JPH0736221B2 - Frequency characteristic measurement method of magnetic disk - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a method for measuring frequency characteristics of a magnetic disk in a magnetic disk tester, and more specifically, the amplitude of a read test signal is 2 minutes in a low frequency range. The frequency (data 50 or D50) lowered to 1 is measured.

[Prior Art] A magnetic disk, which is widely used as an information recording medium, and a magnetic head for the magnetic disk are subjected to various tests in the manufacturing process. One of them is measurement of frequency characteristics for a combination of the recording medium and the head. .

A conventional frequency characteristic measuring method for a combination of a magnetic disk and a magnetic head will be described with reference to FIGS. 3 (a), (b), (c) and (d). With respect to a predetermined track of the magnetic disk 1 to be inspected shown in FIG. 7A, the magnetic head to be inspected at a constant amplitude shown in FIG. The test signal is written and read by the write current Iw having the frequency fw. The frequency fw is gradually changed from a low frequency range, for example, 1 MHz to a high frequency range, for example, 10 MHz, and writing / reading is repeated for one track of each frequency, and ER− shown in FIG. The fw curve is obtained. Here, ER is the amplitude of the read test signal.

The above-mentioned ER-fw curve has a recording characteristic that the amplitude in the low frequency range is constant up to a certain frequency, and when it exceeds this, it gradually decreases, and the amplitude was reduced to half to express this characteristic. The frequency fp with respect to the point p is regarded as an important index, and a person concerned has abbreviated this as data 50 (%) or D50.

[Problems to be Solved] In the above D50 measurement, in order to obtain the ER-fw curve, the frequency of the current Iw is gradually changed from the low frequency region to the high frequency region, and each time the change is made, one cycle of the track is changed. Since the test signal is written / read, the number of tests is large, and it takes a very long time to measure a large number of magnetic disks and magnetic heads in a production plant. As described above, the reason why the data for one track is required for each current value is that the read test signal is accompanied by the duration shown in FIG. 3D due to the distortion of the magnetic disk or the like. Because there is. Since the modulation is periodic for one round of the track, in the above measurement, it is erased by taking the average value of one round of the measurement data. On the other hand, if modulation can be corrected, D50 can be obtained by changing the frequency of the current Iw and writing / reading the test signal for one track, which shortens the measurement time. It should be possible.

The present invention has been made in view of the above, and it is an object of the present invention to provide a frequency characteristic measuring method for a magnetic disk for obtaining D50 by one test of one track.

[Means for Solving the Problems] The present invention is a method for measuring the frequency characteristic of a magnetic disk in a magnetic disk tester, wherein one cycle of a track between index signals of the magnetic disk is controlled by a microprocessor control and calculation. Then, the tester signal is written and read by a write current having a constant amplitude and a frequency that linearly increases. The read test signal is multiplied by the modulation correction coefficient measured in advance and stored in the memory for each rotation angle of the magnetic disk at a constant interval to correct the amplitude, and the amplitude of the corrected test signal becomes low. Find the frequency (D50) that drops to half the amplitude of the frequency range.

In the above-mentioned preliminary measurement, the test signal is written and read by a write current having a constant amplitude and a constant frequency in one round of the track, and the envelope signal of the read test signal is detected. Furthermore, the peak value of the envelope signal at each rotation angle of the magnetic disk is detected, and the average value for one track is calculated,
The moduli of the average value and each peak value are used as the modulation correction coefficient.

[Operation] The operation of the frequency measuring method of the present invention will be described with reference to FIGS. 1 (a), (b), (c) and (d). By the control and calculation of the microprocessor, the frequency f is changed in accordance with the rotation angle θ shown in FIG.
The test signal is written by the write current in which w increases linearly from fL to fH. The amplitude ER of the read test signal is modulated into the shape shown in FIG. When this envelope signal Ee is detected and corrected by multiplying it by a modulation correction coefficient for each rotation angle θ ₂ at the fixed intervals of the disk ... θn, the amplitude variation is eliminated as shown in FIG. Then, one test of one track gives an angle θp at which the amplitude in the low frequency range is reduced to half, and the frequency (D5
0) is obtained from the fw-θ straight line in FIG.

The method for obtaining the above-mentioned modulation correction coefficient is to write a test signal with a write current having a constant amplitude and a constant frequency between track indices, and read the test signal to detect an envelope signal εe shown in FIG. 1 (d).
Furthermore, the crest value for angles θ ₁ , θ ₂ ... θn at regular intervals
e ₁ , e ₂ ... En are detected and their average value M is calculated. The ratio of the pair of the average value M and the peak value e ₁ , e ₂ ... En is calculated and used as the correction coefficient for each angle. In this case, n is the number of divisions of one track and is appropriately determined in consideration of the required accuracy.

[Embodiment] FIG. 2 shows a schematic block configuration of an embodiment of a frequency characteristic measuring method for a magnetic disk according to the present invention. A drive current is supplied from a drive controller 3 to a motor 1a in response to a command from a microprocessor 2. Then, the magnetic disk 1 rotates. Disk index is an index detector
Detected by 1b. First, in order to obtain the modulation correction coefficient, the frequency sweep of the frequency sweep generator 5 is stopped by a command from the microprocessor 2 to generate an appropriate constant frequency with a constant amplitude, and the index detector
A test signal is written by the magnetic head 1c, which is output during the index signal from 1b and passed through a write / read amplifier (R / W AMP) 6. This is read out, the envelope is detected by the envelope detector 7, and the rotation angles θ ₁ , θ ₂ ...
The peak value of the envelope signal by the angle signal for every n
e ₁ , e ₂ ... Transfer en to memory 2a. By the calculation of the microprocessor 2, the average value M of the crest values stored in the memory and the modulation correction coefficient for each rotation angle are calculated.

Next, in the measurement of the frequency characteristics, the frequency sweep generator 5 changes the frequency from, for example, 1 MHz to 10 MH from the index signal as the starting point according to the command of the microprocessor 2.
A write current that linearly increases up to z is output, and the test signal is written on one track of the track by stopping at the next index signal. Envelope detector 7 as above
Each rotation angle θ ₁ , of the envelope signal detected by
The peak value for θ ₂ ... θn is transferred to the microprocessor 2 and is multiplied by the above correction coefficient to obtain normal envelope signal data for the angular rotation angle. In the microprocessor 2, the rotation angle θ and the frequency f
Since the relationship of w is known in advance, the frequency D50 at which the amplitude is halved with respect to the low frequency range is obtained from this data, and is output to the output unit 2b.

[Effects of the Invention] As is clear from the above description, in the frequency characteristic measuring method for a magnetic disk according to the present invention, a test signal is written to one track of a track by a write current whose frequency increases linearly, and this is used. Since the peak value of the envelope signal is read out and corrected by the modulation correction coefficient, the normal read signal amplitude can be obtained as in the case without modulation, and measurement that requires data for one track per frequency as in the past. The measurement time is significantly shortened as compared with the method, and the effect of providing an efficient frequency measurement method for a combination of a large number of magnetic disks and magnetic heads is great.

[Brief description of drawings]

1 (a), (b), (c) and (d) are explanatory views for the operation of the frequency characteristic measuring method of the magnetic disk according to the present invention, and FIG. 2 is the frequency characteristic measuring method of the magnetic disk according to the present invention. A schematic block diagram for an embodiment of the method, FIGS. 3 (a), (b), (c) and (d),
It is explanatory drawing of the conventional frequency measuring method with respect to a magnetic disk. 1 ... magnetic disk, 1a ... motor, 1b ... index detector, 1c ... magnetic head, 2 ... microprocessor, 2a ... memory, 2b ... output section, 3 ... drive controller, 4 ... … Angle detector, 5 …… Frequency sweep generator, 6 …… R / W AMP, 7 …… Envelope detector.

Claims (2)

[Claims] 1. In a magnetic disk tester, a write current having a constant amplitude and a linearly increasing frequency with respect to one round of a track between index signals of a magnetic disk is controlled by a microprocessor control and calculation. A test signal is written and read, and the read test signal is corrected by multiplying it by a modulation correction coefficient measured in advance and stored in a memory for each rotation angle of the magnetic disk at a constant interval. A frequency characteristic measuring method for a magnetic disk, wherein a frequency (D50) at which the amplitude of the corrected test signal is reduced to one half of the amplitude in the low frequency range is obtained. 2. In the above-mentioned measurement, writing and reading are performed in one round of the track with a write current having a constant amplitude and a constant frequency, and the envelope signal of the read test signal and the rotation angle at the constant interval are measured. Detecting the crest value of the envelope signal at, respectively, calculating an average value of one round of the track with respect to the angular crest value, and comparing the average value with each crest value as the modulation correction coefficient.
The frequency characteristic measuring method for a magnetic disk according to claim 1.