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CSME 2024/05
Volume 45 No.2
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169-176
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Grid Gap Measurement Method Based on Machine Vision
Hao Yanga, Li-Xu Kanga, Han-Zhong Taoa, Hao-Yu Lia, Hai-Feng Zhanga and Yu Fanga
aSchool of Mechanical and Automotive Engineering, Shanghai University of Engineering Science, Shanghai 201620, China.
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Abstract:
Grid assembly is the core component of ion thruster. The grid gap is a key thruster parameter that affects the divergence angle and the thrust of ion beams. However, the measurement of grid gap mainly relies on manual methods in practical applications. To solve the technical problem with the automatic detection of grid gaps during the assembly process, a noncontact grid gap detection method based on machine vision is proposed. A mathematical model of grid gaps and small aperture areas is established for the special structure of gate apertures and the characteristics of light propagation. For the extraction of small aperture projection contours, this paper proposes an Otsu multi-threshold fast segmentation method based on LaGrange decomposition, which improves the accuracy and real-time projection area calculation. A 40-times repetition test is conducted for the single-hole pitch of the grid assembly, and the standard deviation of the method is 12 μm, which has high repetition accuracy. The accuracy verification test results show that the detection accuracy of the system is higher than ±20 μm. The results meet the requirements of the ion thruster assembly process. Grid gap measurement is expected to replace the existing manual inspection methods in practical applications.
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Keywords: Ion thruster; Grid gap; Noncontact measurement; Machine vision;
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*Corresponding author; e-mail: fangyu_hit@126.com
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©
2024
CSME , ISSN 0257-9731
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