Femtosecond Laser Fabricated Nitinol Living Hinges for Millimeter-Sized Robots

Nitinol is a smart material that can be used as an actuator, a sensor, or a structural element, and has the potential to significantly enhance the capabilities of microrobots. Femtosecond laser technology can be used to process nitinol while avoiding heat-affected zones (HAZ), thus retaining superelastic properties. In this work, we manufacture living hinges of arbitrary cross sections from nitinol using a femtosecond laser micromachining process. We first determined the laser cutting parameters, $4.1 \,\mathrm{Jcm}^{-2}$ fluence with $5$ passes for $5 \,{\mu }\mathrm{m}$ ablation, by varying laser power level and number of passes. Next, we modeled the hinges using an analytical model as well as creating an Abaqus finite element method, and showed the accuracy of the models by comparing them to the torque produced by eight different hinges, four with a rectangular cross section and four with an elliptic notch cross section. Finally, we manufactured a prototype miniature device to illustrate the usefulness of these nitinol hinges: a piezoelectric actuated robotic wing mechanism, and we characterized its performance.