Design Of Subdivision Control System Of Optical Fiber Positioning For LAMOST

LAMOST(Large sky Area Multi-Object fiber Spectroscopic Telescope) is astronomical telescope with large field and large diameter located at Xinglong of Hebei Province. The optical fiber positioning system of LAMOST which used a technology of "Parallel Control of Fiber Location" was built to solve the problem of optical fiber positioning in order to get spectrum from celestial objects effectively.The optical fiber positioning system of LAMOST is build in this way.First,4000optical fibers are fixed one by one on4000mechanical units. Second, center shaft and eccentric shaft of each mechanical unit are driven by two stepper motors which are installed on the mechanical unit. At last, the stepper motors are driven by a node driver board which is also fixed on the mechanical units. In order to control4000node driver boards, a Zigbee wireless network is designed to realize the communication between main control boards and node driver boards which can avoid complex winding or high power loss compared to traditional cable communication network. The main control boards is working as intermediary between PC and node driver boards, on the one hand, they can communicate with PC through serial port, on the other hand, they can communicate with node driver boards through Zigbee wireless network.But meanwhile, the optical fiber positioning system has two places to be optimized. First, The low frequency open-loop operation of stepper motor has problems of losing steps or more steps so that the positioning accuracy is reduced. So this paper design a subdivision control scheme. Subdivision control can improve the low-frequency instability characteristics of stepping motor by reducing the change rate of current. Second, the node driver boards are fixed on the mechanical units which are hard to remove. So it is quite inconvenience to update the inner program of target node driver boards through hardware connections. This paper proposes a wireless FLASH-update system through Zigbee so that the FLASH of target node driver boards can be updated without hardware connections. In this way, the efficiency can be improved and the operation is convenient in the meanwhile.