Huang Shujun, Liu Yue, Gao Nan, Zhang Zonghua, Gao Feng, Jiang Xiangqian
School of Mechanical Engineering, Hebei University of Technology, Tianjin 300130, China.
Centre for Precision Technologies, University of Huddersfield, Huddersfield HD1 3DH, UK.
Sensors (Basel). 2018 Jan 6;18(1):144. doi: 10.3390/s18010144.
The recently developed direct phase measuring deflectometry (DPMD) method can directly measure the three-dimensional (3D) shape of specular objects with discontinuous surfaces, but requires a calibrated distance between a reference plane and liquid crystal display screen. Because the plane and screen are different distances from the imaging device, they cannot be clearly captured given the limited depth of field (DOF) of the lens. Therefore, existing machine vision-based methods cannot be used to effectively calibrate a DPMD system. In this paper, a new distance calibration method that uses a mirror with a hollow ring matrix pattern and a mobile stage is presented. The direction of the mobile stage in the camera coordinate system is determined by the mirror's pattern at several positions in the camera's DOF so that the reference position outside of the DOF can be calculated. The screen's position can also be calibrated by displaying patterns at a known scale. Therefore, the required distance is accurately obtained in the camera coordinate system. Evaluation results show that the maximum value of the absolute error is less than 0.031 mm. The experimental results on an artificial stepped mirror and a reflected diamond distribution surface demonstrate the accuracy and practicality of the proposed method.
最近开发的直接相位测量偏折术（DPMD）方法可以直接测量具有不连续表面的镜面物体的三维（3D）形状，但需要校准参考平面与液晶显示屏之间的距离。由于该平面和屏幕与成像设备的距离不同，鉴于镜头有限的景深（DOF），它们无法被清晰捕捉。因此，现有的基于机器视觉的方法无法用于有效校准DPMD系统。本文提出了一种新的距离校准方法，该方法使用具有空心环形矩阵图案的镜子和移动平台。通过镜子在相机景深内几个位置的图案来确定相机坐标系中移动平台的方向，从而可以计算出景深外的参考位置。屏幕的位置也可以通过以已知比例显示图案来校准。因此，可以在相机坐标系中准确获得所需的距离。评估结果表明，绝对误差的最大值小于0.031毫米。在人工阶梯镜和反射钻石分布表面上的实验结果证明了该方法的准确性和实用性。
