Research On 3D Measurement Method Of Object Surface Based On Structural Light

Three dimensional measurement based on structural light has been widely used in the reverse engineering,mechanical manufacture,object recognition,medical diagnosis,relics protection and so on because of the following features:non-contact,high precision,low cost and long measurement distance,etc.In the process of three dimensional measurement based on structural light,there is the effect from projector nonlinearity,the effect from projector defocusing levels,the errors from phase unwrapping and the errors from calibration,etc.So the important research direction of three dimensional measurement is how to increase the measurement precision and the speed of measurement.On the basis of domestic and overseas related work,a further research about three dimensional measurement based on structural light is carried out in this dissertation.For the deficiencies of current methods,many effective theories and methods are proposed,then the precision and speed of three dimensional measurement based on structural light are increased.The major research contents and innovative results are shown as following:To solve the phase shifting problem from traditional F-S defocused dithering fringe pattern,a phase optimization method based on F-S dithering fringe pattern is proposed.The symmetrical kernel function is generated via F-S error diffusion kernel function.Then based on the odd lines and even lines,a symmetrical F-S dithering fringe pattern is generated by using continuous path scanning.In order to further increase the phase precision of dithering fringe pattern,a kind of weighted optimization function is proposed to optimize the phase of fringe pattern.Experiment results show that the proposed method can solve the phase shifting problem from F-S defocused dithering fringe pattern effectively.Compared with traditional F-S defocused dithering fringe,the phase precision of F-S dithering fringe pattern with different periods can be increased by the proposed method in this dissertation.To solve the problem that the measurement precision is affected by projector defocusing levels,a kind of fringe pattern generation method based on global optimization and local optimization is proposed.Bayes dithering fringe pattern is generated by using Bayes dithering encoding method.Then the intensity of corresponding points between Bayes dithering fringe patterns and sinusoidal fringe pattern is compared and global optimization is carried out on the dithering fringe pattern.Because three-step phase shifting is robust to triple frequency component,the residual error optimization function is established and the local fringe pattern with half of period is optimized by using residual error optimization function.Based on the periodicity and symmetry of structural light fringe pattern,the global fringe pattern can be generated by joining the best fringe pattern with half of period together.Experiment results show that the effect from periods and projector defocusing levels can be overcome effectively.Compared with traditional dithering fringe pattern,higher measurement accuracy can be obtained by the dithering fringe pattern generated by the proposed method under different conditions.To solve the problem that the speed and precision of phase unwrapping is affected by the period of fringe pattern,a kind of phase unwrapping method based on two kinds of stair modes is proposed.The first kind of stair mode is established by using intensity and the global fringe pattern is divided equally.The grade of the first kind of stair mode is determined from the intensity value.Then the second kind of stair mode is established by using phase and the first kind of stair mode is subdivided.Besides the boundary points are determined from the average value of phase.At last the grades of wrapped phase are determined according to relationship between two kinds of stair modes.Experiment results show that the wrapped phase can be accurately retrieved and the effect from period of fringe pattern can be solved effectively.Compared with traditional phase unwrapping methods,higher speed of phase unwrapping can be obtained from the proposed method in this dissertation and it is robust to the gray change of image.To solve the problem that the calibration precision is affected by defocusing levels of projector,a kind of structural light system calibration based on dithering fringe pattern is proposed.The parameter of camera can be calibrated by using calibration toolbox.Then global optimization and local optimization are carried out on the Bayes fringe pattern.So horizontal and vertical dithering fringe pattern can be generated respectively.These two kinds of fringe patterns are projected to the calibration board and the absolute phase with horizontal and vertical direction are generated.The projector can be seen as a reverse camera,so the relationship between camera image and projector image can be established from calibration corners and absolute phase.At last external parameters of camera and projector can be obtained from by calibrating the whole structural light system.Experiment results show that calibration parameters of structural light system can be obtained accurately and the the proposed method is robust to the projector defocusing levels.Compared with traditional calibration method,higher calibration precision can be obtained from the proposed method in this dissertation.Moreover,it is not required to take the projector nonlinearity into consideration and the calibration process is easier.