Reseach On Decoupling And Coutrol For Magnetic Suspesion Fine Stage Of Lithographic Scanners

Magnetic suspension fine stage is a key component of coarse-fine laminated ultra precision motion stage in lithography machine with short-stroke and high precision, furthermore its movement and positioning accuracy will directly determine the quality of the wafer in photolithography process. This paper have conducted the research in view of the coupling between the different degrees of freedom of motion based on a magnetic suspension fine stage with a novel gravity compensation structure, and the controller have been designed based on exact decoupling to meet the movement performances of the magnetic suspension fine stage.Firstly, considering the electromagnetic force will change when the coil of voice coil motor moves in the air gap of permanent magnets, so the difference of electromagnetic force will cause the imbalanced drive, and each degree of freedom will coupling, thus I have established an analytical model of electromagnetic density flux and electromagnetic force of the coil in magnetic suspension fine stage, and the simulations and experiments have verified the correctness of the analytical model.Secondly, installation, manufacturing and assembly error are inevitably exist in the gravity balance components and drive motor, and will causes inconsistence bettween the actual model and theory model. So making force distribution based on thoretical model will cause the degree of freedom coupling and bring error of driving force, and the results of the analysis have been validated by computer simulations.Moreover, in view of the time-domain and frequency-domain performances of the magnetic suspension fine stage, a lead-lag feedback controllers have been designed for motion control based on the model identification, at the same time, the low pass filter for energy attenuation has been applied to reduce position error in the high frequency flexible oscillation, and these controllers have been verified by experiments.Finally, the six degree of freedom input and output model for magnetic suspension fine stage has been set up, then I have proposed an off-line calculation method of current distribut coefficients for decoupling combined with least square method, and the effectiveness of this method to decouple the six degree of freedom of fine stage has been verified by the experiments.