Three-dimensional Shape Measurement Technology Of Complex Shape Objects

The 3D scale measurement of human teeth is realized by the phase shifting technology of grating fringe projection.In the past,when the 3D scale measurement of object was carried out with the fringe projection phase shifting technology,the object appearance was obtained in phase.Then,the transformation relationship between phase and height was determined by the geometric parameters of the measurement system,so as to get the 3D scale information of the object.In the real measurement system,there exists phase information nonlinear distortion in both the phase-shifting fringe projection and image acquisition system.To fix the system defects,we propose a feasible solution,that is to use a standard flat plate to translate vertically near the position where the measured object is placed,so as to obtain the corresponding phase distribution in a series of different positions on the surface.By making use of the corresponding relationship between the phase distribution information in different positions on the surface and the moving distance of the flat plate,the transformation relationship between phase and height in the phase shifting measurement system is established.This transformation method can help obtain different phase-height calibration coefficients in different parts of teeth,and avoid the system error caused by the single phase-height transformation coefficient in traditional calibration method.(1)A 3D scale measurement system of tooth surface is established.A standard plane is used to move with equidistance in the direction perpendicular to itself.Through the phase distribution of the standard plane in different positions and the corresponding moving distance of the flat plate,the phase-height conversion relationship is established to make it come true for the 3D scale measurement of the objects.This method can effectively avoid the system error caused by single phase-height conversion coefficient in the past.(2)A computer program for the 3D scale measurement of teeth is developed.The grating fringe images used in the four-step phase shifting projection are made with computer image technology.The images needed in the experiment is obtained with the fringe brightness and contrast adjusted by the computer program.The phase of tooth projection fringes is created with flood filling algorithm to start the computer program,so as to get the 3D appearance information of tooth surface in phase.(3)The height distribution of the tooth surface is measured by a 3D phase-shifting measurement system which has established the conversion relationship between the phase and height,and a satisfactory experimental result is obtained in the end.This technology can be widely applied in the 3D measurement of sub-millimeter-level objects with complex appearance..