Mechanical system with an active materials-based actuator
A mechanical system selectively imparts a prescribed motion to an output load using two or more actuators, including at least one having an active material element. The output load can be a locking member when the system is a vehicle transmission, a shuttle car of a linear system, or another device. A controller determines a total motive force required for imparting the prescribed motion, and selectively commands a combination of the actuators to provide the total motive force, apportioning the total motive force between the various actuators to optimize the performance of the system. An algorithm determines which combination of the actuators is the most suitable in moving the output load, and continuously modified this combination as needed as the output load is moved. The other actuator or actuators are then selectively energized as needed to provide the total motive force depending on this suitability determination.
1. A system for selectively moving an output load over a predetermined distance, the system comprising:
at least one energy source:
a first actuator operable for applying a variable first motive force to move the output load:
a second actuator operable for applying a variable second motive force to the output load to move the output load, wherein the second actuator includes an active element having a variable property, and wherein the second actuator is positioned in parallel with the first actuator with respect to the output load; and
a controller operable for determining a total motive force sufficient for moving the output load, and for selectively varying a combination of the first and the second motive force to thereby apply the total motive force;
wherein activating the second actuator includes connecting the active element of the second actuator to the at least one energy source to thereby apply a stimulus sufficient for varying the variable property.
2. The system of claim 1 , wherein the controller is operable for determining an initial combination of the first and the second actuator that is most suitable for imparting the desired motion to the output load, and for selectively varying the combination as needed to thereby impart the desired motion to the output load.
3. The system of claim 2 , further comprising a sensor adapted for detecting a condition of each of the first and the second actuator, and for transmitting the condition to the controller for determining which combination of the first and the second actuator is most suitable.
4. The system of claim 1 , further comprising a sensor adapted for measuring at least one characteristic of the system, and for transmitting the at least one characteristic to the controller for determining the total motive force.
5. The system of claim 1 , wherein the active element has a variable length as the variable property.
6. The system of claim 1 , wherein the system is a transmission interlock system for a vehicle transmission, the stationary member is a member of the transmission that defines a notch, and the output load is a shaped locking member which is selectively engageable with the notch defined by the stationary member in response to the first and second motive forces to thereby provide a positive restraint against motion of the vehicle.
7. A system for selectively imparting a desired motion to an output load, the system comprising:
a voltage supply;
a first actuator operable for applying a variable first motive force sufficient for moving the output load over the predetermined distance;
a second actuator operable for applying a variable second motive force sufficient for moving the output load over the predetermined distance, the second actuator including an active element having a variable property that varies in response to an electrical stimulus from the voltage supply, wherein the first actuator and the second actuator are positioned in parallel with each other with respect to the output load; and
a controller operable for determining a suitable combination of the first and the second actuator for imparting the desired motion to the output load;
wherein the controller is configured for activating the suitable combination when moving the output load over the predetermined distance to thereby impart the desired motion to the output load.
8. The system of claim 7 , wherein activating the suitable combination includes activating the second actuator by varying the variable property.
9. The system of claim 7 , wherein the active element is selected from the group consisting of a shaped-memory alloy (SMA), a magneto-strictive element, an electro-strictive element, a piezo-electric element, and an electro-active polymer (EAP).
10. The system of claim 9 , wherein the active element is an SMA wire.
11. The system of claim 7 , wherein the system is a transmission interlock system for a vehicle transmission, and the output load is a shaped locking member which is selectively engageable with a notch defined by a stationary member of the transmission in response to the first and second motive forces to thereby provide a positive restraint against motion of the vehicle.
12. A method for imparting a desired motion to an output load in a mechanical system a first actuator operable for applying a variable first motive force to the output load, and a second actuator operable for applying a variable second motive force to the output load, the method comprising:
connecting the first actuator to the output load;
connecting the second actuator between a stationary member of the system and the output load such that the second actuator is positioned in parallel with the first actuator with respect to the output load;
detecting a signal requesting the desired motion of the output load from a first position to a second position within a predetermined interval;
determining a total motive force necessary for moving the output load to the second position within the predetermined interval; and
selectively actuating the first actuator to provide the first motive force as a portion of the total motive force; and
selectively actuating an active element of the second actuator to thereby impart the second motive force as another portion of the total motive force;
wherein selectively actuating the active element includes applying a stimulus to the active element to thereby vary a variable property of the active element.
13. The method of claim 12 , wherein applying a stimulus to the active element to thereby vary the variable property includes applying an electrical stimulus to vary a variable length of the active element.
14. The method of claim 12 , wherein a portion of the output load is configured as a locking member for a vehicle transmission, the method further comprising:
moving the output load to the first position to place the vehicle transmission in a park (P) position; and
moving the output load to the second position to place the transmission in an out-of-park (OP) position.
15. The method of claim 12 , wherein the output load is configured as a moveable portion of a linear actuator.