Research On Large Stroke Nan-positioning Technology And Application Based On Dual-frequency Laser Interferometer

Large stroke nano-positioning technology is the key technology in the manufacture of the ruling engine. In this paper, the research is mostly focused on large stroke nano-positioning technology based on dual-frequency laser interferometer combined with the characteristics of the ruling engine. Designed large stroke nano-positioning system contains macro positioning subsystem, micro positioning sub system, measuring feedback subsystem and control subsystem. In chapter two, the configuration of the large stroke nano-positioning system, which consists of macro system and micro system, is designed and then established. Focused accuracy analysis of the dual-frequency laser interferometer measuring subsystem, whose resolving power is 0.15nm, showed results with short-term repeatability of the measurement system to 2nm, meeting the 10nm positioning accuracy requirement of ruling engine. In chapter three, the character of micro and micro positioning subsystem is analysed. In chapter four, the control subsys is established. In chapter five, a method that monitors the state of ruling engine is proposed. The main contents and results are as follows. Firstly, the diffraction grating ruling engine error model which describes the positioning error and the relationship to the grating performance is established. At the same time, a formula for positioning accuracy calculation is provided. Secondly, the establishment and identification by the macro positioning system given sixth-order model parameters, provides a model error of less than 1.6%. Analysing the system’s controllability, observability, frequency domain characteristics and time domain characteristics with transfer function and equation of state, the results show that the system is suitable for ruling engine macro positioning. Thirdly, the establishment and indentification by the second order micro-positioning system transfer function uses an optimal design based on the results of the new micro-positioning stage, given constant natural frequency to increase the damping ratio and improve the system dynamic characteristics. The experimental results show that the micro-positioning system’s resolution is better than 3nm with the angle correction 3σaccuracy of 0.0031″. Fourthly, the traditional PID controller and BP neural network control algorithms are proposed for the large stroke nano-positioning system. Diffraction grating ruling experiment showed that the random errors of these algorithms are 7.548nm(σ) and 4.17nm(σ), the average errors of grooves are 0.23nm(σ) and 0.16nm(σ), the periodic errors are 0.043nm and 0.01nm. The control subsystem corrects the periodic error of ruling engine, and improves the quality of gratings. Among the algorithms, the BP neural network control algorithm can effectively eliminate the errors caused by nonlinearity and increase the robustness of the system. Fifth, the design of the macro positioning control loop real-time compensation system solves the problem of integral saturation to improve positioning stability. Sixth, a normalization model of solving resolution using fitting coefficients of Zernike polynomials are established based on the spectral imaging theory of Fourier optics. The relationship between resolution and wavefront aberration of diffraction gratings is illustrated by this model. Meanwhile a new method of testing resolution using fitting coefficients of Zernike polynomials is proposed. Comparing with directly method, results indicate that the error of indirect method is less than 4.22%, and this method could be an effective way which avoids the difficult of direct method to solve resolution. The same method applied to the grating ruling engine running real-time monitoring, can improve the efficiency of the ruling engine.