Actuator with a wound shape-memory element

Abstract

An actuator comprises an elongated shape-memory element wound around a first element and having one first end connected to the first element and one second end connected to a second element. Heating means are provided for heating the shape-memory element in order to obtain a displacement of one of the ends thereof. The elongated shape-memory element is guided so that it can slide within a closed channel made of a material having a low coefficient of friction, for example defined by a sheath.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention will now be described in detail with reference to the attached plate of drawings, which are provided purely by way of non-limiting example, and in which:

FIG. 1 is a schematic perspective view of the actuator according to the invention in a first end position of its actuation stroke;

FIG. 2 is a schematic perspective view of the actuator according to the invention in a second end position of its actuation stroke;

FIG. 3 is a front view of a first embodiment of the actuator according to the invention;

FIG. 4 is a cross-sectional side view of the actuator according to the line IV-IV of FIG. 3;

FIG. 5 represents, at an enlarged scale, a portion of the cross section of FIG. 4;

FIG. 6 is a front view of a second embodiment of the actuator;

FIG. 7 is a cross-sectional side view of the variant of FIG. 6, according to the line VII-VII of FIG. 6;

FIG. 8 represents, at an enlarged scale, a portion of the cross section of FIG. 7;

FIG. 9 represents a cross-sectional view according to the line IX-IX of FIG. 10 of the actuator applied to an internal thread that actuates a wormscrew, the actuator being in a first position;

FIG. 10 represents a cross-sectional view according to the line X-X of FIG. 9;

FIG. 11 represents the application of FIG. 9, in a cross-sectional view according to the line XI-XI of FIG. 12, the actuator being in a second position; and

FIG. 12 represents a cross-sectional view according to the line XII-XII of FIG. 11.

Claims

1. An actuator for causing a variation in relative position between a first element and a second element, said variation in position occurring from a first relative position as far as at least one second relative position, said actuator comprising: an elongated SMA element wound around said first element, said elongated SMA element having a first end connected to said first element and a second end connected to said second element; andheating means for heating said elongated SMA element in order to obtain a transformation from a martensitic phase into an austenitic phase and to bring about displacement of one of said ends of said elongated SMA element,said actuator being characterized in that said elongated SMA element is guided so that it can slide within a closed channel made of a material having a low coefficient of friction, which is fixed with respect to the first element and has a helical or spiral development.

2. The actuator according to claim 1, wherein said closed channel is defined by a sheath made of a material having a low coefficient of friction.

3. The actuator according to claim 1, wherein said heating means include an electrical-supply source and electrical-conduction terminals for conducting a current through said SMA element.

4. The actuator according to claim 2, wherein said sheath is wound to form a helix.

5. The actuator according to claim 2, wherein said sheath is wound to form a spiral with the turns that are superimposed on one another and lie on one and the same plane.

6. The actuator according to claim 2, wherein said sheath is made of PTFE.

7. The actuator according to claim 1, wherein said SMA element is in the form of a wire with a circular cross section.

8. The actuator according to claim 1, wherein said SMA element is in the form of a strip with a flattened cross section.

9. The actuator according to claim 1, wherein it comprises return means for recalling said first element and said second element into said first relative position.

10. The actuator according to claim 9, wherein said return means are formed by elastic elements.

11. The actuator according to claim 2, wherein said first element has a circular outer side surface made on which is a groove that extends to form a helix throughout the development of said side surface.

12. The actuator according to claim 1, wherein said first element is made up of two ring-shaped blocks which can be coupled concentrically one inside the other.

13. The actuator according to claim 12, wherein the inner surface of the block and the outer surface of the block have helical grooves which, when the two blocks are coupled, constitute as a whole a helical passage.

14. The actuator according to claim 13, wherein moulded on the surface of the helical grooves of the aforesaid blocks are two half-shells made of a material having a low coefficient of friction, for example PTFE, so as to constitute said closed channel having a low coefficient of friction.

15. The actuator according to claim 13, wherein one of the two aforesaid blocks is made entirely of a material having a low coefficient of friction, for example PTFE, so as to define with the other block the aforesaid closed channel having a low coefficient of friction.

16. The actuator according to claim 15, wherein the block made entirely of a material having a low coefficient of friction is the outer block.

17. The actuator according to claim 13, wherein the elongated SMA element is guided within the aforesaid helical passage with interposition of a sheath made of a material having a low coefficient of friction constituting the aforesaid closed channel having a low coefficient of friction.