In the closed-loop fiber positioning control mode of Large Sky Area Multi-Object Fiber Spectroscopic Telescope (LAMOST), there are stringent requirements for time efficiency. However, due to the large size and high resolution of the images required for fiber positioning, the data volume for a single image is extremely large, reaching up to 90 MegaBytes per image. The current time efficiency of the closed-loop control system has yet to meet the requirements. This paper attempts to implement the fiber positioning algorithm, the light centroid algorithm, for calculating fiber positions in an FPGA-based edge fiber positioner detection module. Optimizing this module can significantly save image transmission time. The article mainly utilized Vivado HLS to port the algorithm to an FPGA and achieved improvements to its implementation. To enhance the algorithm's computational efficiency, the labels were assigned to each light spot to calculate the centroid coordinate, which enabled more efficient operation on the FPGA. The results indicated that the new hardware architecture effectively have reduced transmission time, making the improved centroid algorithm more suitable for operation on an FPGA.
Realizing accurate positioning with the Large Sky Area Multi-Object Fiber Spectroscopic Telescope (LAMOST) closed-loop system depends on accurate high-precision calibration of the visual measurement system, which has a great impact on collision avoidance and accurate positioning. We designed fiducial fibers for the calibration of the LAMOST closed-loop system to provide accurate fiducial positions for visual measurement. The benchmark position accuracy of the fiducial fibers is a key factor affecting the accuracy of the visual measurement system; the more accurate the fiducial fiber positions are, the higher the visual measurement correction accuracy. In this study, three measurement methods were used to obtain the fiducial fiber positions, namely, measuring the hole positions using a coordinate measuring machine, imaging the fiducial fibers using a calibrated photographic system, and directly measuring the fiducial fiber spatial positions using a laser tracker. By evaluating the fiber positions obtained via the three methods, we can obtain a stable and reliable fiducial fiber position benchmark. A fiducial fiber positions evaluation method based on an optimal residual criterion is proposed, and the optimal residual solution for a small calibration target (SCT) is used to evaluate the optimal fiducial fiber measurement method. Specifically, the fiducial positions obtained via each of the three methods are used to invert the camera calibration parameters, which are then used to calculate the physical position of an SCT. Finally, the residual value between the calculated and theoretical positions is taken as the standard for evaluating the fiducial fiber measurement benchmark performance. The results show that the fiducial fiber positions measured using the laser tracker can be applied to effectively calibrate the photographic system, enabling the LAMOST vision measurement system to achieve a positioning accuracy of nearly 10 μm with the camera 20 m from the focal surface, whereas the accuracy is within 20 μm for ∼95 % of the measurement points.
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