Mechanical design and finite element analysis of multi-degree-of-freedom transmission for single incision laparoscopic surgery

Instruments with multiple degree-of-freedom (DOF) distal joints may facilitate laparoscopic surgery significantly, but the articulating driving mechanism presents many design challenges. The aim of this study is to investigate the ergonomic requirements for single incision laparoscopic surgery (SILS) and design a flexible driving mechanism which can be used for single port laparoscopic surgery. In order to realize large angulations, transmit force and torque, the flexible driving component will subject to very complex mechanical stresses and strains. Material specifications and particular model parameters have been identified. Superelastic nitinol alloy has been tested, and one structural model has been optimized to realize the clinical requirements. Finite element analysis has been employed to minimize the high stresses during stretching, bending and twisting, while providing adequate transmission force or torque. The evaluation results reveal that the maximum equivalent stresses and strains of the flexible driving component are kept within the material´s safe range. Based on the mechanism, various instruments like tissue forceps and graspers can be very developed for single port surgery.