Remote Membrane Switch

This invention relates to multi-layered membrane switches.

Backlighting is generally provided for switch panels by placing a light source behind transparent switch areas. Because membrane switches typically have opaque electrical contacts within the switches immediately below the switch depressing areas, it is often impossible to have a fully backlit switch area. This creates limitations in low light areas of being able to locate and read the switches on a panel.

I have discovered that full backlighting can be provided for a membrane switch by placing the contacts within the switch remotely from the area to be depressed. The contacts are spaced apart, carried by different layers, and actuated by increased pressure on the non-carrying surface of a flexible contact-supporting layer, the pressure being caused by decreasing the volume in a primary chamber directly below the switch depressing area and communicating with a secondary chamber partially bounded by the non-carrying surface of the flexible contact-supporting layer.

I turn now to description of the drawings and the structure and operation of a preferred embodiment.

FIG. 1 is a diagrammatic plan view of a switch according to the invention.

FIG. 2 is a vertical sectional view, taken at 2--2, of said switch.

In FIG. 1 is shown membrane switch 10 having face layer 12 made of transparent polycarbonate 10 mils thick having a texturized upper surface and line 14 of opaque ink on its bottom surface indicating a switch depressing area 15. Indicia can also be inked on the bottom surface of layer 12. Also shown are primary chamber 16 and passage 18, which connects the primary chamber to the secondary chamber 20 via hole 22.

Referring to FIG. 2, face layer 12 is adhered to primary flexible layer 24 (5 mils thick polyester) by adhesive layer 26 (2 mils thick acrylic thermosetting adhesive). Beneath flexible layer 24 is spacer layer 28 (5 mils thick polyester sandwiched between 2 mils thick layers of acrylic thermosetting adhesive), which is shown diagrammatically in FIG. 2. Therebeneath is less-flexible spacer layer 30 (30 mils thick polycarbonate); spacer layer 32 (similar to layer 28); secondary flexible layer 34 (5 mils thick polyester); contact spacer layer 36 (similar to layer 28); lower contact support layer 38 (5 mils thick polyester); and finally adhesive layer 40 (2 mils thick layer of cured acrylic adhesive). A release sheet (not shown), which will be removed prior to use, is beneath adhesive layer 40. Primary chamber 16 and passage 18 are partially defined by cut out portions within spacer layer 28. Hole 22 is defined by a cut out portion of less-flexible layer 30. Contacts 42, 44 are carried by the lower surface of secondary flexible layer 34 and the upper surface of lower contact support layer 38, respectively, within switch chamber 46 located directly below secondary chamber 20. Contacts 42, 44 are pads of conductive silver paint about 0.4 mil thick and sold by Acheson Colloids of Port Huron, Mich., under the designation Electrodag 415SS. The contacts 42, 44 are connected to external leads (not shown) for connection to external circuitry.

In operation switch 10 is mounted with a light source underneath transparent switch depressing area 15. When face layer 12 is depressed by a finger at area 15, primary flexible layer 24 will be depressed, thereby decreasing the volume of primary chamber 16, forcing air to flow through passage 18 and increasing the pressure in secondary chamber 20, thereby depressing secondary flexible layer 34 and making contact between contacts 42, 44. Less-flexible spacer layer 30 ensures that the volume of primary chamber 16 will decrease when flexible layer 24 is depressed and prevents electrical contact from being made when face layer 12 is depressed in an area other than area 15.