为了抑制激光在线测厚时入射角波动引起的误差, 根据几何光学分析了激光透射式和反射式测厚原理, 发现激光在特定入射角附近波动时, 两种方式的测厚误差一正一负, 具有互补性, 在此基础上提出基于透射和反射同时测量的互补式测厚方法, 该方法可将误差限定在透射式和反射式测量误差之间, 抑制在线测厚误差.对于有机玻璃平板, 理论计算表明, 当激光入射角在67.013°±4°波动时, 相对误差绝对值在1%以内, 误差抑制率均值大于90%; 当入射角为61.536°时, 误差抑制率为100%.利用线结构激光器和两个线阵CCD相机搭建互补式测厚实验系统, 测量了标称厚度为1~5 mm的有机玻璃平板, 与透射式和反射式测厚结果进行对照, 除厚度为1 mm的玻璃外, 互补式测厚误差被限制在透射式和反射式之间, 最大误差抑制率达61%.实验结果表明, 该互补式方法有效抑制了误差, 提高了在线厚度测量准确度, 解决了在线测量不可重复性导致的无法通过均值法减小误差的问题.

For suppressing the error from the incident angle fluctuation during laser thickness measurement online, the principles of laser transmission and reflection thickness measurement were analyzed by geometrical optics, which show that when the fluctuation of laser incident angle is nearby a particular value, the thickness measurement errors of two methods are complementary with one positive and the other negative. On this basis, a complementary thickness measurement method was proposed based on laser transmission and reflection simultaneous measurement, and the error could be limited between the transmission type and reflection type measurement errors, suppressing the online thickness measurement error. For the polymethyl methacrylate sheet, theoretical calculation results show that when the fluctuation span of the incident angle is at 67.013±4 degrees, the relative error absolute value is within 1% and the mean error suppression ratio is greater than 90%. When the incident angle is 61.536 degrees, the error suppression ratio is 100%. Using one line structured light laser and two linear array CCD cameras, a complementary thickness measurement system was set up. The polymethyl methacrylate sheets with the nominal thickness of 1~5 mm were measured. In addition to the 1mm glass, the complementary thickness measurement error is restrained between the transmission and reflection measurement errors, and the maximum error suppression ratio is 61%. Experimental results show that the complementary method can effectively restrain the error and improve the online thickness measurement accuracy.