Design and Optimization of a 3D Printed Distal Flexible Joint for Endoscopic Surgery

This paper presents a flexible joint with excellent motion range, outstanding constant curvature characteristics, tiny hysteresis, and high loading capacity to support distal operation and observation for flexible endoscopy and natural orifice transluminal endoscopic surgery (NOTES). It adopts a rigid-flexible coupling design based on the 3D printing technique and mainly consists of multiple helical segments and rigid segments in a staggered arrangement. This flexible joint relies on the uniform stress distribution on the helical segments to generate a smooth bending shape and is configurated with a central hollow channel to carry surgical instruments instead of the central backbone configuration. Both kinematic modeling and simplified static modeling have been derived. Design optimization has been subsequently conducted to investigate the structural parameters for further performance improvement. Both flexible joints in a single-section and two-section configurations have been utilized for experiments to analyze and validate their performances. The experimental results show that the proposed flexible joints achieve excellent distal end positioning accuracy within [−180°, 180°] with a small distal average positioning error of 2.20% and a tiny hysteresis error of 0.95%. The modeling error between the derived kinematics and experimental results is only 3.8%. Meanwhile, the proposed joint can withstand a large surgical operation loading of 5N. The obstacle avoidance and colorectal phantom experiments have also been performed to demonstrate the great potentials for endoscopic surgery and NOTES.