Design Of 6-PSS Master-Slave Actuator And Gravity Compensation Control For Ophthalmic Surgical Robot

With the increasing demand for ophthalmic surgery,ophthalmic robot technology has entered a period of rapid development.As the key of the surgical robot,the structure and control performance of the actuator will directly affect the overall performance of the system.In ophthalmic surgery,doctors need to complete complex multi-degree of freedom operation in the eye,which requires the actuator with enough freedom and workspace.Besides,the actuator itself will be affected by gravity.For human-computer interaction,gravity leads to the fatigue of the operator,which needs to be reduced.For motion control,gravity is disturbances,and the control accuracy is affected.Therefore,it is necessary to design an actuator for ophthalmic surgery robot which takes into account the accuracy,degree of freedom(DOF),and human-computer interaction performance.This paper focuses on mechanism design,analysis modeling,and gravity compen-sation.The following research are studied:(1)For the operation requirements of ophthalmic surgery,the mechanism design of the master-slave actuator is completed.Based on the 6-PSS parallel mechanism,three-axis translation and three-axis rotation are realized.On this basis,the kinematics modeling and Workspace Analysis of the actuator is carried out.The forward kinematics and inverse kinematics of the actuator are analyzed.The correctness of the modeling results is verified by Matlab/Simulink simulation.The Monte Carlo method is used to analyze the workspace,and the practicability of the design scheme is verified.(2)The dynamic model of the actuator is established by the Newton Euler method.Under the condition of neglecting the friction force,the Newton Euler equations of the moving platform,the branch chain,and the moving pair are established respectively,and the dynamic equations of the whole actuator are established according to the force balance.The dynamic model lays a foundation for the design of the gravity compensation controller.(3)Based on the dynamic model,the gravity compensation of the actuator is studied.The gravity of the mechanism at any position is obtained from the dynamic equation,and the gravity compensation controller is designed.The experimental results show that the gravity compensation for the main actuator can effectively reduce the influence of gravity and improve the performance of human-computer interaction;For the gravity compensation of the slave actuator,the motion control accuracy is effectively improved and the precision control is realized.Based on the application of ophthalmic surgery,The master-slave actuator of the 6-DOF ophthalmic surgery robot is designed by the 6-PSS parallel mechanism.The kinematics and dynamics of the designed actuator are analyzed and modeled,and the gravity compensation is realized based on the dynamic model.The experimental results show that the root mean square error of the actuator is increased by 66%,and the effective control performance is decreased by 54%.