Design And Experimental Research On The Flexible Joint For Endoscopic Surgery

This article is oriented to the operation requirements of NOTES,and the flexible joint integrated at the distal end of the endoscope has the disadvantages of small motion range,poor constant bending curvature performance,and low loading capacity.Therefore,a flexible joint with variable stiffness modules integrated at the distal end of the colonoscopy has been proposed based on the helical structure and low melting point alloy materials.Furthermore,the endoscope can enter the pathological structure through the natural orifice of the human body,and perform complex operations in a narrow environment.The detailed research contents are described as follows:Firstly,the design and analysis of the colonoscopy are carried out.A rigid-flexible coupling’s flexible joint has been designed based on 3D printing technology,and the structure is mainly composed of multiple helical segments and rigid segments arranged in a staggered manner.The designed flexible joint structure relies on the uniform stress distribution on the helical segment to produce a smooth curved shape.A hollow channel at the center of the flexible joint has been reserved to pass through surgical instruments.Furthermore,a two-section flexible joint that can achieve S-shaped bending is proposed.The design of the driving platform of the flexible joint has been proposed.Secondly,the kinematics and dynamics of the flexible joint are modeled respectively.According to the kinematics model,the working space of single-section and two-section flexible joints were drawn and compared.According to the needs of the actual surgery and the dynamic model,combined with the MATLAB genetic algorithm toolbox,the size parameters of the flexible joint were optimized.Then,in order to solve the defects of insufficient loading capacity and low operation accuracy of the flexible joint during complex surgical operations,a variable stiffness tube combined with a 3D cylindrical micro-channel structure was proposed.The proposed variable stiffness structure includes a double-layer micro-channel tube made of rubber-like materials.Liquid metal is filled in the inner micro-channels,and the outer micro-channels pass water.Finally,prototypes of single-section and two-section flexible joints were processed and a four-degree-of-freedom experimental platform based on a lead screw mechanism was built.Experiments show that the designed flexible joint achieves excellent distal positioning accuracy within the range of [-180°,180°].Meanwhile,the proposed flexible joint can withstand a surgical loading of 5N at any bending angle.Obstacle avoidance and colorectal model experiments were also proposed to prove the great potential of the flexible joint for endoscopic surgery and NOTES.