圆锥外螺纹的线阵CCD非接触检测方法

Measurements of non-contact external tapered thread based on linear array CCD

为了提高圆锥外螺纹尺寸检测的精度并实现自动化测量,提出了基于线阵CCD的非接触测量方法.建立了包括计算机运动控制、图像数据自动采集和尺寸计算的测量系统,该系统通过控制高精度的线阵CCD扫描外圆锥螺纹在平行光场中的投影来获取螺纹图像.针对正投影时螺旋线对螺纹牙的投影产生局部遮挡的现象,通过调整螺纹轴线与光轴的角度消除遮挡,获取完整的螺纹牙投影.1维CCD图像信号经过中值滤波处理后进行一阶差分提取螺纹牙的轮廓点.对螺纹轮廓分段拟合并以亚像素级的轮廓推导出螺纹尺寸的计算公式.实验表明,该系统可以完成各项螺纹参数测量,精度高于5μm,重复性好,易于实现自动化测量.

In order to improve the measuring accuracy of external tapered thread and realize automatic measurement, a non-contact method based on linear array CCD is presented, in which a CCD camera is controlled to scan the projection of thread in the parallel optical field to acquire thread images. Considering the block of screw line on the projection of thread teeth, the thread axis was adjusted to a suitable angle with the optical axis to obtain the accurate teeth projection. The accurate digital teeth contour was obtained by the application of high precise CCD in combination with the processing of median filtering and first order difference method. The contour was further fitted to be lines and arcs in different segments to achieve the precise outline with sub-pixel class, from which the measuring equations can be derived and transformed into real values. The experiments show that the system can complete the measurements of thread dimensions with an accuracy of higher than 5 μm, and is easy to realize automatic measurement.