Improved infrared phase measuring deflectometry method for the measurement of discontinuous specular objects

For phase-measuring deflectometry (PMD), the selection of light source is a crucial factor for guaranteeing the measurement accuracy. Since visible light is sensitive to the ambient light, the reconstructed 3D shapes of PMD systems will be affected by the external environment in actual measurements. To tackle this issue, a method named Infrared-PMD (IR-PMD) has been developed, which exploits IR as the light source and directly measures specular objects having discontinuous surfaces from phase data by moving an IR camera and the measured specular surfaces together to realize two screens measurement. However, the movement of the measured objects during the experimental measurement procedure will cause random errors. For further optimizing this system, this paper exploits an IR digital display's movement to substitute the camera and the measured object's movement. A smaller IR projector projecting sinusoidal fringe patterns onto a ground glass is regarded as an IR digital screen. The projector and the ground glass are moved to two positions to realize two screens measurement. Fringe reflection technique is used to obtain the phase information. Then, 3D shape data can be directly calculated by the phase data on the IR digital screen located at two positions. Experimental results demonstrate that 3D shape of discontinuous specular objects can be effectively and accurately measured by the improved IR-PMD.