Design Of The End-effector Arm Of Minimally Invasive Surgical Robots And Cable-driven Transmission Characteristics

With the prospect of future surgery,robot-assisted minimally invasive surgery has become one of the fastest-growing fields in modern surgery.Minimally invasive surgical robotics,as a technological solution for robotassisted minimally invasive surgery,has become one of the robot products that truly achieve global clinical applications in medical surgical robots.Nevertheless,there are problems with the complex structure,limited spatial operation ability,and low control accuracy of the cable-driven system of minimally invasive surgical robots that seriously restrict their development.This article conducts detailed research on the above issues.Firstly,a new 6-DOF cable-driven terminal manipulator prototype was developed.The structural layout,winding scheme,and transmission mode of the manipulator were analyzed theoretically,and the coupling phenomenon ofj oint motion of the cable-driven system was analyzed.A slider decoupling scheme was designed based on the structural principle,and the influence of the front joint motion on the length of the rear joint drive cable was eliminated by the quantitative decoupling relationship.The parameter selection of the driving unit is complete to ensure that the maximum clamping force of the prototype is greater than 12N.The prototype meets the requirement for 6-DOF operation.Secondly,the kinematic characteristics and workspace capabilities of the cable-driven end manipulator are analyzed to verify its operational capability and flexibility.The forward kinematics model of the manipulator based on the improved D-H method is established,and the motion simulation based on the URDF model in the Matlab environment verifies the accuracy of the forward kinematics equation.Based on the Monte Carlo method,the workspace of the manipulator was simulated,and the joint workspace of the the three manipulator was solved as 182 × 134 × 75 mm.By comparing the target workspace of common minimally invasive abdominal surgery robots,it is proven that the end manipulator fully meets the workspace requirements of minimally invasive abdominal surgery.Thirdly,the tendon sheath system(a structural form of the cable-driven system)with a series of nonlinear problems such as hysteresis,time delay,and a dead zone is studied.A dynamic Coulomb friction model with time-varying characteristics is proposed,and atime-varying single tendon sheath transmission model(RT model)with the characteristics of flexible manipulators is established by combining kinematics and the constant curvature assumption.A force and position control algorithm without remote feedback has been proposed to solve the problem of the inability to form closed-loop control for terminal surgical instruments.The influence of velocity on the tendon sheath system was studied,and a tendon sheath transfer model with velocity characteristics(RV model)was proposed.The experimental platform of the flexible manipulator and tendon sheath system is established to provide an experimental basis for exploring the power transmission loss of the tendon sheath system.Finally,through the force and position compensation control experiment,the transmission characteristics of the cable-driven system were analyzed,and the differences in force and displacement transmission characteristics between static and dynamic cable-driven systems were explored.The results indicate that the correlation coefficient(R~2)between force and position transmission reaches at least 96.57%and 99.16%,demonstrating the effectiveness of the time-varying tendon sheath model in compensating for dynamic force and position loss of the tendon sheath.Through the same stroke differential velocity experiment,the hysteresis characteristics of the force profile hysteresis curve under differential velocity were analyzed,and the accuracy of the tendon sheath transmission model with velocity characteristics was verified.Through the positioning and tracking experiment of the flexible arm,the yawing motion of the end manipulator is simulated.The results show that the positioning accuracy of the flexible arm is improved by 15.1%,which proves that the time-varying tendon sheath model is of great significance in improving the actual control accuracy of the cable-driven end manipulator.