Superelastic shape memory alloy overloading and overheating protection mechanism

1. An overload and overheating protection device, comprising:

an austenitic shape memory alloy protection element operable to undergo a solid state transformation from an austenitic phase having a first modulus to a de-twinned martensitic phase having a second modulus smaller than the first modulus when a transforming force is applied to the austenitic shape memory alloy protection element;

wherein:

the austenitic shape memory alloy protection element:

is adapted for use with a shape memory alloy actuator and for protecting the shape memory alloy actuator from an overload condition of the shape memory alloy actuator;

has an austenitic finish temperature less than a lowest operating temperature of the shape memory alloy actuator; and

is communicatively coupled to an electrical circuit;

the shape memory alloy actuator:

is distinct from the austenitic shape memory alloy protection element;

is drivenly coupled to a load;

defines a stroke;

produces an actuating force when activated;

is an element of the electrical circuit; and

is activated by closing the electrical circuit;

the transforming force is caused by the overload condition of the shape memory alloy actuator;

the solid state transformation enables the actuating force to cause tensile strain in the austenitic shape memory alloy protection element, so as to produce a secondary work output path for the shape memory alloy actuator; and

the solid state transformation further enables the shape memory alloy actuator to open the circuit, so as to deactivate the shape memory alloy actuator.

2. The overload and overheating protection device as defined in claim 1 , wherein the austenitic shape memory alloy protection element is connected in series to the shape memory alloy actuator.

3. The overload and overheating protection device as defined in claim 1 , wherein the austenitic shape memory alloy protection element presents at least one wire.

4. The overload and overheating protection device as defined in claim 1 , further comprising:

a lever defining a pivot axis and first and second arms, wherein the shape memory alloy actuator is drivenly connected to the first arm;

the austenitic shape memory alloy protection element is a wire;

the wire is drivenly connected in tension to the second arm antagonistic to the shape memory alloy actuator; and

said lever being operable to open the circuit when the first arm is driven by the shape memory alloy actuator.

5. The overload and overheating protection device as defined in claim 1 , wherein the austenitic shape memory alloy protection element is a wire, and an electrically insulating barrier mechanically connects the wire to the circuit and electrically insulates the wire from the circuit.

6. The overload and overheating protection device as defined in claim 1 , further comprising a holding mechanism to urge the shape memory alloy actuator to close the circuit to activate the shape memory alloy actuator.

7. The overload and overheating protection device as defined in claim 4 , wherein the first arm is longer than the second arm, so as to provide mechanical advantage.

8. The overload and overheating protection device as defined in claim 4 , wherein the second arm is longer than the first, so as to provide mechanical advantage.

9. The overload and overheating protection device as defined in claim 6 , wherein the holding mechanism includes a detent.

10. An actuation assembly adapted for driving a load and for protecting against an overload condition, said assembly comprising:

a shape memory alloy actuator to produce an actuating force and stroke when activated, and the shape memory alloy actuator composing a circuit, wherein the circuit, when closed, is to activate the shape memory alloy actuator; and

an overload and overheating protection device including an austenitic shape memory alloy wire:

having an austenitic finish temperature less than a lowest operating temperature of the shape memory alloy actuator;

distinct from the shape memory alloy actuator;

operable to undergo a solid state transformation from an austenitic phase having a first modulus to a de-twinned martensitic phase having a second modulus smaller than the first modulus when a transforming force is applied to the austenitic shape memory alloy wire;

connected in series to the shape memory alloy actuator, configured such that the transforming force is caused by the overload condition; and

communicatively coupled to the circuit;

said solid state transformation enabling the actuating force to cause tensile strain in the austenitic shape memory alloy wire, so as to produce a secondary work output path for the shape memory alloy actuator; and

said tensile strain being further operable to open the circuit, so as to deactivate the shape memory alloy actuator.

11. The actuation assembly as defined in claim 10 , wherein the shape memory alloy actuator includes a Martensitic shape memory alloy wire.

12. The actuation assembly as defined in claim 10 , wherein the overload and overheating protection device is adjustable so as to modify an overload protection threshold for enabling the actuating force to cause the solid state transformation and tensile strain in the austenitic shape memory alloy wire.

13. The actuation assembly as defined in claim 10 , wherein a holding mechanism is to urge the overload and overheating protection device to close the circuit to activate the shape memory alloy actuator.

14. The actuation assembly as defined in claim 12 , wherein the overload and overheating protection device further includes a lever defining a pivot axis and a plurality of holes spaced differing distances from the pivot axis, and each hole is configured to removably receive the austenitic shape memory alloy wire.

15. An actuation assembly adapted for driving a load and for protecting against an overload condition, said assembly comprising:

an actuator producing an actuating force and stroke when activated, and composing a circuit, wherein the circuit, when closed, activates the actuator;

an overload and overheating protection device including an austenitic shape memory alloy wire operable to undergo a change in fundamental property when exposed to or occluded from a stress activation signal, connected in series to the actuator, configured such that the stress activation signal is caused by the overload condition, and communicatively coupled to the circuit;

said change enabling the actuating force to strain the austenitic shape memory alloy wire, so as to produce a secondary work output path for the actuator; and

said change being further operable to open or close the circuit, so as to deactivate the actuator;

wherein the overload and overheating protection device is adjustable so as to modify the stress activation signal; and

wherein the overload and overheating protection device further includes a lever defining a pivot axis and a plurality of holes spaced differing distances from the pivot axis, and each hole is configured to removably receive the austenitic shape memory alloy wire.

16. An actuation assembly adapted for driving a load and for protecting against an overload condition, said assembly comprising:

an actuator producing an actuating force and stroke when activated, and composing a circuit, wherein the circuit, when closed, activates the actuator; and

an overload and overheating protection device including an austenitic shape memory alloy wire operable to undergo a change in fundamental property when exposed to or occluded from a stress activation signal, connected in series to the actuator, configured such that the stress activation signal is caused by the overload condition, and communicatively coupled to the circuit;

said change enabling the actuating force to cause tensile strain in the austenitic shape memory alloy wire, so as to produce a secondary work output path for the actuator;

said change being further operable to open the circuit, so as to deactivate the actuator;

wherein the overload and overheating protection device is adjustable so as to modify an overload protection threshold for enabling the actuating force to strain the austenitic shape memory alloy wire;

and wherein the overload and overheating protection device further includes a lever defining a pivot axis and a plurality of holes spaced differing distances from the pivot axis, and each hole is configured to removably receive the austenitic shape memory alloy wire.