Stress-wave Actuator and Reducer

Abstract

A stress-wave actuator is disclosed in which a stressed, elastic member is in frictional contact with a rigid element. A stress altering element moves along the elastic element, temporarily altering stress in a portion of it, moving the stressed element relative to the rigid element. When the rigid element is an open ended enclosure, the elastic member is shaped and sized to be slightly larger in circumference than the open ended enclosure so that the elastic member is compressed and stressed. Movingly reducing the stress in a portion of the elastic member causes it to be displaced relative to the rigid member. Stress alteration may be effected by magnetic, electric or physical means depending of the physical nature of the elastic element. The stress wave actuator may be configured to act as a high torque motor, a high gear ration motion transfer device, and as a clutch.

Claims

1. A stress-wave actuator, comprising: a rigid element having a first, smooth, or textured, surface; a stressed, elastic member having a second, surface, said second surface having at least one region in contact with said first surface; and one or more stress altering elements that sequentially and temporarily alter said stress in a portion of said stressed elastic member, thereby displacing said elastic member relative to said rigid element by a first displacement distance.

2. The stress-wave actuator of claim 1, wherein, said stressed, elastic member comprises said one or more stress altering elements.

3. The stress-wave actuator of claim 1, wherein said temporarily altering said stress in said portion of said stressed elastic member results in a part of said second surface in contact with said first surface, becoming a temporarily detached portion, and re-contacting with said second surface, displaced parallel to a direction of said movement of said stress alteration.

4. The stress-wave actuator of claim 1, wherein: said first surface of said rigid element forms an enclosure; and, said stressed elastic member is contained within said enclosure such that it is compressed, and thereby stressed.

5. The stress-wave actuator of claim 1, wherein: said second surface of said stressed, elastic member forms an enclosure; and said rigid element is enclosed within said stressed, elastic member, such that said stressed, elastic member is stretched, and, thereby, stressed.

6. The stress-wave actuator of claim 4, wherein: said rigid element is a rigid outer structure comprising a right cylindrical cavity having a first perimeter; said stressed elastic member is an inner structure having a second, outer perimeter that is greater in length than said first perimeter thereby inducing a stress within inner structure; and, said temporarily, and sequentially, applying a stress altering actuation in said portion of said stressed elastic member results in said outer structure being displaced relative to said inner structure by a distance proportional to a difference between said first and second perimeters.

7. The stress-wave actuator of claim 6, wherein said inner structure comprises a hollow elastic tube.

8. The stress-wave actuator of claim 7, wherein, said induced stress is less than a critical buckling stress.

9. The stress-wave actuator of claim 6, wherein, said inner structure comprises a paramagnetic material; and, further comprising, a drive structure comprising one or more magnets located proximate to an inner surface of said inner structure, such that, when said magnets are rotated by one revolution about an axis of said right circular cylindrical opening, said inner structure is rotated about said axis by an amount proportional to said difference between said first and second perimeters.

10. The stress-wave actuator of claim 9, wherein, said drive structure is functionally connected to an input shaft; and, said inner structure is functionally connected to an output shaft such that said stress-wave actuator functions as a gearless reduction unit between said input and said output shafts.

11. The stress-wave actuator of claim 9, wherein, at least one of said magnets is a permanent magnet.

12. The stress-wave actuator of claim 9, wherein, at least one of said magnet is an electromagnet, thereby providing a clutch mechanism between said input and output shafts.

13. The stress-wave actuator of claim 6, wherein, said inner structure comprises an electroactive material.

14. The stress-wave actuator of claim 13, wherein, said electroactive material is activated at one or more localized regions.

15. The stress-wave actuator of claim 14, wherein, said activation of said localized regions moves sequentially around said second, outer perimeter such that said inner structure rotates with respect to said outer structure.

16. The stress-wave actuator of claim 15, wherein, said inner structure is functionally connected to an output shaft such that said stress-wave actuator functions as an electric motor.

17. The stress-wave actuator of claim 7, wherein, said buckling stress exceeds a critical buckling stress and said inner structure assumes a shape having one or more buckled regions.

18. The stress-wave actuator of claim 17, wherein, said right cylindrical cavity is a right circular cylindrical cavity having a first radius; said inner structure has a uniform wall of a first thickness; and further comprising a drive shaft functionally connected to one or more buckle driving elements located such that rotation of said buckle drive elements about an axis of said right circular cylindrical by one full rotation causes said inner structure to rotate by an amount proportional to said difference between said first and second perimeters about said axis.

19. The stress-wave actuator of claim 18, wherein, said inner structure is functionally connected to an output shaft such that said stress-wave actuator functions as a gearless reduction unit between said drive shaft and said output shaft.

20. The stress-wave actuator of claim 17, wherein, said right cylindrical cavity is a right circular cylindrical cavity having a first radius; said inner structure has a uniform wall of a first thickness and comprises an electroactive material; and, said electroactive material is activated in a vicinity of one or more of said buckles, thereby causing said inner structure to rotate with respect to said outer structure about and axis of said right circular cylindrical opening.

21. The stress-wave actuator of claim 20, wherein, said inner structure is functionally connected to an output shaft such that said stress-wave actuator functions as an electric motor.

Description

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

[0023] FIG. 1 shows a series of schematic views of a stress-wave actuator of one embodiment of the present invention at various stages of activation.

[0024] FIG. 2 A shows a schematic cross-section of a compression stressed stress-wave actuator of the present invention.

[0025] FIG. 2 B shows a schematic cross-section of a tension stressed stress-wave actuator of the present invention.

[0026] FIG. 3 A shows a schematic cross-section of a further embodiment of a compression stressed, stress-wave actuator of the present invention.

[0027] FIG. 3 B shows a schematic cross-section of a further embodiment of a tension stressed, stress-wave actuator of the present invention.

[0028] FIG. 4 A is a diagrammatic representation of the functioning of a portion of a stress-wave actuator, showing the surfaces in a detached state.

[0029] FIG. 4 B is a diagrammatic representation of the functioning of a portion of a stress-wave actuator, showing the surfaces being reattached.

[0030] FIG. 5 A shows a schematic cross-section of a stress-wave actuator of one embodiment of the present invention.

[0031] FIG. 5 B shows a schematic cross-section of a stress-wave actuator having piezoelectric activators of one embodiment of the present invention.

[0032] FIG. 6 shows a schematic cross-section of a magnetically activated stress-wave actuator of one embodiment of the present invention.

[0033] FIG. 7 shows a schematic longitudinal, cross-section of a stress-wave actuator of one embodiment of the present invention configured to operate as a gearless reduction unit.

[0034] FIG. 8 shows a schematic longitudinal, cross-section of a stress-wave actuator of a further embodiment of the present invention configured to operate as a gearless reduction unit.

[0035] FIG. 9 shows a schematic isometric view of an electroactive loop of one embodiment of the present invention.

[0036] FIG. 10 shows a schematic longitudinal, cross-section of a stress-wave actuator of one embodiment of the present invention configured to operate as a motor.

[0037] FIG. 11 shows a schematic cross-section of a stress-wave actuator with a buckled region of one embodiment of the present invention.

DETAILED DESCRIPTION OF THE INVENTION

[0038] The preferred embodiments of the present invention will now be described in more detail with reference to the drawings in which identical elements in the various figures are, as far as possible, identified with the same reference numerals. These embodiments are provided by way of explanation of the present invention, which is not, however, intended to be limited thereto. Those of ordinary skill in the art may appreciate upon reading the present specification and viewing the present drawings that various modifications and variations may be made thereto without departing from the spirit of the invention.

[0039] FIG. 1 shows a series of schematic views of a stress-wave actuator of one embodiment of the present invention at various stages of activation.

[0040] The views in FIG. 1 schematically illustrate six stages of a stressed, elastic member 115 being moved past a rigid element 110 by a stress altering element 120 that may sequentially and temporarily alter a stress. The stress altering element 120 may, for instance, be movable stress reduction element.

[0041] The stressed, elastic member 115 may, for instance, be a material such as, but not limited to, a plastic or a metal of a suitable thickness and composition that it can be relatively easily bent or deformed, but when the bending or deforming force is removed, it may spring back to resume its original shape. At room temperature, typical materials that may be considered elastic members in the context of this patent application include, but are not limited to, plastics such as for instance, nylon, and thin metal materials such as, but not limited to, beryllium copper alloys and suitable thin stainless steel alloys.

[0042] In the region 118, the surface 116 of the elastic member and the surface 111 of the rigid element may be in frictional contact. The frictional forces of the contact may be sufficient to maintain the stresses in the elastic element, which may be compression or tension stresses. Stress may then be altered in a localized portion of the elastic member by reducing, or eliminating, the frictional forces in that localized portion. This may be accomplished by, for instance, separating the surfaces in that localized portion. The localized separation may be achieved using a means 120 for sequentially and temporarily altering a stress that may, for instance, be a physical element such as, but not limited to, a rolling or sliding bar, a sliding wedge, one or more piezoelectric elements, or some combination thereof. Or, if the stressed, elastic member 115 is a ferromagnetic material, the stress altering element 120 may be a magnet, such as, but not limited to, a permeant magnet or an electromagnet. If the elastic member 115 is an electroactive material, the stress altering element 120 may be an application of a voltage or an electric current in the localized region.

[0043] Configuration 131 is an initial configuration showing a rigid element 110 in contact with a stressed, elastic member 115. In a region 118, a first, upper surface 111 of the rigid element 110 may be in contact with a second, lower surface 116 of the stressed, elastic member 115. The elastic member 115 may, for instance, be stressed by a mechanical constraint (not shown in FIG. 1), or it may be pre-stressed, and held in stress by the frictional contact forces, or some combination thereof.

[0044] In configuration 132, a stress altering element 120, such as movable stress reduction element, may be brought into proximity with a region of the stressed, elastic member 115, resulting in stress being altered in a portion 125 of the stressed elastic member. The change of stress may, for instance, be the result of a slight separation of the surfaces in the vicinity of the stress reduction element. The change of stress may, for instance, result in the portion of the stressed elastic member 125 changing in size, by either expanding or shrinking in size. The nature of the stress reduction element may depend on the nature of the elastic member. For instance, if the elastic member is a ferromagnetic material, the stress altering element may be a magnet that may attract a portion of the stressed elastic member 125 away from the rigid element 110, thereby allowing that less stressed region to expand and be displaced along the surface 111 of the rigid element.

[0045] Alternately, if the elastic member is an electroactive material, the stress altering element may apply a suitable voltage, or electric current, to the portion 125 of the stressed elastic member. The applied voltage, or current, may, for instance, allow that region to change and to expand. In expanding, there may be a slight buckling, resulting in a slight separation of the surfaces and a local release of stress. As the stress alteration, or reduction, is moved along the elastic member, and the surfaces re-contact, they may be slightly displaced with respect to each other.

[0046] In a further embodiment, the stress altering element may be a mechanical component such as, but not limited to, a roller that may physically separate the two surfaces in a vicinity of a portion of the stressed elastic member 125. The separation may then allow that portion of the stressed, elastic member 115 to, for instance, expand as the stress is released, and be displaced along the first surface 111 of the rigid element when the surfaces reconnect.

[0047] In configuration 133, the stress altering element is shown moved in a direction 145, resulting in the portion of the stressed elastic member in which the stress is being temporarily altered, also being moved in that direction. As a result, the portion in which the stress was previously altered may now become re-attached to the surface of the rigid element, but now displaced by a distance 140. The reattached portion may also once again be returned to its original lever of stress.

[0048] Configuration 134 shows the stress altering element moved further along the compression stressed, elastic member in the direction 145.

[0049] In configuration 135, the movable stress reduction element, and the resultant stress altered portion of elastic member, are shown at the extreme end of the elastic member.

[0050] Configuration 136 shows the rigid element and the stressed, elastic member after the stress altering element has been moved along the length of the elastic member. The result shown in FIG. 1 is that the stressed, elastic member has been moved by a displacement distance 140 with respect to the rigid element.

[0051] FIG. 2 A shows a schematic cross-section of a compression stressed stress-wave actuator of the present invention.

[0052] As shown in FIG. 2 A, the first surface 111 of the rigid element 110 may form an enclosure 150. In a preferred embodiment, the first surface 111 may be smooth, or it may be textured, or roughened, for additional friction. The stressed, elastic member 115 may be contained within the enclosure 150 such that it is compressed, and thereby stressed.

[0053] The stress altering element 120 may move in a direction 145.

[0054] FIG. 2 B shows a schematic cross-section of a tension stressed stress-wave actuator of the present invention.

[0055] As shown in FIG. 2 B, the stressed, elastic member 115 may form an enclosure 150. The rigid element 110 may be contained within the enclosure 150 such that the stressed, elastic member 115 is stretched and, thereby, stressed in tension. In a preferred embodiment, the second surface 116 that is in contact with the rigid element 110 may be smooth, or it may be textured, or roughened, for additional friction.

[0056] The stress altering element 120 may move in a direction 145.

[0057] FIG. 3 A shows a schematic cross-section of a further embodiment of a compression stressed, stress-wave actuator of the present invention.

[0058] In FIG. 3 A, a rigid outer structure 160 is shown containing an inner structure 175. The rigid outer structure 160 is shown having a right cylindrical cavity 170 with a perimeter 165. The inner structure 175 that may, for instance, be an elastic tube, is shown having a second, outer perimeter 166. In a preferred embodiment of the present invention, the second, outer perimeter 166 of the inner structure may, in an uncompressed state, be longer than the first perimeter 165 of the rigid outer structure. As a result of the difference in perimeters, the elastic, inner structure may be compressed when it is contained within the outer structure and, therefore, be stressed.

[0059] Also shown schematically in FIG. 3 A is a stress altering actuation force 180 that may be provided by a stress reduction element. The stress altering actuation force 180 may be moved around the perimeter of the inner structure in a direction 145.

[0060] FIG. 3 A also shows the localized region 235 in greater detail. This may be the region affected by the stress reducing actuation. As shown, a part of the second surface 116 of the inner structure may be the portion 126 that may be temporarily detached from the surface 111 of the rigid structure's cylindrical opening. As the stress altering actuation force 180 is moved around the perimeter, the slight buckle, or less stressed, temporarily detached portion 126, may also move around the perimeter. As the portions that were temporarily detached become reattached, they may do so slightly displaced with respect to the first surface 111 from where they were before they were detached.

[0061] In this way, the inner structure 175 may be gradually moved with respect to the rigid outer structure 160 so that by the time the stress altering actuation force 180 has moved through 360 degrees, the structures will have moved with respect to each other by an amount proportional to, or even equal to, a difference between the perimeter of the right cylindrical cavity 170 and the perimeter of the elastic inner structure 175 before it was compressed.

[0062] FIG. 3 B shows a schematic cross-section of a further embodiment of a tension stressed, stress-wave actuator the present invention.

[0063] In the embodiment shown in FIG. 3 B, the stressed, elastic member 115 may be situated externally to the rigid element 110. The stressed, elastic member 115 may, for instance, have an unstressed circumference that may be slightly smaller than the circumference of the rigid element 110. When the stressed, elastic member 115 enclosers the rigid element 110, the stressed, elastic member 115 may be stretched, and therefore be stressed in tension. In such an embodiment, the stress altering actuation force 180 may act outwardly from a center of the rigid element. As shown in the lead out, there may be a temporarily detached portion 126 that may form outwardly from the portion of the stressed elastic member 125 at which the stress altering actuation force 180 may be acting.

[0064] As with the embodiment shown previously in FIG. 3 A, as the stress altering actuation force 180 travels around the circumference, the stressed, elastic member 115 may be gradually moved with respect to the rigid element 110 so that by the time the stress altering actuation force 180 has travelled through 360 degrees, the structures will have moved with respect to each other by an amount proportional to, or even equal to, a difference between their unstressed perimeters.

[0065] FIG. 4 A is a diagrammatic representation of the functioning of a portion of a stress-wave actuator, showing the surfaces in a detached state.

[0066] As shown in FIG. 4 A, a portion 126 of the surface 116 of the elastic element may be temporarily detached from the surface 111 of the rigid element. This detachment may be effected by a stress altering actuation force 180 moving in a direction 145. The temporarily detached portion 126 may, for instance, become unstressed, and may expand away from a point 117. The point 117 may, for instance, be where the two surfaces may still be held locked in frictional contact with each other.

[0067] FIG. 4 B is a diagrammatic representation of the functioning of a portion of a stress-wave actuator, showing the surfaces becoming reattached.

[0068] As the stress altering actuation force 180 is moved away, the second surface may become reattached to the first surface. However, as the point 117 may have remained in contact between the two surfaces, the other end of the second surface may now be reattached displaced by a distance 140 with respect to the first surface.

[0069] FIG. 5 A shows a schematic cross-section of a stress-wave actuator 105 of one, exemplary embodiment of the present invention.

[0070] A rigid outer structure 160 having a right circular cylindrical cavity 195 may contain a hollow elastic tube 190. The hollow elastic tube 190 may have a uniform wall of a thickness 210, and a radius 205. The hollow elastic tube 190 may have an uncompressed perimeter that may be larger than the perimeter of the right circular cylindrical opening. When contained within the right circular cylindrical cavity 195, the hollow elastic tube 190 may, therefore, be in a state of stressed compression.

[0071] The tube may have a wall thickness is less than 0.05 of the radius, and the induced stress may, therefore, be less than a critical buckling stress.

[0072] An effective stress altering element 120 may, for instance, be a roller. The roller may, for instance, be inserted between the outer surface of the hollow elastic tube 190, and the inner surface of the right circular cylindrical cavity 195. When so inserted, the roller may temporarily, and locally, reduce the stress in the hollow elastic tube 190 in the portion that it has displaced out of contact with the rigid outer structure 160. By moving the means 120 for sequentially and temporarily altering a stress around the perimeter of the right circular cylindrical cavity 195, a stress wave may be propagated round the perimeter. The moving stress wave may cause the hollow elastic tube 190 rotate in the direction 146 relative to rigid outer structure 160. This relative motion may occur due to mechanisms described in more detail in connection with FIGS. 1, 2, 4 A and 4 B.

[0073] FIG. 5 B shows a schematic cross-section of a stress-wave actuator having piezoelectric activators of one embodiment of the present invention.

[0074] As shown in FIG. 5 B, in such an embodiment, an inner elastic structure 196, that may, for instance, be a hollow elastic tube, may be actuated by piezoelectric elements 120 A-H. These stress altering, or actuation elements may be installed inside the rigid outer structure 160 along the radial directions of the inner elastic structure 196. The stress altering, or actuation elements 120 A-H may be individually activated by applying a suitable electric signal that may be a suitable electric current or electric voltage.

[0075] The stress altering, or actuation elements may, for instance, be actuated temporarily and sequentially from A to H, i.e., the element 120 A may be temporarily actuated followed by element 120 B being temporarily actuated and do on. When the stress altering, or actuation elements are actuated in such a manner, the inner elastic structure 196, may rotate about the central axis 147 of the right circular cylindrical cavity 195 in the direction 146.

[0076] However, when the stress altering, or actuation elements are actuated temporarily and sequentially from 120H to 120A, the inner elastic structure 196 may rotate about a central axis 147 of the right circular cylindrical cavity 195 in the reverse direction, i.e., opposite to the direction 146 of movement of the inner structure/The stress altering, or actuation elements may also be activated in pairs, or other groupings. For instance, in FIG. 5 B, stress altering, elements 120 A and E are shown being activated concurrently. Such concurrent, or simultaneous, actuation of pairs of stress altering, or actuation elements in sequence may double the rotational speed of the inner elastic structure 196 to the case in which the stress altering elements are actuated individually in sequence. The electric signals may also be applied sequentially and temporarily to groups of three, or more, of the stress altering elements, so that the rotational speed of the inner elastic structure 196 may be increased further.

[0077] Although the device shown schematically in FIG. 5 B is described as having piezoelectric actuators, any suitable linear actuator may be used such as, but not limited to, an electro-strictive linear actuator, a magneto-strictive actuator, an electro-active polymer (EAP) linear actuator, or some combination thereof.

[0078] FIG. 6 shows a schematic cross-section of a magnetically activated stress-wave actuator of one embodiment of the present invention.

[0079] As shown in FIG. 6, the rigid outer structure 160 may enclose an inner structure 175 that may be made of a paramagnetic material. The inner structure 175 may be under stress by virtue of having an uncontained perimeter that is slightly larger than the perimeter of the enclosing cavity of the rigid outer structure. In a preferred embodiment, the perimeters may be selected such that the induced stress in the inner structure is less than a critical stress, i.e., the inner structure will not buckle spontaneously. Furthermore, if a slight buckle is formed by an external force, when the force is removed, the inner structure may resume its compression stressed, but unbuckled state.

[0080] The stress-wave actuator may also include one or more magnets 220 that may be located proximate to an inner surface of the inner structure. Each magnet may provide a stress altering actuation force 180 in a portion of the ferromagnetic inner structure 175. The stress altering actuation force 180 may, for instance, be caused by the magnet attracting a portion of the elastic inner structure 175 towards it, thereby forming a slight buckle in the inner structure. In the slight buckle, the outer surface of the elastic inner structure may become temporarily detached from the inner surface of the rigid outer structure 160. The elastic inner structure may become less stressed in the detached portion as it expands slightly. As the magnet is moved round the perimeter, the location of the slight buckle will also move. At the leading edge of the moving buckle, the surfaces will be becoming detached, while at the trailing edge, the surfaces will be becoming re-attached. However, as discussed above in more detail, when the surfaces become re-attached, they will do so displaced a small amount relative to each other. The amount of the displacement may be proportional to, or even equal to, the difference between the outer perimeter of the elastic inner member 175 in its uncompressed state, and the inner perimeter of the enclosing cavity of the rigid outer element 160.

[0081] With such an arrangement, when the magnets are rotated by one revolution about an axis of the right circular cylindrical opening, the inner structure may be rotated about the same axis by an amount that may be proportional to, or equal to, a difference between two perimeters.

[0082] FIG. 7 shows a schematic longitudinal, cross-section of a stress-wave actuator of one embodiment of the present invention configured to operate as a gearless reduction unit 242. In the gearless reduction embodiment shown in FIG. 7, the compression stressed, elastic member 115 contained within the rigid outer structure 160 may be connected to an output shaft by an output-shaft-to-inner-structure connection element 232. The output shaft 230 may be located on a same axis of rotation 147 as an input shaft 225. The input shaft 225 may be connected to one or more movable stress reduction elements 120 via an input-shaft-to-stress-reduction element connector 226.

[0083] In such an arrangement, each complete revolution of the input shaft 225 may result in the output shaft 230 being rotated by an angle proportional to the difference in perimeter of the inner surface of the rigid outer structure 160, and the perimeter of the compression stressed, elastic member 115, when in its uncompressed state.

[0084] In one preferred embodiment of the present invention, the stress altering elements 120 may be movable stress reduction elements that may be magnets, and the compression stressed, elastic member 115 may be, at least in part, made of a ferromagnetic material.

[0085] The magnets may be permanent magnets such as, but not limited to, neodymium rare earth magnets, or they may be electromagnets. In the event they are electromagnets, the arrangement shown in FIG. 7 may also act as a combination clutch and reducing drive. For instance, when the electromagnets are not activated, i.e., no current is flowing through them, turning the input shaft 225 will have no effect on the output shaft 230. However, when the electromagnets are activated by having a current flowing through them, turning the input shaft 225 may cause the output shaft to rotate, albeit at a much lower rate of rotation. If the difference in perimeters is x, and the perimeter of the enclosing surface is y, the ratio of the rate rotation of the output shaft to the rate of rotation of the input shaft will be close to, or equal to x/y. As the difference in perimeters may be of the order of 1/100th of the length of the perimeter, very high gearing ratios may be obtained with such devices. As the torque transmission may be close to, or equal to, the inverse of the gearing ratio, very high torque transmissions may be obtained. This may, for instance, allow small motors, or small turning forces, to be used to turn large loads, something that may, for instance, be of considerable use in the field of robotic actuation.

[0086] In a further embodiment, the arrangement shown schematically in FIG. 7, may be adapted to be a combination reducing element and clutch when the stress altering elements 120 is a permanent magnet, by having a retractable input-shaft-to-stress-reduction element connector 226.

[0087] In yet a further embodiment of the arrangement shown schematically in FIG. 8, the stressed, elastic member 115 may be made of an electroactive material, or have one or more discrete electroactive electrodes on it. The stress altering elements 120 may then be a means of supplying a suitable electrical current or voltage to a portion of the electroactive elastic member. The stress altering elements 120 may, for instance, consist of one or more conductive rollers that may be used as electrical contacts.

[0088] As shown in FIG. 8, the stress altering element 120 may be a mechanical element such as, but not limited to, a metal roller. The stress altering element 120 may be positioned between the stressed, elastic member 115 and the rigid outer structure 160. The stressed, elastic member 115 may be connected to an output shaft 230 via an output-shaft-to-inner-structure connection element 232. The output-shaft-to-inner-structure connection element 232 may, for instance, have a spoked construction, or have some degree of flexibility, especially where it connects to the stressed, elastic member 115. Such arrangements may, for instance, allow the elastic member to flex, but still effectively transmit rotational motion to the output shaft 230. The input shaft 225 may rotate about the same axis of rotation 147 as the output shaft. The input shaft 225 may be connected to the means 120 for sequentially and temporarily altering a stress by an input-shaft-to-stress-reduction-element connector 226.

[0089] In such an arrangement, each complete revolution of the input shaft 225 may result in the output shaft 230 being rotated by an angle proportional to the difference in perimeter of the inner surface of the rigid outer structure 160, and the perimeter of the stressed, elastic member 115. The perimeter of the elastic member may be measured when it is in its uncompressed state.

[0090] FIG. 9 shows a schematic isometric view of an electroactive loop of one embodiment of the present invention.

[0091] The electroactive loop 265 may, for instance, be constructed from a loop of flexible conductive material 270 such as, but not limited to, spring steel, aluminum alloy, copper alloy, or titanium, or some combination thereof. The electroactive loop 265 may also have a plurality of segmented electrodes 260 that may act as localized actuators. The segmented electrodes 260 may, for instance, be made of an electroactive material such as, but not limited to, an electroactive polymer, a piezoelectric material, or some combination thereof. The electroactive loop 265 may also have a first external interconnect 275 and a second external interconnect 276. These external interconnects may be insulated from the flexible conductive material 270. The external interconnects may function as electrodes that allow the segmented electrodes 260 to be activated sequentially so that the electroactive loop 265 may be made to rotate when contained in a state of compression stress within a suitable rigid container.

[0092] FIG. 10 shows a schematic longitudinal, cross-section of a stress-wave actuator of one embodiment of the present invention configured to operate as a motor.

[0093] The stress-wave actuator may have a rigid enclosure 150 that may have a first open end 155 and a second open end 156. The open ends may not be equal in size, and may of any reasonable shape such as, but not limited to, circular, elliptical, or stadium shaped.

[0094] The stressed, elastic member 115 may be made of an electroactive material such as, but not limited to, an electroactive polymer, or it may be an electroactive loop having a construction as described above and shown in FIG. 8. The stressed, elastic member 115 may be connected to an output shaft 230 via an output-shaft-to-inner-structure connection element 232. The connection element 232 may, for instance, have a spoked construction, or have some degree of flexibility, especially where it connects to the stressed, elastic member 115. Such an arrangement may, for instance, allow the elastic member to flex, but still effectively transmit rotational motion to the output shaft 230. The connection element 232 may also provide electrical connections to the stressed, elastic member 115. These electrical connections, that may include active electronic components, may enable regions of the member to be de-stressed in manner that allow a stress-wave to propagate around its circumference. Such a propagating stress wave may, for instance, move the stressed, elastic member 115 rotationally with respect to the enclosure 150. In such an arrangement, the stress-wave actuator may function as an electric motor that may have a high torque.

[0095] FIG. 11 shows a schematic cross-section of a stress-wave actuator with a buckled region of one embodiment of the present invention.

[0096] In the embodiments described above, the stress-wave actuators 105 had, for the most part, a compression stressed, elastic member in which the stress was less than a critical stress. Any slight buckles formed by any activating forces may, therefore, have only been temporary, and disappeared after the activating force was removed. However, if the stress in the elastic element is greater than a critical stress, then one or more permanent buckles may be formed.

[0097] In FIG. 11, a schematic cross-section of a stress-wave actuator 106 with a buckled region is shown. The stressed, elastic member 115 contained within the rigid element 110 may be sufficiently stressed that a permanent buckled region 245 may be formed. Such a buckle may be moved by a suitable buckle driving element 250 that may, for instance, be a stress relieving element such as, but not limited to, a metal roller. The buckle driving element 250 may be moved in a direction 145. As the buckle driving element 250 contacts the stressed, elastic member 115 it may separate the member from the inner wall of the rigid element 110, and may, therefore, cause a local reduction in stress and result in the buckle moving in the direction 146. As the buckle moves, the leading edge may be slightly detached, while at the trailing edge, the elastic element may re-contact the inner surface of the rigid element. However, as detailed above, the re-attachment may occur such that the elastic member is displaced with respect to the rigid element. The amount of the displacement may be proportional to, or even equal to, the difference between the perimeter 165 of the inner surface of the rigid element 110 and the unstressed, outer perimeter 166 of the stressed, elastic member 115. Once the buckle driving element 250 has moved one revolution around the perimeter 165, the stressed, elastic member 115 may have rotated by that amount around the axis of rotation 147.

[0098] Although this invention has been described with a certain degree of particularity, it is to be understood that the present disclosure has been made only by way of illustration and that numerous changes in the details of construction and arrangement of parts may be resorted to without departing from the spirit and the scope of the invention.