Method and system for detecting multiple touches on a touch-sensitive screen

• US 7,023,427 B2
• Filed: 06/28/2002
• Issued: 04/04/2006
• Est. Priority Date: 06/28/2002
• Status: Active Grant

• Current Assignee: Microsoft Technology Licensing LLC (Microsoft Corporation)
• Original Assignee: Microsoft Corporation
• Inventors: Kraus, Mark Gerard, Nguyen, Vu Xuan
• Primary Examiner(s): Mengistu, Amare
• Application Number:
  US10/185,056
• Publication Number:
  US 20040001048A1
• Time in Patent Office: 1,376 Days
• Field of Search: 178/18.02, 345/173, 345/174, 345/178, 345/179
• US Class Current: 345/173
• CPC Class Codes: G06F 2203/04808 Several contacts: gestures triggering a specific function, e.g. scrolling, zooming, right-click, when the user establishes several contacts with the surface simultaneously; e.g. using several fingers or a combination of fingers and pen
• CPC Class Codes: G06F 3/0421 by interrupting or reflecting a light beam, e.g. optical touch-screen
• CPC Class Codes: G06F 3/0436 in which generating transducers and detecting transducers are attached to a single acoustic waves transmission substrate
• CPC Class Codes: G06F 3/04883 for inputting data by handwriting, e.g. gesture or text

Abstract

Disclosed are a method and a system for detecting multiple, simultaneous touches on a touch-sensitive screen of a computing device. The hardware that controls the touch screen performs two measurements to locate a touch location on the screen. If there is a single touch, then the two measurements are equal. A non-zero difference indicates multiple touches and is correlated with the spread of locations simultaneously touched on the screen. If the difference is greater than a set threshold, then an indication is given of multiple touches. The user is warned against multiple touches, and input from the screen is ignored as long as multiple touches are detected. For some embodiments, when multiple touches are detected, the invention also tries to indicate the boundary of the set of locations simultaneously touched. The boundary is used to interpolate the intended single touch from the locations of all the touches.

Claims

1. A method for indicating if a set of simultaneous contact points on a touch-sensitive screen contains a plurality of contact points, the method comprising:

setting a multiple contact point discrimination threshold representing a minimum difference in voltage expected between conductors at opposing edges of the touch-sensitive screen when multiple contact points are presented;

setting a conductor on a first edge of the touch-sensitive screen to a first reference voltage;

setting a conductor on a second edge of the touch-sensitive screen to a second reference voltage, the second edge being across the touch-sensitive screen from the first edge;

taking a first measurement of a voltage associated with a conductor on a third edge of the touch-sensitive screen, the third edge being adjacent to the first and second edges;

taking a second measurement of a voltage associated with a conductor on a fourth edge of the touch-sensitive screen, the fourth edge being adjacent to the first and second edges and across the touch-sensitive screen from the third edge;

comparing the multiple contact point discrimination threshold with a difference between the first and second voltage measurements, the difference reflecting a difference in proximity between the set of simultaneous contact points and the third and fourth edges of the touch-sensitive screen; and

if the difference between the first and second voltage measurements is greater than the multiple contact point discrimination threshold, then indicating that the set of simultaneous contact points contains a plurality of contact points.

2. The method of claim 1 wherein the set of simultaneous contact points consists of a single contact point.

3. The method of claim 1 wherein the multiple contact point discrimination threshold is set to zero.

4. The method of claim 1 wherein setting a multiple contact point discrimination threshold comprises considering a request regarding a value for the threshold from a program configured to receive input from the touch-sensitive screen.

5. The method of claim 1 further comprising:

if the difference between the first and second voltage measurements is not greater than the multiple contact point discrimination threshold, then indicating that the set of simultaneous contact points contains a single contact point.

6. The method of claim 1 further comprising:

setting the conductor on the third edge of the touch-sensitive screen to a third reference voltage;

setting the conductor on the fourth edge of the touch-sensitive screen to a fourth reference voltage;

taking a third measurement of a voltage associated with the conductor on the first edge of the touch-sensitive screen;

taking a fourth measurement of a voltage associated with the conductor on the second edge of the touch-sensitive screen;

comparing the multiple contact point discrimination threshold with a second difference between the third and fourth voltage measurements, the difference between the third and fourth voltage measurements reflecting a difference in proximity between the set of simultaneous contact points and the first and second edges of the touch-sensitive screen; and

if the difference between the third and fourth voltage measurements is greater than the multiple contact point discrimination threshold, then indicating that the set of simultaneous contact points contains a plurality of contact points.

7. The method of claim 6 further comprising:

if the difference between the third and fourth voltage measurements is not greater than the multiple contact point discrimination threshold, then indicating that the set of simultaneous contact points contains a single contact point.

8. The method of claim 6 wherein the first reference voltage equals the third reference voltage and wherein the second reference voltage equals the fourth reference-voltage.

9. The method of claim 1 further comprising increasing the multiple contact point discrimination threshold in response to finding that the difference between the first and second voltage measurements is greater than the multiple contact point discrimination threshold.

10. A computer-readable medium containing computer-executable instruction for performing a method for indicating if a set of simultaneous contact points on a touch-sensitive screen contains a plurality of contact points, the method comprising:

setting a multiple contact point discrimination threshold representing a minimum difference in voltage expected between conductors at opposing edges of the touch-sensitive when detecting multiple contact points are presented;

setting a conductor on a first edge of the touch-sensitive screen to a first reference voltage;

setting a conductor on a second edge of the touch-sensitive screen to a second reference voltage, the second edge being across the touch-sensitive screen from the first edge;

taking a first measurement of a voltage associated with a conductor on a third edge of the touch-sensitive screen, the third edge being adjacent to the first and second edges;

taking a second measurement of a voltage associated with a conductor on a fourth edge of the touch-sensitive screen, the fourth edge being adjacent to the first and second edges and across the touch-sensitive screen from the third edge;

comparing the multiple contact point discrimination threshold with a difference between the first and second voltage measurements, the difference reflecting a difference in proximity between the set of simultaneous contact points and the third and fourth edges of the touch-sensitive screen; and

if the difference between the first and second voltage measurements is greater than the multiple contact point discrimination threshold, then indicating that the set of simultaneous contact points contains a plurality of contact points.

11. A method for indicating if a set of simultaneous contact points on a touch-sensitive screen contains a plurality of contact points, the method comprising:

setting a multiple contact point discrimination threshold representing a minimum combined difference in voltage expected between pairs of conductors at opposite edges of a touch-sensitive screen when multiple contact points are presented;

setting a conductor on a first edge of the touch-sensitive screen to a first reference voltage;

setting a conductor on a second edge of the touch-sensitive screen to a second reference voltage, the second edge being across the touch-sensitive screen from the first edge;

taking a first measurement of a voltage associated with a conductor on a third edge of the touch-sensitive screen, the third edge being adjacent to the first and second edges;

taking a second measurement of a voltage associated with a conductor on a fourth edge of the touch-sensitive screen, the fourth edge being adjacent to the first and second edges and across the touch-sensitive screen from the third edge;

setting the conductor on the third edge of thee touch-sensitive screen to a third reference voltage;

setting the conductor on the fourth edge of the touch-sensitive screen to a fourth reference voltage;

taking a third measurement of a voltage associated with the conductor on the first edge of the touch-sensitive screen;

taking a fourth measurement of a voltage associated with the conductor on the second edge of the touch-sensitive screen;

combining a first difference between the first and second voltage measurements reflecting a difference in proximity between the set of simultaneous contact points and the third and fourth edges of the touch-sensitive screen with a second difference between the third and fourth voltage measurements reflecting a difference in proximity between the set of simultaneous contact points and the first and second edges of the touch-sensitive screen;

comparing the multiple contact point discrimination threshold with a combination of the first and second differences; and

if the combination of the first and second differences is greater than the multiple contact point discrimination threshold, then indicating that the set of simultaneous contact points contains a plurality of contact points.

12. The method of claim 11 wherein the set of simultaneous contact points consists of a single contact point.

13. The method of claim 11 wherein the multiple contact point discrimination threshold is set to zero.

14. The method of claim 11 wherein setting a multiple contact point discrimination threshold comprises considering a request regarding a value for the threshold from a program configured to receive input from the touch-sensitive screen.

15. The method of claim 11 wherein the first reference voltage equals the third reference voltage and wherein the second reference voltage equals the fourth reference-voltage.

16. The method of claim 11 wherein combining the first and second differences comprises taking a sum of a square of the first difference and a square of the second difference.

17. The method of claim 11 further comprising:

if the combination of the first and second differences is not greater than the multiple contact point discrimination threshold, then indicating that the set of simultaneous contact points contains a single contact point.

18. The method of claim 17 further comprising increasing the multiple contact point discrimination threshold in response to finding that the combination of the first and second differences is greater than the multiple contact point discrimination threshold.

19. A computer-readable medium containing computer-executable instructions for performing a method for indicating if a set of simultaneous contact points on a touch-sensitive screen contains a plurality of contact points, the method comprising;

setting a multiple con-tact point discrimination threshold;

setting a conductor on a first edge of the touch-sensitive screen to a first reference voltage;

setting a conductor on a second edge of the touch-sensitive screen to a second reference voltage, the second edge being across the touch-sensitive screen from the first edge;

taking a first measurement of a voltage associated with a conductor on a third edge of the touch-sensitive screen, the third edge being adjacent to the first and second edges;

taking a second measurement of a voltage associated with a conductor on a fourth edge of the touch-sensitive screen, the fourth edge being adjacent to thee first and second edges and across the touch-sensitive screen from the third edge;

setting the conductor on the third edge of the touch-sensitive screen to a third reference voltage;

setting the conductor on the fourth edge of the touch-sensitive screen to a fourth reference voltage;

taking a third measurement of a voltage associated with the conductor on the first edge of the touch-sensitive screen;

taking a fourth measurement of a voltage associated with the conductor on the second edge of the touch-sensitive screen;

combining a first difference between the first and second voltage measurements reflecting a difference in proximity between the set of simultaneous contact points and the third and fourth edges of the touch-sensitive screen with a second difference between the third and fourth voltage measurements reflecting a difference in proximity between the set of simultaneous contact points and the first and second edges of the touch-sensitive screen;

comparing the multiple contact point discrimination threshold with a combination of the first and second differences; and

if the combination of the first and second differences is greater than the multiple contact point discrimination threshold, then indicating that the set of simultaneous contact points contains a plurality of contact points.

20. A system for indicating if a set of simultaneous contacts points on a touch-sensitive screen contains a plurality of contact points, the touch-sensitive screen comprising first, second, third, and fourth edges, each edge comprising a conductor, the first edge being across the touch-sensitive screen from the second edge, the third and fourth edges each being adjacent to the first and second edges, and the third edge being across the touch-sensitive screen from the fourth edge, the system comprising:

a multiple contact paint discrimination threshold representing a minimum combined difference in voltage expected between airs of conductors at opposite edges of a touch-sensitive screen when multiple contact points are presented;

a voltage source for setting the first edge conductor to a first reference voltage and for setting the second edge conductor to a second reference voltage;

a voltage measurement circuit with an input, and an output;

a multiplexor for connecting the input of the voltage measurement circuit alternatively to the third edge conductor and to the fourth edge conductor;

a comparator for comparing the multiple contact point discrimination threshold with a difference between a value produced on the output of the voltage measurement circuit when its input is connected to the third edge conductor and a value produced on the output of the voltage measurement circuit when its input is connected to the fourth edge conductor the difference reflecting a difference in proximity between the set of simultaneous contact points and the third and fourth edges of the touch-sensitive screen; and

an indicator for indicating that the set of simultaneous contacts points on the touch-sensitive screen contains a plurality of contact points, the indicator set based on an output of the comparator.

21. A system for indicating if a set of simultaneous contacts points on a touch-sensitive screen contains a plurality of contact points, the touch-sensitive screen comprising first, second, third, and fourth edges, each edge comprising a conductor, the first edge being across the touch-sensitive screen from the second edge, the third and fourth edges each being adjacent to the first and second edges with the third edge being across the touch-sensitive screen from the fourth edge, the system comprising:

a multiple contact point discrimination threshold representing a minimum combined difference in voltage expected between pairs of conductors at opposite edges of a touch-sensitive screen when multiple contact points are presented;

a first voltage source for setting the first edge conductor to a first reference voltage and for setting the second edge conductor to a second reference voltage;

a first voltage measurement circuit with an input and an output;

a first multiplexor for connecting the input of the first voltage measurement circuit alternatively to the third edge conductor and to the fourth edge conductor;

a first calculator for calculating a first difference between a value produced on the output of the first voltage measurement circuit when its input is connected to the third edge conductor and a value produced on the output of the first voltage measurement circuit when its input is connected to the fourth edge conductor, the first difference reflecting a difference in proximity between the set of simultaneous contact points and the third and fourth edges of the touch-sensitive screen;

a second voltage source for setting the third edge conductor to a third reference voltage and for-setting the fourth edge conductor to a fourth reference voltage;

a second voltage measurement circuit with an input and an output;

a second multiplexor for connecting the input of the second voltage measurement circuit alternatively to the first edge conductor and to the second edge conductor;

a second calculator for calculating a second difference between a value produced on the output of the second voltage measurement circuit when its input is connected to the first edge conductor and a value produced on the output of thee second voltage measurement circuit when its input is connected to the second edge conductor, the second difference reflecting a difference in proximity between the set of simultaneous contact points and the first and second edges of the touch-sensitive screen;

a comparator for comparing the multiple contact point discrimination threshold with a combination of the first and second differences; and

an indicator for indicating that the set of simultaneous contacts points on the touch-sensitive screen contains a plurality of contact points, the indicator set based on an output of the comparator.

22. The system of claim 21 wherein the first and second voltage sources are the same voltage source;

wherein the first and second voltage measurement circuits are the same voltage measurement circuit;

wherein the first and second multiplexors are the same multiplexor; and

wherein the first and second calculators are the same calculator.