Research On Dynamic Error Modeling And Control Strategy Of Medical Flexible Manipulator End

The medical robotic arm is an important equipment in the heavy ion cancer treatment system.In addition to supporting the patient,its end position error directly affects the accuracy of the focus on the beam.Controlling the end error of the robotic arm is one of the key points to achieve precise radiotherapy.This thesis explore the impact of its end space dynamic error on the accuracy of tumor positioning based on the research object—medical robotic arm independently developed by the research group.In this thesis,the lateral dynamic error and the longitudinal dynamic error model are built respectively according to the structural features,and the physical model is idealized and the dynamic model is built through the error comparison analysis.Then,the singular perturbation combined control strategy is proposed to effectively restrain the vibration on the basis of the setting accuracy control;Through comparing and analyzing the PID control strategy and the singular perturbation combined control strategy,the author further shows the rationality and effectiveness of the singular perturbation combined control strategy.The chief research substances and results of this study are as follows:(1)According to the characteristics of the driving joint of the medical manipulator,the main factors causing the transmission error are analyzed,and the dynamic error model of the transmission chain is established by the concentrated mass method in consideration of the helical gear rack meshing damping,error,time-varying meshing stiffness and load change.At the same time,a dynamic transmission error model considering the error factors,such as RV reducer manufacturing,assembly,etc.,is established according to the method of dynamic substructure and concentrated quality.(2)The thesis briefly analyzes the structural characteristics of the medical manipulator,simplify the manipulator arm into a Timoshenko beam,and describe its flexible deformation through the assumed modal method.According to the motion characteristics,the spatial dynamic positioning error of the end of the robot arm is divided into horizontal and vertical.Then,the thesis combines the transmission error model and the arm flexibility to further establish the horizontal and vertical dynamic error model;through numerical solution analysis,the relations between horizontal dynamic error and,the meshing gap,as well as the longitudinal dynamic error and the end load change are obtained.so that a kinetic model of the medical flexible manipulator is built.And the accuracy of the system deformation description is verified through the comparison between the natural frequency of the system acquired through numerical calculation and that acquired through finite element simulation analysis.(3)Based on the established dynamic model of the medical flexible manipulator system,the system is reduced to two subsystems according to the singular perturbation theory.In terms of the obtained slow-varying subsystem,inversion sliding mode variable structure control is adopted for trajectory tracking,while fuzzy self-tuning PID control is applied in the fast-varying subsystem to eliminate the vibration during the movement of the flexible arm,so as to realize the positioning accuracy control of the medical flexible manipulator and effectively suppress vibration.(4)Adams software is used to build a virtual prototype model of a medical flexible manipulator,Matlab is applied to build a singular perturbation combined control strategy model and a PID control strategy model;Obtaining the control effects of angular displacement tracking,angular velocity and end vibration displacement through joint simulation,the thesis compares,analyzes and demonstrate the rationality and effectiveness of the strategy.Based on the research analysis of the dynamic positioning error in the end of the medical flexible manipulator,this thesis proposes a singular perturbation combined control strategy,which improves the accuracy of the end positioning error control,provides a guarantee for the application and popularization of heavy ion precise radiotherapy technology,and offers certain rederences for the research in related technologies field.