Number and Distribution of Fiducial Fibers in a Spectroscopic Survey Telescope

Duan, Shipeng; Zhou, Zengxiang; Zuo, J. C.; Li, Mengtao; Liu, Zhigang; Hu, Hongzhuan; Wang, Jianping; Cui, Xiangqun; Zhang, Yong; Zhang, Haotong

doi:10.1088/1674-4527/ac3e5c

Cited by 7 publications

(7 citation statements)

References 24 publications

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“…As shown in Figure 5, the camera was erected at a certain height, and an electric guide rail was installed approximately 1 m in front of the camera. The fiducial fiber (Duan et al 2021) was installed on the electric guide rail at the same height as the camera. The illumination source was red light with a wavelength of approximately 620-645 nm.…”

Section: Methodsmentioning

confidence: 99%

Research on Autofocus Recognition of the LAMOST Fiber View Camera System Under Front and Back Illumination

Liang¹,

Zhou²,

Duan³

et al. 2022

PASP

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In the closed-loop detection system of the LAMOST, the lens of the fiber view camera system must focus the end of the optical fiber to accurately acquire the fiber position. It is difficult to evaluate the fibers image with a very small proportion of the image with the traditional autofocus algorithm, whether it is recognition of the front illuminated by the fiber ceramic ferrules, or the light-emitting spot of the fibers in the black background, that is, the recognition of the back illumination of the fibers. In this paper, we propose an autofocus determination method for the LAMOST closed-loop control under front and back illumination conditions. Under the condition of front illumination, to greatly reduce the calculation time, the system first pre-recognizes the focusing target through the Faster R-CNN and then uses an optimized contrast algorithm to evaluate the image definition of the corrected focusing target ROI. Then, the algorithm is compared with Tenengrad gradient and Laplacian gradient calculations using the Sobel operator and Laplacian operator in OpenCV. The results show that this method takes only one-ninth of the time required by the other methods to obtain the same accuracy. Under the condition of back illumination, we use the average number and average brightness of spot pixels as the evaluation basis of image sharpness. This method can complete the evaluation of image sharpness in the process of spot recognition and provide initial data for the subsequent detection for closed-loop control. The focus accuracy of the camera is of great significance for thousand-fiber metrology, which will have an important influence on the accuracy of astronomical observations. These focusing methods not only play an important role in the closed-loop control of the LAMOST but also apply to the focusing of closed-loop detection systems of other multi-target optical fiber spectral astronomical telescopes.

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Section: Methodsmentioning

confidence: 99%

Research on Autofocus Recognition of the LAMOST Fiber View Camera System Under Front and Back Illumination

Liang¹,

Zhou²,

Duan³

et al. 2022

PASP

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“…Although our scheme is not superior in coding capacity, it can obtain higher registration point accuracy after subsequent experiments. In addition, when conducting optical fiber positioning in practical applications, approximately 60 fiducial fibres must be distributed in a camera's field of view (Duan et al 2022). Our 12 bit coding scheme can obtain 228 kinds of coding capacity, which can fully meet the measurement requirements.…”

Section: Design Of the Fiducial Fibrementioning

confidence: 99%

“…In the 2022 LAMOST upgrade project, we plan to implement a closed-loop vision measurement scheme to improve the accuracy of fiber positioning (Zhou et al 2021a(Zhou et al , 2022. At present, six fiber view cameras (FVCs) are installed around mirror B (MB), approximately 20 m from the focal plane (Duan et al 2022). Due to the long distance between the camera and the focal plane, the environment has a great influence on the repeatability of the FVC capturing fiber.…”

Section: Introductionmentioning

confidence: 99%

“…In addition, for the 1.75 m diameter LAMOST focal plane, to ensure the accuracy of the system, it is difficult to cover the entire focal plane with one camera under the condition of existing cameras and lenses. In the design of the whole closed-loop detection system, the focal plane is divided into six areas, each corresponding to the standard full-frame sensor size, covering one-sixth of the focal plane, rectangular, and overlapping with each other (Duan et al 2022). The rotation and translation of the LAMOST focal plane during observation will change the number and position of the fiducial fibres in the camera field of view, which will increase the complexity of detecting the fiducial fibres in the focal plane partition.…”

Section: Introductionmentioning

confidence: 99%

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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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“…LAMOST has been operated with a 100 μm positioning accuracy based on an open-loop control mode for 12 yr. The LAMOST improvement project plans to add a fiber metrology system to update the positioning mode to closed-loop control (Duan et al 2022). The fiber metrology system is designed to measure the position of the fiber tips in the focal plane with an accuracy of less than 20 μm.…”

Section: Introductionmentioning

confidence: 99%

Novel Fiducial Fiber Scanning Measurement Method Based on a Polar Coordinate System for LAMOST

Zhang¹,

Chen²,

Liu³

et al. 2023

PASP

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The multiobject fiber-fed spectrograph is the core scientific instrument for large-scale spectroscopic surveys. For closed-loop control of fiber positioning, fiber metrology systems are implemented in numerous fiber-fed spectrographs. The position accuracy of the fiducial fiber in the focal plate directly affects the performance of the fiber metrology system. However, there are currently no suitable methods and devices for measuring the fiducial fibers with high accuracy in the Large Sky Area Multi-Object Fiber Spectroscopic Telescope (LAMOST). To solve this problem, this study proposed a novel online scanning measurement method for fiducial fibers in which a scanning camera was set up in front of the focal plate, and the rotation and translation movements of the focal plate were combined to set a polar coordinate measurement system. First, the pole and polar axis of the polar coordinate frame were determined, and the compensation values of the polar radius and angle of the polar coordinate of the fiducial fibers were solved in the field of view of the scanning camera. A prototype measurement platform was set up to verify the feasibility and scientific validity of the method. Experiment results show that the polar radius accuracy of the proposed method met the measurement requirements. The X–Y measurement accuracy can be further improved when a higher-precision rotary stage is adopted. Thus, the difficulties in online accurate measurement for fiducial fibers can be tackled by the proposed method with good operability in LAMOST.

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Number and Distribution of Fiducial Fibers in a Spectroscopic Survey Telescope

Cited by 7 publications

References 24 publications

Research on Autofocus Recognition of the LAMOST Fiber View Camera System Under Front and Back Illumination

Research on Autofocus Recognition of the LAMOST Fiber View Camera System Under Front and Back Illumination

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

Novel Fiducial Fiber Scanning Measurement Method Based on a Polar Coordinate System for LAMOST

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