SMA actuation apparatus

1. An SMA actuation apparatus for moving a movable element relative to a support structure in any direction perpendicular to a notional primary axis, the SMA actuation apparatus comprising:

a support structure;

a movable element supported on the support structure in a manner allowing movement of the movable element relative to the support structure in any direction perpendicular to said primary axis; and

N pairs of SMA actuator wires extending perpendicular to said primary axis, and extending transverse to respective notional radii extending from the primary axis, as viewed along the primary axis where N is three or more, the SMA actuator wires of each pair extending parallel to each other and being connected at their ends in tension to the movable element and the support structure in opposition so that they apply a force to the movable element in opposite directions, the pairs of SMA actuator wires being arranged around the movable element such that they are capable of being selectively driven to move the movable element in any direction perpendicular to said primary axis.

2. An apparatus according to claim 1 , wherein the SMA actuation apparatus is a camera apparatus further comprising an image sensor fixed to the support structure, and the movable element comprises a camera lens element comprising one or more lenses arranged to focus an image on the image sensor, the primary axis being the optical axis of the camera lens element.

3. An apparatus according to claim 2 , wherein the at least one lens has a diameter of at most 10 mm.

4. An apparatus according to claim 3 , wherein the camera lens element comprises a lens carrier on which the one or more lenses are supported in a manner in which at least one of the one or more lenses is movable along the optical axis.

5. An apparatus according to claim 2 , further comprising:

a vibration sensor arranged to generate output signals representative of the vibration of the apparatus; and

a control circuit arranged to generate drive signals for the SMA actuator wires in response to the output signals of the vibration sensor for stabilising the image sensed by the image sensor, and to supply the generated drive signals to the SMA actuator wires.

6. An apparatus according to claim 5 , wherein the control circuit is arranged to generate drive signals that cause the SMA actuator wires provide no net component of torque around the primary axis.

7. An apparatus according to claim 1 , wherein the pairs of SMA actuator wires are arranged around the outside of the movable element.

8. An apparatus according to claim 1 , wherein the pairs of SMA actuator wires are arranged around the movable element with N-fold rotational symmetry as viewed along the primary axis.

9. An apparatus according to claim 1 , wherein N is four.

10. An apparatus according to claim 1 , wherein the SMA actuator wires of each pair overlie one another as viewed along the primary axis.

11. An apparatus according to claim 1 , wherein the SMA actuator wires have the same length.

12. An apparatus according to claim 1 , further comprising a suspension system supporting the movable element on the support structure in said manner allowing movement of the movable element relative to the support structure in any direction perpendicular to said primary axis, whilst resisting movement of the movable element relative to the support structure along the primary axis.

13. An apparatus according to claim 12 , wherein the suspension system comprises a plurality of beams extending transverse to said two orthogonal directions.

14. An apparatus according to claim 13 , wherein the beams extend parallel to the primary axis.

15. An apparatus according to claim 13 , wherein the beams are formed by wires.