A plate beamsplitter based stereo phase measuring deflectometry for measuring specular structured surfaces

Accurate, fast, embedded and in-line three-dimensional (3D) measurement of specular structured surfaces is an ever-increasing demand in industry but also a great challenge for current metrology. Phase measuring deflectometry (PMD) is an important technique for form measurement of specular surfaces. However, there are problems that prevent PMD from achieving embedded and in-line measurement, such as large system volume and measurement shadows for measuring structured specular surfaces. For traditional PMD techniques, imaging sensor and fringe-displaying screen in a PMD system have to be separated on both sides of the normal of the measured surface in order to guarantee the imaging sensor can capture the reflected fringes through the reflection of the measured surface. This configuration results in large system volume. Here, we present a plate beamsplitter based stereo phase measuring deflectometry (BSPMD) to solve these problems. With the function of plate beamsplitter, imaging sensors and screen in BSPMD can be located in the same direction, which makes the volume of BSPMD is much reduced compared with traditional PMD system. In addition, the imaging sensors in BSPMD can capture the measured surface perpendicularly, which can significantly decrease structure shadows and increase valid measurement data. A comparison study between traditional PMD and BSPMD is conducted by measuring a specular step to show BSPMD has similar measurement accuracy, but smaller system volume compared with traditional PMD.