Phase measuring deflectometry with active display registration
Final Report Abstract
Highly accurate three-dimensional shape measurement is a fundamental requirement for precise manufacturing and quality control. Phase measuring deflectometry (PMD) enables fast, full-field and contact-free shape measurement of specular surfaces. A camera observes, via reflection on the specular surface, patterns on a display, which appear distorted in the camera image due to the surface curvature. For a quantitative evaluation, the display shows sinusoidal patterns. Using phase shifting technique, a so-called phase measurement can be calculated, which is a mapping from camera pixels to the observed display pixels. To measure the shape of the specular surface, the two-dimensional position information on the display must be converted to points in the three dimensional space based on the knowledge of display position and shape. However, display position and shape are not constant but change due to orientation caused by gravitational forces, and also thermal expansion. This necessitates a method to determine display position and shape simultaneous to the PMD measurement. We pursue such a method in this project. A registration camera system directed at the display determines display position and shape (so called active display registration, ADR). The registration cameras perform phase measurements to determine the three dimensional coordinates of the display based on the principle of stereo fringe projection. Therefore, PMD with ADR does not need prior calibration of display position and shape. This enables multiple phase measurements with the display in different positions to resolve the ambiguity in shape reconstruction, that is otherwise inherent to PMD. The aim of project DeflektAktiv is the testing and optimization of PMD with ADR (PMD-ADR) and a quantitative evaluation of measurement uncertainty to establish this technique in metrology. A PMD-ADR experimental setup was realized and calculation methods for simulation, calibration, shape reconstruction and evaluation were implemented. PMD-ADR was successfully applied to the shape measurement of flat, spherical and aspherical mirrors. The measurement uncertainty is comparable to an existing PMD technique. PMD-ADR also enables the measurement of high curvature surfaces. As an interesting further result, ADR is also possible with only one camera.
Publications
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Phasenmessende Deflektometrie mit aktiver Displayregistrierung, in: Proc. of 121th DGaO Conference (2020)
Jonas Bartsch & Ralf B. Bergmann
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Active Display Registration in Phase Measuring Deflectometry, in: 12th High Level Expert Meeting - Asphere Metrology (2022)
Yann Sperling, Jonas Bartsch & Ralf B. Bergmann
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A3.3 Active Display Registration in Phase Measuring Deflectometry. Lectures, 49-50. AMA Service GmbH, Von-Münchhausen-Str. 49, 31515 Wunstorf, Germany.
Sperling, Y. & Bergmann, R.
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Laser-tracker-based reference measurement for geometric calibration of phase-measuring deflectometry with active display registration. Journal of Sensors and Sensor Systems, 13(1), 1-7.
Sperling, Yann & Bergmann, Ralf Bernhard
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Phase measuring deflectometry with monoscopic active display registration. Optics and Photonics for Advanced Dimensional Metrology III, 38. SPIE.
Sperling, Yann & Bergmann, Ralf B.
