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Sensors 2018, 18(1), 144; doi:10.3390/s18010144

Distance Calibration between Reference Plane and Screen in Direct Phase Measuring Deflectometry

1
School of Mechanical Engineering, Hebei University of Technology, Tianjin 300130, China
2
Centre for Precision Technologies, University of Huddersfield, Huddersfield HD1 3DH, UK
*
Author to whom correspondence should be addressed.
Received: 17 November 2017 / Revised: 2 January 2018 / Accepted: 2 January 2018 / Published: 6 January 2018
(This article belongs to the Special Issue Charge-Coupled Device (CCD) Sensors)
View Full-Text   |   Download PDF [6293 KB, uploaded 6 January 2018]   |  

Abstract

The recently developed direct phase measuring deflectometry (DPMD) method can directly measure the three-dimensional (3D) shape of specular objects with discontinuous surfaces, but requires a calibrated distance between a reference plane and liquid crystal display screen. Because the plane and screen are different distances from the imaging device, they cannot be clearly captured given the limited depth of field (DOF) of the lens. Therefore, existing machine vision-based methods cannot be used to effectively calibrate a DPMD system. In this paper, a new distance calibration method that uses a mirror with a hollow ring matrix pattern and a mobile stage is presented. The direction of the mobile stage in the camera coordinate system is determined by the mirror’s pattern at several positions in the camera’s DOF so that the reference position outside of the DOF can be calculated. The screen’s position can also be calibrated by displaying patterns at a known scale. Therefore, the required distance is accurately obtained in the camera coordinate system. Evaluation results show that the maximum value of the absolute error is less than 0.031 mm. The experimental results on an artificial stepped mirror and a reflected diamond distribution surface demonstrate the accuracy and practicality of the proposed method. View Full-Text
Keywords: distance calibration; direct phase measuring deflectometry (DPMD); specular surface measurement; phase measurement; three-dimensional (3D) sensing distance calibration; direct phase measuring deflectometry (DPMD); specular surface measurement; phase measurement; three-dimensional (3D) sensing
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MDPI and ACS Style

Huang, S.; Liu, Y.; Gao, N.; Zhang, Z.; Gao, F.; Jiang, X. Distance Calibration between Reference Plane and Screen in Direct Phase Measuring Deflectometry. Sensors 2018, 18, 144.

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