【作者】 许伟；

【导师】 习俊通；

【作者基本信息】 上海交通大学 ， 机械制造及其自动化， 2010， 硕士

【摘要】 相移结构光三维测量系统因其测量精度高,适应性广等优势在逆向工程、工业检测、人体测量、文物保护等领域得到广泛应用。系统首先通过采集多帧有一定相移的条纹图像计算包含有被测物体表面三维信息的初始相位值,再利用多频相移或与其他编码方式结合的方法实现相位解包。最后采用三角测量法,利用解得的绝对相位值获取物体表面的空间三维信息,用于物体表面的三维重建。相移测量技术有单频相移和多频相移两种方式。单频相移技术测量时只获取一组包裹相位值,故其在解包场景、解包精度以及误差容忍度方面均存在不足。本文结合计算机模拟试验分析多频相移相对于单频相移在解包场景,解包精度,抑制随机误差和系统误差方面的优势。并提出了多频相移测量的技术方案,其中包括光栅设计、解包算法设计、相位波动误差补偿、相位校正以及程序设计等内容。查表法和差分法是多频相移技术中最主要的两种方法,本文详细研究了这两种解包方法的算法原理。在此基础上归纳总结这两种解包算法的具体实施步骤。利用计算机模拟解包过程,对这两种方法在测量场景以及解包容差能力方面进行了理论分析和比较。模拟试验表明查表法在测量场景以及理论容差度上均优于外差法。相位波动误差和相位偏移错误校正是多频相移测量中的两项关键技术。在计算机仿真分析投影仪伽马非线性特性对包裹相位波动误差影响的基础上,提出一种面向相移结构光测量的相位波动误差补偿方法。该方法采用二次多项式最小二乘拟合的方法近似输出条纹光强分布,实现对相位波动误差的补偿。实验结果表明,该方法可大大降低由伽马非线性产生的相位波动误差,补偿后平均相位波动误差小于补偿前的1/5,解包查表误码率比补偿前减少14.5倍。采用基于像素段生长的方法实现对相位偏移错误的校正,该方法利用较小的链表长度实现校正,空间复杂度低,校正健壮性好。在实现对相位波动误差的补偿和相位偏移错误的校正后,本文利用C++实现解包程序的设计。最后,在理论分析的基础上,利用实验室测量系统对本文所提出的解包算法、误差补偿方法以及相位校正技术进行实验验证。同时对查表和差分这两种解包方法在实际测量中的场景、容差度、解包效率以及解包健壮性进行实验比较,并举例说明测量方法在工程中的应用。更多还原

【Abstract】 The structured-light 3D shape measurement technology based on phase shift has been used in many kinds of fields, such as reverse engineering, product quality control, body measurement, heritage repair and so on. This technology grabs images with some phase-shifted grating to compute the wrapped phase which include 3D shape information. And then, using multiple frequency phase-shift technology or other coding method, the unwrapped phase used for 3D-reconstruction can be obtained.The structured-light measurement system has three parts: projection system, image acquisition system and software system. Based on triangulation, the system builds relationship between spatial coordination of object surface and unwrapped phase, and uses the unwrapped phase to get spatial coordination. Single and multiple frequency technology are the most used methods in phase shift technology. In this paper, based on simulation, we prove that compared to single-frequency technology, the multiple-frequency technology has an advantage in reducing random error and system error. Meanwhile we put forward the method of grating design and unwrapping process based on multiple frequency technology.The foremost unwrapping method based multiple frequency technology are look-up table and differential method, in this paper, these two methods are studied intensively. According to the study, unwrapping process of two methods is put forward. Based on computer simulation, we compare and analysis the unwrapping scene and allowance between two methods. Simulation result shows that look-up is better than differential method theoretically.Error compensation and calibration are key technologies of multiple frequency technology. Based on simulation of the impact of gamma nonlinearity of the projector on phase error, a method of phase error compensation for structural light measurement based on phase-shifting is put forward. In this method, binomial curve is used to approximate the intensity of the captured images, meanwhile, least square fitting method is used to compensate the phase error, and in this way, system error caused by the gamma nonlinearity of the projector is reduced greatly. Experimental results show that this method reduces greatly the phase error caused by the gamma nonlinearity of the projector. The average phase error is 5 times smaller than that before error compensation, meanwhile, the error rate of unwrapping based on look-up table method is reduced 14.5 times. This paper uses the method of growth of pixel segment to calibrate phase error. This method has advantages in space complexity and robust. After error compensating and calibrating, programming design of unwrapping is completed based on C++ program.At last, based on Theoretical analysis, experiments are performed to study the performance of Error compensation technology and error calibration technology, and to compare allowance, robust and unwrapping efficiency between look-up table and differential method. Meanwhile, some examples of the system application in projects are illustrated.更多还原