Abstract: Aiming at the problems of helical angle measurement of helical gear, such as high difficulty, complex measurement device, too much measurement time and difficulty in realizing online measurement, helical cylindrical gear was taken as the research object, and a machine vision measurement method combined with curve fitting was proposed. Firstly, a helical gear helix angle visual measurement system combined with the end face measurement system was designed and built.The side image of helical gear was acquired by using a double telecentric lens camera. The tooth profile is modeled and analyzed to verify the feasibility of the method. Then, the rotation direction of the helical gear was determined by the method of statistical structural elements; the rotation direction of helical gear was determined by the method of statistical structural elements. The canny operator combined with homomorphic filtering and the slope screening algorithm based on improved hit miss transformation were used to process the side image of helical gear, and the tooth line edge map was obtained. Finally, the analytical formula of a single tooth line was obtained by fitting, and then the analytical formula was optimized by using the variance between the edge points of the other tooth lines and the analytical coordinates to obtain the helical angle of the helical gear. Combining with the design value, the experimental results were verified. The experimental results show that the measurement speed of the proposed method is about 1 s, the measurement error of helical angle of helical gear can reach 4.38′, and the rotation direction of helical gear is accurate. The measuring system of the proposed method can measure the number of teeth, the diameter of tooth tip circle, the diameter of indexing circle and other parameters of the gear, and measure the helix angle and direction of helical gear at the same time, which can meet the requirements of industrial rapid online detection.

Key words: gear transmission system; cylindrical gear; helical angle of helical gear; edge detection; curve fitting; on-line measurement; morphological processing