JPH10162379A - Optical disk reader and focus offset setting method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an optical disk reader which can reduce a reading error rate of signals at the time of seek of multi-track jump. SOLUTION: This optical disk reader 20 has a focus offset generator 11 for land, a focus offset generator 12 for groove and a focus offset generator 13 for seek, when focus servo control of a light beam is performed and an optical pickup 2 traces a land of an optical disk 1, the focus offset generator 11 for land is selected by a selector 14, when a groove is traced, the focus offset generator 12 for groove is selected. On the other hand, when tracking in not locked, the focus offset generator 13 for seek having an intermediate value between focus offset for land and focus offset for groove is selected, and focus servo control is performed.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to an optical disk reader and a focus offset setting method.

[0002]

2. Description of the Related Art Conventionally, a land-groove recording method has been known as an optical disk format. FIG. 5 is a sectional view showing the recording surface of the optical disk. FIG. 6 is a diagram showing a land-groove recording method. In this recording method, land A
The signal is recorded in both the groove B and the groove B.

When a signal recorded on the land A or the groove B is read by irradiating the recording surface of the optical disk with a light beam, since there is a difference in height between the land A and the groove B, the focal point of the light beam is focused on the land. If it is optimally adjusted by A, the focus of the light beam is not optimal in the groove B. Therefore, since the crosstalk between the land A and the groove B is reduced, the track pitch can be reduced in the land-groove recording method, and high-density recording can be performed.

In order to correctly read a signal recorded on an optical disk by the land / groove recording method, when performing focus servo control for optimizing the focus of a light beam on both the land and the groove, a focus offset is performed on each surface. To be changed.

[0005]

However, the above-mentioned conventional optical disk reader has the following problems. That is, at the time of seek or multi-track jump, the light beam crosses the track at high speed.
For example, when a light beam is tracing a track on a land and the focus offset for the groove is set, the focus of the light beam is not optimal on the land.

Normally, of the signals recorded on the optical disk, the signal of the address portion is easier to read than the signal of the data portion. However, if the focus offset is set differently, the focus of the light beam is not optimal. The read error rate of the address recorded in the optical pickup increases, and it takes time to correctly position the optical pickup, and as a result, the seek time becomes longer.

On the other hand, it is conceivable that the focus offset for lands and grooves is switched every time the track crosses during a seek. However, since the speed across the track is high, it is difficult to set the focus offset correctly, resulting in erroneous reading. Increase. FIG. 7 is a graph showing the relationship between the seek time t and the speed v of the optical pickup. For example, the number of tracks 2000 in 50 msec
When zero seeks are performed, the area of the triangle shown in the figure corresponds to the number of tracks, and therefore, ×× v × 50 [msec]
= 20,000 [lines], the velocity v is 800 [lines / ms]
ec, kHz].

Therefore, the focus offset must be switched every time the track passes in 1.25 μsec, and the land and groove must be specified correctly. It is assumed that the rate will increase. As described above, it is difficult to switch the land and groove focus offsets at the time of seeking.

SUMMARY OF THE INVENTION It is an object of the present invention to provide an optical disk reader and a focus offset setting method capable of reducing a signal read error rate during a seek or a multi-track jump.

[0010]

According to a first aspect of the present invention, there is provided an optical disk reading apparatus according to the present invention, wherein a signal recorded on a land and a groove of an optical disk is changed by changing a focus offset. And a focus offset setting means for setting the focus offset to a substantially intermediate value between the focus offset suitable for the land and the focus offset suitable for the groove.

The focus offset setting means generates a land focus offset as a focus offset suitable for the land, and a groove focus offset as a focus offset suitable for the groove. Groove focus offset generating means; intermediate focus offset generating means for generating an intermediate focus offset that is a substantially intermediate value between the land focus offset and the groove focus offset; the land focus offset; and the groove focus offset. And a selecting unit for selecting any one of the intermediate focus offsets.

Further, it is preferable that the selecting means selects the intermediate focus offset at the time of seeking or at the time of a multi-track jump.

[0013] The intermediate focus offset generating means may include an intermediate focus offset between two focus offsets corresponding to the ascending and descending address signals near the maximum level among the address signals read when the focus offset is changed. Preferably, the intermediate focus offset is set to a value, and the set intermediate focus offset is generated.

According to a fifth aspect of the present invention, there is provided a focus offset setting method for changing a focus offset for reading a signal recorded on each of a land and a groove of an optical disk. It is characterized in that the focus offset is set to a substantially intermediate value from a focus offset suitable for the groove.

In the present invention, at the time of seek or multi-track jump, the focus offset is set to a substantially intermediate value between the focus offset suitable for the land and the focus offset suitable for the groove.

[0016]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of an optical disk reading apparatus and a focus offset setting method according to the present invention will be described. In the optical disk reading apparatus according to the present embodiment, three focus offsets are prepared for the land, groove, and seek when performing focus servo control of the light beam to read data recorded on both the land and the groove of the optical disk. Has been
When tracking is not locked, a seek focus offset which is an intermediate value between the land focus offset and the groove focus offset is set.

FIG. 1 is a block diagram showing a configuration of a focus servo control system of an optical disk reader according to an embodiment. The reading device 20 includes an optical pickup 2 for reading a signal recorded on the optical disc 1, a normalization block 3 for normalizing a focus error signal read by the optical pickup 2 with a sum signal also read by the optical pickup 2, and a normalized block 3. An adder 6 for adding a focus offset to the focus error signal; a loop filter 4 for filtering the focus error signal to which the focus offset has been added; a multiplier 7 for amplifying the filtered focus error signal by a predetermined gain of a gain generator 5; It has a focus drive amplifier 8 for focusing the optical pickup 2 in accordance with the amplified focus error signal.

An RF block 9 for separating an address signal from a read signal of the optical disc 1, a system control unit 10 for controlling the entire servo control system, an external controller 15 for outputting a seek command and the like to the system control unit 10, a system control unit It has a tracking servo and a thread servo 16 for driving the optical pickup 2 in accordance with a command from 10.

Further, a land focus offset generator 11, a groove focus offset generator 1
2. A focus offset generator 13 for seek and a selector 14 are controlled by the system control unit 10. The focus offset generator 11 for land and the focus offset generator 12 for groove are provided.
And one of the seek focus offset generators 13, and selectively outputs the focus offset to the adder 6.

FIG. 2 is a flowchart showing a processing procedure of the system control unit 10 when a command to seek to a different address is issued from the external controller 15. Here, in the following description, it is assumed that an odd track is a land portion and an even track is a groove portion. The system control unit 10 first determines whether a seek command has been output from the external controller 15 and the seek command flag has been set (step S1). If the seek command has not been output, the process ends.

On the other hand, if the seek command has been output in step S1, it is determined whether or not the seek has been completed (step S2). If the seek has been completed, the system control unit 10 determines, based on the address signal output from the RF block 9, whether the track currently traced by the optical pickup 2 is a land or a groove (step S3). . If the track is an odd track, the system control unit 10 selects the land focus offset generator 11 by the selector 14 (Step S).
4) If the track is an even track, select the groove focus offset generator 12 (step S5). Then, the seek command flag is reset (step S
6), end the process.

On the other hand, if there is a command to seek to a different address from the external controller 15 and the seek is not completed in step S2, it is determined whether or not the seek first status flag is set and the seek is the first. (Step S7). If it is not the first seek, the process is terminated. If it is the first seek, the system control unit 10 calculates a track address difference obtained by subtracting the current address from the command address (step S8).

The system control unit 10 outputs a command to seek by the calculated track address difference to the thread servo and the tracking servo 16 (step S).
9) The selector 14 selects the seek focus offset generator 13 (step S10). And
Reset the seek first status flag (step S
11), end the process.

On the other hand, when a seek end signal is received from the thread servo and tracking servo 16 in step S2, it is determined whether the current address is a land or a groove as described above, and the selector 14 responds. Select the focus offset.

As described above, in the optical disk reader 20 of this embodiment, the land focus offset is selected when the optical pickup 2 is tracing the land of the optical disk 1, and when the optical pickup 2 is tracing the groove, the groove is selected. Focus seek offset is selected, and during seek, the seek focus offset is selected and focus servo control is executed.

Next, setting of the seek focus offset which is an intermediate value between the land focus offset and the groove focus offset will be described. FIG.
Is a graph showing the relationship between the focus offset and the address signal. When setting the focus offset for seek, if the focus offset is gradually changed in the state of focus lock and tracking off, the level of the address signal changes. The focus offsets A and B at two points near the maximum level of the address signal are obtained, and the intermediate value (A + B) / 2 is calculated to set the seek focus offset.

FIG. 4 is a graph showing the relationship between the focus offset and the reading error rate (error rate). The focus error (± a, ± 2a in the figure) does not have a linear relationship with the signal reading error rate (error rate), and when the focus error changes from the value ± a to the value ± 2a, the corresponding error rate e2 Is more than twice as bad as the error rate e1.

As described above, in the present embodiment, the intermediate value between the land focus offset and the groove focus offset is set as the seek focus offset. In this seek focus offset, the optimum focus offset is set for each of the land and the groove. However, the error rate at the time of seeking can be remarkably reduced, and address detection with less reading errors can be performed as compared with the related art. The error rate can be reduced by setting the seek focus offset not only at the time of seek but also at the time of multi-track jump. Further, the optical disk reading device of the present invention can be applied to both a reproduction-only device and a device that performs both recording and reproduction.

[0029]

According to the optical disk reading apparatus of the first aspect of the present invention, when reading a signal recorded on each of the lands and grooves of the optical disk by changing the focus offset, the focus offset setting means sets the focus offset. Since the focus offset is set to a substantially intermediate value between a focus offset suitable for a land and a focus offset suitable for the groove, a signal reading error can be set by setting the focus offset to a substantially intermediate value during a seek or a multi-track jump. Rate can be reduced. As described above, the address detection error was high because the seek was conventionally performed at one of the land and groove focus offsets. However, according to the present invention, the address detection with few errors is performed because the seek is performed at the intermediate focus offset. Can be. As a result, the waiting time due to the inability to read the address immediately before the end of the seek is reduced, and the seek time can be reduced.

According to the optical disk reading device of the present invention, the focus offset setting means includes a land focus offset generating means for generating a land focus offset as a focus offset suitable for the land; A groove focus offset generating means for generating a groove focus offset as a suitable focus offset, and an intermediate focus offset generating means for generating an intermediate focus offset that is a substantially intermediate value between the land focus offset and the groove focus offset. A selection means for selecting any of the land focus offset, the groove focus offset and the intermediate focus offset,
The focus offset can be easily switched.

According to the third aspect of the present invention, the selecting means selects the intermediate focus offset at the time of seeking or at the time of a multi-track jump. Can be reduced.

According to the optical disk reading device of the fourth aspect, the intermediate focus offset generating means is configured to output the address signal read when the focus offset is changed, when the signal rises and falls close to the maximum level. Since the intermediate focus offset is set to an intermediate value between the two focus offsets corresponding to the address signals and the set intermediate focus offset is generated, the intermediate focus offset can be easily set.

According to a fifth aspect of the present invention, there is provided a focus offset setting method for changing a focus offset for reading signals recorded on lands and grooves of an optical disc, respectively. Since the focus offset is set to a substantially intermediate value between the offset and the focus offset suitable for the groove, the signal reading error rate can be reduced by setting the focus offset to a substantially intermediate value at the time of seek or multitrack jump.

[Brief description of the drawings]

FIG. 1 is a block diagram illustrating a configuration of a focus servo control system of an optical disk reading device according to an embodiment.

FIG. 2 is a flowchart showing a processing procedure of a system control unit 10 when a command to seek to a different address is issued from an external controller 15;

FIG. 3 is a graph showing a relationship between a focus offset and an address signal.

FIG. 4 is a graph showing a relationship between a focus offset and a reading error rate (error rate).

FIG. 5 is a sectional view showing a recording surface of an optical disc.

FIG. 6 is a diagram showing a land-groove recording method.

FIG. 7 is a graph showing a relationship between a seek time t and a speed v of an optical pickup.

[Explanation of symbols]

1 ... optical disk, 10 ... system control unit,
11 Focus offset generator for land, 12
… Focus offset generator for groove, 13…
Focus offset generator for seek, 14 ... selector.

Claims (5)

[Claims] 1. An optical disk reading apparatus for reading a signal recorded on each of a land and a groove of an optical disk by changing a focus offset, wherein the optical disk has a focus offset suitable for the land and a focus offset suitable for the groove. An optical disk reading device comprising a focus offset setting means for setting the focus offset to a value. 2. The focus offset setting unit generates a land focus offset as a focus offset suitable for the land, and generates a groove focus offset as a focus offset suitable for the groove. Groove focus offset generating means; intermediate focus offset generating means for generating an intermediate focus offset that is a substantially intermediate value between the land focus offset and the groove focus offset; the land focus offset; and the groove focus offset. 2. The optical disk reading apparatus according to claim 1, further comprising: a selection unit for selecting any one of the intermediate focus offset. 3. The optical disk reading apparatus according to claim 2, wherein said selecting means selects said intermediate focus offset at the time of seeking or at the time of a multi-track jump. 4. The method according to claim 1, wherein the intermediate focus offset generating means is configured to output an intermediate signal between two focus offsets corresponding to an ascending and descending address signal close to a maximum level among the address signals read when the focus offset is changed. 3. The optical disk reading device according to claim 2, wherein the intermediate focus offset is set to a value, and the set intermediate focus offset is generated. 5. A focus offset setting method for changing a focus offset for reading a signal recorded on each of a land and a groove of an optical disk, wherein a focus offset suitable for the land and a focus offset suitable for the groove are provided. A focus offset setting method, wherein the focus offset is set to an intermediate value.