A combined binary defocusing technique with multi-frequency phase error compensation in 3D shape measurement. (January 2020) - Hu, Haohui
Highlights: A new binary defocusing method making use of 1D and 2D fringe modulation techniques. The phase errors of binary fringes are analyzed and compensated. A multi-frequency method with the phase error compensation is described. The proposed method can remarkably improve the measurement performance. Abstract: Binary defocusing technology is widely used in three-dimensional (3D) structured light measurement technologies because of its high-speed measurement capability. Owing to the limitations regarding the type of binary fringe and the degree of defocus, the accuracy and speed of 3D measurement may not be satisfactory for certain industrial applications. This paper addresses this problem and proposes a new binary defocusing technique through a combination of a 1D fringe modulation technique with a 2D fringe modulation technique. First, we select a square binary fringe modulation technique for high frequency fringes generation and use an improved Stucki error diffusion dithering technique with serpentine scanning for low frequency fringes generation. Based on the analysis of the theoretical model of the phase error caused by binary fringes, a double three-step phase shifting method is adopted to compensate the phase error in the wrapped phase map. The compensated phase is then unwrapped using a multi-frequency method. The proposed method was verified experimentally through a white board, a real complex object and a standard block with a depth of 1 mm. The measurement errors were shown to be reduced by 16.9% or more with the proposed method.