JPS63113878A - Device for detecting contact between head and media - Google Patents

Abstract

PURPOSE:To attain a highly accurate detection by making coincident the main resonance frequency of an output signal induced to a piezoelectric transducer and the frequency of the sum or difference of the main resonance frequency of the output signal of a local oscillator with the central frequency of a BPF. CONSTITUTION:On a floating type magnetic slider, a piezoelectric transducer 1 is loaded. In order to execute the contact detection between a head and media, the frequency of an oscillator 11 is set so that the frequency of a local oscillator 11 and the frequency of the sum or difference of the main resonance frequency of the output signal induced to the transducer 1 can be coincident to the central frequency of a BPF 13. Thereafter, by an envelope detecting circuit 5, a comparator 6 and a counter 8 to count the number of a wave to exceed a threshold voltage, the number of times of the contact between the head and media is counted. Thus, the output of the erroneous contact detecting signal can be eliminated and the highly accurate detection can be executed.

Description

[Detailed description of the invention] <Technical field to which the invention pertains> This invention detects contact between a magnetic disk medium and a floating magnetic head slider that floats due to air dynamic pressure generated by high-speed rotation of a magnetic disk medium of a magnetic disk recording device. The present invention relates to a head/medium contact detection device.

<Prior art> A floating magnetic head slider floats above a magnetic disk medium at a high speed of several m/s to several tens of m/s and with a minute gap on the order of submicrons. If it comes into contact with minute protrusions or fixed dust on the disk medium, the magnetic head and the magnetic disk medium will be damaged, leading to destruction of information, loss of recording and reproducing functions, etc. Therefore, it is necessary to remove minute protrusions or dust on the magnetic disk medium during manufacturing of the magnetic disk medium, and a highly sensitive head/medium contact detection device is required to inspect the magnetic disk medium after removal. It has become.

A conventional head/medium contact detection device is an acoustic Δ emission sensor (8coustic emission sensor).
r.

Approximately 10
A large vibration sensor with a resonant frequency between 0 KHz and IMHz was mounted at a location away from the floating magnetic head slider via a specially processed gimbal.

In this method, the sensor itself has high sensitivity, but because it uses a gimbal, it is not possible to accurately capture the behavior of the floating magnetic head slider due to waveform distortion and the like.

However, recently, in U.S. Patent No. 4,532,802, a method of attaching a small piezoelectric transducer directly to a floating magnetic head slider has been proposed, which makes it possible to accurately capture the behavior of the floating magnetic head slider. It is considered as a head/medium detection method.

<Problems to be Solved by the Invention> However, although the method of U.S. Pat. It had the disadvantage of being small and having a poor S/N ratio.

As a method to eliminate this drawback, in the conventional technology, it is possible to improve the S/N ratio by optimizing the bandpass filter (narrowing the band). However, the main resonance frequency of the voltage induced in the piezoelectric transducer is not constant because it varies depending on the material of the floating magnetic head slider, the type of piezoelectric transducer, the frequency of contact between the head and the amount of the medium, and there are variations and fluctuations. be. A bandpass filter usually consists of a bypass filter that cuts the low frequency band and a lowpass filter that cuts the high frequency band, and the center frequency of the bandpass filter is the center of the cutoff frequencies of these two filters. Continuously variable etc. are achieved by changing the cutoff frequencies of the two filters. but,
Changing the bandpass frequency requires switching between many high-precision filters, which is not very practical. In particular, it is impossible to change the center frequency of the bandpass filter to follow changes over time. It was possible.

Therefore, in the past, a contact count was detected from the output signal induced in the piezoelectric transducer using a counting circuit having the configuration shown in Fig. 6 in response to variations and fluctuations in the main resonance frequency of the output signal induced in the piezoelectric transducer. Was.

In other words, the counting circuit shown in FIG. 6 calculates the voltage induced in the piezoelectric transducer 1 mounted on the floating magnetic head slider through the amplifier 2, the medium-band bandpass filter 3 with a relatively large band width, the amplifier 4, and the envelope. A detector 5, a comparator 6 for comparison with a reference threshold voltage value, a reference voltage source 7 set to the threshold, a counter 8 for counting the number of waves exceeding the threshold 1, and a recording device. Therefore, since the voltage induced in the piezoelectric transducer 1 passes through the envelope detection circuit and the comparator 6 with a poor S/N ratio, the number of false contacts due to noise frequently accumulates. There was an inconvenience that occurred.

The present invention provides a head/medium contact detection device using a small piezoelectric transducer mounted on a floating magnetic head slider in such a conventional magnetic disk recording device.
The present invention aims to eliminate erroneous contact detection due to noise and provide a hanging device that performs highly accurate head/medium contact detection.

Means for Solving the Problems> In order to achieve the above object, the head/medium contact detection device of the present invention is a floating system that levitates a magnetic head using air dynamic pressure caused by high-speed rotation of a magnetic disk medium. A piezoelectric transducer is provided on the floating magnetic head slider, and the voltage induced in the piezoelectric transducer due to contact between the floating magnetic head slider and the magnetic disk medium is compared with a preset reference voltage value. In a head/medium contact detection device that detects contact between a magnetic disk and a magnetic disk medium, the frequency of the sum or difference between the main resonance frequency of the output induced in the piezoelectric transducer and the output of a variable frequency local oscillator has a predetermined bandwidth. The present invention is characterized in that it includes a tuning circuit that can be set to match the center frequency of the bandpass filter having the following characteristics.

The head/medium contact detection device of the present invention uses the center frequency of the bandpass filter as the intermediate frequency between the main resonance frequency of the output signal induced in the piezoelectric transducer and the frequency of the sum or difference between the output signal generated by the local oscillator and the piezoelectric transducer. The frequency of the local oscillator may be changed in accordance with fluctuations in the main resonant frequency of the output signal induced in the ducer, so that the frequency of the input signal to the bandpass filter is always constant.

<Example> Next, typical embodiments of the present invention will be described.

(Embodiment 1) FIG. 1 shows a head/medium contact detection circuit according to a first embodiment of the present invention. This circuit includes a piezoelectric transducer 1 mounted on a floating magnetic head slider, an amplifier 2, a mixer 10, a local oscillator 11, an amplifier 12, a narrowband bandpass filter 13, an amplifier 14, an envelope detector 5, and a comparator 6. , a reference voltage source 7 set to a threshold value, a counter 8, and a recording device 9.

In order to detect contact between the head and the medium using this head/medium contact detection circuit, the frequency of the local oscillator 11 and the sum or difference of the main resonance frequency of the output signal induced in the piezoelectric transducer 1 must be The frequency of the local oscillator 11 is set so that it matches the center frequency of the bandpass filter 13. Also, band pass filter 1
3 is set at a point with the best S/N, which is 172 to 15 times the half width of the main resonance frequency of the output signal induced in the piezoelectric transducer 1.

After that, the envelope detection circuit 5, the comparator 6:
The number of contacts between the head and the medium is counted by a counter 8 that counts the number of waves exceeding the threshold voltage.

With the above configuration, the main resonant frequency of the voltage induced in the piezoelectric transducer is converted to a constant intermediate frequency by the mixer 10, and the main resonant frequency of the voltage induced in the piezoelectric transducer is converted to a constant intermediate frequency
．． 14 and a bandpass filter 13 having an optimal bandwidth, the S/N can be improved. As a result, the relationship between the running of the magnetic disk medium, the effective voltage at the main resonance frequency of the output signal induced in the piezoelectric transducer 1, and the effective voltage in the conventional head/medium contact detection circuit is shown in a characteristic diagram as shown in Fig. 2. is obtained.

From the characteristic diagram in FIG. 2, it can be seen that in both the circuit according to the present invention and the conventional circuit, as the speed increases, the effective value voltage suddenly decreases at a certain speed. This phenomenon is based on the American Institute of Electronics and Communication Engineers (IEICE).
The Institute of ElecLrica
l and Electronic Engineers
) Published by IEEE Transactions o
nMagnetics J Vol MAG +6. No. 5, p, 873' (1980).
As reported by A et al., this is because as the traveling speed increases, the floating head slider changes from a continuous contact state to an intermittent contact state to a flying state due to air film lubrication. . From the figure, it can be seen that in the conventional circuit configuration, the effective value voltage does not become completely zero even in the flying state. This is because the noise contained in the output induced in the piezoelectric transducer and the amplifier is detected and remains as a DC component.On the other hand, when it passes through the circuit of the example, the noise is reduced and almost no longer occurs. In the actual measurement example of the characteristic diagram shown in FIG. 2, the degree of improvement in S/N is about 10 dB.

Next, we will examine the output of the main resonance frequency induced in the piezoelectric transducer when using a magnetic disk medium partially provided with minute protrusions and a floating magnetic head slider using a conventional circuit and a circuit according to the present invention. Figures 3(a) and 3(b) show a comparison of the output waveforms when In the conventional circuit, the envelope of the contact detection waveform has a poor S/N ratio and not only the contact area is unclear, but also a lot of spike-like noise is observed, but the contact detection circuit of the present invention has a good S/N ratio. A detected waveform is obtained, and it can be seen that almost no spike-like noise occurs.

(Example 2) FIG. 4 shows the second embodiment of the head/medium contact detection device of the present invention.
This circuit is a circuit diagram showing an embodiment of a piezoelectric transducer 1 mounted on a floating magnetic head slider.
, an amplifier 2, a mixer 10, a voltage-controlled local oscillator 15 whose frequency can be varied by voltage, narrow-bandwidth band-pass filters 13, 12 and 14 are amplifiers, and an f-v converter 16 that generates a voltage proportional to the frequency. , envelope detector 5,
a comparator 6, a reference voltage source 7 set to a threshold;
It consists of a counter 8 and a recording device 9.

With this configuration, when the main resonance frequency of the piezoelectric element 1 changes, the output of the f-v converter 16 changes, and the frequency of the voltage-controlled local oscillator 15 changes.
The frequency of the voltage controlled local oscillator No. 5 is controlled so as to reduce the change in the frequency manually applied to the band pass filter No. 13. For this reason, the frequency of the signal entering the bandpass filter 13 is automatically controlled so that it is always constant, and the frequency of the signal entering the bandpass filter 13 is automatically controlled by the temporal fluctuation of the main resonance frequency of the piezoelectric element mounted on the floating head slider 1. Mismatching caused by deviations between the frequency of the signal input to the bandpass filter and the center frequency can be eliminated, and the S/N ratio can always be maximized.

FIG. 2 shows an actual measurement example in this example.

It can be seen that not only the noise is reduced compared to the conventional method, but also the output drop in the intermittent contact state is smaller than that of the first embodiment.

(Embodiment 3) FIG. 5 is a head/medium contact detection circuit diagram of a third embodiment of the present invention, in which 1 is a piezoelectric element mounted on a floating head slider, 2 is an amplifier, and 10 is a mixer. , 11 is a local oscillator, 12 is a plurality of bandpass filter groups with different bandwidths, 18 is a changeover switch, 17.20 is an amplifier, 5 is an envelope detector, 6 is a comparator, and 7 is set to a threshold voltage. 8 is a counter, and 9 is a recording device. With this configuration, 19
The shape of the piezoelectric element,
The optimal bandwidth can be selected in response to changes in the bandwidth of the main resonance frequency of the voltage induced in the piezoelectric element 1 due to differences in the material and shape of the floating head slider, and the best S/N can be achieved. Obtainable.

<Effects of the Invention> As is clear from the above embodiments, the head of the present invention
By using a medium contact detection device, it is possible to eliminate the output of false contact detection signals due to contact between the floating magnetic head slider and the magnetic disk medium, and to detect the presence or absence of minute protrusions or dust on the high-density magnetic disk medium. It is possible to achieve high accuracy as a technology for testing.

[Brief explanation of the drawing]

FIG. 1 is a circuit diagram of a first embodiment of the head/medium contact detection device of the present invention, and FIG. 2 shows the speed and main force induced in the piezoelectric transducer when a magnetic disk medium and a magnetic head slider are used. Characteristic diagrams showing the relationship between the effective value voltage characteristics at the resonance frequency, and FIGS. 3(a) and 3(b) show the contact detection outputs of the conventional device and the device of the present invention when using a magnetic disk medium partially provided with protrusions. A waveform diagram, FIG. 4 is a circuit configuration diagram of the second embodiment of the present invention, and FIG. 5 is a circuit diagram of the third embodiment of the present invention.
FIG. 6 is a circuit diagram of a conventional head/medium contact detection device. In the drawing, 1... a piezoelectric transducer mounted on a floating magnetic head slider, 3... a bandpass filter with medium bandwidth. 5... Envelope detector, 6... Comparator, 7... Reference voltage source set to threshold voltage, 8... Counter, 9... Recording device, lO... Mixer , 11... Local oscillator, 13... Narrow bandwidth band pass filter, 15...
Voltage controlled local oscillator, 16.=f-v converter, 18... Changeover switch, 19... Band pass filter group with different bandwidths.

Claims (2)

[Claims] (1) A piezoelectric transducer is installed in a floating magnetic head slider that levitates the magnetic head using air dynamic pressure generated by high-speed rotation of a magnetic disk medium, and the contact between the floating magnetic head slider and the magnetic disk medium induces energy in the piezoelectric transducer. In a head/medium contact detection device that detects contact between a floating magnetic head slider and a magnetic disk medium by comparing the applied voltage with a preset reference voltage value, the main resonant frequency of the output signal induced in the piezoelectric transducer and A head characterized in that it is provided with a tuning circuit that can set the frequency of the sum or difference of the main resonance frequencies of the output signals of the variable frequency local oscillator to match the center frequency of a bandpass filter having a predetermined bandwidth. Media contact detection device. (2) Set the intermediate frequency of the sum or difference frequency of the output induced by the piezoelectric transducer and the output generated by the local oscillator as the center frequency of the bandpass filter, and respond according to fluctuations in the main resonance frequency of the output signal induced by the piezoelectric transducer. Claim 1, characterized in that the frequency of the local oscillator is changed by changing the frequency of the local oscillator, so that the input signal frequency of the bandpass filter is always kept constant.
The head/medium contact detection device described in section 1).