Three-dimensional shape measurement method based on sinusoidal and triangular fringe projection

In the existing three-dimensional measurement method for the surface topography of complex objects, in order to complete absolute phase measurement, it is usually necessary to process at least 6 fringe images, which limits the measurement speed. A method for obtaining three-dimensional shape of object by using two sinusoidal fringes and two triangle wave fringe patterns was proposed.The two-step phase-shifting sinusoidal fringe and two-step phase-shifting triangular wave fringe were calculated to obtain the wrapped phase, then the two-step phase-shifting triangular wave fringe was used to determine fringe order. Due to the decrease in number of projection images, the speed of measurement increased. In order to obtain the fringe order, the triangular wave fringe intensity modulation and intensity ratio were calculated. Compared with the calculation of the phase, the data processing time can be reduced, and the measurement speed can be further increased. At the same time, the influence on the surface reflectance can be reduced, and the measurement accuracy can be improved.For measuring the stepped standard block with maximum height of 39 mm, the maximum absolute error and the maximum root-mean-square (RMS) error are 0.045 mm and 0.041 mm, respectively. Experimental results demonstrate that the proposed method is effective and practical, the benefits are seen in the high-speed, real-time 3-D shape measurement of complex objects.