Method and system for measuring position on surface capacitance touch panel using a flying capacitor

• US 8,432,375 B2
• Filed: 06/04/2012
• Issued: 04/30/2013
• Est. Priority Date: 11/20/2008
• Status: Expired due to Fees

• Current Assignee: Cirque Corporation
• Original Assignee: Cirque Corporation
• Inventors: Bytheway, Jared G., Paulsen, Keith L.
• Primary Examiner(s): Feild, Joseph
• Assistant Examiner(s): Sasinowski, Andrew
• Application Number:
  US13/488,089
• Publication Number:
  US 20120235954A1
• Time in Patent Office: 330 Days
• Field of Search: 345/173, 345/174, 178/18.06
• US Class Current: 345/174
• CPC Class Codes: G06F 3/044 by capacitive means
• CPC Class Codes: G06F 3/0444 using a single conductive element covering the whole sensing surface, e.g. by sensing the electrical current flowing at the corners

Abstract

A touch panel having a substantially even coating of a conductive material on a non-conductive substrate and then covering the conductive material with a dielectric material, wherein a novel current measuring circuit reduces the effect of stray capacitance on the accuracy of a current measurement so that the relative X and Y position of an object on the touch panel can be determined using simple ratio equations.

Claims

1. A method for determining the position of a pointing object on a first axis of a surface capacitance touch panel, said method comprising:

1) providing a touch panel comprised of an insulating substrate, a resistive material disposed on the substrate, and a dielectric disposed on the resistive material;

2) connecting a charged capacitor to opposite first and second edges of the resistive material and measuring current X1 through a path from the first edge to an electrostatic ground using a current measurement circuit;

3) switching connections of the charged capacitor between the first and second edges of the resistive material and measuring current X2 through a path from the second edge to the electrostatic ground using the current measurement circuit; and

4) determining a position of the pointing object on the first axis between the first and second edges on a surface of the resistive material as a ratio of measured currents X1 and X2.

2. The method as defined in claim 1 wherein the method further comprises determining the position of the pointing object in a second axis that is between different opposite edges of the touch panel.

3. The method as defined in claim 2 wherein the method further comprises:

1) connecting a charged capacitor to opposite third and fourth edges of the resistive material and measuring current Y1 through a path from the third edge to the electrostatic ground using the current measurement circuit;

2) switching connections of the charged capacitor between the third and fourth edges of the resistive material and measuring current Y2 through a path from the fourth edge to the electrostatic ground using the current measurement circuit; and

3) determining a position of the pointing object on the second axis that is between the third and fourth edges on a surface of the resistive material as a ratio of measured currents Y1 and Y2.

4. The method as defined in claim 2 wherein the method further comprises connecting a positive node of the capacitor to the third edge, and a negative node of the flying capacitor to the fourth edge in order to measure current Y1.

5. The method as defined in claim 2 wherein the method further comprises connecting a positive node of the capacitor to the fourth edge, and a negative node of the capacitor to the third edge in order to measure current Y2.

6. The method as defined in claim 2 wherein the method further comprises determining the position of the pointing object in any axis that is defined as being disposed between any two opposite edges of the touch panel.

7. The method as defined in claim 3 wherein the method further comprises increasing accuracy of the method for measuring the position of a pointing object on the touch panel by only allowing the current to drain to the pointing object and to the current measurement circuit.

8. The method as defined in claim 3 wherein the method further comprises determining a position of the pointing object in the first axis using the equation X=X1/(X1+X2).

9. The method as defined in claim 8 wherein the method further comprises determining a position of the pointing object in the second axis using the equation Y=Y1/(Y1+Y2).

10. The method as defined in claim 1 wherein the method further comprises connecting a positive node of the capacitor to the first edge, and a negative node of the capacitor to the second edge in order to measure current X1.

11. The method as defined in claim 1 wherein the method further comprises connecting a positive no of the capacitor to the second edge, and a negative node of the capacitor to the first edge in order to measure current X2.

12. The method as defined in claim 1 wherein the method further comprises providing a known voltage on the capacitor in order to determine how much current is being drained from the resistive material by the presence of the pointing object.

13. The method as defined in claim 12 wherein the method further comprises refreshing the capacitor to the known voltage in order to maintain the voltage gradient across the resistive material.

14. The method as defined in claim 1 wherein the method further comprises creating a linear voltage gradient across the resistive material.

15. The method as defined in claim 1 wherein the method further comprises using an ammeter as the current measuring circuit.

16. A method for determining the position of a pointing object on a first axis of a surface capacitance touch panel, said method comprising:

1) providing a touch panel comprised of an insulating substrate, a resistive material disposed on the substrate, and a dielectric disposed on the resistive material;

2) providing a voltage gradient from a flying capacitor across a resistive material from a first edge to a second edge, and measuring a first current through a path from the first edge to an electrostatic ground using a current measurement circuit;

3) switching connections of the flying capacitor between the first and second edges of the resistive material and measuring a second current through a path from the second edge to an electrostatic ground using the current measurement circuit; and

4) determining a position of the pointing object on the first axis between the first and second edges on a surface of the resistive material as a ratio of measured first and second currents.

17. A surface capacitance touch panel that can determine the position of a pointing object on a first axis thereof, said surface capacitance touch panel comprised of:

an insulating substrate;

a resistive material disposed on the substrate;

a dielectric disposed on the resistive material;

a flying capacitor for that is switchabiy coupled to any opposite edges of the resistive material to thereby selectively provide a voltage gradient across the resistive material from one edge to as opposite edge;

a current measuring circuit that is coupled to one end of the flying capacitor and to electrostatic ground, to thereby measure current through a path from an edge to electrostatic ground; and

s

means for determining a position of the pointing object on the first axis between the opposite edges on a surface of the resistive material as a ratio of measured currents.