Research On Control Of Slave System Of Minimally Invasive Surgical Robot

Compared with traditional minimally invasive surgery(MIS),robotic MIS has more delicate operation,clearer vision and more comfortable operation process.However,there are still some chal enges in the surgical process,such as the inflexibility of preoperative manual adjusting the slave manipulator,asynchronism of master-slave operation and the frequent manipulation of laparoscopy during surgical operation,the joint flexibility of robotic manipulator and the lack of haptic interaction(including tactual sensation and force sensation)of the surgical instruments,which prolongs the operation time,leads to the decline of the quality of surgery and the increase of the cost of surgery.In view of these problems in robotic minimally invasive surgery,the studies on the control of slave manipulator system of MIS robot are carred on in this paper.In the preoperative setting stage,the internal resistance of robotic joints makes it difficult for doctors to insert surgical instruments mounted on the slave manipulator into the patient's body and adjust the position and posture.To this end,it is necessary to study a backdrivability control method is proposed to improve the flexibility and accuracy of the preoperative manual adjustment of slave manipulator.Firstly,the flexible joint dynamic model of the 3-degree of freedom remote center motion(RCM)mechanisms of slave manipulator is deduced and its dynamic parameters are identified.Next,a new static friction compensation method is proposed to compensate the static friction of low-speed moving joints.And a real-time estimation method of joint angular velocity and acceleration based on Kalman filter is developed.Finally,the output torque of the joint motor is controlled to balance the internally generated gravity,friction and inertial force experienced during the positioning and orientating,so as to enhance the backdrivable performance of RCM mechanisms.In the master-slave operation stage of robotic MIS,doctors frequently switch control objects to adjust the position and posture of laparoscopy(in order to obtain better surgical vision)will distract doctor's attention,resulting in the decline of the quality of laparoscopic surgery.Therefore,it is necessary to study a method of laparoscopic automatic follow-up motion planning of MIS robot to achieve rapid and smooth movement of laparoscopic follow-up surgical instruments.Firstly,the common trajectory planning methods for the slave manipulators are analyzed.Next,by analyzing the adjusting conditions of the position and posture of the laparoscope and the requirements of the adjusted visual field,the reference path points and the limited path points of the laparoscopic end point in the task space are determined.The corresponding path points of the driving joint of laparoscopic manipulator in the joint space are obtained by using kinematics model,and then the joint space trajectory planning and optimization(based on time-smoothness optimization)are carried out by using Chebyshev pseudospectral method(CPM)and sequential quadratic programming method.Finally,the simulation results show that CPM has good trajectory planning performance and meets the performance requirements of simultaneous on-line trajectory planning and optimization for multiple joints of slave manipulators.In order to achieve delicate surgical operations such as cutting,suturing and knotting,it is necessary to design a control algorithm that considers joint flexibility,high computational efficiency,and can handle variable constraints to achieve precise position control and vibration suppression for the flexible joint of RCM mechanisms.Firstly,the linearization of the flexible-joint dynamic model is realized by gravity compensation and variable transformation,and its corresponding state space model and extended state space model are established.Secondly,the double closed-loop predictive functional control algorithm based the extended state space model and the cascaded predictive functional control and proportional integral control(PFC-PI)algorithm based the state space model are designed respectively,and the stability of the PFC-PI algorithm is analyzed.Finally,the comparative simulations have verified that the PFC-PI algorithm has better dynamic control performance and vibration suppression effect.Due to the transmission backlash and the lack of force feedback information,it is difficult to accurately control the position and force of the cable-driven surgical instruments.Therefore,it is necessary to study a force/position transmission model based on the cable-pulley transmission to accurately estimate the transmission backlash and output torque of the cable-pulley system of the surgical instruments.Firstly,the transmission structure and force/position transmission characteristics of the cable-pulley system are analyzed,the force/position transmission model of the closed-loop cable-pulley system is established,and the calculation formulas of the transmission backlash and output torque of the end effector of the cable-pulley system during the gripping operation are derived.Then,a PID control algorithm based on feedforward backlash compensation and force saturation limitation is designed to realize safe and accurate position control of the cable-pulley system.Finally,the accuracy of the established model has been verified by the gripping operation of the end effector of the cable-pulley system.Research on the control experiments of slave system of MIS robot is carried out.The validity of the proposed backdrivability control method has been verified by manual adjustment experiments of RCM mechanisms and animal experiments;the effectiveness of the proposed laparoscopic automatic follow-up motion planning method has been verified by laparoscopic automatic follow-up motion experiments;the dynamic control performance and vibration suppression effect of the proposed PFC-PI control algorithm have been verified by the position control experiment of the joint of RCM mechanisms;the correctness of the established cable-pulley transmission model of the surgical instruments has been verified by the gripping operation experiments.