Image Recognition Method for Missing and Looseness of Hexagonal-Head Bolts Based on the Optimal Hexagon Rule

MAO Suyi; ZONG Xiaoheng; WEN Xiaoguang; FENG Xiaorui; CHEN Wenlong; ZHANG Guowei; ZHANG Ji; SUN Yingjie; ZHANG Yongxing; CHEN Dongdong

doi:10.3724/j.gyjzG26033101

Volume 56 Issue 5

May 2026

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Article Navigation > INDUSTRIAL CONSTRUCTION > 2026 > 56(5): 239-247

MAO Suyi, ZONG Xiaoheng, WEN Xiaoguang, FENG Xiaorui, CHEN Wenlong, ZHANG Guowei, ZHANG Ji, SUN Yingjie, ZHANG Yongxing, CHEN Dongdong. Image Recognition Method for Missing and Looseness of Hexagonal-Head Bolts Based on the Optimal Hexagon Rule[J]. INDUSTRIAL CONSTRUCTION, 2026, 56(5): 239-247. doi: 10.3724/j.gyjzG26033101

Citation:

MAO Suyi, ZONG Xiaoheng, WEN Xiaoguang, FENG Xiaorui, CHEN Wenlong, ZHANG Guowei, ZHANG Ji, SUN Yingjie, ZHANG Yongxing, CHEN Dongdong. Image Recognition Method for Missing and Looseness of Hexagonal-Head Bolts Based on the Optimal Hexagon Rule[J]. INDUSTRIAL CONSTRUCTION, 2026, 56(5): 239-247. doi: 10.3724/j.gyjzG26033101

Citation:

MAO Suyi, ZONG Xiaoheng, WEN Xiaoguang, FENG Xiaorui, CHEN Wenlong, ZHANG Guowei, ZHANG Ji, SUN Yingjie, ZHANG Yongxing, CHEN Dongdong. Image Recognition Method for Missing and Looseness of Hexagonal-Head Bolts Based on the Optimal Hexagon Rule[J]. INDUSTRIAL CONSTRUCTION, 2026, 56(5): 239-247. doi: 10.3724/j.gyjzG26033101

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Image Recognition Method for Missing and Looseness of Hexagonal-Head Bolts Based on the Optimal Hexagon Rule

doi: 10.3724/j.gyjzG26033101

1. Jiangsu Expressway Company Limited, Nanjing 210049, China;
2. School of Civil Engineering, Nanjing Forestry University, Nanjing 210037, China;
3. China Railway Major Bridge Reconnaissance & Design Institute Co., Ltd., Wuhan 430056, China;
4. China Railway Bridge and Tunnel Technologies Co., Ltd., Nanjing 210061, China;
5. Beijing Jingneng International Integrated Smart Energy Co., Ltd., Beijing 101204, China;
6. Beijing Energy International Holding Co., Ltd., Beijing 100020, China

Received Date: 2026-03-31
Available Online: 2026-06-06
Publish Date: 2026-05-20

Abstract

Abstract

A vision-based detection method for bolt missing and loosening using the optimal hexagon rule is proposed. High-quality images are obtained through preprocessing operations such as perspective transformation and distortion correction. Based on the optimal hexagon rule， combined with a regional attention mechanism and a residual efficient layer aggregation network， a keypoint detection algorithm based on YOLOv26 is developed to precisely locate the six vertex coordinates of the head of standard hexagonal-head bolts. The Graham scan algorithm is adopted to obtain the convex hull of the circumcircle of the six bolt vertices. Taking the centroid of the convex hull as the center， the sum of deviations between the actual and estimated values of the six vertices is minimized. The Broyden-Fletcher-Goldfarb-Shanno （BFGS） quasi-Newton optimization algorithm is used to adjust the vertex coordinates and generate optimized regular hexagon vertex coordinates. By comparing the coordinate states of bolts， the rotation angle of the bolt can be calculated. Bolt joint rotation tests using 16-hole three-color bolt heads （gray， blue， and red） showed that within the loosening angle range of 0–60°， the absolute error of the identified bolt loosening angle ranged from -2° to 2°， with a maximum relative error of 8%， demonstrating that the proposed optimal hexagon method provided high detection accuracy and stability.
- bolt missing,
- bolt looseness,
- computer vision,
- image recognition,
- optimal hexagon rule

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References(21)

References

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