JP2000057586A - Control device for focus of optical disk - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a control device for focus of an optical disk in which focus-pull-in is performed surely for all layers of optical disks having multi-layer structure. SOLUTION: An object lens is moved in the direction of approaching an optical disk by sampling a focus error FE signal with fixed time intervals t0, t1, t2,... by a reference voltage generating means and comparing successively the present data in sampling and data directly before sampling of one data before. In this case, since a state of variation of each S type curve, that is, each layer is surely recognized, reference voltage is appropriately generated and set using peak values d30, d34 of S type curves of which the amplitude is the minimum out of plural peak values d4, d12,... d30, d34, focus-pull-in of all layers of an optical disk having multi-layer structure can be surely performed.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical disk focus control device for an optical disk apparatus using a multilayer optical disk having a plurality of recording layers.

[0002]

2. Description of the Related Art In recent years, as one method of increasing the recording density, there is an optical disc having a multilayer structure having a plurality of recording layers. When using such an optical disk having a multilayer structure, it is necessary to control the focus pull-in so that the irradiation light is focused on a desired layer.

FIG. 7 shows a configuration example of a conventional optical disk focus control device in an optical disk device using such an optical disk 1 having a multilayer structure. In the figure, reference numeral 2 denotes a focus actuator for displacing the objective lens facing the optical disk 1 in a direction approaching or moving away from the objective lens. Although not specifically shown, the objective lens has a structure included in the focus actuator 2 and also has a tracking actuator and the like. Such a focus actuator 2 is driven by an appropriate amount in an appropriate direction based on a drive signal from a driver 3.

The driver 3 is connected to a focus control switch 4 for switching between a servo signal and a focus search signal. A focus control switching unit 5 for switching the focus control switch 4 is provided. An FE (focus error) indicating a focus shift is provided on the servo signal side of the focus control switch 4.
A phase compensator 6 for generating a servo signal from the signal is connected to the focus search signal side of the focus control changeover switch 4, and the objective lens is moved from bottom to top (to approach) or from top to bottom (to separate). The focus search signal generation unit 7 that outputs a signal (focus search signal) for moving the focus search signal in the direction (direction) is connected.

A comparator 18 for comparing the FE signal with a predetermined reference voltage 1 and a comparator 29 for comparing the FE signal with a predetermined reference voltage 2 are provided. On the output side of these comparators 8 and 9, there is provided a counter 10 for counting at the rise of the output of the comparator 8 or 9. Further, a system controller 11 for issuing a predetermined command signal to the counter 10, the focus control switching unit 5, and the focus search signal generating unit 7 to control the entire system is provided.

[0006] The operation and control when the focus pull-in is performed on a certain layer of the optical disk 1 having a multilayer structure under such a configuration will be described. FIG. 8 is a time chart showing an example of such a waveform at the time of focusing.
First, a focus pull-in command and a focus pull-in target layer are designated from the system controller 11 and output to the focus control switching unit 5. Also, the system controller 11 determines whether the focus pull-in command and the objective lens should be moved in the direction approaching the optical disc 1 and retracted, or whether the objective lens should be moved away from the optical disc 1 and retracted. Output to 10 Here, an example is shown in which the objective lens is moved in a direction approaching the optical disc 1 (from bottom to top) and retracted.

Under such a premise, the focus control switching section 5 switches the focus control switch 4 to the focus search side in response to a focus pull-in command from the system controller 11. In the focus search signal generator 7, the system controller 11 outputs a focus search signal as shown in FIG. Thus, the objective lens is continuously moved via the focus actuator 2 in a direction approaching the optical disc 1 (from bottom to top). As described above, when the objective lens is moved from the bottom to the top, the focus position changes so as to cross each layer in the optical disc 1. Therefore, the focus position is changed by the number of layers of the multilayer structure as shown in FIG. F with S-shaped curve of 3 layers)
An E signal is obtained.

The FE signal is input to comparators 8 and 9 and compared with reference voltages 1 and 2 respectively. The result of the comparison is converted into a pulse signal as shown in FIG.
Is output to Here, since the objective lens is moved upward from below, the counter 10 operates to count at the rising edge of the pulse signal on the comparator 18 side. The count value of the counter 10 is output to the focus control switching unit 5. Therefore, when the focus control target layer specified by the system controller 11 and the count value of the counter 10 match, the focus control switching unit 5 switches the focus control switch 4 to the servo side by detecting a zero cross of the FE signal. The focus is pulled in, and the process shifts to focus servo control.

[0009]

However, in reality,
Since the reflectivity of each layer on the optical disc 1 is different, the magnitude (amplitude) of the FE signal in the S-curve generated by each layer is different as shown in FIG. 8, for example. For this reason,
If the reference voltages 1 and 2 are not set properly, S
In a layer where the amplitude of the curve is small, there is a possibility that the pulse signals are not generated by the comparators 8 and 9.
In that layer, a case occurs in which focus pull-in cannot be performed.

SUMMARY OF THE INVENTION It is an object of the present invention to provide an optical disk focus control device that can always perform focus pull-in on all layers of an optical disk having a multilayer structure.

[0011]

According to the first aspect of the present invention,
Specifying means for specifying a focus pull-in target layer for a multilayer optical disc; reference voltage generating means for setting a reference voltage for comparison with a focus error signal; and a focus error signal and a reference voltage generated by the reference voltage generating means. A focus pull-in unit configured to perform focus pull-in to the focus pull-in target layer based on comparison with a reference voltage, wherein the reference voltage generation unit samples a focus error signal at regular time intervals; Storage means for storing the current data and the data immediately before the previous sampling time;
A comparison means for comparing the stored current data with the immediately preceding data and outputting an H level signal when the current data is equal to or greater than the immediately preceding data and outputting an L level signal when the current data is smaller than the immediately preceding data; A peak value storage means for storing the maximum peak value of the focus error signal based on the rising edge of the output signal, and storing the minimum peak value of the focus error signal based on the falling edge of the output signal from the comparing means. Output means for generating and outputting a reference voltage for the focus pull-in means based on the maximum peak value and the minimum peak value.

Accordingly, the reference voltage generating means samples the focus error signal at fixed time intervals, and sequentially compares the current data at the current sampling time with the data immediately before the immediately preceding sampling time, thereby changing the objective lens to the optical disk. The state of change of each S-curve when moved in the direction of approaching, that is, it is possible to reliably recognize each layer and appropriately generate and set a reference voltage for the S-curve with the smallest amplitude. As a result, it is possible to reliably perform focus pull-in of all layers of the optical disk having a multilayer structure.

According to a second aspect of the present invention, there is provided a designating means for designating a focus pull-in target layer for an optical disc having a multilayer structure, a reference voltage generating means for setting a reference voltage to be compared with a focus error signal, and a focus error signal. A focus pull-in means for performing a focus pull-in on the focus pull-in target layer based on a comparison between a signal and a reference voltage generated by the reference voltage generation means, wherein the reference voltage generation means outputs a focus error signal at regular time intervals. Sampling means for sampling; storage means for storing current data at the current sampling time and data immediately before the previous sampling time; comparing these stored current data with the immediately preceding data to determine whether the current data is the immediately preceding data; In the following cases, an H level signal is output and the current data is larger than the immediately preceding data. Comparing means for outputting an L level signal, and storing the maximum peak value of the focus error signal based on the falling of the output signal from the comparing means, and detecting the focus error signal based on the rising of the output signal from the comparing means. A peak value storage means for storing the minimum peak value of the above, and an output means for generating and outputting a reference voltage for the focus pull-in means based on the stored maximum peak value and minimum peak value.

Accordingly, the reference voltage generating means samples the focus error signal at fixed time intervals, and sequentially compares the current data at the current sampling time with the data immediately before the immediately preceding sampling time, thereby changing the objective lens to the optical disk. The state of the change of each S-curve when moved in the direction to separate from, that is, it is possible to surely recognize each layer and appropriately generate and set the reference voltage for the S-curve with the smallest amplitude. As a result, it is possible to reliably perform focus pull-in of all layers of the optical disk having a multilayer structure. In particular,
Since it is assumed that the objective lens is moved in a direction to separate from the optical disk, the time required for setting the reference voltage can be reduced.

According to a third aspect of the present invention, there is provided a means for designating a layer to be focused on for a multi-layer optical disc, and a pulse signal generating means for generating a pulse signal based on a change in the sampling result of a focus error signal. A counting means for counting the rising edge of the pulse signal generated by the pulse signal generating means; and a focus pull-in means for performing a focus pull-in on the focus pull-in target layer based on a count value of the counting means and a focus error signal. .

Therefore, it is possible to reliably perform the focus pull-in of all the layers of the multi-layered optical disk with a simpler configuration without generating or setting a reference voltage.

[0017]

FIG. 1 shows a first embodiment of the present invention.
A description will be given based on FIG. The same parts as those shown in FIG. 7 are denoted by the same reference numerals. In the present embodiment, F
The reference voltages 1 and 2 are generated based on the E signal to generate comparators 8 and 9.
A reference voltage generating unit (reference voltage generating means) 12 for supplying power to the power supply is added. The function of the designating means according to the present invention is the same as that of the related art, and designates the focus pull-in target layer to the focus control switching unit 5 for the multilayer optical disc 1 under the control of the system controller 11. Also, the function of the focus pull-in means according to the present invention is the same as the conventional one. Under the control of the system controller 11, if the designated focus pull-in target layer and the count value of the counter 10 match, the FE signal is zero-crossed. The detection is performed, and the focus control switching unit 5 switches the focus control changeover switch 4 to the servo side, thereby performing the focus pull-in operation.

FIG. 2 shows an example of the configuration of the reference voltage generator 12. First, an A / D converter 13 is provided, which samples the FE signal by A / D conversion at regular time intervals and outputs data at each sampling time as a digital value. A storage means 14 for storing the sampled data is connected to the output side of the A / D converter 13. The storage means 14 includes a register 115 for sequentially rewriting and storing the current data at the current sampling time output from the A / D converter 13, and a register 1 for storing new current data in the register 115. And a register 216 for storing the immediately preceding data at 15 (that is, the data immediately before the immediately preceding sampling time). A comparator (comparing means) 17 is connected to the output side of these registers 15 and 16. The comparator 17 compares the magnitude of the current data stored in the registers 15 and 16 with the immediately preceding data, and outputs an H level signal when the current data is equal to or more than the immediately preceding data, and outputs an L level signal when the current data is smaller than the immediately preceding data. It is configured to output a signal.

The register 2 is set based on the rising and falling of the output signal (pulse signal) from the comparator 17.
A peak value storage means 18 for storing data stored in the memory 16 as a peak value is provided. The peak value storage means 18 stores a maximum peak value of the FE signal based on the rise of the output signal from the comparator 17, and a minimum peak value of the FE signal based on the fall of the output signal from the comparator 17. And a minimum peak register 20 for storing a value. A reference voltage output section (output means) 21 is connected to these registers 19 and 20. This reference voltage output unit 21
The reference voltages 1 and 2 for the comparators 8 and 9 are generated and output based on the maximum peak value and the minimum peak value stored in the registers 9 and 20, respectively. Specifically, using the data of the maximum peak and the minimum peak, it is generated as a voltage value having a magnitude of, for example, about ２ of the peak of the S-shaped curve having the smallest amplitude.

In such a configuration, the present embodiment is an example in which the objective lens is moved in a direction approaching the optical disc 1 (from bottom to top) and retracted. First, the optical disk 1
Is set, the system controller 11 sends a focus pull-in command to the focus control switching unit 5, and switches the focus control switch 4 to the focus search side. The system controller 11 also sends a focus pull-in command or the like to the focus search signal generator 7 and outputs a focus search signal as shown in FIG. Thus, the objective lens is continuously moved via the focus actuator 2 in a direction approaching the optical disc 1 (from bottom to top). As described above, when the objective lens is moved from the bottom to the top, the focus position changes so as to cross each layer in the optical disc 1. Therefore, the focus position is changed by the number of layers of the multilayer structure as shown in FIG. FE with S-shaped curve of 3 layers)
A signal is obtained.

The FE signal is supplied to the reference voltage generator 1
2, the reference voltages 1 and 2 are generated, and the comparators 8 and
9 is set. Here, the reference voltage generator 1
The generation of the reference voltages 1 and 2 in 2 will be described with reference to FIG. First, it is assumed that the values of the registers 15 and 16 are initialized to 0 in an initial state. Therefore, the data d ₀ sampled by the A / D converter 13 at the first sampling time t ₀ is taken into the register 115. At this time, the data (here, 0) taken in the register 115 is taken into the register 216. Then, the comparator 17 compares the data d ₀ , 0 of these registers 15, 16 and outputs the comparison result. Here, d ₀
Since ≧ 0, the comparator 17 outputs the L level. At the next sampling time t ₁ , similarly, the sampled data d ₁ is taken into the register 115, and the data d ₀ taken into the register 115 is taken into the register 216. Then, the comparator 17 compares the data d ₁ and d ₀ of these registers 15 and 16 and outputs a comparison result. Here, since d ₁ ≧ d ₀ , the comparator 1
7 outputs the L level. In this way, each sampling data is sequentially taken and compared. here,
At the sampling time t ₅ , the current data in the register 115 is d ₅ , the data immediately before the register 216 is d ₄ , and d ₅ <d ₄ , so that the comparator 17 outputs the H level. That is, the output of the comparator 17 rises from the L level to the H level. Therefore, the maximum peak register 19 takes in the data d ₄ stored in the register 216 as one maximum peak data at the rise of the output signal of the comparator 17.

Thereafter, from the sampling time t ₅ to t ₁₂ , the output of the comparator 17 remains at the H level because the current data stored in the register 115 is smaller than the immediately preceding data stored in the register 216. It is. And
Reaches the sampling time point t _13, the output of the register 1 since 15 towards the current data stored in is greater than just before the data stored in the register 2 16 comparator 17 L
Change to a level. That is, the output of the comparator 17 falls from the H level to the L level. Therefore, the minimum peak register 20 takes in the data d ₁₂ stored in the register 2 16 at the falling of the output signal of the comparator 17 as one minimum peak data.

Thereafter, similarly, the sampling time t ₃₅
Then, the maximum peak register 19 and the minimum peak register 20 receive the maximum peak data d ₃₀ and the minimum peak data d ₃₄ of the S-shaped curve having the smallest amplitude.

Therefore, in the reference voltage output section 21, S having the smallest amplitude among the plurality of peak data stored in the maximum peak register 19 and the minimum peak register 20 is set.
With respect to the peak data of the V-shaped curve, for example, voltage values of 、 ２ level are respectively generated as reference voltages 1 and 2 and set in the comparators 8 and 9.

Thereafter, as in the case described above, the FE signal is inputted to the comparators 8 and 9, respectively, and the reference voltages 1 and 2, respectively.
And the result of the comparison is output to the counter 10 as a pulse signal as in the case shown in FIG.
Here, since the objective lens is moved upward from below, the counter 10 operates to count at the rising edge of the pulse signal on the comparator 18 side. The count value of the counter 10 is output to the focus control switching unit 5. Therefore,
The focus controller 5 includes a system controller 11
Focus pull-in target layer and counter 10 specified from
When the count value coincides with the above, the zero-crossing of the FE signal is detected, the focus control changeover switch 4 is switched to the servo side to perform focus pull-in, and shift to focus servo control. In such an operation, since the reference voltages 1 and 2 are appropriately set based on the S-shaped curve having the smallest amplitude, it is possible to reliably perform the focus pull-in on all the layers of the optical disc 1 having the multilayer structure. .

A second embodiment of the present invention will be described with reference to FIG. 1 to 3 are denoted by the same reference numerals, and description thereof will be omitted. The present embodiment is based on a focus search method in which the objective lens is moved in a direction away from the optical disc 1 (from top to bottom) and retracted. 1 and 2 can be used as they are, but the comparator 17 compares the current data stored in the registers 15 and 16 with the immediately preceding data. It outputs a signal and outputs an L level signal when the current data is larger than the immediately preceding data. The peak value storage means 18
Is a maximum peak register 19 for storing the maximum peak value of the FE signal based on the fall of the output signal from the comparator 17.
FE based on the rising of the output signal from the comparator 17
Minimum peak register 20 for storing the minimum peak value of a signal
It is composed of

In such a configuration, first, when the optical disk 1 is set, a command for pulling in the focus is sent from the system controller 11 to the focus control switching unit 5, and the focus control switch 4 is switched to the focus search side. The system controller 11 also sends a focus pull-in command and the like to the focus search signal generator 7 and outputs a focus search signal as shown in FIG. Thus, the objective lens is continuously moved via the focus actuator 2 in a direction away from the optical disc 1 (from top to bottom). As described above, when the objective lens is moved from the top to the bottom, the focus position changes so as to cross each layer in the optical disc 1, and therefore, the number of layers of the multilayer structure shown in FIG. An FE signal having an S-shaped curve (for three layers) is obtained.

The FE signal is supplied to the reference voltage generator 1
2, the reference voltages 1 and 2 are generated, and the comparators 8 and
9 is set. Here, the reference voltage generator 1
The generation of the reference voltages 1 and 2 in 2 will be described with reference to FIG. First, it is assumed that the values of the registers 15 and 16 are initialized to 0 in an initial state. Therefore, the data d ₀ sampled by the A / D converter 13 at the first sampling time t ₀ is taken into the register 115. At this time, the data (here, 0) taken in the register 115 is taken into the register 216. Then, the comparator 17 compares the data d ₀ , 0 of these registers 15, 16 and outputs the comparison result. Here, d ₀
Since ≦ 0, the comparator 17 outputs the L level. At the next sampling time t ₁ , similarly, the sampled data d ₁ is taken into the register 115, and the data d ₀ taken into the register 115 is taken into the register 216. Then, the comparator 17 compares the data d ₁ and d ₀ of these registers 15 and 16 and outputs a comparison result. Here, since d ₁ ≦ d ₀ , the comparator 1
7 outputs the L level. In this way, each sampling data is sequentially taken and compared. here,
At the sampling time t3, the current data in the register 115 is d ₃ , the data immediately before the register 216 is d ₂ , and d ₃ > d ₂ , so that the comparator 17 outputs the H level. That is, the output of the comparator 17 rises from the L level to the H level. Therefore, the minimum peak register 20 takes in the data d ₂ stored in the register 216 as the minimum peak data at the rise of the output signal of the comparator 17.

Thereafter, from the sampling time t ₃ to t ₆ , the output of the comparator 17 remains at the H level because the current data stored in the register 115 is larger than the immediately preceding data stored in the register 216. It is. Then, at the sampling time t ₇ , the output of the comparator 17 changes to L level because the current data stored in the register 115 is smaller than the immediately preceding data stored in the register 216. That is, the output of the comparator 17 falls from the H level to the L level. Therefore, the maximum peak register 19 registers 2216 at the rising edge of the output signal of the comparator 17.
The data d ₆ stored in the capture as the maximum peak data.

In this embodiment, at this point, the reference voltage output unit 21 uses these maximum peak registers 1
9. Assuming that the peak data stored in the minimum peak register 20 is the peak data of the S-shaped curve having the smallest amplitude, for example, a voltage value of ／ level is set to the reference voltage 1, 2 and set in the comparators 8 and 9. That is, although basically the same as the case of the first embodiment, since it is assumed that the objective lens is moved in the direction away from the optical disc, the S at which the amplitude is the smallest at the beginning of the focus search is set. Since the character curve is searched, the time required for setting the reference voltages 1 and 2 can be reduced.

Thereafter, as in the case described above, the FE signal is input to the comparators 8 and 9, respectively, and the reference voltages 1 and 2, respectively.
And the result of the comparison is output to the counter 10 as a pulse signal as in the case shown in FIG.
Here, since the objective lens is moved upward from below, the counter 10 operates to count at the rising edge of the pulse signal on the comparator 18 side. The count value of the counter 10 is output to the focus control switching unit 5. Therefore,
The focus controller 5 includes a system controller 11
Focus pull-in target layer and counter 10 specified from
When the count value coincides with the above, the zero-crossing of the FE signal is detected, the focus control changeover switch 4 is switched to the servo side to perform focus pull-in, and shift to focus servo control. In such an operation, since the reference voltages 1 and 2 are appropriately set based on the S-shaped curve having the smallest amplitude, it is possible to reliably perform the focus pull-in on all the layers of the optical disc 1 having the multilayer structure. .

FIGS. 5 and 6 show a third embodiment of the present invention.
It will be described based on. 1 to 3 are denoted by the same reference numerals, and description thereof will be omitted. In the present embodiment, a layer detector 22 functioning as a pulse signal generator is used instead of the comparators 8 and 9 and the reference voltage generator 12.
Is provided. As shown in FIG. 6, the layer detection unit 22 has a configuration in which the registers 19 and 20 and the reference voltage output unit 21 are removed from the reference voltage generation unit 14, and the FE
A pulse signal is generated and output based on the magnitude change of the signal sampling result (see the comparator output in FIGS. 3 and 4). Further, the counter 10 functions as a counting means for counting at the rising edge of the pulse signal output from the comparator 17. For example, referring to FIG. 3, the counter 10 counts the number of layers at sampling times t ₅ ,..., T ₃₀ at which the pulse signal rises. Therefore, it is possible to cause the layer designated by the designating means to perform focus pull-in as it is based on the count value of the counter 10 and the FE signal. In this embodiment, the direction of the focus search does not matter.

Therefore, according to the present embodiment, it is possible to reliably perform the focus pull-in of all the layers of the multilayer optical disc 1 with a simpler configuration without generating or setting a reference voltage.

[0034]

According to the first aspect of the present invention, the reference voltage generating means samples the focus error signal at regular time intervals, and compares the current data with the current data at the current sampling time by one.
The state of the change of each S-curve when the objective lens is moved in the direction of approaching the optical disk by sequentially comparing the data immediately before the previous sampling time with the data immediately before the sampling time, that is, each layer is surely recognized, and Since the reference voltage is appropriately generated and set for a small S-shaped curve, it is possible to reliably perform the focus pull-in of all the layers of the multilayer optical disc.

According to the second aspect of the present invention, the reference voltage generating means samples the focus error signal at regular time intervals and sequentially outputs the current data at the current sampling time and the data immediately before the immediately preceding sampling time. The state of change of each S-curve when the objective lens is moved away from the optical disk by comparison, that is, each layer is reliably recognized, and the reference voltage is adjusted appropriately for the S-curve having the smallest amplitude. Since it is generated and set, it is possible to reliably perform the focus pull-in of all the layers of the multi-layered optical disc. In particular, since it is assumed that the objective lens is moved in a direction away from the optical disc, Thus, an S-shaped curve having the smallest amplitude appears, and the time required for setting the reference voltage can be reduced.

According to the third aspect of the present invention, the pulse signal generating means for generating a pulse signal based on the change in the sampling result of the focus error signal, and counting at the rising edge of the pulse signal generated by the pulse signal generating means By providing the counting means, it is possible to reliably perform the focus pull-in of all the layers of the multi-layered optical disk with a simpler configuration without generating or setting a reference voltage.

[Brief description of the drawings]

FIG. 1 is a block diagram of an optical disc focus control device according to a first embodiment of the present invention.

FIG. 2 is a block diagram showing a configuration of the reference voltage generator.

FIG. 3 is a time chart showing signal waveforms of respective units accompanying a search operation for generating a reference voltage.

FIG. 4 is a time chart showing signal waveforms of various parts involved in a search operation for generating a reference voltage according to the second embodiment of the present invention.

FIG. 5 is a block diagram of an optical disc focus control device according to a third embodiment of the present invention.

FIG. 6 is a block diagram showing a configuration of the layer detection unit.

FIG. 7 is a block diagram of a conventional optical disc focus control device.

FIG. 8 is a time chart showing signal waveforms of the respective units accompanying the focus search operation.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Optical disk 10 Counting means 12 Reference voltage generation means 13 Sampling means 14 Storage means 17 Comparison means 18 Peak value storage means 21 Output means 22 Pulse signal generation means

Claims (3)

[Claims] 1. A designating means for designating a focus pull-in target layer for an optical disc having a multilayer structure, a reference voltage generating means for generating a reference voltage for comparison with a focus error signal, a focus error signal and the reference voltage generation A focus pull-in means for performing a focus pull-in on the focus pull-in target layer based on a comparison with a reference voltage generated by the means, wherein the reference voltage generating means is a sampling means for sampling a focus error signal at regular time intervals; Storage means for storing the current data at the current sampling time and the data immediately before the previous sampling time; comparing the stored current data with the immediately preceding data; Outputs a signal and L level when the current data is smaller than the immediately preceding data A comparing means for outputting a signal, a maximum peak value of a focus error signal is stored based on a rise of an output signal from the comparing means, and a minimum peak value of the focus error signal is stored based on a fall of the output signal from the comparing means. An optical disc focus control device comprising: a peak value storage means for storing; and an output means for generating and outputting a reference voltage for the focus pull-in means based on the stored maximum peak value and minimum peak value. 2. A designator for designating a focus pull-in target layer for an optical disc having a multilayer structure, a reference voltage generator for setting a reference voltage for comparison with a focus error signal, a focus error signal and the reference voltage generator. A focus pull-in means for performing a focus pull-in on the focus pull-in target layer based on a comparison with a reference voltage generated by the means, wherein the reference voltage generating means is a sampling means for sampling a focus error signal at regular time intervals; Storage means for storing the current data at the current sampling time and the data immediately before the immediately preceding sampling time; comparing these stored current data with the immediately preceding data, and when the current data is lower than the immediately preceding data, the H level Outputs a signal, and when the current data is larger than the immediately preceding data, L level Comparing means for outputting a signal; storing a maximum peak value of the focus error signal based on a falling edge of the output signal from the comparing means; and calculating a minimum peak value of the focus error signal based on a rising edge of the output signal from the comparing means. An optical disc focus control device comprising: a peak value storage means for storing; and an output means for generating and outputting a reference voltage for the focus pull-in means based on the stored maximum peak value and minimum peak value. 3. A specifying means for specifying a focus pull-in target layer for an optical disc having a multilayer structure; a pulse signal generating means for generating a pulse signal based on a change in the sampling result of a focus error signal; and a pulse signal generating means. An optical disc focus control device, comprising: counting means for counting at the rising edge of the pulse signal generated by the following; and focus pull-in means for pulling focus into the focus pull-in target layer based on the count value of the counting means and a focus error signal.