提高相移条纹投影三维测量精度的主值相位反向误差补偿法

The 3D measurement with digital phase-shifting fringe projection techniques is implemented through the serial processes: digital phase-shifting fringe patterns production, the fringe patterns projection, acquisition, phase wrapping and phase unwrapping. Then the unwrapping phase is used to recover the 3D profile of the measured object. Due to the complexities of the surface structure to be measured, and the non-linear responses of the fringe pattern projectors and the imaging system, the phase error inevitably occur. To obtain the unwrapped phase value with high speed and high accuracy for measuring the complex surfaces having holes, steps and gaps as well as those having high dynamic range optical reflectivity, this project will investigate a fast and accurate method of phase recovery and inverse-phase error compensation, which is adaptive and robust to the change of measurement conditions. The method does not require the advance process to calibrate the system phase errors. Only a compensation fringe pattern with the same frequency as the highest one of the measurement fringe patterns and a certain amount of phase shift is required to project to the measured surface. The nonlinear phase error compensation can be conducted in the wrapped map through error average superposition with the same value but having opposite sign. Then the high accuracy unwrapped phase value can be computed in the following process. If the inverse-phase error compensation is used in the multi-frequency phase-shifting fringe projection, the high accuracy absolute unwrapped phase map can be achieved. In one word, the method proposed in this project can improve not only the measurement speed but also the accuracy. It can realize high- efficiency and rapid digital fringe projection 3D profile measurement.

数字相移条纹投影三维测量技术通过数字条纹产生、投影、采集、相位提取和相位展开技术，获取反映物体三维形貌信息的解包裹相位，实现表面三维轮廓的测量。由于被测对象表面结构的复杂性，以及条纹投影仪和成像系统存在非线性响应，必然存在非线性相位测量误差。为了快速准确地获得高精度相位值，本项目针对有孔洞、大台阶、相对分离不连续的，以及光学反射率动态变化范围大的复杂轮廓表面，提出一种具有普适性的，对测量条件变化具有自适应性和鲁棒性的，快速准确的相位恢复和反向误差补偿方法。该方法无需提前标定系统的相位误差，仅通过投影一组与最高频率相同且具有一定相移量的补偿相移条纹，在主值相位图内，通过正负误差叠加相抵，进行相位误差补偿，获得精确的解包裹相位值。并与倍频法相结合，可实现高精度绝对相位测量。因此，该方法既可提高测量速度，又可提高绝对相位测量的精度，能够实现高效快速数字条纹投影三维轮廓高精度测量。

数字相移条纹投影三维测量技术在工业检测、反求工程等领域具有广阔的应用前景。由于被测对象表面结构的复杂性，以及条纹投影仪和成像系统存在非线性响应等干扰，如何提高测量准确性、可靠性和适应性，一直是人们关注的重点内容。为此，本项目针对有孔洞、大台阶、相对分离不连续的物体表面，研究多频条纹投影主值相位反向误差补偿原理与算法，光学反射率动态范围大的表面反向误差补偿技术，高精度绝对相位实现方法与三维重构技术。经过4年的研究，本项目取得的主要研究成果如下：.(1)针对测量系统和测量环境变化等因素产生的非线性误差难题，提出一种利用倍频法与反向误差补偿法相结合的相位误差补偿方法，该方法无需提前标定系统，仅通过投影一组与最高频率相同且具有一定相移量的补偿相移条纹，即可获得精确的解包裹相位值。.(2)针对数字投影仪的伽马效应引起的非线性相位误差问题，提出了一种多预补偿值的方法，可以有效减少伽马非线性效应对测量精度的影响。.(3)针对光学反射率变化剧烈的高动态轮廓三维测量难题，提出了一种基于递归的自适应条纹投影方法和一种高低幅值条纹投影方法，这两种方法可以用于复杂场景和物体轮廓在线自适应测量。.(4)针对光亮三维轮廓测量，提出了两种光学折返相移测量解决方案：单相机+相移条纹投影方案；双相机+相移条纹投影方案。还提出了一种新的共平面约束的系统参数高精度标定方法。.(5)为了实现相移条纹投影三维测量能够用于在线测量场合，提出了三种数据处理加速算法和体系结构：FPGA嵌入系统的加速方法、FPGA和CPU的异构加速方法，以及可扩展的并行处理架构方法。.(6)提出了一种提升系统模型参数标定精度的有效解决方案，即减小棋盘格靶标的角点提取误差，提高亚像素角点坐标位置处的绝对相位值的提取精度。.(7)开发了一款适用于复杂形体结构外观缺陷三维多功能视觉检测仪，可用于工业现场装配环境下机械手驱动多视角检测。