of the sum signal Y by the signal related to the header section (S60). Then, it is determined whether or not the header portion of the optical disc 6 is detected by the signal for detecting the header portion (S61). When it is determined that the header portion is not detected, the sum signal level is measured at each set timing (S62).

In this way, the timing for measuring the sum signal is set so that the sum signal is not measured while the header section is being detected, but the CPU 24 needs to perform higher-level processing other than the sum signal measurement. If this occurs, the timing for measuring the sum signal will be incorrect. Even after setting the timing for measuring the sum signal, it is necessary to determine whether or not the sum signal is measured when the header portion is not detected. Further, it is necessary to make a similar judgment when optical disks having different numbers of sectors are used. Therefore, it is determined whether the measurement of the sum signal does not coincide with the timing of detecting the header portion.

On the other hand, when it is determined that the header portion is detected (S61), the timing set to measure the sum signal level is changed (S63). For example, in the period in which the header portion is detected, the measurement timing cycle is set to, for example, several hundred so that the timing for measuring the level of the sum signal is not set.
Change to make nanoseconds to several milliseconds longer or shorter. ..
As a result, the low-level sum signal when the header part is detected is not measured. In this way, the sum signal level when the header portion is not detected is measured at the set timing (S62) and stored in the memory (not shown).

Subsequently, the control unit 24 calculates an average value of a plurality of measured values of the sum signal level which has already been measured, and multiplies the average value of the sum signal levels by a coefficient to set a threshold value.
(S64). Here, determine whether the header part is detected
(S65) If the header is not detected, the measured sum signal level is compared with the threshold value (S66). If it is determined that the focus servo is not out of order and the level of the sum signal is above the threshold value, the focus error signal X '
The focus servo is performed according to (S67).

Subsequently, it is determined whether or not the focus servo operation is necessary (S68). When it is determined that the focus servo operation is necessary, the same flow is repeated until the level of the measured sum signal falls below the threshold value, and the focus servo is continued. To do. Then, when it is determined that the level of the sum signal has decreased and is equal to or less than the threshold value (S66), the focus error signal X'is cut off by the control unit 24 in the same manner as described above to prohibit the driving of the actuator 7 and focus. Prohibit servo (S6
9). Further, the emission of light by the laser diode 1 is stopped to prohibit recording, reproduction and erasing of data (S70).

Subsequently, it is determined whether or not the track is being accessed (S71). When it is determined that the track is being accessed, the control unit 24 shuts off the focus error signal X ″ to drive the carriage 28. This prohibits the track access (S72), which prevents the focusing lens 4 from running away in the radial direction of the optical disk 6 even if the number of crossed tracks cannot be detected due to the focus servo deviation. Then, it is judged whether or not the focus servo operation is necessary (S68), and when it is judged as necessary, the focusing lens 4 is brought closest to the optical disk 6 and the focusing lens 4 is retracted. Terminate the servo operation to access the track.

According to this focus servo circuit, the level of the sum signal is not measured and the magnitude is not compared with the threshold value while the header portion is being detected. Therefore, the focus servo deviation can be detected with high accuracy by measuring only the level of the sum signal during the period in which the header portion is not detected.

[0059]

As described above in detail, according to the first invention,
When the level of the sum signal is below the threshold value set based on the average value of the measured sum signal levels, the focus servo is prohibited, and according to the second invention, the threshold value set based on the signal level due to stray light. When the level of the sum signal is below, the focus servo is prohibited, and according to the third invention, the level of the sum signal is set to a predetermined value or higher and / or the level of the signal due to stray light is set to a predetermined value or lower. By controlling the gain of the amplifier that amplifies the output of the photodetector, the focus servo is prohibited when the level of the measured sum signal is less than or equal to a preset threshold value, and according to the fourth invention, the header section is detected. Since the sum signal is not measured at the same timing, in any of the inventions, when the light reflectance of the optical disk or the light intensity of the light projected on the optical disk temporarily fluctuates, Even if the light intensity of the reflected light from the optical disk fluctuates temporarily due to dust or scratches on the optical disk, it is possible to reliably detect the focus servo deviation and to detect the focus servo deviation erroneously without being affected by them. Never. Therefore, the present invention has an excellent effect of significantly improving the reliability of the focus servo.

[Brief description of drawings]

FIG. 1 is a block diagram showing a configuration of a focus servo circuit according to the present invention.

FIG. 2 is a flowchart showing control contents of a control unit of the focus servo circuit according to the first invention.

FIG. 3 is a flowchart showing control contents of a control unit of the focus servo circuit according to the second invention.

FIG. 4 is a graph showing the relationship between the level of a sum signal, the threshold value, and the level of a signal due to stray light.

FIG. 5 is a flowchart showing the control contents of the control unit of the focus servo circuit according to the third invention.

FIG. 6 is a graph showing a relationship among a level of a sum signal, a first prescribed value, a threshold value, a second prescribed value, and a signal level due to stray light.

FIG. 7 is a flowchart showing control contents of a control unit of a focus servo circuit according to a fourth invention.

FIG. 8 is a block diagram showing a configuration of a conventional flowchart servo circuit.

FIG. 9 is a graph showing each level change of a sum signal and a difference signal.

[Explanation of symbols]

1 Laser diode 3 Half mirror 4 Focusing lens 6 Optical disk 7 Actuator 9 4 split light detector 12 Differential amplifier 13 Summing amplifier 14,20 Divider 24 Control section 28 Carriage SW ₁ , SW ₂ switches GC1, GC2 Gain switching circuit

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Hiroyuki Onda 3-7-3 Nakamachi, Musashino-shi, Tokyo Inside TAITSUKU CORPORATION (72) Inventor Yoshiki Nakajima 8-1-1 Tsukaguchihonmachi, Amagasaki City, Hyogo Prefecture Ryo Electric Co., Ltd. Industrial Systems Research Institute (72) Inventor ▲ Kichisuke Moto Kyosuke 8-1, Tsukaguchi Honcho, Amagasaki City, Hyogo Sanryo Electric Co., Ltd. Industrial System Research Center (72) Inventor Osamu Amagasaki, Hyogo Prefecture 8-1, 1-1 Tsukaguchihonmachi Sanryo Electric Co., Ltd. Industrial Systems Research Center

Claims (4)

[Claims] 1. A light comprising a plurality of light receiving portions for receiving reflected light from an optical disc, obtaining a difference signal and a sum signal of these outputs, and projecting the difference signal on the optical disc by a signal obtained by normalizing the difference signal with the sum signal. In the focus servo circuit for controlling to obtain the in-focus point of, a means for measuring the level of the sum signal a plurality of times, a means for setting a threshold value based on the average value of the levels of the sum signals measured, and a plurality of measurements. A means for comparing the level of the sum signal measured later with the threshold value a plurality of times, and a means for prohibiting the control operation for obtaining the in-focus point are provided. A focus servo circuit, which is configured to prohibit a control operation to be obtained. 2. A light comprising a plurality of light receiving portions for receiving reflected light from an optical disc, obtaining a difference signal and a sum signal of these outputs, and projecting the difference signal on the optical disc by a signal normalized by the sum signal. In a focus servo circuit that performs control to obtain the in-focus point, a means for measuring the level of the signal due to the stray light received by the light receiving section in the absence of the reflected light from the optical disk, and the level of the sum signal are measured multiple times. Means, a means for setting a threshold value based on the average value of the level of the measured sum signal and the level of the signal due to the measured stray light, a means for comparing the level of the measured sum signal with the threshold value, and a focus point. And a means for inhibiting the control operation to be obtained, and for inhibiting the control operation for obtaining the in-focus point when the level of the measured sum signal is below the threshold value. Focus servo circuit according to claim. 3. A plurality of light receiving portions for receiving the reflected light from the optical disk and an amplifier for amplifying the outputs of these light receiving portions are provided, a difference signal and a sum signal of the outputs of the amplifiers are obtained, and the difference signal is normalized by the sum signal. In a focus servo circuit that controls to obtain the focal point of the light projected on the optical disc by a signal, a means for periodically measuring the level of the sum signal and a means for setting a threshold value to be compared with the level of the measured sum signal. A means for comparing the level of the measured sum signal with the threshold value, a means for controlling the gain of the amplifier, and a level of a signal due to stray light received by the light receiving section in the absence of reflected light from the optical disc. Means for measuring from the output of the amplifier and means for setting at least one predetermined value to be compared with the level of the measured sum signal and / or the level of the signal due to stray light , The level of level and / or signal due to stray light of the measured sum signal and means for comparing the predetermined value,
A means for calculating the signal level due to stray light from the gain of the amplifier and a means for inhibiting the control operation for obtaining the in-focus point are provided, and the level of the sum signal is set to a predetermined value or higher and / or the signal level due to stray light is set to a predetermined value A focus servo circuit, characterized in that the gain is controlled to be equal to or less than a value, and when the measured level of the sum signal is equal to or less than a threshold value, a control operation for obtaining a focused point is prohibited. 4. A plurality of light receiving sections for receiving reflected light from an optical disk having an information recording section and a header section recording information relating to the information recording section are provided, and a difference signal and a sum signal of these outputs are provided. And a means for determining whether or not the header portion is detected in a focus servo circuit that performs control to obtain the in-focus point of the light projected on the optical disc by a signal obtained by normalizing the difference signal with a sum signal,
A means for measuring the level of the sum signal a plurality of times, and means for changing the timing for measuring the level of the sum signal,
A focus servo circuit characterized in that the level of the sum signal is not measured when the header portion is detected.