Research On Dynamic3D Shape Measuring Technology And System Based On Multi-view Phase-shifting Framework

3D shape measurement technology has been widely used in the aerospace, weapons, automobile and other fields. The shape of key parts of these areas (such as the engine block, blades, exhaust pipes, etc.) is usually very complex, and the3D shape measurement technology not only be able to take full advantage of the existing design to improve the design speed and shorten the development cycle, but also control the product quality and reduce production costs. However, most of the existing3D shape measurement techniques can only measure the static objects. Dynamic3D measurement is increasingly important in many applications such as measuring the deformation of the rotating blades, the aircraft wind tunnel experiment, collision experiments and electromagnetic forming process. The dynamic process of continuous3D shape measurement results can be used to verify the computer simulation results, help to delineate and analyze the variation of the surface morphology and improve manufacture process, so it is very important in theoretical and practical researches.This paper presents a novel sinusoidal grating projection-based dynamic3D measurement techniques based on the development of nonlinear error correction technique, multi-view phase-shift framework based dynamic3D measurement, high-precision multi-view system calibration and massive fine-grained parallel computing. By accurate synchronization acquisition hardware design and software design, a high accurate, full temporal and spatial resolution, dynamic3D measurement system is developed.Typically, the phase value accuracy calculated by the three-step phase-shift algorithm will be influenced by the non-linear response of the system. In order to improve phase calculation accuracy, the nonlinear response of the measurement system is modeled. Compared with the existing models, it takes the defocus of projector into consideration and can describe the non-linear distortion of the fringe images in space accurately. On this basis, a gamma parameter calibration algorithm is proposed, and the calibrated gamma value will be encoded into the fringe images before measurement task for phase error compensation. Experimental results showed that the phase error could be control within0.045rad, and the3D measurement error was effectively suppressed, and it laid a good foundation for3D calculation process.It is very important to achieve full temporal and spatial resolution3D measurement of arbitary shape objects in scientific research and engineering application. So a stereo matching method based on multi-view phase-shift framework is proposed for dynamic3D measurement. In this framework, benefited from the trifocal tensor constraint, each pixel can explore its corresponding point independently only in the wrapped phase-map and reconstruct a3D point in space, so arbitrary shape including the discontinuous surfaces or step-like surfaces can be measured with full spatial resolution. Moreover, as any adjacent three images per camera in the continuous capturing stream can be used to reconstruct one3D frame, the3D acquisition speed can be as fast as the camera capturing speed. So our method can also perform full temporal resolution3D measurements. To enhance the resistance to false correspondence caused by multiple fringe number and phase error, a two-stage strategy, using disparity range constraint and mixed consistency check successively, is proposed to reject the wrong candidates. Further, the accuracy of the corresponding points is refined by performing edge point adjustment and correspondence refinement, and makes the3D result insensitive to the phase error.System calibration accuracy is very critical to the measurement accuracy, and a multi-view system calibration method is proposed. The calibration procedure contains two steps:(1) calibrating the internal parameters of each camera individually (2) determining the pose of each camera. For single camera calibration problem, Zhang’s flexible calibration method is used to obtain the initial values, and these values are optimized by the bundle adjustment strategy to eliminate the influence of the inaccuracy of the target. Then the world coordinate is located on the camera coordinate, the pose of each camera is calibrated by epipolar constraint, and the calibrated translation vector has to be revised to remove the scaling factor. In addition, due to the environmental factors, the pose of the camera might slightly change, which will make the measurement result inaccurate. In order to grarantee the measurement accuracy, a fast and enhanced pose calibration method is used to determining the pose of each camera. Experimental results showed that this method is accurate and stable.The large amount of data intensive computing is always the bottleneck of real-time dynamic3D measurement. In order to effectively improve the speed of3D calculation, a large-scale, fine-grained parallel computing model, which take full advantage of the performance of GPU parallel computing, is used to design a high-resolution high-precision, real-time dynamic3D parallel computing algorithms in the conventional mainstream chip. The experiment showed that the computation efficiency in the GPU is nearly400times faster than that in the CPU. And it achieved real-time calculation of32000points per millisecond, which will provide an important foundation in real-time3D measurement applications.On the basis of the above theory and technology researches, a dynamic3D shape measurement equipment is developed. In this equipment, the synchronous timing of the projector with the camera is designed to correctly capture gray scale images. Two test experiments are designed to determine the time delay of DMD flip and time delay of camera receiving a trigger signal and the photosensitive response. The experiments show that the system can achieve precise synchronization acquisition of220per second. On the other hand, a dynamic3D measurement software system is designed to achieve2203D frames per second dynamic measurement with spatial resolution of1024x768. Finally application prospects of this system in material deformation, motion tracking, the face measuring and gestures and gesture recognition is also described.