JPH0435804B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a magnetic head, and more particularly to a magnetic head in which a magnetic gap is provided in a tape sliding portion having a large curvature.

A tape cassette, as typified by a Phillips-type cassette, has a reel for winding and supplying tape stored in a compact storage box, and is equipped with a tape pad for pressing the magnetic tape against a magnetic head.

On the other hand, in a magnetic head mounted on a cassette tape recorder, the magnetic gap is generally placed approximately at the center of the tape sliding surface so that it is always under the direct influence of the pressure contact force of the tape pad. That is,
Whether the coil 1 is wound on both sides of the magnetic core 2 as shown in FIG. 1 or the coil 1 is wound around the base of the magnetic core as shown in FIG.
A magnetic gap 2a is positioned at the center of the tape sliding surface of the magnetic tape 4 from an opening 3a at the tip of the shield case. Then, the tape pad 5 is passed through the magnetic tape 4 to the magnetic gap 2.
A is pressed with a force of F. If such a structure is adopted, the magnetic tape 4 is always kept in the magnetic gap 2a.
Since it is pressed against the surface, recording and reproduction can be performed with almost no spacing loss.

However, the pressure applied by the tape pad 5 usually exceeds the necessary and sufficient pressure to prevent spacing loss, and the pressure applied to the head surface
In particular, the magnetic gap and its vicinity are pressed together. In particular, when felt is used as a tape pad member, the felt fibers scattered in a rough state apply pressure to the head surface one by one through the tape, resulting in dots or spots on the head surface depending on the fiber density. Concentrated pressure is applied unevenly in a line. If the magnetic head is used in this state for a long time, the head surface will exhibit uneven wear, resulting in significant loss of tape touch.

In order to solve these problems, materials such as hard permalloy, sendust, and ferrite, which are highly hard and wear-resistant materials, have been used as core materials for magnetic heads. However, materials with high hardness are difficult to process, and it is extremely difficult to develop materials that have excellent magnetic properties, particularly magnetic permeability, saturation magnetic flux density, etc., and also have good corrosion resistance. Moreover, the wear resistance of the sendust material obtained in this manner is only several times higher than that of hard permalloy material at most.

The present invention was made in view of the above-mentioned drawbacks of the conventional magnetic head, and an object of the present invention is to provide a magnetic head configured to significantly improve wear resistance while using the conventional magnetic core material. The purpose is

In order to achieve the above object, the magnetic head of the present invention has magnetic tape on the upstream side and downstream side of the tape sliding surface along the flow of magnetic tape running. A convex surface part for changing the running direction of the tape pad is formed respectively, a flat part for receiving the tape pad is formed in the middle stream, and the depth direction of the downstream convex part is inclined with respect to the perpendicular direction of the flat part to form a magnetic field. A structure with gaps was adopted.

Hereinafter, details of the present invention will be explained based on embodiments shown in the drawings.

Generally, the function of the tape pad is to press the tape into the head gap by its pressing force, and the mechanism of this pressing is divided into direct force and indirect force as described below.

That is, when a direct force is applied, the magnetic gap is located directly below the fibers of the tape pad, and at this time, the tape is directly pressed against the magnetic gap by the force of the fibers of the pad.

In addition, when applying an indirect force, the magnetic gap is not directly under the fibers of the tape pad, and at this time, the tape running preventing force due to the friction between the tape and the head and the tape pulling force due to the winding shaft are combined. The tape tension generated in between acts on the tape sliding surface of the head, a cylindrical surface with a large curvature (small radius R). In other words, the force acting on the magnetic gap is pressure in the normal direction acting on the cylindrical surface, and is an indirect force.

By the way, the width of the magnetic gap is generally extremely small (1 to 2 μm) compared to the fiber density of the tape pad and the spacing between each fiber, so the direct force mentioned above is extremely small, and most of the tape contact force is due to indirect force. arise.

Now, the coefficient of friction between the tape and the pad during tape running is μ, the width of the tape and the pad is W ₁ ,
If the pad width in the tape running direction is d and the pad pressure contact force is F, then the tape tension Tg generated on the tape on the gap by the pressure contact force F is Tg=1/2×F・μ...(1 ) The pressing force N per unit area on the gap generated by this Tg and the radius R of the tape sliding surface of the head is expressed by the following equation (2).

N=Tg/R・1/W...(2) Here, the tape pressure force required for magnetic recording and reproduction is
Assuming N ₀ , the pad pressure contact force F ₀ required to obtain this pressure contact force with the tape pad is expressed by the following equation.

F ₀ =2・R・W・N ₀ /μ (3) Also, the pressure contact force f ₀ of the part per unit area is expressed by the following formula.

f ₀ =F ₀ /W・d=2R・N ₀ /μ・d ...(4) Therefore, the ratio of f ₀ and N ₀ is f ₀ /N ₀ =2R/μ・d ...(5 ) Generally, in a cassette, R≒10mm, μ≒
0.3, and d≒4 mm, so f ₀ /N ₀ ≒17 (6). Therefore, in order to obtain the necessary pressure contact force _N0 , it is necessary to apply a force 17 times the tape pressure contact force as the pad pressure contact force.

Furthermore, because the fiber density of the tape pad is coarse, these forces are concentrated directly under the fibers, and a locally large force is applied unevenly to the head surface through the tape, causing head wear and unevenness. This causes uneven wear phenomenon.

Therefore, in order to eliminate such negative effects from the tape pad and obtain the necessary tape pressure, it is necessary to release the magnetic gap from under the direct pressure of the tape pad, so that the part without the gap can receive the pressure of the tape pad more strongly. Tape tension must be generated in this way. It is also necessary to position a magnetic gap between the tape winding capstan and the tape pad.

The present invention is based on the above-mentioned principle, and embodiments thereof are shown in FIG. 3 and subsequent figures.

In the embodiment shown in FIG.
A structure is adopted in which the position a is set away from directly below the tape pad 5 (approximately the center of the tape sliding surface) and is set at a position with a large curvature in the peripheral area shifted in the tape running direction.

Further, in the embodiment shown in FIG. 4, a structure is adopted in which the gap 2a of the magnetic core 2 protrudes and faces the tape sliding surface from the opening of the shield case 3. The position of 2a is directly below the tape pad 5 (approximately the center of the tape sliding surface)
It is set at a position with a large curvature at the periphery, which is offset from the tape in the running direction.

If the structure shown in Figures 3 and 4 is adopted, the pressure force of the tape pad will not be applied directly to the magnetic gap part at a large position of the song, but will be applied to the part with small curvature, so that the necessary tape pressure force will be reduced. Therefore, uneven wear of the magnetic gap portion does not occur.

FIG. 5 shows another embodiment of the present invention. In this embodiment, the entire magnetic head having a tape sliding surface with a large curvature is arranged at an angle, and the magnetic gap is released from the tape pad 5. , a structure is adopted in which a device 6 is provided on the side surface of the shield case 3 to receive the pressing force of the tape pad 5 on a tape sliding surface having a small curvature (including a flat surface). In addition, the plane is R=
∞, that is, the curvature is zero, and it can be thought of as the minimum curvature state.

Even if such a structure is employed, the same effects as those of the above-mentioned embodiments can be obtained.

FIG. 6 is a diagram comparing the amount of wear between the magnetic head of the present invention and the magnetic head of conventional structure. Curve A in the figure shows the conventional one, curve B shows the one of the present invention, and the hard The experiment was conducted using a commercially available γ-Fe ₂ O ₃ type cassette C-90 tape whose core was made of palm wood. The test was conducted at a temperature of 30°C and a humidity of 70%.

As is clear from Figure 6, as a result of 1000 hours of tape running, the magnetic head of the present invention was proven to have approximately 10 times more wear resistance than Sendust material while still being made of hard permalloy material. It is clear that the effect that far exceeds the life of the core can be obtained, and it can be seen that the degree of freedom in selecting the core material is significantly expanded.

As is clear from the above description, according to the magnetic head of the present invention, among the upstream, midstream, and downstream sides of the tape sliding surface along the flow of the magnetic tape, the upstream side and the downstream side are Convex portions for changing the running direction of the magnetic tape are formed respectively, a flat portion for receiving the tape pad is formed in the midstream, and the depth direction of the downstream convex portion is inclined with respect to the perpendicular direction of the flat portion. Since we have adopted a structure in which the magnetic gap is arranged at the same time, it is possible to apply uniform tension to the magnetic tape with an extremely simple structure, prevent uneven wear of the magnetic gap part, and significantly improve the service life.
An excellent effect can be obtained in that the degree of freedom in selecting the core material can be expanded.

[Brief explanation of drawings]

1 and 2 are cross-sectional plan views showing different structures of conventional magnetic heads, and FIGS. 3 and 4 are cross-sectional plan views showing different embodiments of the magnetic head of the present invention. FIG. 5 is a plan view showing another embodiment of the present invention, and FIG. 6 is a diagram showing the amount of wear between the magnetic head according to the present invention and the conventional magnetic head. 1... Coil, 2... Magnetic core, 2a... Magnetic gap, 3... Shield case, 4... Magnetic tape, 5... Tape pad, 6... Receiver.

Claims (1)

[Claims] 1. Convex portions for changing the running direction of the magnetic tape are respectively formed on the upstream side and the downstream side of the tape sliding surface along the flow of the magnetic tape running, and on the middle stream. 1. A magnetic head comprising a flat surface for receiving a tape pad, and a magnetic gap disposed on the convex surface on the downstream side with a depth direction inclined with respect to a perpendicular to the flat surface.