JPS59213020A - Magnetic head core loss detecting system - Google Patents

Abstract

PURPOSE:To measure automatically a loss position on a core slider by providing a noise extracting means, and detecting a noise which is generated regularly. CONSTITUTION:A PLL circuit 10 synchronizes if a synchronizable pulse exists in a waveform data, and an output of a filter becomes constant, but it is varied if said circuit cannot synchronize. A lock deciding circuit 9 decides from a state of the filter whether the PLL circuit 10 has synchronized or not and reports it to a controlling circuit 8. The controlling circuit 8 sends out a series of pulses continued as pulses (c), c', and subsequently, sends out a series of pulses continued as pulses (d), d'. Whether the PLL circuit 10 synchronizes or not is decided by a waveform data inputted by a series of pulses. When this operation is repeated and executed N-2 times, if it is reported to the controlling circuit 8 that the PLL circuit 10 has synchronized, a position on a slider is detected from a sequence of a series of pulses, also a level of the pulse of the synchronized waveform data is detected from a level of 1/M, and its result is sent out to the output.

Description

DETAILED DESCRIPTION OF THE INVENTION (a) Technical Field of the Invention The present invention relates to a magnetic head used in a magnetic disk device, etc., and in particular to a magnetic head core defect that detects a defect in a core slider of a magnetic head whose slider has a small equivalent mass. Regarding detection method.

(b) Prior Art and Problems Floating head type magnetic heads are often used in magnetic disk drives and the like. This is because there is surface runout on the surface of the magnetic disk, and in order for the magnetic head to sufficiently follow the linear surface runout,
Balance is maintained by the air film rigidity and the equivalent mass of the slider. The inner slider of these magnetic heads is made of a core, and a gap is provided in a part of the core to form an electromagnetic conversion system, making it possible to start and stop the slider while it is in contact with the magnetic disk surface. . C
It is called SS head.

As mentioned above, in the C8S head, the slider is made of core material, so if the slider is damaged, noise is likely to be picked up. Since defects in the slider cannot be detected visually, they are checked using a microscope, but defects that occur during post-processing cannot be detected. Accordingly, methods have been devised to detect core slider loss during serial/write operations. This is determined by writing a signal on the magnetic disk in a period physically wider than the width of the core slider, reading out the signal and displaying it on an oscilloscope for visual observation.

FIG. 1 is a diagram illustrating the state displayed on the oscilloscope. The waveforms indicated by a and ao are signals recorded at a physically wide period relative to the width of the core slider, and the range indicated by A is the physical width of the core slider.

That is, after the position on the magnetic disk of the a waveform recorded by the cap of the core slider passes under the core slider,
The next a waveform is recorded on the magnetic disk. If there is a defect in the core slider, a noise waveform due to the defect appears as shown in b. Therefore, by measuring the distance from a to b, the position of the defect on the core slider can be determined from the circumferential speed due to rotation of the magnetic disk. However, the conventional core defect detection method as described above has the disadvantage that it cannot be automated and is inefficient because it is displayed on an oscilloscope and measured visually.

(C) Purpose of the Invention An object of the present invention is to provide a magnetic head core defect detection method that can automatically detect defects in the core slider and simultaneously measure the position thereof, in order to eliminate the above-mentioned drawbacks. .

(d) Structure of the Invention The structure of the present invention includes a means for reading a recorded signal to detect a defect in a core slider and generating a pulse that equally divides the signal, and noise generated by the defect in the core slider. A means for generating a dark value for detecting a dark value, and a pulse train sent from the pulse generating means and a dark value from the dark value generating means are used to scan between the signals and generate the dark value regularly. When the noise extraction means detects regularly occurring noise, the defective position on the core slider is automatically subtracted.

(e) Embodiments of the Invention The present invention uses a PLL (phase-locked loop) circuit, and focuses on the fact that if the filter output in the PLL circuit is synchronized, it will not fluctuate, but if it is not synchronized, it will fluctuate. The system detects regularly occurring pulses as shown in the waveform shown in FIG. 2, synchronizes the pulses by applying them to a PLL circuit, and automatically detects the presence or absence of a defect in the core slider. In other words, it can be determined from the waveform (pulses that occur regularly cannot be obtained from normal noise.Also, if there is a defect in the core slider, it is necessary to know its position, so Pulses that open gates for detecting waveforms are sent out to positions sequentially shifted from waveform a, and measurements are made starting from the gate pulse that matches waveform a.

FIG. 2 is a block diagram of a circuit showing one embodiment of the present invention. A write signal enters from the input, and is sent to the magnetic head 1 by the read/write switch 2 and recorded on the magnetic disk. Next, the magnetic node 1 reads out the signal recorded on the magnetic disk, and the read/write switch 2
send to The signal sent to the filter 3 by the switch of the read/write switch 2 enters the automatic gain adjustment amplifier 4, is amplified to the level instructed by the AGC reference voltage circuit 13, and is sent to the peak detection circuit 5 and comparison circuit 12. be done. The peak voltage of the signal detected by the peak detection circuit 5 is
The oscillation frequency of the circuit 6 is synchronized with the period of the signal. P.L.
The L circuit 6 sends pulses with the same period as the signal and an oscillation frequency with a period N times that period to the N equal division circuit 7, and the N (3 pulses) of the signal are sequentially output to the AND circuit 11 under the control of the control circuit 8. i.e. initially c, 'c' in Figure 1.
As shown in , if the time from waveform a to ao is T, then T/H
The time waveforms a and a' are respectively transmitted to positions delayed by T/N. Next, d and d' are transmitted to positions T/N delayed from c and c'', respectively, and then e and e' are transmitted in the same manner. be done.

In this way, by sequentially shifting the positions of the pulses, we can create waveforms from a to ao.
The period up to this point is sent N-2 times. In addition, the control circuit 8 is a digital/
The analog conversion circuit 14 is instructed to send a level (dark value) 1/M of the level instructed by the AGC reference voltage circuit 13 to the comparison circuit 12.

Therefore, the comparator circuit 12 sends to the AND circuit 11 data having a waveform higher than the level of 1/M of the signal input from the automatic gain adjustment amplifier 4. A pulse is input to the AND circuit 11 from the N equal dividing circuit 7 as described above.

Therefore, the PLL 1 path 10 is supplied with a pulse C which is delayed by r/N time from the waveform a from the AND circuit 11 to generate 1/M of the signal.
Hell's waveform data is included. Next, from waveform a” 1゛/
Waveform data at a level of 1/M of the signal is inputted by the pulse C' delayed by N hours. In this way, waveform data is input sequentially. The PLL circuit 10 synchronizes if there is a pulse that can be synchronized with the waveform data, and the output of the filter becomes constant, but if synchronization is not possible, it fluctuates. The lock determination circuit 9 determines whether the PLL circuit 10 is synchronized based on the state of the filter and reports the result to the control circuit 8. The control circuit 8 receives the pulse c as described above.
, c', and then pulses d, d', and so on. It is determined whether the PLL circuit 10 is synchronized with the waveform data input by the series of pulses. When the above operation is repeated N-2 times, when the control circuit 8 receives a report that the PLL circuit 10 is synchronized, the position on the slider is detected from the order of the series of pulses, and synchronization starts from the level of 1'/M. The pulse level of the waveform data is detected and the result is sent to the output.

The numerical values of N and M can be determined in advance, and it is also possible for the control circuit 8 to select and instruct a plurality of numerical values.

(f) As described in detail, the present invention is capable of automatically detecting defects in the core slider, simultaneously measuring the position thereof, and also measuring the noise level associated with the defects.
The effect is great.

[Brief explanation of the drawing]

FIG. 1 is a diagram for explaining the state displayed on an oscilloscope, and FIG. 2 is a block diagram of a circuit showing an embodiment of the present invention. 1 is a magnetic head, 2 is a read/write switch, 3 is a filter, 4 is an automatic gain adjustment amplifier, 5 is a peak detection circuit,
6 and 10 are PLL circuits, 7 is an N equal division circuit, 8 is a control circuit, 9 is a lock judgment circuit, 12 is a comparison circuit, 13 is an AGC
Reference voltage circuit 14 is a digital/analog conversion circuit.

Claims (1)

[Claims] means for reading a recorded signal to detect a defect in the core slider and generating a pulse that equally divides the signal, and means for generating a darkness value for detecting noise generated by the defect in the core slider; means for scanning between the signals and extracting regularly occurring noise using the pulse train sent out from the /< pulse generating means and the dark value from the dark value generating means. . A magnetic held core defect detection method, characterized in that the noise extracting means detects regularly generated noise and automatically measures the defect position on the core slider.