A high-accuracy circular hole measurement method based on multi-camera system

Industrial parts often contain a large number of circular holes that are often used as assembly datums. Measuring circular holes with high accuracy is very challenging due to the low signal-to-noise ratio of the edges on the image. This problem is further complicated when chamfers and nonuniform reflections are present. In this paper, a high-accuracy method for measuring circular holes is proposed to realize on-line inspection under a multi-camera system. In the image processing stage, an ellipse detector is designed based on a high-confidence edge detection algorithm and state-of-the-art ellipse fitting technology to significantly eliminate the ellipse fitting bias caused by blurred edges. In the ellipse matching and validation stage, the ambiguous objects are reconstructed first using ambiguous ellipse pairs matched by the epipolar geometry. Then, the similarity between the reprojected ellipse and the detected ellipse is assessed by calculating the Euclidean distance to significantly eliminate mismatched candidates and select the best matching ones. Subsequently, the discrete 3-D points are calculated by spatial intersection after obtaining the homologous points on the corresponding ellipses. Furthermore, a robust spatial circle fitting method is developed to adapt to discrete 3-D points that are not strictly located on a plane. Finally, extensive experiments on both real-world datasets and simulation datasets demonstrate that the proposed algorithm is beneficial for improving the measurement accuracy compared with the state-of-the-art algorithms and demonstrate great potential for industrial applications.