Scalable rotary actuators with embedded shape memory alloys

Scalable rotary actuators are being developed with the help of Shape Memory Alloy (SMA) wires. Subjected to elevated temperatures SMA wires deliver large strains and high stresses. Yet their bandwidth is limited because of the time required for cooling. Bandwidth can be enhanced by miniaturizing the actuating system, which results in higher cooling rates. Using SMA wires with diameter of about 100 micron, several miniature actuators have been designed and fabricated. For example, a rotary joint with bi-directional actuation, which is about 4mm wide, 9mm long and 3mm high, can achieve angular deflection of around +/- 60 deg. Based on this bi-directional actuator, SMA ratchet mechanisms with minimum feature sizes of about 200 micron have been developed. The ratchet mechanisms can transform angular motion to continuously rotating motion. SMA wires are embedded into polyurethane structures using Shape Deposition Manufacturing (SDM). SDM is a layered manufacturing process capable of building complex 3D parts through the combination of material addition and subtraction. A key advantage of this process is the ease by which process interruption may occur to embed sensors and actuators into components. SDM can also fabricate functional mechanisms in an assembled configuration eliminating the need for assembly. The present article will describe design and manufacturing processes which enable the fabrication of the scalable rotary actuators. System performance and behavior of the SMA actuators will be also discussed in this contribution.