MXPA97008185A - Switch device activated by pres - Google Patents

Abstract

The present invention relates to a switch device without pressure sensitive sparks that includes a layer of piezoresistive polymeric cellular foam, at least two conductive layers and an insulating spacer element having at least one hole. When pressure is applied to the device, the piezoresistive foam itself is distributed through the orifice of the separator element and makes electrical contact between the conductive layers. The strength of piezoresistive foam varies with the amount of pressure applied to provide an analog function as well as on-off. The device can also provide multiple interruption and detection capabilities tangenci

Description

PRESSURE-OPERATED SWITCH DEVICE BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a pressure-operated switch device for closing or opening an electrical circuit, and particularly to a safety mat for operating and stopping machinery in response to movement of personnel. on the carpet. 2. BACKGROUND OF THE INVENTION Electric pressure operated carpet switches are known in the art. Typically, these carpet switches are used as floor mats around machinery to open or close electrical circuits. For example, a floor carpet switch that opens an electrical circuit when stepped on it can be used as a safety device to stop machinery when a person walks in an unsafe area around machinery. Conversely, the floor mat switch can be used to close a circuit and thereby keep the machinery operating only when the person is standing in a safe area. In an alternative mode, the floor mat switch may be used "to sound an alarm when walking on it or to perform any such function." U.S. Patent No. 4,497,989 to Miller discloses an electric switch on a rug that has a pair of outer layers of use, a pair of internal layers that serve as barriers to moisture between the outer layers of use, and a separating layer between the layers that act as a moisture barrier, US Patent 4,661,664 to Miller discloses a highly sensitive switch in carpet including external sheets, an open work separator sheet, conductive sheets interposed between the outer sheets on opposite sides of the separator sheet for flexing contact through the separator sheet, and a compressible deflection sheet interposed between a conductive sheet and the adjacent external sheet, the deflection sheet being compressible in the form of a It lifts for the protrusion through the separating sheet to make contact with the conductive sheets with the movement of the external sheets between them. U.S. Patent No. 4,845,323 to Beggs discloses a flexible touch switch for determining the presence or absence of weight, such as a person on a bed. U.S. Patent No. 5,019,950 to Johnson describes a combination of timed night light, on the side of the bed that lights a lamp on the side of the bed when a person steps on a carpet adjacent to the bed and lights a stopwatch when the person leaves the carpet. The timer turns off the lamp after a predetermined time. U.S. Patent No. 5,264,824 to Hour discloses a carpet floor system for sound emitting flooring. While these rugs have developed useful functions, an improved safety mat is still necessary that can respond not only to the presence of force, but also to the amount and direction of the force applied to it. Likewise, the carpet switches currently used usually have "dead zones". Dead zones are non-reactive areas in which an applied force does not give rise to the breaker action. For example, the peripheral area around the rim of carpets conventionally used is usually a "dead zone". In the active area where the interruption occurs there is a danger of sparking when the two conductive metal sheets touch. It would be advantageous to have a carpet in which dead zones and sparks are reduced or eliminated. Compressible piezoresistive materials having electrical resistance that varies according to the degree of compression of the material are also known in the art. These piezoresistive materials are described in U.S. Patent Nos. 5,060,527, 4,951,985, and 4,172,216, for example.

SUMMARY OF THE INVENTION A pressure sensitive switch device is provided herein. In one embodiment the device consists of a first and second conductive layer; a layer of compressible piezoresistive material positioned between the first and second conductive layer; and at least one isolating spacer element positioned between the piezoresistive material and at least the first or second conductive layer, the spacer element having a plurality of holes. The compressible piezoresistive material preferably has a resistance from about 500 ohms to about 100,000 ohms when it is not compressed and a resistance from about 200 ohms to about 500 ohms when compressed. The first and second conductive layer each preferably has a lower resistance than the piezoresistive layer. Preferably the resistance of the first and second conductive layer is less than half of the piezoresistive layer. More preferably, the resistance of the first and second conductive layer is less than 10% of the piezoresistive layer, and more preferably the conductive layers have a lower resistance of l '? than the piezoresistive layer. These resistances are the resistance measured in the direction of the flow of the current. The compressible piezoresistive material is placed through at least some of the orifices of the spacer element to make electrical contact with the conductive layer separated by the spacer element in response to the force applied thereto. In another embodiment, the device consists of a separating element having an insulating layer and an upper conductive layer, the separating member having at least one hole; a layer of piezoresistive material placed on the separator element and being in electrical contact with the upper conductive layer; and a lower conductive layer placed below the separator element. At least a portion of the lower conductive layer may contain a plurality of small electrodes individually placed in alignment with a respective hole. In another embodiment, the device includes a plurality of isolating spacer elements positioned between the piezoresistive material and the base. The spacer elements, and preferably the base as well, each have an upper layer of conductive material and each has at least one opening. The openings are aligned, configured and dimensioned to form at least one hollow space defined by stepped sides. The void space has a relatively large diameter orifice adjacent the piezoelectric material and a relatively smaller diameter orifice adjacent the base. The separating elements form a vertical stack of layers oriented in the horizontal direction, the conductive layer of the separating element in the uppermost part is an electrical contact with the piezoresistive material. When a force is applied downwards to the device, the piezoresistive material moves through the empty space in successive contact with the other conductive layers. In still another embodiment, the pressure-operated switch means includes the sensing means sensitive to the shear force to make electrical contact between the piezoresistive material and an emitting or receiving electrode. Particularly, the device may include a primary and secondary receiving electrode, the primary electrode making contact in response to the compressive force down applied to the device, and a secondary receiving electrode making contact in response to the shear force. This detection means may include, for example, a separating element that moves in a resilient manner in response to cutting or to a projection of piezoresistive material exposed to the shearing force and movable in contact with a secondary receiving electrode.

BRIEF DESCRIPTION OF THE DRAWINGS Figure 1 is a partially cut away perspective view of the apparatus. Figure IA and IB are transverse elevational views of a carpet switch that has a segmented conductive layer, in conditions not activated and activated, respectively. Figure 2 is a perspective view partly cut away of an alternative embodiment of the apparatus. Figure 3 is a partially cut away perspective view of a unit of the spacer element. Figure 3A is a view of an elevation cut-out of a mode of the switch device having a point separator. Figure 4 is a view of a section in elevation of a stacked multiple switch device. Figure 5 is an elevation view of a section of the device of Figure 4 under compression. Figure 6 is a sectional elevation view of an alternative embodiment of the present invention that detects shear force.

Figure 7 is a view of an elevation cut of the embodiment shown in Figure 6 under vertical compression. Figure 8 is a view of an elevation cut of the embodiment shown in Figure 6 with applied shear stress. Figure 9 is a view of a cut in elevation of an alternative cut detector device. Figure 10 is a sectional elevation view of the embodiment shown in Figure 10 with applied compressive shear force. Figure 11 is an exploded perspective view of one embodiment of the invention of the carpet switch assembled in a frame. Figure 12 is a sectional elevation view showing one embodiment of the carpet switch including the supporting struts. Figure 13 is a partially cut-away sectional view of the embodiment of the carpet switch shown in Figure 12. Figure 14 is a detailed section of the carpet switch mode support area shown in "Figure 12 with compression. Figure 15 is a sectional view showing a lever type marginal device for removing dead areas along the edge of the carpet switch Figure 16 is a spring-loaded coupling device for removing dead areas along the edge of the coupled carpet switches Figure 17 is a diagram of an electrical circuit for use with the apparatus of the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT (S) The term "insulator", "conductor", "strength" and its related forms are used herein to indicate the electrical properties of the materials described, unless Indicate otherwise. The terms "superior", "inferior", "above" and "below" are used interrelated. The terms "elastomer" and "elastomeric" are used herein to indicate the material that can suffer at least 10"of elastic deformation. Commonly, "elastomeric" materials suitable for the purposes described herein include polymeric materials such as natural and synthetic rubbers and the like. As used herein the term "piezoresistive" refers to a material that has an electrical resistance that decreases in response to compression caused by mechanical pressure applied to it in the direction of the current path. These piezoresistive materials are usually resilient cellular polymeric foams with conductive coatings that cover the walls of cells. "Resistance" refers to the opposition of the material to the flow of the electric current along the path of the current in the material and is measured in ohms. The resistance increases in proportion to the length of the current path and the specific resistance or "resistivity" of the material, and varies in inverse proportion to the amount of cross-sectional area available for the current. Resistivity is a property of the material and can be thought of as a measure of (strength / length) / area. More particularly, the resistance can be determined according to the following formula: R = (pL) / A (I) where R = resistance in ohms p = resistivity in ohms-inches L = length in inches A = area in square inches The current through a circuit varies in. ratio to applied voltage and inversely to resistance, as demonstrated by Ohm's law: I = V / R (II) where I = current in amperes V = voltage in volts R = resistance in ohms Typically, resistance of a flat conductive sheet through the plane of the sheet, that is, from one bank to the opposite bank, is measured in units of ohms squared. For any given conductive sheet thickness, the value of the resistance across the square remains the same no matter what size the square has. In applications where the path of the current is from one surface to another, the conductive sheet, ie in a direction perpendicular to the plane of the sheet, the resistance is measured in ohms. Referring to Figure 1, the pressure activated carpet switch 10 of the present invention includes a base 11 having a conductive layer 12 disposed thereon, a compressible piezoresistive material 14 sandwiched between two spacer elements, ie the separators 13. and 15, and preferably an elastomeric protective sheet 17 with a conductive layer or film 17b on the underside thereof adjacent one of the separators. Although two spacer elements are shown, ie, separators 13 and 15, it should be appreciated that only one spacer element is necessary, a second spacer element being preferred and optional.

More particularly, the base layer 11 is a sheet of any type of durable material capable of withstanding the stresses and pressures that are to be printed on the safety mat 10 under the operating conditions. The base 11 can be manufactured from, for example, plastic or elastomeric materials. A preferred material for the base is a thermoplastic such as a polyvinyl chloride ("PVC") sheet, which can be advantageously thermosealed otherwise bonded to a PVC protective sheet at the margins to achieve a tight seal of the carpet of security. The sheet may be, for example, 1/8 inch to inches thick and may be embossed or fluted. Moreover, the base 11 may alternatively be rigid or flexible to accommodate different media or applications. The conductive layer 12 is a metal foil, or film, applied to the upper part of the base 11. Otherwise, the conductive layer 12 can be a plastic foil coated with a conductive film 11. This conductive coating can also be deposited on the base 11 (for example by chemical deposition). The conductive layer 12 can be, for example, a copper or aluminum foil, which has been adhesively bonded to the base 11. The conductive layer 12 should preferably have a strength that is less than the strength of the piezoresistive material 14 that outlined below. Typically, conductive layer 12 has a lateral resistance, or edge-to-edge resistance from about 0.001 to about 500 ohms per square [sic]. Preferably, the resistance of the conductive layer 12 is less than half of the piezoresistive layer 14. More preferably, the resistance of the conductive layer 12 is less than 10% of the piezoresistive layer 14. More preferably, the resistance of the conductive layer 12 is less than 1% than the piezoresistive layer 14. The low relative resistance of the conductive layer 12 helps to ensure that only significant amounts of resistance encountered by the current as it passes through the apparatus 10 is in this portion of the path of the current that is normal to the plane of the layers. The conductive layer 12 remains stationary relative to the base 11. However, another conductive layer 17b, as described below, is resiliently movable when a compression force is applied. The upper conductive layer 17b also has little relative resistance for the piezoresistive material, which is disposed between the upper conductive layer 17b and the lower conductive layer 12. In this manner, the measured resistance is indicative of the vertical displacement of the conductive layer 17b and the Compression of the piezoresistive foam 14, which, in turn, is related to the force applied downwards in the device. The lateral position of the force downwards, that is, whether the force is applied near the center of the device or near one of the edges, does not significantly affect the measured resistance. The separating layer 13 functions as a separating element and comprises a sheet of electrically insulative material having a plurality of holes 13a, which may be an array of holes of similar or dissimilar sizes, or, as shown, a random array of holes with different sizes. The separator 13 is preferably relatively rigid compared to the foam layer 14 on it. Alternatively, the separator 13 can be a resilient, compressible polymer foam. The spacers provide an on-off function. By separating the conductive layer of piezoresistive material 14 from the conductive layer 12, the separator 13 prevents electrical contact therebetween unless a descending force of sufficient magnitude is applied to the upper part of the carpet switch 10. In this way , the size and configuration of the separator 13 can be designed to achieve predetermined threshold values of force, or weight, under which the carpet switch 10 will not be actuated. This feature also controls the force ratio to the analog output when the piezoresistive material or configuration is compressed. Upon application of a predetermined sufficient amount of force the conductive piezoresistive material 14 is pressed through the holes 13a to make electrical contact with the lower conductive layer 12. The amount of predetermined minimum force sufficient to operate the switch depends at least in part on the diameter of the orifice, the thickness of the separator and layer 13 and the degree of stiffness of the separator 13 (a very rigid separator requires a greater activation force than a less rigid separator, ie, compressible). This principle applies to all switching devices in it that use a separator. Commonly, the ranges in the thickness of the separator 13 are from about 1/32 inch to about% inches. The holes 13a in the diameter range from about 1/16 inches to about inches. It is possible to choose other smaller or larger dimensions suitable for the desired application. The dimensions given herein are simply for the exemplification of one of the most suitable size ranges. The piezoresistive material 14 is preferably a conductive piezoresistive foam consisting of a flexible and resilient sheet of a cellular polymeric material having a resistance that changes in relation to the magnitude of the pressure applied to it. Ordinarily, the piezoresistive foam layer 14 may be in the range of 1/16 inch to about. inches, although it is possible to use other thicknesses when appropriate. A conductive polymeric foam suitable for use in the present apparatus is described in U.S. Patent No. 5,060,527. Other conductive foams are described in U.S. Patent Nos. 4,951,985 and 4,172,1216. In general, these conductive foams can be open cell foams coated with a conductive material. When a force is applied the piezoresistive foam is compressed and the total resistance is reduced because the resistivity as well as the current path are reduced. For example, an uncompressed piezoresistive foam can have a resistance of 100,000 ohms, while when compressed, the resistance can drop to 300 ohms. An alternative conductive piezoresistive polymeric foam suitable for use in the present invention is an intrinsically conductive expanded polymeric cellular foam (PEIC) consisting of an expanded polymer with premixed filler material containing finely divided conductive (colloidal) particles and conductive fibers. Commonly, conductive cellular foams consist of a non-conductive expanded foam with a conductive coating dispersed through the cells.These foams are limited to foams with open cells to allow the inner cells of the foam to receive the conductive coating. An intrinsically conductive expanded foam differs from the expanded foams known in the prior art in that the foam matrix is itself conductive.The difficulty in making an intrinsically conductive expanded foam is that the conductive filler particles, which have They are pre-mixed in the unexpanded foam, they separate from each other and lose contact with each other as the foam expands, thereby creating an open circuit. Surprisingly, the combination of finely divided conductive particles with conductive fibers allows the conductive filler material to be premixed into the resin before expansion without loss of conductive capacity when the resin subsequently expands. The conductive filler material may consist of an effective amount of conductive powder combined with an effective amount of conductive fiber. By "effective amount" is meant an amount sufficient to maintain electrical conductance after expansion of the foam matrix. The conductive powder can be pulverized metals such as copper, silver, nickel, gold and the like, or pulverized carbon such as carbon black and powdered graphite. The particle size of the conductive powder is usually in the range from diameters of about 0.01 to about 25 microns. The conductive fibers can be metallic fibers or, preferably, graphite and usually in the range from about 0.1 to about 0.5 inches in length, usually the amount of conductive powder is in the range from about 15% to about 80% by weight of the total composition. Conductive fibers are usually in the range from about 0.1% to about 10% by weight of the total composition. The intrinsically conductive foam can be made according to the procedure described in Example 1 given below. In connection with the example, the silicone resin is obtainable from Dow Corning Company under the designation Silicone resin SILASTIC ™ S5370. The graphite pigment is available as Asbury Graphite A60. The black pigment is available as Shawingigan Black carbon. The graphite rows are obtainable as graphite fibers from Hercules Manamite type A. A significant advantage of intrinsically conductive foam is that it can be a closed cell foam.

Example 1 108 grams of silicone resin was mixed with a filler consisting of 40 grams of graphite pigment, 0.4 grams of carbon black pigment, 3.0 grams of inch graphite fibers. After the filler was dispersed in the resin, 6.0 grams of foaming catalyst was stirred into the mixture. The mixture was emptied into a mold and foam and gel formation was allowed to form a piezoresistive elastomeric polymeric foam having a sheet strength of about 50 K ohms / square. The preformed silicone resin can be thinned with solvent, such as methyl ethyl ketone to reduce the viscosity. The polymer usually forms a "skin" when it foams and gels. The skin decreases the sensitivity of the piezoelectric sheet because the skin usually has a higher resistance value that is less affected by compression. Optionally, a fabric can be coated around the mold in which the preformed resin is emptied. After the resin has been foamed and gelled, the fabric can be detached from the polymer, thereby removing the skin and exposing the polymer cells for greater sensitivity. When loaded, that is, when a mechanical force or pressure is applied, the resistance of a piezoresistive foam descends in a way that is reproducible. That is, the same load applied repeatedly gives consistently the same resistance values. Also, it is preferred that the cellular foam show little or no resistance hysteresis. That is, the measured resistance of the conductive foam for a particular amount of compressive displacement is substantially the same whether the resistance is measured when the foam is being compressed or expanded. Advantageously, the piezoresistive foam layer 14 performs the interruption or connection of the apparatus without spark, which provides a greater margin of safety in media with flammable gases or vapors present. Adjacent to the piezoresistive foam 14 is another separator 15, which has holes 15a. The spacer 15 is preferably identical to the spacer 13. Alternatively, the spacer 15 can be modified to be different from the spacer 13 in the thickness or configuration and dimensions of the holes 13a. The switch device 10 includes a protective sheet 17 consisting of a non-conductive layer 17a which is preferably elastomeric (but may also be rigid); and a conductive layer 17b. The aforementioned comments regarding the negligible resistivity of the conductive layer 12 relative to that of the piezoresistive foam also applies to the conductive layer 17b. The conductive layer 17b can be deposited on top of a non-conductive layer 17a to form a conductive, lower elastomeric surface. The deposited layer 17b can also be a polymeric elastomer or a coating containing a filler material such as metal or finely pulverized carbon to render it conductive. A conductive layer suitable for use in the present invention is described in U.S. Patent No. 5,06,995, it is incorporated herein in its completeness. An elastomeric conductive layer 17b can be fabricated with the powder and conductive fibers as described above in connection with the intrinsically conductive expanded polymeric foam, with the exception that the polymer matrix of the conductive layer 17b does not need to be cellular. Preferably an elastomeric silicone is used as the matrix as set forth in example 2.

Example 2 A conductive filler material was made from 60 g of graphite pigment (Asbury Graphite A60), 0.4 g of carbon black (Shawingigan Black A), 5.0 g of graphite fibers of 1/4 inch (Hercules Magnamiete) type A). This filler was dispersed in 108.0 grams of silicone elastomer (SYLGARD ™ 182 silicone elastomer resin). Then catalyst was added and the mixture was emptied into a mold and allowed to harden. The result was an elastomeric silicone film with a sheet strength of about 10 ohms / square. Alternatively, the protective sheet 17 can be flexible without being elastomeric and can consist of a metallized polymer sheet such as an aluminized MYLAR® polymer film, the aluminum coating provides the conductive layer 17b. As yet another alternative, the protective sheet 17 may consist of a flexible polymer resin of the upper layer 17a, elastomeric or simply flexible, and a continuous layer 17b of metal foil. Preferably the upper layer 17a is a PVC plasticized sheet which can be heat sealed or otherwise bonded (for example, by soldering solvents) to a PVC base 11. The advantage of using a continuous sheet layer is the higher conductivity of the metallic sheet compared to the polymers that become conductive by the mixture of conductive components. The aforementioned layers are assembled as shown in Figure 1 with conductive wires 18a and 18b connected individually, respectively, to the conductive layers 12 and 17b. The wires 18a and 18b are connected to a power source (not shown) and are part of an electrical switch circuit.

Referring to Figures IA and IB, as another modification, the conductive layer 17b may consist of a conductive elastomeric polymer composite bonded to a segmented metal sheet or a corrugated metal sheet, the sheet adjacent to the separator 15a being placed, or, as shown in FIG. shown in Figures IA and IB, the piezoresistive layer 14. The divisions in the segmented sheet (or the corrugations in the corrugated sheet) allow the elastomeric elongation of the conductive layer 17b while providing the high conductivity of the metal through the greater part of the conductive layer 17b. Figure IA shows a carpet switch 10a with a conductive layer 17b attached to an elastomeric insulating protective sheet 17a. The conductive layer 17b consists of an elastomeric conductive sheet 17c to which a segmented layer of metal sheet 17d having grooves 17e is attached to the underside thereof. The piezoresistive material 14 is in contact with the segmented sheet and is placed on the separator 13. As shown in Figure IB, when a downward force F is applied to the upper surface of the carpet switch 10a, the elastomer layers 17a and 17b they flex in a resilient manner downward and elongate in the lateral direction. The piezoresistive material 14 is therefore pressed down through the openings 13a in the separator and makes contact with the conductive layer 12 on the base 11. The holes in the metal sheet 17d defined by slots 17e become a little wider. The electric current passes through these spaces through the elastomeric conductive sheet 17c. Since the spaces are enlarged when the elastomeric sheet 17c is lengthened, the total resistance of the sheet through the conductive layer 17b is slightly increased when the device is operated. However, since the conductivity of the segments of the sheet is much greater than that of the elastomeric conductor 17c, the total conductivity of the elastomeric conductive layer 17b is similar to the aforementioned embodiment of the web although it also provides elastomeric operation. Referring to Figure 2, another embodiment of the apparatus is shown wherein the carpet switch 20 consists of a base layer 21 with an array of small, laterally separate conductive layers 22 which serve as electrodes. The insulating base 21 can be conveniently manufactured from a circuit board with a copper layer. The copper layer can be selectively orchestrated to form electrodes 22 with wires 22a to provide an electrical connection thereto. Alternatively, the electrodes 22 can be deposited or electroplated onto the base layer 21 by means of a pattern. This layer can also be a metallic or otherwise conductive film. Those skilled in the art will recognize many ways of achieving a patterned electrode layer on an insulating substrate (for example, the straight conductive lines found on an axis may be the electrodes). The layer 23 is a separator having an array of holes 23a, each orifice 23a aligned with one of the respective electrodes 22. The upper surface of separator 23 has a conductive layer 24 thereon. The conductive layer 24 can be a sheet, plate or metal film, and can be formed by any of the methods suitable for the purpose such as electroplating, deposition, adhesion of a sheet or plate, etc. Alternatively, this layer can be a circuit of electrodes designed to provide the desired communication to the circuit 22 of the layer 21 (for example, the straight conductive lines running on the orthogonal axes). The piezoresistive foam 25 is placed on the conductive layer 24 and makes electrical contact therewith. The insulating protective sheet 26, which can be an elastomeric or non-elastomeric flexible polymer sheet, covers the piezoresistive foam 25. As can easily be seenWhen a downward force is applied to the upper part of the protective sheet 26, the piezoresistive foam 25 is forced through the holes 23a in contact with the electrodes 22, by means of which the circuit is completed and the current flowing between the conductive layer or circuit 24 and electrodes 22. Unlike the previously described embodiment, the current does not flow from the upper part to the lower part of the piezoresistive foam 25, but through this portion of foam 25 occupying the space defined by the holes 23a. Since the electrodes 22 are small, each with its own cable 22a the lateral position of the applied force can be known by detning which of the electrodes 22 receives the current. In still another alternative, the separator can be combined with a mesh or screen consisting of a network of wires or filaments. Optionally, the sheets of a single piece of insulating material having an array of perforations can be replaced by a filamentary or wire mesh. For example, in relation to Figure 3, the unit of the separator element 19 is a combination of a burdq separator 19c interleaved between two insulating screening nets 19a and 19b. The holes 19d in the separator 19c have relatively wide diameters (as compared to the holes in the sieve) and may be of random size and spacing, ordered or combined.

The insulating screens 19a and 19b are preferably of mesh size 20 and can be in the range of 5 mesh to about 30 mesh. The unit of the spacer element 19 can be replaced by one or the other of the separators 13 or 15 in the safety mat 10. Optionally, the other of the two separators can be removed. For example, a safety carpet switch may be manufactured with a protective sheet 17, including an insulating cover 17a and an electrode film 17b; a piezoresistive foam 14 proximate the electrode layer 17b; the unit of the separator element 19 adjacent the piezoresistive foam 14; a lower electrode 12 and a base 11.

In still another alternative, the unit of the separating element 19 can be manufactured with the coarse separator 19c and only one of the screens 19a and 19b adjacent thereto. In an alternative, the carpet switch 10 can be constructed with a mesh 19a instead of having any of the spacer elements, the mesh itself functioning as the spacer element. Referring to Figure 3A, one mode 80 of the switch device is shown with a base 81, the conductive layers 82 and 85 the piezoresistive layer 84, the protective sheet 86 and two spacers 83 and 87, each of which is a layer which consists of a plurality of pearls separated in the lateral direction, small or points 83a and 87a, respectively, of insulating material. The points 83a and 87a can be applied to the conductive layers 82 and 85, or to the upper and / or lower surfaces of the piezoresistive material, for example, by depositing an insulating fluid (for example synthetic polymers) through a screen with a pattern, then the pattern of dots thus formed is allowed to harden or vulcanize. For example, the material for use in manufacturing the spacer points 83a and 87a can be a polymer (e.g., methacrylate polymers, polycarbonates or polyolefins dissolved in a solvent and applied to the conductive layers 82 and / or 85 as a viscous liquid) . The solvent is then allowed to evaporate, exiting via this from the spots of the deposited polymer. As an alternative, the points 83a and 87a can be deposited as a resin that hardens under the influence of an agent for curing (e.g., ultraviolet light). Silicone and epoxy resins are preferred materials for making points 83a and 87a. The points 83a and 87a are preferably hemispherical but can be manufactured in any shape and are preferably from about 1/32 inch to about H inches in height. The amount of force needed to connect the device 80 depends at least in part on the height of the points.

The operation and construction of the carpet switch 80 is similar to the carpet switch 10 except that small dots 83a and 87a are used as the separator instead of a perforated continuous layer as the separators 15 and 13 of the carpet switch 10, or wire mesh as the mesh 19a or 19b as shown in Figure 3. The margins of the carpet switches 10, 20 and 80 are preferably sealed by, for example, heat sealing. The active surface for activation extends very close to the edges with few dead zones.

Referring to Figure 11, there is shown a pressure operated switch 120 supported by a structure wherein a protective plate of the structure 127 has an annular retaining ring 128. The elastomeric protective sheet 126, the piezoresistive foam 125 and the element separator 123 are maintained by means of retaining ring 128. Separator element 123 includes a metallized upper conductive layer 124 that serves as the emitting electrode, and a plurality of openings 123a. The lower plate 121 includes a plurality of receiving electrodes 122 oriented in alignment with the openings 123a. The conductive wires 122a extend from the respective receiving electrodes to the edge of the lower plate 121 to allow the current to be carried for the measurement. A cable 122b extending between the edge of the bottom plate and the conductive metal film 124 at the top of the spacer member 123 provides a path for the source current to the emitter electrode 124. Referring to FIGS. 12 and 13, one embodiment of the invention with obturating struts is shown. The carpet switch 130 includes a sealed box 131 having a base portion 131a and a cover portion 131b having a top surface with channels 131e and sealed at the ends 131d. For example, the box 131 can be made of polyvinyl chloride with heat seal along the edges 131d. The covered portion 131b has a flat portion 131c aligned with a strut 137 below it. The struts 137 are elongated rigid members that provide support for the carpet switch 130 and that divide the piezoresistive layer 136 into sections. The piezoresistive foam layer 136 is placed over the separator element 133 and is in contact with the upper emitting electrode, ie, the conductive metal film 135 coated on the upper surface of the spacer element 133. The openings 134 of the spacer element 133 allow the resilient piezoresistive foam 136 makes contact with the receiving electrodes 132, whereby a current path between the emitting and receiving electrodes for the on state is provided. The operation of the carpet switch 130 is similar to the operation of the above-described modes 20 and 120 in which the emitting and receiving electrodes are both placed on the same side of the piezoresistive material and activated when, in response to the driving force applied to them. the surface of the carpet switch, the piezoresistive foam is disposed through the openings of the separator element to complete the electric circuit making contact with the receiving electrodes aligned with the openings. The dead zone, the non-reactive area on the struts 137 is reduced having thin flat portions 131c of the covered portion 131b disposed on the struts 137, and with the portion with channels 131e adjacent thereto. The support struts 137 and the planar portions 131c are relatively narrow compared to the amplitude of the carpet switch 130, and usually no more than about 0.125 inches in width. The carpet switch 130 could not register a force distributed only within this narrow area range. However, under actual working conditions almost all forces will be distributed over an area that overlaps the flat portions 131c. The raised channels 131e adjacent to the flat portion 131c allow the covered portion 131b to be depressed by at least a distance equal to the height of the channels. For example, with reference to Figure 14, it can be seen that when a force represented by the weight is caused to rest on the covered portion 131b on the flat area 131c and the strut 137, the overlap of the weight W makes contact with the channels 131e , by means of which the covered portion 131b is forced to descend. This, in turn, pushes the piezoresistive material 136 through the opening 134 and makes contact with the receiving electrode 132 to complete the electrical circuit and put the carpet switch in the "on" state. Now with reference to FIGS. 15 and 16, the use of the transmission means together with the carpet switch 130 to completely eliminate the dead zones is also contemplated. Figure 15 illustrates a lever device 200 that includes an inner body 201 with an arm 202 with sloping shoulder 203, a curved base 204 and a stabilizing buttress 205. The lever 200 is elongated and positioned adjacent the edge of the carpet switch 130 so that the flange 203 engages a valley portion between two channels 131e on the upper surface of the covered portion 131b. The arm 202 extends over the edge of the carpet switch 130. If a downward force F is applied to the arm 202, although the position of the force F is aligned with a marginal strut 137, the lever 200 will rotate to transfer the force to a active region of the carpet switch where the force can be detected. That is to say, the flange 203 is on the piezoresistive material 136 so that the downward force F will be displaced to compress the piezoresistive material. The buttress 205 also serves as a counterweight to hold the lever 200 in an un-activated position, or a non-tilted position, in the absence of the downward force on the arm 202. In this way the lever 200 is in equilibrium so that, when the force F is removed from the lever 200, it automatically returns to its initial position. Now in relation to Figure 16, there is shown a coupling device 210 for joining two carpet switches 130 while removing the dead zones between them and along their respective margins. The coupler 210 includes a T-shaped upper portion 211 that slidably engages the vertical post 214 of the base 212. The T-shaped upper portion includes two arms 213 which hang over the respective carpet switches 130. Each The arm preferably has a sloping shoulder 215 for engaging the ribbed upper surfaces 131b of the carpet switches 130, as described above with respect to the engagement of the flange 203 with the channels 131 E. The trunk portion 217 of the top member includes an inner chamber 218 in which a spring 216 is placed. The spring 216 rests on the vertical post 214 and resiliently urges the upper member 211 to an upward position where the shoulders 215 do not apply any downward force to the surface the covered portion 131b of the carpet switch. When a force is applied to the upper surface of the T-shaped upper portion 211, the upper portion 211 slides down against the urging force of the spring 216. This causes the arms 213 and the shoulders 215 to move downwardly. pressing through this the channel cover portion 131b and driving the carpet switch 130. The force applied downward in what would otherwise be a "dead zone" is transferred to an active area of the carpet switch 130 eliminating this way the dead zone during actual use. Now in relation to Figure 4, an alternative embodiment 40 of the present invention is illustrated. The multiple interrupting device 40 includes a protective layer 41, a piezoresistive layer 42, a base 46 and an activation region 47 that is an empty space. The shape of the activation region 47 is defined by a series of spacer elements in layers 45a, 45b, 45c, 45d and the conductive layers 43 and 44a, 44b, 44c, and 44d. More particularly, the protective sheet 41 is a flexible non-conductive sheet preferably made of an elastomeric synthetic polymer. The piezoresistive material 42 is preferably a piezoresistive cellular foam such as that described above, and is placed on the upper conductive layer 43 with which the piezoresistive layer 42 is in electrical contact. The conductive layers 43, 44a, 44b, 44c and 44d can be, for example, metal foils adhesively bonded to the respective spacer elements directly below, or they can be conductive coatings deposited thereon. The spacer elements 45a, 45b, 45c, and 45d are insulating layers of predetermined thicknesses or heights. As shown in Figure 4, the separating elements have similar heights. However, these can also be manufactured with different heights. The heights determine the amount of pressure or force applied to the upper part of the multiple switch device 40 necessary to activate the next level of the circuit. The base 46 may be rigid or flexible and may be a rigid, non-conductive material as described above. The activation region 47 is funnel-shaped with the stepped sides. As you can see, the top part is preferably circular although you can also work angled shapes like triangles. As you can see in figure 4, the diameter of the orifice 47a in the most upper separating element 45a is greater than the diameter of the orifice 47b in the separating element 45b, each successively lower separating member with a smaller orifice diameter than the previous one. The upper conductive layer 43 is connected to a power source P and is designed as an "emitter" electrode. The remaining conductive layers 44a, 44b, 44c, and 44d are designed as "receiving electrodes" and can be connected individually to different respective circuits Zl t Z¿, Now in relation to Figure 5, when the multiple switch device 40 is actuated by a force F by pressing down on the protective sheet 41, the piezoresistive foam 42 is pressed down to the activation region 47, and makes electrical contact with a or more of the remaining conductive layers 44a, 44b, 44c and 44d depending on the magnitude of the force F. As each successive contact is made, a new circuit is actuated. In this way, for example, the circuit Z] can be used to carry out a function, the circuit Z can be dedicated to another purpose or other machinery, and so on for Z3, and Z4. The conductive layer 43 serves common emitting electrode dome providing the energy for the receiving electrodes 44a, 44b, 44c, and 44d. Although four spacer elements are shown in the multiple switch device 40, it should be recognized that any number of spacer elements may be used, and the heights of the spacer elements may vary according to the application for which the device 40 is used. Referring to Figure 6, there is shown an embodiment of the invention that can detect a shear force, ie, a force parallel to the plane defined by the flat upper surface of the switch device. A force directed vertically downwards on the protective sheet in a direction normal to the plane defined by the upper surface of the switch device has no cutting component. However, if the downward force is at an angle from the vertical orientation, it will have a vector component parallel to the plane of the top surface, this vector component constitutes a shear force or force.

As seen in Figure 6, the switch device 60 includes an insulating protective sheet 61 with a conductive film or coating 62 on the underside thereof. The conductive film 62 serves as an emitting electrode. The protective sheet 61 and the conductive film 62 are preferably elastomeric. The piezoresistive foam layer 63 lies below the conductive film 62 and is in electrical contact therewith. The separating element 64 is an insulating layer of cellular polymer and is deformable in a resilient manner. The separating element 64 has an opening 68 defining a void space in which the piezoresistive foam 63 can enter with the application of a downward force to the protective sheet 61. The primary receiving electrode 65 is aligned with the opening 68 so that When the piezoresistive foam 63 moves to the opening 68, it makes contact between the piezoresistive foam 63 and the primary receiving electrode 65 by means of which it closes the electrical circuit and initiates the interrupting action as the current flows between the electrodes 62 and 65. In addition to the primary receiver electrode 65, the cut detector switch 60 includes at least 1 and preferably 4 or more secondary receiver electrodes 66a and 66b positioned around and placed in the lateral direction of the primary receiver electrode 65, and covered by the element. separator 64. Secondary receiver electrodes 66a and 66b may be connected to different electrical circuits. The base 67 provides support to the device, the primary receiving electrode 65 and the secondary receiving electrodes 66a and 66b are installed thereto. The base 67 can be manufactured from materials as mentioned in the above. Now in relation to FIGS. 7 and 8, it can be seen that when a force F is directed vertically downwards onto the protective sheet without any lateral vector component (ie, without any shearing stress) as shown in FIG. 7, the piezoresistive foam layer 63 fills the opening 68 and contacts the primary receiving electrode 65, but not the secondary receiving electrodes 66a or 66b. In Figure 8, the force F is shown with a cutting component, that is, the force F is at an angle with respect to the vertical orientation. As shown in Figure 8, the secondary receiving electrode 66a is on the side of the primary receiving electrode 65 on which the cutting force is directed. The separating element 64 is thereby moved towards the uncovered secondary receiving electrode 66a, with which the piezoresistive foam makes electrical contact in addition to the primary receiving electrode 65. The secondary receiving electrode 66d on the side of the primary receiving electrode 65 opposite the direction of the cut applied remains covered and not activated. In this way the direction in which the cutting force is applied can be detected. Additionally, the magnitude of the vector components of the force F can also be measured since the strength of the piezoresistive foam will vary according to the compressive force applied, as described above in relation to the aforementioned carpet switch devices. . When the cutting force is removed, the separating element returns resiliently to its initial configuration. Now, with reference to FIGS. 9 and 10, another cut detector detector device 70 is shown. The switch device 70 includes an insulating base 79 with a pattern-like arrangement of primary receiving electrodes 77 placed in alignment with the openings 78 of a Rigid Insulating Separator Element 76. The primary piezoresistive foam layer 75 is placed over the separator element 76 so that in the initial non-compressive configuration of the device 70 there is a space between the primary piezoresistive foam layer 75 and the primary receiving electrodes 77. Above the primary piezoresistive foam layer 75 is an elastomeric insulating sheet 73 having upper and lower conductive coatings 74b and 74c, respectively. The conductive films or coatings 74b and 74c serve as electrodes or emitters and may be electrically connected to each other or to different electrical circuit parts. A secondary layer 72 of piezoresistive foam is stacked on the upper conductive layer 74b and is in electrical contact therewith. The secondary piezoresistive foam layer 72 has a plurality of conical peaks 72a projecting on the upper surface of the protective sheet 71. At least 1, and preferably several secondary electrodes 74a are placed around each opening 71a of the protective sheet 71 on the upper surface of this one. Now in relation to FIG. 10, a downward force F with a cutting component is applied to the switching device 70. The primary piezoresistive layer 75 is moved through the openings 78 in contact with the primary receiving electrodes 77. Likewise, the tapered peaks 72a are bent in the direction of the cutting force to make electrical contact with the secondary receiving electrodes 74a by means of which the electrical circuit path between the upper emitting electrode 74b and the secondary receiving electrodes 74a is completed. The direction and magnitude of both cuts can be measured by determining the secondary receiving electrodes 74a that were activated and the amount of the current flowing from the upper emitting electrode 74b thereto. In the same way, the magnitude of the descending force vector can be determined from the current flowing from the lower emitting electrode 74c to the primary receiving electrodes 67. Moreover, the lateral position of the force F on the upper surface of the device 70 can be indicated by determining the primary receiving electrodes 79 that are activated. In this way a detailed measurement of the position, magnitude and direction of an applied force can be made. The resolution of the measurement depends on the number, size and placement of the receiving electrodes. The corresponding carpet switch 35 has lugs 36 configured and sized to engage slots 32 and areas of slots 37 to receive the lugs 31 of the safety mat 30. The lugs and corresponding slots provide the rugs 30 and 35 interlocking capacity to form a single contiguous structure. The carpets can be electrically connected, as well as physically in series or parallel circuits. The construction of the carpet switch of the present connection allows the active surface area of the carpet up to the lugs 31, 36. In this way, the area of the lugs does not represent a dead zone. Now in relation to Figure 17, a circuit 50 is shown in which any of the carpet switches of the present invention can be used to operate a relay. The circuit 50 is powered by a direct current source, i.e., a battery 51, which provides a voltage Vu of cd in the range from 12 to 48 volts, preferably from 24 to 36 volts. The safety carpet A can be any of the embodiments from the invention described in the above. The potentiometer Ri can be in the range from 1000 ohms to about 10,000 ohms and provides a calibration resistor. The resistor Rz has a fixed resistance from about 1000 ohms to about 10,000 ohms. Transistors Qi and Q¿ give amplification of the signal from safety mat A to operate relay K. Relay K is used to close or open the electrical circuit on which the machinery to be controlled operates. The capacitor d is in the range from about 0.01 microfarads to 0.1 microfarads and is provided to suppress noise. K can be substituted with a measuring device to measure the force in A. This would require adjusting the ratio of Ri and A (compression vs. force) to polarize the transistors Qi and Q¿ in their linear amplification range. This circuit represents an example of how the carpet can be activated. Many other circuits can be used including the use of electronic or triax switches. The various electrodes of the carpet switches 40, 60 and 70 can be incorporated into separate electrical circuits of the type shown in Figure 17. The activation of the relay corresponding to a particular circuit would then indicate that longitudinal pressure or shear force of a Some magnitude or in a certain position has been presented on the carpet. The multiple outputs of the relays may be the input of a pre-programmed guide control or other means of control or response. The present invention can be used in many different applications of machine safety carpets. For example, the invention can be used for intrusion detection, freight diversion detection, shock simulation, athletic objectives, (eg, baseball, karate, boxing, etc.), detector devices on human limbs to provide computer intelligence. for prosthetic control, feedback devices for virtual reality screens, mattress covers to monitor the heartbeat (especially for use in hospitals or to signal the interruption of the heart in the syndrome of sudden death in infants) toys, assistive devices for blindness, computer input devices, ship anchoring aids, keyboards, analog button switches, "smart" joints, weighing scales and the like. It will be understood that various modifications can be made to the embodiments described herein. Therefore, the above description should not be considered as limiting but simply as exemplifications of the preferred embodiments. Those skilled in the art will discover other modifications within the scope and spirit of the claims appended hereto.

Claims (59)

1. CLAIMS A pressure activated switch device consisting of: (a) first and second conductive layer; (b) a layer of compressible piezoresistive material disposed between the first and second conductive layers; (c) at least one isolating spacer element positioned between the piezoresistive material and at least the first conductive layer or the second conductive layer, the spacer element with a plurality of holes; wherein in response to a predetermined amount of force applied thereto, the piezoresistive material is placed through at least some of the orifices of the spacer element to make electrical contact with the conductive layer.
2. The apparatus of claim 1, wherein the compressible piezoresistive material has a resistance of about 500 ohms to about 150,000 ohms when it is not compressed and a resistance of about 200 ohms to about 500 ohms when compressed, and the first and second conductive layer each has a lower resistance than the strength of the compressed piezoresistive layer.
3. 3. The apparatus of claim 1 further includes a protective sheet and a base.
4. The apparatus of claim 3, wherein the first conductive layer is placed between the protective sheet and the piezoresistive material, and the second conductive layer is placed between the base and the piezoresistive material.
5. The apparatus of claim 4, wherein the first conductive layer consists of an elastomeric conductive material and a metal foil layer folded thereto.
6. 6. The apparatus of claim 5, wherein the metal foil is segmented.
7. The apparatus of claim 3, wherein the protective sheet and the first conductive layers are joined together and are elastomeric.
8. The apparatus of claim 1, wherein the first and second conductive layer consists of layers of metal foils.
9. The apparatus of claim 1, wherein the piezoresistive material consists of a cellular polymer foam having a conductive filler material consisting of a mixture of colloidal carbon and graphite fibers.
10. The apparatus of claim 1, wherein at least one spacer element consists of a layer of rigid polymeric material.
11. The apparatus of claim 1, wherein at least one spacer element consists of a sheet of resiliently compressible polymeric material.
12. 12. The apparatus of claim 1, wherein the orifices of the spacer element are substantially dimensioned, placed and / or arranged in a regular manner.
13. The apparatus of claim 1, wherein the orifices of the spacer element are sized, placed and / or ordered substantially randomly.
14. The apparatus of claim 1, wherein at least one spacer element includes a mesh.
15. 15. The apparatus of claim 1 further includes the lug means for interlocking a pressure-operated switch device with another.
16. 16. The apparatus of claim 1 further includes the means responsive to the application of a cutting force to make electrical contact between the piezoresistive material and the first and second conductive layer.
17. The apparatus of claim 1, wherein the predetermined amount of force is related to the size of the holes of the spacer element and the thickness and stiffness of the spacer element.
18. 18. A pressure-operated switch apparatus consisting of: a) a spacer element having an insulating layer and an upper conductive layer, the spacer element having at least one hole; b) a layer of piezoresistive material placed on the separator element and which is in electrical contact with the upper conductive layer; c) a lower conductive layer placed below the separating element, at least a portion of the lower conductive layer aligned with at least one hole, wherein the piezoresistive material is disposed through at least one hole to make electrical contact between the upper and lower conductive layers in response to the pressure of predetermined magnitude applied to it.
19. 19. The apparatus of claim 18It also includes a protective sheet on the piezoresistive material and a bbelow the lower conductive layer.
20. The apparatus of claim 18, wherein the at least one hole in the separator element consists of a plurality of holes, and the lower conductive layer consists of a plurality of small electrodes, each electrode placed in alignment with a respective one of the plurality of holes.
21. The apparatus of claim 18, wherein the piezoresistive material consists of a cellular polymeric material having a conductive filler material consisting of a mixture of colloidal carbon and graphite fibers.
22. The apparatus of claim 18, wherein the spacer element is rigid.
23. The apparatus of claim 18, wherein the spacer member is resiliently flexible.
24. The apparatus of claim 18, wherein the upper and lower conductive layers consist of layers of deposited metal.
25. The apparatus of claim 18 further includes an insulating mesh positioned between the insulating layer of the spacer element and the lower conductive layer.
26. The apparatus of claim 18 further includes the transmission means for transferring the applied force from a non-reactive area of the apparatus to a reactive area of the apparatus.
27. The apparatus of claim 26, wherein the transmission means includes at least one arm that extends over the non-reactive area and engages in an active region, the transmission means being movable in response to a force applied to the arm from a first position to a second position, wherein the applied force is directed to the active zone and the transmission means is pushed to the first position.
28. The apparatus of claim 27, wherein the transmission means is an integrally constructed pivotable member having a counter weight of reinforcement for pushing the transmission means to the first position.
29. The apparatus of claim 27, wherein the transmission means consists of a top member from which at least one arm extends, a bmember having a vertical extension to which the upper member is slidably connected, and a spring for pushing the transmission means to the first position.
30. A pressure-operated switch device, which consists of; a) an insulating protective sheet; b) an isolation basis; c) at least one emitting electrode and at least one receiving electrode; d) at least one layer of piezoresistive material disposed between the protective sheet and the base and further disposed between at least one emitting electrode and at least one receiving electrode; e) the sensing means sensitive to the cutting force to make electrical contact between the piezoresistive material and one of the emitting and receiving electrodes.
31. The device of claim 30, wherein at least one receiving electrode consists of at least one primary receiving electrode and at least one secondary receiving electrode.
32. The device of claim 31, further includes at least one isolating spacer element positioned between the piezoresistive foam and the material and at least one secondary receiving electrode wherein the detection means consists of at least a portion of the spacer element which is moving in response to a cutting force between a first position, wherein the portion of the separating means avoids electrical contact between the piezoresistive material and at least one secondary receiving electrode, and a second position that allows electrical contact between the piezoresistive material and at least one secondary receiving electrode.
33. The device of claim 32, wherein the portion of the spacer element is resiliently pushed towards the first position.
34. The device of claim 31, wherein the protective sheet includes an upper surface and at least one opening, and at least one secondary receiving electrode is placed on the upper surface of the protective sheet in the vicinity of at least one opening .
35. The device of claim 32, wherein the detection means consists of at least one projection of piezoresistive foam disposed through at least one opening of the protective sheet and projecting on the upper surface, the foam projection being piezoresistive mobile in response to a cutting force applied to it from a first position, where the projection of piezoresistive foam is not in electrical contact with the secondary receiver electrode, and a second position where the projection of the piezoresistive foam is found in electrical contact with the secondary receiving electrode.
36. The device of claim 31, wherein at least one emitter electrode consists of at least one primary emitter electrode and at least one secondary emitter electrode.
37. The device of claim 36, wherein the primary and secondary emitting electrodes are separated by an insulating sheet.
38. The device of claim 37, wherein the piezoresistive material consists of a first and second layer of piezoresistive material, the first layer of piezoresistive material being placed between the protective sheet and the primary emitting electrode and the second layer of piezoresistive material placed between the secondary emitter electrode and at least one primary receiving electrode.
39. The device of claim 38 further comprises an isolating element having at least one opening aligned with at least one primary receiving electrode and disposed between the second layer of piezoresistive material and the primary receiving electrode.
40. The device of claim 39, wherein the protective sheet includes at least one upper surface and at least one opening, and the at least one secondary receiving electrode is placed on the upper surface of the auxiliary protective sheet in the vicinity of at least one opening.
41. The device of claim 40, wherein the detection means consists of at least one projection from [sic] piezoresistive disposed through at least one opening of the protective sheet and projecting on the upper surface, the projection of mobile piezoresistive foam in response to a cutting force applied to it from a first position, where the projection of piezoresistive foam is not in electrical contact with the secondary receiving electrode, and a second position where the projection of the foam piezoresistiva is in electrical contact with the secondary receiving electrode.
42. A pressure-operated switch device, which consists of; a) a layer of compressible piezoresistive material; b) a base below the orresistive material layer; c) at least two isolating spacer elements placed between the piezoresistive material and the base, the spacer elements each with an upper layer of conductive material and each with at least one opening, these openings aligned, shaped and sized to form by at least one empty space defined by the stepped sides.
43. 43. The device of claim 42, wherein the void space has a relatively large diameter orifice adjacent the piezoresistive material and a relatively smaller diameter orifice adjacent the base.
44. 44. The device of claim 43, wherein at least two spacer elements form a stack of spacer element layers having a layer of the highest spacer element the conductive layer of which is in electrical contact with the piezoresistive material.
45. 45. The device of claim 44, wherein the piezoresistive material moves resiliently in response to the downward force applied to it through the void space and in successive contact with at least one other conductive layer.
46. 46. The device of claim 45, wherein at least one void space is generally conical in its shape.
47. 47. The device of claim 42 further includes an insulating flexible protective sheet disposed on the layer of piezoresistive material.
48. 48. The device of claim 42, wherein the spacer elements are made of a rigid material.
49. The device of claim 42, wherein the base consists of an insulating layer bonded to an upper layer of conductive material.
50. A pressure operated switch apparatus consisting of: (a) first and second conductive layers; (b) a layer of compressible piezoresistive material disposed between the first and second conductive layers; c) at least one spacer layer positioned between the piezoresistive material and at least the first or second conductive layer, the spacer layer consists of a plurality of small spaced points of insulating material; wherein in response to a predetermined force magnitude applied thereto the compressible piezoresistive material moves through the space between the spacer points to make electrical contact with at least the first conductive layer or the second conductive layer.
51. The apparatus of claim 50, wherein the stitches are made of a synthetic polymer.
52. The apparatus of claim 50, wherein the points are hemispherical in shape and have a height in the range from about 1/32"to about 1/4".
53. 53. The apparatus of claim 50 further includes a protective sheet and a base.
54. 54. The apparatus of claim 53, wherein the first conductive layer is placed between the protective sheet and the piezoresistive material, and the second conductive layer is placed between the base and the piezoresistive material.
55. 55. A piezoresistive material consisting of: a cellular matrix of polymer foam having a conductive filler material that includes a conductive powder and conductive fibers.
56. 56. The piezoresistive material of claim 55, wherein the conductive powder is selected from the group consisting of powdered metal, carbon black, powdered graphite, and combinations thereof.
57. 57. The piezoresistive material of claim 55, wherein the conductive fibers are selected from the group consisting of metal fibers, graphite fibers and combinations thereof.
58. 58. The piezoresistive material of claim 55, wherein the polymeric foam cell matrix is a closed cell foam.
59. 59. The piezoresistive material of claim 55, wherein the conductive powder consists of particles in the range from about 0.01 to about 25 microns in diameter. The piezoresistive material of claim 55, wherein the conductive fibers are in the range from about 0.1 to about 0.5 inches in length.