A semi-supervised deep learning approach for circular hole detection on composite parts

This paper introduces the usage of semi-supervised learning to obtain competitive detection accuracy of measuring drilled holes on composite parts with very limited noisy training data. An improved texture segmentation algorithm based on local binary patterns algorithm is proposed, named local exponential patterns. The algorithm divides the image texture into nine levels, of which the highest level of texture is selected for contour extraction. An ellipse fitting method is used to fit the target contours and vote for the candidate ellipses. The regions inside the candidate ellipses are taken as the semi-supervised semantic label for images. A new loss named round loss is proposed, and a superior circle segmentation model was trained by learning from incompletely annotated data. To verify the effectiveness of the method, experiments were conducted with the drilled holes on the composite parts. The results show that the proposed semi-supervised deep learning approach is exceedingly suitable for circle detection of holes with different texture information commonly found in robotic drilling. Massive data labeling can be completely avoided with proposed method. The measurement accuracy can reach 0.03 mm, which can meet the visual measurement requirements of the circular holes on composite parts in the robotic drilling system.