JPH08147722A - Optical disk device with focus bias means - Google Patents

Abstract

PURPOSE: To provide a focus servo device which allows focus bias to be constantly adjusted at an optimum value and is reduced in cost with simple constitution. CONSTITUTION: The optical disk device 10 performs focus servo by applying focus bias VFB from a focus bias generating circuit 18 to a focus error signal. It is provided with an extracting means 20 which extracts the traverse level of a tracking error signal while varying focus bias when the tracking servo is off, an arithmetic circuit 22 which obtains focus bias corresponding to the maximal value of the traverse level extracted by this extracting means, and a control means 23 which controls the focus bias generating circuit so as to give the focus bias obtained by this arithmetic circuit.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a focus error signal from a focus bias generation circuit for recording and / or reproducing an optical disc used in a compact disc, a magneto-optical disc, or a data storage using these. The present invention relates to an optical disk device provided with a focus bias unit, which is adapted to perform focus servo by applying a focus bias.

[0002]

2. Description of the Related Art Conventionally, the following servo has been performed in such an optical disk device. That is, for example, a light beam from a light source is applied to the surface of the optical disc, and a returning light beam from the optical disc is received by the photodetector. The focus error signal and the tracking error signal are detected based on the outputs of the divided focus sensor units of the photodetector. Further, the focus error signal and the tracking error signal are given to the focus servo circuit and the tracking servo circuit, respectively, so that the focus servo and the tracking servo are performed.

Such an optical disk device is shown in FIG.
It is configured as shown in FIG. In FIG. 4, the optical disc device 1 receives a tracking error signal and a focus error signal, which are obtained based on the light amount difference between the optical pickup 2 and each light receiving portion of the photodetector of the optical pickup 2, via amplifiers 3 and 4, respectively. It has a tracking servo circuit 5 and a focus servo circuit 6.

Further, the optical disk device 1 drives and controls the actuator of the optical pickup 2 based on the servo signal from the tracking servo circuit 5 to move the objective lens in the tracking direction, and the focus servo. Based on the servo signal from the circuit 6, the actuator of the optical pickup 2 is drive-controlled to move the objective lens in the focus direction, and the focus driver 8 outputs a focus error signal output from the amplifier 4. An adding circuit 9a for applying the focus bias from the bias generating circuit 9a is provided.

The optical pickup 2 has a known structure, and an objective lens (not shown) movably supported in two axial directions is supplied to a tracking coil and a focusing coil provided in an actuator. As a result, the objective lens is driven and controlled in the biaxial directions, that is, the tracking direction and the focusing direction.

The tracking servo circuit 5 receives the tracking error signal from the optical pickup 2 after being amplified by the amplifier 3 and is inputted to the driver 7 so as to reduce the tracking error based on the tracking error signal. , Outputs a tracking control signal.

The focus servo circuit 6 receives the focus error signal from the optical pickup 2 after being amplified by the amplifier 4, and inputs it to the driver 8 so as to reduce the focus error based on the focus error signal. , And outputs the focus control signal.

The driver 7 is a tracking servo circuit 5
The actuator of the optical pickup 2 is driven based on the tracking control signal from (1) to move the objective lens in the tracking direction so that the tracking error is reduced.

The driver 8 drives the actuator of the optical pickup 2 based on the focus control signal from the focus servo circuit 6 to move the objective lens in the focusing direction so that the focus error is reduced.

Here, since the minimum point of the focus error signal may not coincide with the minimum jitter point of the reproduction signal, the focus bias from the focus bias generation circuit 9 is applied to the focus error signal. As a result, the minimum point of the focus error signal and the minimum jitter point of the reproduction signal are made to coincide.

In the optical disc device 1 having such a configuration, the focus bias is adjusted as follows. At the time of assembling the optical disk device 1, focusing is performed in a state where the focus servo is on, and the value of the jitter is monitored while observing the RF signal from the optical pickup 2, and the adjusting volume 9b provided in the focus bias generation circuit 9 is provided. The optimum focus bias is determined for each optical disk device 1 by manually operating.

[0012]

However, in the optical disk device having such a structure, the tact time required for determining the focus bias becomes long, and the adjustment volume 9b is required. There was a problem that would be high.

Further, at the time of recording / reproducing of the optical disk, if the material of the optical disk is different, the refractive index with respect to the incident light beam is different, and the incident light amount of the return light beam with respect to the photodetector may change. Furthermore, if the ambient temperature changes, the position of the objective lens may be displaced due to the temperature change. Therefore, there is a problem that it is difficult to always adjust the focus bias to the optimum value when reproducing the optical disc.

In view of the above points, an object of the present invention is to provide a focus servo device having a simple structure in which the focus bias is always adjusted to an optimum value and the cost can be reduced. There is.

[0015]

According to the present invention, a return light beam from an optical disk is received by a photodetector, and a focus error signal is generated based on the output of each of the divided sensor portions of the photodetector. A focus servo device for an optical pickup, which detects and applies a focus bias to the focus error signal by a focus bias generation circuit to perform focus servo, wherein the focus bias is changed while tracking servo is turned off. Extraction means for extracting the traverse level of the tracking error signal calculated based on the output of each sensor section, an arithmetic circuit for obtaining a focus bias corresponding to the maximum value of the traverse level extracted by the extraction means, and this arithmetic circuit Obtained by And control means for controlling the focus bias generating circuit so that the focus bias was, by the optical disc apparatus having a focus bias means having, is achieved.

Here, the traverse level means the peak-to-peak value of the traverse signal based on the tracking signal obtained when the optical pickup moves across the track of the optical disc.

Preferably, the extracting means is a high pass filter for extracting the AC component of the input tracking error signal.

Further, according to the present invention, the arithmetic circuit has a traverse level based on an AC component of the tracking error signal extracted by the high pass filter,
The focus bias may be determined based on a reference voltage corresponding to the reference level obtained by the reference voltage generating circuit.

Further preferably, the arithmetic circuit compares the traverse level with the reference level slightly lower than the maximum value of the traverse level, and detects the traverse level of one traverse level substantially matching the reference level. Obtaining the value, the value of this traverse level and the average value of the values of any traverse level higher than the reference level, the focus bias corresponding to this average value, the focus bias that gives the maximum value of the traverse level It may be configured to do so.

Further, preferably, the arithmetic circuit compares the traverse level with the reference level slightly lower than the maximum value of the traverse level, and two traverse levels in which the traverse level substantially coincides with the reference level. May be obtained, and the focus bias corresponding to the average value of these two traverse level values may be set as the focus bias that gives the maximum value of the traverse level.

According to the above construction, when the tracking servo is off, the extracting means extracts the traverse level from the tracking error signal, and the arithmetic circuit obtains the focus bias corresponding to the maximum value of the traverse level. The control means controls the focus bias generation circuit so that
As a result, the focus bias is adjusted,
The minimum point of the focus error signal and the best point of the jitter will be matched. That is, since the jitter of the reproduction signal becomes the smallest at the maximum value of the traverse level, the focus bias corresponding to the maximum value of the traverse level or a value corresponding thereto is obtained.

When the extracting means is a high-pass filter for extracting the AC component of the input tracking error signal, the traverse level is extracted from the tracking error signal with a simple structure.

The above-mentioned arithmetic circuit compares the reference level slightly lower than the maximum value of the traverse level with this traverse level to obtain the value of one or two traverse levels at which the traverse level matches the reference level, When the focus bias corresponding to the average value of the traverse level of this one value and any other value or a value of 2 or more is set as the focus bias that gives the maximum value of the traverse level, the above average value is approximated. Since it is processed as the focus bias that gives the maximum value of the traverse level, it is not necessary to obtain the maximum value of the traverse level, and the focus bias that gives the maximum value of the traverse level can be obtained with a simple circuit configuration. .

[0024]

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, preferred embodiments of the present invention will be described in detail with reference to FIGS.
Since the embodiments described below are preferred specific examples of the present invention, various technically preferable limitations are attached, but the scope of the present invention particularly limits the present invention in the following description. Unless otherwise stated, the present invention is not limited to these modes.

FIG. 1 shows a preferred embodiment of an optical disk device incorporating a focus servo device according to the present invention. In FIG. 1, the optical disc device 10 receives an optical pickup 11 and a tracking error signal and a focus error signal, which are obtained on the basis of the light amount difference between the respective photodetectors of the photodetector of the optical pickup 11, via amplifiers 12 and 13, respectively. The tracking servo circuit 14 and the focus servo circuit 15 are provided.

Further, the optical disc device 10 drives and controls the actuator of the optical pickup 11 based on the servo signal from the tracking servo circuit 14 to move the objective lens in the tracking direction, and the focus servo. Based on a servo signal from the circuit 15, a focus driver 17 that drives and controls an actuator of the optical pickup 11 to move the objective lens in the focus direction, and a focus error signal output from the amplifier 13 is focused. An adding circuit 19 for applying the focus bias from the bias generating circuit 18 is provided.

The optical pickup 11 has a known structure and supplies an objective lens (not shown) movably supported in two axial directions to the tracking coil and the focusing coil provided in the actuator. As a result, the objective lens is driven and controlled in the biaxial directions, that is, the tracking direction and the focusing direction.

The tracking servo circuit 14 receives the tracking error signal from the optical pickup 11 after being amplified and input by the amplifier 12, and based on the tracking error signal, causes the driver 16 to reduce the tracking error. Output tracking control signal.

The focus servo circuit 15 outputs the focus error signal from the optical pickup 11 to the amplifier 13
Then, a focus control signal is output to the driver 17 so as to reduce the focus error based on the focus error signal.

The driver 16 drives the actuator of the optical pickup 11 based on the tracking control signal from the tracking servo circuit 14 to move the objective lens in the tracking direction (radial direction of the disc) so that the tracking error is reduced. To move.

The driver 17 is the focus servo circuit 1
Based on the focus control signal from 5, the actuator of the optical pickup 11 is driven to move the objective lens in the focusing direction (optical axis direction) so that the focus error is reduced.

The focus bias generation circuit 18 applies a focus bias VFB to the focus error signal so as to match the minimum point of the focus error signal and the best point of the jitter when they do not match.
Generate.

Further, the optical disk device 10 includes the amplifier 1
The high-pass filter 20 to which the tracking error signal from 2 is input, the comparator 22 that compares the signal from the high-pass filter 20 with the reference value from the reference voltage generation circuit 21, and the output signal from the comparator 22. On the basis of,
The mechanical control computer 23 for changing the focus bias from the focus bias generation circuit 18 is included.

The high-pass filter 20 is a filter that allows signals of a predetermined frequency or higher to pass therethrough, and extracts the AC component from the tracking error signal and takes its peak-to-peak value to output the traverse level VTE.

The reference voltage generating circuit 21 outputs the reference voltage VREF adjusted to a predetermined voltage.
This reference voltage VREF is determined from the range of jitter that is practically allowable in obtaining the reproduction signal.

The comparator 22 uses the traverse level VT.
E and the reference voltage VREF are compared, and the traverse level V
When TE is higher than the reference voltage VREF, for example, an H level signal is output, and when the traverse level VTE is equal to or lower than the reference voltage VREF, an L level signal is output.

The mechanical control computer 23 controls the focus bias generation circuit 18 to set the focus bias VFB to -n by the voltage difference Vd.
It is adapted to change from Vd to + nVd (n is an integer). As a result, the focus bias VFB
Is

[Equation 1] (K is an integer). Here, the focus bias VFB is changed by changing k from -n to + n.
Changes stepwise from -nVD to + nVD. It should be noted that the values of -n to n are selected within a range in which the focus servo does not fail when the corresponding focus bias is applied to the focus servo circuit 15 via the focus bias generation circuit.

By the way, when the focus bias VFB changes in this way, the maximum value VTEM of the tracking error signal, that is, the traverse level and the reference voltage V.
The relationship with REF is classified into three cases as shown in each graph of FIG. In these graphs, the vertical axis represents the voltage value and the horizontal axis represents the focus bias value. 1. The maximum value VTEM is always higher than the reference voltage VREF (FIG. 2 (a)). 2. The maximum value VTEM becomes smaller than the reference voltage VREF when the focus bias VFB is low, and becomes larger than the reference voltage VREF midway, and the focus bias VF
When B is high, it becomes lower than the reference voltage VREF (see FIG. 2).
(B)). 3. The maximum value VTEM is smaller than the reference voltage VREF when the focus bias VFB is low, and becomes larger than the reference voltage VREF midway (FIG. 2C).

Based on this, the adjustment of the focus bias in the optical disk device 10 is performed, for example, as follows in accordance with the flowchart of FIG. That is, FIG.
First, in step 1, the focus servo is turned on and the tracking servo is turned off (ST
1). Then, in step 2, the mechanical control computer 23 controls the focus bias generation circuit 18 to give the focus bias VFB k.
Substituting an integer from -n for the value of (ST2), then go to step 3.

In this step 3, the comparator 22
Compares the value of the traverse level VTEM corresponding to the value of k determined by ST2 with the reference voltage VREF given from the reference voltage generation circuit 21, and determines whether the traverse level VTEM is higher than the reference voltage VREF. . If an affirmative result is obtained, the process proceeds to step ST4, in which 1 is sequentially added to the value of k until k becomes n (ST
5) Repeat the comparison in ST3. by this,
When the traverse level VTEM is higher than the reference voltage VREF over the entire range of the value of k from -n to n, the mechanical control computer 23 determines that it is the case of FIG. Level V
In response to the maximum value of TEM, the focus bias generation circuit 18 is instructed to set the focus bias VFB to 0 (zero).

Further, the mechanical control computer 23
However, if a negative result is obtained in step 3, the value of k is 1
Are added (ST7), and the comparator 2 is sequentially operated until k becomes n.
It is determined whether the output of 2 becomes H level (ST8,
9). In step 9, if the traverse level VTEM is lower than the reference voltage VREF in the range of k from -n to n, an error occurs because it does not belong to any case of FIG. 2 (ST10). On the other hand, when ST8 obtains a positive result in the process of sequentially adding the integers to k, the value of k at this time is set as l, and the value of k at this time is set in the memory incorporated in the mechanical control computer 23, for example. Is stored (ST11), and the value of k is further increased by 1 (ST)
12).

Next, the mechanical control computer 2
3 determines whether the output of the comparator 22 is inverted to L (ST13). When a negative result is obtained, the process proceeds to ST14, the value of k is incremented by 1, and ST1 is increased until k becomes n.
Repeat judgment 3 above. In this process, when a positive result is obtained in ST13, that is, when the traverse level VTEM becomes lower than the reference voltage VREF, it is determined that it is the case of (b) of FIG. 2, and the value of k at this time is determined. Minus 1 to m
Is stored in a memory built in the mechanical control computer 23 (ST17).

In this case, as shown in FIG. 2B, since the curve representing the traverse level VTEM shows a parabola convex upward, the traverse level VTEM and the reference voltage VREF are shown. The average value of the value of l and the value of m, which are points at which and substantially match, is calculated. As a result, the mechanical control computer 23 can select the maximum value of the curve of the traverse level VTEM or a portion corresponding thereto. Therefore, a focus bias corresponding to the average value of l and m is given to the focus bias generating circuit 18 (ST18). Here, 1 is subtracted from m when the curve representing the traverse level VTEM and the reference voltage VREF intersect by 1 is defined by k, which is one less than the value m, and the corresponding traverse level VTE.
This is because M always becomes higher than the reference voltage VREF.

On the other hand, if the traverse level VTEM is higher than the reference voltage VREF even if the value of k is increased sequentially in the process of steps 13 to 15 and k becomes n, the mechanical control computer 23 causes the mechanical control computer 23 to operate as shown in FIG. It is determined that it is the case of c). In this case, traverse level VTEM
, The traverse level VTEM is always higher than the reference voltage level VREF even when the value of l is exceeded and k is sequentially increased. Therefore, the mechanical control computer 23
The value of n larger than l is selected, and the average value of l and n is regarded as the maximum value of the traverse level VTEM, and this l
A focus bias corresponding to the average value of the values n and n is given to the focus bias generation circuit 18 (ST16).

In the above description, the traverse level VT
The value of k when EM becomes larger than the reference voltage VREF is set to 1, and the traverse level VTEM is set to the reference voltage VR.
The value of k when it is smaller than EF is (m + 1). That is, in the flowchart of FIG. 3, step 7
From step 1 to step 11, l is obtained, and from step 12 to step 17, m is obtained. By doing so, the maximum value of the traverse level or a value corresponding thereto can be easily obtained, and the focus bias that minimizes the jitter can be obtained based on this value.

As described above, in the above-described embodiment, when the tracking servo is off, the extracting means extracts the traverse level from the tracking error signal, and the arithmetic circuit obtains the focus bias corresponding to the maximum value of the traverse level. Then, the control means controls the focus bias generation circuit so that the focus bias is obtained. As a result, the focus bias is adjusted so that the minimum point of the focus error signal and the best point of the jitter coincide with each other.

Therefore, the focus bias is adjusted at any time when the tracking servo is off, so that the focus bias is adjusted not only when the optical disk device is assembled but also when it is in use. Thus, it is possible to adjust the focus bias at the start of recording / reproducing of the optical disc, so that even if the material of the optical disc is different, the optimum focus bias is adjusted for each optical disc. Even if the ambient temperature changes, the focus bias is adjusted, so that the focus bias is always adjusted to the optimum value.

Further, since the focus bias is adjusted by the control circuit, the conventional adjusting potentiometer is not required, so that the cost of parts can be reduced. When the extraction means is a high-pass filter that extracts the AC component of the input tracking error signal, the traverse level is extracted from the tracking error signal with a simple configuration.
Therefore, the cost is reduced.

[0049]

As described above, according to the present invention, there is provided an optical disk device having a focus bias means which has a simple structure and is capable of reducing the cost so that the focus bias is always adjusted to an optimum value. Will be done.

[Brief description of drawings]

FIG. 1 is a block diagram showing an embodiment of an optical disc device incorporating a focus servo device according to the present invention.

2 is a flowchart illustrating an operation of determining a focus bias in the focus servo apparatus of FIG.

3 is a graph showing a relationship between a focus bias and a traverse level in the focus servo apparatus of FIG.

FIG. 4 is a block diagram showing an example of a conventional optical disc device.

[Explanation of symbols]

 10 Optical Disk Device 11 Optical Pickup 12 Amplifier 13 Amplifier 14 Tracking Servo Circuit 15 Focus Servo Circuit 16 Driver 17 Driver 18 Focus Bias Generating Circuit 19 Adder Circuit 20 High Pass Filter 21 Reference Voltage Generating Circuit 22 Comparator 23 Mechanical Control Computer

Claims (5)

[Claims] 1. A return light beam from an optical disc is received by a photodetector, a focus error signal is detected based on the output of each of the divided sensor parts of the photodetector, and a focus bias signal is focused by the focus bias signal generation circuit. Add a bias,
A focus servo device for an optical pickup, which is configured to perform focus servo, and extracts a traverse level of a tracking error signal calculated based on the output of each sensor unit while changing the focus bias when the tracking servo is off. Extracting means, an arithmetic circuit for obtaining the focus bias corresponding to the maximum value of the traverse level extracted by the extracting means, and a control means for controlling the focus bias generating circuit so as to obtain the focus bias obtained by the arithmetic circuit. An optical disk device provided with a focus bias unit having: 2. The optical disk device according to claim 1, wherein the extraction means is a high-pass filter that extracts an AC component of an input tracking error signal. 3. The focus circuit based on a traverse level based on an AC component of a tracking error signal extracted by the high pass filter and a reference voltage corresponding to a reference level obtained by a reference voltage generation circuit, by the arithmetic circuit. The optical disk device according to claim 1, wherein the bias is determined. 4. The arithmetic circuit compares the reference level slightly lower than the maximum value of the traverse level with this traverse level to obtain a value of one traverse level at which the traverse level substantially matches the reference level. Get,
The value of this traverse level and the average value of any traverse level higher than the reference level are obtained, and the focus bias corresponding to this average value is determined as the focus bias that gives the maximum value of the traverse level. The optical disk device according to claim 1, wherein: 5. The arithmetic circuit compares the traverse level with the reference level slightly lower than the maximum value of the traverse level, and determines the values of two traverse levels at which the traverse level substantially coincides with the reference level. Got
2. The optical disk device according to claim 1, wherein the focus bias corresponding to the average value of the two traverse level values is determined as the focus bias that gives the maximum value of the traverse level.