JP2004146060A - Optical information reproducing method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method for eliminating effectively waveform distortion of a reproduced signal caused by coma aberration generated by an tilted optical disk and an optical head in an optical disk device premised with interchangeability of disks. <P>SOLUTION: This method is an information reproducing method by which information recorded in an optical disk 1 is reproduced using an optical head 2 performing reproduction by irradiating with light spot and an equalizer 7 constituted of transversal filters having taps of three pieces or more, a specific region which is positioned at an inner periphery side and an outer periphery side of an optical disk for the light spot and in which a mark deviated in the peripheral direction is formed is reproduced, a tilt error signal of the optical disk 1 and the optical head 2 is obtained, tilting of the optical disk 1 and the optical head 2 is compensated base on this tilt error signal, and the information recorded on the optical disk 1 is reproduced. <P>COPYRIGHT: (C)2004,JPO

Description

The present invention relates to optical information recording / reproducing, and more particularly to an optical information reproducing method for effectively suppressing deterioration of a reproduced signal caused by an inclination between an information recording / reproducing surface and an optical head when a compatible optical disc is used. .

2. Description of the Related Art In an optical disk apparatus for performing optical information recording / reproduction, an optical beam of a semiconductor laser is narrowed down by an objective lens, a focus is precisely controlled on a recording medium through a transparent substrate, and a minute diameter of about 1 micron is obtained. An information mark is recorded and reproduced. For this reason, as described in, for example, Shigeo Kubota, "Jitter Analysis of Eye Patterns on Optical Disks V", published in "Optics" Vol. 14, No. 4 (August 1985) (see Non-Patent Document 1). The waveform distortion of the reproduction signal occurs due to the aberration of the optical system, and the reproduction signal changes with respect to the change point of the original recording data from "0" to "1" or "1" to "0". A phenomenon occurs in which a point (edge) shifts back and forth on the time axis (edge shift). This causes a detection error in an optical disk device that gives information to a change point of a reproduction signal. This edge shift is particularly remarkable when an information mark recorded at high density is reproduced. The range (tolerance) of the variation (tolerance) with respect to the aberration amount allowed in the optical system constituting the optical head is as follows. It becomes severe.

と お り As described in [Non-Patent Document 1], spherical aberration, astigmatism, coma aberration, defocus, and the like are typical aberrations that cause problems in an optical disk device. Of these, the three aberrations excluding coma mainly depend on variations in assembling the optical head and the amount of electrical offset generated in a servo circuit for focusing. On the other hand, coma is generated as a result of the light beam passing through the disk substrate being refracted by the substrate due to the relative inclination between the objective lens and the disk substrate, thereby changing the optical path length. It largely depends on the mechanical accuracy of the disk.

First, as described in the background art of Japanese Patent Application Laid-Open No. 60-231930 (see Patent Document 1), the mechanical accuracy of a disk substrate is generally large because it is easy to mold. In the case of a polycarbonate or acrylic resin material which is used as a substrate material, deformation or warpage after disk molding is apt to occur. For this reason, the disk tends to warp like an umbrella toward the outer periphery, and the disk is inclined with respect to the optical head. This is defined as a radial inclination, and the coma generated at this time is called a radial coma.

Also, when the disk substrate is detachably fixed to the rotating motor, a concentric hole is made in the center of the substrate, and a metal member is mounted so as to be sandwiched from the front and back of the disk. A method is often employed in which a shaft is provided with a receiving portion to which a permanent magnet is fixed, and the metal member is fixed by its magnetic force. In this case, the reference surface of the optical disc varies depending on the individual optical discs, depending on the mounting accuracy of the metal member. In addition, the inclination of the optical disk in the circumferential direction also occurs depending on the accuracy of the initial adjustment when the optical head is attached. This phenomenon is called a tangential frame with respect to the radial frame.
As described above, in an optical disk device that takes advantage of optical disk compatibility, in principle, the parallelism at the time of mounting varies from optical disk to optical disk, and even if the tilt of the optical head is strictly adjusted at the time of shipment, coma aberration may occur. There is a problem that can not be completely prevented.

As a prior art, an optical recording disk reproducing apparatus proposed in Japanese Patent Application Laid-Open No. 60-231930 (see Patent Document 1) discloses a radial frame which leaks a signal from an information mark on an adjacent track. In order to reduce (−), a method of detecting the tilt angle of the optical disc and adjusting the tilt of the objective lens is adopted. Further, as a conventional technique relating to the removal of tangential frames, for example, as described in Japanese Patent Application Laid-Open No. Sho 60-214463 (see Patent Document 2), interference between adjacent information marks before and after in the track scanning direction (refer to Japanese Unexamined Patent Application, First Publication No. H11-260563). This is effective for reducing intersymbol interference).

On the other hand, many methods for removing the intersymbol interference and the crosstalk by signal processing have been proposed so far. In particular, a method of removing intersymbol interference generated between adjacent information marks before and after in the track scanning direction by waveform equalization has been widely used in the field of communication and magnetic recording. It has been applied as one means for realizing density recording. By the way, as described above, in the optical disk device, since it is necessary to ensure the compatibility of the optical disk, an automatic equalization system that operates adaptively according to the state of the light spot is desirable. As a known example relating to this, for example, Japanese Patent Application Laid-Open No. Hei 2-170613 (see Patent Document 3) is cited. This is a transversal filter type equalizer having a tap coefficient setting circuit having a digitally settable tap coefficient setting circuit. The output signal after equalization is binarized at two determination levels, ie, an equalization error detection level and a data discrimination level, and based on a combination of digital data “0” and “1”, respectively. The update direction (whether to increase or decrease) of the tap coefficient value and the equalization error detection level is determined, and these are sequentially updated. According to this method, it is possible to realize an automatic equalizer with a relatively simple circuit configuration even for data having a high transfer rate.

JP-A-60-231930. JP-A-60-214463. JP-A-2-170613. Shigeo Kubota: "Jitter Analysis of Eye Pattern on Optical Disk V", Optics, Vol. 14, No. 4, August 1985.

In the above-described conventional technique for removing coma aberration, the relative tilt angle between the optical disk surface and the optical head is detected and adjusted to almost zero (0). Since it does not suppress itself, the accuracy is poor, and it is difficult to sufficiently suppress the influence of coma. On the other hand, the method of removing waveform distortion due to coma aberration by an equalizer requires a sufficiently large number of taps, and has many disadvantages such as an increase in circuit scale and accompanying power consumption. When the correction is performed by the automatic equalization circuit, the compatibility of the optical disc can be ensured, but there is a problem that the residual waveform distortion increases as the coma aberration increases.

SUMMARY OF THE INVENTION An object of the present invention is to solve the above-mentioned problems in the prior art, and in an optical information reproducing method for an optical disk device or the like on the premise of optical disk compatibility, a coma aberration generated due to a tilt between an optical disk and an optical head. An object of the present invention is to provide an optical information reproducing method for effectively removing waveform distortion of a reproduced signal caused by the above.

In order to achieve the above object, the present invention is configured as described in the claims. That is,
An optical head for reproducing information recorded on an optical disk by irradiating a light spot, and an equalizer including a transversal filter having three or more taps are provided. An information reproducing method for reproducing information by using:
A specific area in which a mark located on the inner circumference side and the outer circumference side of the optical disc and shifted in the circumferential direction is formed with respect to the light spot is reproduced, and a tilt error signal of a tilt between the optical disc and the optical head is obtained. Then, an information reproducing method for reproducing the information recorded on the optical disk by correcting the inclination between the optical disk and the optical head based on the tilt error signal.

According to a second aspect of the present invention, in the first aspect, the tilt is any one of a circumferential tilt between the optical disc and the optical head, a radial tilt, or a tilt in both the circumferential direction and the radial direction. This is an information reproducing method.

At the time of loading an optical disk in the reproduction of optical information according to the present invention, an area in which a specific recording pattern is recorded is reproduced, and an optimum tap control is performed by an automatic equalizer constituted by a transversal filter of at least three taps. Numerical values are obtained, and based on this, an error signal proportional to the relative tilt between the optical disk surface and the optical head is obtained, and the tilt of the optical head is mechanically adjusted so that the error signal becomes substantially zero (0). After the adjustment, the waveform distortion of the reproduced signal caused by the coma aberration caused by the tilt of the optical disk and the optical head is removed, or the recording data is removed in addition to the waveform distortion removed at the time of loading the optical disk. During data reproduction, the tap coefficient value is finely adjusted so as to remove the waveform distortion remaining in the reproduction signal using the same automatic equalizer as described above, so that the Waveform distortion of the reproduction signal caused by the coma aberration caused by the inclination of the head is to effectively remove.

Means for carrying out the optical information reproducing method of the present invention includes an optical disk which is at least a removable optical recording medium, and an optical head for reproducing information recorded on the optical disk. Signal processing means for removing the waveform distortion of the reproduced signal, and means for obtaining, from the signal processing means, information on the inclination of the optical disc and the optical head in the circumferential direction, or the inclination in the radial direction, or both of the inclination information; Means for mechanically correcting the tilt between the optical disk and the optical head from the tilt information is provided.

The signal processing means for removing the waveform distortion of the reproduction signal from the optical head is a means for equalizing the output signal from the optical head, and has an equalization characteristic adaptive to the equalization means. It is provided with an equalizing means for calculating the inclination between the optical head and the optical disk from the equalizing characteristics optimized using the controlling means.

In addition, the present invention substantially eliminates the inclination between the optical disk surface and the optical head before recording or reproducing information with the optical head, and removes the waveform distortion due to the remaining inclination from the optimized equalization characteristic. It is provided with a circuit for removing by an equalizing means for calculating the inclination between the expression head and the optical disk. The equalizing means for calculating the inclination between the optical head and the optical disk from the optimized equalizing characteristics comprises a circuit constituted by a transversal filter having at least three taps.
[Action]
When there is an inclination between the optical disk and the optical head, waveform distortion that is asymmetric in the front-rear direction occurs in the reproduced signal due to coma aberration. When automatic equalization is performed on the reproduced signal, one of the first and third tap coefficients converges to a large value according to the asymmetry of the waveform distortion. By adjusting the tilt of the head so that these tap coefficient values become equal, the tilt between the optical disk and the optical head is almost eliminated. This operation only needs to be performed once at the time of loading the optical disk, so that there is no waiting time at the time of reproducing the recorded data. At the time of recording data reproduction, the same automatic equalizer is used to finely adjust the tap coefficient value so as to remove the waveform distortion of the reproduction signal that could not be removed only by adjusting the tilt of the optical head. It is possible to correct with high accuracy including the effect of slight coma caused by the above.

As described in detail above, according to the optical information recording / reproducing method and apparatus of the present invention, the relative tilt between the optical disk and the optical head caused by using a compatible disk is indispensable for high-density recording. Since the waveform distortion of the reproduction signal is removed by the equalizer and the inclination information is obtained from the optimum tap coefficient value at this time, the inclination angle can be accurately detected by a small number of additional circuits. Furthermore, after the inclination is corrected at the time of loading the optical disk, the effects of the remaining inclination and the inclination caused by the touching of the optical disk up and down can be automatically equalized to achieve a short convergence time and high reliability. The waveform distortion of the reproduced signal can be removed.

Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. In the following embodiments, a case where the present invention is applied to an optical disk device using a magneto-optical recording medium will be described as an example. However, the present invention is applicable to a write-once optical disk device and an optical disk device using a phase-change recording medium. However, the present invention can be applied without losing its essence. Further, in this embodiment, the specifications of the optical head are described assuming that the laser wavelength is 780 nm (nanometer), the numerical aperture of the objective lens is 0.55, and the mechanical characteristics of the disk substrate are 1.2 mm. The present invention is not limited to this.

<Example 1>
FIG. 1 is a schematic diagram illustrating a configuration of an apparatus for removing waveform distortion caused by the tilt of an optical disk illustrated in this embodiment. In this embodiment, an example will be described in which the waveform distortion generated by detecting the inclination of the optical head in the circumferential direction of the optical disk is removed.
A light spot 9 for recording and reproduction is focused on the recording medium surface of the optical disk 1 from the optical head 2 over the substrate with respect to the optical disk 1 detachably fixed to a spindle (not shown). The light spot 9 is a laser beam diverging from a semiconductor laser (not shown) having a wavelength of 780 nm provided inside the optical head 2 and is not shown, but is collimated by a collimator lens and a prism. After that, the light passes through an optical system including a prism or the like having a polarization characteristic and is finally collected by an objective lens having a numerical aperture of 0.55. The optical head 2 can be driven back and forth in the radial direction of the optical disk along a guide mechanism (not shown). The entire guide mechanism is rotatable with respect to the driving direction of the optical head 2, and its rotation is controlled by the tilt adjustment mechanism 3. On the other hand, the reproduced signal from the optical head 2 passes through four delay lines 4 having a delay time corresponding to the signal identification time interval. The five reproduction signals group-delayed by the identification time interval pass through a weighting circuit (tap coefficient setting circuit) 5 provided in a time series, and are added by an adder 6 to become an output signal. The weights in each weighting circuit 5 are hereinafter referred to as tap coefficients, and are C (-2), C (-1), C (0), C (1), and C (2), respectively. The value of the tap coefficient is variable by a 4-bit digital signal, for example. The output signal of the adder 6 is input to the equalization error detection and tap coefficient control unit 7. In the equalization error detection and tap coefficient control unit 7, tap coefficient values are updated so as to minimize waveform distortion, and these updated values are weighted by tap coefficients in the form of 4-bit digital signals. It is supplied to the circuit 5. Among the tap coefficients, the updated values of C (-1) and C (1) are input to the comparator 8, and as an error signal Δ for inclination adjustment control, Δ = C (1) −C (−1) The value is output. This value is supplied to the tilt adjusting mechanism 3, and the tilt of the optical head is adjusted so that the error signal Δ becomes zero (0). In the present embodiment, the number of taps is described as 5. However, if the number of taps is 3 or more, the present invention can be applied without losing its essence.

Next, the fact that the error signal Δ output from the comparator 8 becomes an error signal for inclination adjustment control will be described with reference to FIGS. When the optical head 2 is inclined with respect to the optical disc 1 by an inclination angle θ> 0, the reproduced signal waveform of the recording pit has a side peak on the front edge side as shown in FIG. Occurs, and the signal level of the trailing edge decreases. To remove such waveform distortion by the equalizer, the tap coefficient C (1) may be increased to raise the signal level of the rear edge. That is, the error signal Δ> 0. On the other hand, when the optical head 2 is inclined with respect to the optical disk 1 by an inclination angle θ <0, as shown in FIG. 2C, the reproduced signal waveform of the recording pit has a side peak on the trailing edge side. At the same time, the signal level of the leading edge decreases. To remove such waveform distortion by the equalizer, the tap coefficient C (-1) may be increased to raise the signal level of the front edge. That is, the error signal Δ <0. As described above, it is expected that the inclination angle θ of the optical disc and the error signal Δ are in direct proportion. Actually, computer simulation is performed in consideration of the tilt of the optical disk, and tap coefficient values obtained by executing equalization on the computer so as to minimize waveform distortion using the obtained reproduced signal waveform. , The relationship between the error signal Δ (%) and the tilt of the optical disk (milliradian: mrad) was obtained. As shown in FIG. Was in a relationship. From the above, it can be confirmed that it is possible to execute the tilt adjustment servo with the error signal Δ = 0 as the target point. In the simulation, the calculation was performed on the assumption that the laser wavelength was 780 nm, the numerical aperture of the lens was 0.55, and the thickness of the disk substrate was 1.2 mm.

(3) Next, FIG. 3 shows a processing flow for adjusting the inclination of the optical disk. After the optical disk is loaded, the optical head moves to a learning area where information pits for learning are recorded. The operation of the automatic equalizer is started, and the value of the tap coefficient is updated. An error signal Δ is calculated from the updated value. If the error signal Δ is larger than a predetermined set value ε, the rotation direction is determined according to the sign, and the head is rotated at an angle proportional to the absolute value of the error signal Δ. The magnitude of the set value ε depends on how much residual strain is to be allowed. For example, if it is to be suppressed to a crossing of inclination from −2 mrad to +2 mrad, it may be set to 2% from FIG. The above flow is repeated until the absolute value of the error signal Δ becomes smaller than the set value ε. After the tilt adjustment is completed when loading the optical disk, the tilt adjustment servo is stopped and the tilt of the optical head is fixed. Waveform distortion occurs in the reproduced signal due to the residual tilt that could not be completely removed by mechanical adjustment and the coma aberration that occurs due to the slight tilt caused by touching up and down when rotating the optical disc. Can be adaptively removed.

The present invention is not limited to the rotation mechanism of the optical head 2 and can be applied to any rotation mechanism without losing the essence of the invention. The pits recorded in the learning area are preferably pre-pits, but may be in the magneto-optical domain, and are not limited to recording pits. Further, the learning area may be provided anywhere on the optical disk surface as long as the optical head can be moved, and it is apparent that the present invention does not lose its essence.

<Example 2>
FIG. 5 is a schematic diagram showing the configuration of an apparatus for removing waveform distortion caused by inclination in the circumferential direction and radial direction of an optical disk exemplified in the present embodiment, and is different from FIG. 1 shown in the first embodiment. A mechanism for detecting and correcting the tilt of the head in the radial direction is added.
In FIG. 5, after the optical disc 1 is mounted, the optical head 2 is sequentially moved from the inner circumference to the outer circumference (or from the outer circumference to the inner circumference) to a track position designated in advance by a head driving mechanism (not shown). Moving. During that time, the optical head position detector 10 reads the address information of each track of the optical disk, stops at the specified track position, and then obtains the tilt information between the disk 1 and the optical head 2 by the radial tilt detection circuit 11. Then, the information is stored in the tilt information memory 12 together with the optical head position information. As the track position for detecting the tilt information in the radial direction, for example, the area from the inner circumference to the outer circumference is divided into eight, and the track substantially at the center of each area is set as the representative track. The tilt information for the other tracks is calculated by the correction value calculator 13 by interpolating from the tilt information of the preceding and following representative tracks. After the operation is completed, when the optical head 2 moves to an arbitrary track, the position information of the track is read by the optical head position detector 10 and the inclination information of the representative track before and after the optical head 2 is stored in the radial inclination information memory. 12 and input it to the correction value calculation unit 13 to obtain tilt correction information. This is sent to the tilt adjusting mechanism 14 in the radial direction and the attitude of the optical head 2 is controlled to correct the tilt in the radial direction. Note that the priority order for correcting the inclination in the circumferential direction is not particularly limited in the present embodiment.

<Example 3>
FIG. 6 is an explanatory diagram for calculating a tilt error signal in the radial direction of the optical disk exemplified in this embodiment. FIG. 7 is a diagram for removing waveform distortion of a reproduced signal caused by tilt (radial and circumferential tilts) of the optical disk. FIG. 1 is a schematic diagram showing an example of the configuration of a device for performing the above.
As shown in FIG. 6, when the optical disk and the optical head are tilted in the radial direction, a side spot 17 due to coma is generated in the main light spot 16 and interferes with an adjacent track. When the inclination is positive [FIG. 6 (a)] or negative [FIG. 6 (b)], the side spots 17 are generated on the inner circumference or outer circumference of the optical disk. By providing the tracks at a fixed interval, it is possible to cause the reproduction signal waveform of the recording pit 19 for learning to be caused by coma in the circumferential direction, similarly to the waveform distortion caused by the tilt of the optical disk shown in FIG. Waveform distortion similar to the above occurs. When the tap coefficient value is optimized to remove this distortion, the value of C (1) -C (-1) changes the polarity according to the positive or negative of the relative tilt between the optical disk and the optical head, and changes in the radial direction. It can be used as a tilt error signal.

Next, a procedure for actually correcting the inclination of the optical head using the apparatus for removing the waveform distortion of the reproduced signal shown in FIG. 7 will be described below.
After the optical disc 1 is loaded, the optical head 2 is moved by a head drive mechanism (not shown) to a learning area where information pits for learning are recorded. The circuit path is switched to the inclination adjustment mechanism 3 in the circumferential direction based on the inclination correction switching signal. Thereafter, as shown in the first embodiment, the correction of the inclination in the circumferential direction is executed. The details of this procedure have already been described in the first embodiment, and a description thereof will be omitted. Next, a switching signal for tilt correction switches the circuit path to the tilt adjustment mechanism 14 in the radial direction. The optical head 2 sequentially moves from an inner circumference to an outer circumference (or from the outer circumference to the inner circumference) to a track position designated in advance by a head driving mechanism (not shown). During that time, the optical head position detector 10 reads the address information of each track of the optical disk, stops at the specified track position, and then calculates the inclination information between the optical disk 1 and the optical head 2 from the error signal Δ = C (1) -C (-1) and stored in the radial tilt error signal memory 15 together with the optical head position information. As a track position for detecting a tilt error signal in the radial direction, for example, the area from the inner circumference to the outer circumference is divided into eight, and a track substantially at the center of each area is set as a representative track. The tilt information for the other tracks is separately calculated by interpolating from the tilt information of the preceding and following representative tracks. After this operation is completed, when the optical head 2 moves to an arbitrary track, the position information of the track is read by the optical head position detector 10, and the tilt error signals in the representative tracks before and after the optical head 2 are converted into the tilt error in the radial direction. By reading from the signal memory 15 and sending it to the radial tilt adjusting mechanism 14 to control the attitude of the optical head 2, the radial tilt can be corrected.

FIG. 1 is a schematic diagram showing a configuration of a device for removing a waveform distortion of a reproduced signal generated due to an inclination of an optical disc exemplified in Embodiment 1 of the present invention. FIG. 3 is an explanatory diagram illustrating a form of waveform distortion of a reproduction signal caused by the tilt of the optical disc illustrated in the first embodiment of the present invention. FIG. 3 is a block diagram illustrating a processing flow of tilt adjustment control of the optical disc illustrated in the first embodiment of the present invention. 4 is a graph showing a relationship between the tilt of the optical disk illustrated in the first embodiment of the present invention and an error signal Δ value. FIG. 9 is a schematic diagram illustrating a configuration of a waveform distortion removal device for a reproduced signal generated due to the tilt of the optical disc illustrated in the second embodiment of the present invention. FIG. 9 is an explanatory diagram showing a form of waveform distortion of a reproduced signal caused by a tilt in the radial direction of the optical disc illustrated in the third embodiment of the present invention. FIG. 9 is a schematic diagram illustrating a configuration of a device for removing a waveform distortion of a reproduction signal caused by an inclination of an optical disc illustrated in a third embodiment of the present invention.

Explanation of reference numerals

DESCRIPTION OF SYMBOLS 1 ... Optical disk 2 ... Optical head 3 ... Circumferential inclination adjustment mechanism 4 ... Delay line 5 ... Tap coefficient setting circuit (weighting circuit)
6 Adder 7 Equalization error detection and tap coefficient control unit 8 Comparator 9 Light spot 10 Optical head position detector 11 Radial tilt detection circuit 12 Radial tilt information memory 13 Correction Value calculator 14: Radial tilt adjustment mechanism 15: Radial tilt error signal memory 16: Main light spot 17: Side spots 18, 19, 20: Learning recording pits

Claims (2)

Information for reproducing information by using an optical head for reproducing information recorded on an optical disk by irradiating a light spot and an equalizer including a transversal filter having three or more taps A playback method,
A specific area in which a mark located on the inner circumference side and the outer circumference side of the optical disc and shifted in the circumferential direction is formed with respect to the light spot is reproduced, and a tilt error signal of a tilt between the optical disc and the optical head is obtained. An information reproducing method comprising: correcting an inclination between the optical disk and the optical head based on the inclination error signal to reproduce information recorded on the optical disk. The information reproducing method according to claim 1, wherein the tilt is any one of a tilt in the circumferential direction, a tilt in the radial direction, and a tilt in both the circumferential direction and the radial direction between the optical disc and the optical head.

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