Felix Tenner

Noncontact optical sensor for bone fracture diagnostics

We present the first steps of a device suitable for detection of broken and cracked bones. The approach is based on temporal tracking of back reflected secondary speckle patterns generated when illuminating the limb with a laser and while applying periodic pressure stimulation via a loud speaker. Preliminary experiments are included showing the validity of the proposed device for detection of damaged bones.

Experimental approach for quantification of fluid dynamics in laser metal welding

Laser metal welding is widely applied in industry. Nevertheless, a complete process understanding which leads to a full control of the process is not available yet. To contribute a solution for this task, we use two high-speed cameras with recording rates of up to 250 kHz and measure the velocity and direction of the fluid flow inside the keyhole with very high precision. Furthermore, we use tracer particles to measure the fluid dynamics in the keyhole. To get a deep view into the keyhole without the use of x-rays, we use a setup which allows us to look inside the keyhole during overlap welding of zinc-coated steel sheets with a spatial resolution of 25 μm per pixel and a temporal resolution of 5.3 μs per frame. Moreover, we quantify the influence of this approach on the process dynamics. Our findings show how the fluid dynamics inside the keyhole are linked to the laser power, the feed rate, and a gap between two zinc-coated steel sheets.

Development of a hyperspectral imaging technique for monitoring laser-based material processing

In this paper, a new observation technique for monitoring laser-based material processing on the basis of hyperspectral imaging (HSI) is presented. HSI techniques integrate both spatial and spectral information upon the object/process to be investigated. Essentially, the spectral information can be used to derive the absolute temperature of the object/process. The presented observation tool employing HSI-techniques comprises a high-speed camera and a self-developed HSI-lens system. It offers a time resolution in the microsecond-range and a spectral resolution of ∼4 nm. A proof-of-concept of temperature determination based upon HSI-derived spectra is given, and the initial observation results of the laser welding process are presented. These observations include the temperature evolution of the melting process of two different metal alloys over time. Moreover, we can show that the maximal temperature in the process zone does not exceed the evaporation temperature when processing construction steel and aluminum.In this paper, a new observation technique for monitoring laser-based material processing on the basis of hyperspectral imaging (HSI) is presented. HSI techniques integrate both spatial and spectral information upon the object/process to be investigated. Essentially, the spectral information can be used to derive the absolute temperature of the object/process. The presented observation tool employing HSI-techniques comprises a high-speed camera and a self-developed HSI-lens system. It offers a time resolution in the microsecond-range and a spectral resolution of ∼4 nm. A proof-of-concept of temperature determination based upon HSI-derived spectra is given, and the initial observation results of the laser welding process are presented. These observations include the temperature evolution of the melting process of two different metal alloys over time. Moreover, we can show that the maximal temperature in the process zone does not exceed the evaporation temperature when processing construction steel and alum...

A ROUND ROBIN STUDY FOR LASER BEAM MELTING IN A METAL POWDER BED

With recent developments in additive manufacturing, there has been a keen interest in understanding its possibilities and limitations specifically with respect to the conventional engineering and manufacturing standards. Although coined as a prototyping technology at the time of its inception, Additive manufacturing with its characteristic layer by layer fabrication methodology is now the focus of end product manufacturing for many niche applications. One of the key additive manufacturing processes leading this evolution is the process of Laser Beam Melting in metal powder bed. With its ability to fabricate fully dense 3-dimensional structures by selectively melting micro-sized metal powder, Laser Beam Melting is being considered by many as a significant complimentary technology to the conventional forming and subtractive manufacturing processes. In order to completely understand the abilities and limitations of the Laser Beam Melting process, a detailed analysis of the system technology, process and user induced variations in relation to the characteristics of the resultant part needs to be performed. With the above motivations in mind, an initiative at the Collaborative Working Group, Lasers in production at the International Academy of Production Engineering (CIRP) was undertaken to conduct a comparative study in the form of a Round Robin test by analyzing the mechanical characteristics of samples fabricated by various users of the Laser Beam Melting technology from volunteers within the members of the academy. The presented paper illustrates the design and methodology of the round robin test in addition to some preliminary results and makes an attempt to connect these results with the various phenomena occurring in the Laser Beam Melting process. Authors of the paper gratefully acknowledge the contributions from the various members of the Collaborative Working Group, Lasers in production at the International Academy of Production Engineering (CIRP) who volunteered for providing the samples for the conducted round robin test.

Detection radius of EMG for fasciculations: Empiric study combining ultrasonography and electromyography

OBJECTIVE The aims of this study were to investigate the detection radius and sensitivity of EMG for fasciculations. METHODS Muscle ultrasonography was performed simultaneously to EMG recordings in patients with fasciculations in the context of amyotrophic lateral sclerosis. Ultrasonography and EMG parameters were analyzed for selected fasciculations. RESULTS A total of 381 fasciculations were detected by ultrasonography in 18 muscles of 10 patients. Out of these, 125 (33%) were EMG-negative. In contrast, none of the fasciculations detected by EMG were ultrasonography-negative. EMG detection probability decreased significantly with increasing distance from the center of the fasciculation. EMG detection rate was 98% when the EMG needle was located within the fasciculation and 50% at 7.75 mm distance from the fasciculation center. In addition, EMG detection depended significantly on cross-sectional area of the fasciculation and presence of neurogenic changes. CONCLUSIONS For detecting the same fasciculations, EMG is less sensitive than ultrasonography. EMG detection probability decreases sharply at a distance comparable to motor unit size. SIGNIFICANCE These results extend previous knowledge about superior sensitivity of ultrasonography for fasciculations. Moreover, our novel bimodal detection method provides first in vivo data about the EMG detection radius for fasciculations in a clinical setting.

Towards a multi-sensor system for the diagnosis of neurological disorders

The occurrence of fasciculations is an indication for several neurological disorders. However, due to the low amplitude and irregular occurrence, these involuntary muscle movements are hard to quantify. Currently used techniques have to be applied manually from a trained specialist and lack the possibility of a remote measurement of fasciculations. Therefore, we introduce a new approach which is able to remotely measure fasciculations with high temporal resolution. Moreover, we compare the sensitivity of our technique with established methods and give an outlook how our technology can be expanded to a multi-sensor system for the automated diagnosis of neurological disorders.

Remote photoacoustic tomography using speckle sensing with a high-speed camera

In the emerging photoacoustic imaging and tomography technique, contactless imaging approaches are of great interest. In this work, a proof of principle for remote photoacoustic tomography using speckle sensing is shown.

Development of a joining gap control system for laser welding of zinc-coated steel sheets driven by process observation

Laser deep penetration welding is already widely used in industry. However, a further increase in the number of possible applications is hindered by process instabilities leading to process defects for a variety of welding scenarios. To overcome this obstacle, sensing and control systems can be used to detect deviations in relevant process features and counteract by adjusting specific process parameters. Hence, there is a demand for process control systems to increase process stability and thus quality. To fulfil this demand, the development of a process sensor which acquires a broad variety of process emissions aiming to gain the full picture of the welding process is the ultimate goal. One way to find relevant relations between defects and process features is the correlation of a vast amount of data to a specific process defect. This approach is very time consuming and did often lead to unsatisfactory results if no correlations could be found between the sensor signals and the occurring process defects. For a more targeted development of a process control system, we propose the use of process observation methods with high temporal and spatial resolution. By the use of image and data analysis process features which characterize the evolution of defects can be extracted and the relation of specific factors to the characteristic process features can be found. Moreover, the mechanisms of the evolution of process defects can be observed and a tailored strategy can be designed to ensure a robust and reliable control of the process. By means of this strategy, sensors to measure the defect-related features, control interfaces, and actuators to change these features can be specifically chosen. In our paper, we illustrate these steps by the development of a joining gap control system for the laser welding of zinc-coated steel sheets in an overlap configuration. This process is a topic of current research and highly relevant for industrial application. In our study, we prove that the keyhole opening is a process feature which correlates with the joining gap between two sheets. Moreover, we show an exemplary design and build of a setup for adapting the joining gap with respect to the requirements given by the real-time applicability during the welding process. Afterwards, we merge sensor and actuator to a control system and validate it on different process situations. The validation shows that the gap can be measured and set during the laser welding process to reliably increase the process stability and quality. We conclude our paper with an outlook on how this system might be applied in an industrial environment.Laser deep penetration welding is already widely used in industry. However, a further increase in the number of possible applications is hindered by process instabilities leading to process defects for a variety of welding scenarios. To overcome this obstacle, sensing and control systems can be used to detect deviations in relevant process features and counteract by adjusting specific process parameters. Hence, there is a demand for process control systems to increase process stability and thus quality. To fulfil this demand, the development of a process sensor which acquires a broad variety of process emissions aiming to gain the full picture of the welding process is the ultimate goal. One way to find relevant relations between defects and process features is the correlation of a vast amount of data to a specific process defect. This approach is very time consuming and did often lead to unsatisfactory results if no correlations could be found between the sensor signals and the occurring process defects....

Analytical model of the laser welding of zinc-coated steel sheets by the aid of videography

Despite several approaches from different research groups, currently the best solution for welding of zinc-coated steel sheets in an overlap configuration is the use of a joining gap between the sheets. However, the introduction of the gap is prone to errors due to dirt or thermal distortion. A too small gap leads to the explosive zinc ejections. In contrast, a too large gap causes false friends where the melt is not able to bridge the gap due to an erroneous clamping of the sheets. Currently, there is no direct measurement of the joining gap available. The reason therefore is the lack in the understanding of the fluid dynamics inside the keyhole in laser welding. To increase the process of understanding, the authors analyzed the correlation between the well visible keyhole opening, the joining gap size, and the welding speed for uncoated and zinc-coated sheets. To scrutinize our findings, the authors present a model of the zinc degassing inside the keyhole which obtains its input parameters directly from our comprehensive high-speed videography analysis of the process. To get a deep view inside the keyhole without the use of x-rays, the authors use a glass plate flanking the keyhole which allows us to look inside the keyhole during overlap welding of steel sheets with very high spatial and temporal resolution. By the aid of tracer particles, the authors measured and modeled the pressure due to the evaporation of the zinc layer without the use of unknown thermodynamic coefficients. Our results show that the joining gap and the welding speed have an influence on the pressure balance inside the keyhole. Hence, our work can be used as a foundation for building a control system for the joining gap for the welding of zinc-coated steel sheets.Despite several approaches from different research groups, currently the best solution for welding of zinc-coated steel sheets in an overlap configuration is the use of a joining gap between the sheets. However, the introduction of the gap is prone to errors due to dirt or thermal distortion. A too small gap leads to the explosive zinc ejections. In contrast, a too large gap causes false friends where the melt is not able to bridge the gap due to an erroneous clamping of the sheets. Currently, there is no direct measurement of the joining gap available. The reason therefore is the lack in the understanding of the fluid dynamics inside the keyhole in laser welding. To increase the process of understanding, the authors analyzed the correlation between the well visible keyhole opening, the joining gap size, and the welding speed for uncoated and zinc-coated sheets. To scrutinize our findings, the authors present a model of the zinc degassing inside the keyhole which obtains its input parameters directly from...

P 157 Detection radius of EMG for fasciculations: combined ultrasonographic-electromyographic analysis

Background Fasciculations are caused by spontaneous discharges of single motor units. In electromyography (EMG), they are characterized by single motor unit action potentials. Muscle ultrasonography is increasingly applied as a non-invasive screening tool for the examination of fasciculations. In the context of motor neuron disease, the sensitivity of muscle ultrasonography to detect fasciculations was superior to EMG. Limited detection radius of concentric needle EMG may explain this discrepancy, but a direct EMG-ultrasonography-correlation of single fasciculations has not been reported so far. In the current study, we aimed to define an “EMG detection radius” of fasciculations by simultaneous recording of EMG and muscle ultrasonography. Methods Parallel to concentric needle EMG, we recorded in-plane high-resolution videos of muscle ultrasonography showing the needle tip within the transverse section of the muscle. A total of 200 fasciculations were acquired during 50 recordings of 10 patients with motor neuron disease. Amplitude and duration of EMG fasciculation potentials were subsequently correlated to the corresponding ultrasonographic muscle displacement and the distance from the EMG needle tip. Results The onset of ultrasonographic muscle displacement was concurrent to its EMG fasciculation potential whereas the plateau phase and the backward movement occurred when the EMG had already returned to baseline. About 40% of fasciculations observed on ultrasonography were not detected in EMG and this included fasciculations located close to the needle tip. The amplitude of EMG-positive fasciculations was negatively correlated to their distance from the needle tip. However, the correlation differed significantly between different patients and between different muscles. Discussion Analysis of fasciculations on simultaneous EMG and ultrasonography recordings improves the understanding of the “EMG-detection radius” of fasciculations. A relevant portion of ultrasonographic fasciculations was not detected on EMG which may in part explain the superior sensitivity of ultrasonography. Different localization of neuromuscular endplates and of myofibrils along the longitudinal axis of the analyzed muscles might explain the occurrence of “EMG-negative” fasciculations. Alternatively, muscle remodeling or changes of axon terminals due to neurodegeneration may alter the sensitivity of EMG. Further studies are needed to classify fasciculations of other entities with this method.