针对钣金零件轮廓尺寸高精度测量面临尺度增大造成的测量精度下降问题, 提出了准确获取零件上表面的边缘方法和厚度转换模型。首先, 结合光学成像理论分析了背光光源下不同厚度钣金零件的边缘特性, 提出厚度零件具有上下边缘特征, 然后根据平板零件图像的边缘分布特征, 采用Canny算子初定位边缘, 用多项式拟合算法实现亚像素边缘精确提取, 对含有上下边缘的轮廓提出平均距离法获得上表面边缘, 并针对厚度引入的误差提出了厚度转换模型进行边缘修正, 获取零件在标定平面上的真实边缘, 最终结合标定数据求取零件尺寸。实验结果表明, 在1×0.75 m2的视场内, 1~5 mm厚、500 mm×500 mm零件的测量精度达到了0.05 mm, 满足了钣金加工测量的需求。

In order to improve the measurement accuracy of planar sheet metal parts when the measurement scales increase, upper and lower edge distinguishing method and thickness converting model were proposed. Firstly, edge distribution characteristics of parts image which include upper edges and lower edges were proposed by analyzing the edge feature of different thickness of metal parts placed in back-lighting. Sub-pixel edges of parts were extracted by the Canny and polynomial fitting algorithm. Then, upper or lower edges were distinguished by distance-mean method. Finally, accurate edges on the calibration plane were located basing on thickness converting model. Dimensional measuring of metal part could be calculated using the calibration data. Experimental result shows that the precision of the 1-5 mm thickness and 500 mm×500 mm parts in the range of 1×0.75 m2 is up to 0.05 mm. It can satisfy the requirement of the sheet metal cutting measurement.