Comparison of Camera Calibration and Measurement Accuracy Techniques for Phase Measuring Deflectometry

Renhao Ge,Wanxing Zheng,Ruiyang Wang,Xiaowei Li,Dahai Li,Wuxiang Zhao,Xinwei Zhang

doi:10.3390/app112110300

Renhao Ge, Wanxing Zheng + Show 5 more

Open Access

https://doi.org/10.3390/app112110300

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Abstract

Phase measuring deflectometry (PMD) is a competitive method for specular surface measurement that offers the advantages of a high dynamic range, non-contact process, and full field measurement; furthermore, it can also achieve high accuracy. Camera calibration is a crucial step for PMD. As a result, a method based on the calibration of the entrance pupil center is introduced in this paper. Then, our proposed approach is compared with the most popular photogrammetric method based on Zhang’s technique (PM) and Huang’s modal phase measuring deflectometry (MPMD). The calibration procedures of these three methods are described, and the measurement errors introduced by the perturbations of degrees of freedom in the PMD system are analyzed using a ray tracing technique. In the experiment, a planar window glass and an optical planar element are separately measured, and the measurement results of the use of the three methods are compared. The experimental results for the optical planar element (removing the first 6 terms of the Zernike polynomial) show that our method’s measurement accuracy reached 13.71 nm RMS and 80.50 nm PV, which is comparable to accuracy values for the interferometer.

Highlights

Phase measuring deflectometry (PMD) with structured light projection and the phaseshifting technique is a highly accurate optical surface measuring method based on the law of light reflection
In the PMD system, rays are considered to be emitted from the projection center of a camera lens and reflected off a planar surface under test (SUT) to reach a liquid crystal display (LCD) screen
The entrance pupil calibration method (EPCM) that we propose is compared with the popular photogrammetric method based on Zhang’s technique (PM) [16], and Huang’s modal phase measuring deflectometry (MPMD) method (MPMD) [7]

Summary

Introduction

Phase measuring deflectometry (PMD) with structured light projection and the phaseshifting technique is a highly accurate optical surface measuring method based on the law of light reflection. The slope data are integrated to obtain the surface information [3,4,5,6,7,8,9,10] Among these variables, the most important are the coordinate positions of the screen, the SUT and the projection center of the camera. Based on Zhang’s technique, Xiao et al proposed a calibration method with a flat mirror to obtain the position of the projection center of the camera [15,16].

Methods

PM The procedure of PM is introduced in detail as follows:

Accuracy Analysis