Abstract: Aiming at the low efficiency of traditional measurement methods in measuring geometric parameters of helical gears, a measurement method based on the principle of vision was proposed. Firstly, the repeatability accuracy test of the circular calibration board was designed to verify the reliability of the measurement system. Secondly, the nonzero pixel coordinates of helical gear contour were obtained by boundary tracking function, 

the distance from the helical gear contour to the center of the mounting hole was calculated, and the radius of the tooth top circle and tooth root circle were obtained. 

Then, aiming at the image of the distance between the edge point and the center point of the tooth profile, a pulse counting method was designed to measure the number of teeth. Then, the Hough transform and the formula of the angle between two lines were introduced to measure the helix angle, and the diameter and modulus of the dividing circle were indirectly calculated according to the relevant formula. Finally, the least square method was used to fit the three edge lines of the keyway, and the width and depth of the keyway were obtained by the intersection of the lines and the information of the gear mounting hole. The two gears were measured 10 times. The experimental results show that the uncertainty of the measurement system is not more than 0.003 pixels, and the gear size can be measured in the range of 10mm~70mm. The relative errors of the parameters of the big and small gears are less than 1% and 2% respectively, which can meet the requirements of automatic and accurate measurement of helical gear geometric parameters.

Key words:  helical gears; visual measurement; geometric parameters; repeatability accuracy test; pulse counting method

LI Jie, LIU Yong, LI Hao-ze, et al. Measurement method of geometric parameters of helical gear based on vision principle［J］.Journal of Mechanical & Electrical Engineering, 2021,38(11):1451-1457.