Browsing by Author "Aach, T."
Results Per Page
Sort Options
-
PublicationAn image-based "click&weld"-method for laser beam positioning in micro welding applications( 2009)
;Stache, N.C. ;Dieckelmann, J. ;Gedicke, J. ;Olowinsky, A.Aach, T.In most laser welding applications the welding result is highly sensitive to the weld position and the initial determination of process parameters requires time-consuming adjustments to be made. In case of manufacturing individual parts with low quantities this is a significant cost driver. State-of-the-art CAD/CAM based manufacturing systems ease the creation of welding contours significantly but position deviations resulting, e.g., from workpiece tolerances or misplacements must still be compensated. Seam tracking systems are rather complicated to handle during process qualification as they require adjustment to a start position and are subject to be misguided by disturbances in the material. Besides, it is difficult to apply seam tracking to scanner-based micro welding operations. Therefore, we developed a system that enables the user to position welds easily and accurately by marking the intended weld position in a calibrated live-image of the workpiece, which is us ed as reference. Thereby, positioning errors are compensated. Because of the live image acquisition, it is also possible to observe the welding process and assess the geometrical properties of the weld surface immediately. Moreover, the paper describes how this idea is extended to a system for more complex weld contours and ends up with a system for image-based contour extraction. -
PublicationApproaches for high-speed melt pool detection in laser welding applications( 2006)
;Stache, N.C. ;Zimmer, H. ;Gedicke, J. ;Regaard, B. ;Olowinsky, A. ;Knepper, A.Aach, T.In this paper several approaches for the detection of the melt pool circle (i.e. its position and radius) in laser welding applications are described. Instead of indirectly examining the evolution of the melt pool via the radiation of plasma that is generated during the welding process, we use a direct view onto the melt pool that is possible in a narrow wavelength band with a coaxial aligned high speed CMOS imaging sensor. Since visual inspection is often a bottleneck in mass production, we focus on high speed approaches that enable real-time monitoring of the melt pool parameters. -
PublicationAutomatic calibration of a scanner-based laser welding system( 2009)
;Stache, N.C. ;Stollenwerk, A. ;Gedicke, J. ;Olowinsky, A. ;Knepper, A.Aach, T.In precision engineering scanners are widely used for laser beam positioning. Equipped with cameras, scanners enable process monitoring or even position recognition of the parts to be welded. To allow precise welding or position recognition, it is essential to calibrate a welding system. Instead of calibrating the whole system, most approaches only help to adjust the laser beam position. Consequently, the varying lateral offset between the laser's focus point and the camera's field of view, due to chromatic aberration of the scanner optics. cannot be compensated. Furthermore, these approaches require manual microscopic measurement of weld seams. which comes along with several downsides. This paper proposes two techniques for automatic calibration without these downsides by use of the system-incorporated camera. The first technique is the calibration at laser wavelength. To this end, the system automatically creates laser spots, evaluates their positions and possible offsets, and finally fits an affine model for compensation. The second technique is based oil a specially coded test pattern, which is used for calibration at camera wavelengths. Experimental results confirm the accuracy of the calibration obtained. -
PublicationAutomatic calibration of a scanner-based laser welding system( 2007)
;Stache, N.C. ;Stollenwerk, A. ;Gedicke, J. ;Olowinsky, A. ;Knepper, A.Aach, T.In precision engineering scanners are widely used for laser beam positioning. Equipped with cameras, scanners enable process monitoring or even position recognition of the parts to be welded. To allow precise welding or position recognition, it is essential to calibrate a welding system. Instead of calibrating the whole system, most approaches only help to adjust the laser beam position. Consequently, the varying lateral offset between the laser's focus point and the camera's field of view, due to chromatic aberration of the scanner optics, cannot be compensated. Furthermore, these approaches require manual microscopic measurement of weld seams, which comes along with several downsides. This paper proposes two techniques for automatic calibration without these downsides by use of the system-incorporated camera. The first technique is the calibration at laser wavelength. To this end, the system automatically creates laser spots, evaluates their positions and possible off sets and finally fits an affine model for compensation. The second technique is based on a specially coded test pattern, which is used for calibration at camera wavelengths. Experimental results confirm the accuracy of the calibration obtained. -
PublicationDeformable 4DCT Lung Registration with Vessel Bifurcations( 2007)
;Hilsmann, A. ;Vik, T. ;Kaus, M. ;Franks, K. ;Bissonette, J.-P. ;Purdie, T. ;Beziak, A.Aach, T. -
PublicationDetection and follow-up assessment of pleural thickenings from 3D CT data( 2008)
;Chaisaowong, K. ;Bross, B. ;Knepper, A. ;Kraus, T.Aach, T. -
PublicationHigh speed video-based melt pool surveillance in laser spot welding( 2008)
;Stache, N.C. ;Dieckelmann, J. ;Firnich, R. ;Gedicke, J. ;Abels, P. ;Olowinsky, A.Aach, T. -
PublicationImage-based creation and positioning of welds for accelerated prototyping( 2010)
;Stache, N.C. ;Dieckelmann, J. ;Gedicke, J. ;Olowinsky, A.Aach, T.In most laser welding applications the welding result is highly sensitive to the weld position. The initial determination of process parameters therefore requires time-consuming adjustments to be made. When manufacturing individual parts with low quantities, this is a significant cost driver. State-of-the-art computer-aided design/computer-aided manufacturing systems ease the creation of weld seams significantly, but position deviations resulting, e.g., from workpiece tolerances or displacement must still be compensated. Seam tracking systems are rather complicated to handle during process qualification as they require adjustment to a start position and are subject to be misguided by disturbances in the material. Besides, it is difficult to apply seam tracking to scanner-based microwelding operations, which are considered in this paper. Therefore, the authors developed a system that enables the user to position welds easily and accurately by marking the intended weld po sition in a calibrated live image of the workpiece, which serves as reference. Thereby, positioning errors are compensated. When executing the welding process it is also possible to observe it in the live image and to assess the geometrical properties of the weld surface immediately. Moreover, the paper describes how this idea is extended to a system for creating more complex weld paths and concludes with an approach for automated image-based path generation by extracting the joint geometry from the workpiece image. -
PublicationRange flow in varying illumination: Algorithms and comparisons( 2010)
;Schuchert, T. ;Aach, T.Scharr, H.We extend estimation of range flow to handle brightness changes in image data caused by inhomogeneous illumination. Standard range flow computes 3D velocity fields using both range and intensity image sequences. Toward this end, range flow estimation combines a depth change model with a brightness constancy model. However, local brightness is generally not preserved when object surfaces rotate relative to the camera or the light sources, or when surfaces move in inhomogeneous illumination. We describe and investigate different approaches to handle such brightness changes. A straightforward approach is to prefilter the intensity data such that brightness changes are suppressed, for instance, by a highpass or a homomorphic filter. Such prefiltering may, though, reduce the signal-to-noise ratio. An alternative novel approach is to replace the brightness constancy model by 1) a gradient constancy model, or 2) by a combination of gradient and brightness constancy constraints used earlier successfully for optical flow, or 3) by a physics-based brightness change model. In performance tests, the standard version and the novel versions of range flow estimation are investigated using prefiltered or nonprefiltered synthetic data with available ground truth. Furthermore, the influences of additive Gaussian noise and simulated shot noise are investigated. Finally, we compare all range flow estimators on real data. -
PublicationRobust high-speed melt pool measurements for laser welding with sputter detection capability( 2007)
;Stache, N.C. ;Zimmer, H. ;Gedicke, J. ;Olowinsky, A.Aach, T.Although lasers are widely used for welding in precision engineering industry, it is still a challenge to achieve high accuracy in creating and positioning welding spots at extremely high processing speed. Towards this end, we propose a system for monitoring the welding process in order to ensure good quality of the welding spots. Our technology enables high speed image acquisition confocally to the laser beam with a direct view onto the melt. This innovative system permits accurate estimation of the melt pool's position and radius, which, however, must be performed at frame rates above 200 fps. We therefore employ fast correlation based approaches for sampling the melt pool's contour and robustly fitting a circle to it. In addition, the approaches enable sputter detection via outlier classification. To assess the performance of each presented method, extensive experiments are conducted. The proposed paradigms can furthermore be conveniently adapted to a variety of prob lems dealing with rapid shape estimation in noisy environments.