JPH0266715A - Gap depth measuring instrument for magnetic head - Google Patents

Abstract

PURPOSE:To measure a gap depth with non-destruction and to discriminate the exchange period of a head by calculating the gap depth of a head from the relation of a measured saturated magnetic flux, the saturated magnetic flux density of a magnetic core and the track width of a magnetic head. CONSTITUTION:The waveform of a current I flowing to a magnetic head 1 is measured with an ammeter 62, the waveform of a voltage E2 generated at both edges of a coil 1b of the head 1 is simultaneously measured by a voltmeter 63, measuring data are processed by a computer 64 and the waveform of a magnetic flux phi and an excited magnetism is obtained. The computer 64 measures the magnetic saturated characteristic of the head 1, a saturated magnetic flux phis of a gap part 1c of the head 1 is detected from a measured hysteresis characteristic, and from an expression Gd=phis/(TwXBs) [provided that Gd: depth of gap, Tw: track width (length of gap 1c) and Bs: saturated magnetic flux density of core 1a], a depth Gd of the gap 1c is calculated.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to an apparatus for measuring the depth of a gap in a magnetic head.

[Prior Art] Among magnetic recording and reproducing devices, in devices in which the recording medium is tape-shaped or sheet-shaped, the magnetic head and the magnetic medium are in contact with each other and move relative to each other. FIG. 6 shows how the magnetic head of a video tape recorder (hereinafter referred to as rVTRJ) contacts the magnetic medium. In the figure (11 is a magnetic head, (la
) is the magnetic head, core, (Ibl is the coil, (Ic) is the gap, Gd is the depth of the gap, Tw is the length of the gap that determines the width of the recording track, (2) is the magnetic recording medium, (10) is the traveling direction of the magnetic head (1).

As shown in FIG. 6, when the magnetic head (1) and the magnetic recording medium (2) move in contact with each other, the magnetic head core (la) is worn away by the magnetic recording medium (2), and the gap (1G)
The depth Gd becomes smaller.

This situation is shown in FIG. Initially, the depth Gd of the gap (lc) is large, as shown in FIG.
) will wear out and become as shown in the same figure (b), and the gap (Ic)
The depth Gd becomes smaller. If further used, the same figure (c
), the depth Gd of the gap (1c) disappears, and it no longer functions as a magnetic head. The amount of wear of the magnetic head (1) per unit usage time increases as the relative speed between the magnetic head (1) and the magnetic recording medium (2) increases. It is known that the higher the pressure, the more people are attracted, and the higher the humidity, the louder the atmosphere.

Further, the amount of wear per unit of use time varies depending on humidity, swelling, and operating conditions (continuous use or intermittent use).

For example, broadcast V, which requires high relative speed and reliability.
With V 1-11 such as TR, the magnetic head (1) is replaced after a certain period of use, and the gap (LC) is removed during use.
This is to ensure that the depth Gd does not disappear.

[Problems to be Solved by the Invention] As described above, in conventional magnetic recording and reproducing devices, the value of the gap depth Gd cannot be known, so the magnetic head is replaced after a certain period of use. Since the amount of wear varies depending on temperature, humidity, dust, etc., the replacement period for the magnetic head must be much shorter than the average lifespan of the magnetic head in order to obtain sufficient reliability, so the gap depth Gd must be large enough. Since the magnetic head may have to be replaced, which is economically disadvantageous, it has been desired to develop an appropriate head gap depth measuring device.

This invention has been made to solve the above-mentioned problems, and provides a measuring device that can non-destructively measure the gap depth of a magnetic head and determine the appropriate time to replace the magnetic head. The purpose is to

[Means for Solving the Problem] A gap depth measuring device according to the present invention includes a means for measuring the saturation characteristic of a magnetic head, and a means for calculating the gap depth from the measured saturation characteristic. .

[Operation] The saturation characteristic measuring means in the present invention measures the magnetic flux at which the gap portion of the magnetic head is saturated, and the head-to-butt depth calculating means calculates the measured saturation magnetic flux and the saturation magnetic flux density of the magnetic core. , the gear A/tube depth of the magnetic head is calculated from the relationship with the track width (gap j) of the magnetic head.

[Embodiment of the Invention] Hereinafter, an example in which an embodiment of the present invention is incorporated into a VTR will be described. In Figure 1, (3) is a rotary transformer, (4) is a switch, (5) is a recording/reproducing device, (52) is a recording circuit, (53) is a reproduction circuit, (51)
(5) is the gap depth measuring device, (61) is the signal source that sends the test signal to the magnetic head (1), (62) is the output current of the signal source (61) (63) is a voltmeter that measures the output voltage waveform of the signal source (61), converts it into digital data, and outputs it. The measurement data of the ammeter (62) and voltmeter (63) and the magnetic head (1
) is a computer that is a means of calculating the gap depth.

In normal use as V i”R, the switch (
4) is closed to the terminal a side, and the magnetic head (1) is connected to a recording/reproducing device (5).

When measuring the gap depth of the magnetic head (1), the switch (4) is closed to the end side, and the magnetic head (1) is connected to the gap depth measuring device (6) side.

FIG. 2 shows an isochoric circuit in this case. However, the rotary transformer (3) is omitted as it is considered ideal.

In Figure 2, (11) is the resistance component of the coil (l b l itself) of the magnetic head (1), and (12) is the resistance component of the magnetic head (1).
The inductance component (61a) of signal source (6
1) internal electromotive force, (61bl is the internal impedance of the signal source (6I), ■ is the current flowing in the magnetic head (1), Φ is the magnetic flux passing through the magnetic core (1), Ti j, trrI
The voltage generated across the coil (Ib) of the electric head (1), F, 2 is the voltage generated in the inductance component (12), and El is the voltage generated in the resistance component (11).

If the number of turns of the coil (lbl) of the magnetic head (1) is N, the voltage E1 generated by the inductance component is (1
), and if the resistance value of the resistance component (11) is F7, the voltage T:2 generated in the resistance component (jl) is (2)
The voltage E generated across the coil (Ibl) of the magnetic head (1) is expressed by the equation (3). In the equation, dΦ is the time differential of the magnetic flux.

d 1−, 2 Also, the magnetomotive force Nl is N I = NX 1...
(5) becomes.

From equations (4) and (5), the coil (1) of the magnetic head (1)
b) By determining the number of turns N and the value R of the resistance component in advance, you can measure the waveform of the current I flowing through the magnetic head (11) with an ammeter (62), and also measure the waveform of the current I flowing through the magnetic head (11) with the coil (1b) of the magnetic head (1).
By simultaneously measuring the waveform of the voltage E generated at both ends with a voltmeter (63) and processing the measured data with a computer (64), the waveforms of the magnetic flux Φ and the magnetomotive force Nl can be determined. The magnetomotive force NI obtained in this way and the magnetic flux Φ
The relationship between the two is a hysteresis group as shown in FIG. 3(a). Figure 4 shows the flow of magnetic flux passing through the magnetic core (Ial). In the figure, ΦC is the magnetic flux that passes only through the magnetic core (1a), and ΦL is the magnetic flux that passes only through the magnetic core (1a), and ΦL is the flow of magnetic flux that passes through the magnetic core (1a). Magnetic core (1 day)
The magnetic flux Φ that leaks out of the coil (1b) and interlinks with the coil (1b) is Φ! is added. Fig. 3 ib) shows the characteristics of the magnetic flux ΦC with respect to the magnetomotive force N1, and Fig. 3 (c) shows the characteristics of the magnetic flux ΦL with respect to the magnetomotive force NI.
a) is expressed as a combination of the characteristics of these ΦG and Φt. In FIG. 3 [bl], the magnetic flux ΦC is saturated at Φs. The value of this Φs is the saturation magnetic flux density B of the magnetic core (1a)
s and the minimum cross-sectional area of the magnetic core (1a), that is, the gap (
It is determined by the cross-sectional area S of the lcl portion, and is expressed as equation (5).

Φs:B5X5-(6) This Φs is calculated by calculation in the computer (64). In FIG. 3(a), the magnetic flux is obtained by extrapolating the portion after the gap portion is saturated until the magnetomotive force Nl is 0 (vertical axis). In this way, the magnetic flux Φs at which the gap portion is saturated can be determined. Gap (1e)
When the cross-sectional shape of the portion is rectangular, the cross-sectional area S is determined by the track width, that is, the length Tw of the gap (lc), and the depth Gd of the gap (lcl), and is expressed as equation (7). ( From Equations 6) and Equations (7), the depth Gd of the gap (IC) is expressed as Equation (8).

S = T”w X Gd = (7
) In equation (8), Φs can be obtained by the above measurement, and '1'w can be measured with high precision by an optical method, and is a value determined by the magnetic head (1). Bs is a value determined by the material of the magnetic core (1a), and it is known that it does not change due to processing, so it may be measured in advance. Thus, in this example,
If the saturation magnetic flux density Bs of the material of the magnetic core (1a), the track width -F'w, and the number of turns N of the coil (Ibl) are known, the gap of the magnetic head (1c ) can be measured, and the appropriate time to replace the magnetic head can be determined.

In addition, in Example 1, the saturation characteristics of the magnetic head were determined using the output current waveform and output voltage waveform of the signal source (61), but other methods may also be used. For example, as shown in FIG. The average value or effective value of the output current of the signal source (61) is measured with an ammeter (62), and the average value or effective value of the output voltage is measured with a voltmeter (63).
The saturation characteristics may be determined by varying the output level of the output of the filter 61) using an attenuator (65). In this case, the voltmeter (63) and ammeter (52) only need to measure the average value or effective value of the voltage and current, respectively, so there is an advantage that the measuring device can be constructed at an inexpensive price.

In addition, in the first embodiment, the gap depth measuring device (6) of the magnetic head was provided inside the v''-t'R, but it could also be constructed as an independent measuring device and connected to the magnetic head during measurement. Good too.

Although the embodiment described in section 1-1 is applied to a broadcasting V'T'R, similar effects can be obtained by applying it to other magnetic recording/reproducing devices, such as floppy disk devices.

[Effects of the Invention] As described above, according to the present invention, the magnetic head saturation f
1 and calculate the gap depth from this measured value, it is possible to know the optimum time to replace the magnetic head.

[Brief explanation of the drawing]

Fig. 1 is a block circuit diagram showing the configuration of an embodiment in which the present invention is applied to a VTR, Fig. 2 is an equivalent circuit diagram when measuring magnetic characteristics of a magnetic head in this embodiment, and Fig. 3 is a block circuit diagram showing the configuration of an embodiment in which the present invention is applied to a VTR. Figure 4(a) is a front view showing the magnetic head, Figure 4(a) is a diagram showing the magnetic saturation characteristics of the magnetic head measured.
b) is a plan view showing the flow of magnetic flux in the magnetic head, FIG. 5 is a block circuit diagram of another embodiment of the present invention, FIG. 6 is a diagram showing the state of contact between the magnetic head and the magnetic recording medium, and FIG. The figure shows how the magnetic head wears. (1)...Magnetic head, (IC)...Gap, (
6)...gap depth measuring device, (61)...signal source, (62)...ammeter, (63)...voltmeter, (
64)...Computer, (65)...Attenuator. In addition, in each figure, the same symbol indicates the same or equivalent part. Agent: Masuo Iwa, Figure 3, Figure 4 Procedure Amendment Kei (voluntarily) Contents of the amendment in the “Detailed Description of the Invention” section of the specification to be amended: (1) Page 2, line 5 to Page 2, line 6; 2. The name of the invention, ``Herad Fist Core,'' is corrected to ``Head Core'' and the gap depth measuring device between the magnetic head. 3. Relationship between the person making the amendment and the case

Claims (1)

[Claims] (1) A means for measuring the magnetic saturation characteristics of a magnetic head, and detecting the saturation magnetic flux Φs in the gap portion of the magnetic head from the hysteresis characteristics measured by this measuring means, using the following formula Gd=Φs/(Tw×Bs) where: Gd: Gap depth Tw: Track width (gap length) Bs: A magnetic head gap depth measuring device comprising means for calculating the gap depth Gd from the saturation magnetic flux density of the magnetic head core.