JPH0355796B2 - - Google Patents

Description

[Detailed Description of the Invention] (1) Technical Field of the Invention The present invention relates to a method and apparatus for inspecting a magnetic recording medium such as a magnetic recording/reproducing disk or a magnetic tape, and particularly relates to a method and apparatus for inspecting a detection signal read from a magnetic medium. The present invention relates to an inspection method and an inspection apparatus for inspecting defects such as pinholes and dropouts occurring in a magnetic medium by comparing with a predetermined slice level.

(2) Conventional technology Magnetic media such as magnetic recording/reproducing disks and magnetic tapes are manufactured by applying magnetic powder onto a substrate, and inspection is required to detect defects such as pinholes and dropouts that occur during this process. The following devices are known as devices. That is, for example, a certain frequency signal is written on a magnetic medium, this written signal is read out, a specific percentage of the average output is set as a slice level, and this is compared with the above-mentioned read signal (detection signal). This is an inspection device that detects defective signals called missing or extra signals, counts these signals, and determines that the defective signal is defective if it exceeds a predetermined count value. The configuration of such an inspection apparatus is shown in FIG. 1, and the signal waveforms of each part thereof are shown in FIG.

In FIG. 1, a magnetic recording/reproducing disk 3 is placed on, for example, a turntable 2 and rotated by a motor 1. As shown in FIG. A recording and erasing head 5 and a reading head 4 are arranged on the magnetic recording/reproducing disk 3. These heads 4 and 5 are disposed in contact with or separated from the surface of the magnetic recording/reproducing disk 3, and along the radial direction of the magnetic recording/reproducing disk 3 on which a plurality of concentric tracks are formed. It is configured to move forward. The recording and erasing head 5 writes a constant frequency signal to the magnetic recording/reproducing disk 3 or erases (demagnetizes) the written signal in response to a signal from the recording and erasing circuit 6. That is, writing is performed on the magnetic recording/reproducing disk 3 by applying a constant frequency signal from the recording and erasing circuit 6 to the recording and erasing head 5, and on the other hand, an erasing current is applied from the recording and erasing circuit 6 to the recording and erasing head 5. By applying it to the head 5, the magnetic recording/reproducing disk 3 is demagnetized.

When the constant frequency signal written on the magnetic recording/reproducing disk 3 is read out by the read head 4, it is sent to the amplification and average output setting circuit 7 as a detection signal. Here, the detection signal is amplified and sent to the error detection circuit 9, and the average output per track of the peak value of the amplified detection signal is determined as the TAA level shown in FIG. 2A, and the slice level is set. It is sent to circuit 8. In the slice level setting circuit 8, as shown in FIG. 2A, a specific ratio of the average output (TAA) is set as a set of positive and negative slice levels SL ₁ , SL ₂ , and this set of slice levels SL ₁ , SL ₂ is error detection circuit 9
sent to. In the error detection circuit 9, the amplified detection signal is compared with the slice levels SL ₁ and SL ₂ to determine the slice levels SL ₁ and SL ₂ of the detection signal.
The following dips are detected as missing.
For example, as shown in FIG. 2D, the magnetic recording/reproducing disk 3
magnetic powder 3b coated on the base 3a of
When there is one defect 3c on the surface of the defect 3c, the detection signal level at the corresponding location drops as shown in FIG.
Or, as shown in C, it is detected as missing.

On the other hand, when the magnetic recording/reproducing disk 3 demagnetized by the recording and erasing head 5 is read out by the reading head 4, the readout detection signal is amplified by the amplification and average output setting circuit 7, and the amplified signal is amplified by the amplification and average output setting circuit 7. The detected signal is at the above slice level SL ₁ ,
It is given to the error detection circuit 9 together with SL ₂ . The error detection circuit 9 compares the detection signal with the slice levels SL ₁ , SL ₂ in the same manner as described above, and the portion of the detection signal that is equal to or higher than the slice levels SL ₁ , SL ₂ is detected as an extra pulse. For example, if a defect 3c as shown in FIG. 2D exists in the magnetic recording/reproducing disk 3, pulse noise as shown in FIG. 2E appears in the detection signal at the corresponding location, and thus is detected as an extra pulse as shown in FIG. 2F.

Defects detected as missing or extra pulses in this way can cause damage to one magnetic recording/reproducing disk 3.
If there are more than a predetermined number of magnetic recording/reproducing disks 3, the magnetic recording/reproducing disk 3 is determined to be defective.

(3) Problems with the prior art In the past, the magnetic recording and reproducing disks were inspected individually as described above, but the equipment that actually uses the magnetic recording and reproducing disks was basically inspected as described above. Magnetic recording and reproducing disks are inspected for defects using the same method as inspection, and shipped to the market after confirming that the number of defects is less than the specified number. However, depending on the device in which the magnetic recording/reproducing disk is mounted, the slice level may differ slightly and may not be the same as the slice level when inspecting the magnetic recording/reproducing disk alone. It was difficult to do so.

The problem of such variations will be explained with reference to FIG. In FIG. 3, the vertical axis represents the number of defects (errors) in the magnetic recording/reproducing disk, and the horizontal axis represents the slice level. Here, for example, the first magnetic recording/reproducing disk 11 has more large defects than small defects, and the second magnetic recording/reproducing disk 12 has, on the contrary, more small defects than large defects. Compare and think. First, two magnetic recording/reproducing disks 1 are prepared using a high slice level C.
1 and 12, the number of defects in the first magnetic recording and reproducing disk 11 is higher than that of the second magnetic recording and reproducing disk 12.
Since the number of defects is greater than the number of defects, there is a high possibility that the first magnetic recording/reproducing disk 11 is determined to be a defective product and the second magnetic recording/reproducing disk 12 is determined to be a good product. However, when the two magnetic recording and reproducing disks 11 and 12 are similarly inspected using the low slice level A, the number of defects obtained by inspecting the second magnetic recording and reproducing disk 12, which has many small defects, is The number of defects is greater than the number of defects in the first magnetic recording and reproducing disk 11, and contrary to the above case, it is possible that the second magnetic recording and reproducing disk 12 is determined to be defective and the first magnetic recording and reproducing disk 11 is determined to be good. It becomes more sexual. That is, after inspecting the magnetic recording and reproducing disk alone,
When installed and tested in equipment that would actually be used, there was a high probability that a good magnetic recording/reproducing disk would be mistakenly judged as defective.

(4) Purpose of the Invention The present invention has been made in view of the above-mentioned conventional problems, and an object of the present invention is to enable accurate determination of the quality of magnetic media without increasing inspection time.

(5) Structure of the Invention The above object of the present invention is to record a predetermined recording signal on a magnetic medium, read out the recorded signal to obtain a detection signal, and convert the detection signal into a set of positive and negative slice levels. A method for inspecting a magnetic medium, characterized in that the magnetic medium is simultaneously compared with a plurality of different slice levels, and defects in the magnetic medium are simultaneously detected based on the respective comparison results, or
a recording means for recording a predetermined recording signal on a magnetic medium; a reading means for reading out the predetermined recording signal recorded on the magnetic medium as a detection signal; a plurality of error detection circuits for detecting defects in the magnetic medium by comparison with a set of slice levels, and each slice level of the plurality of error detection circuits is set to a different level; This is achieved by a magnetic medium inspection apparatus characterized in that it includes an error detection means for simultaneously detecting defects using a detection circuit.

(6) Examples of the invention Examples of the invention will be described below with reference to the drawings.

FIG. 4 shows the configuration of an embodiment of the inspection device of the present invention. Note that the same parts in FIG. 1 are denoted by the same reference numerals, and redundant explanation thereof will be omitted.

In FIG. 4, a constant frequency signal recorded on the magnetic recording/reproducing disk 3 by the recording and erasing head 5 is read out by the reading head 4.
After the read signal is amplified as a detection signal by the amplifier circuit 15, each comparison circuit 14a, .
...14n is added to one input terminal.

Further, the detection signal amplified by the amplifier circuit 15 is inputted to the average value setting circuits 16a,...16n, and thereby the average output (TAA level) of the peak value of the detection signal obtained by reading out one track. is determined, and its DC output is applied to the DC input of digital-to-analog conversion circuits (D/A converters) 17a, . . . 17n. At the same time, mutually different slice level values respectively set by the slice level setting circuits 18a, . . . 18n are given to the digital-to-analog conversion circuits 17a, . Therefore, for example, if the digital-to-analog conversion circuit 17a is given a slice level setting value of 80% and the average output voltage determined by the average value setting circuit 16a is 3V DC, the digital-to-analog conversion circuit ±2.4 (=3×0.8) for the output of 17a
The voltage of V is taken out as a set of positive and negative slice levels and applied to the other input terminal of the comparison circuit 14a. Note that the slice level output from one digital-to-analog conversion circuit here is a set of positive and negative slice levels as described above, and these levels are set for each digital-to-analog conversion circuit according to the slice level setting value of each slice level setting circuit. It is set differently for each conversion circuit. The detection signal amplified by the amplifier circuit 15 is sent to each comparison circuit 14a,...
14n, and defect detection based on a plurality of mutually different sets of slice levels is performed simultaneously. If there is a defect in the magnetic recording/reproducing disk 3, defect detection signals such as extra and missing signals can be obtained according to each slice level, so that the quality of the magnetic recording/reproducing disk 3 can be determined from these signals. Note that reading of the recorded signal is performed on all tracks of the magnetic recording/reproducing disk 3 from the inner or outer track to the outer or inner track.

Next, in the above configuration, as the plurality of error detection circuits, for example, three error detection circuits 13a,
13b and 13c, the operation thereof will be specifically explained based on FIG.

In this case, different slice level values are set in the respective slice level setting circuits 18a, 18b, and 18c, and based on the slice level values, the digital
From the analog conversion circuits 17a, 17b, and 17c, a plurality of mutually different sets of slice levels (SL _a1 , SL _a2 ), (SL _b1 , SL _b2 ),
(SL _c1 , SL _c2 ) is output. These three sets of slice levels are separately compared with the comparator circuit 14a,
14b and 14c, where it is input to the amplifier circuit 15.
A comparison is made with the detection signal obtained from the above, and the presence or absence of a defect is determined based on the comparison result.

For example, consider a case where the magnetic recording/reproducing disk 3 has a relatively small defect 3c and a relatively large defect 3d as shown in FIG. 5A. When a constant frequency signal recorded on such a magnetic recording/reproducing disk 3 by the recording/erasing head 5 is read out by the reading head 4, a detection signal as shown in FIG. 5B is obtained from the amplifier circuit 15. It will be done. That is,
In the locations corresponding to defects 3c and 3d, only a considerably smaller level than the TAA level is obtained, and the degree of level reduction almost corresponds to the size of the defect, and the level reduction in defect 3d is greater than that in defect 3c. It's getting bigger. These detection signals are converted into the three sets of slice levels (SL _a1 , SL _a2 ), (SL _b1 ,
SL _b2 ) and (SL _c1 , SL _c2 ) to obtain defect detection signals as shown in FIG. 5C, D, and E, respectively. Here, according to the defect detection signals obtained from the comparison circuits 14a and 14b (FIG. 5C and D), 2
Both of the two defects 3c and 3d are detected as missing, and on the other hand, according to the defect detection signal obtained from the comparison circuit 14c (FIG. 5E), only the relatively large defect 3d is detected as missing. In this way, each error detection circuit 14a,
Defect detection results are obtained according to each slice level set in steps 14b and 14c.

On the other hand, when the magnetic recording/reproducing disk 3 shown in FIG. 5A is demagnetized by the recording/erasing head 5 and then read by the reading head 4, the amplifier circuit 15 outputs a detection signal as shown in FIG. 5F. can get.
That is, the level does not become zero at locations corresponding to the defects 3c and 3d, but a level of a certain degree of magnitude corresponding to each defect is obtained. These detection signals are converted into the three sets of slice levels (SL _a1 , SL _a2 ), (SL _b1 ,
When compared with SL _b2 ) and (SL _c1 , SL _c2 ), defect detection signals as shown in FIG. 5G, H, and I are obtained, respectively. Here, according to the defect detection signals (H, I in FIG. 5) obtained from the comparison circuits 14b and 14c, the two defects 3c and 3d are both detected as extra pulses, while the comparison circuit 14a
According to the defect detection signal obtained from (FIG. 5G), only the relatively large defect 3d is detected as an extra pulse. In this way, defect detection results are obtained according to each slice level set by each error detection circuit 14a, 14b, 14c.

(7) Effects of the Invention According to the present invention, defects in a magnetic medium are detected using a plurality of different sets of slice levels including positive and negative slice levels. This makes it possible to cover the non-uniform distribution of defects that occur when a magnetic medium is defective. Conversely, it is possible to reduce the probability of erroneously determining that a defective product is a non-defective product, making it possible to perform extremely reliable inspection.

Moreover, since each defect detection based on the plurality of slice levels described above is performed simultaneously, it is possible to accurately evaluate the quality of the magnetic medium with high work efficiency without increasing inspection time.

[Brief explanation of drawings]

Fig. 1 is a configuration diagram of a conventional magnetic medium inspection device, Fig. 2 A to F are signal waveform diagrams for explaining the operation of the inspection device shown in Fig. 1, and Fig. 3 shows the number of defects and slice level. FIG. 4 is a block diagram of an embodiment of the magnetic medium inspection apparatus of the present invention, and FIG. 5 is a signal waveform diagram for explaining the operation of the inspection apparatus shown in FIG. 4. 1...Motor, 3...Magnetic recording/reproducing disk, 4...
...Reading head, 5... Recording and erasing head, 6... Recording and erasing circuit, 13a to 13n
...Error detection circuit, 14a-14n...Comparison circuit, 15...Amplification circuit, 16a-16n...Average value setting circuit, 17a-17n...Digital-to-analog conversion circuit, 18a-18n...Slice level setting circuit .

Claims (1)

[Claims] 1. After recording a predetermined recording signal on a magnetic medium, the recording signal is read out to obtain a detection signal, and the detection signal is divided into a plurality of mutually different sets of slices each having positive and negative slice levels as one set. 1. A method for inspecting a magnetic medium, characterized in that the levels are compared at the same time, and defects in the magnetic medium are simultaneously detected based on the respective comparison results. 2. Recording means for recording a predetermined recording signal on a magnetic medium; reading means for reading out the predetermined recording signal recorded on the magnetic medium as a detection signal; and polarizing the detection signal read by the reading means. a plurality of error detection circuits for detecting defects in the magnetic medium by comparison with a set of slice levels; each slice level of the plurality of error detection circuits is set to a different level; A magnetic medium inspection device comprising: error detection means for simultaneously detecting defects with an error detection circuit.