JP2005056496A - Measuring method of overwrite property - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To accurately measure an overwrite value by preventing the occurrence of a measurement error due to off-track in reading based on large positional deviation of a track position at overwritting. <P>SOLUTION: Signal intensity are detected in a plurality of measurement points between an inner periphery and an outer periphery of the overwritten measurement track, an off-track profile of an amplitude value of a reproduced signal and an off-track profile of a signal component of a low frequency signal are prepared, a position of an effective track is estimated from the off-track profile of the amplitude value of the reproduced signal, a signal component of the residual low frequency signal is calculated from the position of the effective track and the off-track profile of the signal component of the low frequency signal, and the overwrite value is determined by calculating a ratio of the signal component of the residual low frequency signal and the signal component of the low frequency signal before being overwritten. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

The present invention relates to a method for evaluating a magnetic disk medium, and more particularly to a method for evaluating an overwrite characteristic in a read / write test.

  A hard disk device is a large-capacity external storage device that reads and writes digital information from and to a concentric track of a magnetic disk medium that rotates at high speed. The hard disk apparatus employs an overwrite system that does not erase in advance as a system for writing digital information to a magnetic disk medium.

  Since this overwrite method overwrites old data with new data, it is important that the magnetic disk medium has high writing ability. Therefore, in the read / write test of the magnetic disk medium, the overwrite characteristic is quantitatively evaluated.

Here, a conventional method for measuring the general overwrite characteristic will be described.
First, the periphery of the measurement track is demagnetized (that is, DC erase). Next, a low frequency (LF) signal (a signal having a constant frequency of 10 MHz to several tens of MHz) is written to the measurement track, and a signal component (magnitude) of the LF frequency is measured. Further, a high frequency (HF) signal (a signal having a frequency several times that of the LF signal) is overwritten on the track, and the remaining signal component of the LF frequency is measured. The overwrite value is obtained as the ratio (M2 / M1) of the signal component (M2) of the residual LF frequency after overwriting to the signal component (M1) of the LF frequency before overwriting.

Here, how to obtain M2 by the conventional measurement method will be described.
First, as a precondition, it is assumed that the LF signal is written (written) for one round in advance on the measurement track.

  Next, the head 9 (see FIG. 1 described later) is moved to the center position of the measurement track. Then, the HF signal is written for one round on the measurement track. As a result, the HF signal is overwritten on the LF signal.

  Next, the head 9 is offset in the track direction by the write / read offset, and the center position of the reproducing head is adjusted to the center position of the measurement track. As a result, the signal recorded on the measurement track is reproduced by the reproducing head of the head 9. Here, the read / write offset is measured in advance by a known method.

  Then, the LF frequency component of the reproduction signal is measured, and this measured value is M2.

Japanese Patent Laid-Open No. 10-320702 JP 2002-93088 A

  By the way, the performance of hard disk devices has improved year by year due to the progress of various basic technologies, and recent models satisfy very strict design specifications. For example, the track density has reached about 60 kTPI. Along with this, the write width of the recording / reproducing head has become extremely narrow.

  The reduction in the write width of a recording / reproducing head makes it more difficult to measure the read / write characteristics of a magnetic disk medium using the head. This is because the positioning accuracy of the spin stand in the track direction is limited, and as the write width is reduced, the influence of positioning errors increases, which is particularly a serious problem in the measurement of overwrite characteristics. ing. That is, in the measurement of the overwrite characteristic, the head is positioned at each time of overwriting and when the overwritten signal is read, and a position error occurs at that position.

  As shown in FIG. 14, when the head position is shifted in the track direction (radial direction) T during overwriting, the width in the track direction T of the actually overwritten region R1 becomes narrower. Further, a region R2 that remains without being overwritten is generated. When the width of the region R2 in the track direction exceeds a certain ratio with respect to the write width, signal leakage from this region affects and an error occurs in the measurement of the residual LF signal component.

8 and 9 show the track profile of the LF signal component after overwriting.
8 shows a case where the positional deviation ΔT between the track positions of the LF signal and the HF signal is small, and FIG. 9 shows a case where the positional deviation ΔT between the track positions is large. Reference numeral 100 denotes the position of the recording head when the LF signal is written. Reference numeral 200 denotes the position of the recording head when the HF signal is written. Reference numeral 300 denotes an execution track formed by overlapping the tracks of the LF signal and the HF signal, and the track width from one end of 100 to one end of 200 is defined. Reference numeral 310 denotes the center position of the execution track 300.

  When the deviation is small as shown in FIG. 8, the off-track profile is substantially trapezoidal. However, when the deviation increases as shown in FIG. 9, the off-track profile has a peak in the vicinity of the region where the LF signal is not overwritten. Further, the signal intensity Mb at the center of the effective track 300 increases compared to the signal intensity Ma when the deviation is small due to the leakage of the signal from the region that remains without being overwritten, and becomes an inaccurate value.

  Further, when reading the overwritten signal, it is necessary to accurately position the reproducing head at the center position 310 of the effective track 300.

  However, in the conventional measurement method, reading is performed at a position shifted from the center position 310 of the effective track 300 due to the positioning error of the spin stand in the track direction T, which causes an error in the measurement of the residual LF signal component. .

  That is, the conventional measuring method has a problem in that the track position deviation ΔT is allowed without limitation when overwriting using the recording head. Further, there is a problem in that when the overwritten signal is read using the reproducing head, the reading is permitted at a position shifted from the center position 310 of the effective track 300.

  Therefore, an object of the present invention is to avoid the occurrence of measurement errors due to off-tracking at the time of reading (during reproduction) based on a large positional deviation of the track position at the time of overwriting (at the time of overwriting), and to accurately overwrite the overwrite value. An object of the present invention is to provide a method for measuring an overwrite characteristic that can be measured.

  The present invention is a method for measuring an overwrite characteristic of a magnetic disk medium, wherein after demagnetizing a measurement track of the magnetic disk medium, a low frequency signal is written to the track and the low frequency before being overwritten. A measurement step of measuring a signal component of the signal, and after overwriting the measurement track in which the signal component of the low frequency signal is written with a high frequency signal, a plurality of portions between the inner and outer circumferences of the overwritten measurement track A creation step of creating an off-track profile of the amplitude value of the reproduction signal and an off-track profile of the signal component of the low-frequency signal by detecting the signal intensity at the measurement point, and the amplitude value of the created reproduction signal The effective track position is estimated from the off-track profile of the track, and the estimated effective track position and the creation are A calculation step of calculating a signal component of the remaining low-frequency signal based on the off-track profile of the signal component of the low-frequency signal, the signal component of the calculated remaining low-frequency signal, and the measured By providing an overwrite value determination step of determining an overwrite value by calculating a ratio with a signal component of a low frequency signal before being overwritten, a method for measuring an overwrite characteristic is provided.

  The calculating step calculates a head position of a recording head corresponding to an edge of an effective track constituted by the low-frequency signal and the high-frequency signal from an off-track profile of the amplitude value of the generated reproduction signal. And calculating the center position of the execution track from the calculated head position, and based on the calculated center position of the effective track and the off-track profile of the signal component of the generated low-frequency signal. A calculation step of calculating a signal component of the remaining low-frequency signal.

  The track position corresponding to the low frequency signal and the track corresponding to the high frequency signal are compared by comparing the signal intensity at a predetermined measurement point of the off-track profile of the signal component of the generated low frequency signal with a reference value. And a step of evaluating a deviation width of the track position in the track direction, and a step of invalidating the measurement of the overwrite characteristic when the deviation width of the track position in the track direction exceeds a predetermined value. Good.

  As described above, according to the present invention, the signal intensity is detected at a plurality of measurement points between the inner and outer circumferences of the overwritten measurement track, and the off-track profile of the amplitude value of the reproduction signal and the signal of the low frequency signal are detected. Component off-track profile, the effective track position is estimated from the off-track profile of the amplitude value of the playback signal, and the low-frequency signal remaining from the effective track position and the off-track profile of the signal component of the low-frequency signal Since the signal component of the remaining low frequency signal and the ratio of the measured signal component of the low frequency signal before being overwritten are calculated to determine the overwrite value. It is possible to measure the overwrite by adopting the off-track profile of the residual LF signal component at the center position of the effective track. Can, thereby, avoids the occurrence of an error due to the off-track during the read, even when using a narrow head having a write width, the overwrite characteristics can be accurately measured.

  In addition, according to the present invention, the measurement of the overwrite characteristic is made effective only when the positional deviation amount of the track position between the HF signal and the LF signal is within the allowable range. It is possible to avoid occurrence of a measurement error corresponding to a large positional deviation.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.

(Constitution)
First, the configuration of a read / write test apparatus used in the method for measuring the overwrite characteristics according to the present invention will be described.

  FIG. 1 shows a configuration example of a read / write test apparatus 9 used for overwriting measurement. The read / write test apparatus 1 generates a spin stand 3 for rotating the magnetic disk medium 2, a signal generator 4 for generating write data 4 a, a write current 5 a corresponding to the write data 4 a, and inputs the write current 5 a to the spin stand 3. It comprises a write amplifier 5, a read amplifier 6 that amplifies the head signal 6 a output from the spin stand 3, a spectrum analyzer 7, and an oscilloscope 8.

  The spin stand 3 includes a positioning mechanism 10 for positioning the recording / reproducing head 9 on an arbitrary track on the magnetic disk medium 2.

  The head 9 includes an inductive head as a recording head and an MR (Magneto Resistive) head or GMR (Giant Magneto Resistive) head as a reproducing head. The head 9 is mainly a composite head in which a recording element and a reproducing element are independent, but is not limited to this.

(Measuring method)
Next, an overwriting measurement method will be described.
FIG. 2 is a flowchart showing the measurement procedure of the overwrite measurement method.
First, after setting a magnetic disk medium to be measured as a preparatory work on the spin stand 3, the magnetic disk medium is rotated at a constant rotation speed, and the recording head of the head 9 is moved to the measurement track.

Next, the actual measurement work is started.
In step S1, the peripheral tracks including the measurement track are degaussed (DC erased).

  In step S2, an LF signal (for example, a signal having a constant frequency of 10 MHz) is written to the measurement track for one round.

  In step S3, the LF signal component M1 is measured. For this reason, first, the reproducing head of the head 9 is moved onto the measurement track to reproduce the recorded signal.

  Due to this reproduction, the waveform of the reproduction signal as shown in FIG. The waveform of the reproduction signal has a spectrum as shown in FIG. 5 in the frequency domain.

The spectrum includes a fundamental frequency component H _{1 of} 10 MHz and odd harmonic components H ₃ , H ₅ , H ₇ . . . Is included. Among them, the fundamental frequency component _{H 1} of the intensity of 10MHz (unit Volt) measured with a spectrum analyzer 7, and this measured value and the LF signal component M1.

  In step S4, the recording head of the head 9 is moved onto the measurement track, and the HF signal (for example, a signal having a constant frequency of 60 MHz) is overwritten.

  In step S5, an off-track profile of the amplitude value of the reproduction signal and an off-track profile of the residual LF signal component are acquired.

Here, the acquisition procedure will be described.
FIG. 6 shows an off-track profile 20 of the amplitude value of the reproduction signal. FIG. 7 shows an off-track profile 30 of the residual LF signal component.

  First, the reproducing head of the head 9 is moved to a position, for example, 0.4 μm away from the measurement track on the inner circumference side. Then, the peak-to-peak amplitude of the reproduction signal is measured with the oscilloscope 8 and the result is recorded. Further, the signal intensity of the fundamental frequency component of 10 MHz is measured by the spectrum analyzer 7 and the result is recorded. Also, the current head position is recorded.

  Similarly, the head 9 is moved from the current head position in the track direction T (see FIG. 14) to the outer periphery by, for example, 0.05 μm, and the LF signal component and the amplitude value are measured. Record the position.

  Such a series of <movement-measurement-recording> operations are repeated until the reproducing head of the head 9 reaches a position 0.4 μm away from the measurement track on the outer peripheral side.

  As a result, the off-track profile 20 of the amplitude value shown in FIG. 6 and the off-track profile 30 of the LF signal component shown in FIG. 7 are obtained.

  The acquired off-track profile 20 of the amplitude value is composed of amplitude value data AM (n) (unit Volt) and head position data P (n) (unit μm). Here, n is an index number corresponding to the measured head position.

  The LF signal component off-track profile 30 includes signal intensity data LF (n) (unit Volt) and head position data P (n) (unit μm).

  As can be seen from FIG. 6, the off-track profile 20 of the amplitude value is generally bell-shaped and its peak is approximately at the center of the measurement track.

  In step S6, the off-track profile 30 of the residual LF signal component in FIG. 7 is analyzed. Here, the shape of the off-track profile 30 of the residual LF signal component is examined, and based on the result, the magnitude of the deviation width (the positional deviation ΔT shown in FIGS. 8 and 9) between the LF signal track and the HF signal track is determined. To evaluate.

  As the evaluation method, as shown in FIG. 7, the signal intensity value LF (n) at each head position measurement point in the off-track profile 30 of the residual LF signal component is compared with a threshold value Mmax. This comparison processing is performed for all measurement points n (n = 1, 2,..., N, N is the number of measurement positions).

  In step S7, it is determined whether the overwriting process is OK or NG. From the comparison result, when the signal intensity value satisfies the condition of LF (n) ≦ Mmax, the process proceeds to step S8, and overwrite processing is executed. However, if the condition is not satisfied, the measurement result is invalidated, the process returns to step S1 without performing the overwriting process, and the measurement is restarted from the beginning.

Here, the determination process in step S7 will be described with an example.
8 and 9 are examples of the off-track profile 30 of the residual LF signal component.
FIG. 8 shows an example in which the shift between the track positions of the LF signal and HF signal is small. FIG. 9 is an example when the deviation is large.

  When the positional deviation ΔT of the track position is small as shown in FIG. 8, the off-track profile 30 is substantially trapezoidal. However, when the positional deviation ΔT is large as shown in FIG. 9, the off-track profile 30 has a peak in the vicinity of the region where the LF signal is not overwritten. Since this peak value increases as the positional deviation ΔT increases, it is possible to determine the magnitude of the positional deviation width based on the peak value.

  In step 8, a residual LF signal component at the center of the effective track 300 shown in FIG. 9 is obtained.

  FIG. 3 is a flowchart showing the detailed overwriting process in step S8. This overwriting process will be described with reference to FIGS.

In step S11, the head positions P ₁ and P ₂ at the edge of the effective track 300 are obtained from the off-track profile 20 of the amplitude value of the reproduction signal shown in FIG.

In step S12, it obtains the head position _{P 0} at the center of the effective track 300 by the following equation.
P ₀ = (P ₁ + P ₂ ) / 2

As shown in FIG. 10, the edge positions P ₁ and P ₂ of the effective track 300 correspond to head positions where the amplitude of the off-track profile 20 of the amplitude value of the reproduction signal is 50% of the maximum value.

In step S13, it obtains the signal intensity M2 in residual LF signal head position _{P 0} of the off-track profile 30 of the components shown in FIG. 11.

  The signal strength M2 is obtained by interpolation processing of the signal strength data LF (n) of the off-track profile 30 of the residual LF signal component. Here, linear interpolation is used, but not limited to linear interpolation, other known interpolation methods can be applied.

  Finally, returning to step S9 in FIG. 2, the ratio (M2 / M1) between the residual LF signal component M2 obtained in step 8 and the LF signal component M1 obtained in step 3 is calculated based on the definition of the overwrite characteristic. The calculated value is used as an overwrite value.

(Comparative example)
Next, an example in which the overwrite characteristic is compared with the conventional method will be described.
Here, the result of applying the measurement method of the overwrite characteristic to the measurement of an actual magnetic disk medium is shown.

FIG. 12 shows a method according to the present invention, FIG. 13 shows a conventional method, and the results of measuring the overwrite characteristics of the same magnetic disk medium were compared. Each measurement is performed a plurality of times, and the measurement results are shown as histograms 400 and 410.
The measurement conditions are as follows.
LF frequency: 10 MHz
HF frequency: 60MHz
Write current value: 49.7 mA
Disc media: 3.5 inch
Rotation speed: 5400rpm
Radius value: 32mm
Skew angle: 3.187deg

  12 and 13, the horizontal axis represents the overwrite value (M2 / M1), and the vertical axis represents the frequency (frequency) at which each bar graph appears.

  In the case of the method according to the present invention shown in FIG. 12, the average overwrite value is -28.49 dB, and the standard deviation is 1.2 dB. In the case of the conventional system shown in FIG. 13, the average value of the overwrite value is −27.78 dB, and the standard deviation is 3.0 dB.

  When compared with the standard deviation, it can be seen that the overwrite value is greatly reduced to 1.2 dB in the method according to the present invention, compared to 3.0 dB in the conventional method. Ideally, it is desirable that the measurement values are aggregated into a single bar graph having no variation, but the method according to the present invention clearly has less variation in the measurement value than the conventional method. I understand.

  From the above comparison results, it is proved that the method for measuring the overwrite characteristics according to the present invention is much more effective than the conventional method.

  In this example, in order to simplify the explanation, an example in which the off-track profile 20 of the amplitude value and the off-track profile 30 of the LF signal component are obtained only once for each measurement.

  However, in practice, it is desirable to acquire each off-track profile M times (M is a value of about 5 to 10) for each measurement. In this case, in Step 8 of the flowchart of FIG. 1, the residual LF signal component M2 at the center position of the effective track is calculated for each of the M off-track profiles. A value obtained by averaging the M residual LF signal components M2 is used for the calculation of the overwrite characteristic (M2 / M1). By this calculation, the influence of the positioning error of the head position of the spin stand 3 and the measurement error due to other factors is removed, and the measurement accuracy of the overwrite characteristic can be further improved.

  The present invention relates to a method for evaluating a magnetic disk medium, and more particularly to a method for evaluating an overwrite characteristic in a read / write test. It is possible to avoid the occurrence of measurement errors due to off-tracking at the time of reading (during reproduction) based on a large positional deviation of the track position at the time of overwriting (at the time of overwriting), and to accurately measure the overwrite value.

It is a block diagram which shows the structure of the read / write test apparatus used for this invention. 3 is a flowchart showing a method for evaluating overwrite characteristics according to the present invention. It is a flowchart which shows the process of the overwrite which concerns on this invention. It is explanatory drawing which shows the waveform of a reproduction signal. It is explanatory drawing which shows the spectrum of a reproduction signal. It is a wave form diagram which shows the off-track profile of the amplitude value of a reproduction signal. It is a wave form diagram which shows the off-track profile of a residual LF signal component. It is explanatory drawing which shows the off-track profile of LF signal component after overwriting. It is explanatory drawing which shows the off-track profile of LF signal component after overwriting. It is explanatory drawing which shows the method of calculating | requiring the edge and center position of an effective track. It is explanatory drawing which shows the method of calculating | requiring a residual LF signal component. It is explanatory drawing which shows the measurement result of the overwrite value by the system of this invention. It is explanatory drawing which shows the measurement result of the overwrite value by a conventional system. It is explanatory drawing which shows the mode of a shift | offset | difference of a track position.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Read / write test apparatus 2 Magnetic disk medium 3 Spin stand 4 Signal generator 4
4a Write data 5 Write amplifier 5a Write current 6 Read amplifier 6a Head signal 7 Spectrum analyzer 8 Oscilloscope 9 Head 10 Positioning mechanism 100 Recording head position 200 when writing LF signal Recording head position 300 when writing HF signal Execution track 310 Center position of execution track

Claims (3)

A method for measuring the overwrite characteristics of a magnetic disk medium,
A measurement step of demagnetizing a measurement track of the magnetic disk medium, writing a low frequency signal to the track, and measuring a signal component of the low frequency signal before being overwritten;
After overwriting the measurement track in which the signal component of the low frequency signal is written with a high frequency signal, detecting signal strength at a plurality of measurement points between the inner and outer circumferences of the overwritten measurement track, A creation step of creating an off-track profile of the amplitude value of the reproduction signal and an off-track profile of the signal component of the low-frequency signal;
An effective track position is estimated from the off-track profile of the amplitude value of the generated reproduction signal, and based on the estimated effective track position and the off-track profile of the signal component of the generated low-frequency signal, A calculation step of calculating a signal component of the remaining low-frequency signal; and calculating a ratio between the calculated signal component of the remaining low-frequency signal and the measured signal component of the low-frequency signal before being overwritten. And an overwrite value determination step for determining an overwrite value. The calculation step includes
Calculating a head position of a recording head corresponding to an edge of an effective track constituted by the low frequency signal and the high frequency signal from an off-track profile of the amplitude value of the created reproduction signal;
Calculating a center position of the execution track from the calculated head position;
A calculation step of calculating a signal component of the remaining low-frequency signal based on the calculated center position of the effective track and an off-track profile of the signal component of the generated low-frequency signal. The method for measuring an overwrite characteristic according to claim 1. The track position corresponding to the low frequency signal and the track corresponding to the high frequency signal are compared by comparing the signal intensity at a predetermined measurement point of the off-track profile of the signal component of the generated low frequency signal with a reference value. A step of evaluating the deviation width in the track direction from the position;
3. The overwrite characteristic according to claim 1, further comprising a step of invalidating measurement of the overwrite characteristic when a deviation width of the track position in the track direction exceeds a predetermined value. Measuring method.

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