JPH0514964B2 - - Google Patents

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to a method for sorting magnetic heads, and is applicable, for example, to selecting acceptable heads from manufactured magnetic heads for use in video tape recorders (VTRs). It is suitable for this purpose.

[Conventional technology]

The optimum recording depth d of the magnetic tape is determined by the wavelength λ of the recording current flowing through the head, and is approximately λ/4. However, in VTRs, from the point of view of magnetic tape recording efficiency, the chroma signal is reduced and converted and assigned to a lower range than the luminance signal, and when other signals are superimposed on the video signal and recorded, the lower range is A recording method has been proposed in which the chroma signal is allocated to a band in which there is no chroma signal. For example, convert audio signal to FM
The so-called modulated and superimposed video signal is recorded.
The AFM method has been proposed, and the so-called ATF method records a pilot signal used for head tracking during playback by superimposing it on the video signal.
(Automatic Tracking Follow) method has been proposed.

When recording such a reduced signal on a magnetic tape, the wavelength λ of the recording signal becomes longer, so the optimum recording depth d for the tape becomes deeper. Therefore, it is necessary to increase the recording current flowing through the head to strengthen the recording magnetic field.

Therefore, a magnetic head used in a VTR is required to have as wide a range of linear portions as possible in its saturation characteristics. Incidentally, since the magnetic head has saturation characteristics, even if a large recording current is passed to generate a strong magnetic field, the resulting magnetic field will be ST1 as shown in Figure 6.
As shown in , the isomagnetic interface is distorted as if it were crushed compared to the magnetic field ST2 when the recording current is small and not saturated. There is no problem if the head has a sufficiently large current value at which it begins to exhibit saturation characteristics and can secure the necessary optimum recording depth d for the recording current, but if the head starts to exhibit saturation characteristics at a small value, it may be necessary to use a large recording current value range. In this case, the level of the reproduced signal decreases due to the influence of the saturation characteristics, and the waveform reproducibility deteriorates.

Conventionally, therefore, a method has been adopted in which signals are recorded on a table and reproduced in a manner similar to the manner in which the head is actually used, and the output level of the reproduced chroma signal is detected to determine whether the head is acceptable or not. That is,
As shown in Fig. 7, a predetermined video signal is recorded on a tape 2 by the magnetic head 1 to be inspected, which is reproduced by the reproducing head 3, and the output level of the chroma signal component of the reproduced signal VPB is detected and selected. Ta. At that time, the video signal used for recording is standardized so that it is the same for all heads 1 to be tested. It consists of a superimposed signal with a chroma signal whose level is -12 [dB] lower than the signal. Further, the reproducing head 3 is commonly used by all the heads 1 to be inspected.

In this way, since the recorded video signal and reproduction conditions are the same for each head 1 to be tested, the difference in the output level of the reproduced chroma signal component represents the difference in the recording characteristics of the head 1 to be tested. Become.
Therefore, it is possible to judge whether the head to be inspected 1 passes or fails using a predetermined judgment level.

In this way, the head 1 to be inspected is selected based on the chroma signal component, and the head 1 selection judgment is not made again based on the ATF signal and AFM signal. This is because there is a correlation between the output level of the chroma signal and the output level of the AFM signal.

[Problem that the invention seeks to solve]

However, although the above-described head selection method has the advantage of selecting the heads by inspection in the same manner as when the heads are actually used, it is difficult to select each head individually when selecting a large number of heads to be inspected. Since the recording and reproducing inspection process must be performed, there are problems in that the time required for the sorting operation is long and the effort is complicated.

In addition, the output level of the chroma signal, which determines whether or not to be selected, is lower than the output level of the luminance signal, so the conditions for the filters, amplifier circuits, etc. used to extract and amplify the chroma signal components must be made stricter. , the sorting device must be expensive.

The present invention has been made in consideration of the above points,
The object of the present invention is to provide a magnetic head selection method that can simply and accurately determine whether a magnetic head is acceptable or not, without going through a recording/reproducing inspection process for all magnetic heads.

[Means for solving problems]

In order to achieve this purpose, a biased low frequency current signal i _R is applied to the magnetic head 10 to be tested.
At that time, measure the inductance L of the head 10, and vary the bias value _iHF to increase the inductance L.
The inflection point of the inductance is detected, and the magnetic head 10 to be inspected is selected based on the bias value i _HFS that provides the inflection point of the inductance.

[Effect]

The saturation characteristics of the head are divided into the unsaturated region HR and the saturated region.
The inflection point between HS and VAR is represented by VAR, and the inflection point
Detects VAR and selects heads. by the way,
The head inductance L changes rapidly between the unsaturated region HR and the saturated region HS. Therefore, by detecting the inflection point of the inductance L, selection can be made.

To detect the inflection point of the inductance L, apply a bias i _HF to a low frequency signal i _LF with small amplitude change, measure the inductance L in a minute range H _c corresponding to the amplitude of the low frequency signal i _LF , and measure the bias amount. i Perform by changing _HF . Then, based on the bias amount i _HFS that provides the inflection point of the inductance L, the magnetic head 10 is determined to be acceptable when the bias amount i _HFS is larger than the pass/fail determination criterion.

〔Example〕

An embodiment of the magnetic head sorting method according to the present invention will be described in detail below with reference to the drawings.

Since the magnetic head is made of soft magnetic material,
The B-H characteristics of the head are as shown in Figure 2A.
Almost regardless of the history, in the non-saturated region HR, the magnetic flux density B changes with a large slope μ1 as the magnetic field strength H changes, and in the saturated region HS, the magnetic flux density B changes with the change in the magnetic field strength H.
As , the magnetic flux density B changes with a slope μ2 close to 0.

Therefore, the inflection point of the slope in this B-H characteristic, that is, the point where the slope changes from μ1 to μ2 VAR
The saturation characteristic is represented by VAR, and this inflection point VAR is detected to select the head.

In order to detect the inflection point VAR, the magnetic field strength H
must be changed and the corresponding slope μ must be detected. Of these, the magnetic field strength H is the recording current
Since it is proportional to i _R , the magnetic field strength H can be changed by changing the recording current i _R. On the other hand, the slope μ represents the ratio of the magnetic flux density B to the magnetic field strength H, as shown in μ=B/H (1), and means magnetic permeability. Here, the magnetic permeability μ is proportional to the head inductance L as shown in μ∝L (2). Therefore, a change in the slope μ in the B-H characteristic can be detected by detecting the inductance L.

Therefore, in order to detect the inflection point VAR of the slope of the B-H characteristic, it is sufficient to change the recording current i _R and detect it as the inflection point of the inductance L.

By the way, as a method for detecting the inflection point of the inductance L with respect to the recording current i _R , firstly, the inductance L is detected for each minute range of the recording current i _R , and the inductance L is changed by changing the minute range for detection. A second method is to detect the inflection point of the inductance L by gradually increasing the recording current i _R and detecting the inductance L each time.

However, according to the second method, the recording current
The change in inductance L appears gradually with respect to the change in i _R , and the inflection point of inductance L is difficult to distinguish, so that it is still insufficient.

As shown in Figure 2A, when looking at the B-H characteristic in a minute range _Hc of the magnetic field strength corresponding to the minute range of the recording current _iR , the inductance L is determined by the magnetic permeability as shown in Figure 3. When there is a minute range H _c in the unsaturated range HR that changes with μ1, a value proportional to the magnetic permeability μ1
If L1 is taken, and there is a minute range H _c in the saturation range HS that changes with magnetic permeability μ2, a value proportional to magnetic permeability μ2
When the minute range H _c covers both the unsaturated range HR and the saturated range HS, the value L3 is taken as the intermediate value between L1 and L2.

Detection of the inflection point of the inductance L according to the first method can be realized by the configuration shown in FIG. In FIG. 1, a head to be inspected 10 has one end of a coil grounded, and the other end of the coil connected to a recording current generating circuit 20 so that a recording current _iR is applied thereto.

The recording current generation circuit 20 generates a low frequency signal _iLF which is obtained by amplifying a signal of, for example, 100 [KHz] outputted by a low frequency signal oscillation circuit 21 to a peak-to-peak level of 2 [mA] by a low frequency signal amplification circuit 22, and a high frequency signal. A recording current i _R is generated by superimposing a high frequency signal i _HF amplified by a high frequency signal amplification circuit 24 on a signal of, for example, [MHz] outputted by the oscillation circuit 23 .

Here, the low frequency signal i _LF has a frequency suitable for detecting the recording characteristics in the low range of the video signal, and its amplitude gives a minute range for detecting the inductance L. In contrast, high-frequency signals
i _HF acts as a bias signal for the low frequency signal i _LF ,
The detection microrange is changed, and the bias is changed by changing the amplification factor of the high frequency signal amplification circuit 24. The high frequency signal amplification circuit 24 is configured to conduct a high frequency signal i _HF between the peaks of 0 to 40, which is sufficient to detect the inflection point of the inductance L.
The oscillation signal can be amplified so as to be variable within the [mA] range.

When the recording current i _R flows through the head 10 to be inspected, magnetic fields H1, H2, H3 (FIG. 2B,
C, D) are generated. The inductance L of the head 10 at this time can be detected by the voltage drop v _L across the coil of the head 10.

In order to detect the inflection point of the inductance L, the low-pass filter 30 only needs to detect the voltage drop component with respect to fluctuations within a minute range of the recording current i _R , so it generates a bias signal (high frequency signal) from the voltage drop v _L component. Remove ingredients. Therefore, the cutoff frequency of the low-pass filter 30 is such that the low frequency signal component passes through (100 [KHz]) and the high frequency signal component (5 [MHz]) passes through.
For example, the frequency is selected to be 1 [MHz] so as to be able to cut the frequency (Hz).

The voltage measurement circuit 40 includes an oscilloscope 41 and a spectrum analyzer 42, and measures the voltage signal _vLL from the low-pass filter 30, and its measurement accuracy is, for example, 0.3 to 1.0 [dB].
was selected to be able to measure voltage fluctuations.

In the configuration shown in FIG. 1, in a range where the degree of amplification of the high-frequency signal amplification circuit 24 is small and the amount of bias in the recording current i _R is small, the magnetic field due to the recording current i _R is as shown in H1 shown in FIG. 2B. unsaturated region
It changes only within HR. Therefore, the voltage v _LL corresponding to the inductance extracted by the low-pass filter 30 for the low frequency component, that is, the envelope component of the magnetic field H1, is a constant value corresponding to the magnetic permeability μ1.
v _LL 1 (Figure 3).

As the amplification factor of the high-frequency signal amplification circuit 24 is increased and the bias amount of the recording current _iR is increased, the magnetic field due to the recording current iR eventually becomes larger as shown in FIG.
Unsaturated region HR and saturated region as shown in H2
Varies across HS. At this time, the voltage v _LL is the value v _LL 3 corresponding to the intermediate value of magnetic permeability μ1 and μ2 (Figure 3)
decreases to

Therefore, this drop from v _LL 1 to v _LL 3 is measured by the voltage measuring circuit 40, and the amount of the drop is, for example, 0.3 [dB].
The recording characteristics of the head 10 to be tested can be specified by the bias current i _HFS .

Figure 4 shows the bias current in the configuration of Figure 1.
The figure shows the change in the voltage signal _vLL at the three tested heads 10a, 10b, 10c when the peak-to-peak value of _iHF is changed. As shown in Figure 4, 15 [mA] for head 10a, 26.6 [mA] for head 10b, and 26.6 [mA] for head 10c.
33.2 [mA] is the value i _HFS that indicates the recording characteristics of the head. Therefore, based on this value, each head to be inspected 10
can be sorted.

The relationship between the inflection point bias current value i _HFS obtained in this way and the output level e _OUT of the chroma signal component according to the conventional recording/reproducing method (Fig. 7) for the 42 heads 10 to be inspected is shown in the fifth table. As shown in the figure. As shown in Fig. 5, there is a strong correlation between the inflection point bias current value i _HFS and the output level e _OUT , and even if the heads 10 are selected based on the inflection point bias current value i _HFS , the output level e _OUT Almost the same result is obtained even if the heads 10 are selected using the same method.

For example, if in the conventional method a head with an output level of -15 [dB] or more was judged to be good (that is, passed), if a similar sorting is performed using the configuration shown in Figure 1, the output level will be The inflection point bias current value i _MFS for -15 [dB] has a certain range due to head variations, but it is desirable for quality control to take a value as large as possible, so the output level -
The judgment can be made based on the upper limit inflection point bias current value i _MFS of 16.6 [mA] among heads showing 15 [dB]. When the three heads 10a, 10b, and 10c shown in FIG. 4 are selected and determined based on this criterion, head 10a is determined to be a defective product (that is, rejected), and heads 10b and 10c are determined to be non-defective products.

In this way, by using the configuration shown in FIG. 1 and selecting heads based on the change in inductance L, the heads to be tested can be easily selected without going through the tape recording/reproducing testing process.

Note that in the configuration shown in Figure 1, the low frequency signal i _LF
The frequency of is not limited to 100 [KHz] and is a high frequency signal.
i Any frequency that changes slowly enough with respect to the _HF frequency (5 [MHz]) is sufficient. however,
For example, if a fairly small value such as 20 [KHz] is selected, the impedance ωL due to the inductance L of the head 10 is proportional to the frequency, so the value of the voltage drop _vL due to that impedance becomes small, making it difficult to distinguish it from noise. As a result, the measurement sensitivity of the voltage measurement circuit 40 deteriorates. Conversely, when the frequency of the low frequency signal i _LF is increased, distortion occurs in the voltage signal v _LL in relation to the frequency of the high frequency signal i _HF , and measurement sensitivity also decreases in this case. Therefore, as in the configuration of FIG. 1, around 100 [KHz] is appropriate.

Incidentally, the frequency of the low frequency signal i _LF is approximately 700 [KHz],
If the frequency of the high frequency signal i _HF is selected to be 5 [MHz], the recording current i _R can be made to correspond to the video signal in the _VTR , which is desirable for determining recording characteristics. The frequency is large, distortion occurs, and sensitivity inevitably deteriorates.

Furthermore, in the above-described embodiment, the inflection point of the inductance was detected by applying an AC bias to vary the recording current detection minute range, but by applying a DC bias to vary the recording current detection minute range. The range may be varied and similar effects can be obtained.

〔Effect of the invention〕

As described above, according to the present invention, it is possible to detect the inductance by simply flowing a biased low-frequency current signal to the head, without having to go through the trouble of actually performing recording/reproducing operations on the magnetic head to be tested. This allows you to easily and quickly determine whether the head is acceptable or not.

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing the configuration for implementing the magnetic head sorting method according to the present invention, FIG. 2 is a schematic diagram showing the B-H characteristics of the head, and FIG. 3 is a diagram showing the relationship between magnetic field strength and inductance. A schematic diagram showing the relationship,
Figure 4 is a graph showing the experimental results of changes in inductance with respect to changes in recording current, Figure 5 is a graph showing the correlation between the conventional selection method and the selection method of the present invention, and Figure 6 is a graph showing the correlation between the recording characteristics of saturation characteristics. FIG. 7 is a schematic diagram used to explain the conventional magnetic head sorting method. 10...Head to be inspected, 21...Low frequency signal oscillation circuit, 23...High frequency signal oscillation circuit, 24...
High frequency signal amplification circuit, 30...Low pass filter, 40...Voltage measurement circuit, i _LF ...Low frequency signal,
i _HF ...High frequency signal (bias), v _L ...Voltage drop due to inductance.

Claims (1)

[Claims] 1 Measure the inductance of the magnetic head to be tested by passing a biased low frequency current signal through the magnetic head to be tested, detect the inflection point of the inductance by changing the bias amount of the low frequency current signal, and measure the inductance of the magnetic head to be tested. A magnetic head selection method for determining whether the magnetic head to be inspected passes or fails based on the bias amount that provides an inflection point.