Shape memory alloy actuator system and method

1. An actuator system, comprising:

a housing;

a clutch having clutch plates and a clutch shaft, the clutch plates being axially engageable with one another causing the clutch shaft to be coupled to an output shaft;

a shape memory alloy (SMA) torque tube for rotating the clutch shaft;

a first unidirectional bearing limiting rotation of the clutch shaft relative to the SMA torque tube to a first direction;

a second unidirectional bearing preventing rotation of the clutch shaft relative to the housing along a second direction opposite the first direction and

an over-center linkage coupled to the clutch and configured to axially disengage the clutch plates.

2. The actuator system of claim 1 wherein:

at least one of the first and second unidirectional bearings is configured as a sprag bearing.

3. The actuator system of claim 1 further comprising:

an SMA linear actuator linearly contracting when heated in a manner causing engagement of the clutch.

4. The actuator system of claim 3 further comprising:

an SMA ribbon;

the SMA linear actuator being coupled to the over-center linkage and linearly contracting when heated causing locking of the over-center linkage and engagement of the clutch;

the SMA ribbon linearly contracting when heated causing collapse of the over-center linkage and disengagement of the clutch.

5. An actuator system, comprising:

a clutch having clutch plates and a clutch shaft;

an over-center linkage;

a shape memory alloy (SMA) linear actuator coupled to the over-center linkage and linearly contracting when heated causing locking of the over-center linkage and causing the clutch plates to axially engage with one another and causing the clutch shaft to be coupled to an output shaft; and

an SMA ribbon coupled to the over-center linkage and linearly contracting when heated causing collapse of the over-center linkage and axial disengagement of the clutch plates from one another.

6. The actuator system of claim 5 further comprising:

a bellcrank configured to collapse the over-center linkage in response to heating of the SMA ribbon.

7. The actuator system of claim 5 further comprising:

an SMA torque tube;

the clutch including a clutch shaft; and

the SMA torque tube being coupled to the clutch shaft for rotating the clutch shaft.

8. The actuator system of claim 7 further comprising:

a housing;

a first unidirectional bearing limiting rotation of the clutch shaft relative to the SMA torque tube to a first direction; and

a second unidirectional bearing preventing rotation of the clutch shaft relative to the housing along a second direction opposite the first direction.

9. The actuator system of claim 7 further comprising:

an output shaft;

the clutch coupling the clutch shaft to the output shaft during engagement of the clutch by the SMA linear actuator.

10. A method of rotating a shaft relative to a housing, comprising the steps of:

coupling a clutch to an over-center linkage;

axially engaging clutch plates of the clutch having a clutch shaft;

coupling the clutch shaft to an output shaft in response to axially engaging the clutch plates;

heating an SMA torque tube;

twisting the SMA torque tube in response to heating thereof;

rotating the output shaft in response to twisting the SMA torque tube;

limiting rotation of the clutch shaft relative to the SMA torque tube to a first direction using a first unidirectional bearing;

preventing rotation of the clutch shaft relative to the housing along a second direction opposite the first direction using a second unidirectional bearing; and

disengaging the clutch plates using the over-center linkage.

11. The method of claim 10 further comprising the steps of:

heating an SMA linear actuator;

linearly contracting the SMA linear actuator in response to heating thereof; and

engaging the clutch in response to linearly contracting the SMA linear actuator.

12. The method of claim 10 further comprising the steps of:

coupling a deployable device to the output shaft; and

rotating the deployable device in response to heating the SMA torque tube.

13. The method of claim 10 further comprising the steps of:

coupling the SMA linear actuator to the clutch using the over-center linkage;

locking the over-center linkage in response to linearly contracting the SMA linear actuator; and

engaging the clutch in response to locking the over-center linkage and linearly contracting the SMA linear actuator.

14. The method of claim 13 further comprising the steps of:

coupling an SMA ribbon to the over-center linkage ;

heating the SMA ribbon;

linearly contracting the SMA ribbon in response to heating;

collapsing the over-center linkage in response to linearly contracting the SMA ribbon; and

disengaging the clutch in response to collapsing the over-center linkage .

15. A method of disengaging a clutch, comprising the steps of:

coupling the clutch to an over-center linkage , the clutch having clutch plates being axially engaged to one another, the clutch plates being coupled to an output shaft;

heating an SMA ribbon coupled to the over-center linkage;

linearly contracting the SMA ribbon in response to the heating thereof;

collapsing the over-center linkage in response to linearly contracting the SMA ribbon; and

disengaging the clutch plates in response to collapsing the over-center linkage.

16. The method of claim 15 further comprising the steps of:

coupling the over-center linkage to an SMA linear actuator;

heating the SMA linear actuator;

linearly contracting the SMA linear actuator in response to heating thereof; and

engaging the clutch plates in response to linearly contracting the SMA linear actuator.

17. The method of claim 15 wherein the clutch includes a clutch shaft, the method further comprising the steps of:

coupling an SMA torque tube to the clutch shaft in response to the clutch plates being axially engaged to one another;

heating the SMA torque tube; and

rotating the clutch shaft in response to heating the SMA torque tube.

18. The method of claim 17 wherein the step of coupling the SMA torque tube to the clutch shaft comprises:

coupling the SMA torque tube to the clutch shaft using a first unidirectional bearing;

coupling the clutch shaft to a housing using a second unidirectional bearing;

limiting rotation of the clutch shaft relative to the SMA torque tube to a first direction; and

preventing rotation of the clutch shaft relative to the housing along a second direction opposite the first direction.

19. The method of claim 18 further comprising the steps of:

coupling a deployable device to the output shaft; and

rotating the deployable device in response heating the SMA torque tube.