基于视觉测量的回转轴线标定方法研究

Study on calibration method of rotary axis based on vision measurement

为了实现高压涡轮叶片上的气膜孔特征的高精高效测量,设计并搭建了一套非接触式的四轴视觉坐标测量系统。针对其中的回转轴线的空间位置标定难题,结合工业影像测头的成像特点,提出了一种基于视觉测量的回转轴线标定方法。在标定过程中,采用了定制的长方体标定块,并通过回转工作台与三坐标测量机之间的配合,使工业影像测头对焦于标定块的表面并采集到其锋利棱边的图像,而后再通过边缘提取、像素距离计算、物理距离转化和代数运算等步骤,最终确定了回转工作台的轴线在机器坐标系中的空间方位。最后,选用一个标称尺寸为80 mm的标准量块作为被测物体,以对标定方法及标定结果进行验证,各次测量结果的误差均小于±0.01 mm,并进行了合成标准不确定度的分析。实验结果表明:文中所提出的回转轴线标定方法能够达到较高的标定精度和较好的重复性,能够满足气膜孔形位参数的检测要求。

For the purpose of inspecting the film cooling holes on high-pressure turbine blade in a rapid and accurate manner, a non-contact four-axis vision coordinate measuring system was designed and established in the paper. With regard to the determination difficulty of the spatial location of the rotary axis, a calibration method based on vision measurement was proposed in the paper, which fully considered the imaging characteristics of industrial CCD used in the system. In the calibrating procedure, a specially designed cuboid mental block was applied as the target. Through the coordination between the turntable and the coordinate measuring machine, the industrial CCD focused on the block surface and then captured the sharp edges of the block. And then, the spatial orientation of the rotary axis in the machine coordinate system could be determined by edge extraction, pixel distance calculation, physical distance conversion and algebraic operation etc. Finally, a gauge block was selected to be inspected by the measuring system to verify the calibration method and results, whose nominal size was 80 mm.As the experimental results showed, the measuring errors were all smaller than ±0.01 mm. Therefore, the calibration method of rotary axis proposed in the paper showed higher calibration precision and repeatability,which could meet the inspecting requirements of the shape and position parameters of film cooling holes.