Optimal Design and Fabrication of Narrow-Gauge Compliant Forceps

This paper describes a multidisciplinary project focused on developing design and fabrication methods for narrow-gauge compliant mechanisms expected to be useful in advanced minimally invasive surgery. In this paper, three aspects of the project are discussed: meso-scale fabrication, compliant mechanism design, and experimental determination of mechanical properties and forceps performance. The selected manufacturing method is a lost mold rapid infiltration forming process that is being developed at Penn State University. The process is capable of producing hundreds of freestanding metallic and ceramic parts with feature sizes ranging from sub-10 μm to approximately 300 μm. To fulfill surgical and manufacturing requirements, a contact-aided compliant mechanism design is proposed. A finite element analysis solution, used to evaluate large deformation and contact, is implemented into an optimization routine to maximize tool performance. A case study demonstrates the design and manufacturing processes for a 1 mm diameter austenitic (300 series) stainless steel forceps. Due to manufacturing variables that affect grain size and particle adhesion, the strength of the fabricated parts are expected to vary from the bulk material properties. Therefore, fabricated parts are experimentally tested to determine accurate material properties. Three point bend tests reveal yield strengths between 603 and 677 MPa. Results from the design optimization routine show that material strengths within this range require large instrument aspect ratios between 40 and 50 with anticipated blocked forces as high as 1.5 N. An initial prototype is assembled and tested to compare experimental and theoretical tool performance. Good agreement between the computational and experimental data confirms the efficacy of the processes used to develop a meso-scale contact-aided compliant forceps.