A Novel Asymmetric Pneumatic Soft-Surgical Endoscope Design with Laminar Jamming

Soft pneumatic endoscopes developed for Minimally Invasive Surgeries (MIS) are designed upright which means that the starting positions straight. As the internal chambers are pressurized the endoscopic module starts bending. The relation between the pneumatic pressure and bending is nonlinear as the air needs first to fill the chamber before bending, and additionally frictional interaction to the sheath adds more to this start-up transient behaviour. This highly nonlinear behaviour severely limits the actuator sensitivity, accuracy, and repeatability near the endoscope's center of operating range. This paper introduces a novel pre-bent MR-compatible soft-surgical pneumatic endoscope design aimed to improve the bending performance of soft endoscopes by shifting the start-up transient out of the operating range. The pre-bent design of 12 mm diameter consists of an actuation and stiffening chamber, inextensible shell reinforcement with a backbone and rings, and external sheathing. The design parameters that include cross-sectional area, number of rings and backbone width are determined using Finite Element (FE) analysis. The motion profile of the fabricated endoscope, determined via experimentation, shows a successful shift of the start-up transient while the jamming structure increases the stiffness of the endoscope but limits the bending range. Further design developments of the endoscope are required for clinical application.