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BETA
Christiansson, Anna-KarinORCID iD iconorcid.org/0000-0001-5608-8636
Alternative names
Publications (10 of 54) Show all publications
Elefante, A., Nilsen, M., Sikström, F., Christiansson, A.-K., Maggipinto, T. & Ancona, A. (2019). Detecting beam offsets in laser welding of closed-square-butt joints by wavelet analysis of an optical process signal. Optics and Laser Technology, 109, 178-185
Open this publication in new window or tab >>Detecting beam offsets in laser welding of closed-square-butt joints by wavelet analysis of an optical process signal
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2019 (English)In: Optics and Laser Technology, ISSN 0030-3992, E-ISSN 1879-2545, Vol. 109, p. 178-185Article in journal (Refereed) Published
Abstract [en]

Robotized laser beam welding of closed-square-butt joints is sensitive to the positioning of the laser beam with respect to the joint since even a small offset may result in a detrimental lack of sidewall fusion. An evaluation of a system using a photodiode aligned coaxial to the processing laser beam confirms the ability to detect variations of the process conditions, such as when there is an evolution of an offset between the laser beam and the joint. Welding with different robot trajectories and with the processing laser operating in both continuous and pulsed mode provided data for this evaluation. The detection method uses wavelet analysis of the photodetector signal that carries information of the process condition revealed by the plasma plume optical emissions during welding. This experimental data have been evaluated offline. The results show the potential of this detection method that is clearly beneficial for the development of a system for welding joint tracking.

Place, publisher, year, edition, pages
Elsevier, 2019
Keywords
Laser beam welding, Joint tracking, Butt joints, Photodiode, Wavelet analysis
National Category
Manufacturing, Surface and Joining Technology
Research subject
Production Technology
Identifiers
urn:nbn:se:hv:diva-12832 (URN)10.1016/j.optlastec.2018.08.006 (DOI)000446949600023 (Scopus ID)
Funder
VINNOVA, 2016-03291
Available from: 2018-08-21 Created: 2018-08-21 Last updated: 2018-10-25Bibliographically approved
Nilsen, M., Sikström, F., Christiansson, A.-K. & Ancona, A. (2018). In-process Monitoring and Control of Robotized Laser Beam Welding of Closed Square Butt Joints. Paper presented at 8th Swedish Production Symposium (SPS 2018), Stockholm, Sweden, May 16-18, 2018. Procedia Manufacturing, 25, 511-516
Open this publication in new window or tab >>In-process Monitoring and Control of Robotized Laser Beam Welding of Closed Square Butt Joints
2018 (English)In: Procedia Manufacturing, E-ISSN 2351-9789, Vol. 25, p. 511-516Article in journal (Other academic) Published
Abstract [en]

In robotized laser welding of technical zero gap closed square butt joints it is critical to position the laser beam correct with regardsto the joint. Welding with an offset from the joint may cause lack of sidewall fusion, a serious defect that is hard to detect and gives a weak weld . When using machined parts with gap and misalignment between the parts that is close to zero, existing joint tracking systems will probably fail to track the joint. A camera based system using LED illumination and matching optical filters is proposed in this paper to address this issue. A high dynamic range CMOS camera and the LED illumination is integrated into the laser tool. The camera captures images of the area in front of the melt pool where the joint is visible and an algorithm based on the Hough transform and a Kalman filter estimates the offset between the laser spot and the joint position. Welding experiments, using a 6 kW fiber laser, have been conducted to evaluate the performance of the system. Promising results are obtained that can be used in the further development of a closed loop controlled joint tracking system.

Place, publisher, year, edition, pages
Elsevier, 2018
Keywords
Laser welding, Butt joints, Joint tracking, Camera
National Category
Production Engineering, Human Work Science and Ergonomics Manufacturing, Surface and Joining Technology
Research subject
ENGINEERING, Manufacturing and materials engineering; Production Technology
Identifiers
urn:nbn:se:hv:diva-12828 (URN)10.1016/j.promfg.2018.06.123 (DOI)
Conference
8th Swedish Production Symposium (SPS 2018), Stockholm, Sweden, May 16-18, 2018
Projects
VINNOVA project VarGa (2016-03291)MoRE program project Hy-Las - Hybrid sensing for understanding of laser welding technology for process control, no 608473
Funder
VINNOVA, 2016-03291EU, European Research Council, FP7/2007-2013
Note

Del av specialnumret Proceedings of the 8th Swedish Production Symposium (SPS 2018) Redaktörer: M. Onori, L. Wang, X. V. Wang och W. Ji

This work was supported by the VINNOVA project VarGa (2016-03291) and also the People Programme (MarieCurie Actions) of the European Unions Seventh Framework Programme (FP7/2007-2013) under REA grant agreement no 608473 (MoRE program project Hy-Las - Hybrid sensing for understanding of laser welding technology for processcontrol).

Available from: 2018-08-28 Created: 2018-08-28 Last updated: 2018-08-31Bibliographically approved
Nilsen, M., Sikström, F., Christiansson, A.-K. & Ancona, A. (2017). Monitoring of Varying Joint Gap Width During Laser Beam Welding by a Dual Vision and Spectroscopic Sensing System. Paper presented at 16th Nordic Laser Materials Processing Conference, NOLAMP16. Physics Procedia, 89, 100-107
Open this publication in new window or tab >>Monitoring of Varying Joint Gap Width During Laser Beam Welding by a Dual Vision and Spectroscopic Sensing System
2017 (English)In: Physics Procedia, ISSN 1875-3892, E-ISSN 1875-3892, Vol. 89, p. 100-107Article in journal (Refereed) Published
Abstract [en]

A vision and spectroscopic system for estimation of the joint gap width in autogenous laser beam butt welding is presented. Variations in joint gap width can introduce imperfections in the butt joint seam, which in turn influence fatigue life and structural integrity. The aim of the monitoring approach explored here is to acquire sufficiently robust process data to be used to guide post inspection activities and/or to enable feedback control for a decreased process variability. The dual-sensing approach includes a calibrated CMOS camera and a miniature spectrometer integrated with a laser beam tool. The camera system includes LED illumination and matching optical filters and captures images of the area in front of the melt pool in order to estimate the joint gap width from the information in the image. The intensity of different spectral lines acquired by the spectrometer has been investigated and the correlation between the intensity of representative lines and the joint gap width has been studied. Welding experiments have been conducted using a 6 kW fiber laser. Results from both systems are promising, the camera system is able to give good estimations of the joint gap width, and good correlations between the signal from the spectrometer and the joint gap width have been found. However, developments of the camera setup and vision algorithm can further improve the joint gap estimations and more experimental work is needed in order to evaluate the robustness of the systems.

Place, publisher, year, edition, pages
Elsevier, 2017
Keywords
Laser beam welding; Butt joints; Varying gap width; Vision sensor; Spectroscopic sensor
National Category
Manufacturing, Surface and Joining Technology
Research subject
Production Technology
Identifiers
urn:nbn:se:hv:diva-11898 (URN)10.1016/j.phpro.2017.08.014 (DOI)2-s2.0-85037711817 (Scopus ID)
Conference
16th Nordic Laser Materials Processing Conference, NOLAMP16
Available from: 2017-12-11 Created: 2017-12-11 Last updated: 2018-01-06Bibliographically approved
Nilsen, M., Sikström, F., Christiansson, A.-K. & Ancona, A. (2017). Vision and spectroscopic sensing for joint tracing in narrow gap laser butt welding. Optics and Laser Technology, 96, 107-116
Open this publication in new window or tab >>Vision and spectroscopic sensing for joint tracing in narrow gap laser butt welding
2017 (English)In: Optics and Laser Technology, ISSN 0030-3992, E-ISSN 1879-2545, Vol. 96, p. 107-116Article in journal (Refereed) Published
Abstract [en]

The automated laser beam butt welding process is sensitive to positioning the laser beam with respect to the joint because a small offset may result in detrimental lack of sidewall fusion. This problem is even more pronounced incase of narrow gap butt welding, where most of the commercial automatic joint tracing system fail to detect the exact position and size of the gap. In this work, adual vision and spectroscopic sensing approach is proposed to trace narrow gap butt joints during laser welding. The system consists of a camera with suitable illumination and matched optical filters and a fast miniature spectrometer. An image processing algorithm of the camera recordings has been developed in order to estimate the laser spot position relative the joint position. The spectral emissions from the laser induced plasma plume has been acquired by the spectrometer, and based on the measurements of the intensities of selected lines of the spectrum, the electron temperature signal has been calculated and correlated to variations of process conditions. The individual performances of these two systems have been experimentally investigated and evaluated offline by data from several welding experiments where artificial abrupt as well as gradual excursions of the laser beam out of the joint were produced. Results indicate thata combination of the information provided by the vision and spectroscopic systems is beneficial for development of a hybrid sensing system for joint tracing.

Place, publisher, year, edition, pages
Guildford, Surrey: , 2017
Keywords
Laser beam welding, Joint tracing, Butt joints, Optical spectroscopy, Vision sensor, Hybrid sensing
National Category
Manufacturing, Surface and Joining Technology
Research subject
Production Technology; ENGINEERING, Manufacturing and materials engineering
Identifiers
urn:nbn:se:hv:diva-10639 (URN)10.1016/j.optlastec.2017.05.011 (DOI)000405051800015 ()2-s2.0-85019735734 (Scopus ID)
Note

Ingår i lic. avhandling

Available from: 2017-02-03 Created: 2017-02-03 Last updated: 2017-12-11Bibliographically approved
Nilsen, M., Sikström, F. & Christiansson, A. K. (2016). Joint tracking in zero gap laser beam welding using a vision sensor. In: The 7th International Swedish Production Symposium, SPS16, Conference Proceedings: 25th – 27th of October 2016. Paper presented at 7th Swedish Production Symposium (SPS), Lund, Sweden, October 25-27, 2016 (pp. 1-7). Lund: Swedish Production Academy
Open this publication in new window or tab >>Joint tracking in zero gap laser beam welding using a vision sensor
2016 (English)In: The 7th International Swedish Production Symposium, SPS16, Conference Proceedings: 25th – 27th of October 2016, Lund: Swedish Production Academy , 2016, p. 1-7Conference paper, Published paper (Refereed)
Abstract [en]

The paper describes a robust vision sensor system that can find very narrow gaps between metal sheets to be butt welded together. The use of automated laser beam welding is seen as a key enabler for efficient manufacturing by enabling narrow and deep welds with a limited heat affected zone and low thermal distortion of the welded components. It is sensitive to positioning the laser beam with respect to the joint position. Even a small off-set from the actual joint could result in detrimental lack of fusion. The system comprises a CMOS camera with optic filters integrated in the welding optics and appropriate LED illumination of the work piece. By analysing the spectral emissions during welding, illumination and matching optic filters have been chosen in a spectral range where the process disturbances are relatively low. In this way it has been shown possible to detect the joint position even during harsh welding conditions. Preliminary results from the first experiments show promising results, however more tests will be performed using different weld geometries etc. to verify the robustness of the algorithm.

Place, publisher, year, edition, pages
Lund: Swedish Production Academy, 2016
Keywords
Laser beam welding, joint tracing, narrow gap, butt weld
National Category
Manufacturing, Surface and Joining Technology
Research subject
ENGINEERING, Manufacturing and materials engineering
Identifiers
urn:nbn:se:hv:diva-10162 (URN)
Conference
7th Swedish Production Symposium (SPS), Lund, Sweden, October 25-27, 2016
Available from: 2016-12-07 Created: 2016-11-23 Last updated: 2018-08-12Bibliographically approved
Hagqvist, P., Christiansson, A.-K. & Heralic, A. (2015). Automation of a laser welding system for additive manufacturing. In: Kazuhiro Saitou, Univ. of Michigan (Ed.), Proceedings of the 2015 IEEE International Conference on Automation Science and Engineering: . Paper presented at 11th IEEE International Conference on Automation Science and Engineering, CASE 2015; Elite Park Avenue HotelGothenburg; Sweden; 24 August 2015 through 28 August 2015 (pp. 900-905). IEEE
Open this publication in new window or tab >>Automation of a laser welding system for additive manufacturing
2015 (English)In: Proceedings of the 2015 IEEE International Conference on Automation Science and Engineering / [ed] Kazuhiro Saitou, Univ. of Michigan, IEEE, 2015, p. 900-905Conference paper, Published paper (Refereed)
Abstract [en]

This paper presents the benefits and challenges ofusing a standard robotised laser welding cell for additive manufacturing(AM). Additive manufacturing, sometimes denoted3D-printing or rapid prototyping, has lately met strong interestin several areas of society, and a variety of technologies andmaterials have been in focus. The current paper summarisesautomation efforts for AM of advanced aero engine componentsusing high power laser with welding optics as power source formelting metal wire and using an industrial robot for obtaininga 3-dimensional feature shape. The challenges are related to theprocess itself encountering high and repeated temperatures withmelting and solidification of the metal as the main players. Themajor research solutions discussed in this paper are relatedto automation issues for obtaining a stable process and tohave control of the temperatures and temperature changes thatthe metals encounter during the process. The solutions aresuccessfully implemented in an industrial laser welding cell.

Place, publisher, year, edition, pages
IEEE, 2015
Keywords
Additive manufacturing, laser welding
National Category
Control Engineering Aerospace Engineering Manufacturing, Surface and Joining Technology
Research subject
ENGINEERING, Manufacturing and materials engineering; Production Technology
Identifiers
urn:nbn:se:hv:diva-8015 (URN)10.1109/CoASE.2015.7294213 (DOI)2-s2.0-84952778708 (Scopus ID)978-1-4673-8182-6 (ISBN)
Conference
11th IEEE International Conference on Automation Science and Engineering, CASE 2015; Elite Park Avenue HotelGothenburg; Sweden; 24 August 2015 through 28 August 2015
Note

Article number 7294213

Available from: 2015-08-31 Created: 2015-08-31 Last updated: 2018-08-12Bibliographically approved
Sikström, F., Christiansson, A.-K. & Lennartson, B. (2015). Model based feedback control of gas tungsten arc welding: An experimental study. In: Automation Science and Engineering (CASE), 2015 IEEE International Conference on: . Paper presented at 11th IEEE International Conference on Automation Science and Engineering, CASE 2015; Elite Park Avenue HotelGothenburg; Sweden; 24 August 2015 through 28 August 2015 (pp. 411-416). IEEE conference proceedings
Open this publication in new window or tab >>Model based feedback control of gas tungsten arc welding: An experimental study
2015 (English)In: Automation Science and Engineering (CASE), 2015 IEEE International Conference on, IEEE conference proceedings, 2015, p. 411-416Conference paper, Published paper (Refereed)
Abstract [en]

In order to obtain high structural integrity and joint performance in welding a transient heat conduction model has been utilized to design a model based feedback controller.Gas tungsten arc welding of work-pieces of austenitic steel have been simulated by the finite element method. The basis for controller design is a low order model obtained from parametric system identification. The identification has been performed both on the finite element simulation and on physical welding. The low order model responses show a good agreement with both the finite element simulation result and the physical process response. An experimental study has been performed to verify the approach. This study also explores what experiments are needed for a successful design. It is shown that model based control successfully mitigates perturbations that occur during welding.

Place, publisher, year, edition, pages
IEEE conference proceedings, 2015
National Category
Manufacturing, Surface and Joining Technology
Research subject
ENGINEERING, Manufacturing and materials engineering
Identifiers
urn:nbn:se:hv:diva-8299 (URN)10.1109/CoASE.2015.7294113 (DOI)2-s2.0-84952778514 (Scopus ID)
Conference
11th IEEE International Conference on Automation Science and Engineering, CASE 2015; Elite Park Avenue HotelGothenburg; Sweden; 24 August 2015 through 28 August 2015
Note

Article number 7294113

Available from: 2015-09-29 Created: 2015-09-29 Last updated: 2016-02-08Bibliographically approved
Hagqvist, P., Heralic, A., Christiansson, A.-K. & Lennartson, B. (2015). Resistance based iterative learning control of additive manufacturing with wire. Mechatronics (Oxford), 31, 116-123
Open this publication in new window or tab >>Resistance based iterative learning control of additive manufacturing with wire
2015 (English)In: Mechatronics (Oxford), ISSN 0957-4158, E-ISSN 1873-4006, Vol. 31, p. 116-123Article in journal (Refereed) Published
Abstract [en]

This paper presents successful feed forward control of additive manufacturing of fully dense metallic components. The study is a refinement of former control solutions of the process, providing more robust and industrially acceptable measurement techniques. The system uses a solid state laser that melts metal wire, which in turn is deposited and solidified to build the desired solid feature on a substrate. The process is inherently subjected to disturbances that might hinder consecutive layers to be deposited appropriately. The control action is a modified wire feed rate depending on the surface of the deposited former layer, in this case measured as a resistance. The resistance of the wire stick-out and the weld pool has shown to give an accurate measure of the process stability, and a solution is proposed on how to measure it. By controlling the wire feed rate based on the resistance measure, the next layer surface can be made more even. A second order iterative learning control algorithm is used for determining the wire feed rate, and the solution is implemented and validated in an industrial setting for building a single bead wall in titanium alloy. A comparison is made between a controlled and an uncontrolled situation when a relevant disturbance is introduced throughout all layers. The controller proves to successfully mitigate these disturbances and maintain stable deposition while the uncontrolled deposition fails.

Keywords
Additive manufacturing, Metal deposition, Automatic control, Resistance, Process measurement, Iterative learning control
National Category
Manufacturing, Surface and Joining Technology
Research subject
ENGINEERING, Manufacturing and materials engineering
Identifiers
urn:nbn:se:hv:diva-7429 (URN)10.1016/j.mechatronics.2015.03.008 (DOI)000367772000013 ()
Note

Available online 10 April 2015. Ingår i avhandling

Available from: 2015-03-06 Created: 2015-03-06 Last updated: 2018-06-18Bibliographically approved
Svenman, E., Rosell, A., Runnemalm, A., Christiansson, A.-K. & Henrikson, P. (2015). Weld gap position detection based on eddy current methods with mismatch compensation. In: Proceedings of JOM 18 International conference on joining materials, Helsingör, Danmark, april 26-29, 2015: . Paper presented at 18th International Conference on Joining Materials In association with the IIW Helsingør-Denmark, April 26 to 29, 2015 (pp. 1-9). JOM-institute
Open this publication in new window or tab >>Weld gap position detection based on eddy current methods with mismatch compensation
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2015 (English)In: Proceedings of JOM 18 International conference on joining materials, Helsingör, Danmark, april 26-29, 2015, JOM-institute , 2015, p. 1-9Conference paper, Published paper (Refereed)
Abstract [en]

The paper proposes a method for finding the accurate position of narrow gaps, intended for seam tracking applications. Laser beam welding of butt joints, with narrow gap and weld width, demand very accurate positioning to avoid serious and difficult to detect lack of fusion defects. Existing optical and mechanical gap trackers have problems with narrow gaps and surface finish. Eddy current probes can detect narrow gaps, but the accuracy is affected by mismatch in height above the surface on either side of the gap. In this paper a non-contact eddy-current method, suitable for robotic seam tracking, is proposed. The method is based on the resistive and inductive response of two absolute eddy current coils on either side of the gap to calculate a position compensated for height variations. Additionally, the method may be used to estimate the values of height and gap width, which is useful for weld parameter optimization. To investigate the response to variations in height, the method is tested on non-magnetic metals by scanning one commercially available eddy current probe across an adjustable gap and calculating the expected response for a two-probe configuration. Results for gap position are promising, while mismatch and gap width results need further investigation.

Place, publisher, year, edition, pages
JOM-institute, 2015
Series
JOM, ISSN 2246-0160
Keywords
laser welding, seam finding, inductive, eddy current
National Category
Manufacturing, Surface and Joining Technology
Research subject
Production Technology
Identifiers
urn:nbn:se:hv:diva-8991 (URN)
Conference
18th International Conference on Joining Materials In association with the IIW Helsingør-Denmark, April 26 to 29, 2015
Available from: 2016-02-04 Created: 2016-02-04 Last updated: 2018-08-12
Hagqvist, P., Sikström, F., Christiansson, A.-K. & Lennartson, B. (2014). Emissivity compensated spectral pyrometry for varying emissivity metallic measurands. Measurement science and technology, 25(2), 025010
Open this publication in new window or tab >>Emissivity compensated spectral pyrometry for varying emissivity metallic measurands
2014 (English)In: Measurement science and technology, ISSN 0957-0233, E-ISSN 1361-6501, Vol. 25, no 2, p. 025010-Article in journal (Refereed) Published
Abstract [en]

A novel method for converting electromagnetic spectral radiance information into emperature measurements is presented. It allows for varying spectral emissivity of the metallic measurand during the course of the measurement. Such variations are due to e.g. thermal oxidation or temperature dependent emissivity. Based on the assumption that emissivity changes with time and temperature in a continuous manner, it is further assumed that an emissivity estimate at one sample instance can be derived from the estimated emissivity found at the previous samples together with updated spectral information. This leads to successive recalculations of spectral emissivity together with corresponding temperature values. The proposed algorithm has been proven to give accurate temperature estimates from a measurement based on data captured by a standard UV-Vis spectrophotometer even for an oxidizing Ti-6Al-4V specimen in a temperature range between 900K and 1400K. The method however, is not limited to these wavelength- or temperature-ranges.

Place, publisher, year, edition, pages
Bristol: IOP Publ.,, 2014
Keywords
Emissivity Compensated Spectral Pyrometry
National Category
Robotics
Research subject
ENGINEERING, Manufacturing and materials engineering
Identifiers
urn:nbn:se:hv:diva-5607 (URN)10.1088/0957-0233/25/2/025010 (DOI)000332697800010 ()2-s2.0-84892898937 (Scopus ID)
Note

Del av lic.  

Available from: 2013-09-18 Created: 2013-09-18 Last updated: 2017-12-06Bibliographically approved
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ORCID iD: ORCID iD iconorcid.org/0000-0001-5608-8636

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