Preliminary study on the measurement system for LAMOST small focal plane fiber positioning system

摘要

LAMOST is National Ninth Five Great Scientific Project. In the fiber positioning system, geometrical coordinates of fibers need to be measured in order to verify the precision of fiber positioning. The small focal plane system for LAMOST includes more than 200 fiber positioning units and its diameter is 500mm, so it's difficult to cover it using only one area CCD. For measuring wide field of view, the measurement system based on one CCD rotating is designed. The CCD camera is placed on a mechanism liked a pan head and can rotate around two vertical axes. When the CCD camera rotates in a certain way, the measuring scope becomes a ring. When the initial angle of CCD is changed the size of the ring changed too, so the wide field of view is measured. In this plan different measuring has overlapped regions and one fiber point may be measured for several times. After the camera's calibration the different imaging points will be transformed to the same coordinate system using photogrammetry method and the average value of them is the final value in order to eliminate the imaging error and transformation error. The realization of the measurement system based on CCD rotation is described.