Fiber positioning of LAMOST

LAMOST is a 4m class wide field of view telescope special designed for multi-object spectroscopic observation. For the observing mode of low spectral resolution, 4000 fibers are employed. 4000 fibers is a challenge to the positioning of multi-object spectroscopy nowadays. We are going to use a method that each fiber is controlled by independent positioner, like MX. But the working area of every fiber is limited in quite small a region comparing with whole focal plane to reduce the size of the position device so that 4000 positioners could be homed inside focal plate. The first problem of the method we have considered is the usable rate of fibers. Because 4000 fibers employed by LAMOST and a couple of times of targets in a field of view of LAMOST, a reasonable usable rate of fiber is expected,. But there are still a few problems we have to solve before the method could be used. Paralleled control of 4000 positioners, the electronic and mechanical interference between positioners may be a trouble. And the stability of bases plate should be considered Some models of positioners has been proposed and made for test in past two years. They have been examined in laboratory and in observatory.