Modeling and motion control of 6-DOF ultra-precision stage based on iterative learning and fractional-order PID

Both the high positioning accuracy and the high moving speed are critical performance pursued in motion control of the precision stage, especially in semiconductor industry. To satisfy these requirements simultaneously, a novel control strategy is proposed in this paper, which combines the iterative learning control and fractional-order PID control together. Based on the kinematical analysis and the motion decoupling model, the control framework is constructed. The ILC-fractional-order PID controller is used for the position loop, while the classical PID controller is chosen for the current loop and the speed loop. Considering the dynamical motion performance, the parameters adjusting method is illustrated in detail by discussing different effects of control factors. By simulation analysis, the proposed strategy could maintain high positioning accuracy with high-frequency periodical input. And the experiments carried on a reticle stage for the lithography machine verified the effectiveness of this novel method. The positioning accuracy could reach nano-scale with the movement speed of 1.2m/s.