Helical gears are widely used in engineering. Compared with straight gears, helical gears have the advantages of smooth operation, high bearing capacity and low noise. There is no fixed standard for the helical angle of helical gears, and the helical angles of helical gears produced by different manufacturers are often different. Industrial measurement of helical gear helix angle mainly adopts contact measurement method, which is divided into universal angle ruler method, rubbing method, lead meter method, hobbing machine method, etc. According to GB / T 6315-2008, the measurement accuracy of universal angle ruler is 2 ‘or 5’, and the measurement time is generally about 18 s. Contact measurement consumes more man hours and is increasingly difficult to adapt to rapid industrial production.
The non-contact measuring methods of helical gear helix angle mainly include laser measuring method, structured light method and machine vision method. Zi Hao et al. Proposed a measurement method of helical angle of helical cylindrical gear based on laser displacement sensor. The laser probe in this method needs a precise mechanical transmission device. Shi Wei et al. Proposed a helical gear helix angle measurement method based on image processing of upper and lower end faces of helical gears, which requires manual operation and is slow. Song shuanjun et al. Proposed a helical gear angle measurement method based on gear side image processing, and Li Jie et al. Proposed a helical angle detection method combining Hough transform and the formula of the angle between two straight lines; These two methods can be applied to the on-line measurement, but the error is large when measuring the helical gear with large helix angle, and the image processing effect on the gear side is poor.
The projection analytical formula of helical gear tooth line in two-dimensional space is obtained through calculation, and the uniqueness of tooth line shape is verified by MATLAB simulation; By processing the helical gear side image, the edge image of the tooth line is obtained, the helical gear rotation direction is obtained by counting the number of structural elements, and the helical angle is obtained by curve fitting. The algorithm proposed by the author can be combined with the gear end face measurement system to achieve fast on-line measurement.