3D Measurement Method And Technology Based On Combined Time Encoding Structured Light

The three-dimensional (3D) measurement technology of structured light has a board prospect for application in non-contact measurement of 3D visual effect with fantastic speed, high efficiency and low cost. The coding structured light measurement, renowned for high efficiency and easy identification has become the main development trend in the 3D measurement technology of structured light. Compared to space coding and direct coding, time coding has advantages of higher accuracy and sampling density, which contributes to the development direction of coding structured light technology. Thus, it is an eternal goal for the researchers to enhance comprehensive technical index like accuracy and sampling density while accelerating the speed. In this dissertation, the author mainly analyzes the 3D measurement methods and technology of the combined time coding structured light so as to improve accuracy and sampling density while ensuring measurement speed.Basing on the systematically theoretical analysis of the traditional combined-cycle sinusoidal phase-shifting method, this dissertation at the outset, demonstrates combined-cycle method, which combines trapezoidal phase-shifting intensity ratio and trapezoidal phase-shifting. In addition, the complex arctangent operation is replaced by the simple arithmetic operation while ensuring the high sampling density in phase-shifting method. Therefore the calculating speed has been changed to merely ten percent of that in combined-cycle sinusoidal phase shift method, and it effectively improves the measurement speed.Furthermore, the asymmetrical combined-cycle trapezoidal phase-shifting intensity ratio method is presented targeting for the error of one bit gray code and the periodic dislocation caused by measuring principle of the combined-cycle trapezoidal phase-shifting intensity ratio method. Then, through the combination of trapezoidal phase-shifting, the code yard of the encoding period and its corresponding location, one bit gray code error has been reduced to one bit intensity code error from cycling error which brings about elimination of periodic dislocation in principle and the improvement in measurement accuracy. In order to improve the accuracy in decoding gray code, the author creatively proposes the adaptive threshold-belt binarization method, through sacrificing part of the sampling points with improving the accuracy of binarization and anti-jamming capability in the measurement.Basing on the 3D MAX and the MATLAB environment, this research has established the 3D measurement emulation system, and completed the emulation system calibration. For a variety of typical three-dimensional surface, the author has adopted combined-cycled sinusoidal phase shift method, combined-cycled trapezoidal phase-shifting intensity ratio method and asymmetrical combined-cycled trapezoidal phase-shifting intensity ratio method to conduct emulation comparative experiments of three-dimensional measurement.Then, the author designs and sets up experimental apparatus as well as its calibration equipment and completes calibration experiment of system. Meanwhile, asymmetrical combined-cycle trapezoidal phase-shifting intensity ratio method is used to three-dimensionally measure the typical surface and the result has been verified.Theoretical analysis and emulation result:The result of reconstruction measured by combined-cycle sinusoidal phase-shifting method is confirmed with visual effect. And the plane maximum error is less than 2.304mm in the range from 700mm to 1000mm. But reconstructed plane and complex surface have periodic dislocation error. Compared with the former, symmetric combined-cycle trapezoidal phase-shifting intensity ratio method after the amendment dislocation causes the smooth surface with some small fluctuations. However, it eliminates the periodic dislocation error, and its maximum error is less than 0.753mm. In addition, the reconstruction surface is not smooth and even does not match with the measured object in vision. The reconstruction plane and complex surface used by asymmetric combined-cycle trapezoidal phase-shifting intensity ratio method is much smoother and less fluctuating and having no cycle dislocation error, and the plane maximum error is less than 0.514mm.Device measurement results:It is shown that the maximal error of plane is less than 3mm in the range from 700mm to 1000mm, and the measuring accuracy is 0.3%. The 3D reconstruction method orienting structured light is used to reconstruct the measured object. And the result clearly illustrates that the measured surface and reconstruction result are commensurate in visual effect, and it can reflect the measured surface topography smoothly and carefully.