JPH03280222A - Method for inspecting defect of optical recording medium - Google Patents

Abstract

PURPOSE:To provide the method for inspecting the defects of an optical recording medium which can make stable defect detection without depending on the sizes of defects and specification of the factors for the generation of the defects by detecting the medium modulating signal in a recording region and detecting the size and length of the signal level change of the medium modulating signal. CONSTITUTION:A prebit signal 3 and the medium modulating signal 4 are obtd. by using an optical head with the optical recording medium 1 in the state of previously erasing the recording region. The prebit signal 3 is inputted to a recording region detector 10 and the medium modulating signal 4 is inputted to comparators 7, 8. The comparator 7, which is used to detect the presence and length of the defect, detects the defect by using a predetermined reference level and outputs a pulse signal according to the length thereof. The comparator 8, which is used to discriminate the kind of the defect by judging the magnitude of the amplitude, judges the amplitude by using the predetermined reference level and outputs a pulse signal. The defect inspection, the detection accuracy of which does not depend on the size of the defect, and which can discriminate the factors for generation is executed in such a manner.

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 a 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 10 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 15 based on the inspection recording data stored in the pattern ROM 14, 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 5, and after unnecessary components in the signal are removed by a filter 6, reproduced data is obtained by a data discriminator 16. This playback data and pattern RO
A data comparator 17 checks whether the recorded data stored in M14 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 13.

Recorded data for inspection is data whose recording signal is a single frequency signal in order to equalize the resolution when detecting defects and to simplify the circuit configuration of the recording signal generator, data discriminator, etc. is often used. 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.

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 in a place where we provide.

[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. a group of signal level change detection means for detecting a medium modulation signal in a recording area and detecting a signal level change using at least two or more reference signal levels with respect to the medium modulation signal; and the signal level change detection means. Among the means group, a signal level change time measuring means for receiving an output from a predetermined signal level change detecting means and measuring the time interval; a flag generating means for receiving an output from the signal level change detecting means and generating a flag indicating the presence or absence of a level change; and a counting means for totaling the data from the signal level change time measuring means and the flag from the flag generating means. It is characterized by having

[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 comparator 7.8.

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 FIG. 3(b), the waveform is slow with a small amplitude, and in the case of a defect caused by a scratch, the waveform is steep with a large amplitude as shown in FIG. 3(a).

The comparator 7 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 of width T.

Further, the comparator 8 is used to judge the magnitude of the amplitude, that is, to judge the type of defect, and judges the amplitude using a predetermined reference level R2, and depending on the result, the signal shown in FIG. 2(d) is used. , outputs a pulse signal as shown in FIG. 3(C).

The counter 12 receives the output from the comparator 7,
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 11 and the count control signal from the recording area detector 10.

Further, the flag generator 9 generates different flags depending on whether a pulse exists in the output of the comparator 8 or not.

The error counter 13 receives two data, the defect length data output from the counter 12 and the flag output from the flag generator 9, and records and totals the type and length of the defect.

[Effects of the Invention] As explained above, according to the present invention, by detecting the magnitude and length of a signal level change of a medium modulation signal,
Defect inspection can be performed in which the detection accuracy does not depend on the size of the defect and the cause of its occurrence can be determined.

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. 7.8 0 Optical recording medium Optical head Comparator Flag generator Recording area detector 1 2 3 4 5 6 7 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 at least two a group of signal level change detection means for detecting a change in signal level using one or more reference signal levels; A signal level change time measuring means for measuring the interval, and a flag that receives an output from a predetermined signal level change detecting means of the group of signal level change detecting means and generates a flag indicating the presence or absence of a level change. 1. A defect inspection method for an optical recording medium, comprising a generating means and a counting means for totaling data from the signal level change time measuring means and a flag from the flag generating means.