EP0353058A1

EP0353058A1 - Charge discharge touchplate for video display terminals

Info

Publication number: EP0353058A1
Application number: EP89307621A
Authority: EP
Inventors: Mark Gart
Original assignee: SUN-FLEX Co Inc; SUN FLEX CO Inc
Current assignee: SUN-FLEX Co Inc; SUN FLEX CO Inc
Priority date: 1988-07-28
Filing date: 1989-07-27
Publication date: 1990-01-31
Also published as: JPH0412993B2; NO893031D0; AU3806089A; DK366189A; JPH02167179A; NO893031L; DK366189D0

Abstract

Apparatus for use with a video display terminal (12) for the discharge of static electricity accumulated on a user to the ground circuit of the terminal. The apparatus includes a touchplate (40, 76) of conductive material adapted to be electrically connected to a conductive filter screen (17, 70) mounted over the display surface (18) of the video display terminal. The touchplate (40, 76) may be attached to the frame (16, 74) of the filter screen or may be a means remote from the screen but electrically connected to the screen. An indicator light (82) may also be interposed in the discharge path to indicate that the static charge has been discharged. The user of the terminal merely touches the touchplate to discharge static electricity to the filter screen.

Description

This invention relates to a device that may be added to or near the face of a display surface of a video display terminal for the purpose of discharging static electrical energy existing on or generated by a user of the terminal.
Video display terminals are now commonplace as a result of the rapid increase in the use of computers and the like. The usual display surface of such a terminal is a cathode ray tube. Electromagnetic energy is generated from within the terminal from the electrical components therein and from the beam of the cathode ray tube, which produces electrostatic and electromagnetic fields emanating from the terminal. The user of the terminal also frequently generates static electric energy from the materials surrounding the terminal and from the user's clothing and movement. These electromagnetic and static electric energies need to be withdrawn or conducted from the terminal for reasons that include operator comfort, reduction in possible loss of memory within the storage of the terminal, and/or damage to the electronics within the terminal.
Filter screens are known which may be positioned over the face of the video display terminal for the purpose of suppressing or reducing the electromagnetic and/or electrostatic fields emanating from the terminal. The screens are electrically connected to the ground system of the terminal so that such fields are shunted to terminal ground at the filter screen. The screen is capable of collecting any static electricity generated at the terminal and conducting that energy to terminal ground.
The cabinet enclosing the terminal and the keys of the terminal keyboard are not usually grounded to the electrical ground of the terminal even though they are isolated from the supply service electrical ground to protect the user of the terminal from electrical shock. The static electrical energy generated by the user of the terminal is not grounded to the terminal ground with the mere use of the terminal keyboard or controls. There has therefore developed a need for a system that will permit the user of the terminal to discharge static electricity to the terminal ground so as to reduce or eliminate the operator annoyance or the possibility of data loss or equipment damage.

SUMMARY OF THE INVENTION

The present invention is directed to apparatus for discharging electrical charge, sometimes referred to as personal static, accumulated on a user of a video display terminal of the type having a cathode ray tube (CRT) for generating the video display and a conductive mesh filter screen mounted over the display surface of the CRT and grounded to the display terminal for reducing or suppressing electric fields emanating from the terminal. The invention provides an electrically conducting contact surface at a convenient location which is electrically connected for discharge to ground through the conducting mesh filter screen. When the user touches the contact surface, any accumulated personal static is safely discharged through the mesh filter.
In one embodiment of the invention the apparatus may be secured to the frame of the filter screen at a convenient location so as to make electrical contact with the mesh filter and to present a convenient contact surface to the user. In another embodiment of the invention an indicator light responsive to the discharging personal static is electrically interposed in the discharge path between the contact surface and the mesh filter to assure the user that the personal static has been removed.
It is an object of the present invention to provide a simple attachment to a video display terminal that will permit the user of the terminal to discharge static electricity from the user to the terminal ground.
The attachment may be fixed to the grounded filter screen associated with the face of a video display terminal in an easily accessible and visible location on the terminal.
The attachment may be clamped on the frame of a grounded filter screen with the attachment being formed of conductive material that will make electrical contact with either or both of the screen material of the filter screen and the frame of the screen.
There may be a visible indication to the user that accumulated static charge has been discharged.
Further features of the present invention will be readily apparent to those skilled in the art from the appended drawings and specification illustrating a preferred embodiment wherein:

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view of a video display terminal and the associated structure along with an embodiment of a filter screen for the suppression of radiation and static electricity generated within and around the cathode ray tube of the terminal.
FIG. 2 is a front view of the radiation and static electricity suppression filter screen of FIG. 1 with the addition of a touchplate of the present invention.
FIG. 3 is a side view of the device shown in FIG. 2.
FIG. 4 is an elevational view of an embodiment of the touchplate of the present invention.
FIG. 5 is a sectional view taken along the lines 5 - 5 of FIG. 4.
FIG. 6 is an assembly drawing showing the touchplate of FIG. 4 mounted on the frame of a filter screen of a video display terminal.
FIG. 7 is a perspective view illustrating the touchplate in an alternative placement on the terminal.
FIG. 8 is an enlarged showing of the alternative placement of a touchplate.
FIG. 9 illustrates access to a touchplate mounted behind the terminal bezel.
Fig. 10 is a perspective view of a front-mount filter screen embodying the present invention.
Fig. 11 is a cut-away perspective view of an indicator light in a filter frame according to the invention.
Fig. 12 is a top plan view of the indicator light of Fig. 11.
Fig. 13 is a side cross-sectional view of the indicator light and frame of Fig. 11.
Fig. 14 is an end elevational view, partially in section, of the indicator light and frame of Fig. 11.

DETAILED DESCRIPTION OF THE INVENTION

Referring now to FIG. 1, a video display terminal with keyboard is illustrated in the form that is typical of a computer terminal device 12. The terminal includes a cathode ray tube display device 10 having a display surface 18; the cathode ray tube 10 is supported within the case 13 of the device 12 behind a bezel 15.
For the purposes of this specification and appended claims, the term "cathode ray tube" and "video display terminal" will be used to encompass the cathode ray tube itself, the associated circuitry necessary to drive the electron beam or beams utilized in the cathode ray tube for display of intelligence on the screen surface, and further will include the grounding chassis which may or may not include the housing of the terminal or a like device. In summary, the term cathode ray tube would encompass what is currently sold in the marketplace as a television set, a remote display device, a video display tube and associated circuitry used in a word processor, or any other installation where a cathode ray tube is utilized for electronic display of information on the surface of the tube itself.
Referring now to Fig. 2, a radiation and static electricity suppression device is shown in the form of a filter screen 17, which includes a conductive mesh fabric screen 14, or similarly functioning material, and a frame 16. Mesh screen 14 may be held in frame 16 such that the screen 14 may be conformably positioned against the display surface 18 of the cathode ray tube or, alternatively, mounted on the front of the terminal 12 between the user and the surface 18. Such a conformably mounted framed mesh screen for reducing glare as well as radiation and static electricity is disclosed in U.S. Patent No. 4,468,702 issued to Louis H.M. Jandrell on August 28, 1984. In that patent a filter screen is disclosed wherein a conductive mesh fabric coated with conductive plastics or the like is electrically connected through a grounding wire 26 to ground of the terminal. As shown in FIG. 3 the mesh fabric 14 of the filter screen is glued by a conductive glue at 24 to the frame 16 of the filter screen and to the grounding wire 26 at 28.
The filter screen of the device shown in U.S. Patent No. 4,468,702 is effective in the suppression of certain radiation and static electricity generated within the terminal. The screen does not reduce the effects of static electricity generated by the user of the device or by other sources external to the terminal. That static electricity could cause operator discomfort by discharge "shock" to the terminal or could possibly cause loss of storage memory within the terminal and might distort the display on the surface of the terminal. It is the purpose of the present invention to provide a means for discharging that static electricity easily, conveniently, comfortably and safely.
In some video display terminals the manufacturers have placed the frame 16 of a filter screen in front of the bezel at the face of the terminal case or at least in the opening of the bezel adjacent to the face of the cathode ray tube. Such filter screens are commonly referred to as front-mount screens. In those positions the frame is accessible from the front of the terminal. The usual frame of a filter screen may not itself be conductive even though the fabric within the screen is conductive because of its coating or its construction. In accord with the present invention, a touchplate device is adapted to be attached to the frame of the filter screen in a manner to provide an electrical connection between the touchplate and the mesh of the filter screen. As shown in FIGS. 2 and 3, a touchplate 40 is attached to the frame 16 of the filter screen in a location where a portion of the touchplate is in contact with the mesh 14 of the screen.
FIGS. 4 and 5 illustrate the touchplate 40 in elevation and cross section. As shown, the touchplate member 40 is formed of a conductive material in a channel or U-shape with a body portion 42 and legs 44 and 46. The interior portions of the legs 42 and 46 are formed with shoulder extensions 48 directed toward each other so that the touchplate has an interior portion 50 that is wider than the space between the extensions 48. The touchplate has a linear dimension that is substantially larger than its lateral dimension; however, the linear dimension can be any desired length to serve the purpose intended.
The touchplate 40 is formed of a flexible material that will permit the legs 44 and 46 to pivot about their connection to the body portion 42. Those skilled in the plastics arts will readily be able to select from a variety of plastic compositions which may be used for this purpose. The extensions 48 are formed in a form to permit a frame to be easily passed toward the interior 50 but to restrict the retraction of the frame from the interior. Further, the extensions are formed with sloping surfaces on their interiors to be effective in pressing the frame firmly into the interior 50. The entire touchplate is conductive so that the exterior ends of the legs 44 or 46 will make good electrical contact with the mesh 14 of the filter screen.
The touchplate 40 is designed to enclose a portion of the frame 16 of a filter screen as shown in FIGS. 2 and 3, and in more detail in FIG. 6, in a manner to enclose the frame within the interior portion 50 between the legs 44 and 46 and with the extensions 48 retaining the frame within the interior. The ends of the legs 44 or 46 make their contact with the mesh 14 and present the exterior of the body portion at the exterior of the frame 16. As shown in FIG. 6, the touchplate 40 is mounted on a filter screen frame 16 behind the bezel 15.
The user of the terminal merely touches the touchplate 40 with the first use of the terminal or at any time during the use of the terminal. That touch permits any static electricity existing on the user to be discharged through the touchplate to the ground circuit of the terminal through the filter screen. If the user generates static electricity during use of the terminal as by moving on the flooring surface, by movement of the clothing of the user or by contact with another source of static electricity, that static electricity can be discharged to the terminal ground by merely again touching the touchplate.
It should be understood that the touchplate of the present invention can be attached to any form of conductive filter screen whether the screen is in front of the display surface or in contact with the display surface. The present invention is particularly effective where the filter screen is not removable from the face of the display terminal. If the user were to repeatedly touch the filter screen for the purpose of discharging static electricity, the screen could become soiled to the degree that it would interfere with the viewing of the display. With the use of the touchplate of the present invention, only the touchplate is soiled and it is removable from the frame to permit cleaning.
FIGS. 7 and 8 illustrate an alternative form of operation for the touchplate of the present invention. In these FIGS. the touchplate 40 is mounted remotely from the frame or the filter screen and is connected by a conductor or pair of conductors to the screen 14 at the display surface. In FIG. 7 the screen is behind the bezel 15 and the conductor is connected by suitable conducting connection to the screen at the face of the display surface. In FIG. 8 the screen is at the exterior of the bezel 15 and the conductor is attached to the screen 14 or could be attached to a frame if the screen has a frame. In the alternative forms of FIG. 7 and 8 the touchplate is touched to discharge the static electricity from the user.
FIG. 9 illustrates an alternative form of access to the touchplate 40 when the screen 14 and its frame 16 are mounted behind the bezel 15 and not accessible from the front of the terminal. In this alternative, the touchplate 40 is fixed to the frame as in Fig. 6 and the bezel 15 is provided with an access hole 62 through which contact may be made with the touchplate 40. In the alternative form of FIG. 9, the touchplate is contacted through the access hole 62 to discharge static electricity from the user.
To alert the user to the fact that personal static is being discharged, the apparatus according to the invention may include an indicator light. An embodiment of such apparatus in a front-mount filter screen is illustrated in Fig. 10. The front-mount filter 70 includes the conductive mesh fabric 72 and supporting frame 74. Disposed within the frame is a conductive member 76, which presents a contact surface 78, which the user may touch to allow any personal static to discharge. The conductive member 76 may be formed, for example, of a carbon-filled conductive nylon, although those skilled in the art will recognize that other conductive materials may also be used for this purpose. The conductive member 76 is formed with a display window 80, through which an indicator light 84 may be viewed. The conductive mesh fabric 72 may be connected to the terminal ground by grounding cable 84.
Within the frame 74 behind the display window 80 a cavity is formed, in which the indicator light 82 is mounted. In the embodiment of Fig. 11, a top wall 86 of the cavity is provided by a portion of the conductive member 78. A bottom wall of the cavity 88 is provided by the back portion of the filter screen frame 74. In Figs. 11, 13, and 14, the conductive mesh filter screen is indicated at reference numeral 90.
To electrically connect the conductive member 76 to the indicator light 82, the conductive top wall 86 of the cavity makes electrical contact with the metallic contact member 92, which in turn makes electrical contact with a lead 94 at a first side of the indicator light 84. Electrical connection is made with the conductive mesh filter screen 90 through a metallic plate 96 overlying the mesh filter screen 90. The lead 98 at a second side of the indicator light 82 lies in contact with the plate 96. The plate 96 in effect provides electrical contact with the mesh over a small area rather than at a point.
It is, of course, necessary that the indicator light 82 be of such characteristics that it will respond to the discharge of the relatively low levels of personal static typically accumulated by a user. A Gilway neon bulb, Model No. N501, having an ionization potential of 85 volts has been found sufficient for this purpose. With this or lower threshold potential for energizing the bulb, the operation of the bulb as an indicator of static discharge has been found to be independent of prevailing atmospheric conditions.
In this way, the indicator light is interposed in the discharge path between the conductive member 76 and the conductive mesh filter screen 90. Discharging the accumulated charge through the conductive mesh in this manner, the mesh may perform the function of a current limiting fuse in the event of an electrical problem in the CRT or grounding system.
While certain illustrative embodiments of the present invention have been specifically described and disclosed, it should be understood that the invention is not limited thereto as many variations will be readily apparent to those skilled in the art. For example, given the disclosure presented here, variations in the manner of establishing the electrical connections, such as alternative configurations of the electrical contact members or use of conductive adhesives, will readily suggest themselves to persons of ordinary skill and are therefore within the intended scope of the present invention.

Claims

1. Apparatus for use with a video display terminal for discharging a charge accumulated on a user, said video display terminal including a cathode ray tube and a conductive mesh filter screen mounted over the display surface of said cathode ray tube and grounded thereto, the filter screen comprising a conductive mesh material disposed in a frame, said apparatus being characterized by:
a conductive member having a body portion of predetermined length defining a contact surface for contact by said user; and
means for mechanically and electrically attaching said conductive member to said grounded filter screen;
wherein said body portion of said member is formed and arranged to be accessible to a user of said video display terminal whereby said user may touch said member at said contact surface and discharge any accumulated static charges to the terminal ground.

2. The apparatus of claim 1, wherein at least a portion of said frame is visible to said user, said apparatus being further characterized in that said conductive member is mounted in a section of said frame at said visible portion.

3. The apparatus of claim 1, further characterized by:
first and second legs extending from said body portion to form a channel-shaped cross section transverse of said member, said legs being formed and arranged to enclose said frame of said filter screen and to establish electrical contact with said filter screen.

4. The apparatus of claim 3 further characterized in that said legs are resiliently self-biased inwardly of said channel shape so as to firmly engage said frame of said filter screen.

5. The apparatus of claim 4 wherein said member is adapted to be removably mounted to said frame.

6. The apparatus of claim 1, further characterized in that said conductive member is formed of an electrically conductive plastic material.

7. The apparatus of claim 1, further characterized by:
an indicator light energizable in response to static discharge from said user and electrically connected at a first side to said conductive member and at a second side to said conductive mesh material;
whereby said user may touch said member at said contact surface and discharge accumulated charge to the video display terminal ground through said indicator light and mesh material.

8. The apparatus of claim 7, further characterized in that said indicator light is electrically connected to said conductive mesh material over an extended region thereof.

9. The apparatus of claim 8, wherein at least a portion of said frame is visible to said user, said apparatus being further characterized in that said conductive member and indicator light are mounted in said frame at said visible portion.

10. The apparatus of claim 9, further characterized by:
means defining a cavity within said frame;
said indicator light being mounted within said cavity;
said conductive member defining a top wall of said cavity: and
said indicator light being electrically connected to said conductive member at said top wall.

11. A method of discharging a charge accumulated on a user of a video display terminal, said terminal including a cathode ray tube and a conductive mesh filter screen mounted over the display surface of said cathode ray tube and grounded thereto, said method comprising the steps of:
providing a conductive member having a contact surface for contact by said user;
providing an indicator light energizable in response to static discharge from said user;
providing a series discharge path from said conductive member through said indicator light and through said conductive mesh filter screen to ground; and
touching said contact surface, whereby charge accumulated on said user is discharged to the video display terminal ground through said indicator light and throughout said mesh filter screen.