The measurement of profile tolerance for the small focal plane plate of LAMOST

摘要

One essential technology of the entire project of LAMOST(Large-sky-area multiobjec fiber spectroscopic telescope) is the focal plane plate on which is installed over 4000 fiber units. The telescope receives the light passes through the reflector of MA (the reflecting Schmidt plate) and MB (the spherical mirror), forms focusing image in the focal plane. And through optical fiber the light is introduced to the spectroscope by the fiber units. So the focal plane is the basic of the plane installed 4000 fiber units, and influence the imaging quality of the whole system. In the project of LAMOST, the focal plane plate is a part of sphere which radius is 19880mm and the diameter of it is about 1750mm, but the surface area of the focal plane plate approximate 1/8000 of the whole global. Thereby the measurement of the focal plane plate which profile tolerance low than 40μm to obtain the reliable and accurate results is a difficult problem to deal with. All the installation of the fiber units and mending the focal plane are based on the measurement. We try to use CMM(Coordinate Measurement Machine) to survey the processed Small Focal Plane which diameter is 445mm. And we will carry on the analysis for several kinds of test and the data processing method to compare and optimize, finally determines the actual application plan.