Effects of multi-point contacts during object contour scanning using a biologically-inspired tactile sensor

Vibrissae are an important tactile sense organ of many mammals, in particular rodents like rats and mice. For instance, these animals use them in order to detect different object features, e.g., object-distances and -shapes. In engineering, vibrissae have long been established as a natural paragon for developing tactile sensors. So far, having object shape scanning and reconstruction in mind, almost all mechanical vibrissa models are restricted to contact scenarios with a single discrete contact force. Here, we deal with the effect of multi-point contacts in a specific scanning scenario, where an artificial vibrissa is swept along partly concave object contours. The vibrissa is modeled as a cylindrical, one-sided clamped Euler-Bernoulli bending rod undergoing large deflections. The elasticae and the support reactions during scanning are theoretically calculated and measured in experiments, using a spring steel wire, attached to a force/torque-sensor. The experiments validate the simulation results and show that the assumption of a quasi-static scanning displacement is a satisfying approach. Beyond single- and two-point contacts, a distinction is made between tip and tangential contacts. It is shown that, in theory, these contact phases can be identified solely based on the support reactions, what is new in literature. In this way, multipoint contacts are reliably detected and filtered in order to discard incorrectly reconstructed contact points

Investigations on the mechanical relevance of prominent vibrissa features for surface texture detection

The tactile hairs of animals are used as paradigm for artificial tactile sensors. In the case of mystacial vibrissae, the animals can determine the distance to an object, recognize the shape of the object and detect the surface texture of the object. The goal is to design an artificial tactile sensor inspired by the natural paradigm. In the present work, the vibrissa and the follicle-sinus-complex are modeled as a one-sided clamped beam within the limits of the non-linear Euler-Bernoulli beam theory. The theoretical background of the function principle and the effects of typical properties of the natural vibrissa, e.g., a tapered shape and a pre-curvature while operating in surface texture detection are analyzed. The beam-surface contact is described by Coulomb’s law of friction. When the beam is in touch with the surface, a quasi-static displacement of the support takes place. As a consequence of the displacement the support reactions are changing. The resulting support reactions are analyzed in parameter studies and beneficial levels of tapering and pre-curvature are identified

An artificial vibrissa-like sensor for detection of flows

In nature, there are several examples of sophisticated sensory systems to sense flows, e.g., the vibrissae of mammals. Seals can detect the flow of their prey, and rats are able to perceive the flow of surrounding air. The vibrissae are arranged around muzzle of an animal. A vibrissa consists of two major components: a shaft (infector) and a follicle–sinus complex (receptor), whereby the base of the shaft is supported by the follicle-sinus complex. The vibrissa shaft collects and transmits stimuli, e.g., flows, while the follicle-sinus complex transduces them for further processing. Beside detecting flows, the animals can also recognize the size of an object or determine the surface texture. Here, the combination of these functionalities in a single sensory system serves as paragon for artificial tactile sensors. The detection of flows becomes important regarding the measurement of flow characteristics, e.g., velocity, as well as the influence of the sensor during the scanning of objects. These aspects are closely related to each other, but, how can the characteristics of flow be represented by the signals at the base of a vibrissa shaft or by an artificial vibrissa-like sensor respectively? In this work, the structure of a natural vibrissa shaft is simplified to a slender, cylindrical/tapered elastic beam. The model is analyzed in simulation and experiment in order to identify the necessary observables to evaluate flows based on the quasi-static large deflection of the sensor shaft inside a steady, non-uniform, laminar, in-compressible flow

Validation of a Mechanical Model of the Active Scanning Process in the Rat Vibrissal System

The rat vibrissal system shows a sophisticated functionality in tactile discrimination, therefore it is analyzed in various works out of the perspective of neuroscience and bio-engineering. The present work focuses on the vibrissal system of rodents during tactile exploration in terms of mechanics. In this way, a mechanical model of the natural vibrissa is designed in order to determine the forces and moments at the base while the modeled vibrissa contacts a rough surface. The results of the mechanical simulation are compared to electrophysiological measurements of the afferent activity from vibrissal nerve in consequence of a contact between the vibrissa and real surface. This comparison gives information about the principal relation between mechanical and neuronal signals and furthermore about the electromechanical properties of the system.La sobresaliente capacidad de discriminación táctil del sistema vibrisal ha sido motivo de estudio en áreas de las neurociencias y bioingeniería. Este trabajo aborda los aspectos mecánicos de la exploración táctil efectuada a través del sistema vibrisal en roedores. Para ello se propone un modelo mecánico el cual permite predecir/determinar las fuerzas y momentos evocados en la base de la vibrisa durante el contacto activo con superficies rugosas. Asimismo, se realiza una validación electrofisiológica del modelo en base a registros de la actividad aferente del nervio vibrisal, evocados por el contacto activo. La estimación de estos parámetros mecánicos en el folículo vibrisal, no solo permite comprender los procesos que subyacen a la codificación neuronal, sino también aquellos relacionados a la transducción electromecánica del sistema.Fil: Scharff, Moritz. Pontificia Universidad Católica de Perú; Perú. Technische Universität Ilmenau; AlemaniaFil: Lucianna, Facundo Adrián. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Tucumán. Instituto Superior de Investigaciones Biológicas. Universidad Nacional de Tucumán. Instituto Superior de Investigaciones Biológicas; ArgentinaFil: Pizá, Alvaro Gabriel. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Tucumán. Instituto Superior de Investigaciones Biológicas. Universidad Nacional de Tucumán. Instituto Superior de Investigaciones Biológicas; ArgentinaFil: Albarracin, Ana Lia. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Tucumán. Instituto Superior de Investigaciones Biológicas. Universidad Nacional de Tucumán. Instituto Superior de Investigaciones Biológicas; ArgentinaFil: Alencastre Miranda, Jorge H.. Pontificia Universidad Católica de Perú; PerúFil: Farfan, Fernando Daniel. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Tucumán. Instituto Superior de Investigaciones Biológicas. Universidad Nacional de Tucumán. Instituto Superior de Investigaciones Biológicas; Argentin

Bio-inspired Tactile Sensing: Analysis of the inherent characteristics of a vibrissa-like tactile sensor

Tactile sensing is a fast-developing research area that is important, e.g., for autonomous robot systems in the context of path planning and navigation in uncertain terrains. One possibility for novel enhanced designs of tactile sensors is to analyze and adapt natural paragons. Rodents like rats have tactile sensory hairs, so-called vibrissae, on both sides of their muzzle. These hairs exhibit a sophisticated structure and geometrical shape. The slender, tapered, and inherent curved hair shaft is supported by a hair follicle that includes mechanoreceptors. Touching an object with their vibrissae, rats can recognize the shape of an object or determine properties of its surface texture by evaluating only the signals inside the hair follicle. The present work contributes to the overall goal to unfold the ability of natural vibrissa with view to applications in engineering like surface metrology or autonomous robots. The vibrissal system is described in detail, analyzed, and interpreted using the idea of a biomechatronic system and stimulus leading apparatus. The properties of a natural vibrissa contribute in a complex manner and in various ways to its functionality and determine its inherent characteristics. Therefore, properties of a natural vibrissa are systematically adapted to an artificial tactile sensor. Using this artificial vibrissa-like sensor, it is shown that three different kinds of information about the scanned object are present in the captured data: the overall object shape, a macroscopic, and a microscopic surface texture. The regarding information is encrypted in the signals at the base of the sensor and must be processed to recognize each type of information. To support this process, it is found that a larger distance to an object, around 80\% of the length of the sensor shaft, permits a good detectability of properties regarding the macroscopic surface texture. For a moderate distance, e.g., 60\% of the length of the sensor shaft, the detection of a microscopic surface texture works best. Finally, a closer distance, below 45\% of the length of the sensor shaft, is advantageous for a recognition of the overall shape. These characteristics -strongly depending on the distance- are closely related to the elasticity of the sensor shaft. For example, scanning a close object with distinct macroscopic surface texture, proper detection of the macroscopic surface texture is not possible because the bending induced curvature of the sensor shaft prevents contact between the sensor shaft and small shapes of macroscopic surface features like grooves and gaps. Therefore, the deformed sensor shaft fulfills the task of a morphological filter. The diameter of the sensor defines the limit between macroscopic and microscopic surface texture. Surface texture elements smaller than this limit belonging to the microscopic surface texture. Therefore, also the tip diameter is an inherent characteristic of the sensor. A further inherent characteristic is found while scanning a microscopic surface texture and retracting the sensor shape in the way that the concave side of the deformed elastica points in the displacement direction.\newpage This configuration and displacement cause an amplification of the recorded support reactions. Following these kinds of ideas, the inherent characteristics of the sensor system are analyzed in the present work.Die Weiterentwicklung taktiler Sensoren gewinnt an Bedeutung bspw. durch eine verstärkte Anwendung taktiler Sensoren zur Navigation in unbekannten Umgebungen von autonomen mobilen Robotern. Eine Möglichkeit taktile Sensoren weiter zu entwickeln ist, sich -wie auch schon andere Entwicklungen zeigen- der Natur zu bedienen, Vorbilder zu identifizieren, diese fundamental zu analysieren und als wesentlich befundene Eigenschaften und Funktionstüchtigkeiten zu adaptieren. Ratten besitzen auffällige Tasthaare an beiden Seiten der Schnauze, sogenannte Vibrissen. Diese sind gekennzeichnet durch einen langen, schlanken und natürlich vorgekrümmten Haarschaft mit konischem Querschnittsverlauf. Der Haarschaft wird von einem Haarfollikel gehalten, der sich unter der Haut befindet und in dem überdies Mechanorezeptoren zur Reizdetektion zu finden sind. Während der Erkundung von unbekannten Umgebungen und Objekten setzen Ratten ihre Vibrissen ein, um bspw. die Form oder Textur eines Objektes zu bestimmen, indem die Vibrisse daran entlang bewegt wird. Die Informationsaufnahme wird im Haarfollikel durch die Mechanorezeptoren realisiert. Die vorliegende Arbeit leistet einen Beitrag zum übergeordneten Ziel, die Eigenschaften und Einsatzmöglichkeiten dieses komplexen und hochentwickelten Sensorsystems der Natur für technische Anwendungen nutzbar zu machen. Die Eigenschaften einer Vibrisse sind synergetisch und beeinflussen ihre Funktionen in bedeutendem Maß. Deshalb wird das natürliche Vorbild detailliert analysiert und mit den Konzepten des biomechatronischen Systems und des Reizleitungsapparats beschrieben und auf dieser Basis ein Vibrissen-ähnlicher Sensor entworfen, um die inhärenten Eigenschaften eines solchen Sensorsystems zu untersuchen. Um die Funktionstüchtigkeit des entworfenen Protoyps, aufgebaut auf Basis der detaillierten Vorabanalyse, zu untersuchen, werden verschiedene Testobjekte, einschließlich verschiedener Oberflächenbeschaffenheiten, mit dem Sensor vermessen. Anhand der aufgezeichneten Messsignale zeigt sich, dass ein Objekt durch seine generelle Form sowie seine makroskopische und mikroskopische Oberflächenstruktur beschrieben werden kann. Die genannten Informationen überlagern sich in den gemessenen Signalen und müssen für eine weiterführende Auswertung extrahiert werden. Der Abstand zwischen Sensorlagerung und Objekt hat entscheidenden Einfluss. Makroskopische Oberflächenelemente lassen sich im Abstand von 80\% der Länge des Sensorschafts besonders gut detektieren. Ein mittlerer Abstand, ca. 60\% der Länge des Sensorschafts, unterstützt die Erfassung der Eigenschaften einer mikroskopischen Textur. Hingegen ist ein kleiner Abstand von 45\% der Sensorschaftlänge besonders geeignet zur Detektion der generellen Form des Objekts. Diese Effekte sind in enger Verbindung zur Elastizität des Sensorschafts zu interpretieren.\newpage Beispielsweise verhindert die starke Krümmung des Sensorschafts in Folge eines kleinen Objektabstandes eine Detektion von makroskopischen Oberflächenelementen wie Rillen und Stufen, da sich der Sensorschaft in dieser Konfiguration wie ein adaptiver morphologischer Filter auswirkt und damit eine inhärente Eigenschaft des Sensorsystems ist. Der Übergang zwischen der makroskopischen und mikroskopischen Oberflächenstruktur wird durch den Durchmesser der Spitze des Sensorschafts bestimmt. Oberflächenstrukturelemente, die kleiner als dieser Durchmesser sind, gehören zur mikroskopischen Oberflächenstruktur. Daraus folgt, dass auch der Durchmesser der Spitze eine inhärente Eigenschaft ist. Eine weitere inhärente Eigenschaft wird bei der Detektion einer mikroskopischen Oberflächenstruktur erkennbar. Wenn der, sich im Kontakt befindende, stark verformte, Sensorschaft so bewegt wird, dass die konkave Seite des Sensorschafts in Bewegungsrichtung zeigt, werden die erfassten Signale verstärkt - im Vergleich zur entgegengesetzten Bewegungsrichtung. Unter Berücksichtigung der genannten und weiterer Ideen, wird der durch eine natürliche Vibirsse inspirierte Sensor in der vorliegenden Arbeit untersucht

Artificial tactile sensors for surface texture detection - analytical and numerical investigations

Natural vibrissae fulfill a lot of functions. Next to object distance detection and object shape recognition, the surface texture can be determined. Inspired by the natural process of surface texture detection, the goal is to adapt it by technical concepts. Modeling the vibrissa as an Euler­Bernoulli bending beam and the vibrissa-surface contact with respect to Coulomb's Law of Friction, the first approach is formed by the group of Steigenberger and Behn. Due to the surface contact, the vibrissa gets deformed. Initiating a linear movement of the beam support in the way that the bearn tip gets pushed, first the beam tip is sticking to the surface. The acting friction force prevents a movement of the beam tip until the static friction coeflicient is reached. The displacement of the support corresponds to changes in the acting forces and moment. Out of these changes the coeflicient of static friction can be determined. Advancing the present model, the effects of an elastic support, a conical shape of the considered beam, a natural pre-curved (stress free) beam and an inclined contact plane on the resulting forces and moments are analyzed in an analytical way, and then discussed by numerical simulations in performing parameter studies. All these special features of the beam as a tactile sensor are successfully studied. The results for the conical beam shape are only of theoretical relevance. In a next step, a quasi-static model is compared to experimental data to verify the concept. The displacement is represented by a linear, stepwise change of the support of the sensor. By image processing the deformations of the beam for every support position are analyzed. This information is compared to the simulation. The concept in principal is confirmed by the experiments.Tesi

Strategic Anti-SARS-CoV-2 Serology Testing in a Low Prevalence Setting: The COVID-19 Contact (CoCo) Study in Healthcare Professionals.

Background: Serology testing is explored for epidemiological research and to inform individuals after suspected infection. During the coronavirus disease 2019 (COVID-19) pandemic, frontline healthcare professionals (HCP) may be at particular risk for infection. No longitudinal data on functional seroconversion in HCP in regions with low COVID-19 prevalence and low pre-test probability exist. Methods: In a large German university hospital, we performed weekly questionnaire assessments and anti-severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) immunoglobulin G (IgG) measurements with various commercial tests, a novel surrogate virus neutralisation test, and a neutralisation assay using live SARS-CoV-2. Results: From baseline to week 6, 1080 screening measurements for anti-SARS CoV-2 (S1) IgG from 217 frontline HCP (65% female) were performed. Overall, 75.6% of HCP reported at least one symptom of respiratory infection. Self-perceived infection probability declined over time (from mean 20.1% at baseline to 12.4% in week 6, p < 0.001). In sera of convalescent patients with PCR-confirmed COVID-19, we measured high anti-SARS-CoV-2 IgG levels, obtained highly concordant results from enzyme-linked immunosorbent assays (ELISA) using e.g. the spike 1 (S1) protein domain and the nucleocapsid protein (NCP) as targets, and confirmed antiviral neutralisation. However, in HCP the cumulative incidence for anti-SARS-CoV-2 (S1) IgG was 1.86% for positive and 0.93% for equivocal positive results over the study period of 6 weeks. Except for one HCP, none of the eight initial positive results were confirmed by alternative serology tests or showed in vitro neutralisation against live SARS-CoV-2. The only true seroconversion occurred without symptoms and mounted strong functional humoral immunity. Thus, the confirmed cumulative incidence for neutralizing anti-SARS-CoV-2 IgG was 0.47%. Conclusion: When assessing anti-SARS-CoV-2 immune status in individuals with low pre-test probability, we suggest confirming positive results from single measurements by alternative serology tests or functional assays. Our data highlight the need for a methodical serology screening approach in regions with low SARS-CoV-2 infection rates