Femtosecond laser fabricated nitinol living hinges for millimeter-sized robots

TL;DR

This paper demonstrates femtosecond laser micromachining to create nitinol living hinges with arbitrary cross-sections, enabling the development of miniature robotic mechanisms with preserved superelastic properties.

Contribution

It introduces a precise laser fabrication process for nitinol hinges and validates analytical and finite element models against experimental torque data.

Findings

Laser parameters for nitinol hinge fabrication identified

Models accurately predict hinge torque behavior

Prototype miniature robots successfully demonstrate hinge functionality

Abstract

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.