| Needle puncture surgery is mainly used in biopsy,local injection and radioactive particle implantation because of its many advantages such as low trauma,fast recovery and high precision.However,the passive oblique tip flexible needle has a relatively fixed puncture radius,which makes it difficult to achieve variable curvature puncture.The active flexible needle proposed in this thesis can change the tip deflection angle by flexure transmission,and then change the puncture radius of the flexible needle.In this thesis,we first study the relationship between preload force and flex cable transmission efficiency,establish the flex cable tension ratio mechanics model,and further establish the tension transmission and displacement transmission model of the flex cable to realize the accurate control of the active flexible needle tip movement.Based on the requirements of the working environment of the active flexible needle,the long-distance transmission method is analyzed,and the flexible cable is determined as the driving method of the active flexible needle.Based on the requirements of the needle tip deflection,the configuration of the flexible cable drive system is analyzed,and a closed-loop transmission structure with two drive units for the same direction transmission is determined.The mechanical characteristics of the flex cable and the pulley are analyzed,and the radius of the flex cable and the shape of the pulley are selected.Simulation analysis of the flex cable drive,based on the relationship between the flex cable drive and the friction force,the relationship between the preload force and the accuracy of the flexible needle tip deflection is obtained.Analyze the force of flex cable between pulleys,consider the radius ratio of flex cable to pulley,bending stiffness of flex cable and friction coefficient,study the mechanical characteristics of flex cable,and derive the mechanical model of tension ratio of flex cable at any position in the pulley.The geometric structure relationship between the position of the flex cable and the contact with the side wall of the pulley is studied at the rope exit end of the pulley,and the maximum deflection angle of the flex cable at the rope exit end is determined,and the relationship between the deflection angle of the flex cable and the deflection of the needle tip is derived.Analyze the force during the motion of the flex cable and the pulley,and get the friction loss between the flex cable in the pulley according to Hooke’s law,and then get the output tension of the flex cable in the tight side and the loose side respectively.The elastic extension of the flexible cable in the pulley is analyzed,and the relationship between the elastic extension of the flexible cable and the rotation angle of the active and passive pulleys is obtained.Analyze the driving characteristics of the flexible cable between pulleys,and establish the tension transmission and displacement transfer model of the flexible cable based on the established tension ratio mechanics model,and then obtain the end needle tip deflection displacement and output moment.The experimental platform of the puncture and transmission characteristics of the flexible needle is built,and the transmission characteristics and puncture experiments of the active flexible needle are completed.The experimental results show that the absolute error of tension is within 1.1N,which verifies the accuracy of the tension ratio mechanics model;the average error of the tip deflection angle is 1.69°,and the root mean square error is 1.85°,which verifies the accuracy of the transmission characteristics model;furthermore,the bending characteristics of the active flexible needle are verified by the experiments of the bionic tissue puncture of the flexible needle with different tip deflection angles. |
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