Active material actuation utilizing tunable magnetic overload protection

1. An active material actuation system adapted for driving a load over an actuation cycle, and preventing an overload condition during the cycle, the system comprising:

an active material actuator operable to undergo a reversible transformation in fundamental property when exposed to or occluded from an activation signal, having a work output end and a securing end, and configured to apply a driving force to the load;

a fixed structure coupled to the actuator; and

a magnetically functioning mechanism intermediate and physically coupled to the securing end and structure, and configured to produce a selected holding force opposite the driving force and operable to retain the securing end and structure in a relatively fixed condition over the cycle;

wherein the mechanism is tunable, so as to produce a plurality of differing holding forces, including the selected holding force, the mechanism being configured such that the structure and securing end are disconnected when the driving force is greater than the selected holding forces, so as to provide a secondary work output path;

and wherein the mechanism includes a combination of at least one electromagnet, permanent magnet, and ferrous material communicatively coupled to the magnets cooperatively producing the selected holding force.

2. The system as defined in claim 1 wherein the mechanism further includes a magnetorheological fluid defining a selectively modifiable yield strength, and the selected holding force is produced at least in part by the yield strength.

3. The system as defined in claim 1 wherein the mechanism includes at least one ferromagnetic electromagnet.

4. The system as defined in claim 2 wherein the at least one electromagnet is configured to selectively expose the fluid to a magnetic field.

5. The system as defined in claim 4 wherein the electromagnet is adjustably energized, so as to vary the field, and thereby produce the plurality of holding forces.

6. The system as defined in claim 1 , further comprising:

a sensor operable to detect a load influencing condition, and communicatively coupled to the mechanism;

wherein the mechanism is configured to produce the selected holding force in response to the condition.

7. The system as defined in claim 6 wherein the condition is selected from the group consisting essentially of the slope of the actuator, the acceleration or deceleration of the load, a crash event, a pre-crash event, the ambient temperature, atmospheric pressure, lubrication presence, the application, and surrounding fluid, ice, or particulate matter characteristics.

8. The system as defined in claim 6 , further comprising:

a controller communicatively coupled to and intermediate the sensor and mechanism, and having stored thereupon a condition threshold;

wherein the controller, sensor, and mechanism are cooperatively configured to autonomously adjust the holding force only when the condition exceeds the threshold.

9. The system as defined in claim 1 , further comprising:

a global positioning system communicatively coupled to the mechanism, and operable to determine the geographic location of the actuator, and the slope of the location;

wherein the holding force is autonomously adjustable and responsive to the slope.

10. An active material actuated assembly adapted to protect against systemic overload conditions, the assembly comprising:

a driven structure presenting a structural capacity, operable to sustain a maximum load at a location based on the capacity, and exposable to an applied load at the location;

an active material actuator operable to undergo a reversible transformation in fundamental property when exposed to or occluded from an activation signal, and configured to apply a driving force to the structure;

a fixed base coupled to the actuator opposite the driven structure; and

a magnetically functioning mechanism configured to produce a holding force opposite the driving force, so as to retain the structure and base in a coupled condition;

wherein the holding force is not greater than the maximum load, such that the structure and base are disconnected when the applied load is greater than the maximum load, so as to free the structure from the base.

11. The assembly as defined in claim 10 wherein the mechanism is intermediate the actuator and base.

12. The assembly as defined in claim 10 wherein the mechanism is intermediate the actuator and driven structure.

13. The assembly as defined in claim 10 wherein the mechanism is tunable so as to achieve a plurality of holding forces.

14. The assembly as defined in claim 13 wherein the mechanism includes an electromagnet, a permanent magnet, and ferrous material communicatively coupled to the magnets, and the holding forces are achieved by selectively energizing the electromagnet.

15. The assembly as defined in claim 14 wherein the electromagnet is adjustably energized, so as to produce a greater plurality of differing holding forces.

16. The assembly as defined in claim 13 , further comprising:

a sensor operable to detect a load influencing condition, and communicatively coupled to the mechanism;

wherein the mechanism is configured to produce the selected holding force in response to the condition.

17. The system as defined in claim 16 wherein the condition is selected from the group consisting essentially of the ambient temperature, atmospheric pressure, lubrication presence, an inputted characteristic at the location, and usage/age of the structure.