Robust vision-based joint tracking for laser welding of curved closed-square-butt joints

  • Morgan NilsenEmail author
  • Fredrik Sikström
  • Anna-Karin Christiansson
  • Antonio Ancona
Open Access


Robotized laser beam welding of closed-square-butt joints is sensitive to how the focused laser beam is positioned in relation to the joint, and existing joint tracking systems tend to fail in detecting the joint when the gap and misalignment between the work pieces are close to zero. A camera-based system is presented based on a high dynamic range camera operating with LED illumination at a specific wavelength and a matching optical filter. An image processing algorithm based on the Hough transform extracts the joint position from the camera images, and the joint position is then estimated using a Kalman filter. The filter handles situations, when the joint is not detectable in the image, e.g., when tack welds cover the joint. Surface scratches, which can be misinterpreted as being the joint, are handled by a joint curve prediction model based on known information about the nominal path defined by the robot program. The performance of the proposed system has been evaluated off line with image data obtained during several welding experiments.


Laser beam welding Joint tracking Butt joints Camera Hough transform Kalman filter 


Funding information

This work was supported by the VINNOVA project VarGa (2016-03291) and the SWE-DEMO MOTOR (2015-06047).


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Copyright information

© The Author(s) 2018

Open Access This article is distributed under the terms of the Creative Commons Attribution 4.0 International License (, which permits unrestricted use, distribution, and reproduction in any medium, provided you give appropriate credit to the original author(s) and the source, provide a link to the Creative Commons license, and indicate if changes were made.

Authors and Affiliations

  1. 1.Department of Engineering SciencesUniversity WestTrollhättanSweden
  2. 2.Physics Department, IFN-CNR Institute for Photonics and NanotechnologiesBariItaly

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