分析了大口径衍射光栅的焦斑特点, 研究了衍射光栅非规则图像自适应调焦过程中出现的各种问题及处理方案。提出了适用于此类光栅非规则焦斑自适应调焦的控制技术和数据处理方法, 并设计了一套自适应调焦装置用于离线检测衍射光栅的取样距离和取样角度。提出的方法用最优域值法将图像分割为焦斑和背景两部分, 基于数学形态学求取光斑面积、以及长短轴长及图像中心。通过分析图像中心位置与水平电机的对应关系, 以及长短轴长与轴向电机的对应关系, 设计出自适应调焦方法。最后, 结合面积最小化原则使用黄金分割算法进行对焦迭代和形心搜索。测试结果得到取样距离标准差为412.5 μm, 取样角度标准差为10.35″, 满足取样距离优于1 000 μm, 取样角度优于30″的精度要求。该装置具有结构简单、可靠性高、抗干扰能力强等特点,已在大口径衍射光栅综合诊断平台上得到验证和应用。

The characteristics of faculae for a larger diameter diffraction grating were analyzed, and different problems and their processing methods in self-adaptive auto-focusing of irregular images for the diffraction grating were discussed. A group of methods to control the auto-focusing of the irregular facula of the diffraction grating were proposed and a self-adaptive auto-focusing device were developed to achieve the offline detection of sampling distance and sampling angle for the diffraction grating. By optimizing threshold theory, the image was divided into two parts, facula area and background. On the basis of the mathematical morphology theory, the facula area, major and minor axis lengths and image center were calculated. Then, the adaptive focusing methods were implemented by analyzing the corresponding relationship between image center position and leveling motor, the lengths of major and minor axes and the axial motor. Finally, focusing iteration and centroid search were performed by combining the area minimization with the golden section algorithm. Test results show that the standard deviation of sampling distance is 412.5 μm and that of sampling angle is 10.35″, which meets the requirements for sampling distance and sampling angle less than 1 000 μm and 30″, respectively. This device is characterized by simple structure, high reliability, strong anti-interference ability, and has been applied in a large aperture diffraction grating comprehensive diagnosis platform.