JPH0528525A - Track positional deviation signal generator for optical disk device and tracking controller - Google Patents

Abstract

PURPOSE:To improve the stability of the track follow-up control of an light beam by enlarging a range capable of detecting almost linearly a track positional deviation in an optical disk device. CONSTITUTION:A corrective track error signal is generated by an inversion circuit 32, a sample holding circuit 33 and an adder 35 based on a track error signal, the sum signal of a light quantity received with a track error detector 15 is compared with a reference level by a level comparator circuit 34, a fact that the positional deviation exceeds a fixed value is detected, when the positional deviation is large, the tracking control of the light beam is performed by the corrective track error signal. The track positional follow-up operation of the light beam is stabilized.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION The present invention relates to optical recording of information,
BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical disk device for reproduction, and more particularly to a tracking servo control device for making its light beam follow an information track accurately.

[0002]

2. Description of the Related Art In an optical disc device for focusing and irradiating a recording surface with a laser beam to optically record and reproduce information, a light beam is aligned with an extremely narrow information track, and It is required to keep the beam position at the track center following the fluctuation. Therefore, tracking control is performed to optically detect a position deviation (track error) of the light beam with respect to the information track, and to move the objective lens for beam focusing or the mirror for beam deflection in the lateral direction of the track so as to correct the deviation. Be seen.

The detection of the track error signal generally utilizes the fact that the intensity distribution of the reflected light of the light beam irradiated by a minute guide groove formed on the recording surface of the record carrier (disk) changes, and the track lateral signal changes. The reflected light is received by a photodetector divided into two in the direction, and the difference between the outputs of the divided elements of the photodetector is calculated. For this reason, the track error signal is a sinusoidal signal having a period of one track crossing, and the range in which the positional deviation with respect to the track center is relatively accurate is at most ± 1/4 of the track interval. The nature of such a track error signal is essentially the same using other error detection methods.

[0004]

In a conventional tracking control device which controls the position of a light beam by directly inputting such a track error signal as an error signal, it is appropriate that the deviation of the light beam from the information track center becomes large. There is a problem that the track following control operation cannot be performed. That is, as described above, it is possible to expect a roughly proportional relationship (linearity) between the position deviation of the light beam and the value of the track error signal, as described above, within the range of ± 1/4 track interval, and the position deviation exceeding that occurs. Then, the restoring force to return to the central position becomes rather weak. Further, when the positional deviation becomes larger, a force for moving the light beam rather acts on the center of the adjacent track. Therefore, if the position of the light beam is displaced due to a defect of the record carrier (disk) or disturbance, tracking is easily lost (error that the light beam moves from a predetermined track).
There was a problem of causing. Also, during track access to move the light beam to a different track, if the light beam enters the target track while the speed of the light beam is high, the light beam will not be emitted even if the tracking control operation is performed to stop the light beam on the track. The amount of overshooting the center of the track (position overshoot) becomes too large,
The light beam could not be stopped on the desired track, and the light beam (or the optical head) sometimes caused runaway.

Due to such a problem, in the conventional tracking control device of the optical disk device, it is necessary to avoid the state where the positional deviation of the light beam from the track center is excessive, which causes a disturbance. There has been an excessive demand for suppressing the vibration shock of the device and reducing the defects of the record carrier. Further, when the light beam is moved between tracks, it is required to strictly control the speed, which complicates the speed control for track access.

In order to solve these problems, it suffices that a signal indicating the positional deviation relatively accurately can be obtained even if the positional deviation of the light beam with respect to the track center becomes large, but there has been no suitable method in the past. It was

An object of the present invention is to provide a track position deviation signal generating device and a tracking control device for an optical disk device, which solves the above problems.

[0008]

SUMMARY OF THE INVENTION The present invention is directed to illuminating an information track on a record carrier with a focused light beam,
In a track position deviation signal generating device of an optical disk device for recording and reproducing information, an optical head equipped with a photodetector for detecting a position deviation of a light beam with respect to an information track, and information of the light beam from an output of the photodetector. A means for generating a track error signal indicating a positional deviation with respect to a track, a means for generating a signal indicating a total light amount received by the photodetector, and a signal indicating the total light reception amount are compared with a predetermined reference level. , Means for detecting that the light beam deviates from the center of the information track by a certain value or more,
When it is detected that the light beam deviates from the information track by the predetermined value or more, a means for generating a track error signal corrected based on the track error signal, and the track error signal and the corrected track error signal A track error signal is input, and normally, the track error signal is selected and output as a track position deviation signal, and when it is detected that the light beam deviates from the information track by the predetermined value or more, And a means for selecting the corrected track error signal and outputting it as a track position deviation signal.

Further, the tracking control device of the present invention comprises the track position deviation signal generating device and means for driving the position of the light beam in the lateral direction of the track, and the track output from the track position deviation signal generating device. The means for driving the position of the light beam in the lateral direction of the track by the position shift signal is controlled so as to keep the position of the light beam at the center of the track.

[0010]

Embodiments of the present invention will now be described with reference to the drawings.

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

FIG. 2 is a signal waveform diagram for explaining the operation of the embodiment shown in FIG.

A semiconductor laser 1 arranged in an optical head 2.
0 is supplied with a current from the laser drive circuit 20 and emits a laser beam. The divergent laser light emitted from the semiconductor laser 10 is converted into parallel light by the collimator lens 11, passes through the beam splitter 12, and enters the objective lens 13.

The objective lens 13 focuses the light flux and forms a minute light spot on the recording surface of the record carrier 1. Track position information is formed on the recording surface of the record carrier 1 in an optically detectable form, and the record information is recorded and reproduced along this track. The objective lens 13 is attached to the track actuator 14 and can move laterally with respect to the information track.

The light reflected from the record carrier 1 passes through the objective lens 13 again and enters the beam splitter 12.
The beam splitter 12 is composed of a half mirror or a polarization beam splitter, and bends the optical path so that a part of the reflected light is incident on the track error detector 15.

The light whose optical path is bent by the beam splitter 12 remains substantially parallel light, and the track error detector 15
Incident on and project a far-field image of the reflected light. The track error detector 15 is a photodetector (photodetector) divided into at least two parts so that the incident reflected-light far-field image is divided in the lateral direction of the track and received.
The position deviation (track error) of the light beam with respect to the track is detected by the so-called push method. That is, the differential amplifier 30 obtains and amplifies the difference between the outputs of the divided elements of the track error detector 15 to obtain a signal (track error signal 101) corresponding to the track position deviation.

FIG. 2A shows the change of the track error signal 101 with respect to the positional deviation of the light beam. The signal shows a substantially sinusoidal change with respect to the position shift of the light beam with respect to the track center P, and the signal shows the same change at the center Q of the adjacent track as at the track center P. Positive and negative peak values are taken at points L ₁ and L ₂ , respectively, which are separated from each other by about 1/4 track from the track center, and when the positional deviation becomes larger than that, the signal level decreases in accordance with the increase in the positional deviation. , The proportional relationship with respect to the positional deviation is no longer maintained. For this reason, in the past, the allowable value of the positional deviation in the tracking control loop was approximately ±
It was limited to within 1/4 track interval.

On the other hand, by summing the outputs of the respective elements of the track error detector 15, a signal indicating the total amount of light received by the track error detector can be obtained. Minute grooves are formed on the recording surface of the record carrier 1 in a substantially concentric circle or spiral shape, which gives track position information, but at the same time changes the amount of reflected light 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 when the light beam is at an intermediate position from the center of the adjacent track. Therefore, the sum of the outputs of the respective elements of the track error detector 15 that receives the reflected light is a value (maximum value) when the light beam exists at the center of the track and a light beam exists between the tracks. It is possible to judge whether or not the light beam position is largely displaced from the track center (close to the middle position between the tracks) by comparing it with a value substantially in the middle of the value (minimum value).

The summing amplifier 31 sums and amplifies the outputs of the respective divided elements of the photodetector 15, and amplifies the sum to output a sum light amount signal 102 indicating the total amount of light received by the track error detector 15.

FIG. 2B shows changes in the light quantity sum signal 102. The amount of reflected light is large near the track center P, and the light amount sum signal 102 has a maximum value, and has a minimum value at an intermediate position Z between the track center P and the adjacent track center Q.

The level comparison circuit 34 uses the light quantity sum signal 10
2 is compared with the reference level E _R set to a value approximately midway between the maximum value and the minimum value as described above, and it is determined whether or not the light beam is separated from the track center by approximately ¼ of the track interval, The switching signal 103 is output. FIG. 2C shows the waveform of this switching signal.

The sample and hold circuit 33 receives the track error signal 101, and when the switching signal 103 is at a high level, for example, indicating that the light beam is near the center of the track, the track and error signal is passed through as it is. When the signal 103 changes from the high level to the low level and it is shown that the light beam deviates from the track center by about ¼ track interval or more, the change of the track error signal 101 immediately before the switching signal 103 changes to the low level. Hold the value.

FIG. 2D shows a sample hold circuit 33.
The change of the output signal of is shown. When the light beam is within the range of about ¼ track interval from the track center P, the same signal as the track error signal 101 is output. When the positional deviation of the light beam becomes large and the switching signal 103 becomes low level, the value of the track error signal 101 immediately before it becomes low level is sampled and held. This level is maintained until the switching signal 103 becomes the high level again next time, that is, until the original track center of the light beam approaches the center of the adjacent track.

The output of the sample hold circuit 33 is
The signal is amplified twice by the amplifier 40 and input to the adder 35. The adder 35 adds the track error signal whose polarity is inverted by the inverting circuit 32 and the signal obtained by doubling the output of the sample hold circuit 40 to generate a corrected track error signal 104. This correction track error signal 1
Reference numeral 04 is a signal that shows a change substantially proportional to the positional deviation of the light beam even when the track positional deviation of the light beam exceeds 1/4 of the track interval and the track error signal 101 does not accurately indicate the positional deviation. Becomes

FIG. 2E shows changes in the output signal of the inverting circuit 32. This is the track error signal 1 shown in FIG.
The signal has the polarity of 01 inverted.

The selector 36 selects either the track error signal 101 or the corrected track error signal 104 according to the state of the switching signal 103, and inputs it to the servo loop filter 37 as an enlarged track error signal 105.

FIG. 2F shows an enlarged track error signal 10
5 changes are shown. The change shown by the dotted line in the figure shows the change in the original track error signal 101.

Output of the sample hold circuit 33 (see FIG. 2)
(D)) and the output of the inverting circuit (FIG. 2 (E)) are added, the change in the linear region of the track error signal is approximately extrapolated when the positional deviation of the light beam exceeds about 1/4 track interval. A corrected track error signal 104 is obtained.
When the switching signal 103 (FIG. 2 (C)) becomes low level, the corrected track error signal 104 is output instead of the track error signal 101, so that the positional deviation of the light beam is almost equal to the track interval. ± 3
In the range up to / 4, the enlarged track error signal 105 is obtained in which the linearity with respect to the positional deviation is almost ensured. That is,
If the switching signal is high, indicating that the light beam is near the center of the track, the track error signal 101
Is selected, the switching signal is at a low level, and the light beam position is a fixed distance from the track center (about 1/4 of the track interval).
, The corrected track error signal 104 is selected. The expanded track error signal 105 output from the selector 36 indicates the track position deviation approximately accurately until the track position deviation of the light beam becomes large and approaches the center of the adjacent track. When the position of the light beam approaches the adjacent track, the light amount sum signal 102 becomes large, and the switching signal 103 becomes high level again, the selector 36 switches so as to select the track error signal 101. At this time, the expanded track error signal 105 can no longer show the displacement of the light beam with respect to the original track center, but shows the displacement of the light beam with respect to the adjacent track center. However, such a state is reached when the position of the light beam is about 1 / the track interval with respect to the adjacent track center.
4 and the positional deviation from the original track center is within about 3/4 track interval, the enlarged track error signal 105 changes substantially in proportion to the track positional deviation.

The servo loop filter 37 is the selector 3
In response to the enlarged track error signal 105 output from the control unit 6, the gain adjustment and the phase compensation are performed. Power amplifier 38
Receives and amplifies the output of the servo loop filter 37, and supplies the track actuator 14 with power for moving the objective lens 13.

When the objective lens 13 is moved by the track actuator 14, the position of the light beam applied to the record carrier 1 moves, and tracking control is performed to follow (hold) the light beam position with respect to the center of the information track. Be seen.

As described above, the expanded track error signal 1
In No. 05, since the linearity (proportional relationship) is maintained even if the position deviation of the light beam with respect to the track center becomes large, good restoration control is performed even if the light beam is greatly deviated from the track center due to disturbance, speed abnormality, or the like. A stable tracking follow-up operation is realized.

[0032]

As described above, according to the present invention, the total received light amount of the track error detector is compared with the reference level to detect that the light beam deviates from the track center by a certain value or more, and the position of the light beam is detected. When the deviation becomes large, a corrected track error signal is generated based on the track error signal instead of the track error signal, and it is used as an expanded track error signal for tracking control. Even if the deviation becomes large, the control for returning the light beam position to the original track center is faithfully performed, and stable tracking of the light beam track does not occur even if disturbance or disturbance of the tracking operation occurs. There is an effect that can be realized. Further, when the light beam moves between tracks, there is an effect that the light beam can be stably stopped on the target track even if the position of the light beam causes an over short circuit.

[Brief description of drawings]

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

FIG. 2 is a diagram showing signal changes for explaining the operation of the embodiment of FIG.

[Explanation of symbols]

1 record carrier 2 optical head 10 Semiconductor laser 11 Collimating lens 12 Beam splitter 13 Objective lens 14-track actuator 15 Track error detector 20 Laser drive circuit 30 differential amplifier 31 Addition amplifier 32 inversion circuit 33 Sample and hold circuit 34 level comparison circuit 35 adder 36 Selector 37 Servo loop filter 38 Power Amplifier

Claims (2)

[Claims] 1. A track position deviation signal generating device for an optical disk apparatus for irradiating a focused light beam onto an information track on a record carrier to record and reproduce information, wherein the position deviation of the light beam with respect to the information track. And an optical head having a photodetector for detecting, a means for generating a track error signal indicating the positional deviation of the light beam with respect to the information track from the output of the photodetector, and the total amount of light received by the photodetector. Means for generating a signal, means for comparing the signal indicating the total received light amount with a predetermined reference level, and detecting that the light beam deviates from the center of the information track by a certain value or more, When it is detected that the deviation is more than the predetermined value, a corrected track error signal is generated based on the track error signal. Means, the track error signal and the corrected track error signal are input, and normally, the track error signal is selected and output as a track position deviation signal, and the light beam is equal to or more than the predetermined value with respect to the information track. And a unit for selecting the corrected track error signal and outputting the corrected track error signal as a track position deviation signal when the deviation is detected. 2. A track position deviation signal generating device according to claim 1, and means for driving the position of the light beam in the lateral direction of the track, and the track position deviation signal output from the track position deviation signal generating device. The tracking control device is characterized in that the means for driving the position of the light beam in the lateral direction of the track is controlled so as to keep the position of the light beam at the center of the track.