Study on Measurement Error of Fibers' Space Coordinates Detection Using an Area CCD Camera for LAMOSTPositioning System

摘要

An area CCD camera is used to detect space coordinates of fibers in LAMOST positioning system, which is National Ninth Five Great Scientific Project, in order to achieve the detection of real-time, un-touched and high accuracy. This measurement method is based on photogrammetry and is applied in many other photometric measurement systems. The positioning accuracy for LAMOST is less than 40m, so fibers' position detection accuracy is at least one-third of it. The position detection of static goals through general photogrammetry can achieve high accuracy, about several microns. But fibers are active in LAMOST, so the systematic research about CCD measurement under this circumstance is carried on in this paper, which includes measurement error magnitude, form of expression, influencing factors, causes and ways to reduce measurement error. Some conclusions can be obtained through position detection experiments for movement fibers: The measurement method with a CCD camera for position detection has a good measurement stability, its accuracy can achieve about 2 microns for 8 hours; This method also has a high accuracy for position detection of one-dimensional movement fibers, which is less than 5 microns within the movement distance of several millimeters; But when fibers move in a curtain space freely, F number, lamp-house, speckle status and imaging size will probably cause additional measurement error. It is about a dozen microns to tens of microns and it stems from the changes of light intensity distribution of imaging speckles while fibers are moving. Finally, it is discussed simply to improve the measurement method and reduce measurement error.