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Robust vision-based joint tracking for laser welding of curved closed-square-butt joints
University West, Department of Engineering Science, Division of Production Systems. (PTW)ORCID iD: 0000-0002-8771-7404
University West, Department of Engineering Science, Division of Production Systems. (PTW)ORCID iD: 0000-0001-5734-294X
University West, Department of Engineering Science, Division of Production Systems. (PTW)ORCID iD: 0000-0001-5608-8636
University West, Department of Engineering Science, Division of Production Systems. Physics Department, IFN-CNR Institute for Photonics and Nanotechnologies, Bari, Italy. (PTW)ORCID iD: 0000-0002-6247-5429
2019 (English)In: The International Journal of Advanced Manufacturing Technology, ISSN 0268-3768, E-ISSN 1433-3015, Vol. 101, no 5-8, p. 1867-1978Article in journal (Refereed) Published
Abstract [en]

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.

Place, publisher, year, edition, pages
2019. Vol. 101, no 5-8, p. 1867-1978
Keywords [en]
Laser beam welding, Joint tracking, Butt joints, Camera, Hough transform, Kalman filter
National Category
Materials Engineering Manufacturing, Surface and Joining Technology
Research subject
ENGINEERING, Manufacturing and materials engineering
Identifiers
URN: urn:nbn:se:hv:diva-13211DOI: 10.1007/s00170-018-3044-0OAI: oai:DiVA.org:hv-13211DiVA, id: diva2:1271709
Projects
VINNOVA project VarGa
Funder
Vinnova, 2016-03291
Note

First Online: 27 November 2018

Funders: SWE-DEMO MOTOR ; [2015-06047]

Available from: 2018-12-18 Created: 2018-12-18 Last updated: 2019-05-10Bibliographically approved
In thesis
1. Monitoring and control of laser beam butt joint welding
Open this publication in new window or tab >>Monitoring and control of laser beam butt joint welding
2019 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Laser beam welding is one important technology in automated production. It has several advantages, such as the ability to produce deep and narrow welds giving limited heat induced deformations. The laser beam welding process is however sensitive to how the high power laser is positioned with regards to the joint position. Therefore, to achieve a seam without defects, the joint position needs to be measured and controlled. The laser beam welding process is also sensitive to variations in joint gap width. Costly joint preparations are required to achieve the tight fit up tolerances needed to produce high quality welds. However, the demand on joint preparation can be somewhat relaxed by allowing the joint gap width to vary and controlling the process. One way of doing this is to control the filler wire feed rate based on joint gap width measurements.This thesis presents experimental studies on how to track closed-square-butt joints and also how to handle varying square-butt joints in laser beam welding.

Different optical sensor systems are evaluated for their performance to estimate the joint position and the joint gap width. The possibility of detecting beam offsets is studied by using sensors systems based on a photo diode and on a spectrometer. Estimations of the joint position, to be used for closed loop position control, is studied by using a camera and external LED illumination. Variations in joint gap width is evaluated using a spectrometer, a camera and a laser profile sensor. Experimental results show that both the photodiode system and the spectometer system is able to detect beam offsets and that the beam position can be estimated with sufficient accuracy when welding closed-square-butt joints. It is also shown that the joint gap width can be estimated by the selected sensor systems and that the estimates can be used for controlling the wire feed rate in order to obtain a constant weld geometry and avoid defects related to the gap width.

Place, publisher, year, edition, pages
Trollhättan: University West, 2019. p. 84
Series
PhD Thesis: University West ; 27
Keywords
Laser beam welding, Optical sensors, Joint tracking, Varying gap
National Category
Manufacturing, Surface and Joining Technology
Research subject
Production Technology
Identifiers
urn:nbn:se:hv:diva-13650 (URN)978-91-88847-23-2 (ISBN)978-91-88847-22-5 (ISBN)
Public defence
2019-02-05, F104, Albertsalen, Trollhättan, 10:15 (English)
Opponent
Supervisors
Available from: 2019-03-15 Created: 2019-02-28

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Nilsen, MorganSikström, FredrikChristiansson, Anna-KarinAncona, Antonio

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