Research on Closed-Loop Control Algorithm for Fiber Positioning in Fiber Spectroscopy Telescope Based on SMART
YANG Hao-jie1, GAN Zhao-xu1, WANG An-zhi1, WANG Jia-bin1, SUI Xiang1, DOU Zhi1, XUE Wei-xi1, LUO Jia-shun1, YAN Yun-xiang1, 2, GENG Tao1, SUN Wei-min1*
1. Key Laboratory of Fiber Integrated Optics of Ministry of Education, College of Physics and Optoelectronic Engineering, Harbin Engineering University, Harbin 150001, China
2. Qingdao Innovation and Development Center, Harbin Engineering University, Qingdao 266000, China
Abstract：A control algorithm for realizing closed-loop fiber positioning was proposed with the structure of the special-shaped micro-lens aimer (SMART) that can achieve real-time fiber positioning, to fit the requirement of the dual-rotary positioning device on the focal plane of the Large Sky Area Multi-Object Fiber Spectroscopic Telescope (LAMOST). During the closed-loop control process, if the fiber and the star image were misaligned, the starlight would deviate from the center plate of the SMART and enter the special-shaped micro-lens, which would deflect part of the starlight into the corresponding feedback fiber. Based on the light intensity signals received by the six feedback optical fibers, the light intensity contrast relative to the feedback optical fibers is calculated to obtain the azimuth information of the misalignment, and a control signal is sent back to the optical fiber positioning unit to drive the dual-rotation positioning device to adjust the angle, thereby achieving high-precision alignment dynamically. Its design logic closely aligns with the optical fiber alignment requirements of the dual-rotation positioning device, as the device relies on two independent rotation axes (a central axis and an eccentric axis) to achieve two-dimensional positioning. The closed-loop control dynamically corrects the dual-axis angle using real-time feedback signals to compensate for mechanical errors and environmental disturbances, ultimately meeting the requirements of large-scale optical fiber arrays for high-precision, high-efficiency alignment. The correspondence between the rotation angle and the movement distance of the dual-rotary positioning device was analyzed, and a two-round, multi-step convergence method was developed. The calculation formulas for the alignment path between the fiber and the star image under different dual-axis expansion conditions were analyzed. In the first round of positioning, the single-step length was set to 30 μm, and the contrast threshold was set to 0.9; in the second round, the single-step length was set to 10 μm, and the contrast threshold was set according to the calibration. The fiber needs to undergo multiple movements, from misalignment to alignment. After each movement of the positioning unit, the control system would again obtain the real-time feedback signal from the detection system to determine whether the fiber had reached the threshold. A simulation system of LAMOST was built in the laboratory, and the lengths of the dual axes were calibrated. The positioning accuracy and positioning time of the fiber closed-loop positioning system were tested. The results showed that the positioning system could make any initially misaligned fiber return to the aligned state. The average correction time was 27.6 s. There were 72.5% fibers of 10 μm correction accuracy, and 97.5% fibers of 30 μm correction accuracy.
Key words：Astronomical spectroscopy; The large sky area multi-object fiber spectroscopic telescope (LAMOST); Optical fiber positioning; Closed-loop control; Special-shaped micro-lens aimer(SMART)
杨浩杰，甘兆虚，王安之，王佳斌，隋 响，窦 智，薛维玺，罗佳顺，严云翔，耿 涛，孙伟民. 基于SMART的光纤光谱望远镜中光纤定位闭环控制算法研究[J]. 光谱学与光谱分析, 2025, 45(12): 3455-3464.
YANG Hao-jie, GAN Zhao-xu, WANG An-zhi, WANG Jia-bin, SUI Xiang, DOU Zhi, XUE Wei-xi, LUO Jia-shun, YAN Yun-xiang, GENG Tao, SUN Wei-min. Research on Closed-Loop Control Algorithm for Fiber Positioning in Fiber Spectroscopy Telescope Based on SMART. SPECTROSCOPY AND SPECTRAL ANALYSIS, 2025, 45(12): 3455-3464.
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