Research Of Non-contact Detection System For YTG-type External Thread Parameters

The subject benefits from the cooperation project between Heilongjiang University and YiLangSiTe Petroleum Special Thimble Co. Ltd. in DaQing.Aiming at the problems of low efficiency and low reliability in the detection of thimble thread parameters, according to API standard (American Petroleum Institute) about thread size and existing image detection theory, A non-contact detection way for external thread parameters is presented, the geometric parameters of thimble external thread is detected and image processing technologies are discussed in the paper.The principle of the detection system is: by action of 2DOF platform, we take a thread picture by CCD camera and generate image file by image acquisition card, and get the thread contour by digital image processing technology. The contour in picture is proportional to the actual one, and the ratio is a constant K determined by CCD camera magnified ratio. By calculating the geometry parameters and comparing with the definition size, we can judge whether it is qualified.According to the site conditions and image processing requirements, we design the camera removing dust mechanical structure, closed box mechanical structure and reduction vibration mechanical structure. And assembly drawing is completed.This paper adopts the median filter to reduce the interferers, uses image enhancement to enhance image clarity. According to testing, we can make the conclusion that the median filter is better than other ways. The image is clearer and the contour line is well preserved. The key of detection thread parameters is extraction of image contour. The paper analyzes several the thread contour extraction algorithms, including to Roberts algorithm, Sobel algorithm, Laplacian algorithm and Canny algorithm. We choose Canny contour detection algorithm through analysis and comparison. Contour joint is necessary after getting thread contour. So the paper presents two ways: line joint and circle joint. At last we choose circle joint way to process contour.According to testing, the system realizes non-contact detection of thimble thread parameters, and results to fast detection speed and well precision. Therefore, it is an effect way for thimble thread non-contact detection.