Research On Three-dimensional Shape Measurement Method Of High-reflective Object Based On Adaptive Fringe Projection

Digital fringe projection technique has been widely used in industrial manufacturing,reverse engineering,virtual reality,academic research and so on,because of the advantages in their non-contact operation,high precision and fast measurement speed.However,the method still has some limitations,when the coded fringe images are projected to measure surface with large reflectivity variations,the high-reflective region is too bright to result in image saturation,which will easily lead to large error in the threedimensional(3D)measurement.Therefore,it is an intractable challenge to measure the object with high-reflective surface accurately.It is of great significance and application value to study how to apply digital fringe projection technology to obtain 3D morphology information of high reflective objects.In this paper,the measurement of the 3D morphology of high reflective object is studied based on adaptive digital fringe projection.The main work and innovation of this paper are as follows:(1)In order to solve the problem about local overexposure of modulated fringe image captured in the 3D measurement of high reflective surface,an algorithm based on mask image fusion and interpolation prediction is proposed to obtain the optimal projection gray level adaptively and effectively.Compared with the adaptive fringes generated by the traditional method and the existing research methods,our method has better modulation and higher contrast.In addition,the proposed method neither needs to attach or improve any hardware devices,nor needs to capture and project a large number of fringe patterns with different exposure and exposure time,which can effectively measure the 3D surface shape of high reflective object and obtain the relatively complete point cloud information of measured surface.(2)To solve the problem of large measurement error caused by Gamma distortion in digital fringe projection measurement,an active precoding calibration Gamma coefficient method is proposed in this paper.And the phase error caused by the Gamma nonlinear error and the accuracy of phase calculation,this paper proposes a reverse calculation initial phase method based on three-frequency with three phase shifts,and a phase error compensation method based on phase offset method.Compared with the traditional threefrequency with four phase shifts method,the proposed method has higher phase accuracy and better noise resistance.Most importantly,compared with the traditional threefrequency whit four phase shifts,the proposed method needs less compensation fringe patterns and has less phase error.The experimental results demonstrate that the phase information in local overexposure region is obtained completely,the average error and standard deviation in absolute direction and forward direction are smaller than those obtained by traditional method,the average error in absolute direction is reduced by 84.1% and forward direction deviation is reduced by 69.4%,which effectively achieves 3D shape measurement of high-reflective surface.Simulation experiments show that the proposed pre-calibration Gamma coefficient method can effectively improve the error accuracy in nearly 80% by projecting fewer fringe patterns.And the experiments has indicated that the proposed phase error compensation method can effectively reduce the phase error by the Gamma effect.