COMPLIANT MECHANISMS USING SUPERELASTIC NITINOL
Open Access
- Author:
- Liu, Jiening
- Graduate Program:
- Mechanical Engineering
- Degree:
- Master of Science
- Document Type:
- Master Thesis
- Date of Defense:
- November 07, 2012
- Committee Members:
- Mary I Frecker, Thesis Advisor/Co-Advisor
Jason Zachary Moore, Thesis Advisor/Co-Advisor - Keywords:
- compliant mechanism
nitinol
superelastic modelling
NOTES
flapping wing - Abstract:
- NiTiNOL which is a nickel and titanium alloy exhibits the superelastic effect at desired temperature so that it can provide large strain up to 10% under loading. The superelastic property of NiTiNOL could benefit compliant mechanisms which relays on elastic deformation of the material to transfer motion, force or energy. The goal of this research is to explore compliant mechanisms using superelastic NiTiNOL in new or current applications and evaluate the performance of new designed compliant mechanisms with superelastic NiTiNOL. Two applications are investigated in this thesis. First, a device that can provide articulation to surgical tool tips is needed in natural orifice transluminal endoscopy surgery (NOTES). 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 64.8o 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. Second, a contact-aided compliant mechanism, or compliant spine, that was previously developed in our Engineering Design and Optimization Lab at the Pennsylvania State University is redesigned and modeled using superelastic NiTiNOL. The new one-joint compliant spine using superelastic NiTiNOL can reduce 50% of the size compared to Delrin design while not exceeds the weight of Delrin design. The tip deflection and length ratio of NiTiNOL design is about 150% of Delrin design, which means that NiTiNOL could make the compliant spine much smaller thus possibly lighter while still provide large deformation.