Abstract
Phase-measuring deflectometry (PMD)-based methods have been widely used in the measurement of the three-dimensional (3D) shape of specular objects, and the existing PMD methods utilize visible light. However, specular surfaces are sensitive to ambient light. As a result, the reconstructed 3D shape is affected by the external environment in actual measurements. To overcome this problem, an infrared PMD (IR-PMD) method is proposed to measure specular objects by directly establishing the relationship between absolute phase and depth data for the first time. Moreover, the proposed method can measure discontinuous surfaces. In addition, a new geometric calibration method is proposed by combining fringe projection and fringe reflection. The proposed IR-PMD method uses a projector to project IR sinusoidal fringe patterns onto a ground glass, which can be regarded as an IR digital screen. The IR fringe patterns are reflected by the measured specular surfaces, and the deformed fringe patterns are captured by an IR camera. A multiple-step phase-shifting algorithm and the optimum three-fringe number selection method are applied to the deformed fringe patterns to obtain wrapped and unwrapped phase data, respectively. Then, 3D shape data can be directly calculated by the unwrapped phase data on the screen located in two positions. The results here presented validate the effectiveness and accuracy of the proposed method. It can be used to measure specular components in the application fields of advanced manufacturing, automobile industry, and aerospace industry.
Highlights
With the advent of the information age, optical methods for the acquisition of three-dimensional (3D)-shape information of objects has an increasingly important role in various application fields, such as advanced manufacturing, automotive industry, aerospace industry, and so on
Phase-measuring deflectometry (PMD)-based methods have been widely used in 3D shape measurement of specular objects, because they offer the advantages of a large dynamic range, high accuracy, and full-field, noncontact, and automatic data processing [11,12,13]
This paper presents a new full-field 3D shape measurement method by using infrared phase-measuring deflectometry (IR-PMD) to obtain specular components having discontinuous surfaces
Summary
With the advent of the information age, optical methods for the acquisition of three-dimensional (3D)-shape information of objects has an increasingly important role in various application fields, such as advanced manufacturing, automotive industry, aerospace industry, and so on. The classical PMD calculates the gradient distribution of specular surfaces by displaying sinusoidal fringe patterns, and the 3D shape can be obtained by integrating the gradient data. The sinusoidal fringe patterns are displayed on a digital screen, such as a liquid-crystal display (LCD) These fringe patterns are reflected by the specular object and are deformed with respect to the gradient and height variation of the measured surface. The classical PMD methods cause cumulative errors during gradient data integration They cannot be used to measure multiple discontinuous and/or isolated specular surfaces. Guo et al [16] proposed an improved PMD to determine the corresponding reflected rays by calibrations without knowing the incident rays This method provides a new tool for quantitative measurements of aspheric surfaces in full field of optical manufacturing. Xiao et al [17] presented a PMD calibration method using a markerless flat mirror to simplify the system calibration and reduce the error of the system calibration and the image noise
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