SMART : the closed-loop control system for LAMOST

The accuracy of fiber positioning is crucial for the observation of multi-target fiber spectral telescopes such as LAMOST (Large Sky Area Multi-Object Fiber Spectroscopy Telescope). Most of the methods used for fiber positioning are open-loop control or semi-closed-loop control, the efficiency cannot meet the requirements of next-generation spectral telescopes. Considering that, this paper proposes a fiber positioning method that can achieve a completely closed loop without blind spots based on SMART (Special-shaped Micro-lens Aimer for Real-time Targeting) and a dual-rotary positioning mechanism. The entire correction process can be described as follows: first, the light intensity obtained by the 6-channel photodetector is stored in a buffer. Then the pulses required for correction are calculated based on the data in the buffer and the correction algorithm by the computer. The running command is then sent to the stepper motor controller using serial communication to drive the stepper motor. After the movement, the program will run again to verify if the correction is done. After selecting a position in the first quadrant, 8 directions were selected to conduct automatic correction experiments after the optical fiber position offset. The experimental results show that the average farthest distance that the method could correct is 600 mu m, and 75.9% positioning accuracy under our closed control method can reach 10 mu m, 94.8% positioning accuracy can reach 20 mu m, 100% positioning accuracy can reach 30 mu m. For corrections within the 500 mu m offset distance, 97.5 % of the correction time is within one minute.