Piezoelectric motors and methods for the production and operation thereof

• US 20050127790A1
• Filed: 10/22/2004
• Published: 06/16/2005
• Est. Priority Date: 04/22/2002
• Status: Active Grant

• Current Assignee: Thorlabs Elliptec GmbH
• Original Assignee: Elliptec Resonant Actuator AG (Pantec Engineering AG)
• Inventors: Hagemann, Benjamin, Wolf, Kai, Davidson, Erick M., Schuler, Dieter A., Magnussen, Bjoern B., Varadi, Peter C.
• Granted Patent: US 7,368,853 B2
• Time in Patent Office: Days
• US Class Current: 310/328
• CPC Class Codes: H02N 2/003 using longitudinal or radial modes combined with bending modes
• CPC Class Codes: H02N 2/004 Rectangular vibrators
• CPC Class Codes: H02N 2/006 Elastic elements, e.g. springs in general F16F1/00
• CPC Class Codes: H02N 2/0075 Electrical details, e.g. drive or control circuits or methods
• CPC Class Codes: H02N 2/026 by pressing one or more vibrators against the driven body
• CPC Class Codes: H02N 2/103 by pressing one or more vibrators against the rotor
• CPC Class Codes: H10N 30/202 using longitudinal or thickness displacement combined with bending, shear or torsion displacement

Abstract

The invention relates to a piezoelectric motor comprising a piezoelectric component that is connected to a resonator and a two-dimensional resonator that interacts with a movable element, the resonator having principal surfaces that are parallel to each other and that are also identical in shape and size. The invention further relates to methods for producing such piezoelectric motors, wherein the resonators are manufactured by cutting a profiled, extruded bar into lengths or by cutting, preferably by punching, from sheet metal having constant thickness. Finally, this invention relates to a method for exciting such a piezoelectric motor, wherein the excitation frequency or frequencies is/are generated by the control electronics as a function of time in response to the respective peak current and/or in response to the respective phase minimum between current and voltage and/or in response to the change in phase.

Claims

1. A piezoelectric motor for moving a movable element in at least two directions, comprising:

a resonator having a plane of symmetry;

at least one piezoelectric component connected to the resonator for exciting the resonator to vibrate when an electric signal is applied to the piezoelectric component;

wherein the piezoelectric element is located asymmetrically with respect to the resonator in such a way that the plane of symmetry of the resonator is not a plane of symmetry of the combination of resonator and piezoelectric component to cause the combination of resonator and piezoelectric component to have two distinct frequencies of operation f₁ and f₂ for moving the movable element; and

resonance/anti-resonance pairs (f₁, f₁′

) and (f₂, f₂′

) such that the phase between the electric current and the electric voltage of a sinusoidal electric signal that is applied to the piezoelectric component declines for frequencies of the sinusoidal electric signal that lie inside each of the resonance/anti-resonance pairs.

2. The piezoelectric motor of claim 1, further comprising an elastic element urging the resonator onto the movable element.

3. The piezoelectric motor of claim 2, wherein the elastic element is located asymmetrically with respect to the resonator in such a way that the plane of symmetry of the resonator is not a plane of symmetry of the combination of resonator and elastic element.

4. The piezoelectric motor of claim 1, wherein the two frequencies of operation cause the movable element to move in opposite directions.

5. The piezoelectric motor of claim 1, wherein the piezoelectric component is located asymmetrically with respect to the resonator so that the two frequencies of operation f₁ and f₂ are each less than half of the frequency that is calculated as the longitudinal wave speed of the resonator material divided by the largest resonator dimension.

6. The piezoelectric motor of claim 5, wherein the resonator has an elongated shape.

7. The piezoelectric motor of claim 6, wherein the resonator has an opening for receiving the piezoelectric component.

8. The piezoelectric motor of claim 7, wherein the opening comprises notches.

9. The piezoelectric motor of claim 7, wherein the resonator forms side walls of the opening, and wherein at least one of the side walls is not straight in the longitudinal direction of the resonator.

10. The piezoelectric motor of claim 1, wherein the piezoelectric component is located asymmetrically with respect to the resonator so one frequency of operation is no more than 1.5 times the other frequency of operation.

11. The piezoelectric motor of claim 1, wherein the resonator comprises two principal surfaces that are parallel to the plane of symmetry, and wherein the cross-sections of the resonator between the principal surfaces are the same.

12. The piezoelectric motor of claim 1, wherein the at least one piezoelectric component comprises a layered configuration of electrodes and ceramics.

13. The piezoelectric motor of claim 12, wherein the at least one piezoelectric component comprises two electric terminals for applying electric signals.

14. The piezoelectric motor of claim 13, wherein the ceramics has a monolithic structure.

15. The piezoelectric motor of claim 1, wherein the resonator has an elongated shape and wherein the resonator does not execute vibrations that are pure longitudinal, torsional, or bending modes of the resonator.

16. The piezoelectric motor of claim 1, wherein the resonator comprises a single contact area for drivingly engaging the movable element during use of the piezoelectric motor.

17. The piezoelectric motor of claim 1, wherein the resonator comprises a contact area for drivingly engaging the movable element during use of the piezoelectric motor, and wherein the piezoelectric element is further located to cause the resonator vibrations at the two frequencies of operation to have speed profiles that are not parallel to each other in the contact area.

18. The piezoelectric motor of claim 16, wherein the piezoelectric element is further located to cause the contact area of the resonator to vibrate with amplitudes that have the same order of magnitude for both frequencies of operation.

19. The piezoelectric motor of claim 1, wherein the ratio of the distance f₁ to f₁′

and the distance f₂ to f₂′

has a value between 0.25 and 4.

20. The piezoelectric motor of claim 1, wherein the distance from f₁ to f₁′

or the distance from f₂ to f₂′

is at least 500 Hz.

21. The piezoelectric motor of claim 1, wherein the distance from f₁ to f₁′

or the distance from f₂ to f₂′

is more than 2 kHz.

22. The piezoelectric motor of claim 1, wherein the phase declines inside the resonance pairs (f₁, f₁′

) and (f₂, f₂′

) by at least 45°

.

23. The piezoelectric motor of claim 1, wherein the phase declines inside the resonance pairs (f₁, f₁′

) and (f₂, f₂′

) by at least 60°

.

24. The piezoelectric motor of claim 1, wherein the phase declines by the same amount for both modes of operation.

25. The piezoelectric motor of claim 22, further comprising coil spring for urging the resonator onto the movable element, the coil spring comprising windings and a foamed material that is pressed into the windings sufficiently to dampen spring vibrations and to assist the phase decline.

26. The piezoelectric motor of claim 22, wherein the piezoelectric motor is driven by a resonator circuit with an admittance that increases during f₁ and decreases during f₂.

27. The piezoelectric motor of claim 22, wherein the piezoelectric motor is driven by a resonator circuit with an admittance that increases during f₁ and decreases during f₂ with a maximum admittance occurring between f₁ and f₂.

28. The piezoelectric motor of claim 22, wherein the piezoelectric motor is driven by a resonator circuit at frequencies f₁ and f₂ within the range of 73 kHz to 84 kHz for f₁ and about 91 kHz to 108 kHz for f₂.

29. A piezoelectric motor for moving a movable element, the motor comprising a coil spring on opposing sides of a resonator which is in driving communication with a piezoelectric element, the spring connected to the resonator to elastically urge a contacting portion on the resonator against the movable element.

30. The piezoelectric motor of claim 29, wherein the resonator has a recess on a surface of the resonator for receiving a connecting portion of the coil spring.

31. The piezoelectric motor of claim 30, wherein the coil spring comprises a wire and wherein at least the connecting portion of the coil spring has a non-circular cross-section to make the joint between the resonator recess and the connecting portion of the coil spring more twist resistant.

32. The piezoelectric motor of claim 30, wherein the coil spring comprises two connecting portions and wherein the resonator has a plane of symmetry with a recess located on either side of the plane of symmetry to receive one of the contacting portions each.

33. The piezoelectric motor of claim 29, wherein the coil spring comprises windings that do not touch each other.

34. A method for configuring a piezoelectric motor to have two frequencies of operation for moving a movable element in two opposite directions, the method comprising:

providing an elongated resonator having a plane of symmetry;

providing a piezoelectric component having a plane of symmetry;

connecting the piezoelectric component to the resonator such that the resonator plane of symmetry and the piezoelectric component plane of symmetry are parallel but offset from each other;

offsetting the resonator plane of symmetry and the piezoelectric component plane of symmetry sufficiently causes the piezoelectric component to excite the elongated resonator to vibrate in a manner that is neither purely longitudinal nor purely bending, and

exciting the piezoelectric component with a first and second signal f₁ and f₂ to cause the motor to move in first and second directions, respectively, with the frequency f₁ falling within a wide-band signal having a frequency interval Δ

f₁ and with the frequency f₂ falling within a wide-band signal having a frequency interval Δ

f₂, with the frequency bands Δ

f₁ and Δ

f₂ falling within the domain of influence of a resonant circuit having an admittance that increases during Δ

f₁ and decreases during Δ

f₂.

35. The method of claim 34, wherein the resonator is symmetric about two perpendicular planes intersecting along the longitudinal axis of the resonator.

36. The method of claim 34, wherein the combination of resonator and piezoelectric component has a plane of symmetry.

37. The method of claim 34, wherein the offset between the resonator plane of symmetry and the piezoelectric component plane of symmetry is sufficiently large to cause the two frequencies of operation to each be less than half of the frequency that is calculated as the longitudinal wave speed of the resonator material divided by the largest resonator dimension.

38. The method of claim 34, wherein the offset between the resonator plane of symmetry and the piezoelectric component plane of symmetry is sufficiently large to cause one frequency of operation to be no more than 1.5 times the other frequency of operation.

39. The method of claim 34, further comprising providing a single contact portion on the resonator for drivingly engaging the movable element.

40. The method of claim 35, wherein the resonator is manufactured by cutting it to a desired thickness from a rod having a continuous, constant profile, the cut being perpendicular to the longitudinal direction of the rod.

41. The method of claim 35, wherein the resonator is manufactured by cutting or punching it from a sheet of constant thickness.

42. The method of claim 35, wherein the resonator is manufactured by extrusion

43. A method for configuring a piezoelectric motor to have two frequencies of operation for moving a movable element in two different directions, the method comprising:

providing an elongated resonator having an axial symmetry about an axis of symmetry;

providing a piezoelectric component having an axial symmetry about an axis of symmetry;

connecting the piezoelectric component to the resonator such that the resonator axis of symmetry and the piezoelectric component axis of symmetry are coaxial;

configuring the contact surfaces between the piezoelectric component and the resonator to be asymmetric to cause the piezoelectric component to excite the elongated resonator to vibrate in a manner that is neither purely longitudinal nor purely bending;

exciting the piezoelectric component at first and second frequencies of operation f₁ and f₂ to cause the motor to move in first and second directions, respectively, with the frequency f₁ falling within wide band signal having a frequency interval Δ

f₁ and with frequency f₂ falling within a wide-band signal having a frequency interval Δ

f₂, with the frequency bands Δ

f₁ and Δ

f₂ falling within the domain of influence of a resonant circuit having an admittance that increases within the frequency range Δ

f₁ and decreases within the frequency range Δ

f₂.

44. The method of claim 43, wherein the frequency ranges Δ

f₁ and Δ

f₂ are each about 10 kHz or less.

45. The method of claim 43, wherein the frequencies of operation f₁ and f₂ each lie within a respective frequency band Δ

f₁, Δ

f₂ having a minimal distance Δ

f between the bands Δ

f₁, Δ

f₂ where Δ

f is about 7 kHz or less.

46. The method of claim 45 wherein the bands Δ

f₁, Δ

f₂ are within a maximal bandwidth Δ

f_max having a width of about 27 kHz

47. The method of claim 45, wherein the minimal distance Δ

f and the frequency of operation f₁ are related as follows;

0.025 f₁≦

Δ

f≦

f₁.

48. The method of claim 45, wherein the minimal distance Δ

f and the frequency of operation f₁ are related as follows;

0.1 f₁≦

Δ

f≦

0.3 f₁

49. The method of claim 45, wherein the electrical current consumption of the piezoelectric motor is at a maximum at the respective frequencies of operation f₁, f₂ are within the frequency bands Δ

f₁ and Δ

f₂.

50. A piezoelectric motor having two frequencies of operation for moving a movable element in two different directions, comprising:

an elongated resonator having an axial symmetry about a first axis of symmetry;

a piezoelectric component having an axial symmetry about a second axis of symmetry, the piezoelectric component being connected to the resonator and exciting the elongated resonator to vibrate in a manner that is neither purely longitudinal nor purely bending;

a resonant circuit in electrical communication with the piezoelectric component and exciting the piezoelectric component at first and second frequencies of operation f₁ and f₂ to cause the motor to move in first and second directions, respectively, with frequency f₁ falling within wide band signal 1 having a frequency interval Δ

f₁ and with frequency f₂ falling within wide-band signal Δ

f₂, with the frequency bands Δ

f₁ and Δ

f₂ falling within the domain of influence of the resonant circuit having an admittance that increases within the frequency range Δ

f₁ and decreases within the frequency range Δ

f₂.

51. The piezoelectric motor of claim 50, wherein the first and second axes are inclined relative to each other.

52. The piezoelectric motor of claim 50, wherein the first and second axes are parallel, but offset.

53. The piezoelectric motor of claim 50, wherein the frequency ranges Δ

f₁ and Δ

f₂ are each about 10 kHz or less.

54. The piezoelectric motor of claim 50, wherein the frequencies of operation f₁ and f₂ each lie within a respective frequency band Δ

f₁, Δ

f₂ having a minimal distance Δ

f between the bands Δ

f₁, Δ

f₂ where Δ

f is about 7 kHz or less and the frequency band Δ

f, is about 11 kHz and the frequency band Δ

f₂ is about 17 kHz.

55. The piezoelectric motor of claim 50, wherein the bands Δ

f₁, Δ

f₂ are within a maximal bandwidth Δ

f_max having a width of about 35 kHz

56. The piezoelectric motor of claim 50, wherein a minimal distance Δ

f between and the frequencies of operation f₁ and f₂ are related to the frequency f₁ as follows;

0.025 f₁≦

Δ

f≦

f₁.

57. The piezoelectric motor of claim 50, wherein the minimal distance Δ

f between and the frequencies of operation f₁ and f₂ are related to the frequency f₁ are related as follows;

0.1 f₁≦

Δ

f≦

0.3 f₁.

58. The piezoelectric motor of claim 50, wherein the electrical current consumption of the piezoelectric motor is at a maximum at the respective frequencies of operation f₁, f₂.