Intelligent detection method for tapping omitting of internal thread based on computer vision

Tapping plays an important role in machining internal thread, whereas tapping omitting is inevitable in automated mass production. In this paper, a method for interior thread detection is presented for its efficiency, stability and robustness. Some key technologies such as imaging scheme and image processing algorithms were studied on the basis of the self-designed online detecting device. Firstly, the global threshold segmentation algorithm and local region growing segmentation algorithm are combined to precisely segment the imaging region of screw holes, while the imaging region of thread region is acquired based on the previous orientation. Then, the shape descriptors of the hole and texture descriptors of thread region are computed, respectively. And each descriptor's attribute importance is obtained using rough set. Finally, based on significant classification descriptors, semantic recognition of tapping omitting is achieved by heuristic rules. The experiment shows that the proposed classification algorithm using semantic features can identify the internal thread. The average detection time is 0.256 s, the detection accuracy of tapping omitting is 95.88%, and the detection accuracy of tapping thread is 100%.