WANG Sen， LIU Shugui， MAO Qing
（State Key Laboratory of Precision Measuring Technology and Instruments， Tianjin University， Tianjin 300072, China）
Abstract： Light pen coordinate measuring system (LPCMS) is a kind of portable coordinate measuring technique based on vision metrology. In classical LPCMS, the measuring range is limited to the camera’s field of view. To overcome this defect, a new LPCMS is designed in this paper to fulfil whole space coordinate measurement. The camera is installed on a turntable instead of a tripod, so that the camera can rotate to track the movement of the light pen. The new system can be applied to large scale onsite measurement, and therefore it notably extends the application of LPCMS. To guarantee the accuracy of the new system, a method to calibrate the parameters of the tracking turntable is also proposed. Fixing the light pen at a stationary position, and changing the azimuth angles of the turntable’s two shafts, so that the camera can capture the images of the light pen from different view angles. According to the invariant spatial relationship between the camera and the pedestal of the tracking turntable, a system of nonlinear equations can be established to solve the parameters of the turntable. Experimental results show that the whole space coordinate measuring accuracy of the new system can reach 0.25 mm within 10 m. It can be concluded that the newly designed system can significantly expand the measuring range of LPCMS without losing too much accuracy.
Key words： light pen； whole space coordinate measuring system； tracking turntable； vision metrology； parameter calibration； homogeneous coordinate transformation matrix
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基于跟踪转台的光笔式全空间坐标测量系统
王森， 刘书桂， 毛晴
（天津大学精密测试技术及仪器国家重点实验室， 天津 300072）
摘要:光笔式坐标测量系统是一种基于视觉测量的便携式坐标测量技术。 在经典的光笔式坐标测量系统中， 其测量范围被限制在相机的视场范围之内。 为了克服这种缺陷， 本文设计了一种新的光笔式坐标测量系统以实现全空间坐标测量。 相机被安装在一个转台而不是三脚架上， 因而， 相机能够进行旋转从而对光笔的移动进行跟踪。 新系统能够被用于大范围的工业现场测量， 因此极大地扩展了光笔式坐标测量系统的应用范围。 为了保证新设计系统的测量精度， 本文还提出了一种对跟踪转台参数进行标定的方法。 将光笔放置在固定的位置， 并改变转台两个旋转轴的方位角， 让相机从不同的视角采集光笔的图像。 根据相机和转台基座之间不变的坐标变换关系， 可以建立起一个非线性方程组来对跟踪转台的参数进行求解。 实验结果表明， 新系统在测量距离为10 m内的全空间， 其坐标测量精度能够达到0.25 mm。 可以得出， 新设计系统能够在不损失太多精度的情况下显著扩大光笔式坐标测量系统的测量范围。
关键词:光笔； 全空间坐标测量系统； 跟踪转台； 视觉测量； 参数标定； 齐次坐标变换矩阵
引用格式：WANG Sen, LIU Shugui, MAO Qing. Light pen whole space coordinate measuring system based on a tracking turntable. Journal of Measurement Science and Instrumentation, 2021, 12（4）： 379-389. DOI： 10.3969／j.issn.1674-8042.2021.04.001
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