中径是决定螺纹联接质量的重要参数, 为了能够利用机器视觉技术实现对螺纹中径的高效测量, 提出了一种基于虚拟三针法的螺纹中径测量方法。建立虚拟三针法测量螺纹中径的理论计算模型;对螺纹图像进行了预处理和边缘提取, 并利用最小一乘法对提取的螺纹轮廓进行拟合, 获取中径值;以螺纹塞规为对象进行了对比实验。实验数据表明, 利用虚拟三针法测得的中径方差较传统三针法降低了51.8%。测量效率上虚拟三针法是传统三针法的2倍以上, 较触针扫描方法提高了52%。说明所提出的虚拟三针法也可以作为一种测量螺纹中径的手段。

Pitch diameter is an important parameter to decide thread connection quality, in order to be able to use machine vision technology to realize the high efficiency measurement of the thread diameter, a method based on virtual three ball method was proposed. Firstly, a theoretical calculation model for measuring the pitch diameter of the thread by virtual three ball method was established, the thread image is preprocessed and the edge is extracted, and the extracted thread contour is fitted with the least linear method to obtain the value of pitch diameter. Finally, a comparative experiment is carried out with thread plug gauge as the object, experimental datas show that the variance of pitch diameter measured by virtual three ball method is 51.8% lower than that by traditional three ball method. In terms of measuring efficiency, the virtual three ball method is more than 2 times of the traditional three ball method, and 52% higher than the stylus scanning method. It is shown that the proposed virtual three ball method can also be used as a means to measure the pitch diameter of thread.