编码光场偏折术及其在高反射自由曲面三维测量中的应用

Specular free-form surfaces are ubiquitous in industrial production. They occur on objects ranging from impeller blades, optical parts, and lacquered automobile parts. Specular free-form surfaces own the characters of high surface finishment, preponderant specular reflectivity and complex surfaces, so that it is a great challenge for 3D measurement. The traditional deflectometry can not meet the practical demands, because its shortcoming is obvious in regularization, the angle resolution, the ability of identifying the input light and the light inter-reflection. This project explores a new method for measuring specular surfaces based on light field theorem. We call it the coded light field deflectometry, which acquires 3D information from the reflected light field. The coded light field is generated with a multilayer mask system. The light in it is transmitted onto the surface and reflected. The reflected light field is captured using a multimodal light field camera. The 3D information of the surface is in the reflected light field in a special manner, and the mechanism of the light field is the key to restore the information. Thus, the multiplexing theorem of the light field is studied firstly. A general model would be developed to depict the process of multiplexing the dimensions (such as time, space and frequency) of the plenoptic function onto an image. Based on this theory, the mechanisms of light field imaging and the principle of light field recovery will be studied respectively. The light can be determined from its position and direction, when the relationship between the out light field and inner light field is calibrated. After that, the code strategy of the input light field and the decoding method are studied to determine the correspondence of between the input light field and the reflected light field. Finally, the surface is obtained from the norm results through optimizing the energy of light field. In a word, this project provides a new perspective of measuring specular surfaces and is the supplement of the traditional theory based on light reflection. A variety of innovative research results are expect and can be demonstrate superior application in related areas.

高反射自由曲面具有高表面光洁度，高反射和面形复杂的特点，要求测量时零损伤，避免方向依赖性，实现高测量精度。然而基于反射光线模型的传统偏折术在规则化，角度分辨力，入射光线分辨能力，互反射等方面的不足，使其无法满足在航空航天、精密光学、模具制造、汽车、家用消费类越来越迫切的高反射自由曲面测量要求。本项目提出全新的编码光场偏折术，从高反射曲面的畸变光场中恢复三维信息。研究统一的全光函数复用理论，探讨光场恢复的多模态方法，构建多层掩模的光场投射系统和多模态光场感知系统，对内在光场与外在场景光场进行标定，研究光场的时空编码理论，解码确定光场对应性，以机器人抛磨系统中的叶片在线测量为对象开展编码光场偏折术的应用研究。该项目将揭示偏折术中光线传播、反射和接收的光场本质，形成全新的编码光场偏折术方法体系，是对高反射自由曲面光学测量理论的进一步完善和补充，有望促进相关应用行业的发展和进步。

镜面反射表面的非接触、高精度测量已成为三维光学测量领域的重要科学问题。相位测量偏折术以其原理简单、成本低、动态测量范围大、全场测量快速等优点成为研究热点。本项目针对相位偏折术的测量模型、对应性相位求解、系统参数标定、梯度积分等方面展开了研究。在高精度相位求解，高精度标定方法研究，高精度测量方法等方面取得了研究进展。.针对移动屏幕偏折术测量方法中的重复标定问题，提出了基于单相机监控的偏折术测量方法。辅助相机监控显示屏幕的两个位置，通过 Perspective-n-Point （PnP）方法和坐标系变换确定显示屏幕在主相机中的位姿关系。利用绝对相位追踪对应同一像素的显示屏幕两个位置上的同名相位点，确定入射光线，最终确定法线和梯度信息，并根据径向基函数插值法精确重建镜面面形。采用镜面标定法对具有不同视场的主辅相机进行标定，从而通过坐标系变换将入射光线和反射光线统一到主相机坐标系下。该方法只需标定一次，不会产生重复标定误差。.针对传统空间结构偏折术测量视场受限、结构复杂的问题，提出了空间结构双层平面偏折术。通过透明面光源构建用于确定入射光线的双平面结构而不是通过普通面光源的空间复用。透明面光源被建模为一块厚度和折射率均匀的透明玻璃。入射光线传播路径通过厚度和折射率参数精确描述。通过多立体视觉方法标定透明光源的折射参数，通过改进平面镜标定法标定系统参数。标定完成后，系统测量精度可以达到微米级。.为提高相位偏折术系统位姿关系标定精度和效率，提出了平行镜面标定方法。旋转矩阵只需要一个镜面位置直接通过PnP方法和镜像原理计算得到。平移矩阵的求解有两种模式：单相机模式和双相机模式。在单相机模式下，平移矩阵需要两个镜面位置通过求解线性方程组得到；在双相机模式下，平移矩阵被转换为一维搜索镜面到相机距离最优解来确定。平行镜面标定方法的双相机标定模式可用于立体偏折术实现系统位姿关系的自动标定。.将传统的反射光线与入射光线求交问题转化为反射光线与入射光线所在平面的求交问题并构建线面模型，从而构建了线面偏折术。基于镜面位姿标定方法提出线面偏折术系统的标定方法，只需一次标定即可用于镜面测量。线面偏折术有两种测量模式：单线面模式和双线面模式。单线面模式下，系统测量最大误差为0.25mm，误差均方根值为0.073ｍｍ；双线面模式下系统测量精度可达到微米级。