Design and identification of the precision feeding system of a grating ruling engine

The transport of the grating blank at the nanometer scale is the key to the diffraction grating fabrication technology. This paper describes in detail the design of the precision grating blank feeding system of a diffraction grating ruling engine. In order to accurately control this system, nonlinear characteristic cannot be neglected in the system model. So empirical mode decomposition (EMD) and Hilbert transform are combined to identify and analyze the fine-actuate stage (FAS) in the dual-actuated stage, because this method has been shown to be suitable for characterizing nonstationary signals. Comparing the nonlinear characteristic of FAS with some typical nonlinear system, the nonlinear mathematical model can be properly simplified for easy control. All the identification work is performed based on the impulse excitation signal obtained from the laser interference measurement system. Numerical simulation of the system is introduced to verify the mathematical model. Results of the experimental identification and simulation demonstrate that the dynamic characterization identified corresponds with the actual physical structure, so the Hilbert transform combined with EMD is effective to identify the nonlinear system mathematical model to establish better control in the ruling process of the grating fabrication.