Dynamic And Control Of Robot Drilling End-effector Based On 3-SPR Parallel Mechanism

A new type of robot drilling end-effector for curved surface is designed by using 3-SPR parallel mechanism.According to the characteristics of the 3-SPR parallel mechanism and the design requirements of the drilling end-effector for curved surface,the parallel mechanism is used as the adjusting and pressing mechanism of the drilling end-effector.This dissertation presents a posture adjustment algorithm for the drilling end-effector on the basis of kinematic analysis of the mechanism.Based on the data of four points around drilling area obtained by the four distance sensors arranged evenly around drill bit at the end-effector,The coordinates of the four points in the same coordinate system are obtained.Combined with the known coordinates of drilling point,a vector weighted sum new algorithm of surface normal measurement is presented.Compared with the normal measurement algorithm of spherical surface fitting,the results show that the new algorithm has higher precision in normal measurement.Adjusting parallel mechanism of drilling end-effector,the dynamic model of the mechanism is established by using Lagrange equation.The solution of driving force is obtained,which provide a mathematical model for further analysis of the dynamic control of the actuator.Based on the mathematical model,the simulation analysis of the dynamic characteristics of adjusting parallel mechanism of drilling end-effector is made.According to the display of the driving force,the change of driving force is obtained in the posture adjustment.At the same time,the change of driving force is compared when the platform is loaded or not loaded.The relationship between the change of the driving force and the structural parameters of the mechanism is analyzed,which provides a reference for the further analysis of the dynamic characteristics of the mechanism and the optimization design of the actuator.Based on the dynamic equation of the mechanism,the modified PD control strategy and the sliding mode variable structure control strategy(SMC)are designed.The simulation results show that the sliding mode variable structure controller based on reaching law is more robust than the PD controller for the dynamic model.Based on the mathematical model of the feed system of the end-effector,the traditional PID controller and fuzzy PID controller are used.The simulation results show that the fuzzy PID strategy is more suitable to be used as the controller of the feed system of the drilling unit.