A membrane switch assembly for cathode ray tubes and mounting thereof

Abstract

 A transparent membrane switch assembly (10) and mounting means (118) for mounting the assembly (10) to a cathode ray tube (CRT) (68) are disclosed. The assembly (10, 10') is comprised of two layers (12, 16) of transparent film having spaced-apart parallel double fineline conductors (20) deposited on the internal surfaces (14, 18) of both layers (12, 16). The mounting means (118) comprise extension (114) protruding from the perimeter (116) of at least one of the layers of film, and a patch of a coupled fastening assembly (120) attached to each extension (114). Each fastening assembly comprises two separable parts, an outer surface (124) of one part being attachable to a side surface of a CRT when the switch assembly is registered with the CRT face.

Description

[0001] This invention relates to membrane switch assemblies of the type that are used on cathode ray tubes.

[0002] In today's technological world, there is an increasing need for membrane switch assemblies that can be mounted on cathode ray tubes (CRT's). An ever-increasing amount of software is becoming available that requires the user to answer questions by pressing appropriate areas of a CRT equipped with a membrane switch assembly.

[0003] These assemblies are generally made from two layers of essentially transparent film, the internal surfaces of each layer having conductors deposited thereon, separated by a third layer of film containing openings for switch sites. The conductors on the layers cross and are normally spaced from each other at the switch sites.

[0004] Membrane switches were initially developed for use in such items as calculators, computer keyboards, cash registers, games, and the like. In manufacturing these items, the membrane switches are essential to the operation of the device. Housings for the items had to be developed to encase the switches.

[0005] A membrane switch used on a CRT, however, is an optional piece of equipment. The CRT can be fully operational without the membrane switch. The switch must be designed to fit an existing object. Mounting the switches to CRT's, therefore, presents unique problems.

[0006] Mounting is a particular problem with switches made from successive layers of essentially transparent film. It is essential that the film be held securely in place against the firm surface of the CRT. It is desirable that the means for mounting the switch not block any of the operable areas of the switch. Furthermore, the method of mounting should permit realignment of the switch should the switch become distorted during use and easy replacement should the switch become damaged.

[0007] Heretofore, membrane switches for CRT's have been profiled to the shape of a CRT. The methods used for mounting these switches include the use of adhesive gaskets to adhere the switch to the face of the CRT and the use of brackets to surround a portion, or all, of the outer perimeter of the switch and a portion of the face of the CRT. There are problems associated with the above methods, particularly in aligning and replacement of the switch.

[0008] The disclosed invention solves the problems associated with mounting membrane switches on CRT's. An essential part of the means for mounting, integral with the switch itself, eliminates the use of gaskets and brackets. The means for mounting is comprised of a plurality of extensions of film along the perimeter of at least one layer of the film and a plurality of coupled fastening assemblies. The assemblies are comprised of two separable parts, the inner surfaces of which have a very large number of closely spaced hooking elements of the hook and loop type that engage with each other when the two parts are pressed together. One outer surface of the assembly is adhered to the film extensions and the second outer surface is fastened to the sides of the CRT. The fastening assemblies hold the switch securely to the CRT without blocking any of the face of the CRT, and at the same time permit easy realignment if the film becomes distorted during use. Furthermore, the switch can be removed and replaced with a minimum of effort.

[0009] When a switch assembly mounted on a CRT is operated, it is highly desirable that the assembly be essentially optically clear to the operator. For this reason, assemblies having wide conductive ink or electrodeposited traces are generally unacceptable. The widths of the traces are visible to the naked eye. Assemblies of the type having fineline conductors are generally more acceptable. The conductors can be electrodeposited metal or deposits of conductive ink.

[0010] Use of fineline conductors, however, can cause other problems. An electrical circuit can be completed only when the conductors from the two layers are brought in contact with each other. The conductors, being extremely fine, present a relatively small switch site area. Failure to press on the point at which the conductors cross usually means the circuit is not completed. Furthermore, a break in a fineline conductor also prevents the completion of the circuit.

[0011] The invention disclosed herein solves the above problems by using essentially parallel double fineline conductors instead of single fineline conductors. The double fineline conductors provide a larger area for applying pressure to complete the circuit and also provide for redundancy in the event a break should occur in a fineline conductor. At each switch site there are four possible points of electrical contact. In addition to the double fineline conductor, the disclosed invention uses a polymer spacer that is deposited on both layers of film over the fineline conductors themselves, except for the switch sites.

[0012] Plating of electrodeposited conductors in membrane switches of this type is often desirable. When electrodeposited conductors are used, the polymer is a plating mask as well as a spacer. It is more economical to plate just the switch sites rather than the complete conductors. Having a spacer that also serves as a plating mask eliminates the need to apply and then remove a separate plating mask from the conductors.

[0013] In a membrane switch assembly having mounting means for mounting the assembly to a cathode ray tube, the assembly is comprised of two layers of substantially transparent film having internal surfaces that are separated from each other by spacing means, the spacing means having openings therein constituting switch sites. The internal surfaces of each layer have conductors thereon, the conductors crossing and being normally spaced from each other at the switch sites. The mounting means is characterized in that a plurality of extensions protrude from the perimeter of at least one of the layers of film; a patch of a coupled fastening assembly is attached to each extension; and the fastening assembly is comprised of two separable parts, the inner surfaces of which have a very large number of closely spaced hooking elements of the hook and loop type that engage with each other when the two parts are pressed together, whereby when the switch assembly is aligned against the CRT, the extensions wrap around the perimeter of the CRT enabling the outer surfaces of the coupled fastening assemblies to be attached to one or more sides of the CRT.

[0014] A membrane switch assembly is comprised of two layers of substantially transparent film having internal surfaces that are separated from each other by spacing means, the spacing means having openings therein constituting switch sites. The internal surfaces of each layer have fineline conductors thereon, the conductors crossing and being normally spaced from each other at the switch sites. The assembly is characterized in that the internal surface of the first layer has a plurality of spaced=_apart parallel double fineline conductors, each double conductor having a first portion, an intermediate portion and a second portion, the first and second portions of the double conductor being essentially parallel to each other with the intermediate portion connecting the first and second portions, the distance between the first and second portions of each double conductor being less than the distance between adjacent conductors. The internal surface of the second layer has a plurality of spaced-apart parallel double fineline conductors applied in a direction normal to the direction of the first layer conductors, the switch sites being created by the crossing double fineline conductors of the first and second circuit layers when they are assembled, thus giving four points of contact at each site. The spacing means is comprised of an insulating ultraviolet curable polymer applied in parallel strips over the conductors, the spacer being discontinuous at the switch sites, whereby, as force is applied at the switch site to bring the two layers of conductors together, an electrical circuit can be completed at any one of the four contact points thus providing redundancy and insuring the completion of the electrical circuit even if the force has been applied at the periphery of the switch site.

FIGURE 1 is a three-dimensional view of the preferred embodiment of the membrane switch assembly having mounting means and a fitter having similar mounting means, mounted on a cathode ray tube.

FIGURE 2 is an exploded view of the devices shown in Figure 1.

FIGURE 3 is an exploded view of one embodiment of the mounting means.

FIGURE 4 is an exploded view of an alternative embodiment of the mounting means.

FIGURE 5 is a side view of the embodiment shown in Figure 4.

FIGURE 6 is a three-dimensional view of an alternative embodiment of the membrane switch assembly and a filter mounted on a cathode ray tube.

FIGURE 7 is an exploded view of the device shown in Figure 6.

FIGURE 8 is an orthographic view of the pattern of double conductors deposited on one layer of the film.

FIGURE 9 is an orthographic view of the polymer spacer pattern deposited on the double conductors of Figure 8.

FIGURE 10 is an orthographic view of the pattern of double conductors deposited on the second layer of film.

FIGURE 11 is an orthographic view of the polymer spacer pathern deposited on the double conductors of Figure 10.

FIGURE 12 is an orthographic view of the double conductor pattern of the completed membrane switch assembly.

FIGURE 13 is an orthographic view of the polymer spacer pattern deposited on the double conductors in the completed membrane switch assembly.

FIGURE 14 is a fragmentary view of the membrane switch assembly illustrating the pattern of double conductors and polymer spacer in the completed membrane switch assembly.

FIGURE 15 is an enlarged view of a switch site.

FIGURE 16 is a cross-sectional side view taken along the lines 16-16 of Figure 15.

[0015] Referring to Figures 1 and 2, membrane switch assembly 10 having mounting means 118 is intended for mounting on a CRT 68. These figures also illustrate the use of a filter 70 disposed over the external surface 72 of the assembly.

[0016] Referring now to Figures 2 and 3, the mounting means 118 is comprised of extensions 114 which protrude from the outer perimeter 116 of the membrane switch assembly and coupled fastening assemblies 120 having two outer surfaces 122 and 124, the first outer surface 122 for attaching to extension 114 and the second outer surface 124 for attaching to the sides of the CRT. The inner surfaces 126 and 128 have a very large number of closely spaced hooking elements of the hook and loop type that engage with each other when the two parts are pressed together.

[0017] Figure 3 is an exploded view illustrating the mounting means 118, comprised of extension 114 and coupled fastening assembly 120 where surface 122 of the assembly 120 is adhered directly to the extension 114.

[0018] Figures 4 and 5 show an alternative embodiment of the mounting means 118. In this embodiment, extension 114 has an opening 130. Surface 122 of the coupled fastening assembly 120 is mounted to the first side 134 of a snap-in plate 132. The plate has a boss 138 extending from the opposite side 136. The boss 138 then snaps into the extension opening 130.

[0019] Figures 1 and 2 illustrate the use of the same type of mounting means as 118 for attaching the filter 70 to sides 142 of the CRT. The extensions 146 on the filter 70 are offset from extensions 114 on the switch for purposes of mounting.

[0020] Figures 6 and 7 illustrate an alternative embodiment of a membrane switch assembly 10' which is intended for mounting on a cathode ray tube 68. This embodiment requires alternative mounting means such as a clamp around the edge of the CRT or other means to adhere the switch to the face of the CRT. These figures also illustrate the use of filters 70, 70' disposed over the external surface 72, 72' of the membrane switch assembly 10, 10'.

[0021] Referring now to Figure 14, the assembly 10 is comprised of two layers 12 and 16 of substantially transparent film, the internal surfaces 14 and 18 of layers 12 and 16 having a plurality of double fineline conductors 20 thereon, ,the conductors crossing and being normally spaced from each other at the switch sites 34, the layers 12 and 16 being separated from each other by polymer spacer 32, applied over the conductors, the spacer being discontinuous at switch sites 34.

[0022] The double conductors 20 as shown in Figures 8 and 10 have a first portion 22, an intermediate portion 24, and a second portion 26. Each conductor 20 is reversely bent in its intermediate portion 24 so that the first and second portions 24 and 26 of the conductor are spaced apart and essentially parallel to each other.

[0023] As further illustrated in Figures 8 and 10, the conductors 20 are deposited on the internal surface 14 of the first layer 12 in a direction normal to the direction of the double conductors 20 deposited on the second layer 16. As is shown in Figure 12, the conductors 20 on the two layers 12 and 16 cross and are normally spaced apart at the switch points 34.

[0024] Referring to Figures 9, 11 and 13, the polymer spacer 32 is applied over the double conductors 20. For purposes of clarity, the double conductors 20 have been eliminated from these figures. The spacer 32 is discontinuous at the switch sites 34. Figure 9 shows the polymer spacer pattern 36 deposited on the first layer 12. Figure 11 shows the polymer spacer pattern 38 deposited on the second layer 16. Figure 9 also illustrates the isolated cross-shaped deposit 40 of polymer spacer deposited at the center 42 of the switch sites 34. This cross-shaped deposit can be made on either layer 12 or 16 of the film. Figure 13 illustrates the pattern 44 of the polymer spacer in the completed membrane switch assembly.

[0025] Referring now to Figures 14 and 15, Figure 14 is a fractional view of a portion of the membrane switch assembly 10. The lower layer conductors 46 are represented by a solid line and the upper layer conductors 50 are represented by broken lines. The lower layer polymer spacer 48 and the cross-shaped center spacer 40 are stippled, while the upper layer polymer spacer 52 is represented by broken lines. As is illustrated by these drawings, the spacer 32 is not deposited over the conductors in the switch site areas 34.

[0026] The operation of the invention is best illustrated by referring to Figure 15. When the switch site 34 is pressed, the double fmeline conductors 46 and 50 are compressed around the spacer to make electrical contact. Because each conductor 20 is a double fineline conductor at each switch site, the lower and upper conductors 46 and 50 cross at four locations 54, 56, 58 and 60, thus enabling the circuit to be completed at any of these locations. Thus, when force is applied in the center 42 of the switch site, electrical contact may actually be made at all four locations. If force is applied, for example, at the outer area 62 of the switch site, electrical contact will still be made at location 58.

[0027] Figure 16 is a cross-sectional view taken along line 16-16 of Figure 15. The upper layer 64 of film is separated from the lower layer 66 of film by the upper spacer 48, the cross-shaped center spacer 40. The upper and lower layer conductors cross at locations 58 and 60.

[0028] The mounting means are intended for use with membrane switches comprised of two layers of film having conductors deposited on their internal surfaces, the internal surfaces being separated by an insulating spacer containing openings for switch sites. Various spacing means can be used, including a third layer of film or deposits of polymer applied over the traces.

[0029] In the preferred embodiment, extensions of film were profiled on both layers of film having conductors thereon. In practicing the invention, however, it is only necessary that at least one layer of film have extensions protruding therefrom. The extensions should be of sufficient length to wrap around the perimeter of the CRT and be mounted on the tension band of the CRT.

[0030] Coupled fastening assemblies were adhered to the extensions after the switch had been formed and assembled. In the preferred embodiment, fastening assemblies having a pressure sensitive adhesive backing protected by release liners were used. Assemblies without the adhesive backing and a separate adhesive can also be used. Fastening assemblies of the type used are available from Velcro, USA, Inc., New York, New York 10022, and from Minnesota Mining and Manufacturing Co., St. Paul, Minnesota 55101.

[0031] In mounting the switches to a CRT, the CRT is removed from the housing. The switch is aligned in its proper place, release liner is removed from the second side of the fastening assembly, and the assembly is adhered to the side of the CRT. The film extensions being thin do not interfere when the housing is replaced.

[0032] The switch can be removed from the CRT, if necessary, by separating the individual coupled fastening assemblies. Furthermore, this invention permits easy realignment of the switch should the film stretch after prolonged use owing to the heat generated by the CRT, no longer lying flat against the CRT.

[0033] An alternative embodiment of the mounting means is shown in Figures 4 and 5. This embodiment permits the customer to snap in the fastener at the time the switch is ready for mounting on a CRT. Use of this embodiment eliminates bulk at the outer edges of the membrane switches, thus enabling the switches to be packaged closer together during shipping.

[0034] In making the membrane switch assembly, the double fineline, essentially parallel conductors can be electrodeposited metal such as copper or can be lines of conductive ink. Methods to deposit the conductors are known in the art.

[0035] The conductors are deposited as double finelines in order to provide for redundancy at the switch sites. Redundancy is a desirable feature to ensure that electrical contact will still be made at the site in the event force is applied at the outside edge of the switch site rather than the center of the site. Redundancy is also a desirable feature to ensure that electrical contact will be made in the event there is a break somewhere in one of the lines.

[0036] In the preferred embodiment, the lines of the double fineline conductors are approximately .013 cm wide, but other width lines may also be used. The distances between the two lines of each conductor and the adjacent conductors varies according to the number and size of switch sites. The switch sites need to be sufficiently spaced apart so that when force is applied to the site, the circuit is completed only at the desired site. Furthermore, the size and curvature of the cathode ray tube presents problems of parallax. The switch site must be of sufficient size to permit actuation even when the force is not applied in a direction normal to the site. The distance between the lines of a double conductor also determines whether an isolated spacer is needed at the center of the switch site to prevent sagging of the upper film layer and accidental completion of the electrical circuit. For example, with membrane switch assemblies having parallel lines of each double conductor ₀.₅ cm apart, a center spacer was also required to keep the first and second film layers separate.

[0037] In the preferred embodiment, after the double conductors were deposited on the film layers, an ultraviolet curable polymer was applied parallel to and over the traces, except at the switch sites. The polymer may be applied using a variety of methods including silkscreening and transfer printing. This polymer is the spacer which keeps the two layers separated until force is applied to complete a circuit. An isolated deposit may be applied to one layer at the center of the switch site.

[0038] A number of polymers can be used for this purpose. The polymer used should meet the following criteria. The cured polymer should be essentially optically dear. The means of curing the polymer must be one that will not adversely effect the performance of the switch. It should also be sag resistant and stable at the temperature of the operating cathode ray tube and the temperature required for manufacturing the assembly. One polymer which can be used in Colonial 580-319 available from Colonial Printing Ink Co., East Rutherford, New Jersey 07073.

[0039] When electrodeposited conductors are used, the polymer can be used as a mask for plating. If additional plating is desired, use of the polymer spacer according to the disclosed invention minimizes the amount of precious metal needed and thereby reduces the cost of the assembly. Gold, silver and palladium can all be used.

[0040] After the polymer spacer has been deposited on the film and any additional plating has been completed, individual layers are profiled to shape and formed to the desired spherical radius. The formed layers are then adhered together along their perimeters to complete the assembly.

[0041] The double fineline conductors being only .013 cm or less wide are nearly invisible when the assembly is mounted on a cathode ray tube.

[0042] It is often desirable to use filters with membrane switches mounted on CRT's to reduce glare and to protect the surface of the switches. Filters can be profiled and mounted in the same manner as the switch. The extensions on the filter are offset from those of the switch for ease in mounting. This permits easy replacement of filters should they become scratched or otherwise unusable.

Claims

1. A membrane switch assembly (10) having mounting means (118) for mounting the assembly (10) to a cathode ray tube (68) the assembly (10) comprised of two layers (12, 16) of substantially transparent film having internal surfaces (14, 18) that are separated from each other by spacing means, the spacing means having openings therein constituting switch sites (34), the internal surfaces (14, 18) of each layer having conductors (20) thereon, the conductors (20) crossing and being normally spaced from each other at the switch sites (34), the mounting means (118) being characterized in that:

a plurality of extensions (114) protrude from the perimeter (116) of at least one of the layers of film,

a patch of a coupled fastening assembly (120) is attached to each extension (114),

the fastening assembly (120) is comprised of two separable parts, the inner surfaces (126, 128) of which have a very large number of closely spaced hooking elements of the hook and loop type that engage with each other when the two parts are pressed together, whereby,

when the switch assembly (10) is aligned against the CRT (68), the extensions (114) wrap around the perimeter of the CRT (68) enabling the outer surfaces (122, 124) of the coupled fastening assemblies (120) to be attached to one or more sides of the CRT (68).

2. An assembly as claimed in claim 1 characterized in that the coupled fastening assembly (120) is attached to the extension (114) by means of a snap-in plate (132), the plate having one side (134) for attaching to the coupled fastening assembly (120) and a second side (136) having a boss (138) sized to snap into an opening (130) in the extension (114).

3. A membrane switch assembly (10, 10') comprised of two layers (12, 16) of substantially transparent film having internal surfaces (14, 18) that are separated from each other by spacing means, the spacing means having openings therein constituting switch sites (34), the internal surfaces (14, 18) of each layer having fineline conductors (20) thereon, the conductors crossing and being normally spaced from each other at the switch sites (34), the assembly (10, 10') being characterized in that:

the internal surface of the first layer (14) has a plurality of spaced-apart parallel double fineline conductors (20), each double conductor having a first portion (22), an intermediate portion (24) and a second portion (26), the first and second portions (22, 26) of the double conductor (20) being essentially parallel to each other with the intermediate portion (24) connecting the first and second portions (22, 26), the distance between the first and second portions (22, 26) of each double conductor (20) being less than the distance between adjacent conductors (20),

the internal surface (18) of the second layer (16) has a plurality of spaced-apart parallel double fineline conductors (20) applied in a direction normal to the direction of the first layer conductors, the switch sites (34) being crested by the crossing double fineline conductors (20) of the first and second circuit layers (14, 18) when they are assembled, thus giving four points of contact (54, 56, 58, 60) at each site,

the spacing means is comprised of an insulating ultraviolet curable polymer (32) applied in parallel strips over the conductors, the spacer being discontinuous at the switch sites (34), whereby,

as force is applied at the switch site (34) to bring the two layers (14, 18) of conductors together, an electrical circuit can be completed at any one of the four contact paints (54, 56, 58, 60) thus providing redundancy and insuring the completion of the electrical circuit even if the force has been applied at the periphery of the switch site (34).

4. A membrane switch assembly (10, 10') as set forth in claim 1 or 3 characterized in that the spacing means is an essentially optically clear polymer (32).

5. The membrane switch assembly (10, 10') as set forth in claim 1 or 3 characterized in that the polymer spacer (32) also serves as a plating mask.

6. The membrane switch assembly (10, 10') as set forth in claim 1 or 3 characterized in that a noble metal, selected from the group consisting of gold, silver and palladium, has been plated on the switch site (34).

7. The membrane switch assembly (10, 10') as set forth in claim 1 or 3 characterized in that the assembly (10, 10') is mounted on a cathode ray tube (68).

8. The membrane switch assembly (10, 10') as set forth in claim 1 or 3 characterized in that a substantially transparent filter (70, 70') is dispersed over the external surface of the outermost layer of the switch assembly (10, 10').

9. The membrane switch assembly (10, 10') as set forth in claim 1 or 3 characterized in that the conductors (20) are electrodeposited fineline conductors.

10. The membrane switch assembly (10, 10') as set forth in claim 1 or 3 characterized in that the conductors (20) are lines of conductive ink.

Drawing