Closed loop control systems employing relaxor ferroelectric actuators

• US 6,707,230 B2
• Filed: 05/29/2002
• Issued: 03/16/2004
• Est. Priority Date: 05/29/2001
• Status: Expired due to Fees

• Current Assignee: Insitutec LLC
• Original Assignee: University of North Carolina At Charlotte (University of North Carolina System)
• Inventors: Smith, Stuart T., Woody, Shane C., Seugling, Richard M.
• Primary Examiner(s): BUDD, MARK OSBORNE
• Application Number:
  US10/157,095
• Publication Number:
  US 20030006676A1
• Time in Patent Office: 657 Days
• Field of Search: 310/316.01, 310/317, 310/319, 310/330-332, 310/328, 310/357-359, 310/321, 310/326
• US Class Current: 310/316.01
• CPC Class Codes: H02N 2/0095 producing combined linear and rotary motion, e.g. multi-direction positioners
• CPC Class Codes: H02N 2/043 Mechanical transmission means, e.g. for stroke amplification
• CPC Class Codes: H02N 2/062 Small signal circuits; Means for controlling position or derived quantities, e.g. for removing hysteresis
• CPC Class Codes: H10N 30/8548 Lead based oxides

Abstract

A closed loop motion control system employing at least one relaxor actuator which controls the position of a moving member having mass by controlling an electric field applied to the relaxor actuator. The actuator comprises a body of relaxor material dimensionally variable under the influence of the electric field applied in the form of a voltage to electrodes on at least two surfaces of the actuator. The voltage is applied in response to a feedback signal produced by at least one feedback sensor, which may be a displacement sensor or some other type of sensor. Thus, by constantly monitoring the displacement or other variable of the actuator device, the position of the moving member may be precisely controlled.

Claims

1. An electromechanical actuator system comprising:

at least one actuator device having an actuator body formed from a relaxor-based piezoelectric material and a mechanical system driven by the actuator body;

a sensor for sensing a phenomenon produced by the mechanical system in response to piezoelectric movement of the actuator body; and

a driver, having an input connected to the sensor, for applying a variable electric field to the actuator body.

2. The electromechanical actuator system of claim 1, wherein the sensor produces an output corresponding to the phenomenon produced by the mechanical system, and wherein the driver applies the electric field in response to the sensor output.

3. The electromechanical actuator system of claim 2, wherein piezoelectric movement of the actuator body causes a first surface to move relative to a second surface, wherein the sensor measures the separation between the first and second surfaces, and wherein the output of the sensor is a function of the separation measurement.

4. The electromechanical actuator system of claim 3, wherein the sensor measures the separation between a point on the first surface and a point on the second surface.

5. The electromechanical actuator system of claim 3, wherein the first surface defines a first plane and the second surface defines a second plane, and wherein the sensor measures the separation between the first plane and the second plane.

6. The electromechanical actuator system of claim 3, wherein the piezoelectric movement of the actuator body defines a direction of movement, and wherein the direction of movement intersects the first and second surfaces.

7. The electromechanical actuator system of claim 6, wherein the actuator body defines a central axis parallel to the direction of piezoelectric movement, and wherein the central axis intersects the first and second surfaces.

8. The electromechanical actuator system of claim 3, wherein the magnitude of the piezoelectric movement of the actuator body is substantially equivalent to the magnitude of change caused by the piezoelectric movement in the separation between the first and second surfaces.

9. The electromechanical actuator system of claim 3, wherein the sensor is disposed generally adjacent to the actuator body.

10. The electromechanical actuator system of claim 3, wherein the mechanical system includes a first moving member in direct physical contact with the actuator body, wherein the area of contact generally defines a first location in the mechanical system, and wherein the movement of the first surface relative to the second surface occurs in a second location in the mechanical system.

11. The electromechanical actuator system of claim 10, wherein the mechanical system includes a lever, and wherein the movement of the first surface relative to the second surface is transmitted from the actuator body via the lever.

12. The electromechanical actuator system of claim 2, wherein the phenomenon produced by the mechanical system is a displacement.

13. The electromechanical actuator system of claim 12, wherein the displacement is the displacement of at least a portion of the mechanical system.

14. The electromechanical actuator system of claim 12, wherein the displacement is a linear displacement.

15. The electromechanical actuator system of claim 12, wherein the displacement is a rotational displacement.

16. The electromechanical actuator system of claim 2, wherein the sensor is a proximity probe.

17. The electromechanical actuator system of claim 2, wherein the sensor is a strain gage.

18. The electromechanical actuator system of claim 2, wherein the sensor detects a phenomenon other than displacement.

19. The electromechanical actuator system of claim 2, further comprising a comparator for comparing the sensor output to a signal representing a desired state.

20. The electromechanical actuator system of claim 2, further comprising a controller for controlling the driver to variably apply the electric field to the actuator body.

21. The electromechanical actuator system of claim 20, wherein the controller controls the driver in response to the output produced by the sensor.

22. The electromechanical actuator system of claim 20, further comprising at least a second driver for applying a variable electric field to the actuator body.

23. The electromechanical actuator system of claim 22, wherein the controller also controls the second driver to variably apply an electric field to the actuator body.

24. The electromechanical actuator system of claim 22, further comprising a second controller for controlling the second driver to variably apply the electric field to the actuator body.

25. The electromechanical actuator system of claim 2, further comprising at least a second sensor for sensing a second phenomenon produced by the mechanical system in response to the piezoelectric movement of the actuator body, wherein the second sensor produces an output corresponding to the second phenomenon produced by the mechanical system.

26. The electromechanical actuator system of claim 25, wherein the driver applies the electric field in response to the second sensor output.

27. The electromechanical actuator system of claim 25, wherein at least one sensor is a displacement sensor and at least one sensor is not a displacement sensor.

28. The electromechanical actuator system of claim 27, wherein the first sensor is not a displacement sensor and the second sensor is a displacement sensor, and wherein the second phenomenon is a displacement caused by the piezoelectric movement of the actuator body in response to the output of the first sensor.

29. The electromechanical actuator system of claim 25, wherein at least two sensors are displacement sensors.

30. The electromechanical actuator system of claim 2, further comprising a first support structure and a second support structure, wherein the actuator body is supported by the first support structure and the sensor is supported by the second support structure, and wherein the first and second support structures are structurally independent of each other.

31. The electromechanical actuator system of claim 1, wherein the relaxor-based piezoelectric material is a relaxor ferroelectric material.

32. The electromechanical actuator system of claim 1, wherein the relaxor-based piezoelectric material is PMN, PZN, a solid solution of PMN and PT, or a solid solution of PZN and PT.

33. The electromechanical actuator system of claim 32, wherein PT is 8% of the solid solution of PZN and PT.

34. The electromechanical actuator system of claim 32, wherein PT is 4.5% of the solid solution of PZN and PT.

35. The electromechanical actuator system of claim 32, wherein PT is 24% of the solid solution of PMN and PT.

36. The electromechanical actuator system of claim 1, wherein the actuator body is rectilinear in shape.

37. The electromechanical actuator system of claim 1, wherein the actuator body is curvilinear in shape.

38. The electromechanical actuator system of claim 1, wherein the actuator body is formed from at least two bi-morph elements.

39. A method of controlling an electromechanical actuator system, the method comprising the steps of:

applying an electric field to an actuator body formed from a relaxor-based material to generate a piezoelectric movement in the actuator body;

in response to the piezoelectric movement of the actuator body, producing a phenomenon in a mechanical system;

sensing the phenomenon produced by the mechanical system; and

varying the applied electric field according to the outcome of the sensing step.

40. The method of claim 39, further comprising the step of generating an output signal corresponding to the phenomenon produced by the mechanical system.

41. The method of claim 40, further comprising the step of comparing the output signal to a signal representing a desired state.

42. The method of claim 41, wherein the step of varying the applied electric field is carried out according to the outcome of the comparing step.

43. The method of claim 39, wherein the step of producing a phenomenon includes causing a first surface to move relative to a second surface, and wherein the step of sensing includes measuring the separation between the first and second surfaces.

44. The method of claim 43, wherein the step of causing a first surface to move relative to a second surface includes causing the first surface to move in a first direction defining an axis, and wherein the axis intersects the first and second surfaces.

45. The method of claim 43, wherein the magnitude of the piezoelectric movement of the actuator body is substantially equivalent to the magnitude of change caused by the piezoelectric movement in the separation between the first and second surfaces.

46. The method of claim 43, wherein the sensing step is carried out in a location generally adjacent to the actuator body.

47. The method of claim 43, wherein the step of producing a phenomenon in the mechanical system includes physically contacting a first moving member of the mechanical system with the actuator body, wherein the area of physical contact between the first moving member and the actuator body generally defines a first location in the mechanical system, and wherein the movement of the first surface relative to the second surface occurs in a second location in the mechanical system.

48. The method of claim 47, wherein the mechanical system includes a lever, and wherein the step of causing movement of the first surface relative to the second surface includes transmitting movement from the actuator body via the lever.

49. The method of claim 39, wherein the step of producing a phenomenon includes producing a displacement of at least a portion of the mechanical system.

50. The method of claim 47, wherein the step of producing a displacement includes producing a linear displacement.

51. The method of claim 47, wherein the step of producing a displacement includes producing a rotational displacement.

52. The method of claim 47, wherein the step of sensing includes sensing the proximity of a surface to the tip of a proximity probe.

53. The method of claim 47, wherein the step of sensing includes measuring strain.

54. The method of claim 47, wherein the step of sensing includes detecting a phenomenon other than displacement.

55. An electromechanical actuator system, comprising:

an actuator device having an actuator body formed from a relaxor-based piezoelectric material and a mechanical system driven by the actuator body;

a driver for variably applying an electric field to the actuator body; and

a feedback loop for providing input to the driver in response to at least one phenomenon produced by the mechanical system.

56. The electromechanical actuator system of claim 55, wherein the phenomenon produced by the mechanical system is in response to piezoelectric movement of the actuator body, and wherein the driver applies the electric field in response to the input from the feedback loop.

57. The electromechanical actuator system of claim 56, wherein piezoelectric movement of the actuator body causes a first surface to move relative to a second surface, and wherein the feedback loop provides input to the driver regarding the separation between the first and second surfaces.

58. The electromechanical actuator system of claim 57, wherein the input provided regarding the separation between the first and second surfaces is based on a measurement of the separation between the first and second surfaces.

59. The electromechanical actuator system of claim 57, wherein the piezoelectric movement of the actuator body defines a direction of movement, and wherein the direction of movement intersects the first and second surfaces.

60. The electromechanical actuator system of claim 57, wherein the mechanical system includes a first moving member in direct physical contact with the actuator body, wherein the area of contact generally defines a first location in the mechanical system, and wherein the movement of the first surface relative to the second surface occurs in a second location in the mechanical system.

61. The electromechanical actuator system of claim 60, wherein the mechanical system includes a lever, and wherein the movement of the first surface relative to the second surface is transmitted from the actuator body via the lever.

62. The electromechanical actuator system of claim 56, wherein the phenomenon produced by the mechanical system is a displacement of at least a portion of the mechanical system.

63. The electromechanical actuator system of claim 56, wherein the feedback loop provides input to the driver regarding a phenomenon other than displacement.

64. The electromechanical actuator system of claim 56, further comprising a comparator for comparing input from the feedback loop to a signal representing a desired state.

65. The electromechanical actuator system of claim 56, further comprising a controller for controlling the driver to variably apply the electric field to the actuator body in response to the input from the feedback loop.

66. The electromechanical actuator system of claim 65, further comprising at least a second driver for applying a variable electric field to the actuator body.

67. The electromechanical actuator system of claim 56, wherein the feedback loop further provides input to the driver in response to at least a second phenomenon produced by the mechanical system, and wherein the second phenomenon is produced in response to piezoelectric movement of the actuator body.