Acoustic touch position sensor with shear to lamb wave conversion

• US 5,072,427 A
• Filed: 11/16/1990
• Issued: 12/10/1991
• Est. Priority Date: 11/16/1990
• Status: Expired due to Term

• Current Assignee: The Whitaker Corporation (Meggitt PLC)
• Original Assignee: Exzec Incorporated
• Inventors: Knowles, Terence J.
• Primary Examiner(s): Pihulic, Daniel T.
• Application Number:
  US07/614,494
• Time in Patent Office: 389 Days
• Field of Search: 367/907, 367/118, 367/129, 178/18, 310/313 R, 310/313 D, 340/712
• US Class Current: 367/118
• 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: H03K 2217/96011 with propagation, SAW or BAW
• CPC Class Codes: Y10S 367/907 Coordinate determination

Abstract

An acoustic touch position sensor is shown wherein a transducer coupled to a side of a substrate imparts a shear wave into the substrate that propagates along a first axis. A shear to Lamb wave converting array disposed along the first axis converts the shear wave to Lamb waves propagating along a plurality of parallel paths where each path is associated with a different axial position on the substrate relative to the first axis. The Lamb waves are converted back to shear waves by a Lamb to shear wave converting array disposed along an axis parallel to the first axis, the second converting array being spaced across a touch surface of the substrate from the first array. The shear wave from the second converting propagate to a receiving transducer that provides a signal representative of the waves. A touch on the substrate results in a partial absorption of the energy in the Lamb wave propagating along a path intersection the touch position so as to produce a perturbation therein which is sensed to determine the axial position of the touch on the substrate. In a second embodiment a single transducer and reflective array is provided for each axis, a coordinate on which is to be determined. In a third embodiment of the present invention, a single transducer is provided for two axes.

Claims

1. A touch position sensor comprising:

a substrate capable of supporting shear waves and Lamb wave propagating therein, said substrate having a touch surface;

first means coupled to said substrate for imparting a shear wave into said substrate, said shear wave propagating along a first axis;

first means disposed along said first axis for converting portions of said shear wave to Lamb waves propagating along first paths parallel to each other and extending across the touch surface of said substrate, each first path representing a different axial position, a touch on said substrate touch surface forming a perturbation in a Lamb wave propagating along a first path intersecting the position of said touch; and

means for sensing the occurrence of a perturbation in said Lamb waves to determine the axial position of a touch on said substrate relative to said first axis.

2. A touch position sensor as recited in claim 1 wherein said converting means converts said shear wave into Lamb waves having a first mode and second mode, said converting means further including means for suppressing one of the said modes to prevent interference with the other of said modes.

3. A touch position sensor as recited in claim 2 wherein said first and second modes are symmetric and anti-symmetric Lamb wave modes and said suppressing means includes means for suppressing said symmetric Lamb wave mode.

4. A touch position sensor as recited in claim 2 wherein said first and second modes are symmetric and anti-symmetric Lamb wave modes and said suppressing means includes means for suppressing said anti-symmetric Lamb wave modes.

5. A touch position sensor as recited in claim 1 wherein said sensing means includes

means disposed along an axis generally parallel to said first axis for converting said Lamb waves to shear waves;

and

means coupled to said substrate for receiving shear waves to provide a signal representative thereof.

6. A touch position sensor as recited in claim 5 wherein said imparting means includes a transmitting transducer coupled to a side of said substrate perpendicular to said first axis and said receiving means includes a transducer coupled to said substrate side spaced from said transmitting transducer and generally perpendicular to the axis of said Lamb to shear wave converting means.

7. A touch position sensor as recited in claim 1 wherein said substrate includes means disposed across said substrate touch surface from said converting means for reflecting Lamb waves propagating along said first paths back along said first paths to said converting means, said converting means converting said reflected Lamb waves to shear waves propagating along said first axis to said imparting means and said imparting means being responsive to shear waves propagated thereto to provide a signal representative of said shear waves, said signal being coupled to said sensing means.

8. A touch position sensor as recited in claim 1 further including

second means for imparting a shear wave into said substrate, said shear wave propagating along a second axis generally perpendicular to said first axis;

second means disposed along said second axis for converting portions of said shear wave propagating along said second axis to Lamb waves propagating along parallel paths extending across the touch surface of said substrate, each path representing a different axial position relative to said second axis, a touch on said substrate touch surface forming a perturbation in a Lamb wave propagating along a path intersecting the position of said touch;

said sensing means sensing the occurrence of a perturbation in said Lamb wave to determine the axial position of a touch on said substrate relative to said second axis.

9. A touch position sensor recited in claim 1 wherein said substrate is formed of glass.

10. A touch position sensor as recited in claim 9 wherein said glass is tempered.

11. A touch position sensor as recited in claim 9 wherein said glass is frosted.

12. A touch position sensor as recited in claim 1 wherein said substrate is formed of metal.

13. A touch position sensor as recited in claim 1 wherein said substrate is formed of plastic.

14. A touch position sensor as recited in claim 1 wherein said substrate is formed of a ceramic.

15. A touch position sensor as recited in claim 1 wherein said imparting means imparts a zeroth order horizontally polarized shear wave into said substrate.

16. A touch position sensor as recited in claim 15 wherein said imparting means includes a transducer, said transducer being coupled to said substrate by a flexible connector capable of transmitting said shear wave to allow said transducer to be positioned remote from said substrate.

17. A touch position sensor as recited in claim 16 wherein said flexible connector is formed of a metal strip.

18. A touch position sensor as recited in claim 17 wherein said metal strip has a variable thickness, the thickness of said strip adjacent to said plate being equal to the thickness of said plate.

19. A touch position sensor as recited in claim 17 further including a sheathing for said metal strip.

20. A touch position sensor as recited in claim 19 wherein said sheathing is plastic.

21. A touch position sensor as recited in claim 1 wherein said imparting means includes a transducer, a conductive frit bonding said transducer to said substrate.

22. A touch position sensor as recited in claim 21 wherein the height of said transducer is equal to the thickness of said substrate.

23. A touch position sensor comprising:

a substrate capable of supporting shear waves and Lamb waves propagating therein said substrating having a touch surface;

means coupled to said substrate for imparting a shear wave into said substrate, said shear wave propagating along a first axis;

a first array of converting elements disposed on said substrate along said first axis for converting said shear wave to Lamb waves having a symmetric mode and an anti-symmetric mode;

means disposed on said substrate relative to said first array for suppressing one of said modes, said converting means propagating the other of said modes along first parallel paths extending across the touch surface of said substrate, each first path representing a different axial position relative to said first axis and a touch on said substrate touch surface forming a perturbation in a Lamb wave propagating along a first path intersecting the position of said touch;

a second array of converting elements disposed along an axis generally parallel to said first axis for converting said Lamb waves to shear waves propagating along an axis generally parallel to said first axis, a perturbation in a Lamb wave forming a perturbation in the shear wave to which said Lamb wave is converted; and

means coupled to said substrate for sensing shear waves propagating along said parallel axis to provide a signal representative thereof; and

means responsive to said signal for determining the position of a touch on said substrate touch surface relative to said first axis.

24. A touch position sensor as recited in claim 23 wherein said first array is disposed on a first surface of said substrate and said suppressing means includes an array of converting elements disposed on a surface of said substrate opposite to said first surface and aligned with the elements of said first array to suppress said anti-symmetric mode.

25. A touch position sensor as recited in claim 23 wherein said first array is disposed on a first surface of said substrate and said suppressing means includes an array of converting elements disposed on a surface of said substrate opposite to said first surface and shifted relative to the first array by an amount approximately equal to the wavelength of a symmetric mode Lamb wave divided by two to suppress said symmetric mode.

26. A touch position sensor as recited in claim 25 wherein said shear waves are first order horizontally polarized shear waves, said Lamb waves are first order Lamb waves and the thickness of said substrate is set to a value for which the phase velocity of said shear wave is equal to the phase velocity of said first order symmetric Lamb wave.

27. A touch position sensor as recited in claim 25 wherein the elements of said suppressing array are shifted from the elements of said first converting array in the direction at right angles to said first axis.

28. A touch position sensor as recited in claim 25 wherein the elements of said suppressing array are shifted from the elements of said first converting array in a direction along said first axis.

29. A touch position sensor as recited in claim 23 further including

second means coupled to said substrate for imparting a shear wave propagating along a second axis, said second axis intersecting said first axis;

a third array of converting elements disposed along said second axis for converting portions of said shear wave to Lamb waves having a symmetric mode and an anti-symmetric mode;

means disposed on said substrate relative to said third array for suppressing one of said modes, converting means propagating the other of said modes along second parallel paths extending across the touch surface of said substrate, each second path representing a different axial position relative to said second axis and a touch on said substrate touch surface forming a perturbation in a Lamb wave propagating along a second path intersecting the position of said touch;

a fourth array of converting elements disposed along an axis generally parallel to said second axis for converting Lamb waves propagating on said second paths to shear waves propagating along an axis generally parallel to said second axis; and

second means coupled to said substrate for sensing shear waves propagating along said axis parallel to said second axis to provide a signal representative thereof, said determining means being coupled to said sensing means to determine the position of a touch on said substrate touch surface relative to said second axis.

30. A touch position sensor as recited in claim 23 wherein said substrate is formed of glass.

31. A touch position sensor as recited in claim 30 wherein said glass is tempered.

32. A touch position sensor as recited in claim 30 wherein said glass is frosted.

33. A touch position sensor as recited in claim 23 wherein said substrate is formed of metal.

34. A touch position sensor as recited in claim 23 wherein said substrate is formed of plastic.

35. A touch position sensor as recited in claim 23 wherein said substrate is formed of a ceramic.

36. A touch position sensor as recited in claim 23 wherein said imparting means imparts a zeroth order horizontally polarized shear wave into said substrate and said converting means converts said shear waves to first order Lamb waves.

37. A touch position sensor as recited in claim 23 wherein said imparting means includes a transducer, said transducer being coupled to said substrate by a flexible connector capable of transmitting said shear wave to allow said transducer to be positioned remote from said substrate.

38. A touch position sensor as recited in claim 37 wherein said flexible connector is formed of a metal strip.

39. A touch position sensor as recited in claim 38 wherein said metal strip has a variable thickness, the thickness of said strip adjacent to said plate being equal to the thickness of said plate.

40. A touch position sensor as recited in claim 38 further including a sheathing for said metal strip.

41. A touch position sensor as recited in claim 40 wherein said sheathing is plastic.

42. A touch position sensor as recited in claim 23 wherein said imparting means includes a transducer, a conductive frit bonding said transducer to said substrate.

43. A touch position sensor as recited in claim 42 wherein the height of said transducer is equal to the thickness of said substrate.

44. A touch position sensor comprising:

a substrate capable of supporting shear waves and Lamb waves propagating therein said substrating having a touch surface;

means coupled to said substrate for imparting a shear wave into said substrate, said shear wave propagating along a first axis;

a first array of converting elements disposed on said substrate along said first axis for converting said shear wave to Lamb waves having a symmetric mode and anti-symmetric mode;

means disposed on said substrate relative to said first array for suppressing one of said modes, said converting means propagating the other of said modes along first parallel paths extending across the touch surface of said substrate, each first path representing a different axial position relative to said first axis and a touch on said substrate touch surface forming a perturbation in a Lamb wave propagating along a first path intersecting the position of said touch;

means disposed generally parallel to said first axis and spaced from said first array for reflecting Lamb waves propagating along said first parallel paths back along said first parallel paths to said first array of converting elements, said converting elements converting said reflected Lamb waves to shear waves propagating along said first axis to said first imparting means and said first imparting means being responsive to shear waves propagated thereto to provide a signal representative of said shear waves; and

means responsive to said signal for determining the position of a touch on said substrate relative to said first axis.

45. A touch position sensor as recited in claim 44 wherein said first array is disposed on a first surface of said substrate and said suppressing means includes an array of converting elements disposed on a surface of said substrate opposite to said first surface and aligned with the elements of said first array to suppress said anti-symmetric mode.

46. A touch position sensor as recited in claim 44 wherein said first array is disposed on a first surface of said substrate and said suppressing means includes an array of converting elements disposed on a surface of said substrate opposite to said first surface and shifted relative to the first array by an amount approximately equal to the wavelength of a symmetric mode Lamb wave divided by two to suppress said symmetric mode.

47. A touch position sensor as recited in claim 46 wherein said shear waves are first order horizontally polarized shear waves, said Lamb waves are first order Lamb waves and the thickness of said substrate is set to a value for which the phase velocity of said shear wave is equal to the phase velocity of said first order symmetric Lamb wave.

48. A touch position sensor as recited in claim 46 wherein the elements of said suppressing array are shifted from the elements of said first converting array in the direction at right angles to said first axis.

49. A touch position sensor as recited in claim 46 wherein the elements of said suppressing array are shifted from the elements of said first converting array in a direction along said first axis.

50. A touch position sensor as recited in claim 44 wherein said reflecting means includes a reflective edge of said substrate.

51. A touch position sensor as recited in claim 44 further including

second means coupled to said substrate for imparting a shear wave propagating along a second axis, said second axis intersecting said first axis;

a second array of converting elements disposed along said second axis for converting portions of said shear wave to Lamb waves having a symmetric mode and an anti-symmetric mode;

means disposed on said substrate relative to said second array for suppressing one of said modes, said converting means propagating the other of said modes along second parallel paths extending across the touch surface of said substrate, each of said second paths representing a different axial position relative to said second axis and a touch on said substrate touch surface forming a perturbation in a Lamb wave propagating along a second path intersecting the position of said touch;

means disposed generally parallel to said second axis and spaced from said second array for reflecting Lamb waves propagating along said second parallel paths back along said second paths to said second array of converting elements, said converting elements converting said reflected Lamb waves to shear waves propagating along said second axis to said second imparting means and said second imparting means being responsive to shear waves propagated thereto to provide a signal representative of said shear waves said position determining means being coupled to said second imparting means to determine the position of a touch on said substrate relative to said second axis.

52. A touch position sensor as recited in claim 44 wherein said substrate is formed of glass.

53. A touch position sensor as recited in claim 52 wherein said glass is tempered.

54. A touch position sensor as recited in claim 52 wherein said glass is frosted.

55. A touch position sensor as recited in claim 44 wherein said substrate is formed of metal.

56. A touch position sensor as recited in claim 44 wherein said substrate is formed of plastic.

57. A touch position sensor as recited in claim 44 wherein said substrate is formed of a ceramic.

58. A touch position sensor as recited in claim 44 wherein said imparting means imparts a zeroth order horizontally polarized shear wave into said substrate and said converting means converts said shear waves to first order Lamb waves.

59. A touch position sensor as recited in claim 44 wherein said imparting means includes a transducer, said transducer being coupled to said substrate by a flexible connector capable of transmitting said shear wave to allow said transducer to be positioned remote from said substrate.

60. A touch position sensor as recited in claim 59 wherein said flexible connector is formed of a metal strip.

61. A touch position sensor as recited in claim 60 wherein said metal strip has a variable thickness, the thickness of said strip adjacent to said plate being equal to the thickness of said plate.

62. A touch position sensor as recited in claim 60 further including a sheathing for said metal strip.

63. A touch position sensor as recited in claim 62 wherein said sheathing is plastic.

64. A touch position sensor as recited in claim 44 wherein said imparting means includes a transducer, a conductive frit bonding said transducer to said substrate.

65. A touch position sensor as recited in claim 64 wherein the height of said transducer is equal to the thickness of said substrate.

66. A touch position sensor comprising:

a substrate capable of supporting shear waves and Lamb waves propagating therein, said substrating having a touch surface;

means coupled to said substrate for imparting a shear wave into said substrate, said shear wave propagating along a first axis;

a first array of converting elements disposed on said substrate along said first axis for converting said shear wave to Lamb waves having a symmetric mode and anti-symmetric mode;

means disposed on said substrate relative to said first array for suppressing one of said modes, said converting means propagating the other of said modes along first parallel paths extending across the touch surface of said substrate, each of said first paths representing a different axial position relative to said first axis and a touch on said substrate touch surface forming a perturbation in a Lamb wave propagating along a first path intersecting the position of said touch;

means disposed generally parallel to said first axis and spaced from said first array for reflecting Lamb waves propagating along said first parallel paths back along said first parallel paths to said first array of converting elements, said converting elements converting said reflected Lamb waves to shear waves propagating along said first axis to said imparting means and said imparting means being responsive to shear waves propagated thereto to provide a signal representative of said shear waves;

a second array of converting elements disposed along a second axis intersecting said first axis for converting portions of a shear wave reflected thereto to Lamb waves having a symmetric mode and an anti-symmetric mode;

means for reflecting a shear wave propagating along said first axis to said second array for propagation along said second axis;

means disposed on said substrate relative to said second array for suppressing one of said modes, said converting means propagating the other of said modes along second parallel paths extending across the touch surface of said substrate, each of said second paths representing a different axial position relative to said second axis and a touch on said substrate touch surface forming a perturbation in a Lamb wave propagating along a second path intersecting the position of said touch;

means disposed generally parallel to said second axis and spaced from said second array for reflecting Lamb waves propagating along said second parallel paths back along said second paths to said second array of converting elements, said converting elements converting said reflected Lamb waves to shear waves propagating along said second axis to said reflecting means and said reflecting means reflecting said shear waves for propagation along said first axis to said imparting means, said imparting means being responsive to shear waves propagated thereto to provide a signal representative thereof; and

means responsive to said signals for determining the position of a touch on said substrate touch surface relative to said first and second axes.

67. A touch position sensor as recited in claim 66 wherein said substrate is formed of glass.

68. A touch position sensor as recited in claim 67 wherein said glass is tempered.

69. A touch position sensor as recited in claim 67 wherein said glass is frosted.

70. A touch position sensor as recited in claim 66 wherein said substrate is formed of metal.

71. A touch position sensor as recited in claim 66 wherein said substrate is formed of plastic.

72. A touch position sensor as recited in claim 66 wherein said substrate is formed of a ceramic.

73. A touch position sensor as recited in claim 66 wherein said imparting means imparts a zeroth order horizontally polarized shear wave into said substrate and said converting means converts said shear waves to first order Lamb waves.

74. A touch position sensor as recited in claim 66 wherein said imparting means includes a transducer, said transducer being coupled to said substrate by a flexible connector capable of transmitting said shear wave to allow said transducer to be positioned remote from said substrate.

75. A touch position sensor as recited in claim 74 wherein said flexible connector is formed of a metal strip.

76. A touch position sensor as recited in claim 75 wherein said metal strip has a variable thickness, the thickness of said strip adjacent to said plate being equal to the thickness of said plate.

77. A touch position sensor as recited in claim 75 further including a sheathing for said metal strip.

78. A touch position sensor as recited in claim 77 wherein said sheathing is plastic.

79. A touch position sensor as recited in claim 66 wherein said imparting means includes a transducer, a conductive frit bonding said transducer to said substrate.

80. A touch position sensor as recited in claim 79 wherein the height of said transducer is equal to the thickness of said substrate.