JPH0628679A - Optical disk device - Google Patents

Abstract

PURPOSE:To prevent unstability in drawing operation due to a pseudo S-shape curve caused by a disk surface at a focus drawing time when a focus error signal is normalized with total reflection light quantity in a recording type optical disk device. CONSTITUTION:In a recording type optical disk, the intensity of beams at a recording time and at a reproducing time are different from each other, and the values as well of the focus error signals vary according to that. By using a divider 15 for preventing that, a ratio between the magnitudes of the total reflection light quantity and the error signal is taken, and a servo is applied by using the ratio. At a focus servo drawing time, by a controller 17, the value of a denominator in the divider 15 is fixed to a prescribed value, influence by a pseudo focus error signal due to the optical disk surface is reduced, and focus servo drawing is per formed stably.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a recording / reproducing type optical disk device.

[0002]

2. Description of the Related Art In recent years, recording type optical discs such as magneto-optical discs and phase change type optical discs have been actively researched. In such a recordable optical disc, generally, data is recorded at the time of recording by irradiating a light beam having an intensity several times higher than that at the time of reproduction and changing the property of the recording layer.

Further, in the case of recording / reproducing information on a magneto-optical disk or a phase change type optical disk, a focus servo for accurately focusing on a recording layer or a reflective layer in the disk and a light spot for following a track. Tracking servo is essential. In many cases, the error signals necessary for these servos are obtained by irradiating an optical disk with a light beam and receiving the reflected light with a plurality of light receiving elements, and adding or subtracting the output of each light receiving element. . For example, in the generation of the focus error signal by the astigmatism method described in “Optical Disc Technology” Morio Onoue, Radio Technology Co., Ltd., pages 83 to 85, astigmatism is generated in the optical path as shown in FIG. The optical component 61 to be generated is placed and the error signal is obtained as follows. Each of the light receiving elements a, b, c, and d constituting the four-division photodetector 62 receives light and outputs an electric signal according to the amount of light. Adder 6
Reference numerals 3 and 64 denote light receiving elements b and d, and a and c on diagonal lines, respectively.
Then, the focus error signal FE1 (hereinafter referred to as the FE1 signal) is obtained by adding the outputs of the above and subtracting by the subtractor 65. Further, the adder 66 includes the light receiving elements a, b,
The outputs c and d are added together, and the total reflection light amount signal RF (hereinafter, referred to as RF signal) received by the four-division detector 62 is obtained.
Is obtained. In the case of an optical disc in which data is recorded by changing the amount of reflected light, such as a phase change type optical disc, the data is reproduced from this signal.

However, in the case of a recordable optical disk, the intensity of the reflected light changes at the same time because the intensity of the light beam applied to the optical disk at the time of recording is different from that at the time of reproducing, and the magnitude of the error signal changes at the time of recording and reproducing. In some cases, the servo may be lost when switching from recording to reproduction or switching from reproduction to recording. In order to solve this, in the conventional optical disk device, in addition to the focus error signal and the tracking error signal, a signal indicating an average total reflected light amount is generated, and the error signal is divided by the total reflected light amount signal to perform irradiation. An error signal that does not depend on the intensity of the light beam is generated, and this is used to perform focus servo and tracking servo.

A conventional optical disk device will be described below with reference to the drawings. FIG. 5 is a block diagram of a servo loop of a focus servo of a conventional optical disc device. In FIG. 5, 51 is a recordable optical disc,
For example, data recording is performed by irradiating a light beam stronger than during reproduction such as magneto-optical type or phase change type during recording to change the state of the recording layer. An optical head 52 has a focus actuator 521 that moves the objective lens up and down, and a light receiving portion 522 that receives reflected light from the optical disc 51. The light receiving section 522 is provided with the above-mentioned four-division photodetector and adder / subtractor, and outputs the FE1 signal and the RF signal according to the reflected light beam. In the case of a phase change type optical disc, the RF signal is sent to the reproduction circuit 53 as it is, and the data recorded on the optical disc 51 such as music data is reproduced.

The RF signal enters the low pass filter 54 in addition to the reproduction circuit 53, and only low frequency components are extracted.
This signal is called an AS signal. It can be considered that the AS signal indicates the average value of the reflected light from the optical disc 51, which is obtained by removing the noise having a high frequency component such as the disturbance of the reflected light amount due to the scratch from the RF signal. Now, the FE1 signal from the light receiving unit 522 and the AS signal described above enter the divider 55, and are subjected to calculation using the FE1 signal as the numerator and the AS signal as the denominator, and output. Hereinafter, this calculation result will be referred to as an FE2 signal. The drive circuit 56 inputs the FE2 signal and drives the focus actuator 521 so that the FE2 signal becomes zero.

Here, the output of each photodetector of the four-division photodetector during reproduction is a, b, c, d, the value of the FE1 signal is FE1, the value of the AS signal is AS, and the value of the FE2 signal is the value of the FE2 signal. FE
Assuming 2, these relationships are as follows.

[0008]

[Equation 1]

[0009]

[Equation 2]

[0010]

[Equation 3]

On the other hand, if the output of the light beam at the time of recording is set to G times that at the time of reproducing (G> 1), FE1,
AS1 and FE2 are as follows, respectively.

[0012]

[Equation 4]

[0013]

[Equation 5]

[0014]

[Equation 6]

From (Equation 3) and (Equation 6), it can be seen that the value of FE2 does not change even if the output intensity of the light beam changes. Therefore, by applying servo using the FE2 signal as an error signal, it is possible to prevent the servo from becoming unstable due to a change in the intensity of the irradiation light beam during recording and reproduction.

[0016]

In the above-mentioned conventional optical disk device, the error signal is normalized by the total reflected light amount to eliminate the influence of the change in the emitted light amount of the error signal, and the intensity of the recording and reproducing light beams. Although the instability of the servo due to the change of was eliminated, there were the following problems when the focus servo was pulled in.

FIG. 7 is a graph of the FE1 signal, the AS signal and the FE2 signal with the horizontal axis representing the distance between the objective lens and the optical disk. The pulling of the focus servo is usually performed by causing the laser diode to emit light, moving the lens away from the optical disc once, and moving the lens closer to the lens, and detecting a change in the focus error signal due to reflection of the recording layer, a so-called S-shaped curve 71. This is shown in Figure 7.
It is (a). However, in reality, the light beam is reflected not only on the recording layer but also on the disk surface, and a pseudo S-shaped curve 72 is detected. Normally, the reflectivity of the disk surface is sufficiently smaller than the reflectivity of the recording layer, and this pseudo S-shaped curve 72 does not cause any problem, but division by the AS signal has an adverse effect. That is, when the objective lens is approached from a distance and the distance at which the S-shaped curve 72 due to the disk surface appears, an AS signal corresponding to the reflectance of the disk surface appears as shown in FIG. 7B. In such a situation, if the normalization by the AS signal is performed, as shown in FIG. 7C, the pseudo S-shaped curve 73 due to the surface of the disc is formed.
Then, the level of the normal S-curve 74 due to the recording layer becomes the same, and there is a situation in which the focus servo is erroneously pulled into the disk surface. This is the above (Equation 6)
It is also clear from. The present invention focuses on this point and eliminates the influence of the pseudo S-time curve 72 due to the disk surface while having the advantage of the division described in the conventional example.

[0018]

According to the present invention, a first focus error signal output from an error signal generating means and a total reflection light amount signal output from a total reflection light amount calculating means are input, and a first focus error signal is input during focus servo pull-in. The focus error signal of 1 is divided by a fixed value and the result is output as a second focus error signal. After the focus servo is pulled in, the first focus error signal is divided by the total reflection light amount signal, and the result Is a second focus error signal, and an optical disk device provided with a control means for controlling the controlled object based on the second focus error signal.

[0019]

By providing the above means, the present invention prevents the focus servo pull-in failure due to the reflection of the disk surface at the time of pulling in the focus servo, and after the focus servo pull-in, changes the irradiation light beam intensity of the error signal. Dependency can be eliminated, and focus servo or tracking servo can be stably applied regardless of recording and reproduction.

[0020]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A first embodiment will be described below with reference to the drawings.

FIG. 1 is a block diagram of the first embodiment of the present invention. Reference numeral 11 denotes a recording type optical disk such as a magneto-optical type or a phase change type. The optical head 12 irradiates the optical disc 11 with a light beam, and the light beam reflected by the optical disc 11 is received by the light receiving section 122 of the optical head 12. In the light receiving section 122, the optical disc 1 is received based on the received light.
1 and the FE1 signal (focus error signal) corresponding to the distance between the objective lens of the focus actuator 121 and the RF signal indicating the total sum of the light reflected by the optical disk 11. The RF signal enters the reproduction circuit 13 and the low-pass filter 14, and the AS signal which is a low-frequency component is extracted. Both the FE1 signal and the AS signal described above enter the divider 15, where FE1 is the numerator and AS is the denominator, and a focus error signal FE2 that is not affected by the change in the amount of reflected light is obtained. In normal focus servo, the FE2 signal is used as an error signal, and the loop filter 16 generates a drive signal that reduces the FE2 signal and supplies the drive signal to the focus actuator 121.

When the focus is pulled in, the controller 17 operates according to the flowchart shown in FIG. First, in step 21, the denominator of the divider 15 is fixed to a predetermined value. This value is sufficiently larger than the size of the S-shaped curve 72 formed by the surface of the disc, and is sufficiently compressed, so that the value is too large compared to the size of the S-shaped curve 71 formed by the recording layer, and is set to a value that is not too small. . When the denominator is fixed, the process proceeds to step 22, and the drive signal supplied to the focus actuator 121 is supplied to the triangular wave generation circuit 1
With the output of 8, the S-curve is detected with the servo loop open. In step 23, it is determined whether or not the focus can be pulled in, and if it is possible, the process proceeds to step 24. The state in which focus can be pulled in refers to a state in which the servo cannot be disengaged even if the servo loop is closed. Specifically, it is near the 0 cross point of the S-shaped curve and the slope of the S-shaped curve is not so large. Refers to the state. Now, when the focus pull-in is enabled and the process proceeds to step 24, the focus actuator 12
The drive signal supplied to 1 is switched to the output from the loop filter 16, and the process proceeds to step 25, where the denominator of the divider 15 is switched to the dynamic value of the AS signal. Here, either step 24 or step 25 may be performed first. This completes the focus pull-in operation.
The focus servo loop operates using the FE2 signal which is the quotient of the S signal and the FE1 signal.

As described above, according to this embodiment, by setting the denominator of the divider 15 to a fixed value when pulling in the focus, it is possible to eliminate the adverse effect of the false S-curve due to the reflection on the disk surface. Thus, the focus pull-in operation can be completed stably.

In the above-described embodiment, the predetermined value used for fixing the denominator in step 21 is preferably the predicted AS signal when the focus servo is on. This value can be calculated in advance from the intensity of the light beam at the time of focus pull-in (usually the intensity for reproduction, which is predetermined) and the reflectance of the optical disk 11 used. The magnitude of the AS signal can be estimated by the following formula.

[0025]

[Equation 7]

Where k is a constant, P is the intensity of the light beam,
R is the reflectance of the optical disc when the recording surface is focused. By fixing the denominator to the predicted value of the AS signal, the fluctuation of the calculation result FE2 when the denominator is switched to the AS signal in step 25 can be kept small, and the deviation of the focus servo can be prevented.

Next, a second embodiment of the present invention will be described with reference to the drawings. In the first embodiment described above,
By setting the denominator of the divider to a fixed value when pulling in the focus, it was possible to prevent the focus servo from being pulled into the disk surface. As described above, the fixed value at this time is preferably the value of the AS signal when the focus servo is turned on, which is calculated from the reflectance of the optical disc and the intensity of the irradiation light beam. The reflectance of an optical disk recorded / reproduced by a reproducing apparatus is not constant, and almost always takes a different value depending on the material of the recording layer, the wavelength of the light beam, and the like. For example, in some types of magneto-optical discs, the reflectivity is greater than 15% and 25
It is said that it is necessary to consider that the variation is less than%, and the variation with wavelength is about ± 30%. In such a situation, if the denominator of the divider at the time of pulling in the focus is set to a fixed value, the size of the focus error signal FE2 after division will vary from optical disc to optical disc. There is a risk that the amplitude is too small to perform focus pull-in, and in some cases, the amplitude of the S-shaped curve is too large to make pull-in unstable. In the second embodiment, attention is paid to this point, and while having the advantage described in the first embodiment, it is intended to follow the variation of the reflectance of each disk and to reliably pull in the focus. is there.

FIG. 3 is a block diagram of an optical disk device according to the second embodiment of the present invention. Reference numeral 31 is a recording type optical disk such as a magneto-optical or phase change type. Reference numeral 32 is an optical head having a focus actuator 321 for moving the objective lens up and down and a light receiving portion for receiving the reflected light from the optical disc 31. With the focus servo already applied, the light beam reflected from the optical disc 31 is received by the light receiving unit 322. The light receiving section 322 incorporates the focus error detection circuit shown in the conventional example, and generates and outputs the focus error signal FE1 and the total reflection light amount signal RF. In the case of a disc in which data is recorded depending on the amount of light reflected from the disc, such as a phase change type, the RF signal is directly input to the reproduction circuit 33, demodulated, and output as music data or computer program data. It Also, the RF signal is transmitted through the low pass filter 3
4, the AS signal which is a low frequency component is extracted. A
Both the S signal and the FE1 signal enter the divider 35, where AS
Division is performed using the signal as the denominator and the FE1 signal as the numerator.
The FE2 signal that is the result of this division is the loop filter 36.
to go into. The loop filter 36 uses the FE2 signal as an error signal, and supplies a drive signal such that this value approaches 0 to the focus actuator 321. As described above, by adopting the above-described configuration, the servo loop operates stably even if the intensity of the light beam applied to the optical disc 31 changes.

Now, when the focus servo is pulled in, the controller 37 controls the optical disk device based on the flowchart shown in FIG. First, as in the first embodiment, the denominator of the divider 35 is fixed at a predetermined value (step 41), and the signal supplied to the focus actuator 321 is switched to the output signal from the triangular wave generation circuit 38 (step 42). . In this case, the predetermined value is preferably a predicted value of the AS signal when the focus servo is turned on, which is calculated from the average reflectance of the optical disc used and the intensity of the light beam to be irradiated. By driving the focus actuator 321 with the output signal from the triangular wave generation circuit 38, the objective lens moves up and down, and an S-shaped curve appears in the FE2 signal. An amplitude measuring circuit 39 measures the amplitude of the FE2 signal, and the measurement result is sent to the controller 37.
The controller 37 inputs the amplitude data of the FE2 signal, which is the measurement result from the amplitude measuring circuit 39, and adjusts the value of the denominator of the divider 35 so that the maximum amplitude becomes a predetermined value (step 43). . This predetermined value is a number uniquely determined by the method of generating the FE1 signal or AS signal, the circuit configuration of the servo loop, and the like. For example, in the circuit configuration shown in FIG. 3, the maximum positive value is "1" from (Equation 8), the maximum negative value is "-1" from (Equation 9), and the maximum amplitude is "2".

[0030]

[Equation 8]

[0031]

[Equation 9]

The size of the denominator is set by calculation from the amplitude data, or by taking a value from a list of amplitude data and denominator values that is provided in advance. Now, when the value of the denominator is decided, the controller 37
Observes the FE2 signal and determines whether or not the focus servo pull-in is possible (step 44). The state in which the focus servo can be pulled in has been described in the first embodiment, and is omitted here. When the focus servo pull-in is enabled, the signal supplied to the focus actuator 321 is switched to the output from the loop filter 36 to close the servo loop (step 4).
5). Then, the denominator of the divider 35 is the dynamic signal A
Switching to the S signal (step 46), the focus servo pull-in operation is completed.

As described above, according to this embodiment, the divider 3
5 is provided with an amplitude measuring circuit 39 for measuring the amplitude of the FE2 signal, which is used when the focus servo is pulled in.
By adjusting the value of the denominator of the divider 35 so that the amplitude of the two signals becomes a predetermined value, it is possible to eliminate the focus servo pull-in defect due to the difference in reflectance of the optical disc.

In the second embodiment, the controller 37
Adjusts the maximum amplitude of the FE2 signal, but it is also possible to obtain a positive maximum value or a negative maximum value and adjust the value to a predetermined value.

[0035]

As described above, according to the present invention,
The first focus error signal output from the error signal generation unit and the total reflection light amount signal output from the total reflection light amount calculation unit are input, and the first focus error signal is input when the focus servo is pulled in.
The focus error signal of is divided by a fixed value and the result is output as a second focus error signal. After the focus servo is pulled in, the first focus error signal is divided by the total reflection light amount signal, and the result is By providing a calculation means for outputting as a second focus error signal and a control means for controlling a controlled object based on the second focus error signal, recording and reproduction can be performed in a servo-on state. The difference in the intensity of the light beam at that time does not affect the focus error signal, and stable recording and reproduction can be performed.Furthermore, at the time of pulling in the focus servo, the part corresponding to the denominator of the divider that is the calculating means is set. By setting the value to a fixed value, the influence of reflection on the disk surface can be eliminated and the focus servo can be pulled in stably. As the fixed value at this time, it is desirable to use a predicted value of the AS signal calculated from the intensity of the light beam applied to the optical disc when pulling in the focus servo and the assumed reflectance of the optical disc.

Also, in the focus servo pull-in, the amplitude of the FE2 signal which is the output of the divider which is the calculating means is monitored, and the denominator of the divider is adjusted based on this value, so that the optical discs having different reflectivities are obtained. However, in each case, the focus servo can be pulled in stably, and the practical effects are large.

[Brief description of drawings]

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

FIG. 2 is a flowchart for explaining a focus servo pull-in operation of the first embodiment.

FIG. 3 is a block diagram showing a configuration of an optical disc device according to a second embodiment of the present invention.

FIG. 4 is a flowchart for explaining a focus servo pull-in operation of the second embodiment.

FIG. 5 is a block diagram showing a configuration of a conventional optical disc device.

FIG. 6 is a block diagram showing a configuration of a light receiving portion of an optical head in the conventional example.

FIG. 7 is a waveform diagram showing signal waveforms of various parts of the conventional example.

[Explanation of symbols]

 11,31 Optical head 12,32 Optical head 121,321 Focus actuator 122,322 Light receiving part 14,34 Low-pass filter 15,35 Divider 16,36 Loop filter 17,37 Controller 18,38 Triangular wave generating circuit 39 Amplitude Measuring circuit

Claims (3)

[Claims] 1. A pickup which irradiates an optical disc with a light beam, receives reflected light from the optical disc by a plurality of light receiving elements, converts the electric signal into an electric signal according to the amount of received light, and outputs the electric signal. Error signal generating means for performing addition or subtraction to generate and output a first focus error signal; total reflection light amount calculation means for performing addition of electric signals from the pickup and generating and outputting a total reflection light amount signal; 1 focus error signal and the total reflection light amount signal are input, the first focus error signal is divided by a fixed value when the focus servo pull-in is performed, and the result is output as a second focus error signal. After the focus servo pull-in, the first focus error signal is output. Calculation of dividing the focus error signal of No. 1 by the total reflection light amount signal and outputting the result as the second focus error signal An optical disc apparatus comprising: a control unit and a control unit that controls a control target based on the second focus error signal. 2. The optical disk device according to claim 1, wherein the fixed value is a predicted value of the total reflection light amount signal calculated from the reflectance of the optical disk to be used and the intensity of the light beam emitted when the focus servo is pulled in. 3. A pickup which irradiates an optical disc with a light beam, receives reflected light from the optical disc by a plurality of light receiving elements, converts the electric signal into electric signals corresponding to the respective amounts of received light, and outputs the electric signals. Focus error signal generation means for performing addition or subtraction to generate and output a first focus error signal; total reflection light amount calculation means for performing addition of an electric signal from the pickup to generate and output a total reflection light amount signal; An arithmetic means for inputting a first focus error signal and the total reflection light amount signal, performing a division process, and outputting as a second focus error signal; and an amplitude measuring means for measuring the amplitude of the second focus error signal. And a control means for controlling the controlled object based on the second focus error signal, and the amplitude when the focus servo is pulled in. The arithmetic means is controlled so that the amplitude data output from the measuring means becomes a predetermined value, and the arithmetic means is controlled so as to divide the first focus error signal by the total reflection light amount signal after the focus servo is pulled in. An optical disk device including a system controller.