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清华大学学报(自然科学版)  2024, Vol. 64 Issue (4): 738-748    DOI: 10.16511/j.cnki.qhdxxb.2024.26.003
  机械工程 本期目录 | 过刊浏览 | 高级检索 |
冯宇星, 郑军, 林劲松
清华大学 机械工程系, 先进成形制造教育部重点实验室, 北京 100084
Calibration method of laser profiler based on constant focusing optical path
FENG Yuxing, ZHENG Jun, LIN Jinsong
Key Laboratory of Materials Processing Technology of the Ministry of Education, Department of Mechanical Engineering, Tsinghua University, Beijing 100084, China
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摘要 传统线激光视觉传感器受到相机景深的限制, 高精度测量范围有限。 通过倾斜镜头以满足Scheimpflug定律, 能在视觉传感器内建立恒聚焦光路, 使可见范围均清晰成像。 该文针对改进后的线激光视觉传感器, 提出了一套完整且有效的标定方案。 相机内参标定方面, 建立了倾斜相机成像模型, 并提出了新的参数初值获取方法和非线性优化流程。 光平面标定方面, 设计了双台阶形状的新标定靶物, 只需要采集一次标志物轮廓信息就能通过最优化求解快速完成光平面标定。 实际测量结果显示, 完成标定的传感器对标准陶瓷量块尺寸的检测偏差均值约为0.028 0 mm, 表明该文提出的标定方案可靠有效, 符合实际应用需求。
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关键词 线激光视觉传感器Scheimpflug定律恒聚焦光路相机标定光平面标定    
Abstract:[Objective] Laser profilers are widely utilized in various fields owing to their high precision, noncontact, and low cost. However, the lens plane for traditional laser profilers is parallel to the imaging plane. Thus, the high-precision measurement range of a traditional laser profiler is limited by the camera's restricted depth of view. To address this issue, this study optimizes the traditional laser profiler design and proposes a calibration method. [Methods] Specifically, this study establishes a constant focus optical path in the laser profiler by tilting the lens to meet the Scheimpflug condition, wherein the imaging, lens, and light planes intersect in a single line, called the Scheimpflug line. Furthermore, the traditional imaging model is not suitable for the detection principle of the laser profiler; hence, the corresponding calibration ideas must be improved and optimized. This study proposes a complete and effective calibration method for the laser profiler, which can be divided into two parts: camera calibration and light plane calibration. For the camera calibration part, a tilt camera imaging model is established based on the traditional camera imaging model using a two-dimensional tilt angle. A method of obtaining the initial parameters and a nonlinear optimization process for the parameters are presented to rapidly obtain the tilt camera imaging model parameters. For the light plane calibration part, a calibration target, which has a double-step shape, is designed. Precise subpixel coordinates of the feature points on the laser profiler are obtained through image processing algorithms by collecting the contour image of the calibration target once the laser profiler is used. The light plane parameters are acquired using the subpixel coordinates for the least squares fitting, which quickly completes the light plane calibration. This study also designs a three-degree-of-freedom automatic calibration device to address various issues, including the removal of the laser profiler's filter, the manual adjustment of the laser profiler's pose, and the complex operating procedures in traditional calibration experiments. [Results] This study used the automatic calibration device to complete the calibration and accuracy evaluation experiments and verify the correctness and effectiveness of the proposed scheme. The experimental results revealed of the following: (1) The laser profiler designed herein could clearly capture all the feature points on the light plane, thereby effectively solving the limited measurement range problem of the traditional laser profiler. (2) The reprojection errors of the laser profiler's camera were 0.487 with the traditional camera calibration method and 0.129 with the camera calibration method. (3) The calibration target could complete the light plane calibration by collecting only one image according to the expected goal. (4) After completing all the calibration steps, the average detection deviation of the laser profiler for measuring the size of the standard ceramic gauge block was approximately 0.028 0 mm. [Conclusions] Thus, this study significantly improves the profiler's high-precision measurement range by establishing a constant focus optical path in the laser profiler. A calibration method with higher accuracy and efficiency is proposed herein for the laser profiler. The detection accuracy of the calibrated laser profiler meets the actual industrial requirements.
Key wordslaser profiler    Scheimpflug condition    constant focusing optical path    camera calibration    light plane calibration
收稿日期: 2023-08-16      出版日期: 2024-03-27
通讯作者: 郑军,副研究员,     E-mail:
作者简介: 冯宇星(1998—),男,硕士研究生。
冯宇星, 郑军, 林劲松. 基于恒聚焦光路的线激光视觉传感器的标定方案[J]. 清华大学学报(自然科学版), 2024, 64(4): 738-748.
FENG Yuxing, ZHENG Jun, LIN Jinsong. Calibration method of laser profiler based on constant focusing optical path. Journal of Tsinghua University(Science and Technology), 2024, 64(4): 738-748.
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