JP2652883B2 - Method for measuring current saturation characteristics of magnetic disk - Google Patents

Description

The present invention relates to a method for measuring a current saturation characteristic of a magnetic disk, and more particularly, to a method of erasing a modulation generated in a read signal due to distortion of a magnetic disk or the like. A correct saturation characteristic is required.

[Prior Art] Magnetic disks, which are frequently used as information recording media,
Various tests are performed during the manufacturing process. One of the test items is the saturation characteristic of the recording medium with respect to the write current, and an appropriate write current is determined based on the saturation characteristic.

4 (a), 4 (b), 4 (c) and 4 (d), a conventional method for measuring the current saturation characteristic of a magnetic disk will be described. With respect to a predetermined track of the magnetic disk 1 shown in FIG. 5A, between the indexes (IND), that is, in one round of the track, a write current Iw having a constant frequency shown in FIG.
, A test signal is written and read.
In this case, the relationship between the amplitude of the current Iw and the amplitude ER of the read test signal is such that, as shown in FIG. 9C, ER rises proportionally rapidly to a certain degree as the Iw increases, and saturates at the peak value Ep. After that, it gradually decreases. The cause of the decrease is Iw
Is too large, the magnetic field of the recording head affects and the immediately preceding recording code is demagnetized.

According to the above characteristics, before saturation, ER greatly changes due to a small change in Iw, and is unstable, and when too large, it adversely affects the immediately preceding recording code, which is not preferable. On the other hand, a point q where the change is small immediately after the peak point p is taken, and the current value Iwc for the point q is determined to be an appropriate current value. The point q is obtained by multiplying the peak value Ep by an appropriate coefficient k smaller than 1.

It is necessary to measure the saturation characteristic in order to obtain the above appropriate current or to know the recording performance of the medium,
Conventionally, a method of obtaining the (ER-Iw) curve of FIG. 4C, that is, a saturation characteristic, by repeating writing and reading on the same track a plurality of times using Iw as a parameter has been performed.

[Problem to be Solved] In the above-described measurement of the saturation characteristic, writing and reading for one round of the track are performed for each current value Iw, respectively. The modulation shown in FIG. 4 (d) occurs in the read test signal due to distortion or the like existing on the magnetic disk, so that the modulation is erased by calculating the average value of one round. In such a test method,
When the number of tests is large and a large number of magnetic disks are used in a production factory, the measurement takes a very long time and is not efficient. On the other hand, the inventor of the present invention performs writing and reading with a write current of varying amplitude for one round of a track on the assumption that there is no modulation or that this can be corrected.
A method of efficiently finding the saturation characteristic and the appropriate current in the test of the circumference was proposed. On the same day, a method for measuring the write current value of a magnetic disk was disclosed in Japanese Patent Application No. 1-68765 (JP-A-2-247805). And its current value measuring device. Therefore, there is a problem in a method of eliminating the modulation and obtaining a correct saturation characteristic.

The present invention has been made in view of the above, and writes a test signal with a write current of which amplitude changes over one round of a track of a magnetic disk, erases a modulation generated in the read signal, and corrects a current saturation characteristic. It is an object of the present invention to provide a measuring method for outputting the data of (1) and the data of an appropriate write current value.

[Means for Solving the Problems] A feature of the method for measuring a current saturation characteristic of a magnetic disk according to the present invention for achieving the above object is that a constant rotation is maintained for one round of a track between index signals of the magnetic disk. A write current having a frequency and an amplitude that increases stepwise by a constant amount at every fixed rotation angle of the magnetic disk, and whose maximum increase is larger than a point at which storage of the magnetic disk is saturated. The test signal is written, the written test signal is read, the envelope signal of the read test signal is detected, and the envelope signal at the rotation angle at a fixed interval is measured in advance and stored in the memory. Modulation correction coefficient corresponding to each rotation angle at regular intervals Envelope signal value for each rotation angle at regular intervals , And outputs a proper write current value exceeding a saturation point determined according to the saturation characteristic data.

As a specific example of measuring the above-described modulation correction coefficient, for example, writing and reading of a test signal are performed with a current having a constant amplitude and frequency for one round of a track. An envelope signal corresponding to the read test signal and peak values at rotation angles at fixed intervals are detected. The average value of each peak value for one round of the track is calculated, and the ratio between the average value and each peak value is used as a modulation correction coefficient.

[Operation] With reference to FIGS. 1 (a), (b) and (c), the procedure of the method for measuring the current saturation characteristic according to the present invention will be described. Under the control of the microprocessor, the writing is performed such that the amplitude increases stepwise for each rotation angle θ ₁ , θ ₂ ... Θ _n (n is the number of divisions of one track round) at fixed intervals of rotation of the magnetic disk shown in FIG. The test signal is written to one round of the track between the indexes of the magnetic disk by the current Iw. When this is read out and its envelope signal Ee is detected, a modulated waveform shown in FIG. 7B is obtained, and its peak value is indicated by Ep. By multiplying the peak value at each rotation angle of the envelope signal Ee by a modulation correction coefficient, a corrected envelope signal Ee 'shown in FIG. 3C is obtained, and this is the saturation curve to be obtained. From the rotation angle θq with respect to kEp obtained by multiplying the peak value Ep by an appropriate constant k smaller than 1, the appropriate current Iwc is obtained by the curve Iw = θ in FIG.
Is required. These operations are performed by a microprocessor.

Next, a procedure for obtaining a modulation correction coefficient will be described with reference to FIG. When a test signal is written to a circumference of the track of the magnetic disk by a write current having a constant frequency and a constant amplitude, and the test signal is read out, a waveform shown in the drawing is obtained. The detected envelope εe waveform, and each rotation angle theta _1, detects the peak value e _1, e ₂ ...... e _n in θ _{2 ......} θ _n. An average value M of each peak value is calculated, and a ratio between the average value M and each peak value is obtained as a modulation correction coefficient for each rotation angle. In this case, n is the number of divisions in one round of the track, and is appropriately determined in consideration of the required accuracy.

As a result, saturation characteristic data is obtained by writing data for one track and modulation correction for the data, and an appropriate write current value can be obtained based on the data.
Thus, each time the write current is changed as in the prior art, writing is performed for one round of the track corresponding to each current value, and then read out, and further, one round of the track is compared with the measured value obtained as a result of the measurement. This eliminates the need for modulation correction, and enables efficient measurement.

Embodiment FIG. 3 is a schematic block diagram showing an embodiment of a current saturation characteristic measuring method according to the present invention. In the figure,
In response to a command from the microprocessor 2, a drive current is supplied from the drive controller 1a, the motor 1b and the magnetic disk 1 rotate, and an index signal is output from the index detector 1c. The angle detector 1d outputs angle signals at regular intervals. In the write current register 3, data for a current value having a constant amplitude from the microprocessor and a write current value in which the amplitude increases stepwise with a constant magnitude for each rotation angle at a predetermined interval are set in advance.

In order to obtain the modulation correction coefficient, the current generator 4 outputs data for a write current having a constant amplitude from the write current register 3 in accordance with an instruction from the microprocessor and an index signal from the index detector 1c.
And a test signal is written by a write / read amplifier (R / W · AMP) 5 and a magnetic head 6. This is read out, the envelope signal is detected by the envelope detector 7, and the peak value of the envelope signal is A / D converted at a constant angular interval by the A / D converter 8 by the angle signal from the angle detector 1d. The data is transferred to and stored in the memory 2a. By the operation of the microprocessor 2, the average value of each peak value for one round of the track is calculated, and the ratio between the average value and each peak value, that is, a modulation correction coefficient is calculated and stored in the memory 2a.

In the measurement of the current saturation characteristic, the above data is sequentially input to the current generator 4 from the write current register 3 by the above angle signal with the index signal as a starting point, in accordance with a command from the microprocessor 2, and the rotation angle is stepwise. , And the test signal is written, and the process ends with the next index signal. After the completion, the read test signal is output for each angle signal in the same manner as in the case of the correction coefficient described above.
The data is D-converted, transferred to the memory 2a, and multiplied by the modulation correction coefficient by the microprocessor 2 to obtain data of the saturation characteristic. At the same time, an appropriate write current value is calculated, and these data are stored in the memory 2a and output to the output unit 2b.

[Effects of the Invention] As is apparent from the above description, in the method for measuring the current saturation characteristics of a magnetic disk according to the present invention, a test signal is written by a current that increases stepwise around one track, and a modulation correction coefficient is added to a read signal. , The correct current saturation characteristic and the appropriate write current value are quickly measured and the data is output.
Saturation characteristic data is obtained by writing for the track and modulation correction for the track, and an appropriate write current value can be obtained based on the data.

As a result, each time the write current is changed as in the prior art, writing is performed for one round of the track in accordance with each current value, and is read out. Further, one round of the track is compared with the measured value obtained as a result of the measurement. This eliminates the need for the modulation correction, and greatly contributes to the efficiency of measurement work on a large number of magnetic disks in a production factory.

[Brief description of the drawings]

FIGS. 1 (a), 1 (b) and 1 (c) are explanatory diagrams of a procedure of a method for measuring a current saturation characteristic of a magnetic disk according to the present invention.
FIG. 2 is an explanatory view of a procedure of measuring a modulation correction coefficient with respect to the procedure of FIG. 1, FIG. 3 is a schematic block diagram of an embodiment of a method for measuring a current saturation characteristic of a magnetic disk according to the present invention, and FIG. FIGS. 2A, 2B, 2C and 2D are explanatory diagrams of a conventional current saturation measuring method for a magnetic disk. DESCRIPTION OF SYMBOLS 1 ... Magnetic disk, 1a ... Drive controller, 1b ... Motor, 1c ... Index detector, 1d ... Angle detector, 2 ... Microprocessor, 2a ... Memory, 2b ... Output part, 3 ... Write current register, 4 current generator, 5 R / W AMP, 6 magnetic head, 7 envelope detector, 8 A / D converter.

Claims (2)

(57) [Claims] In a magnetic disk tester, for one round of a track between index signals of a magnetic disk,
Up to a point where the frequency has a constant frequency and the amplitude increases stepwise by a constant magnitude at every fixed rotation angle of the magnetic disk, and the maximum increase is further than the point where the recording of the magnetic disk is saturated. The test signal is written by the write current of the test signal, the written test signal is read, the envelope signal of the read test signal is detected, and the envelope signal at the fixed rotation angle is measured in advance. Then, saturation characteristic data for recording on the magnetic disk is obtained by multiplying an envelope signal value by a modulation correction coefficient corresponding to each of the rotation angles at the constant intervals stored in the memory and corresponding to the rotation angles at the constant intervals. Outputting an appropriate write current value exceeding the saturation point determined according to the characteristic data; Wherein, current saturation characteristic measuring method of the magnetic disk. 2. The method according to claim 1, wherein in the pre-measurement, a signal is written in one round of the track with a write current having a constant amplitude and a constant frequency, the written signal is read, and the read signal is read. Of the envelope signal and the peak value at each of the rotation angles of the envelope signal, and calculates an average value of the peak values of the track for one round, and determines the ratio of the average value and the peak value to the constant value. 2. The method according to claim 1, wherein the modulation correction coefficient corresponds to each rotation angle of the interval.