Vision-Based Detection of Bolt Loosening Using YOLOv5

Abstract

Bolted connections have been widely applied in engineering structures, loosening will happen when bolted connections are subjected to continuous cyclic load, and a significant rotation between the nut and the bolt can be observed. Combining deep learning with machine vision, a bolt loosening detection method based on the fifth version of You Only Look Once (YOLOv5) is proposed, and the rotation of the nut is identified to detect the bolt loosening. Two different circular markers are added to the bolt and the nut separately, and then YOLOv5 is used to identify the circular markers, and the rotation angle of the nut against the bolt is calculated according to the center coordinate of each predicted box. A bolted connection structure is adopted to illustrate the effectiveness of the method. First, 200 images containing bolts and circular markers are collected to make the dataset, which is divided into a training set, verification set and test set. Second, YOLOv5 is used to train the model; the precision rate and recall rate are respectively 99.8% and 100%. Finally, the robustness of the proposed method in different shooting environments is verified by changing the shooting distance, shooting angle and light condition. When using this method to detect the bolt loosening angle, the minimum identifiable angle is 1°, and the maximum detection error is 5.91% when the camera is tilted 45°. The experimental results show that the proposed method can detect the loosening angle of the bolted connection with high accuracy; especially, the tiny angle of bolt loosening can be identified. Even under some difficult shooting conditions, the method still works. The early stage of bolt loosening can be detected by measuring the rotation angle of the nut against the bolt.

YOLOv7-RAR for Urban Vehicle Detection

“…This idea omits the complex candidate box selection and calculation steps in the two-stage algorithm. Therefore, the running speed of the algorithm is far faster than that of the two-stage detection algorithm [ 27 , 28 , 29 ]. The representative algorithms are the YOLO algorithm and the SSD algorithm.…”

Image-based bolt self-localization and bolt-loosening detection using deep learning and an improved homography-based prospective rectification method

“…Zhang (2020) et al proposed a bolt loosening detection method based on Fast-RCNN algorithm, using the bolt thread heights under different loosening states. Sun et al (2022) identified the marks on the nut and the screw to determine the loosening of bolt based on YOLOv5.…”

Bolt looseness detection based on Canny edge detection algorithm

“…Pan et al 35 combine target detection algorithm and target tracking algorithm to detect and track bolt looseness. Sun et al 36 use YOLOv5 algorithm to detect bolts and marks on bolts, and calculate the bolt loosening angle according to the central coordinates of two types of boundary frames. Huynh et al 37 detected and cut the bolt area through convolutional neural network, and then identified the bolt loosening angle based on Hough transform.…”