Method of reducing the effect of preheat time variation during shape memory alloy actuation

1. A method of activating a shape memory alloy (SMA) actuator, comprising the steps of:

a) exposing the SMA actuator to an activation signal wherein the SMA actuator is responsive to the activation signal by a microstructure transformation to activate the SMA actuator;

b) sensing an observable property of a portion of the SMA actuator or of a component in a drive-train driven by the SMA actuator wherein the observable property is indicative of an amount of motion delay between a beginning of the exposing of the SMA actuator to the activation signal and an onset of the activation of the SMA actuator;

c) autonomously detecting a change in the observable property based on the sensing;

d) autonomously determining a reduction in the amount of motion delay based on the detecting of the change in the observable property wherein the reduction in the amount of motion delay is caused by the activation of the SMA actuator; and

e) autonomously determining the onset of the activation of the SMA actuator based on the determining of the reduction in the amount of motion delay.

2. The method as claimed in claim 1 , wherein the motion delay is due to a tolerable degree of slack within the SMA actuator.

3. The method as claimed in claim 2 , wherein:

the SMA actuator comprises:

a point; and

a tab defining a surface, the tab being attached to the SMA actuator at the point;

the method further comprises the step of securely positioning a position sensor relative to the actuator, such that the position sensor is operable to selectively engage the tab and determine a change in position by the point;

the observable property is a position of the point;

the position of the point is indicative of the degree of slack; and

the degree of slack is indicative of the amount of motion delay.

4. The method as claimed in claim 3 , wherein the sensor is photoelectric in operation and the tab defines a plurality of through-holes.

5. The method as claimed in claim 3 , wherein:

the position sensor includes a lateral contact operable to physically engage the SMA actuator only when the SMA actuator is deactivated; and

the method further comprises the step of determining disengagement between the actuator and the contact.

6. The method as claimed in claim 3 , wherein the position sensor is positioned at a predetermined location, so as to maximize the observable change in position of the point caused by the activation of the SMA actuator.

7. The method as claimed in claim 1 , wherein the motion delay is due to a tolerable degree of compliance within the drive-train.

8. The method as claimed in claim 1 , wherein the motion delay is due to a tolerable degree of backlash in the drive-train.

9. The method as claimed in claim 8 , wherein:

the SMA actuator is operatively connected to an active vent system;

the drive-train further includes at least one gear and rack cooperatively presenting intermeshed teeth; and

the backlash is presented by a spacing between the intermeshed teeth.

10. The method as claimed in claim 9 , wherein the sensing is performed by a potentiometer operable to detect rotation by a driven one of said at least one gear.

11. The method as claimed in claim 1 , wherein:

the method further comprises the step of securing a linear position sensor relative to the drive-train;

the observable property is a position of the component in the drive-train;

the position of the component is indicative of the amount of motion delay; and

the sensing is performed by the linear position sensor.

12. The method as claimed in claim 11 , wherein the linear position sensor is positioned at a predetermined location proximate the actuator, so as to maximize a change in the observable property caused by the activation of the SMA actuator.

13. The method as claimed in claim 1 , wherein:

the sensing is performed by a sensor;

a controller operable to perform an action is communicatively coupled to the sensor; and

said method further comprises a step of:

f) causing the controller to perform the action in response to the step of determining the onset of the activation of the SMA actuator.

14. The method as claimed in claim 13 , wherein:

the controller is operable to perform an overload protection action; and

the step f) further includes the step of terminating the activation signal.

15. The method as claimed in claim 1 , wherein after the step of determining the onset of the activation of the SMA actuator, the method further comprises the steps of:

f) returning the SMA actuator, the drive-train, or a combination thereof, to a de-actuated state; and

g) autonomously regenerating the motion delay.

16. The method as claimed in claim 15 , wherein step f) further includes the step of engaging the SMA actuator with magnetism, so as to induce strain.

17. The method as claimed in claim 15 , wherein the drive-train comprises a plurality of racks or gears cooperatively presenting intermeshing teeth, and step f) further includes the step of engaging the racks or gears with biasing springs operable to regenerate the motion delay after activation of the SMA actuator.

18. A method of activating a shape memory alloy (SMA) actuator, comprising the steps of:

a) continually exposing the SMA actuator to an activation signal operable to cause preheating of the SMA actuator to start a microstructure transformation of the SMA actuator wherein:

a system includes the SMA actuator, a drive-train driven by the SMA actuator, or a combination thereof; and

the system has a movable output responsive to an activation of the SMA actuator;

b) monitoring a duration of the exposure to the activation signal by the actuator, and observing over time an observable property of a portion of the SMA actuator or of a component in a drive-train driven by the SMA actuator wherein:

the observable property is indicative of an amount of motion delay between a beginning of the exposing of the SMA actuator to the activation signal and the output motion of the system; and

the amount of motion delay includes a preheat delay between the beginning of the exposing of the SMA actuator to an onset of the activation of the SMA actuator;

c) autonomously detecting a reduction over time of the amount of the motion delay based on the observing of the observable property by a sensor, wherein the reduction in the amount of motion delay is caused by the activation of the SMA actuator, and determining the onset of activation of the SMA by the actuator;

d) determining a secondary information, based on the monitoring, the observing and the autonomous detecting;

e) adjusting an algorithm, a timer, or a threshold based on the secondary information; and

f) improving a performance of the system based on the adjusting the algorithm, timer, or threshold.

19. The method as claimed in claim 18 , wherein the secondary information is the preheat delay of the SMA actuator.

20. The method as claimed in claim 18 , wherein the secondary information is an overall actuation time of the system.