Research On Methods To Enhance Force Feedback Fidelity Of Virtural Surgery

Virtual surgery is an application branch of virtual reality technology.It reappears visual and force information in real surgery through computer and interactive device,which can let surgeons get operation experience of real surgery.Fidelity is not only the basic requirement of virtual reality system,but also the ultimate aim of virtual reality technology.This paper analyzes major factors affecting force fidelity and explores the evaluation methods and criteria of force feedback fidelity in virtual surgery.And this paper takes virtual thoracoscopic cardiac surgery and virtual cardiovascular intervention surgery as the study objects to study the strategies to enhance force feedback fidelity in virtual surgery from the perspective of force feedback control.This paper first introduces evaluation methods of fidelity,including the structure and mode of operation of the force feedback device,dynamical modeling of virtual environment and force rendering.Then it explores evaluation methods of force feedback fidelity from three aspects: the quantitative index requirements of different operation types of force perception models to fidelity evaluation,evaluation method of device transparency and force feedback fidelity to the performance requirements of the actuator,and putting up the evaluation methods and indexes of force feedback fidelity.According to the above analysis,the paper evaluates the force feedback control effects of virtual thoracoscopic cardiac surgery and virtual cardiovascular intervention surgery.In rigid force feedback interaction device,friction and gravity would affect transparency of the device;while inaccurate modeling,variable parameter,slip of the linear drive and other factors would affect the force feedback control accuracy,it puts forward requirements to system robustness.This paper uses sliding mode control to eliminate parameter variety,inaccurate modeling and other factors to improve system robustness,and designs disturbance observer to eliminate gravity inaccuracy to improve device transparency,which can reduce the control error angle,ease sliding mode switch control pressure and suppress chattering.Then,the paper evaluates the enhancement of force feedback fidelity.The key issue of virtual cardiovascular intervention surgery is to simulate feedback force of human hands brought by multiple point collision of the guide wire in the bifurcation of the blood vessel.This study firstly uses a glass vessel to simulate the collision process of guide wire in the vessel,and measures the force feedback of the human hand in real-time to buildthe virtual environment.Then it analyzes force response model of guide wire in the pipeline of force feedback device and uses Adams software to simulate the collision and stress process of guide wire in the blood vessel.Through numerical simulation,the collision force data of the guide wire in the real vessel is obtained.By changing the length from guide wire to handheld terminal in force feedback device and the length from front-end of guide wire to handheld terminal,the paper analyzes the influence of the length variety of the guide wire on its dynamic characteristics,which is the reference to the design of force feedback device.Force involved in cardiovascular intervention surgery is low,easily affected by the motion and friction of the actuator and hand tremor,which puts up the requirement for system robustness.In this paper,the design of terminal sliding mode controller is designed to improve the robustness and convergence of the force feedback control in virtual cardiovascular interventional surgery.With low-pass filter and the controller were softened,it can suppress inaccurate modeling and system chattering caused by measurement noise.This research studies force change of two degrees of freedom by push and revolve when guide wire enters into vascular branches,and evaluates the effects that used control method improving fidelity of force feedback from three aspects: the force feedback control error,the environmental equivalent stiffness error and the real-time performance of the force information.