| In recent years,compared with traditional rigid needle puncture,the targeted puncture technology using flexible needles can get curved trajectory in minimally invasive surgery,which provides the possibility of obstacle avoidance.Therefore,it increases the safety of surgery and has become an important medical method for the diagnosis and treatment of various organs.However,due to the complex distribution of arterys and organs in human body,the targeted puncture technology using flexible needles faces more challenges.Under the control of non duty cycle,the single curvature characteristic of flexible needle can not meet the needs of targeted puncture with obstacle avoidance.Under the control of duty cycle,the curvature of the flexible needle can be reduced,but it will cause additional damage,and the change of small curvature cannot change the current situation.Therefore,the probe research tends to the active needle steering scheme aiming at realizing controllable deflection,so as to deal with the complex puncture environment and complete the targeted puncture with higher accuracy.In order to improve the safety of puncture,the active needle steering scheme should reduce the damage to the tissue.In order to meet the obstacle avoidance puncture in complex environment,the active needle steering scheme should be able to obtain a wider range and more controllable radius of curvature.In this paper,based on the flexible probe with tubes,the flexible probe guided by the pre-bent needle wire is adopted,and the uncoupled rotary feed mechanism is designed to drive the pre-bent flexible probe,which realizes the independent rotation and feed movement of the pre-bent needle wire relative to the flexible needle tube.The active steering of the flexible needle is divided into two parts:curvature change and direction change,and can be uncoupled controlled.The relationship between the elongation of pre-bent needle wire and the curvature of puncture trajectory is obtained through experiments.An interpolation method based on experimental data is proposed to deal with the problem that flexible needle can obtain different curvature through puncture in different soft tissues.The curvature of puncture arc trajectory can be predicted after six times of puncture,and 31 puncture trajectories with controllable curvature can be obtained.The numerous number of controllable curvature can be obtained in a large curvature range,which is 82.2%better than other active needle steering schemes and exhibits greater curvature controllability.And the additional damage is much less than the tip control scheme.In order to predict the multi-curvature characteristics of the pre-bent flexible probe and reduce the auxiliary experimental process,an Euler-Bernoulli quasi-static model of the pre-bent flexible probe based on the fitting deflection curve is established to carry out simulation experiments.The spring model is used to simulate the coupling process of the probe puncture,the quasi spring coefficients of different tissues can be obtained,and the adaptability of the model to different puncture tissues can be improved.The path planning is based on the multi-curvature feature trajectory model of the pre-bent flexible probe.When the existing random search algorithm is applied to the probe path planning,the path is not optimized enough and the path is not applicable.Therefore,based on the Rapidly-exploring Random Trees star algorithm,the path fitting based on multi curvature feature is added in the pruning optimization process.Continuous optimization is carried out based on the path length to obtain the optimized path suitable for the pre-bent flexible probe.The convergence speed is 8.8%better than the ordinary Rapidly-exploring Random Trees star algorithm,and the path length is 21%better than the fast expanding random tree algorithm.Based on the research of pre-bent flexible probe drive device and path planning,a set of path planning and tracking control system is designed.The appropriate two-dimensional plane is selected in three-dimensional space for plane path planning and tracking control.One of the specific functions is to realize the optimal planning of target obstacle avoidance path by using the optimized Rapidly-exploring Random Trees star algorithm according to the path characteristics of the pre-bent flexible probe.Another function is that the position compilation and speed control of the motor are carried out,and the real-time trajectory is obtained and tracked to improve the accuracy of targeted puncture.The research work of this paper provides the research of active needle scheme based on pre-bent flexible probe,and provides the research basis for its application of targeted puncture. |
