Actuator arrangement

1. An actuator arrangement comprising:

a piezoelectric actuator having a body section, said body section defining a central longitudinal axis;

a shroud which enshrouds at least part of the body section of the actuator at a location along said central longitudinal axis; and

at least one constrictive member, positioned at said location along said central longitudinal axis and disposed externally with respect to the shroud;

wherein the constrictive member applies a constrictive force, to the shroud and generally toward said central longitudinal axis, so as to maintain a seal between the shroud and the underlying body section of the actuator;

wherein the constrictive member is a helical coil, has an inner surface facing the enshrouded body section of the actuator, and said inner surface is cylindrical.

2. The actuator arrangement of claim 1 , wherein the shroud is flexible.

3. The actuator arrangement of claim 1 , wherein the shroud conforms to the contours of the underlying body section.

4. The actuator arrangement of claim 1 , wherein the shroud presents a male seat surface to a female surface of the constrictive member.

5. The actuator arrangement of claim 1 , wherein the body section of the actuator is inserted into the shroud.

6. The actuator arrangement of claim 5 , wherein the shroud is a sleeve.

7. The actuator arrangement of claim 6 , wherein the sleeve is composed of a heat-shrinkable material.

8. The actuator arrangement of claim 1 , wherein at least one intermediate layer is disposed between the shroud and the underlying body section of the actuator.

9. The actuator arrangement of claim 8 , wherein the intermediate layer is an adhesive layer or a filler layer.

10. The actuator arrangement of claim 8 , wherein there are at least two intermediate layers including at least one adhesive layer and at least one filler layer.

11. The actuator arrangement of claim 1 , wherein the shroud is formed on the body section of the actuator.

12. The actuator arrangement of claim 11 , wherein the shroud is formed by over-moulding, painting, dipping or spraying.

13. The actuator arrangement of claim 1 , wherein the shroud is in contact with the underlying body section of the actuator.

14. The actuator arrangement of claim 1 , wherein the constrictive member applies the constrictive force to the shroud resiliently.

15. The actuator arrangement of claim 14 , wherein the constrictive member has a diameter that is expanded resiliently to accommodate the underlying enshrouded body section of the actuator.

16. The actuator arrangement of claim 1 , wherein the constrictive member applies the constrictive force to the shroud by plastic deformation.

17. The actuator arrangement of claim 16 , wherein the constrictive member is of heat-contractible material.

18. The actuator arrangement of claim 16 , wherein the constrictive member is of a shape-memory material.

19. The actuator arrangement of claim 18 , wherein the actuator arrangement has an operational temperature range and wherein the shape-memory material of the constrictive member has a defined martensitic transformation temperature that is outside that temperature range.

20. The actuator arrangement of claim 1 , wherein the constrictive member is generally annular.

21. The actuator arrangement of claim 20 , wherein the constrictive member is generally tubular.

22. The actuator arrangement of claim 1 , wherein the straight side defines a cylindrical female surface.

23. The actuator arrangement of claim 20 , wherein the constrictive member comprises at least one coil.

24. The actuator arrangement of claim 23 , wherein the constrictive member comprises a plurality of coils and the coils of the plurality co-operate to define a cylindrical female surface.