Study Of High-speed And High-robust Dynamic Three-dimensional Shape Measurement (Doctor Thesis)

High-speed and high-robust three-dimensional(3D)shape measurement has important scientific significance and extensive applied value in 3D modeling of dynamic scenes and deep analysis of dynamic process,such as digital modeling in virtual reality(VR)and augmented reality(AR),detection of intelligent manufacture and test of material performance.3D shape measurement based on structured light projection has been widely applied in measurement of different static scenes owing to its advantages of high precision,high flexibility and full-field measurement.With the rapid development of hardware and the increased demand of measuring high-speed dynamic scenes,research interest of scholars is attracted to 3D shape measurement of complex dynamic scenes from simple static scenes.However,many contradictions still exist among measuring accuracy,stability and efficiency for the existing measurement techniques based on structured light and it is hard to simultaneously satisfy the requirements of high anti-noise ability,high robustness and high efficiency in highspeed 3D shape measurement.In addition,limited by measuring principle,regular measuring system based on structured light cannot accurately track and analyze 3D displacement and deformation information of dynamic scenes,which restricts the further application of structured light techniques.This thesis researches the topic of high-speed and high-robust 3D shape measurement technology.Based on the combination of Gray code and phase-shifting technique,it makes full use of the high anti-noise ability of Gray code patterns.Aiming at three technical difficulties: jump error,low coding efficiency,and inability to complete displacement and deformation analysis,this thesis researched and proposed the corresponding effective solutions,and finally solved the problem of 3D digital measurement of complex and isolated scenes.This thesis comprehensively and systematically studies the related techniques and methods of high-speed and high-robust dynamic 3D shape measurement assisted by Gray code.A set of complete,efficient,reliable and accurate technical solution was provided to achieve high-speed dynamic 3D shape measurement and 3D deformation analysis of complex isolated or even scattered objects under high noise interference.The main works and innovations of this thesis are summarized as follows:(1)Aiming at the problem of the selection of the measurement method,the performance evaluation model of multi-frequency phase-shifting method and Gray code-assisted method is established,which provides a quantitative comparison standard for the selection of dynamic measurement methods based on structured light.Through simulations and experiments,the comparative analysis of the anti-noise ability,coding efficiency and anti-motion blur error ability between these two types of methods are realized,and finally the Gray code-assisted method with the highest antinoise performance is selected,which establishes the base of high anti-noise measurement.(2)Aiming at the problem of jump errors in the combined technique of Gray code and phase-shifting method for dynamic measurement,the cyclic complementary Gray code(CCGC)coding strategy and the shifting Gray code(SGC)coding strategy are respectively studied and proposed.These two strategies recode the traditional Gray code in spatial and temporal domains to avoid the jump errors caused by the projection system’s active defocusing,ununiform reflectivity of the object surface and random noise of the system.And finally,it can achieve high-robust and high-speed 3D shape measurement.A simple,efficient,and robust phase unwrapping process is implemented in the measurement of the dynamic scenes using two proposed strtegies.The experiment proves that the proposed method has better measurement robustness compared with the traditional Gray code method and can complete 3D shape measurement of complex dynamic scenes of moving objects,including Newtonian pendulum impact and building block collapse,at 310 frame per second(fps).(3)Aiming at the problem of low coding efficiency of the combined technique of Gray code and phase-shifting method in dynamic measurement,a high-speed and highefficiency 3D shape measurement method based on Gray code light is proposed.Tripatate phase unwrapping(Tri-PU)strategy is proposed to avoid the jump errors caused by the projector defocus and object motion.On this basis,the time overlapping gray code(TOGC)coding strategy is proposed.The pattern number of each projection sequence is reduced from 7 to 4,which greatly improves the coding and reconstructed efficiency.These two presented techniques for the first time preserve the high antinoise ability of the Gray code-based method while overcoming the drawbacks of jump errors and low coding efficiency.Experimental results demonstrate the proposed method is superior to the traditional Gray code method in anti-noise ability and coding efficiency.And it also veritys the proposed method can reconstruct the dynamic scenes including building blocks collapsing under force and rotating fan blades at 542 fps without any jump errors.(4)Aiming at the problem that it is difficult to further realize the 3D deformation measurement using the traditional structured light measurement system for dynamic scenes,the digital image correlation(DIC)assisted fringe projection method is proposed.Firstly,based on the proposed high-speed 3D shape measurement system based on Gray code,the 3D shape information of the textured surface at different moments is obtained.Then,the texture extraction method based on modulation is proposed to extract high-quality texture information from the three phase-shifting fringes,which eliminates the influence of the nonuniform and time-varying ambient light.Finally,DIC is used to complete point-by-point matching of the measured 3D shape result and realize further 3D displacement and deformation measurement.The experiment successfully achieved 3D shape,displacement and deformation measurement of the dynamic scene including the rotating fan blade and the deformed membrane at 542 fps,and the results proved the effectiveness of the proposed method.Compared with the traditional structured light system,the proposed method does not require additional hardware costs or calibration compensation,and the presented method is reliable and promising for further 3D displacement mapping and deformation analysis of dynamic scenes using structured light system.The works of this thesis are driven by the needs of high-end intelligent manufacturing and the main battlefield of VR/AR national economy to break through the technical bottlenecks of existing methods and to solve the problem of being unable to simultaneously achieve high-speed 3D shape measurement and deformation analysis of high-noise complex dynamic scenes.The goal is to carry out in-depth research on this problem and finally form the complete and efficient technical solution,which realizes the accurate recording and reconstruction of the 3D shape,displacement and deformation of complex,isolated and even scattered dynamic objects.With the obvious features of high-speed,high-efficiency and high-robust,the new developed dynamic 3D measurement techniques and systems in the thesis expand the application fields and objects of structured light-based 3D measurement,and can meet the application requirements of dynamic deformation detection for complex surface in the revolution of manufacturing and the performance test of defense equipment.The research results are expected to be applied to online inspection of industrial production and processing,performance testing of national defense equipment,and high-speed3 D modeling of complex dynamic scenes in VR/AR and subsequent displacement,deformation and force analysis.