Compliant Articulation Structure Using Superelastic NiTiNOL

A device that can provide articulation to surgical tool tips is needed in natural orifice transluminal endoscopy surgery (NOTES). In this paper, we propose a compliant articulation structure that uses superelastic NiTiNOL to achieve a large deflection angle and force in a compact size. Six geometric parameters are used to define this structure, and constraints based on the fabrication process are imposed. Using finite element analysis, a family of designs is evaluated in terms of the free deflection angle and blocked force. The same family of designs is evaluated for both NiTiNOL and stainless steel. It can be seen that significant benefits are observed when using NiTiNOL compared to 316 stainless steel; a maximum free deflection angle of 64.8° and maximum blocked force of 24.7 N are predicted. The designs are refined to avoid stress concentrations, and design guidelines are recommended. The meso-scale articulation structure is fabricated using both a Coherent Avia Q-switched, 355 nm laser and a Myachi Unitek 200 W single mode pulsed fiber laser with active water cooling. Select fabricated structures are then tested to validate the finite element models.