JPH1011770A - Focusing control method, device therefor, and master di sk exposure device for optical disk - Google Patents

Abstract

PROBLEM TO BE SOLVED: To perform stable focusing control by using a simple sequence. SOLUTION: The interval between an optical master disk 2 and an objective lens 6 is adjusted so that the focusing point of the objective lens 6 becomes on the optical master disk 2 by driving a Z stage 5 based on a fine focusing signal Fc showing the focusing state of the objective lens 6, thereafter, by rotating the optical master disk 2 and vertically moving the Z stage 5 so that the fine focusing signal Fc falls within a fixed range, and the interval between the optical master disk 2 and the objective lens 6 is adjusted.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a focus control method and an apparatus for adjusting a focus point of an objective lens on an optical disk master when manufacturing an optical disk master, and an optical disk master exposure apparatus to which these focus controls are applied. About.

[0002]

2. Description of the Related Art FIG. 6 is a block diagram of such an optical disk master exposure apparatus. A turntable 3 on which an optical disk master 2 is placed is connected to a rotation shaft of the spindle motor 1. The optical disk master 2 is obtained by applying a resist on a glass master.

On the other hand, an X stage 4 is provided, and a Z stage 5 is provided at the tip of a moving end 4a of the X stage 4. The Z stage 5 has an objective lens 6
Is provided with a voice coil motor (VCM) 7 incorporating the same.

The moving end 4a of the X stage 4 is moved in the X direction by the driving of an X axis motor 4b.
Move in the Z direction by driving the Z-axis motor 5b.

The recording optical system 8 outputs a laser beam 9 for exposure. The laser beam 9 for exposure is reflected by a mirror 10 and enters the objective lens 6. With such a configuration, when the optical disk master 2 is rotated by the driving of the spindle motor 1 and at the same time the exposure laser light 9 is output from the recording optical system 8, the exposure laser light 9 The light is reflected by 19 and enters the objective lens 6, where it is condensed on the optical disk master 2.

When the objective lens 6 and the mirror 10 move integrally in the radial direction of the optical disk master 2 by driving the X stage 4, the exposure laser beam 9 is scanned on the optical disk master 2 to expose the disk. I do.

When manufacturing the optical disk master 2, the exposure laser beam 9 focuses on variations in the thickness of the glass master, irregularities on the surface of the glass master, and runout of the turntable 3. It is necessary to perform focus control so that the point is always on the optical disk master 2.

For this reason, the focus control is performed by arranging the coarse focus detection system 11 and the fine focus detection system 12 on the optical path of the exposure laser beam 9. The coarse focus detection system 11 and the fine focus detection system 1
The incidence of the exposure laser beam 9 to the beam 2 is branched and guided by beam splitters 11a and 12a, respectively.

FIG. 7 is a block diagram of such a focus control device. Each of the coarse focus detection system 11 and the fine focus detection system 12 has a configuration in which a cylindrical lens 13 and a four-divided detector 14 are combined as shown in FIG.

That is, when the exposure laser light 9 is focused on the optical disk master 2 through the objective lens 6 and the exposure laser light 9 reflected by the optical disk master 2 is incident on the four-divided detector 14 through the cylindrical lens 13, The focus points f ₁ , f ₀ , f _{2 of the} cylindrical lens 13 are shifted according to the focus point of the objective lens 6 with respect to the optical disc master 2.

The cylindrical lens 13
Focus point f ₁ of, f _0, the beam shape h ₁ for condensing the 4-split detector 14 at f _2, h _0, h ₂
Are different.

Accordingly, the respective light amounts incident on the respective light receiving elements A to D of the four-segment detector 14 differ depending on the beam shapes h ₁ , h ₀ and h ₂ as shown in FIGS. 9 (a) to 9 (c). For example, at the focus point, the respective light amounts of the respective light receiving elements A to D become substantially the same as shown in FIG. 3B, and when the light amount shifts from the focus point, each of the light receiving elements B as shown in FIGS.
The light reception amount of C or A, D becomes large.

However, these coarse focus detection systems 1
1. The fine focus detection system 12 calculates (A + C)-(B + D) from the amount of light received by each of the light receiving elements A to D of the four-divided detector 14, and calculates this as the coarse focus signal Fa or the fine focus signal Fc. Output as

The difference between the coarse focus detection system 11 and the fine focus detection system 12 is that the detection range of the cylindrical lens 13 and the quadrant detector 14 is changed.
Has a low detection sensitivity in a wide detection range, and the fine focus detection system 12 has a high detection sensitivity in a narrow detection range. In particular, the fine focus detection system 12 has a configuration in which, for example, the focus error is controlled to about 0.1 μm. ing.

FIG. 10 shows a coarse focus sum signal Fb indicating the characteristics of the coarse focus signal Fa output from the coarse focus detection system 11, and the sum of the respective light receiving elements A to D of the four-divided detector 14 obtained by the coarse focus detection system 11. And the characteristic of the fine focus signal Fb output from the fine focus detection system 12.

The coarse focus detection system 11 and the fine focus detection system 12 are connected to gain adjustment units 13 and 14 for gains G _A and G _B , respectively. Power amplifier 17
Is connected.

Therefore, the coarse or fine focus signals Fa and Fc output from the coarse focus detection system 11 and the fine focus detection system 12 are supplied from the gain adjustment units 13 and 14 to the focus switching unit 15, the phase compensation circuit 16, It is supplied to the voice coil motor 7 through the amplifier 17.

The coarse focus sum signal Fb output from the coarse focus detection system 11 is sent to the control device 19 through the comparator 18 and is output from the coarse focus detection system 11 and the fine focus detection system 12, respectively. The Fa and fine focus signal Fc are sent to the control device 19 through the window comparator 20.

The control device 19 has a sequence function of driving the spindle motor 1 to rotate the turntable 3 and driving the Z stage 5, switching control of the focus switching unit 15, and performing focus control. .

The focus control sequence in the above-described focus control device is as follows. First, the controller 19 drives the Z stage 5 to lower the objective lens 6 from above to below the optical disc master 2.

At this time, it is detected whether or not the coarse focus sum signal Fb output from the coarse focus detection system 11 has reached a certain value which is compared by the comparator 18. When the coarse focus sum signal Fb reaches a certain value or more and the level determination signal la is sent to the control device 19, the control device 19 receives Z
The driving of the stage 5 is stopped.

Next, the controller 19 controls the spindle motor 1
To rotate the optical disk master 2. In this state, the control device 19 drives the Z stage 5 and moves the objective lens 6 for the optical disk until the coarse focus signal Fa output from the coarse focus detection system 11 reaches a certain range in comparison with the window comparator 20. The master 2 is further lowered.

The control unit 19 switches the focus switching unit 15 to the terminal A, and transmits the coarse focus signal Fa output from the coarse focus detection system 11 to the voice coil motor 7 through the gain adjustment unit 13, the phase compensation circuit 16 and the power amplifier 17. And the servo control of the voice coil motor 7 is performed.

It is determined whether the fine focus signal Fc output from the fine focus detection system 12 is within a certain range by comparison in the window comparator 20, and a level determination signal lb indicating that the fine focus signal Fc is within the certain range is obtained. When sent to the control device 19, the control device 19 switches the focus switching unit 15 to the terminal B, and
2 is supplied to the voice coil motor 7 through the gain adjustment unit 13, the phase compensation circuit 16 and the power amplifier 17, and the voice coil motor 7 is servo-controlled. Thereby, the voice coil motor 7 is servo-controlled by the fine focus signal Fc,
The recording on the optical disk master 2 can be started.

[0025]

However, in the above-mentioned focus control device, two detection systems 11 and 12 corresponding to two coarse and fine focuses are required, and accordingly, each of the coarse and fine focus circuit systems is required. Required.

In executing the focus control sequence, the sequence of switching the focus switching unit 15 to switch from coarse focus to fine focus is also complicated.

Further, the coarse focus signal F shown in FIG.
If the zero-cross point between a and the fine focus signal Fc deviates from the optical characteristics, the servo control system becomes unstable when switching from coarse focus to fine focus, and the servo control system may not be able to pull in.

An object of the present invention is to provide a focus control method and a focus control method capable of performing stable focus control with a simple sequence. Another object of the present invention is to provide an optical disk master exposure apparatus capable of controlling a focus point of an objective lens on an optical disk master by performing stable focus control and recording information with high accuracy.

[0029]

According to a first aspect of the present invention, there is provided a focus control method for adjusting a focus point of an objective lens based on a focus signal corresponding to a focus state of the objective lens for irradiating an optical disk with light. And a second step of starting the adjustment of the focus point based on the detected zero cross.

According to a second aspect of the present invention, there is provided a focus control method for adjusting a focus point of an objective lens based on a focus signal corresponding to a focus state of the objective lens for irradiating the optical disk with light, wherein the objective lens for the stopped optical disk And a second step of adjusting the focus point based on a focus signal obtained by rotating the optical disc after the first step.
And a step of controlling the focus.

According to a third aspect of the present invention, there is provided a focus control method for adjusting a focus point of an objective lens based on a focus signal corresponding to a focus state of an objective lens which irradiates an optical disk with light, wherein peaks of irregularities on the optical disk are respectively adjusted A focus control method includes a first step of detecting and a second step of adjusting a focus point between peaks.

According to a fourth aspect of the present invention, there is provided a focus detection system for outputting a focus signal according to a focus state of the objective lens with respect to the disk, and a focus point of the objective lens is set based on the focus signal output from the focus detection system. In the focus control device for adjusting the position on the disk, a drive mechanism for changing the distance between the disk and the objective lens, a rotation mechanism for rotating the disk, and a drive mechanism for adjusting the focus point of the objective lens on the disk based on the focus signal are provided. First adjusting means for driving to adjust the distance between the disk and the objective lens, and driving the rotating mechanism to rotate the disk and driving the driving mechanism so that the focus signal falls within a predetermined range, and Second adjusting means for adjusting the distance from the objective lens;
Is a focus control device provided with:

With such a focus control device,
The distance between the disk and the objective lens is adjusted by the drive mechanism based on the focus signal indicating the focus state of the objective lens so that the focus point of the objective lens is on the disk.

Thereafter, the disk is rotated by the rotation mechanism, and the drive mechanism moves the disk and the objective lens so that the focus signal falls within a predetermined range in consideration of variations in the thickness of the disk and surface irregularities. Adjust the interval.
After this adjustment, switch to servo control.

According to the fifth aspect, there is provided a focus detection system for outputting a focus signal according to a focus state of the objective lens with respect to the disk, and a focus point of the objective lens is set based on the focus signal output from the focus detection system. In a focus control device for adjusting on a disk, a drive mechanism for changing the distance between the disk and the objective lens, a rotation mechanism for rotating the disk, and positive and negative peaks of a focus signal when the disk is rotated by driving this rotation mechanism. A peak detecting means for detecting the value, and a drive mechanism for calculating a center value of the focus signal based on the positive and negative peak values detected by the peak detecting means, so that the center value of the focus signal falls within a predetermined range. Adjusting means for adjusting the distance between the disc and the objective lens by driving the It was a focus control device.

With such a focus control device,
The disk is rotated by a rotation mechanism to detect the disk runout and the like, and at this time, the positive and negative peak values of the focus signal are detected by peak detecting means. Then, the adjusting means calculates the center value of the focus signal based on the positive and negative peak values, and adjusts the distance between the disc and the objective lens so that the center value of the focus signal falls within a predetermined range.

According to a sixth aspect of the present invention, there is provided an optical disc master exposure apparatus for irradiating a recording light onto an optical disc master through an objective lens to record information on the optical disc master.
A focus detection system for detecting a focus state of the objective lens with respect to the optical disk master and outputting a focus signal according to the focus state, a drive mechanism for changing an interval between the optical disk master and the objective lens, and rotating the optical disk master A rotation mechanism, first adjustment means for adjusting a distance between the optical disk master and the objective lens by driving a drive mechanism such that a focus point of the objective lens is positioned on the optical disk master based on the focus signal, and a rotation mechanism And a second adjusting means for driving the drive mechanism to rotate the optical disc master and driving the drive mechanism so that the focus signal falls within a predetermined range to adjust the distance between the optical disc master and the objective lens. This is an optical disk master exposure apparatus.

With such an optical disk master exposure apparatus, during the recording operation on the optical disk master, the focus point of the objective lens is set on the optical disk master based on the focus signal indicating the focus state of the objective lens. The distance between the optical disk master and the objective lens is adjusted by the drive mechanism.

After that, the optical disk master is rotated by the rotating mechanism, and the drive mechanism drives the optical disk so that the focus signal falls within a predetermined range in consideration of variations in the thickness of the optical disk master and surface irregularities. Adjust the distance between the master and the objective lens. After this adjustment, switch to servo control.

According to a seventh aspect of the present invention, there is provided an optical disk master exposure apparatus for irradiating a recording light onto an optical disk master through an objective lens to record information on the optical disk master.
A drive mechanism that changes the distance between the optical disk master and the objective lens, a rotation mechanism that rotates the optical disk master, and detection of the positive and negative peak values of the focus signal when the rotary mechanism is driven to rotate the optical disk master And a driving mechanism that calculates a center value of the focus signal based on each of the positive and negative peak values detected by the peak detecting unit, and that the center value of the focus signal falls within a predetermined range. And an adjusting means for adjusting the distance between the optical disc master and the objective lens.

With such an optical disk master exposure apparatus, during a recording operation on the optical disk master, the optical disk master is rotated by a rotating mechanism in order to detect surface runout and the like of the optical disk master. The positive and negative peak values of the focus signal are detected by peak detecting means. Then, the adjusting means calculates the center value of the focus signal based on these positive and negative peak values, and adjusts the distance between the master optical disc and the objective lens so that the center value of the focus signal falls within a predetermined range. After this adjustment, switch to servo control.

[0042]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS First, a focus control method according to the present invention will be described. In a focus control method for adjusting a focus point of an objective lens based on a focus signal corresponding to a focus state of an objective lens for irradiating an optical disk with light. A first step of driving the objective lens to detect a zero cross, and a second step of starting adjustment of a focus point based on the detected zero cross.

The focus control method according to the present invention is a focus control method for adjusting a focus point of an objective lens based on a focus signal corresponding to a focus state of an objective lens for irradiating the optical disc with light. A first step of adjusting the position of the objective lens with respect to the focus point based on the focus signal, and a second step of adjusting the focus point based on the focus signal obtained by rotating the optical disc after the first step And

Further, the focus control method of the present invention is a focus control method for adjusting a focus point of an objective lens based on a focus signal corresponding to a focus state of an objective lens for irradiating an optical disk with light. The method includes a first step of detecting each peak and a second step of adjusting a focus point between the peaks. (1) Next, a first embodiment of the present invention will be described with reference to the drawings. 6 and 7 are denoted by the same reference numerals, and detailed description thereof will be omitted.

FIG. 1 is a block diagram of an optical disk master exposure apparatus to which the above-described focus control method is applied. The fine focus detection system 12 is connected to a zero cross detection circuit 30 and a window comparator 31, and the output terminals of the zero cross detection circuit 30 and the window comparator 31 are connected to a control device 32.

The focus point of the objective lens 6 is set on the optical disk master 2 based on the fine focus signal Fc output from the fine focus detection system 12 by the zero-cross detection circuit 30 and the control device 32 as first adjusting means. Has a function of driving the Z stage 5 to adjust the distance between the optical disc master 2 and the objective lens 6 so as to conform to the above.

[0047] That is, the zero-crossing detection circuit 30 receives the fine focus signal Fc output from the fine focus detection system 12, have the function of outputting a determination signal H ₁ detects a zero-cross point of the fine focus signal Fc doing.

The controller 32 drives the Z stage 5 lowers the objective lens 6, receiving the judgment signal H _1, which indicates the detection of the zero cross point of fine focus signal Fc from the zero-cross detection circuit 30 in this state Sometimes, it has a function of stopping driving of the Z stage 5.

On the other hand, the window comparator 31 and the control device 32 act as a second adjusting means to drive the spinned motor 1 to rotate the optical disk master 2 so that the fine focus signal falls within a certain range. 5 has a function of moving the objective lens 6 in the vertical direction by adjusting the distance between the objective lens 6 and the optical disk master 2.

That is, the window comparator 31
It determines fine focus signal Fc is within the predetermined range, fine focus signal Fc has a function of outputting a determination signal H ₂ indicating that falls within a certain range.

The controller 32, in addition to the above functions, drives the Z stage 5 drives the spindle motor 1 stops driving of the Z stage 5 when receiving a determination signal of H ₂ from the window comparator 31 And a function of transmitting an open / close signal K to the changeover switch SW and switching to servo control by the voice coil motor 7.

Next, the operation of the above-configured apparatus will be described with reference to the control flowchart shown in FIG.
The control device 32 determines that the Z stage 5
Issues a descending command to The Z stage 5 moves downward from above to bring the voice coil motor 7 incorporating the objective lens 6 closer to the optical disk master 2.

On the other hand, the exposure laser beam 9
Is output, the exposure laser light 9 is
And is condensed on the optical disk master 2 by the objective lens 6, and the reflected exposure laser light 9 is again reflected on the mirror 10.
And is branched by the beam splitter 12a and enters the fine focus detection system 12.

The fine focus detection system 12 receives the reflected exposure laser beam 9 and outputs a fine focus signal Fc corresponding to a focus point of the objective lens 6 with respect to the optical disk master 2. The characteristics of the fine focus signal Fc are shown in FIG.

The zero-crossing detection circuit 30 determines in step # 2
, The fine focus signal Fc output from the fine focus detection system 12 is input, and it is detected whether or not the fine focus signal Fc has reached the zero cross point.

If the zero-cross point of the fine focus signal Fc is not detected by the zero-cross detection circuit 30, the lowering operation of the Z stage 5 is continued. When the zero-crossing point of the fine focus signal Fc is detected, the zero crossing detection circuit 30 outputs a determination signal H ₁ showing a zero-cross point detection of the fine focus signal Fc.

Upon receiving the determination signal H ₁ , the control device 32 stops driving the Z stage 5 and sets the focus point of the objective lens 6 on the optical disk master 2 in step # 3.

Here, the focus point of the exposure laser beam 9 is always set to the variation in the thickness of the glass master of the optical disk master 2, the unevenness of the surface of the glass master, and the runout of the turntable 3. It is necessary to perform focus control so as to be on the second position.

Accordingly, the control device 32 executes the following step #
In step # 5, the spindle motor 1 is driven to rotate the optical disk master 2, and in step # 5, the Z stage 5 is driven up and down to move the objective lens 6 up and down with respect to the optical disk master 2 surface.

At this time, the fine focus detection system 12 outputs a fine focus signal Fc corresponding to the focus point position of the objective lens 6 with respect to the optical disk master 2 in the same manner as described above.

On the other hand, in step # 6, the window comparator 31 determines that the fine focus signal Fc is within a certain range, that is, the variation of the thickness of the glass master forming the optical disk master 2, the unevenness of the surface of the glass master, the turntable Then, it is determined whether or not it is within a certain range allowing the surface runout of No.3.

[0062] When the fine focus signal Fc falls within a predetermined range, the window comparator 31 outputs the determination signal H ₂ to indicate that this fine focus signal Fc is within the predetermined range.

The control device 32 includes a window comparator 3
When receiving the determination signal H ₂ from 1, at step # 7, stops the vertical drive of the Z stage 5. Subsequently, in step # 8, the control device 32
, An open / close signal K is transmitted to switch to servo control by the voice coil motor 7.

That is, the fine focus signal Fc output from the fine focus detection system 12 is supplied to the voice coil motor 7 through the gain adjustment unit 13, the phase compensation circuit 16 and the power amplifier 17, and the servo control of the voice coil motor 7 is started. I do.

As described above, in the first embodiment, based on the fine focus signal Fc indicating the focus state of the objective lens 6, the Z stage 5 is set so that the focus point of the objective lens 6 is on the optical disk master 2. The distance between the optical disc master 2 and the objective lens 6 is adjusted by driving the optical disc. Then, the optical disc master 2 is rotated, and the Z stage 5 is driven up and down so that the fine focus signal Fc falls within a certain range. Since the distance between the optical disc master 2 and the objective lens 6 is adjusted, the focus point of the objective lens 6 can be adjusted on the optical disc master 2 by using a simpler configuration and control sequence than before without using a coarse focus detection system. Thus, stable focus control can be performed, and the time required for the focus control sequence can be reduced.

Further, since the switching from the coarse focus to the fine focus is not performed, a pull-in error does not occur due to the instability of the servo control system which tends to occur conventionally. Therefore, after adjusting the focus point of the objective lens 6 on the optical disk master 2, the servo control of the objective lens 6 using the voice coil motor 7 is performed so that the focus point of the objective lens 6 is on the optical disk master 2. Control enables high-accuracy information recording. (2) Next, a second embodiment of the present invention will be described with reference to the drawings. 6 and 7 are denoted by the same reference numerals, and detailed description thereof will be omitted.

FIG. 3 is a block diagram of an optical disk master exposure apparatus to which the above-described focus control method is applied. The fine focus detection system 12 includes a positive peak detection circuit (hereinafter, referred to as a + peak detection circuit) 40 and a negative peak detection circuit (hereinafter, referred to as a-peak detection circuit) that constitute peak detection means.
41 are connected.

Each of the + peak detection circuit 40 and the −peak detection circuit 41 receives the fine focus signal Fc from the fine focus detection system 12 when the optical disc master 2 is rotating. It has a function of detecting a positive peak value (hereinafter, referred to as a + peak value) and a negative peak value (hereinafter, referred to as a -peak value).

Note that these + peak detection circuits 40 and-
The peak detection circuit 41 is connected to one of the turntables 3.
The + peak value and the-peak value of the fine focus signal Fc in rotation are detected, and these + peak value and-peak value are updated by the origin signal once per rotation of the turntable 3. .

The output terminals of the + peak detection circuit 40 and the −peak detection circuit 41 are connected to an addition circuit 42, a window comparator 43, and a control device 44. The addition circuit 42, the window comparator 43, and the control device 44 adjust the center value of the fine focus signal Fc based on the positive and negative peak values detected by the + peak detection circuit 40 and the -peak detection circuit 41, respectively, as adjusting means. The distance between the master disc 2 for the optical disc and the objective lens 6 is adjusted by driving the Z stage 5 and moving the objective lens 6 up and down so that the center value of the fine focus signal Fc falls within a certain range. It has the function to do.

That is, the adding circuit 42 has a function of adding the respective peak values output from the + peak detecting circuit 40 and the −peak detecting circuit 41 to calculate the center value of the fine focus signal Fc. .

The window comparator 43 includes an adder 4
It is determined whether or not the center value of the fine focus signal Fc obtained in step 2 is within a certain range, and when the center value of the fine focus signal Fc is within a certain range, the determination signal H is determined.
_It has a function to output ₃ .

The control device 44 drives the spindle motor 1 and the Z stage 5 in the vertical direction, and the window comparator 43 outputs a determination signal H indicating that the center value of the fine focus signal Fc has entered a predetermined range. When receiving ₃ , the Z-stage 5 has a function of stopping the vertical drive and sending an open / close signal K to the changeover switch SW to switch to servo control by the voice coil motor 7.

Next, the operation of the apparatus configured as described above will be described with reference to the control flowchart shown in FIG.
The controller 44 issues a drive command to the spindle motor 1 in step # 10 to rotate the optical disc master 2, and in the next step # 11, the Z stage 50
The objective lens 6 is lowered by being driven, and the objective lens 6 is brought closer to the optical disk master 2 from above.

On the other hand, the exposure laser beam 9
Is output, the exposure laser light 9 is
And is condensed on the optical disk master 2 by the objective lens 6, and the reflected exposure laser light 9 is again reflected on the mirror 10.
And is branched by the beam splitter 12a and enters the fine focus detection system 12.

The fine focus detection system 12 receives the reflected exposure laser light 9 and outputs a fine focus signal Fc corresponding to the focus point of the objective lens 6 with respect to the optical disk master 2.

The + peak detection circuit 40 determines in step # 12
During the rotation of the optical disk master 2, the fine focus signal Fc from the fine focus detection system 12 is input, and a + peak value in the fine focus signal Fc is detected.

At the same time, the negative peak detection circuit 41
While the optical disk master 2 rotates once, the fine focus signal Fc from the fine focus detection system 12 is input, and a negative peak value in the fine focus signal Fc is detected.

The positive peak value and the negative peak value of the fine focus signal Fc are determined by the variation in the thickness of the glass master of the optical disk master 2, the unevenness of the surface of the glass master, and the runout of the turntable 3, as shown in FIG. And so on.

The + peak value and the-peak value of the fine focus signal Fc are updated by the origin signal once per rotation of the turntable 3. The + peak value and the −peak value detected by the + peak detection circuit 40 and the −peak detection circuit 41 are sent to the addition circuit 42.

In step # 13, the adding circuit 42 inputs the + peak value and the −peak value, and calculates the center value of the fine focus signal Fc by adding the + peak value and the −peak value.

Next, in step # 14, the window comparator 43 inputs the center value of the fine focus signal Fc obtained by the adding circuit 42, and determines whether or not this center value falls within a certain range.

If the result of this determination is that the center value of the fine focus signal Fc is not within a certain range, the controller 4
In step 4, the steps # 11 to # 13 are repeated again to move down the Z stage 5, and bring the objective lens 6 closer to the optical disk master 2.

When the center value of the fine focus signal Fc falls within a certain range as a result of the determination by the window comparator 43, the window comparator 43 enters the center value of the fine focus signal Fc within a certain range. and it outputs a determination signal H ₃ indicating that.

The control device 44 includes the window comparator 4
When receiving the determination signal H3 from Step ₃ , the vertical drive of the Z stage 5 is stopped in Step # 15. Subsequently, the control device 44 determines in step # 16 that the changeover switch S
An open / close signal K for W is transmitted to switch to servo control by the voice coil motor 7.

That is, the fine focus signal Fc output from the fine focus detection system 12 is supplied to the voice coil motor 7 through the gain adjustment unit 13, the phase compensation circuit 16 and the power amplifier 17, and the servo control of the voice coil motor 7 is started. I do.

As described above, in the second embodiment, during the recording operation on the optical disk master 2, the optical disk master 2 is rotated in order to detect the surface deflection or the like of the optical disk master 2. Fine focus signal Fc
, The center value of the fine focus signal Fc is calculated based on these ± peak values, and the Z stage 5 is driven so that the center value of the fine focus signal Fc falls within a certain range. Since the distance between the optical disk master 2 and the objective lens is adjusted, the objective lens 6 can be formed with a simpler configuration and control sequence than the conventional one without using a coarse focus detection system, as in the first embodiment. Can be adjusted on the optical disk master 2, stable focus control can be performed, and the time required for the focus control sequence can be reduced.

Further, since the switching from the coarse focus to the fine focus is not performed, a pull-in error does not occur due to the instability of the servo control system, which tends to occur in the past. Furthermore, since the control is performed by a single determination process of detecting the ± peak values of the fine focus signal Fc and controlling the center value of the fine focus signal Fc to be within a certain range based on the ± peak values, high accuracy is achieved. In addition, the focus point of the objective lens 6 can be adjusted on the optical disk master 2 at a higher speed as compared with the first embodiment.

Therefore, after the focus point of the objective lens 6 is set on the optical disc master 2,
By performing servo control using the voice coil motor 7, the focus point of the objective lens 6 can be controlled on the optical disk master 2 to record information with high accuracy.

The present invention is not limited to the first and second embodiments, but may be modified as follows. For example, in the first and second embodiments, the present invention is applied to the adjustment of the focus point of the objective lens 6 on the optical disk master 2. However, the present invention is not limited to this optical disk master 2, and a disk-shaped one such as a compact It can also be applied to adjust the focus point on the disc.

The focus point of the objective lens 6 is determined not only by moving the objective lens 6 up and down by the Z stage 5 but also by rotating the spindle motor 1 and the turntable 3.
May be moved up and down integrally, or the objective lens 6 and the spindle motor 1 and the turntable 3 may be moved up and down with respect to each other.

Although the focus point of the objective lens 6 is adjusted on the optical disk master 2 using the fine focus signal Fc output from the fine focus detection system 12, a focus signal equivalent to the fine focus signal Fc is obtained. Any focus detection system that can be obtained can be applied. Further, a detection beam may be separately provided.

[0093]

As described in detail above, claims 1 to 5 of the present invention.
According to (3), a focus control method capable of performing stable focus control by a simple sequence can be provided.
According to the fourth and fifth aspects of the present invention, it is possible to provide a focus control device capable of performing stable focus control with a simple sequence.

Further, according to the fourth and fifth aspects of the present invention, the focus point of the objective lens can be adjusted on the disk by a simple configuration and control sequence without using the coarse focus detection system. It is possible to provide a focus control device capable of performing a stable focus control by reducing the time required for a focus control sequence without causing a pull-in error due to instability of a servo control system without switching to fine focus.

Also, according to the sixth and seventh aspects of the present invention, there is provided an optical disk master exposure apparatus capable of controlling a focus point of an objective lens on an optical disk master by stable focus control to record information with high accuracy. it can.

[Brief description of the drawings]

FIG. 1 is a configuration diagram of an optical disc master disc exposure apparatus to which a first embodiment of a focus control method according to the present invention is applied.

FIG. 2 is a control flowchart in the apparatus.

FIG. 3 is a configuration diagram of an optical disc master disc exposure apparatus to which a second embodiment of the focus control method according to the present invention is applied.

FIG. 4 is a control flowchart in the apparatus.

FIG. 5 is a diagram showing ± peak values of fine focus signals caused by variations in the thickness of an optical disc master.

FIG. 6 is a configuration diagram of a conventional optical disk master exposure apparatus.

FIG. 7 is a configuration diagram of a conventional focus control device.

FIG. 8 is a configuration diagram of a coarse focus detection system and a fine focus detection system.

FIG. 9 is a diagram showing a beam shape incident on a four-divided detector.

FIG. 10 is a characteristic diagram of each focus signal output from a coarse and fine focus detection system.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... Spindle motor, 2 ... Optical disk master, 3 ... Turntable, 4 ... X stage, 5 ... Z stage, 6 ... Objective lens, 7 ... Voice coil motor (VCM), 8 ... Recording optical system, 12 ... Fine focus Detection system, 30: zero cross detection circuit, 31: window comparator, 32, 44: control device, 40: + peak detection circuit, 41:-peak detection circuit, 42: addition circuit, 43: window comparator.

Claims (7)

[Claims] 1. A focus control method for adjusting a focus point of an objective lens based on a focus signal according to a focus state of an objective lens that irradiates an optical disc with light, wherein a first cross-point is detected by driving the objective lens to detect a zero cross. And a second step of starting the adjustment of the focus point based on the detected zero cross. 2. A focus control method for adjusting a focus point of the objective lens based on a focus signal according to a focus state of the objective lens that irradiates the optical disc with light, wherein the position of the objective lens with respect to the stopped optical disc. A second step of adjusting the focus point based on the focus signal obtained by rotating the optical disc after the first step. And a focus control method comprising: 3. A focus control method for adjusting a focus point of the objective lens based on a focus signal according to a focus state of an objective lens that irradiates the optical disc with light, wherein a peak of unevenness on the optical disc is detected. 1. A focus control method, comprising: a first step; and a second step of adjusting the focus point between the peaks. 4. A focus detection system for outputting a focus signal according to a focus state of the objective lens with respect to the disk, and a focus point of the objective lens is adjusted on the disk based on a focus signal output from the focus detection system. A focus control device, wherein: a drive mechanism that changes an interval between the disc and the objective lens; a rotation mechanism that rotates the disc; and a focus point of the objective lens on the disc based on the focus signal. First adjusting means for driving a driving mechanism to adjust the distance between the disc and the objective lens; and driving the rotating mechanism to rotate the disc so that the focus signal falls within a predetermined range. By driving the drive mechanism, the disk and the objective lens Focus control apparatus characterized by comprising second adjusting means for adjusting the spacing, the. 5. A focus detection system for outputting a focus signal according to a focus state of an objective lens with respect to a disk, wherein a focus point of the objective lens is adjusted on a disk based on a focus signal output from the focus detection system. In the focus control device, a driving mechanism that changes an interval between the disk and the objective lens; a rotation mechanism that rotates the disk; and a positive or negative focus signal when the rotation mechanism is driven to rotate the disk. Peak detecting means for detecting a peak value; calculating a center value of the focus signal based on the positive and negative peak values detected by the peak detecting means so that the center value of the focus signal falls within a predetermined range. The drive mechanism to drive the disc and the objective lens Focus control apparatus characterized by comprising an adjustment means for adjusting the septum, the. 6. An optical disk master exposure apparatus for irradiating a recording light onto an optical disk master through an objective lens to record information on the optical disk master, wherein a focus state of the objective lens with respect to the optical disk master is detected. A focus detection system that outputs a focus signal according to the focus state; a drive mechanism that changes an interval between the optical disc master and the objective lens; a rotation mechanism that rotates the optical disc master; First adjusting means for adjusting the distance between the optical disc master and the objective lens by driving the drive mechanism so that the focus point of the objective lens is aligned with the optical disc master, and driving the rotating mechanism. The optical disk master is rotated in such a manner that the focus signal falls within a predetermined range. Wherein a master for the optical disc by driving the drive mechanism so that the objective lens and the optical disk master exposure apparatus that the second adjusting means for adjusting the spacing, characterized by comprising a. 7. An optical disk master exposure apparatus for irradiating a recording light onto an optical disk master through an objective lens and recording information on the optical disk master, wherein a drive mechanism for changing a distance between the optical disk master and the objective lens. A rotating mechanism for rotating the optical disc master; peak detecting means for detecting the positive and negative peak values of the focus signal when the rotating mechanism is driven to rotate the optical disc master; Calculating the center value of the focus signal based on each of the positive and negative peak values detected by,
Adjusting means for adjusting the distance between the optical disc master and the objective lens by driving the drive mechanism so that the center value of the focus signal falls within a predetermined range. Master exposure equipment.