JPS59110006A - Magnetic erasing method - Google Patents

Abstract

PURPOSE:To secure head quality close to that of an AC erasing head with regard to a noise and distortion, not to mention an erasure rate, by rotating a magnet type erasing head which is formed by magnetizing the surface of a cylindrically shaped magnetic material to an N and an S poles alternately to almost equal magnetic field intensity at a specific speed, and running a magnetic tape. CONSTITUTION:The surface of the cylindrically shaped magnetic material 6 is magnetized to the N and S poles alternately. A surface magnetic field is set above the residual magnetic flux density of the tape to be erased. The magnetized material is linked to a motor 7 through a driving shaft 8 and rotated as shown by an arrow 9. The tape 3 runs to right in contact with part of the surface of the rotating magnetic material 6. One point on the tape aproaches the rotating magnetic material 6 gradually from a far distant point and contacts the magnetic material 6 eventually to be influenced by a maximum magnetic field. Variation of the magnetic field on the tape is in exactly the same shape as variation of the magnetic field applied to the magnetic tape. Therefore, the quality of erasure is close to that of the AC erasing head.

Description

DETAILED DESCRIPTION OF THE INVENTION FIELD OF INDUSTRIAL APPLICATION The present invention relates to a method for erasing signals recorded on a magnetic tape, and in particular to recording after erasing.

The present invention aims to provide a magnetic erasing method that maintains a high quality of reproduced audio and video signals.

Conventional structure and its problems Conventionally, the erasing head 2 page in a tape recorder or video tape recorder (hereinafter abbreviated as VTR) has been constructed by passing a high frequency signal through the magnetic head winding and applying a high frequency magnetic field to the magnetic tape. In addition, erasing is possible, however, this method requires a very large amount of high-frequency power for frl erasing, which is disadvantageous both economically and in terms of miniaturizing the device. Furthermore, high-power high-frequency oscillators have problems such as the placement of each circuit and the difficulty in determining I > pA-, since they can cause major interference by entering audio amplification circuits and video processing circuits through power lines, ground lines, or directly. Ta.

In the meantime, there are erasing heads that use permanent magnets to avoid rifling.The simplest method of saturation erasing is that the erasing magnetic field remains on the tape, resulting in large noise after erasing.
However, there are problems such as significant distortion of recorded and reproduced signals after erasing, so it has not been put into practical use. The magnetic erasing heads currently in use for erasing audio signals include:
In order to bring the residual magnetization of the tape close to zero, there are tapes in which the surface of the magnetic material is magnetized in such a way that the polarity is successively different and the strength of the magnetic field is gradually attenuated. Such an erasing head
Normally, the 1.degree.-co magnetic field distribution has an important influence on the erasing quality, and there are difficult problems such as the design of the surface magnetic field distribution and magnetization variations. Furthermore, even if the magnetic field distribution on the surface is magnetized in an ideal form, if the contact state between the running tape and the multipolar magnetic erasing head changes, the magnetization given to the tape will change, resulting in quality There was a problem in that it was not possible to perform good erasure. For example, in the case of audio signals erased, recorded, and reproduced with the multi-polar magnetic erasing head used in the Ushi, the distortion rate is as high as 3 to 5%. Therefore, it is mainly used in popular tape recorders and cannot be used in high-end Hi-Fi tape recorders or VTRs. It is important to control the magnetization method and the state of contact between the tape and the erase head during tape running.
Because of these difficulties, it can be said that the erasing quality of the magnetic erasing head is not comparable to that of the AC erasing head.

OBJECTS OF THE INVENTION The present invention is directed to solving the problems associated with magnetic erase heads. Of course, the present invention aims to provide a magnetic erasing method 111' that can ensure quality close to that of AC erasing in terms of noise and distortion.

Structure of the Invention The present invention has a cylindrical shape and a magnetic field strength of approximately equal to 1 to 1'll on the surface of the cylindrical material. By rotating the magnetic erasing head at a predetermined medium speed and bringing the magnetic tape into contact with a part of the surface of the magnetic erasing head, the magnetic tape is erased. It erases noise.

High 1'l-1'l (eliminate l>! for strain, etc.)
1. ! In addition to showing the 1' case, the tongue l-magnetic v11-
The method of magnetizing the erase head is much simpler than that of the attenuating magnetic field of (Y:'q), since it is only necessary to magnetize it strongly.

High-quality erasing is possible/) C1: Magnetic tape If you look at it from one point, the N and S magnetic fields will gradually become stronger and then gradually attenuate. This shows that it is possible to obtain a magnetic field change equivalent to that of an AC erasing head, and furthermore, even if the contact state between the tape and the erasing head changes, the attenuation magnetic field that the tape receives does not change much. In other words, whereas conventional multi-pole magnetic erase heads apply an attenuating magnetic field to the tape by the magnetic field intensity distribution itself on the surface and require close contact between the tape and the head, in the present invention, the tape and the erase head are in close contact. As the distance gradually increases, the contact between the tape and the head becomes less important in order to obtain an attenuating magnetic field. This will be explained by comparing.

FIG. 1(A) is a diagram for explaining erasing by a conventional multi-polar magnetic erasing head. It is magnetized so that the magnetic field distribution is such that N poles and S poles alternate and attenuate sequentially as shown in FIG. Then, attach the magnetic tape 3 to the tape contact surface 2.
If the magnetic tape 3- is brought into contact with the magnetic tape 3- and the magnetic field is run from the stronger side to the weaker side (in one direction indicated by the arrow), a magnetic field almost equal to the surface magnetic field distribution shown at one point C-1, 4 on the magnetic tape 3- is generated. The recorded signal will be erased. When recording and reproducing are performed on the magnetic tape 3- erased in this way, the quality of the reproduced signal (S/N, distortion, etc.) largely depends on the shape of the magnetic field distribution shown in 1.4. Therefore, when manufacturing the head, the surface magnetic field distribution is J
$ L <Tube 1'l! Must be 1~.

If the contact between the tape and the head is poor, for example, if the tape comes off the head at the right end of the figure, the tape will appear as if the number of poles has decreased (17), as shown by 5 in Figure 1 (C). 31: Since it receives a magnetism of 1/, l, the DC residual magnetization increases. This is due to the linearity of magnetic pole conversion characteristics and 3
It can affect the KI sound. The nonlinearity of electromagnetic conversion appears conspicuously as second-order harmonic distortion in the case of audio signals, and in the case of 5° video conversion, it appears as cross-modulation of the luminance signal and color signal, the former being a distorted sound of the sound.

The latter becomes the extra 1st stripe on the screen 1-, deteriorating the reproduction quality and increasing the 1-dimension.

7. Figure 2 is a diagram of the principle of the present invention. In the same figure (A),
The surface of the cylindrical magnetic material 6 is alternately magnetized with north and south poles as shown in (B). The surface magnetic field is set to be larger than the residual magnetic flux density of the tape to be erased. Number of magnetic poles d: many culms = 1 to ease of magnetization. Unlike conventional attenuation magnetization, it is possible to easily magnetize several dozen poles on a surface with a diameter of 20 mJI using the same magnetic field. The magnetic material 6 magnetized in this manner is connected to a motor through a drive shaft 8, and is rotated in the direction of the arrow 9. The tape 3 travels to the right while contacting a part of the surface of the rotating magnetic material 60. At this time, if we consider the magnetic field that a single point on the tape receives, as shown in Figure 2 (G), it increases gradually, reaches the maximum value, and then decreases gradually, during which the polarity alternates with N. It changes into pole and south pole.

This is because a point on the tape starts from a point far away from the rotating magnetic material 6, gradually approaches it, finally comes into contact with the magnetic material 6 and receives the maximum magnetic field, and then gradually moves away from it. . Figure 2 (C) 11 Tomorrow n59-11
000G (3) shows the magnetic l/]I- on the tape
Change 1ll-1 The change in the magnetic field that an AC erase head exerts on a magnetic tape is exactly the same as that of the magnetic tape.
Erasing quality: far superior to that used in AC erasing heads.

Furthermore, this high-quality in)'s eraser 11; function r11, tape 3 and magnetic material l.16; ”, is a major feature not found in conventional multi-pole magnetic erase heads, in that it is maintained even when the magnetic erase head changes to a magnetic field. 1: is formed at a spatial distance 1-1 from the erasing head.

Therefore, no matter where the tape leaves the erase head, no significant difference h''11 occurs in the shape of the attenuated magnetic field.

Multi-pole magnetization j ~ cylindrical magnet An inexpensive motor can be used if not required.

How to rotate the erase head? ):, ni+: In addition to the embodiments described above, it is also possible to transmit the signal from, for example, a cylinder motor, a gear bus stan motor, or a reel motor or roping motor using an idler or a belt.

It is also possible to use a structure in which the rotation is performed by a running tape, such as an impedance roller, without providing any particular rotation drive source.

Although the erasing head of the present invention has been described as an example in which an integral body of magnetic material is magnetized, this is not limited to an integral body, but is also applicable to magnetic materials magnetized to a structure of separate thorns in a cylindrical shape. Of course, it may be formed.

Effects of the Invention - F1 As described in detail, the present invention provides an erasing method using a magnetic erasing head suitable for suppressing noise, second harmonic distortion rate of an audio signal, and cross-modulation of a video signal. , it is possible to achieve almost the same performance as an AC erase head.

Then, all you have to do is alternately magnetize the surface of the cylindrical magnetic material with the same magnetic field strength and with different polarities.This is a technique that has been used for example in motor magnets, etc. This is extremely easy compared to the conventional multi-rod reduced magnet head.

There are no strict restrictions on the contact between the tape and the erasing head on the spatula. ?] Y: In the case of future AC erasing, a large erasing current is required, and there is a strong demand for lower power consumption in tape recorders and VTRs. This is extremely effective for such requests.

[Brief explanation of the drawing]

Figure 1), (B), and (C) 1. The principle of the conventional multipolar erase head (?) A schematic diagram of the head, a surface magnetic field distribution diagram, and a diagram showing changes in the magnetic field to which the tape is subjected. ,
Figure 2 (A). (B) and (C) are diagrams showing the relative relationship between the erasing head and the tape, the surface magnetic field distribution diagram of the erasing head, and the changes in the magnetic field that the tape undergoes to explain one embodiment of the present invention. 3...Magnetic tape, 6...Magnetic material, 7.
... Drive motor, 8... Rotating shaft 6, Fig. 1/ Fig. 2 □ Time

Claims (1)

[Claims] A plurality of magnetic poles having approximately equal magnetic field strength and alternately different polarities are formed into a cylindrical shape, and a magnetized body having different cylindrical shapes is rotated at a predetermined speed, and a recorded magnetic tape is attached to a part of the surface of the magnetized body. 1. A magnetic erasing method characterized in that information on a magnetic tape is erased by running the tape in contact with the magnetic tape.