Ultrasonic Actuator

Abstract

A hollow-cylindrical ultrasonic actuator is disclosed a central axis, an inner peripheral surface facing the central axis and an outer peripheral surface facing away from the central axis and spaced apart from the inner peripheral surface, a closed inner contour curve, a closed outer contour curve, at least one electrode, and an electromechanical material provided between opposed electrodes. In a non-actuated state of the ultrasonic actuator, a curvature of the inner contour curve or of an outer contour curve includes at least three mutually spaced-apart local maximum points.

Claims

1. A hollow-cylindrical ultrasonic actuator comprising: a central axis (ZA); an inner peripheral surface facing the central axis (ZA) and an outer peripheral surface facing away from the central axis (ZA) and spaced apart from the inner peripheral surface, wherein in a cross-section perpendicular to the central axis (ZA) the inner peripheral surface defines a closed inner contour curve and the outer peripheral surface defines a closed outer contour curve; at least one electrode arranged on each of the inner peripheral surface as well as the outer peripheral surface; and an electromechanical material provided between opposed electrodes, vibration deformations to be excited in the ultrasonic actuator by electrically actuating the electrodes, these vibration deformations being utilizable for driving an element when in frictional contact with the ultrasonic actuator, wherein in a non-actuated state of the ultrasonic actuator, at least one of the inner contour curve or the outer contour curve includes at least three spaced-apart local points of maximum curvature.

2. The hollow-cylindrical ultrasonic actuator according to claim 1, wherein the points of maximum curvature are spaced apart equidistantly along the inner and/or outer contour curve.

3. The hollow-cylindrical ultrasonic actuator according to claim 1, wherein the number of points of maximum curvature corresponds to an odd natural number.

4. The hollow-cylindrical ultrasonic actuator according to claim 1, wherein a curvature of the inner contour curve or of the outer contour curve changes continuously along its respective profile.

5. The hollow-cylindrical ultrasonic actuator according to claim 1, wherein a shape of the inner contour curve is geometrically similar to a shape of the outer contour curve and wherein a thickness of the hollow-cylindrical ultrasonic actuator is equal along a periphery.

6. The hollow-cylindrical ultrasonic actuator of claim 1 in combination with: a support device to form an arrangement, wherein the support device contacts the inner peripheral surface of the ultrasonic actuator at a section where a curvature of the inner contour curve exhibits a local maximum.

7. The combination according to claim 6, wherein contacts of the support device with the inner peripheral surface of the ultrasonic actuator comprise: spherical sections or spherical elements.

8. The combination according to claim 7, wherein the spherical sections or the spherical elements are elastically deformable.

9. The combination according to claim 6, wherein the support device comprises: elastically deformable sections configured as flexure hinges.

10. The combination according to claim 6, wherein the support device has a star-shaped geometry which comprises: arm sections which extend from a common center.

11. The arrangement according to claim 10, wherein a distal end of each arm section comprises: a spherical element, and wherein each arm section includes a deformable section formed integrally therewith and configured as a flexure hinge.

12. A method for driving an element, the method comprising: providing a hollow-cylindrical ultrasonic actuator having electrodes, an electromechanical material provided between opposed electrodes, a central axis (ZA), and an inner peripheral surface facing the central axis (ZA) and an outer peripheral surface facing away from the central axis (ZA) and spaced apart from the inner peripheral surface, wherein in a cross-section perpendicular to the central axis (ZA) the inner peripheral surface defines a closed inner contour curve and the outer peripheral surface defines a closed outer contour curve, the method comprising: arranging at least one electrode on each of the inner peripheral surface as well as the outer peripheral surface; and electrically activating the electrodes to excite the vibration deformations, these vibration deformations driving an element in frictional contact with the ultrasonic actuator, wherein in a non-actuated state of the ultrasonic actuator, at least one of the inner contour curve or the outer contour curve include at least three spaced-apart local points of maximum curvature.

13. The hollow-cylindrical ultrasonic actuator according to claim 2, wherein the number of points of maximum curvature corresponds to an odd natural number.

14. The hollow-cylindrical ultrasonic actuator according to claim 13, wherein a curvature of the inner contour curve or of the outer contour curve changes continuously along its respective profile.

15. The hollow-cylindrical ultrasonic actuator according to claim 14, wherein a shape of the inner contour curve is geometrically similar to a shape of the outer contour curve and wherein a thickness of the hollow-cylindrical ultrasonic actuator is therefore equal along a periphery.

16. The hollow-cylindrical ultrasonic actuator of claim 15 in combination with: a support device to form an arrangement, wherein the support device contacts the inner peripheral surface of the ultrasonic actuator at a section where a curvature of the inner contour curve exhibits a local maximum.

Description

[0025] In the following, an embodiment of the ultrasonic actuator according to the present invention and embodiments concerning the arrangement of such an ultrasonic actuator on a support device will be described with respect to the respective figures. Like reference numerals refer here to like components of the different figures,

[0026] in which

[0027] FIG. 1 shows representations (a) to (c): an ultrasonic actuator according to the present invention in different views

[0028] FIG. 2 shows representations (a) and (b): an arrangement of the ultrasonic actuator according to the present invention, as shown in FIG. 1, on different support devices

[0029] FIG. 3 shows representations (a) and (b): an arrangement of the ultrasonic actuator according to the present invention, as shown in FIG. 1, on further possible support devices

[0030] FIG. 1 (a) shows, in a top view, a possible embodiment of an ultrasonic actuator 1 according to the present invention. The latter has a hollow-cylindrical geometry comprising a central axis ZA, an inner peripheral surface 2 facing the central axis and an outer peripheral surface 3 facing away from the central axis. The area defined or enclosed or circumscribed by the inner peripheral surface 2 has here a center of area through which a centroidal axis, which is coincident with the central axis ZA, extends in a direction perpendicular to the circumscribed area.

[0031] The curve of intersection formed by a cross-section, perpendicular to the central axis, with the inner peripheral surface 2 defines an inner closed contour curve 4, while the curve of intersection formed analogously with the outer peripheral surface 3 defines an outer closed contour curve 5.

[0032] The inner peripheral surface 2 has arranged thereon a single electrode 7 covering the entire inner peripheral surface 2, while the outer peripheral surface 3 has arranged thereon a plurality of electrodes 6 that are distributed over the periphery and spaced apart from one another. Between the respective opposed electrodes, i.e. in the overlapping area of the respective electrodes 6 and 7, an electromechanical material is arranged.

[0033] A flat end face 8 of the ultrasonic actuator has arranged thereon a plurality of peripherally distributed friction elements 9 in the form of half-spheres or partial spheres. These spheres are provided for frictional contact with an element to be driven, which is not shown in FIG. 1. By applying a suitable electric voltage to the electrodes 6 and 7, deformation vibrations can be excited in the electromechanical material of the ultrasonic actuator. These deformation vibrations propagate to the friction elements 9, and the respective movements of the friction elements 9 can then be transmitted to the element to be driven, so that the latter will, in the final analysis, carry out a desired drive movement. The ultrasonic actuator 1 according to FIG. 1 is here preferably used for the rotary drive of an element to be driven, but linear drives can also be realized in this way.

[0034] FIG. 1 (b) shows the ultrasonic actuator according to FIG. 1 (a) in a perspective view, while FIG. 1 (c) shows the ultrasonic actuator according to FIG. 1 (a) in a side view. On the basis of FIGS. 1 (b) and 1 (c), in particular the electrodes 6 arranged on the outer peripheral surface 3 can be seen more clearly.

[0035] FIG. 2 shows in representations (a) and (b) an arrangement of the ultrasonic actuator according to FIG. 1 on different support devices, as disclosed by the present invention. According to FIG. 2 (a), the support device 10 has a star-shaped geometry with three arm sections 15 extending outwards from a common center 14, each arm section 15 being formed integrally with a spherical section 11 and an elastically deformable section 13. Each of the deformable sections 13 is here configured as a flexure hinge.

[0036] The spherical sections 11 contact the inner peripheral surface 2 of the ultrasonic actuator 1 at the sections where the inner contour curve 4 exhibits a local minimum with respect to the radius of curvature and a local maximum with respect to the curvature.

[0037] Other than the embodiment according to FIG. 2 (a), the support device 10 according to FIG. 2 (b) comprises arm sections 15, which each have two webs, each web comprising a deformable section 13 configured as a flexure hinge and the two webs being connected to each other at their respective distal end via a spherical section 11. The center 14 of the support device 10 is configured as a circular section to which the respective other ends of the webs of the arm sections 15 are integrally connected.

[0038] FIG. 3 shows in representations (a) and (b) two additional embodiments of support devices for arranging the ultrasonic actuator according to FIG. 1. According to FIG. 3 (a), the support device 10 is star-shaped and comprises three arm sections 15 having at their respective distal end a receiving section for receiving and supporting, respectively, a spherical element 12, which is elastically deformable. The support device 10 according to FIG. 3 (b) differs from the support device shown in FIG. 3 (a) only insofar as elastically deformable sections 13 in the form of flexure hinges are formed integrally with the arm sections 15.