JPH067414B2 - Optical disk device - Google Patents

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical disc device, and more particularly to an optical disc device that performs astigmatism focus servo.

2. Description of the Related Art Conventionally, there have been read-only optical disks such as compact disks (CDs), and recently writable and rewritable optical disks have been developed.

In such an optical disk recording apparatus and reproducing apparatus, it is necessary to focus the laser beam on the signal surface of the optical disk with high accuracy, and the signal surface moves up and down with the rotation of the optical disk. Therefore, focus servo control Are doing.

2. Description of the Related Art Conventionally, there is an astigmatism method as focus servo control.

This astigmatism method uses the fact that the laser light passing through the cylindrical lens becomes a perfect circle at the focal position, becomes a vertically long ellipse before the focus, and becomes a horizontally long ellipse behind the focus, and this is divided into four. This is a method of detecting with a light sensor.

For example, if the optical disk is too close, the diameter of the light projected on the divided parts a, b, c, d of the four-divided optical sensor becomes an ellipse descending to the right as shown in FIG. 8 (A). As shown in (b), the shape of the light is a perfect circle, and when it is too far, it becomes an ellipse that descends to the left (the major axis is rotated 90 degrees with respect to the ellipse in (A) in the figure). .

As a result, when the division units a to d output electric power proportional to the amount of received light, an error signal obtained by taking the difference between the sum of the output voltages of the division units a and c and the sum of the output voltages of the division units b and d is obtained. It is possible to know whether the optical disk is in focus, too close or too far, and the focus servo moves the focus position according to the error signal.

DISCLOSURE OF THE INVENTION Problems to be Solved by the Invention In an optical disk device, a relative position between an optical system and an optical sensor is displaced due to a change with time, a rapid change in temperature and humidity,
The optical axis shifts on the optical sensor. For example, FIG. 8 (D) shows the focal point and the optical axis shifts only in the x direction, FIG. 8 (E) shows the focal point and the optical axis shifts only in the y direction, and FIG. 8 (F) shows the focal point and the optical axis shifts. x
The state is shifted in the direction.

When the optical axis is deviated in the xy directions at the in-focus point as shown in FIG. 6F, the error signal does not become zero and the focus is moved by the focus servo, and a focus error, that is, defocus occurs. This focus error reduces the laser light energy on the signal surface of the optical disc,
There is a problem that the recording performance and the reproducing performance of the optical disk device are deteriorated.

The present invention has been made in view of the above points,
An object of the present invention is to provide an optical disk device that corrects errors and prevents deterioration of recording performance and reproduction performance.

Means for Solving the Problems In the optical disk device of the present invention, the first arithmetic means calculates the amount of deviation of the optical axis with respect to the sensor in the y direction from the output of each division part of the four-division optical sensor, and the second arithmetic means. Then, the shift amount of the optical axis with respect to the sensor in the x direction is calculated from the output of each division unit, and the maximum shift amount of the optical axis with respect to the sensor in the x direction and the y direction is calculated from the output of each division unit by the third computing means. The fourth arithmetic means calculates the error signal from the output of each division unit, the fifth arithmetic means calculates the deviation component of the optical axis in the error signal from the outputs of the first to third arithmetic means, The error signal of only the focus error in which the deviation component of the optical axis is removed from the outputs of the fourth and fifth calculating means is calculated by the operation means of 6, and the error signal of only the focus error in which the deviation component of the optical axis is removed. Focus servo with.

Further, the amount of laser light to be irradiated onto the optical disk is varied by the varying means according to the deviation component of the optical axis output from the fifth computing means, and the focus signal is focused by the error signal output from the fourth computing means.
Servo.

Further, the seventh calculating means calculates the deviation rate of the optical axis in the y direction from the outputs of the first to third calculating means, and the eighth calculating means calculates from the outputs of the second and third calculating means. The relative position between the sensor and the optical axis is calculated so that the deviation rate of the optical axis in the x direction is calculated, and the deviation amount in the y direction is eliminated according to the deviation rate of the y direction output from the seventh computing means by the first driving means. Is moved and the relative position between the sensor and the optical axis is moved by the second drive means so as to eliminate the amount of deviation in the x direction in accordance with the deviation rate in the x direction output from the eighth calculating means. Focus servo is performed by the error signal output from the means.

Action To explain the principle of the method of the present invention, as shown in FIG. 2, the output levels of the divided portions a, b, c, d of the optical sensor when the optical axis is deviated in the xy directions are A, B, and C and D, and the output level when there is no deviation in the xy direction is A ₀ ,
Represented as B ₀ , C ₀ , D ₀ . That is, the shaded area in FIG. 2 (A) corresponds to the output level A, and the shaded area in FIG. 2 (B) corresponds to the output level A ₀ . Here, the shift amount x in the x direction corresponding to the area of the hatched portion in FIG.

X = (B + C)-(A + D) (1) Further, the maximum displacement amount X _{M in the} x direction is expressed by the following equation.

X _M = A + B + C + D (2) Similarly, the shift amount Y in the y direction and its maximum value Y _M are represented by the following equations.

Y = (A + B) − (C + D) (3) Y _M = A + B + C + D (4) If the above-mentioned shift amounts X, X _M , Y, Y _M are used, the area of the downward-sloping diagonal line in FIG. 2 (D) The area Xa and the area Ya of the diagonally downward-sloping portion are expressed by the following equation.

Xa = {(A + B) / 2} · (X / X _M ) ... (5) Ya = {(A + D) / 2} · (Y / Y _M ) ... (6) Using this, the output level A is approximate. Is expressed as

A = A ₀ − {(A + B) / 2} · (X / X _M ) + {(A + D) / 2} · (Y / Y _M ) ... (10) Similarly, the output levels B, C and D are as follows. It is expressed as a formula.

B = B ₀ + {(A + B) / 2} · (X / X _M ) + {(B + C) / 2} · (Y / Y _M ) ... (11) C = C ₀ − {(C + D) / 2} _{· (X / X M) +} {(B + C) / 2} · (Y / Y M) ... (12) D = D 0 - {(C + D) / 2} · (X / X M) - {(A + D) / 2} · (Y / Y _M ) ... (13) Here, the error signal of the focus error is (A + C) −
It is given by (B + D), and by substituting the equations (10) to (13), the following equation is obtained.

(A + C) − (B + D) = (A ₀ + C ₀ ) − (B ₀ + D ₀ ) − (A + B−C−D) · (X / X _M ) + (A + D−B−C) · (Y / Y _M ) (14) From this, the following equation is obtained.

(A + C) − (B + D) = (A ₀ + C ₀ ) − (B ₀ + D ₀ ) −2 · X · Y / (A + B + C + D) (15) The first term on the right side of the equation (15) is a true error signal component. The second term is the optical axis shift component.

In the present invention, the focus error is corrected by performing the focus servo by obtaining the error signal in which the second term on the left side of the equation (15) is removed by the sixth calculating means, so that the recording performance and the reproducing performance are deteriorated. Is prevented.

Further, the focus servo is performed by the error signal represented by the equation (15), and the laser light amount is changed by the changing means, so that the focus error is corrected and thereby the deterioration of the recording performance and the reproducing performance can be prevented.

Further, the relative position between the sensor and the optical axis is moved so as to eliminate the deviations of the optical axis in the y direction and the x direction, respectively, and the focus error is corrected, thereby preventing the deterioration of the recording performance and the reproducing performance.

First Embodiment FIG. 1 shows a block diagram of a first embodiment of the method of the present invention.

In the figure, 10 is an optical disk, which is rotated by a motor 11. The laser beam output from the laser diode 12 is collimated into a parallel beam by the collimator lens 13, is guided to the objective lens 16 through the beam splitter 14 and the tracking mirror 15, and is converged on the signal surface of the optical disc 10 to record and record a signal. Playback is performed. The reflected light of the optical disk 10 is guided to the beam splitter 17 through the objective lens 16, the tracking mirror 15 and the beam splitter 14, and most of the reflected light is guided to the optical sensor 18 for signal reproduction. In addition, part of the reflected light is mirror 1
Focus from 9 through the cylindrical lens 29
It is led to the four-division optical sensor 20 for servo.

The outputs A, B, C, D of the respective divided parts a, b, c, d of the four-division optical sensor 20 are supplied to the arithmetic circuit 21, and the arithmetic circuit 21, the arithmetic circuit 22 and the subtraction circuit 23 determine the optical axis of the optical axis. An error signal from which the shift component has been removed is obtained, and this error signal is supplied to the drive coil 25 through the amplifier 24, whereby the objective lens 16 is moved in the direction in which the laser light converges on the signal surface of the optical disc 10.

FIG. 3 shows a circuit diagram of the arithmetic circuits 21 and 22 described above.

In the figure, the arithmetic circuit 21 is composed of addition circuits 30 to 35 and subtraction circuits 36 to 39. The adder circuit 30 adds the output levels A and B of the division parts a and b of the four-division sensor 20 and outputs a signal A + B. The adder circuit 31 includes a division unit c,
The output levels C and D of d are added and the signal C + D is output. Similarly, the adder circuits 32 to 35 add the output levels A to D of the sensors a to c, respectively, and output signals B + C, A + D and A +.
Outputs C and B + D respectively.

The subtractor circuit 7 subtracts the output signal A + B of the adder circuit 30 and the output signal C + D of the adder circuit 31 to obtain a signal (A + B) −.
(C + D) That is, the signal Y representing the shift amount Y shown in the equation (3)
Is output. The subtracting circuit 8 subtracts the output signals of the adding circuits 32 and 33 and outputs a signal representing the shift amount X shown in the equation (1). Similarly, the adder circuit 36 adds the output signals of the adder circuits 34 and 35 and outputs a signal (A + B + C + D) representing the shift amount Xa ₁ or Ya ₁ shown in the equation (2) or (4).
The subtraction circuit 39 subtracts the output signals of the addition circuits 34 and 35 and outputs the error signal (A + C)-(B + D) shown in the equation (15).

Here, the addition circuits 30 and 31 and the subtraction circuit 37 constitute a first calculation means, the addition circuits 32 and 33 and the subtraction circuit 38 constitute a second calculation means, and the addition circuits 34 to 36 form a third calculation means. Addition circuits 34 and 35, and a subtraction circuit 39, which constitute arithmetic means.
And constitutes a fourth arithmetic means.

The arithmetic circuit 22 which is the arithmetic means of FIG.
38 and output signals X, Y, (A + B) of the adder circuit 36, respectively.
+ C + D), that is, a signal {2 · X · Y / (A + B) that represents the shift component of the optical axis represented by the second term of Expression (15).
+ C + D)} is output. Arithmetic circuit 22 and arithmetic circuit 3
The respective output signals of 9 are supplied from the terminals 40 and 41 to the subtraction circuit 23 of FIG.

As a result, the output signal of the subtraction circuit 23 becomes only the true error signal component represented by the first term of the expression (15), and the focus error due to the deviation of the optical axis can be prevented. Therefore, the deterioration of the recording performance and the reproducing performance of the optical disc device can be prevented.

FIG. 4 shows a block diagram of a second embodiment of the system of the present invention.
In the figure, those parts which are the same as those corresponding parts in FIG. 1 are designated by the same reference numerals, and a description thereof will be omitted.

In FIG. 4, the signal output by the arithmetic circuit 21 from the terminal 41 and represented by the equation (15) is directly supplied to the amplifier 24 for focus servo control.

For this reason, although the same defocus as in the conventional case occurs, the signal representing the deviation component of the optical axis output from the terminal 40 from the arithmetic circuit 22 is supplied to the laser diode drive circuit 50 as the variable means. The laser diode drive circuit 50 increases the drive current of the laser diode 12 and increases the laser light amount as the absolute value of the output signal of the arithmetic circuit 22, which is a component of optical axis deviation, increases. As a result, the laser light energy on the signal surface of the optical disc 10 increases to compensate for the focus error, and the deterioration of the recording performance and the reproducing performance can be prevented.

FIG. 5 shows a block diagram of a third embodiment of the method of the present invention.
In the figure, those parts which are the same as those corresponding parts in FIG. 4 are designated by the same reference numerals, and a description thereof will be omitted.

In FIG. 5, instead of the arithmetic circuit 22, arithmetic circuits 26a and 26b which are seventh and eighth arithmetic means are provided. Arithmetic circuit 26a as shown in FIG. 6, and the output from the terminal 42 generates the signal Y / _{Y M} representing the signal Y and the signal (A + B + C + D ) and more y direction deviation rate, the arithmetic circuit 26
b generates a signal X / X _M representing the deviation rate in the x direction from the signal X and the signal (A + B + C + D) and outputs it from the terminal 43.

The signals Y / Y _M and X / X _M are respectively supplied to the drive coils 27a and 27b which are the first and second drive means, whereby the mirror 19 is rotated and the optical axis of the reflected light is changed to the signal Y / Y _M. Y
_M , X / X _M, respectively, in the y direction of the four-division sensor 20,
By moving them in the respective x-directions, the deviation of the optical axis with respect to the sensor 20 is compensated.

As a modification of this, as shown in FIG. 7, the signal Y /
Y _M and X / X _M are respectively supplied to the drive coils 28a and 28b which are the first and second drive means, and the four-division sensor 20 is provided.
The displacement of the optical axis with respect to the sensor 20 can be compensated by moving in the y direction and the x direction respectively.

EFFECTS OF THE INVENTION As described above, according to the optical disk device of the present invention, it is possible to correct the focus error caused by the shift of the optical axis with respect to the sensor, and prevent the deterioration of the recording performance and the reproduction performance.
It is extremely useful in practice.

[Brief description of drawings]

1, 4, 5, and 7 are block diagrams of respective embodiments of the method of the present invention, FIG. 2 is a diagram for explaining the principle of the present invention, and FIG. 3 is FIG. 6 is a circuit configuration diagram of a partial circuit of FIG. 6, FIG. 6 is a circuit configuration diagram of the partial circuit of FIG. 5, and FIG. 8 is a diagram for explaining the deviation of the optical axis. 12 ... Laser diode, 20 ... 4-division sensor, 2
1, 22, 26a, 26b ... Arithmetic circuit, 23 ... Subtraction circuit, 27a, 27b, 28a, 28b ... Driving coil, 29 ... Cylindrical lens.

Claims (3)

[Claims] 1. An optical disk for projecting reflected light from an optical disk through a cylindrical lens onto a four-division optical sensor, and obtaining a focus error error signal from the output of each division of the sensor to perform astigmatism focus servo. In the apparatus, first computing means for calculating the amount of deviation of the optical axis with respect to the sensor in the y direction from the output of each dividing unit, and calculating the amount of deviation of the optical axis for the sensor with respect to the x direction from the output of each dividing unit. Second calculating means, third calculating means for calculating the maximum deviation amount of the optical axis with respect to the sensor in the x-direction and the y-direction from the output of each dividing portion, and the error signal calculated from the output of each dividing portion. Means for calculating the deviation component of the optical axis in the error signal from the outputs of the first to third arithmetic means, and the outputs of the fourth and fifth arithmetic means From the optical axis shift component An optical disc having a sixth arithmetic means for calculating an error signal of only the removed focus error, and performing focus servo with an error signal of only the focus error from which the deviation component of the optical axis is removed. apparatus. 2. An optical disk for performing astigmatism focus servo by projecting reflected light of an optical disk through a cylindrical lens onto a four-division optical sensor and obtaining a focus error error signal from the output of each division of the sensor. In the apparatus, first computing means for calculating the amount of deviation of the optical axis with respect to the sensor in the y direction from the output of each dividing unit, and calculating the amount of deviation of the optical axis for the sensor with respect to the x direction from the output of each dividing unit. Second calculating means, third calculating means for calculating the maximum deviation amount of the optical axis with respect to the sensor in the x-direction and the y-direction from the output of each dividing portion, and the error signal calculated from the output of each dividing portion. Means for calculating the deviation component of the optical axis in the error signal from the outputs of the first to third arithmetic means, and the light output by the fifth arithmetic means. Depending on the axis deviation component And a varying means for varying the amount of laser light to be irradiated to the optical disk, an optical disk apparatus and performing the focus servo in error signal output of the arithmetic means of the fourth. 3. An optical disk for projecting reflected light of an optical disk through a cylindrical lens onto a four-division optical sensor, and obtaining an error signal of a focus error from the output of each divided portion of the sensor to perform focus servo of an astigmatism method. In the apparatus, first computing means for calculating the amount of deviation of the optical axis with respect to the sensor in the y direction from the output of each dividing unit, and calculating the amount of deviation of the optical axis for the sensor with respect to the x direction from the output of each dividing unit. Second calculating means, third calculating means for calculating the maximum deviation amount of the optical axis with respect to the sensor in the x-direction and the y-direction from the output of each dividing portion, and the error signal calculated from the output of each dividing portion. From the outputs of the first to third arithmetic means, the seventh arithmetic means for calculating the deviation rate of the optical axis in the y direction, and the outputs of the second and third arithmetic means. Deviation rate of optical axis in x direction An eighth calculating means for calculating, and a first moving means for moving the relative position between the sensor and the optical axis so that the shift amount in the y direction disappears in accordance with the shift rate in the y direction output from the seventh calculating means. Driving means, and second driving means for moving the relative position between the sensor and the optical axis so as to eliminate the shift amount in the x direction in accordance with the shift ratio in the x direction output from the eighth computing means. And an optical disc device, wherein focus servo is performed by an error signal output from the fourth arithmetic means.