JP2001067686A - Optical disk device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To surely detect the defocusing of an objective lens. SOLUTION: When a period when the value of a sum signal SUM indicating a reflected total light quantity to be outputted from an optical pickup becomes lower than a prescribed threshold by comparing the value of the sum signal SUM with the prescribed threshold continues for a prescribed threshold period, a focusing servo is stopped by judging that the focus of an objective lens is deviated from a magneto-optical disk. The threshold is set between a detected peak vaiue and a detected bottom value by detecting the peak value and the bottom value of the sum signal SUM which is to be generated when the objective lens is moved in its optical axis direction by gradually lowering a driving signal DV.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical disk device, and more particularly, to an optical disk device capable of detecting out-of-focus of an objective lens.

[0002]

2. Description of the Related Art In an optical disk apparatus for recording a signal on an optical disk or reproducing a signal from the optical disk, the optical disk is irradiated with laser light using an optical pickup, and reflected light from the optical disk is detected. The optical pickup has an objective lens for focusing a laser beam on the optical disk, and this objective lens is amplitude-controlled in the optical axis direction by focus servo control so that the focus follows the signal surface of the optical disk.

[0003]

However, when a large external impact is applied or a large scratch is formed on the optical disk, the focus of the objective lens may be largely deviated from the optical disk. If the focus is slightly deviated, the focus returns to the optical disk by the focus servo control, but if the focus deviates greatly, the focus no longer returns to the optical disk. If this is left unchecked, the focus servo actuator will continue to move the objective lens in the direction of the optical axis and shake it off to either side, and accurate focus servo control cannot be performed.

An object of the present invention is to provide an optical disk device capable of performing accurate focus servo control.

[0005]

An optical disc apparatus according to the present invention includes an objective lens, an optical sensor, a focus error signal generating means, a focus servo control means, a sum signal generating means, and a defocus detecting means. . The objective lens focuses the laser light on the optical disc. The optical sensor is divided into a plurality of areas, and detects light reflected from the optical disc in each area. The focus error signal generating means calculates a signal output from each area of the optical sensor to generate a focus error signal. The focus servo control means performs focus servo control of the objective lens in response to the focus error signal. The sum signal generation means includes:
A signal output from each area of the optical sensor is added to generate a sum signal. The out-of-focus detecting means determines that the focus of the objective lens is out of the optical disk when the value of the sum signal is lower than a predetermined threshold.

In this optical disk device, focus servo control of the objective lens is performed in response to the focus error signal. However, when the focus of the objective lens is largely out of the optical disk, the level of the sum signal is greatly reduced. When the value of the sum signal is lower than a predetermined threshold value, it is determined that the focus of the objective lens has deviated from the optical disk.

Preferably, the optical disk apparatus further includes servo control stopping means for stopping the focus servo control when the out-of-focus detecting means determines that the focus of the objective lens is out of the optical disk.

In this optical disk device, when it is determined that the focus of the objective lens has deviated from the optical disk, the focus servo control is stopped. Therefore, there is no possibility that the objective lens keeps moving on the optical axis and shakes off to any one side.

Preferably, the optical disk apparatus further detects a peak value and a bottom value of a focus error signal generated when the objective lens is moved in the optical axis direction, and detects the detected peak value and bottom value. And learning means for setting a threshold value between.

In this optical disk apparatus, the objective lens is continuously moved in the direction of the optical axis, the peak value and the bottom value of the focus error signal generated at this time are detected, and the detected peak value and bottom value are detected. The above threshold value is set between. Therefore, an appropriate threshold value is automatically set according to each optical disc.

Preferably, the out-of-focus detecting means includes a value comparing means, a time measuring means, and a period comparing means. The value comparing means compares the value of the sum signal with a threshold value.
The timer measures a period during which the value of the sum signal is lower than the threshold according to the comparison result by the value comparator. The period comparison unit compares the period measured by the time measurement unit with a predetermined threshold period.

In this optical disk device, a period during which the value of the sum signal is lower than the threshold value is measured, and the measured period is compared with a predetermined threshold period. Thus, when the measured period exceeds a predetermined threshold period, it is determined that the focus of the objective lens has deviated from the optical disk.
Therefore, even if the value of the sum signal instantaneously falls below the threshold value, the focus of the objective lens is not determined to be out of the optical disk, and the out-of-focus state is not erroneously detected.

[0013]

Embodiments of the present invention will be described below in detail with reference to the drawings. In the drawings, the same or corresponding portions have the same reference characters allotted, and description thereof will not be repeated.

Referring to FIG. 1, this optical disk apparatus comprises:
An optical pickup 12 irradiates a magneto-optical disk 10 such as an AS-MO (Advanced Storage Magneto Optics) with a laser beam to record and reproduce signals.
, Amplifiers 14 and 16, A / D converters 18 and 20,
It includes a DSP (Digital Signal Processor) 22, a D / A converter 24, and a driver 26.

The optical pickup 12 irradiates a laser beam onto the magneto-optical disk 10, detects reflected light from the magneto-optical disk 10, and outputs reproduced signals such as a sum signal SUM and a focus error signal FE, which will be described in detail later. . Amplifier 14
Amplifies the sum signal SUM output from the optical pickup 12. The A / D converter 18 digitizes the analog sum signal SUM output from the amplifier 14. The amplifier 16 amplifies the focus error signal FE output from the optical pickup 12. The A / D converter 20 outputs the analog focus error signal F output from the amplifier 16.
Digitize E.

The DSP 22 modulates a recording signal and demodulates a reproduction signal, and also performs focus servo control, tracking servo control, thread servo control, spindle servo control, and the like. In the focus servo control, the objective lens (128 in FIG. 2) in the optical pickup 12 is caused to swing in the optical axis direction so that the laser beam is always focused on the signal surface of the magneto-optical disk 10. In the tracking servo control, the laser light is
The objective lens is made to oscillate in the radial direction of the magneto-optical disk 10 so as to always follow the upper track. The thread servo control is to move the optical pickup 12 (objective lens) in the radial direction of the magneto-optical disk 10 by a feed mechanism such as a linear motor in order to move the laser light to a desired track on the magneto-optical disk 10 at high speed. is there. In the spindle servo control, the magneto-optical disk 10 is rotated at a predetermined speed by a spindle motor.

For focus servo control, a DSP 2
2 outputs a digital drive signal DV for driving the objective lens in response to the digital focus error signal FE output from the A / D converter 20. When the level of the digital sum signal SUM output from the A / D converter 18 becomes lower than a predetermined level, the DSP 22 determines that the focus of the objective lens has deviated from the signal surface of the magneto-optical disk 10 and performs focus servo control. Stop control.

The D / A converter 24 converts the digital drive signal DV output from the DSP 22 into an analog signal. This D
Instead of the / A converter 24, PWM (Puls) that performs focus servo control according to the duty ratio of the drive signal DV
e Width Modulation) circuit may be used. Driver 2
6 increases the drive capability of the analog drive signal DV output from the D / A converter 24.

Referring to FIG. 2, optical pickup 12 includes
A semiconductor laser 120, a diffraction grating 122 that separates laser light emitted from the semiconductor laser 120 into three, a collimator lens 124 that parallelizes the laser light from the diffraction grating 122, a beam splitter 126, and a beam splitter 126 An objective lens 128 for focusing the transmitted laser light on the signal surface of the magneto-optical disk 10. The beam splitter 126 transmits 80% of the P-polarized laser light emitted from the semiconductor laser 120 and parallel to the plane of the drawing, and reflects the remaining 20%. Beam splitter 126 also
The reflected light from the magneto-optical disk 10 is reflected.

The optical sensor 130 monitors the laser light emitted from the semiconductor laser 120, and the power of the semiconductor laser 120 is controlled in response to an output signal from the sensor 130. The condenser lens 132 is provided for the semiconductor laser 1
The laser light emitted from 20 and reflected by the beam splitter 126 is focused on the optical sensor 130. Optical sensor 13
Numeral 4 is for detecting the reflected light from the magneto-optical disk 10, and various reproduction signals are generated in response to the output signal from the optical sensor 134. Wollaston prism 136
Separates the laser light reflected on the magneto-optical disk 10 and further reflected by the beam splitter 126 into a P-polarized component and an S-polarized component. The condenser lens 138 focuses the laser light from the Wollaston prism 136 on the optical sensor 134.

The optical pickup 12 further moves the objective lens 128 so that the focal point of the objective lens 128 is always located on the signal surface of the magneto-optical disk 10 in response to the drive signal DV output from the driver 26 in FIG. A focus servo actuator 140 for making the amplitude in the optical axis direction is included.

Referring to FIG. 3, lands 100 and grooves 102 are formed on magneto-optical disk 10. A magneto-optical recording film is formed on both the land 100 and the groove 102, and the land 100 and the groove 102 form a track of the magneto-optical disk 10. The tracks are formed spirally or concentrically on the magneto-optical disk 10. Land 100
In the groove 102, a large number of fine clock marks 104 and 106 are formed at regular intervals. Fine clock mark 104 is land 100
The fine clock mark 106 is formed by a land-shaped discontinuous region formed in the groove 102. The fine clock mark 106 is formed by a groove-shaped discontinuous region formed therein.

Since the optical pickup 12 employs the three-beam system as described above, the main beam spot MB and the two sub-beam spots SB are formed on the magneto-optical disk 10.
1 and SB2 are formed. In FIG. 3, the main beam spot MB is formed on the groove 102.

Referring to FIG. 4, optical sensor 134 is arranged to receive reflected light from main beam spot MB1 and to receive reflected light from sub-beam spot SB1. A sub sensor 1342,
And a sub sensor 1344 arranged to receive the reflected light from the sub beam spot SB2. Here, the main sensor 1340 has four regions 1340A, 1340B, and 134.
0C and 1340D. The area 1340A receives the reflected light of the main beam spot MB from the area A, the area 1340B receives the reflected light from the area B, and
0C receives the reflected light from area C, and area 1340D receives the reflected light from area D.

Referring to FIG. 5, optical pickup 12 further includes regions 1340A and 1340 of main sensor 1340.
B, output signals A, B from 1340C, 1340D,
It includes a sum signal generation circuit 141 that adds C and D to generate a sum signal SUM, and a focus error signal generation circuit 147 that calculates the output signals A, B, C, and D to generate a focus error signal FE. . Sum signal generation circuit 141
Includes adders 142, 144, and 146. The focus error signal generation circuit 147 includes adders 148 and 150 and a subtractor 152. The adder 142 is connected to the main sensor 1
The output signal A from the area 1340A of 340 and the area 134
And the output signal B from 0B. The adder 144
The output signal C from the area 1340C and the output signal D from the area 1340D are added. The adder 146 is the adder 1
The sum signal SUM (= A + B + C +) is obtained by adding the output signal A + B from the F.42 and the output signal C + D from the adder 144.
D) is obtained. Adder 148 adds output signal A from area 1340A and output signal C from area 1340C. Adder 150 provides output signal B from region 1340B.
And the output signal D from the area 1340D. The subtracter 152 subtracts the output signal B + D from the adder 150 from the output signal A + C from the adder 148 to obtain a focus error signal FE (= (A + C) − (B +) which is a difference signal.
D)) is obtained.

The optical pickup 12 further includes a sub sensor 1
342, 1344 are output from DPP (Differenti
al Push Pull) method and includes a circuit (not shown) that generates a tracking error signal.

Next, the operation of the optical disk device will be described. The DSP 22 operates according to the program shown in FIG. That is, first, in step S1, the drive signal DV for driving the focus servo actuator 140 is decremented as shown in FIG.

Subsequently, at step S2, the A / D converter 18
Is taken in.

Subsequently, in step S3, the value of the obtained sum signal SUM is compared with a peak value previously written in the memory. In this memory, the value of the ground voltage which is the lowest value is previously written as the initial value of the peak value.

As a result of the comparison in step S3, the sum signal S
If the value of UM is higher than the peak value stored in the memory, the value of the sum signal SUM is overwritten in the memory as a new peak value in step S4. Conversely, if the value of UM is low, such overwriting is not performed. In these steps S3 and S4, the peak value of the sum signal SUM can be detected.

Subsequently, in step S5, the value of the sum signal SUM fetched in step S2 is compared with a bottom value previously written in the memory. In this memory, the value of the power supply voltage which is the highest value is previously written as the initial value of the bottom value.

As a result of the comparison in step S5, the sum signal S
If the value of UM is lower than the bottom value stored in the memory, the value of the sum signal SUM is overwritten in the memory as a new bottom value in step S6, and if it is higher, such overwriting is not performed. In steps S5 and S6, the bottom value of sum signal SUM can be detected.

When the value of the drive signal DV is gradually reduced in step S 1, when the focus of the objective lens 128 passes through the signal surface of the magneto-optical disk 10, a substantially S-shaped focus error signal FE is generated by the optical pickup 12. Output from Zero-cross point Z of this focus error signal FE
C is the focal point. On the other hand, while the sum signal SUM has a bottom value while largely deviating from the focal point, it rises as it approaches the focal point and reaches a peak value at the focal point.

Referring again to FIG. 6, in step S7, it is determined whether or not the value of drive signal DV has reached the lowest point. When the value of the drive signal DV has not reached the lowest point, the operations of the above steps S1 to S6 are repeated, and when the value of the drive signal DV has reached the lowest point, the process proceeds to the next step S8. Therefore, the DSP 22 can detect the peak value and the bottom value of the focus error signal FE generated when the objective lens 128 is continuously moved in the optical axis direction.

Subsequently, in step S8, a threshold value of the sum signal SUM which is out of focus is calculated according to the following equation.

Threshold value = bottom value + α (peak value−bottom value) where 0 <α <1, preferably 0.4 <α <
0.6, and more preferably α = 0.5.

Then, in step S9, the focus servo control is turned on. After completing the focus search operation as described above, the DSP 22 operates according to the program shown in FIG. That is, first, in step S10,
Calculate parameters required for phase compensation of focus servo control.

Subsequently, in step S11, parameters required for phase compensation of tracking servo control are calculated.

Subsequently, in step S12, a parameter necessary for phase compensation of thread servo control is calculated, or in step S13, a parameter required for phase compensation of spindle servo control is calculated. To detect.

The routine shown in FIG. 8 is repeatedly performed, of which steps S12 to S14 are performed only once every 16 times.

Next, the details of step S14 for detecting out-of-focus will be described with reference to FIG.

First, in step S141, the A / D converter 1
8 is taken in.

Subsequently, in step S142, the value of the obtained sum signal SUM is compared with the threshold value preset in step S8. While the focal point of the objective lens 128 is located at or very close to the signal surface of the magneto-optical disk 10, the value of the sum signal SUM is almost at the peak value as shown in FIG. High. In this case, the timer (for example, the value of the memory area prepared as the timer area) is cleared in step S143.

On the other hand, when the focal point of the objective lens 128 deviates significantly from the signal surface of the optical disk 10, the value of the sum signal SUM greatly decreases as shown in FIG. Sum signal SUM
Is smaller than the threshold value, the timer is incremented by one in step S144.

Subsequently, in step S145, the period measured by the timer is compared with a predetermined threshold period (for example, 30 milliseconds or more).

If the period measured by the timer exceeds the threshold period, all the servo controls including the focus servo control are stopped in step S146. If the period measured by the timer does not exceed the threshold period, this step is performed. S
Skip 146.

Therefore, when the value of sum signal SUM becomes lower than the threshold value and the state continues for a predetermined threshold period, all servo controls are stopped.

As described above, according to this embodiment, the value of sum signal SUM is compared with a predetermined threshold value,
Since it is determined whether or not the value of M is lower than the threshold value, it is possible to detect that the focus of the objective lens 128 has largely deviated from the signal surface of the magneto-optical disk 10.

Further, when such out-of-focus is detected, all the servo controls including the focus servo control are stopped, so that the focus servo actuator 140 does not shake the objective lens 128 to one side. Absent.

The peak value and the bottom value of the sum signal SUM generated when the objective lens 128 is continuously moved in the direction of the optical axis are detected in advance, and the sum of the detected peak value and the bottom value is calculated. Since the threshold value appropriate for each magneto-optical disk 10 is obtained by learning so that the threshold value is set in advance, the out-of-focus state is reliably detected, for example, in a magneto-optical disk with many scratches or a magneto-optical disk with few scratches. be able to.

When the period during which the value of the sum signal SUM becomes lower than the threshold value continues for a predetermined threshold period, it is determined that the focus of the objective lens 128 has deviated from the signal surface of the magneto-optical disk 10. Therefore, when the value of the sum signal SUM becomes momentarily low, an out-of-focus state is not erroneously detected.

It should be understood that the embodiments disclosed this time are illustrative in all aspects and not restrictive. The scope of the present invention is defined by the terms of the claims, rather than the description above, and is intended to include any modifications within the scope and meaning equivalent to the terms of the claims.

[0053]

According to the present invention, when the value of the sum signal is lower than the predetermined threshold value, it is determined that the focus of the objective lens has deviated from the optical disk, so that the defocus can be reliably detected. As a result, accurate focus servo control can be performed.

[Brief description of the drawings]

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

FIG. 2 is a diagram illustrating a configuration of an optical pickup in FIG. 1;

FIG. 3 is a plan view showing the structure of the magneto-optical disk shown in FIGS. 1 and 2 together with a beam spot.

FIG. 4 is a plan view showing the structure of an optical sensor for detecting reflected light from the magneto-optical disk in FIG.

FIG. 5 is a circuit diagram showing a configuration of a sum signal generation circuit and a focus error signal generation circuit included in the optical pickup in FIG. 1;

FIG. 6 is a flowchart showing a focus search operation by the DSP in FIG. 1;

FIG. 7 shows drive signals when the optical disc apparatus shown in FIG. 1 performs a focus search operation and a normal operation;
6 is a timing chart showing waveforms of a focus error signal and a sum signal.

FIG. 8 is a flowchart showing a normal operation by the DSP in FIG. 1;

FIG. 9 is a flowchart showing details of a step of detecting out-of-focus in FIG. 8;

[Explanation of symbols]

10 magneto-optical disk, 12 optical pickup, 22
DSP, 128 objective lens, 134 optical sensor, 13
40 main sensor, 1340A, 1340B, 1340
C, 1340D area, 141 sum signal generation circuit, 14
7 Focus error signal generation circuit.

Claims (4)

[Claims] 1. An optical disk device for recording and / or reproducing signals by irradiating an optical disk with a laser beam, comprising: an objective lens for focusing the laser beam on the optical disk; An optical sensor that detects reflected light from the optical disc in each area; a focus error signal generating unit that calculates a signal output from each area of the optical sensor to generate a focus error signal; and responds to the focus error signal. A focus servo control means for performing focus servo control of the objective lens; a sum signal generation means for adding a signal output from each region of the optical sensor to generate a sum signal; Out-of-focus detecting means for determining that the focus of the objective lens has deviated from the optical disk when the focus is lower than the threshold value of Optical disk device. 2. The optical disk device according to claim 1, further comprising: a servo control stop unit that stops the focus servo control when the out-of-focus detection unit determines that the focus of the objective lens is out of the optical disk. Optical disk device. 3. The optical disk device further detects a peak value and a bottom value of a focus error signal generated when the objective lens is moved in the optical axis direction, and detects the detected peak value and bottom value. The optical disk device according to claim 1, further comprising a learning unit that sets the threshold value between the optical disk device and the optical disk device. 4. An out-of-focus detecting means, comprising: a value comparing means for comparing a value of the sum signal with the threshold value; and a value of the sum signal being lower than the threshold value according to a comparison result by the value comparing means. Time measuring means for measuring the period during which the time is also low, comparing the period measured by the time measuring means with a predetermined threshold period, and when the measured period exceeds the threshold period, the focus of the objective lens is The optical disk device according to claim 1, further comprising a period comparison unit that determines that the optical disk has deviated from the optical disk.