A Braided Skeleton Surgical Manipulator with Tunable Diameter

In natural orifice transluminal endoscopic surgery (NOTES), the manipulator design is a great challenge because it needs to meet different requirements for stiffness and size during the whole process. In our recent work, a braid-based manipulator has been proposed, which behaves as a stand-alone braid to fold and deploy in normal state, but turns to be rigid when a negative pressure is applied. It exhibits a stiffness ratio of 6.85 and diameter variability, but the control of the tunable diameter was not declared. In this paper, a bi-directional tunable-diameter mechanism for the braided skeleton is proposed, which uses shape memory alloy (SMA) braided fibers to deploy to a large profile state by electric heating, and rubber bands to force the skeleton back to the slim state when cooled. The mechanism is validated with a physical model, which can achieve a ratio of 1.46 between the maximum and minimum diameters. A theoretical model is also established based on the open-coiled theory, and parametric analysis is conducted to further detail the mechanism. The results show the promise of the mechanism in braided manipulator.