KR20000038810A - Method for detecting tilt of optical disc drive - Google Patents

Abstract

PURPOSE: A method is provided to compensate an effect by a defocus in a method for detecting a tilt component by using a head signal in an optical disc drive to record and to play a recordable disc having a header pre-pitted for distinguishing a physical sector. CONSTITUTION: A size of a signal detected in a synchronous signal area recorded on a middle line of track is V1 and a size of a signal detected in the synchronous signal area recorded on a middle line of track is V3. And tilt amounts and defocus amounts are detected by a difference between V1 and V3 in points having a different focus each other. The tilt amount is decided by operating a rate between a changed amount of tilt amounts and a changed amount of defocus amounts detected in two points. The tilt method has a benefit to stably compensate the tilt by compensating an effect from the defocus in detecting the tilt and the defocus amounts using the synchronous signal recorded in a header area of a disc.

Description

Tilt detection method of optical disc drive

The present invention relates to a method of detecting a tilt component using a header signal in an optical disc drive for recording and reproducing a recordable disc having a pre-pitted header for determining a physical sector. It is about how to compensate for the impact.

In addition to playback-only discs such as DVD-ROMs, as well as recordable discs such as DVD-RAMs, as the recording density increases, signal quality deterioration due to the disc tilt increases.

In the recordable disc, if the tilt is present during recording, the recording quality is deteriorated due to the influence thereof. If the tilt is also present during the playback of the part, the quality of the reproduction signal is increased, causing data error.

Tilts often occur depending on the state of the disk or driver, and a method and apparatus for adjusting / removing these two components are required.

A method of detecting the tilt component using the header signal recorded on the disc is used. This method detects the magnitude difference of the reproduced signals in the headers arranged up and down at the centerline of the track. Even if the tracking of the disc is maintained correctly, the distribution of the laser beam is distributed according to the tilt when the disc is tilted. Therefore, the intensity of the laser beam irradiated to the headers arranged up and down at the center line of the track changes according to the tilt, and the tilt amount can be detected by detecting the degree of the change.

However, the intensity of the laser beam irradiated onto the headers can also be changed by focus, so a method must be devised to compensate or eliminate the effects of focus.

An object of the present invention is to provide a method for compensating the influence of defocus in a method of detecting a tilt component of an optical disk drive, which is devised to meet the above requirements.

FIG. 1A shows the physical shape of the land track, and FIG. 1B shows the waveform of the push-pull signal in the land track.

2A shows the physical shape of the groove track, and FIG. 2B shows the waveform of the push-pull signal in the groove track.

3 is an enlarged view of the header area illustrated in FIGS. 1A to 2A.

4A and 4B show a push-pull signal and a sum signal obtained when the laser spot passes through the header section of the groove track, respectively, in FIG. 3.

FIG. 5 shows the configuration of a device for obtaining the push-pull signal shown in FIG. 4.

6 shows various signals and timings for detecting the magnitude of the synchronization signal.

7 is V ₁ and V ₃ The configuration of the measuring device will be shown.

8 shows various signals and timings for detecting the magnitude of a mirror signal.

9 is a radial tilt and balance value K This graph shows the relationship of.

10 shows defocus and balance values K This graph shows the relationship of.

11 is a block diagram showing the configuration of a conventional radial tilt correction device.

12 is a block diagram showing a detailed configuration of the radial tilt adjustment unit shown in FIG.

13 is a flowchart illustrating an embodiment of a tilt detection method according to the present invention.

14 is a flowchart illustrating another embodiment of a tilt detection method according to the present invention.

15 is a flowchart illustrating still another embodiment of the tilt detection method according to the present invention.

One embodiment of the tilt detection method according to the present invention to achieve the above object

A tilt detection method of an apparatus for reproducing an optical disc having at least a synchronous signal region in which a synchronous signal is recorded up and down at a track center line, the tilt detection method comprising: adjusting the defocus of the optical disc to be minimum; And the magnitude of the signal detected in the synchronization signal area recorded on one side of the track center line. V ₁ And the magnitude of the signal detected in the synchronization signal area recorded on the other side of the track center line. V ₃ When we say V ₁ and V ₃ Difference V ₁ -V ₃ It characterized in that it comprises a process of detecting the amount of tilt by.

Another embodiment of the tilt detection method according to the present invention which achieves the above object is a tilt detection method of an apparatus for reproducing an optical disc having synchronization signal regions in which at least a synchronization signal is recorded up and down at the track center line. Size of the detected signal in the sync signal area V ₁ And the magnitude of the signal detected in the synchronization signal area recorded on the other side of the track center line. V ₃ When we say V ₁ and V ₃ Difference V ₁ -V ₃ Detecting the amount of tilt by; And said V ₁ -V ₃ It characterized in that it comprises a process of compensating by the defocus amount.

Still another embodiment of the tilt detection method according to the present invention to achieve the above object

A tilt detection method of an apparatus for reproducing an optical disc having sync signal regions in which at least a sync signal is recorded above and below a track center line, the tilt detection method comprising: a magnitude of a signal detected in a sync signal region recorded above the track center line; V ₁ And the magnitude of the detected signal in the synchronization signal area recorded above the track center line. V ₃ So, at two different points of focus V ₁ and V ₃ Difference V ₁ -V ₃ Tilt amount by K _t1 , K _t2 ) And defocus amount ( d ₁ , d ₂ Detecting); And determining the tilt amount by calculating a ratio of the change amount of the tilt amount and the change amount of the defocus amount detected at the two points. Hereinafter, the configuration and operation of the present invention will be described in detail with reference to the accompanying drawings.

In a DVD-RAM disc, information is recorded in a track, and the track is composed of a land track and a groove track, and the land track and the groove track intersect with each revolution of the disc. The reason why the land track and the groove track intersect in a DVD-RAM disc is to provide a tracking guide initially, and also to reduce crosstalk between adjacent tracks in a high density narrow track.

The track is composed of sectors divided into constant lengths. As a means for enabling physical division of such sectors, the header area is pre-pitted at the time of disc manufacture. The physical address of the sector is recorded in this header area.

That is, each sector is largely composed of a header area and a data area in which physical address information (hereinafter referred to as PID) is recorded.

1A shows the physical shape of the land track in a DVD-RAM disc, and FIG. 1B shows the waveform of a push-pull signal in the land track.

The header area is repeatedly arranged in a predetermined section (sector) of the track, and the so-called Complementary Allocation of Pit Address method in which four PIDs (PID1 to PID4) having the same value are alternately arranged from the center of the track to one header area is arranged side by side. Is recorded. That is, in order to accurately read the PID even when the laser spot 22 is out of the center of the track, PID1 and PID2 are arranged a certain amount out of the center of the track, and PID3 and PID4 are arranged in the opposite direction from the center of the track. do. In the land track and groove track, the arrangement of PID1, 2 and PID3, 4 is reversed. In the land track, a push-pull signal as shown in Fig. 1B can be obtained. In FIG. 1B, the large rectangles correspond to PID1 to PID4 from the left side, and PID1 and 2 are located at the bottom of the track center line (bottom header), and therefore have a low DC value and PID3 and 4 are upwards from the track center line. It has a high DC value because it is located at (peak header).

2A shows the physical shape of the groove track in the DVD-RAM disc, and FIG. 2B shows the waveform of the push-pull signal in the groove track. In FIG. 2B, the large rectangles correspond to PID1 to PID4 from the left side, and PID1 and 2 are located at the top of the track center line (peak header), and therefore have a high DC value and PID3 and 4 are lower from the track center line. It has a low DC value because it is located at (bottom header).

3 is an enlarged view of the header area illustrated in FIGS. 1A to 2A. In the structure of the header area, PID1,2 and PID3,4 are arranged to be shifted by a certain amount from side to side with respect to the track center, and each PID has an ID representing a physical address of a sector and a vfo signal of the same frequency for synchronization for ID detection. The signal is recorded. The vfo signal has a recording pattern of 4T (where T is the basic length of the recording signal).

As shown in Fig. 3, the header areas include vfo1 33 and ID1 34 (more than PID1), vfo2 35 and ID2 36 (more than PID2), vfo3 37 and ID3 38 (more than PID3). ), And vfo4 39 and ID4 40 (above PID4).

In FIG. 3, when the laser spot 32 passes through the header section of the groove track, the push-pull signal RF_pp as shown in FIG. 4A and the sum signal RF_sum as shown in FIG. 4B may be obtained. 4A and 4B, the vfo1 signal 42 corresponds to the vfo1 signal region 33 of FIG. 2, and the vfo3 signal 43 corresponds to the vfo3 signal region 37.

FIG. 5 shows the configuration of a reproduction signal generator for obtaining the push-pull signal RF_pp shown in FIG. 4A and the sum signal RF_sum shown in FIG. 4B. In Fig. 5, reference numeral 50 denotes a four-part photodetector, 52 and 54 are adders, and 56 denotes a calculation unit.

The apparatus shown in Fig. 5 is a sum signal of the radial pairs B and C, A and D of the light receiving elements A to D of the quadrature photodetector. I ₁ , I ₂ ), I ₁ Wow I ₂ Difference between I ₂ -I ₁ Push-pull signal RF_pp, and I ₁ Wow I ₂ Sum of I ₁ + I ₂ Outputs the sum signal RF_sum.

6 shows various signals and timings for detecting the magnitude of the synchronization signal. The detection output of header12 and the detection output of header34 of FIG. 6 are generated for the header section, and the enable 12 and enable 34 of FIG. 6 are generated for the synchronization signal section.

When enable 12 of FIG. 6 becomes “high” V ₁ If enable 34 becomes "high" V ₃ Detect.

7 is V ₁ and V ₃ As shown in FIG. 7, the signals input to the enable terminal of FIG. 7 become enable 12 and enable 34 of FIG. 6.

In the case of enable 12 is input to the device shown in FIG. V ₁ If enable 34 is input, V ₃ Outputs

The magnitude of the vfo1 signal when the laser spot crosses the track center line V ₁ Magnitude of vfo3 signal V ₃ Matches, but when a radial tilt occurs, one side gets bigger and the other gets smaller.

This is because the intensity of light reflected from the signal planes of PID1, 2 and PID3, 4 arranged to be different from each other is different. When tilting and detracking occur, the intensity of the light reflected by the upper header (peak header) becomes larger than that reflected by the lower header (bottom header).

Accordingly, the magnitude of the vfo1 signal V ₁ And vfo3 signals V ₃ The ratio is different. The magnitude of the vfo2 signal V ₂ Magnitude of vfo4 signal V ₄ The ratio between them is likewise different.

Thus, the magnitude of the vfo1 signal V ₁ And vfo3 signals V ₃ By detecting the ratio (balance) therebetween, the tilt amount and the detrack amount can be detected.

Where the balance value K is

It is obtained by K = (V ₁ -V ₃ ) / (V ₁ + V ₃ ).

here, (V ₁ + V ₃ ) Is the term for normalization.

In Equation 1 V ₁ and V ₃ Although the balance value was calculated using, it is also possible to use the magnitude of the synchronization signal detected in the vfo2 and vfo4 regions. It is also possible to use a value obtained by the combination of the synchronization signals detected in the vfo1 and vfo2 regions and a value obtained by the combination of the synchronization signals detected in the vfo3 and vfo4 regions. However, vfo1 and vfo3 are easier to detect than vfo2 and vfo4.

If there is no tilt K Value K _o When the tilt occurs K Value K ₁ Is the difference between the two values K _t Is defined as

K _t = K _o -K ₁

In other words, K _t The direction and magnitude of the tilt can be known according to the value and the sign of.

here, K _o May be a value measured in the absence of a tilt, a default value determined by the system controller of the recording / reproducing apparatus, or a value measured in a reference state determined by the system.

In the land track and groove track, the positions of PID1,2 and PID3,4 are reversed. K _t To compute K ₁ The polarity of must change from track to track.

K _t The radial tilt value in the actual system using R _t Is calculated as:

R _t = α * K _t

here, α Is a proportional constant with a constant value.

Radial Tilt Value Detected R _t Operate the tilt correction mechanism or change the recording / playback signal according to the direction and size of the. When operating the tilt correction mechanism K _t or R _t Control the value of to be zero. When changing the recording / playback signal R _t Apply. Where proportional constant α Has a constant value determined in accordance with the characteristics of the recording / reproducing apparatus and the method of manufacturing the disc.

Another example for tilt detection is to change the normalization method shown in Equation 1 by using the signal size of the mirror area immediately after the header section as follows.

K = (V ₁ -V ₃ ) / I ₀

here, Io Is a term for normalization and is the magnitude of the sum signal RF_sum in the mirror region.

At this time Io Can be obtained by applying the sum signal RF_sum to the input of FIG. 6 using the mirror interval detection signal and enable 5 shown in FIG. 8.

9 is a radial tilt and balance value K This graph shows the relationship of. In Fig. 9, the vertical axis represents the radial tilt value, and the horizontal axis represents the balance value. K Indicates. In FIG. 9, the graph indicated by ▲ shows the case where the sum signal RF_sum and the balance value according to Equation 1 are used, and the symbol indicated by ▼ shows the case where the sum signal RF_sum and the balance value according to Equation 4 are used. Denoted by the push-pull signal RF_pp and the balance value according to the equation (4), and denoted by ■ shows the case of using the push-pull signal RF_pp and the balance value by the equation (1).

As shown in FIG. 9, the best showing the radial tilt is a case in which the push-pull signal RF_pp and the balance value according to Equation 1 are used as indicated by s.

In addition, it can be seen that the? Indicates a linear result for the radial tilt although the slope is small even when the push-pull signal RF_pp and the balance value according to Equation 4 are used.

In addition, when the push-pull signal RF_pp and the balance value according to the equation (1) are used as shown in FIG. 9, the radial tilt is almost linearly affected, and thus it is very suitable for detecting the radial tilt. Able to know.

11 is a block diagram showing the configuration of a conventional tilt adjustment device. The apparatus shown in FIG. 10 includes a header section signal generator 142, a first synchronous signal level detector 144, a second synchronous signal level detector 146, a mirror section signal generator 150, a mirror level detector 152, A balance calculator 154, a comparator 156, a land / groove detector 158, and a polarity inverter 160 are provided.

An operation of adjusting the radial tilt in the apparatus shown in FIG. 11 will be described.

The header section signal generator 152 generates a header section signal (header section signal 12, header section signal 34) indicating a header region from the push-pull signal RF_pp generated by the reproduction signal generator 130. Here, the header section signal 12 is a signal indicating the PID1, 2 areas, and the header section signal 34 is a signal indicating the PID3, 4 areas. Since the header region has a larger envelope than the data region, a header section signal representing the header region can be obtained using an envelope detector and a comparator for detecting the envelope of the reproduction signal.

The first synchronous signal level detector 144 is the size of the vfo1 signal shown in FIG. 6 in synchronization with the header section signal 12 generated by the header section signal generator 142. V ₁ Is detected. Specifically, after generating the first enable signal enable 12 having a predetermined interval and a predetermined width from the start point of the header interval signal 1, gating the push-pull signal RF_pp by the first enable signal enable 12 By detecting the peak-peak value of the gated reproduction signal V ₁ Is detected.

The second synchronous signal level detector 146 synchronizes the header section signal 34 generated by the header section signal generator 142 with the magnitude of the vfo3 signal shown in FIG. 6. V ₃ Is detected. In more detail, a second enable signal enable 34 having a predetermined interval and a predetermined width is generated from the start point of the header section signal 34, and the gate pull signal RF_pp is gated by the second enable signal enable 34, and then gated. By detecting the peak-peak value of the reproduction signal V ₃ Detect. The first synchronous signal level detector 144 and the second synchronous signal level detector 146 are implemented with the apparatus shown in FIG.

The balance calculator 154 is detected by the first synchronous signal level detector 144 as shown in equation (1). V ₁ Detected by the second synchronous signal level detector 146 V ₃ Calculate the ratio of and. Here, the balance calculator 154 may output an average value of balance values obtained from several consecutive sectors.

The comparator 156 calculates a balance value calculated by the balance calculator 164 as shown in Equation 2. K ₁ And the predetermined reference value K _o Compare and compare the two values K _t Outputs here, K _o May be a value measured in the absence of a detrack, a default value determined by the system controller of the recording / playback apparatus, or a value measured in a reference state determined by the system.

The land / groove detector 158 introduces RF_pp to detect whether the current track is a land track or a groove track. As shown in Fig. 1B, the push-pull signal RF_pp in the land track is larger than the size of PID3,4, and in the groove track, the size of PID1,2 is smaller than the size of PID3,4. The land / groove detector 138 uses the same to determine a land / groove track.

The polarity inversion unit 160 outputs a difference value output from the comparator 156 according to a result detected by the land / groove detector 158. K _t Invert the polarity of.

The radial tilt adjustment unit 134 is a polarity inverted difference value output from the polarity inversion unit 160. K _t Adjust the radial tilt accordingly. Difference K _t Since the sign and magnitude of represents the direction and magnitude of the radial tilt, the tilt is adjusted by feeding back the tilt.

The mirror section signal generator 150 generates a mirror section signal representing the mirror area from the sum signal RF_sum generated by the reproduction signal generator 130. In the case of the push-pull signal RF_pp, since the mirror signal becomes zero, the mirror section signal cannot be obtained by the push-pull signal RF_pp.

Since the mirror signal has a very low envelope compared to the data region and the header region, the mirror signal may be generated by the envelope detector and the comparator.

The mirror signal level detector 152 detects the level of the mirror signal from the sum signal RF_sum based on the mirror section signal generated by the mirror section signal generator 150. The mirror signal level detector 152 generates a third enable signal enable 5 having a predetermined section and a predetermined width by the mirror section signal generated by the mirror section signal generator, and by the third enable signal enable 5. The sum signal RF_sum is gated and the peak-peak value of the gated sum signal RF_sum is detected. The mirror signal level detector 152 is implemented with the apparatus shown in FIG. 7.

The balance calculator 154 may level the vfo1 signal detected by the first synchronous signal level detector 144. V ₁ , The level of the vfo3 signal detected by the second synchronous signal level detector 156 V ₂ Mirror signal level detected by mirror signal level detector 162. I ₀ Balance value as shown in equation (4) by K ₁ To calculate. Here, the balance calculator 164 may output an average value of balance values obtained from several sectors consecutive in the tangential direction.

Sum signal of radial pair instead of sum signal RF_sum I ₁ , I ₂ You can also use In this case, the first synchronous signal level detector 144 I ₁ Is input to the second synchronous signal level detector 146. I ₂ Enter.

FIG. 12 is a block diagram illustrating a detailed configuration of the radial tilt control unit illustrated in FIG. 11. The apparatus shown in FIG. 12 includes a radial tilt servo 170, a radial tilt driver 172, and an equalizer controller 174.

10 to calculate the balance value RF _pp Defocus amount when using d Wow K _t This graph shows the relationship with. In FIG. 10, the solid line in the center shows the case where the radial tilt is zero, the solid line in the upper side shows the case where the radial tilt is 0.5, and the solid line in the lower side shows the case where the radial tilt is -0.5.

According to the defocus amount as shown K _t It can be seen that the linearly fluctuates. therefore, K _t It is necessary to correct according to the defocus amount.

13 is a flowchart showing a tilt component detection method according to the present invention.

First, defocus amount d The defocus is minimized. For example, the point where the defocus is minimized is set to, for example, a point where the focus error signal is minimized.

next K _t (S1310) K _t Can be detected by the method disclosed in Equations 1 to 6.

14 is a flowchart illustrating another embodiment of a method of detecting a tilt component according to the present invention.

first, K _t (S1400) K _t Can be detected by the method disclosed in Equations 1 to 6.

Defocusing d (S1410) The defocus amount is detected by the magnitude of the focus error signal.

K _t Is corrected by the defocus amount d (S1420).

K _t Defocusing amount d The correction by is determined by the following equation.

here, K _c Is the amount of radial tilt in which the effect due to defocus is compensated for.

Defocusing Amount d Wow K _t Has a linear relationship, so Equation 7 can be modified as follows.

here, a Is a proportional constant.

Defocusing Amount d Wow K _t Since 1 has a linear relationship, Equation 8 can be modified as follows.

here, b Is the threshold.

15 is a flowchart illustrating still another embodiment of the tilt detection method according to the present invention. Unlike the method shown in Figs. 13 to 14, the method shown in Fig. 15 determines the amount of tilt by detecting a difference in the amount of tilt detected at two points with different focus.

First, the amount of tilt at a point K _t1 Measure (S1500

Defocusing amount at this time d ₁ This is called.

Next tilt amount at different points K _t2 Measure (S1510

Defocusing amount at this time d ₂ This is called.

Next, the tilt amount is determined by the change value of the tilt amount and the change value of the defocus amount. (S1520) The correction equation is as follows.

As described above, the tilt method according to the present invention can perform the tilt correction more stably by compensating the effect of defocus in detecting the tilt and detrack amounts using the sync signal recorded in the header area on the disk. There is an advantage to that.

Claims (17)

A tilt detection method of an apparatus for reproducing an optical disc having sync signal regions in which at least a sync signal is recorded above and below a track center line, the apparatus comprising: Adjusting defocus of the optical disk to a minimum; And The magnitude of the signal detected in the synchronization signal area recorded on one side of the track center line V ₁ And the magnitude of the signal detected in the synchronization signal area recorded on the other side of the track center line. V ₃ When we say V ₁ and V ₃ Difference V ₁ -V ₃ A tilt detection method comprising the step of detecting the amount of tilt by. The tilt detection method of claim 1, wherein the adjusting of the defocus is minimized so that the size of the focus error signal is substantially zero. A tilt detection method of an apparatus for reproducing an optical disc having sync signal regions in which at least a sync signal is recorded above and below a track center line, the apparatus comprising: The magnitude of the signal detected in the synchronization signal area recorded on one side of the track center line V ₁ And the magnitude of the signal detected in the synchronization signal area recorded on the other side of the track center line. V ₃ When we say V ₁ and V ₃ Difference V ₁ -V ₃ Detecting the amount of tilt by; And remind V ₁ -V ₃ Tilt detection method comprising the step of compensating for by the defocus amount. The process of claim 3, wherein the process of compensating by the defocus amount K _c Is the amount of radial tilt compensated for by the defocus effect, K _t Is the detected detrack amount, d Is the defocus amount Tilt detection method, characterized in that The method of claim 3, K _c Is the amount of radial tilt compensated for by the defocus effect, K _t Is the detected detrack amount, d Is called the defocus amount, a When is called proportional constant Tilt detection method characterized in that it is determined. The method of claim 3, K _c Is the amount of radial tilt compensated for by the defocus effect, K _t Is the detected detrack amount, d Is called the defocus amount, a Is called the proportional constant, b When is called threshold Tilt detection method characterized in that it is determined. The method according to claim 4, wherein d The defocus amount is detected from the focus error signal. A tilt detection method of an apparatus for reproducing an optical disc having sync signal regions in which at least a sync signal is recorded above and below a track center line, the apparatus comprising: The magnitude of the detected signal in the sync signal area recorded above the track center line V ₁ And the magnitude of the detected signal in the synchronization signal area recorded above the track center line. V ₃ So, at two different points of focus V ₁ and V ₃ Difference V ₁ -V ₃ Tilt amount by K _t1 , K _t2 ) And defocus amount ( d ₁ , d ₂ Detecting); And And a tilt amount is determined by calculating a ratio of a change amount of the tilt amount and a change amount of the defocus amount detected at the two points. The method of claim 8, K _c Is the amount of radial tilt compensated for by the defocus effect. Tilt detection method characterized in that it is determined. The method of claim 3, wherein V ₁ -V ₃ The process of detecting V ₁ -V ₃ To V ₁ + V ₃ Tilt and detrack control method characterized in that the normalization. The method of claim 3, wherein V ₁ -V ₃ The process of detecting V ₁ -V ₃ The magnitude of the mirror signal detected from the mirror area where no pit is recorded I ₀ Tilt and detrack control method characterized in that the normalization. The method of claim 3, wherein V ₁ -V ₃ The process of detecting And a tilt amount is detected from the push-pull signal reproduced in the synchronization signal region. The method of claim 3, wherein V ₁ -V ₃ The process of detecting And a detrack amount from the sum signal reproduced in the synchronization signal region. The method of claim 3, wherein V ₁ -V ₃ The process of detecting Detected from a plurality of adjacent synchronization signal regions V ₁ -V ₃ A tilt detection method characterized by detecting an average value of. 4. The tilt and detrack control method according to claim 3, wherein the disc is a DVD-RAM disc. The method of claim 15, V ₁ -V ₃ And a process for inverting the polarity of each land / groove track. The recording area is divided into sectors, each sector having a header indicating an address, the header having a first header and a second header which are recorded staggered from side to side at the center point of the track, and the first header and the second header have the address of the sector. A tilt and detrack detection method of an apparatus for reproducing an optical disc having an address area in which is recorded and a sync signal area in which a sync signal for detecting address signals recorded in the address area is recorded The magnitude of the signal detected in the synchronization signal region in the first header V ₁ The magnitude of the signal detected in the synchronization signal region of the second header V ₃ When we say V ₁ and V ₃ Difference V ₁ -V ₃ Detecting the amount of tilt by; And remind V ₁ -V ₃ Tilt detection method comprising the step of compensating for by the defocus amount.