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. 2020 Nov 6;20(21):6341.
doi: 10.3390/s20216341.

Improvement of Robot Accuracy with an Optical Tracking System

Ying Liu  1 , Yuwen Li  1 , Zhenghao Zhuang  1 , Tao Song  2
Affiliations

Improvement of Robot Accuracy with an Optical Tracking System

Ying Liu et al. Sensors (Basel). .

Abstract

Robot positioning accuracy plays an important role in industrial automation applications. In this paper, a method is proposed for the improvement of robot accuracy with an optical tracking system that integrates a least-square numerical algorithm for the identification of kinematic parameters. In the process of establishing the system kinematics model, the positioning errors of the tool and the robot base, and the errors of the Denavit-Hartenberg parameters are all considered. In addition, the linear dependence among the parameters is analyzed. Numerical simulation based on a 6-axis UR robot is performed to validate the effectiveness of the proposed method. Then, the method is implemented on the actual robot, and the experimental results show that the robots can reach desired poses with an accuracy of ±0.35 mm for position and ±0.07° for orientation. Benefitting from the optical tracking system, the proposed procedure can be easily automated to improve the robot accuracy for applications requiring high positioning accuracy such as riveting, drill, and precise assembly.

Keywords: kinematic parameter identification; optical tracking system; robot.

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Conflict of interest statement

The authors declare no conflict of interest.

Figures

Figure 1
Figure 1
Robot calibration system configuration.
Figure 2
Figure 2
Measurement range of the optical tracking system used in this work (unit: mm).
Figure 3
Figure 3
System integration diagram.
Figure 4
Figure 4
Kinematic scheme of a serial robot.
Figure 5
Figure 5
Definition of D-H parameters.
Figure 6
Figure 6
Nominal and actual coordinate frames.
Figure 7
Figure 7
Specific process of the robot to accurately track the trajectory.
Figure 8
Figure 8
Nominal position and corrected positions.
Figure 9
Figure 9
Pose errors before and after calibration for simulation: (a) X axis; (b) Y axis; (c) Z axis; (d) roll α; (e) pitch β; (f) yaw γ.
Figure 10
Figure 10
Experimental setup.
Figure 11
Figure 11
The nominal and corrected positions.
Figure 12
Figure 12
Pose errors before and after calibration for test: (a) X axis; (b) Y axis; (c) Z axis; (d) roll  α; (e) pitch  β; (f) yaw  γ.
Figure 13
Figure 13
Pose errors before and after calibration of 10 data points: (a) X axis; (b) Y axis; (c) Z axis; (d) roll α; (e) pitch β; (f) yaw γ.
Figure 14
Figure 14
Teaching the robot insertion at three points.
Figure 15
Figure 15
Alignment of rod and hole (a) before calibration and (b) after calibration.
Figure 16
Figure 16
Difference between the joint angles before and after calibration: (a) joint 1; (b) joint 2; (c) in joint 3; (d) joint 4; (e) joint 5; (f) joint 6.
Figure 17
Figure 17
Difference between the end-effector position before and after calibration: (a) X axis; (b) Y axis; (c) Z axis; (d) roll α; (e) pitch β; (f) yaw γ.
Figure 18
Figure 18
Misalignment of the tip.
Figure 19
Figure 19
Corrected misalignment for each hole.
See this image and copyright information in PMC

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