Publikationen

Ocular current stimulation (CS) exhibits potential for the treatment of neurodegenerative ocular diseases. For a full field electroretinogram (ffERG) we found no CS effect on the characteristic waves (a-wave, b'-wave, and b-wave). To investigate whether the orientation of the generated electric field has an influence on the CS effect, this study repeated the previous ffERG study with changing one CS electrode position and compared the results of both studies. In the first study 15 (8 m, 27.5 ± 4.5 years) and in the second study 17 (7 m, 22.0 ± 1.9 years) healthy volunteers were stimulated with an anodal, cathodal, and sham direct CS of 800 [my]A for 5 min in three sessions (randomized, different days). For both studies, a cut-sized ring rubber electrode was placed around the eye. A square rubber electrode was placed for the first study at the ipsilateral temple and for the second study at the visual cortex. Before (ERG 1) and during (ERG 2) the CS, the ffERG was measured. For both studies, the difference between the ERG 1 and ERG 2 measurement (CS effect) for the three characteristic waves was analyzed and compared between the studies. For statistical analysis, the Mann-Whitney U test with Bonferroni correction was applied (α = 0.05). The comparison of the data distribution showed only slight differences between the studies. The Mann-Whitney U test found no significant difference of the CS effect between the studies for all amplitudes and CS groups (p ≥ 0.0055). In the mean, the latency differences were smaller than the time resolution, therefore no statements for latency effects were possible. It can be concluded that the retinal cells generating the ffERG are not affected by ocular CS in either electrode montages tested.

Dry electrodes enable a shorter preparation time for infant EEG. Since infant skin is more sensitive than adult skin, soft electrodes are required to reduce the mechanical stress for this sensitive skin. Thus, soft electrodes are crucial for eventual repetitive and long-term use like in neonatal intensive care units. A biocompatible polyurethane (PU) can be produced in low hardness resulting in a soft and flexible electrode substrate. Silver/silver chloride (Ag/AgCl) electroless plating provides a conductive, electrochemically stable coating but the process may alter the mechanical properties of the electrode substrate. In this study, we assess the hardness of PU material before and after Ag/AgCl plating. The test sample design for Shore hardness measurement is based on ISO 7619-1:2010. Sample production consists of a 3D print master model, silicone molding, PU casting, and finally electroless plating. UPX 8400-1 (Sika AG, Switzerland) is used for the sample substrates. Test samples are produced with 7 different Shore hardness (range A40-A95) and 14 samples (each hardness: 1 uncoated and 1 coated). The hardness measurements are carried out with a lever-operated test stand Shore hardness tester model with a digital hardness tester (TI-AC with HDA 100-1, KERN & SOHN GmbH, Germany). It is shown that there is a hardness increase (Shore A) due to Ag/AgCl coating with a grand average of 1.1±0.7 (p<0.05). The largest increase of 2.1±0.2 is seen on the initial lowest Shore hardness sample (Shore hardness: 43.4±0.1). The absolute increase of hardness due to the Ag/AgCl coating decreases with increasing substrate hardness. It is concluded that there is no strong hardness increase of PU substrates due to Ag/AgCl plating. Therefore, the material is suitable as a soft electrode for repetitive and long-term use in infant applications.

Seit seiner Einführung vor etwas mehr als 20 Jahren hat das Verfahren Interconnection and Damping Assignment Passivity-based Control (IDA-PBC) zu vielen theoretischen Erweiterungen und praktischen Anwendungen geführt. Diese Regler zeichnen sich unter anderem durch i) robuste Eigenschaften, ii) die Ausnutzung der strukturellen Eigenschaften des Systems und iii) ihre universelle Stabilisierungseigenschaft aus. Dies spiegelt sich in der großen Vielfalt der Anwendungen von elektrischen, mechanischen, allgemein nichtlinearen und sogar unendlich-dimensionalen Systemen wider. Das größte Problem für die Implementierung dieser Regelverfahren ist die Erfüllung der sogenante matching condition, die sich als ein System von partiellen Differentialgleichungen herausstellt. Weitere wichtige Probleme sind die Dissipationsbedingung in unteraktuierten mechanischen Systemen, die Aufteilung der Regelverfahren in zwei Stufen und die unvollständige Theorie für Systeme in impliziter Darstellung, d.h. für Systeme, die durch differential-algebraische Gleichungen beschrieben werden. In diesem Zusammenhang gliedert sich die vorliegende Arbeit in zwei Teile. Zunächst werden algebraische Lösungen für eine Klasse von nichtlinearen Systemen mit Polynomstruktur vorgestellt. Die vorgeschlagene Methode vermeidet einige der zuvor erwähnten Standardprobleme von IDA-PBC und führt zu Bedingungen, die als Summen-Quadrate-Programme umformuliert werden können. Außerdem erlaubt sie die Einbeziehung von Eingangssättigungs- und Minimierungszielen, um den Regler zu parametrieren. Im zweiten Teil verallgemeinern wir die Gesamtenergieumformung bei IDA-PBC auf mechanische Systeme in impliziter Darstellung, d.h. mit kinematischen Nebenbedingungen. Weiterhin stellen wir eine heuristische Formulierung und einige konstruktive Methoden zur Lösung der partiellen Differentialgleichungen der matching conditions vor. Schließlich stellen wir eine Methode zur Eliminierung von kinematischen Zwangsbedingungen und Zwangskräften vor, d. h. zur Reduzierung der impliziten auf die explizite Darstellung. Die Beiträge werden in zwei Polynomsystemen zweiter Ordnung, einem rationalen System dritter Ordnung, dem einfachen Pendel, der rollenden Scheibe, dem PVTOL-Flugzeug, dem cart-pole System und dem Portalkran validiert. Für die beiden letztgenannten werden reale Experimente durchgeführt, die beide im Labor des Fachgebiets Regelungstechnik an der TU Ilmenau angesiedelt sind.

An online model-based fault detection and isolation method for salient-pole permanent magnet synchronous motors over a finite horizon is proposed. The proposed approach combines parity-space-based residual generation and modulation-function-based filtering. Given the polynomial model equations, the unknown variables (i.e. the states, unmeasured inputs) are eliminated resulting in analytic redundancy relations used for residual generation. Furthermore, in order to avoid needing the derivatives of measured signals required by such analytic redundancy relations, a modulation-function-based evaluation is proposed. This results in a finite-horizon filtered version of the original residual. The fault detection and isolation method is demonstrated using simulation of various fault scenarios for a speed controlled salient motor showing the effectiveness of the presented approach.

Industrial processes are large scale, highly complex systems. The complex flow of mass and energy, as well as the compensation effects of closed-loop control systems, cause significance cross-correlation and autocorrelation between process variables. To operate the process systems stably and efficiently, it is crucial to uncover the inherent characteristics of both variance structure and dynamic relationship. Long-term dependency slow feature analysis (LTSFA) is proposed in this paper to overcome the Markov assumption of the original slow feature analysis to understand the long-term dynamics of processes, based on which a monitoring procedure is designed. A simulation example and the Tennessee Eastman process benchmark are studied to show the performance of LTSFA. The proposed method can better extract the system dynamics and monitor the process variations using fewer slow features.