Research On Controllable Stiffness Of Continuum Robot For Minimally Invasive Surgery

Compared with traditional porous minimally invasive surgery,single port surgery and natural orifice translumenal endoscopic surgery have the advantages of less iatrogenic trauma,less pain and shorter postoperative recovery time,so they are more favored by patients and doctors.Robot-assisted single port surgery and natural orifice translumenal endoscopic surgery can effectively reduce the labor intensity of doctors and improve the accuracy of surgery.Related technologies are gradually becoming a research hotspot in the field of robotics.The limited single-port approach of this kind of robot-assisted minimally invasive surgery requires the minimally invasive surgical robot to integrate more freedom of movement in a limited external size and provide sufficient operation accuracy and operation force in a more limited operating space.The contradiction between the need for good flexibility of the robot due to the narrow and multi-curved approach and the need for stiffness of the robot due to surgical operation is an important problem that restricts the wide application of minimally invasive surgical robots.In order to achieve stable,accurate and safe single port surgery invasive surgery and natural orifice translumenal endoscopic surgery,a minimally invasive surgical robot with variable stiffness continuum structure was developed in this paper to solve the core problems of natural luminal stenosis and multicurvature and insufficient freedom and stiffness of flexible surgical instruments.Based on the analysis of the structure and physiological characteristics of human digestive tract,the configuration requirements and design requirements of the minimally invasive surgery variable stiffness continuum robot are studied.The characteristics and surgical applicability of different variable stiffness methods and driving modes of continuum robot were analyzed and compared,and a flexible variable stiffness robot structure based on cascade hemispherical cylinder was proposed.Compared with the cascaded ring structure,the flexible variable stiffness robot structure has the advantages of large axial stiffness and simple variable stiffness.At the same time,the single tensioning rope of the central channel is used to control the stiffness,and the four driving ropes of the surrounding channel are used to control the bending motion,thus the separation of motion control and stiffness control is realized.On this basis,the motion constraint conditions are analyzed,and the motion capability of robot matrix is analyzed and the scale optimization design is made according to the motion capability requirements.Then,according to the medical and mechanical properties of minimally invasive surgery,the operating forces of various surgical actions in minimally invasive surgery were analyzed,and the stiffness requirements of the variable stiffness robot were obtained.Based on the proposed variable stiffness joint structure,the stiffness composition of the variable stiffness continuum surgical robot was analyzed,and a variable stiffness control method of the continuum robot was proposed based on the principle of single rope force locking,which could realize the continuous stiffness control of the robot.The intrinsic stiffness of the variable stiffness joint was analyzed according to the deformation characteristics of the driving rope,the variable stiffness model was established based on the mechanical balance equation,and the quantitative model between the tension force and stiffness was established,and the variable stiffness capability of the variable stiffness continuum robot was deduced.Based on the structural characteristics,the pressure transfer efficiency of joints with variable stiffness under non-ideal arc curve was analyzed.Based on Workbench,the finite element simulation analysis of the variable stiffness characteristics of the continuum robot was carried out to verify the variable stiffness characteristics of the continuum robot.Secondly,aiming at the precise guidance requirements of the robot in cruise mode and the requirement of surgical action reproduction in surgical mode,the kinematic model of the minimally invasive surgery continuum robot was constructed by analyzing the mapping relationship among drive space,joint space and Cartesian space based on d-H method and constant curvature hypothesis.Based on Monte Carlo method and Matlab programming,the space of robot movement is simulated and analyzed.The bending motion of the variable stiffness continuum robot is simulated and analyzed by Matlab.Based on the kinematic model,the master-slave control system of the minimally invasive surgery continuum robot was designed by using CAN bus communication.In the Visual Studio environment,using C#programming language to write the control program of the system.Finally,based on the proposed variable stiffness continuum structure and control system,the experimental system of the robot principle prototype for minimally invasive surgery variable stiffness continuum was established.Experiments on single-joint bending ability and double-joint bending motion control of the variable stiffness continuum robot are carried out.The experiments show that the robot has good bending ability and can meet the requirements of the robot in the narrow and multi-curved natural cavity.Meanwhile,the correctness of the proposed kinematic model is verified.The experiments of variable stiffness and maximum static load verify the correctness of the stiffness model and the good load capacity of the surgical robot.Gastric stromal tumor resection was simulated to verify the feasibility of the proposed minimally invasive surgical continuum robot.