Research on reference fiber for closed-loop measurement of Spectral Survey Telescope

Duan, Shipeng; Zuo, Jiale; Li, Mengtao; Liu, Zhigang; Hu, Hongzhuan; Wang, Jianping; Chu, Jiaru; Zhou, Zengxiang

doi:10.1117/12.2560310

Cited by 4 publications

(2 citation statements)

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“…Moreover, the center of the structure is designed as a cone for target positioning and is equipped with a magnet for attaching a 1.5-inch target for the laser tracker. 21 The pixel center coordinates of such a multi-head fiducial fiber cannot be measured directly. Instead, we investigate a fiducial fiber inspection algorithm for the identification and coordinate acquisition of the center positions of the fiducial fibers.…”

Section: Fiducial Fiber Inspection Algorithmmentioning

confidence: 99%

“…This design allows the fiducial fibers to be encoded on the basis of the light and dark distribution of the different fibers, which can improve the fiducial fiber recognition efficiency. Moreover, the center of the structure is designed as a cone for target positioning and is equipped with a magnet for attaching a 1.5-inch target for the laser tracker 21 . The pixel center coordinates of such a multi-head fiducial fiber cannot be measured directly.…”

Section: Algorithms For Obtaining Fiducial Fiber Positionsmentioning

confidence: 99%

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Evaluation method to obtain a fiducial fiber metrology benchmark for the Large Sky Area Multi-Object Fiber Spectroscopic Telescope

Liu,

Du,

Wang

et al. 2023

J. Astron. Telesc. Instrum. Syst.

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.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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Section: Fiducial Fiber Inspection Algorithmmentioning

confidence: 99%

Section: Algorithms For Obtaining Fiducial Fiber Positionsmentioning

confidence: 99%

Evaluation method to obtain a fiducial fiber metrology benchmark for the Large Sky Area Multi-Object Fiber Spectroscopic Telescope

Liu,

Du,

Wang

et al. 2023

J. Astron. Telesc. Instrum. Syst.

Self Cite

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Research on the Fiducial Fibre Coding and Identification Algorithm of the LAMOST Fibre Positioning System

Duan¹,

Liang²,

Cai³

et al. 2022

PASP

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To obtain the world coordinates of a measured object in camera measurement, a certain number of image control points should be established around the detected object as fiducial points for data processing. The precision of a fiducial point directly determines the measurement accuracy of the measured object in the camera measurement. Fiducial points in camera measurement are widely used in various fields of measurement, such as aerial surveys, close-range surveys, and 3D reconstruction. In addition, a fiducial point generally adopts an encoding structure to reduce the search cost in the detection. Camera measurement is used in the LAMOST fiber positioning system, which also requires fiducial points to ensure the accuracy of fiber positioning. Different from a general fiducial point, the whole system needs to operate under dark conditions during LAMOST observation, and optical fiber positioning is carried out by the “backlighting method”, which measures the optical fiber spot under a dark background. In addition, fiber positioning needs to reach an accuracy of 40 μm at a distance of 20 m, which is difficult to achieve with the fiducial points used in general vision measurements. To meet the requirements of LAMOST optical fiber positioning with high accuracy, this paper presents a fiducial fiber and its recognition algorithm for optical fiber positioning of optical fiber spectroscopic telescopes. The fiducial fiber can be applied to a wide-field optical fiber spectroscopic telescope measurement system in a high-precision long-distance measurement environment. The experimental results show that fiducial fiber can ensure the accuracy of closed-loop positioning for LAMOST fiber units.

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Research on Calibration Method of off-axis Closed-loop Detection System for Multi-target Spectral Telescope

Du¹,

Wang²,

Duan³

et al. 2023

PASP

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The LAMOST telescope has been operating steadily for more than 10 yr and is currently undergoing an upgrade to its fiber-optic positioning system on the telescope’s focal plane. By adding a vision detection system to accurately measure the current position of the optical fibres and carry out closed-loop feedback control, the positioning accuracy of the original optical fiber system is greatly improved. Due to the limitation of the existing optical path of the telescope, to avoid blocking the optical path, the detection system camera cannot be placed on the optical axis of the telescope, which makes the camera and the optical fiber end face at a relatively inclined position. However, the angle between the camera and an object will introduce errors to the polynomial calibration method used in the visual detection system. To address this problem, by analyzing the relationship between the camera imaging principle and the polynomial calibration method, this paper studies the influence of distortion and imaging angle on polynomial calibration results under different angle conditions and proposes an improved high-precision polynomial calibration method. First, the distortion parameters are calculated using Zhang’s method, and the image distortion is removed. Then, a mapping model between oblique plane image and nonoblique plane image is established through a homography matrix. The coordinates of all oblique plane feature points are mapped one by one to the nonoblique plane positions on the image space, and a good correction effect is obtained. Finally, the calibration images from different angles are calculated and analyzed through simulation experiments and compared with Zhang’s method. The results show that this method has a 10%–40% improvement over Zhang’s method.

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Research on reference fiber for closed-loop measurement of Spectral Survey Telescope

Cited by 4 publications

References 0 publications

Evaluation method to obtain a fiducial fiber metrology benchmark for the Large Sky Area Multi-Object Fiber Spectroscopic Telescope

Evaluation method to obtain a fiducial fiber metrology benchmark for the Large Sky Area Multi-Object Fiber Spectroscopic Telescope

Research on the Fiducial Fibre Coding and Identification Algorithm of the LAMOST Fibre Positioning System

Research on Calibration Method of off-axis Closed-loop Detection System for Multi-target Spectral Telescope

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