Hypercentric Imaging in Coherent Optical Metrology (HyperCOMet)

相干光学计量中的超中心成像 (HyperCOMet)

• 批准号: 430572965
• 负责人: Professor Dr. Ralf Bernhard Bergmann
• 金额: --
• 依托单位: BIAS - Bremer Institut für Angewandte Strahltechnik GmbH
• 依托单位国家: 德国
• 项目类别: Research Grants
• 财政年份: 2019
• 资助国家: 德国
• 起止时间: 2018-12-31 至 2023-12-31
• 项目状态: 已结题
• 来源: https://gepris.dfg.de/gepris/projekt/430572965?language=en
• 关键词: Hypercentric; Imaging; Coherent; Optical; Metrology

During production, technical parts are subject to unwanted geometrical distortions and surface defects such as fractures, scratches and dents. Therefore, shape inspection is a mandatory perquisite for industrial quality assurance. If high precision is required, interferometric methods are well established, because they work contactless and provide a measurement uncertainty down to a fraction of the illumination’s wavelength.Advancements in micro cold forming and micro systems engineering allow for the production of increasingly complex shaped micro parts, which leads to new challenges in optical metrology. Thus, in addition to the high precision, future interferometric measurement systems have to meet these requirements by offering the ability to measure highly complex shaped objects in a reasonable time frame. Currently available systems based on standard imaging systems cannot accomplish this task, because they have a limited viewing angle, and measuring the full 3D form of a complex geometry often requires a number of individual measurements from different observation directions. This requires extensive hardware and involves time-consuming calibration and stitching procedures to reconstruct the object’s form.A solution to this problem could be hypercentric (or pericentric) imaging, which has recently been introduced to the field of machine vision. It enables circumferential visibility (simultaneous imaging of the front and the side surfaces) of convex objects. Currently the technique is mainly used in combination with image processing, e.g. to rapidly detect irregularities of an object's surface texture. Even though interferometric shape measurement techniques could largely benefit from this imaging modality, an application of hypercentric imaging to the field of coherent optical metrology has, to the best of our knowledge, not been reported.The aim of the proposed project is to introduce hypercentric imaging to the field of interferometric shape measurement. It is expected that this concept provides fast and precise form determination in industrial quality inspection of complex shaped objects for all cases in which the objects have convex shape. Exemplarily, the two coherent optical shape measurement methods of multi wavelengths phase shifting interferometry (MW-PSI) and frequency domain white light interferometry (FD-WLI) will be adapted. This requires understanding of the hypercentric imaging process on a wave optics level with a focus on speckle statistics and coherence properties of the light in the image plane. Furthermore, a specific geometry model has to be developed, that links the observed path differences to the actual shape of the object, while taking the reversed magnification of hypercentric lenses into account. The results of the project could lead to a new generation of compact, flexible and precise interferometric sensors offering circumferential shape data with a measurement uncertainty down to the sub micrometer range.

在生产过程中，技术零件会出现不必要的几何变形和表面缺陷，例如断裂、划痕和凹痕，因此，如果需要高精度，则必须采用干涉测量方法，因为它们很有效。非接触式测量，测量不确定度低至照明波长的一小部分。微冷成型和微系统工程的进步允许生产形状日益复杂的微型零件，这给光学计量带来了新的挑战。未来的高精度干涉测量系统必须能够在合理的时间范围内测量高度复杂的形状物体，从而满足这些要求。目前基于标准成像系统的系统无法完成这项任务，因为它们的视角有限。测量复杂几何形状的完整 3D 形状通常需要从不同观察方向进行多次单独测量，这需要大量硬件，并涉及耗时的校准和缝合程序来重建对象的形状。解决此问题的方法可能是超中心的（或中心周围）成像，最近它已被引入机器视觉领域，能够实现凸面物体的周向可见性（正面和侧面的同时成像），目前该技术主要与图像处理结合使用，例如快速检测物体的表面。尽管干涉形状测量技术可以在很大程度上受益于这种成像方式，但据我们所知，尚未报道超中心成像在相干光学计量领域的应用。该项目的目的是引入干涉形状测量领域的超中心成像预计可以在复杂形状物体的工业质量检测中为物体具有凸形状的所有情况提供快速和精确的形状确定。多波长相移干涉测量 (MW-PSI) 和频域白光干涉测量 (FD-WLI) 的技术将得到调整，这需要了解波动光学层面的超中心成像过程，重点关注散斑统计和此外，必须开发一个特定的几何模型，将观察到的路径差异与物体的实际形状联系起来，同时考虑超中心镜头的反向放大率。新一代紧凑、灵活且精确的干涉传感器，可提供测量不确定度低至亚微米范围的圆周形状数据。