JPS59146432A - Ac erasing head - Google Patents

Abstract

PURPOSE:To attain the high-quality recording/reproducing of sounds with a low level of power consumption and reduced noises and distortions for an AC erasing head, by giving an azimuth angle tilting to the orthogonal direction to the traveling direction of a magnetic tape to at least the gap where the tape passes last among those gaps generated by an erasing magnetic field. CONSTITUTION:For an AC erasing head, a gap 41 where a magnetic tape passes first is formed in the direction orthogonal to the traveling direction 43 of the tape. At the same time, a gap 42 where the tape passes last has an inclination by an angle theta to the direction orthogonal to the direction 43. In other words, the magnetic tape is erased from its magnetization facilitating axis with an erasing magnetic field leaked out of the gap 41 which is orthogonal to the direction 43 when an erasing current is supplied from an erasing power supply 47 to a coil 46 wound around a center core 44 made of a material of high permeability. Furthermore the erasion is performed by a magnetic field leaked out of the gap 42 tilted to the direction orthogonal to the direction 43 after the remaining magnetization is reduced.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to an AC erasing head suitable for audio tape recorders. In particular, the present invention is useful as a low-power erasing head for a portable battery-powered tape recorder, or as an erasing head for a cassette tape recorder or cassette tape deck with a radio receiver that is equipped with a dubbing function at a tape speed higher than a constant running speed. This invention relates to an AC erase head used as an AC erase head.

Conventional configuration and its problems Conventional methods for erasing information recorded on magnetic tape include:
Broadly speaking, there are DC elimination method and AC elimination method.

The DC erasure method is a method in which a strong DC magnetic field is applied to the magnetic tape to erase all the residual magnetization caused by the recorded signal by magnetizing it to the magnetic saturation point. However, there are two types: a direct current type erasing head that uses a direct current magnetic field leaking from the cap portion by passing a large direct current through the coil, and a magnetic type erasing head that uses a ferromagnetic magnet. This DC erasure method has the advantage of consuming less power, especially the magnetic type, which consumes no power at all, but it leaves a saturated residual magnetism on the magnetic tape, which causes large noise during subsequent recording and playback, and distorts the playback signal. There was a big drawback:

On the other hand, the AC erasing head has a coil 16 wound around high magnetic permeability material cores 14 and 15 having two gaps as shown in FIG. This system utilizes a leaking alternating current magnetic field, and a magnetic tape running in the direction of arrow 13 receives a strong alternating magnetic field when passing through a gap. As the magnetic tape moves away from the gap, the alternating current magnetic field acting on the magnetic tape gradually decreases while reversing in the positive and negative directions, so that the magnetization on the magnetic tape reaches a magnetic neutral point and is erased to a state where residual magnetism is almost zero. In general, two or more gaps are provided to improve erasing efficiency. In this case, the cancellation frequency is selected to be at least 3 to 4 times the audio signal band so as not to be reproduced by the playback head, and is usually 60
An alternating current of KHz or higher is used. For this reason, a high magnetic permeability ferrite material, which has a high specific resistance and low eddy current loss, is generally used as the core material. This AC erasing head has advantages over the DC erasing method, such as lower noise during subsequent recording and playback, and less distortion of the audio signal, but it consumes a lot of energy, especially when erasing high coercive force tapes (such as metal tapes). The drawback is that it requires a large amount of power and is difficult to install in a portable battery-powered tape recorder.

Furthermore, it is impossible to install the AC erasing head described above in a tape recorder equipped with a radio receiver or a cassette tape recorder that is equipped with the function of dubbing tapes at a speed faster than the constant running speed, for the reasons described below. Ta. That is, during high-speed dubbing, the audio signal is shifted to a high frequency range according to the dubbing speed. For this reason, the erasure frequency during high-speed dubbing must also be shifted to a higher frequency range.

However, since the AC erasing head has a structure in which a coil is wound around a core made of a high magnetic permeability material, its impedance increases in proportion to an increase in the erasing frequency. Moreover, in order to obtain the same magnetomotive force as when running at constant speed, the applied current must be the same as when running at constant speed, which has the disadvantage of requiring a high voltage, high power consumption power source for the AC erase head. there were.

In addition, when conventional AC erase heads are used at higher frequencies, power consumption increases, and due to the heat generation phenomenon, the AC erase heads reach high temperatures, resulting in decreased magnetic permeability of the core material and short circuits due to melting of the winding coating. However, it has been impossible to mount the conventional AC erasing head on a cassette tape recorder with a radio receiver or a cassette tape deck that can perform dubbing at a speed four times faster than the constant running speed.

Purpose of the Invention The purpose of the present invention is to solve the problems of the conventional AC erasing head.
We provide a low power consumption AC erasing head, which enables the installation of an AC erasing head in battery-powered portable cassette tape recorders, realizing high-quality audio recording and playback with less noise and distortion, and at a constant speed. To provide an AC erasing head for a tape recorder with a radio receiver or a cassette tape deck capable of dubbing at four times the running speed or more.

Structure of the Invention The present invention provides an AC erasing head in which, among the gaps in which an erasing magnetic field is generated, at least the gap through which the magnetic tape passes last has an azimuth angle that is inclined with respect to a direction perpendicular to the direction in which the magnetic tape travels. be. Therefore, the small magnetization remaining in the erasing process is not reproduced due to azimuth loss caused by the angle of intersection between the magnetization pattern and the reproduction head gap being tilted at a certain angle.
This means that it is possible to set the cancellation frequency within the audio band.

Generally, the recording wavelength on a magnetic tape is λ, the track width is W,
When the azimuth angle is θ, the azimuth loss L_A is expressed by the following equation.

If this is illustrated with L_A on the vertical axis and θ on the horizontal axis, the second
The graph becomes as shown in the figure, and the loss becomes infinite at an angle θ such that tanθ=nλ/W (n is an integer) (2).

The curve connecting the peaks of each mountain, that is, the azimuth loss L_A' when is given by the following equation.

This equation (3) is the minimum azimuth loss guarantee level when considering azimuth loss considering variations in azimuth angle.

Now, if the running speed of the magnetic tape is v and the erasing frequency is f, then the following equation is obtained.

Taking a cassette tape recorder as an example, v=4.75cm
/s, and the erasure frequency is taken as a parameter, 5KHz, 1
When the frequencies are 0 KHz and 20 KHz, equation (3) becomes as shown in FIG. That is, in the erasing process of an AC erasing head having an azimuth angle, even if residual magnetization remains on the magnetic tape, the erasing frequency component will not be reproduced by the reproducing head due to azimuth loss.

In particular, if the azimuth angle is set to 10 degrees or more, the azimuth loss will be at least 30 dB at any frequency. An erasing head with an azimuth angle of 10 degrees was prepared, and according to this erasing experiment, the residual magnetization level of the erasing frequency component was about -30 dB at maximum with respect to the saturation level. Therefore, the reproduction level of the erased frequency component by the reproduction head is -60 dB or less, and no practical problem occurs.

Another major feature of the present invention is that of the two or more gaps, at least the gap through which the magnetic tape passes first is formed in a direction perpendicular to the traveling direction of the magnetic tape.

This involves first erasing the magnetic tape in the axis of easy magnetization, that is, in the longitudinal direction of the magnetic tape, and then using a gap formed so as to be inclined with respect to the direction perpendicular to the traveling direction of the magnetic tape. It means.

DESCRIPTION OF THE EMBODIMENTS One embodiment of an AC erase head according to the present invention is shown in FIG. As shown in FIG. 4, in the AC erasing head according to the present invention, a gap 41 through which a magnetic tape (not shown) first passes is formed in a direction perpendicular to a magnetic tape running direction 43, and a gap 41 through which a magnetic tape (not shown) passes first is formed in a direction perpendicular to a magnetic tape running direction 43, and a gap 41 through which a magnetic tape (not shown) passes first is formed in a direction perpendicular to a running direction 43 of the magnetic tape. The gap 42 passing through is at an angle θ with respect to the direction perpendicular to the magnetic tape running direction 43.
Only slanted.

That is, when an erasing current is supplied from the erasing power supply 47 to the coil 46 wound around the center core 44 made of a high magnetic permeability material provided at the center of the core 45, first the gap 41 perpendicular to the traveling direction of the magnetic tape is supplied. Erasing is performed from the direction of the axis of easy magnetization of the magnetic tape by the erase magnetic field leaking from the magnetic tape to reduce the residual magnetization, and then erasing is performed by the leak magnetic field from the gap 42 which is oblique to the direction perpendicular to the direction of travel of the magnetic tape. It will be done.

In this erasing process, even if residual magnetization due to the erasing current remains on the magnetic tape, the residual magnetization pattern on the magnetic tape is also inclined by an angle θ with respect to the direction perpendicular to the running direction of the magnetic tape. It will not be played back by the playback head due to azimuthal loss. As a result, as mentioned above, the erasing frequency can be increased from 5KHz to 20KHz.
It becomes possible to select within the audio signal band such as .

Although this embodiment has been described with respect to a two-gap erase head, a head having three or more gaps may also be used in which the first gap through which the magnetic tape passes is formed orthogonally to the running direction of the magnetic tape, and the magnetic tape is As long as the last gap to be passed is inclined with respect to the direction perpendicular to the running direction of the magnetic tape, the essence of the present invention is not affected in any way even if other gaps in between are inclined or perpendicular to each other. .

When the AC erasing head according to the present invention was used as an erasing head for a portable type cassette tape recorder driven by dry batteries at an azimuth angle of 30 degrees and an erasing frequency of 10 KHz, the results shown in the following table were obtained.

Effects of the Invention As described above, the AC erasing head according to the present invention has a high erasing rate,
Even though both the S/N and the distortion rate are on the same level as the conventional AC erase head, the power consumption can be reduced to one-sixth of that of the conventional AC erase head.

That is, generally a magnetic tape has an axis of easy magnetization in the running direction, and therefore, when erasing a magnetic tape from a direction different from the axis of easy magnetization, the magnetomotive force is increased to increase the erasing magnetic field leaking from the gap. However, in the AC erasing head according to the present invention, erasing is first performed in the direction of the easy axis of magnetization as in the conventional method, and after the residual magnetization is extremely reduced, erasing is performed from a direction different from the axis of easy magnetization of the magnetic tape. Therefore, there is no need to particularly increase the magnetomotive force, and the same erase current as in the conventional method is sufficient.

On the other hand, the erasure frequency ranges from 60 KHz to 10 KHz as mentioned above.
Since the frequency is reduced to KHz, the impedance of the coil of the erasing head is reduced to one-sixth, and the voltage to be applied can be reduced to about one-sixth.

As a result, the power consumption of the AC erasing head according to the present invention is reduced to one-sixth of that of the conventional erasing head. According to experiments, especially when the azimuth angle is 15 degrees or more,
The effect of reducing power consumption was particularly large when the setting was within 30°F. Note that the erasing frequency cannot be set too low because the noise characteristics after erasing depend on the number of magnetic field reversals while the magnetic tape passes through the gap. According to experiments, there was no practical problem if the erasing frequency was set to 5 KHz or higher.

On the other hand, the erasing power supply may be of low voltage and low power consumption, and can be made smaller and lower in cost than conventional ones. Further, in a tape recorder with a radio receiver, a cassette tape deck, etc., which are equipped with a high-speed dubbing function, the AC erasing head according to the present invention can be used at an erasing frequency corresponding to the dubbing speed. For example, when dubbing at 6x speed, 60 KHz may be used, and when dubbing at 10x speed, it is sufficient to use 100 KHz, and it is possible to drive at the conventional erasing frequency and with the same power consumption.

In addition, the erasing frequency when running at constant speed is 5KHz to 20KHz.
Since it can be set within the KHz audio band, metal cores with high saturation magnetic flux density such as sendust, permalloy, and amorphous magnetic materials can be used as the core material, and metal tapes with high saturation magnetic flux density and coercive force can be erased efficiently. It is something that can be done.

[Brief explanation of the drawing]

Figure 1 is a block diagram of a conventional AC erasing head, Figure 2 is a diagram showing the relationship between azimuth loss and azimuth angle, and Figure 3 is an envelope connecting the peaks of each peak in Figure 2. FIG. 4 is a block diagram showing an embodiment of an AC erasing head according to the present invention. 41, 42...gap, 44...center core,
46...Coil.

Claims (2)

[Claims] (1) An AC erasing head that has at least two or more gaps and erases the magnetic tape by applying an AC magnetic field generated from the gap portion to the magnetic tape, wherein at least one of the gaps includes at least two gaps. A gap through which the magnetic tape first passes is formed in a direction perpendicular to the traveling direction of the magnetic tape, and at least a gap through which the magnetic tape passes last among the gaps is formed in a direction perpendicular to the traveling direction of the magnetic tape. An AC erasing head characterized by being inclined with respect to an angle. (2) The direction of the gap through which the magnetic tape passes last is set at 15 degrees or more and within 60 degrees with respect to the direction perpendicular to the traveling direction of the magnetic tape. AC erase head.