Mr. Zhi Pan Profile

Zhi Pan

at Univ of Science and Technology of China

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Proceedings Article | 15 February 2022 Paper

Collision-free motion planning approach for multi-object spectrographs with equal-arm fiber positioners

Yinjie Wu, Zhigang Liu, Zhi Pan, Zengxiang Zhou

Proceedings Volume 12166, 121663R (2022) https://doi.org/10.1117/12.2616855

KEYWORDS: Oxygen, Spectrographs, Astronomical imaging

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The fiber positioner plays an important role in carrying the fiber in the Fiber Multi-Object Spectrograph. Most spectrographs such as the Large Sky Area Multi-Object Fiber Spectroscopic Telescope (LAMOST) and the Dark Energy Spectroscopic Instrument (DESI) have thousands of fiber positioners shared working space. However, the overlap of motion areas increases the possibility of collisions for fiber positioners within a confined space. The collision prevents fiber positioners from reaching the designated observation position, which reduces the observation accuracy of the telescope and the service life of fiber positioners. This study proposed a collision-free motion planning approach based on the collision risk function for the fiber positioner. By using this method, a collision-free trajectory can be planned before positioners run, avoiding the discontinuity of trajectory caused by collision avoidance while running. Simulated experiments validated that our method has the advantages of easy operation, complete avoidance of collision, and less accumulation of motion errors compared with the existing anti-collision motion trajectory planning methods.

Proceedings Article | 15 February 2022 Paper

Closed-loop control system based on visual measurement for LAMOST optical fiber positioning

Zhi Pan, Yinjie Wu, Zhigang Liu, Zengxiang Zhou

Proceedings Volume 12166, 1216644 (2022) https://doi.org/10.1117/12.2617169

KEYWORDS: Optical fibers, Control systems, Visualization, Detection and tracking algorithms, Calibration, Telescopes, Spectroscopy

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With the development of optical fiber positioning, the LAMOST (Large Sky Area Multi-Object Fiber Spectroscopy Telescope) system requires higher positioning accuracy. Despite the great success of open-loop control mode in previous techniques, it would be hard to meet the strict requirements of the next-generation optical fiber positioning techniques. In contrast to the open-loop system, in this paper, we focus on the closed-loop control of fiber positioning based on visual measurement. In our proposed framework, by measuring the actual position of the optical fiber positioner and feeding it back to the control system, we control the positioner to approach the target position multiple times to improve the accuracy of optical fiber positioning. Nevertheless, the challenges such as cross-border phenomenon and collision of the fiber positioner still hinder the accuracy of our designed system. To tackle the former challenge, we normalize the central axis angle of the positioner according to the algorithm we proposed, which alleviates the problem that the positioner cannot move successfully due to the cross-border phenomenon near the mechanical zero position in the central axis. Extensive experimental results show that closed-loop control consistently improves the positioning accuracy of the unit. After ignoring the lens positioning error, 95% fiber unit positioning error under our proposed closed-loop control method is less than 40um after three steps of approximation, 98% fiber unit positioning error is less than 40um after four steps of approximation, which meets the requirements of high precision fiber positioning. It is worth noting that our experiments also exhibit the insensitivity of the closed-loop positioning scheme to the initial unit parameters, verifying the satisfactory robustness of our proposed method.

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