Analysis of Twist Deformation in Wire-driven Continuum Surgical Robot

Wire-driven continuum surgical robots are attracting significant interest in minimally invasive surgeries owing to their high dexterity level and miniaturization. However, twist deformation due to the external force at the end effector decreases the accuracy and controllability of these robots. In this study, we analyze the two factors responsible for twist deformation and propose models incorporating these factors. In our analyses, we first consider twist deformation due to the elastic deformation of the wire; when a tensioned wire is subjected to normal force, a sag effect occurs, which results in twist deformation in the robot. We analyze this sag effect statically considering the material properties of the wire. We also analyze the twist deformation due to the clearance between the wire and hole boundary in the spacer of the robot. Clearance is required in a wire-driven continuum robot to realize bending motion; however, this is considered one of the main causes of twist deformation and is referred to as the clearance effect. Subsequently, we propose sag and clearance effect models that quantitatively predict the twist deformation. The results of the experiments conducted to verify the accuracy of the proposed models, including a payload test using a conventional continuum robot comprising spherical joints, indicate that the accuracy of the proposed models is 95%.