Research On Control Strategy Of Six Degrees Of Freedom Magnetic Levitation Micro Motion Stage

The six-degree-of-freedom magnetic levitation micro-motion stage has the potential ability to obtain multiple degrees of freedom,high speed,high acceleration,and high positioning accuracy under high cleanliness and high vacuum environments.Its drive units are voice coil motors.However,the structure and electrical characteristics of the voice coil motor make the thrust coefficient of the voice coil motor change with the relative position and angle of the primary and secondary,causing main thrust fluctuations and parasitic forces.At the same time,there are certain mechanical errors in the design,manufacture and installation of the micro-motion stage,which causes the actual installation position and angle of each voice coil motor to be different from the theoretical design.The actual center of mass of the micromotion table body does not coincide with the theoretical center of mass,which leads to incomplete decoupling of the system,resulting in thrust crosstalk during the control of their degrees of freedom.Therefore,how to suppress the disturbance and ensure the strong robustness of the system has become the key in the control system of the 6-degree-of-freedom magnetic levitation micro-movement stage.In this paper,the motion control algorithm is studied for the decoupling control and disturbance suppression of a 6-degree-of-freedom magnetic levitation micro-motion platform.First of all,this paper carries out the model establishment of single-degree-of-freedom voice coil motor and the analysis of thrust fluctuation.Furthermore,according to the structure of the micro-motion table,the conversion relationship between the driving force of each voice coil motor and the motion of the solution point is derived,and the differential model of the micro-motion table including the installation error and the shift of the center of mass is established.At the same time,the six-degree-of-freedom attitude solution of the solution point is performed according to the installation position of the displacement sensor.Secondly,the dynamic coupling of the micro-motion table is divided into two parts:position-dependent coupling and force-dependent coupling for dynamic decoupling,and the logic control forces/torques at the solution point are converted into the driving force of each voice coil motor.The MIMO control system is transformed into 6 independent SISO control systems to realize the decoupling control of the micro-motion platform.In order to take into account both the dynamic response and the steady-state response of the system,the position loop PID controller and the phase lead-lag controller are designed based on the minimum ITAE criterion.Through simulation experiments to verify the effectiveness of the decoupling model,and compare controller performance.Thirdly,the design is based on the first-order exponential reaching law sliding mode controller to improve the ability to suppress disturbances,and for the chattering problems of traditional sliding mode control,the boundary layer method is used for optimization.In order to eliminate the effect of chattering in principle and improve the response speed and robustness of the system,a second-order sliding mode controller based on Super-Twisting algorithm is designed and stability analysis is performed.Through simulation comparison,the superiority of Super-Twisting algorithm in control accuracy and chatter suppression is verified.The second-order sliding mode disturbance observer based on Super-Twisting algorithm is designed to observe and feed-forward compensation of the individual degree of concentrated disturbance.The simulation and loading simulation verify the accuracy and disturbance suppression ability of the observer for load disturbance and concentrated crosstalk observation.Finally,an experimental test platform is built based on RT-LAB semi-physical simulation controller.Through experiments,the correctness of the designed decoupling algorithm and the solution of the attitude of the solution point are further proved;comparing the control effect of the PID controller and the second-order sliding mode controller based on the Super-Twisting algorithm,the experiment proves the second-order sliding mode controller It has higher control precision and robustness,can realize six-degree-of-freedom closed-loop experiments with different trajectory tracking,and has higher tracking accuracy and positioning accuracy.