Topology Optimization of Compliant Mechanism for Laparoscopic Surgery Instruments

Abstract

Compliant mechanisms are flexible single-piece structures that produce the desired movement by going through elastic deformation, which is different from the traditional mechanisms that are joined by rigid bodies. Some of the advantages of compliant mechanisms include reduced friction, wear, noise and the possibility to generate unconventional actuation as well as ease of manufacture and assembly. A critical step in the design of compliant mechanisms is topology optimization for material distribution. It helps designers to extend and fine-tune a design that already has near-optimum material distribution. It involves determining the shape and location of holes of a structure as well and the connectivity of the domain. This study presents a compliant mechanism design for laparoscopic surgery instrument in which a feasible topology (configuration) is evolved to fulfil a prescribed input-output force-displacement relationship. Two different methods are used for this purpose. In the first method, an objective function is formulated to capture the need for compliance by going through the desired deformation (kinematic requirement) and stiffness to resist external loads (structural requirement) once the mechanism adopts the desired configuration. In the second method, the objective function is to minimize the volume fraction given the design constraints as limitation to translation of nodes. The optimization process is implemented in MATLAB and Altair OptiStruct software. The resulting topology is converted into 3-D CAD model followed by Finite Element Analysis to determine the stress and deformations. Some observations and recommendations are noted based on these studies.