JP2577949B2 - Unnecessary magnetic influence removal device - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an apparatus for removing the influence of unnecessary magnetism, such as an electronic apparatus, in which, for example, a shadow mask type color cathode ray tube is hardly affected by an ambient magnetic field such as terrestrial magnetism. Things.

[Conventional technology]

There are many known devices, such as a shadow mask type color cathode ray tube, that eliminate the influence of unnecessary magnetism such as terrestrial magnetism during operation.

Such devices are known in various ways to prevent the magnetic effects of interest. The first is the use of known magnetic shields. The magnetic shield is formed by surrounding the device in question, or a specific portion therein, with a magnetic material of high magnetic permeability.

For example, in the case of the above-mentioned shadow mask type color cathode ray tube, the outside of a funnel portion having a substantially funnel shape, which is a main traveling path of the electron beam, is surrounded by a magnetic material so that the influence of geomagnetism does not affect the traveling path of the electron beam. It is common to use a magnetic shield. In some cases, the magnetic shield is provided in a vacuum portion inside the funnel.

As the shield material, a special alloy such as permalloy having a large initial magnetic permeability or an inexpensive soft iron plate is used. The soft iron plate has a small initial permeability, so the effect is small as it is, but in the presence of a magnetic field to be shielded, it is degauss (usually translated as demagnetization,
Operation (not pure non-magnetization operation in the presence of an ambient magnetic field) can increase the effective permeability and is commonly used as such.

The degauss operation is an operation in which an alternating magnetomotive force is applied to the shield member in which the polarity of the shield material is magnetically saturated or larger and the positive and negative polarities are substantially symmetric and gradually decrease toward zero.

Assuming that this is done, the soft iron plate can obtain a shielding effect that is quite close to that of a special material such as permalloy with a similar configuration (plate thickness and shape).

However, as is well known, perfecting a magnetic shield is very difficult, and even in the case of the color cathode ray tube mentioned earlier, the usual shield is quite imperfect, If this is to be ensured, the thickness and area of the shielding material (for example, the surrounding ratio of the color cathode ray tube in question) must be increased.

However, such a shield is accompanied by an increase in the weight of the device and an increase in the price, and the degree of improvement in the effect is small for that. In particular, in the case of a color cathode ray tube, the fluorescent screen portion cannot be surrounded by a shielding material, so this tendency is remarkable.

According to a second method for eliminating the influence of unnecessary magnetism, a coil is wound around the device in question, and a continuous magnetic current is continuously applied to the coil during use of the device to cancel the unnecessary magnetism in question. There is also a way to actively create

However, this requires a new DC current source,
There is a drawback that power consumption increases, and furthermore, the direction of the current is problematic. The troublesome work of adjusting the direction of the DC current in the direction of canceling the magnetic field is required, and the effect is not practically applicable in any case.

The third method to eliminate the influence of unnecessary magnetism
There is a special method disclosed in Japanese Patent Publication No. 49-49. This is because a member exhibiting a magnetic shield function is disposed near a device that is not affected by unnecessary external magnetism, and the member exhibiting the magnetic shield function is magnetically saturated or positive or negative starting from an amplitude larger than that. The function of the magnetic shield is defined as the sum of the alternating supermagnetic force, whose polarity is almost symmetric and the amplitude gradually decreases, and another magnetomotive force that does not converge to zero until at least a predetermined time has elapsed and monotonically decreases toward zero. In this case, in addition to the members provided, the other magnetomotive force is applied in a direction to strengthen the unnecessary magnetism, which is a problem.

[Problem to be Solved by the Invention] This method can achieve a better effect than the first method if the size of the member corresponding to the magnetic shield is the same, and can be continuously performed during the use period of the problem device. Although it has the advantage that it is not necessary to keep the DC current flowing, for its practical use, it is necessary to know the direction of the unnecessary magnetism that originally exists in order to determine the direction of the above “another magnetomotive force”, and It is necessary to set a different direction of the magnetomotive force (adjustment of the direction of the flowing current, though temporarily), and there are many troublesome elements similar to the second method for the effect, and it is not necessarily practical. Was.

The present invention has been made in order to solve the above-described problems, and can be used without checking each direction of the magnetic field from which the influence should be removed. One specific direction (regardless of sign)
It is an object of the present invention to obtain a device for removing the influence of unnecessary magnetism, which is effective against unnecessary magnetism and can improve the magnetic shielding effect only by controlling the current waveform flowing through the degauss coil.

[Means for solving the problem]

An apparatus for removing influence of unnecessary magnetism according to the present invention includes a magnetic member having a magnetic shield function, a coil disposed close to the magnetic member, and a current waveform control circuit connected in series to the coil. The current waveform control circuit makes the peak value of the current flowing through the coil due to the external magnetism positive and negative asymmetric, and converges the current flowing through the coil to zero while maintaining the positive / negative asymmetric state. And two sets of impedance control circuits connected in anti-parallel.

[Action]

In the current waveform control circuit according to the present invention, an alternating current having an amplitude exceeding a level at which the magnetic member is magnetically saturated flows through the coil. And the current is gradually converged to zero while maintaining the asymmetric tendency, thereby eliminating the influence of unnecessary magnetism.

〔Example〕

Hereinafter, an embodiment of a device for removing influence of unnecessary magnetism of the present invention will be described with reference to the drawings. FIG. 1 is a circuit diagram showing the configuration of one embodiment, and FIG. 1 shows a color CRT as a device for eliminating the influence of unnecessary magnetism.

In FIG. 1, 1 is a color CRT,
It has a tube axis Z-Z1 and has the property of eliminating the influence of magnetism in this method. Reference numeral 2 denotes a magnetic member having a magnetic shielding function, which is made of a magnetic metal as described later. When a magnetic flux in the Z-Z1 direction is applied to the color cathode-ray tube 1, it surrounds a main portion of the color cathode-ray tube 1 so as to bypass the magnetic flux. In. Hereinafter, the magnetic member 2 is simply referred to as a magnetic shield.

Numeral 3 is a coil wound on the magnetic shield 2 in a plane orthogonal to the tube axis (to avoid the influence of magnetism in this direction). Reference numeral 4 denotes a current waveform control circuit which is a main part of the present invention, which is connected in series to the coil 3, and is supplied with an AC input from an input terminal 5. The details are described below.

As shown in the figure, the current waveform control circuits 4 in this embodiment are arranged in opposite directions (inverted symmetry) and in parallel with each other.
Two capacitors 11a, 11b having a relatively large capacity are connected in series with the respective emitters of the power transistors 10a, 10b.
Is connected.

Time constant adjusting resistors 12a and 12b are connected in parallel to the capacitors 11a and 11b, respectively. The emitter of the power transistor 10a is connected to a connection point B via a parallel circuit of a resistor 12a and a capacitor 11a. The connection point B is connected to one of the input terminals 5.

The connection point B is connected to the collector of the power transistor 10b via a diode 14b for preventing discharge of the capacitor 11b.

The emitter of the power transistor 10b is connected to the connection point A via a parallel circuit of a resistor 12b and a capacitor 11b. The connection point A is connected to the other of the input terminals 5 via the coil 3 and to the collector of the power transistor 10a via a diode 14a for preventing discharge of the capacitor 11a.

A posistor 13 is connected between the connection points A and B.
The posistor 13 is in parallel with the current waveform control circuit 4 as if it were short-circuited as a whole.

Next, the operation will be described. Member averse influence of terrestrial magnetism, i.e., it is assumed that the magnetic field H _E should shield the Z-Z1-direction of the color picture tube 1 is present. The magnetization curve (BH curve) of the material of the magnetic shield 2 is shown in FIG. And the magnetic field in the drawings are filled with H _E is due geomagnetism in question now magnetic field in the material to provide a saturation magnetic flux density, respectively + H _M, and -H _M.

Returning to FIG. 1, an AC power supply is connected to the input terminal 5 when the color cathode ray tube 1 operates in the same manner as the operation usually called degauss. At the beginning of this operation, it is assumed that the posistor 13 is in a conductive state and the current waveform control circuit 4 has no special function.

In this state, a current (initial current) flows through the coil 3, and the initial current is determined in the magnetic shield 2 at least under the influence of the back electromotive force due to the magnetic flux generated by the current itself.

Now, if this initial current when a no magnetic field H _E by geomagnetism in the magnetic shield 2 of FIG. 1, back and forth between the magnetic field + H _M and -H _M to give just saturation magnetic flux density, slightly larger than Number of turns, resistance,
It is assumed that the applied voltage has been adjusted in advance. It is assumed that the current in this case has a waveform as shown by a solid line 100 in FIG.

Then the Moto the presence of a magnetic field H _E by geomagnetism, if used to connect to the input terminal 5 of the same power source as described above, the change in the magnetic field in the magnetic shield 2 by the immediately following initial current fourth
Overall it is assumed that leaning to the right (towards the positive H when H _E is positive) around the substantially H _E as shown in 110 in the figure, the peak towards positive exceeds saturation field + H _M It will be.

The current I at this time has a waveform as shown by a dotted line 101 in FIG. 5, that is, the peak on the positive side becomes higher and the peak on the negative side becomes lower. The peak of the positive side becomes high when the value of the magnetic field H shown in 110 in Figure 4 exceeds the saturation magnetic field + H _M,
This is because the magnetic flux density B does not increase from there, and the back electromotive current which suppressed the increase of the current I suddenly decreases.

On the other hand, the opposite tendency appears to some extent in the negative peak, and the peak becomes lower on the contrary.

That is, when the terrestrial magnetism H _E is present, the coil 3 of FIG. 1
Large next peak of the initial current waveform when applying an alternating current magnetomotive force produced by it in the direction of strengthening the H _E in,
In the opposite direction, it is asymmetrical to a small extent.

Returning to FIG. 1, if the initial current waveform as described above continues for a while (several tens of cycles or less), the temperature of the posistor 13 increases, its resistance increases, and the current no longer flows through the posistor 13. The current flows through the power transistors 10a and 10b.

Now, the direction in which the current flows in the current waveform control circuit 4 from the connection point A to the direction B shown in the figure is defined as the positive direction in FIG.

Considering this positive half cycle, the capacitors 11a,
11b is not charged, so that it is considered to be in a conducting state when an alternating current is flown.Therefore, the power transistor 10a has the same potential at the base and the emitter, and the positive current is the connection point A-diode 14a-power transistor 10a
-Capacitor 11a (resistors 12a and 12b are assumed to be negligibly large when considering this phenomenon)-flow in the direction of connection point B.

At this time, a slight charge is stored in the capacitor 11a. Although a small amount of charge is stored in the capacitor 11b, it is small and negligible due to the base current of the power transistor 10a. Hereinafter, the base current is assumed to be sufficiently small.

Next, the current of the negative half cycle similarly flows in the direction of the connection point B, the diode 14b, the power transistor 10b, the capacitor 11b, and the connection point A. At this time, the base potential of the power transistor 10b is applied to the capacitor 11a. Since a small current blocking bias is applied due to the stored charge, a small amount of current flows in the negative direction shown by the dotted line 101 in FIG.

The above process is repeated, and each time the capacitor 12a,
The charge is stored little by little in 12b, but as is clear from the process described above, the capacitor 11a, through which the current in the positive direction, which initially had a large amount of current, passes through the capacitor 11b, through which the current in the negative direction passes. Many charges can be saved.

In the positive half cycle, the current flowing through the coil 3 is blocked by charging the capacitor 11a, and in the negative half cycle, it is blocked by the power transistor 10b being biased to the cutoff, and the current gradually decreases. The current hardly flows through.

Moreover, the current in the positive direction is consistently maintained larger during the process. (Note that the diodes 14a and 14b are arranged to prevent the charge once stored in the capacitors 11a and 11b from being discharged through the transistor circuit in the next half cycle).

That is, asymmetric initial current generated for existed originally H _E is maintained or proportionally enlarged current amplitude is reduced while, eventually hardly current flows. That is, a current as shown by 102 in FIG. 6 can be automatically passed through the coil 3.

If any terrestrial magnetism H _E is the above explanation the opposite direction that was initially present, who from the connection point B of the current towards the A is increased, the positive half cycle that the transistor 10a is cut off Blocking, capacitor 11 in negative half cycle
6 is stabilized in the state of being blocked by charging, and the waveform during this period is the reverse of that shown in FIG.

Furthermore, if the component of the geomagnetism in the Z-Z1 direction is zero from the beginning,
Then, the current of the positive half cycle (current flows from the connection point A to B) and the negative half cycle (current flows from the connection point B to A) of the power transistors 10a and 10b at least. The values are almost the same at the beginning of the flow.

In general, in such a circuit, a certain degree of characteristic variation is unavoidable, so that the charge that accumulates in one of the capacitors becomes larger than the other in several cycles of current reciprocation, and finally either Becomes the predominant unbalanced current waveform, which converges to zero, but if the peak of the current value becomes sufficiently small before the unbalance becomes noticeable, the degauss operation substantially known from the related art can be realized. The same effect will be obtained.

Eventually, as will be described later, the increase in the effect of the magnetic shield 2 due to the alternating current having a special waveform is automatically performed without performing the operation of measuring the direction of the terrestrial magnetism and setting the waveform accordingly. Become.

In order for this automatic waveform control to be performed stably, the charge is not stored very quickly in the capacitor 11a, and it is necessary that this be performed by repeating a number of cycles. The resistor 12a is also used for this purpose. Its value should be determined by experiment.

If this value is too small, the current will continue to flow through the coil 3 forever, which may adversely affect the operation of the device to be shielded, for example, the color cathode ray tube 1. A technology conventionally known as a degauss circuit in color television, such as connecting an element whose resistance becomes 0 with a certain time constant when a known voltage is applied, that is, a thermistor or the like in parallel with the coil 3. Can be applied.

This example is shown in FIG. In FIG. 2, reference numeral 15 denotes a thermistor. The time constant of the thermistor 15 must be larger than the time constant of the current waveform control circuit 4.

The posistor 13 is used to prevent the phase of the power supply voltage at the moment when the AC power supply is connected to the input terminal 5 from affecting the asymmetry of the current of the coil 3 later. For example in the example a positive previous H _E, if the AC power is turned on with a negative current flows phase, initially will be charged the capacitor 11b is earlier, quite the opposite to those required subsequent current waveform May be asymmetric.

The choice of the size of the resistors 12a, 12b mentioned above is also important in connection with such problems. If the resistances 12a and 12b are set low enough to reduce the charge per cycle,
13 may be omitted.

If the resistors 12a and 12b are reduced, a resistor such as the thermistor 15 described with reference to FIG. 2 is required, so that the resistors 12a and 12b can be configured by the posistor 13 from the beginning. It is.

This example is shown in FIG. In FIG. 3, 16a, 16
b is a posistor replacing the resistors 12a and 12b.

Returning to FIG. 1 again, this embodiment is effective when the unnecessary magnetic (geomagnetic) component is oriented in the Z-Z1 direction. It only gives the same effect as the shield and the usual degaussing operation (due to the symmetrically decaying alternating current).

However, in the case where the device that suppresses the influence of magnetism is the color cathode ray tube 1, the direction of the most harmful magnetism is often determined, so that the coil arrangement should be performed mainly considering the direction.

It is needless to say that the material of the magnetic shield 2 can be selected and the structure can be determined based on this method.

The gist of the present invention described above is that when a coil 3 having a winding surface orthogonal to the magnetism is provided in a magnetic substance placed in a space where unnecessary magnetism exists, and a sine wave AC voltage having an appropriate amplitude is applied thereto. If the impedance of the AC power supply is sufficiently low, the current waveform flowing is asymmetrical in the positive and negative directions. Based on this, the current waveform control circuit 4 is operated. The current waveform control circuit 4 need not be limited to the one described here.

In some cases, it is possible to make more precise ones using complex waveform analysis circuits.

Incidentally, the asymmetry of the current waveform can also be known approximately by the magnitude of the phase of the second harmonic component of the original AC power supply frequency. Therefore, the second harmonic component is detected and the current waveform control circuit 4 Of course, a method of determining the operation is also possible.

It goes without saying that auxiliary means for stabilizing the operation of the power transistors 10a and 10b can be considered even with a simple circuit as described in this embodiment.

Next, the principle that the current waveform control according to the present invention is effective in removing the influence of unnecessary magnetism will be described below.

First, the principle of a general magnetic shield will be described. In order to make the problem easy to understand, it is assumed to be a model. As shown in Fig. 7, a rod-shaped equivalent to a magnetic shield such as mild steel is placed in a space where a uniform unnecessary magnetic flux having a density B ₀ corresponding to geomagnetism exists. When a ferromagnetic rod ba (hereinafter simply referred to as a magnetic rod) is placed (a place to be placed is indicated by a dotted line in the figure), a place near the place, for example, a place indicated by an α point Consider how the magnetic flux density changes.

Now, FIG. 8 shows the state of the magnetic flux distribution when the magnetic rod ba is placed at the portion indicated by the dotted line shown in FIG. Considering the total magnetic flux crossing the X-XI plane in FIG. 8, the total magnetic flux at sufficiently far left and right must be the same as in FIG.

However, the magnetic flux tends to collect in the magnetic bar ba having a small reluctance, and therefore, α near the magnetic bar ba
Conversely, near the point, the magnetic flux density decreases. This is the principle of the magnetic shield.

That is, in order to obtain the effect of the magnetic shield, in FIG. 8, it is desirable to increase the number of magnetic fluxes passing through the magnetic rod ba, that is, the magnetic flux density.

FIG. 9 shows a so-called magnetization curve of the material of the magnetic rod ba for considering the change of the magnetic flux in the magnetic rod ba.
Now, the magnetized state of the magnetic rod ba will be described with reference to FIG.

For convenience of explanation, the magnetic flux density and the like in the magnetic rod ba slightly vary depending on the location inside the magnetic rod ba itself, but in the following description, it is considered as uniform.

Now, it is assumed that the magnetic rod ba is initially magnetically neutral, that is, in the state of the point 0 in FIG.

When such a magnetic rod ba is placed in a space having a magnetic flux density B ₀ corresponding to uniform geomagnetism as shown in FIG. 8, the magnetic state of the magnetic rod ba is at a point P (magnetic field H _P , magnetic flux Move to density _BP ).

At this time, as described above, the magnetic flux due to the terrestrial magnetism tends to gather in the magnetic body, so that B _P > B ₀ .

Further, the magnetic field H _P is smaller than the magnetic field in the space in the case of Figure 7 by the geomagnetism, which is magnetized slightly magnetic bar ba, as a result, the so-called self-down force occurs.

In order for the magnetic rod ba in FIG. 8 to at least increase the apparent effect as a magnetic shield for the point α, it is preferable that the value of the magnetic flux density _BP be as high as possible.

For this reason, in an apparatus such as an ordinary color television receiver, an operation called apparent degauss of the magnetic shield is performed so as to increase the effect of the magnetic shield.

Degauss operation of the magnetic shield is, as already mentioned, a strong alternating magnetomotive force (the magnetic field is used as it is by the alternating current of the electric light line) to the shield material, and this alternating magnetic force is positive and negative symmetry. This is an operation of gradually weakening while substantially maintaining, and finally converging to zero.

FIG. 10 shows a state in which a conventional degauss operation is performed on the magnetic rod ba in FIG. In FIG. 10, reference numeral 20 denotes a coil wound around the magnetic rod ba, and reference numeral 21 denotes the coil 20.
Shows a power supply for supplying a current to the power supply.

As shown in FIG. 11, the power supply 21 can supply the coil 20 with an alternating current whose amplitude decreases with time. The peak value of this current is such that at least in the first few cycles of the alternating current, a supermagnetic force sufficient to saturate the magnetic flux passing through the magnetic rod ba is generated.

FIG. 12 shows a change in magnetic state when a conventional degauss operation is performed on the magnetic bar ba in FIG. 8 as it is, and the magnetic state of the magnetic bar ba is at point P at first. However, when an alternating magnetomotive force is applied, the peak is sufficiently strong at first, and the point representing the state is the outermost circumference of the magnetization curve, that is, the point ab-b in FIG.
When the peak is slightly reduced, the apparent supermagnetic force due to the terrestrial magnetism and the alternating magnetomotive force due to the coil are added, that is, a
During part of the points alternating ultrasonic force is mutually subtracted phase by ultra force and coils on geomagnetic apparent against ready-for, i.e., c point is no longer pass status point, as a-b-c ₁ -d ₁ To follow a simple route.

Further, when the peak value of the alternating magnetic field becomes small, the state point does not pass through the point a, for example, the state point follows a path such as a ₁ −b ₁ −c ₂ −d ₂ , and the figure becomes small as it is. When the alternating supermagnetic force converges to zero, the magnetic state point of the magnetic rod ba is point P '(magnetic field H _P ′, not shown).
Move to the magnetic flux density _BP ').

At this time, as can be inferred from the convergence process as described above, the point P ′ is higher than the point P in FIG. 12, that is, _BP ′>
B _P , or in other words, the magnetic flux passing through the magnetic rod ba increases before the degauss operation is performed, and the magnetic flux density decreases by a corresponding amount near the point α in FIG. 8, resulting in a magnetic shielding effect. Will be enhanced.

In a general color television receiver, as shown in FIG. 13, the shapes and arrangements of the color cathode ray tube 1 and the magnetic shield 2 are different from the schematic one as shown in FIG. Compare FIG. 7 or FIG. 8 with the magnetic shield 2 on the magnetic rod ba, the degauss coil 3 on the coil 20 in FIG. 10, the alternating current supply device 4a on the power supply 21 in FIG. If one point in a portion substantially surrounded by the magnetic shield 2 in the cathode ray tube 1 corresponds to the point α, the same description as above can be applied in terms of the operation principle.

However, color TV receivers cannot perform degauss operation when the screen is displayed, so that this operation can be performed automatically when the screen is not displayed, for example, when the power switch is turned on. It is devised.

Hereinafter, returning to FIG. 8 again, the magnetic rod ba
By reducing the magnetic flux density near the α point, that is, in order for the magnetic bar ba to exhibit at least an apparently higher shielding effect on the space near the point, the magnetic bar ba It was important that the magnetic flux was concentrated.

In other words, in order to increase the shielding effect, after applying a degauss operation to the magnetic rod ba, the state point of the magnetic rod ba on the magnetization curve phase diagram as shown in FIG. Just do it up.

Incidentally, in FIG. 12, the point P 'is higher than the point P,
In other words, B _P <B _P ′ can be satisfied because, when the alternating supermagnetic force that attenuates while maintaining the positive and negative symmetries is applied to the magnetic rod ba as a degauss operation, the geomagnetism This is because the added alternating supermagnetic force is asymmetrical.

The method described here, focusing on this point, deliberately imparts an asymmetric characteristic to the magnetic shield, that is, the alternating supermagnetic force applied to the magnetic bar ba schematically shown in FIG. This is to improve the above shielding effect.

FIG. 14 shows the waveform of the alternating supermagnetic force when the degauss operation is performed on the magnetic bar ba of the model shown in FIG. 10 by this method, and the waveform of the current flowing through the coil 20 is shown in FIG.

This current waveform is classified as Category t ₁ of substantially symmetrical attenuating alternating electromotive force relative to the DC component I _0, attenuation period t ₂ of the DC component I ₀
It consists of The direction of the current I ₀ is a direction to increase further the magnetic flux by the geomagnetism passing through the magnetic rod ba, that is, it is assumed that the pick in a direction to strengthen the external magnetic field to be now shielding.

The description is returned to FIG. Given the effects of this degaussing operation in the state diagram of the magnetization curve, the end of the section t ₁ in Figure 14, i.e., at the time when the attenuation of the alternating damped ultrasonic force has been completed, the magnetization of the magnetic pole ba state, for example, the magnetic flux density B as P ₁ point moves to the place where the magnetic field H both are large. This is because a supermagnetic force of a DC component is applied from the outside.

Then the end of the partition t ₂ in Figure 14, i.e., at the time when the attenuation of the ultrasonic force due to the DC current component has been completed, the magnetization state of a magnetic material bar ba proceeds at such as P "point. This At this time, the point P "on the magnetization state diagram of the magnetization curve in FIG. 12 is necessarily located on the upper left as compared with the point P '.

This is, as is clear from the above operation, the magnetic rod ba
Is slightly permanent magnetized by the supermagnetic force generated by the direct current component.

However, because of this, the magnetic flux density in the magnetic rod ba, and therefore the total magnetic flux has increased, and as described above, the total magnetic flux crossing the X-XI plane in FIG. Taking into consideration that the magnetic flux must be the same as the total magnetic flux, the magnetic flux density can be further reduced at a point slightly away from the magnetic rod ba, for example, at a point such as the point α, as compared with the conventional degauss operation.

By the way, in the above description, it is a formal discussion focusing only on the magnetic flux density, and in fact, the magnetic rod ba is slightly permanent magnetized as is apparent from the above operation. Therefore, assuming that the point P ′ on the magnetization diagram of the magnetization curve in FIG. 12, that is, the distribution of the magnetic field lines corresponding to the completion of the conventional degauss operation is as shown by the solid line in FIG. At the point P ″ in the drawing, that is, at the time of completion of the degauss by this method, the fifteenth bar is attached to the magnetic rod ba.
It can be considered that magnetic lines of force indicated by dotted lines in the figure are newly added.

As a result, if the point generally considered is very close to the magnetic rod ba, for example, a point like the α ′ point in FIG. 15, a magnetic field opposite to the terrestrial magnetism may be generated, and This amount is the DC component I ₀ described in connection with FIG.
Greatly depends on the magnitude of the DC supermagnetism corresponding to.

However, even if a slightly opposite magnetic field is generated at a position very close to the magnetic rod ba, the magnitude of the DC supermagnetic force corresponding to the DC component I ₀ is adjusted appropriately to achieve the purpose. Certainly, the magnitude of the magnetic field at the point, for example the point α, and thus the magnetic flux density, can be significantly smaller than when a conventional degaussian operation is applied.

The following description is based on a model using the magnetic rod ba, but the same principle can be applied to a color CRT as shown in FIG.

To apply the unnecessary external magnetism to the color cathode ray tube 1, in the case of FIG. 13, if the tube axis Z-Z1 is in the direction of the unnecessary magnet, an alternating current supply for supplying a current to the degauss coil 3 is assumed. A current as shown in FIG. 14 may be supplied by the device 4a.

In this case, the direction of the DC component I ₀ of current, selects the undesired magnetic running through the time middle color CRT 1 in a direction such that substantially increases the size of the DC component I ₀ is related to FIG. 15 The selection should be made in consideration of the phenomenon described above.

According to experiments, if the symmetry of the geomagnetism, the size of the super-magnetic force due to the DC component I ₀ in the case of a color television receiver having a common magnetic shield, is within a few times of substantially super-magnetic force generated by the geomagnetism.

As is clear from the principle, this value is also related to the material of the magnetic shield, and should be mainly determined experimentally in combination with the selection of the material.

Since the magnitude and direction of the DC component I ₀ must be selected according to the direction of the color cathode-ray tube 1, in practice, the alternating current supply device 4a has a built-in device for changing the magnitude and magnetism of the DC component inside itself. Is preferred.

In the example of FIG. 13, this method is effective only for the component of the unnecessary magnetism parallel to the tube axis Z-Z1.

However, the same effect as that of a normal degauss is guaranteed for a component perpendicular to this.

In this method, the supermagnetic force applied to the magnetic shield does not have to be as shown in FIG.
For example, the one shown in FIG. 16 may be used. In essence, a positively and negatively symmetric damped alternating supermagnetic force starting from a sufficiently large amplitude and a supermagnetic force that monotonically decreases toward zero only in one direction without converging to zero at least earlier than this damped alternating supermagnetic force. Anything that can be regarded as the sum of

〔The invention's effect〕

As described above, according to the present invention, a magnetic member having a magnetic shielding function, a coil disposed close to the magnetic member, and a current waveform control circuit connected in series to the coil are provided. When a peak waveform of a current flowing through the coil is detected to be asymmetrical due to external magnetism while an alternating voltage whose voltage changes symmetrically is applied to the coil, the asymmetric tendency is maintained. The current flowing through the coil is gradually converged to zero while the current is flowing, so that the influence of the external magnetism can be effectively removed without sequentially examining the direction of the external magnetism, such as a shadow mask type color CRT device. There is an effect that a device for eliminating the influence of unnecessary external magnetism can be operated with high performance.

[Brief description of the drawings]

FIG. 1 is a circuit diagram of a device for removing the influence of unnecessary magnetism according to an embodiment of the present invention, FIGS. 2 and 3 are circuit diagrams showing another embodiment of the present invention, and FIG. 4 is a principle of the present invention. FIG. 5 is an explanatory diagram showing that an asymmetric current flows through a coil by the asymmetric magnetic field of FIG. 4, and FIG. 6 is a waveform diagram showing a current waveform of a current waveform control circuit according to the present invention. 7 and 8 are explanatory diagrams showing the relationship between the unnecessary magnetism and the magnetic shield for explaining the unnecessary magnetism removal according to the present invention, and FIG. 9 is a magnetization curve for explaining the unnecessary magnetism removal according to the present invention. FIG. 10, FIG. 10 is a view showing a state of performing a degauss operation on the magnetic rod in FIG. 8, FIG. 11 is a waveform chart showing a current of the coil in FIG. 10, and FIG. 12 is a magnetic rod in FIG. Magnetic field when degauss operation is performed Magnetization curves illustrating the change in state, 13
FIG. 14 is a diagram showing an example in which the magnetic member and the coil according to the present invention are applied to a general color receiver, FIG. 14 is a waveform diagram showing a current waveform for obtaining a magnetization curve in FIG. 12, and FIG. Is an explanatory diagram showing the state of distribution of magnetic field lines corresponding to the completion of the degauss operation in the magnetization curve of FIG. 12, and FIG. 16 is a waveform diagram showing a current waveform different from FIG. 14 for obtaining the magnetization curve of FIG. It is. 1 ... A device for eliminating the influence of unnecessary magnetism, 2 ... A magnetic member, 3 ... A coil, 4 ... A current waveform control circuit. In the drawings, the same reference numerals indicate the same or corresponding parts.

Claims (1)

(57) [Claims] A magnetic member having a magnetic shielding function;
A coil disposed in close proximity to the magnetic member; and a current waveform control circuit connected in series to the coil, wherein the current waveform control circuit has a peak of a current flowing through the coil due to external magnetism. It is configured by two sets of impedance control circuits connected in anti-parallel to make the value positively and negatively asymmetric, and to gradually converge the current flowing through the coil to zero while maintaining the positive-negative asymmetric state. Unnecessary magnetic influence removing device.