JP2616068B2 - Cathode ray tube device - Google Patents

Description

Description: FIELD OF THE INVENTION The present invention relates to a cathode ray tube device having a novel magnetic shield device operated in a constantly changing environmental magnetic field.

[Conventional technology]

In a cathode ray tube of a type in which an electron beam is deflected in two directions perpendicular to each other horizontally and vertically and a raster is drawn on a fluorescent screen of the tube surface, the electron beam is deflected under the influence of an environmental magnetic field. It is not uncommon for the image projected on the screen to be unsightly.

Under the influence of an undesirable environmental magnetic field which is not expected at the beginning, an image may move from a position where it should be in the phosphor screen or may be distorted. Particularly, in a shadow mask type color cathode ray tube, an undesired phenomenon occurs in which the color purity is impaired due to the influence of an environmental magnetic field.

Therefore, in a cathode ray tube which is easily affected by an environmental magnetic field, for example, a shadow mask type cathode ray tube which is affected by terrestrial magnetism, a magnetic shield is provided around the cathode ray tube or inside the cathode ray tube in order to eliminate the influence of the environmental magnetic field. This magnetic shield is often made of an inexpensive soft iron plate. As is well known, a soft iron plate is a material having a relatively small initial magnetic permeability, and has almost no shielding effect against an environmental magnetic field which is relatively weak such as terrestrial magnetism but is harmful to a cathode ray tube. For this reason, a magnetic shield using a soft iron plate is subjected to a degauss operation (generally referred to as demagnetization) in order to reduce the shielding effect against environmental magnetic fields. This degauss operation is
By passing an alternating current starting from a sufficiently large value and gradually converging to zero through the coil wound around the magnetic shield, an alternating magnetic field (magnetomotive force) starting from a value sufficiently magnetically saturated and gradually converging to zero on the magnetic shield ) Is forcibly applied, thereby increasing the apparent permeability of the magnetic shield made of a soft iron plate to eliminate the influence of the environmental magnetic field. The reason why the shielding effect is improved when the apparent permeability of the magnetic shield is improved by performing the degauss operation is disclosed in, for example, Japanese Patent Publication No. 54-31649 (method for reducing the influence of unnecessary magnetism). Although the description is omitted, the degauss operation in the presence of the environmental magnetic field does not demagnetize or demagnetize the shield material.

In an ordinary household color television set, the coil for degauss operation and a circuit device associated therewith are built in the television set, and each time the power switch of the television set is turned on. Degauss operation is performed automatically, and a device is devised so that the magnetic shield works effectively.

It is very important that this degauss operation be performed in the presence of environmental magnetic fields that are expected to have deleterious effects. For example, a color television set that performs a degauss operation with the screen positioned eastward in the presence of a horizontal environmental magnetic field can almost eliminate the influence of the environmental magnetic field that is received while the screen remains eastward it can. However, if the screen of the color television set is replaced, for example, to the west, it is almost impossible to remove the influence of the environmental magnetic field on the west. In order to remove the influence of the environmental magnetic field when the screen is facing west, it is necessary to perform the degauss operation again in this state. The degaussian device for the degauss operation usually generates a very strong leakage magnetic field. During the degauss operation, the image of the color television set becomes completely unreadable due to the influence of the stray magnetic field because its stray magnetic field is not synchronized with the deflection state of the electron beam and is indefinite.

As described above, in order to prevent an adverse effect of an environmental magnetic field on a cathode ray tube, a magnetic shield of a soft iron plate provided with a degauss device is often used. However, the effect of the magnetic shield is effective when the environmental magnetic field is constant with respect to the cathode ray tube, but the effect of the magnetic shield is very small when the environmental magnetic field changes over time with respect to the cathode ray tube. Become.

Therefore, for example, in a cathode ray tube affected by a magnetic field due to geomagnetism or a DC current in a vehicle whose traveling direction changes or near a track of an electric railway where a large DC current constantly changes, the image is regarded as normal. In order to do this, special measures are required. As a first example of this ingenuity, it is conceivable that the magnetic shield is made of a material having a sufficiently high initial magnetic permeability, such as a permalloy alloy. However, for this purpose, it is necessary to use a special alloy containing a large amount of nickel component, and the magnetic shield becomes very expensive and is not useful.

Secondly, a method is conceivable in which an inexpensive shielding material such as a soft iron plate requiring a degauss device is used and the degauss operation is constantly repeated. In this case, since a strong magnetomotive force for degauss operation is applied to the magnetic shield, the electron beam is affected by the leakage magnetic field, and the image is significantly disturbed. Therefore, the degauss operation needs to be performed during a period when the electron beam is not scanning the phosphor screen. For this reason, it has been devised that the degauss operation is constantly and automatically performed during the retrace period of the raster, particularly during the period corresponding to the vertical retrace period in television.

[Problems to be solved by the invention]

Since the conventional cathode ray tube apparatus is as described above, it is necessary to perform the degauss operation in an extremely short period. For example, when the vertical scanning is performed 60 times per second, the vertical retrace period is one.
As less than 10% of the scanning period per time It is necessary to perform one degauss operation within this time. During this time, a large-scale circuit device is required to pass through the degauss coil an alternating decay current that generally converges to zero from a sufficiently large current by repeatedly repeating positive and negative for 10 cycles or more, and a circuit device for degauss operation. There was a problem that the cost of the system became high.

In addition, for example, when 10 cycles of alternating decay current are applied to the coil during 1/600 second, the frequency of the degauss current becomes 6000
Due to the Hz, the magnetic shield caused some mechanical vibration during degauss operation, generating abnormal noise, which was extremely annoying.

The present invention has been made in order to solve the above-described problems, and eliminates the influence of a change in an environmental magnetic field on a cathode ray tube without stopping the operation of the cathode ray tube and performing a degauss operation. An object of the present invention is to provide a cathode ray tube device that does not affect a picture by a leakage magnetic field generated by supplying a current to a coil for applying a magnetomotive force to a body and does not generate a high-frequency unpleasant abnormal sound. .

[Means for solving the problem]

A cathode ray tube device according to the present invention includes an electron gun for acceleratingly emitting an electron beam, a cathode ray tube having a phosphor screen on which the electron beam collides, a horizontal deflection of the electron beam at a constant cycle, and a horizontal deflection of the electron beam. A deflecting device that performs vertical deflection at a constant cycle larger than the cycle of the magnetic shield body made of a magnetic material arranged near the traveling path of the electron beam, and arranged around or near the outside of the magnetic shield body, A coil for generating a magnetic field in the magnetic shield, and a repetitive current having the same cycle as the vertical deflection of the electron beam by the deflection device and having the same waveform synchronized with the vertical deflection is supplied to the coil throughout the operation period of the cathode ray tube. And a power supply device for constantly applying a predetermined level of reciprocating magnetomotive force to the magnetic shield body.

(Operation)

In the cathode ray tube device according to the present invention, the power supply device has the same period as the period of the vertical deflection of the electron beam by the deflecting device and supplies a repetitive current of the same waveform synchronized with the vertical deflection to the coil throughout the operation period of the cathode ray tube. Thus, since a predetermined level of reciprocating magnetomotive force is always applied to the magnetic shield, the effective magnetic permeability of the magnetic shield can be maintained at a large value at all times.

Furthermore, since the repetitive current supplied to the coil by the power supply during the operation of the cathode ray tube is synchronized with the vertical deflection, the leakage magnetic field generated by repeatedly supplying the current to the coil during the operation of the cathode ray tube causes a traveling magnetic field of the electron beam. Even if the path is affected, the effect is synchronized with the vertical deflection.

Further, since the repetitive current supplied to the coil by the power supply device during the operation period of the cathode ray tube is the same as the period of the vertical deflection, the frequency of the mechanical vibration generated in the magnetic shield decreases.

〔Example〕

 Hereinafter, an embodiment of the present invention will be described with reference to the drawings.

In the present embodiment, as an example of a cathode ray tube device, a cathode ray tube device which has a horizontal and vertical deflecting device such as a television and draws a raster on a phosphor screen will be described as an example.

In FIG. 1, reference numeral 1 denotes a cathode ray tube device as a cathode ray tube device, which comprises the following components. 2
Is an electron gun 10 that accelerates and emits an electron beam according to the video signal
The cathode ray tube has a rear surface and a front surface, and a deflection yoke 3 is mounted between the electron gun 10 and the phosphor surface 11. The deflection yoke 3 includes a horizontal deflection circuit 12 for inputting a horizontal synchronization signal from an input terminal 12a and a vertical deflection circuit 13 for inputting a vertical synchronization signal from an input terminal 13a. A deflection current is supplied to deflect the beam in both the horizontal and vertical directions at a constant period.
This period is controlled to be constant in synchronization with the horizontal synchronizing signal and the vertical synchronizing signal supplied to each of the deflection circuits 12 and 13.

Reference numeral 4 denotes a magnetic shield which is disposed at least partially around the electron beam travel path of the cathode ray tube 2 and is made of a high permeability metal plate having a small coercive force such as a soft iron plate. Each has a conical cylindrical shape and an annular shape. In the present embodiment, the magnetic shield 4 surrounds the outer periphery of the cathode ray tube 2 between the mounting portion of the deflection yoke 3 and the fluorescent screen 11. Reference numeral 5 denotes a coil wound in a toroidal shape over the entire annular body of the magnetic shield 4, and is a repetitive signal of the same waveform having a constant period and generated by a synchronous oscillator 14 in synchronization with a vertical synchronous signal input from an input terminal 13a. The power amplifier 15
, A repetitive current having the same waveform and a constant cycle amplified by the above is supplied. 6 is a constant cycle in the coil 5 in synchronization with the vertical synchronizing signal.
This is a power supply device that supplies a repetitive current having the same waveform, and includes a synchronous oscillator 14 and a power amplifier 15.

Next, the operation of this embodiment will be described with reference to FIG. The electron gun 10 of the cathode ray tube 2 of the cathode ray tube device 1 accelerates and emits an electron beam toward the phosphor screen 11 according to the video signal. This electron beam is generated by a magnetic field from a deflection yoke 3 from which a deflection current having a cycle synchronized with the horizontal synchronization signal is supplied from the horizontal deflection circuit 12 and a deflection current having a cycle synchronized with the vertical synchronization signal is supplied from the vertical deflection circuit 13. The phosphor screen 11 is raster-scanned while being deflected horizontally and vertically at a constant period. As a result, an image corresponding to the video signal is displayed on the fluorescent screen 11 of the cathode ray tube 2.

On the other hand, in the cathode ray tube device 1, during the above-described operation of the cathode ray tube 2, a repetitive current having a constant waveform is continuously supplied to the coil 5 by the power supply device 6 in synchronization with the vertical synchronization signal. As a result, the magnetic shield 4 cuts the influence of the environmental magnetic field on the electron beam. The operation principle will be described in detail below.

FIG. 2 is a hysteresis curve (BH curve) showing the magnetic characteristics of the soft iron plate as the material of the magnetic shield 4.
The magnetic field generated at each point in the magnetic shield 4 by the current flowing through the coil 5 changes with a repetition of a constant waveform according to the coil current. Thus, assuming that the magnitude of the holding force of the magnetic shield body 4 is Hc, a predetermined level of reciprocal magnetomotive force is applied to the magnetic shield body 4 so as to reciprocate between + Hc and -Hc. Is set. If it is more than that, the leakage magnetic field inside the outside of the magnetic shield 4 increases, which is not preferable.

The dotted line in FIG. 2 is the initial magnetization curve 100. The gradient μ _i = tan ^{−1 of the} initial magnetization curve 100 near the origin.
_i (where _i is the angle between the H axis and the tangent of the initial magnetization curve 100 near the origin) is called the initial magnetic permeability. In the case of a material such as a soft iron plate, the initial magnetic permeability μ _i is considerably smaller than the magnetic permeability when the material is used as a normal ferromagnetic material in a magnetic field range that does not cause extreme magnetic saturation. This is the reason why the magnetic shield formed of a soft iron plate or the like has a small shielding effect against a weak environmental magnetic field and requires a so-called degauss operation.

Now, the case of applying a reciprocating magnetomotive force causing a magnetic field to the extent that reciprocates between the the magnetic shield 4 + H _c and -H _c by passing a reciprocating current to the coil 5 as described above,
The locus of the B (magnetic flux density) -H (magnetic field) state point in the magnetic material of the magnetic shield 4 becomes considerably complicated, and the coil 5
It cannot be explained simply because the waveform of the current flowing through is also involved.

However, when another small magnetic field ΔH is generated by the environmental magnetomotive force in the magnetic shield 4 to which the reciprocating magnetomotive force is applied by the reciprocating current, the magnetic flux density ΔB that passes through the magnetic shield 4 due to the magnetic field ΔH is considerably large. It will be big. That is, the effective permeability of the + H _c and the material of the magnetic shield member 4 with respect to small magnetic field ΔH separately from joining the reciprocating magnetomotive force of such a degree that reciprocates between the -H _c is considerably greater.

Such a method is known as a shaking effect of a magnetic shield, and is described, for example, in the literature: IEEE TRANSAC on magnetics (IEEE TRANSAC).
SIONS ON MAGNETICS), M.G.
4, July 1980, "Zefect of Jaking
On Magnetic Shields. "

Generally, when a reciprocating magnetomotive force (shaking magnetomotive force) of an appropriate frequency is applied to a magnetic material, an initial magnetization curve for a magnetic field ΔH due to an environmental magnetomotive force is generally called an ideal magnetization curve. The gradient near the origin becomes relatively steep. In the case of, for example, a soft iron plate material, this ideal magnetization curve does not show a so-called hysteresis phenomenon or a phenomenon in which the initial magnetic permeability decreases near the origin, as shown by a curve 101 shown by a dashed line in FIG.
That is, the magnetic shield 4 against the environmental magnetic field (magnetomotive force)
Is always maintained at a large value when the magnetic shield 4 is applied with a reciprocating magnetomotive force. For this reason, the magnetic shield 4 can exhibit the substantially highest shielding effect of the material without performing the degauss operation.

If the coil 5 is wound around the magnetic shield 4 in a toroidal shape as in the present embodiment, the leakage of the magnetic field for shaking into the outside of the magnetic shield 4 is minimized. Because of this, a strong leakage magnetic field
It does not act directly on the electron beam inside, and the appearance of undesirable symptoms on the image can be minimized. The shaking magnetic field generated by the energization of the coil 5 is applied to the magnetic shield 4 as shown by an arrow 102 in FIG.
It goes around inside and hardly leaks outside the magnetic shield 4. However, in practice, the shaking magnetic field flowing through the coil 5 is so large that the shaking magnetic field leaks somewhat into the electron beam traveling space of the Fraun tube 2 and tends to have an undesirable effect on the image. In order to prevent this, the shaking current flowing through the coil 5 is repeated by the power supply device 6 with a constant waveform synchronized with the vertical synchronization signal. The vertical deflection current 103 flowing in the deflection yoke 3 and having a waveform shown in FIG. 4 (a) and the shaking electrode 10 having a waveform shown in FIG. 4 (b) simply reciprocating once between positive and negative peaks.
4 is synchronized with the vertical deflection current 103 because it is synchronized with the vertical synchronization signal. Accordingly, even if the shaking magnetic field leaks and affects the trajectory of the electron beam in the cathode ray tube 2, the effect is synchronized with the deflection of the electron beam by the magnetic field of the deflection yoke 3. That is, the position at which the electron beam repeatedly arrives is constant at each location of the phosphor screen at the same phase, and the temporal change phenomenon such as image distortion does not appear, and is always constant for the same video signal. If image distortion occurs, the image distortion can be eliminated by appropriately arranging a small permanent magnet near the electron beam exit of the deflection yoke 3. If there is a problem with the color purity of the shadow mask type color cathode ray tube, the problem can be eliminated by modifying a correction lens for printing the phosphor screen. When these inconvenient phenomena occur, undesired symptoms in the image can be removed using known correction methods for the phenomena.

In FIG. 4 (b), the shaking current 104 is a sinusoidal one. However, the shaking current 104 is not limited to this, and may have the same waveform as the vertical deflection current 103 as long as it has a sufficient magnitude and stability. In some cases, the vertical deflection current itself may be used also as the shaking current. The shaking current only needs to generate a repetitive magnetic field of a certain magnitude in the magnetic shield body. If the magnitude of the amplitude is appropriate, the shaking current does not necessarily have to be positive / negative symmetric. It is not necessary to limit to a) and (b).

Also, if the environmental magnetic field to be shielded changes relatively slowly and the effect of this change during one cycle of shaking (eg, one vertical scan period) is almost negligible to the image, then The king current may be such that a portion where the current is zero repeatedly appears for a predetermined time like the current 104a shown in FIG. 4 (c).

Furthermore, the shaking current is a repetitive signal waveform whose fundamental wave is synchronized with the fundamental wave of the vertical synchronization signal (thus, generally 50 to 60).
(Frequency of Hz), but the present invention is not limited to this, and it is sufficient if the frequency is synchronized with the deflection of the electron beam. However, shaking with a fundamental wave having a frequency higher than the order of the vertical deflection frequency causes problems such as generation of eddy current generated in the magnetic shield, generation of noise due to vibration of the magnetic shield, and generation of electromagnetic interference (EMI). And is not necessarily recommended. It has been stated that if an undesirable phenomenon of the image caused by the leakage of the shaking magnetic field appears, it can be corrected by a known method.However, in order to make this correction possible, the image generated by the influence of the leakage magnetic field of the electron beam must be corrected. It is important that undesired phenomena such as distortion appear on the phosphor screen in as simple a form as possible. Therefore, it is best that the shaking magnetic field, that is, the shaking current simply reciprocates once between a positive peak and a negative peak during one cycle of vertical deflection without a local maximum or minimum. This is preferable also from the viewpoint of economical efficiency of the power supply device.

Although a soft iron plate was used as a material for the magnetic shield, a phenomenon in which the initial permeability is smaller than the initial permeability according to the ideal magnetization curve is generally observed for any magnetic material. The effect of the magnetic shield can be further improved by using a material such as a permalloy.

Moreover, although a cylindrical thing was used as a magnetic shield body,
It is not limited to the cylindrical shape, and may be a flat annular shape. For example, a pair of coils formed by winding a coil in a toroidal shape around this annular magnetic shield body may be disposed so as to be opposed to the upper and lower sides of the traveling path of the electron beam. good.

Further, the coil may not be wound in a toroidal shape, and a planar spiral coil may be arranged near the outside of the magnetic shield. Also in this case, the shaking magnetic field generated by the energization of the spiral coil passes through the magnetic shield.

The present invention can be variously modified and applied in addition to the above.
The combination of the magnetic shield and the coil may have any other shape as long as attention is paid to leakage of the shaking magnetic field.

As described above, a cathode ray tube device has been described as an example of the cathode ray tube device. However, the application of the present invention is not limited to the cathode ray tube device, but is also applicable to an imaging tube device using a cathode ray tube. The deflection of the electron beam is not limited to the electromagnetic deflection by the deflection yoke, but may be an electrostatic deflection.

〔The invention's effect〕

According to the cathode ray tube device of the present invention, the power supply device has the same period as the period of the vertical deflection of the electron beam by the deflecting device and supplies a repetitive current of the same waveform synchronized with the vertical deflection to the coil throughout the operation period of the cathode ray tube. By applying a predetermined level of reciprocal magnetomotive force to the magnetic shield, the effective magnetic permeability of the magnetic shield can always be maintained at a large value, and the operation of the cathode ray tube can be performed even when the environmental magnetic field changes. , The influence of the environmental magnetic field on the cathode ray tube can be eliminated without performing the degauss operation.

Furthermore, since the repetitive current supplied to the coil by the power supply unit during the operation of the cathode ray tube is synchronized with the vertical deflection, the leakage magnetic field generated by repeatedly supplying the current to the coil affected the traveling path of the electron beam. However, since the influence is synchronized with the vertical deflection, there is no phenomenon that the image is distorted due to the leakage magnetic field.

Furthermore, since the repetitive current supplied to the coil by the power supply unit during the operation period of the cathode ray tube is the same as the period of the vertical deflection, the frequency of the mechanical vibration generated in the magnetic shield becomes low. No unpleasant abnormal sounds.

[Brief description of the drawings]

FIG. 1 is a configuration diagram of a cathode ray tube device according to one embodiment of the present invention, FIG. 2 is a BH curve diagram for explaining the principle of one embodiment of the present invention, and FIG. FIG. 4 is an explanatory view showing a relationship between the coil and a coil wound in a toroidal shape.
The figure is a signal waveform diagram showing the timing of the vertical deflection current and the current flowing through the coil. In the figure, 1 ... CRT device, 2 ... CRT, 3 ...
... deflection yoke, 4 ... magnetic shield, 5 ... coil,
6 ... power supply unit, 10 ... electron gun, 11 ... phosphor screen, 12 ...
Horizontal deflection circuit, 13 Vertical deflection circuit, 14 Synchronous oscillator, 15 Power amplifier. In the drawings, the same reference numerals indicate the same or corresponding parts.

Claims (1)

(57) [Claims] An electron gun for acceleratingly emitting an electron beam, a cathode ray tube having a phosphor screen on which the electron beam collides, a horizontal deflection of the electron beam at a constant cycle, and a cycle of the horizontal deflection. A deflecting device that performs vertical deflection at a large fixed period; a magnetic shield body made of a magnetic material disposed near the traveling path of the electron beam; and a magnetic shield body disposed around or outside the magnetic shield body.
A coil for generating a magnetic field in the magnetic shield body, and a repetitive current having the same cycle as the vertical deflection of the electron beam by the deflection device and having the same waveform synchronized with the vertical deflection throughout the operation period of the cathode ray tube. A cathode-ray tube device comprising: a power supply device that constantly applies a predetermined level of reciprocating magnetomotive force to the magnetic shield by supplying the coil to the coil.