A Vibrissa-Inspired Highly Flexible Tactile Sensor: Scanning 3D Object Surfaces Providing Tactile Images.

Just as the sense of touch complements vision in various species, several robots could benefit from advanced tactile sensors, in particular when operating under poor visibility. A prominent tactile sense organ, frequently serving as a natural paragon for developing tactile sensors, is the vibrissae of, e.g., rats. Within this study, we present a vibrissa-inspired sensor concept for 3D object scanning and reconstruction to be exemplarily used in mobile robots. The setup consists of a highly flexible rod attached to a 3D force-torque transducer (measuring device). The scanning process is realized by translationally shifting the base of the rod relative to the object. Consequently, the rod sweeps over the object's surface, undergoing large bending deflections. Then, the support reactions at the base of the rod are evaluated for contact localization. Presenting a method of theoretically generating these support reactions, we provide an important basis for future parameter studies. During scanning, lateral slip of the rod is not actively prevented, in contrast to literature. In this way, we demonstrate the suitability of the sensor for passively dragging it on a mobile robot. Experimental scanning sweeps using an artificial vibrissa (steel wire) of length 50 mm and a glass sphere as a test object with a diameter of 60 mm verify the theoretical results and serve as a proof of concept.

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.

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.

Simulations and experiments of the balloon dilatation of airway stenoses.

This article investigates the mechanics of balloon dilatation in the treatment of bronchotracheal stenosis. The "scar stricture"-type stenosis examined in this paper is typically dilated manually, using a dilatation balloon. If indicated, this is followed by stent implantation. The selection of the stent with proper characteristics is performed empirically, based on personal experience and preference. In order to optimize the therapeutic outcome, however, it is necessary to match the stent with the stress-strain properties of the stenosis, which are not determined during manual balloon dilatation. The objective is to utilize models to experimentally and theoretically establish the correlation between the pressure/volume curve measured during the dilatation and the stress-strain properties of the stenosis, taking into account that during dilatation of scar strictures the balloon is only partially compressed, as it extends beyond both ends of the stenosis. Experiments are carried out using stenosis models with various extensibilities and lengths. As expected, more hardened stenosis resulted in steeper pressure/volume curves during the dilatation. On the other hand, the comparison between stenosis of equal extensibilities, but different length, showed an initially unexpected larger distension of the shorter stenosis, at equal pressure increases. This is caused by the fact that the margins of the stenosis are allowed more time to distend, compared to the central areas of the stenosis. The term "effect of margin expansion" was introduced to describe this behavior. The modeling of the dilatation process is based on the equilibrium conditions of cut-free balloon portions. The balloon/stenosis system is divided into three areas with different characteristics: (1) the proximal and distal area of the balloon outside the stenosis; (2) the area of contact between the balloon and the stenosis; and (3) the transition area between (1) and (2). Numerical simulations of the balloon dilatation confirm the conclusions from the experimental results and the theoretical considerations regarding the correlation between the pressure/volume curve of the dilatation and the stress-strain properties of the stenosis.