光学非球面三坐标测量中的像散补偿

利用三坐标测量仪在光学非球面镜研磨与粗抛阶段进行面形检测时,测量结果常由于补偿程序不完善而出现像散误差。本文分析了非球面三坐标测量得到的数据,指出测量结果中出现像散误差是测头半径补偿不准确所致。然后,提出了一种离线数据处理方法对测量数据进行补偿来消除像散误差。该方法通过计算网格排列的测头中心点行和列方向的切向量得出曲面上每个点的法向矢量;根据测头半径计算出测头球心到接触点的偏移量,从而实现三坐标测量仪的三维测头半径补偿。球面样板实验显示这种方法可以将该样板测量中的像散峰谷值(PV)由4.921 9μm减小到0.065 2μm,基本消除了测量结果中的像散误差,提高了三坐标测量结果的准确度。实验结果验证了提出的三维测头半径补偿程序的有效性。

Compensation of astigmatism in coordinate measurement for optical aspheric elements

When a three Coordinate Measurement Machine is used to test the surface shape of an aspheric element in grinding and polishing, obtained result often shows astigmatism errors due to an imperfect compensation programming. This paper analyzes these measurement data, and points out that the astigmatism errors comes from the imprecise compensation programming for the radius of three-dimensional probe in the CMM. Then, It presents an off-line data processing method to compensate the measurement data and to eliminate the astigmatism. By calculation of the tangent vectors of row and column at the meshed central point, the normal vector of each point on the surface is obtained. By calculation of the offsets between the centers of probe and the contact points, the radius of the tree-dimensional probe in the CMM is compensated. The experiment of a standard sphere show that this method decreases the astigmatism PV(Peak-to-Valley) of the measurement result from 4.921 9 μm to 0.065 2 μm, eliminating basically the astigmatism errors and improving the accuracy of the coordinate measurement. Obtained results verify the effectiveness of the proposed compensation programming for the radius of tree-dimensional probe in the CMM.