Optimization Design And Reverse Drive Of Remote Centre Mechanism For Minimally Invasive Surgery

The minimally invasive surgical robot applies robot technology to the field of minimally invasive surgery,not only effectively utilizing the strengths of robot technology,but also making up for the many shortcomings of traditional minimally invasive surgery.However,it still has some shortcomings,such as collision problems during multi-arm coordinated movement and lack of flexibility in preoperative reverse drive.This article carries out optimization design and reverse drive control research on the remote center mechanism of the minimally invasive surgical robot to address these issues.The minimally invasive surgical robot requires multiple operating arms to coordinate work from the console.In order to reduce the collision probability of mechanical arm and improve the flexibility of operation,a parallelogram mechanism with a redundant rotational degree of freedom is proposed.First,the forward kinematics model of the operating arm(including the parallelogram remote center mechanism with redundant degrees of freedom)is established through an improved D-H parameter method.Then,the inverse kinematics of the intraoperative mechanism(including the remote center mechanism and surgical instruments)are solved using an analytical method.Next,the correctness of the forward and inverse kinematics models of the operating arm is verified through a hybrid simulation of Simulink and Sim Mechanics toolboxes.Finally,based on the previous work,a multi-objective optimization model with four optimization objective functions(kinematics,stiffness,compactness,and dynamic performance indicators)and three optimization variables(two link lengths and joint angles)is proposed.The optimal values are obtained through multi-objective genetic algorithm(NSGA-II)optimization,and a remote center mechanism prototype is built based on the optimal values.Based on the optimal size parameters of the remote center mechanism obtained from the previous work,an experimental platform with a redundant degree of freedom remote center mechanism is constructed.Prior to the surgery,the operator needs to adjust the position of the remote center mechanism to an ideal state.However,the process of reverse driving is very difficult due to the influence of the remote center mechanism’s own gravity and joint resistance.Therefore,a feedforward resistance compensation reverse driving control method is proposed to assist with preoperative adjustment of the remote center mechanism.First,a dynamic model is constructed using Newton-Euler method and Coulomb viscous friction force.The problem of high-order terms in the model is solved using the translation axis theorem,and linearization is achieved.The coupling relationship between various dynamic parameters is analyzed using QR decomposition method to obtain the minimum parameter set and full-rank observation matrix of the dynamics.Then,to obtain better reverse driving effect,the dynamic parameters of the remote center mechanism are identified using both direct and indirect methods.The direct method uses the optimized finite Fourier series as the excitation trajectory,while the indirect method uses a special symmetric trajectory to excite gravity and friction parameters.Finally,after processing the experimental data,two sets of dynamic parameters are fitted using an improved least squares method.Random complex trajectories are used to verify the results and it is found that the direct method identification results have good tracking performance under most conditions except for certain errors when the torque has sudden fluctuations.The indirect method can predict the basic trend of the torque when predicting any complex trajectory,but the deviation is large.Therefore,the dynamic parameter model obtained from the direct method identification is used as the feedforward resistance model for reverse driving.To verify the effectiveness of the reverse drive algorithm,reverse drive experiments were conducted.Firstly,the resistance model was constructed based on the parameter identification results of the direct and indirect methods.Secondly,the resistance model was used as feedforward to real-time compensate for the joint torque in torque mode.Then,under different pushing speeds,the pushing force required for forward and reverse joint motion was respectively collected by a thin film pressure sensor.The experimental results show that although the reverse drive control based on feedforward resistance torque compensation identified by the indirect method can achieve significant labor-saving effects,it has shaking and cannot guarantee the smoothness and stability of reverse drive.The reverse drive control based on feedforward resistance torque compensation identified by the indirect method has a good torque compensation effect.The torque applied at the torque compensation peak only accounts for one-sixth of the original required torque.The adjustment posture process does not shake and achieves good reverse drive effect,which verifies the effectiveness of reverse drive.