  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 Jcm^-2 fluence
with 5 passes for 5 um 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 arc cross-section. Finally, we
manufactured three prototype miniature devices to illustrate the usefulness of
these nitinol hinges: a sample spherical 5-bar mechanism, a sarrus linkage, and
a piezoelectric actuated robotic wing mechanism.
