Method Of Identification And Control For Ultra-Precision Stage With Nonlinear Character

Variable slit system is a key sub-system of a scanning lithography, playing an important role during the process of exposure. An ultra-precision motion stage is in turn the kernel part of the variable slit system, whose control faces the issue of nonlinearity not ignorable. Therefore, this paper studies the mathematical modeling, identification and control of the ultra-precision motion stage in the presence of non-smooth nonlinear characteristics.Firstly, the function of the variable slit system in the operation of a scanning lithography is described, and the design of its mechanical structure and electrical control system is analyzed. In particular, the electrical control system is described from the system level, while the mechanical system is investigated using motion component modal analysis. Meanwhile, the selection or designing of the main devices are explained.Secondly, based on Wiener-Hammerstein structure, the key-term separation principle is introduced to model the typical single-valued non-smooth nonlinear characteristics that could be present in an ultra-precision motion stage, such as dead zone and saturation. Then, these models are identified by the method based on RGIA,with or without output white noise, and simulation results confirms the effectiveness of the models and methodsNext, as apposed to typical single valued nonlinear characteristics, a more complex multiple-valued one, the backlash characteristic, is considered. When identifying the backlash Wiener-Hammerstein system based on the key-term separation principle,simulation results of a numerical example indicate the limitation of RGIA for such a system. Therefore, an improved Particle Swarm Optimization algorithm is introduced for the identification of a backlash Wiener-Hammerstein system, and the related simulation and comparison results are provided.Finally, based on the identification results above, Inner Mode Control is employed to makes use of the identified system model to control the system. According to the parameters of the variable slit ultra-precision motion stage, and with dead zone characteristic considered, simulation of the stage control using IMC is performed. The simulation results show the satisfying performance of IMC.