模压成型非球面镜残余应力与折射率的三维无损重建研究

Residual stresses and refractive index variation were observed in compression molded aspherical glass lenses. These both affect the optical performance and constrain the usage of molded aspherical lenses. In order to improve the quality of molded aspherical lenses, concurrent three characterization of residual stresses and refractive index are studied in this research. There are two major difficulties during the study. First, the nonlinear property of the residual stress makes reconstruction process complexity. Second, how to find the relationship between residual stresses and refractive index from the measurement results. Therefore, three dimensional photoelasticity, computerized tomography and numerical simulation are employed to study the reconstruction of nonlinear residual stresses. An experiment setup is designed to measure the residual stresses and refractive index concurrently. Then, a numerical model is built to calculate the optical performance through residual stresses and refractive index. The simulated optical performance is compared with experimental measurement to confirm and improve the measurement method. Finally, the experimental calculated residual stresses and refractive index are compared with numerical simulation results to analyzed the mechanism of residual stresses and refractive index. The theoretical analysis, numerical simulation and experimental measurement are combined to study the concurrent reconstruction of residual stresses and refractive index. And results can be used as a guidance for compression process.

残余应力和折射率偏差影响模压成型非球面镜的光学性能，制约了它的推广应用。为了提高非球面镜的光学性能，本项目对残余应力和折射率的无损检测技术展开研究。研究存在以下技术难点：残余应力重建的非线性；残余应力和折射率的对应关系。本项目运用三维光弹性法、计算机断层扫描、数值模拟等知识，以模压成型非球面镜为研究对象，研究非线性残余应力的三维重建方法；设计残余应力与折射率无损检测方法，建立残余应力和折射率的对应关系；建立残余应力和折射率对光学性能影响计算模型，结合实验测量与仿真计算结果，对检测方法进行改进和优化，最后将实验结果与有限元仿真计算的残余应力和折射率进行对比分析，研究模压工艺参数对残余应力和折射率的影响规律，残余应力与折射率的产生机理。本项目采用理论分析、数值模拟与实验测试相结合的研究方法，为残余应力和折射率的三维重建，模压成型工艺设计提供理论支持。

残余应力和折射率偏差影响模压成型透镜的光学性能，制约了它的推广应用。为了提高模压成型透镜的光学性能，本项目对残余应力和折射率的无损检测技术展开研究。利用圆偏光器测量的光强图像，采用积分光弹性法对柱透镜和非球面透镜中的残余应力分布进行三维无损重建。采用TNM模型仿真研究了模压成型透镜工艺过程，发现转折温度前的冷却速率为影响透镜的残余应力与透镜曲面形貌的重要参数，可以利用两步冷却方式来减少工艺过程时间。为了研究积分光弹性法的应力三维重建误差，利用琼斯矩阵模拟计算仿真的应力在圆偏光器中六步相移法下的光强图像，通过该图像计算了等倾角与相位延迟，然后重建残余应力场分布。将重建的三维应力场与有限元仿真的应力场进行对比分析，发现由于在计算过程中采用了三维区域的力平衡条件来分离轴向应力，而由于透镜上下两端存在着应力方向的变动，使分离的轴向应力在上下两端产生了一定的偏差，由此将误差引入了应力的三维重建，且使得中心部位产生了累积误差。该误差可以通过多项式对应力进行拟合，进行消解。为了提高生产效率，提出了透镜模压成型质量控制方法，该方法在冷却过程中采用略高的冷却速率以提高生产效率，然后通过批量退火减小残余应力与折射率偏差，提高透镜的性能。提出了在线检测透镜质量的方法，该方法通过测量、三维重建，建立残余应力-折射率-光强图像的对应数据库，在之后的测量过程中，只需要将测量的光强数据与数据库进行对比即可获取折射率偏差、残余应力分布。