Cable-driven pulleyless rolling joint with elastic fixtures for medical applications

Abstract

This dissertation proposes a novel miniature cable-driven joint mechanism, named PREF joint. PREF stands for Pulleyless Rolling with Elastic Fixtures. Pulleys prevent miniaturization of the cable-driven joints and medical instruments using them. A rolling mechanism stabilizes the movement of the pulleyless cable-driven joint, and elastic fixtures guarantee a steady rolling contact with a small size. Because its driving range is quite limited, a bending joint is composed with some of PREF joints. This bending mechanism can be actuated with a small number of actuation cables, and it has a special property of resistance to the buckling-like S-shaped curvature. A small radius of bending curvature and a low tension of the actuation cables are also its great strengths. In this dissertation, fundamental characteristics are analyzed and some design rules are suggested. Using two different types of 1-DOF underacuted bending joint prototypes, various experiments were performed to understand the characteristics. The motion accuracy and payload capacity were measured from various angles to evaluate the efficacy of an improved design that enhances the payload on the distal end. And a new computation model considering friction is suggested to demonstrate the hysteresis motion. Moreover, experiments were performed to measure the bending tendency and the motion accuracy at the unit joint level. Vision based shaped sensing was used to measure every angle of composing unit joints for the evaluation of the efficacy of the proposed joint and its computation model. At the end, this mechanism is applied to develop flexible surgical robot arms for NOTES (Natural Orifice Transluminal Endoscopic Surgery). They are easily exchangeable and maneuverable with 4 or 5 DOF motion. A simple tension controller, which converts between a flexible insertion mode and a rigid operation one. They were verified with laboratory level experiments and animal tests. This innovative joint can be actuated...