Abstract
With the rapid development of modern manufacturing processes, ultra-precision structured freeform surfaces are being widely explored for components with special surface functioning. Measurement of the 3D surface form of structured specular objects remains a challenge because of the complexity of the surface form. Benefiting from a high dynamic range and large measuring area, phase measurement deflectometry (PMD) exhibits great potential in the inspection of the specular surfaces. However, the PMD is insensitive to object height, which leads to the PMD only being used for smooth specular surface measurement. Direct phase measurement deflectometry (DPMD) has been introduced to measure structured specular surfaces, but the surface form measurement resolution and accuracy are limited. This paper presents a method named stereo-DPMD for measuring structured specular objects by introducing a stereo deflectometor into DPMD, so that it combines the advantages of slope integration of the stereo deflectometry and discontinuous height measurement from DPMD. The measured object is separated into individual continuous regions, so the surface form of each region can be recovered precisely by slope integration. Then, the relative positions between different regions are evaluated by DPMD system to reconstruct the final 3D shape of the object. Experimental results show that the structured specular surfaces can be measured accurately by the proposed stereo-DPMD method.
Highlights
With the emergence of ultra-precision manufacturing technology, a large number of complex and precision components and objects were fabricated to meet various needs, which pushed the development of many cutting-edge industries
Experimental data proves that the proposed method can effectively improve the measurement accuracy of surface topography while maintaining the advantages of Direct phase measurement deflectometry (DPMD) technology for measuring discontinuous surfaces
The proposed stereo-DPMD method combines the advantages of slope integration and discontinuous height calculation
Summary
With the emergence of ultra-precision manufacturing technology, a large number of complex and precision components and objects were fabricated to meet various needs, which pushed the development of many cutting-edge industries (such as aerospace, automobile manufacturing, large scale integrated circuit, etc.). Once the deformed fringe pattern is demodulated, the 3D coordinate of the measured surface can be accurately obtained. The fringe projection technology has made great progress in speed, accuracy, size, and other measurement aspects. This technique is only suitable for diffused surface measurement. A traditional way to solve this problem is to spray coating materials on the specular surface to make it show diffuse reflection characteristics, the fringe projection technique can be applied to obtain its 3D data, but this behavior may damage the optical properties of the precision specular surface [10]
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