JPS59215040A - Device for detecting defect of picture information disc - Google Patents

Abstract

PURPOSE:To detect stably a defect signal existing on a disc face and a defect signal mixed in a picture signal by detecting the envelope from a detected signal including a pulse formed defect signal and detecting the defect signal only through circuits such as differentiation and comparison or the like. CONSTITUTION:A reproducing signal supplied to an input terminal 21 and including a synchronizing signal a1, and defect signals a2, a3 and a4 is envelope- detected by an envelope detecting circuit 22 and outputted as defect detected outputs h1, h2 by an upward defect pulse detecting circuit 30 comprising a differentiation circuit 23, a comparator 24 and a monostable multivibrator 25 or the like. Further, the reproducing signal supplied to the input terminal 21 is inputted also to an inverse circuit 28 and outputted as a defect pulse h3 by a downward defect detecting circuit 29.

Description

DETAILED DESCRIPTION OF THE INVENTION [Technical Field of the Invention] The invention relates to an apparatus for detecting defects in image information discs during the manufacturing process of video discs.

[Technical background of the invention and its problems-1 In recent years, image information discs have come to be used as video recording and reproducing systems. There are optical reading methods, needle reading methods, etc., but both of them have advantages such as the disks that serve as image sources can be mass-produced at low cost using a press, and high-speed image access is possible compared to conventional VTR devices. It is excellent. However, since information is recorded by adding uneven shapes to the disk surface or reflective surface, any defects in the shape on the recording surface will greatly deteriorate the image quality.Therefore, it is difficult to detect defects that occur on the recording surface. is especially important in the manufacturing process.

Conventional one stroke 18! The method for detecting defects in the information disk is to play one track at a time in the same way as normal screen playback.7 Since the playback signal is FM modulated, the envelope of the signal is detected, and the point at which it drops is detected. methods etc. are used. However, this method has the disadvantage that the inspection time is long because each track is inspected. Therefore, a method is used in which information on several tracks is extracted at once by, for example, shining a light beam on the disk, and defects can be inspected in a short period of time. However, in this case, since several tracks are detected at once, the detection signal is an FM signal obtained at the time of detection of only one track.
A signal that is different from the modulated signal, such as a synchronization error signal or a control signal for tracking, appears as a defect (and a pulse shape similar to No. 4 (No. 8). Therefore, the synchronization signal and control signal also appear as defects. The defect is that the detection is rarely detected.One possible way to improve this is, for example, to not perform detection in the sync signal section.In this case, defective signals other than the sync signal section can be detected, but the sync signal It has been impossible to detect defect signals that appear mixed with the defect signal.In addition, a method of frequency discrimination is generally used for defect detection, but in image information disks, the synchronization signal and control signal are very similar to the defect signal. Since they are in similar frequency bands, it is difficult to detect only the defective signal using a frequency discrimination method.

[Purpose of the invention]

SUMMARY OF THE INVENTION An object of the present invention is to provide an image information disc defect detection device that can stably detect defects (mth number) on the surface of an image information disc and defect signals mixed in image signals in a short time.

[Summary of the invention]

The present invention extracts a detection signal including a pulsed defect signal from a reflected beam obtained from a disk on which image information is recorded, inputs this detection signal (No. 1) to an envelope detection circuit, extracts the envelope signal, and outputs the detected signal. is differentiated and input to a comparator to obtain a signal for detecting the rise of the envelope.This envelope rise detection signal inverts the monostable multivibrator for a time shorter than the synchronization signal period and longer than the defect signal period.

The detection signal and the output of the monostable multivibrator are input to an AND circuit. The defect signal is usually a pulse-like signal shorter than the synchronization signal. Therefore, if the falling detection signal obtained during the time when the inverted monostable multivibrator is inverted from the rising detection signal V is selected by the AND circuit, a defect is detected and I is entered.

〔Effect of the invention〕

According to the present invention, defects on the recording surface of an image information disk can be detected stably in a short time, and in particular, defects on synchronization signals and control signals can also be detected.
And image information obtained during the manufacturing process can be efficiently inspected for defects on the master disk.

[Embodiments of the invention]

Hereinafter, one embodiment of the present invention will be described in detail using the drawings.

FIG. 1 is a diagram showing an optical system from which a reproduction signal is obtained from reflected light from an image information disk. The laser beam output from the laser oscillation device aυ passes through the beam splitter 02 and forms a small light spot on the image disk I by the lens +13. At this time, the disk I is being rotated by the motor OS.

In order to perform inspection in a short time, the light spot is focused sufficiently large on the recorded bits and tracks on disk I.
Several tracks (for example, about 5 tracks) are being played at once.

The reflected beam that is reflected by the surface of the disk 1141 and contains image No. 16 and defect information passes through the lens f131 again, is reflected by the beam splitter 0, and is received by the photodetector fil. Here, the original signal becomes an electrical signal and is output to the output terminal surface. Further, the focus adjuster 1181 receives a signal from the photodetector aO and operates the lens +131 so that the shape of the light spot on the board surface is always the optimum size.

FIG. 2 is a simple example of a defect detection circuit according to the present invention,
FIG. 3 is a diagram showing waveforms of various parts in FIG. 2. A reproduced signal from the optical detection device shown in FIG. 1 is supplied to the reproduced signal input terminal C21) in FIG.

FIG. 3(a) is a diagram showing the waveform of this reproduced signal.

When several tracks of the 0th place on the disc are reproduced at once, the same signals are always recorded in adjacent tracks in the synchronization signal section, so they are added in the same phase, and a signal like &1 in FIG. 3 (&) appears. Furthermore, in the video signal section, since there is no signal correlation between adjacent tracks, the signals are averaged over several tracks and no large amplitude changes appear. Furthermore, if there are defects over several tracks, the amount of reflected beam light may decrease or increase, resulting in large amplitude 1d such as a2 and a3 in Fig. 3, 1c&).
A number appears.

This reproduced signal is envelope-detected by the envelope detection circuit +221, and the diagram showing this waveform is shown in FIG. 3(b). Only the upper envelope in FIG. 3(a) is detected, and the downward Please remove defective Itt No. a3. The output of this envelope detection circuit (4) is input to the differentiator circuit r!sae. The output waveform of this differentiator circuit is shown in Figure 3(c). This output is input to the comparator (2, 0). .Comparator +24) is shown in Figure 3(c).
Compare the output of the differential circuit shown in (the output of the arrogance) and level C1, and
Create a pulse train to detect the rising edge of the envelope as shown in Figure (d). The output of this comparator C4 is input to a monostable multivibrator (c), and its output becomes a pulse train of the formula frf)7 shown in FIG. 3(e). Here, τ is shorter than the length of the synchronization signal and longer than the length of the defective signal.

On the other hand, the output of the differentiating circuit Qkon is also input to the comparator (c),
It is compared with the level C2 shown in FIG. 3(o), and the level C2 shown in FIG.
Detect the falling pulse of the envelope shown in ). The output of this comparator t21i) is a monostable multivibrator (
It is input to the AND circuit (27) together with the output of 2!9. This AND circuit outputs the signal shown in FIG. 3(g) only when there is a falling pulse within one equation from the rising edge of the envelope. In this way, the upward defect signals a2 and a4 on the reproduced signal shown in FIG.
The detection formula is as shown in ). Further, the reproduced signal supplied to the input terminal CD reverses the polarity of the defective pulse in an inversion circuit (to) and inputs it to the downward defect detection circuit (21).This downward defect pulse detection circuit 01 is connected to the envelope detection circuit, This circuit is similar to the circuit consisting of a differential circuit, two comparators, a monostable multivibrator, and an AND circuit.In this way, the downward defective pulse a3 of the reproduced signal shown in Fig. 3 (11) is detected. The upward and downward defect detection signals of the GE signal are added by an OR circuit 01), and a defect detection signal 0 is output as shown in FIG. 3 (1).

As described above, according to this embodiment, the output signals after the differentiating circuit can be digitally processed, so the stability of the detection ability is excellent, and the manufacturing and adjustment of the circuit is easier than with analog circuits. In addition, the defect detection signal is outputted with almost no time delay relative to the defect position of the reproduced signal, which is convenient in practice.

According to the above embodiment, a method of optically reading information in several tracks each was shown, but even with a contact type, a reproduction signal can be obtained using a needle large enough to be divided into several tracks. You can also do it. Also, in Figure 2, the lower envelope 4! without inverting the reproduced signal with the inverting circuit! ! Using a circuit that detects
It is also possible to detect only downward defect signals.

[Brief explanation of the drawing]

FIG. 1 is a diagram showing an optical system 1 for obtaining an external signal, FIG. 82 is a diagram showing an embodiment of the present invention, and FIG. 3 is a diagram showing waveforms at various parts in FIG. DESCRIPTION OF SYMBOLS 11... Laser oscillation device, 12... Beam splitter 13... Lens, 14... Image disk, 15...
7-tater, 16... photodetector, 17... output terminal, 1
8... Focus adjuster, 21... Playback signal input terminal, 2
2... Envelope detection circuit, 23... Differential circuit, 24.
26... Comparator, 25... Monostable multivibrator, 27... AND circuit, 28... Inverting circuit, 29
... Downward defect pulse detection circuit, 30 ... Upward defect pulse detection circuit, 31 ... OR circuit, 32 ... Defect detection signal. Bow, Q

Claims (1)

[Claims] Means for detecting the envelope of a reproduced signal including a pulse-like defect signal obtained from a recording medium on which image information is recorded, means for differentiating the envelope signal obtained from the detecting means, and a differential signal obtained from the differentiating means. a first detection means for detecting a pulse of one predetermined polarity; a pulse generation means for generating a signal of a predetermined pulse width based on the detection signal obtained by the detection means; and the other of the differential signals. and an AND circuit that takes a logical product of the output obtained from the pulse generation means and the output obtained from the second detection means. Image information disk defect detection device.