JPH09185815A - Contactless magnetic head abrasion loss measuring device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To measure abrasion loss of a precision head in noncontact manner without being affected by form tolerances, mounting errors, etc., of a magnetic head. SOLUTION: Two magnetic sensors 30A and 30B are arranged so as to have gaps β1, β2 (>β1) as opposed to a magnetic head 20 respectively. The magnetic sensors are connected to variable oscillation circuits 40A, 40B as variable oscillation elements, and a same oscillation frequency is outputted when both gaps opposed to the drum are the same. Head abrasion loss is measured based on a difference between individual oscillation frequencies fa, fb measured at a rotation position where the magnetic head is opposed to the magnetic heads. Since a variation of magnetic reluctance is obtained for measuring the head abrasion loss, the head abrasion loss can precisely be measured in accordance with a projection value of the head. Due to a non-contact type, there is no fear of damaging the magnetic head to be measured. Since the head abrasion loss is measured by utilizing the difference between the two oscillation frequencies, the measurement results are not affected by form tolerances or mounting errors of the magnetic head.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a non-contact type magnetic head wear amount measuring apparatus suitable for application to a rotating drum device using a magnetic head such as a video tape recorder, and more particularly to a rotating magnetic head device. The present invention relates to a measuring device in which a magnetic sensor is disposed in a non-contact manner and a wear amount of the magnetic head is measured in a non-contact manner by a change in total magnetic resistance between the magnetic head and the magnetic sensor. More specifically, it is possible to eliminate variations in measured values that occur due to tolerances in the shape of the magnetic head, mounting errors, and the like by using the differences in oscillation frequencies obtained from a plurality of magnetic sensors.

[0002]

2. Description of the Related Art Video tape recorders (VTRs), data recorders, digital audio tape recorders (D)
In an AV device such as an AT) which uses a rotary drum device equipped with a magnetic head, a magnetic head is brought into contact with a magnetic tape to run the tape. The moving parts wear.

When the amount of wear reaches several tens of microns,
In a normal magnetic head, the area (head depth) that forms the magnetic head gap disappears, so if the head depth is worn to the point where it is completely lost, recording and reproduction may be hindered. If the head sliding portion wears out until the head depth completely disappears, the worst case will occur and the signal cannot be recorded or reproduced.

In this case, when the head wear reaches several tens of microns during signal reproduction, the reproduced signal from the tape becomes zero, so that an abnormality of the magnetic head can be immediately known.

However, when the amount of head wear reaches several tens of microns during recording of the signal, there is a possibility that the signal cannot be normally recorded. This abnormal situation cannot be confirmed without reproducing the recorded signal. Therefore, when such an AV device is used for business purposes, important information may be missed. Such a situation must be avoided.

Therefore, it is preferable to monitor the amount of wear of the head, especially in the AV equipment for business use, and to warn the user when the amount of wear reaches a specified amount to prompt maintenance and inspection. For that purpose, it is necessary to measure the amount of head wear, and as this measuring device, a contact type measuring device and a non-contact type measuring device can be considered.

When the magnetic head wear amount measuring device is constructed as a contact type, a measuring jig such as a tracing stylus is attached so as to come into contact with the magnetic head to be measured.
The tape sliding surface of the magnetic head to be measured may be scratched, or in the worst case, the magnetic head to be measured may be damaged.
In addition, the measurement result varies depending on how the measuring element is attached, and the influence on the measurement accuracy cannot be overlooked.

When the amount of wear is measured in a non-contact type, the problem of the contact type does not occur. In the non-contact type, the amount of head wear is measured using light. In this case, it is necessary to use a laser beam or the like and focus the laser beam to accurately irradiate the tape sliding surface of the magnetic head to be measured, so that the arrangement and adjustment of the laser optical system becomes very troublesome. In addition to the fact that the measuring device itself is bulky due to the use of the optical system, it requires considerable nerves to assemble it into the rotary drum device.

In order to solve these problems, a magnetic sensor is used, which is arranged so as to face the rotary magnetic head device with a predetermined gap, and a magnetic circuit formed when the magnetic head and the magnetic sensor face each other. It is conceivable to obtain the head protrusion amount from the change in the magnetic resistance and measure the head wear amount based on this.

[0010]

When measuring the amount of head wear in a non-contact manner by using the magnetic sensor as described above, there are problems in the shape tolerance of the magnetic head and the mounting of the magnetic head to the rotary magnetic head device. It is an error.

Such variations in shape tolerances and variations in mounting accuracy result in variations in oscillation frequency, so that the measurement accuracy of the head wear amount is finally affected. For example, when the shape tolerance and the mounting error of the magnetic head are the smallest, the oscillation frequency f1 at the initial protrusion amount of the head, and the limit wear amount at which recording and reproduction are possible due to wear of the head as shown in FIG. It is assumed that the prediction curve obtained based on the oscillation frequency f2 is L1.

On the other hand, when variations in the shape tolerance and mounting error of the magnetic head to be used increase, the actual head wear amount changes even at the same oscillation frequency f2, so the prediction curves at that time are L2 and L3. May be. That is, even when the same oscillation frequency f2 is obtained, the head wear amount does not reach the limit wear amount (in the case of curve L3), or exceeds the limit wear amount (in the case of curve L2). Can be considered. This makes it impossible to measure the head wear amount with high accuracy, and it becomes impossible to replace the magnetic head or issue a warning at an appropriate time.

Therefore, the present invention solves such a problem, and makes it possible to measure the amount of head wear in a non-contact manner without being affected by the shape tolerance or mounting error of the magnetic head. The amount of head wear can be measured with high accuracy.

[0014]

In order to solve the above-mentioned problems, the invention described in claim 1 is such that a plurality of magnetic sensors have different facing gaps with respect to a rotary magnetic head device to which a magnetic head is attached. And each magnetic sensor is connected to a variable oscillation circuit as a variable oscillation element, and when the facing gap to the rotary magnetic head device is the same, the same oscillation frequency is output.
It is characterized in that the wear amount of the magnetic head is measured based on the change in the difference between the oscillation frequencies measured at the rotational position where the magnetic head faces the magnetic sensor.

In the present invention, a pair of magnetic sensors are arranged and fixed at a position outside the tape wrap angle while maintaining a predetermined gap with the rotary magnetic head device. One of the facing gaps is arranged farther from the rotary magnetic head device.

The magnetic sensor has a U-shaped core.
The width of the winding groove is made wider than the gap width of the magnetic head and narrower than the width of the magnetic head.

At the rotational position when the magnetic head faces the magnetic sensor, the total value of the magnetic resistance including the magnetic head and the magnetic sensor changes as the head wears. Is regarded as a change in inductance. Since the inductance is a part of the oscillation circuit element, when the inductance changes, the oscillation frequency also changes. Since the amount of head wear and the fluctuation of the oscillation frequency are related to each other, the oscillation frequency when the amount of head wear is zero is stored in memory, and if the fluctuation of the oscillation frequency after that is monitored, the amount of head wear at the time of measurement You can know. In order to eliminate the influence of the shape tolerance and mounting error of the magnetic head, the difference between the oscillation frequencies detected by the pair of magnetic sensors is required.

Since the difference is not affected by variations in the shape tolerance of the magnetic head, the difference between the two magnetic sensors (absolute value of (β2-β1)) can be obtained from the difference when it is managed with high accuracy. The amount of head wear is accurate. Therefore, when the head wear amount calculated from this difference exceeds the limit wear amount, for example, a warning is given to the user. By doing so, it is possible to avoid an unexpected situation in which the signal is suddenly not recorded while the signal is being recorded.

The rotational position of the magnetic head facing the magnetic sensor is detected based on the reference signal indicating the rotational position reference of the rotary magnetic head device. When multiple magnetic heads are attached with a step difference in the direction of rotation, these can be covered with a single magnetic sensor.
That is, the size (thickness) of the magnetic sensor is selected so that the plurality of magnetic heads are all included in the magnetic gap of the magnetic sensor.

[0020]

BEST MODE FOR CARRYING OUT THE INVENTION Next, one embodiment of the non-contact type magnetic head wear amount measuring apparatus according to the present invention will be described with reference to the above-mentioned V.
A case where the present invention is applied to a rotary drum device mounted on a TR will be described in detail with reference to the drawings. For convenience of explanation, an outline of a head wear amount measuring device which is a premise of the present invention will be described with reference to FIG.

FIG. 5 is a conceptual diagram of a non-contact type magnetic head wear amount measuring device 10 for explaining the present invention, in which the rotary magnetic head device 12 has a predetermined wrap angle α defined by a guide pin 16. The magnetic tape 14 is helically wound around a rotating drum (not shown), and information is recorded on the magnetic tape 14 by the mounted magnetic head 20 and reproduced from the information.

A base 22 is attached to a predetermined position of the rotary magnetic head device 12, and the magnetic head 20 is mounted and fixed on the base 22. The magnetic head 20 is attached in a state of protruding by a specified amount from the drum surface. The signal winding 24 is wound around both legs of the head core 23.

The drum surface 12 of the rotary magnetic head device 12
a, specifically, a position which is separated from the head sliding surface of the magnetic head 20 by a predetermined gap β and does not reach the tape wrap angle α,
For example, when the wrap angle α is approximately 180 ° as shown, the magnetic sensor 30 is arranged at a position 90 ° away. The magnetic sensor 30 includes a U-shaped core 31 and a detection coil 32 wound around the winding groove 31a. The detection coil 32 wound around the magnetic sensor 30 functions as a part of an oscillating element of a variable oscillating circuit (V.OSC) described later.

As shown in FIG. 6, the rotary drum device has the lower drum 3
When 2 is fixed and only the upper drum 34 is configured to rotate, the upper drum 34 also functions as the rotary magnetic head device 12. Then, at this time, the above-described magnetic sensor 30 is mounted on the mounting member 38 having an L-shaped cross section provided on the lower drum 32, and the magnetic head 20 of the upper drum 34.
It is attached and fixed so as to face with.

On the other hand, as shown in FIG. 7, a rotary drum device having a middle drum (rotary drum) 36 to which the magnetic head 20 is attached, and the upper and lower drums 32 and 34 thereof are fixed is used. In this case, the magnetic sensor 30 is attached and fixed to the U-shaped attachment member 38 attached between the upper and lower drums 32 and 34.

As shown in FIG. 8A, the magnetic head 20 is composed of a pair of cores 23 and a signal winding 24, and both sides of the head protruding portion (tape sliding portion) 25 including the tape sliding surface 25a are shown in FIG. 8B. The core portion other than the head protrusion 25 formed by the notch is called a back core 23a.

Even if the core 23 has a single-layer structure composed of only a magnetic material as shown in FIG.
Alternatively, a laminated core in which a metal 23b is arranged in the middle and nonmagnetic materials (ceramics) are arranged above and below the metal 23b may be used, as shown in FIG.

Since the magnetic head 20 is rotating, a state in which the magnetic head 20 faces the magnetic sensor 30 and a state in which it does not occur during one rotation. Magnetic head 2
When 0 is facing the magnetic sensor 30 as shown in FIG. 5,
A magnetic circuit formed by the magnetic head 20 and the magnetic sensor 30 is as shown in FIG.

In the equivalent circuit shown in FIG. 9, Ra represents the magnetic resistance of the head protrusion 25, and Rb represents the magnetic resistance of the back core 23a. Similarly, the detection coil 3 of the magnetic sensor 30
The resistance of 2 is indicated by Rc. Also, the magnetic resistance in the magnetic gap 36 when both are opposed is shown by Rd and Re.
Here, the magnetic resistances Rd and Re are magnetic resistances between both legs of the U-shaped core 31 and the head protrusion 25.

When the head protruding portion 25 is worn, the thickness of the head protruding portion 25 decreases, and the magnetic resistance Ra changes. At the same time, the facing gap length between the head protrusion 25 and the magnetic sensor 30 also changes, so that the magnetic resistance Rd, R
e also changes. Therefore, the value of the total magnetic resistance when the magnetic head 30 is viewed from the magnetic sensor 30 changes due to head wear.

The change in the inductance due to the change in the magnetic resistance is guided to the variable oscillation circuit. FIG. 10 is a system diagram showing an outline of a circuit system of the non-contact magnetic head wear amount measuring device 10. The variable oscillating circuit 40 has an amplifying stage 42 composed of a transistor which is an oscillating amplifying device, and in this example, an LC device is connected as an oscillating device to a parallel feedback path to the amplifying stage 42. Capacitor 4 which is a capacitive element
The variable inductance element 46 is connected in parallel with the wiring 4.
This variable inductance element 46 shows the total inductance Lx shown in FIG.

When the inductance Lx fluctuates, the oscillation frequency also fluctuates, and the oscillation output is measured by the measuring circuit 5.
It is guided to 0 and converted into a level (for example, a voltage level) proportional to the frequency. For example, the oscillation frequency is counted using a counter and converted into a voltage according to the count value. The measurement data proportional to the oscillation frequency is supplied to the wear amount calculating means 52 in the subsequent stage.

A CPU is provided in the wear amount calculation means 52, and the wear amount of the magnetic head 20 is calculated based on the obtained measurement data. The data such as the calculated wear amount is stored in the memory 54, and is also supplied to the display unit 56 to display the calculated value and the like.

Apart from this processing, when the amount of wear exceeds a specified value, a notification means such as an alarm means (not shown)
If it is left as it is, the information may not be recorded correctly, and the user may be notified immediately that the head should be replaced. The prescribed value can be selected, for example, to a value immediately before the critical wear amount at which the depth of the head protrusion 25 (the region forming the head depth) disappears. For example, when the depth of the head protrusion 25 is about 25 μm, about 20 μm can be selected as the specified value.

The measurement process of FIG. 10 can be performed, for example, immediately after the power of the device is turned on. Usually 500-1
It has been empirically known that the limit wear amount will be reached after 000 hours of use, and recording and reproduction will be hindered. Therefore, even if the software is constructed so that the measurement process is executed immediately before this usage time is used as a guide. Good. In addition to this measurement process, control may be performed such that the value of the recording current is reduced as the wear amount increases, and the head replacement is performed only when the limit wear amount is detected.

The amount of wear can be measured over the entire circumference of the drum.
It is also possible to carry out only the section facing. In any case, as shown in FIG. 5, a rotation detecting means (for example, pulse generator PG) 58 is attached to the drum rotation shaft, and one PG pulse is used as a reference for one rotation of the drum obtained from the drum. The rotational position is detected. This is because the relationship between the timing at which the PG pulse is obtained and the mounting position of the magnetic head 20 mounted on the drum is known, and the relative positional relationship between the two is clear in advance.

As shown in FIG. 5, the magnetic sensor 3 described above is used.
Width W of winding groove 31a formed in core 31 forming 0
The width a is selected to be larger than the width Wb of the gap g of the magnetic head 20 and narrower than the width Wc of the head itself. This is because the magnetic gap is formed between the magnetic sensor 30 and the magnetic head 20 as described above, and the magnetic resistance formed by the magnetic head 20 and the magnetic sensor 30 is caused by the abrasion of the head sliding surface 25a of the magnetic head 20. This is to change the value of. To give an example of these concrete numerical values,
It is as follows.

Wa = 250 μm, Wb = 0.5 μm, W
c = 1.5 mm If the width Wa of the winding groove 31a is narrower than the width Wb of the gap g of the magnetic head 20 (although such a shape is actually impossible) or wider than the width Wc of the head itself, This is because the amount of wear cannot be accurately grasped as a change in magnetic resistance. Since the facing gap β affects the detection sensitivity, the optimum gap value is selected.

The present invention follows the basic structure of the measuring device 10 described with reference to FIGS. 5 to 10 as it is, and further takes measures so as not to be influenced by the shape tolerance and mounting error of the magnetic head 20. is there. One embodiment thereof is shown in FIG.

Therefore, in the present invention, as shown in FIG. 1, at a position facing the rotary magnetic head device 12,
In addition, a plurality of, in this example, a pair of magnetic sensors 30 (30A, 30B) having the same structure are arranged in a region that does not reach the wrap angle α with a predetermined facing gap.

The pair of magnetic sensors 30A and 30B are arranged so that the facing gaps are different from each other. For example, when the facing gap of the first magnetic sensor 30A (distance from the tape sliding surface 25a of the magnetic head 20) is β1, the second magnetic sensor 30B is selected to be β2 (> β1). β1 and β2
The difference (step) with is always constant.

The mounting angle ε of both magnetic sensors 30A and 30B with respect to the center of rotation of the rotary magnetic head device 12 is arbitrary. Although not particularly limited, it is appropriate that ε be several degrees to 10 degrees in consideration of mounting and fixing on the mounting member 38 and easiness of mounting.

The magnetic sensors 30A and 30B are used as a part of the oscillation elements of the variable oscillation circuit 40 (40A and 40B), respectively. The variable oscillating circuits 40A and 40B have the same configuration as described above, and when the facing gaps with the rotary magnetic head device 12 are the same, the variable oscillating circuits 40A and 40B are the same.
It is assumed that the circuit constants of A and 40B are adjusted so that the same oscillation frequency is output.

Oscillation frequency f obtained when the magnetic heads 20 face the respective magnetic sensors 30A and 30B.
a and fb (≠ fa) are corresponding measurement circuits 50 (50A, 50A,
50B) and the oscillation frequencies fa and fb are converted into corresponding levels (measurement data).

The respective measured data are the wear amount calculation means 5
2, the measurement data corresponding to the difference between the oscillation frequencies fa and fb is calculated, the prediction curve is obtained from the difference measurement data, the head protrusion amount is calculated from this prediction curve, and then the head wear amount is calculated. It The calculated head wear amount is stored in the memory 54 and is also supplied to the display means 56 including a warning means to display the head wear amount as a numerical value or to warn that when the wear amount is close to the limit wear amount. This is the same as the basic configuration of FIG.

As described above, the oscillation frequency fluctuates due to the shape tolerance of the magnetic head 20 and the mounting error of the magnetic head 20 with respect to the rotary drum device. This is because both of them cause fluctuations in the magnetic resistance of the magnetic circuit.

Therefore, the pair of magnetic sensors 30A, 30B
Variable oscillation circuits 40A, 40 when using
The difference between the oscillation frequencies fa and fb obtained from B is obtained.
Even if the facing gap β1 is deviated due to the shape tolerance or the mounting error of the magnetic head 20, the gap (β2-β1) = Δ
As long as is constant, the frequency difference is constant. That is,
By taking the difference of the oscillation frequencies, it is possible to eliminate all the influences of the variation factors due to the shape tolerance.

From the above, a head wear prediction curve can be obtained from both the oscillation frequency fa obtained from the variable oscillation circuit 40A and the oscillation frequency fb obtained from the variable oscillation circuit 40B when the initial protrusion amount of the magnetic head 20 is obtained. You can ask. The curve La in FIG. 2 shows this prediction curve. Ideally, by obtaining the curve La, the oscillation frequency f during measurement is measured.
The amount of head wear can be predicted almost accurately from the values of a and fb. Here, the gap Δ is adjusted to fall within a predetermined range.

By the way, the relative positional relationship between the magnetic sensor 30 and the magnetic head 20 is as shown in FIG. The relationship between the magnetic head 20 and the magnetic sensor 30 indicated by the solid line corresponds to the relationship between the magnetic sensor 30A and the magnetic head 20 having the facing gap of β1. The relationship between the magnetic head 20 and the magnetic sensor 30 indicated by the chain line corresponds to the relationship between the magnetic sensor 30B and the magnetic head 20 having β2 as the facing gap. Then, Δ corresponds to (β2-β1).

Since the oscillating frequency when the magnetic head 20 retracts to the position of the chain line is fb, this oscillating frequency fb
To satisfy the above condition, the magnetic head 20 must be retracted uniformly from the solid line position to the broken line position. However, it is the head protrusion 2 that actually wears due to contact with the tape.
Since there are only 5 areas, only the shaded area 36a has a small area, and the areas of the remaining shaded areas 36b and 36c remain unchanged.

Considering the above, the magnetic head 20
When the tape slides and the tape sliding surface recedes to the position of the chain line only in the shaded area 36a, the oscillation frequency may be a frequency fc different from fb (see FIG. 4). This depends on the configuration of the core of the magnetic head 20.

For example, as shown in FIG. 8C, the laminated core 2
3 is used, the metal 23b and the non-magnetic body 23a
And the shaded areas 36b, 36
There is no influence of c on the magnetic resistance. Therefore, as long as the magnetic head 20 composed of this laminated core is used, even if only the shaded area 36a recedes, when it recedes to the position of the chain line, the oscillation frequency at that time becomes fb, and FIG.
The relationship of is established as it is.

However, when the core having the single-layer structure shown in FIG. 8B is used, since it is composed of a ferrite core, when the entire shaded regions 36a to 36c are retracted,
The obtained oscillation frequency differs when only the shaded area 36a is retracted. Therefore, a prediction curve in which the relationship of FIG. 2 is modified is necessary.

In this case, it is necessary to replace the magnetic circuit of the magnetic head 20 among the equivalent magnetic circuits shown in FIG. 9 with a finer magnetic circuit. For example, instead of simply dividing the head projecting portion 25 and the back core 23, the back core 23 is divided into three parts in the direction of the head projecting portion 25 to give a magnetic resistance to each, and accordingly, the resistance of the magnetic gap. It is necessary to change the equivalent circuit by increasing.

When the oscillation frequency at this time is fc instead of fb and the predicted curve is Ld in FIG. 4, the head wear amount is measured and predicted using this predicted curve Ld. Even when the prediction curve Ld is used, a slight variation occurs, but it is so small that the curve Ld may be used in this case as well.

When the magnetic sensor 30 is used to measure the amount of head wear from the change in the magnetic resistance as in the present invention, the gap (β2-β1) is set to a predetermined value. Even if there is a shape tolerance of the magnetic head 20 or a mounting error with respect to the drum, it is possible to realize highly accurate wear amount measurement by only finely adjusting the mounting positional relationship.

Experiments have confirmed that the head wear amount can be measured (including prediction) with an accuracy of ± 1 μm. Especially when using a magnetic head with a laminated core, zero error (±
It was confirmed that the head wear amount can be measured with an accuracy of 0 μm). The magnetic sensor 30 itself is an ultra-small element, and the rest is a circuit component, so the scale of the measuring device is very small.

In the rotary magnetic head device 12 shown in FIG. 1, the magnetic head 20 mounted on the rotary magnetic head device 12 is 1 for convenience of description.
Are shown. In practice, several magnetic heads 20
Are usually arranged at a specific interval in the rotation direction. Even in the case of measuring the amount of wear of each head when a plurality of magnetic heads are attached in this way, it is advantageous in terms of measurement accuracy and configuration if two magnetic sensors are used as the magnetic sensors.

FIG. 11 is a conceptual diagram of the measuring apparatus 10 considering such points. The example shown in the drawing is an example in which four magnetic heads 20A to 20D are arranged with a predetermined level difference with respect to the rotation direction. Figure 1 based on the end face of the drum
The magnetic heads 20B, 20C, and 20D having the same configuration are arranged with the steps m2, m3, and m4 with respect to the reference magnetic head 20A as shown in FIG. ga, gb,
gc and gd represent respective gaps. Gap ga
As is well known, the glass material 27a is provided at both upper and lower ends of the gd.
27d is filled.

The magnetic sensor 30A (30B) arranged facing the plurality of magnetic heads 20 is constructed as shown in FIG. Assuming that the thickness of the magnetic head 20 (axial direction of the rotating drum) is Ha, the magnetic heads 20A to 20D
The thickness Hb up to is Hb = Ha + m4. Therefore, the thickness Hc of the magnetic sensor 30A (30B) is selected as Hc ≧ Hb so as to cover all the magnetic heads 20. By doing this, the two magnetic sensors 30
It is possible to measure the amount of head wear for all magnetic heads 20 alone. The PG pulse described above is used in order to know the position of the magnetic head 20 for wear measurement. This is because the PG pulse generation timing and the positional relationship between the magnetic heads are uniquely determined.

When the thickness of the magnetic sensor 30A (30B) is selected to the value Hc as described above, the magnetic head 20 to be measured.
It can be considered that the magnetic resistances Rc and Rd of the magnetic gaps differ depending on A to 20D, and the measurement accuracy may differ, but there is practically no difference. It is considered that this is because the magnetic resistance of the core 31 itself is small.

Since the variable oscillation circuit 40 described above has a semiconductor element, its oscillation frequency varies depending on the ambient environmental temperature. The extent to which it fluctuates is shown below. First, as shown in FIG. 14, the magnetic head 20, the magnetic sensor 30, and the variable oscillation circuit 40 are housed in a constant temperature bath 62, respectively. In this state, the internal temperature of the thermostat 62 is changed. For example, when the internal temperature was changed from −5 ° C. to 45 ° C. at 10 ° C. intervals, the oscillation frequency at that time became a curve as shown in FIG.

As is clear from FIG. 15, at room temperature (25
Draw a parabola so that the oscillation frequency f25 at (° C.) becomes the bottom. Thus, the oscillation frequency f
Therefore, accurate measurement of the amount of wear is impossible.
In the above-described AV equipment, since the internal temperature of the apparatus increases as the time after the power is turned on becomes longer, there is a possibility that a large difference may occur in the wear amount calculation result between when the power is turned on and immediately before the power is turned off. Therefore, measurement conditions such as measurement immediately after power-on are set, or temperature compensation is preferably performed. Next, an example of temperature compensation will be described.

16 and 17 are specific examples of the measuring device 10 with temperature compensation. The calculation of the oscillation frequency for temperature compensation cannot use the magnetic head 20 itself used for recording and reproduction. This is because the head wears with use time.

Therefore, when the drum surface 12a where the magnetic head 20 does not exist and the magnetic sensor 30 are opposed to each other, the oscillation frequency measurement process for temperature compensation is performed in the example of FIG. is there.

Therefore, the temperature compensating means 100 is provided as shown in FIG. As many temperature compensating means 100 as the magnetic sensors 30 are provided. In FIG. 16, only the first magnetic sensor 30A is shown for convenience of explanation, and therefore only the temperature compensating means 100A is shown. The variable oscillation circuit 40A is also included in the loop of the temperature compensation means 100A. The capacitance element 44 provided in the variable oscillation circuit 40A is changed to a variable element, and in this example, a variable capacitance diode (varicap) is used as shown in FIG.

The measurement circuit 50A is configured as a digital measurement circuit, and the measurement data (digital data) output from the measurement circuit 50A and corresponding to the oscillation frequency at that time is supplied to the D / A converter 102 to obtain an analog level. (For example, voltage). This analog level is compared with the reference level REF by the level comparator 104.
The reference level REF can be set to a value corresponding to the analog level at the oscillation frequency obtained at normal temperature (25 ° C.).

The capacitance value of the variable capacitance diode 44 is controlled by the comparison output obtained from the level comparator 104 so that the oscillation frequency f25 at room temperature is maintained regardless of temperature fluctuation. The temperature compensation operation can be performed intermittently or continuously during the head wear amount measurement period. Whether or not the drum surface 12a where the magnetic head 20 does not exist faces the magnetic sensor 30 is determined as follows.
It is clear that the determination can be made from the output timing of the PG pulse.

The drum surface 12 without the magnetic head 20
Instead of using a, a dummy head HD can be used separately from the recording / reproducing head. FIG. 17 is an example thereof. For this purpose, the head protrusion amount is adjusted so that the dummy head HD used for temperature compensation does not protrude from the drum peripheral surface. Dummy head HD in use
This is to prevent them from wearing.

Then, the value of the oscillation frequency when the dummy head HD faces the magnetic sensor 30A is read,
As in the case of FIG. 16, feedback control is performed so that the value at that time becomes the reference level REF. The rotation timing at which the dummy head HD faces the magnetic sensor 30A is determined based on the PG pulse. The rest of the configuration is the same as that of FIG. 16, and the description is omitted.

Digital processing is suitable for the measuring device 10 shown in FIG. 1 or FIG. A concrete example is shown in FIG.
8 and below. FIG. 18 is a conceptual diagram of digital processing, and the configuration of the second magnetic sensor 30B is omitted in this figure as well.

In this measuring device 10, the measuring circuit 50A
Is configured as a digital processing system, which is commonly provided with a reference clock source 68, and digital processing is performed based on the reference clock CK from this point.

In the case of digital processing, one rotation of the drum is divided into n divisions, and the head wear amount is calculated based on the measurement data of the divisional area where the magnetic head 20 is actually located among the measurement data obtained every n divisions. To be done. Figure 1
As shown in FIG. 9, one rotation of the drum is divided into 256 (2 to the 8th power) to obtain.

FIG. 20 shows a concrete example of the digital measuring circuit 50A when one rotation of the drum is divided into 256. Terminal 5
0a is the oscillation output of the variable oscillation circuit 40A (frequency is f2
5) Fa (Fig. 21E) is supplied, and the clock CK (C in Fig. 21) from the reference clock source 68 is supplied to the terminal 50b. The terminal 58a is supplied with a pulse Fd (B in the figure) obtained by differentiating one PG pulse (A in the figure) output for one rotation of the drum.

The clock CK is used by the frequency dividing circuit 72 for the drum 1
The frequency division is performed with a division ratio such that 256 pulses (divided pulse) can be obtained per rotation. Since the PG differential pulse Fd is supplied as a reset pulse to the frequency dividing circuit 72, a frequency dividing pulse Pa (D in the figure) synchronized with the rotation of the drum is obtained.

The oscillation output Fa is differentiated by the differentiating circuit 71,
The differential pulse Pb (FIG. F) is supplied to the counter 73. The counter 73 outputs a first counter pulse P1 (G in the figure) at the timing when the first pulse of the differential pulses Pb input after reset is input, and m
The second counter pulse Pm (H in the figure) is output at the timing when the second pulse is input. Since the divided pulse Pa is supplied as a reset pulse to the counter 73, the counter pulses P1 and Pm are divided pulse P respectively.
The pulse is synchronized with a.

Since the counter pulses P1 and Pm are supplied as the set pulse and the reset pulse of the flip-flop circuit 74, the measurement window pulse M (I in the same figure) having a width corresponding to m oscillation output Fa is obtained. To be
This measurement window pulse Mi is 2 per drum rotation.
You can get 56 pieces.

The measurement window pulse Mi is supplied to the measurement counter 75, and the number of clocks CK supplied to the counter 75 is counted by the pulse width of the measurement window. Since the pulse width of the measurement window differs depending on the oscillation frequency, the value of the measurement output Xi also differs. The measurement output Xi is latched by the latch circuit 76. Therefore, the second counter pulse Pm is supplied to the 1-bit shift register 77 to generate the latch pulse Pr (J in the same figure) slightly delayed from the second counter pulse Pm, and the measurement is completed with this latch pulse Pr. The subsequent measurement output Xi is latched. The measurement output X0 is latched when the measurement window pulse is M0, and the X1 is latched when it is M1 (K in the figure).

Further, in order to know at which position (the drum rotation position when the magnetic sensor 30 is a reference) the measured output Xi, the divided pulse Pa indicates the drum rotation position (measurement angular position). It is supplied to the address counter 78 shown. When one rotation of the drum is divided into 256, an 8-bit counter is used. Then, the measured angle address Ai obtained from the counter 78 is latched by the latch circuit 79 (L in the figure). As the latch pulse, the same pulse Pr as described above is used.

Therefore, at the measurement window pulse M0, the measurement angle address A0 (00000000) and the measurement output X0 are obtained at the corresponding output terminals 52a and 52b. For example, at the measurement window pulse M255, the measurement angle address A255 (11111111). And the measured output X255 at that time is obtained.

These measurement data (measurement angle address Ai
And the measurement output Xi) are supplied to the wear amount calculating means 52 shown in FIG. 18, and the head protrusion amount from the drum surface is calculated based on the difference between the measurement data corresponding to the section where the magnetic head 20 is located. The wear amount of the magnetic head 20 is predicted from the initial head protrusion amount (stored in the memory 54) and the measured head protrusion amount.

As described above, when the width Wc of the magnetic head 20 is about 2.5 mm, it corresponds to about 2.5 ° when converted into an angle as shown in FIG. When one rotation of the drum is divided into 256, the measurement angle γ is approximately 1.4 °. As a result, the head protrusion amount is calculated based on the measurement outputs Xi from two measurement window pulses Mi.

However, this calculation is only for the magnetic head 2.
This is an example when the timings of the core end surface of 0 and the measurement window pulse Mi match, and when the timings do not match, at least three measurement outputs Xi
The head protrusion amount is calculated based on

It is clear that the accuracy of measuring the wear amount is improved if the head protrusion amount can be calculated based on a large number of measurement outputs Xi. That is, the measurement resolution is improved. FIG. 23 and the following are examples in which the measurement resolution is increased and the head wear amount can be measured with high accuracy. In the example described below, one rotation of the drum is divided into 256 as shown in FIG. 23, and these are further divided into 16 to make a total of (256 ×
This is an example in which 16) measurement outputs Xi are obtained and the head wear amount is calculated from them.

As a method of dividing one rotation of the drum into 256 and further dividing them into 16
In the case of using the measurement cycle pulse Ti corresponding to the division, by sequentially shifting this by 1/16 for one rotation of the drum, it is possible to obtain just 256 in 16 rotations of the drum.
× 16 pieces of measurement data can be obtained.

FIG. 24 shows a concrete example of the digital measuring circuit 50A for realizing the above-mentioned processing. The clock CK supplied to the terminal 50b is supplied to the frequency dividing circuit 72 to form the first frequency dividing pulse Pa (FIG. 25B), which is further supplied to the second frequency dividing circuit 83 to provide 256 per rotation of the drum. Measurement cycle pulse Ti output only for pulse
(FIG. F) is formed.

The oscillation output Fa is given to the terminal 50a,
This is differentiated by the differentiating circuit 71 to generate the oscillation differential pulse Pb.
(H in the same figure) is formed, and the oscillation differential pulse Pb is supplied to the counter 73 to generate the first and second counter pulses P1.
And Pm are generated (I and K in the same figure). Since the measurement period pulse Ti is given to the counter 73 as a reset pulse, the counter pulses P1 and Pm are the measurement period pulse T.
It is synchronized with i.

The counter pulses P1 and Pm are applied to the flip-flop circuit 74 in the subsequent stage to form the measurement window pulse Mi as shown in FIG. This pulse Mi
Also, 256 will be generated. In the measurement counter 75, the number of clocks CK supplied within the section of the measurement window pulse Mi is counted, and the measurement output Xi (M in the figure) which is the count value is latched by the latch circuit 76. The latch pulse Pr shown in O of the figure uses the one generated by the shift register 77 for 1-bit shift.

On the other hand, the PG differential pulse Fd (A in the figure) supplied to the terminal 58a is supplied to the address forming counter 82. As described above, the measurement is performed by further dividing the measurement angle obtained by dividing one rotation of the drum into 256 into 16 divisions. In order to give an address in synchronization with the rotation of the drum at each division point at the 16 divisions, a counter is added. 82
Is provided. Therefore, the counter 82 is composed of a 4-bit counter, and the address data contents are sequentially updated by 1 per one rotation of the drum as shown in FIGS. 26A to 26C, and the original address data U0 is returned after 16 rotations.

The above-mentioned first frequency-divided pulse Pa is further supplied to the shift register 81, and shift pulses Pc for 16 pulses are generated (C in the same figure). This shift pulse P
c is a phase shift pulse used to divide the unit measurement angle into 16 parts, and only 16 pulses are output per one rotation of the drum. The phase shift pulse Pc is obtained in synchronization with the PG differential pulse Fd, and the phase shift pulse Pc is always output at the same timing.

As shown in FIG. 25C, the phase shift pulse Pc is 4-bit digital data, which is supplied to the measurement reference pulse forming means 90 together with the drum rotation address Ui.

FIG. 27 shows a concrete example of the forming means 90, in which the phase shift pulse Pc is given to the 4-bit counter 91 through the terminal 90a to output digital data which is sequentially updated bit by bit, which is the coincidence circuit. 92
At, the drum rotation address Ui given from the terminal 90b is compared with the data content. For example, in FIG.
While the drum rotation address Ui is "0000" when the drum is the first rotation as in C and D, the phase shift pulse Pc has a data content (bit data) for each pulse from the initial value "0000". Since they are updated sequentially, in this case, the contents of both data coincide only with the first phase shift pulse Pc “0000”.

The gate circuit 93 is opened by this coincidence pulse, and the input phase shift pulse Pc itself is gated. Therefore, as shown in FIGS. 25C and 25D, when the drum rotation address Ui is “0000”, the measurement reference pulse R0 (FIG. 25E) is output at the first pulse timing. In the second rotation, as shown in FIGS. 25C, 25D, 25E,
Since the drum rotation address becomes "0001", the measurement reference pulse R1 is output at this time at the timing when the second phase shift pulse Pc "0001" is obtained. As a result, it is understood that the second measurement reference pulse R1 is shifted by one pulse with respect to the first measurement reference pulse R0 and is output. Therefore, in terms of the measurement angle γ, the position shifted by 1/16 is the position of the measurement reference pulse R1.

As shown in FIG. 24, since the measurement reference pulse Ri is supplied to the frequency dividing circuit 83 as its reset pulse, the frequency dividing operation is performed after the measurement reference pulse Ri is input. It can be seen that the measurement cycle pulse Ti is generated in synchronization with the reference pulse Ri.

As a result, in the case of FIG. 25 (first rotation of the drum), the measurement reference pulse Ri is generated in synchronization with the 0th phase shift pulse Pc, and the relationship between this and the measurement window pulse Mi is shown in FIGS. become that way.

Similarly, in the case of FIG. 25 (the second rotation of the drum), the measurement reference pulse Ri is generated in synchronization with the first phase shift pulse Pc, and the relationship with the measurement window pulse Mi at that time is shown in FIG. 28B, It becomes like F. Then, at the 16th rotation of the drum, the measurement reference pulse R15 is generated in synchronization with the 15th phase shift pulse Pc.
The relationship of D and H is obtained.

As described above, since the generation timing of the measurement reference pulse Ri, and hence the measurement period pulse Ti, is sequentially shifted by the rotation of the drum, the measurement position of the drum is gradually shifted even within the same measurement angle γ. Then, the measurement data Xi at each position obtained by dividing the measurement angle γ into 16 equal parts is obtained.

The frequency-divided pulse Ti is also supplied to the measurement angle address counter 84 to generate one rotation 256 address (measurement angle address) Li. Since the counter 84 is reset by the measurement reference pulse Ri, the address generation is repeated every one rotation of the drum. The measurement angle address Li is latched by the latch circuit 85, and the current measurement data Xi is obtained by using this measurement angle address Li.
It is possible to determine at which measurement angle the data is.

The measurement reference pulse Ri is further supplied to the latch circuit 8
6, the content of the drum rotation address Ui is latched, and this is latched again by the latch pulse Pr. The number of rotations of the measured data can be determined by the drum rotation address Ui latched by the latch circuit 87. Therefore, one round of the drum is 256 × 1 by the measurement data Xi, the drum rotation address Ui and the measurement angle address Li obtained at the terminals 52a, 52b and 52c.
It is possible to reliably determine at which position of the six measured positions the data is given to the wear amount calculation means 52.

The head wear amount measuring apparatus according to the present invention is
As described above, it is obvious that the invention can be applied to all the devices having the rotating magnetic head. Two or more magnetic sensors may be used to measure the amount of head wear.

[0101]

As described above, in the non-contact type magnetic head wear amount measuring apparatus according to the present invention, the magnetic sensor is arranged in a non-contact state with the rotary magnetic head apparatus, and the magnetic circuit of the magnetic circuit including the magnetic sensor is arranged. By detecting a change in resistance, the amount of protrusion of the magnetic head from the drum surface, and hence the amount of head wear, is measured.

According to this, it is possible to prevent damage to the magnetic head to be measured in advance, as compared with a contact type measuring device using a contactor or the like. Also, unlike a non-contact measuring device that uses a laser beam, the amount of head wear is measured by the change in magnetic resistance, so the measurement accuracy is high and the measuring device itself can be miniaturized. It has the feature that it can be installed without receiving it. Therefore, it can be easily applied to a rotary drum device having a small drum diameter.

Further, according to the present invention, a plurality of magnetic sensors are further provided, and the difference in the oscillation frequency obtained from them is detected to measure (predict) the amount of head wear. It is possible to eliminate any influence on the measurement value due to the error in mounting the magnetic head on the drum or drum. Therefore, more accurate measurement becomes possible. Therefore, the present invention is extremely suitable when applied to AV equipment such as VTR, DAT, and data recorder.

[Brief description of the drawings]

FIG. 1 is a configuration diagram of essential parts showing an embodiment of a non-contact magnetic head wear amount measuring device according to the present invention.

FIG. 2 is a characteristic diagram showing a relationship between an oscillation frequency and a head wear amount.

FIG. 3 is a diagram showing a relative positional relationship between a magnetic head and a magnetic sensor.

FIG. 4 is a characteristic diagram showing a relationship between an oscillation frequency and a head wear amount.

FIG. 5 is a conceptual diagram showing an outline of a non-contact magnetic head friction amount measuring device provided for explaining the present invention.

FIG. 6 is a configuration diagram showing an example of a rotary magnetic head device.

FIG. 7 is a configuration diagram showing an example of a rotary magnetic head device.

FIG. 8 is a configuration diagram of a magnetic head for measurement.

FIG. 9 is an equivalent magnetic circuit diagram including a magnetic head and a magnetic sensor.

FIG. 10 is a system diagram showing an embodiment of a non-contact magnetic head friction amount measuring device used for explaining the present invention.

FIG. 11 is a conceptual diagram showing the same concept as in FIG. 5 when a plurality of magnetic heads are used.

FIG. 12 is a development view of FIG. 11;

FIG. 13 is a layout view of FIG. 11 viewed from the side.

FIG. 14 is a diagram of a frequency fluctuation measuring device according to a change in environmental temperature.

FIG. 15 is a characteristic diagram showing the relationship between temperature and oscillation frequency.

FIG. 16 is a system diagram of a main part showing an example of a measuring device with temperature compensation in which one magnetic sensor is omitted.

FIG. 17 is a system diagram of essential parts showing an example of a measuring device with temperature compensation in which one magnetic sensor is omitted.

FIG. 18 is a conceptual diagram of a digital magnetic head friction amount measuring device in which one magnetic sensor is omitted.

FIG. 19 is a diagram showing a relationship of a measured angle with respect to one round of a drum.

FIG. 20 is a system diagram showing an example of a measuring circuit used in the non-contact magnetic head friction amount measuring device.

FIG. 21 is an operation waveform diagram thereof.

FIG. 22 is a diagram showing a relationship between a magnetic head and a measurement range.

FIG. 23 is an explanatory diagram of high resolution measurement.

FIG. 24 is a system diagram showing an example of a digital measuring circuit therefor.

FIG. 25 is a waveform diagram (No. 1) for explaining the operation.

FIG. 26 is a waveform chart showing an example of drum address generation.

FIG. 27 is a system diagram of measurement reference pulse forming means.

FIG. 28 is an operation waveform diagram for achieving high resolution by phase shifting.

FIG. 29 is a waveform diagram (part 2) for explaining digital measurement.

FIG. 30 is a prediction curve diagram when calculating a head wear amount.

[Explanation of symbols]

 10 Measuring Device 12 Rotating Magnetic Head Device 14 Tape 20 (20A to 20D) Magnetic Head 30 (30A, 30B) Magnetic Sensor 40 (40A) Variable Oscillation Circuit 44 Variable Capacitance Diode 50 (50A) Measuring Circuit 52 Friction Amount Calculation Means 54 Memory

Claims (5)

[Claims] 1. A rotary magnetic head device to which a magnetic head is attached, wherein a plurality of magnetic sensors are arranged so as to have different facing gaps, and each magnetic sensor is connected to a variable oscillation circuit as a variable oscillation element. The same oscillation frequency is output when the opposing gap to the rotary magnetic head device is the same, and based on the change in the difference between the respective oscillation frequencies measured at the rotational position where the magnetic head faces the magnetic sensor. A non-contact type magnetic head wear amount measuring device characterized in that the wear amount of the magnetic head is measured. 2. The non-contact type magnetic head wear amount measuring device according to claim 1, wherein the magnetic sensor is a fixed type. 3. The non-contact type magnetic head wear amount measuring device according to claim 1, wherein the magnetic head has a single-layer core. 4. A core constituting the magnetic head,
2. The non-contact type magnetic head wear according to claim 1, wherein a composite magnetic head is used in which a metal is arranged in an intermediate portion, and a composite core in which upper and lower parts of the metal are laminated and combined is used. Quantity measuring device. 5. The rotation position of the magnetic head facing the magnetic sensor is detected based on a reference signal indicating a rotation position reference of the rotary magnetic head device. Non-contact type magnetic head wear measuring device.