Anisotropic touch screen element

Abstract

A touch sensitive position sensor for detecting the position of an object in two dimensions is described. The position sensor has first and second resistive bus-bars spaced apart with an anisotropic conductive area between them. Electric currents induced in the anisotropic conductive area by touch or proximity flow preferentially towards the bus-bars to be sensed by detection circuitry. Because induced currents, for example those induced by drive circuitry, flow preferentially along one direction, pin-cushion distortions in position estimates are largely constrained to this single direction. Such one-dimensional distortions can be corrected for very simply by applying scalar correction factors, thereby avoiding the need for complicated vector correction.

1 . A touch sensitive position sensor comprising: 
 a substrate defining a touch sensitive platform;    first and second resistive bus-bars arranged spaced apart on the substrate; and    an anisotropic conductive area arranged between the bus-bars such that currents induced in the anisotropic conductive area flow preferentially towards the bus-bars.    
     
     
         2 . A touch sensitive position sensor according to  claim 1 , wherein the bus-bars each have a resistance of between 1 kΩ and 50 kΩ.  
     
     
         3 . A touch sensitive position sensor according to  claim 1 , wherein the bus-bars have substantially the same resistance.  
     
     
         4 . A touch sensitive position sensor according to  claim 1 , wherein the anisotropic conductive area provides a resistance between the bus-bars of between 1 kΩ and 50 kΩ.  
     
     
         5 . A touch sensitive position sensor according to  claim 1 , wherein the resistance of each of the bus-bars is less than the resistance between them provided by the anisotropic conductive area.  
     
     
         6 . A touch sensitive position sensor according to  claim 1 , wherein the anisotropic conductive area comprises a film of molecular substance having anisotropic conduction supported on a substrate.  
     
     
         7 . A touch sensitive position sensor according to  claim 1 , wherein the anisotropic conductive area comprises a plurality of resistive stripes connecting in parallel between the bus-bars.  
     
     
         8 . A touch sensitive position sensor according to  claim 7 , wherein the resistive stripes are formed from sections of resistive wire.  
     
     
         9 . A touch sensitive position sensor according to  claim 7 , wherein the resistive stripes are formed from a resistive material deposited on a substrate.  
     
     
         10 . A touch sensitive position sensor according to  claim 7 , wherein the resistive stripes have widths that are greater than gaps formed between adjacent ones of the resistive stripes.  
     
     
         11 . A touch sensitive position sensor according to  claim 1 , further comprising a conductive overlay separated from the anisotropic conductive area such that the conductive overlay and the anisotropic conductive area may be brought into contact by externally applied pressure.  
     
     
         12 . A touch sensitive position sensor according to  claim 1 , wherein the first resistive bus-bar extends between a first and a second electrode and the first resistive bus-bar extends between a third and a fourth electrode, the position sensor further comprising first, second, third and fourth drive channels associated with respective ones of the first, second, third and fourth electrodes, each drive channel being operable to generate an output signal dependent on the resistance between its electrode and the position of the object.  
     
     
         13 . A touch sensitive position sensor according to  claim 12 , further comprising a processor operable to generate an estimate for the position of the object by comparing the output signals from the drive channels.  
     
     
         14 . A touch sensitive position sensor according to  claim 13 , wherein the processor is configured to estimate the position of the object in a first direction running between the bus-bars from a ratiometric analysis of the sum of the signals associated with the first and second electrodes and the sum of the signals associated with the third and fourth electrodes.  
     
     
         15 . A touch sensitive position sensor according to  claim 13 , wherein the processor is configured to estimate the position of the object in a second direction running along the bus-bars from a ratiometric analysis of the sum of the signals associated with the first and third electrodes and the sum of the signals associated with the second and fourth electrodes.  
     
     
         16 . A touch sensitive position sensor according to  claim 13 , wherein the processor is further operable to apply a correction to the estimated position according to a pre-determined distortion associated with the platform.  
     
     
         17 . A touch sensitive position sensor according to  claim 16 , wherein the pre-determined distortion is a one-dimensional pin-cushion distortion.  
     
     
         18 . A control panel incorporating a touch sensitive position sensor comprising: 
 a substrate defining a touch sensitive platform;    first and second resistive bus-bars arranged spaced apart on the substrate; and    an anisotropic conductive area arranged between the bus-bars such that currents induced in the anisotropic conductive area flow preferentially towards the bus-bars.    
     
     
         19 . An apparatus having a control panel incorporating a touch sensitive position sensor comprising: 
 a substrate defining a touch sensitive platform;    first and second resistive bus-bars arranged spaced apart on the substrate; and    an anisotropic conductive area arranged between the bus-bars such that currents induced in the anisotropic conductive area flow preferentially towards the bus-bars.