Abstract:
An electronic resistor user interface comprises flexible conductive materials and a flexible variably resistive element capable of exhibiting a change in electrical resistance on mechanical deformation and is characterised by textile-form electrodes ( 10,12 ) a textile form variably resistive element ( 14 ) and textile-form members ( 16 ) connective to external circuitry.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
   This is a national phase of PCT/GB01/02183, filed May 17, 2001, which claims priority to Great Britain Application No. 0011829.9, filed May 18, 2000 each incorporated herein by reference in its entirety. 
   TECHNICAL FIELD 
   This invention relates to electrical switching devices and more particularly to the architecture and construction of flexible switching devices and the use thereof in switching and proportional control of electric/electronic currents. 
   The working components of these devices can appear as and perform similarly to conventional textile materials and thus have applications as user-interfaces (including pressure sensors) particularly in the field of textile/wearable electronics. The devices are applicable as alternatives to hard electronic user-interfaces. Generally the devices can be produced using commercial textile manufacturing processes but the invention is not limited to such processes. 
   In this specification: 
   ‘textile’ includes any assemblage of fibres, including spun, monofil and multifilament, for example woven, non-woven, felted or tufted; and the fibres present may be natural, semi-synthetic, synthetic, blends thereof and metals and alloys; 
   ‘electronic’ includes ‘low’ currents as in electronic circuits and ‘high’ currents as in circuits commonly referred as ‘electric’; 
   ‘user interface’ includes any system in which a mechanical action is registered as a change in electrical resistance or conductance. The mechanical action may be for example conscious bodily action such as finger pressure or footfall, animal movement, pathological bodily movement, expansion or contraction due to bodily or inanimate temperature variation, displacement in civil engineering structures. 
   ‘mechanical deformation’ includes pressure, stretching and bending and combinations of these. 
   SUMMARY OF THE INVENTION 
   The invention provides an electronic resistor user-interface comprising flexible conductive materials and a flexible variable resistive element capable of exhibiting a change in electrical resistance on mechanical deformation, characterised by textile-form electrodes, a textile-form variably resistive element and textile-form members connective to external circuitry. 
   It will be appreciated that the textile form of each component of the user-interface may be provided individually or by sharing with a neighbouring component. 
   The electrodes, providing a conductive pathway to and from either side of the variably resistive element, generally conductive fabrics (these may be knitted, woven or non-woven), yarns, fibres, coated fabrics or printed fabrics or printed fabrics, composed wholly or partly of conductive materials such as metals, metal oxides, or semi-conductive materials such as conductive polymers (polyaniline, polypyrrole and polythiophenes) or carbon. Materials used for coating or printing conductive layers onto fabrics may include inks or polymers containing metals, metal oxides or semi-conductive materials such as conductive polymers or carbon. Preferred electrodes comprise stainless steel fibres, monofil and multifilament or stable conducting polymers, to provide durability under textile cleaning conditions. 
   The electrodes can be supported by non-conducting textile, preferably of area extending outside that of the electrodes, to support also connective members to be described. 
   Methods to produce the required electrical contact of the electrode with the variably resistive element include one or more of the following:
         a) conductive yarns may be woven, knitted, embroidered in selected areas of the support so as to produce conductive pathways or isolated conductive regions or circuits;   b) conductive fabrics may be sewn or bonded onto the support;   c) conductive coatings or printing inks may be laid down onto the support by techniques such as spraying, screen printing, digital printing, direct coating, transfer coating, sputter coating, vapour phase deposition, powder coating and surface polymerisation.       

   Printing is preferred, if appropriate using techniques such as resist, to produce contact patterns at many levels of complexity and for repetition manufacture. 
   The extension of the support outside the electrode region is sufficient to accommodate the connective members to be described. It may be relatively small, to give a unit complete in itself and applicable to a user-apparatus such as a garment. 
   Alternatively it may be part of a user-apparatus, the electrodes and variably resistive element being assembled in situ. It may carry terminals at which the connective members pass the electric current to other conductors. 
   The variably resistive element, providing a controllable conductive pathway between the two electrodes, may take a number of forms, for example
         a) a self-supporting layer;   b) a layer containing continuous or long-staple textile reinforcement;   c) a coating applied to the surface of textile eg. as fabrics, yarns or fibres. This coating preferably contains a particulate variably resistive material as described in PCT/GB99/00205, and may contain a polymer binder such as polyurethane, PVC, polyacrylonitrile, silicone, or other elastomer. Alternatively the variably resistive material may be for example a metal oxide, a conductive polymer (such as polyaniline, polypyrrole and polythiophenes) or carbon. This coating may be applied for example by commercial methods such as direct coating, transfer coating, printing, padding or spraying;   d) it may contain fibres that are inherently electrically conductive or are extruded to contain a variably resistive material as described in PCT/GB99/00205;   e) it may be incorporated into or coated onto one of the electrodes in order to simplify manufacturing processes or increase durability in certain cases.       

   The variable resistor generally comprises a polymer and a particulate electrically conductive material. That material may be present in one or more of the following states:
         a) a constituent of the base structure of the element;   b) particles trapped in interstices and/or adhering to surfaces;   c) a surface phase formed by interaction of conductive particles (i or ii below) with the base structure of the element or a coating thereon.       

   Whichever state the conductive material of the variably resistive element is present in, it may be introduced:
         i) ‘naked’, that is, without pre-coat but possibly carrying on its surface the residue of a surface phase in equilibrium with its storage atmosphere or formed during incorporation into the element. This is clearly practicable for states a) and c), but possibly leads to a less physically stable element in stage b);   ii) lightly coated, that is, carrying a thin coating of a passivating or water-displacing material or the residue of such coating formed during incorporation into the element. This is similar to i) but may afford better controllability in manufacture;   iii) polymer-coated but conductive when undeformed This is exemplified by granular nickel/polymer compositions of so high nickel content that the physical properties of the polymer are weakly if at all discernable. As an example, for nickel starting particles of bulk density 0.85 to 0.95 this corresponds to a nickel/silicone volume ratio (tapped bulk: voidless solid) typically over about  10 . Material of form iii) can be applied in aqueous suspension. The polymer may or may not be an elastomer. Form iii) also affords better controllability in manufacture than i).   iv) Polymer-coated but conductive only when deformed. This is exemplified by nickel/polymer compositions of nickel content lower than for iii), low enough for physical properties of the polymer to be discernible, and high enough that during mixing the nickel particles and liquid form polymer become resolved into granules rather than forming a bulk phase. This is preferred for b) an may be unnecessary for a) and c). It is preferred for the present invention: more details are given in co-pending application PCT/GB99/00205. An alternative would be to use particles made by comminuting materials as in v) below. Unlike i) to iii), material iv) can afford a response to deformation within each individual granule as well as between granules, but ground material v) is less sensitive. In making the element, material iv) can be applied in aqueous suspension;   v) Embedded in bulk phase polymer. This relates to a) and c) only. There is response to deformation within the bulk phase as well as between textile fibres.
 
The general definition of the preferred variably resistive material exemplified by iv) and v) above is that it exhibits quantum tunnelling conductance (‘QTC’) when deformed. This is a property of polymer compositions in which a filler selected from powder-form metals or alloys, electrically conductive oxides of said elements and alloys, and mixtures thereof are in is admixture with a non-conductive elastomer, having been mixed in a controlled manner whereby the filler is dispersed within the elastomer and remains structurally intact and the voids present in the starting filler powder become infilled with elastomer and particles of filler become set in close proximity during curing of the elastomer.
       

   The connective textile member providing a highly flexible and durable electrically conductive pathway to and from each electrode may for example comprise conductive tracks in the non-conducting textile support fabric, ribbon or tape. The conductive tracks may be formed using electrically conductive yarns which may be woven, knitted, sewn or embroidered onto or into the non-conducting textile support. As in the construction of the electrodes, stainless steel fibres, monofil and multifilament are convenient as conductive yarns. The conductive tracks may also be printed onto the non-conducting textile support. In certain cases the conductive tracks may need to be insulated to avoid short circuits and this can be achieved by for example coating with a flexible polymer, encapsulating in a non-conducting textile cover or isolating during the weaving process. Alternatively the yarns may be spun with a conductive core and non-conducting outer sheath. In another alternative at least one connective member comprises variably resistive material pre-stressed to conductance, as described in PCT/GB99/02402. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  shows a basic switch; 
       FIG. 2  shows a switch adaptable to multiple external circuits; 
       FIG. 3  shows a multiple key device; and 
       FIG. 4  shows a position-sensitive switch. 
   

   DESCRIPTION OF THE PREFERRED EMBODIMENTS 
   In conjunction with appropriate electronics the devices may be used for digital type switching, analogue switching, proportional control, pressure sensing, flex sensing in the following applications, for example: 
   interfaces to electronic apparatus such as:
         computers, PDA, personal audio, GPS;   domestic appliances, TV/video, computer games, electronic musical instruments, toys lighting and heating, clocks and watches;   personal healthcare such as heart rate monitors, disability and mobility aids;   automotive user controls;   controls for wearable electronics;   educational aids;   medical applications such as pressure sensitive bandages, dressings, garments, bed pads, sports braces;   sport applications such as show sensors, sensors in contact sport (martial arts, boxing, fencing), body armour that can detect and measure hits, blows or strikes, movement detection and measurement in sports garments;   seat sensors in any seating application for example auditoria and waiting rooms;   garment and shoe fitting;   presence sensors, for example under-carpet, in-flooring and in wall coverings.       

   Referring to  FIG. 1 , the basic textile switch/sensor device comprises two self-supporting textile electrodes  10 , 12  sandwiching variably resistive element  14  made by applying to nylon cloth an aqueous suspension of highly void-bearing granular nickel-in-silicone at volume ratio within the composition of 7:1 capable of quantum tunneling conduction, as described in PCT/GB99/00205. Electrodes  10 , 12  and element  14  are fixed in intimate contact so as to appear and function as one textile layer. Each electrode  10 , 12  is conductively linked to a connective textile element  16  consisting of stainless steel thread in nylon tape  18  extending from electrodes  10 , 12 . When pressure is applied to any area of electrode  10 , 12  the resistance between them decreases. The resistance between electrodes  10 , 12  will also decrease by bending. 
   Referring to  FIG. 2 , in a variant of the basic textile switch/sensor, upper payer  20  is a non-conducting textile support under which adheres the upper electrode constituted by a discrete electrically conductive textile member to sub-area  22  and conductively linked to connective member  24 , which is a conductive track in extension  26  of support  20 . Variably resistive element  28 , similar to that of element  12  above but containing polyurethane binder, is provided as a coating on lower electrode  29 , the area of which is greater than that of upper electrode  22 . Lower electrode  29  is formed with lower connective member  24 , a conductive track on an extension  26  of electrode  29 . When pressure is applied to sub-area  22 , the resistance between elements  22  and  29  changes. Effectively this define a single switching or pressure sensitive area  22  in upper layer  20 . 
   Referring to  FIG. 3 , a multiple key textile switch/sensor device is similar in form to that shown in  FIG. 2  except that under upper layer  30  are adhered three discrete electrodes constituted by electrically conductive sub-areas  32 , 34  and  36  isolated from each other by the non-conducting textile support and electrically linkable to external circuitry by way of connective members  33 , 35 , 37  respectively, which are conductive tracks on extension  31  of layer  30 . Variably resistive element  38  is provided as a coating on lower electrode  39 ; it is of the type decreasing in resistance when mechanically deformed, since it depends on low or zero conductivity in the plane of element  38 . Electrical connection to lower electrode  39  is by means of conductor  24  and extension  26 , as in  FIG. 2 . When pressure is applied to any of areas overlying electrodes  32 , 34  and  36 , the resistance between the relevant electrode(s) and lower electrode  39  decreases. Effectively this defines three separate switching or pressure sensitive areas  32 , 34  and  36 , suitable as individual keys in a textile keypad or individual pressure sensors in a textile sensor pad. If the sensor is to respond to bending, other electrodes in contact with lower layer  39  would be provided to measure changes in conductivity in the plane of that layer; at the same time the external circuit would temporarily switch out the measurement perpendicular to the plane of layer  39 . 
   Referring to  FIG. 4 , in a matrix switch/sensor device the upper layer  40  and lower layer  42  each contains parallel linear electrodes consisting of isolated rows  44  and columns  46  of conductive areas woven into a non-conducting textile support. Conductive areas  44 ,  46  are warp yarns that have been woven between non-conductive yarns. Variably resistive element  48  is a sheet of fabric carrying nickel/silicone QTC granules as in  FIG. 1  applied by padding with an aqueous dispersion of the granules, which are of the type decreasing in resistance on mechanical deformation. Layer  48  is supported between layers  40  and  42  and coincides in area with electrodes  44  and  46 . When pressure is applied to a localised area of  40  or  42  there is a decrease in resistance at the junctions of the conductive rows  44  and columns  46  which fall within the localised area of applied pressure. This device can be used as a pressure map to locate force applied within the area of the textile electrodes. By defining areas of the textile electrodes as keys, this device can also be used as a multi-key keypad. 
   EXAMPLE 
   One electrode is a fabric consisting of a 20 g/m2 knitted mesh containing metallised nylon yarns. The variably resistive element was applied to this-fabric by transfer coating of: 
   75% w/w water based polyurethane (Impranil-Dow chemical); and 
   25% w/w nickel/silicone QTC granules (size 45–70 μm) and was cured on the fabric at 110° C. The other textile electrode element is another piece of the same knitted mesh. Each electrode was then sewn onto a non-conducting support fabric sheet of greater area than the electrode. The sensor was assembled with the coated side of the first electrode element facing the second electrode. Separate connective textile elements each consisting of metallised nylon thread were sewn up to each electrode so that good electrical contact was made with each. On the non-conducting support fabric outside the electrodes two metal textile press-studs were fixed such that each was in contact with the two conductive yarn tails. An electrical circuit was then connected to the press-studs so that a sensor circuit was completed.