| Three-dimensional measurement technology can be divided into contact measurement and non-contact measurement,contact measurement mainly use probe contact object surface to get the object’s three-dimensional coordinates,so as to get the object’s three-dimensional surface data,its measuring principle is simple,the process is convenient,the precision is high,but the drawback is that the measuring speed is slow,can not be soft and ultra-thin object measurement,and the cost is expensive;The non-contact measurement method is based on photoelectric,electromagnetic technology,and obtains the three-dimensional data of the surface without touching the surface of the object.As one of the non-contact measuring methods,the optical three-dimensional measuring technology is faster,more accurate and more adaptable than the contact measuring method,the advantages of real-time measurement and low cost are widely used.A three-dimensional profile measurement system based on grating projection is designed and built in this paper,which measures the height of naphthalene sublimation in the process of naphthalene sublimation,the results provide experimental basis for obtaining more accurate local heat transfer coefficient of brake disc.The research contents and results of the thesis can be summarized as follows:(1)The basic working principle and mathematical model of phase measurement profilometry are studied,the noise types of the images collected by the camera are analyzed,and different filtering measures are adopted for different noises,combining median filter and threshold wavelet transform to write the filter program,through experimental analysis,verify the applicability and correctness of the filter function.(2)The realization principle of phase unwrapping is studied,and the corresponding algorithm programs are compiled for several commonly used spatial phase unwrapping algorithms.In order to solve the problem that the branch-cut method can not perform the phase unwrapping effectively in the area where the residuals are too dense or in the area where the branch-cut lines are closed,a fusion algorithm based on the branch-cut method and the quality graph-oriented method is proposed.The simulation results of the fusion algorithm by MATLAB show that the root mean square error of the fusion algorithm is reduced by 52%and 77%compared with the branch-cut method and the quality map-oriented method when the noise is maximum,it is proved that the phase unwrapping ability of the fusion algorithm is better than the branch-cut method and the quality graph-oriented method.(3)Studying and analyzing the transformation from a two-dimensional plane to a 3D,and deriving the transformation relationship between image coordinates and camera coordinates,and then to a three-dimensional spatial coordinate system,using the camera calibration toolbox built in MATLAB,the internal and external parameters of the camera are calibrated by using the checkerboard calibration board.In this paper,the mapping relation between phase and height is studied,and the differences,advantages and disadvantages between the traditional display calibration method and the implicit calibration method are analyzed,the phase-height mapping is obtained according to the experimental structure,and the error is calculated.(4)According to the content of the study,build the experimental platform of three-dimensional measurement,and carry out the actual measurement.First,the continuous phase of the reference plane is measured with a three-dimensional measurement system,and then the three-dimensional profile of the naphthalene surface before and after sublimation is measured,finally,the height of naphthalene sublimation was obtained. |
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