Experiment And Analysis Of Variable Stiffness Theory For LESS Instrument

With the development of minimally invasive surgery,the novel single-site minimally invasive surgical skills are getting mature gradually and widely applied in surgical robots,especially for urinary surgeries.Compared with robotic surgery with multiple ports,the single-port surgery has the advantages of small injury and better recovery after operation.However,there still exist practical problems in laparoendoscopic single-site surgery(LESS)and LESS robot operation,including easy collisions between the instruments and insufficient control power.Thus,in this paper,based on the stiffness and flexibility issues of the LESS robot and LESS surgery,with the design concept of material-structure integration,the author proposes a novel structure with tunable-stiffness through integration of new liquid metal materials and the relevant instrument structure.This structure is successfully applied in LESS surgery instrument.The main work of this study is as follows.Firstly,after analyzing the related parameters of the existing surgery robots,a solution based on the mechanism of variable stiffness is proposed to solve the problems of collision and lack of operating force.Through analyzing the mechanism of tunable-stiffness,the author chooses to change the phase of the materials,namely the In-Sn alloy and the polyethylene glycol,to do the research.The microscopic metallographic structure of the materials is observed,and then their physical and mechanical properties in liquid state are tested.A preliminary verification experiment using the corrugated pipe has been carried out to prove the validity of this solution.Secondly,the structure of the LESS instruments is designed according to the characteristics of the materials.The matrix theory is used to work out the solution of forward kinematics and inverse kinematics of the proposed structure,after which its motion space is analyzed.After that,the Jacobi transform matrix is applied to analyze its mechanism singularity.At the same time,the problems in actuation and errors in the control wire are analyzed according to the characteristics of the structure.At last,the heat exchange in the instrument is analyzed,and on this basis,the flexibility test and load test of the constructed structure are carried out.Finally,the integrated structure suitable for the polyethylene glycol is confirmed through multi-factor test experiment.