Testing an aspheric mirror based on phase measuring deflectometry

Abstract

A method based on basic phase measuring deflectometry is proposed for testing the aspherical mirror. The method uses a reference screen in two different distances from the mirror under test. The sinusoidal, intensity-modulated patterns generated by the computer are displayed on the LCD screen, and the camera observes the patterns reflected off the testing mirror. The observed pattern appears distorted depending on the shape of the mirror. Using the phase-shifting technique, the original ray of every image point and its corresponding deflected ray can be constructed. Their intersection points and the surface normal are obtained. Then the mirror surface is reconstructed with high accuracy by numerically integrating the surface normals. The proposed method is robust against noise and can test the mirror full field. In this work, the method is introduced, and computer simulation and experimental results are shown.

Photogrammetry for Concentrating Solar Collector Form Measurement, Validated Using a Coordinate Measuring Machine

“…Slope measurement methods currently implemented include pattern reflection techniques, such as deflectometry and laser reflection techniques, such as VSHOT. One method of deflectometry is to use a known pattern, such as linear stripes, and to view this pattern by reflection in the mirror [8][9][10]. The pattern will be distorted by the shape of the mirror, and so by calculating the difference between known and reflected patterns, the shape of the mirror is determined.…”

Three-dimensional shape measurement of aspheric mirrors with fringe reflection photogrammetry

“…To alleviate the cumbersome calibration process, Tang et al proposed a concept named "dummy paraboloid," which is based on geometrical optics [7][8] in PMD. Zhao et al [9] applied PMD to aspheric mirror testing, and Huang et al [10] utilized it for dynamic 3D sensing for water waves. PMD obtains the relative 3D shape through integration of gradient information that is computed by phase measuring.…”

Real-Time Measurement of Three Dimensional Weld Pool Surface in GTAW

“…The measurement of 3D surface has been recently studied extensively with techniques which can be roughly categorized into three branches: 1) reflectometry/deflectometry with fringe reflection technique [31][32][33]; 2) phase shifted digital fringe projection technique for diffuse objects [34,35]; 3) shape from shading technique [36]. Unfortunately, the dynamic and specular nature of the weld pool and the interference from the strong arc radiation complicate the observation and deteriorate the effectiveness of most of those methods.…”