用空间载频法测量玻璃平板的厚度均匀性

设计了一种基于迈克耳逊干涉光路的相位测量系统,将单臂作为检测端完成了对玻璃平板厚度均匀性的直接测量和分析。该系统由CCD采集干涉图样,利用傅里叶变换条纹分析术和相位解包裹技术提取干涉图中所包含的待测相位信息;对于傅里叶变换法中频谱旁瓣中心无法准确定位的问题,采用三角变换法去载频,从而不需要准确地得知频谱旁瓣的中心位置就可以计算出相位结果,消除了人为估算和垂轴方向上的微小载频分量给测量结果带来的误差。实验测量了多块玻璃平板的厚度均匀性。测量结果显示：使用像元大小为4.65 μm×4.65 μm的CCD相机,测量玻璃平板两表面在长度方向和宽度方向上的厚度均匀性的理论精度分别达到0.93%和0.92%,表明本系统基本满足玻璃平板厚度均匀性测量的要求,且对干涉图频谱旁瓣的定位精度和载频的方向精度要求较低。

Measurement of thickness uniformity for glass plate by spatial carrier

On the basis of the Michelson interferometer, a phase interference measurement system with one single arm as the measurement output port was designed to measure and analyze the thickness uniformity of a glass plate. In the system, a CCD camera was used to collect the interference pattern and the Fourier transform fringe analysis and phase unwrapping techniques were used to extracted the phase information contained in the interference pattern. For the problem that the sidelobe center of Fourier transform spectrum could not be accurately located, an applicable triangular transformation method was proposed to extract the volume of phase change directly. With this approach, the phase results could be obtained more accurately without knowing the central location of the spectral sidelobe, meanwhile, the errors induced by man-made estimation and the small carrier frequency component in vertical axis were eliminated. The thickness uniformity of a group of glass plates was measured in both of the length and width directions. The experimental results show that the theoretical accuracy is 0.93% and 0.92% in two directions, respectively, when they measured by a CCD camera with a unit size of 4.65 μm×4.65 μm. The system can measure the thickness uniformity of the glass plates, and has lower demands for the location accuracy of frequency spectral sidelobe and the direction precision of carrier frequency.