JPH03705B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Technical Field of the Invention] The present invention relates to an image information disc defect detection apparatus during a video disc manufacturing process.

[Technical background of the invention and its problems]

In recent years, image information disks have come into use as video recording and reproducing systems. There are optical reading systems, needle reading systems, etc., but both of them have advantages such as the discs 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 in many respects. However, in both cases, information is recorded by adding uneven shapes to the disk surface or reflective surface, so any defects in the shape on the recording surface greatly deteriorate the image quality. Therefore, it is important to detect defects occurring on the recording surface, especially in the manufacturing process.

Conventionally, the method for detecting defects in image information disks was to play back one track at a time in the same way as normal screen playback, detect the envelope of the signal since the playback signal is FM modulated, and then detect the point at which the envelope drops. A detection method etc. is used. However, with this method, 1
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, several tracks are detected at once, so the detection signal is different from the FM modulated signal obtained when only one track is detected, and the synchronization signal and control signal for tracking are similar to the defect signal. It appears as a pulse-like signal. This has resulted in the drawback that even synchronization signals and control signals may be mistakenly detected as defects. As a method to improve this, for example, a method of not performing detection in the synchronization signal section can be considered. In this case, it is possible to detect defective signals other than the synchronizing signal portion, but it is impossible to detect defective signals that appear mixed with the synchronizing signal. Generally, a method of detecting defects by frequency discrimination is used, but in image information disks, the synchronization signal and control signal are in a frequency band very close to the defect signal, so only the defect signal is detected by simply frequency discrimination. It was also difficult to do.

[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 defect signals on the image information disc surface and defect signals mixed in the 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 to an envelope detection circuit, extracts the envelope signal, and differentiates the output. and input it to a comparator to obtain a signal for detecting the rising edge of the envelope. This envelope rise detection signal causes the monostable multivibrator to be inverted for a period shorter than the synchronization signal period and longer than the defect signal period. On the other hand, the differential signal is input to another comparator to obtain a signal for detecting the fall of the envelope. This falling 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 monostable multivibrator inverted by the rising detection signal is inverted, is selected by the AND circuit, a defect can be detected.

〔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. The image information obtained can be used to efficiently inspect defects on master discs.

[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 11 passes through the beam splitter 12 and is sent to the image disk 1 by the lens 13.
4 Connect a small light spot on the top. At this time, disk 1
4 is rotated by a motor 15. In order to perform the inspection in a short time, the light spot is focused sufficiently on the recorded bits and tracks on the disk 14, and several tracks (for example, about five) are reproduced at once. The reflected beam that is reflected by the 14 surfaces of the disk and contains image signals and defect information is returned to the lens 13.
The light is reflected by the beam splitter 12 and received by the photodetector 16. Here, the optical signal becomes an electrical signal and is output to the output terminal 17. In addition, the focus adjuster 18 receives a signal from the photodetector 16 and adjusts the lens 1 so that the shape of the light spot on the board is always the optimal size.
Operate 3.

FIG. 2 shows an embodiment of the defect detection circuit according to the present invention, and FIG. 3 is a diagram showing waveforms of various parts in FIG. A reproduced signal from the optical detection device shown in FIG. 1 is supplied to the reproduced signal input terminal 21 in FIG. FIG. 3a is a diagram showing the waveform of this reproduced signal. When several tracks on the disk 14 are played back at once, since the same signal is always recorded on adjacent tracks in the synchronization signal section, they are added in the same phase, resulting in the output shown in Figure 3a.
A signal like a ₁ 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 defects exist over several tracks, the amount of reflected beam light decreases or increases, resulting in the appearance of signals with large amplitudes such as a ₂ and a ₃ in FIG. 3a. The envelope of this reproduced signal is detected by the envelope detection circuit 22, and a diagram showing this waveform is shown in FIG. 3b.
, only the upper envelope in Figure 3a is detected,
The downward defect signal _a3 is removed. The output of this envelope detection circuit 22 is input to a differentiating circuit 23. The output waveform of this differentiator circuit is shown in FIG. 3c. This output is input to comparator 24. The comparator 24 compares the level _C1 with the output of the differentiating circuit 23 shown in FIG. 3c, and creates a pulse train for detecting the rise of the envelope as shown in FIG. 3d. The output of this comparator 24 is input to a monostable multivibrator 25, and its output becomes a pulse train having a width .tau.sec shown in FIG. 3e. Here τ is shorter than the length of the synchronization signal,
Make it longer than the length of the defect signal. On the other hand, differentiator circuit 2
The output of 3 is also input to the comparator 26, where it is compared with the level _C2 shown in FIG. 3c, and the falling pulse of the envelope shown in FIG. 3f is detected. This comparator 26
The output is input to the AND circuit 27 together with the output of the monostable multivibrator 25. This AND circuit outputs the signal shown in FIG. 3g only when a falling pulse occurs within .tau.sec from the rising edge of the envelope. In this way, upward defect signals a ₂ and a ₄ on the reproduced signal shown in FIG. 3a are detected as shown in FIG. 3g. Further, the reproduced signal supplied to the input terminal 21 has the polarity of the defective pulse reversed by the inverting circuit 28 and is inputted to the downward defect detection circuit 29 . This downward defect pulse detection circuit 29 is a circuit similar to the circuit 30 which includes the envelope detection circuit, a differentiation 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. 3h is detected. The upward and downward defect detection signals of the reproduced signal are added by an OR circuit 31, and the defect detection signal 32
is output as shown in Figure 3i.

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. Furthermore, 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.

Although the above embodiment shows a method of optically reading information on several tracks at a time, it is also possible to obtain a reproduction signal using a contact type or using a needle large enough to span several tracks. Further, in FIG. 2, it is also possible to detect only the downward defect signal by using a circuit for detecting the lower envelope without inverting the reproduced signal using an inverting circuit.

[Brief explanation of the drawing]

FIG. 1 is a diagram showing an optical system up to obtaining a reproduced signal, FIG. 2 is a diagram showing an embodiment of the present invention, and FIG. 3 is a diagram showing waveforms at various parts in FIG. 2. 11... Laser oscillation device, 12... Beam splitter, 13... Lens, 14... Image disk, 1
5...Motor, 16...Photodetector, 17...Output terminal, 18...Focus adjuster, 21...Reproduction signal input terminal, 22...Envelope detection circuit, 23...Differential circuit, 24, 26 ... Comparator, 25 ... Monostable multivibrator, 27 ... AND circuit, 28 ...
...Inversion circuit, 29...Downward defective pulse detection circuit, 30...Upward defective pulse detection circuit, 31...
...OR circuit, 32...defect detection signal.

Claims (1)

[Claims] 1. A first detection means for detecting an envelope of a reproduced signal including a pulse-like defect signal obtained from a recording medium on which image information is recorded; and means for differentiating the envelope signal obtained from the first detection means; a second detection means for detecting a pulse of one predetermined polarity of the differential signal obtained from the differentiation means;
pulse generating means for generating a signal of a predetermined pulse width based on the detection signal obtained by the detection means; and a third pulse generating means for detecting a pulse of the other polarity of the differential signal.
An image information disk defect detection apparatus comprising: a detection means; and an AND circuit that performs a logical product of an output obtained from the pulse generation means and an output obtained from the third detection means.