Curved LCD based deflectometry method for specular surface measurement. (April 2022)

• Record Type: Journal Article
• Authors: Han, Hao; Wu, Shiqian; Song, Zhan
• Is Part Of: Optics and lasers in engineering. Volume 151(2022)
• Publication Date: 2022-04
• Subjects: Phase measuring deflectometry -- Curved LCD -- Calibration -- Registration; Lasers in engineering -- Periodicals; Optical measurements -- Periodicals; Optics -- Periodicals; Lasers en ingénierie -- Périodiques; Mesures optiques -- Périodiques; Optique -- Périodiques; 621.36605
• DOI: 10.1016/j.optlaseng.2021.106909
• Languages: English
• ISSNs: 0143-8166

Abstract

Highlights: The curved LCD is first applied to the PMD, which increases the measurable curvature than the planar LCD. A calibration method is proposed for the system based on the 3D fiducials on the curved LCD rather than the 2D fiducials on the planar one. Different from the traditional stereo-PMD in which only areas that has common FOV with phase information of two cameras can be reconstructed, the proposed stereo-PMD reconstruction and registration algorithm can reconstruct the surface in FOV of each camera, respectively, and then register together. The reconstructed error of RMS is less than 100 nm for the concave mirror of ROC 1000 mm. Abstract: Phase measuring deflectometry (PMD) technique is widely used to measure the specular surface. However, the Current PMD methods are generally based on the planar LCD for the measurement, which limits the measurable curvature of the surface under test (SUT). To increase the measurable range of curvature, this paper proposes a novel PMD method by using a curved LCD monitor. A calibration method based on the cylindrical coordinate system is introduced for the proposed system calibration. To extend the measurable range further, the curved LCD is applied in stereoscopic PMD. The partial surface of SUT in the field of view (FOV) of each camera and curved LCD are reconstructed with iterative algorithm respectively, the calibration parameters as well as the seed point are used for point cloud registration. Simulations show the advantage of a curved LCD over a planar one and the feasibility of the proposed method. The actual performance is demonstrated in the experiments for specular optics and a phone touchscreen.