JPH0562217A - Tracking controller - Google Patents

Abstract

PURPOSE:To reduce the speed of the movement of a light beam even when the following operation of the light beam to a track is deviated and to stop the movement on other track by the movement within a few tracks. CONSTITUTION:Based on the detected result of a tracking error detector 12, an enlarged positional error signal 103 changing in saw-tooth-wave shape over roughly one period of a tracking error signal 101 to the positional deviation to the track is outputted by a differential amplifier 21, an addition amplifier 22, a level comparator circuit 33, a sample-hold circuit 32, an amplifier 34, an inversion circuit 31 and an adder 35. By a lead lag filter 40, phase the enlarged positional error signal 103 is compensated and an output signal 104 is outputted and by an amplitude limitter 41, the amplitude of the output signal 104 is limitted and a tracking control signal 105 is outputted.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention is used in a tracking control device of an optical disk device for optically recording and reproducing information. In particular, the present invention relates to a tracking control device that causes a light beam of an optical disk device to accurately follow an information track.

[0002]

2. Description of the Related Art In an optical disk device that focuses laser light and irradiates it on a recording surface to optically record and reproduce information, a light beam is aligned with an extremely narrow information track, and track position fluctuations occur. It is necessary to follow the beam position with respect to and keep it at the center of the track.

For this reason, a positional deviation of the light beam with respect to the information track (hereinafter referred to as a tracking error) is technologically detected, and the object lens for beam focusing or the beam deflection is used so as to correct the deviation. Tracking control is performed to move the movable mirror in the track lateral direction (tracking direction).

Conventionally, a tracking controller detects a tracking error by changing the intensity distribution of reflected light of a light beam emitted by a minute guide groove (groove) formed on a recording surface of a record carrier (disk). Taking advantage of the occurrence, the reflected light is received by the photodetector divided into two in the track lateral direction, and the difference between the outputs of the respective divided elements of the photodetector is taken. For this reason, the tracking error signal becomes a substantially sinusoidal signal with one cycle crossing one cycle, and the range in which the positional deviation of the light beam with respect to the track center is relatively accurately shown is at most "± 1 /" of the track interval.
It was in the range of "4".

Therefore, if the positional deviation of the light beam exceeds “± 1/4” of one track interval due to external impact, vibration of the disk, excessive distortion of the information track, etc., tracking is easily lost. However, there is a risk that so-called runaway may occur in which the light beam moves in the lateral direction of the track. Once the tracking is off, the tracking error signal is sinusoidal, so a control signal is generated at a position off the center of the track to accelerate the deviation of the light beam. May cause serious damage. In order to avoid such danger, conventional tracking control detects that the tracking error signal exceeds a certain level,
A method has been used in which it is determined that tracking is out of order, the tracking control operation is once stopped (off) to prevent runaway of the light beam, the optical head is returned to a predetermined position, and the track pull-in operation is performed again.

As a prior art, Japanese Patent Laid-Open No. 63-2638
There are techniques disclosed in Japanese Patent Publication No. 27, Japanese Patent Application Laid-Open No. 63-291223 and Japanese Patent Application No. 1-1139239.

[0007]

However, in such a conventional tracking control apparatus, it is necessary to detect the tracking deviation very sensitively, and the light beam (optical head) is detected at the time when the deviation is detected. Since it is completely unknown whether it is in the position or not, there is a problem that the recovery work for carrying out the tracking pull-in again is complicated and takes a lot of time.

Further, even if the tracking shift is detected and the tracking control operation is stopped, the movement of the light beam (optical head) is not stopped and the runaway cannot be completely prevented.

Due to the above-mentioned problems, in the conventional optical disk device, it is necessary to avoid a state in which the positional deviation of the light beam from the track center is excessively large. Therefore, the vibration of the device causing a disturbance, It has been excessively necessary to suppress the impact and reduce the distortion (defect) of the track guide groove of the record carrier (disk).

The present invention solves the above problems,
Even if the tracking operation of the light beam for the track is off, the movement of the light beam can be quickly decelerated and stopped on another track within a few tracks of movement, so the light beam does not run away and stable tracking operation It is an object of the present invention to provide a tracking control device capable of performing the following.

[0011]

SUMMARY OF THE INVENTION The present invention is a recording / reproducing means for irradiating a focused light beam onto an information track on a record carrier to optically record and reproduce information, and a reflected light of this light beam. In the tracking control device provided with an optical head including a detection means for detecting the positional deviation by generating a periodic tracking error signal corresponding to the positional deviation with respect to the information track by detecting the tracking error signal, Generating means for generating a position error signal that changes in a saw-tooth wave shape over approximately one cycle of the tracking error signal with respect to a position shift of the light beam with respect to the information track, and a phase with respect to the position error signal. The lead-lag filter for compensation and the output of this lead-lag filter exceed the specified positive and negative values. Oddly a limiter for limiting the amplitude, the optical head is characterized in that it comprises a driving means for moving the light beam based on the output of the limiter in the tracking direction.

According to the present invention, the detection means includes two photodetection elements that receive the reflected light by dividing the reflected light into two in the lateral direction of the information track, and the generation means includes the two photodetection elements. A differential amplifier that takes the difference between the detection lights and amplifies and outputs the tracking error signal; an addition amplifier that takes the sum of the detection lights of the two photodetecting elements and amplifies and outputs a light quantity sum signal; and this addition amplifier. Level comparison circuit for comparing the output of the differential amplifier with a predetermined reference level and outputting a switching signal, and holding the output tracking error signal of the differential amplifier when the level of the switching signal switches between the high level and the low level by passing the output tracking error signal as it is. A sample and hold circuit, an amplifier that amplifies the output of the sample and hold circuit by a factor of two, and the polarity of the output tracking error signal of the differential amplifier is reversed. An inverting circuit for, may include an adder for adding the output of the inverting circuit and the amplifier.

[0013]

The generating means generates a position error signal which changes in a sawtooth waveform over approximately one period of the tracking error signal with respect to the positional deviation of the light beam with respect to the information track based on the detection result of the detecting means. The lead-lag filter performs phase compensation on the position error signal. The limiter limits the amplitude so that the output of the lead-lag filter does not exceed the specified positive and negative values. The optical head moves the light beam in the tracking direction based on the output of the limiter by the driving means.

As described above, even if the tracking operation of the light beam with respect to the track is deviated, the movement of the light beam can be quickly decelerated, and the light beam can be stopped on another track within a few tracks, and the light beam can run away. Without this, stable tracking operation can be performed.

[0015]

Embodiments of the present invention will be described with reference to the drawings. FIG. 1 is a block diagram of a tracking control device according to an embodiment of the present invention.

In FIG. 1, the tracking controller is
Recording / reproducing means for irradiating a focused light beam onto an information track on the record carrier 1 to optically record and reproduce information, and a periodical corresponding to a positional deviation with respect to this information track by reflected light of this light beam. An optical head 2 including a tracking error detector 12 is provided as a detection means for detecting a positional error by generating a different tracking error signal and detecting the tracking error signal.

The feature of the present invention is that the tracking error signal changes in a sawtooth waveform over almost one cycle with respect to the positional deviation of the light beam with respect to the information track based on the detection result of the tracking error detector 12. The output signal 104 of the lead-lag filter 40 and the lead-lag filter 40 that performs phase compensation on the enlarged-position error signal 103 and outputs the output signal 104 are generated by the generating unit that generates the enlarged-position error signal 103 as the position-error signal. An amplitude limiter 41 for outputting the tracking control signal 105 and a power amplifier 42 are provided as limiter means for limiting the amplitude so as not to exceed the positive and negative specified values, and the optical head 2 outputs a light beam based on the output of the power amplifier 42. It is to include drive means for moving in the tracking direction.

Further, the tracking error detector 12 includes two photodetection elements which receive the reflected light by dividing the reflected light into two in the lateral direction of the information track, and the generation means includes the detection light of the two photodetection elements. A differential amplifier 21 that outputs the tracking error signal 101 by amplifying the difference between the two, a summing amplifier 22 that sums and amplifies the detection light of the two photodetection elements, and outputs a light quantity sum signal 102; Two
The switching signal 11 is compared by comparing the output of 2 with a predetermined reference level.
A level comparison circuit 33 that outputs 0, and a sample hold circuit 32 that passes the output tracking error signal 101 of the differential amplifier 21 as it is and holds it when the level of the switching signal 110 switches between a high level and a low level.
An amplifier 34 that amplifies the output of the sample hold circuit 32 by a factor of 2, an inverting circuit 31 that inverts the polarity of the output tracking error signal 101 of the differential amplifier 21, and an output of the inverting circuit 31 and the amplifier 34. And an adder 35.

The operation of the tracking control device having such a configuration will be described. FIG. 2 is a diagram showing signal changes for explaining the operation of the tracking control device of the present invention. 2A shows a tracking error signal, FIG. 2B shows a light amount sum signal, FIG. 2C shows an enlarged position error signal, and FIG. 2D shows a tracking control signal.

In FIG. 1, an optical head 2 is a record carrier 1
An optical system that irradiates a focused laser beam to record and reproduce information and detects a focus shift signal and a tracking shift signal (tracking error signal) from reflected light is provided.

In order to realize these functions, the optical head 2
Although a complicated optical system is configured in the inside of the above, there are many publicly known examples of these and the description thereof will be omitted.

The tracking error detector 12 arranged in the optical head 2 is a photodetector element (photodetector) divided into at least two so that the reflected light from the record carrier 1 is divided and received in the lateral direction of the track. It is configured and outputs a signal indicating a positional deviation (tracking error) of a light beam with respect to a track by a so-called push-pull method.
The differential amplifier 21 receives the respective outputs of the divided photodetection elements of the tracking error detector 12, detects the difference between them, and outputs the tracking error signal 101.

On the other hand, if the sum of the outputs of the respective photodetection elements of the tracking error detector 12 is taken, a signal indicating the total amount of light received by the tracking error detector 12 (that is, corresponding to the amount of reflected light from the record carrier) is obtained. can get. A minute groove is formed on the recording surface of the record carrier 1 and provides track position information, but at the same time, changes the reflected light amount according to the position of the light beam with respect to the track. For example, the amount of reflected light is large when the light beam is near the center of the track, and the amount of reflected light is small at a position near the middle of the adjacent track. Therefore, by monitoring the level change of the total amount of light received by the tracking error detector 12, it is possible to determine whether the light beam is near the center of the track or between the tracks.

The summing amplifier 22 sums and amplifies the outputs of the respective elements of the tracking error photodetector 12 and amplifies the sum to output the sum signal 1 of light quantity corresponding to the quantity of reflected light from the record carrier 1.
02 is output. The level comparison circuit 33 uses the light intensity sum signal 1
02 is compared with a reference level that is set to a value approximately halfway between the maximum value and the minimum value, and a switching signal 110 indicating whether or not the light beam is away from the track center by a certain distance or more is output. The sample and hold circuit 32 receives the tracking error signal 101 and passes the tracking error signal 101 as it is when the switching signal 110 is at a high level and it is shown that the light beam is near the center of the track, but the switching signal 110 is at a high level. When it is shown that the light beam is deviated from the track center by a certain distance or more, the value of the tracking error signal 101 immediately before the switching signal 110 is changed to the low level is held.

On the other hand, the inverting circuit 31 receives the tracking error signal 101, inverts its polarity and outputs it. The amplifier 34 doubles the output of the sample hold circuit 32, and the adder 35 adds the output of the amplifier 34 and the output of the inverting circuit 31 and outputs the result as an enlarged position error signal 103.

The process of generating the enlarged position error signal 103 will be described in more detail with reference to the signal waveforms shown in FIG.

FIG. 2A shows a tracking error signal 101.
3 shows a change with respect to the positional deviation (X) of the light beam. As described above, the tracking error signal 101 changes in a substantially sinusoidal manner with the track interval as a cycle. FIG. 2B shows a change of the light intensity sum signal 102 with respect to the positional deviation of the light beam. FIG. 2B shows a change of the light intensity sum signal 102 with respect to the positional deviation of the light beam. As described above, the amount of light reflected is large near the track center position (P ₁ , P ₂ , P ₃ , P ₄ ) and the light amount sum signal 102 takes the maximum value, and is between the tracks (for example, between P ₁ and P _2). ) Is almost maximum. Therefore, by comparing the light level sum signal 102 with the reference level E _{R that} is approximately between the maximum value and the minimum value, it is possible to determine whether or not the light beam position deviates from the track center by approximately ¼ or more of the track interval. When the switching signal 110 is at a high level, indicating that the light beam is near the center of the track, the sample hold circuit 32 allows the tracking error signal 101 to pass through.

Therefore, the enlarged position error signal 103 obtained by adding the signal obtained by doubling the output of the sample hold circuit 32 (the same as the tracking error signal 101) and the signal obtained by inverting the polarity of the tracking error signal 101 is the switching signal 11
While 0 is high level, it is the same as the tracking error signal 101. On the other hand, the switching signal 110 is switched to the low level, and the light beam moves from the track center to 1 / of the track interval.
When it is shown that the deviation is 4 or more, the sample hold circuit 32 holds the value of the tracking error signal 101 at the moment when the switching signal 110 is switched to the low level. The held value is close to the positive or negative peak value of the tracking error signal 101.

Whether the held value becomes positive or negative depends on the moving direction of the light beam. While the switching signal 110 is at the low level, the peak value of the positive (or negative) tracking error signal 101 thus held is set to 2
Since the doubled signal and the signal obtained by inverting the polarity of the tracking error signal 101 are added by the adder 35, the expanded position error signal 103 is tracked by the positional deviation of the light beam as shown by the solid line in FIG. It continues to increase (or decrease) even if it exceeds 1/4 of the interval, and shows a substantially sawtooth-like change with respect to the displacement of the light beam with respect to the track position. Figure 2
The waveform indicated by the broken line in (C) represents the change in the original tracking error signal 101 for comparison.

The expanded position error signal 103, which shows a substantially sawtooth-like change with respect to the positional deviation of the light beam generated as described above, is input to the lead-lag filter 40. The lead-lag filter 40 is a filter for compensating the phase lead of the tracking control loop, and has a characteristic in which proportional amplification and differential amplification are combined. When the light beam is near the track center, the lead-lag filter 40 performs phase compensation and generates a control signal for keeping the light beam at the track center. When the light beam loses tracking due to disturbance or the like, and the light beam moves in one direction, the expanded phase error signal 103 changes in a sawtooth wave shape, so that the output of the lead-lag filter 40 is a component obtained by proportionally amplifying this. And the differentially amplified component are combined.

Where the expanded position error signal 103 changes with a gentle slope (slope portion), the output of the lead lag filter 40 becomes a control signal for returning the light beam to the track center position. Where the signal 103 suddenly changes from positive to negative, the output of the lead lag filter 40 becomes a large level in the direction of removing the light beam from the track due to the differential effect. Therefore, when the light beam moves in one direction in this way, the output of the lead-lag filter 40 becomes almost "0" level on average, and there is no effect of stopping the light beam on the track.

However, although the output of the lead-lag filter 40 at the point where the enlarged position error signal 103 suddenly changes from positive to negative (or from negative to positive) is at an extremely large level, the period during which the level is output is extremely large. It's a short time. Therefore, if a limiter is attached so as to limit the amplitude of the output of the lead-lag filter 40, the output of the lead-lag filter when the enlarged position error signal 103 changes abruptly is suppressed, and the control for removing the light beam from the track is performed. The signal component becomes smaller.

An amplitude limiter 41 arranged after the lead-lag filter 40 limits the amplitude of the output signal 104 of the lead-lag filter 40, and the output signal 104 at the slope portion where the enlarged position error signal 103 changes gently. Is passed through as it is, but acts to limit the amplitude for the output of the lead-lag filter where the enlarged position error signal 103 changes abruptly. This amplitude limiter 41
The output tracking control signal 105 has a greater effect of pulling the light beam back on the track even if the light beam moves in one direction, and the movement of the light beam is suppressed.

Tracking control signal 1 shown in FIG.
Further description will be made with reference to the waveform of 05. The output signal 104 of the lead-lag filter 40 is in the negative direction (in the case where the moving direction of the light beam is opposite) where the enlarged position error signal 103 (FIG. 2C) changes rapidly as shown by the broken line in FIG. 2D. Becomes a positive direction), and the signal level becomes large. This acts so as to cancel the signal component that tends to pull back and stop the light beam output from the lead lag filter 40 on the track at the slope portion of the expanded position error signal 103.

However, the amplitude of the tracking control signal 105 is limited by the amplitude limiter, and the level in the negative direction is suppressed so as not to become excessive as shown by the solid line in FIG. For this reason, the average level of the tracking control signal 105 becomes close to the output level of the lead lag filter 40 generated in the slope portion of the enlarged position error signal 103, and the movement of the light beam out of the track is suppressed and the light beam on the track is suppressed. Has the effect of stopping.

In this embodiment, the lead-lag filter 40 and the amplitude limiter 41 are separate components, but they may be integrated and the lead-lag filter 40 itself may have the amplitude limiting function. The tracking control signal 105 output from the amplitude limiter 41 is input to the power amplifier 42, and the power amplifier 42 amplifies it and supplies the track actuator 11 with a current for driving the light beam in the lateral direction of the track (tracking direction). With this loop configuration, tracking control is performed in which the light beam is kept on the desired track center so as to follow the track position variation, and the light beam is quickly and stably stopped on the track even if the tracking is deviated.

[0037]

As described above, according to the present invention, the movement of the light beam is promptly decelerated and the movement of the light beam is stopped on another track within a few tracks even if the tracking operation of the light beam deviates. In addition, there is an excellent effect that a stable tracking operation can be performed without causing the light beam to run away.

[Brief description of drawings]

FIG. 1 is a block configuration diagram of a tracking control device according to an embodiment of the present invention.

FIG. 2 is a diagram showing signal changes for explaining the operation of the tracking control device of the present invention.

[Explanation of symbols]

 1 record carrier 2 optical head 11 track actuator 12 tracking error detector 21 differential amplifier 22 summing amplifier 31 inversion circuit 32 sample hold circuit 33 level comparison circuit 34 amplifier 35 adder 40 lead-lag filter 41 amplitude limiter 42 power amplifier 101 tracking error Signal 102 Light intensity sum signal 103 Enlarged position error signal 104 Output signal 105 Tracking control signal 110 Switching signal

Claims (2)

[Claims] 1. A recording / reproducing means for irradiating a focused light beam onto an information track on a record carrier to optically record and reproduce information, and a position deviation with respect to the information track by reflected light of the light beam. In a tracking control device provided with an optical head including a detecting means for detecting a positional deviation by generating a corresponding periodic tracking error signal and detecting the tracking error signal, Generating means for generating a position error signal that changes in a sawtooth wave shape over substantially one cycle of the tracking error signal with respect to a position shift with respect to the information track; and a lead lag filter for performing phase compensation on the position error signal. Limit the amplitude so that the output of this lead-lag filter does not exceed the specified positive and negative values. And a limiter, the optical head tracking control apparatus comprising a drive means for moving the light beam based on the output of the limiter in the tracking direction. 2. The detecting means includes two photodetecting elements that receive the reflected light by dividing the reflected light into two in the lateral direction of the information track, and the generating means includes a difference between the detected lights of the two photodetecting elements. A differential amplifier that amplifies and outputs the tracking error signal; a summing amplifier that sums and amplifies the detection light of the two photodetector elements and outputs a light quantity sum signal; And a sample and hold circuit for passing the output tracking error signal of the differential amplifier as it is and holding it when the level of the switching signal switches between a high level and a low level. And an amplifier for doubling the output of the sample and hold circuit, and an inverting circuit for inverting the polarity of the output tracking error signal of the differential amplifier. The tracking control device according to claim 1, further comprising: an adder that adds outputs of the inverting circuit and the amplifier.