JP2006260618A - Evaluation method and device of magnetic recording medium - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a simple method based on the actual operating environments to evaluate the magnetic layer surface projections causing a thermal asperity phenomenon or spacing losses which degrades the error rates when recording or reproducing a magnetic recording medium. <P>SOLUTION: This is an evaluation method of the surface projections on a magnetic recording medium based on the reproduced signals after recording signals on the medium. It has a step of recording signals of a predetermined frequency, a step of reproducing the signals, a step of monitoring the output power and frequency of the reproduced signals, and a step of comparing and operating the output power and frequency with the predetermined values (L, H) each other. When the output power exceeds the threshold L, it decides there are projections, and detects the surface projections at the same time by classifying them depending on whether the frequency exceeds the threshold H or not. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a method for evaluating a magnetic recording medium, and more particularly, to an evaluation method and apparatus capable of evaluating protrusions of a magnetic layer under the same conditions as when a magnetic recording medium is actually reproduced.

  Magnetic recording media have various uses such as audio tapes, video tapes, computer tapes, magnetic disks, etc., especially in the field of magnetic tapes for data backup (backup tapes), as the capacity of hard disks to be backed up increases, Those with a storage capacity of more than several hundred GB per volume have been commercialized. In order to cope with the further increase in capacity of hard disks in the future, it is essential to increase the capacity of this type of backup tape.

  To increase the capacity per roll of backup tape, the total tape thickness is reduced to increase the tape length per roll, and the magnetic layer thickness is reduced to reduce the thickness demagnetization. Thus, increasing the short wavelength output, and increasing the recording density in the width direction by reducing the recording track width to 25 μm or less, particularly 15 μm or less, are being studied.

  Further, when the recording track width is narrowed to 25 μm or less, particularly 15 μm or less and the recording density in the width direction is increased, the leakage magnetic flux from the magnetic tape is reduced. The mainstream is to use an MR head using an MR element. In recent years, with the rapid increase in data backup capacity, data backup tape drives equipped with MR heads for signal reproduction have become widespread in the field of data storage. The MR head replaces a change in magnetic flux with a change in resistance value by an MR element, and does not have an induction coil. Therefore, a high S / N ratio can be obtained as compared with an inductive head.

  However, the characteristics of MR elements are likely to change due to temperature changes, and when they collide with protrusions existing on the recording surface of a magnetic recording medium during reproduction, the temperature of the MR element rises rapidly due to the heat (friction heat) generated during the collision. However, the resistance value changes, which causes noise. The MR head has a structure in which an MR element is provided in a portion recessed by a predetermined depth with respect to the sliding surface with the magnetic layer of the head. Usually, a small protrusion collides with the MR element. It is designed not to happen.

  When the recording track width is narrowed and the recording wavelength is shortened, the output of the reproduction signal becomes sensitive to the distance (spacing) between the surface of the tape magnetic layer and the MR element. For example, if there are protrusions or dents on the surface of the magnetic layer of the magnetic tape, the error rate increases due to a decrease in output due to spacing loss. In addition, since characteristics (resistance values) of MR elements are likely to change due to temperature changes, the MR element temperature changes when it collides with protrusions existing on the magnetic tape magnetic layer surface during reproduction of recorded data on the magnetic tape. Therefore, an unexpected fluctuation of the voltage value output from the MR element may occur, and a reading error may occur due to a so-called thermal asperity phenomenon.

  Thermal asperity not only leads to data reading failure, but is also recognized as a very undesirable phenomenon because it damages the MR element due to a rapid temperature change that occurs when the protrusion collides with the MR element. For this reason, a number of methods for preventing and reducing thermal asperities and methods for evaluating and measuring have been proposed. For example, Patent Document 1 discloses a thermal asperity phenomenon caused by protrusions present on the surface of a magnetic tape magnetic layer and a measuring method thereof in a data reproducing method using an MR element. In the measuring method of Patent Document 1, a magnetic tape on which no signal is recorded is run, and the distance between the MR element and the shield surface (sliding surface with the magnetic layer of the head) is different while the magnetic tape is running. A plurality of MR heads are arranged in parallel in the width direction of the magnetic tape, and for each MR head, the result of frequency analysis of the signal output during reproduction of the magnetic tape and the signal output during non-reproduction are Thermal asperity noise is detected by comparing the result of frequency analysis.

  In Patent Document 2, a test signal is recorded by an inductive magnetic head, a signal is reproduced by a magnetoresistive magnetic head, and this signal is converted into a first signal component having a frequency lower than a predetermined frequency by a filter. A magnetic disk inspection method is disclosed that separates into a high-frequency second signal component, detects a protrusion on the surface of the magnetic disk with a low-frequency signal component, and detects an error with a high-frequency signal component. .

On the other hand, with the further increase in capacity of backup tape media, the data recording track width is narrowed, and the optimum value of the distance (spacing) between the tape magnetic layer surface and the MR element is reduced. For this reason, protrusions on the magnetic tape magnetic layer surface that do not collide with the MR element but cause spacing loss are starting to affect the error rate more than ever, and the spacing loss phenomenon caused by protrusions is also a thermal asperity phenomenon. Similarly, the situation cannot be ignored when using the tape.

JP 2003-346331 A Japanese Patent Laid-Open No. 11-328670

  The method for evaluating protrusions on the surface of the tape magnetic layer in the above-mentioned Patent Document 1 is intended for the one that causes thermal asperity, and does not collide with the MR element and does not cause thermal asperity. Small protrusions that would cause reading errors were not subject to evaluation. In addition, this evaluation method requires a plurality of heads having different distances between the MR element and the shield surface, and there is a problem that the evaluation apparatus is expensive.

  On the other hand, evaluation of protrusions on the surface of the magnetic layer that affects the function of the MR head has been performed using a laser interference microscope, an atomic force microscope (AFM), or the like. It is limited to a very narrow range, and in order to obtain a correlation with actual error occurrence, it is necessary to observe a very large number of places, and the comparison and verification work is difficult.

  In the present invention, protrusions on the surface of the magnetic layer causing thermal asperity phenomenon and spacing loss, which cause the error rate at the time of recording / reproducing of the magnetic recording medium to be deteriorated, are easily evaluated according to actual use conditions and classified. It is to provide a way to do.

  In order to solve the above-mentioned problem, the magnetic recording medium evaluation method according to claim 1, wherein a step of recording a signal having a predetermined frequency, a step of reproducing the signal, and an output and a frequency of the reproduction signal are monitored. And a step of comparing and calculating the output and frequency of the reproduction signal with predetermined values (L, H), respectively, and when the output exceeds a threshold value L, it is determined as a protrusion, and at the same time The surface protrusions are classified and detected depending on whether the frequency exceeds a threshold value H or below.

The apparatus for evaluating a magnetic recording medium according to claim 2 is an apparatus for evaluating a magnetic recording medium that records and reproduces a signal on the magnetic recording medium and evaluates a surface protrusion of the magnetic recording medium based on the reproduction signal.
Means for recording a signal of a predetermined frequency, means for reproducing the recorded signal, means for monitoring the output and frequency of the reproduction signal, and comparing the output and frequency with predetermined values (L, H), respectively A means for calculating, and when the output exceeds a threshold L, it is determined as a protrusion, and at the same time, the surface protrusion is classified and detected depending on whether the frequency exceeds a threshold H or below. It is characterized by that.

  In the evaluation method described in Patent Document 2, a test signal is recorded by an inductive magnetic head, a signal is reproduced by a magnetoresistive magnetic head, and this signal is reduced to a frequency lower than a predetermined frequency by a filter. The first signal component and the second signal component of high frequency are separated, the protrusion on the surface of the magnetic disk is detected by the low frequency signal component, and the error is detected by the high frequency signal component. It is an inspection method, and the output of the reproduction signal of the present invention is compared with a threshold value L. When the output exceeds the threshold value L, it is determined that it is a protrusion, and at the same time, the frequency exceeds the threshold value H or below. Therefore, the method is different from the method of detecting the surface protrusions by classification.

  According to the evaluation method of the present invention, a step of recording a signal of a predetermined frequency, a step of reproducing the signal, a step of monitoring the output and frequency of the reproduction signal, and the output and frequency are set to a predetermined value. (L, H) and a step of performing a comparison operation, detecting a protrusion based on the threshold value L of the output and determining whether the protrusion is caused by a spacing loss or a thermal asperity phenomenon based on the frequency threshold value H. And the existence frequency of each can be evaluated.

According to the apparatus for evaluating a magnetic recording medium according to claim 2, means for recording a signal, means for reproducing the recorded signal, means for monitoring the output and frequency of the reproduction signal, and the output Means for comparing and calculating the frequency with a predetermined value (L, H), respectively, and detecting the protrusion by the threshold values L and H and whether the protrusion is caused by the spacing loss or the thermal asperity phenomenon, as described above. It is possible to distinguish and detect whether it is a thing, or to collect and output and save the analysis results by an output device (not shown).

  The present invention relates to a magnetic recording medium. Hereinafter, an evaluation method and an evaluation apparatus of the present invention will be described with reference to the drawings, taking a magnetic tape as an example. In the drawings to be referred to, FIG. 1 is a schematic diagram showing an example of the configuration of a magnetic tape evaluation apparatus according to an embodiment of the present invention.

  As shown in FIG. 1, the evaluation apparatus of the present invention guides the running reel 1 for feeding the magnetic tape T, the take-up reel 2 for taking up the fed magnetic tape T, and the running direction of the running magnetic tape T. It comprises a plurality of travel guides 3, a signal processing circuit C, a magnetic head 4, and a driving device (not shown) for driving the take-up reel 1 and take-up reel 2. The traveling system of the magnetic tape T may be any traveling system device as long as it has a function of traveling the magnetic tape T. There are no particular limitations on the material, surface state, etc. of the magnetic tape T. The signal processing circuit C and the running system may be those included in a data backup tape drive.

  The signal processing circuit C is a signal generation circuit 5 that constitutes a means for recording a signal, a signal reproduction circuit 6 that constitutes a means for reproducing a signal, and an output that is means for monitoring the output and frequency of a reproduction signal The frequency detection circuit 7 is composed of a comparison operation circuit that compares the output and frequency with predetermined values (L, H).

First, a signal having a predetermined frequency (H ₀ ) is recorded on the magnetic tape T by a signal generating circuit 5 which is a means for recording a signal and a recording head (inductive head) (not shown) disposed in the magnetic head 4. Is done. The value of H ₀ is not particularly limited, but a range of 1 to 50 MHz is preferable. Usually, it is preferable to use the recording frequency used in the data backup tape drive. The signal recorded on the magnetic tape T is reproduced by a reproduction head (MR head) (not shown) disposed in the magnetic head 4 which is a means for reproducing the signal and the signal reproduction circuit 6 and shown in FIGS. Such a reproduced signal waveform is obtained. FIG. 2 shows the waveform of the normal part of the magnetic tape T, and FIGS. 5 and 8 show the waveform of the protrusion on the surface of the magnetic tape T (no thermal asperity) and the protrusion that caused thermal asperity, respectively.

  The output / frequency detection circuit 7 which is means for monitoring the output and frequency of the reproduction signal includes a waveform squaring circuit, a noise removal circuit, and a peak hold circuit (not shown), and has a positive polarity as shown in FIG. Extract the square signal waveform. The output value indicated by the square signal waveform and the threshold value L are compared by a comparison operation circuit 8 described later. FIG. 3 shows the square signal waveform of the normal part of the magnetic tape T, and FIGS. 6 and 9 show the square signal waveform of the protrusion on the surface of the magnetic tape T (without thermal asperity) and the protrusion that caused thermal asperity, respectively.

  Further, the output / frequency detection circuit 7 includes a frequency count circuit (not shown), and extracts a frequency from a certain section (200 μs in the drawing) of the reproduction waveform by a change in the polarity of the reproduction signal at the baseline. FIG. 4 shows an enlarged waveform of the normal part of the magnetic tape T, and FIGS. 7 and 10 show an enlarged waveform of the time axis of the protrusion having no thermal asperity and the thermal asperity on the surface of the magnetic tape T (5 μs interval in the figure). In the enlarged waveform of the protrusion portion without thermal asperity in FIG. 7, no change in frequency is observed compared to the normal portion. However, in the enlarged waveform of the thermal asperity protrusion in FIG. 10, the count frequency decreases because there is a non-frequency-counting portion with no polarity change at the baseline.

  When the output value of the square signal waveform exceeds a predetermined threshold value L, the comparison operation circuit 8 as means for comparing the output and frequency with predetermined values (L, H) respectively has a protrusion on the magnetic layer. It is determined that it was correct. At the same time, a comparison is made as to whether the value of the frequency exceeds a predetermined threshold value H or below, and if it exceeds H, thermal asperity does not occur but a projection causing spacing loss. It is determined that the protrusion causes asperity. This makes it possible to distinguish the protrusions according to the type of error that causes them. A flowchart of the comparison operation circuit 8 is shown in FIG.

The threshold value L may be set to a value larger than L ₀ when the output of the normal part is L ₀ , but if a value that is too close to L ₀ is set, even a small protrusion that does not cause an error will be detected. If an excessively large value is set, an error-protruding protrusion will not be detected. Therefore, it is preferable to set it appropriately according to the conditions of the data backup tape drive, but normally 1.2 ≦ (L / L ₀ ) ≦ 5 The range is preferably set, and 1.5 ≦ (L / L ₀ ) ≦ 3 is more preferable. The threshold value H may be set to a value smaller than H ₀ when the recording frequency is H ₀ , but if the value is set too close to H ₀ , correct detection cannot be performed due to the influence of noise and travel speed fluctuations. If a value that is too small is set, a small thermal asperity cannot be detected. Therefore, it is preferable to set it appropriately according to the conditions of the tape drive for data backup. Usually, however, 5 ≦ (H ₀ -H) ≦ 50 The range is preferably set, and more preferably 10 ≦ (H ₀ −H) ≦ 30. The section for counting the frequency may normally count the frequency in the section of 100 to 500 μs. 2 to 10 show data in a 200 μs section.

Further, when the output waveforms of the protrusions in FIGS. 6 and 9 and the frequency countless width in FIG. 10 are observed in detail, the following can be found based on the evaluation method (apparatus) of the present invention. That is, the value of the output of the protrusions has a height and the correlation of the projections, also, the time width of the output is L ₀ smaller portions before and after the output waveform of the projections (W), the magnetic tape T longitudinal projection The frequency countless width correlates with the size of the portion corresponding to the magnetoresistive effect element of the protrusion, so based on this information, the protrusions are separated and aggregated to determine the state of the surface protrusion of the magnetic tape T. A more detailed analysis is possible.

The schematic diagram which shows an example of a structure of the magnetic tape evaluation apparatus which is one Embodiment of this invention Normal part waveform diagram Normal part square signal waveform diagram Enlarged waveform diagram of normal part Protrusion (without thermal asperity) waveform diagram Square signal waveform diagram of protrusion (no thermal asperity) Enlarged waveform diagram of protrusion (no thermal asperity) Protrusion (thermal asperity) waveform diagram Square signal waveform diagram of protrusion (thermal asperity) Enlarged waveform diagram of protrusion (thermal asperity) Flowchart of comparison operation circuit 8

Explanation of symbols

T magnetic tape C signal processing circuit 1 unwinding reel 2 take-up reel 3 traveling guide
4 Magnetic head (including MR head and inductive head)
5 Signal Generation Circuit 6 Signal Recovery Circuit 7 Output / Frequency Detection Circuit 8 Comparison Operation Circuit

Claims (2)

  A method for evaluating a magnetic recording medium that records and reproduces a signal on a magnetic recording medium and evaluates surface protrusions of the magnetic recording medium based on the reproduced signal, the step of recording a signal of a predetermined frequency, and reproducing the signal And a step of monitoring the output and frequency of the reproduction signal, and a step of comparing the output and frequency of the reproduction signal with predetermined values (L, H), respectively, the output being a threshold value L A method for evaluating a magnetic recording medium comprising: determining that the protrusion is a protrusion when the frequency exceeds the threshold value, and simultaneously detecting the surface protrusion depending on whether the frequency exceeds a threshold value H or below. An apparatus for evaluating a magnetic recording medium that records and reproduces a signal on a magnetic recording medium and evaluates surface protrusions of the magnetic recording medium based on the reproduced signal, the means for recording the signal, the means for reproducing the recorded signal, Means for monitoring the output and frequency of the reproduction signal, and means for comparing the output and the frequency with predetermined values (L, H), respectively, and when the output exceeds a threshold value L, An apparatus for evaluating a magnetic recording medium, characterized in that it is determined that the surface protrusion is present and at the same time, the surface protrusions are classified and detected depending on whether the frequency exceeds a threshold value H or below.

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