Simulations of Collision between Optical-Fiber Positioning Units of the LAMOST Using Single-Chip Microprocessors

To avoid missing survey areas, the light-collection areas of focal-plane optical fibers of the LAMOST (Large sky Area Multi-Object Fiber Spectroscopic Telescope) are set to overlap. Collision between adjacent optical-fiber positioning units may thus occur during their adjustments and affect the instrumental work efficiency. We propose a system based on AT89C51 microprocessors to reverse instrumental state changes caused by collision. During positioning each optical fiber is driven by two stepping motors, which control its central shaft and off-center shaft, respectively. Pulses generated by a delay procedure run in one SCM (Single-Chip Microprocessor) of the system have three patterns which have the same frequency but different phases. Such pulses serve as signals for detecting collision. The counter in each SCM controlling an optical-fiber positioning unit accumulates counts of pulses during a step of the stepping motor. A collision between two units causes pulses to be double counted, which triggers the SCMs to stop the two units and drive them backward. This collision-processing system has succeeded in boosting the work efficiency of optical fibers and improving the LAMOST observation efficiencies. As reported in the paper, we have carried out simulations to test the feasibility of the system using a PROTEUS software package.