JPH02163605A - Disk medium projection inspecting signal processing circuit - Google Patents

Abstract

PURPOSE:To use an oscillator of a fixed frequency as an oscillator in a frequency converting means for bringing an inspecting signal to frequency conversion by providing a floating type head slider, an elastic resonance frequency signal generating circuit, a first and a second frequency mixers and a band pass filter. CONSTITUTION:An elastic resonance frequency signal generating circuit 40 generates a signal of almost the same frequency as an elastic resonance fre quency of a floating type head slider 7. An oscillator 50 outputs a signal of almost the same frequency as the center frequency of a band pass filter 33. A first frequency mixer 60 mixes an output signal of the oscillator 50 and an output signal of the circuit 40. A second frequency mixer 31 mixes a disk medium projection inspecting signal outputted from a piezoelectric element 10 provided on a slider 7 and an output signal of the circuit 40. In this regard, a filter 33 has band width of about 0.1-fold - 10-fold of band width of a peak in a frequency spectrum spectrum of an inspecting signal induced in an element 10. According to this constitution, an oscillator of a fixed frequency can be used as an oscillator for outputting a prescribed frequency signal.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention provides a floating head slider used in a magnetic recording device equipped with an elastic wave detection element such as a piezoelectric element, and a disk output by this elastic wave detection element. The present invention relates to a circuit for processing a medium protrusion inspection signal.

[Prior Art] A floating head slider used in a magnetic recording device travels above a magnetic disk medium at high speed (several m/s to several tens of m/s) and flies in a minute gap on the order of submicrons. . Therefore, if the floating head slider comes into contact with minute protrusions or fixed dust on the magnetic disk medium, the floating head slider and the disk medium will be damaged, information will be destroyed, and the recording/reproducing function will be lost. .

Therefore, when manufacturing magnetic disk drives, it is essential to remove minute protrusions on the surface of the magnetic disk medium. To remove these protrusions, a vanish slider with a special taper on the slider running surface is used to Travels while flying low above the medium. After removing the protrusions in this way, when inspecting the surface of the disk medium for the presence or absence of protrusions, an inspection method that uses a detection element to mechanically and electrically convert the elastic waves generated in the head when the protrusions and the head come into contact is used. Generally used.

However, in recent years, there has been a trend to reduce the flying height of the head, and in this case, the SN of the mechanically-electrically converted test signal
Since the ratio decreases, a highly accurate and sensitive medium protrusion inspection method is desired.

FIG. 4 is an explanatory diagram of a conventional example of protrusion inspection.

This conventional example uses AE (acoustic emission)
A large vibration sensor 1, called a sensor, having a resonant frequency at at least one point in the range of a few kHz to several MHz is mounted on an arm 2 remote from the floating head slider 7 to perform protrusion inspection.

A gimbal 3 is provided to support the floating head slider 7, and as the magnetic disk medium 4 rotates, an air flow 5 is provided.
In this case, fine protrusions 6 are formed on the disk medium 4.
Suppose that it is stuck and dust 8 is attached. When the protrusion 6 or the dust 8 comes into contact with the floating head slider 7, the floating head slider 7 vibrates elastically, and the elastic wave propagates through the gimbal 3 and the arm 2, and reaches the AE sensor 1.

In this conventional example, although the sensitivity of the sensor 1 itself is high,
The gimbal 3 and arm 2 are specially processed to guide the elastic waves generated by the floating head slider 7 to the AE sensor l.
A propagation path is required.

Therefore, the problem is that it is not possible to accurately grasp the impact force acting on the floating head slider 7 because waveform distortion, time delay, etc. occur due to the long transmission path including the gimbal 3 and the arm 2. There is. Furthermore, since the large AE sensor 1 is mounted on the arm 2, mechanical noise is easily picked up during head seeking, making it difficult to distinguish between impact force and noise.

FIG. 5 is an explanatory diagram of a conventional example in which a small piezoelectric element is directly attached to a floating head slider.

This conventional example is a contact detection method/medium protrusion inspection method that can accurately grasp the behavior of a floating head slider, and is patented in the United States (U.S., PAT 4532802. Aug.
8゜1985), etc. However, in this conventional example, although the behavior of the floating head slider 7 can be accurately grasped by the detection circuit 9, when the piezoelectric element 10 is made smaller in accordance with the miniaturization of the floating head slider 7, the output signal becomes smaller. , there is a problem that the signal-to-noise ratio decreases.

FIG. 6 is a circuit diagram of a conventional example in which the SN ratio is improved by narrowing the band of a bandpass filter.

In this conventional example, the main resonance frequency of the voltage induced in the piezoelectric element 10 varies depending on the material and dimensions of the floating head slider 7, the frequency of contact between the floating head slider 7 and the disk medium 4, temperature changes, etc. , Therefore, the main resonance frequency varies and fluctuates.

By the way, the bandpass filter 21 is normally used.

Bandpass filter 2 consists of a bypass filter that cuts low frequencies and a low-pass filter that cuts high frequencies.
The center frequency of 1 is the center of the cutoff frequencies of the two filters. In order to make the center frequency continuously variable, it is necessary to make the cutoff frequencies of the two filters variable.

Therefore, in order to change the center frequency of a bandpass filter, a large number of highly accurate filters must be installed.

Since they have to be switched and used, it is not very practical, and it is also difficult to make the center frequency of the bandpass filter 21 follow temporal fluctuations. Therefore, in order to cope with the dispersion and fluctuation of the main resonance frequency induced in the piezoelectric element 10, the current situation is to set the bandwidth to be relatively large, which prevents the improvement of the S/N ratio.

In addition, in FIG. 6, a circuit is provided that counts the number of times of contact with the protrusion 6 based on the voltage induced in the piezoelectric element IO (disk medium protrusion inspection signal), and this circuit includes an amplifier 20, 22, A bandpass filter 21, a detection circuit 23, a comparator 24 for comparing with a threshold voltage generated by a reference voltage source 25, a counter 26 for counting the number of waves exceeding the threshold voltage, and a recording device 27 are provided.

However, in this conventional example, there is a problem in that the number of times of contact with the protrusion 6 is erroneously accumulated frequently due to noise such as external noise.

FIG. 7 is a circuit diagram of a conventional example in which the signal-to-noise ratio is improved by converting the frequency of a disk medium protrusion test signal from a piezoelectric element and passing it through a narrow band pass filter.

In this conventional example, as shown in Japanese Patent Application No. 61-257,016, the piezoelectric element 1 is
The signal of the main resonance frequency induced at zero (disk medium protrusion test signal) and the output signal of the local oscillator 30 are mixed, and the sum or difference between the frequency of the disk medium protrusion test signal and the frequency of the output of the local oscillator 30 is calculated. Outputs a signal with a frequency of Then, this output signal passes through a narrowband bandpass filter 33, creates an envelope in a detection circuit 23, is compared with a threshold voltage in a comparator 24, and counts the number of waves exceeding the threshold voltage in a counter 26. The number of times of contact with the protrusion 6 is counted. Note that the local oscillator 30 is a frequency variable oscillator.

As a result, noise contained in the voltage induced in the piezoelectric element IO and noise generated by the amplifier etc. are blocked by the bandpass filter 33, and a contact signal waveform with a good S/N ratio can be obtained. In addition, the material of the floating head slider 7,
When the main resonant frequency changes due to dimensions, contact conditions, etc., it is relatively easy to automatically follow the frequency of the local oscillator 30 so that the intermediate frequency entering the bandpass filter 33 is always constant.

FIG. 8 is a diagram showing the relationship between the relative velocity between the magnetic disk medium and the floating head slider and the effective voltage value of the main resonance frequency output (disk medium protrusion inspection signal) induced in the piezoelectric element IO. .

In FIG. 8, as the relative speed increases, the effective voltage drops rapidly at a certain speed. This is the reference (Ki
ta, Kogure, Mitsuya, Naka
Nishi.

IEEE, Vol WAG-18, No-5, 198
0,873), as the relative speed increases, the floating head slider 7 floats above the magnetic disk medium 4 from a continuous contact state to an intermittent contact state due to the air film lubrication effect. This is to move to a running state.

Here, in the circuit shown in FIG. 6, the effective value voltage does not become completely zero even in the flying state.

This is because the output induced in the piezoelectric element 10 and the noise contained in the amplifier are detected and remain as DC components. On the other hand, as shown in Fig. 7, when the disk medium protrusion inspection signal is frequency-converted and passed through a narrow band pass filter, the above noise is removed and the effective value voltage becomes almost zero even in the flying state. Become.

In the actual measurement example shown in Figure 8, the degree of improvement in the S/N ratio is approximately 16 dB.
That's about it. Therefore, as shown in FIG. 7, by converting the frequency of the disk medium protrusion inspection signal and using a narrow band pass filter, it is possible to clearly distinguish between the contact sliding state and the flying running state, thereby improving the accuracy of the protrusion inspection. It can be made higher.

FIGS. 9(a) and 9(b) show the output waveform of the main resonance frequency ( 7 is a diagram showing the case of the circuit shown in FIG. 6 and the case of the circuit shown in FIG. 7 regarding the disc medium protrusion test signal). FIG.

In the circuit shown in FIG. 6, the envelope of the disk medium protrusion test signal has a poor SN ratio, and not only the protrusion detection portion is unclear, but also many spike-like noises are observed. However, when the disk medium protrusion test signal is frequency-converted and passed through a narrow band pass filter as shown in FIG.
A detection waveform with an excellent signal-to-noise ratio can be obtained, almost no spike-like noise is generated, and therefore erroneous output of a disk medium protrusion test signal due to noise can be removed.

[Problem N to be solved by the invention] However, when the disk medium protrusion inspection signal is frequency-converted and passed through a narrow band pass filter as described above, first, the resonant frequency of the floating head slider 7 and It is necessary to be able to match the sum or difference frequency with the frequency of the local oscillator 30 to the center frequency of the bandpass filter 33, and consider that there are variations in the resonant frequency of the floating type slider 7. Therefore, a local oscillator 30 that can change the frequency is required, and there is a problem that the variable frequency local oscillator 30 is expensive.

Further, a tuning operation is required to match the frequency of the local oscillator 30 necessary for frequency conversion to the resonance frequency of the floating head slider 7, and there is a problem that the operation is complicated.

The present invention provides a disk medium protrusion inspection signal processing circuit that can use a fixed frequency oscillator as an oscillator in a frequency conversion means for frequency converting a disk medium protrusion inspection signal (acoustic wave signal) generated in a floating head slider. The purpose is to provide

[Means for Solving the Problems] The present invention provides an oscillator that outputs a predetermined frequency signal, generates a signal with a frequency substantially the same as the elastic resonance frequency of the floating head slider or a pseudo head slider, and combines the predetermined frequency signal with the above-mentioned one. A device that mixes a signal at an elastic resonance frequency, mixes this mixed signal with a disk medium protrusion inspection signal output from the above-mentioned elastic wave detection element, and sends this second mixed signal to a narrow band bandpass filter. It is.

[Function] The present invention provides an oscillator that outputs a predetermined frequency signal, and generates a signal with approximately the same frequency as the elastic resonance frequency of the floating Hent slider or pseudo head slider, and makes the difference between the predetermined frequency signal and the elastic resonance frequency. This mixed signal is mixed with the disk medium protrusion inspection signal output from the elastic wave detection element, and this second mixed signal is sent to the narrowband bandpass filter, so that the predetermined frequency is A fixed frequency oscillator can be used as the oscillator for outputting the signal.

[Example] FIG. 1 is a diagram showing a first embodiment of the present invention.

Note that the same members as the part ν shown in the above conventional example are given the same reference numerals. The same applies to the following examples.

When compared with the conventional example shown in FIG. 7, this first embodiment has the following:
Instead of the local oscillator 30 whose oscillation frequency is variable,
The difference is that an elastic resonance frequency signal generation circuit 40, an oscillator 50 with a fixed oscillation frequency, and a first frequency rationalizer 60 are provided.

The elastic resonance frequency signal generation circuit 40 is an example of an elastic resonance frequency signal generation means that generates a signal having approximately the same frequency as the elastic resonance frequency of the floating head slider 7, and includes a white noise signal source 41 and the floating head slider 7. The head slider 47 has a pseudo head slider 47 made of the same material, size, and shape as the head slider 47, piezoelectric elements 42 and 43 provided at the input end and output end of the pseudo head slider 47, respectively, and an amplifier 44. The pseudo head slider 47 is a floating head slider 7.
It is located near the.

The oscillator 50 is an oscillator that outputs a signal having approximately the same frequency as the center frequency of the bandpass filter 33.

The first frequency rationalizer 60 is a circuit that mixes the output signal of the oscillator 50 and the output signal of the elastic resonance frequency signal generation circuit 40.

The second frequency rationalizer 31 is a circuit that mixes the disk medium protrusion test signal output from the piezoelectric element 10 provided on the floating slider 7 and the output signal of the first frequency rational circuit 60 .

The band pass filter 33 is a narrow band pass filter, and has a width of 0.1 to 10 times the peak bandwidth in the frequency spectrum of the output signal (disk medium protrusion inspection signal) induced in the piezoelectric element IO. It has about twice the bandwidth.

Next, the operation of the first embodiment will be explained.

When a white noise signal from a white noise signal source 41 is applied to a piezoelectric element 42, a pseudo slider 47
is excited, and at this time, the resonance frequency of the pseudo head slider 47 (same as the resonance frequency of the floating head slider 7, Fl, F2, F3, F4, etc.) is applied to the piezoelectric element 43.
. . .) outputs a signal having a peak at . The amplifier 44 amplifies this output signal, and the first frequency rationalizer 6
Send to 0.

On the other hand, the center frequency (F sp
) is generated by the oscillator 50 and supplied to the first frequency rationalizer 60 . Therefore, the first frequency rationalizer 60 selects Fl±Fep, F2±Fep, F3 upper FB
A signal having a peak at P, F4 above F8P, . . . is output, and this signal is supplied to the second frequency grain warming device 31. The second frequency grain temperature mixer 31 receives a signal (disk medium protrusion test signal).

Therefore, the second frequency grain temperature mixer 31 is Fl±FBpf
F1, F2±Fep+F2, F3±FBP±F3, F4
A signal having a peak at ±Fep±F4, . . . is output. Among these, Fl±(±Fl), F
2 above (±F2), F3 above (±F3), F4 above (±F4)
,...... parts cancel each other out,
Only the component of the center frequency Fep of the band pass filter 33 passes through the narrow band band pass filter 33. At this time, the noise component is prevented from passing through the bandpass filter 33.

Then, the signal that has passed through the band pass filter 33 is DC-detected by the wave detector 23, the signal exceeding the threshold voltage is extracted by the comparator 24, and counted by the counter 26. 6
The number of collisions is shown, and data such as the number of collisions is recorded in the recording device 27.

In the first embodiment, the frequency of the disk medium protrusion test signal induced in the piezoelectric element IO when the floating head slider 7 collides is converted to a low frequency by the second frequency grain temperature mixer 31, and Since the low frequency signal passes through the narrow band band pass filter 33, the noise (especially external noise) from the floating head slider 7 to the second frequency grain temperature mixer 31 is filtered through the band pass filter 33. will definitely be removed.

Furthermore, since a signal that is a mixture of the signal from the elastic resonance frequency signal generation circuit 40 and the signal from the oscillator 50 is sent to the second frequency grain warming device 31, it is necessary to make the oscillation frequency of the oscillation W50 variable. The oscillator 50 can be made at a fixed cost, and the cost of the oscillator 50 can be reduced.

Furthermore, even if the elastic resonance frequency of the floating head slider 7 is uneven or fluctuates due to temperature or the like, the oscillator 50
There is no need to adjust the oscillation frequency. In other words, even if the elastic resonance frequency of the floating head slider fluctuates due to temperature, since the floating head slider 7 and the pseudo slider 47 are provided close to each other, the output from the elastic resonance frequency signal generation circuit 40 Since the frequency of the signal also changes accordingly, the fluctuation is canaled, and the oscillation frequency of the oscillator 50 can be fixed without having to be adjusted.

FIG. 2 is a circuit diagram showing a second embodiment of the present invention.

In this second embodiment, an elastic resonance frequency signal generation circuit 70 is provided in place of the elastic resonance frequency signal generation circuit 40.

The elastic resonance frequency signal generation circuit 70 is an example of an elastic resonance frequency signal generation means that generates a signal having approximately the same frequency as the elastic resonance frequency of the floating type slider, and includes the pseudo head slider 47 and the piezoelectric elements 42 and 43. and amplifier 44
, a phase shifter 71 provided between the amplifier 44 and the piezoelectric element 42 , and an attenuator 72 that attenuates the output signal of the amplifier 44 .

That is, a feedback loop is formed by the piezoelectric element 43, the amplifier 44, the phase shifter 71, the piezoelectric element 42, and the pseudo head slider 47, and the phase shifter 71 is adjusted so that a positive feedback loop is applied. Therefore, the feedback loop circuit oscillates at the main resonance frequency determined by the elastic vibration of the pseudo head slider 47.

Next, the operation of the second embodiment will be explained.

The elastic resonance frequency signal generation circuit 70 performs positive feedback using a piezoelectric element 43, an amplifier 44, a phase shifter 71, a piezoelectric element 42, and a pseudo head slider 47 as a feedback loop. The output signal of the attenuator 72 is applied to the first frequency rationalizer 60. The first frequency rationalizer 60 is then mixed with the fixed frequency signal from the oscillator 50.

In this second embodiment as well, the bandpass filter 33 reliably removes noise (particularly external noise) from the floating head slider 7 to the second frequency grain warming device 31. Furthermore, the oscillation frequency of the oscillator 50 does not need to be made variable, but can be fixed;
0 cost can be lowered. Further, even if the elastic resonance frequency of the floating head slider 7 varies or fluctuates, there is no need to adjust the oscillation frequency of the oscillator 50.

FIG. 3 is a diagram showing a third embodiment of the present invention.

In this third embodiment, an elastic resonance frequency signal generation circuit 80 is provided in place of the elastic resonance frequency signal generation circuit 40 in the first embodiment.

The elastic resonance frequency signal generation circuit 80 is an example of an elastic resonance frequency signal generation means that generates a signal having approximately the same frequency as the elastic resonance frequency of the floating Hent slider, and includes a white noise signal source 81, a switch 82, and a floating type Hent slider. A piezoelectric element 83 mounted on the head slider 7, a floating head slider 7, a piezoelectric element 10, a switch 84 for switching the output signal of the piezoelectric element 10 between an A terminal and a B terminal, an amplifier 85, and an amplifier. 85, and oscillators 87a, 87b, and 87c that output signals of different frequencies.

Note that the frequency analyzer 86 includes one oscillator 87a, 87b, 8
By commanding the oscillators to be driven among the oscillators 7c, that is, by changing the combination of drive oscillators, the frequency of the signal from the amplifier 85 and the frequency of the combined and synthesized signal are made the same.

Furthermore, the A terminal of switch 84 is connected to amplifier 85 and the B terminal thereof is connected to amplifier 20. Further, the switches 82 and 84 are switched in conjunction with each other, so that when one switch is connected to the A terminal, the other switch is also connected to the A terminal.

Next, the operation of the third embodiment will be explained.

Before checking the number of protrusions 6 on the disk medium 4, as a preparatory step, as shown in FIG.
4 to the A terminal, and the white noise signal from the white noise signal source 81 is supplied to the piezoelectric element 83. As a result, the floating head slider 7 is excited and resonates.
A frequency analyzer 86 analyzes the peak frequency of the elastic resonance frequency signal output by the piezoelectric element 10, and stores the peak frequency.

When inspecting the number of protrusions 6, the switch 82
, and switch 84 to the B terminal. At this time, the frequency analyzer 86 controls the driving combination of the first oscillators 87a to 87c so that a signal having the same frequency as the frequency stored therein is supplied to the first mixer 60. and,
The first frequency rationalizer 60 mixes the signal from the first oscillator 50 and the signal from the elastic resonance frequency signal generation circuit 80,
The mixed signal is supplied to the second frequency grain warming device 31.

The other input terminal of the second frequency mixer 31 has a piezoelectric element 1
The F4 body protrusion test signal from 0 is supplied. The subsequent operation is similar to that of the first embodiment.

In this third embodiment as well, the noise (especially external noise) from the floating slider 7 to the second frequency rationalizer 31 is reliably removed by the light filter 33. Furthermore, there is no need to make the oscillation frequency of one oscillator 50 variable; it can be fixed, and the cost of the oscillator 50 can be reduced. Further, even if the elastic resonance frequency of the floating head slider 7 is constant or fluctuates, there is no need to adjust the oscillation frequency of the oscillator 50.

Furthermore, according to the third embodiment, the pseudo head slider 47
The same effects as in the first and second embodiments can be obtained without using. Note that the oscillators 87a and 87b
, 87C are shown as examples, and the number of oscillators may be other than three.

Further, instead of the piezoelectric element, other elastic wave detection elements may be used, such as those that detect elastic waves based on magnetic or capacitance changes.

[Effects of the Invention] According to the present invention, there is no need to use an oscillator with a variable oscillation frequency as an oscillator in the frequency conversion means for converting the frequency of the elastic wave signal generated in the floating head slider, so the entire device is inexpensive. In addition, even if the elastic resonance frequency of the floating head slider varies or fluctuates, there is no need to adjust the oscillation frequency of the oscillator, and the entire device can be easily operated.

[Brief explanation of the drawing]

FIG. 1 is a diagram showing a first embodiment of the present invention. FIG. 2 is a diagram showing a second embodiment of the present invention. FIG. 3 is a diagram showing a third embodiment of the present invention. FIG. 4 is an explanatory diagram of a conventional example of protrusion inspection. FIG. 5 is an explanatory diagram of a conventional example in which a small piezoelectric element is directly attached to a floating slider. FIG. 6 is a circuit diagram of a conventional example in which the SN ratio is improved by narrowing the bandpass filter. FIG. 7 is a circuit diagram of a conventional example in which the signal-to-noise ratio is improved by converting the frequency of a disk medium protrusion test signal from a piezoelectric element and passing it through a narrow band pass filter. FIG. 8 is a diagram showing the relationship between the relative speed between the magnetic disk medium and the floating slider and the effective voltage value of the output of the main resonance frequency induced in the piezoelectric element 10. FIGS. 9(a) and 9(b) show the output waveform of the main resonance frequency induced in the piezoelectric element 10 when a magnetic disk medium 4 partially provided with protrusions and a floating head slider 7 are used. , is a diagram showing the case of the circuit shown in FIG. 6 and the case of the circuit shown in FIG. 7. 7...7 slider to floating type, 10.42.43.83... Piezoelectric element, 31... Second frequency mixer, 33... Narrowband band pass filter, 40.70.8
0...Elastic resonance frequency signal generation circuit, 47...Pseudo slider, 50...Fixed frequency oscillator. 60...first frequency converter. Patent Applicant Nippon Telegraph and Telephone Co., Ltd. Agent: Arata Kubo

Claims (1)

[Claims] A floating head slider equipped with an elastic wave detection element to detect protrusions on a disk medium; An oscillator that outputs a signal at a predetermined frequency; A frequency substantially the same as the elastic resonance frequency of the floating head slider. elastic resonance frequency signal generation means for generating a signal; first frequency mixing means for mixing the output signal of the oscillator and the output signal of the elastic resonance frequency signal generation means; a disk medium output by the elastic wave detection element; a second frequency mixing means for mixing the protrusion inspection signal and the output signal of the first frequency mixing means; inputting the output signal of the second frequency mixing means, the center frequency of which is approximately the same as the frequency of the output signal of the oscillator; A disk medium protrusion inspection signal processing circuit comprising: a bandpass filter; and a bandpass filter.