Smart material actuator

1. An actuator assembly comprising:

a frame structure including a pair of axially spaced apart, laterally extending crossheads and a pair of laterally spaced apart, axially extending side frame members connected between respective ends of the crossheads, the side frame members being laterally deflectable in opposite directions at mid-sections thereof in response to movement of the crossheads toward or away from one another;

a smart material device extending axially between the crossheads and operative upon expansion or contraction to move the crossheads away from or towards one another to cause lateral deflection of the mid-sections of the side frame members away from or towards one another and thereby vary the spacing between the mid-sections of the side frame members;

a support;

a constraint mechanism on the support which constrains movement of the mid-sections of the side frame members along respective paths but in opposite directions, each path having an axial component such that as the spacing between the side members is varied the frame structure will be caused to be rotated relative to the support; and

an output member rotatable with the frame structure for outputting the rotational motion of the frame structure relative to the support.

2. An actuator according to claim 1 , wherein the constraint mechanism comprises a pair of rocker arms each having a first end connected to the mid-section of a respective one of the side frame members and a second end pivotally connected to the support at a pivot location axially offset from the pivot connection of the other rocker arm, whereby expansion or contraction of the smart material device will cause the side frame members to deflect in opposite directions to vary the spacing therebetween, which in turn will cause the frame structure to be rotated about a pivot axis by the interaction between the rocker arms and the support.

3. An actuator according to claim 1 , wherein the smart material device includes an electro-responsive smart material.

4. An actuator according to claim 1 , wherein the smart material device includes one or more axially elongated piezoelectric stacks captured between the crossheads.

5. An actuator according to claim 1 , wherein each side frame member includes a toggle linkage connected between the ends of the crossheads.

6. An actuator according to claim 5 , wherein the toggle linkage is formed by a resiliently flexible blade bowed at its mid-section and connected at its ends to the crossheads.

7. An actuator according to claim 6 , wherein the flexible blade is clamped to the end of the rocker arm.

8. An actuator according to claim 7 , wherein the ends of the blades are fixed in slots in the crossheads by set screws.

9. An actuator according to claim 6 , wherein the blades are normally bowed inwards towards the smart material device.

10. An actuator according to claim 1 , wherein the crossheads are held under a pre-load against the ends of the smart material device.

11. An actuator according to claim 10 , wherein the pre-load is effected by high tensile wire wrapped around the crossheads.

12. An actuator according to claim 11 , wherein the pre-load is adjustable by means of a wire tensioner drum.

13. An actuator according to claim 1 , wherein the output device includes an actuator arm connected to one of the crossheads and extending radially outwardly with respect to the pivot axis of the frame structure such that expansion movement of the smart material device is amplified at the distal end of the actuator arm.

14. An actuator according to claim 1 , wherein the output device is used to actuate a valve or other control device.

15. An actuator according to claim 1 , wherein the side frame members are in tension, thereby applying a pre-load to the smart material device.