LiDAR measurement system and the calibration method of loading robot

Wang Chunmei; Huang Fengshan; Xue Ze

doi:10.12086/oee.2019.190002

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Wang Chunmei, Huang Fengshan, Xue Ze. LiDAR measurement system and the calibration method of loading robot[J]. Opto-Electronic Engineering, 2019, 46(7): 190002. doi: 10.12086/oee.2019.190002

Citation:

Wang Chunmei, Huang Fengshan, Xue Ze. LiDAR measurement system and the calibration method of loading robot[J]. Opto-Electronic Engineering, 2019, 46(7): 190002. doi: 10.12086/oee.2019.190002

LiDAR measurement system and the calibration method of loading robot

1.
School of Electrical Engineering, Hebei University of Science and Technology, Shijiazhuang, Hebei 050018, China
2.
School of Mechanical Engineering, Hebei University of Science and Technology, Shijiazhuang, Hebei 050018, China

Fund Project: Supported by National Natural Science Foundation of China (51075119), Key Basic Research Project of Hebei Province (18961825D), and the Natural Science Foundation of Hebei Province (E2017208111)

More Information

Corresponding author: Huang Fengshan, E-mail: hfs_high@126.com

Received Date 07 January 2019

Revised Date 03 April 2019

Published Date 01 July 2019

Abstract

Abstract

To carry out the measurement of vehicle body position and dimension of loading robot before loading, an intelligent vehicle body measurement system based on two-dimensional LiDAR was provided, and the calibration method of this system was studied as a key point. The two-dimension LiDAR was driven by rotating the platform, and the three-dimensional information of car body measured was obtained by using the single two-dimensional laser radar. In allusion to the complexity of calibration method of LiDAR measurement system and the difficulty in making calibration pieces, a system parameter calibration method was proposed based on 321 coordinate system building method, and mathematical models of calibration was established, with the principle and procedure of calibration method in detail. Measurement system was set up in a laboratory to carry out calibration experiment and measurement experiment on simulation vehicle body, and the measurement experiment for real vehicle body was conducted outside. The experiment result shows that the maximum measurement error of vehicle body size and length of this measurement system was 26.4 mm; maximum angle measurement error was 0.18 degree, which fully meets the precision requirements of loading.
- vehicle body position measurement /
- LiDAR /
- loading robot /
- calibration

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References

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Overview

Overview

Overview: At present, the material loading in China is basically in semi-automatic phase. The loading work is mainly completed by manpower and trolley, fork lift truck and telescopic belt conveyor, which is with low loading efficiency, large labor intensity. The industry crying needs intelligent loading robot to achieve the intelligent loading of the materials, while the vehicle shape and bucket size of the vehicle to be loaded should be firstly determined to achieve intelligent loading. Therefore, this paper established an intelligent vehicle body measurement system based on two-dimensional LiDAR, a system parameter calibration method was proposed based on 321 coordinate system building method, and mathematical models of calibration was established, giving the principle and procedure of calibration method in detail. The result shows that the maximum measurement error of vehicle body size and length of this measurement system was 26.4 mm; maximum angle measurement error was 0.18°, which fully meets the precision requirements of loading.

The specific calibration steps are: 1) establish LiDAR coordinate system, rotation center coordinate system, and robot loading coordinate system. The origin of LiDAR coordinate system o₀ is located at the optical center of LiDAR.y₀o₀z₀ plane is the scanning plane of LiDAR, axis o₀y₀ corresponds to the 45° line scan direction of LiDAR, axis o₀x₀ points in the dead ahead of LiDAR in front. The intersection o₁ of rotation axis l of rotating platform and plane x₀o₀y₀ is the origin of rotation center coordinate system. Three coordinate axes of rotation center coordinate system are parallel to the three axes of radar coordinate system. Loading coordinate system o₂-x₂y₂z₂ is located in the right front of the vehicle under test; 2) obtain the conversion relation between LiDAR coordinate system and rotation center coordinate system according to the installation location relationship of LiDAR and rotating platform; 3) assume that the coordinate-transformation matrix of rotation center coordinate system and loading coordinate system is T. Then calculate matrix T by substituting in special point coordinates from which we could transfer the calibration problem to looking for special point; 4) suspend a calibration board (about 2 m×2 m) over the axis o₂x₂ and axis o₂y₂ of loading coordinate system to ensure that the calibration plate is suspended directly above the axis; 5) scan the calibration plane and its adjacent ground, and two calibration plates and flat area are used as three calibration planes, then fit three plane equations, establish the coordinate system by means of 321 method and obtain the coordinates of four special points, and then solve the Tmatrix. Finally, the calibration of vehicle body measurement system is completed.