| This dissertation concentrates on the technique research and implementation which is minute position displacement detection and system control in the shadow mask motherboard automatic alignment procedure. The mathematical model between displacement of double diffracting gratings and the intensity of Moire signal was established, and simulate with MATLAB simulation software. The results showed that the intensity of Moire signals varied periodically when relative displacement of the gratings changed, thus Moire signal can be used for minute displacement measurement of shadow mask motherboard.A compound double drive alignment system was proposed and could achieve precise alignment in the wide work range, in which combined coarse alignment with fine alignment. Coarse alignment relies on the coarse platform of precision ball guide screw driven by stepper motor, obtains a displacement signal from the coarse grating. By analyzing Moire signals, the industry control computer sent out the driven pulses and the stepper motor drives the ball guide screw for coarse alignment.The alignment range can be narrowed down to within ±220μm and work range could be 1000nm. Once coarse alignment is finished, the industry control computer sent out the driven voltage according to the displacement signal, driving piezoelectric ceramics brake to produce the corresponding deformation. And then move the flexure hinge to the expected position. The final accuracy of the system could be ±100nm.The system met both requirements of the wide work range and the alignment accuracy.Adaptive fuzzy control was proposed and the corresponding control flow chart also was designed, aimed at the nonlinear and complexity in the piezoelectric ceramic. The experimental results show that the designed control strategy alleviated the nonlinear problem of piezoelectric ceramics and could perform excellent control effect such as faster response and better stability. It could effectively improve positioning speed with high accuracy. |
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