足部三维测量系统中CCD传感器的全局标定

Global calibration of CCD cameras in measurement system for 3-D foot shapes

介绍了足部三维形貌测量系统的原理以及利用测量系统已有的一维运动机构和专用标定组件对测量系统所有CCD进行全局标定的实用方法。建立了基于光平面坐标系、标定坐标系、一维运动机构坐标系和CCD图像坐标系的测量系统模型;在测量系统一维运动机构的控制下,光平面分别对标定组件中两个斜面进行扫描,求取两个斜面上扫描线在光平面坐标系中的交点坐标,并根据光平面坐标系中交点坐标和CCD图像坐标系中交点坐标的对应关系,采用坐标映射方法建立光平面与CCD图像坐标系之间的坐标转换关系;确定了基于坐标系之间转换参数的优化目标函数,并根据标定块的标称值和实际测量结果,利用POWEL直接优化方法对坐标系之间的转换参数进行了优化。测量结果表明,单个CCD重复测量误差<0.062 5%;4个CCD测量值相对误差<0.365%。实验结果表明,所述全局标定方法减小了一维运动机构、光平面和足支撑玻璃平板之间安装调节误差以及CCD等器件非线性带来的影响,且简便、实用、不需要其它精密标定仪器,可以对测量系统进行现场标定。

A measurement system for 3-D foot shapes under different loads and the practical global calibration principle of CCD cameras based on coordinate mapping and POWEL optimization method were described. The model of the measurement system was constructed based on four coordinate systems, the visual point-net grid in light plane and in CCD camera image planes was formed through the scanning of two inclined planes and the mapping relations were constructed. Finally, the objective function based on transform coefficients between different coordinate systems was defined and the transform parameters were optimized by POWEL method. Measurement results show that the repetitive error of single CCD camera is 0.0625% and the relative measuring error of four CCDs is 0.365%. Experimental results prove that the simple and practical global calibration method can be used in the spot calibration of the measurement system, and installation errors and nonlinearity of CCD cameras can be reduced.