JPH06168424A - Inspection method for magnetic head - Google Patents

Abstract

PURPOSE:To quantitatively obtain the extent of the waviness (noise) in the bottom part of signal waves obtained by samplings at different times. CONSTITUTION:A measuring instrument in which a regenerative signal 2 outputted by a magnetic head 1 is amplified by an amplifier 3 and the amplified regenerative signal 4 is calculated by an arithmetic unit 5 is provided. In the device, an average signal wave form 7 is obtained by averaging plural wave forms (a typical example is a wave form 6), a difference wave form 8 is obtained by calculating the difference between each of observed signal wave forms (a typical example is the wave form 6) and the average wave form 7, the extent of the waviness (noise) in the bottom part of the signal is quantitatively obtained by calculating the wave high value or the square mean value of the difference wave form.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention is used for magnetic heads such as fixed disk devices and video tape recorders, and is capable of measuring the noise amount of signal waveforms sampled at different times as clear numerical values. The present invention relates to a method for inspecting a head.

[0002]

2. Description of the Related Art FIG. 5 shows an example of a reproduction waveform of a conventional magnetic head. As shown in the broken line in FIG. 5 (a), waviness occurs especially in the tail portion of the signal waveform. Moreover, the shape of the swell changes at each observation time as shown in FIGS. 5 (b), 5 (c) and 5 (d) (hereinafter, this swell is referred to as irregular noise). Conventionally, the irregular noise has been visually determined. That is, the magnitude of the irregular noise was judged by visually judging the magnitude of the swell of the tail portion of the signal waveform displayed on the oscilloscope.

This irregular noise strongly affects the phase margin important for the recording / reproducing apparatus. The phase margin is an index indicating how much the time positions of the peaks of the positive and negative pulses in the signal waveform have a margin with respect to the time width of the data detection window (data window). In a magnetic head having a large amount of irregular noise, the fluctuation of the phase margin tends to be large, but there has been no method for accurately examining the correlation so far. That is,
This is because the amount of noise could not be accurately quantified in order to visually judge the irregular noise.

[0004]

In such a conventional method of inspecting a magnetic head, an operator must spend time with great care and attention. Further, since the work depends on intuition, it is easy for the workers to make a difference in the determination results, and a highly skilled worker is required. MEANS TO SOLVE THE PROBLEM The present invention solves the above-mentioned problem, and does not visually judge the irregular noise of the signal waveform, and anyone can easily and accurately quantify the irregular noise. It is an object of the present invention to provide a method for inspecting a head.

[0005]

In order to achieve the above object, the present invention provides a measuring device for inputting a reproduced signal output from a magnetic head to an amplifier and inputting the amplified reproduced signal to an arithmetic unit. Compose and obtain an average signal waveform that averages multiple signal waveforms sampled at different times,
The difference between the average signal waveform and each of the signal waveforms is calculated to obtain the difference waveform, and the irregular noise included in the signal waveform can be quantitatively obtained by the peak value or the root mean square value of the difference waveform. The magnetic head inspection method described above is used.

[0006]

Therefore, in the present invention, since a plurality of signal waveforms sampled at different times are averaged by the above configuration, irregular noise is canceled out in the average signal waveform, and the waviness of the tail portion is eliminated. become.
Therefore, the difference waveform can be extracted as irregular noise by subtracting the average signal waveform from the signal waveform.

[0007]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A first embodiment of the present invention will be described with reference to FIGS. FIG. 1 (a) shows the configuration of a measuring apparatus according to the first embodiment of the present invention, and FIGS. 1 (b), (c) and (d) show signal waveforms measured by the measuring apparatus,
An average signal waveform and a difference waveform are shown. 2 (a),
(b), (c) and (d) show the differential waveform of the present invention. In FIG. 1, the data recorded on the magnetic disk is reproduced by the magnetic head 1, the reproduced signal 2 thus reproduced is amplified by the amplifier 3, and the amplified reproduced signal 4 is taken into the arithmetic unit 5. The calculation program pre-installed in the calculation device 5 has a plurality of signal waveforms (a typical example is shown in FIG.
Signal waveform example 6) is averaged to obtain an average signal waveform 7 shown in FIG. 1C, and each signal waveform (a representative example is the signal waveform example 6 of FIG. 1B) and the average signal waveform 7 And the difference waveform 8 is obtained. The peak value is calculated from the difference waveform 8 and the irregular noise included in the signal waveform is quantitatively obtained.

The arithmetic unit 5 performs the arithmetic operation of the signal waveform, which is composed of, for example, a combination of a digitizing oscilloscope and a computer. The digitizing oscilloscope is an oscilloscope that can input a continuous analog signal waveform, sample the value of the continuous waveform at constant time intervals, and output the discrete sampling data. The amplified signal waveform 4 is input to a digitizing oscilloscope, the sampling data output from the digitizing oscilloscope is captured by a computer, and the data is processed according to a program incorporated in the computer in advance.

A method of obtaining the differential waveform and the peak value will be described. The signal waveform at a certain first time
₁ and (t)), the observation of n waveform from the signal waveforms in another second time (this V ₂ (t) and) so that such V ₁ (t) to V _n (t) Suppose First, an average signal waveform 7 (this is V (t)) obtained by averaging these n waveforms is obtained. The calculation formula of the average signal waveform V (t) is as shown in the formula (1).

[0010]

## EQU1 ## V (t) = {V ₁ (t) + V ₂ (t) + ... + V _n (t)} / n This average signal waveform V (t) is not calculated by averaging each signal waveform. The regular noise is canceled out, and the tail portion becomes a smooth shape.

Next, each signal waveform (V ₁ (t), V ₂ (t),
, V _n (t)) and the average signal waveform V (t) are calculated. For example, the difference waveform ΔV _i (t) is obtained by subtracting the average signal waveform V (t) from the i-th signal waveform V _i (t), which is expressed by the equation (2).

[0012]

[Number 2] _{ΔV i (t) = V i} (t) -V (t) such calculations the n (= 1,2, ..., n ) performed on pieces of each waveform. Difference waveform ΔV obtained by this method
An example of _i (t) is shown in the difference waveform 8 of FIG. 1 (d). The average signal waveform V (t) is obtained by averaging a plurality of signal waveforms, and since apparently irregular noise is canceled out, the average signal waveform from each signal waveform V _i (t) The difference waveform ΔV _i (t) obtained by subtracting V (t) can be treated as noise.

Here, the peak value in the difference waveform ΔV _i (t) is taken as the magnitude of noise. That is, as shown in FIG. 2 signal waveforms V _i average signal waveform V from (t) differential waveform [Delta] V _i obtained by subtracting the (t) the signal waveform peak value V _pi of (t) V _i (t) Is defined as the noise amount for (i = 1, 2,
…, N). Peak values (V _p1 , V _p2 , ..., V of the differential waveform
By determining the maximum V _pmax among _pn ), it is possible to measure which signal waveform has large random noise as a numerical value.

The greatest feature of the first embodiment is that only the noise waveform can be extracted separately from the original signal waveform. Therefore, the present invention is characterized by noise characteristics.
(Amplitude and phase relationship of noise) can be more accurately grasped, and it becomes an effective means for inspecting irregular noise at the time of manufacturing a magnetic head.

Next, a second embodiment of the present invention will be described. In the measuring apparatus of the second embodiment, each signal waveform V
Since _i until it obtains a difference waveform [Delta] V _i (t) of (t) is the same as the first embodiment will be described subsequent calculation processing. Peak value V of each signal waveform obtained in the first embodiment
Based on _pi , not only the maximum V _{pmax of} each peak value (V _p1 , V _p2 , ..., V _pn ) but also their average and standard deviation were obtained. Equation 3 shows the average X calculation method, and Equation 4 shows the standard difference σ calculation method.

[0016]

X = (V _p1 + V _p2 + ... + V _pn ) / n

[0017]

[Equation 4]

By thus _obtaining the average X and the standard deviation σ of the peak value V _pi of the differential waveform, the stochastic property of the irregularly changing waveform can be quantified more accurately. That is, the distribution state (histogram) of the peak value V _pi of the difference waveform can be accurately grasped, and each peak value V _pi
It is also possible to determine whether _pi is out of its distribution.

When the magnetic head of the 3.5-inch fixed disk device was inspected based on the method of the second embodiment, when the number of signal waveforms was set to n = 20, variation in judgment between workers was reduced and The magnetic head could be inspected in a short time. Further, 3% of defective products with irregular noise could be detected.

A third embodiment of the present invention will be described with reference to FIG. FIG. 3 (a) shows i when the present invention is used.
The third difference waveform ΔV _i (t) is shown, and FIG. 3B is a diagram showing an area calculation method for the squared waveform ΔV _i ² (t). The process up to the step of obtaining the difference waveform ΔV _i (t) of each signal waveform V _i (t) is the same as that of the first embodiment, so the calculation process of the root mean square value (effective value) after that will be described.

With the sampling time of the i-th difference waveform ΔV _i (t) set to ΔT, the root mean square value in the section from time t ₀ to time t _m is obtained. Although the width of ΔT in FIG. 3B is wide for convenience of explanation, the actual ΔT is set to a sufficiently small time so that high calculation accuracy can be obtained. For example, when the time period of the signal waveform is 2 microseconds,
The sampling time ΔT may be set to 5 nanoseconds or less.

The envelope curve of FIG. 3 (b) is ΔV _i (t) squared Δ
V _i ² (t) is shown, and the area S _i obtained by adding ΔV _i ² (t) multiplied by ΔT from t ₀ to t _m-1 is given by the equation (5).

[0023]

## EQU5 ## S _i = ΔT {ΔV _i ² (t ₀ ) + ΔV _i ² (t ₁ ) + ... + ΔV _i ² (t _m-1 )} This area represents S _i at time T (= t _m −t ₀ If the square root divided by) is defined as the effective value RMS _i , RMS _i is expressed by the equation (6).

[0024]

[Equation 6]

By calculating the maximum, average, standard deviation, etc. of the effective value RMS _i of each differential waveform obtained by the above method,
The magnitude of random noise can be measured as an accurate numerical value.

In the first and second embodiments described above, since the peak value of the differential waveform is used, only the instantaneous magnitude can be obtained, but in the third embodiment, the square of the voltage is calculated. Since it is a time average, it can be regarded as the average power of noise. Based on the method of the third embodiment
When the magnetic head of the 3.5-inch fixed disk device was inspected, when the number of signal waveforms was set to n = 20, it was possible to reduce the variation in the judgment between workers and to inspect the magnetic head in a short time. . Furthermore, 5% of defective products with irregular noise could be detected. This further improves the determination accuracy as compared with the second embodiment.

This irregular noise strongly affects the phase margin important for the recording / reproducing apparatus. The phase margin is an index indicating how much the time positions of the peaks of the positive and negative pulses in the signal waveform have a margin with respect to the time width of the data detection window (data window). In a magnetic head having a large amount of irregular noise, the fluctuation of the phase margin tends to be large, but there has been no method for accurately examining the correlation so far. By using the effective value RMS shown in the third embodiment, the correlation relation between the random noise and the fluctuation of the phase margin could be clarified. FIG. 4 shows the experimental result of the correlation between the standard deviation of the phase margin and the average of the effective value RMS for the 3.5 inch fixed disk device. As shown in FIG. 4, the effective value RM
It was possible to quantitatively analyze that the standard deviation of the phase margin increases as the average of S increases. This correlation analysis is made possible by accurately quantifying the irregular noise, unlike the conventional case where the signal waveform is visually judged.

[0028]

As is apparent from the above embodiments, according to the present invention, irregular noise can be distinguished from the original signal waveform and extracted. Therefore, the peak value or the root mean square value of the differential waveform can be calculated. By this, anyone can easily and accurately measure the magnitude of irregular noise, which enables stable inspection of the magnetic head. Therefore, the method of inspecting a magnetic head according to the present invention has an effect of having high industrial utility value.

[Brief description of drawings]

FIG. 1 is a diagram showing a configuration, a signal waveform, an average signal waveform and a difference waveform of a measuring device according to a first embodiment of the present invention.

FIG. 2 is a diagram showing a differential waveform in the second embodiment of the present invention.

FIG. 3 is a diagram showing an area calculation method for a differential waveform and its squared waveform in a third embodiment of the present invention.

FIG. 4 is a diagram showing a correlation between an average RMS value and a standard deviation of a phase margin in the third embodiment of the present invention.

FIG. 5 is a diagram showing a signal waveform of a conventional magnetic head.

[Explanation of symbols]

1 ... Magnetic head, 2, 4 ... Playback signal, 3 ... Amplifier,
5 ... Arithmetic device, 6 ... Signal waveform example, 7 ... Average signal waveform, 8 ... Difference waveform.

Claims (1)

[Claims] 1. A measuring device for inputting a reproduction signal output from a magnetic head to an amplifier and inputting the amplified reproduction signal to an arithmetic device, and averaging a plurality of signal waveforms sampled at different times. The average signal waveform obtained is calculated, the difference between the average signal waveform and each of the signal waveforms is calculated to obtain a difference waveform, and the irregular noise included in the signal waveform by the peak value or the root mean square value of the difference waveform. A method of inspecting a magnetic head, which is capable of quantitatively obtaining the value.