| 1. |
- Van Bulck, Liesbet, et al.
(författare)
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Patient-reported outcomes of adults with congenital heart disease from eight European countries : scrutinising the association with healthcare system performance
- 2019
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Ingår i: European Journal of Cardiovascular Nursing. - : Sage Publications. - 1474-5151 .- 1873-1953. ; 18:6, s. 465-473
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Tidskriftsartikel (refereegranskat)abstract
- Background: Inter-country variation in patient-reported outcomes of adults with congenital heart disease has been observed. Country-specific characteristics may play a role. A previous study found an association between healthcare system performance and patient-reported outcomes. However, it remains unknown which specific components of the countries’ healthcare system performance are of importance for patient-reported outcomes.Aims: The aim of this study was to investigate the relationship between components of healthcare system performance and patient-reported outcomes in a large sample of adults with congenital heart disease.Methods: A total of 1591 adults with congenital heart disease (median age 34 years; 51% men; 32% simple, 48% moderate and 20% complex defects) from eight European countries were included in this cross-sectional study. The following patient-reported outcomes were measured: perceived physical and mental health, psychological distress, health behaviours and quality of life. The Euro Health Consumer Index 2015 and the Euro Heart Index 2016 were used as measures of healthcare system performance. General linear mixed models were conducted, adjusting for patient-specific variables and unmeasured country differences.Results: Health risk behaviours were associated with the Euro Health Consumer Index subdomains about patient rights and information, health outcomes and financing and access to pharmaceuticals. Perceived physical health was associated with the Euro Health Consumer Index subdomain about prevention of chronic diseases. Subscales of the Euro Heart Index were not associated with patient-reported outcomes.Conclusion: Several features of healthcare system performance are associated with perceived physical health and health risk behaviour in adults with congenital heart disease. Before recommendations for policy-makers and clinicians can be conducted, future research ought to investigate the impact of the healthcare system performance on outcomes further.
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| 2. |
- Ancona, Antonio, 1974-, et al.
(författare)
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Monitoring and control of directed energy deposition using a laser beam
- 2023. - 1.
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Ingår i: Additive Manufacturing of High-Performance metallic Materials. - : Elsevier. - 9780323918855 - 9780323913829 ; , s. 612-638
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Bokkapitel (refereegranskat)abstract
- To be a successful competitor among other technologies, metallic laser-directed energy depositionusing a laser beam would benefit from the support of intelligent automation making the processrobust, repeatable, and cost-efficient. This calls for technology leaps towards robust and accuratedetection and estimation of the conditions during processing and control schemes for robustperformance. This chapter discusses how developments in sensor technology and model-basedsignal processing can contribute to advancements in in-process monitoring of directed energydeposition using a laser beam and how developments in model-based feedforward- and feedbackcontrol can support automation. The focus is on how machine vision, optical emission spectroscopy,thermal sensing, and electrical process signals can support monitoring, control and better processunderstanding. These approaches are industrially relevant and have a high potential to support amore sustainable manufacturing.
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| 3. |
- Elefante, Arianna, et al.
(författare)
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Detecting beam offsets in laser welding of closed-square-butt joints by wavelet analysis of an optical process signal
- 2019
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Ingår i: Optics and Laser Technology. - : Elsevier BV. - 0030-3992 .- 1879-2545. ; 109, s. 178-185
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Tidskriftsartikel (refereegranskat)abstract
- 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.
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| 4. |
- Nilsen, Morgan, et al.
(författare)
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A study on change point detection methods applied to beam offset detection in laser welding
- 2019
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Ingår i: Procedia Manufacturing. - : Elsevier BV. - 2351-9789. ; 36, s. 72-79
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Tidskriftsartikel (refereegranskat)abstract
- This paper presents an experimental study where a photodiode integrated into a laser beam welding tool is used to monitor laser beam spot deviations fromthe joint, the beam offset. The photodiode system is cost effective and typically easy to implement in an industrial system. The selected photodiode is a silicondetector sensitive in the spectral range between 340-600nm which corresponds to the spectral emissions from the plasma plume. The welding application is closed-square-butt joint welding where a laser beam offset can cause lack of fusion in the resulting weld. The photodiode signal has been evaluated by two different change point detection methods, one off-line and one on-line method, with respect to their detection performance. Off-line methods can be used to guide post weld inspection and on-line methods have the potential to enable on-line adaptive control or the possibility to stop the process for repair. The performance of the monitoring system and the change point detection methods have been evaluated from data obtained during laser beam welding experiments conducted on plates of stainless steel. The results clearly indicates the possibility to detect beam offsets by photodiode monitoring.
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| 5. |
- Nilsen, Morgan, et al.
(författare)
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Adaptive control of the filler wire rate during laser beam welding of squared butt joints with varying gap width
- 2019
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Ingår i: The International Journal of Advanced Manufacturing Technology. - : Springer Science and Business Media LLC. - 0268-3768 .- 1433-3015. ; 102:9-12, s. 3667-3676
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Tidskriftsartikel (refereegranskat)abstract
- Adding filler wire control to autogenous laser beam welding of squared butt joints offers a means to widen up the tight fit-up tolerances associated with this process. When the gap width varies, the filler wire rate should be controlled to assure a constant geometry of the resulting weld seam. A dual mode sensing system is proposed to estimate the joint gap width and thereby control the filler wire rate. A vision camera integrated into the welding tool together with external LED illumination and a laser line projection enables two sensing modes, one surface feature extraction mode and one laser triangulation-based mode. Data from the both modes are fused in a Kalman filter, and comparisons show that the fusing of the data gives more robust estimation than estimates from each single mode. A feed-forward control system adaptively adjusts the filler wire rate based on the estimations ofthe joint gap width in front of the keyhole. The focus is on keeping the data processing simple and affordable, and the real-time performance of the sensor and control system has been evaluated by welding experiments. It is shown that the proposed system can be used for on-line control of the filler wire rate to achieve a constant weld geometry during varying joint gap widths
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| 6. |
- Nilsen, Morgan, et al.
(författare)
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In-process Monitoring and Control of Robotized Laser Beam Welding of Closed Square Butt Joints
- 2018
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Ingår i: Procedia Manufacturing. - : Elsevier BV. - 2351-9789. ; 25, s. 511-516
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Tidskriftsartikel (refereegranskat)abstract
- 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.
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| 7. |
- Nilsen, Morgan, et al.
(författare)
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Joint tracking in zero gap laser beam welding using a vision sensor
- 2016
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Ingår i: The 7th International Swedish Production Symposium, SPS16, Conference Proceedings. - Lund : Swedish Production Academy. ; , s. 1-7
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Konferensbidrag (refereegranskat)abstract
- 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.
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| 8. |
- Nilsen, Morgan
(författare)
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Monitoring and control of laser beam butt joint welding
- 2019
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- 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.
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| 9. |
- Nilsen, Morgan, et al.
(författare)
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Monitoring of Varying Joint Gap Width During Laser Beam Welding by a Dual Vision and Spectroscopic Sensing System
- 2017
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Ingår i: Physics Procedia. - : Elsevier BV. - 1875-3892. ; 89, s. 100-107
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Tidskriftsartikel (refereegranskat)abstract
- 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.
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| 10. |
- Nilsen, Morgan
(författare)
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Optical detection of joint position in zero gap laser beam welding
- 2017
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Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- This thesis presents an experimental study on how to track zero gaps between metal sheets to be joined by laser beam butt welding. Automated laser beam welding is gaining interest due to its ability to produce narrow and deep welds giving limited heat input and therefore less distortions compared to other processes, such as arc-welding. The automated laser beam welding process is however sensitive to how the high power laser is positioned with regards to the joint position. Deviations from the joint position may occur due to inaccuracies of the welding robot and fixturing, changes in joint geometry, process induced distortions, etc. Welding with an offset from the joint position can result inlack of sidewall fusion, a serious defect that is hard to detect. This work develops and evaluates three monitoring systems to be used during welding in order to be able to later control the laser beam spot position. (i) A monitoring systemis developed for three different photo diodes, one for the visual spectrum of the process emissions, one for the infrared spectrum, and one for the reflected highpower laser light. The correlation between the signals from the photodiodes and the welding position relative to the joint is analysed using a change detection algorithm. In this way an indication of a path deviation is given. (ii) A visual camera with matching illumination and optical filters is integrated into the laser beam welding tool in order to obtain images of the area in front of the melt pool. This gives a relatively clear view of the joint position even during intense spectral disturbances emitted from the process, and by applying animage processing algorithm and a model based filtering method the joint positionis estimated with an accuracy of 0.1 mm. (iii) By monitoring the spectral emissions from the laser induced plasma plume using a high speed and high resolution spectrometer, the plasma electron temperature can be estimated from the intensities of two selected spectral lines and this is correlated to the welding position and can be used for finding the joint position.
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