A new method for measuring the position of the end of optical fibers for LAMOST

Abstract

Measuring the position of the end of 4000 optical fibers on the spherical focal plate for the LAMOST (Large Sky Area Multi-Object Fiber Spectroscopy Telescope) optical fibers positioning system is one of the key problems for LAMOST. Currently, the area CCD camera is used to measure the positions conveniently and quickly. However, due to too small size of area CCD, the large-size focal plate should be reduced large multiples to image on the area CCD, and in this process, there is error amplification which will disturb the improvement of measuring precision. So far, the precision of this method does not meet the requirement. Therefore, a new method with linear CCD sensors is created. The device consists of a rotary encoder and a scanning frame on which several linear CCD sensors are spliced into a measuring baseline. The scanning frame can be driven by step motor and take a slow rotation around the center axis of the focal plate and close to the surface of the focal plate. In the course of rotation, each time the scanning frame turns a very small angle, the linear CCD sensors take an acquisition and get the radial coordinate of the end of optical fibers, the rotary encoder records the angle coordinate, and this polar coordinates can be used to express the position of the end of optical fibers. This new method is a 1:1 measurement, and it hasn't error amplification but has high precision in theory. The main content of this paper is to build the measuring model of the new method with linear CCD.