CCD Camera Calibration Of The Focal Plane Positioning System For LAMOST

The Large Sky Area Multi-Object Fiber Spectroscopic Telescope (LAMOST) is an innovative reflecting Schmidt telescope, promising a very high spectrum acquiring rate of several ten-thousands of spectra per night. By using the parallel controllable fiber positioning technique, LAMOST makes reconfiguration of fibers accurately according to the positions of objects in minutes and fine adjusting the fibers.4000 fiber positioning units are accommodated on the focal plane with a 25.6 mm distance between each others. Each unit drives a fiber moving in a circle of 33 mm in diameter. The unit is driven by two step motors in double rotation movement. The positioning error is 40 micron maximum. The parallel controllable fiber positioning technique solves the problem how to precise positioning 4000 observation target. It is an international leader in technological innovation. LAMOST is located at the Xinglong Station of National Astronomical Observatories, Chinese Academy of Sciences, as a national facility open to the whole astronomical community. It will bring Chinese astronomy into the 21st century with a leading role in wide field spectroscopy and in the fields of large scale and large sample astronomy and astrophysics.Camera measurement calibration system is one key system of the parallel controllable fiber positioning technique. The accomplished tasks are as following:(1) Two CCD camera calibration models are briefly introduced, one is camera calibration based on intrinsic and extrinsic parameters, the other is camera calibration arithmetic based on integration of multinomial, the latter model is based on the theory of the former model. The algorithms describes in detail, include optical center of gravity method, least squares fitting analysis, LM algorithm and so on The results of the experiment prove the precision of these two methods of camera calibration.(2) Based on the latter camera calibration model, differential splicing camera calibration method was presented with multi-position, single calibration jig in wide view. The experiment results show that high precision calibration can be achieved in the measurement with differential splicing camera calibration. And this calibration method has used in running-in testing for 4000 fiber positioning units in small focal plane system for LAMOST.(3) In accordance with the requirements of the star-observations and the positioning modes of units, we work-out seven necessary precise positioning parameters in complex field environment by a specific process and a series of practicable algorithms. The algorithms include fitting circle arithmetic based on least squares analysis, coordinate rotation algorithm and so on. Through the simulation test and field test of stellar image observation, has proved that the accuracy of parameters could meet stellar image observation's need. The stellar image spectrum acquiring rate of LAMOST telescope is more than 90 percents now.