Touch sensitive screen with improved corner response

• US 5,045,644 A
• Filed: 04/16/1990
• Issued: 09/03/1991
• Est. Priority Date: 04/16/1990
• Status: Expired due to Term

• Current Assignee: Tyco Electronics Corporation (TE Connectivity Ltd. (United Kingdom))
• Original Assignee: Elographics Incorporated (Elo Touch Solutions, Inc.)
• Inventors: Dunthorn, David I.
• Primary Examiner(s): SCHREYER, STAFFORD
• Application Number:
  US07/509,601
• Time in Patent Office: 505 Days
• Field of Search: 178/18, 178/19, 382/13, 382/59
• US Class Current: 178/18.05
• CPC Class Codes: G06F 2203/04113 Peripheral electrode pattern in resistive digitisers, i.e. electrodes at the periphery of the resistive sheet are shaped in patterns enhancing linearity of induced field
• CPC Class Codes: G06F 3/045 using resistive elements, e.g. a single continuous surface or two parallel surfaces put in contact

Abstract

A resistor electrode type of gradient sheet for a touch sensor having reduced ripple and bow of equipotential lines along edges and in the corners of the sensor. Orthogonal electrical fields are produced on a resistive surface so as to give coordinates of a selected position. T-shaped electrodes of a selected effective length and spacing are attached to the resistive surface, the length and spacing selected to substantially eliminate the bow of the equipotential fields. Each electrode is connected to a selected connection point along a resistor chain positioned along each edge of the resistive surface to provide selected voltages to the surface. Preferably, each resistance chain is made up of at least one resistance unit between each electrode connection point, with each unit formed of a pair of spaced-apart conductive lines applied to the resistive surface. In addition, the gradient sheet has corner electrodes that are connected to corner junctions of the resistor chains, preferably through a resistor of a selected value. This results in a sensor having an increased linear work area as compared with the prior art.

Claims

1. A position touch sensor having resistive electrodes which provides a linear output response over an enhanced proportion of the surface area of said sensor by reducing the ripple and bow or equipotential lines along edges of said sensor and reducing ripple or equipotential lines in corner areas, which comprises:

a resistive surface having a selected resistivity throughout said surface, said resistive surface defining perimeter edges and corners;

a resistor chain positioned proximate each of said perimeter edges of said resistive surface for providing orthogonal electrical fields on said resistive surface, each of said resistor chains having opposite ends joined at junction points proximate said corners to proximate ends of adjoining resistor chains;

a plurality of edge tee electrodes positioned on, and electrically connected to, said resistive surface along a path proximate each perimeter edge of said surface, said edge tee electrodes each being electrically connected to selected points along said resistor chains and having a selected spacing and an effective length along said path, said length and spacing selected to produce a selected voltage gradient at each of said edge tee electrodes to compensate for any cumulative voltage drop along said resistor chain perpendicular to current flow in said resistive surface to thereby reduce bow in said equipotential lines at said edges; and

a corner electrode positioned so as to be at an intersection of adjacent of said paths of said edge tee electrodes proximate each corner of said resistive surface, and electrically connected to said resistive surface, said corner electrode connected by an electrical connection to an adjacent of said junctions joining said resistor chains so as to be electrically in parallel with said resistor chains and produce a selected voltage at said corner electrode, said corner electrode provided for the reduction of ripple of equipotential lines in said resistive surface along said edges and at said corners.

2. The sensor of claim 1 wherein said electrical connection connecting said corner electrode to said adjacent junction includes a series resistance of a selected value whereby said corner electrode and series resistance are electrically in parallel with said resistor chains and edge tee electrodes.

3. The sensor of claim 2 wherein said series resistance in said electrical connection connecting said corner electrode to said junction is an independent resistor.

4. The sensor of claim 2 wherein said series resistance in said electrical connection connecting said corner electrode to said junction is an overlap resistor comprising a pair of lines of conductive material in electrical contact with said resistive surface and spaced apart a selected distance and overlapping a selected length to provide said selected value of resistance.

5. The sensor of claim 4 wherein said selected value of resistance is established by said resistivity of said resistive surface at said pair of lines of conductive material and by said selected separation distance and said overlap length of said pair of lines of conductive material.

6. The sensor of claim 1 wherein each of said resistor chains has at least one resistance unit interposed between adjacent selected connection points for said edge tee electrodes, each said resistance unit formed by a pair of lines of conductive material being in electrical contact with said resistive surface and spaced apart a selected distance and overlapping a selected length whereby said resistance unit has a resistance value established by said resistivity of said resistive surface and by said selected separation distance and said overlap length.

7. A position touch sensor having resistive electrodes which provides a linear output response over an enhanced proportion of the surface area of said sensor by reducing the ripple and bow of equipotential lines along edges of said sensor and reducing ripple of equipotential lines in corner areas, which comprises:

a resistive surface having a selected resistivity throughout said surface, said resistive surface defining perimeter edges and corners;

a resistor cain positioned proximate each of said perimeter edges of said resistive surface for producing orthogonal electrical fields on said resistive surface, each of said resistor chains having opposite ends joined at junction points proximate said corners to proximate ends of adjoining resistor chains;

a plurality of tee electrodes positioned on, and electrically connected to, said resistive surface along a path proximate each perimeter edge of said surface, said tee electrodes each being electrically connected to selected points along said resistor chains and having a selected spacing and an effective length along said path, said length and spacing selected to produce a selected voltage gradient at each of said tee electrodes to compensate for any cumulative voltage drop along said resistor chain perpendicular to current flow in said resistive surface to thereby reduce bow in said equipotential lines at said edges; and

a corner electrode positioned so as to be at an intersection of adjacent of said paths of said edge tee electrodes proximate each corner of said resistive surface, and electrically connected to said resistive surface, said corner electrode connected by a resistor of a selected resistance value to an adjacent of said junctions joining said resistor chains so as to be electrically in parallel with said resistor chains and to provide a selected voltage on said corner electrode, said corner electrode providing for the reduction of ripple of equipotential lines in said restrictive surface along said edges and at said corners.

8. The sensor of claim 7 wherein said resistor connecting said corner electrode to said junction is an overlap resistor comprising a pair of lines of conductive material in electrical contact with said resistive surface and spaced apart a selected distance and overlapping a selected length to provide said selected value of resistance.

9. The sensor of claim 8 wherein said selected value of resistance is established by said resistivity of said resistive surface and by said selected separation distance and said overlap length of said pair of lines of conductive material.

10. The sensor of claim 7 wherein each of said resistor chains has at least one resistance unit interposed between adjacent selected connection points for said edge tee electrodes, each said resistance unit formed by a pair of lines of conductive material being in electrical contact with said resistive surface and spaced apart a selected distance and overlapping a selected length whereby said resistance unit has a resistance value established by said resistivity of said resistive surface and by said selected separation distance and said overlap length.

11. A position touch sensor having resistive electrodes which provides a linear output response over an enhanced proportion of the surface area of said sensor by reducing the ripple and bow of equipotential lines along edges of said sensor and reducing ripple of equipotential lines in corner areas, which comprises:

a resistive surface having a selected resistivity throughout said surface, said resistive surface defining perimeter edges and corners;

a resistor chain positioned proximate each of said perimeter edges of said resistive surface for producing orthogonal electrical fields on said resistive surface, each of said resistor chains having opposite ends joined at junction points proximate said corners to proximate ends of adjoining resistor chains, each of said resistor chains having at least one resistance unit interposed between adjacent selected connection points, each said resistance unit formed by a pair of lines of conductive material being in electrical contact with said resistive surface and spaced apart a selected distance and overlapping a selected length whereby said resistance unit has a resistance value established by said resistivity of said resistive surface and by said selected separation and said overlap length;

a plurality of tee electrodes positioned on, and electrically connected to, said resistive surface along a path proximate each perimeter edge of said surface, said tee electrodes each being electrically connected to selected points along said resistor chains and having a selected spacing and an effective length along said path, said length and spacing selected to produce a selected voltage gradient at each of said tee electrodes to compensate for any cumulative voltage drop along said resistor chain perpendicular to current flow in said resistive surface to thereby reduce bow in said equipotential lines at said edges; and

a corner electrode positioned so as to be at an intersection of adjacent of said paths of said edge tee electrodes proximate each corner of said resistive surface, and electrically connected to said resistive surface, said corner electrode connected by a series resistor of a selected resistance value to an adjacent of said junctions joining said resistor chains so as to be electrically in parallel with said resistor chains and to provide a selected voltage on said corner electrode, said corner electrode and said series resistor providing for the reduction of ripple of equipotential lines in said resistive surface along said edges and at said corners.