JPH0434734A - Focus servo fault detector - Google Patents

Abstract

PURPOSE:To prevent mis-detection such as the production of a secondary zero cross point in a fault detection signal resulting in detection of a focal point by comparing a total sum of electric signals generated from plural designated split photodetector faces with a preset reference value and discriminating it as a focus servo error when the total sum is less than the reference value. CONSTITUTION:A sum voltage V1+V2 being a focus servo error detection signal has a flat area near a focus, the sum voltage rises once when a point is parted from the focal position and reaches again another flat area and then the level is gradually decreased in the waveform. Then a reference voltage VR being a criterion of a focus servo error is set in a way that the sum voltage V1+V2 and the reference voltage VR cross with each other at a distance from the focal point closer to the secondary zero cross point of a focus error signal voltage VFES. Thus, only the focus point is included in a range of the area B between two points Pa and Pb and the secondary zero cross point exists in a range C1 discriminated to be a focus servo error, then the zero cross point is not discriminated to be a focal point and mis-detection is prevented.

Description

Detailed Description of the Invention (Industrial Application Field) The present invention relates to an optical information recording/reproducing device for optically recording or reproducing information on an optical information recording carrier, and particularly relates to an optical information recording/reproducing device. The present invention relates to a focus servo abnormality detection device that detects servo abnormality.

(Prior Art) Conventionally, as an optical information recording carrier, there is, for example, a card-shaped recording carrier (hereinafter referred to as an optical card) disclosed in Japanese Utility Model Application No. 63-145669 filed by the applicant. The structure of an example of this optical card is shown in FIG.

This optical card 1 has storage areas of a predetermined width called tracks 2 arranged in parallel in a plurality of stages in the longitudinal direction on the main surface. In the center of this track 2, a data section 4 in which bits for recording data are formed is arranged.
Seek sections 3a and 3b are arranged at both ends thereof. Further, track numbers are recorded in the seek sections 3a and 3b, respectively, so that data can be easily searched. Here, the longitudinal direction of the optical card 1 is defined as the track direction, and the direction perpendicular to this is defined as the theta direction.

This optical card 1 records data by irradiating the track 2 with a light beam such as a laser. When reading out the data, the data is read out by irradiating a light beam and converting the presence or absence and strength of the reflected light into electrical signals.

Next, FIG. 'iB6 shows the area A surrounded by the dotted line shown in FIG. 5, and the structure of the track 2 will be explained.

The track 2 is divided into a seek section 3a and a data section 4. The data section 4 includes a clock pattern 6 recorded in advance in the center of the clock/servo line 5;
5A data of 8 bits each (total 16 bits) on both sides
Data bits 5A-1 to 5A that can store
-18 is placed.

Next, FIG. 7 is a block diagram showing the configuration of an optical information recording/reproducing apparatus for recording or reproducing data on the optical card 1, and the configuration will be explained.

First, the optical pickup 8 that records or reads data from the optical card 1 polarizes a light beam generated from a light source 10 such as a semiconductor laser driven by a light source drive circuit 9 so that it becomes parallel using a collimator lens 11. After passing through the polarizing beam splitter 12, the light is focused by the objective lens 13 and irradiated onto the recording surface of the optical card 1 to physically change the recording surface and form bits, thereby recording information on the recording surface. Record.

Furthermore, when reading the information recorded on the optical card 1,
The reflected light from the recording surface is sent to the polarizing beam splitter 1.
2 and detected by a photodetector 14.

The light detected here is converted into an electrical signal and sent to the demodulation circuit 15 as a detection signal. The demodulation circuit 15 outputs the input detection signal as a read signal 16a which is a recording/reproduction signal and a clock signal 16b which is a reference timing for reading information from the optical card 1.

Further, the aforementioned detection signal is input to the demodulation circuit 15, and is also sent to a tracking control system and a focus control system, and is used for tracking control and focus control, respectively.

In the tracking control system, first, the detection signal from the photodetector 14 is input to a tracking error signal (hereinafter referred to as TES) detection circuit 17, and the TES detection circuit 17 outputs a tracking error signal 18. Next, the tracking error signal 18 is passed through a phase compensation circuit 19 to compensate for its phase, and then inputted to a drive circuit 21 via an analog switch 20.

Based on the phase-compensated tracking error signal 18, the drive circuit 21 uses a tracking coil 22 provided in the optical pickup 8 to adjust the objective lens 13 within the linear range of the tracking error signal 18.
is driven in the seek direction to correct the irradiation position of the light beam so that it irradiates along the track 2 when the optical card 1 is driven in the track direction. The on/off operation of the analog switch 20 is controlled by a control circuit 23.

In this way, the tracking control system performs auto-tracking control to correct the deviation between the recording/reproducing position of the optical pickup 8 and the track 2 of the optical card 1.

In the focus control system, first, the photodetector 1
4 to the focus error signal (hereinafter referred to as FES) detection circuit 24, and the FES detection circuit 2
4 outputs a focus error signal 25. Next, the focus error signal 25 is sent to the phase compensation circuit 26, and after compensating the phase, the control circuit 23 turns on/off the focus error signal 25.
Power is applied to the drive circuit 28 via the analog switch 27 whose OFF operation is controlled.

Based on the focus error signal 25, the drive circuit 28 moves the objective lens 13 to the optical card 1 using a focus coil 29 provided in the optical pickup 8.
It is driven back and forth in a direction perpendicular to the surface to focus on the recording surface of the optical card 1.

The optical card 1 and the optical pickup 8 are driven by a guard motor 30 and a seek motor 31 which are controlled by the control circuit 23.

Here, an example of the configuration of the photodetector 14 is shown in FIG. The detection surface 14a of the photodetector 14 has the track 2 described above.
16 data reading light-receiving cells 5B-1 to 5B-18 are formed so that 16 pieces of data in the theta direction can be read simultaneously. Pattern 6 (not shown)
1 for receiving the image of and generating the clock signal 16b.
0 clock signal generation light receiving cells 51-1 to 51-
10 is formed. In addition, on the detection surface 14a, there are four pairs of servo light receiving cells 52- which are spaced apart and opposed to each other in the seek direction.
1 to 52-4, and 53-1 to 53-4 are formed.

Electrical signals extracted from these cells serve as detection signals.

FIG. 9 shows a diagram in which the track 2 shown in FIG. 6 and the detection surface 14a of FIG. 8 are superimposed and corresponded to each other. Here, the reference numbers in the drawings are the same as those in FIG. 6.8, and the explanation thereof will be omitted.

That is, in the detection signals of the servo light receiving cells 53-1 to 53-4, the theta direction is detected by comparing the signals detected from the servo light receiving cells on both sides of the clock pattern 6 in the seek direction. positional deviation is detected. In addition, servo light receiving cells 53-1 to 53
-4. In the detection signals 52-1 to 52-4, the vertical positional deviation with respect to the optical card 1 is determined by comparing the signal values detected from the servo light receiving cells on both sides of the clock pattern 6 in the track direction. Detected.

There is no positional deviation of these, and the clock signal 16b
When the data bits 5A-1 to 5A-18 of the data section 4 are synchronized with each other, the photodetector 14
The desired information is read out.

Further, a dotted circle 32a indicates the position of the maximum value of the illuminance distribution when the distance between the optical card 1 and the objective lens 13, which will be described later, is at the in-focus position.

FIG. 10 shows the illuminance distribution on the detection surface 14a of the photodetector 14 when a light emitting diode (hereinafter referred to as LED) is used as the light source 10. In other words, due to the spherical aberration caused by the spherical lens inside the LED 10, an image (illuminance distribution) having two protruding parts is formed on the surface of the optical card and is projected onto the detection surface 14g.

Illuminance distribution 32a1 when the distance between the optical card 1 and the objective lens 13 is at the in-focus position 32a1 Illuminance distribution 50 μm away from the in-focus position 32b1 Illuminance distribution 32 50 μm closer than the in-focus position
Let it be c. At this time, the corresponding servo light receiving cell 52-1
52-4 and 53-1 to 53-4 are arranged as shown.

The outputs of the servo light receiving cells 52-1 to 52-4 are converted into voltages and are used as detection voltages VCI to VC4, and the outputs of the servo light receiving cells 53-1 to 53-4 are converted into voltages. When the detection voltages are VDI to VD4, G -X, VC-G (VC1+ VC2+ VC3
+ VC4)...(1), I VD -VDl+ VD2+ VD3+ VD4
...(2) becomes.

Focus error signal (FES) from equations (1) and (2)
25 FES voltage V FES is VFES-G・ΣVC
-ΣVD (G is a constant)...(3).

Next, FIG. 11 shows the FES voltage V FES with respect to the distance between the optical card 1 and the objective lens 13. Here the above (
3) The voltage is the FES voltage VFES, the voltage G-Σ in the above (1)
VC to FES voltage V FESa, (2) l' pressure IV
Let D be the FES voltage VFESb. As shown in this figure, the FES voltage V FES has a secondary zero-crossing point at the same potential as the focal point that is the reference for focus servo.

In addition, the focus control system is, for example,
In some cases, a focus servo abnormality detection device configured as shown in FIG. 12 for detecting a focus servo abnormality as disclosed in No. 7 is provided. Here, the focus servo abnormality means that the focus servo goes from normal operation to abnormal operation due to dust, scratches, defects, etc. on the optical card l, or disturbances such as vibrations. In order to detect this abnormal operation, a focus servo abnormality detection device was provided.

In other words, the focus servo abnormality detection signal is detected by a low-pass filter (hereinafter referred to as LPF) 33 connected to take in the drive current of the focus coil 29 output from the drive circuit 28 of the focus control system described above, and detects the DC component. do. Two comparators 34a are provided at the output end of the LPF 3B.

34b are connected at one end. A first reference voltage VR)I is applied to the other end of the comparator 34Jl,
[2 reference voltage VRL is applied to the other end of the comparator 34b. Comparison of these: 834g.

34b, the DC component is a second reference voltage VRH.
Abnormality detection signal 3 when exceeding the range up to the reference voltage VRL
5 to the control circuit 23 to notify that the focus servo is abnormal.

(Problem to be Solved by the Invention) However, in the conventional optical information recording and reproducing device described above, when there is a secondary zero-crossing point in the focus error signal voltage V FES, the secondary zero-crossing point is mistakenly regarded as the focal point. When detected, the focus servo may be pulled in incorrectly. Therefore, the secondary zero-crossing point is determined to be the focal point, and it is impossible for the focus servo abnormality detection device to determine whether or not there is a focus servo abnormality.

Furthermore, the focus servo abnormality detection device requires an LPF 3B with a large time constant in order to capture the DC component of the drive current flowing through the focus coil 29. Therefore, a long delay occurs in order to detect the DC component, resulting in a long detection time, resulting in poor responsiveness and failure to follow the situation. However, in an attempt to shorten the detection time, the time constant of the LPF 33 was reduced (then the detection sensitivity became too sensitive, resulting in erroneous detection even though the focus servo was operating normally).

Therefore, the present invention prevents erroneous detection such as generation of a secondary zero cross point in the abnormality detection signal and detecting it as a focused point, and also enables accurate detection of abnormality of the focus servo in a short time, and prevents overcurrent in the focus coil. It is an object of the present invention to provide a focus servo abnormality detection device that prevents focus servo from drifting.

(Means for Solving the Problems) In order to achieve the above object, the present invention includes a focus servo means for irradiating a light beam onto an optical information recording carrier, and a response light of the light beam irradiated from the focus servo means. A photodetecting means having a plurality of divided light receiving surfaces that are converted into electrical signals, a focus error signal generating means that generates a focus error signal from the electric signal, and a plurality of specified divided light receiving surfaces of the light detecting means. A focus servo abnormality detection signal generation means that calculates the sum of each electric signal generated compares the sum value by the arithmetic processing means with a predetermined reference value set in advance, and determines that the sum value is less than or equal to the reference value. It is possible to provide a focus servo abnormality detection device having a determining means that determines that there is a focus servo abnormality when there is a focus servo abnormality.

(Function) The focus servo abnormality detection device configured as described above compares the reading ratio signal value detected from the photodetector with a predetermined reference value, and determines whether the readout signal value reaches a predetermined value. When it is determined that the value is larger than the reference value, a focus servo abnormality detection signal is sent to the control circuit to stop focus control, thereby preventing overcurrent from flowing through the focus coil.

(Example) Hereinafter, an example of the present invention will be described in detail with reference to the drawings.

FIG. 111 is a block diagram showing the configuration of a focus servo abnormality detection device according to an embodiment of the present invention. Here, the same reference numerals are given to the same members as in the conventional optical information recording/reproducing device, and detailed explanation thereof will be omitted.

In the configuration of this focus servo abnormality detection bag W36, first, clock signal generation light receiving cells 5I-1 to 51-10 are formed in the photodetector 14. These light receiving cells are odd numbered light receiving cells 51-1, 3.5, 7 .
9 and even numbered light receiving cells 51-2.4.6. Il.

10, and the respective output lines are internally connected to the output ends 37.10 of the odd-numbered light receiving cells. It is connected to the output end 38 of the even numbered light receiving cells.

The output terminal 37 is a current-voltage (hereinafter referred to as I-V)
It is connected to the conversion circuit 39, and the current If detected by the odd-numbered light receiving cells and subjected to photo-electrical conversion is connected to the 1-V conversion circuit 39.
It is output as a detection voltage ■1. Similarly, the output terminal 38 is connected to a 1-V conversion circuit 40, and the current 12 detected by the even-numbered light receiving cells and converted from light to electricity.
is outputted by the 1-V conversion circuit 40 as a detection voltage v2.

Further mentioned above! The respective output terminals of the -V conversion circuits 39 and 40 are connected to an adder circuit 41, and together with the
The respective output terminals of the conversion circuits 39 and 40 are connected to the subtraction circuit 4.
Connected to 2.

Therefore, the detection voltages Vl and V2 are supplied to an adding circuit 41 to calculate and output an added voltage (Vl + V2), and are also supplied to a subtracting circuit 42 to calculate a subtracted voltage (Vl - V2).
V2) is calculated and output.

The output end of the adder circuit 41 is connected to one end of the input end of the comparator circuit 43, and the other end is connected to a predetermined reference voltage VR.
is applied. Therefore, the comparison circuit 43 compares the added voltage (Vl + V2 > with the reference voltage VR, and when the added voltage (Vl + V2 ) exceeds the reference voltage VR, sends a focus servo abnormality detection signal to the control circuit 23. 44 is sent.

Next, the control circuit 23 determines that the focus servo is abnormal, and
A control signal 45 is sent to turn off the analog switch 27 to cut off input of the focus error signal 25 to the drive circuit 28. As a result, the focus error signal 25
Based on this, the focus coil 29 that drives the objective lens 13 back and forth is protected from overcurrent.

Also, the subtraction voltage Vl calculated and output from the subtraction circuit 42
-V2 is binarized as a clock signal and used as a synchronization signal for simultaneously reproducing 16-bit data recorded on the optical card 1.

Further, FIG. 2 is a block diagram showing the configuration of an optical information recording/reproducing apparatus having a focus servo abnormality detection device. Here, the main body of the optical information recording and reproducing apparatus of the present invention is similar to a conventional optical information recording and reproducing apparatus, and the added focus servo abnormality detection device of the present invention will be explained.
Other equivalent parts will be given the same reference numerals and detailed description thereof will be omitted.

This focus servo abnormality detection device is included in the demodulation circuit 15. This detection device 36 includes an optical pickup 8
It is connected so that a detection signal is input from the photodetector 14 in the control circuit, and when it is determined that there is an abnormality in the focus servo, an abnormality detection signal 44 is sent to the control circuit 23 and the analog switch 27 is turned off (non-conducting). Then, the input to the drive circuit 28 is cut off. As a result, the focus error signal 2
5, the focus coil 29 that drives the objective lens 13 back and forth is stopped to protect it from overcurrent.

Next, the operation of determining a focus servo abnormality by the focus servo abnormality detection device described above will be explained with reference to FIG.

The voltage is plotted on the vertical axis, and the focal length between the optical card 1 and the objective lens is plotted on the horizontal axis, and the conventional focus error signal voltage V
PES is shown as a dotted line.

Then, the additional voltage that becomes the focus servo abnormality detection signal (
2) has a flat region near the focal point, and as the distance from the focal point increases, the added voltage rises once more and has a flat region again, and then gradually decreases (waveform becomes.

Therefore, the reference voltage VR, which is the criterion for determining focus servo abnormality, is set at a distance from the in-focus position that is closer than the secondary zero cross point of the FES voltage V F'ES, and the additional voltage CVl + V2
') and the reference voltage VR so that the reference voltage VR intersects with the reference voltage VR.
Set.

With this setting, the area B between the two points Pa and Pb where the addition voltage (Vl + V2) and the reference voltage VR intersect is set as the range in which the focus servo normally operates, and the areas C1 and C2 outside area B are set as the range where the focus servo normally operates. The range in which the focus servo operates abnormally is detected by the focus servo abnormality detection device.

In particular, within the range of the region B, only the focused point is included, and 2
Since the secondary zero-crossing point is within the range C1 in which focus servo abnormality is determined, the secondary zero-crossing point is not determined as the in-focus point.

Further, FIG. 4 shows respective signal waveforms when the addition voltage (Vl +V2) and the reference voltage VR intersect at point pb and it is determined that the focus servo is abnormal.

When the focus servo abnormality starts, the clock signal (subtraction voltage Vl - V2
) 16b becomes out of synchronization with the clock pattern 6 of the optical card 1, and the amplitude of the clock signal 16b decreases. At the same time, since the amount of light received by each servo light-receiving cell changes, the voltage generated by one of the light-receiving cells increases, disrupting the equilibrium state, and the FES voltage VFES also temporarily increases and then decreases. Therefore, the added voltage (Vl +V2
) rises temporarily, then falls and the reference voltage VR
When the value is below, the focus servo abnormality detection device sends an abnormality detection signal 44 for focus servo abnormality detection to the control circuit 23. Then, the analog switch 27 is turned off by the control signal 45 of the control circuit 23, and the input to the drive circuit 28 is cut off.

The optical information recording/reproducing apparatus of this embodiment does not detect a focus servo abnormality at -degrees, but instead makes a determination as to whether or not there is a focus servo abnormality.
If the abnormality detection operation described above is repeated a plurality of times and the abnormality detection signal 44 for focus servo abnormality detection is still sent to the control circuit 23, it is determined that the focus servo is abnormal,
Stops the optical information recording and reproducing device and notifies the outside of the abnormality.
Take measures such as ejecting the optical card.

The focus servo abnormality detection device having the above configuration has two
Set the next zero cross point to focus servo abnormality range H,
By preventing erroneous detection such as detection as a focused point and cutting off input to the drive circuit, overcurrent is prevented from flowing through the focus coil.

Note that when the abnormality detection signal 44 is sent to the control circuit 23,
In the tracking control system as well, the analog switch 20 is turned off by the control circuit 23, the input of the tracking error signal 18 to the drive circuit 21 is cut off, and overcurrent is prevented from flowing through the tracking coil 22.

In addition, although the optical information recording carrier in the above-described embodiment is a card-shaped recording carrier, the present invention is not limited to this, and can be applied to compact discs, etc., without departing from the gist of the invention. Various modifications and applications are possible.

(Effects of the Invention) As described in detail above, according to the present invention, it is possible to prevent an abnormality detection signal that incorrectly detects a secondary zero cross point generated in a focus error signal as a focused point, and to achieve accurate focus servo control in a short time. Abnormality can be detected and overcurrent can be prevented from flowing through the focus coil and tracking coil.

[Brief explanation of the drawing]

FIG. 1 is a configuration diagram showing the configuration of an embodiment of a focus servo abnormality detection device according to an embodiment of the present invention, and FIG.
FIG. 3 is a block diagram showing the configuration of an optical information recording/reproducing device having the focus servo abnormality detection device shown in FIG.
The figure is a waveform diagram showing each signal waveform during focus servo abnormality determination, Figure 5 is a structural diagram showing the structure of an example of an optical card, Figure 6 is a structural diagram showing the structure of a track, and Figure 7 is a conventional optical card. FIG. 8 is a block diagram showing the structure of a conventional information recording and reproducing device, FIG. 9 is a block diagram showing the structure of a conventional photodetector, and FIG. 9 is a block diagram showing the structure of a conventional photodetector. FIG. 10 is a distribution diagram showing the illuminance distribution on the detection surface of a conventional photodetector. FIG. 11 is a waveform diagram showing the waveform of the focus error signal voltage with respect to the distance between the optical card and the objective lens. FIG. 12 is a configuration diagram showing the configuration of a conventional focus servo abnormality detection device. DESCRIPTION OF SYMBOLS 1... Optical card, 2... Track, 8... Optical pickup, 14... Photodetector, 15... Demodulation circuit,
19°26... Phase compensation circuit, 20.27... Analog switch, 21.28... Drive circuit, 23...
control circuit, 24... focus error signal detection circuit,
25... Focus error signal, 29... Focus coil, 44... Abnormality detection signal.

Claims (1)

[Scope of Claims] Focus servo means for controlling a light beam irradiated onto an optical information recording carrier into a focused state, and converting a response light of the light beam irradiated onto the optical information recording carrier into an electrical signal. A light detecting means having a plurality of divided light receiving surfaces, and a focus for calculating the sum of each electric signal generated from a specific plurality of divided light receiving surfaces within the plurality of divided light receiving surfaces of the light detecting means. A servo abnormality detection signal generating means compares the total value obtained by the arithmetic processing means with a predetermined reference value set in advance, and when the total value is less than the reference value, the focus servo means performs focusing. What is claimed is: 1. A focus servo abnormality detection device comprising: determination means for determining that a control state is abnormal.