JPH03280223A - Method for inspecting defect of optical recording medium - Google Patents

Abstract

PURPOSE:To provide the method for inspecting defects, the detection accuracy of which does not depend on the sizes of the defects and which can discriminate the factors for the generation of the defects by detecting the fluctuation in reproduction signals by the influence of the defects with respect to a prebit signal and a medium modulating signal. CONSTITUTION:A prebit signal 3 and the medium modulating signal 4 are obtd. by using an optical head 2 with an optical recording medium 1 in the state of previously erasing the recording region. The medium modulating signal 4 is inputted via a filter 6 to a differentiator 7 and a comparator 8. The comparator 8 outputs a pulse signal according to the length of the detected defect by using a reference level. A comparator 9 judges the magnitude of the output amplitude from the differentiator 7 by using a reference level, discriminates the kind of the defect from the steepness of the level change in accordance with the result thereof and outputs a pulse signal. The output from the comparator 8 is received in a counter 13 where the data on the defect length is formed from the medium modulating signal in the recording region. A flag generator 10 generates the flag based on the output of the comparator 9. The outputs of the flag generator 10 and the counter 13 are inputted to an error counter 14.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to an inspection method for inspecting defects in optical recording media in which information is recorded, reproduced, and erased by focusing light from a laser or the like into a minute spot. .

[Prior Art] In an optical recording medium typified by magneto-optical recording, one data recording unit (sector) is composed of a recognition area and a recording area, as shown in FIG.

The recording area is an area for recording, reproducing, and erasing desired data using the properties of an optical recording medium. On the other hand, the recognition area is an area in which recognition data regarding the sector, such as track number and sector number, is recorded in advance by physical irregularities (pre-pits) on the surface of the recording medium. To reproduce this recognition data, pre-pits are detected from a medium surface reflection signal (pre-pit signal) which is a reflected light signal.

The conventional defect inspection method has the configuration shown in FIG.

First, a pre-pit signal from the optical recording medium 1 is obtained by the optical head 2, and the recording area detector 15 determines a sector, a recognition area within the sector, and a recording area. When the recording area is recognized, a recording signal is generated by the recording signal generator 17 based on the test recording data stored in the pattern ROM 16, and this is recorded using the optical head 2.

Next, this recorded signal is reproduced by the optical head 2 to obtain a medium modulation signal. This medium modulation signal is amplified to a desired signal level by an amplifier 6, and after unnecessary components in the signal are removed by a filter 8, reproduced data is obtained by a data discriminator 18. This playback data and pattern RO
A data comparator 19 checks whether the recorded data stored in M16 matches. If the two do not match, it is determined that a defect exists in the written portion of the recording signal, and this is recorded in the error counter 14.

The recording data for lateral displacement is recorded in such a way that the recording signal becomes a single frequency signal in order to equalize the resolution during defect detection and to simplify the circuit configuration of the recording signal generator, data discriminator, etc. Often uses data. FIG. 6 shows waveform examples of a normal reproduced signal when such recorded data is used and a reproduced signal that causes a data error due to the presence of a defect.

(a) is the reproduced signal when there is no defect, (b)
) is a reproduced signal when a defect exists in the section indicated by T.

[Problems and objects to be solved by the invention] However, in the conventional technology, even if a defect is detected, it is impossible to distinguish whether the cause is a scratch or a physical property of the recording medium such as birefringence. has.

Furthermore, although it is possible to detect defects that are longer than the cycle of the recording signal, it is not always possible to detect defects that are shorter than the cycle, depending on deviations caused by various fluctuation factors when writing the recording signal. That is, depending on the relationship between the defect on the recording medium and the physical position of the recorded signal, a phenomenon occurs in which even if a defect exists, it does not necessarily affect the reproduced signal. To solve this problem, it is possible to shorten the period of the recording signal, that is, increase the frequency of the recording signal, but the quality of the reproduced signal deteriorates due to the recording and reproduction characteristics of the optical head and the frequency characteristics of the recording medium. However, there is also the problem that even if there is no defect, the reproduced data may be erroneous due to other factors such as noise.

In addition, when inspecting a large-capacity recording medium, it is necessary to record the measurement signal over the entire measurement target area.
Another problem is that it is very time consuming.

Therefore, the present invention is intended to solve these problems, and its purpose is to provide a defect inspection method for optical recording media that can stably detect defects that do not depend on the size of the defect and identify the cause of defect occurrence. It is located in a place that provides.

[Means for Solving the Problems] The defect inspection method for an optical recording medium of the present invention uses an optical head to inspect an optical recording medium from which data in a recording area has been erased in advance. level change detection means for detecting a medium modulation signal in a recording area and detecting a change in signal level with respect to the medium modulation signal; and receiving a signal from the signal level change detection means and measuring a change time interval. A signal level change time measuring means, a differentiating means for differentiating the medium modulation signal, a differential signal level change detecting means for receiving the output of the differentiating means and detecting a change in the differentiated signal level, and the differential signal level change detecting means The present invention is characterized by comprising: a flag generating means for generating a flag indicating the presence or absence of a level change in response to an output from the signal level change time measuring means; and a counting means for totaling the data from the signal level change time measuring means and the flag from the flag generating means. shall be.

[Example] The present invention will be explained in detail below.

FIG. 1 shows an embodiment of the optical recording medium defect inspection method of the present invention.

A pre-pit signal 3 and a medium modulation signal 4 are obtained using an optical head 2 on an optical recording medium 1 whose recording area has been erased in advance. Pre-pit signal 3 is recorded area detector 10
On the other hand, the medium modulation signal 4 is amplified to a desired signal level by an amplifier 5, unnecessary noise components etc. are removed by a filter 6, and the medium modulated signal 4 is input to a differentiator 7 and a comparator 8.

When there is no defect, the medium modulation signal is a signal with zero amplitude as shown in Figure 2 (a), but when a defect exists, an extra pulse as shown in Figure 2 (b) and Figure 3 (a) is generated. becomes. In general, defects caused by birefringence are shown in Figure 2 (
As shown in b), the waveform becomes a gentle waveform with a small amplitude, and its differential waveform becomes a waveform with a small amplitude as shown in FIG. 2(d).

On the other hand, a defect caused by a scratch results in a steep waveform with a large amplitude as shown in FIG. 3(a), and its differential waveform becomes a waveform with a large amplitude as shown in FIG. 3(C).

The comparator 8 is for detecting the presence and length of a defect, and detects the defect using a predetermined reference level R1, and depending on the length, it detects the defect as shown in FIGS. b
) outputs a pulse signal with a radiation T.

Further, the comparator 9 is connected to a predetermined reference level R2.
is used to judge the magnitude of the output amplitude from the differentiator 7, and thereby judge the suddenness of the level change, that is, to judge the type of defect. A pulse signal is output as shown in FIG. 3(e) and FIG. 3(d).

The counter 13 receives the output from the comparator 8,
Defect length data from the medium modulation signal in the recording area is generated based on the clock signal for pulse width measurement from the clock generator 12 and the count control signal from the recording area detector 11.

Further, the flag generator 10 generates different flags depending on whether a pulse exists in the output of the comparator 9 or not.

The error counter 14 receives two data, the defect length data output from the counter 13 and the flag output from the flag generator 10, and records and totals the type and length of the defect.

[Effects of the Invention] As described above, according to the present invention, by detecting fluctuations in the reproduced signal due to the influence of defects for the pre-pit signal and the medium modulation signal, the detection accuracy does not depend on the size of the defect. In addition, defect inspection can be performed to determine the cause of the occurrence.

Furthermore, since there is no need to record or erase a signal for defect detection on a recording medium, there is also the effect that the time for defect inspection can be shortened.

[Brief explanation of drawings]

FIG. 1 is a block diagram showing one embodiment of the present invention. FIG. 2 is a waveform diagram of a medium modulation signal when the signal level change is small in the embodiment shown in FIG. FIG. 3 is a waveform diagram of a medium modulation signal when the signal level changes are large in the embodiment shown in FIG. FIG. 4 is a configuration diagram of a data recording unit. FIG. 5 is a block diagram showing a conventional example. FIG. 6 is a waveform diagram of a medium modulation signal in the conventional example shown in FIG. 8.9 0 1 2 3 4 5 6 7 8 Optical recording medium Optical head Differentiator Comparator Flag generator Recording area detector Clock generator Counter Error counter Pattern ROM Recording signal generator Data discriminator Data comparator and above

Claims (1)

[Claims] An optical head is used to detect a medium modulation signal in the recording area of the optical recording medium on which data in the recording area has been erased in advance, and a signal level change is detected with respect to the medium modulation signal. a level change detection means for detecting a change; a signal level change time measurement means for receiving a signal from the signal level change detection means and measuring a time interval of the change;
Differentiating means for differentiating the medium modulation signal; differential signal level change detecting means for receiving the output of the differentiating means and detecting a change in the differentiated signal level; and receiving the output from the differential signal level change detecting means and detecting a level change. A defect in an optical recording medium, comprising: a flag generating means for generating a flag indicating the presence or absence of a defect; and a counting means for totaling the data from the signal level change time measuring means and the flag from the flag generating means. Test method.