Precise feedback control of optic fiber positioning system based on time synchronization algorithm in LAMOST

LAMOST(Large Sky Area Multi-Object Fiber Spectroscopy Telescope) is an Extremely Large Active Reflective Schmidt Telescope. In present LAMOST control system, 4,000 optical fiber control units run to specific positions under the commands of control computer, completing the observation of 4,000 celestial bodies. In order to increase the observation efficiency significantly, the second generation of LAMOST system is designed. In the new system, optical fiber control unit is miniaturized, and increased from 4,000 to 12,000. ZigBee wireless communication in former system is replaced completely by CAN bus communication, increasing the system’s efficiency and stability. The most significant problem of the new system is how to realize real-time precise feedback control of so many control units. In order to solve this problem, we introduced a time synchronization algorithm based on PTP(Precision Time Protocol) into the system. This algorithm realizes precise time synchronization among the upper computer, primary control nodes, subordinate control nodes and control units, thus obtains the planned operation status of each control unit. CCD cameras are used to capture the real-time operation status of control units and transmit the images to upper computer, which are processed and compared with the planned status. Then the control computer sends follow-up commands to control units to compensate the calculated errors. This makes it possible to realize precise feedback control on each control unit, avoiding common problems such as mispositioning and collision.