Spiral angle is an important parameter of helical gears. Currently, the traditional methods for measuring spiral angle mainly include cardboard imprinting method and modulus inference method. Gao Liqin [15] summarized several traditional methods for detecting the helix angle, and Shi Wei [6] proposed a method based on the helix angle of helical gears to detect the helix angle of helical gears. This article proposes a spiral angle detection method based on machine vision, which indirectly calculates the spiral angle of the indexing circle by detecting the spiral angle of the tooth tip circle. According to the formula:
In the equation, 𝛽𝑘 refers to the helix angle on any circle of the helical gear. Therefore, as long as the area of the tooth top is measured and its inclination angle is calculated, the helix angle of the tooth top circle can be obtained, as shown in Figure 1. By using the relationship between 𝛽 and 𝛽𝑎 in the equation, the helix angle 𝛽 on the indexing circle can be obtained.
Firstly, a template matching algorithm based on shape matching is used to obtain the tooth top area of the helical gear, as shown in Figure 2. After morphological optimization, calculate the point with the maximum distance between the contour line and the center of gravity in the region, that is, calculate the inclination angle of the tilted tooth top surface relative to the horizontal axis, and the obtained value is the helix angle of the tooth top circle. By bringing the value into equation 9, the helix angle of the indexing circle 𝛽 can be obtained.
