METHOD AND APPARATUS FOR DETERMINING COORDINATES OF SIMULTANEOUS TOUCHES ON A TOUCH SENSOR PAD

• US 20080296073A1
• Filed: 04/22/2008
• Published: 12/04/2008
• Est. Priority Date: 04/25/2007
• Status: Active Grant

• Current Assignee: William J. Mcdermid
• Original Assignee: William J. Mcdermid
• Inventors: McDermid, William J.
• Granted Patent: US 8,355,009 B2
• Time in Patent Office: Days
• US Class Current: 178/18.05
• CPC Class Codes: G06F 2203/04104 Multi-touch detection in digitiser, i.e. details about the simultaneous detection of a plurality of touching locations, e.g. multiple fingers or pen and finger
• CPC Class Codes: G06F 3/045 using resistive elements, e.g. a single continuous surface or two parallel surfaces put in contact

Abstract

Apparatuses and methods are provided for determining coordinates of simultaneous touches on a touch sensor pad. A touch sensor pad includes a first plurality of resistive sensor strips on a first resistive sheet and a second plurality of resistive sensor strips on a second resistive sheet. A user touches the touch sensor pad at multiple locations simultaneously. A controller of the touch sensor pad determines coordinates of each of the multiple locations of touch independently of other touches. To determine coordinates for a touch, the controller identifies a first strip of the first plurality of resistive sensor strips of the first resistive sheet making contact with a second strip of the second plurality of resistive sensor strips of the second resistive sheet in response to the touch. The controller measures voltages of the strips to determine coordinates of the touch and measures resistance shifts in the strips due to touches to determine contact area of the touch which correlates to the types of objects causing the touch and the pressure of the touch.

Claims

1. A method for determining coordinates of simultaneous touches on a touch sensor pad, the touch sensor pad including a first plurality of resistive sensor strips on a first resistive sheet and a second plurality of resistive sensor strips on a second resistive sheet, the method of determining comprising the steps of:

determining coordinates of each of the multiple locations of touch independently of other touches, the determining step for a touch comprising;

identifying a first strip of the first plurality of resistive sensor strips of the first resistive sheet that is physically contacting a second strip of the second plurality of resistive sensor strips of the second resistive sheet in response to the touch;

identifying the second strip;

measuring a first voltage of the second strip applied by the first strip while in contact with the second strip in response to the touch;

measuring a second voltage of the first strip applied by the second strip while in contact with the first strip in response to the touch; and

determining coordinates of the touch based on the first voltage and the second voltage.

2. The method of claim 1, wherein the first strip has a base resistance and the determining step for a touch further comprises:

measuring a measured resistance of the first strip during contact between the first strip and the second strip in response to the touch; and

determining an area of contact of the touch based on a difference between the measured resistance and the base resistance.

3. The method of claim 2 further comprising:

identifying a type of object contacting the touch sensor pad at the coordinates of the touch based on the area of contact; and

determining an action corresponding to the coordinates based on the type of object contacting the touch sensor pad.

4. The method of claim 2, wherein the first strip has a first resistance per unit length that is less than a second resistance per unit length of the second strip.

5. The method of claim 2 further comprising:

correlating a pressure to the area of contact applied by an object to the touch sensor pad at the coordinates of the touch; and

determining an action corresponding to the coordinates based on the pressure of the object contacting the touch sensor pad.

6. The method of claim 1 further comprising:

determining whether a first strip of a first touch and a first strip of a second touch are the same resistive sensor strip;

determining a first resistance of a second strip of the first touch;

determining a second resistance of a second strip of the second touch; and

adjusting first coordinates of the first touch and second coordinates of the second touch based on the first resistance and the second resistance.

7. The method of claim 1, wherein measuring the first voltage further comprises:

energizing the first strip to generate a voltage gradient along the first strip; and

measuring a voltage of the second strip to determine the first voltage applied by the first strip in response to the touch.

8. The method of claim 1, wherein measuring the first voltage further comprises:

energizing terminals of the first strip to a terminal voltage to generate a voltage gradient along the first strip;

measuring a third voltage of the second strip applied by the first strip in response to the touch; and

subtracting an offset voltage from the third voltage to determine the first voltage.

9. The method of claim 8, wherein each of the first plurality of resistive sensor strips are assigned a sequential index value, and wherein the offset voltage is determined based on the terminal voltage times an index value of the second strip divided by a number of the first plurality of resistive sensor strips.

10. The method of claim 1, wherein identifying the first and second strips of each of the simultaneous touches further comprises:

conducting a parallel search of the of the resistive sensor strips to identify the first strip and second strip.

11. The method of claim 10, wherein conducting the parallel search further comprises:

raising the voltage of all of the resistive sensor strips on a second sheet;

detecting the resistive sensor strips on a first sheet that experience a voltage raise;

clearing the voltages;

raising the voltage of a detected resistive sensor strips on the first sheet;

detecting the resistive sensor strips on a second sheet that experience a voltage raise; and

repeating clearing the voltages and raising the voltage of a detected resistive sensor strips on the first sheet until all the detected resistive sensor strips on a first sheet have been processed.

12. The method of claim 1, wherein identifying the first strip further comprises:

stepping through the first plurality of resistive sensor strips individually in a predefined order to identify the first strip.

13. The method of claim 1 further comprising:

tracking a minimum voltage and a maximum voltage measured on the first strip, wherein the minimum voltage represents a first physical location of a first boundary of the first strip, and the second boundary represents a second physical location of a second boundary of the first strip; and

calculating the coordinates of the touch by interpolating between the first and second physical locations of the first and second boundaries based on where the second voltage falls between the minimum and maximum voltages.

14. The method of claim 1, wherein each of the first plurality of resistive sensor strips include a terminal, and the method further comprises:

drawing a line across the first resistive sheet proximate at least one terminal;

measuring a sequence of calibration voltages of each of the first plurality of resistive sensor strips in response to drawing the line; and

determining a position of each terminal based on the sequence of calibration voltages of each of the first plurality of resistive sensor strips.

15. The method of claim 14 further comprising:

determining a position error of the first strip based on a position of a terminal of the first strip; and

adjusting the coordinates of the touch based on the position error.

16. A method for determining coordinates of simultaneous touches on a touch sensor pad, the method of determining comprising the steps of:

providing a touch sensor pad including a first plurality of resistive sensor strips on a first resistive sheet and a second plurality of resistive sensor strips on a second resistive sheet;

determining coordinates of each of the multiple locations of touch independently of other touches, the determining step for a touch comprising;

identifying a first strip of the first plurality of resistive sensor strips of the first resistive sheet that is physically contacting a second strip of the second plurality of resistive sensor strips of the second resistive sheet in response to the touch;

identifying the second strip;

measuring a first voltage of the second resistive sheet;

measuring a second voltage of the first resistive sheet; and

determining coordinates of the touch based on the first voltage and the second voltage.

17. An apparatus for determining coordinates of simultaneous touches on a touch sensor pad, the apparatus comprising:

an interface coupled to a first plurality of resistive sensor strips on a first resistive sheet of the touch sensor pad and coupled to a second plurality of resistive sensor strips on a second resistive sheet of the touch sensor pad; and

a processing system coupled to the interface and adapted to determine coordinates of each of the multiple locations of touch independently of other touches, the processing system adapted to determine coordinates for a touch by;

identifying a first strip of the first plurality of resistive sensor strips of the first resistive sheet that is physically contacting a second strip of the second plurality of resistive sensor strips of the second resistive sheet in response to the touch;

identifying the second strip of the second plurality of resistive sensor strips of the second resistive sheet;

measuring a first voltage of the second strip applied by the first strip while in contact with the second strip in response to the touch;

measuring a second voltage of the first strip applied by the second strip while in contact with the first strip in response to the touch; and

determining coordinates of the touch based on the first voltage and the second voltage.

18. The apparatus of claim 17, wherein the first strip has a base resistance and the processing system is further adapted to:

measure a measured resistance of the first strip during contact between the first strip and the second strip in response to the touch; and

determine an area of contact of the touch based on a difference between the measured resistance and the base resistance.

19. The apparatus of claim 18, wherein the first strip has a first resistance per unit length that is less than a second resistance per unit length of the second strip.

20. The apparatus of claim 18, wherein the processing system is further adapted to:

identify a type of object contacting the touch sensor pad at the coordinates of the touch based on the area of contact; and

determine an action corresponding to the coordinates based on the type of object contacting the touch sensor pad.

21. The apparatus of claim 18, wherein the processing system is further adapted to:

identify the pressure of an object contacting the touch sensor pad at the coordinates of the touch based on the area of contact; and

determine an action corresponding to the coordinates based on the pressure of an object contacting the touch sensor pad.

22. The apparatus of claim 17, wherein the processing system is further adapted to:

determine whether a first strip of a first touch and a first strip of a second touch are the same resistive sensor strip;

determine a first resistance of a second strip of the first touch;

determine a second resistance of a second strip of the second touch; and

adjust first coordinates of the first touch and second coordinates of the second touch based on the first resistance and the second resistance.

23. The apparatus of claim 17, wherein the processing system is further adapted to:

energize the first strip to generate a voltage gradient along the first strip; and

measure a voltage of the second strip to determine the first voltage applied by the first strip.

24. The apparatus of claim 17, wherein the processing system is further adapted to:

energize a first terminal of the first strip to a terminal voltage to generate a voltage gradient along the first strip;

measure a third voltage of the second strip applied by the first strip; and

subtract an offset voltage from the third voltage to determine the first voltage.

25. The apparatus of claim 24, wherein each of the first plurality of resistive sensor strips are assigned a sequential index value, and wherein the offset voltage is determined based on the terminal voltage times an index value of the second strip divided by a number of the first plurality of resistive sensor strips.

26. The apparatus of claim 17, wherein the processing system is further adapted to:

conduct a parallel search of the resistive sensor strips to identify the first strip and second strip of a touch.

27. The apparatus of claim 26, wherein the processing system is further adapted to:

raise the voltage of all of the resistive sensor strips on a second sheet;

detect the resistive sensor strips on a first sheet that experience a voltage raise;

clear the voltages;

raise the voltage of a detected resistive sensor strip on a first sheet;

detect the resistive sensor strips on a second sheet that experience a voltage raise; and

repeat clearing voltages and raising the voltage of a detected resistive sensor strip on the first sheet until all the detected resistive sensor strips on a first sheet have been processed.

28. The apparatus of claim 17, wherein the processing system is further adapted to:

step through the first plurality of resistive sensor strips individually in a predefined order to identify the first strip and second strip.

29. The apparatus of claim 17, wherein the processing system is further adapted to:

track a minimum voltage and a maximum voltage measured on the first strip, wherein the minimum voltage represents a first physical location of a first boundary of the first strip, and the second boundary represents a second physical location of a second boundary of the first strip; and

calculate the coordinates of the touch by interpolating between the first and second physical locations of the first and second boundaries based on where the second voltage falls between the minimum and maximum voltages.

30. The apparatus of claim 17, wherein each of the first plurality of resistive sensor strips include a terminal, and wherein the processing system is further adapted to:

measure a sequence of calibration voltages of each of the first plurality of resistive sensor strips in response to an operator drawing a line across the first resistive sheet proximate at least one terminal; and

determine a position of each terminal based on the sequence of calibration voltages of each of the first plurality of resistive sensor strips.

31. The apparatus of claim 30, wherein the processing system is further adapted to:

determine a position error of the first strip based on a position of a terminal of the first strip; and

adjust the coordinates of the touch based on the position error.