Research On The Geometrical Parameters Fitting Method For High Accuracy Mirror

The beamline is one of the most important components of the synchrotron radiation facility which is used to generate high-performance synchrotron radiation light, and it is the important connection between the synchrotron radiation source and the experimental station. It is mainly used to transmit beam, split the synchrotron radiation light into monochromatic light and focus the beam. The focus is mainly realized by the large reflective optical surface. The size of the focus spot is an important performance evaluation index of the synchrotron radiation beamline. And the shape error of the surfaces has a great influence on the focus spot. Therefore it is very important to measure the profile of the optical surface accurately and evaluate the quality of the optical surface reasonably.The long trace profiler(LTP) has been widely used to measure the profile of the optical surface. It obtains the profile by integrating the slope data. The shape error is obtained by subtracting the ideal profile from the measurement height data. Because the curvature radius of the mirror is too big and can not to be measured directly, the ideal profile can only be obtained by fitting. In order to find an appropriate fitting algorithm for LTP, we do the research about curve fitting algorithm. Our main works are presented as following.(1) Based on the principle of the LTP, we analyze the factor which may influence the accuracy of the fitting algorithm.(2) By the numerical simulation, we compare the fitting results of the least square method based on algebraic distance, the least square method based on geometric distance, hough transform and genetic algorithm. The result shows that the least square method based on geometric distance is the most appropriate algorithm for LTP.(3) We have done some preliminary research about the ellipse fitting.