JPH0439736B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION (a) Field of Industrial Application The present invention relates to a magnetic head, and particularly to an erasing head used in a rotary manner in an 8 mm VTR or the like.

(b) Prior art The ferrite core halves face each other with the working gap and the metal magnetic layer sandwiched between them at the surfaces that contact the recording medium, and the pseudo-gap portion on the side of the gap widens as it goes outward from the working gap. For example, the type of magnetic head is disclosed in Japanese Patent Application Laid-Open No. 60-89807.
It is stated in the number. When a magnetic head of this type is used as a rotary erasing head for an 8 mm VTR, the structure shown in FIG. 6 has been proposed as a contact surface configuration for a recording medium (magnetic tape).

In FIG. 6, 1 and 2 are first and second ferrite core halves, and 3 is an operating gap made of glass material. 4 is the second ferrite core half 2
This is a sendust film that is coated in advance on the Instead of the sendust film 4, a metal magnetic material film such as amorphous or permalloy may be used. The track width regulating grooves 5 on both sides are filled with glass 6 forming the working gap 3 at the same time. The glass in the track width regulating groove 5 ensures a tape contact area and protects the operating gap. for example
The rotary erasing head used in VTRs needs to be able to erase any single frame in order to achieve clear transition shots. What is required of this erase head is a sufficient erasing rate and a stable erasing width, but in order to obtain a sufficient erasing rate, as shown in Figure 5, a current of at least 150 mA (normal recording current (approximately 10 times larger current consumption compared to
It is necessary to flow. In FIG. 5, the horizontal axis shows the 6MHz erasing current applied to the magnetic head, and the vertical axis shows the erasing rate. In the figure, Y indicates the luminance signal C indicates the color signal, and P indicates the erasing characteristic of the pilot signal for tracking.

(c) Problems to be Solved by the Invention However, in a magnetic head having a structure as shown in FIG. 6, the gap length G is approximately constant, and the sendust _film is In an erase head with a structure in which the track side T _S on the 4th side is slightly larger, when a large current consumption of about 10 times the normal recording current is applied, the leakage magnetic field becomes large and the apparent track width (T _F )
There was a problem that the actual erased width (erased width) was larger than that of the original. This erasure width is larger than T _F
There is also the problem that it depends on T _S and is likely to change depending on the current value. That is, as shown by the solid line a in FIG. 2, in the conventional structure, the erase current is
At 400 mA or more, the spread of the erase width becomes approximately constant, but it changes linearly especially from 150 mA to 300 mA. Therefore, when the erase current is about 10 times as large as the recording current (250 mA to 300 mA), the spread of the erase width (therefore, the erase width) changes greatly in response to changes in the erase current value. On the other hand, erase current circuits often employ a resonant circuit using the coil of the erase head, and the erase current changes with slight changes in the inductance of the magnetic head or the Q of the resonant circuit. There was also the problem that things were changing. In order to prevent this problem from occurring, the standards for the inductance and Q may be made stricter to reduce their variations, but this is difficult in terms of yield and productivity. It is also conceivable to increase the erase current, but this is not preferable from the viewpoint of reliability of the electric circuit and power consumption.

(d) Means for Solving the Problems In the present invention, the ferrite core halves face each other with the actuating gap and the metal magnetic layer sandwiched between them at the surfaces that contact the recording medium, and the track width regulating grooves on the side of the gap are arranged as described above. In a magnetic head that widens outward from the working gap,
The metal magnetic layer is notched at an angle facing the working gap.

(e) Effect According to the above configuration, a head with a constant spread of erase width can be obtained. That is, in the case of a current consumption of 150 mA or more, a leakage magnetic field is generated at both ends of the track T _S1 even at about 200 mA, and the erase width hardly changes even when the current is 300 mA or 400 mA.

(F) Embodiment FIG. 1 shows the contact surface of a magnetic head embodying the present invention against a tape, and the same parts as in FIG. 6 are given the same reference numerals. A feature of the present invention is that the corners 7 and 8 of the sendust film 4 (another metal magnetic film may be used instead of the sendust film) facing the first ferrite core half 1 and the working gap 3 are cut. This is because the notch 9 is provided. As shown in Figure 1, the notch 9 allows you to
The gap between the ferrite core half body 1 gradually increases and becomes about twice as large. As a result, the magnetic field leaks from this notch 9, and the erase width increases. The expansion of the erase width with respect to the erase current of this erase head is shown by the broken line b in FIG.
Even with an erase current of 200 mA to 300 mA, the erase width hardly changes. That is, the erase width is the sum of the track width T _S1 on the sendust film 4 side and the gap length G, and is substantially constant. Regarding the shape of the notch 9, in order to generate an appropriate leakage magnetic field, the value of θ is preferably 30° θ60°, and in particular, θ = 45°, which satisfies the relationship T _S2 - T _S1 = G, is optimal. Ta. Third
4 and 4 respectively show other embodiments of the present invention, and FIG. 3 shows that the corners 10 and 11 of the second ferrite core half 2 are processed in advance before forming the sendust film. Notches 9 are automatically provided at the corners of the sendust film 4 by forming the sendust film thereon. On the other hand, FIG. 4 is obtained by simultaneously processing with a dicing saw or the like after forming the sendust film 4. In the above, 8 mm
Although the explanation has been given using a rotary erasing head for a VTR as an example, the present invention can be similarly applied to a rotary erasing head for a normal 1/2 inch VTR. It goes without saying that the present invention can also be applied to the magnetic head in which a metal film such as sendust is formed on the first ferrite core half 1 side in the above embodiment.

(G) Effects of the Invention According to the present invention, an erase head with a constant erase width regardless of the value of the erase current can be realized without significantly increasing the erase current. Therefore, the specifications for the inductance of the magnetic head and the Q of the resonant circuit can be expanded, and the yield can be greatly improved.

[Brief explanation of drawings]

FIG. 1 is a front view of essential parts of a magnetic head embodying the present invention, and FIG. 2 is an explanatory diagram thereof. 3 and 4 are front views of essential parts of other embodiments of the present invention, respectively. FIG. 5 is a diagram showing the erasing characteristics of the erasing head, and FIG. 6 is a front view of the main parts of a conventional magnetic head. 1, 2...first and second ferrite core halves, 5...
Track width regulation groove, 9...notch.

Claims (1)

[Scope of Claims] 1 A metal magnetic layer is provided on one of the pair of ferrite core halves, and the pair of ferrite core halves form an operating gap and the metal magnetic layer on the surface that contacts the recording medium. In an erasing magnetic head having a structure in which track width regulating grooves are located on sides of the working gap and are opposed to each other with a layer in between, a corner of the metal magnetic layer located between the working gap and the track width regulating groove is provided. An erasing magnetic head characterized by having a notched portion. 2. The erasing magnetic head according to claim 1, wherein the length of the notch in the corner is approximately half the length of the working gap.