JPH0449501A - Track quality inspection instrument for magnetic recording medium - Google Patents

Abstract

PURPOSE:To take out a true defect to set the degree of the defect in details by detecting a minimum level of the part where the level is continuously reduced for a certain time in the envelope of a reproduced signal. CONSTITUTION:A DC converting means 3 converts the reproduced signal to a DC, and the envelope of the DC signal is detected by an envelope detecting means 4. The envelope signal passes a time constant means 5 and has the minimum level detected by a minimum level detecting means 6, and the minimum level in one cycle is detected and is outputted to an output terminal 7 at the end of one cycle of a magnetic disk. An average level detecting means 8 outputs an average output level of one cycle to an output terminal 9. Levels appearing in output terminals 7 and 9 are compared with each other to detect the track quality in a prescribed time in details. Thus, a false signal excluded to take out and evaluate only the true defect against which a countermeasure should be taken.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to a magnetic recording medium track quality inspection apparatus for inspecting the track quality of a disc-shaped magnetic recording medium such as a flexible magnetic disk.

BACKGROUND OF THE INVENTION Evaluation of the track quality of a conventional magnetic recording medium is carried out by checking whether there is an output portion that is below a predetermined percentage of the average output level for a predetermined period of time or longer. For example, the part below -10dB relative to the average output level is 30dB.
The presence or absence of something that lasts for more than μs was inspected.

#J Problem to be Solved by the Invention According to the above method, the presence or absence of a predetermined defect, for example, the presence or absence of a 10 dB and 30 μs, can be inspected.
It was not possible to tell whether it was 30 dB or 30 dB.

Even if the output decrease is large, the output decrease continues for a short time, and is often due to a temporary output decrease due to dust adhering to the media surface (even if it is a real defect, the error correction method This does not pose much of a problem in practice since it is possible to adopt methods such as the following.

These temporary output drops (called temporary errors) mentioned above naturally have no reproducibility and complicate the results, so it is desirable to exclude them by some means when evaluating track quality. .

The present invention aims to solve the above-mentioned problems, and aims to provide an inspection device that discards short-duration output decreases, extracts true defects, and measures the degree of defects in more detail.

Means for Solving the Problems In order to solve the above-mentioned problems, the present invention provides an AGC amplification means for amplifying a reproduced signal from a magnetic recording medium to a substantially constant amplitude, and a DC for converting the output of the AGC amplification means into DC. an envelope detecting means for detecting an envelope of the output of the DC converting means; and an average for outputting an average output level for a predetermined period, for example, a period corresponding to one track of a magnetic disk, when the output of the envelope detecting means is inputted. output level detection means; attenuation means to which the output of the envelope detection means is input and attenuates with a predetermined time constant;
The output of the damping means is inputted and includes a minimum level detection means for detecting the lowest level among the outputs that continuously decrease for a certain period of time, and is configured to obtain a ratio of the minimum level to the average output level for the predetermined period. That's what happens.

The present invention has the above-described configuration, detects the envelope of the reproduced signal of the magnetic recording medium, detects the lowest level if there is a part of the envelope where the level continues to decrease for more than a certain period of time, and calculates the average output level for the predetermined period. and the lowest level can be obtained.

EXAMPLE Hereinafter, an example of the present invention will be described with reference to FIG. In the figure, 1 is an input terminal to which a reproduced signal from a magnetic recording medium is applied, 2 is an AGC amplification means for amplifying the reproduced signal to a substantially constant amplitude, and 3 is a DC converter for converting the output of the AGC amplification means into DC. Means 4 is envelope detection means for detecting the envelope of the output of the DC converting means; 5
6 is a damping means to which the output of the envelope detection means is applied and attenuates with a predetermined time constant, and 6 is the lowest level among the levels to which the output of the damping means is applied and continues to decrease beyond the time determined by the time constant. 7 is an output terminal of the lowest level detecting means; 8 is an average level detecting means to which the output of the envelope detecting means 4 is applied and detects the average output level for a predetermined period; 9 is an average level detecting means of the average level detecting means; It is an output terminal.

Next, the operation of the magnetic recording medium track quality inspection apparatus having the above configuration will be explained with reference to FIG. FIG. 2 schematically shows an example of the operation of the magnetic recording medium track quality inspection apparatus according to the present invention.

FIG. 2(a) shows an index signal corresponding to one period of a magnetic recording medium, for example, a magnetic disk. (b) is a reproduced signal from a magnetic recording medium that is applied to the input terminal 1 in FIG. 1 and amplified to a substantially constant amplitude by the AGC amplification means 2. The DC converting means 3 converts this reproduced signal into DC and outputs a DC signal shown in C). The envelope detection means 4 detects the envelope of this DC signal and outputs an envelope signal shown in d). The time constant means 5 has a discharge time constant τ
The envelope signal shown by the solid line in (e) is output. The lowest level detection means 6 detects the lowest level of the envelope signal as shown by the - dotted chain line in (e), and at the end of one cycle of the magnetic disk, detects the lowest level within one cycle and outputs it to the output terminal 7. . On the other hand, the average level detection means 8 (
As shown in d), the average output level of one cycle is output to the output terminal 9.
Output to. Therefore, by comparing the levels appearing at the output terminals 7 and 9, the track quality within one period, that is, a predetermined period can be known in detail.

Although the above description is an example of the operation for one track, if the operation is performed for all tracks, the track quality of the entire magnetic disk can be known in detail.

Further, it is more effective to configure the damping means to selectively use two or more types of time constants.

Furthermore, it goes without saying that the present invention can be applied not only to magnetic disks but also to magnetic tapes, and in this case, for example, one second can be used as the predetermined period.
You can know the track quality every second in detail.

Effects of the Invention As is clear from the above embodiments, the present invention extracts and evaluates the output drop that occurs continuously for a certain period of time or more in a magnetic recording medium such as a flexible magnetic disk or magnetic tape, and detects a predetermined value within the output drop. This provides a track quality inspection device for magnetic recording media that can determine the lowest level within a period as a ratio to the average output, and eliminates the unreproducible "temporary error" that traditionally complicates measurement results. It also has the effect of filtering out "false signals" and identifying and evaluating only true defects that require countermeasures.

[Brief explanation of the drawing]

FIG. 1 is a block diagram of a main part of a magnetic recording medium track quality inspection apparatus according to an embodiment of the present invention, and FIG. 2 is a schematic diagram illustrating an example of its operation. l...Input terminal, 2...AGC amplification means, 3...DC conversion means, 4...Envelope detection means, 5... Attenuation means, 6...
...Minimum level detection means, 8...Average level detection means.

Claims (1)

[Claims] AGC amplification means for amplifying a reproduced signal from a magnetic recording medium to a substantially constant amplitude;
an envelope detection means for detecting an envelope of the output of the DC conversion means; an average level detection means for outputting an average output level for a predetermined period in which the output of the envelope detection means is input; A means for receiving the output of the detecting means and attenuating it with a predetermined time constant; and a lowest level detecting means for receiving the output of the attenuating means and detecting the lowest level among the outputs that continuously decrease for a certain period of time. A track quality inspection device for magnetic recording media, characterized by: