JPH067415B2 - Track error detection method - Google Patents

Description

The present invention relates to a track error detecting method, and more particularly to an optical information reproducing apparatus for reproducing information by irradiating a recording medium having a track on which information is recorded with a light beam, which is modulated by the recorded information. The light beam is received by a photodetector having four detection areas, which are divided in a direction substantially parallel to the track and a direction substantially perpendicular to the track, and a deviation of the light beam from the track in the direction perpendicular to the track is detected. The present invention relates to a method for detecting a track error signal representing a quantity and a direction.

(Prior Art) In the recording medium used in the optical information reproducing apparatus as described above, the width of the information track and the interval between the information tracks are very narrow in order to increase the recording density. In order to accurately read the original information from the information track having a narrow width and a small pitch, it is necessary to accurately project the light beam on the information track of the medium. However, the relative position between the light beam and the information track will change during information reproduction due to the influence of media installation error or vibration. Therefore, in such an optical information reproducing apparatus, a signal indicating the amount and direction of deviation between the light beam and the information track in the direction perpendicular to the track, a so-called track error signal, is detected, and the light beam is generated based on this signal. The servo mechanism controls the displacement in the direction perpendicular to the track. A method for detecting the track error signal is proposed in, for example, Japanese Patent Laid-Open No. 57-74837.

An optical disc reproducing device will be described below as an example of the optical information reproducing device, and the conventional track error detecting method as described above will be described.

FIG. 6 shows an optical system of the optical disc reproducing apparatus. The disc 1 is rotated by the spindle 2 at, for example, 30 minutes per minute.
It rotates at a speed of 0 rotation. Concentric or spiral tracks are recorded on the disc 1. A light beam emitted from a light source 4 such as a laser is collimated by a collimator lens 5, is transmitted through a half mirror 6, is reflected by a mirror 7 and is condensed on a disk 1 by an objective lens 8. . The condensed light beam is reflected by the disk 1, reflected by the half mirror 6 and condensed by the lens 9 and projected onto the photodetector 10. The photodetector 10 detects the information on the disk by the change in the light intensity.

FIG. 7 is a block diagram showing a signal processing system of the output of the photodetector 10. The photodetector 10 has four detection areas 4 divided in a direction substantially parallel to the track of the disk 1 (Y-axis direction) and a direction perpendicular to the track (X-axis direction).
It has 1,42,43,44. These four detection areas 41 ~
Assuming that the outputs of 44 are a, b, c, and d, the sum U ₁ = a + c and U ₂ = b + d of the outputs of the detection areas located at the diagonal positions are added to the adder circuit 4
5 and 46 respectively. Further, the sum signal U ₃ = U ₁ + U ₂ of these sums U ₁ and U ₂ is obtained by the adder circuit 47, and the difference signal U ₄ = U ₁ -U ₂
Is obtained by the subtraction circuit 48. As shown in the signal waveform diagram of FIG. 8, the difference signal U ₄ has opposite polarities depending on the direction of deviation. Further, as shown in FIG. 8, the sum signal U ₃ is an information signal modulated by an information structure, has a pit frequency, and has a π / 2 phase shift with respect to the difference signal U ₄ . The output U ₃ of the adder circuit 47 is the rising pulse generation circuit 4
9 and the falling pulse generation circuit 50, and the output U ₄ of the subtraction circuit 48 is supplied to the gate circuits 51 and 52, respectively. The rising and falling pulse generation circuits 49 and 50 detect the zero-cross points at the rising and falling edges of the sum signal U ₃ , respectively, and output the eighth signal, respectively.
It produces first and second sampling pulse signals U ₅ and U ₆ as shown. These U ₅ and U ₆ are gate circuits 5
1 and 52 to sample the difference signal U ₄ and supplied to sample hold these sampled difference signal U ₄ at the hold circuits 53 and 54, respectively. U _{7 in} FIG. 8 shows the output of the hold circuit 53 sampled by the sampling pulse signal U ₅ from the rising pulse generation circuit 49, and U _{8 in} FIG. 8 shows the sampling pulse signal U from the falling pulse generation circuit 50. The output of the hold circuit 54 sampled by ₆ is shown. The output signals U ₇ and U ₈ of the hold circuits 53 and 54 are supplied to an RF signal differential amplifier 55 to obtain the difference between them, and a tracking signal U ₉ as shown in FIG.

However, in such a conventional track error detection method, a correct track error signal may not be detected if optical or electrical noise is mixed between the photodetector and the gate circuits 51 and 52. there were.

The above reason will be described in detail with reference to the signal waveform diagram of FIG.

Optical noise typified by changes in the emission intensity of the radiation source or changes in the amount of light reaching the photodetector due to changes in the emission wavelength, and electrical noise that is generated in the photodetector or the circuits up to the gate circuits 51 and 52 or that is externally mixed. The noise appears in the sum signal U ₃ and the difference signal U ₄ shown in FIG. Here the sum signal U ₃ for generating sampling pulses in the track or on the track near the small ratio of the noise component to the signal component, but not too large influence of noise, the difference signal U ₄ to be sampled, on the track or In the vicinity of the track, the ratio of the noise component to the signal component becomes large, and the sample and hold signals output from the sample and hold circuits 53 and 54 become signals affected by noise as shown in U ₂₁ and U ₂₂ in FIG. . Therefore U ₂₁ ,
The track error signal obtained by the difference of U ₂₂ is shown in Fig. 9U.
_As shown in _23, there were two zero points and the track servo became unstable.

(Summary of the Invention) An object of the present invention is to solve the above-mentioned drawbacks of the prior art and to provide a method of detecting a track error signal capable of performing stable track servo with less influence of noise.

In order to achieve the above object, the track error detecting method of the present invention irradiates a recording medium having a track on which information is recorded with a light beam, and directs the light beam modulated by the recording information in a direction substantially parallel to the track. And in order to detect a track error signal by receiving light with a photodetector having four detection areas each divided in a direction perpendicular to it,
When the outputs of two detection areas are a, b, c, and d, the sum of the outputs of the detection areas diagonally located S ₁ = a + c, S ₂ = b + d
Look, these S _1, S ₂ of the sum signal S ₃ = S ₁ + S ₂ and the difference signal S ₄ =
S ₁ -S ₂ is obtained, zero-crossing points of the rising and falling edges of the difference signal S ₄ are detected to generate first and second sampling pulse trains, respectively, and the sum is calculated by the first and second sampling pulse trains. The signal S ₃ is sampled and held to obtain the first and second sample values, the difference signal S ₅ between the first and second sample values is obtained, and L ₁ > 0 and L ₁ > 0 and
From the predetermined values L ₁ and L ₂ set to satisfy L ₂ <0 and the difference signal S ₅ , when S ₅ > L ₁ , S = L ₁ − (S ₅ −L ₁ ) L ₂ ≦ When S ₅ ≦ L ₁ , when S = S ₅ S ₅ <L ₂ , a tracking error signal S represented by S = L ₂ + (L ₂ −S ₅ ) is obtained.

The track error detecting method of the present invention also irradiates a recording medium having a track on which information is recorded with a light beam, and causes the light beam modulated by the recording information to be in a direction substantially parallel to the track and a direction perpendicular thereto. When the outputs of the four detection areas are set to a, b, c, and d in order to detect a tracking error signal by receiving light with a photodetector having four detection areas that are divided, The sum S ₁ = a + c and S ₂ = b + d of the outputs of a certain detection area is calculated, and
Seeking S _1, S sum signal of _{2 S 3 = S 1 + S} 2 and the difference signal S ₄ = S ₁ -S _2, by detecting either one of the zero-cross point of the rising or falling of the difference signal S ₄ A sampling pulse train is generated, the sum signal S ₃ is sampled and held by this sampling pulse train to obtain a signal S ₅ indicating a sample value, and L ₁
When S ₅ > L ₁ from the predetermined values L ₁ and L ₂ set to satisfy> L ₂ and the signal S ₅ described above, S = L ₁ − (S ₅ −L ₁ ) L ₂ ≦ S ₅ ≦ when L _1, S = the time of the _{S 5 S 5 <L 2,} S = L 2 + (L 2 -S 5) obtains the signal S represented by the track error signal by comparing the signal S with a reference value It is characterized by obtaining.

That is, according to the present invention, of the sum signal S ₃ and the difference signal S ₄ obtained from the outputs of the four detection areas, at the timing of the sampling pulse obtained from the difference signal S ₄ , the sum signal S ₃ relatively less affected by noise is generated. Is sample-held and the tracking error signal is calculated from this sample value, so that it is possible to perform stable track servo that is resistant to noise and is always stable.

(Example) Hereinafter, an example of the present invention will be described in detail with reference to the drawings.

FIG. 1 is a block diagram showing an example of a signal processing circuit for realizing the track error detecting method of the present invention, and FIG. 2 is a diagram showing signal waveforms of outputs at respective positions of the circuit shown in FIG. . In FIG. 1, the same members as those in FIG. 7 are designated by the same reference numerals. Here, 10 indicates a photodetector, and the configuration for obtaining the light beam received by the photodetector 10 can be applied with the conventional technique described in FIG.

The photodetector 10 has four detection areas 41, 42, 43, 44 which are divided in a direction substantially parallel to the track of the disc (Y-axis direction) and a direction perpendicular to the same (X-axis direction). . The outputs of these four detection areas 41 to 44 are a, b, c, d
Then, the sums S ₁ = a + c and S ₂ = b + d of the outputs of the diagonal detection positions are calculated by the adder circuits 20 and 21, respectively. Further, the sum signal S ₃ = S ₁ + S ₂ of these S ₁ and S ₂ is obtained by the addition circuit 23, and the difference signal S ₄ = S ₁ -S ₂ between S ₁ and S ₂ is obtained by the subtraction circuit 22. As shown in FIG. 2 (B), the difference signal S ₄ has opposite polarities depending on the direction of the positional deviation between the light beam and the track. The sum signal S ₃ is an information signal modulated by the information structure recorded on the recording medium as shown in the second (A) (the average level of the signal is indicated by L ₀ ),
It has a pit frequency corresponding to the recorded pit and is out of phase by π / 2 with respect to the difference signal S ₄ . Therefore, in the optical information reproducing apparatus, this adding circuit 23
Information is reproduced from the output of.

On the other hand, the difference signal S ₄ is supplied to the rising pulse generating circuit 24 and the falling pulse generating circuit 25 having different threshold levels. Regarding the threshold levels of the two pulse generation circuits, the threshold level of the falling pulse generation circuit 25 is lower than the threshold level of the rising pulse generation circuit 24, and the difference between the two threshold levels is different. Is set larger than the amplitude of the noise component of the difference signal S ₄ . The outputs of the pulse generating circuits 24 and 25 are shown in FIGS. 2 (C) and (D). this
The pulses (C) and (D) are supplied to the gate circuits 26 and 27, and the sum signal S ₃ is sampled. Further, the signals sampled by the gate circuits 26 and 27 are supplied to the hold circuits 28 and 29 and held therein. This is shown in FIGS. 2 (E) and (F). The subtraction circuit 30 outputs the difference between these two sample hold signals. The output S ₅ of the subtraction circuit 30 is shown in FIG.

Then supplying the difference signal S ₅ to the comparison circuits 31 and 32, if greater than the predetermined value L _1, if L ₂ is less than performs when divided into three types of cases L ₂ or L ₁ or less. Note that L ₁ is larger than 0 and L ₂ is smaller than 0. The switch 33 switches the difference signal S ₅ according to the three cases. When the difference signal S ₅ is larger than L ₁ , the subtraction circuit 34 obtains the difference signal S ₆ = S ₅ −L ₁ . The difference signal S ₆ is shown in FIG. 6 (H). Further, the subtraction circuit 35 obtains a difference signal S ₇ = L ₁ -S ₆ . If the difference signal S ₅ is smaller than L ₂ , the subtraction circuit 36 subtracts the difference signal S ₈ = L ₂
-Get S ₅ . The difference signal S ₈ is shown in FIG. 6 (I). Further, the adder circuit 37 obtains the sum signal S ₉ = L ₂ + S ₇ . Difference signal S ₅ is L ₂ or more L ₁
In the following cases, the difference signal S ₅ is directly supplied to the adder circuit 38. The output terminals of the subtraction circuit 35 and the subtraction circuit 37 are also connected to the addition circuit 38, and any of the signals S ₅ , S _7, and S ₉ is input to the addition circuit 38 by the switching. The output S ₁₀ of the adder circuit 38 becomes the track error signal. The signal waveform of the track error signal S ₁₀ is shown in FIG.

In this way, by generating a sampling pulse with the difference signal S ₄ and sampling the sum signal S ₃ , even if the light beam is on or near the track, it is not affected by optical or electrical noise and is accurate. It is possible to obtain various track error signals.

Here, L _{1, which} is the comparison reference of the comparison circuit 31, is the difference signal S ₅
By setting a half or more of the maximum value M ₁ or less and the maximum value M ₁ of the difference signal S ₇ is S _5> As shown in FIG. 3 in the range of _{L 1 (A) S 7 =} 2L _1- M ₁ > 0. L _{2 which} is the comparison reference of the comparison circuit 32 is the minimum value M ₂ of the difference signal S ₅ or more and the minimum value.
By setting it to 1/2 of M ₂ or less, the difference signal S ₉ becomes S ₅ <L ₂
In the range, S ₉ = 2L ₂ -M ₂ <0 as shown in FIG. 3 (B). Therefore, if L ₁ and L ₂ are set as described above, the track error signal S ₁₀ has a zero cross point and is stable only when the light beam is on the track as shown in FIG. 3 (C). Servo can be performed.

FIG. 4 is a block diagram showing an example of a signal processing circuit for realizing another track error detecting method according to the present invention,
FIG. 5 is a diagram showing signal waveforms of outputs at respective positions of the circuit shown in FIG. Incidentally, in FIG. 4, the same members as those in FIG. 1 are designated by the same reference numerals, and detailed description thereof will be omitted. Also,
Also in the present embodiment, as the configuration for obtaining the light beam received by the photodetector 10, the conventional technique described in FIG. 6 can be applied as it is.

In FIG. 4, the optical signal received by the photodetector 10 is
The sum signal S ₃ (the average level of the signal is shown by L ₀ ) shown in FIG. 5 (A) from the adder circuit 23 is processed in exactly the same way as in the case of FIG. Difference signal S shown in (B)
You get ₄ . The difference signal S ₄ is supplied to the rising pulse generation circuit 61 and generates the sampling pulse shown in FIG. 5 (C). This sampling pulse is supplied to the gate circuit 62 to sample the sum signal S ₃ . Further, the signal sampled by the gate circuit 62 is supplied to the hold circuit 6
The signal S ₅ corresponding to the sample value shown in FIG. 5 (D) is obtained by being held at 3.

Then supplies the signal S ₅ to the comparison circuits 31 and 32, if greater than the predetermined value L _1, if L ₂ is less than, L ₂ or L ₁
Cases are divided into the following three cases. Note that L ₁ is larger than L ₂ . The signal S ₅ is switched by the switching 33 according to the three cases. Signal S ₅ is L ₁
If it is larger, the subtraction circuit 34 obtains the difference signal S ₆ = S ₅ -L ₁ . The difference signal S ₆ is shown in FIG. Further subtraction circuit 35
The difference signal S ₇ = L ₁ -S ₆ is obtained at. When the signal S ₅ is smaller than L ₂ , the subtraction circuit 36 obtains the difference signal S ₈ = L ₂ -S ₅ . The difference signal S ₈ is shown in FIG. Further, the sum signal S is added by the adder circuit 37.
We get ₉ = L ₂ + S ₇ . If signal S ₅ is between L _{2 and} L ₁ , inclusive, signal S ₅
Is directly supplied to the adder circuit 38. . The output terminals of the subtraction circuit 35 and the subtraction circuit 37 are also connected to the addition circuit 38, and any of the signals S ₅ , S _7, and S ₉ is input to the addition circuit 38 by the switching. And
The difference between the output of the adder circuit 38 and the reference value of an appropriate level supplied from the potentiometer 65 is determined by the difference amplifier 6.
As shown in FIG.
A track error signal S ₁₀ as shown in (H) is obtained. Also in this embodiment, the same effect as that of the example described with reference to FIG. 1 can be obtained by sampling and holding the sum signal with the sampling pulse obtained from the difference signal S ₄ .

Here, the comparison reference L ₁ of the comparison circuit 31 is set to be equal to or less than the maximum value of the signal S ₅ and equal to or more than the value obtained by adding 1/2 of the amplitude of the signal waveform of S _{5 to} the average level L ₀ of S _5. The difference signal S
A _{S 7 = 2L 1 -M 1>} L 0 in the range of _7> L _1. Also, comparison circuit 3
L _{2 which} is the reference for comparison of ₂ is greater than or equal to the minimum value of the difference signal S ₅ and
By setting the average level L ₀ of the S ₅ below minus half the amplitude of the signal waveform S _5, the difference signal S ₉ is S ₉ = 2L ₂ -M in the range of S ₅ <L _{2 2} <L ₀ . Therefore, if L ₁ and L ₂ are set as described above, the track error signal S ₁₀ when the reference value is L ₀ has a zero cross point and is stable only when the light beam is on the track. Servo can be performed.

The present invention is not limited to the embodiments described above, and various applications are possible. For example, in FIGS. 1 and 4, the signal
Since S ₇ and S ₉ can be written as S ₇ = 2L ₁ -S ₆ and S ₉ = 2L ₂ -S ₅ , respectively, the subtraction circuits 34 and 35 are combined into a single subtraction circuit to which 2L ₁ and S ₅ are input, and , The subtraction circuit 36 and the addition circuit 37 are 2L
It can be replaced with a single subtraction circuit that inputs ₂ and S ₅ . Further, in the example of FIG. ₄ , the sampling is performed at the rising timing of the difference signal S ₄ , but even if the sampling is performed at the falling timing of the difference signal S ₄ , the track error signal can be detected in exactly the same manner. . Further, in the example of FIG. 4, the difference from the reference value is not limited to the subsequent stage of the adder circuit 38, but any stage such as the stage where the sum signal S ₃ is calculated or the stage where the signal S ₅ corresponding to the sample value is calculated. You can do it in.

(Effect of the Invention) As described above, according to the present invention, of the sum signal and the difference signal obtained from the outputs of the four detection areas, the sum signal is sample-held at the timing of the sampling pulse obtained from the difference signal to track error. By obtaining the signal, the effect of noise can be reduced and the effect of stabilizing the track servo can be obtained.

[Brief description of drawings]

FIG. 1 is a block diagram showing an example of a signal processing circuit for implementing the track error detecting method according to the present invention, and FIG.
(J) is a diagram showing signal waveforms in respective portions of the circuit shown in FIG. 1, and FIGS. 3 (A), (B), and (C) are predetermined values L shown in FIG. 2, respectively.
FIG. 4 is a signal waveform diagram for explaining the setting of ₁ and L ₂ , FIG. 4 is a block diagram showing an example of a circuit for carrying out another example of the track error detection method according to the present invention, and FIGS. H) is a diagram showing signal waveforms in respective portions of the circuit shown in FIG. 4, FIG. 6 is a schematic diagram showing a configuration of an optical system of an optical disk reproducing apparatus to which the present invention can be applied, and FIG. 7 is a conventional track error detection. A block diagram showing a circuit used in the method, FIGS. 8 and 9 are diagrams showing signal waveforms in respective portions of the circuit shown in FIG. 7, respectively. 10 …… Photodetector 41,42,43,44 …… Detection area 20,21,23,37,38 …… Adding circuit 22,30,34,35,36 …… Subtracting circuit 24 …… Rising pulse generation circuit 25 …… Falling pulse generation circuit 26,27 …… Gate circuit 28,29 …… Hold circuit 31,32 …… Comparison circuit 33 …… Switch 38 …… Output terminal

Claims (4)

[Claims] 1. A recording medium having a track on which information is recorded is irradiated with a light beam, and the light beam modulated by the record information is divided into four directions, which are substantially parallel to the track and perpendicular to the track. In a method of detecting a track error signal indicating the amount and direction of deviation between a light beam and a track in a direction perpendicular to a track, the output of the four detection areas is detected by a, b , c, d, the sum of the outputs of the detection areas diagonally located S ₁ = a + c, S
₂ = b + d is obtained, the sum signal S ₃ = S ₁ + S _{2 of} these S ₁ and S ₂ and the difference signal S ₄ = S ₁ -S ₂ are obtained, and the rising and falling of the difference signal S ₄ is calculated. A zero-cross point is detected to generate first and second sampling pulse trains, and the sum signal S ₃ is sampled and held by the first and second sampling pulse trains to obtain first and second sample values, The difference signal S ₅ between the first and second sample values is obtained, and the predetermined value L ₁ and L ₂ set to satisfy L ₁ > 0 and L ₂ <0 respectively, and the difference signal S _{5 are used} to track When the error signal S is under the following conditions, S ₅ > L ₁ , S = L ₁ − (S ₅ −L ₁ ) L ₂ ≦ S ₅ ≦ L ₁ , S = S ₅ S ₅ <L ₂ , S = L ₂ + (L ₂ −S ₅ ). Wherein said predetermined value L ₁ is set to 1/2 or more of the maximum value of and S ₅ greater than the maximum value of the difference signal S _5, at the predetermined value L ₂ is less than the minimum value of the difference signal S ₅ The track error detection method according to claim 1, wherein the value is set to 1/2 or less of the minimum value of S ₅ . 3. A recording medium having a track on which information is recorded is irradiated with a light beam, and the light beam modulated by the record information is divided into four directions, which are substantially parallel to the track and perpendicular to the track. In a method of detecting a track error signal indicating the amount and direction of deviation between a light beam and a track in a direction perpendicular to a track, the output of the four detection areas is detected by a, b , c, d, the sum of the outputs of the detection areas diagonally located S ₁ = a + c, S
₂ = b + d is obtained, the sum signal S ₃ = S ₁ + S _{2 of} these S ₁ and S ₂ and the difference signal S ₄ = S ₁ -S ₂ are obtained, and the difference signal S ₄ rises or falls. A sampling pulse train is generated by detecting one of the zero-cross points, and the sum signal S ₃ is sampled and held by this sampling pulse train to obtain a signal S ₅ indicating a sample value, so that L ₁ > L ₂ is satisfied. From the set predetermined values L ₁ and L ₂ and the signal S ₅ , the signal S is set to the following condition, when S ₅ > L ₁ , S = L ₁ − (S ₅ −L ₁ ) L ₂ ≦ S ₅ ≦ L _{When 1} , S = S _{5 When} S ₅ <L ₂ , obtain as shown by S = L ₂ + (L ₂ -S ₅ ) and compare this signal S with a reference value to obtain the track error signal. A method for detecting a track error characterized by: 4. The predetermined value L ₁ is set to be less than or equal to the maximum value of the signal S ₅ and more than or equal to a value obtained by adding 1/2 of the amplitude of the signal waveform of S _{5 to} the average level of S _{5 and} the predetermined value. L ₂ is the amplitude of the signal waveform S ₅ from the average level of the minimum value or more and S ₅ of the signal S ₅
The track error detection method according to claim 3, wherein the track error detection method is set to a value less than 1/2.