Advanced VDT screen shielding method and apparatus

An advanced video display terminal (VDT) screen shielding method and apparatus includes an electric resistance lower than or equal to 10.sup.5 .OMEGA.(R.ltoreq.10.sup.5 .OMEGA.), a transmittance between 1/3 to 2/3, a fiber diameter D.ltoreq.MIN(D.sub.1,D.sub.2). Wherein D.sub.1 =VD.times.25.4.times.0.8/RV.times.0.16 or D.sub.1 =VD.times.25.4.times.0.6/RH.times.0.16, D.sub.2 =VD.times.PA.sup.3 -QA.sup.2 +RA-S, P=1.342.+-.0.002, Q=2.032.+-.0.002, R=1.011.+-.0.002, S=0.116.+-.0.002 and the aperture is a circle, ellipse, polygon, square or other transfigure. A formed angle .ltoreq.45.degree. of the fabric is horizontally against cathode ray tube. This screen-shielding method could suitably reduce glare and reflected lights, eliminate electrostatic charges and low frequency radiation, and prevent Moires and/or Newton Rings. This screen-shielding apparatus includes a frame, the high conductive fabric and a suitable ground wire, and is installed in front of the surface of the CRT.

FIELD OF THE INVENTION 
The present invention relates to an advanced shielding method and apparatus 
for use in reducing glare and reflected light, eliminating electrostatic 
charges and low frequency radiation, and preventing Moires and/or Newton 
Rings from occurring. 
BACKGROUND OF THE INVENTION 
Use of video display terminals (VDT) in data processing equipment, office 
automation equipment, video games and TV is increasing rapidly. But as 
know, the glare and reflected light generated from the surface of a 
cathode ray tube (CRT) can cause eye fatigue, added eye pressure, 
headache, etc. Emission of low frequency radiation and electrostatic 
charges from a VDT can be even more harmful. At the 1986 and 1989 
International Scientific Conference, aimed at Work With Display Units 
(WWDU), a number of such cases were reported by scientists and doctors. In 
their reports, it was noted that electrostatic charges can attract 
bacteria or pollutants with an opposite charge to the screen. Thereafter, 
other bacteria or pollutants having the same charge can bombard the 
operator when replaced by the bacteria on the screen. 
In addition, a controversy over non-ionization radiation has continued on 
for years. Though electromagnetic radiation generated from screen is well 
below an injury-causing level, such low frequency radiation does exist. 
Some old-fashioned or inferior VDTs emit radiation over the limit 
permitted by government regulations and guidelines. A prior art 
anti-static CRT has been developed to overcome this problem. The prior art 
method of coating the CRT surface with a thin, transparent conductive 
layer leaves a high electric resistance impending conduction. Moreover, 
the thin transparent layer, results in reflection and diffusion of light. 
VDTs are available with many different characteristics. For instance, they 
can vary in viewing diagonal from 5" to 40"; in screen surface they can 
vary from cylinderical, spherical to flat surfaces; in color from 
mono-chrome, 2-color, 4-color, 16-color, even to 160-million color; in 
resolution from 160X200, 320X200, 640X200, 640X480, to 4096X4096. In fact, 
in any type of CRT whether monochromatic or color, a few naturally 
defective points like missing phospher dots (M.P.D.), blemishes and small 
scratches are admitted. In color CRT especially, a heat-causing expansion 
of aperture of the shadow mask thereof, which is generally iron material 
or iron-nickel alloy, may sometimes lead to the phenomenon of distorted 
images, Moires and/or Newton Rings. In prior art U.S. Pat. Nos. 4,253,737; 
4,468,702; 4,760,456; 4,788,597; 4,974,935, solution of such problems are 
not presented. 
The device of patent '737 is directed to overcoming glare and reflected 
light. However, because pollutants can easily be attracted to and stick to 
the mesh, the viewing is obstructed and Moires and/or Newton Rings occur. 
The device of patent '702 uses nylon yarns with a conductive thread-woven 
central area. This weaving is very complicated, but does not produce any 
better result than the present invention. The device of patent '597 
includes a conductive mesh, a moveable frame in size adapted to CRT front 
frame (bezel) and a ground wire. The bezel construction result is very 
complicated resulting in a significant increase in cost. 
The device of patent '935 includes a conductive mesh, a rigid frame and a 
ground wire, and is characterized by a fiber diameter between 20-100 
.mu.m, an aperture between 45-230 .mu.m and formed angle with frame 
between 10.degree.-45.degree.. In experiments it was found to be unable to 
fit any kind of VDT. 
OBJECTS OF THE INVENTION 
In view of above-mentioned problems, the present invention is directed to 
new VDT screen shielding method and apparatus whose features include: 
1. A black conductive fabric to fit the viewing of CRT's, to reduce glare 
and reflected light. 
2. Means to increase the contrast of VDT to lower the burden on the eye. 
3. The high conductive fabric further absorbs electrostatic charges and ion 
frequency radiation and a ground wire eliminates such charges and 
radiation. 
4. The black conductive fabric further eliminates Moires and/or Newton 
Rings which may disturb viewing conditions. 
5. The prevention of distorted images and abnormal colors produced by 
magnetism. 
SUMMARY OF THE INVENTION 
A new VDT screen shielding apparatus that includes a frame, a high conduct 
fabric and a ground wire is in a suitable way positioned in front of the 
surface of a CRT. Wherein characteristics of the high conductive fabric 
are listed as below: 
(A) Resistance: R.ltoreq.10.sup.5 .OMEGA.: 
(B) Transmittance: 1/3.ltoreq.T.ltoreq.2/3: 
(C) Fiber diameter: D.ltoreq.MIN (D.sub.1,D.sub.2): 
Wherein 
D.sub.1 =VD.times.25.4.times.0.8/RV.times.0.16 or 
D.sub.1 =VD.times.25.4.times.0.6/RH.times.0.16 
D.sub.2 =PA.sup.3 QA.sup.2 +RA-S 
P=1.342.+-.0.002 
Q=2.032.+-.0.002 
R=1.011.+-.0.002 
S=0.116.+-.0.002 
Wherein 
VD stands for viewing diagonal; 
RH stands for numbers of horizontal scanning lines; 
RV stands for numbers of vertical scanning lines; 
A stands for dot pitchs; and 
(D) is types aperture: circle, ellipse, polygon, square or other 
transfigure, and 
(E) is formed angle of the fabric horizontally against the CRT: 
.theta..ltoreq.45.degree..