This paper presents a dual iterative learning control strategy for a dual stroke actuator system in the lithography scanner. The motion control strategy is employed, in which the trajectory of a short stroke stage is followed by one of a long stroke stage. A short stroke stage is used for improving the system response performance while a long stroke stage is introduced for the purpose of long motion stroke of the system. Combining the dynamic model of the system, the coupling effects between two actuators are analyzed, and the system model is simplified. This model is used for the design of a dual iterative learning control strategy and decoupling controllers. As a result, the heavy proportion of the recurrent coupling force on the long stroke stage is eliminated by the decoupling feedforward action from the output of the short stroke stage in the scanning process. The rest of the coupling force is removed by the first iterative learning control between two subsystems. The impact on the short stroke stage from the long stroke stage is weakened, and the short stroke stage is then designed independently by the two degree of freedom control strategy combining feedback control with the second iterative learning control. The convergence of the iterative learning control system is shown, and the effectiveness of the combined method is verified by a simulated wafer stage.
A new method to reduce the residual pulse peak in stimulated Brillouin scattering (SBS) optical limiting by an injected seed is presented. The pulse shapes of the transmitted pump beam are studied for various delay times and injected seed powers theoretically. The numerical simulated results show that the height of the residual pulse peak can be controlled by changing the delay time and injected seed intensity. Experimentally, various optical limiting pulse shapes with different heights of the residual peak are observed by changing the delay time and intensity of the seed injected into the SBS optical limiter. The experimental and theoretical results show that the residual pulse peak in SBS optical limiting can be controlled by the delay time and power of an injected seed.
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