Electric lamp and discharge devices – Cathode ray tube – Plural beam generating or control
Reexamination Certificate
2000-02-29
2002-09-03
Patel, Ashok (Department: 2879)
Electric lamp and discharge devices
Cathode ray tube
Plural beam generating or control
C313S414000, C315S003000
Reexamination Certificate
active
06445117
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to a cathode ray tube, and in particular to a color cathode ray tube having an electron gun employing an internal voltage-dividing resistor.
Color cathode ray tubes used in TV receivers or information terminals, house an electron gun for emitting a plurality (usually three) of electron beams at one end of an evacuated envelope, a phosphor screen formed of phosphors coated on an inner surface of the evacuated envelope at the other end thereof for emitting light of a plurality (usually three) of colors, and a shadow mask which is closely spaced from the phosphor screen and serves as a color selection electrode. The electron beams emitted from the electron gun are deflected to scan the phosphor screen horizontally and vertically to form a rectangular raster by magnetic fields generated by a deflection yoke mounted externally of the evacuated envelope and display a desired image on the phosphor screen.
FIG. 12
is a cross-sectional view for explaining an exemplary configuration of a color cathode ray tube, and in FIG.
12
. In this color cathode ray tube, an evacuated envelope is formed by a panel portion
1
, a neck portion
2
and a funnel portion
3
, and electron beams
16
emitted from an electron gun
9
housed in the neck portion
2
scan a phosphor screen
4
two-dimensionally by being subjected to horizontal and vertical deflection magnetic fields produced by a deflection yoke
10
.
The electron beams
16
are modulated in amount by video signals supplied via stem pins
15
, are color-selected by a shadow mask
5
disposed immediately in front of a phosphor screen
4
, and impinge upon the phosphors of the corresponding primary colors to reproduce a desired color image. In
FIG. 12
, reference numeral
6
is a mask frame,
7
is a magnetic shield,
8
is a mask suspension mechanism,
11
is an internal conductive coating,
12
is a shield cup,
13
is a contact spring, and
14
is a getter.
Such cathode ray tubes employ a multistage focus lens system to obtain sufficiently small electron beam spots over the entire phosphor screen.
Japanese Patent Application Laid-open No. Hei 10-255682, for example, discloses an “extended field lens” serving as a main lens formed by disposing an intermediate electrode between an anode electrode and a focus electrode.
FIG. 13
is a schematic longitudinal cross-sectional view of an electron gun of a cathode ray tube disclosed in Japanese Patent Application Laid-open No. Hei 10-255682 and
FIG. 14
is a cross-sectional view taken along line XIV—XIV of the electron gun shown in FIG.
13
. The electron gun is of the extended field lens type comprising three equally spaced coplanar cathodes
309
(one for each electron beam), a first electrode
301
, a second electrode
302
, a third electrode
303
, a fourth electrode
304
, a 5-1st electrode (a focus electrode)
305
, a 5-2nd electrode (a focus electrode)
306
, an intermediate electrode
310
, a sixth electrode (an anode electrode)
307
and a shield cup
308
arranged coaxially in the order named from the cathodes
309
, and the cathodes and the electrodes are fixed in predetermined spaced relationship on a pair of glass beads
311
.
A voltage-dividing resistor
312
fabricated on a ceramic substrate is housed within the cathode ray tube to obtain a voltage to be supplied to the intermediate electrode
310
within the cathode ray tube, and the voltage-dividing resistor
312
is fixed to one of the glass beads
311
. A metal wire
314
a
surrounds the glass beads
311
and the voltage-dividing resistor
312
and is welded to the intermediate electrode
310
as shown in FIG.
14
.
The electrons emitted from the cathodes
309
are focused by a prefocus lens formed by the cathodes
309
, the first electrode
301
, the second electrode
302
and the third electrode
303
, next by a pre-main lens formed by the third electrode
303
, the fourth electrode
304
and the 5-1st electrode
305
, and then by a main lens formed by the 5-2nd electrode
306
, the intermediate electrode
310
and the sixth electrode
307
, onto a phosphor screen, and form an image on the viewing screen of the cathode ray tube.
The voltage applied to the intermediate electrode
310
is selected lower than an anode voltage, but higher than voltages applied to the focus electrodes by dividing the anode voltage using the voltage-dividing resistor
312
. Provision of the intermediate electrode
310
forms a lens of the extended field type in which the potential distribution along the tube axis is made gentle from the anode electrode to the focus electrodes, reduces spherical aberration and consequently the diameter of the electron beam spots is reduced.
As shown in
FIG. 14
, the amount of electrical charges accumulated on the inner wall of a neck glass
317
is stabilized by attaching the metal wire
314
a
to the intermediate electrode
310
such that the metal wire
314
a
surrounds the glass bead
311
and the voltage-dividing resistor
312
.
SUMMARY OF THE INVENTION
In the manufacture of a cathode ray tube, after the cathode ray tube has been exhausted of gases and sealed, so-called spot-knocking (high-voltage stabilization) of applying a high voltage of about twice the normal operating voltage for the cathode ray tube to its anode electrode is carried out to remove projections in electrodes of the electron gun or foreign particles within the cathode ray tube by forcing arcing between the electrodes and between the electrodes and the inner wall of the neck portion and to thereby prevent occurrence of arcing within the cathode ray tube during the normal operation of the completed cathode ray tube.
But, in a cathode ray tube employing the extended field lens formed by applying a voltage divided from the anode voltage using an internal voltage-dividing resistor to the intermediate electrode and the above-mentioned metal wire for suppression of discharge attached to and facing a focus electrode upstream of the intermediate electrode, when the spot-knocking of applying a high voltage of about 60 kV, for example, to the anode electrode is carried out with all the electrodes except for the anode electrode and the intermediate electrode being grounded, there has been a problem in that arcing occurs between the metal wire for suppression of discharge and the resistance element of the voltage-dividing resistor and consequently, an overcoat glass film covering a resistance element or an alumina ceramic substrate of the voltage-dividing resistor is often fractured, because the metal wire for suppression of discharge surrounding the voltage-dividing resistor is grounded and therefore a voltage difference of about 30 kV is produced between the metal wire and the resistance element.
It is an object of the present invention to provide a cathode ray tube incorporating an internal voltage-dividing resistor and having withstand voltage characteristics improved by heightening effects of spot-knocking sufficiently preventing fracture of the internal voltage-dividing resistor during the spot-knocking procedure.
A cathode ray tube in accordance with the present invention achieves the above object with the following representative configuration. A color cathode ray tube in accordance with the present invention is provided with a voltage-dividing resistor producing a voltage to be applied to one of focus electrodes of a focus lens for focusing an electron beam on a phosphor screen by dividing a voltage applied to an anode electrode and a metal conductor disposed to surround the voltage-dividing resistor for suppression of discharge. The voltage-dividing resistor comprises an overcoat insulating film, a resistance element and an insulating substrate stacked, and the resistance element comprises major resistance-forming regions disposed on opposite sides of the metal conductor where the resistance element extends meanderingly in a direction of a cathode ray tube axis, and another resistance-forming region containing a portion thereof facing the metal conductor where minimum distances L
1
and
Miyamoto Satoru
Noguchi Kazunari
Antonelli Terry Stout & Kraus LLP
Guharay Karabi
Patel Ashok
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