Image-based bolt-loosening detection using an improved homography-based perspective rectification method

In this paper, a new perspective rectification method for image of bolts in flange joint is proposed and the image-based bolt-loosening detection process for the flange joint is established. The presented method can correct the perspective distortion for the picture using the four center points of corner bolts in bolt-group connection. However, it would be difficult to find the four known points when the picture comes from a flange joint, because of the occlusion of component and the definition of picture. In this paper, a new homography-based perspective rectification method is proposed to correct the perspective distortion for image of each nut based on the identified corners of the gasket. The method to determine the corners of the partially obscured gasket is also a novelty of this paper. Based on the proposed perspective rectification method, the image-based bolt-loosening detection process for the flange joint is proposed. The proposed method is verified using a bolt connection in laboratory. The results show that the proposed method can effectively correct the perspective distortion for image of each nut and identify the bolt-loosening of the flange joint.