Wu Dongxu, Liang Fusheng, Kang Chengwei, Fang Fengzhou
Centre of Micro/Nano Manufacturing Technology (MNMT-Dublin), University College Dublin, Dublin 4, Ireland.
School of Control Engineering, Northeastern University at Qinhuangdao, Qinhuangdao 066004, China.
Micromachines (Basel). 2021 Feb 8;12(2):164. doi: 10.3390/mi12020164.
Optical interferometry plays an important role in the topographical surface measurement and characterization in precision/ultra-precision manufacturing. An appropriate surface reconstruction algorithm is essential in obtaining accurate topography information from the digitized interferograms. However, the performance of a surface reconstruction algorithm in interferometric measurements is influenced by environmental disturbances and system noise. This paper presents a comparative analysis of three algorithms commonly used for coherence envelope detection in vertical scanning interferometry, including the centroid method, fast Fourier transform (FFT), and Hilbert transform (HT). Numerical analysis and experimental studies were carried out to evaluate the performance of different envelope detection algorithms in terms of measurement accuracy, speed, and noise resistance. Step height standards were measured using a developed interferometer and the step profiles were reconstructed by different algorithms. The results show that the centroid method has a higher measurement speed than the FFT and HT methods, but it can only provide acceptable measurement accuracy at a low noise level. The FFT and HT methods outperform the centroid method in terms of noise immunity and measurement accuracy. Even if the FFT and HT methods provide similar measurement accuracy, the HT method has a superior measurement speed compared to the FFT method.
光学干涉测量法在精密/超精密制造中的表面形貌测量与表征方面发挥着重要作用。合适的表面重建算法对于从数字化干涉图中获取准确的形貌信息至关重要。然而，干涉测量中表面重建算法的性能会受到环境干扰和系统噪声的影响。本文对垂直扫描干涉测量中常用的三种用于相干包络检测的算法进行了对比分析，包括质心法、快速傅里叶变换（FFT）和希尔伯特变换（HT）。开展了数值分析和实验研究，以从测量精度、速度和抗噪声能力方面评估不同包络检测算法的性能。使用研制的干涉仪测量了台阶高度标准，并通过不同算法重建了台阶轮廓。结果表明，质心法的测量速度高于FFT法和HT法，但它仅在低噪声水平下能提供可接受的测量精度。FFT法和HT法在抗噪声能力和测量精度方面优于质心法。即使FFT法和HT法提供相似的测量精度，与FFT法相比，HT法具有更高的测量速度。
