JP2010040068A - Optical disk apparatus and tracking control method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an optical disk apparatus and a tracking control method wherein information recorded on an optical disk is reproduced stably and information is stably recorded on the optical disk by precisely detecting a tracking off. <P>SOLUTION: A comparator of a tracking off detection circuit compares a TE signal with a first threshold, and outputs a low-to-high signal when the TE signal exceeds the first threshold. A counter counts the number of times when the TE signal is turned from low to high. A CPU compares the number of the times with a second threshold and determines the occurrence of the tracking off when the number of times is increased to be larger than the second threshold. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to an optical disk apparatus and a tracking control method for recording information on or reproducing information from an optical disk such as a CD system, DVD system, BD system, or HD DVD system.

  A plurality of types of recording density optical disks called CD (Compact Disc) standards and DVD (Digital Versatile Disk) standards are already widely used. In recent years, by recording information using laser light of a blue-violet wavelength, Furthermore, BD (Blu-ray Disc) standard and HD DVD (High Definition Digital Versatile Disk) standard optical disks, which are ultra-high density optical disks with higher recording density, have been put into practical use.

  Of DVD standard and HD DVD standard optical discs, optical discs other than the read-only ROM type, such as a write-once disc (-R) in which information can be written only once, and a rewritable disc in which information can be rewritten repeatedly ( In (-RW, -RAM), a recording track (guide groove) is formed on the information recording surface of the optical disc.

  The recording track is the one in which the center of the light spot of the laser beam used when recording information on the optical disk and reproducing information from the optical disk is the same, and the center of the light spot cannot trace the center of the recording track. Becomes off track, making it difficult to record and reproduce information.

  Against this background, the optical pickup supporting the objective lens that provides the light spot of the laser beam is sequentially moved in the radial direction of the optical disc so that the center of the light spot coincides with the center of the recording track by tracking control. Recording or reproduction of information is continued. For tracking control, a photodetector is used that is capable of detecting the component of the recording track included in the laser beam reflected by the recording surface of the optical disc.

  The output signal of the photodetector is processed to generate a tracking error signal and a tracking control signal, which are output to a tracking actuator and tracking control is performed so that the light spot always traces the objective lens on the recording track.

  If a large noise is mixed in the output signal of the photodetector due to scratches, dirt on the surface of the optical disk, or a defect in the optical disk, and the tracking error signal is disturbed, tracking may be lost from the target recording track. If the data is being recorded, the recorded data in the neighboring recording tracks may be destroyed, so that the off-tracking must be detected quickly.

Patent Document 1 proposes a method for accurately detecting tracking errors. In Patent Document 1, a tracking error signal output from an optical pickup is compared with two comparison values using two comparators, a period in which the tracking error signal is larger than a positive comparison value, a period smaller than a negative comparison value, and Measure the length of the period between the positive comparison value and the negative comparison value, and use this measurement result to determine whether the light spot has approached an adjacent track or whether the moving speed at that time is fast, etc. In addition, it is assumed that a tracking error is detected.
JP-A-8-30990

  In Patent Document 1, it is assumed that the tracking signal amplitude value exceeds the positive threshold value and the negative threshold value when detecting the tracking error, and the tracking error signal exceeds the positive threshold value or the negative threshold value. By measuring the time, the time once between the positive and negative thresholds, and the time exceeding the threshold of the opposite polarity to the first one, the position of the light spot and each state Detecting tracking out of speed.

  FIG. 6 is a diagram illustrating a case where the tracking error signal is shifted from the steady position. In the case where the tracking error signal as shown in FIG. 6 is shifted from the steady position, the threshold value S on the plus side and the threshold value −S on the minus side may not be reached. In such a case, it is not possible to detect a tracking error. FIG. 6 shows a state in which the level of the negative threshold −S cannot be detected because the tracking error signal is shifted in the positive direction.

  As a factor for shifting the tracking signal as shown in FIG. 6, there is a groove shape characteristic of the recording track of the optical disc. The tracking error signal may shift due to mismatch between the performance of the optical pickup of the optical disk apparatus and the groove shape characteristics of the recording track. In addition, when the objective lens of the optical pickup is shifted from the optical axis, the tracking error signal may shift due to the balance with the groove shape characteristics of the recording track. For this reason, it is desirable to accurately detect the tracking error even when the tracking error signal is shifted from the steady position.

  FIG. 7 is a diagram showing a residual deviation of a normal tracking servo. Although the tracking signal temporarily increases, the tracking servo is maintained without losing tracking, but in order to continue continuous recording or reproduction without interruption, such residual deviation In this state, even if the tracking signal exceeds the positive threshold value S, it is better not to detect that the tracking is out of tracking.

  The present invention has been made in view of the circumstances as described above, and an optical disc apparatus capable of accurately detecting tracking errors and stably reproducing information recorded on the optical disc and recording information on the optical disc. It is an object to provide a tracking control method.

  In order to achieve the above object, an optical disc apparatus of the present invention includes an optical pickup that irradiates an optical disc with laser light, receives reflected light from the optical disc and outputs a photoelectric conversion signal, and outputs a tracking error signal from the photoelectric conversion signal. Tracking error signal generating means for generating, comparing means for comparing the magnitude of the tracking error signal with a first threshold value and outputting a comparison result; and in the comparison result, the tracking error signal is greater than the first threshold value. Counting means for counting the number of times of increase, and control means for comparing the number of times with a second threshold value and determining that an out-of-tracking has occurred when the number of times is greater than the second threshold value. It is characterized by that.

  The tracking control method of the present invention includes an output step in which an optical pickup irradiates a laser beam on an optical disc, receives reflected light from the optical disc, and outputs a photoelectric conversion signal; and a tracking error signal generating means generates a photoelectric conversion signal from the photoelectric conversion signal. A generating step for generating a tracking error signal, a comparison result outputting step in which the comparison means compares the magnitude of the tracking error signal with a first threshold and outputs a comparison result, and a counting means in the tracking result among the tracking results A counting step for counting the number of times when the error signal becomes larger than the first threshold value, and the control means compares the number of times with the second threshold value, and tracking when the number of times becomes larger than the second threshold value. And a determination step for determining that a detachment has occurred.

  According to the present invention, it is possible to provide an optical disc apparatus and a tracking control method capable of accurately detecting a tracking error and stably reproducing information recorded on the optical disc and recording information on the optical disc.

  Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a block diagram showing an optical disc apparatus according to Embodiment 1 of the present invention. The optical disc 2 is a CD-type, DVD-type, BD-type, or HD DVD-type reproduction-only or recordable optical disc. For example, the DVD system includes a read-only DVD-Video, a DVD-ROM (Read Only Memory), a recordable DVD-R (Recordable) / RW (Rewritable) / RAM (Random Access Memory), and the like. The optical disk 2 is rotationally driven by a disk motor 3. The disk motor 3 is controlled by a disk motor control circuit 4.

  Information recording and reproduction with respect to the optical disc 2 are performed by the optical pickup 5. The optical pickup 5 is provided with an objective lens 6. The objective lens 6 can be moved in the focusing direction (the optical axis direction of the lens) by driving a focusing actuator 7, and tracking can be performed by driving a tracking actuator 8. It is possible to move in the direction (the direction perpendicular to the optical axis of the lens and the radial direction of the optical disk).

  The recording data generation circuit 9 adds an error correction code to the data supplied from the host device 25 via the interface circuit 24 at the time of information recording, adds a synchronization code, etc., changes to a recording format, further modulates, and modulates Provided data to the laser control circuit 10. The laser control circuit 10 supplies a writing signal to the laser diode 11 in the optical pickup 5 based on the data supplied from the recording data generation circuit 9 during information recording (mark formation).

  The laser diode 11 includes a CD laser diode 11a having a wavelength of about 780 nm (nano meter), a DVD laser diode 11b having a wavelength of about 650 nm, and an HD DVD laser diode 11c having a wavelength of about 405 nm. Depending on the type of optical disk mounted on the optical disk, the laser beam is selected and emitted according to the signal supplied from the laser control circuit 10.

  Laser light emitted from the laser diode 11 is irradiated onto the optical disc 2 through the optical unit 12 and the objective lens 6. The reflected light from the optical disk 2 of the laser light emitted from the laser diode 11 is guided to the photodetector 13 through the objective lens 6 and the optical unit 12. The photodetector 13 photoelectrically changes the received light and outputs a photoelectric conversion signal. The photoelectric conversion signal is supplied to the RF amplifier 14.

  The RF amplifier 14 processes the photoelectric conversion signal from the photodetector 13, a focus error signal (FE signal) indicating an error from the just focus, and a tracking error signal indicating an error between the laser beam spot center and the track center. (TE signal) and a reproduction signal (RF signal) are generated, and the generated FE signal, TE signal, and RF signal are supplied to the A / D converter 15. When the RF amplifier 14 processes the photoelectric conversion signal from the photodetector 13, the RF amplifier 14 sets the parameters for generating the signal according to the type of the laser diode 11 used to respective appropriate values and outputs the signal. Generate. A signal output from the A / D converter 15 is supplied to a CPU (Central Processing Unit) 21 and the like via the bus 20.

  The focus / tracking control circuit 16 generates a focus control signal and a tracking control signal in accordance with the FE signal and the TE signal supplied from the A / D converter 15, and outputs them to the focusing actuator 7 and the tracking actuator 8 to output the objective lens 6. Drive. Thereby, focusing control in which the laser beam is always just focused on the information recording surface of the optical disc 2 and tracking control in which the laser beam is always traced on the track formed on the optical disc 2 are performed.

  The RF signal is converted into a digital signal by the A / D converter 15 and supplied to the PLL circuit 17 as channel bit data. The PLL circuit 17 generates a clock synchronized with data from the data supplied from the A / D converter 15 and a channel data signal in channel bit units, and outputs the data to the data reproduction circuit 18. The data reproduction circuit 18 decodes the format, demodulates the channel data signal to reproduce the byte data, and the reproduced data is output to the error correction circuit 19. The error correction circuit 19 performs error correction using the error correction code to which the reproduction data is assigned, and then outputs the error correction code to the host device 25 via the interface circuit 24.

  The disk motor control circuit 4, modulation circuit 9, laser control circuit 10, A / D conversion circuit 15, focus / tracking control circuit 16, PLL circuit 17, data reproduction circuit 18, error correction circuit 19, etc. are connected via a bus 20. It is controlled by a CPU (Central Processing Unit) 21.

  The CPU 21 comprehensively controls the optical disc recording / reproducing apparatus 1 in accordance with an operation command supplied from the host apparatus 25 via the interface circuit 24. The CPU 21 uses a RAM (Random Access Memory) 22 as a work area such as a buffer memory at the time of recording and reproduction, and performs predetermined control according to a program stored in a ROM (Read Only Memory) 23.

  The off-tracking detection circuit 26 processes the tracking error signal (TE signal) output from the A / D converter 15 and supplies data serving as a basis for determining the off-track to the CPU that is the control unit. The out-of-tracking detection circuit 26 compares the magnitude of the TE signal with the first threshold value, outputs a comparison result, and the number of times when the TE signal is greater than the first threshold value in the comparison result. Counting means (counter). The output counted by the counter is supplied to the CPU 21 via the bus 20.

  FIG. 2 is a block diagram of the off-tracking detection circuit 26. FIG. 3 is a waveform diagram showing the operation of the off-tracking detection circuit 26. The off-tracking detection circuit 26 includes a filter 27, an absolute value circuit 28, a comparator 29, and a counter 30.

  The TE signal output from the A / D converter 15 is first sent to the filter 27. The filter 27 is a filter that extracts only frequency components in the vicinity of frequencies at which tracking error occurs with respect to the TE signal. Although the TE signal contains a high-frequency noise component, it is possible to improve the detection accuracy of the tracking error by extracting only the frequency component near the frequency where the tracking error occurs. For example, extraction is performed with the tracking servo band frequency as the center. FIG. 3A is a diagram illustrating a TE signal waveform after passing through the filter 27. The vertical axis represents the amplitude of the signal. The horizontal axis is time.

  The absolute value circuit 28 obtains a positive absolute value regardless of whether the input voltage is positive or negative. As shown in FIG. 3B, the negative portion of the tracking waveform is inverted, and the positive absolute value is the same. The waveform is as follows.

  The comparator 29 compares the magnitude of the TE signal with the first threshold value and outputs the comparison result. As shown in FIG. 3B, the comparator 29 compares the first threshold value with A, for example, with A. When the TE signal exceeds A, a signal that changes from L to H is output as shown in FIG. When the TE signal becomes A or less, it changes from H to L. When the TE signal again exceeds A, a signal that changes from L to H is output. This signal is supplied to the CPU 21 via the bus 20. The first threshold value is determined by the allowable value of the tracking control system of the optical disc apparatus 1.

  The counter 30 is a counting unit that counts the number of times when the TE signal becomes larger than the first threshold in the comparison result. FIG. 3 (d) shows counter values, which are counted up when the signal shown in FIG. 3 (c) changes from L to H.

  FIG. 4 is a waveform diagram showing the operation of the off-tracking detection circuit 26 when the TE signal is shifted in the plus direction. FIG. 4A is a diagram showing a TE signal waveform after passing through the filter 27. As shown in FIG. 4B, the output signal from the absolute value circuit 28 is a positive waveform in which the negative portion of the tracking waveform is inverted and the absolute value is the same.

  As shown in FIG. 4 (b), the output value of the comparator 29 is compared with A as the first threshold value, for example, A, and when the TE signal exceeds A, as shown in FIG. 4 (c). , A signal from L to H is output. When the TE signal becomes A or less, it changes from H to L. When the TE signal again exceeds A, a signal that changes from L to H is output. This signal is supplied to the CPU 21 via the bus 20. FIG. 4 (d) shows counter values, which are counted up when the signal shown in FIG. 4 (c) changes from L to H.

  FIG. 5 is a flowchart of control for detection of tracking loss. In S10, when reproduction or recording is started, the CPU 21 monitors whether the signal of the comparator 29 of the tracking error detection circuit 26 has changed from L to H. If the signal has changed from L to H, the process proceeds to S12.

  In S12, the CPU 21 sets the timer value of the timer 31 to 0 (zero). In S14, the counter 30 adds 1 to the counter value. The counter value of the counter 30 represents the number of times when the TE signal exceeds A.

  In S16, the CPU 21 compares the counter value with the second threshold value, and moves to S18 when the counter value becomes larger than the second threshold value. In S <b> 18, the CPU 21 determines that a tracking error has occurred, and ends the tracking error detection. Thereafter, the CPU 21 temporarily stops reproduction or recording and performs retry processing.

  The second threshold value can be arbitrarily selected, but when quick detection is necessary, for example, if it is 1, it is detected that the tracking value is off when the counter value becomes 2. When the second threshold value is set to 0 (zero), the counter value is detected as 1. Therefore, even in the case of a residual deviation as shown in FIG. You should do it.

  If it does not change from L to H in S10, it moves to S20. In S20, the CPU 21 determines whether the timer value of the timer 31 is greater than the third threshold value. If the timer value is larger than the third threshold value, the process proceeds to S22. In S22, the CPU 21 sets the counter value of the counter 30 to 0 (zero) and returns to S10.

  The third threshold value is time, and sets a threshold value from when L changes to H until the next appearance of L to H. If a signal that changes from L to H does not occur after a predetermined time, the counter value of the counter 30 is set to 0 (zero).

  If the timer value is not greater than the third threshold value in S20, the process returns to S10. This series of loops continues during the playback or recording operation.

  As described above, the comparator 29 compares the TE signal with the first threshold, outputs a signal that changes from L to H when the TE signal exceeds the first threshold, and the counter 30 changes from L to H. The number of cases is counted, and the CPU 21 compares the number of times with the second threshold value, and determines that the tracking error has occurred when the number of times becomes larger than the second threshold value.

  Further, the elapsed time is measured from when the TE signal exceeds the first threshold value by the timer 31, and the CPU 21 compares the elapsed time with the third threshold value, and the elapsed time is thirdly larger than the threshold value. At this time, the counter 30 is set to 0 (zero).

  By doing this, even when the TE signal is shifted, it is possible to detect the tracking error quickly and accurately, and reproduction of information recorded on the optical disc and recording of information on the optical disc. Can be performed stably. Further, in the case of the residual deviation shown in FIG. 7, it is not determined that the tracking is off, and unnecessary retry operation is not performed, so that the operation time can be shortened and a stable operation can be ensured.

  The present invention is not limited to the above configuration, and various modifications are possible.

1 is a block diagram showing an optical disc apparatus according to Embodiment 1 of the present invention. FIG. 3 is a block diagram of a tracking out detection circuit. The wave form diagram which shows the operation | movement of an off-tracking detection circuit. The wave form diagram which shows the operation | movement of a tracking off detection circuit when TE signal shifts. FIG. 5 is a flowchart of control for detection of tracking loss. The figure which shows the case where the tracking error signal has shifted from the steady position. The figure which shows the residual deviation of a tracking servo.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Optical disk apparatus 2 Optical disk 5 Optical pick-up 14 RF amplifier 15 A / D conversion circuit 21 CPU
26 Out-of-tracking detection circuit 27 Filter 28 Absolute value circuit 29 Comparator 30 Counter 31 Timer

Claims (6)

An optical pickup that irradiates an optical disc with laser light, receives reflected light from the optical disc, and outputs a photoelectric conversion signal;
Tracking error signal generating means for generating a tracking error signal from the photoelectric conversion signal;
Comparing means for comparing the magnitude of the tracking error signal with a first threshold and outputting a comparison result;
Counting means for counting the number of times when the tracking error signal is greater than the first threshold in the comparison result;
An optical disc apparatus comprising: a control unit that compares the number of times with a second threshold value and determines that a tracking error has occurred when the number of times exceeds the second threshold value. A time measuring means for measuring an elapsed time from when the tracking error signal becomes larger than the first threshold in the comparison result;
The control means compares the elapsed time with a third threshold value, and sets the number of times of the counting means to zero when the elapsed time exceeds the third threshold value. The optical disk device described.   3. The optical disc apparatus according to claim 1, further comprising a filter that extracts a frequency component near a frequency at which the tracking error occurs with respect to the tracking error signal. An output step in which the optical pickup irradiates the optical disc with laser light, receives the reflected light from the optical disc, and outputs a photoelectric conversion signal;
A generating step in which a tracking error signal generating means generates a tracking error signal from the photoelectric conversion signal;
A comparison result output step in which the comparison means compares the magnitude of the tracking error signal with a first threshold value and outputs a comparison result;
A counting step in which the counting means counts the number of times when the tracking error signal is larger than the first threshold in the comparison result;
A tracking control method, comprising: a determination step in which the control unit compares the number of times with a second threshold value, and determines that a tracking error has occurred when the number of times exceeds a second threshold value. A time measuring unit has a measuring step of measuring an elapsed time from when the tracking error signal is larger than the first threshold in the comparison result;
The control means includes a step of comparing the elapsed time with a third threshold value, and setting the number of times of the counting means to zero when the elapsed time exceeds the third threshold value. The tracking control method according to claim 4.   6. The tracking control method according to claim 4, further comprising a step of extracting a frequency component in the vicinity of a frequency at which the tracking error occurs with respect to the tracking error signal.

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