Rolled electroactive polymers

• US 20030006669A1
• Filed: 05/21/2002
• Published: 01/09/2003
• Est. Priority Date: 05/22/2001
• Status: Active Grant

• Current Assignee: SRI International, Inc.
• Original Assignee: SRI International, Inc.
• Inventors: Kornbluh, Roy D., Heim, Jonathan R., Pelrine, Ronald E., Bonwit, Neville A., Pei, Qibing, Stanford, Scott E.
• Granted Patent: US 6,891,317 B2
• Time in Patent Office: Days
• US Class Current: 310/309
• CPC Class Codes: A61M 5/142 Pressure infusion, e.g. using pumps
• CPC Class Codes: A61M 5/14276 specially adapted for implantation
• CPC Class Codes: F01L 2301/00 Using particular materials
• CPC Class Codes: F04B 35/00 Piston pumps specially adapted for elastic fluids and characterised by the driving means to their working members, or by combination with, or adaptation to, specific driving engines or motors, not otherwise provided for
• CPC Class Codes: F04B 43/043 Micropumps
• CPC Class Codes: H02N 11/006 Motors
• CPC Class Codes: H10N 30/098 Forming organic materials
• CPC Class Codes: H10N 30/204 using bending displacement, e.g. unimorph, bimorph or multimorph cantilever or membrane benders
• CPC Class Codes: H10N 30/206 using only longitudinal or thickness displacement, e.g. d33 or d31 type devices
• CPC Class Codes: H10N 30/302 Sensors
• CPC Class Codes: H10N 30/506 of cylindrical shape with stacking in radial direction, e.g. coaxial or spiral type rolls
• CPC Class Codes: H10N 30/802 Drive or control circuitry or methods for piezoelectric or electrostrictive devices not otherwise provided for
• CPC Class Codes: H10N 30/857 Macromolecular compositions
• CPC Class Codes: Y10S 310/80 Piezoelectric polymers, e.g. PVDF

Abstract

The invention describes rolled electroactive polymer devices. The invention also describes employment of these devices in a wide array of applications and methods for their fabrication. A rolled electroactive polymer device converts between electrical and mechanical energy; and includes a rolled electroactive polymer and at least two electrodes to provide the mechanical/electrical energy conversion. Prestrain is typically applied to the polymer. In one embodiment, a rolled electroactive polymer device employs a mechanism, such as a spring, that provides a force to prestrain the polymer. Since prestrain improves mechanical/electrical energy conversion for many electroactive polymers, the mechanism thus improves performance of the rolled electroactive polymer device.

Claims

1. A device for converting between electrical and mechanical energy, the device comprising:

a transducer comprising at least two electrodes and a rolled electroactive polymer in electrical communication with the at least two electrodes;

a mechanism having a first element operably coupled to a first portion of the polymer and a second element operably coupled to a second portion of the polymer; and

wherein the mechanism provides a force that strains at least a portion of the polymer.

2. The device of claim 1 wherein the force varies with deflection of the polymer.

3. The device of claim 1 wherein the mechanism is a spring.

4. The device of claim 1 wherein the mechanism allows linear motion of the first portion of the polymer relative to the second portion of the polymer.

5. The device of claim 1 wherein the mechanism provides anisotropic prestrain on the rolled electroactive polymer.

6. The device of claim 1 wherein the mechanism provides prestrain in an axial direction on the rolled electroactive polymer.

7. The device of claim 1 wherein the mechanism provides prestrain in a circumferential direction on the rolled electroactive polymer.

8. The device of claim 1 wherein the mechanism provides tensile prestrain on the polymer.

9. The device of claim 1 wherein the electroactive polymer is a dielectric elastomer.

10. The device of claim 1 wherein the polymer has an elastic modulus at most about 100 MPa.

11. The device of claim 1 further comprising a substantially rigid member coupled to a third portion of the polymer.

12. The device of claim 1 wherein the device comprises a multilayer polymer stack before rolling.

13. The device of claim 12 wherein each polymer layer in the multilayer polymer stack comprises a different level of prestrain before rolling.

14. The device of claim 12 wherein the multilayer polymer stack comprises more than one type of polymer.

15. The device of claim 1 further comprising a second electroactive polymer roll disposed in a hollow central part of the rolled electroactive polymer, and wherein the two electroactive polymer rolls provide a cumulative output for the device.

16. The device of claim 15 wherein mechanical deflection of the rolled electroactive polymer and the second electroactive polymer is in the same direction.

17. The device of claim 15 wherein one of the rolled electroactive polymer and the second electroactive polymer is used for actuation or generation

18. The device of claim 15 wherein the second electroactive polymer roll has a different length than the rolled electroactive polymer.

19. The device of claim 1 wherein the mechanism comprises a rigid frame that maintains prestrain on polymer.

20. The device of claim 19 wherein the frame includes a hole that allows deflection of the polymer normal to the hole.

21. The device of claim 1 wherein the mechanism comprises a magnet that varies its magnetic force with deflection of the polymer.

22. A device for converting between electrical and mechanical energy, the device comprising:

a transducer comprising at least two electrodes and a rolled electroactive polymer in electrical communication with the at least two electrodes; and

a spring having a first spring portion operably coupled to a first portion of the polymer and a second spring portion operably coupled to a second portion of the polymer.

23. The device of claim 22 wherein the spring is a compression spring.

24. The device of claim 22 further comprising a rigid end piece attached to an end portion of the rolled polymer.

25. The device of claim 24 wherein an end portion of the spring is attached to the rigid end piece.

26. The device of claim 24 wherein the rigid end piece comprises an internal thread capable of threaded interface with a threaded member.

27. The device of claim 24 further comprising a second rigid end piece attached to an opposite end portion of the rolled polymer.

28. The device of claim 22 wherein the electroactive polymer is rolled about the outside of the spring.

29. The device of claim 22 further comprising a second electroactive polymer rolled about the spring.

30. The device of claim 22 wherein the rolled electroactive polymer comprises between about 2 and about 200 layers.

31. The device of claim 22 wherein the rolled electroactive polymer comprises between about 5 and about 100 layers.

32. The device of claim 22 wherein the rolled electroactive polymer comprises between about 15 and about 50 layers.

33. The device of claim 22 further comprising a stiff member passing through the spring core that substantially prevents bending of the spring and the polymer about the spring axis.

34. The device of claim 22 wherein the spring provides a force that strains the polymer.

35. The device of claim 34 wherein the spring provides a force that results in anisotropic prestrain on the polymer.

36. The device of claim 34 wherein the spring provides a force that results in prestrain in an axial direction for the rolled electroactive polymer.

37. The device of claim 34 wherein the spring provides prestrain in a circumferential direction for the rolled electroactive polymer.

38. The device of claim 22 wherein an outermost layer portion of the rolled electroactive polymer does not comprise an electrode disposed thereon.

39. The device of claim 22 wherein the device is used in one of a robot, toy, actuator, motor, generator, or sensor.

40. The device of claim 22 wherein the electroactive polymer is a dielectric elastomer.

41. The device of claim 22 wherein the device comprises a multilayer polymer stack before rolling.

42. The device of claim 41 wherein each polymer layer in the multilayer polymer stack comprises a different level of prestrain before rolling.

43. The device of claim 41 wherein the multilayer polymer stack comprises more than one type of polymer.

44. The device of claim 22 further comprising a second electroactive polymer roll disposed in a hollow central part of the rolled electroactive polymer, and wherein the two electroactive polymer rolls provide a cumulative output for the device.

45. The device of claim 44 wherein the output of the two electroactive polymer rolls is in the same direction.

46. The device of claim 44 wherein second electroactive polymer roll has a different length than the rolled electroactive polymer.

47. The device of claim 22 further comprising a magnet that varies its magnetic force with deflection of the polymer.

48. The device of claim 41 wherein the polymer is a monolithic polymer.

49. The device of claim 48 further comprising a common electrode that services multiple active areas on the monolithic polymer.

50. The device of claim 49 wherein the common electrode provides graduated control of the multiple active areas.

51. The device of claim 48 wherein the monolithic polymer comprises radially aligned active areas.

52. The device of claim 51 wherein the radially aligned active areas are configured to provide two dimensional deflection.

53. The device of claim 51 wherein the radially aligned active areas are configured to provide three dimensional deflection.

54. A method for fabricating an electroactive polymer device, the method comprising:

disposing at least two electrodes on an electroactive polymer;

rolling the electroactive polymer to produce a rolled electroactive polymer; and

securing the rolled electroactive polymer to maintain its rolled configuration.

55. The method of claim 54 wherein the disposing comprises spraying the electrodes on the polymer.

56. The method of claim 54 wherein the disposing uses a stencil.

57. The method of claim 54 further comprising prestraining the electroactive polymer before rolling the electroactive polymer.

58. The method of claim 57 wherein the prestraining uses a prestrain fixture that stretches the electroactive polymer and holds the electroactive polymer in a prestained state.

59. The method of claim 54 further comprising, before rolling the electroactive polymer, disposing a second electroactive polymer layer on top of the electroactive polymer having the at least two electrodes.

60. The method of claim 59 wherein the second electroactive polymer does not include an electrode.

61. The method of claim 59 further comprising prestraining the electroactive polymer before rolling the electroactive polymer;

and further comprising imposing a different level of prestrain on the second electroactive polymer before the rolling.

62. The method of claim 61 wherein the different levels of prestrain are achieved by soaking a liquid into one of the first and second electroactive polymer.

63. The method of claim 54 wherein the polymer is rolled about a spring.

64. The method of claim 63 further comprising compressing the spring during the rolling.

65. The method of claim 63 further comprising attaching a rigid end piece to an end portion of the spring.

66. The method of claim 65 further comprising adding an adhesive such that the adhesive contacts an end portion of the polymer when rolled and contacts the rigid end piece.

67. The method of claim 54 further comprising adding a barrier outside the rolled electroactive polymer.

68. The method of claim 54 wherein rolling the electroactive polymer uses a rolling fixture having a substantially smooth rolling surface.

69. The method of claim 68 wherein the substantially smooth rolling surface adheres to the polymer such that prestrain of the polymer is maintained while the polymer adheres to the rolling surface.

70. The method of claim 54 wherein the electroactive polymer is a dielectric elastomer.