JPH0877583A - Information reproducing device - Google Patents

Abstract

PURPOSE: To reduce the quantity of cross talk from an adjacent track by detracking a reproducing light beam in accordance with an inclining direction between a recording medium and an optical system. CONSTITUTION: A detracking amt. is obtained from regenerative signals recorded in prescribed tracks in inner and outer circumferential test areas of a magneto- optical disk or a cross talk amt. leaked from a prescribed track, and is stored in an internal memory by a CPU 18. At the time of reproducing information of the magneto-optical disk 1, the detracking direction and amt. are read out of the internal memory by the CPU 18 to control an AT offset adding circuit 19 according to the direction and the amt. When an offset corresponding to the detracking direction and amt. is impressed upon the AT.AF circuit 12 from the circuit 19, a driving signal corresponding to the offset is supplied from the circuit 12 to an objective lens actuator 14, so as to control an objective lens 8. By this method, a reproducing light beam emitted from a semiconductor laser 5 is detracted by a prescribed amt., and afterward, recorded information is reproduced under the state of this condition.

Description

Detailed Description of the Invention

[0001]

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

[0002]

2. Description of the Related Art Conventionally, as an apparatus for irradiating a recording medium with a light beam to optically record or reproduce information, a reproduction-only apparatus or recording apparatus for reproducing a reproduction-only recording medium in which information is recorded in advance is used. There are a write-once type device that opens information films by heat to record information pits, and a rewritable device that changes the direction of magnetization of a perpendicular magnetization film to form information pits.

FIG. 9 is a block diagram showing a rewritable magneto-optical disk device among them. In FIG. 9, reference numeral 1 is a magneto-optical disk which is an information recording medium, and a magnetic film 2 is formed on a transparent substrate such as glass or plastic. The magneto-optical disk 1 is mounted on the rotating shaft of a spindle motor 3 and is rotated at a predetermined speed by driving the motor 3. An optical head 4 is arranged on the lower surface of the magneto-optical disk 1, and a bias magnet 13 is arranged on the upper surface so as to face the optical head 4.

A semiconductor laser 5 as a recording / reproducing light source is provided in the optical head 4. When recording information, the light beam of the semiconductor laser 5 is modulated by a laser driving circuit (not shown) according to an information signal. . The light beam emitted from the semiconductor laser 5 is collimated by the collimator lens 6 and then transmitted through the polarization beam splitter 7 to obtain the objective lens 8.
Incident on. The incident light beam then passes through the objective lens 8
And the light is focused on the magnetic film 2 of the magneto-optical disk 1 as a minute light spot. On the other hand, the bias magnet 13
From this, a magnetic field in a fixed direction is applied to the magneto-optical disk 1, and a series of information is recorded by the application of this magnetic field and the irradiation of the modulated light beam.

The light beam applied to the magneto-optical disk 1 is reflected by the medium surface. This reflected light again passes through the objective lens 8 and enters the polarization beam splitter 7,
The light is reflected by the plane of polarization toward the beam splitter 9 and separated from the incident light from the semiconductor laser 5. The beam splitter 9 splits the incident light beam into two light beams, and one light beam is received by the optical sensor 11 via the sensor lens 10. The light reception signal of the optical sensor 11 is input to the AT / AF circuit (auto tracking, auto focus control circuit) 12, and A
The T / AF circuit 12 generates a tracking error signal and a focus error signal based on the received light signal. Then, the objective lens actuator 14 is driven based on the obtained tracking error signal and focus error signal to displace the objective lens 8 in the tracking direction and the focus direction, thereby performing tracking control and focus control.

On the other hand, when the recorded information on the magneto-optical disk 1 is reproduced, the light beam of the semiconductor laser 5 is set to a reproducing power at which recording is not possible, and the reproducing light beam is scanned to a target track. The recorded information is reproduced. That is, the reflected light of the reproduction light beam from the disc surface is received by the optical sensor 16 via the objective lens 8, the polarization beam splitter 7, the beam splitter 9, and the sensor lens 15. The light reception signal of the optical sensor 16 is sent to a reproduction signal processing circuit (not shown), and the recorded information is reproduced by performing a predetermined signal processing there. Of course, during reproduction, the reflected light of the reproduction light beam is received by the optical sensor 11,
The T / AF circuit 12 performs tracking control and focus control based on the received light signal.

[0007]

By the way, recently, the density of information pits has been increased to meet the demand for higher capacity of information. However, if the density of the information pits is increased as described above, there is a problem that crosstalk from pits of adjacent tracks is mixed in addition to intersymbol interference from the pits before and after. Therefore, such crosstalk will be described with reference to FIGS. First, FIG. 10 is a diagram for explaining crosstalk in an ideal state, and FIG. 10A shows pits recorded in the information track. Here, an 8T continuous signal is recorded on the (N-1) th track, a 2T continuous signal is recorded on the Nth track, and a 7T continuous signal is recorded on the (N + 1) th track. Therefore,
When the reproduction light spot is scanned and reproduced on the N-th track, an adjacent track is overlapped with the reproduction spot as shown in FIG. 10A. Therefore, the reproduction signal of the N-th track has 8T and 7T signal components. When this signal is observed with a spectrum analyzer, the reproduced signal component of 2T is mixed with the signals of 8T and 7T as shown in FIG. 10B. This difference in carrier level is called the crosstalk amount. Since the explanation of FIG. 10 is for the crosstalk in the ideal state, the crosstalk amounts from the adjacent tracks on both sides are equal and are relatively small values.

However, in practice, as shown in FIG. 11 (a), the center positions of the reproduction spot and the recording pit are deviated due to detrack generated during recording, and aberrations peculiar to the optical system and tilt of the magneto-optical disk cause a disc surface error. Playback spots in asymmetry are asymmetrical, or crescent-shaped sub-spots occur. Therefore, when the N-th track is reproduced, the leaks from the tracks adjacent to each other are also shifted to one side, resulting in an imbalance in the crosstalk amounts of 8T and 7T. In FIG. 11A, since the reproduction light spot is offset to the (N + 1) th track, the 7T signal component is large in the crosstalk leaking into the reproduction signal as shown in FIG. 11B. Thus, in the ideal state, the amount of crosstalk from both sides does not exceed a certain value,
If the leakage from both sides is biased to one side, the crosstalk amount from one side becomes large and exceeds a certain value, and there is a problem that the reproduction signal quality is degraded.

The present invention has been made in view of the above-mentioned conventional problems, and an object of the present invention is to make a reproducing light beam track in accordance with a tilt direction of a recording medium and an optical system.
An object of the present invention is to provide an information reproducing apparatus capable of reducing crosstalk leaking from adjacent tracks.

[0010]

SUMMARY OF THE INVENTION An object of the present invention is to provide an information reproducing apparatus for reproducing recorded information by irradiating a disc-shaped optical information recording medium with a light beam, and the recording medium and the light beam on the medium. Means for determining the direction of the detrack of the reproduction light beam according to the direction of the tilt of the optical system for condensing the light, means for determining the amount of detrack of the reproduction light beam, and the obtained detrack Direction and the amount of detrack, the reproducing light beam is detracked according to the direction and the amount of detrack stored in the memory when reproducing the recorded information on the recording medium. By doing so, it is achieved by an information reproducing apparatus characterized by correcting crosstalk leaking from an adjacent track.

[0011]

Embodiments of the present invention will now be described in detail with reference to the drawings. FIG. 1 is a block diagram showing an embodiment of the information reproducing apparatus of the present invention. In FIG. 1, the same parts as those of the conventional device of FIG.
In FIG. 1, reference numeral 17 is an amplitude detection circuit for detecting the amplitude of the reproduction signal based on the light reception signal of the optical sensor 16.
As will be described later in detail, the amplitude detection circuit 17 detects the amplitude of the reproduction signal when determining the detrack direction of the reproduction light beam and when determining the detrack amount. The detected value is taken into the CPU 18 by the A / D converter in the CPU 18. The CPU 18 is a processor circuit for controlling each part of the device, and when the magneto-optical disk 1 is set in the device, as described later, the CP
In U18, control is performed to control each part to determine the direction and amount of detrack of the reproduction light beam. 19 is CPU1
8 is an AT offset application circuit for applying an offset to the AT / AF circuit 12 based on the instruction 8 to detrack the reproduction light beam by a desired amount in a desired direction. Other configurations are the same as those in FIG.

Next, the relationship between the relative tilt between the objective lens 8 and the magneto-optical disk 1 and crosstalk will be described with reference to FIG. First, when the objective lens 8 and the magneto-optical disk 1 are relatively inclined toward the outer peripheral side as shown in FIG. 2A, a crescent-shaped sub-spot is generated on the outer peripheral side on the board surface, and a sub-spot from the outer track is generated. Crosstalk increases. When the objective lens 8 and the magneto-optical disk 1 are relatively inclined toward the inner peripheral side as shown in FIG. 2B, a crescent-shaped sub-spot is generated on the inner peripheral side on the board surface and the inner track is formed. The crosstalk from is increased. Therefore, by measuring the amount of crosstalk from both adjacent tracks, the objective lens 8
The relative tilt direction of the magneto-optical disk 1 can be specified, and the detrack direction of the light spot for reducing the crosstalk amount can also be determined.

In general, a recording medium such as a magneto-optical disk often has different inclination directions on the inner and outer circumference sides, and even if the crosstalk amount from both adjacent tracks is measured at one point. , It is not possible to specify the direction of the relative tilt between the objective lens and the disc over the entire circumference. But,
The majority of magneto-optical disks are upside down, and there is no such thing as waviness, so when measuring the crosstalk amount from both adjacent tracks on the inner and outer circumferences,
An approximate tilt shape can be inferred.

For example, when the objective lens is tilted toward the outer peripheral side, when the crosstalk amount from both adjacent tracks is measured on the inner and outer peripheral sides, there are six cases as shown in FIG. 3, and the shape of the recording medium can be estimated to some extent. . Further, it can be seen that the pattern of the combination of the detrack directions that reduces crosstalk may be four patterns. Hereinafter, the six cases of FIG. 3 will be described in detail. In the case of (1), the crosstalk from the outer track is large on both the inner and outer circumferences of the recording medium, and there is no difference in the amount of crosstalk on the inner and outer circumferences. . In this case, the detrack direction is inward and crosstalk is reduced. In the case of (2), the crosstalk from the outer track is large on both the inner and outer circumferences of the recording medium, and the crosstalk amount decreases toward the inner circumference. The medium shape is reversed upward (on the side opposite to the objective lens), and the amount of the reverse is larger than the inclination of the objective lens. In this case, the detrack direction is inward and crosstalk is reduced. In the case of (3), crosstalk from the inner track on the inner circumference of the recording medium and from the outer track on the outer circumference is large. The shape of the medium is upward, and the amount of the reverse is equal to or smaller than the inclination of the objective lens. In this case, crosstalk decreases in the direction of detrack from the inner circumference to the inflection point on the outside and from the inflection point to the outer circumference on the inner side. In the case of (4), the crosstalk from the inner track is large both on the inner and outer circumferences of the recording medium, and there is no difference in the amount of crosstalk on the inner and outer circumferences. is there. In this case, crosstalk is reduced outward in the detrack direction. In the case of (5), crosstalk from the outer track is large on both the inner and outer circumferences of the recording medium, and the crosstalk amount decreases toward the outer circumference. The medium shape is downward (on the side of the objective lens), and the amount of the reverse is larger than the inclination of the objective lens. In this case, crosstalk is reduced outward in the detrack direction. In case (6), the crosstalk from the outer track on the inner circumference of the recording medium and from the inner track on the outer circumference is large. The shape of the medium is downward, and the amount of the reverse is equal to or smaller than the inclination of the objective lens. In this case, the crosstalk decreases in the direction of detrack from the inner circumference to the inflection point and inside from the inflection point to the outer circumference.
In addition, in the cases of (3) and (6), the positions of the existing inflection points can be obtained from the intersections of the graphs of (3) and (6) of FIG. 3, respectively.

FIG. 4 is a diagram summarizing the above results. As is clear from FIG. 4, there are four combinations of detrack directions. That is, the above (1), (2),
In the case of (5), the crosstalk decreases in the detrack direction from the inner circumference to the inflection point inward, and from the inflection point to the outer circumference inward. In the case of (3), the crosstalk decreases in the detrack direction from the inner circumference to the inflection point on the outside and from the inflection point to the outer circumference on the inner side. Further, the cases (6) and (4) are as shown in FIG.

On the other hand, when the objective lens is inclined toward the inner peripheral side, the relationship between the crosstalk amount and the medium shape is shown as in FIG. 3, and as shown in FIG. 5, 6 of (1) to (6). There are two cases. Further, FIG. 6 is a diagram collectively showing the directions of detrack at this time. As is clear from FIG. 6, even when the objective lens is inclined toward the inner peripheral side, there are four detrack directions as in FIG.

Next, a specific operation of the above embodiment will be described. First, a method of measuring crosstalk and determining the direction of detrack will be described with reference to FIG. Figure 7
First, when the magneto-optical disk 1 is set in the apparatus, the CPU 18 accesses the optical head 4 to a predetermined inner peripheral side test area (S1) and records a predetermined signal on a predetermined Nth track (S1). S2). Here, it is assumed that the longest pattern 8T signal is recorded. When the recording is completed, the CPU 18 controls each unit to record the signal first.
The N-1th track adjacent to the inner side of the 9th track is reproduced, and the amplitude detection circuit 17 detects the amplitude I.D. O is detected (S3). The signal amplitude I.D. O is the crosstalk amount from the Nth track and is stored in the internal memory of the CPU 18. Then C
The PU 18 reproduces the N + 1th track adjacent to the outside of the Nth track, and the amplitude detection circuit 17 reproduces the reproduction signal amplitude I.S. I is detected (S4). The obtained amplitude value I.D. I is similarly stored in the internal memory of the CPU 18.

When the measurement of the crosstalk in the inner peripheral side test area is completed, the CPU 18 accesses the predetermined outer peripheral side test area of the optical head 4 (S5) and outputs a predetermined signal to a predetermined N'th track. Record (S6). Here again, it is assumed that the longest pattern 8T signal is recorded. Then, the N′−1th track adjacent to the inside of the N′th track is reproduced to reproduce the reproduction signal amplitude O.S. O is detected (S7), and the N '+ 1th track adjacent to the outside of the N'th track is reproduced to reproduce the reproduced signal amplitude O.O. I
Is detected (S8). The obtained amplitude value is the CPU
It is stored in 18 internal memories. This completes the measurement of crosstalk on the inner and outer circumferences of the magneto-optical disk 1.

Next, the CPU 18 performs a process for measuring the detrack direction of the reproduction light spot based on the measurement result. Specifically, the reproduction signal amplitude I.D. O and I. I, and the reproduced signal amplitude O.I. detected in the outer peripheral side test area. O and O. I is compared (S9). Here, the I.D. O and I. The comparison result of I.I. I <I. O in the outer peripheral side test area. I and O. The comparison result of O is O. I <
O. If it is O, (1), (2), (5) in FIG.
In this case, or the case of (1) in FIG. 5, the direction of detrack is determined to be inward. In addition, I. I>
I. O, O. I <O. If it is O, (3) in FIG.
In this case, the position of the inflection point of the disk is obtained.
To obtain the position of the inflection point, (3) in FIG. 3 or FIG.
The position of the inflection point is obtained from the intersection of two crosstalk straight lines connecting the inner circumference and the outer circumference of (6), and the direction of the detrack is as shown in (3) of FIG. 4 or (6) of FIG. From the inner circumference side to the inflection point, the outside is determined, and from the inflection point to the outer circumference is determined to the inside.

Further, the comparison result shows that I <I. O, O. I
> O. If it is O, it is the case of (6) in FIG. 3 or the case of (3) in FIG. 5, so the position of the inflection point of the disk is similarly obtained. Also in this case, the position of the inflection point is obtained from the intersection of two crosstalk straight lines connecting the inner circumference and the outer circumference of (6) of FIG. 3 or (3) of FIG.
The direction of detrack is (6) in FIG. 4 or (3) in FIG.
As shown, the inside is determined from the inner circumference to the inflection point, and the outside is determined from the inflection point to the outer circumference.

Finally, I. I> I. O, O. I> O. O
If it is, (4) in FIG. 3 or (2) in FIG.
Since it corresponds to the cases of (4) and (5), the direction of detrack is (4) in FIG. 4 or (2), (4) in FIG.
It is determined to be outside as in (5). The detrack direction of the reproduction light beam is thus determined, and the obtained detrack direction is stored in the internal memory of the CPU 18.

Next, a method of determining the detrack amount of the reproduction light beam will be described. When determining the detrack amount, the detrack amount is obtained from the reproduction signal of the signal recorded on the predetermined track of the test area on the inner and outer circumferences of the magneto-optical disk or the crosstalk amount leaking from the predetermined track as described above. To be That is, the reproduction light beam is scanned a predetermined number of times while changing the detrack amount on the track in which the 8T pattern signal in the inner or outer test area is recorded, and the reproduction signal amplitude at this time is detected by the amplitude detection circuit 1 each time.
Detected at 7. When changing the detrack amount, the CPU
At 18, the AT offset adding circuit 19 is controlled to gradually change the detrack amount of the reproduction light beam from the center of the track to the left and right sides. When the amplitude of the reproduced signal is measured while changing the detrack amount in this way, a reproduced signal amplitude curve can be obtained as shown in FIG. This measurement result is CPU18
Stored in the internal memory of. In addition, the detrack amount when the reproduction signal amplitude value is the largest is the detrack amount to be obtained, but in order to determine the detrack amount more accurately, from the predetermined track where the previous signal is recorded to the adjacent track. The crosstalk leaking into is measured.

The track for measuring the crosstalk may be a track adjacent to the inner side of the track on which a signal is recorded or a track adjacent to the outer side thereof, and the track adjacent to the inner side or the outer side thereof is scanned with the reproduction light beam. Then, the crosstalk is measured. Also during this crosstalk, the reproduction light beam is scanned a predetermined number of times while changing the detrack amount of the reproduction light beam, and the crosstalk amount at this time is detected by the amplitude detection circuit 17 each time. When crosstalk is measured by changing the detrack amount in this way,
A crosstalk curve can be obtained as shown in FIG. The obtained measurement result is stored in the internal memory of the CPU 18.

Here, when the detrack amount is determined, the detrack amount when the reproduction signal amplitude becomes maximum and the detrack amount when the crosstalk becomes minimum may not always match, and therefore, in FIG. As described above, it is desirable to determine the detrack amount when the difference between the two becomes maximum as the optimum value. Of course, the detrack amount when the reproduction signal amplitude becomes maximum or the detrack amount when the crosstalk becomes minimum may be determined as the detrack amount to be obtained.
When determining the amount of detrack in this way, if there is no inflection point on the disc, measure the reproduced signal amplitude and crosstalk in either the inner or outer test area of the disc as described above. The optimum value of the detrack amount may be determined, but when the disc has an inflection point, the playback signal and crosstalk are measured at the inner and outer rims to determine the detrack amount at the inner and outer rims of the disc. To do. The detrack amount is determined in this way, and the obtained detrack amount is calculated by the CPU.
It is stored in 18 internal memories. As described above, the direction of detrack and the amount of detrack are determined, and the apparatus is ready for operation.

Next, the operation of reproducing information from the magneto-optical disk 1 using the detrack direction and amount determined as described above will be described. First, the CPU 18 reads the detrack direction and amount from the internal memory, and controls the AT offset adding circuit 19 according to the direction and amount. For example, when the detrack direction is the inner circumference side and the detrack amount is n μm, the CPU 18 outputs a corresponding control signal to the AT offset adding circuit 19.
When the AT offset adding circuit 19 receives this, AT
An offset corresponding to the direction and amount of detrack is applied to the AF circuit 12. As a result, the AT / AF circuit 12 supplies a drive signal according to the offset to the objective lens actuator 14, and the objective lens 8 is controlled according to the drive signal. In this way, the reproduction light beam emitted from the semiconductor laser 5 is detracked by n μm toward the inner peripheral side of the disk, and thereafter, the recorded information is reproduced with the reproduction light beam being detracked in this manner.

In the above embodiments, the magneto-optical disk device has been described as an example, but the present invention is not limited to this, for example, a device for reproducing a read-only recording medium or a reproducing device for a write-once recording medium. It can also be applied to.

[0027]

As described above, according to the present invention, the reproduction light beam is detracked in accordance with the tilt direction of the recording medium and the optical system, so that the cross from the adjacent track caused by the tilt of the recording medium and the optical system. The amount of talk can be reduced,
There is an effect that the reproduction signal quality can be maintained at high quality.

[Brief description of drawings]

FIG. 1 is a block diagram showing an embodiment of an information reproducing apparatus of the present invention.

FIG. 2 is a diagram showing the states of spots on the board surface when the objective lens and the recording medium are relatively inclined to the outer peripheral side and when they are inclined to the inner peripheral side.

FIG. 3 is a diagram for explaining the relationship between crosstalk and tilt of the recording medium when the objective lens and the recording medium are relatively inclined toward the outer peripheral side.

FIG. 4 is a diagram collectively showing the detrack direction of the reproduction light beam for each case of FIG.

FIG. 5 is a diagram for explaining the relationship between the crosstalk and the tilt of the recording medium when the objective lens and the recording medium are relatively inclined toward the inner peripheral side.

6 is a diagram collectively showing the detracking direction of the reproduction light beam for each case of FIG.

7 is a flowchart showing a processing procedure for determining a detrack direction in the embodiment of FIG.

FIG. 8 is a diagram showing a measurement result when the reproduction signal amplitude and crosstalk are measured while changing the detrack amount of the reproduction light beam.

FIG. 9 is a configuration diagram showing a conventional magneto-optical disk device.

FIG. 10 is a diagram for explaining crosstalk mixed from adjacent tracks on both sides in an ideal state.

FIG. 11 is a diagram for explaining crosstalk mixed from adjacent tracks on both sides in an actual state.

[Explanation of symbols]

 1 Magneto-optical disk 3 Spindle motor 4 Optical head 5 Semiconductor laser 8 Objective lens 12 AT / AF circuit 13 Bias magnet 17 Amplitude detection circuit 18 CPU 19 AT offset application circuit

Claims (3)

[Claims] 1. An information reproducing apparatus which reproduces recorded information by irradiating a disc-shaped optical information recording medium with a light beam, and in the tilt direction of the recording medium and an optical system for converging the light beam on the medium. Means for determining the detrack direction of the reproduction light beam according to the above, means for determining the detrack amount of the reproduction light beam, and the obtained detrack direction and detrack amount are stored. When reproducing the record information of the recording medium, the cross section leaks from the adjacent track by detracking the reproduction light beam according to the direction and amount of the detrack stored in the storage means. An information reproducing apparatus characterized by correcting talk. 2. The information reproducing apparatus according to claim 1, wherein the detrack direction deciding means causes crosstalk of a signal recorded on a predetermined track in each of two areas on an inner peripheral side and an outer peripheral side of the recording medium. A means for reproducing and measuring tracks adjacent to the inner and outer sides of the track, a value measured on a track adjacent to the inner side of a predetermined track in the inner peripheral side region, and a value measured on a track adjacent to the outer side, and Means for respectively comparing the values measured on the tracks adjacent to the inside of the predetermined track in the outer peripheral side area and the values measured on the tracks adjacent to the outside, and the detracking of the reproduction light beam based on the comparison result of the comparison means. And a means for determining the direction of the information reproducing apparatus. 3. The information reproducing apparatus according to claim 1, wherein the detrack amount determining means reproduces a track on which a predetermined signal is recorded while changing a detrack amount of a reproduction light beam to measure a reproduction signal amplitude. , And the amount of detrack when the difference between the reproduced signal amplitude and the crosstalk is maximum by measuring the crosstalk from the track by reproducing the track adjacent to the track while changing the detrack amount of the reproduction light beam. Is determined as an optimum value.