Inner shield coupling structure for CRT

Details Inner shield coupling structure for CRT Inner shield coupling structure for CRT

1999-09-17

2001-12-18

Patel, Vip (Department: 2879)

Electric lamp and discharge devices

Cathode ray tube

Shadow mask, support or shield

Reexamination Certificate

active

06331751

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an inner shield for cathode ray tube, and more particularly, to an improved inner shield capable of maintaining its tubular shape without distortion.
2. Description of the Related Art
A cathode ray tube (CRT) is generally used as an image displaying unit for television, computer monitors, etc. The CRT displays images by emitting visual rays when electron beams emitted from an electron gun hit a screen panel coated with red, green, and blue phosphors.
A CRT includes a screen panel for showing an image, an electron gun for emitting electron beams, a deflection yoke for deflecting a travel direction of electron beams, a shadow mask for transmitting electron beams, and a funnel holding the above elements.
The screen panel and funnel are sealed together for maintaining a vacuum inside the funnel such that electrons progress in a suitable manner therein.
The electron gun is installed inside the funnel, and the deflection yoke is circumferentially mounted around the funnel. The shadow mask is attached by welding to a mask frame, which is mounted inside the screen panel by means of springs and stud pins. The screen panel is patterned by red, green, and blue phosphors on an inner surface of the screen panel.
The elements such as the shadow mask, mask frame, and plate springs installed inside the CRT are made of ferromagnetic materials, i.e. Fe, such that the elements are magnetized to like poles according to variation of earth magnetic field, resulting in distorting the reflection of the electron beams. Accordingly, the electron beams may not hit correct phosphors.
In the conventional CRT, to solve the above described problems, an inner shield is mounted by using a clip on a rear part of the mask frame.
The inner shield is made out of a steel sheet having low permeability and in a similar shape with the funnel for preventing the reflection of the beam from being obstructed. The inner shield is either an integral type or a separable type of which two parts are assembled.
FIG. 5
is a drawing overlapping a development view with a top plane view of a prior art inner shield.
In
FIG. 5
, reference numeral
2
denotes workpieces cut and bent according to a predetermined design. In one workpiece
2
a
, a first protrusion part
4
is formed with indented portions
4
a
and
4
b
, and in the other workpiece
2
b
, a second protrusion part
6
is formed with a plurality of bands
6
a
and
6
b.
The inner shield is integrated by binding the bands
6
a
and
6
b
of the second protrusion part
6
around the first protrusion part
4
.
The inner shield includes opposite side walls
10
having windows
8
and flanges
12
continuously formed in a lower part of the side walls
10
. A central opening
14
is formed in a longitudinal direction of an axis of the CRT such that the electron beams pass through the central opening
14
. The flanges
12
are welded to the mask frame (not shown).
To assemble the inner shield precisely, widths of the indented portions
4
a
and
4
b
may be formed 2 mm wider than the width of the bands
6
a
and
6
b
such that a gap of approximately 1 mm is formed between side walls of the indented portion
4
a
and
4
b
and side edges of the bands
6
a
and
6
b
when the indented portions
4
a
and
4
b
are bound by the bands
6
a
and
6
b
. The inner shields assembled in this manner are typically stacked for subsequent process.
However, if a plurality of inner shields are stacked, the inner shields, except for the one on top of the stack, receive a load equal to the number of inner shields stacked thereon, such that gaps between the indented portions
4
a
and
4
b
and the bands
6
a
and
6
b
are distorted.
That is, a left side wall of the upper indented portion
4
a
and a left side edge of the upper band
6
a
contact each other, and a right side wall of the lower indented portion
4
b
and a right side edge of the lower band
6
b
contacted each other by concentration of the load.
Accordingly, the coupling portion of the first and second protrusions
4
and
6
droops so as to distort the contour of the inner shield. Particularly, the distortion of the central opening and the window deteriorates the ability of the inner shield to block the earth magnetic field so as to cause deterioration in purity of the CRT.
In more serious cases, the distorted inner shield obstructs the progress of the electron beams such that the electron beams do not reach the screen panel of the CRT.
SUMMARY OF THE INVENTION
The present invention has been made in an effort to solve the problems of the prior art.
It is an object of the present invention to provide an improved inner shield which prevents a central opening and window from being permanently distorted.
To achieve the above object, the inner shield of the present invention comprises a first protrusion having upper and lower indented portions, and a second protrusion having upper and lower bands, wherein the bands are formed asymmetrically.

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