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.
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.
Fig.2Binocular vision system extracts spot locations model
Fig.3Calibration model of laser displacement sensor
Fig.4Coordinate 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轴
${x_{\rm{T}}}$
机器人末端坐标系x轴
${y_{\rm{B}}}$
机器人基座坐标系y轴
${y_{\rm{T}}}$
机器人末端坐标系y轴
${z_{\rm{B}}}$
机器人基座坐标系z轴
${z_{\rm{T}}}$
机器人末端坐标系z轴
${O_{\rm{O}}}$
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轴
${x_{\rm{O}}}$
标定板坐标系x轴
${y_{\rm{C}}}$
双目视觉系统坐标系y轴
${y_{\rm{O}}}$
标定板坐标系y轴
${z_{\rm{C}}}$
双目视觉系统坐标系z轴
${z_{\rm{O}}}$
标定板坐标系z轴
${}_{\rm{B}}^{\rm{T}}{\boldsymbol{H}}$
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.1Calibration model parameter definition
Fig.5Illustration zero position calculation
Fig.6Experimental platform of laser displacement sensor calibration
Fig.7Experimental procedure of laser displacement sensor calibration
Fig.8Eye-to-hand calibration experiment scene
Fig.9Binocular camera collect calibration image
Fig.10Image coordinate extraction process of spot center point
Fig.11The position of the spot of binocular vision acquisition in the robot terminal coordinate system
Fig.12Effect diagram of light spot fitting beam in robot terminal coordinate system
Fig.13Residual diagram of light spot fitting beam in robot terminal coordinate system
Fig.14Calculation results laser zero position in robot terminal coordinate system
Fig.15Measuring system collect spherical data points
Fig.16Spherical data point acquisition results in robot base coordinate system
Fig.17Spherical 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.2Spherical fitting results and measurement errors
Fig.18Normal 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.3Curvature at processing point m−1
Fig.19Measure angle distribution of residuals
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