JPS6232521B2 - - Google Patents

Description

[Detailed description of the invention] The present invention relates to a method for demagnetizing a magnetic tape.

Magnetic tapes used in cassettes, audio, video, electronic computers, etc. are oriented along the length of the tape in order to increase sensitivity, so a high residual magnetism remains in the magnetic tape after manufacture. It's on. Additionally, the tape is magnetized for some reason during the tape manufacturing process, which also causes residual magnetism. If a tape has residual magnetism, it cannot be used as is, and therefore tape manufacturers demagnetize the tape to a level below a specified level (for example, below -60 dB) before shipping.

Conventionally, as shown in FIG. 1, a conventional method for demagnetizing a magnetic tape is to move a magnetic tape 5 in the direction of arrow A at a predetermined speed v by a conveyor 4 between demagnetizers 2 and 3 of an electromagnet 1 generating an alternating magnetic field H. It was transferred and demagnetized.

However, in this method, the portions 5a and 5b (indicated by diagonal lines) on both sides parallel to the transport direction A of the tape 5 are well demagnetized;
The front and rear portions 5c and 5d, which are orthogonal to each other, are not demagnetized very well. This is because the tape 5 is oriented in the longitudinal direction (arrow BB' direction) as described above. That is, as shown in FIG. 2a, the tape 5 has a constant velocity v with respect to the alternating magnetic field H.
5 of this tape 5 to move in the direction of arrow A.
The alternating magnetic field H' is applied to the parts a and 5b from an oblique direction, and therefore, these parts 5
a and 5b are well demagnetized. On the other hand, the direction of the alternating magnetic field H applied to the front and rear portions 5c and 5d of the tape 5 is always in the vertical direction (Fig. 2b) regardless of the movement of the tape 5. , these portions 5c and 5d are difficult to demagnetize, and residual magnetism inevitably remains above the specified value.

If such an incompletely demagnetized tape 5 is used, for example, as a music tape and double-speed recording is performed, the residual magnetism remains as a noise component because the double-speed recording device is not equipped with a demagnetizer. This occurs as periodic noise during playback.

For this reason, tape manufacturers are strongly required to completely demagnetize to below a specified value. In particular, metal tapes in recent years have very high coercive force (approximately
Hc = 1100 Oe) and to demagnetize portions 5c and 5d of the tape 5 to a specified level, a high magnetic field of approximately 4000 Oe must be applied.

However, the design of an electromagnet that generates such a high magnetic field is extremely difficult, and it is also extremely large and expensive to manufacture, and requires a huge amount of power, making it difficult to put it into practical use. be.

The present invention has been made in view of the above-mentioned points, and a vertical demagnetizing magnetic field is applied to both sides parallel to the conveying direction of the tape in plan view, and a rotating demagnetizing field rotating in a vertical plane is applied to the front and rear parts forming a right angle. The present invention provides a method for demagnetizing a magnetic tape in which the entire tape is demagnetized extremely well by applying a magnetic field.

The present invention will be described in detail below based on one embodiment of the accompanying drawings.

In FIG. 3, magnetic poles 11 and 12 of the electromagnet 10
are arranged facing each other at a predetermined interval in the vertical direction, and each of these magnetic poles 11, 12 has a coil 15,
16 is wrapped. These coils 15 and 16 are connected in series, and the coil 15
The winding start 15a and the winding end 16b of the coil 16 are connected to connection terminals T ₁ and T ₄ , respectively.

The electromagnet 20 is arranged horizontally at a predetermined distance from the electromagnet 10, and has four magnetic poles 21, 22, 23, and 24. The magnetic poles 21 and 23, 22 and 24 are arranged facing each other at a predetermined interval in the vertical direction, and the magnetic poles 21 and 22, 23 and 24 are arranged parallel to the magnetic poles 11 and 12 of the electromagnet 10, respectively. has been done. Coils 31 to 34 are wound around each of these magnetic poles 21 to 24, respectively. The coils 31 and 3 are arranged so that the magnetic poles 21 and 24 and 22 and 23 are paired, respectively.
4, 32 and 33 are connected in series (FIG. 4). Then, the winding start 3 of the coils 31 and 32
1a and 32a connect the coil 3 to the connection terminals T ₂ and T ₃ .
The ends 33b and 34b of each winding 3 and 34 are connected to the common connection terminal _T4 , respectively, and these connection terminals
_T1 to _T3 and _T4 are connected to a three-phase AC power source 60 as shown in FIG. In addition, the connection terminals T ₁ , T ₂ ,
The alternating current voltages applied to T ₃ are each 120° out of phase. Therefore, a vertical alternating magnetic field H ₁ (FIG. 5a) is generated between the magnetic poles 11 and 12 of the electromagnet 10. Furthermore, a rotating magnetic field H ₂ (FIG. 5b) is generated between the magnetic poles 21 to 24 of the electromagnet 20, which rotates in a vertical plane.

Note that the electromagnets 10 and 20 do not necessarily need to be connected to the same three-phase power source, and the electromagnet 10 may be connected to another AC power source. Of course, even in this case, it is necessary for the electromagnet 20 to shift the phase of the AC voltage applied to the connecting terminals T ₂ and T ₃ by 120° so as to generate a rotating magnetic field.

A belt conveyor 40 (indicated by a chain line in FIG. 3) has opposing magnetic poles 11, 12; 2 of electromagnets 10, 20.
1, 23; 22, 24 horizontally in the direction of arrow C at a predetermined speed v, and conveys a tape to be demagnetized, for example, a cassette tape 50 (shown by a chain line in FIG. 3). It's becoming like that.

Now, when the cassette tape (left end in FIG. 6) placed on the belt conveyor 40 passes between the electromagnets 10, it is affected by the alternating magnetic field _H1 on both sides 50a,
The portion 50b is demagnetized. This means that when passing between the electromagnets 10, the alternating magnetic field _H1 is generated in the tape orientation processing direction (B,
This is because the alternating magnetic field H ₁ ' is applied in an oblique direction with respect to the magnetic field B' direction).

Next, when the tape 50 passes between the electromagnets 20, a rotating magnetic field _H2 as shown in FIG. 7B is applied to the front and rear portions 50c and 50d of the tape 50. This rotating magnetic field _H2 is applied so as to rotate the orientation processing direction (B, B' direction) of the tape. Therefore, when this rotating magnetic field H ₂ is applied,
The portions 50c and 50d are also demagnetized without any problem.

Thus, after passing through these two electromagnets 10 and 20, the tape 50 (right end in FIG. 6) is demagnetized to below a specified level over the entire area.

As explained above, according to the present invention, even a metal tape with high coercive force can be easily demagnetized to below a specified level with a relatively low magnetic field, and the demagnetizing device can be made inexpensive and compact. It has excellent effects such as

[Brief explanation of the drawing]

FIG. 1 is an explanatory diagram showing a conventional magnetic tape demagnetization method, FIGS. 2a and b are explanatory diagrams of a magnetic field applied to a magnetic tape by the demagnetization method shown in FIG. 1, and FIG. 3 is an explanatory diagram showing the present invention. FIG. 4 is a diagram showing an example of the circuit of the demagnetizing device shown in FIG. 3; FIG. 5 a, b is an explanatory diagram of the magnetic field generated by each electromagnet of the demagnetizing device shown in FIG. 3, FIG. 6 is a diagram showing a method of demagnetizing a magnetic tape by the demagnetizing device shown in FIG. 3, and FIGS. FIG. 3 is an explanatory diagram of a magnetic field applied to a magnetic tape by the demagnetization method of the present invention. 10, 20...Electromagnet, 11, 12, 21-24
...Magnetic pole, 15, 16, 31-34...Coil, 40
...Belt conveyor, 50...Cassette tape, 60
...3-phase AC power supply.

Claims (1)

[Claims] 1 A first electromagnet that generates a predetermined alternating magnetic field between opposing magnetic poles and a second electromagnet that generates a predetermined rotating magnetic field between opposing magnetic poles are arranged at a predetermined interval,
A magnetic tape wound between the magnetic poles of these electromagnets is moved at a predetermined speed so that the width direction of the tape is perpendicular to the magnetic poles. A method for demagnetizing a magnetic tape, in which the entire tape is demagnetized to below a specified level by demagnetizing each with a second electromagnet.