JPS60170018A - Degausser of magnetic head - Google Patents

Abstract

PURPOSE:To perform an assured degaussing job according to the material of a magnetic head and at the same time to avoid the useless consumption of a power supply battery, by changing the initial value of an alternating magnetic field reducing gradually which is produced at a degaussing head after changing freely the initial voltage obtained at the start of oscillation of an oscillation circuit. CONSTITUTION:A power supply battery 1 is provided together with a DC booster circuit 3 connected to the battery 1, a switching circuit 5, a capacitor C4, an oscillation circuit connected to the C4 and degaussing head 8. For the C4 of large capacity connected to a constant voltage circuit 6, the terminal voltage can be changed by connecting selectively a variable contact (d) of a switch device SW to either one of fixed contacts (a)-(c). In other words, the circuit 6 consisting of Zener diodes ZD1-3 and the device SW serves as a terminal voltage changing part of the C4. Then the terminal voltage of the C4 inresponse to the level of the coercive force of a magnetic head to be degaussed. Thus it is possible to change the initial value of an alternating magnetic field reducing gradually which is produced at the head 8.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a degaussing device for a magnetic head, and in order to correspond to the magnitude of the coercive force of the magnetic head to be demagnetized, the magnitude of the initial value of the alternating gradually decreasing magnetic field generated in the degaussing head is adjusted. It is made to be changeable.

A degaussing device for demagnetizing a recording/playback magnetic head of a tape recorder, etc., generally consists of a degaussing head and a driving circuit for the degaussing head, and the degaussing head is brought close to the magnetic head to gradually reduce the magnetization. By generating a magnetic field, the magnetization of the magnetic head is erased. Incidentally, in recent years, magnetic tapes have been made to have higher coercive force, and 1-metal tapes have gradually become popular.However, this metal tape has a higher surface hardness than conventional magnetic powder tapes, and the recording bias signal must also be increased. Therefore, magnetic heads made of permalloy, which have been widely used in the past, are easily worn out due to the sliding friction.For this reason, high bias heads made of materials with a high degree of hardness, such as Sendust, are used as magnetic heads for metal tapes. These high-bias heads have high magnetic permeability and a large coercive force, but their cores are more susceptible to magnetism, which makes them more suitable for tape than magnetic heads made of permalloy. There is a disadvantage that noise is easily recorded and signals are erased, so it is necessary to perform degaussing work more reliably.However, when demagnetizing a high bias head using an alternating gradually decreasing magnetic field, the saturation magnetic flux density of the high bias head is Since it is larger than that of a magnetic head made of permalloy, it is necessary to increase the initial value of the alternating gradually decreasing magnetic field by that much, but in order to completely erase the magnetization of the high bias head, the initial value of the alternating gradually decreasing magnetic field is increased. Therefore, when demagnetizing a magnetic head made of a material with relatively low coercive force, such as permalloy, the alternating gradually decreasing magnetic field becomes excessive, and in addition, the power supply battery is wasted. In the case of the popular cassette type degaussing device, the capacity of the power supply battery is relatively small, so if an unnecessarily large discharge current is passed through the battery, the battery will be rapidly consumed, and the battery will have to be replaced frequently.

Therefore, the present invention has been devised in consideration of the above points, and includes a degaussing device in which an oscillating circuit is oscillated by the discharge current of a capacitor to generate an alternating gradually decreasing magnetic field in a degaussing head. The initial voltage can be changed freely to change the initial value of the alternating gradually decreasing magnetic field generated in the degaussing head.This makes it possible to change the initial value of the alternating gradually decreasing magnetic field generated in the demagnetizing head. For example, by raising the terminal voltage of the capacitor that supplies power to the oscillation circuit and causing a large discharge current to flow, an alternating gradually decreasing magnetic field with a large initial value is generated in the degaussing head, and a magnetic field made of a material with a relatively low coercive force such as permalloy is used. When demagnetizing the head, for example, the terminal voltage of the capacitor is lowered to cause a small discharge current to flow, and an alternating gradually decreasing magnetic field with a relatively small initial value is generated in the degaussing head. Accordingly, the degaussing work can be performed reliably and unnecessary consumption of the power source battery can be prevented. Embodiments of the present invention will be explained below with reference to the drawings. ◎ Figure 1 is an electrical circuit diagram of the degaussing device built into the cassette case, where l is the power supply battery, 2 is the switch circuit, and 3 is the DC booster. It is a DC-Do converter circuit as a circuit, and the switch circuit 2 is a variable contact 2 &
, consists of a fixed contact 2b on the negative electrode side of the power supply battery l and a fixed contact 2c on the side of the capacitor σ3, which will be described later.When the cassette case is set in the tape recorder, the variable contact 2a is connected to the contact 2b side and removed from the tape recorder. and is thrown into the contact 2c side. Converter circuit 3 includes resistor R1, coils L1 and R2, and capacitors 01 and 02.
, diode DI, ) transistor QISCL2, etc., and boosts the terminal voltage of the power supply battery I.

A resistor R2 and a capacitor 03 are connected to the output stage of the converter circuit 3, and a drive display circuit 4 is connected to the resistor R2 and the capacitor 03. The drive display circuit 4 includes a light emitting diode D2 as a light emitting element, a transistor Q3,
The light emitting diode D2 is connected in parallel with the capacitor Q3, and each of the resistors R3 and R4 is connected to the base side of the transistor Ql. The resistor R2 side of the capacitor 03 is connected to the fixed contact 2C of the switch circuit 2, and is also connected to the base side of a transistor Q5, which will be described later, via a diode D3.

5 is a switching circuit connected to the display circuit 4, which includes transistors Q4, q5, resistors R5, R6, and R'7.
, R8, the base side of the transistor q4 is connected to the base side of the transistor q3 via resistors R6 and R7, and the resistors R6 and R7 are connected to the transistor Q
It is connected to the collector side of 5. Also transistor Q
The base side of 5 is connected to the collector side of the transistor Q3 via the resistor n3, and is also connected to the capacitor 03 via the diode D3 as described above.

6 is a constant voltage circuit connected to the switching circuit 5, and is connected to three Zener diodes ZDl, ZD2, and ZD3 connected between the positive and negative lines, and each Zener diode ZDINZD3. Fixed contact a
, b, c and each contact a, bS connected to the negative line side
The switch device SW consists of a variable contact d selectively connected to the switch d. Each Zener diode ZDI~
The breakdown voltages of ZD3 are different in magnitude, and are in the following order: Zener diode ZDI, Zener diode ZD2, and Zener diode ZD3.

04 is a short-capacity capacitor connected to the constant voltage circuit 6, and by selectively connecting the variable contact d of the switching device SW to any of the fixed contacts a, b, and c, its terminal is Voltage can be changed. That is, the constant voltage circuit 6 consisting of the Zener diodes ZDI NZD3 and the switch device SW also serves as a terminal voltage changing section of the capacitor 04, and changes the terminal voltage of the capacitor a4 according to the magnitude of the coercive force of the magnetic head to be demagnetized. By changing the voltage, it is possible to change the initial value of the alternating gradually decreasing magnetic field generated in the degaussing head 8, which will be described later.

7 is an oscillation circuit driven by the discharge current of capacitor a4, which includes capacitor 05.06, resistor R9, RIO
, transistors Q6, Q7, etc., and the oscillation circuit 7 is connected to a degaussing head 8 consisting of degaussing coils L3, L4, and a capacitor 07. Also, transistors Q6 and Q7
The emitter side of each is connected to the collector side of the transistor Q5.

This device has the above-mentioned configuration, and its operation will be explained next.

When demagnetizing the high bias head, the variable contact d is connected to the contact a side of the Zener diode zDl having the maximum breakdown voltage, and the cassette case is set in the tape recorder. Then, the degaussing head 8 is pushed back by the head on the tape recorder side, and in conjunction with this, the variable contact 2a of the switch circuit 2 is closed to the contact 2b side, and the terminal voltage of the S power supply battery l, for example, 1.5 V, is , the voltage is boosted by the converter circuit 3 to about 167, for example, and the transistor q4 becomes conductive, and the capacitor 04 is charged until its terminal voltage becomes equal to the breakdown voltage of the Zener diode ZDI. When it is charged and its terminal voltage rises to a predetermined value, the transistor Q5 becomes conductive due to its discharge current, and the oscillation circuit 7 begins to drive.The transistor q3 also becomes conductive, and the light emitting diode D2 rises well and lights up, and continues to operate during driving. On the other hand, due to conduction of transistor Q3, transistor q4
At the same time, the capacitor 04 starts discharging the stored charge, and the discharge current drives the oscillation circuit 7, creating an alternating magnetic field in the degaussing head 8 that gradually decreases based on the discharge time constant, and the tape The high bias head for recording and playback of the recorder is demagnetized. Here, the variable contact d is the contact on the Zener diode zDl side having the maximum breakdown voltage ak:, vf! Since the terminal voltage of the capacitor o4 is high, the initial value of the alternating gradually decreasing magnetic field generated in the degaussing head 8 is large and completely eliminates the magnetization of the high coercivity and high bias head. Furthermore, when transistor Q3 becomes conductive, a base current flows through transistor q1, transistor Ql becomes conductive, transistor Q2 becomes cutoff, converter circuit 3 stops driving, and power supply battery l and booster circuit 3 switch off from light emitting diode D2. However, the light emitting diode D2 is thereafter sufficiently driven by the discharge current of the capacitor σ2 and continues to light up.

When the discharge of capacitor a4 is completed and the degaussing operation is completed, the cassette case is removed from the tape recorder. Then, the variable contact 2a switches to the contact 2C side, the capacitors 02 and σ3 immediately finish discharging, the light emitting diode D2 goes out, and all driving stops.

Next, when demagnetizing a magnetic head having a relatively small coercive force, such as permalloy, the variable contact d is connected to the fixed contact or to the fixed contact C side. Then capacitor o4
The terminal voltage becomes smaller than in the above case, and the initial value of the alternating gradually decreasing magnetic field generated in the degaussing head 8 also becomes smaller. In other words, when demagnetizing a magnetic head with a relatively low coercive force, if the terminal voltage of capacitor 04 is increased as in the case of demagnetizing a high bias head, the initial value of the alternating gradually decreasing magnetic field becomes excessive and power is wasted. This causes the power supply battery to run out faster. Therefore, when demagnetizing a magnetic head with a relatively small coercive force, use the capacitor 04 as described above.
By reducing the terminal voltage of , so that the degaussing head 8 generates the minimum necessary alternating gradually decreasing magnetic field, it is possible to prevent unnecessary consumption of the power supply battery l.

In addition to the above-mentioned embodiments, the present invention allows for changes in the glaze settings. For example, in the above-mentioned embodiment, three fixed contacts a, b to
Although the terminal voltage of capacitor C4 can be changed in three steps by increasing C, the terminal voltage of capacitor C4 may be changed in any number of steps. Further, the oscillation start timing of the oscillation circuit 7 is controlled by the time determined by the time constant of the resistor R2 and the capacitor 03, but in order to further save the power supply battery, the current flowing through the Zener diodes ZDI-ZD3 is detected, Thus, a configuration may be adopted in which the oscillation circuit 7 is driven by driving the transistor Q5.

As explained above, the magnetic head degaussing device according to the present invention includes a power supply battery 11, a DC booster circuit 3 connected to the power supply battery 1, a switching circuit b, a capacitor 04, and an oscillation circuit 7 connected to the capacitor a4. , demagnetizing head 8
Since the initial voltage for starting oscillation of the oscillation circuit 7 can be changed, the initial value of the alternating gradually decreasing magnetic field generated in the demagnetizing head 8 can be adjusted according to the magnitude of the coercive force of the magnetic head to be demagnetized. Since it can be changed, the magnetization of the magnetic head can be reliably erased, and the necessary minimum alternating gradually decreasing magnetic field can be generated to prevent wasteful consumption of the power supply battery 1.

[Brief explanation of the drawing]

The figure is a 1u circuit diagram of an embodiment of the present invention. 1... Power supply battery 3... DC booster circuit 580. Switching circuit 7...Oscillation circuit 8...Degaussing head a4...Capacitor Applicant Kyushu Hitachi Maxell Co., Ltd. Agent Patent attorney Toshiyuki Takamatsu

Claims (1)

[Claims] Power supply battery 11 DC booster circuit 3 connected to the power supply battery 1
, a switching circuit 5, a capacitor 04, an oscillation circuit 7 connected to the capacitor 04, and a degaussing head 8, characterized in that the initial voltage at which oscillation of the oscillation circuit 7 starts can be changed. Device.