WO2006101007A1

WO2006101007A1 - Method for adjusting tilt of information recording medium and information recording/reproducing device for such method

Info

Publication number: WO2006101007A1
Application number: PCT/JP2006/305261
Authority: WO
Inventors: Masatsugu Ogawa; Shuichi Ohkubo
Original assignee: Nec Corporation
Priority date: 2005-03-18
Filing date: 2006-03-16
Publication date: 2006-09-28

Abstract

Ina method for adjusting a tilt of an information recoding medium, the information recording medium is provided with tracks in parallel and some of the tracks are set as a measuring track group. A reproduction signal is outputted by reproducing information recorded in the tracks arranged at both ends of the measuring track group. Based on the reproduction signal, a tilt indicating the tilt of the information recording medium is calculated. Based on the calculated tilt, the tilt of the information recording medium is corrected. In the track or the track group adjacent to the measuring track group, information is not recorded. Thus, the tilt can be accurately detected by directly using the reproduction signal.

Description

Specification

Information recording medium tilt adjustment method and information recording / reproducing apparatus therefor

The present invention relates to a tilt adjustment method for a high-density optical disc and a recording / reproducing apparatus thereof.

Background art

In an optical disc apparatus, information is recorded on an optical disc or recorded information is read using an optical head. In such an optical disk device, the tilt angle between the optical disk and the optical head greatly affects the performance of the optical disk device. If there is no tilt between the optical disc and the optical head, a good laser beam is applied to the information recording surface of the optical disc and good recording and reproduction is performed. However, if tilt occurs between the optical disc and the optical head, the information recording surface of the optical disc Aberrations occur in the laser beam applied to the recording medium, degrading recording / reproducing performance. Tilt is generally defined by the normal of the recording surface of the optical disk and the tilt of the optical axis of the light beam. The tilt in the radial direction of the optical disk is called radial tilt and the tilt in the track direction is called tangential tilt.

FIG. 2 is a graph showing the relationship between error rate and radial tilt. Referring to Fig. 2, when radial tilt occurs, the error rate increases and the recording / reproduction performance deteriorates significantly. Therefore, several methods for correcting the tilt and improving the reproduction signal have been considered so far.

[0004] For example, Japanese Patent Application Laid-Open No. 2003-157553 discloses a method of controlling an optical disk or an optical head by beam splitting. This method first generates one main beam and two sub-beams from the reflected light received from the optical disk force. Next, the tilt is detected based on the detection results of these beams. The optical disk or the optical head is controlled so that the tilt is eliminated by using the tilt detection signal.

[0005] Further, Japanese Patent Application Laid-Open No. 09-054953 discloses a method using a plurality of beams. The optical head irradiates the optical disc with three or five beams. Tilt is detected using the reflected intensity of each irradiated beam. Depending on the degree of tilt detected, the 3 or 5 beams with the best playback signal quality are selected. The signal is played back. According to this method, since the output of either 3 or 5 beams is used as a reproduction signal, the light intensity of each beam must be reasonably high from the viewpoint of increasing the signal-to-noise ratio (SNR). . Therefore, it is necessary to use a laser diode with a very high output, which is difficult to realize.

[0006] JP 2000-149298 A discloses a method for detecting a radial tilt angle of an optical disc. In this optical disk tilt detection method, a DPP (Differential Push-Pull) and DPD (Differential Phase Detection) signals, which are tracking error signals, are generated by using a main spot and both side spots, or detection signals of both side spots. Based on the difference calculation value of these two signals, the tilt angle of the optical disc is detected, and the radial tilt of the optical disc is controlled.

However, with these methods, it is necessary to irradiate or generate a plurality of beams, which has a great demerit that the optical head becomes complicated. In addition, even if a tilt detection signal is obtained that is directly related to the recorded signal or the reproduction signal, the recording and reproduction characteristics are not necessarily improved optimally.

[0008] Further, Japanese Patent Application Laid-Open No. 2003-16677 discloses a method for controlling tilt using a quadrant photodetector. In the case of radial tilt, the tilt is detected by the light quantity balance of detectors (detectors divided in the radial direction) on the left and right with respect to the optical head scanning direction. In the case of tangential tilt, the tilt is detected by the light quantity balance of the detectors (detectors divided in the scanning direction) that are in front of and behind the optical head scanning direction. This is a method of controlling the tilt based on these tilt detection results. This method has a relatively simple configuration, but in reality, such a tilt detection cannot obtain a tilt detection signal with sufficient accuracy.

[0009] In addition, Japanese Patent Laid-Open No. 2001-256652 discloses a method for eliminating the adverse effects of tilt in terms of signal processing. The outputs of the detectors on the left and right of the optical head scanning direction (detectors divided in the radial direction) are added together by changing the ratio in conjunction with the tilt. In this way, adverse effects due to tilt in signal processing are eliminated without performing mechanical tilt control.

[0010] In Japanese Patent Laid-Open No. 2001-357537, a reproduction signal is generated using three recorded tracks. A method is shown in which the optical head is corrected to a tilt that can be measured to obtain the minimum value. Since this method performs adjustment using jitter that has a high correlation with the reproduction signal that is close to the actual reproduction, good accuracy can be obtained. However, jitter is a value with no polarity. For this reason, when such parameters are used for adjustment, for example, in tilt control, it is unclear which is optimal for driving the tilt. Therefore, there is a need for a so-called hill-climbing method in which the tilt is changed positively and negatively to adjust while searching for the best signal position. This takes time to learn and results in a very large overall performance degradation for an optical disc device.

As described above, most of the currently known tilt detection methods indirectly perform tilt detection using a signal different from the actual reproduction signal. Therefore, the optimal tilt point of the playback signal quality is often misaligned with the optimal tilt point found from the tilt detection signal. Absent. Also, even if the playback signal quality itself is used, time-consuming methods such as hill climbing are used, which causes the overall performance degradation of the optical disc device!

In relation to the above description, a tilt detection device is disclosed in Japanese Patent Laid-Open No. 2001-84621. In this conventional example, a data string having data having a pulse width smaller than the minimum pulse width formed on a normal disk is formed on the optical disk. The reproduction unit reproduces the RF signal from the optical detector, and the tilt detection unit detects the tilt based on the data signal having a small pulse width out of the reproduction RF signal from the reproduction unit.

An optical disk device is disclosed in Japanese Patent Laid-Open No. 2001-266382. In this conventional example, the optical unit simultaneously irradiates a light beam onto the target track on the optical disc and the three adjacent tracks on both sides of the target track, and detects the reflected light reflecting the information recorded on these three tracks. The reproduction unit converts information reflected in the reflected light detected by the optical unit into an electrical signal and provides it as a reproduction signal. The delay unit delays the playback signals of the three tracks for a predetermined time. The equalization unit has a transversal filter and corrects the frequency characteristics of the playback signals of the three tracks provided from the delay unit. The control unit controls the correction amount of the frequency characteristic by the equalization unit. The tilt calculation unit calculates the tilt amount of the optical disc based on the control of the correction amount of the frequency characteristic of the equalization unit by the control unit. The control unit controls the correction amount of the frequency characteristic by changing the tap coefficient group of the transversal filter. That When the signal value sequence reproduced from the three tracks is an observation value sequence, a predetermined signal value sequence corresponding to the signal value sequence reproduced from the target track is an ideal value sequence, and the control unit A relational expression for tap coefficient groups, which satisfies the condition that the sum of squares over multiple channel bits of the residual of the measured value series and ideal value series obtained by the linear expression of the tap coefficient group is minimized. The tap coefficient group is obtained by batch processing. The tilt calculator obtains the relative inclination between the optical disc and the optical means by calculating between tap coefficient groups.

An optical recording medium evaluation system is disclosed in Japanese Patent Application Laid-Open No. 2004-303356. In this conventional example, the reproduction signal read out via the optical pickup head is amplified by the amplifier. The amplified reproduction signal is AZD converted, and the processing device numerically processes the reproduction waveform after AZD conversion. In numerical processing, the amplitude data of the reproduction signal is obtained, the amplitude data is normalized by the average value, and the standard deviation is calculated. In addition, the amplitude data is Fourier transformed and the subsequent SZN ratio is also calculated.

Disclosure of the invention

[0013] An object of the present invention is to provide an accurate tilt detection method that directly uses a reproduction signal, and an information recording / reproducing apparatus therefor.

Another object of the present invention is to provide a tilt detection method capable of further reducing the adjustment time and an information recording / reproducing apparatus therefor.

In an aspect of the present invention, in the information recording medium tilt adjustment method, the information recording medium includes parallel tracks, and a part thereof is set as a measurement track group. Information recorded on tracks arranged at both ends of the measurement track group is reproduced and a reproduction signal is output. A tilt indicating a relative inclination between the information recording medium and the optical head is calculated based on the reproduction signal. The relative tilt is corrected based on the calculated tilt. Information is recorded in the track or track group adjacent to the measurement track group.

In addition, in the information recording medium tilt adjustment method of the present invention, predetermined information is recorded on tracks arranged at both ends of the measurement track group.

Also, a tilt indicating the tilt of the information recording medium is calculated based on the SNR (ratio of signal component to noise component) calculated based on the reproduction signal. Ε = (ε 1, ε 2, ..., ε m), the noise n representing the difference between the ideal signal waveform and the actual signal waveform is n = (nl, n2, ..., nm), and the symbol representing the expected value is E []. Calculated from the following equation.

[Number 1]

Further, this SNR may be selected as a medium force calculated for a plurality of vectors ε. In that case, the minimum value of the results is taken as the SNR. The multiple vectors ε are ε 1 = (1, 2, 2, 2, 1),

ε 2 = (1, 2, 1, 0, -1, -2, —1),

ε 3 = (1, 2, 1, 0, 0, 0, 1, 2, 1)

There are three types.

This SNR is P RSNR defined as SNR in PR (Partial Response) method.

In another aspect of the present invention, an information recording / reproducing apparatus includes a reproducing unit and a tilt detecting unit. The information recording medium includes parallel tracks. A measurement track group is set on the information recording medium. The reproduction unit reproduces information recorded on the tracks arranged at both ends of the measurement track group and outputs a reproduction signal. The tilt detection unit calculates a tilt indicating the tilt of the information recording medium based on the reproduction signal. This information recording / reproducing apparatus includes a tilt correction unit. The tilt correction unit) corrects the relative tilt between the information recording medium and the optical head based on the calculated tilt.

No information is recorded in the track or track group adjacent to the measurement track group. The information recording / reproducing apparatus of the present invention further includes a recording unit for recording predetermined information on tracks arranged at both ends.

The tilt detector of the present invention calculates the tilt based on the SNR (ratio of signal component to noise component) calculated based on the reproduction signal. The vector ε is expressed as ε = (ε 1, ε 2, ..., ε m) The noise n that represents the difference between the ideal signal waveform and the actual signal waveform is n = (nl, n2, ..., nm).

If the symbol representing the expected value is E [], SNR is calculated by the following equation.

[Equation 2]

ε 2 = (1, 2, 1, 0, -1, -2, —1),

ε 3 = (1, 2, 1, 0, 0, 0, 1, 2, 1)

There are three types.

This SNR is P RSNR defined as SNR in PR (Partial Response) method.

Brief Description of Drawings

FIG. 1 is a block diagram showing a configuration of an information recording / reproducing apparatus according to an embodiment of the present invention.

FIG. 2 is a diagram showing the radial tilt dependence of the error rate.

FIG. 3 is a diagram showing a signal recording form according to an embodiment of the present invention.

FIG. 4 is a diagram showing the reproduction characteristics of a recording signal by the information recording / reproducing apparatus in the example of the present invention.

FIG. 5 is a diagram showing a difference in reproduction characteristics of recorded signals by the information recording / reproducing apparatus according to the embodiment of the present invention.

FIG. 6 is a block diagram showing a configuration of an RF circuit unit of the information recording / reproducing apparatus in the example of the present invention.

FIG. 7 is an information recording medium used in the information recording / reproducing apparatus according to the embodiment of the present invention. It is sectional drawing of (disk).

FIG. 8 is a diagram showing a processing procedure when tilt correction is performed using the information recording / reproducing apparatus according to the embodiment of the present invention.

FIG. 9 is a diagram showing the radial dependence of radial tilt in an information recording medium (disc) used in the information recording / reproducing apparatus in the example of the present invention.

[FIG. 10] FIG. 10 is a diagram showing the dependence of the error rate on the radius of the information recording medium (disk) when tilt correction is performed using the information recording / reproducing apparatus according to the embodiment of the present invention and when the tilt correction is not performed. FIG.

[FIG. 11] FIGS. 11A to 11C are some examples of signal recording forms.

BEST MODE FOR CARRYING OUT THE INVENTION

Hereinafter, the present invention will be described in detail with reference to the accompanying drawings.

First, the principle of the present invention will be described. In the present invention, the crosstalk of the adjacent track force (signal leakage from the adjacent track) is used, and the shift of the radial tilt is detected by observing the shift of the crosstalk balance. Generally, guide grooves for scanning with a laser beam are formed on a recording type optical disc. The part of the hill as seen from the laser beam is called a group, and the part of the groove is called a land.

FIG. 3 is a diagram showing an example of a data recording state on the optical disc in the embodiment of the present invention. Referring to FIG. 3, group Gl, land L2, group G3, land L4, group G5, land L6, and group G7 are formed from the inner periphery to the outer periphery. Among them, the recording marks 17 are formed in the group G5 and the group G3, and the measurement track group is constituted by the group G5, the land L4, and the group G3. Group G5 is called Track 1 and Group G3 is called Track 2. That is, data is recorded only in two groups G3 and G5 adjacent to each other with the land L4 interposed therebetween, and at least the land L6 and the group G7 adjacent to the outside of the track 1 and the land L2 and the group G1 adjacent to the inside of the track 2 are recorded. No data is recorded. That is, no data is recorded on the track adjacent to the measurement track group.

When the radial tilt dependence of the PRSNR in track 1 and the PRSNR in track 2 recorded in this way is measured, the result shown in FIG. 4 is obtained. About PRSNR This will be described later. Referring to Fig. 4, it can be seen that the change in PRSNR in track 1 and the change in PRSNR in track 2 differ depending on the degree of radial tilt. In other words, when radial tilt occurs, there is a difference between the PRSNR in track 1 and the PRSNR in track 2, and the magnitude relationship of each PRSNR is reversed depending on the polarity of the radial tilt. In this case, a radial tilt of 0 degrees (deg) is the best tilt for recording / reproducing characteristics.

[0020] When the difference between the PRSNR of track 1 and the PRSNR of track 2 is plotted corresponding to the radial tilt, the result is as shown in FIG. The difference is 0 at the best radial tilt point of 0 degrees (deg). It can also be seen that the difference value has a value and polarity corresponding to the radial tilt amount. Therefore, if the difference between the PRSNR of track 1 and the PRSNR of track 2 can be known, the direction and degree of tilt (tilt amount) can be determined instantly. By performing feedback control based on this difference value, it is possible to always optimally control the tilt between the optical head and the optical disk.

In other words, the present invention creates a track in which the crosstalk (signal leakage) balance from the adjacent track is lost, and sees the deviation of the balance to see the deviation of the radial tilt. In other words, track 1 shown in Fig. 3 is in a state where crosstalk enters only the inner track force, and track 2 is in a state where crosstalk enters only from the outer track. Therefore, at least data is not recorded in the adjacent land L6 and the adjacent group G7 on the outer peripheral side of the track 1 and in the adjacent land L2 and the adjacent group G1 on the inner peripheral side of the track 2.

[0021] Next, PRSNR will be described. Recently, PRML (Partial Response Maximum Likelihood) signal processing is also used in optical disks. PR SNR is ISOM2003 (International Symposium Optical Memory 2003 S. OHKUBO et al. "Signal-to-Noise Ratio in a PRML Section, (Japanese Journal of Applied Physics Vol. 43, No. 7B, 2 004, pp 4859— 4862), and also ίoma JP 2004-213862 [This is the definition of SNR (Signal to Noise Ratio) in the PR (Partial Response) system described above. With the short Euclidean distance and the bottleneck of the system The following equation (1) is calculated for the path. When there are multiple paths that become the bottleneck, the following formula is calculated separately for each path, and the path value with the smallest value is defined as the SNR of the PRML system. .

[Equation 3]

Here, ε = (ε, ε,..., Ε) is a vector representing the difference between the paths, and η = (η, η,

1 2 m 1 2

···, η) represents noise representing the difference between the ideal signal waveform and the actual signal waveform, and Ε [] represents the expected value. The expected value is a value expected when the following formula (2) is calculated at each time, and may be considered as an average value. The numerator is exactly the Euclidean distance between paths.

[Equation 4]

∑s _m n _a (2) Here, the Euclidean distance between paths represents a time-series difference in signal level. For example, a path with a signal level time series of (—4, -3, -1, 1, 3) (in this case, five times are shown) and (1, 3, — 1, 1, 3, 4) When the difference between paths with signal level time series is obtained, the difference between both time series is (1, 2, 2, 2, 1) or (1, 1, -2, -2, -2, 1). . The distance of this time series difference is called the Euclidean distance, which is a vector distance. In this case, the short distance is calculated as IX 1 + 2X2 + 2X2 + 2X2 + IX 1 = 14.

In Fig. 4, the force at which PRSNR is measured for Track 1 and Track 2 Basically the normal SNR may be measured. Also, instead of SNR, an index close to SNR, for example, jitter on both tracks may be measured.

In Fig. 3, two groups G3 and G5 are adjacent to each other with two lands 4 in between. Although recording was performed, recording may be performed on two tracks on adjacent lands. At this time, even if there is a recording mark on land L4 (or a group between two tracks of adjacent lands) sandwiched between two tracks of adjacent groups, the crosstalk balance relationship does not change. Therefore, there is no problem even if data is recorded on the land L4 (or a group between two adjacent land tracks).

In addition, FIG. 3 shows an example of a land / groove * format. The present invention can be applied to an in-groove 'format (recording only in a group) or an on-groove' format (recording only in a land) in which recording is performed only on a group or land. In that case, data is recorded on the adjacent two tracks of the group or the adjacent two tracks of the land, and the same measurement is performed.

Referring to FIG. 1, the information recording / reproducing apparatus records information on optical disc 10 and reproduces information from optical disc 10. The information recording / reproducing apparatus includes a spindle drive system 9, an optical head unit 20, an RF circuit unit 30, a tilt detector 3, a demodulator 4, a system controller 5, a modulator 6, an LD drive unit 7, and a servo controller 8.

The spindle drive system 9 drives the optical disc 10. The optical head unit 20 includes a laser diode (LD) 26, a beam splitter 25, an objective lens 28, and a light receiving unit 22, and irradiates the optical disc 10 with laser light and detects the reflected light. The laser light is emitted from a laser diode (LD) 26, reflected by the beam splitter 25, and applied to the optical disc 10 through the objective lens 28. The reflected light reflected by the optical disk 10 is collected by the objective lens 28, passes through the beam splitter 25, and is detected by the light receiving unit 22. The input signal detected by the light receiving unit 22 is output to the RF circuit unit 30. The RF circuit unit 30 performs processing such as filtering on the input signal, outputs the equalized reproduction signal and the data string signal to the tilt detector 3, and outputs the data string signal to the demodulator 4. The configuration of the RF circuit unit 30 will be described later. The tilt detector 3 calculates a signal for tilt detection based on the equalized reproduction signal and the data string signal input to the RF circuit unit 30 and outputs the result to the system controller 5. The demodulator 4 demodulates the data string signal output from the RF circuit unit 30 and outputs it to the system controller 5. The modulator 6 modulates the signal to be recorded input from the system controller 5 and outputs it to the LD driver 7 To do. The LD drive unit 7 drives the laser diode 26 based on the modulated signal to be recorded input from the modulator 6 and records it on the optical disc 10. The servo controller 8 controls a servo signal that controls the optical head unit 20. This includes a tilt correction mechanism. The system controller 5 takes in demodulated data from the demodulator 4 and outputs data to be recorded in the modulator 6. The system controller 5 takes over the tilt detection signal from the tilt detector 3, instructs the servo controller 8 to perform tilt correction, and controls the spindle drive system 9 and the servo controller 8. . A feature of the present invention lies in the tilt detector 3 that calculates a signal for tilt detection using the output of the RF circuit 30. In this embodiment, PRSNR is also calculated here. As shown in FIG. 6, the RF circuit unit 30 includes a pre-filter 31, an auto gain control (AGC) 32, an AZD converter (ADC) 34, a phase-locked loop (PLL) 35, an adaptive equalizer 37, and a Viterbi decoding. A vessel 38 is provided. An input signal input from the optical head unit 20 is filtered by the prefilter 31, subjected to amplitude control by the auto gain control 32, and then digitized by the AZD converter 34. From the digitalized input signal, a clock signal is extracted by the phase lock droop 35 and output to the adaptive equalizer 37 in synchronization with the channel frequency of the input signal. The adaptive equalizer 37 corrects the frequency characteristic so that the frequency characteristic of the input signal approaches the PR characteristic. The equalized reproduction signal whose frequency characteristics have been corrected by the adaptive equalizer 37 is output to the Viterbi decoder 38 and also to the tilt detector 3. The Viterbi decoder 38 receives the equalized reproduction signal from the adaptive equalizer 37 and converts it into binary information. The converted binary information is fed back to the adaptive equalizer 37 and output to the tilt detector 3 and the demodulator 4 as a data string signal. The equalized reproduction signal that is a signal after adaptive equalization output from the adaptive equalizer 37 and the data string signal after Viterbi decoding output from the Viterbi decoder 38 are input to the tilt detector 3. The tilt detector 3 calculates PRSNR based on the equalized reproduction signal and the data string signal. The noise at each time required for PRSNR calculation is calculated as the difference between the ideal signal waveform obtained based on the data string signal after Viterbi decoding and the actual signal waveform that is the signal after adaptive equalization. . The ideal signal waveform is obtained by the convolution product of the data string signal after Viterbi decoding and the vector (1, 2, 2, 2, 1). [0026] The tilt detector 3 is equipped with memories for track 1 and track 2. This memory can temporarily hold the PRSNR of each track. If the PRSNR of track 1 and track 2 can be calculated, the difference between the two can be found. The difference between the two is output to the system controller 5 as a tilt detection signal. Since the tilt detection signal changes monotonously with respect to the tilt as shown in FIG. 5, the system controller 5 controls the tilt in the direction toward the tilt detection signal force. Thus, the tilt is always controlled to be optimal.

In this embodiment, an example in which an optical head unit 20 having an LD wavelength of 405 nm and NA (numerical aperture) of 0.65 has been shown. Further, the RF circuit unit 30 is exemplified as having a Viterbi decoder for PR (12221).

Further, the optical disk 10 having a structure as shown in FIG. 7 was used. In the optical disk 10, a dielectric film 12, a phase change recording film 13, a dielectric film 14, and a reflective film 15 are laminated on a substrate 11. The substrate 11 is made of polycarbonate and has a transparent disk shape with a thickness of 0.6 mm and a diameter of 12 cm. Guide grooves (not shown) called pre-groups are formed on the substrate 11. At the time of recording and reproduction, an optical beam of an optical information recording apparatus, that is, an optical disk drive can be scanned along this guide groove. On this substrate 11, a dielectric film 12 made of ZnS—SiO 2, a phase change recording film 13 made of AglnSbTe, a dielectric film 14 made of ZnS—Si02, and a reflective film 15 made of AlTi are laminated in this order. The dielectric films 12 and 14 are for protecting the phase change recording film 13 and controlling a laser beam interference condition to obtain a larger signal. The phase state of the phase change recording film 13 is a crystalline state in the initial state, and information is recorded by being irradiated with a recording laser beam to be in an amorphous state. A protective film such as an ultraviolet curable resin may be provided on the reflective film 15.

[0028] The format used was a land 'group' format with a bit pitch of 0.13 µm and a track pitch of 0.34 µm. The land 'groove' format refers to a format in which recording is performed on both the hill (group) and the groove (land) when viewed from the incident light side of the guide groove.

[0029] The information recording / reproducing apparatus corrects the radial tilt according to the processing procedure shown in FIG.

First, when the optical disk 10 is inserted into the apparatus, the optical head is moved to a desired radial position. (Step SI 1). A recording state as shown in FIG. 3, that is, a measurement track group is created. In this case, group G3, land L4, and group G5 are measurement tracks. Predetermined data is recorded only in groups G3 and G5, which are the tracks at both ends of the measurement track group. That is, in the optical disk 10, data is recorded only in two groups G3 and G5 adjacent to each other across the land L4, and at least the land L6 adjacent to the outside of the track 1 and the group G7 and the inside of the track 2 are adjacent. When the data is recorded in the land L2 and the group G1, the recording state is reached (step S12).

Thereafter, track 1 and track 2 in which data is recorded are reproduced (step S14). Tilt detector 3 calculates PRSNR based on the signal reproduced from track 1, and sets the value as S1. The PRSNR is calculated based on the signal reproduced from track 2, and the value is S2. The difference Sl—S2 (or S2—S1) of PRSNR of each track is calculated (step S15). The tilt detector 3 estimates the radial tilt amount by using this differential SI-S2 (or S2-S1) force (step S16). The estimated radial tilt amount is sent to the system controller 5 and held together with the radial position (step S18).

When measuring the state of the other radial position of the optical disc 10, the process returns to step S11, and the radial tilt amount is estimated at another radius (step S19—YES). When the tilt state of the entire disk surface can be estimated (step S19—NO), the tilt detector 3 waits for a recording command from the system controller 5 (waiting for the next measurement).

[0030] In the present example, the above-described treatment was performed at three locations with a radius of 25 mm, 45 mm, and 57 mm. Radial tilt at locations other than the above three radii is estimated by the system controller 5 from the radial tilt amount at the above three radii.

Next, practical verification as the apparatus of the present invention is performed. Figure 9 shows the radius dependence of the radial tilt of the newly created disc. The radial tilt at a position with a radius of 50 mm or more exceeds 0.3 degrees (deg), and there is a concern that the error rate will rise rapidly. In addition, as shown in Fig. 9, in the actual device, radial tilt occurs even at the innermost radius of the disk (in this case, about 0.15 degrees (deg)), and the radial tilt margin is improved. It turns out that it is urgent.

Insert the disk into this device and observe the radius dependence of the error rate. Figure 10 The result is shown. By performing tilt correction, it is possible to suppress the deterioration of the error rate even at the outer periphery, and it is certain that this device can greatly improve the margin of the reproduced signal quality.

As described above, in this embodiment, when the optical disc 10 is inserted, the tilt measurement may be performed appropriately in the meantime without first performing force recording that grasps the state of the tilt of the entire surface of the optical disc. Further, the recording may be temporarily interrupted to measure the tilt. At that time, the data to be recorded should be stored in the buffer of the system controller 5.

If a large amount of data has already been recorded on the optical disc 10, the end of the recorded data or the recorded data should be used appropriately.

The data recording position for measurement has been described as two adjacent groups as shown in FIG. 3, but as shown in FIGS. 11A to 11C, it may be in a recording state for measurement other than FIG. . FIG. 11A shows a recording state when a recording signal is also present in the track (land L4) between track 1 (group G5) and track 2 (group G3). Land L6 and group G7 adjacent to the outer periphery of track 1 and land 2 and group 1 adjacent to the inner periphery of track 2 have no recording signal.

Fig. 11B shows the recording status when track 1 (group G6) and track 2 (group G4) should be recorded on the outer and inner tracks, and only the track is unrecorded. Indicated. That is, group G6 is recorded as track 1, and group G4 is recorded as track 2. The land L7 and the group G8 adjacent to the outer peripheral side of the track 1 do not record signals as tracks that should not be recorded, but there is a recording mark 17 on the further outer land L9, where signals are recorded. Similarly, land L3 and groove G2 adjacent to the inner periphery of track 2 should not be recorded, and no signal is recorded as a track. Further, a recording signal is present on the inner land L1. Signals may or may not be recorded on land 5 between track 1 and track 2.

Also, lands and groups are interchangeable, and the recording states for measurement exemplified so far can reverse the descriptions of lands and groups. Fig. 11C shows the recording state shown in Fig. 3 with the grooves replaced with lands. That is, a signal is recorded on the land L5 as the track 1, and a signal is recorded on the land L3 as the track 2. Sandwiched between track 1 and track 2 There are no signals recorded in group 4. Also, signals are recorded on the outer periphery of track 1 and the inner periphery of track 2.

[0033] In this embodiment, the class PR (12221) is used, but other classes such as PR (1221) can be used in the same manner.

In this embodiment, the PRSNR is used as the SNR. However, the present invention can also be implemented using various SNRs, such as using a simple SNR calculated as ε = (1). It is.

In this embodiment, the case where PRML is used has been described. However, a system that does not use PRML can be used in the same manner.

Further, the present invention is applicable to any wavelength and NA without being limited to a wavelength of 405 nm and NAO.

As described above, the power exemplified for the optical disk apparatus can be used as a method of correcting the signal quality deterioration due to the tilt of the magnetic head with respect to the disk surface in the magnetic disk apparatus.

[0035] According to the present invention, unlike the conventional example in which the tilt is corrected by an indirect signal, a signal for tilt detection is obtained directly from the reproduction signal itself, so that a change due to the tilt of the reproduction signal is very small. It can be detected with high accuracy.

In addition, according to the present invention, since the direction and magnitude of the tilt are strong, it is possible to instantly know which direction the tilt is made. Therefore, the adjustment time that does not require the use of the hill-climbing method can be shortened.

Claims

The scope of the claims

[1] Reproducing information recorded on tracks arranged at both ends of a measurement track group set on an information recording medium having parallel tracks and outputting a reproduction signal;

Calculating a tilt indicating a relative tilt between the information recording medium and the optical head based on the reproduction signal;

Correcting the relative tilt based on the tilt; and

An inclination adjustment method for an information recording medium comprising:

[2] No information is recorded on the track or track group adjacent to the measurement track group.

The method for adjusting the inclination of the information recording medium according to claim 1.

[3] A recording step for recording predetermined information on tracks arranged at both ends of the measurement track group is provided.

The method of adjusting the tilt of the information recording medium according to claim 1 or 2.

[4] In the tilt detection step, the tilt is calculated based on SNR (ratio of signal component to noise component) calculated based on the reproduction signal.

The method for adjusting the tilt of the information recording medium according to any one of claims 1 to 3.

[5] Let the vector ε be ε = (ε 1, ε 2, ···, ε m), and the noise n representing the difference between the ideal signal waveform and the actual signal waveform be n = (nl, n2, ···, nm ) And the symbol E [] representing the expected value, the SNR is given by

[Equation 5]

Calculated from

The method for adjusting the inclination of the information recording medium according to claim 4.

The minimum value among the results calculated for multiple vectors ε is the SNR. The method for adjusting the inclination of the information recording medium according to claim 5.

[7] The plurality of vectors ε are

ε 1 = (1, 2, 2, 2, 1),

ε 2 = (1, 2, 1, 0, -1, -2, —1),

ε 3 = (1, 2, 1, 0, 0, 0, 1, 2, 1)

Is

The method for adjusting the inclination of the information recording medium according to claim 6.

[8] The SNR is a PRS defined as an SNR in PR (Partial Response) method.

NR

The method for adjusting the inclination of the information recording medium according to any one of claims 4 to 7.

[9] A reproduction unit that reproduces information recorded on tracks arranged at both ends of a measurement track group set in an information recording medium including parallel tracks and outputs a reproduction signal, and based on the reproduction signal A tilt detector for calculating a tilt indicating the tilt of the information recording medium;

An information recording / reproducing apparatus comprising:

[10] The apparatus further includes a tilt correction unit that corrects the tilt of the information recording medium based on the tilt.

The information recording / reproducing apparatus according to claim 9.

[11] The information recording / reproducing apparatus according to claim 9 or 10, wherein no information is recorded in a track or a track group adjacent to the measurement track group.

12. The information recording / reproducing apparatus according to any one of claims 9 to 11, further comprising a recording unit that records predetermined information on the tracks arranged at both ends.

[13] The tilt detection unit calculates the tilt based on SNR (ratio of signal component to noise component) calculated based on the reproduction signal.

The information recording / reproducing apparatus according to claim 9.

[14] Let the vector ε be ε = (ε 1, ε 2, ..., ε m), and the noise n representing the difference between the ideal signal waveform and the actual signal waveform be n = (nl, n2, ..., nm ) And the symbol E [] representing the expected value, the SNR is given by [Equation 6]

Calculated from

14. The information recording / reproducing apparatus according to claim 13.

15. The information recording / reproducing apparatus according to claim 14, wherein the minimum value among the results calculated for a plurality of vectors ε is the SNR.

The vectors ε are

ε 1 = (1, 2, 2, 2, 1),

ε 2 = (1, 2, 1, 0, -1, -2, —1),

ε 3 = (1, 2, 1, 0, 0, 0, 1, 2, 1)

Is

16. The information recording / reproducing apparatus according to claim 15.

The SNR is a PRS NR defined as an SNR in a PR (Partial Response) scheme

The information recording / reproducing apparatus according to any one of claims 13 to 16.