Baselining techniques in force-based touch panel systems

• US 20030210235A1
• Filed: 05/08/2002
• Published: 11/13/2003
• Est. Priority Date: 05/08/2002
• Status: Active Grant

• Current Assignee: 3M Innovative Properties Company (3M Company)
• Original Assignee: 3M Innovative Properties Company (3M Company)
• Inventors: Roberts, Jerry B.
• Granted Patent: US 7,532,202 B2
• Time in Patent Office: Days
• US Class Current: 345/173
• CPC Class Codes: G06F 3/0414 using force sensing means to determine a position

Abstract

In connection with establishing a touch location on a touch screen, a number of reference levels are developed. One or more of the reference levels may be used to determine a differential change in the touch signal between a zero touch force condition and a touch event. In one approach, one or more reference levels are selected to compensate for various conditions affecting the touch screen at the time a touch is applied. Using one or more reference levels to compensate for conditions affecting the touch signal at the time touch location information is obtained can provide improved accuracy in determining touch location.

Claims

1. A method for determining a touch location of a touch on a touch screen, comprising:

acquiring a plurality of reference levels for a force responsive touch signal;

selecting one or more of the plurality of reference levels based on information acquired from the touch signal; and

determining the touch location using the one or more selected reference levels.

2. The method of claim 1, further comprising using more than one reference level of the plurality of reference levels.

3. The method of claim 1, further comprising transitioning from using one of the plurality of reference levels as a touch signal reference to using another of the plurality of reference levels as the selected reference level during the touch.

4. The method of claim 3, wherein transitioning from one reference level to another reference levels occurs as the touch is moved across the touch screen.

5. The method of claim 1, further comprising eliminating an effect associated with the one or more selected reference levels from the determined touch location after a predetermined time interval.

6. A method for determining a touch location of a touch on a touch screen, comprising:

developing a first reference level for a force responsive touch signal;

developing a second reference level for the force responsive touch signal; and

determining the touch location using at least one of the first and second reference levels.

7. The method of claim 6, wherein both the first and second reference levels are used to determine the touch location.

8. The method of claim 6, wherein developing the first reference level comprises performing a weighted average of two or more touch signal samples taken during a touch signal quiescent period.

9. The method of claim 6, wherein developing the first reference level comprises adjusting the first reference level by a predetermined amount when a difference between a magnitude of a touch signal sample and a magnitude of the first reference level is less than a predetermined value.

10. The method of claim 9, wherein the first reference is not updated during the time that the touch is applied to the touch screen.

11. The method of claim 6, wherein developing the first reference level comprises:

developing a tentative first reference level; and

saving the tentative first reference level as the first reference level if the difference between the touch signal and the tentative first reference level is less than a predetermined amount for a predetermined number of touch signal samples.

12. The method of claim 11, wherein developing the tentative first reference level comprises:

acquiring two or more touch signal samples during a quiescent period of the touch signal; and

adjusting the tentative first reference level by a first predetermined amount if a first difference between a touch signal sample and a first reference value is greater than a second predetermined amount, and a second difference between the touch signal sample and the tentative first reference level is less than a third predetermined amount.

13. The method of claim 6, wherein developing the second reference level comprises using a touch signal sample taken at a predetermined time before touch location information is first obtained.

14. The method of claim 13, wherein touch location information is first obtained at a peak of the touch signal.

15. The method of claim 13, wherein the predetermined time before touch location information is obtained is in a range of about 50 to 100 ms.

16. The method of claim 6, wherein developing the second reference level comprises acquiring the second reference level in response to a triggering event associated with an application of a touch.

17. The method of claim 16, wherein the second reference level is updated using one or more touch signal samples before the triggering event is detected.

18. The method of claim 16, wherein the second reference level is held unchanged during the time the touch signal is not in a quiescent period.

19. The method of claim 18, wherein the touch signal is determined to be in a quiescent period when the touch signal is below a predetermined threshold and at least one touch signal sample has a value less than an immediately preceding sample.

20. The method of claim 18, wherein the touch signal is determined to be in the quiescent period if a predetermined number of successive samples remain within a predetermined range of values.

21. The method of claim 18, wherein the triggering event is a rise rate of the touch signal exceeding a predetermined rate.

22. The method of claim 18, wherein the triggering event is a magnitude of the touch signal exceeding a predetermined value.

23. The method of claim 6, wherein developing the second reference level comprises using an extrapolated value as the second reference level.

24. The method of claim 23, wherein using an extrapolated value as the second reference level comprises:

acquiring a first touch signal sample during a quiescent period;

acquiring a second touch signal sample during the quiescent period, the second touch signal sample acquired a predetermined number of sample times after the first touch signal sample;

determining a rate of change of the touch signal during the quiescent period using the first and the second touch signal samples;

extrapolating a value of the touch signal at the time the touch location information is obtained from the first touch signal sample, the second touch signal sample and the rate of change of the touch signal; and

using the extrapolated value as the second reference level.

25. The method of claim 6, wherein developing the second reference level comprises using an interpolated value as the second reference level.

26. The method of claim 25, wherein using an interpolated value as the second reference level comprises:

acquiring a first touch signal sample during a quiescent period;

acquiring a second touch signal sample when the touch signal returns to a quiescent state following application of a touch;

determining a rate of change of the touch signal between the first touch signal sample and the second touch signal sample;

interpolating a value of the touch signal at the time the touch location information is obtained from the first touch signal sample, the second touch signal sample and the rate of change of the touch signal; and

using the interpolated value as the second reference level.

27. The method of claim 6, wherein determining the touch location includes transitioning from using the first reference level to using the second reference level.

28. The method of claim 27, wherein transitioning from using the first reference level to using the second reference level comprises:

calculating touch signal location values using each of the first and second reference levels;

assigning weights to each touch signal location value; and

determining the touch location based upon the weighted touch signal location values.

29. The method of claim 28, wherein the weights assigned to each touch signal location value vary with distance as the touch is moved across the touch screen.

30. The method of claim 27, wherein transitioning from using the first reference level to using the second reference level comprises eliminating an effect associated with either the first or the second reference level from the touch location determination when the touch is moved a predetermined distance.

31. The method of claim 27, wherein transitioning from using the first reference level to using the second reference level comprises eliminating an effect associated with either the first or the second reference level from the touch location determination after a predetermined time interval.

32. The method of claim 27, wherein transitioning from using the first reference level to using the second reference level comprises calculating X and Y touch location coordinates as:

X=WX_ref2+(1−

W)X_ref1, Y=WY_ref2+(1−

W)Y_ref1,

where;

W is a weighting factor,

X_ref2 and Y_ref2 are touch location coordinates calculated using the second reference level, and

X_ref1 and Y_ref1 are touch location coordinates calculated using the first reference level.

33. The method of claim 32, wherein the weighting factor, W, is calculated as:

34. The method of claim 32, wherein the weighting factor, W, declines linearly from 1 to 0 over a period of one second.

35. A method of establishing a reference level for a touch signal, comprising:

sensing a quiescent touch signal prior to an application of a touch force;

detecting a touch signal responsive to the application of the touch force; and

establishing a reference level for the touch signal based on one or more values of the touch signal acquired contemporaneously with the detection of the touch force.

36. The method of claim 35, wherein establishing the reference level for the touch signal based on one or more values of the touch signal acquired contemporaneously with the detection of the touch force comprises establishing the reference level using one or more values of the touch signal occurring within a predetermined time interval prior to the detection of the touch force.

37. The method of claim 36, wherein the predetermined time interval is about 100 ms.

38. The method of claim 35, wherein establishing a reference level for the touch signal based on a value of the touch signal acquired contemporaneously with the detection of the touch force comprises using as the reference level a touch signal sample taken a predetermined time before touch location information is first obtained.

45. The method of claim 35, wherein the reference level is held unchanged after detection of the application of the touch force.

48. The method of claim 35 wherein establishing the reference level comprises establishing the reference level based on a particular time at which touch location information is obtained.

49. The method of claim 48, wherein establishing the reference level comprises:

detecting a quiescent touch signal, the quiescent touch signal representing the force responsive touch signal during a period in which no touch force is applied to the touch screen;

extrapolating the quiescent touch signal to the particular time of the touch location measurement; and

using a value of the extrapolated quiescent touch signal at the particular time at which the touch location is determined as the reference level.

50. The method of claim 48, wherein determining the reference level comprises:

detecting a first quiescent touch signal, the first quiescent touch signal representing the force responsive touch signal before the touch is applied to the touch screen;

detecting a second quiescent touch signal, the second quiescent touch signal representing the force responsive touch signal after the touch is removed from the touch screen;

determining an interpolated touch signal between the first and the second quiescent touch signals; and

using a value of the interpolated touch signal at the particular time at which the touch location is determined as the reference level.

51. The method of claim 50, wherein the second quiescent touch signal is detected if a touch signal sample is below a predetermined threshold and at least one subsequent touch signal sample has a value less than the touch signal sample.

52. The method of claim 50, wherein the second quiescent touch signal is detected if a predetermined number of successive samples remain within a predetermined range of values.

39. The method of 38, wherein touch location information is first obtained at a peak of the touch signal.

40. The method of 38, wherein the predetermined time before touch location information is obtained is in a range of about 50 to 100 ms.

41. The method of 35, wherein detecting the touch signal responsive to the application of the touch force comprises detecting a triggering event associated with the application of the touch.

42. The method of claim 41, wherein establishing the reference level comprises using a delayed sample of the touch signal as the reference level.

43. The method of claim 42, wherein the delayed sample of the touch signal is the previous sample of the touch signal before the triggering event.

44. The method of claim 41, wherein establishing the reference level in response to a triggering event comprises storing each touch signal sample as a possible second reference level until the triggering event is detected.

46. The method of claim 41, wherein the triggering event is a rise rate of the touch signal exceeding a predetermined rate.

47. The method of claim 41, wherein the triggering event is a magnitude of the touch signal exceeding a predetermined value.

53. A touch screen system, comprising:

a touch surface;

a plurality of touch sensors, each of the touch sensors physically coupled to the touch surface and producing a force responsive signal in response to a touch applied to the touch surface; and

a control system, coupled to the touch sensors and receiving the sensor signals, the control system configured to acquire a plurality of reference levels for the force responsive signal, select one or more of the plurality of reference levels based on information acquired from the force responsive signal, and determine the touch location using the one or more selected reference levels.

54. The system of claim 53, wherein the touch sensors comprise capacitive force sensors.

55. The system of claim 53, wherein the touch surface is substantially rectangular with one of the plurality of touch sensors located at each corner of the touch screen.

56. The system of claim 53, wherein each touch sensor produces a sensor signal indicative of a force passing through the location of that touch sensor.

57. The system of claim 53, wherein the control system derives one or more force responsive touch signals by combining one or more sensor signals.

58. The system of claim 53, wherein the control system develops a first and a second reference level and determines the touch location using at least one of the first and the second reference levels.

59. A touch screen display system, comprising:

a touch screen system, including;

a touch surface;

a plurality of touch sensors, each of the touch sensors physically coupled to the touch surface and producing a force responsive signal in response to a touch applied to the touch surface; and

a control system, coupled to the touch sensors and receiving the sensor signals, the control system configured to acquire a plurality of reference levels for the force responsive signal, select one or more of the plurality of reference levels based on information acquired from the force responsive signal, and determine the touch location using the one or more selected reference levels; and

a display for displaying information through the touch screen system.

60. The system of claim 59, wherein the display is a liquid crystal display, a light emitting diode display, a plasma display, and organic electroluminescent display, or a cathode ray tube display.

61. The system of claim 59, wherein each touch sensor produces a sensor signal indicative of a force of a touch passing through that touch sensor.

62. The system of claim 59, wherein the control system derives one or more touch signals by combining one or more sensor signals.

63. A display system, comprising:

a touch screen system, including

a touch surface;

a plurality of touch sensors, each of the touch sensors physically coupled to the touch surface and producing a force responsive signal in response to a touch applied to the touch surface; and

a control system, coupled to the touch sensors and receiving the sensor signals, the control system configured to acquire a plurality of reference levels for the force responsive signal, select one or more of the plurality of reference levels based on information acquired from the force responsive signal, and determine the touch location using the selected reference levels;

a display for displaying information; and

a processor coupled to the display and the touch screen system for processing data to be displayed on the display and information received from the touch screen system.

64. The system of claim 63, wherein the display displays information through the touch screen.

65. The system of claim 63, wherein the display is a liquid crystal display, a light emitting diode display, a plasma display, and organic electroluminescent display, or a cathode ray tube display.

66. The system of claim 63, wherein the processor receives information regarding a touch made on the touch screen relative to information displayed on the display.

67. The system of claim 63, wherein each touch sensor produces a sensor signal indicative of a force passing through the location of that touch sensor.

68. The system of claim 63, wherein the control system derives one or more touch signals by combining one or more sensor signals.

69. The system of claim 63, further comprising:

one or more data storage devices coupled to the processor for storing data;

one or more input devices for transferring information to the processor; and

one or more output devices for transferring information from the processor.

70. The system of claim 63, further comprising one or more interfaces for coupling the system to one or more networks.

71. A system for determining a location of a touch on a touch screen, comprising:

means for developing a plurality of reference levels for a force responsive touch signal; and

means for determining the location of the touch using one or more of the plurality of established reference levels.

72. The system of claim 71, wherein means for determining the location of the touch comprises means for transitioning from using one reference level as a touch signal reference to using other reference levels as the touch signal reference.

73. The system of claim 72, wherein transitioning from using one reference level as the touch signal reference to using other reference levels as the touch signal reference comprises means for eliminating an effect associated with one or more reference levels from the touch location determination after a predetermined time period.

74. A system for determining a touch location on a touch screen, comprising:

means for developing a first and a second reference level for a force responsive touch signal; and

means for determining the touch location using at least one reference level of the first and the second reference levels.

75. The system of claim 74, wherein means for developing the first reference level comprises means for adjusting the first reference level by a predetermined amount when a difference between a magnitude of a touch signal sample and a magnitude of the first reference level is less than a predetermined value.

76. The system of claim 74, wherein means for developing the second reference level comprises means for establishing a touch signal value acquired contemporaneously with the detection of a touch force as the second reference level.

77. The system of claim 76, wherein means for establishing a touch signal value acquired contemporaneously with the detection of the touch force comprises means for detecting a triggering event.

78. The system of claim 77, wherein means for detecting a triggering event comprises means for detecting a rise rate of the touch signal exceeding a predetermined rate.

79. The system of claim 77, wherein means for detecting a triggering event comprises means for detecting a touch signal magnitude exceeding a predetermined value.

80. A system for establishing a reference level for a touch signal used to determine a touch location, comprising:

means for sensing a quiescent touch signal prior to an application of a touch force;

means for detecting a touch signal responsive to the application of the touch force;

means for establishing a reference level for the touch signal based on a value of the touch signal acquired contemporaneously with the detection of the touch force.

81. The system of claim 80, wherein means for detecting the touch signal responsive to the application of the touch force comprises means for detecting a triggering event associated with the application of the touch force.

82. The system of claim 81, wherein means for detecting the triggering event comprises means for detecting a rise rate of the touch signal exceeding a predetermined rate.

83. The system of claim 81, wherein means for detecting the triggering event comprises means for detecting a magnitude of the touch signal exceeding a predetermined value.

84. The system of claim 80 wherein means for establishing the reference level comprises means for establishing the reference level based on a particular time at which touch location information is obtained.

85. A computer-readable medium configured with executable instructions for causing one or more computers to perform a method of determining a location of a touch on a touch screen, the method comprising:

acquiring a plurality of reference levels for a force responsive touch signal;

selecting one or more of the plurality of reference levels based on information acquired from the touch signal; and

determining the touch location using the selected reference levels.