JPS6285592A - Color cathode ray tube - Google Patents

Abstract

PURPOSE:To prevent the occurrence of a color blurring phenomenon on a large- sized color cathode ray tube by installing a degaussing coil inside an external magnetic shield with the prescribed plate thickness, which encloses from a funnel part to the forward side part of a panel part. CONSTITUTION:The external magnetic shield EMS4 exists expanding to the front of the color CRT1 in order to cover practically the entire part of the panel 1P as well as the funnel 1F. A magnetic cancel coil 2 or a pair of magnetic cancel coils 3a and 3b are interposed between the CRT1 and the EMS4. Thus even a clearance between a screen and a shadow mask can be covered by the EMS4, whereby external magnetic fluxes in directions E/W and BV can be effectively reduced.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application] This invention relates to a color cathode ray tube having a magnetic shield.

[Conventional technology]

Measures against unnecessary external magnetism such as earth's magnetism in color cathode ray tubes that are currently in common use are shown in Figure 3 (a).
) as shown in color cathode ray tube (1) (color CRT
Internal magnetic shield plate (1 et al.) (abbreviated as IMS) attached to the shadow mask (1 &) inside the shadow mask (1&) (abbreviated as IMS) -Internal Magnetic Shie
ld). This IM
S (1b) is generally composed of an iron plate, and includes a degaussing coil (8
) is designed to provide a magnetic shielding effect and make it difficult for external magnetic fields to affect the electron beam inside the color CRT (1). Before the so-called IMS method using the above-mentioned IMS (To) became mainstream as a countermeasure against external magnetism for color CRTs (1), the mounting of color CRTs (11) was used as shown in Figure 3(b). is an external magnetic shield plate ([31 (EMS) of the type that locks with the hole in the lug (7)
Abbreviated as -External Magnetie 5
A shield (shield) is provided outside the color CRT (11).

Here, (5) shown in Fig. 3 (a) and (b) is the deflection.
Although it covers most of the funnel (IF) of fil,
Most of the panel (IP) is uncovered and therefore
Its magnetic shielding effect is insufficient, it is bulky inside a color television receiver, it is expensive, and its installation increases the amount of work, so it is gradually no longer used. IM shown in a)
The S method has become the mainstream and is widely used.

On the other hand, recently there has been a trend toward larger size color CRTs (11), and models of around 40 inches have been developed, especially for high-definition TVs.
As the size of the illumination progresses, the travel distance of the electron beam from the electron gun to the screen increases dramatically, making it extremely difficult to take measures against external magnetism. Figure 4 shows 3 finches 11
4
The figure plots the amount of horizontal electron beam landing shift on the phosphor screen at the corner of the screen when the external magnetic field is changed by 0.8 Gauss. The reason why the amount of horizontal electron beam shift is shown in Fig. 4 is that the phosphor screen of a 3-inch 110° a color CRT is assumed to have a striped structure, whereas in a dot structure it is vertical. Although the amount of directional electron beam shift is also a problem, an example of a stripe structure will be explained here.

In FIG. 4, E/Wl means a magnetic field in the east-west direction, N/S means a magnetic field in the north-south direction, and BV means a magnetic field in the vertical direction. As is clear from Figure 4, each IMS, EMS
Each NONXMS that is not provided.

It is clear that in the NONEMS method, the amount of movement of the electron beam is extremely large except in the E/W direction, making it useless.

Similarly, in Fig. 4, the color CRT (IMS system) in a conventional color television receiver, although the movement of the electron beam is considerably suppressed, does not reach the practical limit of movement of 150 μm. This limit movement amount differs depending on the type of color CRT film, but in this example, the 3-inch 110° deflection color CRT
Now, let's move on to the above limit! The value of l amount (150 μff1) is a value that is a guideline for whether or not it can be put to practical use. Therefore, the EMS method shown in FIG. 3(b) described above has a further problem in that the amount of electron beam movement is larger than the IMS method shown in FIG. 3(a), making it impractical.

The amount of movement of the electron beam in Fig. 4 is EM 5 (61, I M S (1
b), shadow mask (1a), etc., with a hand-type degaussing coil, and shows the amount of movement after sufficiently degaussing the color 〇 RT (11) from the outside.In actual practical conditions, color c RT (Demagnetization is performed by a degaussing coil (8) wound around the IJ.

[Problem that the invention seeks to solve]

However, in ultra-large color CRTs such as those with a 3-inch 110-degree deflection, the magnetized volume increases, resulting in poor demagnetization efficiency in the degaussing coil.Also, as a measure to reinforce the ultra-large external magnetic shield, the board thickness is increased. A method has been adopted,
After all, this deteriorates the demagnetization efficiency.

This invention was made in order to solve such problems, and in large inch-sized color CRTs, it optimizes the relationship between the reinforcing measures for the ultra-large external magnetic shield and the demagnetizing efficiency of the demagnetizing coil. The objective is to obtain a color cathode ray tube with practical external magnetic countermeasures that suppresses the amount of movement of an electron beam relative to a magnetic field, obtains an extremely large shielding effect, and eliminates color shift.

[Means for solving problems]

The color cathode ray tube according to the present invention is provided with an external magnetic shield plate having a shape that integrally surrounds the funnel part to the front of the side surface of the panel part continuing from the funnel part, and the thickness of the external magnetic shield plate is 0.5.
-1.5 ms, and a demagnetizing coil is provided inside this external magnetic shield plate.

[For production]

In the color cathode ray tube according to the present invention, an external magnetic shield plate is provided on the outside of the color cathode ray tube to cover most of the funnel and panel side surface to reduce the amount of movement of the electron beam due to the external magnetic field, and the degaussing coil is connected to the external magnetic shield plate. By providing the external magnetic shield plate inside the magnetic core, an efficient demagnetizing effect can be obtained using the external magnetic shield plate as the magnetic core, making it possible to reduce the weight of the external magnetic shield.

〔Example〕

FIG. 1(a) is a perspective view showing a color cathode ray tube used in a color television receiver which is an embodiment of the present invention;
FIG. 1(b) is a schematic side sectional view of the color cathode ray tube shown in FIG. 1(a). In the figure, (1) is color CR
T, (IF) is tyler-CRT (11(7)77
Funnel, (IP)l; tColor CRTfl) Nozf*le, +41 Color CRT (1) Funnel (IF
) and an external magnetic shield plate (EMS) that covers most of the side surfaces of the panel (IP).
S (41c, Fig. 3(b) d shows E M S +
Unlike 81, there is a panel (I) outside the funnel (IF) U.
As shown in Fig. 1(b), it has a structure that extends to a considerable extent in front of the color CRT (11) so as to cover most of the color CRT (11). Magnetic cancellation coils (3m) and (3b) are a pair of magnetic cancellation coils for external magnetic fields in the E/W direction, and a magnetic cancellation coil (2) is installed between the color CRT (1) and the EMS (4). or, in some cases, a pair of magnetic cancellation coils (3m
), (3b) are interposed.

Note that the pair of magnetic cancellation coils (3m) and (3b) are omitted in FIG. 1(b) for convenience of explanation of the drawing. In addition, (5) is a deflection yoke, (7) is a lug for attaching a color CRT, and (9) is an E M S (41
This is a degaussing coil installed inside the

The color CRT (11) shown in FIGS. 1(a) and (b), as is clear from FIG.
S (41 alone or E M S (41 and the third
In the magnetic shielding method that combines the conventional IMS (lb) shown in Figure (a), both conventional IMS
The amount of movement of the electron beam is significantly reduced compared to the single system (lb), and in particular, the amount of movement of the electron beam is reduced to less than the limit amount (150μ111) for external magnetic fields in each E/W direction and BV force direction. There is.

However, the amount of movement still exceeds the limit for the external magnetic field in the N/S direction. The reason for this is that color CRT
(This is due to the physical restriction that it is not possible to cover the screen of the image projection part, which is the front of the 11, with a magnetic shield plate. However, the above
The reason why M S (41) is effective against external magnetic fields in the E/W and B directions is thought to be due to the configuration in which the air gap between the screen and the shadow mask is also covered by E M S (41). In particular, it is very effective for color CRTs (11) because the above-mentioned dimensions become large in the case of large inch size.

Now, regarding the external magnetic field in the N/S direction at E M S +41, the limit movement amount of the electron beam is exceeded, resulting in insufficient magnetic shielding. Regarding this lack of magnetic shielding, as shown in Figure 1 (a) and (b), color C
RT (number 10 to number 10 provided to surround the outer circumference of 11
By interposing a ring-shaped magnetic canceling coil (2) wound with 0 turns inside the EMS (41) and passing a direct current through this magnetic canceling coil (2), as shown in FIG. By generating a canceling magnetic field (indicated by a solid line in Fig. 2) to cancel the magnetic field (indicated by a broken line in Fig. 2), and making it appear that the above external magnetic field does not exist, it is possible to effectively Movement of the electron beam can be prevented.In such a system, the E M S
It is possible to generate the above canceling magnetic field very efficiently using +41 as the magnetic core. For example, the amount of current required for the magnetic cancellation coil (2) to cancel an external magnetic field in the N/S direction of 0.3 gauss was 4 ampere-turns (AT). This is IM
In the case of a single S system, the amount of current required to cancel the external magnetic field in the same manner is approximately 172, which means that the ampere-turn efficiency is twice as good (four times as much in terms of power efficiency). Furthermore, in the case shown in Fig. 4, the magnetic shield is sufficient against the external magnetic field in the BV force direction, but there is no practical problem with the external magnetic field in the E/W direction. It is approaching the limit of movement 1. In this case,
As shown in Fig. 1(a), a pair of magnetic cancellation coils (3m) are placed opposite the side surface of the color CRT fil.
, (3b) is interposed between the color CRT (11) and the EMS (41) in the same way as the magnetic cancellation coil (2), and the above pair of magnetic cancellation coils (3m),
It can be corrected by applying direct current to (3b).

Figure 5 shows a 3-inch 110-degree deflection color CRT model.
FIG. 3 is an explanatory diagram showing the relationship between the plate thickness of S (41) and the amount of movement of the electron beam by the magnetic cancellation coil (2).

Figure 5 shows the external magnetic field in the N/S direction, which is a particular problem.
．． It shows the amount of movement of the electron beam in a part of the screen corner when changing by 8 Gauss, and shows the amount of movement of the electron beam after sufficient demagnetization with a hand-type degaussing coil! II (a). As is clear from FIG.
As a result of investigating the demagnetizing characteristics of the conventional type degaussing coil (8) installed around the outer periphery of a color CRT using M S (41), the values shown by the dot-dash dot (b) in Figure 5 were obtained. E M S (For 41, as the magnetized volume increases, the degaussing ability decreases.In order to match the characteristic (a) of the hand type degaussing coil, the ampere turns of the degaussing coil must be increased. According to experiments conducted by the inventor using the demagnetizing filter (9) of the present invention shown in FIG.
) As shown in <, up to the plate thickness of EMS (41) around 1.5 -, the demagnetizing effect can be equivalent to that of using a hand-type degaussing coil. (This is because it generates a magnetic field.In actual practical use, the E M
is the effective plate thickness range.

〔Effect of the invention〕

As explained above, this invention provides an external magnetic shield having a shape that integrally surrounds the area from the funnel part to the front of the side surface of the panel part, and has a thickness of 0.5 to 1 mm.
5■ range, and a degaussing coil is installed inside this external magnetic shield, so that a degaussing effect comparable to that of a hand-type degaussing coil can be obtained, especially for large inch-sized color cathode ray tubes. This has the excellent effect of practically eliminating the problem of color shift by reducing as much as possible the large amount of movement of the electron beam caused by the external magnetic field, which is unique to this method.

[Brief explanation of drawings]

FIG. 1(a) is a perspective view showing one embodiment of this explanation;
Figure (b) is a schematic side sectional view of the color cathode ray tube shown in Figure 1 (a), Figure 2 is a diagram for explaining the operation of the color cathode ray tube shown in Figure 1 (a), and Figure 3 is a schematic side sectional view of the color cathode ray tube shown in Figure 1 (a). A diagram for explaining the magnetic shielding method for a color cathode ray tube. FIG. 4 is an explanatory diagram showing the relationship between the magnetic shielding method and the movement amount of an electron beam for a 3-inch 110° a color cathode-ray tube. FIG. FIG. 3 is an explanatory diagram showing the relationship between the thickness of the external magnetic shield of the °-deflection color cathode ray tube and the amount of movement of the electron beam. 1...Color cathode ray tube, IP...panel, IF...
Funnel, 4 - External magnetic shield plate, 9 - Demagnetizing coil ◎ In each figure, the same reference numerals indicate the same or equivalent parts.

Claims (1)

[Claims] The external magnetic shield is constructed in a shape that integrally surrounds the funnel part to the front of the side surface of the panel part following this, and the thickness of the external magnetic shield is set in the range of 0.5 to 1.5 mm,
A color cathode ray tube characterized in that a degaussing coil is provided inside the external magnetic shield.