JP2002319155A - Focus offset adjustment method - Google Patents

Abstract

(57) [Summary] [Problem] To provide a focus offset adjusting method of an optical disc apparatus for reproducing information from an optical disc in which a groove and a land are coupled at one place in one round, wherein a light spot has passed through a joint between the groove and the land. Immediately after that, a reproduction operation with little jitter is realized. SOLUTION: A focus offset for optimizing a predetermined evaluation amount is obtained for a groove and a land, and a focus error signal immediately after a light spot passes through a joint between the groove and the land is measured for a predetermined period, and the measured value is measured. The focus offset between the groove and the land is corrected so that the amount of change in the focus error signal is reduced.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for adjusting a focus offset of an optical disk apparatus for reproducing information, and in particular, it is possible to reduce a reproduction error immediately after a light spot passes through a joint between a groove and a land. The present invention relates to a focus offset adjustment method.

[0002]

2. Description of the Related Art In an optical disk drive, a focus offset applied to a focus error signal is adjusted in order to improve the accuracy of positioning a light spot irradiated on an optical disk. As the evaluation amount at the time of the adjustment, reproduction error information such as the jitter of the reproduction signal and the number of bits reproduced erroneously is used. In the conventional adjustment method, a signal is reproduced by giving a different focus offset to the focus error signal, and the reproduction error information is repeatedly obtained, and a focus offset with less reproduction error information is obtained by a least square method or the like.

At present, in order to reduce signal leakage from an adjacent track, an optical disk having a groove as a guide groove and a land between the guide grooves as a track is commercialized. Since the characteristics of the focus error signal are different between the groove and the land, the groove focus offset and the land focus offset that minimize the above-described reproduction error information for the groove and the land are determined. When reproducing information on an optical disc, when a light spot is located on a land, a focus error signal is given a land focus offset, and when it is located on a groove, a focus error signal is given a groove focus offset. .

[0004]

In the prior art described above, the target focal position differs between the groove and the land.
That is, the relative distance between the disk and the lens differs between the groove and the land. Therefore, immediately after the position of the light spot is switched from the groove to the land or from the land to the groove, a reproduction error is likely to occur.

Accordingly, it is an object of the present invention to provide a focus offset adjusting method capable of improving the focus positioning accuracy immediately after a light spot has passed a joint between a groove and a land.

[0006]

In order to attain the above object, first, as in the prior art, a groove focus offset and a land focus offset for optimizing a predetermined evaluation amount with respect to a groove and a land are set. Ask.

Next, a focus error signal immediately after the light spot has passed through the joint between the groove and the land is measured for a predetermined period. If the target focal position of the light spot is different between the groove and the land, for example, when the light spot moves from the groove to the land, the focal position immediately after moving to the land becomes the optimal focal position for the groove. I have.

Thereafter, the focus position of the light spot is moved to a position optimal for the land by the focus servo system. By measuring the focus error signal during the period in which the focus servo system is settled, it is possible to measure an amount proportional to the displacement difference between the target focal position of the groove and the land.

In order to reduce the displacement difference, when the light spot settles in the negative direction of the focus error signal on the land, the land focus offset is corrected in the positive direction or the groove focus offset is changed. Correct in the negative direction.

The amount of correction need not be the same for the groove and the land. From the relationship between the focus offset and the reproduction error measured earlier, only the one with the larger allowable amount of focus offset deviation may be corrected.

[0011]

DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described with reference to FIGS.

First, an optical disk will be described with reference to FIG. FIG. 1 is a schematic diagram showing a part of an optical disk, in which an originally arcuate track is linearly described. On the optical disk, a track 16 is defined by a groove 12 as a guide groove and a land 14 between the guide grooves, and the groove 12 and the land 14 are joined at one place per circumference at a joint portion 18.

Next, a method of adjusting the focus offset for optimizing the evaluation amount and its problems will be described with reference to FIGS. FIG. 2 is a block diagram of the focus servo circuit. FIG. 3 is a diagram showing the focus offset and the jitter of the reproduction signal. FIG. 4 is a diagram showing a focus operation at a joint between a groove and a land. FIG. 5 is a diagram showing focus error signals for grooves and lands.

First, after the light spot is located in the groove, the focus servo circuit shown in FIG. The focus actuator drive signal 3 is added by the controller 28 using the sum.
Generate 0.

In this focus servo circuit, it is possible to change the focal position of the light spot by changing the value of the groove focus offset 22. In order to obtain the optimum value of the focal position, reproduction error information, for example, jitter of a reproduction signal or the number of reproduction errors is obtained while changing the groove focus offset 22. Similarly, after the light spot is located on the land,
The reproduction error information is acquired while changing the land focus offset 24.

FIG. 3 shows an example in which the jitter of a reproduced signal is used as error information. A focus offset that minimizes the jitter of the groove reproduction signal is Gopt, and a focus offset that minimizes the jitter of the land reproduction signal is Lopt. In the method of adjusting the focus offset that optimizes the evaluation amount, the focus offset 22 for the groove is Gopt,
Lopt is set to the land focus offset 24.
However, in this adjustment method, the jitter of the reproduction signal is not always the minimum immediately after the light spot moves from the groove to the land or from the land to the groove. This is because the focal position of the light spot set by the above-described adjustment method differs between the groove and the land.

As shown in FIG. 4A, the focus position is not an optimum position immediately after the light spot passes through the groove-land joint 18 and during the settling period 40 of the focus servo. FIG. 4B shows a focus error signal corresponding to FIG. When the light spot scans the groove, it is located at the target focal position corresponding to Gopt. Since the focal position does not change in a minute period before and after the light spot passes through the groove-land joint 18,
The difference between the land and groove focus error signals is observed. After passing through the coupling section, control is performed such that the light spot is located at the target focal position corresponding to Lopt by the settling operation of the focus servo. FIG. 5 shows the locus.

Next, a method of correcting a focus offset which solves the above-described problem will be described with reference to FIGS. FIG. 6 is a diagram showing a focusing operation at a joint between a groove and a land improved by the present invention. FIG. 7 is a diagram illustrating a focus operation at a joint between a groove and a land improved according to another embodiment of the present invention.

In order to reduce the jitter of the reproduced signal immediately after the light spot passes through the joint between the groove and the land, it is necessary to bring the focus positions of the groove and the land closer. As shown in FIG. 5, since the characteristics of the focus error signal are different between the groove and the land, the focus positions of the groove and the land are different even when the same focus offset is given to the groove and the land. FIG. 5 is a schematic diagram, which is a characteristic that is extremely difficult to measure in an experiment. That is, it is extremely difficult to bring the focus positions of the groove and the land closer. A method for solving the problem will be described.

As is apparent from FIG. 4B, when the target focal position is shifted between the groove and the land, the settling operation is performed immediately after the light spot passes through the joint between the groove and the land. By measuring the focus error signal during the settling period 40 of the focus servo system, it is possible to measure the amount 42 that is proportional to the displacement difference between the target focal position of the groove and the land. In order to reduce the displacement difference, when the light spot settles in the negative direction of the focus error signal in the land, the land focus offset is corrected in the positive direction, or the groove focus offset is changed in the negative direction. Should be corrected.

FIGS. 6A and 6B show the operation of the light spot when a correction amount of -.DELTA. Is applied to the groove focus offset and a correction amount of + .DELTA. Is applied to the land focus offset, and the waveform of the focus error signal. . Where Δ
Is a positive constant. Since the characteristics of the focus error signal are different between the groove and the land, it is difficult to calculate Δ as an analytical solution. An appropriate Δ can be obtained by gradually increasing the amount of Δ until the displacement difference between the target focal position of the groove and the land becomes smaller than a predetermined value.

When the value of Δ is large, the deviation from the focus offset Gopt or Lopt that optimizes the evaluation amount becomes large. In order to solve the problem, the correction is performed only on the one with the larger allowable amount of the focus offset shift.
For example, in the example shown in FIG. 3, only the land is corrected because the allowable amount of the land is large. The operation is shown in FIG.
(B).

According to the above-described focus offset adjustment method, the focal position of the light spot substantially matches before and after passing through the joint between the groove and the land, and both the groove and the land are adjusted to a position near the position where the jitter is minimized.

The example used in the description is the case where the light spot moves from the groove to the land, but it is obvious that the same adjustment method can be applied to the case where the light spot moves from the land to the groove.

[0025]

As described above, since the focal position does not change even immediately after the light spot has passed through the joint between the groove and the land, a reproducing operation with less jitter can be realized in the entire area of the optical disk.

[Brief description of the drawings]

FIG. 1 shows an optical disk.

FIG. 2 is a block diagram of a focus servo circuit.

FIG. 3 is a diagram showing a focus offset and a jitter of a reproduction signal.

FIG. 4 is a diagram showing a focus operation at a joint between a groove and a land.

FIG. 5 is a diagram showing focus error signals for grooves and lands.

FIG. 6 is a diagram showing a focus operation at a joint between a groove and a land.

FIG. 7 is a diagram showing a focus operation at a joint between a groove and a land.

[Explanation of symbols]

12 ... groove, 14 ... land, 16 ... track, 18
…… Connection part, 20… Focus error signal, 22…
Groove focus offset, 24: Land focus offset, 26: Groove / land switching signal, 28: Controller, 30: Focus actuator drive signal, 40: Focus servo system settling period, 42:
An amount proportional to the displacement difference between the target focal position of the groove and the land

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Claims (3)

[Claims] A track is defined by a groove as a guide groove and a land between the guide grooves, and a focus error signal is differently applied to the groove and the land on an optical disk in which the groove and the land are coupled at one place in one circumference. A focus offset adjusting method for an optical disc device for giving an offset and reproducing information, wherein a focus offset for optimizing a predetermined evaluation amount is obtained for the groove and the land, and a light spot is formed at a joint between the groove and the land. A focus error signal measured immediately after passing through a predetermined period, and a focus offset between the groove and the land is corrected so that a fluctuation amount of the measured focus error signal is reduced. 2. The focus offset adjusting method according to claim 1, wherein said evaluation amount is a jitter of a reproduction signal or a reproduction error number. 3. The focus offset adjusting method according to claim 1, wherein said focus offset correction corrects one of said groove and land focus offsets.