Anisotropic, resistance-based determination of a position of an object with respect to a touch screen element
View Patent ↗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:
a first resistive bus-bar on the substrate;
a second resistive bus-bar substantially parallel to the first resistive bus-bar on the substrate;
a third resistive bus-bar substantially parallel to the first resistive bus-bar and the second resistive bus-bar on the substrate, the third resistive bus-bar being between the first resistive bus-bar and the second resistive bus-bar;
wherein the first resistive bus-bar extends between a first and a second electrode, the second resistive bus-bar extends between a third and a fourth electrode, and the third resistive bus-bar extends between a fifth and a sixth electrode;
a first, second, third, fourth, fifth, and sixth drive channel associated with respective ones of the first, second, third, fourth, fifth, and sixth electrodes; each drive channel being operable to generate an output signal dependent on the resistance between the respective first, second, third, fourth, fifth, and sixth electrode and a position of an object;
an anisotropic conductive area having a non-zero resistance arranged between the first, second and third resistive bus-bars such that currents induced in the anisotropic conductive area flow preferentially towards the first, second, and third resistive bus-bars; and
a processor operable to generate an estimate for the position of the object by comparing the output signals from the fifth and sixth drive channels and a sum of the output signals selected from one of the first and second drive channels or the third and fourth drive channels;
wherein processor is configured to estimate the position of the object in a first direction running between the resistive bus-bars from a ratiometric analysis of a sum of the output signals from the fifth and sixth drive channels and the sum of the selected output signals.
2. A touch sensitive position sensor according to claim 1 , wherein the processor is configured to estimate the position of the object in a second direction running along the resistive bus-bars from a ratiometric analysis of the sum of the output signal from the fifth drive channel and the output signals of the first and second drive channel associated with the first resistive bus-bar, and the sum of the output signal from the sixth drive channel and the output signals from the third and fourth drive channel associated with the second resistive bus-bar.
3. A touch sensitive position sensor according to claim 1 , wherein the anisotropic conducting area includes a plurality of resistive strips such that some of the resistive strips extend between the first resistive bus-bar and the third resistive bus-bar and other of the resistive strips extend between the second resistive bus-bar and the third resistive bus-bar.
4. A touch sensitive position sensor according to claim 3 , wherein the resistance of the resistive strips is five to ten times greater than the resistance of the first, second, and third resistive bus-bars.
5. A touch sensitive position sensor according to claim 3 , wherein the resistive strips are in a zigzag pattern.
6. A touch sensitive position sensor according to claim 1 , wherein the anisotropic conducting area includes a plurality of resistive strips that extend between the first resistive bus-bar and the second resistive bus-bar.
7. A touch sensitive position sensor according to claim 6 , wherein the resistance of the resistive strips is five to ten times greater than the resistance of the first, second, and third resistive bus-bars.
8. A touch sensitive position sensor according to claim 6 , wherein the resistive strips are in a zigzag pattern.