Active material actuator having a magnetorheological overload protector
View Patent ↗A system for and method of providing overload protection for actuators, such as shape memory alloy wires, including and utilizing a magnetorheological fluid mechanism connected in series with or parallel to the load driven by the actuator, and operable to effect tunable 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 actuator defining a maximum threshold force, and drivenly coupled to the load, so as to apply a driving force thereto;
a fixed structure coupled to the actuator; and
an overload protector, including:
a mechanism further including magnetorheological fluid defining a yield strength, and a translatable part disposed within the fluid; and
at least one magnet communicatively coupled to the fluid, so as to further define the yield strength, the protector producing a selectively modifiable resistive force based on the yield strength, wherein the resistive force is less than the maximum threshold force, the mechanism being driven by the actuator such that the resistive force opposes the driving force, and caused to reconfigure, so as to create a secondary work output path, when the driving force is greater than the resistive force.
2. The system as defined in claim 1 wherein the actuator is an active material actuator operable to undergo a reversible transformation in fundament property when exposed to or occluded from an activation signal, having a work output end and a securing end.
3. The system as defined in claim 2 wherein the actuator is a shape memory alloy wire.
4. The system as defined in claim 1 wherein the at least one magnet includes an electromagnet configured to selectively produce and/or modify a magnetic field.
5. The system as defined in claim 4 wherein the electromagnet is a ferromagnetic electromagnet.
6. The system as defined in claim 4 wherein the electromagnet composes a circuit, and the actuator is configured to open the circuit, so as to deactivate the electromagnet, when the driving force is greater than the resistive force.
7. The system as defined in claim 6 wherein the circuit further comprises a switch, and the actuator is drivenly coupled to the switch.
8. The system as defined in claim 7 wherein the circuit further comprises the actuator.
9. The system as defined in claim 1 wherein the mechanism is connected to the actuator serially with the load.
10. The system as defined in claim 1 wherein the mechanism is connected to the actuator parallel to the load, such that the load and mechanism cooperatively define a modifiable overall load.
11. The system as defined in claim 10 wherein the mechanism, load, and actuator are interconnected by at least one pivot joint.
12. The system as defined in claim 10 wherein the actuator is connected to the mechanism and load at an equilibrium point, so as to produce only linear motion.
13. The system as defined in claim 10 wherein the protector further includes an extension spring intermediate the actuator and fixed structure.
14. The system as defined in claim 1 wherein the actuator applies an angular driving force to the load, and the mechanism defines a clutch.
15. The system as defined in claim 14 wherein the translatable part is a clutch disc, and the mechanism further includes a flywheel selectively engaged by the disc.
16. The system as defined in claim 1 , further comprising a return element drivenly coupled to the actuator and operable to produce a biasing force to the mechanism, so as to return the protector to a pre-actuated state.
17. The system as defined in claim 1 , further comprising a sensor operable to detect a load influencing condition, and communicatively coupled to the mechanism, the mechanism being configured to produce the resistive force in response to the condition.
18. The system as defined in claim 17 wherein the condition is selected from the group consisting of the slope of the actuator, the acceleration or deceleration of the load, the ambient temperature, atmospheric pressure, lubrication presence, the application, and surrounding fluid, ice, or particulate matter characteristics.
19. The system as defined in claim 17 , further comprising a controller communicatively coupled to and intermediate the sensor and mechanism, and having stored thereupon a condition threshold, the controller, sensor, and mechanism being cooperatively configured to autonomously adjust the holding force only when the condition exceeds the threshold.
20. The system as defined in claim 1 wherein the mechanism is formed of ferrous material communicatively coupled to the magnet, and the resistive force is further produced as a result thereof.