Bolt loosening angle measurement along full range of screw exposure length based on 3D point cloud

The existing two-dimensional (2D) vision-based bolt loosening measurement range is generally limited to 0–60°. To overcome this limitation, a bolt loosening angle measurement method along full range of screw exposure length based on three-dimensional (3D) point cloud is proposed. Initially, 3D point clouds of bolt groups were reconstructed using 2D images under 18 working conditions, and the 3D point cloud of a single bolt was extracted from the bolt group. Subsequently, the bolt loosening angle along full range of screw exposure length was measured by calculating the rotation angle derived from the change in screw exposure length before and after loosening. The average relative error of all bolt loosening angle measurement results under the 18 working conditions was 3.46 %. Finally, the factors influencing the proposed method were analyzed. The results demonstrated that the proposed method could accurately measure the bolt loosening angle along full range of screw exposure length.