Research On Control Of 5 DOF Magnetic Levitation Actuator For EDM

Unlike traditional machining,electrical discharge machining(EDM)relies on spark discharge,during which the electrode does not contact with the workpiece,but melts the workpiece by the instant high temperature of spark discharge between the tool electrode and the workpiece,which has the advantage of not being limited by the hardness and strength requirements of the workpiece material.Due to its unique processing advantages,it has been developed rapidly in the field of precision machining.In response to the problem of low efficiency of EDM,this thesis introduces a five degrees of freedom magnetic levitation actuator that can be combined with EDM machine tools for EDM machining.The internal mechanical structure of the magnetic levitation actuator can clamp the electrode to move in five degrees of freedom in a fully levitated state,and the variable universe fuzzy PID control is used to control the displacement of the magnetic levitation actuator to achieve high-speed and precise positioning and improve the machining speed.Firstly,the overall structure of the magnetic levitation actuator is introduced and the working principle of the magnetic levitation actuator is explained.The radial electromagnetic force and axial electromagnetic force of the magnetic levitation actuator are simulated and experimentally compared and analyzed,the displacement stiffness coefficient and current stiffness coefficient of the magnetic levitation actuator are obtained,and the mathematical model of the magnetic levitation actuator is established.Secondly,the PID control system is built in MATLAB/Simulink,and the displacement control simulation experiments are carried out for the Z,X(Y)and θ(φ)directions of the magnetic levitation actuator,due to the lack of control effect of PID controller for non-linear,time-varying objects and the introduction of fuzzy control,the PID parameters are dynamically adjusted during the fuzzy control process,which improves the control effect.In response to the defect that the proportional and quantization factors of fuzzy PID control cannot be changed during the control process once they are preset,a variable universe fuzzy PID control is proposed to adjust the proportional and quantization factors in real-time by using the scaling factor,which improves the control accuracy and adjustment speed of the system and effectively reduces the overshoot.The experimental platform of displacement control is built,and the displacement control experiments are conducted for five degrees of freedom of the magnetic levitation actuator respectively.The experimental and simulation results verify the superiority of the variable universe fuzzy PID.Finally,the EDM control experiment platform was built,and the magnetic levitation actuator was combined with EDM machine tool as the local actuator of EDM process,and the three control strategies of PID control,fuzzy PID control and variable universe fuzzy PID control were carried out for the magnetic levitation actuator.The variable universe fuzzy PID control can effectively accelerate the system response speed and improve the machining efficiency by 41.1%.