JP3067529B2 - Optical disk drive - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical disk apparatus for recording or reproducing information on an optical disk.

[0002]

2. Description of the Related Art In recent years, optical disks for recording and reproducing information on and from optical disks, such as magneto-optical disk devices, have been put to practical use. In such an optical disc device, a so-called tracking loss, in which a light beam cannot follow an information track, has become a problem, and several tracking tracking detection methods have been proposed.

A conventional read-only optical disk device monitors the continuity of address information read from a disk to detect an off-track. However, when this method is used in a recordable optical disk device, even if an off-track occurs during recording, it takes tens of milliseconds to tens of milliseconds to detect it, and a considerable amount of time There was a problem that a track was overwritten. Various proposals have been made to solve this problem. For example, the optical disk device disclosed in Japanese Patent Application Laid-Open No. 64-79942 detects a tracking error when the tracking error signal has exceeded a predetermined value, and stops the recording operation at the same time as detecting the tracking error. .

FIG. 10 shows a block diagram of a conventional optical disk device. A portion 106 surrounded by a broken line is a conventional tracking-off detecting section. 101 is an optical disc having information tracks for recording data, 102 is the optical disc 10
1 is irradiated with a light beam, and a tracking error signal indicating a deviation between the light beam and the information track is generated from the reflected light,
An optical head for outputting. The optical head 102 is the comparator 10
3 and the output of the comparator 103 is the D latch circuit 10
4 clock terminals. D latch circuit 10
4, the data input terminal D and the set terminal S are fixed at "H", and the reset terminal R is connected to the system controller 105. Further, the D latch circuit 104
Is connected to the system controller 105.

[0005] The operation of the optical disk device configured as described above will be described. First, the system controller 105 sets the output Q of the D latch circuit 104 to “L” by setting the reset terminal R of the D latch circuit 104 to “L”.
The optical head 102 generates a tracking error signal,
It is supplied to the value conversion circuit 103. The binarization circuit 103 compares the input tracking error signal with a comparison value, and outputs “H” when the value of the tracking error signal is larger than the comparison value. When the output of the comparator 103 becomes “H”, the D latch circuit 104 latches and outputs “H” of the data input terminal D 1. Since the amplitude of the tracking error signal increases as the light spot deviates from the track, the fact that the output Q of the D-latch circuit 104 is "H" means that the deviation between the light spot and the track exceeds a predetermined value even for a moment. Indicates that. The system controller 105 inputs this signal as an out-of-tracking signal. When the out-of-tracking signal becomes "H", the system controller 105 performs processing such as interruption of the recording / reproducing operation. 11A shows an input signal of the comparator 103, FIG. 11B shows an output signal of the comparator 103, and FIG. 11C shows a tracking-off signal.

[0006]

However, such a tracking error detection method has a problem that erroneous detection occurs when the magnitude of the tracking error signal temporarily increases due to a scratch on the optical disk or the like. Also, when recording data having a time axis attribute such as audio, even if some data to be recorded or data to be read is missing, the less interruption of the recording operation itself may be more convenient as an optical disc device. is there. For example, in the case of audio data, it is possible to add an error detection / correction code at the time of encoding or to perform interpolation processing of data that cannot be completely corrected at the time of decoding. Acceptable. However, in the conventional method, if the light spot deviates from the track even a little, tracking is determined to be deviated. Therefore, there is a problem that the deviated track is frequently detected, the recording process is interrupted, and the usability is poor.

SUMMARY OF THE INVENTION The present invention has been made to solve the above problems, and has as its object to accurately detect a tracking error by capturing a positional relationship between a light beam and an information track and a relative moving speed.

[0008]

To achieve the above object, an optical disk apparatus according to the present invention compares a tracking error signal with a positive comparison value and outputs a first comparison result.
And a second level comparing means for comparing the tracking error signal with a negative comparison value and outputting a second comparison result; and a first comparison result or the second comparison result, A first period measuring means for measuring a period in which the tracking error signal is larger than the positive comparison value or a period smaller than the negative comparison value; a measurement result of the first period measuring means and a first reference period; A first period comparing means for comparing the lengths of the first and second comparison results, and a first comparison result and a second comparison result, and the tracking error signal becomes smaller than the positive comparison value. A second period measuring means for measuring a length of a period from the time when the value becomes smaller than the negative comparison value or a length of time from a time when the value becomes larger than the negative comparison value to a value larger than the positive comparison value; Measurement result of period measurement means and second standard A second period comparison unit that compares the lengths of the intervals and outputs a fourth comparison result; and a third and fourth comparison result that are input and the measurement result of the first period measurement unit is a first reference. Off-track output means for outputting an off-track signal when the measurement result of the second period measurement means is longer than the length of the period and shorter than the length of the second reference period.

[0009]

According to the present invention, the tracking servo is deviated and the light beam approaches the adjacent track beyond the midpoint between the adjacent track and the moving speed at that time. Generate an off-tracking signal.

[0010]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A first embodiment of the present invention will be described below with reference to the drawings.

First, the configuration of the optical disk device of the present embodiment will be described. FIG. 1 is a block diagram of the first embodiment. 1
0 is an optical disk, 11 is an optical head for reading and writing information by irradiating the optical disk 10 with a light beam, 12 is a comparator for comparing a tracking error signal output by the optical head 11 with a positive comparison value, and 13 is a tracking error signal. A comparator that compares the signal with a negative comparison value. Here, “positive” or “negative” refers to a voltage when the tracking error signal has an error of 0 as a reference, and when the voltage is larger than the voltage, it is positive and when it is smaller, it is negative. The outputs of the comparators 12 and 13 are connected to an OR circuit 14, and the output of the OR circuit 14 is connected to the clear terminal CLR of the counter 15, the inverter 18, the clock terminal of the D latch circuit 114, and the AND circuit 117. The counter 15 measures the length of the period during which the output of the OR circuit 14 is “H” using the clock output from the oscillator 16.
Carry output terminal C is the set terminal of SR latch circuit 17
Connected to S. The reset terminal R of the SR latch circuit 17 is connected to the system controller 120,
The output terminal Q is connected to the AND circuit 19 and the inverter 118. The output of the inverter 18 is connected to the other input terminal of the AND circuit 19. AND circuit 19
Is connected to the clear terminal CLR of the counter 111. The counter 111 measures the length of the period during which the clear terminal CLR is "H" using the clock signal from the oscillator 110, and outputs a count value. Output terminal of counter 111
DATA is connected to the input terminal B of the comparator 112. The comparator 112 compares the reference value 113 input to the input terminal A with the output of the counter 111, and outputs "H" if the reference value is large. The output A> B of the comparator 112 is connected to the data input terminal D of the D latch circuit 114. The D latch circuit 114 latches the output A> B of the comparator 112 when the rising edge is input to the clock terminal. Output to the output terminal Q. Output terminal Q of D latch circuit 114
Is connected to the clear terminal CLR of the counter 116.
The counter 116 measures the time during which the output Q of the D-latch circuit 114 is "H" using a clock signal generated by the oscillator 115, and outputs a carry signal when the output Q reaches a predetermined time. The carry output terminal C is connected to the AND circuit 117. The output of the AND circuit 117 is the SR latch circuit 11
9 is connected to the set terminal S, and the SR latch circuit 1
The 19 reset terminal R is connected to the inverter 118. The output Q of the SR latch circuit 119 is connected to the system controller 120. This signal is the tracking error signal. A portion 121 surrounded by a broken line is shown in FIG.
0 corresponds to the conventional tracking-off detection unit 106.

The operation of the optical disk device configured as described above will be described below with reference to waveforms. First, the system controller 120 controls the SR latch circuit 1
7 and the reset terminal R of the SR latch circuit 119 are set to "H", whereby the output Q of both SR latch circuits is set to "L". The optical head 11 outputs a tracking error signal as shown in FIG. 2A based on the reflected light from the optical disk 10. When the tracking error signal exceeds the positive comparison value AA, the comparator 12 outputs "H" as shown in FIG.
Output level signal. When the value becomes smaller than the negative comparison value BB, the comparator 13 outputs an "H" level signal as shown in FIG. The OR circuit 14 is inserted so that by adding these, the track deviation can be detected regardless of the direction of the track deviation in either the inner or outer direction. The output of the OR circuit 14 is shown in FIG. The light spot is shifted to either the inner side or the outer side, and the first "H" signal is the clear terminal of the counter 15.
When input to the CLR, the counter 15 starts counting. When the count value reaches a predetermined number, the counter 15 outputs "H" to the carry output terminal C as shown in FIG. 2E, whereby the output Q of the SR latch circuit 17 becomes "H". ((F) of FIG. 2). This indicates that the time during which the light spot is displaced by a considerable amount (the period Ta in FIG. 2A) is long, which means that tracking is coming off. When the output Q of the SR latch circuit 17 becomes “H” and the first “H” period has passed, the AND circuit 1
9 becomes "H" as shown in FIG. 2 (g), and the counter 111 starts operating. This period ((a) in FIG. 2)
The period Tb) is a period in which the light spot is located between the adjacent tracks. The counter 111 measures the time during this period, and the comparator 112 determines whether this time is shorter than the reference time. If shorter, "H" is output. The fact that the time during which the light spot is located between adjacent tracks is short indicates that the moving speed is high, that is, the servo brake is not effective. Conversely, a long time indicates that the servo brake is effective and is likely to be pulled back. By the way, when the second “H” period of the output of the OR circuit 14 comes while the output A> B ((h) of FIG. 2) from the comparator 112 is “H”, the D latch circuit 114 outputs “H”. Is latched ((i) of FIG. 2). When the output Q of the D latch circuit 114 becomes “H”, the counter 116 starts counting,
When the count value reaches a predetermined value, the carry output C is set to "H" as shown in FIG. 2 (j). This indicates that the length of the period Tc in FIG. 2A is longer than a predetermined value. The AND circuit 117 performs an AND operation on the output of the OR circuit 14 and the carry output C of the counter 116 to form the OR circuit 1
The carry output C is masked during the period when the output of No. 4 is not at "H" to prevent malfunction. When the carry output C of the counter 116 becomes "H", the SR latch circuit 119
Output "H" (FIG. 2 (k)). This indicates that the light spot has moved to the adjacent track side past the intermediate point with the adjacent track, and is riding on the adjacent track. Using this signal as a tracking error signal, the system controller 120 immediately stops the recording operation.

As described above, in the first embodiment, the time when the tracking error signal exceeds the positive or negative threshold value, the time when the tracking error signal once falls between the positive and negative threshold values, and the first time are opposite. By measuring the time when the polarity threshold value is exceeded, tracking out is detected from the position of the light spot and the speed in each state. In this method, the time when the value of the tracking error signal is large is measured, so that the influence of the noise of the tracking error signal due to scratches on the disk can be reduced to a negligible extent, and the position of the light spot can be reduced. By measuring the speed and the speed, it is possible to accurately and surely detect the tracking deviation. By the way, when the tracking loss occurs at the acceleration of 5 G, the period Ta in FIG.
The second and the period Tc are about 50 μsec. Also, since the period of Tb can be said to be an indication of whether the light spot is pulled back by the action of the servo, a relatively long time of about 300 μsec is set.

In the method of the first embodiment, it is assumed that the condition is satisfied when the time exceeding the positive or negative threshold value is long. However, when a strong shock exceeding the assumed acceleration is applied, tracking is lost. May occur at higher frequencies and may not be detectable. As a second embodiment, an optical disk device that addresses this problem will be described.

FIG. 3 is a block diagram of the second embodiment.
Reference numerals 10, 11, 12, and 13 are the optical disk, optical head, and comparator described in the first embodiment. Reference numeral 122 denotes a tracking-off detection unit described in the first embodiment, which corresponds to a portion 122 surrounded by a broken line in the inside of FIG.
Is referred to as a tracking-off detection unit. ). Two comparators 1
The outputs from 2 and 13 are connected to the first tracking-off detection unit 122 and the SR latch circuit 30. SR
The output terminal Q of the latch circuit 30 is connected to the clock terminal of the counter 31 that is periodically reset by the oscillator 32. The carrier output terminal C of the counter 31 is S
It is connected to the set terminal S of the R latch circuit 33. The reset terminal R of the SR latch circuit 33 is connected to the system controller 34. The tracking error signal output from the first tracking error detecting unit 122 and S
The output Q of the R latch circuit 33 is ORed by an OR circuit 35 and input to the system controller 34 as a new tracking-off signal. Further, the system controller 34 also sends a reset signal to the first tracking-off detection unit 122. Portion 36 surrounded by broken line
Is a block added to the first tracking deviation detection unit 122, and shows a characteristic portion of the present embodiment.

The operation of the optical disk device having such a configuration will be described with reference to waveform diagrams. First, the system controller 34 resets the first tracking-off detection unit 122 and the SR latch circuit 33. When a strong shock is applied from the outside, the optical head 11 outputs a tracking error signal as shown in FIG. If this frequency is 1
Assuming that the frequency is 0 KHz, the period Ta, in FIG.
The portion corresponding to Tc is less than or equal to 50 μsec, and the first tracking-off detection unit 122 cannot detect it.
The output of the comparator 12 at this time is shown in FIG.
The output of No. 3 is shown in FIG. The output of the comparator 12 is S
Since the output of the comparator 13 is connected to the set terminal S of the R latch circuit 30 and the reset terminal R, the output Q of the SR latch circuit 30 becomes a pulse as shown in FIG. The output Q of the SR latch circuit 30 enters the clock terminal of the counter 31, and the counter 31 is reset every predetermined time by a signal output from the oscillator 32.
It is possible to know whether or not the frequency of the tracking error signal has become equal to or higher than a predetermined value, depending on whether or not the carry output C becomes “H” within a predetermined time. When the frequency is equal to or higher than the predetermined value, the carry signal C of the counter 31 becomes "H" as shown in FIG. 4E, and the output Q of the SR latch circuit 33 as shown in FIG. Becomes “H”. As a result, tracking deviation with a high frequency is detected. The OR circuit 35 adds the output of the first tracking-off detection unit 122 and the output Q of the SR latch circuit 33 to enable detection of tracking-off with one signal line.

As described above, in the second embodiment, by monitoring the frequency of the tracking error signal, even if a tracking error having an acceleration larger than the acceleration assumed in the first embodiment occurs, It is possible to detect tracking loss.

In the third embodiment, an optical disk device capable of reliably detecting tracking error by a simpler method will be described. FIG. 5 is a block diagram of the third embodiment.
In the figure, reference numerals 10, 11, 12, and 13 denote an optical disk, an optical head and a comparator similar to those of the first embodiment. Comparator 12
Is connected to the set terminal S of the SR latch circuit 50, and the output of the comparator 13 is connected to the reset terminal R of the SR latch circuit 50 and the clock terminal of the D latch circuit 55. S
The output Q of the R latch circuit 50 is the clear terminal of the counter 51
The counter 51 is connected to CLR, and the counter 51 measures the length of time when the clear terminal CLR is at "H" using the clock output from the oscillator 52. The output DATA (count value) of the counter 51 is connected to the input terminal B of the comparator 53. Comparator 53
The reference value 54 is input to the input terminal A of the comparator 53. The comparator 53 outputs "H" when the reference value is larger than the count value of the counter 51. The output A> B of the comparator 53 is connected to the data terminal D of the D latch circuit 55, and the D latch circuit 55 outputs the value of the data terminal D when a rising edge is input to the clock terminal. The clear terminal CLR of the D latch circuit 55 is connected to the system controller 56. The output Q of the D latch circuit 55 is a tracking-off signal. The out-of-tracking signal is input to the system controller 56. A portion 57 surrounded by a broken line is a tracking deviation detecting unit of the third embodiment, and corresponds to the conventional tracking deviation detecting unit 106 in FIG.

The operation of the optical disk device configured as described above will be described with reference to waveforms. Optical head 11
Generates and outputs a tracking error signal as shown in FIG. 6A from the reflected light from the optical disk 10. The comparator 12 compares the tracking error signal with the positive comparison value AA, and outputs a signal as shown in FIG. By this signal, the output Q of the SR latch circuit 50 is changed as shown in FIG.
Becomes "H" as shown in FIG. Output of SR latch circuit 50
When Q becomes “H”, the clear of the counter 51 is released, and the count-up starts by the clock output from the oscillator 52. The comparator 53 compares the reference value 54 input from the input terminal A with the count value input from the input terminal B, and outputs "H" if the reference value is large. Immediately after the count is started, the output A> B of the comparator 53 is “H” because the count value of the counter 51 is 0, and after a predetermined time, the count value exceeds the reference value and the output A> B of the comparator 53
Becomes “L”. Since the D latch circuit 55 latches the output A> B of the comparator 53 at the moment when the output of the comparator 13 becomes “H”, the output Q of the D latch circuit 55 becomes “H” when the output of the comparator 12 becomes “H”. After that, the signal indicates whether the count value has exceeded the reference value before the output of the comparator 13 becomes “H”. The time from when the output of the comparator 12 changes to “H” to when the output of the comparator 13 changes to “H” is from the point where the light spot deviates from the desired track to the point where the light spot crosses the intermediate point with the adjacent track. This shows the time required to approach an adjacent track. If this is short, it indicates that the moving speed of the light spot is high, and it can be said that the stability of the servo is no longer effective. Conversely, if this is long, the tracking error signal has temporarily increased, but it can be considered that it has been returned to a normal position by the servo. Therefore, the output Q of the D latch circuit 55 can be used as a tracking-off signal. FIG. 6E shows the output A> B of the comparator 53 when the count value does not exceed the reference value within a predetermined time, that is, when tracking loss occurs, and FIG. 6F.
Indicates the output Q of the D latch circuit 55 at that time. When the tracking loss is detected, the system controller 5
6 performs processing such as interrupting recording.

FIG. 7A shows a tracking error signal when the tracking servo comes off and is pulled back by the servo, and then comes off again and is pulled back. In such a case, the outputs of the comparators 12 and 13 are as shown in FIGS.
Is "H" for a long period as shown in FIG. 7 (d). During this time, the count value of the counter 51 increases,
Exceeding the reference value, the output A> B of the comparator 53 becomes "L" as shown in FIG. Even if the output of the comparator 13 becomes “H” (FIG. 7C), the output Q of the D latch circuit 55 becomes “L” since the output A> B of the comparator 53 is “L”.
(F in FIG. 7), and tracking deviation is not detected.

As described above, according to the third embodiment, it is possible to detect that the light spot has passed the midpoint between the adjacent track and the simpler hardware configuration, and it is possible to detect tracking error at low cost. A detection mechanism can be constructed. In addition, in this method, when the absolute value of the positive and negative comparison values is the same, the length of the tracking error signal is measured in exactly a half cycle, so that the tracking error signal has an amplitude larger than the interval between the positive and negative comparison values. If it does, tracking loss can be detected, and it is characterized by being hardly affected by constant fluctuations due to temperature changes.

In the optical disk device of the present invention, the tracking error signal is compared with two comparison values, positive and negative, and the tracking error is detected using the result. Therefore, the relationship between the tracking error signal and the comparison value is as expected. It is important. For example, if for some reason the amplitude of the tracking error signal becomes narrower than the width of the positive / negative comparison value as shown in FIG. 9A, it is impossible to detect tracking loss at all. When the amplitude of the tracking error signal becomes extremely large as shown in FIG. 9B, a period 91 in which the tracking error signal is larger than the positive comparison value and a period 93 in which the tracking error signal is smaller than the negative comparison value. Is longer than in the normal case, and the period 92 between the positive comparison value and the negative comparison value is short. Therefore, particularly when the method described in the first embodiment is used, the tracking error is detected. It will be easier. In order to solve this problem, a method of measuring whether or not the relationship between the tracking error signal and the comparison value is correct and adjusting the same will be described below.

FIG. 8 is a block diagram of the fourth embodiment.
81 is an optical disk, 82 is an optical head including a tracking actuator for moving an objective lens, 83 is a phase compensation circuit that receives a tracking error signal output from the optical head 82, performs phase compensation, and outputs it, and 84 is an optical head 8
A kick pulse generating circuit for generating a kick pulse for moving the objective lens in the radial direction in the optical head 2;
A switch circuit for switching a signal to be applied to the tracking actuator in the unit, 86 is a variable gain amplifier for changing the amplitude of the tracking error signal entering the comparator, and 87 is a unit for comparing the tracking error signal output from the variable gain amplifier 86 with a positive comparison value. A comparator 88 compares the tracking error signal output from the variable gain amplifier 86 with a negative comparison value. A comparator 122 detects a tracking error described in the first embodiment and the second embodiment. This is the same as the first off-tracking detection unit 122 described above. 89 is a system controller.

In the optical disk device configured as described above, first, the system controller 89 tilts the switch circuit 85 toward the phase compensation circuit 83 so that the tracking servo is applied. Next, the gain of the variable gain amplifier 86 is reduced, and as shown in FIG.
The tracking error signals entering the comparators 87 and 88 are set to fall between the positive and negative comparison values, and a reset signal is sent to the first tracking error detection unit 122 to set the tracking error signal to “L”. Next, the system controller 8
Numeral 9 turns the switch circuit 85 toward the kick pulse generation circuit 84 and applies a jump pulse to the tracking actuator. When a tracking pulse is applied, the tracking actuator moves the light spot on an adjacent track by driving the objective lens according to the jump pulse. In this case, since the amplitude of the tracking error signal is small, the tracking error is not detected, and the tracking error signal output from the first tracking error detection unit 122 remains “L”. The system controller 89 monitors the tracking-off signal, and in the case of “L”, increases the gain of the variable gain amplifier 86 and performs the same processing.
When the gain of the variable gain amplifier 86 increases and the relationship between the tracking error signal and the positive / negative comparison value assumes an assumed relationship, tracking loss is detected, and the tracking loss signal becomes “H”. When the tracking loss signal becomes “H”, the system controller 89 sets the variable gain amplifier 8
The gain of 6 is fixed, and the adjustment is completed.

As described above, according to the fourth embodiment, the tracking error state is created by performing the track jump, and by changing the amplitude of the tracking error signal while monitoring the tracking error signal, the tracking error signal and the tracking error signal are changed. Positive and negative comparison values can be made to have a correct relationship, and it is possible to accurately detect out-of-tracking.

In the second embodiment and the third embodiment,
The result of comparing the tracking error signal with the positive comparison value is S
The result of comparison with the negative comparison value was input to the reset terminal at the set terminal of the R latch circuit. Conversely, the result of comparison with the positive comparison value was set at the reset terminal, and the result of comparison with the negative comparison value was set. It may be input to the terminal.

In the second embodiment, a block for detecting tracking error by frequency measurement is added to the tracking error detecting section described in the first embodiment.
May be combined with the out-of-tracking detection unit described in the embodiment.

In the fourth embodiment, the relationship between the tracking error signal and the comparison value is adjusted by changing the amplitude of the tracking error signal using the variable gain amplifier. However, means for changing the comparison value is provided. The adjustment may be performed by fixing the amplitude of the tracking error signal and changing the comparison value.

In the fourth embodiment, the gain of the variable gain amplifier is reduced in advance, the gain is increased, and the adjustment is performed by fixing the gain of the variable gain amplifier when tracking loss is detected. However, the adjustment may be performed by increasing the gain of the variable gain amplifier in advance, gradually decreasing the gain, and fixing the variable gain amplifier to the gain immediately before detection of tracking loss is not detected.

Further, in the fourth embodiment, the track jump is performed in order to create a state of tracking loss.
For example, the tracking servo is released while the optical disc is rotated, and tracking is lost due to eccentricity. In the case of performing two-step servo with the optical head and the head transporting means, the head transporting means is driven to reduce the tracking loss state. It does not matter how you make it.

Further, in the fourth embodiment, the method of performing the adjustment using the tracking error detecting section described in the first embodiment has been described. However, the tracking error detecting method described in the second and third embodiments has been described. It goes without saying that similar adjustments can be made to the parts.

[0032]

As described above, according to the present invention,
It is possible to realize an optical disk apparatus that can detect the position of the light spot with fine precision, accurately detect out-of-tracking, and perform stable recording and reproducing operations with little interruption of the recording operation.

[Brief description of the drawings]

FIG. 1 is a block diagram illustrating a configuration of an optical disc device according to a first embodiment of the present invention.

FIG. 2 is a waveform chart showing the operation of the optical disc device in the first embodiment.

FIG. 3 is a block diagram showing a configuration of an optical disk device according to a second embodiment of the present invention.

FIG. 4 is a waveform chart showing the operation of the optical disc device in the second embodiment.

FIG. 5 is a block diagram showing a configuration of an optical disc device according to a third embodiment of the present invention.

FIG. 6 is a waveform chart showing an operation of the optical disk device according to the third embodiment when detecting an off-track;

FIG. 7 is a waveform chart showing an operation of the optical disc device according to the third embodiment in the case where no out-of-track is detected.

FIG. 8 is a block diagram showing a configuration of an optical disk device according to a fourth embodiment of the present invention.

FIG. 9 is a waveform chart for explaining the operation of the optical disc device in the fourth embodiment.

FIG. 10 is a block diagram showing a configuration of a tracking-off detection circuit of a conventional optical disk device.

FIG. 11 is a waveform chart showing an operation of a tracking-off detection circuit of a conventional optical disk device.

[Explanation of symbols]

 12, 13, 112 Comparator 15, 111, 116 Counter 17, 119 SR latch circuit 114 D latch circuit

──────────────────────────────────────────────────続 き Continuation of the front page (56) References JP-A-61-168136 (JP, A) JP-A-62-102432 (JP, A) JP-A-4-28022 (JP, A) JP-A-7-128 287856 (JP, A) (58) Field surveyed (Int. Cl. ⁷ , DB name) G11B ^7/ 09-7/095

Claims (3)

(57) [Claims] An information track on an optical disc is irradiated with a light beam, and information is read out by optical means.
An optical head that outputs a tracking error signal indicating a displacement between the information track and the light beam; and a first comparing the tracking error signal with a positive comparison value.
A first level comparing means for outputting a comparison result of the following, and comparing the tracking error signal with a negative comparison value;
A second level comparing means for outputting a comparison result of the first comparison result or the second comparison result, and a period during which the tracking error signal is larger than a positive comparison value, or a negative comparison value A first period measuring unit that measures the length of a smaller period, a first period that compares a measurement result of the first period measuring unit with a length of the first reference period, and outputs a third comparison result. A period comparing means, the first comparison result and the second comparison result being input, and a period from when the tracking error signal becomes smaller than a positive comparison value until it becomes smaller than a negative comparison value, or A second period measuring means for measuring the length of a period from when the comparison value becomes larger than the positive comparison value to when the measurement result of the second period measuring means and the second reference period are longer. And outputs the fourth comparison result Inputting the third and fourth comparison results, wherein the measurement result of the first period measuring means is longer than the length of the first reference period, and An off-track output means for outputting an off-track signal when the measurement result of the means is shorter than the length of the second reference period. 2. An information track on an optical disk is irradiated with a light beam, and information is read out by optical means.
An optical head that outputs a tracking error signal indicating a displacement between the information track and the light beam; and a first comparing the tracking error signal with a positive comparison value.
A first level comparing means for outputting a comparison result of the following, and comparing the tracking error signal with a negative comparison value;
A second level comparing means for outputting a comparison result of the first and second comparison results, wherein the first comparison result and the second comparison result are inputted, and after the tracking error signal becomes larger than a positive comparison value, Time to get smaller, or
A period measuring means for measuring a time from when the period becomes smaller than the negative comparison value to when the period becomes larger than the positive comparison value; and when the time measured by the period measuring unit is smaller than a predetermined value, it is determined that tracking loss has occurred. And an out-of-track detecting means for outputting an out-of-track signal. 3. An optical recording medium for an information track of an optical disk.
At the same time as reading the information by optical means
A track indicating a displacement between the information track and the light beam.
An optical head for outputting Kkingu error signal, comparing said tracking error signal a positive comparison value, the first
A first level comparing means for outputting a result of the comparison, and comparing the tracking error signal with a negative comparison value;
A second level comparator means for outputting a comparison result of said first comparison result and inputs the second comparison result, at a given time, the tracking error signal from becoming larger than the positive reference value of the negative Frequency measurement means for measuring the number of times until the value becomes smaller than the comparison value, or the number of times until the value becomes smaller than the negative comparison value and becomes larger than the positive comparison value, and the frequency measured by the frequency measurement means is a predetermined value. Off- track output that outputs off-track signal when exceeding
Optical disc and means.