Staggered Nitinol Wire Actuator Array for High Linear Displacement and Force-to-Mass Ratio.

We present the design and performance of a unique Nitinol (NiTi) actuator design for high linear displacement and force generation through joule heating. The device is comprised of a staggered linear array of NiTi in wire form that, as a shape memory alloy, can achieve linear displacement through material phase change when heated. This change allows the crystal lattice within the material to displace/adjust. The design results in strain levels of 20.4% that are comparable to those of biological muscles and provides potential for additional strain. Three- to seven-staggered NiTi wires are tested to demonstrate the different levels of strain that are achieved with a range of wires in a staggered array. In addition, we measure and compare force generated to the mass of each wire to show system force-to-mass ratio. The effective force to mass for the system is greater than 5500 combined with a seven-wire staggered array. The device shows that a lightweight, high-strain actuator can be developed, and our research demonstrates its potential use in prosthetic actuation.