Agour Mostafa, Falldorf Claas, Bergmann Ralf B
BIAS-Bremer Institut für angewandte Strahltechnik, 28359 Bremen, Germany.
Physics Department, Faculty of Science, Aswan University, Aswan 81528, Egypt.
Sensors (Basel). 2024 May 12;24(10):3072. doi: 10.3390/s24103072.
We have recently demonstrated that the 3D shape of micro-parts can be measured using LED illumination based on speckle contrast evaluation in the recently developed SPICE profilometry (shape measurements based on imaging with spatially partially coherent illumination). The main advantage of SPICE is its improved robustness and measurement speed compared to confocal or white light interferometry. The limited spatial coherence of the LED illumination is used for depth discrimination. An electrically tunable lens in a 4f-configuration is used for fast depth scanning without mechanically moving parts. The approach is efficient, takes less than a second to capture required images, is eye-safe and offers a depth of focus of a few millimeters. However, SPICE's main limitation is its assumption of a small illumination aperture. Such a small illumination aperture affects the axial scan resolution, which dominates the measurement uncertainty. In this paper, we propose a novel method to overcome the aperture angle limitation of SPICE by illuminating the object from different directions with several independent LED sources. This approach reduces the full width at half maximum of the contrast envelope to one-eighth, resulting in a twofold improvement in measurement accuracy. As a proof of concept, shape measurements of various metal objects are presented.
我们最近证明，基于最近开发的SPICE轮廓测量法（基于空间部分相干照明成像的形状测量）中的散斑对比度评估，使用LED照明可以测量微零件的三维形状。与共焦或白光干涉测量法相比，SPICE的主要优点是其更高的鲁棒性和测量速度。LED照明的有限空间相干性用于深度辨别。4f配置中的电可调透镜用于快速深度扫描，无需机械移动部件。该方法效率高，捕获所需图像不到一秒钟，对眼睛安全，并且提供几毫米的焦深。然而，SPICE的主要限制是其对小照明孔径的假设。如此小的照明孔径会影响轴向扫描分辨率，而轴向扫描分辨率主导着测量不确定性。在本文中，我们提出了一种新颖的方法，通过用几个独立的LED光源从不同方向照射物体来克服SPICE的孔径角限制。这种方法将对比度包络的半高全宽减小到八分之一，从而使测量精度提高了两倍。作为概念验证，展示了各种金属物体的形状测量结果。
