WO1989003631A1

WO1989003631A1 - Crt shield with double coated mesh

Info

Publication number: WO1989003631A1
Application number: PCT/US1988/003481
Authority: WO
Inventors: Michael L. Hiles; Roger Peterson; Donald Firth
Original assignee: Norad Corporation
Priority date: 1987-10-16
Filing date: 1988-10-07
Publication date: 1989-04-20

Abstract

A CRT shield (10) comprising a woven monofilament mesh (14) coated with a plurality of metallic coatings (32, 34), at least one of which is an efficient conductor of electricity, the final one of which is a black metal in crystalline form, having light-diffusing and absorbing properties, in a frame (18) which holds the mesh (14) flat. The frame (18) is fitted with a means (24) for conducting electricity from the mesh to a fitting (24) for an external grounding cable (26) or other means by which electrical energy can be conducted to a suitable ground.

Description

CRT SHIELD WITH DOUBLE COATED MESH

BACKGROUND OF THE INVENTION

1. Field of the Invention.

The present invention relates to a CRT shield and particularly to a shield which combines anti-glare, anti-static and anti-radiation properties. 2. Description of Related Art.

A cathode ray tube, particularly as used as a video display terminal unit or terminal ("VDU" or "VDT") for computer applications, frequently has a shiny front display surface, which reflects incident light and glare, and a relatively light-colored display surround, resulting in low contrast between the lighted elements of the display and the surround. These characteristics contribute to fatigue, error and low productivity on the part of users of the VDT. In addition, a cathode ray tube is capable of producing an electrostatic field at its face and extending for some distance in front of its face, which attracts dust to the face of the cathode ray tube, and has been implicated by some medical re¬ searchers as a cause of dermatitis and other adverse skin conditions. In addition, a cathode ray tube is capable of producing electromagnetic emanations or radiation. This radiation is suspected by some medical researchers of causing adverse health effects on users. The radiation may also be received and decoded at a distance to reproduce the information displayed on the screen of the cathode ray tube. Various prior art discloses techniques for reducing glare and reflection, such as U.S. Pat. No. 4,253,737 granted on March 3, 1981, to Erik J. Thomsen, et al., comprising a micro- weave screen of black filaments mounted in a flexible mount. It is also well known to suppress static and radiation by interposing a mesh screen between the cathode ray tube and the user, in which electrically conductive strands forming a portion of the mesh are connected to a grounding means, as taught by U.S. Pat. No. 4,468,702 granted on August 28, 1984, to Louis H. M. Jandrell. It is also well known to combine the func¬ tions of anti-glare and reflection with radiation suppression, as taught by U.S. Pat. No. 4,246,613 issued on January 20, 1981, to Jerome Choder, et al. Prior art screens have certain disadvantages. Those which are specialized for reduction of reflection and glare do not alleviate the problems of static and radiation. Those specialized for control of electrical phenomena do little or nothing to reduce the problem of glare and reflection. Those which combine, to some extent, a partial reduction of more than one of the adverse phenomena do not perform any single function as well as a screen specialized for that task.

SUMMARY OF THE INVENTION

It is a general object of the present invention to provide a screen for cathode ray tubes used as VDTs which overcomes the disadvantages of the prior art.

It is a further object of the present invention to provide a screen for a cathode ray tubes used as a VDT which provides a high degree of reduction of glare and reflection, and increase of perceived contrast, while simultaneously reducing the electrostatic field, and while also simultaneously substantially reducing the electromagnetic emanations from the face of the cathode ray tube. It is a further object of the present invention to provide an anti-glare, anti-static and anti-radiation screen for a cathode ray tube used as a VDT which is simple in constriction, and which requires little maintenance by the user.

These and other objects of the present invention are achieved by providing a screen for a video display terminal comprising a mesh consisting of a plurality of monofila ent strands having a diameter of not more than 60 microns, which strands are woven into a mesh having a strand count of not less than 200 threads to the linear inch, and which are uniform in the vertical and horizon¬ tal directions, which strands are coated with a plura¬ lity of metallic coatings of which at least one is highly conductive of electricity and of which the final one is black in color and is deposited in a crystalline state such that its surface exhibits microscopic roughness and acts to diffuse and scatter incident light, which mesh is contained in a frame or other retaining means which keeps it taut, which frame or other retaining means provides a means of attachment to the case of the video display terminal such that the screen is situated in front of and not more than one and one-half inches from the face of the cathode ray tube, and which frame also comprises a means for electrically connecting the conductive mesh to an external grounding cable and connector whereby the mesh may be connected to a relative ground.

Other objects and many of the attendant advantages of the invention may be readily appreciated as the same becomes better understood by reference to the following detailed description when considered in connection with the accompanying drawings. BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a front elevational view of a video display terminal utilizing the screen of the present invention; FIG. 2 is a sectional view taken along line 2 - 2 of FIG. 1; and

FIG. 3 is an enlarged sectional view, similar to that shown in FIG. 2, but enlarged approximately 400 times to show the monofilament strands and the succes- sive metallic coatings thereon.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Referring now to the various figures of the drawing wherein like reference characters refer to like parts, there is shown an anti-glare, anti-reflection, contrast- enhancing screen 10 of the present invention having anti-static and anti-radiation properties, mounted on a conventional video display terminal 12.

The mesh screen portion 14 of the instant inven- tion, by reason of its construction, to be described in detail below, reduces the perceived glare and reflection on the face of the video display terminal. By "glare" is meant the general non-specular reflection of ambient light from the face of the cathode ray tube of the video display terminal or from any glass, plastic or other transparency installed in front of such cathode ray tube; by "reflection" is meant the specular reflection of ambient light from the same. Moreover, by reason of its construction, the mesh screen 14 of the present invention increases the perceived contrast of the alphanumeric or graphic display of the video display terminal in that the video display terminal in that the illuminated display elements are perceived against a perceived background comprising the black, non-reflec- tive surface of the strands 16 (see FIG. 3) comprising the mesh 14. Moreover, by reason of its construction, the mesh screen 14 of the present invention reduces and attenuates the electrostatic field at the face of the video display terminal 12 and the electromagnetic radiation or emission through the face of the cathode ray tube in such terminal 12.

As can be clearly seen in FIGS. 1 and 2, the screen 10 basically consists of a mesh screen 14 constructed in accordance with the present invention as elsewhere described in more detail, held taut in a retaining means or frame 18. In one embodiment of such invention, such retaining means or frame 18 consists of two identical frame halves 20 and 22 produced by injection molding, glued together at 24 as a sandwich with the mesh screen 14 forming the middle by means of a suitable adhesive. In another embodiment, which is not illustrated but the details of the construction of which will be obvious when its description is understood, the retaining means or frame consists of two aluminum or other metal frame halves cut or stamped from sheet metal, or produced by casting, fastened together by means of rivets, screws, or other suitable fasteners, or with a suitable adhe¬ sive, as a sandwich with the mesh screen forming the middle.

The retaining means or frame 18 is also provided with a suitable means for attaching it to the cabinet of the video display terminal 12. In a preferred embodi¬ ment such retaining means or frame is provided with spacers made of a foam rubber or vinyl or similar compressible substance, which are added to its edges to enable it to fit the recess provided in the cabinet of many types of video display terminal, and with paired fabric hook-and-loop fasteners, which spacers and fasteners are coated on one side with a pressure- sensitive adhesive, so that the user can easily install the screen in the manner most suitable for the particu¬ lar video display terminal. The retaining means or frame 18 can be manufactured in various lengths and heights to enable fitting various video display terminals. The retaining means or frame 18 is fitted with a means for conducting electricity from the conductive mesh to an external grounding cable and connector. In a preferred embodiment, such means consists of a ferrule 24 (FIG. 1) made of a conductive metal, inserted in a hole provided for such purpose in the frame half which forms the front of the screen, which ferrule 24 makes contact with the conductive mesh screen 14, and which serves as a jack into which a suitable plug connected to a grounding cable 26 can be fitted. In another embodiment, which is not illustrated but the construction of which will be obvious when the description is understood, the grounding cable 26 is permanently fastened by means of a wire terminal, rivet, screw or similar means.

As can be seen clearly in FIG. 3, the mesh screen is made of a plurality of strands 16 of monofilament woven so that they form a precise mesh 30 of evenly spaced strands of not fewer than 200 strands to the linear inch, each strand 16 having a diameter of not more than 60 microns. Many previous mesh screens used as filters for video display terminals have been made of coarser strands or have had wider spacing, and such previous screens caused annoying moire and Newton's Ring effects, especially when used in connection with color displays or high-resolution displays. It is an object of the present invention, by means of the fine strands 16 and mesh 30 which are employed in its construction, to provide a mesh screen 14 which does not produce significant distortion and moire and Newton's Ring effects, even when used on color displays or high- resolution displays. The strands 16 of the present invention include a monofilament 17 which is coated with a plurality of metallic coatings such that at least one such coating is highly conductive of electricity, and the final coating is black in color and deposited in crystalline form so that its surface exhibits microscopic roughness and acts to diffuse ambient light. In a preferred embodiment, the first metallic coating 32 (FIG. 3) is of nickel, which forms an excellent bond to the underlying mono¬ filament; the second coating 34 is of copper, which provides a high degree of electrical conductivity. In certain prior art screens, the mesh screen was made of a woven metal wire, such as stainless steel. Such woven metal cloth has many disadvantages including the facts that it is expensive, takes a permanent set when bent, and has a shiny surface so that it does not effectively reduce glare and reflection and increase contrast. It is an object of the present invention to provide a highly conductive mesh screen with its electrical advantages while at the same time utilizing relatively inexpensive materials which can be woven with a high degree of precision and which retain their precision character in use. The final coating 36 is of black chrome or black nickel, either of which deposit in a crystalline form and have the requisite properties.

Without further elaboration, the foregoing will so fully illustrate the invention that others may be applying current or future knowledge readily adapt the same for service under various conditions. The above description, while it contains many specifities, exemplifies certain embodiments of the invention; the scope of the invention, however, should be determined by the appended claims and their legal equivalents.

Claims

CLAIMS What is claimed is:

1. A screen for a cathode ray tube, said screen being disposed to reduce glare and reflection and increase perceived contrast of the cathode ray tube display, while reducing and attenuating the electro¬ static field at the face of said tube and the electro¬ magnetic radiation emissions through the face of said tube, said screen comprising: a woven mesh of a plurality of strands having a diameter of not more than 60 microns, said, woven mesh having a strand count of not less than 200 threads per linear inch, said strand count being uniform in the vertical and horizontal directions, wherein each of said strands comprises a centrally located monofilament, and wherein each of said monofilaments is individually coated with at least one electrically conductive interior layer and an electrically conductive outer layer, said outer layer being black in color and deposited in a crystalline state such that the outer surface of said outer layer exhibits microscopic roughness which acts to diffuse and scatter incident light; and a frame for supporting said woven mesh in front of said cathode ray tube face to provide said reduction and attenuation in said electrostatic field at the face of said tube and the electromagnetic radiation emissions through the face of said tube.

2. A screen according to claim 1 wherein one or more of said electrically conductive interior layers is nickel or copper.

3. A screen according to claim 2 wherein there are two electrically conductive interior layers, a first inner coating adjacent to said monofilament and a second outer coating adjacent to said outer layer.

4. A screen according to claim 3 wherein said first inner coating is nickel and said second outer coating is copper.

5. A screen according to claim 1 wherein the cross section of said monofilament and electrically conductive layers is circular.

6. A screen according to claim 1 wherein at least one of said interior electrically conductive layers is copper.

7. A screen according to claim 1 wherein said outer layer is black chrome.

8. A screen according to claim 1 wherein said outer layer is black nickel.

9. A screen according to claim 1 further includ¬ ing means for externally grounding said screen.