Study On The Dynamics Of Surgical Instruments For Robot-assisted Minimally Invasive Surgery Based On Steel Cable-driven Transmission

Minimally invasive surgery is widely used in surgical operations due to its advantages of small wounds to the human body and quick recovery time after surgery.With the rapid development of robotics technology,robot-assisted minimally invasive surgery(RMIS)came into being by combining robotic technology with assisted minimally invasive surgery.The end effector of the robot-assisted minimally invasive surgery system is a surgical instrument,and multiple free surgical instruments make the doctor more flexible during surgery.In order to meet the requirements of minimally invasive surgery,the axial length of surgical instruments is generally no less than400 mm,and the radial dimension is generally no more than 10 mm.At present,most surgical instruments are driven by steel wires.The application of wire transmission is beneficial to realize the lightweight design,improve the transmission accuracy,and effectively improve the function and performance of surgical instruments.However,its special layout,the characteristics of the flexible body of the wire rope under load,the loss of tension during the transmission process,the high safety and high accuracy requirements of the surgical instruments bring many practical application problems.Therefore,this article studies the relationship between movement and force of the wire drive system of surgical instruments to ensure the accuracy of the movement of the end effector of surgical instruments.The specific research content is as follows:Based on the requirements of working environment,working space and transmission accuracy of surgical instruments in the human body,by comparing several long-distance transmission methods and wire transmission configurations,it is determined that the transmission system of surgical instruments is a wire transmission system with an open loop configuration.The shape and size of the pulley groove in the wire transmission system and the mechanism of the deflection angle of the wire rope passing through the pulley are analyzed.Based on the minimum wear of the wire rope,suggestions for the selection of the pulley groove shape and size and the deflection angle of the pulley are given.Finally,through the simulation modeling of the wire transmission system,the relationship between the preload force and the friction force of the system is analyzed,and the selection of the preload force is given.The tension ratio of the wire rope before and after passing the guide wheel was studied.According to the structural characteristics of surgical instruments,the ratio of the radius of the guide wheel to the wire rope is introduced to characterize the bending stiffness of the wire rope.Through the force analysis of the contact area and non-contact area between the wire rope and the guide wheel,the calculation formula of the tension ratio before and after the wire rope is guided by the guide wheel is obtained.The design experiment verifies that the tension calculated by using the tension ratio formula is in good agreement with the tension measured by the force sensor.Finally,according to the calculation formula of the obtained tension ratio,the influence of the structural parameters of the surgical instrument(radius ratio,wire rope diameter,wrap angle and friction coefficient)on the change of the wire rope tension is analyzed,which can provide theoretical guidance for the structural design of surgical instruments.In order to improve the safety and accuracy of surgical instruments,based on the tension ratio formula obtained in the previous chapter,combined with the structure of the surgical instrument wire transmission system,based on the elastic Hooke’s law,the tension-displacement model is established.The model can calculate the output displacement and output torque of the small paw at the end of the surgical instrument,thereby obtaining the hysteresis angle of the transmission system.Finally,a control strategy for the wire drive system is written,which can be used to compensate for the hysteresis error of the transmission system and improve the transmission accuracy.The creep characteristics of the wire rope in the wire drive system of surgical instruments have been studied.Based on the viscoelastic and linear characteristics of the wire rope,through the analysis of the three mechanical models of the linear viscoelastic material Maxwell model,Kelvin model and Burgers model,a new fiveelement model is proposed on the basis of the Burgers model,and the robot is carried out according to the surgical instruments.Assist the different working stages of the wire drive system in minimally invasive surgery,and give the wire rope creep model for each stage.Design experiments to measure the creep of the wire rope,and determine the unknown parameters in the model.