显微成像测量精密狭缝的重复精度

High precision measurement of the micro-imaging system to check repeatability of precision optical slits in SSRF beamlines

上海光源(SSRF)光束线站上使用的精密光学狭缝要求重复精度小于1μm,在精密狭缝安装到光束线站前需要在线或者离线对其进行重复精度测量。提出了基于高分辨率CCD和高倍率镜头的机器视觉测量系统,设计出一种图像多级滤波的数据处理方法,从而实现了精密光学狭缝重复精度的测量。测量之前,通过测量系统对光学分辨率板标准小孔采集图像,完成了高倍率放大镜头倍率标定。利用代数均值滤波、统计中值滤波、最小均方误差滤波有效降低图像随机噪声。提出将狭缝图像二值化,并将狭缝刀片移动前后两帧二值图像差值,从而得到狭缝的重复精度。该系统的测量分辨率达到0.3μm。结果表明,该测量系统能够满足精密狭缝的重复精度的测量。

The beamlines slits of Shanghai Synchrotron Radiation Facility （SSRF） are required to have a repeatability of better than 1 μm. Before the slits installation, the off-line and/or on-line repeatability measurements must be conducted. A machine vision measuring system based on high resolution CCD and adjustable high magnification lens was used in this regard. A multi-level filtering method was used to treat the imaging data. After image binarization, the imaging noises were depressed effectively by using of algebraic mean filtering, statistics median filtering, and the least square filtering. Using the subtracted image between the images before and after slit movement, an average displacement of slit blades could be obtained, and the repeatability of slit could be measured, with a resolution of 0.3 μm of the measurement system. The experimental results show that this measurement system meets the requirements for non-contact measurements to the repeatability of slits.