JPH0370860B2 - - Google Patents

Description

[Detailed Description of the Invention] Industrial Application Field The present invention relates to an optical reproducing device for optically reading information recorded on a disc such as a video disc, or for optically recording and reproducing information on a disc. Regarding optical recording and reproducing devices,
In particular, when the disk is wobbling in the direction perpendicular to the rotation direction as the disk rotates, it is possible to always irradiate a minute spot light onto the disk.
This relates to focus control for tracking the optical system.

Conventional configurations and their problems In general, in video discs and optical recording and reproducing devices, in order to record and reproduce information at high density,
For example, the width of the track on the disk is 0.6 μm,
The pitch is 1.6 μm, making it a fine spiral or concentric circle shape. The disk is irradiated with a minute spot of light having a diameter of 1 μm or less, and the information on the disk is read from the reflected light. In such a device, when the disk causes surface wobbling in a direction perpendicular to the direction of rotation as the disk rotates, the minute spot light focused to φ1 μm or less can always be irradiated onto the disk in response to the surface wobbling. In order to make the optical system follow this, so-called focus control is applied (hereinafter referred to as focus servo). On the other hand, as the disk rotates, the track moves in the radial direction of the disk due to eccentricity, etc., but a tracking servo is required to make the optical system follow this so that the minute spot light always illuminates the track. It is.

Servo error signals for performing such focus servo and tracking servo are obtained from reflected light from the disk system, and a conventional example will be explained with reference to FIG. Note that the tracking control is not directly related to the present invention, and therefore will not be described in detail. 1 is a light source made of, for example, a semiconductor laser; 2 is a condenser lens that collects the light emitted from the semiconductor laser beam 1; and 3 is a polarizing beam splitter that bends the light emitted from the semiconductor laser beam 1 as shown in FIG. Te disk 6
lead upwards. Reference numeral 4 denotes a λ/4 plate, and 5 an aperture lens for concentrating the light into a minute spot light.The minute spot light is irradiated onto the disk 6, and only the recording and reproduction of signals is performed. The reflected light from the disk 6 passes through the λ/4 plate 4 again, its polarization direction is changed, and after passing through the polarizing beam splitter 3, it is condensed by a convex lens 7, split into two by a total reflection mirror 8, and one The light is guided to a photodetector 9 used for tracking control as shown in the figure. The photodetector 9 is divided into two parts as shown at 9a and 9b when viewed from the direction of light incidence. The other of the two divided lights is guided to a photodetector 10 placed approximately at the condensing position of the convex lens 7.

In the above optical system, the principle of obtaining a focus error signal for focus servo will be described with reference to FIG. FIG. 2 is a simplified diagram of FIG. 1 for explaining the method of obtaining a focus error signal, and the same components as in FIG. 1 are given the same reference numerals. In Figure 2, a
is when the aperture lens 5 and the disk 6 are too close to each other than the desired distance, b is exactly the desired distance, that is, when the incident light is focused on the disk surface, c
indicates the case where the distance is longer than the desired distance.

As shown in FIG. 2a, if the aperture lens 5 and the disk 6 are brought closer than the desired distance, the condensing position P ₁ of the reflected light focused by the convex lens 7 will be further away from the photodetector 10. Therefore, in this case, the amount of light received by the photodetector 10a
The amount of light received at point b is greater. On the other hand, as shown in FIG.
The amount of light received by the photodetector 10a is greater than the amount of light received by the photodetector 10a. Further, when the incident light on the disk 6 is focused as shown in FIG. 2b, the focused light is projected onto the photodetector 10 by the convex lens, so
The amount of light received by 0b becomes equal.

Therefore, by inputting the outputs of both photodetectors 10a and 10b to the differential amplifier circuit 11, an S-shaped focus error signal as shown in FIG. 3A can be obtained.
The focus error signal is supplied via the drive circuit 12 to the pick-up 13 that moves the aperture lens 5 up and down to drive it, and the photodetectors 10a, 10
Focus servo may be applied so that the amount of light received at b is equal. Fig. 3A shows the focus error signal in the optical system shown in Fig. 1, the vertical axis V _f shows the focus error signal, and the horizontal axis x shows the amount of focus deviation from the just focus position (Fig. 2 b). ing.

As mentioned above, the mounting position of the photodetector 10 is the target reference value of the focus servo, so if the mounting position deviates from the normal position, the target value of the focus servo will deviate, causing surface wobbling, etc. When the aperture is on the disk 6, control is performed so that the minute spot light is irradiated onto a location different from the actual aperture position on the disk 6. Now, if the amount of focal shift is x, the amount of shift of the photodetector 10 is y, the focal length of the aperture lens 5 is f ₁ and the focal length of the convex lens 7 is f ₂ , then y=1/2・f ₂ /f ₁・x...The relational expression (1) is obtained, for example, f ₁ = 4.54mm, f ₂ = 30mm
Then, equation (1) becomes y=3.3x...(2).

Even if the amount of defocus x is allowed up to ±1 μm, the amount of deviation of the photodetector 10 is ±3.3 μm from equation (2).
must be kept within. The positional deviation of the photodetector 10 from its normal position should be kept within the above ±3.3 μm, considering the position adjustment and locking of the photodetector 10, distortion of the optical bench (caused by secular change and temperature change), etc. That is extremely difficult.

Purpose of the Invention The present invention improves the above-mentioned drawbacks, and provides a focus control system with a detection means for obtaining a focus control error that remains stable even if its mounting position deviates from its normal position due to temperature fluctuations or vibrations. The purpose of this is to enable a focus servo to be applied.

Structure of the Invention In order to achieve the above object, the present invention provides a converting means for reproducing a signal from a signal track on a disk record carrier, and a converting means for keeping the relative position of the disk record carrier and the converting means constant. focus control means;
a peak hold means for holding the maximum value of the envelope of the reproduced signal obtained from the conversion means; an envelope detection means for the reproduced signal; and an output difference between the peak hold means and the envelope detection means exceeds a predetermined threshold. a detecting means for detecting the detection of the detected value and generating a detected output; and a detecting means for generating a detection output by detecting the detection means; and a focal position variable signal generating means for varying the relative position.

DESCRIPTION OF EMBODIMENTS Hereinafter, one embodiment of the present invention will be described based on the drawings.

In FIG. 4, the same parts as in FIG. 1 are given the same numbers, and detailed explanations are omitted. After the focus servo is applied in the same way as in the example shown in FIG. The mixed output signal is amplified by the amplifier circuit 42 and inputted to the video signal reproducing circuit 43 as well as the envelope detection circuit 4.
Enter 4. On the other hand, the output of the amplifier circuit 42 is also input to a peak hold circuit 45 . This peak hold circuit 45 only needs to hold the maximum value of the envelope of the reproduced signal, which is the output of the envelope detection circuit 44, for a relatively long period of time, and even if the hold voltage decreases due to discharge, there is no problem. The charging time constant of the envelope detection circuit 44 is set to an appropriate length in consideration of sudden changes in envelope voltage caused by the nozzle, etc., and the discharging time constant is set to be appropriately long compared to the charging time constant. A generally known circuit as shown in FIG. 5 can be used. The output of the peak hold circuit 45 and the output of the envelope detection circuit 44 are applied to a comparator 46. As shown in FIG. 6, the comparator 46 detects that when the output voltage V _P of the peak hold circuit 45 is outputting the envelope maximum value E _A , the output voltage V _e of the envelope detection circuit 44 is V _e
＞E _A −e ₀ When E _C and E _B become positive voltage V ₁ , V _e
When E _BO satisfies ≦E _A −e ₀ , the voltage becomes negative V ₂ . That is, when the comparator 46 is outputting the envelope maximum value E _A of the output voltage V _P of the peak hold circuit 45, the output voltage of the envelope detection circuit 44
Threshold voltage with an appropriate voltage difference from V _e
e less than ₀ (E _A −V _e <e ₀ ) or greater (E _A −
_{V e ≧} e ₀ This circuit determines whether the difference between E _A and V _e exceeds the threshold voltage e ₀ .

The output of the comparator 46 is applied to a differentiating circuit 49, which generates positive and negative pulses each time the output of the comparator 46 is inverted. Flip-flop 48 is triggered only by the negative pulse output of differentiator circuit 47 to flip between positive and negative output voltage levels.
The output of the flip-flop 48 is applied to an integrating circuit 49, where it is integrated and changed into an increase/decrease signal depending on the polarity of the output voltage of the flip-flop 48, which is mixed and input to the drive circuit 12 described above.

With this configuration, good focus servo is always applied even when the photodetector 10 deviates from its normal position due to temperature changes, etc., which will be explained in detail with reference to FIG. 3. In the configuration of FIG. 1, as described above, in the focus servo, the pickup 13 moves up and down with the target position being point A in FIG. 3A where the focus error signal V _f becomes zero.

The output voltage of the envelope detection circuit 44 at this time is shown in FIG. 3B, and the output voltage of the peak hold circuit 45 is shown in FIG. 3C. If the mounting position of the photodetector 10 moves due to a change in temperature or the like, the target position where the focus error signal V _f becomes zero will move to point B ₀ in FIG. 3A. Therefore,
Focus servo is always applied at point _B0 , which is shifted from point A in FIG. 3A, and the output of the envelope detection circuit 44 at that time becomes E _B0 shown by the broken line in FIG. 3B. On the other hand, the video signal reproducing circuit 43
Considering the ratio, it is desirable that the envelope is at its maximum, and even after the mounting position of the photodetector 10 is moved, it is desirable that the focus state be at point A, at which the envelope is at its maximum.

The present invention searches for a focal state where the envelope is maximum, and maintains that focal state by constantly reciprocating the focal position. For this purpose, for example, when the output voltage of the flip-flop 48 is at a positive voltage level and the output of the integrating circuit 49 is in the increasing direction, this output is mixed into the drive circuit 12, and the DC component output of the differential amplifier 11 is equivalently Therefore, the focus error voltage V _f changes in the direction of point A. Accordingly, the output of the envelope detection circuit 44 increases sequentially from B _B0 as shown in FIG. 3B, and decreases again after reaching the envelope maximum value _EA . When the focus shift amount position X reaches point C,
Envelope voltage of envelope detection circuit 44
E _C (shown in Figure 3B) and peak hold circuit 45
The difference between the hold voltage E _A (holding the maximum envelope voltage E _A at point A as shown in FIG. 3C) is the threshold voltage determined by the characteristic diagram of FIG. 6 of the comparator 46. When e becomes ₀ , the comparator 46 is inverted from a positive level to a negative level.
Therefore, the differentiating circuit 47 generates a negative pulse,
Flip-flop 48 is inverted to a negative voltage level. As a result, the output of the integrating circuit 48 begins to decrease, and the DC component of the differential amplifier 11 decreases again, changing toward point B. Similarly, when reaching point B via point C, the envelope detection circuit 44 at this time is
The difference between the output voltage E _B of and the hold voltage E _A of the peak hold circuit 45 becomes e ₀ , and the direction is reversed,
Head towards point C again. Peak hold circuit 4
5 is thus conveniently recharged to the maximum value E _A each time it passes through point A. Threshold voltage e ₀
A good focus state can be maintained by setting appropriately. The DC voltage of the drive circuit 12 is C
The same applies when the operation is started in a direction decreasing from a point.

In addition, as an example, the optimum position is focused by increasing or decreasing the envelope of the reproduced signal, but the change in the envelope of the reproduced signal is obvious when a recorded track is being reproduced. In the case of unrecorded tracks, the envelope of the reproduced signal itself is small, so it is difficult to detect changes in its increase or decrease. In this case, concave grooves for recording tracks are provided on the disk in advance in a concentric or spiral manner across the inner and outer circumferences of the disk, and addresses corresponding to each track are provided in the concave grooves as concave and convex signals. If the present invention is applied to a disc by extracting only the reproduced signal portion of an address as an envelope and detecting changes in increase or decrease in the envelope, it is possible to obtain the best focus even on tracks in unrecorded portions.

Effects of the Invention As described above, according to the present invention, a good focus state can always be maintained even if the mounting position of the photodetector for the focus servo moves due to temperature changes or loosening of the lock. is possible.

[Brief explanation of drawings]

Figure 1 is a configuration diagram of the conventional example, Figure 2 is a diagram showing the state of reflected light when defocus occurs, and Figure 3 A, B, and C are focus error signals, envelope detection output signals, and peak hold. 4 is a block diagram showing an embodiment of the present invention, FIG. 5 is an electrical connection diagram of the main parts, and FIG. 6 is a characteristic diagram of the comparator. 9...Photodetector for tracking control, 10...
...Photodetector for focus control, 12...Drive circuit, 13...Pickup, 41...Mixing circuit,
44... Envelope detection circuit, 45... Peak hold circuit, 46... Comparator, 47...
Differential circuit, 48...Flip-flop, 49...
Integral circuit.

Claims (1)

[Scope of Claims] 1. Conversion means for reproducing a signal from a signal track on a disc record carrier, focus control means for keeping the relative position of the disc record carrier and the conversion means constant, and the conversion means a peak hold means for holding the maximum value of the envelope of the reproduced signal obtained from the reproduction signal, an envelope detection means for the reproduction signal, and a detection means for detecting that an output difference between the peak hold means and the envelope detection means exceeds a predetermined threshold A detection means for detecting and generating a detection output; and a focus position variable signal that generates a focus position variable signal whose level sequentially increases or decreases with the passage of time until the next detection output is generated according to the output of the detection means, and supplies the focus control means to the detection means. an optical recording/reproducing apparatus comprising: focal position variable signal generating means for adding and varying the relative position; 2. The optical recording and reproducing apparatus according to claim 1, wherein the envelope detection means and the peak hold means use an envelope of a partial section of the reproduced signal obtained from the conversion means.