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Journal of ZheJiang University (Engineering Science)  2021, Vol. 55 Issue (9): 1634-1642    DOI: 10.3785/j.issn.1008-973X.2021.09.004
    
Calibration method of laser displacement sensor based on binocular vision
Hao-ran MA(),Ya-bin DING*()
School of Mechanical Engineering, Tianjin University, Tianjin 300350, China
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Abstract  

A laser displacement sensor calibration method based on binocular visual technology was proposed, in order to increase the calibration precision of laser displacement sensor under the robot end-effector coordinate system. Through binocular visual technology, the location of laser spots projected on the flat was reconstructed. The eye-to-hand calibration parameters were used to transform the light spots into the robot end-effector coordinate system, meanwhile least squares method were used to match light spots into the line of the laser beam and obtain the beam direction as well as zero position of the laser displacement sensor to complete calibration. This method can simultaneously calibrate multiple laser displacement sensors on the robot end-effector coordinate system. No auxiliary component with precision requirement is needed in the calibration process, so the precision is high and the robustness is strong. Result based on standard ball measurement precision evaluation experiment shows that the laser displacement sensor measurement precision range after calibration by this method is 0.038 6±0.025 8 mm, within the range of three standard deviation, which satisfies the requirement of robot processing.



Key wordsbinocular vision system      laser displacement sensor      measurement system      sensor calibration      industrial robot     
Received: 22 September 2020      Published: 20 October 2021
CLC:  TH 161  
Fund:  国家重点研发计划资助项目(2017YFB1301800);国家自然科学基金资助项目(51775376,91948301,51721003,51675369);天津市自然科学基金资助项目(17JCZDJC40100)
Corresponding Authors: Ya-bin DING     E-mail: mahaoran@tju.edu.cn;ybding@tju.edu.cn
Cite this article:

Hao-ran MA,Ya-bin DING. Calibration method of laser displacement sensor based on binocular vision. Journal of ZheJiang University (Engineering Science), 2021, 55(9): 1634-1642.

URL:

https://www.zjujournals.com/eng/10.3785/j.issn.1008-973X.2021.09.004     OR     https://www.zjujournals.com/eng/Y2021/V55/I9/1634


基于双目视觉的激光位移传感器标定方法

为了提高激光位移传感器在工业机器人末端坐标系下的标定精度,提出基于双目视觉的激光位移传感器标定方法. 该方法通过双目视觉技术重建激光光束投影在平面上的光斑位置,利用手眼标定参数将光斑位置转换至机器人末端坐标系,同时利用最小二乘方法将光斑拟合成光束直线,获得机器人末端坐标系下的传感器光束方向及零点位置以完成标定. 该方法可同时标定机器人末端上的多个激光位移传感器,无须采用有精度要求的辅助工件标定,具备精度高,鲁棒性强优势. 基于标准球的精度评价实验结果显示,在3倍标准差范围内该方法标定后的激光位移传感器测量精度范围为0.038 6±0.025 8 mm,满足机器人加工要求.


关键词: 双目视觉系统,  激光位移传感器,  测量系统,  传感器标定,  工业机器人 
Fig.1 Simplified beam model
Fig.2 Binocular vision system extracts spot locations model
Fig.3 Calibration model of laser displacement sensor
Fig.4 Coordinate transformation relation of calibration model
符号 定义 符号 定义
${O_{\rm{B}}}$ 机器人基座坐标系 ${O_{\rm{T}}}$ 机器人末端坐标系
${x_{\rm{B}}}$ 机器人基座坐标系x ${x_{\rm{T}}}$ 机器人末端坐标系x
${y_{\rm{B}}}$ 机器人基座坐标系y ${y_{\rm{T}}}$ 机器人末端坐标系y
${z_{\rm{B}}}$ 机器人基座坐标系z ${z_{\rm{T}}}$ 机器人末端坐标系z
${O_{\rm{O}}}$ 双目视觉系统坐标系 ${O_{\rm{O}}}$ 标定板坐标系
${x_{\rm{C}}}$ 双目视觉系统坐标系x ${x_{\rm{O}}}$ 标定板坐标系x
${y_{\rm{C}}}$ 双目视觉系统坐标系y ${y_{\rm{O}}}$ 标定板坐标系y
${z_{\rm{C}}}$ 双目视觉系统坐标系z ${z_{\rm{O}}}$ 标定板坐标系z
${}_{\rm{B}}^{\rm{T}}{\boldsymbol{H}}$ 机器人末端相对于机器人基座的位姿转换矩阵 ${}_{\rm{C}}^{\rm{O}}{\boldsymbol{H}}$ 标定板相对于双目视觉系统的位姿转换关系
${}_{\rm{T}}^{\rm{O}}{\boldsymbol{H}}$ 标定板相对于机器人末端的位姿转换矩阵 ${}_{\rm{C}}^{\rm{B}}{\boldsymbol{H}}$ 机器人基座相对于双目视觉的位姿转换矩阵
Tab.1 Calibration model parameter definition
Fig.5 Illustration zero position calculation
Fig.6 Experimental platform of laser displacement sensor calibration
Fig.7 Experimental procedure of laser displacement sensor calibration
Fig.8 Eye-to-hand calibration experiment scene
Fig.9 Binocular camera collect calibration image
Fig.10 Image coordinate extraction process of spot center point
Fig.11 The position of the spot of binocular vision acquisition in the robot terminal coordinate system
Fig.12 Effect diagram of light spot fitting beam in robot terminal coordinate system
Fig.13 Residual diagram of light spot fitting beam in robot terminal coordinate system
Fig.14 Calculation results laser zero position in robot terminal coordinate system
Fig.15 Measuring system collect spherical data points
Fig.16 Spherical data point acquisition results in robot base coordinate system
Fig.17 Spherical data point fitting results of ceramic standard sphere in robot base coordinate system
实验序号 ${d_f}/{\rm{mm}}$ ${d_e}/{\rm{mm}}$ ${\varepsilon _{\max }}/{\rm{mm}}$ ${\delta _{}}/{\rm{mm}}$
1 19.996 0.007 0.019 0.026
2 20.002 0.013 0.023 0.036
3 19.968 ?0.021 0.027 0.048
4 20.004 0.015 0.020 0.035
5 19.998 0.009 0.018 0.027
6 19.978 ?0.011 0.023 0.034
7 20.006 0.017 0.025 0.042
8 20.010 0.021 0.029 0.050
9 20.014 0.025 0.024 0.049
10 19.970 ?0.019 0.020 0.039
Tab.2 Spherical fitting results and measurement errors
Fig.18 Normal measurement of workpiece surface
$u$ Kmax Kmin ${K_{\rm{m}}}$ ${K_{\rm{g}}}$
1 43.10 0 21.55 0
2 37.88 0 18.94 0
3 33.78 0 16.89 0
4 25.00 0 12.50 0
5 25.00 0 12.50 0
Tab.3 Curvature at processing point m−1
Fig.19 Measure angle distribution of residuals
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