United States Patent (11) 72) 21 ) 22) () 73 (54) (52) (51) Inventor Alfred J. MacIntyre Nashua, N.H. Appl. No. 884,530 Filed Dec. 12, 1969 Patented Dec. 7, 1971 Assignee Sanders Associates, Inc. Nashua, N.H. PRESSURE-SENSITIVE INDICATINGSWITCH 14 Claims, 4 Drawing Figs. U.S. Cli... 35/149, 313/108,315/159 int. Cli... H05b 37/02 Field of Search... 313/108, 108 E; 31.5/55, 149, 159, 169; 200/66 C; 338/47 56) References Cited UNITED STATES PATENTS 2,816,236 12/1957 Rosen. 315155 X 2,951,817 9/1960 Myers... 338/47 X 3,358,185 12/1967 Lally... 315/169 X 3,379,927 4/1968 Yando.... 315155 Primary Examiner-Roy Lake Assistant Examiner-Lawrence J. Dahl Attorney-Louis Etlinger ABSTRACT: A pressure-sensitive indicating switch comprises an electroluminescent lamp assembly having a pressure-sensi tive variable resistance layer interposed between the phosphor and one conductor thereof. Depression of the switch com presses the pressure-sensitive layer, reducing its resistance and allowing current flow through the phosphor thereby illuminat ing the lamp. Additional provisions include an optical feed back means and means for remotely activating the lamp as sembly. 4.
PRESSURE-SENSTEVE INDICATINGS WITCH BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates generally to the field of elec- 5 trical switching apparatus and more particularly to pressure sensitive switches having an electroluminescent indicating ele ment as an integral part thereof. 2. Description of the Prior Art O Prior to the present invention the field of pressure-sensitive indicating switches was typified by assemblies using mechani cal switch contacts and a filament bulb in series with the con tacts. A number of problems attend the use of such switches including the difficulty presented in sealing mechanical switch 15 contacts against humidity and the catastrophic failure mode of lamp filaments as well as their relatively high current con sumption and heat generation characteristics. Objects and Summary of the invention 20 It is therefore a primary object of the present invention to provide a new and novel pressure-sensitive indicating switch. It is another objective of the present invention to provide apparatus of the above-described character having no 25 mechanical switch contacts. It is an additional object of the present invention to provide apparatus of the above-described character which is not sub ject to catastrophic failure. It is a further object of the present invention to provide ap- 30 paratus of the above-described character having an optical latch to maintain switch illumination after removal of pres SC. It is also an object of the present invention to provide ap paratus of the above-described character including means for 35 remotely activating the switch indicating means. The foregoing and other objectives of the present invention are achieved by providing an electroluminescent lamp as sembly having a pressure-sensitive variable resistance layer in terposed between the phosphor and one conductor of the as- 40 sembly. Depression of the switch compresses the variable re sistance layer thus permitting current to flow through the phosphor layer thereby illuminating the lamp. In one embodi ment a second pressure-sensitive variable resistance layer is disposed between conductive layers and the assembly is disposed adjacent a pressure-sensitive electroluminescent in dicating assembly. Depression of the switch compresses both variable resistance layers thereby closing an electrical circuit coupled across the second variable resistance and activating the electroluminescent phosphor. A photoconductive optical feedback feature may be used to provide switch illumination which persists for a period of time after pressure is removed from the switch. In a further embodiment of the invention a transducer activated by closure of an external circuit may be 55 provided whereby the pressure-sensitive electroluminescent lamp assembly is activated. These and other objects, features and advantages of the present invention will become more apparent from the follow ing detailed description taken in conjunction with the ap- 60 pended drawings. BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a schematic cross section view of a pressure-sensi- 65 tive indicator constructed in accordance with the principles of the present invention. FIG. 2 is a schematic cross section view of a pressure-sensi tive indicating switch in accordance with the present inven tion. 70 FIG. 3 is a schematic cross section view of a pressure-sensi tive switch indicator having an optical feedback means. FIG. 4 is a schematic cross section view of a pressure-sensi tive indicator having means for remotely applying activating pressure thereto. 75 2. DESCRIPTION OF PREFERRED EMBODMENTS With reference now to FIG. there is schematically illus trated in cross section a pressure-sensitive indicator in ac cordance with the present invention. A layer of pressure-sensi tive variable resistance material 2.0 is disposed between a layer of electroluminescent phosphor 2 and a rigid substrate con ductor 4. The other electrically conductive layer 16 essential to the electroluminescent lamp assembly is formed of an opti cally transmissive and preferably flexible material such as metallized mylar. The flexible conductor 16 may then be covered with an optically transmissive, flexible layer of insula tion 18. The pressure-sensitive variable resistance layer 10 may comprise a pressure cell made from the rare earths processed with zirconium tetra-chloride as described by Dudley B. Clark in an article entitled "Pressure-Sensitive Material Measures Explosion Forces...or Footfall of a Fly' ap pearing in the Sept. 16, 1957 issue of Product Engineering. In the alternative a variable resistance material formed of pliable polyvinyl chloride with a conductive filler as described in U.S. Pat. No. 2,951,817 which issued to T. E. Myers on Sept. 6, 1960 may also be of utility in the practice of the present inven tion. In either case the effect of the Pressure-sensitive variable resistance layer 0 is to prevent current flow through the elec troluminescent phosphor when no pressure is applied to the flexible front surface 18 of the cell. When pressure is applied to surface 18 the flexible conductor 16 and phosphor layer 12 are deformed such that the pressure-sensitive variable re sistance layer 10 is compressed. This compression lowers the electrical resistance of the layer 10 and current from the AC source 29 flows from the rigid conductor 14, through the pres sure-sensitive layer 0 and the phosphor layer 12 to the flexi ble conductor 6 thereby causing the emission of light from the phosphor layer 2 and illuminating the switch. Removing pressure from the surface 18, due to the resiliency of the pres sure-sensitive material 10, raises the resistance of layer 10 thus causing a voltage drop sufficient to prevent the emission of light from the phosphor layer 12. It will be understood that a particular application of the invention may require the use of an additional light reflecting layer between the phosphor and pressure-sensitive layers to enhance the switch illumination in accordance with known electroluminescent fabrication techniques. Being known to those skilled in the art such reflecting layer is not illustrated for the purposes of clarity, A pressure-sensitive indicating switch according to the present invention is schematically illustrated in the cross sec tion view of FIG. 2. This embodiment comprises a pressure sensitive indicating element 22 which is of the same construc tion and operation as the apparatus shown in FIG. and wherein like elements are identified by like numerals and switching element 24. The switching element 24 includes a second layer 26 of pressure-sensitive variable resistance material of the character described above which is disposed between electrically conductive layers 28 and 30. An external circuit, schematically shown for illustrative purposes only as a power supply 32 and a utilization means 34, is coupled across the conductive layers 28 and 30. The indicating element 22 and switching element 24 are electrically isolated from one another by a layer of insulation 36 of any suitable type. In practice the indicating and switching elements 22 and 24 together with the insulating layer 36 may be laminated together to form the complete pressure-sensitive indicating switch. in operation when pressure is applied to the front sur face 18 of the indicating element both layers of pressure-sensi tive variable resistance material 19 and 26 are compressed, and the respective resistances thereof are lowered permitting current to flow therethrough. The current flow from AC source through the indicating element 22 causes emission of light from the electroluminescent phosphor layer 12 thereby illuminating the switch face. The lowering of the electrical re sistance of layer 26 operates to close the external circuit and permit current flow from the power supply 32 through the utilization means 34.
3 FIG. 3 is a schematic cross section view of an embodiment of the present invention wherein an optical feedback feature is provided. In this embodiment an optically transparent electri cally conductive layer 38 is interposed between a layer of elec troluminescent phosphor 40 and an annular layer of pressure sensitive variable resistance material 42. A photoconductive element 44 is disposed through the pressure-sensitive layer 42 such that it is in electrical contact with the transparent con ductor 38 and the rear substrate conductor 46. The front con ductor 48 is both flexible and optically transparent as discussed hereinabove and may have a layer of insulation disposed over the front surface thereof. When pressure is ap plied to the front surface of the indicator the electrical re sistance of the pressure-sensitive material 42 is lowered in the above-described manner and current flows from the AC source 52 through the substrate conductor 46, pressure-sensi tive resistance 42, transparent conductor 38, electrolu minescent phosphor 40 and front conductor 48 and light is emitted by the phosphor 40. Some of the light from the phosphor 40 is fed back through the transparent conductive layer 38 to the surface of the photoconductive element 44 thereby lowering the electrical resistance thereof. Thus when pressure is removed from the front surface of the indicator of FIG. 3 the resistance decay characteristic of the photocon ductive. element 44 continues to permit current flow through the phosphor layer 40 and once activated the indicator remains illuminated. It will be apparent that the indicator of FIG. 3 is directly applicable to use in combination with the switching element discussed hereinabove with reference to FIG 2. Turning now to FIG. 4 there is schematically illustrated in cross section a pressure-activated switch indicator in ac cordance with the present invention. The indicating element 53 comprises a flexible conductive layer 54, a layer of pres sure-sensitive variable resistance material 56, a layer of elec troluminescent phosphor 58 and an optically transparent front conductor 60 which may be provided with a layer 62 of insu lating material. The activating element 64 comprises a trans ducer layer 66 formed of one of a class of ceramic materials typified by barium titanate. These materials inhibit the piezoelectric effect and enhance the electrostrictive effect; thus when laminated between first and second flexible con ductive layers 68 and 70 across which an electric field is ap plied, the transducer deforms in a cupping action. The trans ducer 66 together with its flexible conductive layers 68 and 70 is electrically isolated from the indicating element 53 by a layer of insulation 69 and is placed in an external electrical circuit herein illustrated merely as a power supply 72, utiliza tion means 73 and switch 74. When switch 74 is closed an electric field is applied across the transducer 66 and the ac tivating element 64 deforms in a cupping action thus applying pressure to the flexible conductor 54 and pressure-sensitive variable resistance layer 56. Compression of the pressure-sen sitive layer 56 causes a reduction in the electrical resistance thereof and current flows from the AC source 76 activating the electroluminescent phosphor 58 in the above-described manner. Thus the present invention provides a pressure-sensi tive electroluminescent indicator which is activated by a remote switch. It will be apparent that the optical feedback feature illustrated in FIG.3 may further be incorporated in the embodiment of FIG. 4 and thereby provide a latching-type in dicator. It will be apparent from the foregoing description that the objectives of the present invention have been efficiently met and since certain changes in the above-described construction will become apparent to those skilled in the art it is intended that all matter contained in the foregoing description or shown in the appended drawings shall be interpreted as illustrative rather than in a limiting sense. Having described what is new and novel and desired to secure by Letters Patent, what is claimed is: 1. A pressure-sensitive indicating switch comprising: a layer of electroluminescent phosphor material, 10 15 20 25 30 35 40 55 60 65 70 75 4 a layer of optically transmissive electrically conductive material disposed in electrical contact with said phosphor layer, a layer of pressure-sensitive variable resistance material disposed in electrical contact with said phosphor layer opposite said optically transmissive conductive layer, an electrically conductive substrate layer disposed in elec trical contact with said pressure-sensitive variable re sistance layer opposite said phosphor layer, and a source of electrical power coupled between said optically transmissive and substrate conductive layers whereby pressure applied to said optically transmissive conductive layer produces compression of said pressure-sensitive variable resistance material reducing the resistance thereof and causing current from said source to flow through the assembly activating said phosphor material. 2. Apparatus as recited in claim 1 wherein: formed of a rare earth treated with zirconium tetra chloride. 3. Apparatus as recited in claim 1 wherein: formed of pliable polyvinyl chloride having an electrically conductive filler distributed therein. 4. Apparatus as recited in claim 1 wherein: said optically transmissive layer is formed of a flexible elec trically conductive material. 5. Apparatus as recited in claim 4 wherein: said flexible optically transmissive conductive material is metallized mylar. 6. Apparatus as recited in claim 1 further including: a layer of optically transmissive electrical insulation disposed on the surface of said optically transmissive con ductive layer opposite said phosphor layer. 7. Apparatus as recited in claim 1 further including: a second optically transmissive electrically conductive layer disposed between said phosphor layer and said pressure sensitive variable resistance layer, and a photoconductive element disposed through said pressure sensitive variable resistance layer in electrical contact with said substrate conductive layer and said second opti cally transmissive conductive layer whereby optical feed back is provided such that phosphor material remains ac tivated subsequent to removal of pressure from said switch. 8. Apparatus as recited in claim 1 further including: a second layer of pressure-sensitive variable resistance material, first and second layers of electrically conductive material disposed in electrical contact with opposed surfaces of said second pressure-sensitive layer, a layer of electrical insulation disposed between one of said first and second conductive layers and said substrate con ductive layer, and an external circuit coupled across said first and second con ductive layers whereby pressure applied to said optically transmissive conductive layer produces compression of said first and second pressure-sensitive variable resistance layers thereby activating said phosphor material and said external circuit. 9. A pressure-activated switch indicator comprising: a transducer layer which undergoes predetermined defor mation under the influence of an electrical field, first and second flexible electrically conductive layers disposed in electrical contact with opposed surfaces of said transducer layer, a selectively activated external electrical circuit coupled between said first and second conductive layers, a layer of electrical insulation disposed adjacent one of said first and second conductive layers opposite said trans ducer layer, a third electrically conductive layer disposed adjacent said insulation layer,
5 a layer of pressure-sensitive variable resistance material disposed in electrical contact with said third conductive layer opposite said insulation layer, a layer of electroluminescent phosphor material disposed in electrical contact with said pressure-sensitive layer op posite said third conductive layer, an optically transmissive electrically conductive layer disposed in electrical contact with said phosphor layer opposite said pressure-sensitive layer, and a source of electrical power coupled between said optically transmissive and third conductive layers whereby activa tion of said external circuit produces an electric field across said transducer causing deformation thereof such as to apply pressure to said pressure-sensitive variable re sistance layer thereby activating said phosphor material. 10. Apparatus as recited in claim 9 further including: a second optically transmissive electrically conductive layer disposed between said phosphor layer and said pressure sensitive variable resistance layer, and a photoconductive element disposed through said pressure 10 15 20 6 sensitive variable resistance layer in electrical contact with said third conductive layer and said second optically transmissive conductive layer whereby optical feedback is provided such that said phosphor material remains ac tivated subsequent to deactivation of said external circuit. 11. Apparatus as recited in claim 9 wherein: formed of a rare earth treated with zirconium tetra chloride. 12. Apparatus as recited in claim 9 wherein: said pressure-sensitive variable resistance layer is formed of pliable polyvinyl chloride having an electrically conduc tive filler distributed therein. 13. Apparatus as recited in claim 9 wherein: said transducer is formed of a ceramic material which in hibits the piezoelectric effect and enhances the electros trictive effect under the influence of an electric field. 14. Apparatus as recited in claim 13 wherein: said transducer is formed of barium titanate. 25 30 35 40 55 60 65 70 75