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An improved vision calibration method for coaxial alignment microassembly

Xin Ye (School of Mechanical Engineering, Beijing Institute of Technology, Beijing, China)
Jun Gao (School of Mechanical Engineering, Beijing Institute of Technology, Beijing, China)
Zhijing Zhang (School of Mechanical Engineering, Beijing Institute of Technology, Beijing, China)
Chao Shao (School of Mechanical Engineering, Beijing Institute of Technology, Beijing, China)
Guangyuan Shao (School of Mechanical Engineering, Beijing Institute of Technology, Beijing, China)

Assembly Automation

ISSN: 0144-5154

Article publication date: 29 July 2014

339

Abstract

Purpose

The purpose of this paper is to propose a sub-pixel calibration method for a microassembly system with coaxial alignment function (MSCA) because traditional sub-pixel calibration approaches cannot be used in this system.

Design/methodology/approach

The in-house microassembly system comprises a six degrees of freedom (6-DOF) large motion serial robot with microgrippers, a hexapod 6-DOF precision alignment worktable and a vision system whose optical axis of the microscope is parallel with the horizontal plane. A prism with special coating is fixed in front of the objective lens; thus, two parts’ Figures, namely the images of target and base part, can be acquired simultaneously. The relative discrepancy between the two parts can be calculated from image plane coordinate instead of calculating space transformation matrix. Therefore, the traditional calibration method cannot be applied in this microassembly system. An improved calibration method including the check corner detection solves the distortion coefficient conversely. This new way can detect the corner at sub-pixel accuracy. The experiment proves that the assembly accuracy of the coaxial microassembly system which has been calibrated by the new method can reach micrometer level.

Findings

The calibration results indicate that solving the distortion conversely could improve the assembly accuracy of MSCA.

Originality/value

The paper provides certain calibration methodological guidelines for devices with 2 dimensions or 2.5 dimensions, such as microelectromechanical systems devices, using MSCA.

Keywords

Acknowledgements

This work was financially supported by the National Natural Science Foundation of China (51127004) and (51105036). Any opinions, findings and conclusions or recommendations expressed in this material are those of the authors and do not necessarily reflect the views of the National Science Foundation.

Citation

Ye, X., Gao, J., Zhang, Z., Shao, C. and Shao, G. (2014), "An improved vision calibration method for coaxial alignment microassembly", Assembly Automation, Vol. 34 No. 3, pp. 237-243. https://doi.org/10.1108/AA-10-2013-092

Publisher

:

Emerald Group Publishing Limited

Copyright © 2014, Emerald Group Publishing Limited

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