Monitoring system and method

• US 6,819,254 B2
• Filed: 04/03/2001
• Issued: 11/16/2004
• Est. Priority Date: 03/05/1999
• Status: Expired due to Term

• Current Assignee: Hill-Rom Services Incorporated (Baxter International Inc.)
• Original Assignee: Hill-Rom Services Incorporated (Baxter International Inc.)
• Inventors: Riley, Carl William
• Primary Examiner(s): Lieu, Julie
• Application Number:
  US09/825,392
• Publication Number:
  US 20010010497A1
• Time in Patent Office: 1,323 Days
• Field of Search: 340/665, 340/666, 340/667, 340/657, 340/658, 340/573.1, 737/60, 738/620.45, 738/620.46, 345/173, 345/174
• US Class Current: 340/665
• CPC Class Codes: G01L 1/162 using piezoelectric resonators

Abstract

A system including piezoelectric material wherein a force exerted on the piezoelectric material is determined by subjecting the piezoelectric material to an input signal of sweeping frequency and evaluating the response of the piezoelectric material to the applied signal.

Claims

1. A monitoring system comprising a first, piezoelectric device which is subject to a force to be monitored, and a second device for determining the first device'"'"'s output and for correlating the first device'"'"'s output with the force, the second device including a sweep signal generator for causing a sweeping signal to be applied to the first device and an impedance determining circuit for causing the impedance of the first device to the applied swept signal to be determined.

2. The apparatus of claim 1 comprising a plurality of said first devices coupled together in an array.

3. The apparatus of claim 1 wherein the second device comprises a switch for controlling the second device for determining the first device'"'"'s output and for correlating the first device'"'"'s output with the force, the switch having a first state corresponding to a first mode of operation of the second device and a second state corresponding to a second mode of operation of the second device.

4. The apparatus of claim 3 wherein switching of the switch to the second state causes a signal to be applied by the signal generator to the first device and causes the second device to determine the impedance of the first device to the applied signal.

5. The apparatus of claim 4 wherein the second device comprises a second device for determining from the impedance the force applied to the first device.

6. The apparatus of claim 5 wherein the second device comprises a second device for determining from the determined force whether an object is on the first device.

7. The apparatus of claim 3 wherein the second device comprises a second device for detecting a relatively large signal generated by the first device, placing the second device in a second state when the relatively large signal is detected, then determining if the signal generated by the first device varies at a predetermined rate over a predetermined time, and then concluding that an object is still exerting force on the first device.

8. The apparatus of claim 3 wherein the second device comprises a second device for detecting a relatively large signal generated by the first device, then placing the second device in a second state when the signal decreases over a brief time interval below some minimum threshold, then switching to the second mode, and determining if a relatively constant force is being applied.

9. The apparatus of claim 4 wherein the second device comprises a second device for determining from the first device'"'"'s impedance the force that is being applied to the first device.

10. The apparatus of claim 1 wherein the first device comprises a piezoelectric ceramic transducer.

11. The apparatus of claim 10 comprising an array of said piezoelectric ceramic transducers.

12. The apparatus of claim 10 wherein the ceramic transducer is custom fabricated to a particular size, shape, and electrical properties.

13. The apparatus of claim 2 further comprising a third device for holding the plurality of first devices in the array.

14. The apparatus of claim 10 wherein the first device is oriented at a strategic load-bearing point.

15. The apparatus of claim 10 comprising a plurality of first devices coupled together and oriented at a plurality of strategic load bearing points.

16. The apparatus of claim 10 wherein the second device comprises a switch for controlling the second device for determining the first device'"'"'s output and for correlating the first device'"'"'s output with the applied force, the switch having a first state corresponding to a first mode of operation and a second state corresponding to a second mode of operation.

17. The apparatus of claim 16 wherein switching of the switch to the second state causes a signal to be applied by the signal generator to the first device and causes the second device to determine the impedance of the first device to the applied signal.

18. The apparatus of claim 17 wherein the second device comprises a second device for determining from the impedance the force on the first device.

19. The apparatus of claim 18 wherein the second device comprises a second device for determining from the determined force whether an object is exerting force on the first device.

20. The apparatus of claim 16 wherein the second device comprises a second device for detecting a relatively large signal generated by the first device, placing the second device in a second state when the relatively large signal from the first device is detected, then determining if the signal generated by the first device varies at a predetermined rate over a predetermined time, and then concluding that an object is exerting force on the first device.

21. The apparatus of claim 16 wherein the second device comprises a second device for detecting a relatively large signal generated by the first device, placing the second device in a second state when the signal decreases relatively rapidly to below a minimum threshold, then switching to the second mode, and then determining if a relatively constant force is being applied on the first device.

22. The apparatus of claim 17 wherein the second device comprises a second device for determining from the first device'"'"'s impedance the force applied to the first device.

23. The apparatus of claim 1 wherein the first device comprises a flexible piezoelectric film.

24. The apparatus of claim 23 wherein the flexible piezoelectric film is custom fabricated to a particular size, shape, and electrical properties.

25. The apparatus of claim 23 wherein the flexible piezoelectric film comprises an array of said first devices.

26. The apparatus of claim 23 wherein the second device comprises a switch for controlling the second device for determining the first device'"'"'s output and for correlating the first devices'"'"'s output with the force, the switch having a first state corresponding to a first mode of operation and a second state corresponding to a second mode of operation.

27. The apparatus of claim 26 wherein switching of the switch to the second state causes a signal to be applied by the signal generator to the first device and causes the second device to determine the impedance of the first device to the applied signal.

28. The apparatus of claim 27 wherein the second device comprises a second device for determining from the impedance the force on the first device.

29. The apparatus of claim 28 wherein the second device comprises a second device for determining from the determined force whether an object is exerting force on the first device.

30. The apparatus of claim 26 wherein the second device comprises a second device for detecting a relatively large signal generated by the first device, placing the second device in a second state when the relatively large signal from the first device is detected, then determining if the signal generated by the first device varies at a predetermined rate over a predetermined time, and then concluding that an object is exerting force on the first device.

31. The apparatus of claim 26 wherein the second device comprises a second device for detecting a relatively large signal generated by the first device, placing the second device in a second state when the signal decreases relatively rapidly to below a minimum threshold, then switching to the second mode, and then determining if a relatively constant force is being applied on the first device.

32. The apparatus of claim 27 wherein the second device comprises a second device for determining from the first device'"'"'s impedance the force applied to the first device.

33. A monitoring system comprising a first, piezoelectric device which is subject to a force to be monitored, and a second device for determining the first device'"'"'s output and for correlating the first device'"'"'s output with the force, the second device including a signal generator for causing a signal to be applied to the first device and an impedance determining circuit for causing the impedance of the first device to the applied signal to be determined, and the first device including a coaxial cable including a center conductor, a shield, and a piezoelectric material between the center conductor and shield.

34. The apparatus of claim 33 wherein the second device comprises a switch for controlling the second device for determining the first device'"'"'s output and for correlating the first device'"'"'s output with the force, the switch having a first state corresponding to a first mode of operation and a second state corresponding to a second mode of operation.

35. The apparatus of claim 34 wherein switching of the switch to the second state causes a signal to be applied by the signal generator to the first device and causes the second device to determine the impedance of the first device to the applied signal.

36. The apparatus of claim 35 wherein the second device comprises a second device for determining from the impedance the force on the first device.

37. The apparatus of claim 36 wherein the second device comprises a second device for determining from the determined force whether an object is exerting force on the first device.

38. The apparatus of claim 34 wherein the second device comprises a second device for detecting a relatively large signal generated by the first device, placing the second device in a second state when the relatively large signal from the first device is detected, then determining if the signal generated by the first device varies at a predetermined rate over a predetermined time, and then concluding that an object is exerting force on the first device.

39. The apparatus of claim 34 wherein the second device comprises a second device for detecting a relatively large signal generated by the first device, placing the second device in a second state when the signal decreases relatively rapidly to below a minimum threshold, then switching to the second mode, and then determining if a relatively constant force is being applied on the first device.

40. The apparatus of claim 35 wherein the signal generator comprises a sweep signal generator for sweeping the signal frequency and determining the first device'"'"'s impedance in response to the swept signal frequency.

41. The apparatus of claim 35 wherein the second device comprises a second device for determining from the first device'"'"'s impedance the force applied to the first device.

42. A monitoring method comprising providing a first, piezoelectric device which is subject to a force to be monitored, determining the first device'"'"'s output, and correlating the first device'"'"'s output with the force, determining the first device'"'"'s output including providing a sweep signal generator for causing a sweeping signal to be applied to the first device and providing an impedance determining circuit for causing the impedance of the first device to the swept applied signal to be determined.

43. The method of claim 42 wherein providing a first device comprises providing a plurality of said first devices coupled together in an array.

44. The method of claim 42 wherein determining the first device'"'"'s output comprises providing a switch having a first state corresponding to a first mode of operation when the force applied to the first device is being modulated and a second state corresponding to a second mode of operation when the force applied to the first device is not being modulated.

45. The method of claim 44 wherein switching of the switch to the second state causes a signal to be applied to the first device and causes the impedance of the first device to the applied signal to be determined.

46. The method of claim 45 further comprising determining from the impedance the force applied to the first device.

47. The method of claim 46 further comprising determining from the force whether an object is on the first device.

48. The method of claim 44 wherein determining the first device'"'"'s output and correlating the first device'"'"'s output with the force comprise detecting a relatively large signal generated by the first device, then determining if the signal generated by the first device varies at a predetermined rate over a predetermined time, and then concluding that an object is still on the first device.

49. The method of claim 44 wherein determining the first device'"'"'s output and correlating the first device'"'"'s output with the force comprise detecting a relatively large signal generated by the first device, then detecting when the signal decreases relatively rapidly to below a minimum threshold, and then determining if a relatively constant force is being applied.

50. The method of claim 45 wherein providing a signal generator for causing a signal to be applied to the first device and providing an impedance determining circuit for causing the impedance of the first device to the applied signal to be determined comprise sweeping the signal frequency and determining the first device'"'"'s impedance in response to the swept signal frequency.

51. The method of claim 45 wherein determining the first device'"'"'s output and correlating the first device'"'"'s output with the force comprise determining from the first device'"'"'s impedance the force that is being applied the first device.

52. The method of claim 46 wherein providing a first device comprises providing a piezoelectric ceramic transducer.

53. The method of claim 52 wherein providing a piezoelectric ceramic transducer comprises providing an array of piezoelectric ceramic transducers.

54. The method of claim 52 wherein providing a piezoelectric ceramic transducer comprises custom fabricating a piezoelectric ceramic transducer to a particular size, shape, and electrical properties.

55. The method of claim 53 wherein providing an array of said first devices coupled together further comprises providing a third device for holding the plurality of first devices in the array.

56. The method of claim 52 further comprising orienting the first device at a strategic load-bearing point.

65. The method of claim 42 wherein providing a first device comprises providing a flexible piezoelectric film.

66. The method of claim 65 wherein providing a flexible piezoelectric film comprises custom fabricating a flexible piezoelectric film to a particular size, shape, and electrical properties.

67. The method of claim 65 wherein providing a flexible piezoelectric film comprises providing an array of said first devices.

57. A monitoring method comprising providing a first, piezoelectric device which is subject to a force to be monitored, determining the first device'"'"'s output, and correlating the first device'"'"'s output with the force;

wherein determining the first device'"'"'s output comprises providing a switch having a first state when the force applied to the first device is being modulated and a second state when the force applied to the first device is not being modulated, providing a signal generator for causing a signal to be applied to the first device, and providing an impedance determining circuit for causing the impedance of the first device to the applied signal to be determined.

58. The method of claim 57 wherein determining the first device'"'"'s output and correlating the first device'"'"'s output with the force comprise determining from the impedance the force on the first device.

59. The method of claim 58 wherein determining the first device'"'"'s output and correlating the first device'"'"'s output with the force comprise determining from the determined force whether an object is exerting force on the first device.

60. The method of claim 57 wherein determining the first device'"'"'s output and correlating the first device'"'"'s output with the object'"'"'s status comprise detecting a relatively large signal generated by the first device, then determining if the signal generated by the first device varies at a predetermined rate over a predetermined time, and then concluding that the object is exerting force on the first device.

61. The method of claim 57 wherein determining the first device'"'"'s output and correlating the first device'"'"'s output with the object'"'"'s status comprise detecting a relatively large signal generated by the first device, then detecting when the signal relatively rapidly to below a minimum threshold, and then determining if a constant force is being applied.

62. The method of claim 57 wherein providing a signal generator for causing a signal to be applied to the first device and providing an impedance determining circuit for causing the impedance of the first device to the applied signal to be determined comprise sweeping the signal frequency and determining the first device'"'"'s impedance in response to the swept signal frequency.

63. The method of claim 57 wherein determining the first device'"'"'s output and correlating the first device'"'"'s output with the object'"'"'s status comprise determining from the first device'"'"'s impedance the force applied to the first device.

64. The method of claim 62 wherein providing a first device comprises providing a plurality of first devices coupled together and oriented at a plurality of strategic load-bearing points.

68. A monitoring method comprising providing a first, piezoelectric device which is subject to a force to be monitored, determining the first device'"'"'s output, and correlating the first device'"'"'s output with the force;

determining the first device'"'"'s output including providing a signal generator for causing a signal to be applied to the first device and providing an impedance determining circuit for causing the impedance of the first device to the applied signal to be determined; and

wherein providing a first device includes providing a coaxial cable including a center conductor, a shield, and a piezoelectric material between the center conductor and shield.

69. The method of claim 68 wherein determining the first device'"'"'s output comprises providing a switch having a first state when the force applied to the first device is being modulated and a second state when the force applied to the first device is not being modulated.

70. The method of claim 69 wherein determining the first device'"'"'s output and correlating the first device'"'"'s output with the object'"'"'s status comprise determining from the impedance the force on the firs device.

71. The method of claim 70 wherein determining the first device'"'"'s output and correlating the first device'"'"'s output with the object'"'"'s status comprise determining from the determined force whether the object is exerting force on the first device.

72. The method of claim 69 wherein determining the first device'"'"'s output and correlating the first device'"'"'s output with the object'"'"'s status comprise detecting a relatively large signal generated by the first device, then determining if the signal generated by the first device varies at a predetermined rate over a predetermined time, and then concluding that the object is exerting force on the first device.

73. The method of claim 69 wherein determining the first device'"'"'s output and correlating the first device'"'"'s output with the object'"'"'s status comprise detecting a relatively large signal generated by the first device, then detecting when the signal relatively rapidly to below a minimum threshold, and then determining if a constant force is being applied.

74. The method of claim 69 wherein providing electrical signals for exciting the first device and determining the impedance of the first device to the electrical signals comprise sweeping the signal frequency and determining the first device'"'"'s impedance in response to the swept signal frequency.

75. The method of claim 69 wherein determining the first device'"'"'s output and correlating the first device'"'"'s output with the object'"'"'s status comprise determining from the first device'"'"'s impedance the force applied to the first device.

76. A monitoring system comprising:

a piezoelectric device which is subject to static forces whose magnitude is to be monitored;

a voltage source providing variable frequency sweep signals to the piezoelectric device; and

a second device determining the reactance of the piezoelectric device from the piezoelectric device response to the variable frequency sweep signals and determining the magnitude of the static force from the reactance.

77. A monitoring method comprising:

providing a piezoelectric device which is subject to static forces whose magnitude is to be monitored;

providing variable frequency sweep signals;

applying variable frequency sweep signals to the piezoelectric device;

determining the reactance of the piezoelectric device from the piezoelectric device response to the variable frequency sweep signals; and

determining the magnitude of the static force from the determined reactance.