Phase measuring deflectometry with active display registration

高度精确的三维形状评估是精密制造和质量控制的基本要求。相位测量偏折术（PMD）通过跟踪从显示器经由被测表面处的反射到相机的光路，提供镜面表面的快速、全场和非接触式形状评估。通常，计算机显示器被应用于该任务，使得能够通过使用相移技术的空间编码来确定反射的相机视觉射线的参考点。因此，三维空间坐标的评估需要已知显示器的形状。然而，形状不是恒定的，而是取决于其取向而受到诸如重力的物理应力的影响，特别是受到热膨胀的影响。这种行为需要一个程序，用于在每次PMD测量的同时确定显示器的形状。这种方法是由立体条纹投影技术提供的。在这里，由两个摄像机从一个表面上捕获的图像专门编码的结构照明用于识别的瞬态点，通过确定相应的视觉rays.The建议的项目旨在提高PMD的精度和灵活性，通过引入一个额外的立体摄像系统直接观察显示器的设置提供相关的坐标。由于PMD中的显示器已经提供了结构化照明，因此条纹投影原理在没有投影仪的情况下也适用。该立体系统提供了显示器的独立信息，以改善PMD测试下表面的形状确定。它还能够精确确定显示器的姿态。因此，不再需要将显示器的姿态和形状存储为系统校准数据。相反，立体相机系统提供与PMD测量的相位数据相关的绝对坐标。显示器可以自由定位，仅受所有相机的视场在显示表面上充分重叠的条件限制。大多数PMD系统缺乏访问弯曲样品的整个表面的能力，因为无法实现所有相机视觉光线与显示器相交的系统几何形状。所提出的PMD设置提供了显示器的可变定位，并且通过使得能够针对不同的显示器姿态对多个相位测量进行组合评估来改善对被测表面的访问。使用多个显示姿态还允许通过为反射的视觉光线提供多个参考点来解决偏转测量的模糊性。最后，该方法通过提供独立的显示形状信息来避免系统误差。不再需要为校准的系统假设恒定的显示形状。

Highly accurate three-dimensional shape assessment is a fundamental requirement for precise manufacturing and quality control. Phase measuring deflectometry (PMD) provides fast, full-field and contact-free shape assessment of specular surfaces by tracing the path of light from a display via the reflection at the surface under test to a camera. Typically, computer displays are applied for this task, enabling the determination of reference points of reflected camera vision rays by spatial coding using the phase shifting technique.Phase shifting provides two-dimensional localization on the display surface. Therefore, the assessment of three-dimensional spatial coordinates requires the shape of the display to be known. However, the shape is not constant but affected by physical stress such as gravity depending on its orientation and particularly by thermal expansion. This behavior requires a procedure for simultaneous shape determination of the display with each PMD measurement. Such an approach is provided by the stereoscopic fringe projection technique. Here, images captured by two cameras from a surface specially coded by structured illumination are used for identification of transient points, providing the correlated coordinates by determination of intersections of corresponding vision rays.The proposed project aims at the improvement of accuracy and flexibility of PMD by introducing an additional stereoscopic camera system into the setup directly observing the display. Since the display in PMD already provides structured illumination, the fringe projection principle is applicable without a projector. The stereo system provides independent information of the display for improved shape determination of the surface under test with PMD. It additionally enables precise determination of the pose of the display. Therefore, storing pose and shape of the display as system calibration data is no longer required. Instead, the stereo camera system provides absolute coordinates related to the phase data of the PMD measurement. The display can be positioned freely, only confined by the condition that fields of view of all cameras sufficiently overlap on the display surface. Most PMD systems lack the ability to access the full surface of curved samples, since system geometries with all camera vision rays intersecting the display cannot be realized. The proposed PMD setup provides variable positioning of the display and improves access to the surface under test by enabling combined evaluation of multiple phase measurements for varying display poses. Using multiple display poses furthermore allows to solve the ambiguity of deflectometric measurements by providing multiple reference points for reflected vision rays. Finally, the proposed approach avoids systematic errors by providing independent display shape information. Assuming a constant display shape for a calibrated system is not required any more.