Research On 3D Object Morphology Measurement And Key Technology Based On Fringe Projection

With the continuous development of the digital age,people are no longer satisfied with the traditional way of obtaining three-dimensional information.Therefore,the structured light 3D measurement technology,which has the advantages of simple system setup,fast measurement speed,high robustness,flexible installation,and dense point cloud,has been widely and deeply studied.It has shown great application prospects in the fields of smart city,production inspection,emergency surveying and mapping,electric power inspection,forestry and water conservancy,virtual reality technology,and human-computer interaction.This paper focuses on the 3D measurement method of digital streak projection,and conducts an in-depth study of the system model,the phase calculation of streak maps,the non-linear response of the system,the phase error compensation,the calibration of the camera and projector,and the 3D reconstruction principle of the system,in order to build and develop a digital streak projection 3D measurement system with technical characteristics such as high accuracy,fast and easy to implement.In the research and development of the 3D measurement system,this paper focuses on the following aspects.(1)Acquisition of absolute phase.Based on the composition and measurement principle of the fringe projection 3D measurement system,a mathematical model is established.The high-efficiency triangular model is used for the follow-up research.Then,the phase unwrapping methods of the Gray code phase shift method,the multi-frequency heterodyne method and the multi-frequency fringe method are comparatively studied.The comparative experimental results show that the multi-frequency fringe method has the characteristics of high phase precision and good robustness.According to the influence rule of fringe frequency on phase accuracy shown by experimental results,it is found that reasonable selection of fringe frequency can further improve the accuracy of phase calculation.(2)System nonlinear phase error compensation.The fringe non-sinusoidal phenomenon is analyzed,and it is verified by simulation experiments that the Gamma nonlinearity of the projector will cause periodic phase errors in the phase calculation results.The grayscale response of the system is studied,and based on the grayscale response function,the nonlinear effect of the system is corrected through experiments,and the experimental results before and after the nonlinear correction of the system are analyzed and compared.Aiming at the noise and system nonlinear error,an improved phase error compensation algorithm is proposed.The phase calculation accuracy of the improved method is increased by 15 times,and the maximum phase error does not exceed 0.01 rad.The experimental results show that the improved method can largely eliminate the influence of system nonlinearity and improve the phase calculation accuracy.(3)Calibration of cameras and projectors.The calibration principle of the camera and the projector in the system are introduced respectively;the imaging model and calibration method of the camera are analyzed,and the calibration experiment is carried out based on Zhang’s calibration method;for the projector calibration,an improved Gauss radial basis interpolation algorithm is proposed.Using the proposed method to perform projector calibration experiments,the re-projection error is 0.0487 pixel.Compared with point-to-point mapping,homographs matrix and optical coaxial calibration methods,the calibration accuracy is improved by about 4 times.The experimental results verify the effectiveness,accuracy and feasibility of the proposed method.(4)System construction and software program design.According to the selected hardware,a set of experimental platform of digital fringe projection 3D measurement system was built,and the software program was written based on Matlab platform.The software provides a better human-computer interaction interface and improves the efficiency of system measurement.The standard measuring blocks,plaster heads,ceramic vases and other objects were measured through the built experimental platform.The accuracy of the measurement results of the standard block is evaluated,and its measurement error is stable within 0.06 mm,which proves the stability of the system measurement.In addition,the measurement results of other objects with complex morphologies and discontinuous surfaces are ideal,which further verifies the reliability and accuracy of the system.