JP2007035086A - Optical disk drive - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an optical disk drive capable of preventing tracking servo pull-in from being performed at erroneous timing and erroneous trace (track running state). <P>SOLUTION: The optical disk drive is provided with an abnormality detection circuit 23 for detecting an abnormal state of a tracking error signal TE, inhibits a tracking servo pull-in operation so as not to make a tracking control means operate when the abnormality detection circuit 23 detects an abnormal state of the tracking error signal TE, and stops a tracking servo when the abnormality detection circuit 23 detects an abnormal state of the tracking error signal TE while performing a tracking servo pull-in operation and when the abnormality detection circuit 23 detects an abnormal state of the tracking error signal TE after the completion of the tracking servo pull-in operation. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to an optical disc device (optical disc recording device, optical disc playback device, or optical disc recording / playback device). An optical disk refers to a storage medium that uses a light beam for reading or writing information, and a magneto-optical disk or the like is also included in the optical disk.

  In general, in an optical disc apparatus, tracking servo, which is a servo in the radial direction of an optical disc for irradiating laser light along a groove of the optical disc, is performed. The tracking servo drives a tracking actuator in the optical pickup to appropriately move the objective lens in the optical pickup in the radial direction of the optical disc, and includes a sled mechanism that moves the tracking actuator and the entire optical pickup in the thread direction. This is realized by driving in a complementary manner.

  As a conventional technique for supplementing tracks of an optical disc apparatus, for example, the flow direction is detected from the phase relationship between an envelope of an RF signal recorded on the optical disc and a zero cross signal of a tracking error signal, and the target track is supplemented in a short time. The technique which can be mentioned is mentioned (refer patent document 1).

  Further, as a conventional technique related to the tracking servo pull-in of the optical disk apparatus, for example, an invention made by the present inventor and the like and applied for a patent (Japanese Patent Application No. 2005-212135) by the applicant of the present application can be cited.

  Hereinafter, an optical disk apparatus proposed in Japanese Patent Application No. 2005-212135 will be described. An outline of the optical disk apparatus proposed in Japanese Patent Application No. 2005-212135 will be described with reference to FIG. FIG. 5 is a diagram showing a schematic configuration of an optical disc apparatus proposed in Japanese Patent Application No. 2005-212135.

  The optical disk apparatus shown in FIG. 5 includes a spindle motor 2, an optical pickup 3, a thread mechanism 4, an RF processing circuit 5, a signal processing circuit 6, a servo circuit 7, a driver 8, a system control circuit 9, And an interface unit 10.

  The optical disk 1 is mounted on a spindle motor 2 and driven to rotate during reproduction. Information recorded on the optical disc 1 is read by the optical pickup 3. In order to perform focus control and tracking control of the beam spot, an actuator (focusing actuator and tracking actuator) that moves the objective lens 3a of the optical pickup 3 in the vertical direction and the horizontal direction (radial direction of the disc) with respect to the optical disc 1 is light. It is provided in the pickup 3. The optical pickup 3 is configured to be slid and moved in the radial direction of the optical disk 1 by a thread mechanism 4. When a slide motor (not shown) inside the sled mechanism 4 is driven, the driving force is transmitted to a gear system (not shown) inside the sled mechanism 4 and the entire optical pickup 3 is moved.

  The amount of light detected by a photodetector (not shown) in the optical pickup 3 is sent to the RF processing circuit 5 as a current signal. The RF processing circuit 5 performs processing such as current-voltage conversion, calculation, and amplification on the current signal sent from the optical pickup 3, and then, with the main data (RF signal), the tracking error signal TE and the focus error signal FE. Etc. are extracted. An RF signal as reproduction information is sent from the RF processing circuit 5 to the signal processing circuit 6, subjected to decoding and error correction processing in the signal processing circuit 6, and then as reproduction data from the interface unit 10 to an external device or the like ( (Not shown).

  The system control circuit 9 controls the servo circuit 7 and the signal processing circuit 6 based on a disk access request such as a reproduction command or a recording command from an external connection device (not shown) input via the interface unit 10. The tracking error signal TE and the focus error signal FE output from the RF processing circuit 5 are supplied to the servo circuit 7. The servo circuit 7 is constituted by a DSP (digital signal processor) having an A / D converter (not shown) for converting various analog signals for servo control to digital signals.

  The tracking error signal TE and the focus error signal FE supplied to the servo circuit 7 are supplied to the driver 8 as a tracking control signal TC and a focus control signal FC after being subjected to processing such as phase compensation. The driver 8 applies a drive voltage corresponding to the tracking control signal TC to the tracking actuator in the optical pickup 3, and applies a drive voltage corresponding to the focus control signal FC to the focusing actuator in the optical pickup 3. Thereby, the movement of the objective lens 3a in the optical pickup 3 is controlled so that the focus error signal FE and the tracking error signal TE become zero. The driver 8 also applies drive voltages to the spindle motor 2 and the sled mechanism 4 respectively.

  Next, the tracking servo pull-in procedure of the optical disk apparatus shown in FIG. 5 will be described in detail with reference to FIGS. FIG. 6 is a schematic block diagram of the tracking servo circuit, FIGS. 7 and 9 are timing charts of signals of the respective parts of the tracking servo circuit, and FIG. 8 is a waveform diagram of the tracking error signal TE indicating the kick start timing.

  The tracking servo circuit shown in FIG. 6 is a part of the servo circuit 7 of the optical disk apparatus shown in FIG. 5, and includes an A / D converter 11, a track cross detection circuit 12, a frequency detection circuit 13, and a delay circuit 14. A target speed setting register 15, a slip direction detection circuit 16, a speed error detection circuit 17, a kick / brake pulse output circuit 18, a sequence changeover switch 19, a phase correction circuit 20, and a servo switch 21. ing.

  Tracking servo pull-in is roughly divided into four sequences. Hereinafter, the operation of each sequence will be sequentially described.

[Sequence 1]
Before starting the tracking servo pull-in (when the tracking servo is OFF), the servo switch 21 selects the contact a, the contact a of the servo switch 21 and the pole z are electrically connected, and the sequence changeover switch 19 selects the contact c. Then, the contact c and the pole z of the sequence changeover switch 19 are electrically connected. In this case, the output voltage of the tracking servo circuit becomes zero.

  When the tracking servo pull-in is started after the spin motor motor 2 (see FIG. 5) is activated and the focus servo is turned on, the tracking error signal TE output from the RF processing circuit 5 (see FIG. 5) is generated. It is converted into a digital signal by the A / D converter 11.

A tracking error signal (hereinafter referred to as a digital tracking error signal) converted into a digital signal is sent to the track cross detection circuit 12. The track cross detection circuit 12 compares the digital tracking error signal with the reference voltage V _REF and generates a count signal COUT based on the comparison result. As shown in FIG. 7, the count signal COUT is the tracking error signal TE becomes the reference voltage V _REF is greater than the High level, a signal tracking error signal TE becomes the reference voltage V _REF is less than the Low level.

  The frequency detection circuit 13 receives the count signal COUT from the track cross detection circuit 12, and measures the time (t0, t1, t2, t3, t4, t5,...) Between the rising edges of the count signal COUT, that is, the cycle of the count signal COUT. To do. Since the measured time is the reciprocal of the frequency of the tracking error signal TE, the frequency detection circuit 13 detects the frequency of the tracking error signal TE.

The frequency detection circuit 13 monitors the frequency of the tracking error signal TE. Within the frequency range of the tracking error signal TE is given (hereinafter 1/2 or more target frequency f _TG of the target frequency f _TG to be described later in the present embodiment), the process proceeds to the next sequence i.e. sequence 2.

  Here, the purpose of monitoring the frequency of the tracking error signal TE is to detect the flow direction of the track by the method of sequence 3 described later in the vicinity of the return of the tracking error signal TE (periods P1, P5, P9 in FIG. 8). In this case, it is known from experiments that the flow direction of the track has a high probability of reversal and the flow direction cannot be determined stably, and the track flow is detected by the method of sequence 3 described later when the frequency of the tracking error signal TE is high. This is because, when the direction is detected, the frequency of the tracking error signal TE may be ½ or more of the sampling frequency of the digital servo. Since the determination frequency and limit frequency near the return are different depending on the optical disk device, they are determined by experiments, and the predetermined range is set so as not to include the determination frequency and limit frequency near the return.

  When the frequency of the tracking error signal TE is out of the predetermined range for a certain period, the process may proceed to sequence 2 even though the frequency TE of the tracking error signal is out of the predetermined range. Good. In this case, also in the sequence 2, the fact that the frequency of the tracking error signal TE is within the predetermined range is excluded from the condition for shifting to the sequence 3.

[Sequence 2]
A range frequency continues the prescribed tracking error signal TE (hereinafter 1/2 or more target frequency f _TG of the target frequency f _TG to be described later in the present embodiment), the frequency of the tracking error signal TE is rising (When the time between the rising edges of the count signal COUT decreases sequentially), the next sequence, that is, the sequence 3 is started and the kick is started.

  Here, the determination in the sequence 1 and the sequence 2 will be specifically described with reference to FIG. The periods P1, P5, and P9 in FIG. 8 are near the return of the tracking error signal TE as described above, and the periods P2, P3, and P4 in FIG. 8 are periods in which the track flow direction is the outer peripheral direction. Periods P6, P7, and P8 in period 8 are periods in which the track flow direction is the inner circumferential direction.

  In the periods P1, P5, and P9 in FIG. 8, the frequency of the tracking error signal TE is too low to fall within the predetermined range, so that the transition to the sequence 2 is not permitted by the sequence 1. On the other hand, in the periods P3 and P7 in FIG. 8, the frequency of the tracking error signal TE is too high to be within the predetermined range, so that the transition to the sequence 2 is not permitted by the sequence 1.

  In the periods P4 and P8 in FIG. 8, since the frequency of the tracking error signal TE is lowered, the transition to the sequence 3 by the sequence 2 is not permitted. On the other hand, in the periods P2 and P6 in FIG. 8, since the frequency of the tracking error signal TE is within the predetermined range and is rising, the transition to the sequence 3 is permitted by the sequence 2 and the kick is started.

[Sequence 3]
The sequence changeover switch 19 selects the contact a, and the contact a of the sequence changeover switch 19 and the pole z are electrically connected. The kick / brake pulse output circuit 18 outputs a kick pulse signal. As a result, a kick pulse signal KIC (see FIG. 9) is output from the tracking servo circuit, and the objective lens 3a (see FIG. 5) is driven to the inner or outer periphery of the optical disc 1 (see FIG. 5) by driving the tracking actuator. Force to move in the direction. Hereinafter, the case where the objective lens 3a is forcibly moved in the outer peripheral direction of the optical disc 1 will be described as an example.

  During such a kicking operation, the slip direction detection is performed by subtracting the period of the count signal COUT (output of the delay circuit 14) measured last time from the period of the count signal COUT (output of the frequency detection circuit 13) measured this time. If the difference value obtained by the circuit 16 and kicked in the outer peripheral direction is positive by the slip direction detection circuit 16, the track flows in the outer peripheral direction with respect to the objective lens 3a, and the difference value obtained by the slip direction detection circuit 16 is If it is negative, the track flows in the inner circumferential direction with respect to the objective lens 3a. In this way, the flow direction is detected, and the flow direction of the track is determined.

  In the section P2 of FIG. 8, when the kick / brake pulse output circuit 18 outputs a kick pulse signal that causes the objective lens 3a to kick in the outer circumferential direction, the frequency of the tracking error signal TE decreases. From this, it can be seen that the track moves in the outer circumferential direction with respect to the objective lens 3a. However, if the kick pulse is applied to the tracking actuator and the objective lens 3a is continuously accelerated, the moving speed of the objective lens 3a overtakes the moving speed of the track, and then the moving direction of the track is reversed with respect to the objective lens 3a. Detection is also very difficult.

  Further, in the section P6 in FIG. 8, when the kick / brake pulse output circuit 18 outputs a kick pulse signal that similarly causes the objective lens 3a to kick in the outer circumferential direction, the frequency of the tracking error signal TE increases. This shows that the track moves in the inner circumferential direction with respect to the objective lens 3a. However, if the kick pulse is applied to the tracking actuator and the objective lens 3a is continuously accelerated, the frequency of the tracking error signal TE may increase too much and exceed the sampling limit.

  In order to solve these problems, when the frequency of the tracking error signal TE increases (when the time between the rising edges of the count signal COUT decreases sequentially), the process proceeds to the next sequence, that is, the sequence 4, and conversely the tracking error When the frequency of the signal TE falls (when the time between the rising edges of the count signal COUT increases sequentially), the output of the kick pulse signal from the kick / brake pulse output circuit 18 is temporarily stopped and output again, and then the objective lens 3a is temporarily output. Is stopped and re-accelerated to prevent the track moving direction from reversing with respect to the objective lens 3a, and if the increase or decrease of the frequency of the tracking error signal TE cannot be detected for a certain period of time, excessive acceleration of the objective lens 3a is performed. To prevent the kick pulse from the kick / brake pulse output circuit 18 Output once and then stop the re-output of No. temporarily accelerated again to stop acceleration of the objective lens 3a.

  When the player kicks in the outer circumferential direction by the above operation, it is always determined that the moving direction of the track is the inner circumferential direction, and the process proceeds to the next sequence, that is, sequence 4. The kick pulse signal output from the kick / brake pulse output circuit 18 is set to a voltage that does not cause the tracking error signal TE to suddenly increase in frequency.

[Sequence 4]
By the sequence 3, the objective lens 3a is moved in the outer circumferential direction, and the moving direction of the track with respect to the objective lens 3a is also known as the inner circumferential direction. In sequence 4, the sequence changeover switch 19 selects the contact b, the contact b of the sequence changeover switch 19 and the pole z are electrically connected, and the tracking servo circuit is set so that the frequency of the tracking error signal TE becomes the target frequency _fTG. Control the tracking actuator.

The target speed setting register 15 is set in advance with the target moving speed of the objective lens 3a at the time of tracking servo pull-in. This setting is set as a time between rising edges of the count signal COUT. The speed error detection circuit 17 generates a speed error signal VE (see FIG. 7) by subtracting the current cycle of the count signal COUT from the time _VTG set in the target speed setting register 15. The speed error signal VE is positive if the moving speed of the objective lens 3a is smaller than the target speed, and is negative if the moving speed of the objective lens 3a is larger than the target speed. The tracking servo circuit applies the speed error signal VE to the tracking actuator to drive the tracking actuator, and controls the moving speed of the objective lens 3a to be the target speed. When the speed error detection circuit 17 confirms that the moving speed of the objective lens 3a has reached the target speed, the servo switch 21 selects the contact b and the contact b of the servo switch 21 and the pole z are electrically connected. This pulls in the tracking servo.

  Note that the target speed set in advance in the target speed setting register 15 is set so that the moving speed of the objective lens 3a is sufficiently faster than the eccentricity of the track, as in the case of track jump.

  Also, instead of pulling the tracking servo as soon as the moving speed of the objective lens 3a reaches the target speed, a roller that avoids a transient response portion and the moving speed of the objective lens 3a is sufficiently stable (for example, the movement of the objective lens 3a). If the laser spot passes a predetermined number of tracks after the speed reaches the target speed, the moving speed of the objective lens 3a is assumed to be sufficiently stable. This improves the stability of tracking servo pull-in.

  Furthermore, when the tracking servo is pulled in, the objective lens 3a is braked in the direction opposite to the moving direction of the objective lens 3a with respect to the track, that is, the sequence changeover switch 19 selects the contact a before the servo switch 21 selects the contact b. The kick / brake pulse output circuit 18 outputs a brake pulse signal and the tracking servo circuit generates a brake pulse signal BRK (see FIG. 9), so that the relative speed of the objective lens 3a with respect to the track is decreased. Good. As a result, the tracking servo pull-in stability can be further improved.

By the operations of sequence 1 to sequence 4 described above, the flow direction of the track with respect to the objective lens is the same regardless of the eccentricity of the optical disk, and the relative speed of the objective lens with respect to the track at the time of tracking pull-in is always constant. Since it becomes constant, the tracking servo can be pulled in stably.
JP 60-52932 A

  However, when the tracking servo is a digital servo, the tracking error signal from the optical pickup is sampled by the A / D converter, so that aliasing noise occurs. In order to prevent occurrence of the aliasing noise, an anti-aliasing filter that cuts half or more of the sampling frequency of the A / D converter is usually provided in the front stage of the A / D converter. In the optical disk apparatus shown in FIG. 5, since the tracking servo is a digital servo, an anti-aliasing filter is usually provided between the RF processing circuit 5 and the servo circuit 7.

  In the optical disc apparatus having the anti-aliasing filter described above, the capture of the track fails due to an optical disc defect or external vibration, and the speed at which the light beam spot crosses the track becomes the cutoff frequency of the anti-aliasing filter. When the speed exceeds the corresponding speed, there is no tracking error signal input to the servo circuit, and the servo circuit cannot measure the flow direction of the light beam spot, and as a result, the track cannot be captured.

  Even if the speed at which the light beam spot crosses the track is less than the speed corresponding to the cutoff frequency of the anti-aliasing filter, the tracking error signal may be lost due to dirt on the recording surface of the optical disk or optical disk defects. Also in this case, there is no tracking error signal input to the servo circuit, and the servo circuit cannot measure the flow direction of the light beam spot, and as a result, the track cannot be captured.

  For example, when an anti-aliasing filter is provided between the RF processing circuit 5 and the servo circuit 7 of the optical disk apparatus shown in FIG. 5, the tracking error information of the optical disk 1 is detected by a photodetector (not shown) in the optical pickup 3. ) → RF processing circuit 5 → anti-aliasing filter → servo circuit 7 The servo circuit 7 performs the arithmetic processing necessary for the tracking servo, and then the driver 8 → the tracking actuator in the optical pick-up 3 leads to tracking / tracking. A servo loop is formed.

  Due to the band limitation by the anti-aliasing filter, the tracking error after passing through the anti-aliasing filter during the period P10 in which the frequency of the tracking error signal TE is equal to or higher than the cutoff frequency of the anti-aliasing filter as shown in FIG. The signal TE ′, that is, the input signal of the A / D converter in the servo circuit 7 is in a no-signal state. As a result, the tracking error signal TE ′ after passing through the anti-aliasing filter is converted into a digital signal by an A / D converter, and the digital signal is hysteresis-compared at levels HL and LL. The value signal DS is also in the no signal state during the period P10, and the servo circuit 7 cannot detect a tracking error signal exceeding the cutoff frequency band of the anti-aliasing filter.

  In view of the above problems, an object of the present invention is to provide an optical disc apparatus capable of performing tracking servo pull-in at an incorrect timing and preventing an erroneous trace (track flow state).

  In order to achieve the above object, an optical disc apparatus according to the present invention includes a light source, an objective lens that focuses the beam from the light source on the optical disc, and the objective lens is slightly moved parallel to the surface of the optical disc and in the radial direction of the optical disc. A tracking actuator, an optical pickup having a photoelectric conversion unit that converts return light from the optical disk into an electrical signal, tracking error signal generation means for generating a tracking error signal based on the electrical signal, and the tracking error signal In response, the tracking actuator is driven so that the beam spot focused by the objective lens follows the track of the optical disc, the abnormality detecting means for detecting an abnormality of the tracking error signal, and the tracking error signal of An abnormality detecting means for detecting normality, a speed detecting means for detecting the moving speed of the objective lens, a kick means for supplying a kick pulse signal to the tracking actuator, and after the kick means is operated, the objective of the track A slip direction detecting means for detecting a moving direction with respect to the lens; and an output of the speed detecting means so that the moving speed of the objective lens is substantially constant in the same direction as the slip direction detected by the slip direction detecting means. And a tracking servo pull-in means for actuating the tracking control means after the constant speed control means is actuated, and the abnormality detecting means detects the tracking error signal. If an abnormality is detected, tracking servo pull-in movement And the tracking control means is not operated, and a tracking servo pull-in operation is performed by the speed detection means, the kick means, the slip direction detection means, the constant speed control means, and the tracking servo pull-in means. If the abnormality of the tracking error signal is detected by the abnormality detection means when the abnormality is detected, and if the abnormality of the tracking error signal is detected by the abnormality detection means after the tracking servo pull-in operation is completed, the tracking servo is turned off. I am doing so.

  According to the above optical disk apparatus, since the tracking servo pull-in operation is prohibited when an abnormality of the tracking error signal is detected, it is possible to prevent the tracking servo pull-in from being performed at an incorrect timing.

  Further, according to the optical disc apparatus, the objective lens is kicked in the inner or outer peripheral direction of the optical disc, and then the moving direction of the track with respect to the objective lens is detected. Since the tracking actuator is controlled so that the speed is constant, the flow direction of the track relative to the objective lens and the relative speed are always the same when the tracking servo is pulled in, the tracking polarity is not reversed, and the tracking servo is pulled in. Can be performed stably.

  Further, according to the optical disc apparatus, the abnormality detection is performed when a tracking servo pull-in operation is performed by the speed detection unit, the kick unit, the slip direction detection unit, the constant speed control unit, and the tracking servo pull-in unit. When an abnormality of the tracking error signal is detected by the means, and when an abnormality of the tracking error signal is detected by the abnormality detection means after the tracking servo pull-in operation is completed, the tracking servo is turned off. A wrong trace (track flow state) can be stopped and the re-drawing process can be started.

  According to the optical disk apparatus of the present invention, tracking servo pull-in can be performed at an incorrect timing and an erroneous trace (track flow state) can be prevented.

  Embodiments of the present invention will be described below with reference to the drawings. A schematic configuration of an optical disk apparatus according to the present invention is shown in FIG. 1, the same parts as those in FIG. 5 are denoted by the same reference numerals, and detailed description thereof is omitted.

The tracking error signal TE and the focus error signal FE output from the RF processing circuit 5 reach the servo circuit 7 after being band-limited by the anti-aliasing filter 22. The anti-aliasing filter 22 has the frequency characteristics shown in FIG. 2, and cuts frequencies of f _S / 2 or higher. Note that f _S is the sampling frequency of the A / D converter (A / D converter 11 in FIG. 6) in the servo circuit 7.

  The abnormality detection circuit 23 detects an abnormality in the tracking error signal TE output from the RF processing circuit 5 and outputs the detection result to the servo circuit 7. When the abnormality detection circuit 23 detects an abnormality in the tracking error signal TE, the servo circuit 7 does not perform the above-described sequences 1 to 4 before the operations of the above-described sequences 1 to 4, and does not perform the above-described sequences 1 to 4. If it is in operation, the operation is stopped so that tracking servo pull-in is not performed, that is, the tracking servo is turned off. Further, the servo circuit 7 turns off the tracking servo when the abnormality detection circuit 23 detects an abnormality in the tracking error signal TE after the tracking servo pull-in is completed.

  Next, a configuration example of the abnormality detection circuit 23 will be described. FIG. 3 is a diagram illustrating a configuration example of the abnormality detection circuit 23. The abnormality detector shown in FIG. 3 includes a hysteresis comparator 24, a mono multi 25, a mono multi 26, a latch circuit 27, an amplitude determiner 28, and an adder 29.

  The tracking error signal TE is divided into two parts, one being sent to a frequency abnormality detection unit comprising a hysteresis comparator 24, mono-multi 25, mono-multi 26, and latch circuit 27, and the other to an amplitude abnormality detection unit comprising an amplitude determiner 28. Sent out.

First, the operation of the frequency abnormality detection unit will be described. The hysteresis comparator 24 sends a signal OS ₂₄ obtained by comparing the tracking error signal TE with the first reference level and the second reference level (<first reference level) to the mono multis 25 and 26. When the tracking error signal TE becomes higher than the first reference level, the signal OS ₂₄ becomes high level, and then the signal OS ₂₄ maintains the high level until the tracking error signal TE becomes lower than the second reference level. Further, when the tracking error signal TE becomes smaller than the second reference level, the signal OS ₂₄ becomes the low level, and thereafter, the signal OS ₂₄ maintains the low level until the tracking error signal TE becomes larger than the first reference level.

The mono multi 25 sends a signal OS ₂₅ obtained by generating a pulse having a pulse width W 1 in synchronization with the rising edge of the signal OS ₂₄ output from the hysteresis comparator 24 to the latch circuit 27. As can be seen from FIG. 4A, when the period of the signal OS ₂₄ is shorter than the pulse width W1, the signal OS ₂₅ becomes a continuous signal. However, when the period of the signal OS ₂₄ becomes longer than the pulse width W1, the signal OS ₂₅ becomes an intermittent signal. Become.

The mono multi 26 sends a signal OS ₂₆ obtained by generating a pulse having a pulse width W2 (> W1) in synchronization with the rising edge of the signal OS ₂₄ output from the hysteresis comparator 24 to the latch circuit 27. As can be seen from FIG. 4A, when the period of the signal OS ₂₄ is shorter than the pulse width W2, the signal OS ₂₆ becomes a continuous signal. However, when the period of the signal OS ₂₄ becomes longer than the pulse width W2, the signal OS ₂₆ becomes an intermittent signal. Become.

The latch circuit 27 sends a signal OS ₂₇ obtained by holding the state of the signal OS ₂₅ at the falling edge of the signal OS ₂₆ to the adder 29. Note that the latch circuit 27 sets the initial state of the signal OS ₂₇ to the high level.

The signal OS ₂₇ is a signal that becomes high level and notifies the frequency error of the tracking error signal TE when the frequency of the tracking error signal TE is abnormal.

Next, the operation of the amplitude abnormality detection unit will be described. The amplitude determination unit 28 generates a signal OS ₂₈ that is at a high level when the amplitude of the tracking error signal is equal to or less than the threshold value TH, and that is at a low level when the amplitude of the tracking error signal is greater than the threshold value TH. 29.

The signal OS ₂₈ is a signal that indicates a high level and notifies the amplitude abnormality of the tracking error signal TE when the amplitude of the tracking error signal TE is abnormal (when the amplitude of the tracking error signal TE is equal to or less than a threshold value).

The adder 29 sends the signal OS ₂₇ output from the latch circuit 27 and the signal OS ₂₈ output from the amplitude determiner 28 to the servo circuit 7 as an output of the abnormality detection circuit 23. Therefore, when the output signal of the abnormality detection circuit 23 is not at the low level, the abnormality detection circuit 23 has detected an abnormality.

  From the output of the abnormality detection circuit 23, the servo circuit 7 can know whether or not the frequency of the tracking error signal is equal to or higher than the cutoff frequency of the anti-aliasing filter. Since the tracking servo pull-in is not performed when the frequency is equal to or higher than the cut-off frequency of the filter, it is possible to prevent the tracking servo pull-in from being performed at an incorrect timing.

  Further, the output of the abnormality detection circuit 23 allows the servo circuit 7 to know whether or not the amplitude of the tracking error signal is equal to or smaller than a threshold value. When the amplitude of the tracking error signal is equal to or smaller than the threshold value, tracking servo pull-in is performed. Since this is not performed, it is possible to prevent the tracking servo from being pulled in at an incorrect timing. Note that tracking error signal amplitude abnormalities may occur due to contamination of the recording surface of the optical disk, optical disk defects, etc., so detection of tracking error signal amplitude abnormality is also effective for optical disk devices that do not have an anti-aliasing filter. It is.

These are figures which show schematic structure of the optical disk apparatus based on this invention. FIG. 4 is a diagram showing a band of an anti-aliasing filter. These are figures which show the example of a structure of an abnormality detection circuit. These are the timing charts of each part signal of the abnormality detection circuit shown in FIG. These are the timing charts of each part signal of the abnormality detection circuit shown in FIG. These are figures which show schematic structure of the conventional optical disk apparatus. These are schematic block diagrams of a tracking servo circuit. These are the timing charts of the respective signals of the tracking servo circuit. FIG. 4 is a waveform diagram of a tracking error signal indicating kick start timing. These are the timing charts of the respective signals of the tracking servo circuit. These are the timing charts of each part signal of the conventional optical disc apparatus provided with the anti-aliasing filter.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Optical disk 2 Spindle motor 3 Optical pickup 3a Objective lens 4 Thread mechanism 5 RF processing circuit 6 Signal processing circuit 7 Servo circuit 8 Driver 9 System control circuit 10 Interface part 11 A / D converter 12 Track cross detection circuit 13 Frequency detection circuit 14 Delay Circuit 15 Target speed setting register 16 Slip direction detection circuit 17 Speed error detection circuit 18 Kick / brake pulse output circuit 19 Sequence changeover switch 20 Phase correction circuit 21 Servo switch 22 Antialiasing filter 23 Abnormality detection circuit 24 Hysteresis comparator 25, 26 Monomulti 27 Latch circuit 28 Amplitude determiner 29 Adder

Claims (1)

A light source, an objective lens that focuses the beam from the light source on the optical disc, a tracking actuator that slightly moves the objective lens parallel to the surface of the optical disc and in the radial direction of the optical disc, and return light from the optical disc as an electrical signal An optical pickup having a photoelectric conversion unit for conversion;
Tracking error signal generating means for generating a tracking error signal based on the electrical signal;
Tracking control means for driving the tracking actuator in accordance with the tracking error signal and causing a beam spot focused by the objective lens to follow the track of the optical disc;
An abnormality detecting means for detecting an abnormality of the tracking error signal;
Speed detecting means for detecting the moving speed of the objective lens;
Kick means for supplying a kick pulse signal to the tracking actuator;
A slip direction detecting means for detecting a moving direction of the track with respect to the objective lens after the kick means is activated;
Constant speed control means for driving the tracking actuator in accordance with the output of the speed detection means so that the moving speed of the objective lens becomes substantially constant in the same direction as the slip direction detected by the slip direction detection means. When,
A tracking servo pull-in means for activating the tracking control means after the constant speed control means is activated,
When the abnormality of the tracking error signal is detected by the abnormality detection means, the tracking servo pull-in operation is prohibited and the tracking control means is not operated,
Abnormality of the tracking error signal by the abnormality detection means when the tracking servo pull-in operation is performed by the speed detection means, the kick means, the slip direction detection means, the constant speed control means, and the tracking servo pull-in means The optical disk apparatus is characterized in that the tracking servo is turned off when the tracking error signal is detected and when the abnormality of the tracking error signal is detected by the abnormality detecting means after the tracking servo pull-in operation is completed.

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