One of the great obstacles to designing shape memory alloy devices is their low movement (strain), which for a straight wire is only 4-8% of the wire length. This invention uses an insulated, braided NiTi to increase the strain (up to 50% of the actuator length) and multiply the force, while providing airflow to cool the actuator and allow it to cycle quickly. The invention relates to electrical paths through the braid which keep the resistance of the device high, allowing simple circuits and common batteries to easily heat the material. By varying the angle of the braid, a designer can directly trade power for strain and design a device suited for their particular application. From the patent abstract:
One embodiment of an electro-mechanical actuator, comprised of a braid (1) of insulated wires of shape memory material, trained to a contracted length, connected at the ends to primary fixture (2) and secondary fixture (3). These fixtures guide the electrical path through the braid from the electrical power source (4), in a winding path through the braid (5-10), and to electrical ground (11). Other embodiments are described and shown.
Read the entire patent here. Available for licensing.
