Electric lamp and discharge devices – Cathode ray tube – Plural beam generating or control
Reexamination Certificate
2002-05-28
2004-03-16
Patel, Vip (Department: 2879)
Electric lamp and discharge devices
Cathode ray tube
Plural beam generating or control
C313S269000
Reexamination Certificate
active
06707244
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates generally to a cathode-ray tube (CRT) apparatus, and more particularly to a CRT apparatus having an electron gun assembly capable of effecting dynamic astigmatism compensation.
2. Description of the Related Art
In general terms, a color CRT apparatus comprises an in-line electron gun assembly that emits three electron beams, and a deflection yoke that produces deflection magnetic fields for deflecting the three electron beams emitted from the electron gun assembly and causing them to horizontally and vertically scan the phosphor screen. The deflection yoke produces non-uniform magnetic fields comprising a pincushion-shaped horizontal deflection magnetic field
74
, as shown in
FIG. 11
, and a barrel-shaped vertical deflection magnetic field.
An electron beam
63
(B, G, R) that has passed through the non-uniform magnetic fields suffers a deflection aberration, i.e. astigmatism due to the deflection magnetic fields. Specifically, the electron beam
63
traveling to a peripheral portion of the phosphor screen suffers a force as indicated by arrows
a
and
b
by the deflection magnetic field
74
. Consequently, as shown in
FIG. 12
, the beam spot on the peripheral portion of the phosphor screen deforms to have a vertically elongated low-luminance halo portion
76
and a horizontally elongated high-luminance core portion
75
. Such deformation of the beam spot occurs at peripheral portions of the screen in the vertical direction V, horizontal direction H and diagonal direction D, as shown in FIG.
13
. The deformation considerably degrades the resolution.
In order to improve the degradation in resolution, an electron gun assembly has been proposed, for example, in Jpn. Pat. Appln. KOKAI Publication No. 3-93135 and Jpn. Pat. Appln. KOKAI Publication No. 3-95835. In the proposed electron gun assembly, as shown in
FIG. 14
, a fourth grid G
4
and a sixth grid G
6
are supplied with a dynamic focus voltage obtained by superimposing an AC component E
4
varying in synchronism with the deflection magnetic fields upon a DC voltage E
3
. Thereby, a first quadrupole lens is created between the third G
3
and fourth grid G
4
, and a second quadrupole lens is created between the fifth grid G
5
and sixth grid G
6
.
In this electron gun assembly, the first quadrupole lens corrects image-magnifications which differ in horizontal and vertical directions. At the same time, the second quadrupole lens and an ultimate focusing lens, which is created between the sixth grid G
6
and seventh grid G
7
, function to prevent the electron beam
63
, which is ultimately deflected onto the peripheral portion of the screen, from being extremely deformed by the deflection aberration due to the deflection magnetic fields.
With the deflection of the electron beams, potential differences vary between the fourth grid G
4
and sixth grid G
6
supplied with the dynamic focus voltage, on the one hand, and the adjacent third grid G
3
, fifth grid G
5
and seventh grid G
7
, on the other. Accordingly, the coulomb force varies between the grids G
3
through G
7
. Owing to the variation in coulomb force, mechanical vibrations occur in the grids G
3
through G
7
. The mechanical vibrations are transmitted to the funnel via insulating supports, which support the grids G
3
to G
7
, and stem pins electrically connected to the grids G
3
to G
7
. Consequently, the funnel vibrates, and abnormal noise is produced from the funnel.
The third grid G
3
is a main factor that increases the amplitude of vibration of the funnel. The first reason is that the distance between the third grid G
3
and fourth grid G
4
is narrower than that between the third grid G
3
and second grid G
2
. Thus, the variation in coulomb force between the third grid G
3
and fourth grid G
4
is greater than that between the second grid G
2
and third grid G
3
, and vibration easily occurs between the third grid G
3
and fourth grid G
4
. The second reason is that the third grid G
3
is formed of a plate-shaped electrode. Therefore, compared to a cup-shaped electrode body such as the fifth grid G
5
that extends in the tube-axis direction, the third grid G
3
has a lower flexure rigidity to vibration in the tube-axis direction and tends to vibrate easily.
More specifically, the third grid G
3
is a plate-shaped electrode and is supported and fixed by insulating supports at its upper and lower portions. The coulomb force acting between the electrodes is mainly applied to an intermediate portion between the two support points at the upper and lower portions of the third grid G
3
when the third grid G
3
is supported at these two points. Consequently, as shown in
FIG. 16
, the third grid G
3
flexes in the tube-axis direction and vibrates.
The vibration occurring at the third grid G
3
and fourth grid G
4
is modulated while being transmitted to the funnel. The vibration is frequency-modulated or increased by a resonance phenomenon due to the frequency of the dynamic focus voltage and the natural vibration characteristics of the third grid G
3
and fourth grid G
4
in the tube-axis direction. Consequently, the funnel vibrates at audio frequencies (20 Hz to 20 kHz) and produces abnormal noise. The natural vibration characteristics, that is, the characteristic frequency, are determined by the distance between the paired insulating supports that fix the electrode, the thickness of the electrode, the hardness of the electrode material, the electrode structure, etc.
In particular, when such a high-frequency voltage as to vary in synchronism with the horizontal deflection magnetic field is applied as the dynamic focus electrode, abnormal noise at a higher level may be produced due to resonance. Moreover, it has been made clear by experiments that the abnormal noise increases as the fourth grid G
4
and sixth grid G
6
supplied with the dynamic focus voltage are disposed closer to the cathodes K (on the stem section side) accommodating heaters.
The reasons appear to be that (1) the stem pins are firmly fixed to the stem section by means of welding, and so vibration occurring in each grid may easily be transmitted, (2) the electrode supplied with the dynamic focus voltage is formed of a plate-shaped electrode, and so it may easily transmit the vibration, and (3) the electrode supplied with the dynamic focus voltage is disposed near the heaters, and thus it may easily thermally expand. It is assumed that these factors may be combined in a complex fashion and a large abnormal noise is produced.
A dynamic focus voltage including an AC component E
4
of 40 kHz to 100 kHz was applied to the fourth grid G
4
and sixth grid G
6
of the CRT apparatus with the electron gun assembly
64
shown in FIG.
14
. The level of produced abnormal noise was measured.
FIG. 15
shows the measured results.
In
FIG. 15
, the abscissa indicates the frequency of the AC component E
4
included in the dynamic focus voltage, and the ordinate indicates the level of sound pressure sensed by humans in 10 grades. Normally, the level of abnormal noise needs to be suppressed to level 2 or less, at which the noise is hardly sensed by humans or negligible as being not unpleasant. According to the measured results shown in
FIG. 15
, the noise level exceeds level 2 at many frequency bands. If abnormal noise of level 2 or more has occurred, even if good image characteristics are obtained by the application of the dynamic focus voltage, the viewer feels unpleasant, and the product value and reliability of the CRT apparatus are greatly degraded.
BRIEF SUMMARY OF THE INVENTION
The present invention has been made in consideration of the above problems, and its object is to provide a cathode-ray tube apparatus which can suppress abnormal noise and has a high product value and reliability.
According to an aspect of the invention, there is provided a cathode-ray tube apparatus comprising: a substantially rectangular face panel; a funnel made continuous with the face panel; a phosphor screen formed on an inner surface of t
Hasegawa Takahiro
Kimiya Junichi
Oda Hiroyuki
Kabushiki Kaisha Toshiba
Oblon & Spivak, McClelland, Maier & Neustadt P.C.
Patel Vip
LandOfFree
Cathode-ray tube apparatus does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Cathode-ray tube apparatus, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Cathode-ray tube apparatus will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-3260667