Toward Robotic Puncture Based On Flexible Bevel-Tip Needle Insertion

External pressure gas bearings have the advantages of high precision,low friction,small thermal deformation,long life,no pollution,etc.They have been widely used in aviation,semiconductor,textile,measuring instruments and other fields.On the basis of summarizing the research results at home and abroad,this paper considers that minimally invasive surgery has the characteristics of small trauma,rapid recovery and low risk of treatment,and is a commonly used treatment method in clinic.Percutaneous puncture technique is an important method in minimally invasive.As one of the main methods to diagnose and treat the early-stage cancer,percutaneous puncture technique have great application value in biopsy,melting,short-range radiation therapy and targeted injection.The rigid needle is frequently used in the conventional percutaneous puncture operation.Since the rigid needle can only move rectilinearly,it is difficult to meet the obstacle avoidance requirement during puncturing.To solve this problem,researchers proposed flexible needle with bevel tip,whose puncturing path is a curve with constant radius caused by the yawing force from the tissue.Therefore,various intricacy path can be controlled via changing the direction of the bevel during the puncturing,which makes the operation touched on the important issues can be carried out.The bevel-tip flexible needle is not large-scale application because it is restricted by some technical issues such as low accuracy of rotational motion,no real-time information for the puncturing needle,simple and rough control method.This project attempt addressing these issues by reconsidering driving,sensing,and controlling of the percutaneous puncture system.We will deeply research the force model,innovative design of the structure,trajectory planning,real-time supervision of the needle path,and needle-issue control.Regarding to the force model,the influence of the path curve and the friction between the needle body and issue is analyzed.The mathematic model of the friction and the incision during the puncturing is established,which is benefit reduce the errors of the trajectory prediction,furthermore,the axial force for the needle propelling can be obtained via the model.Currently,all the bevel-tip flexible needle is controlled applying rotating the base of the needle to change the direction of the bevel.However,since the friction between the needle and the issue is exiting and the needle has super-elastic character,deviation between the base of the needle and the tip of the needle is large,which will cause trajectory errors.To solve this problem,the tip-separated flexible needle based on piezo actuation is proposed,based on which the kinematics model is established and.Furthermore,the trajectory plan of the flexible needle in the homogeneous medium is studied.The “needled control” with large radius curve trajectory will cause issue tearing.In addition,the trajectory plan can not realize needle state feedback.Inspiring by the issue control in the rigid needle puncture technique,the “needle-issue” hybrid control method based on the flexible needle is proposed.Through the hybrid control method,the target point can be moved to a relative simple puncture trajectory,thus the operation will become simple and the injury caused by the needle will be reduce.Although the real-time information of the needle can be captured via the conventional medical image equipment,its accuracy is coarse and it is difficult to be integrated together.This paper focus on the study of the trajectory character of the needle in the inhomogeneous tissue,and proposed a novel real-time system to rebuild the curve of the puncturing needle based on the strain gage,based on which the arrangement strategy of the sensing unit is studied to give consideration to both the cost and the accuracy.Considering that human tissue has not priori knowledge,a control arithmetic for the tissue control based on the uncalibrated visual servo is analyzed.Finally,an experimental setup is built according the theory mentioned above.Firstly,the influence of the angle of the bevel tip and the radius of the bending needle and the influence of the bending trajectory of the needle in inhomogeneous tissue are verified,based on which two key parameters was obtained,i.e.,the friction on unit length of the needle and the optimal stiffness value of the spring.Furthermore,the feasibility of the tip-separated flexible needle based on piezo actuation is validated,whose driven signal and rotational performance is deeply studied.In addition,the rebuilding needle curve applying strain gage is verified via the experiment study,where the planar single curve,planar double curve and the space curve is studied.Finally,the control of the tissue is realized aimed at specific task by trajectory optimization.The deformation of the tissue is achieved in the experiment study.