Research On 3D Shape Reconstruction Based On Grating Projection

Three dimensional shape measurement is widely used and developed in today's production and life,such as the manufacturing industry,the restoration of archaeological artifacts,biomedical and robotic identification systems.With the development of science and technology,the traditional 3D measurement method has made great progress.However,the complexity of the measurement structure and its contact with the measured object have not been overcome.The grating projection method rapidly becomes one of the main methods to measure the 3D topography at present because of its non-contact,high precision,fast speed and simple structure.Grating projection method combines image processing with computer technology.A series of sinusoidal grating fringes are projected to the measured object,and the fringes are deformed due to the modulation of the measured objects.The deformed fringes are stored in the computer for processing,so that the 3D shape information of the measured object can be separated from the fringes.In this paper,three kinds of phase demodulation methods,such as convolution demodulation method,Fourier transform profilometry and phase shift method,are analyzed.According to the characteristics of the measured object and the characteristics of the demodulation algorithm,phase shifting method is chosen as the demodulation method.The influence of the phase shift error of the traditional mechanical device on the measurement results is analyzed.In order to avoid the phase shift error,the computer software is used to control the fringe phase shift;The basic principle of the phase unwrapping method is analyzed,like rank expansion method,Goldstein branch cut method,least squares based on Fourier transform and discrete cosine and so on,the simulation is carried out to calculate the error parameters of the results,and the least squares method is used as the expansion algorithm compare with others.The combination of the least squares method and the rank expansion method is used to improve the quality of phase unwrapping.The relationship between the phase and height is obtained by using the mathematical model of the cross axis measurement system,the measurement system is calibrated by the method of solving the equations of phase height transformation,and the unknown parameters are solved.To interpolate the continuous phase obtained by phase unwrapping,the data obtained from the system are combined with the parameters of the system to restore the three-dimensional shape of the object.An experimental system is built to reconstruct the 3D shape of the object,and the cause of the error is analyzed.