Electric lamp and discharge devices – Cathode ray tube – Shadow mask – support or shield
Reexamination Certificate
2002-12-03
2004-02-03
Patel, Vip (Department: 2879)
Electric lamp and discharge devices
Cathode ray tube
Shadow mask, support or shield
C313S402000
Reexamination Certificate
active
06686685
ABSTRACT:
BACKGROUND OF THE INVENTION
A conventional “Trinitron” cathode ray tube (CRT) employs an aperture grill welded to a frame under tension. The frame adds weight and cost to the CRT. One conventional implementation of the aperture grill consists of parallel strips or tapes of metal attached to the frame. Each of the tape strips is called an aperture grill tape.
One of the key considerations for the size (and thus the weight) of the aperture grill frame is the tension required to produce a specified natural frequency for each of the aperture grill tapes. The natural frequency is in turn associated with the visual picture quality.
The natural frequency for each of the aperture grill tapes is described by the equation of a standing wave:
F
n
=
n
2
L
(
T
μ
)
1
/
2
where F
n
=natural frequency (Hertz), n=1, 2, 3, . . . represents the order of the mode, L=length (m), T=tension (kg), &mgr;=linear density (mass per unit length, kg/m). From the above equation, one critical factor for the aperture grill tape is the linear density (&mgr;), which in turn is a function of the cross-sectional area of the aperture grill tape.
One technique for reducing the cross-sectional area of the aperture grill tape is to produce the aperture grill from thinner material. Thinner aperture grill material costs more than thicker aperture grill material due to the additional processing required to achieve the thinner material. Moreover, thinner material generally has lower manufacturing yields than a comparable aperture grill of thicker material, which also increases the cost of aperture grill manufacturing.
Another technique for reducing the aperture grill tape cross-sectional area is to vary the screen side bevels (or tapers). One difficulty with this approach is that it can create or compound other subtle visual defects, which reduce manufacturing yields.
The present invention is therefore directed to the problem of reducing the manufacturing cost of a cathode ray tube.
SUMMARY OF THE INVENTION
The present invention solves this problem by reducing the cross-sectional area of the aperture grill tape. One exemplary embodiment of the reduced cross-sectional area aperture grill tape includes a central longitudinal channel in a side of the aperture grill tape that faces away from the screen. The reduction in cross-sectional area reduces the linear density of the aperture grill tape, thereby decreasing the tension (F
n
) required to achieve the desired natural frequency of the aperture grill tape. As each of the aperture grill tapes includes this central longitudinal channel, the weight of the overall aperture grill is significantly reduced. The weight of the aperture grill frame is reduced due to the overall reduction of required tension.
The present invention also includes a method for producing the reduced cross-sectional area aperture grill tape without significantly increasing the cost of manufacturing the tape. One exemplary embodiment of this method includes a two-step etching process, in which one of the etching steps involves etching both sides of the aperture grill, during which step a central longitudinal channel is etched in each of the aperture grill tapes and the other etching step involves etching the screen side of the aperture grill only.
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Fortkort Michael P.
Mayer Fortkort & Williams PC
Patel Vip
Sony Corporation
Williams Karin L.
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